Feasibility Study of Power Generation from Rice husk in Bangladesh
Background of the Study
In this modern world ‘Power’ and ‘Power Crisis’ are probably the most discussed issues. Along with the advancement of human civilization, the demand of power has increased with proportional quantity. Meeting the ever rising demand of energy is a challenging task for the nations to survive. In search of newer sources of power and for development of the existing systems, continuous research is going on in this field.
In a third world country like Bangladesh, power crisis has been an important issue since her birth. The recent discovery about the limited gas reserve in the country has worsened this condition as most of her present power plants use gas as fuel. So it is high time for the Govt. to look for other options like coal or renewable energy as sources of power. For an agricultural country like ours, rice husk is a probable source of fuel for generation of power. In this paper, we have tried to discover whether rice husk is a feasible option in respect of Bangladesh or not.
1.2 Renewable Energy
Renewable energy is energy generated from natural resources—such as sunlight, wind, rain, tides, and geothermal heat—which are renewable (naturally replenished) . In 2006, about 18% of global final energy consumption came from renewable sources, with 13% coming from traditional biomass (Global Status Report 2007).
Renewable energy sources are those energy sources which are not destroyed when their energy is harnessed . Renewable energy sources are distinct from fossil fuels, which must be consumed to release energy. Human use of renewable energy requires technologies that harness natural phenomena, such as sunlight, wind, waves, water flow, biological processes such as anaerobic digestion, biological hydrogen production and geothermal heat.
Traditional uses of wind, water, and solar power are already widespread; but the mass production of electricity using renewable energy sources has become popular only recently, reflecting the major threats of climate change, concerns about the exhaustion of fossil fuels and the environmental, social and political risks of extensive use of fossil fuels and nuclear power.
Renewable energies are sustainable energies. Renewable energy sources may be harnessed directly, such as in solar ovens, geothermal heating, watermills, and windmills. They may require energy harvesting through appropriate technologies such as: electricity generation through wind turbines or photo electrochemical cells (PEC)s, or photovoltaic cells, production of biofuels such as biogas from anaerobic digestion, or ethanol from biomass .
1.3 Bio Energy and Biomass
Biopower is the process of using biomass (plant and organic matter) to generate electricity. Biomass is organic material made from plants and animals. Biomass contains stored energy from the sun . The chemical energy in plants gets passed on to animals and people that eat them. When burned, the chemical energy in biomass is released as heat. Biofuels can be of three types- solid biomass, liquid Biofuel, biogas.
The term biomass is especially useful for plants, where some internal structures may not always be considered living tissue, such as the wood (secondary xylem) of a tree. Direct use is usually in the form of combustible solids, either wood, the biogenic portion of municipal solid waste or combustible field crops. Field crops may be grown specifically for combustion or may be used for other purposes and the processed plant waste then used for combustion .
Solid biomass is most commonly used directly as a combustible fuel, producing 10-20 MJ/kg of heat. Biomass can also be used to feed bacteria, which can transform it in another form of energy such as hydrogen, using a process called Fermentative hydrogen production. Its forms and sources include wood fuel, the biogenic portion of municipal solid waste, or the unused portion of field crops. Field crops may or may not be grown intentionally as an energy crop, and the remaining plant byproduct used as a fuel. Paddy is such a crop with the byproduct of rice husk. Rice husk can be used as the fuel for power generation.
1.3 Bangladesh Perspective
Power sector is one of the most important criterions in the development process of any country. In a third world country like Bangladesh, its condition has always been a very burning question. In spite of the prevailing problems, the power organizations are trying to maximize the output power.
The physical problems in the power sector consist of infrastructural & technological problems. Bangladesh has very limited resources to utilize in the power sector. Bangladesh does not have enough infrastructures to cope with the demand of the population of the country. Government of Bangladesh has not been consistent in financing the power sector. In previous national budgets, power sector was not given enough money. Also GOB does not have any particular policy on power sector. For the improvement of that sector, short term policies as well as long term policies are necessary. Poor policy making worsens the situation. The problem of corruption really has also crippled our power sector.
The huge shortage of electricity is hurting Bangladesh quite hard in each and every development sector. At present electricity coverage in Bangladesh is only 42% and per capita electricity consumption is about 140 kWh  which is one of the lowest in the World
For the solution of the problems renewable energy can be used as a weapon. Renewable resources offers many benefits compared to other conventional generation like they reduce reliance on fossil fuels, air emissions and other negative environmental impacts, protect against the exhaustion of non-renewable resources, provides provision of electricity in remote locations far from the main grid. Along with solar cell and biogas rice husk has also emerged as an alternative source of power in these days in Bangladesh.
Rice husk presently has been identified as a highly potential source of renewable energy. Based on the experience of other rice growing countries like China, Vietnam and Thailand, we can also opt for husk based cogeneration plant if proper study is carried out before the venture.
In the next few chapters, we will try to depict a true picture of the prevailing condition of Bangladesh in this field and try to analyze the condition from various perspectives.
1.4 Structure of the Thesis
This thesis paper has been divided into 6 chapters including this one. In Chapter 2 we include the different aspects of rice husk. This chapter gives us a brief idea about the definition of husk, sources and uses of it and the role of rice mills in this field. Our visit to a automatic rice mill has been included as a case study in this chapter.
In chapter 3, the conditions for a plant site and power generation process from husk have been mentioned. Also we include our findings from the visit to ‘Dreams Power Ltd’. In chapter 4, we enter the main section of the thesis and study the feasibility of plants in respect of Bangladesh. In chapter 5, we have mentioned some recommendations based on our study that we felt would be helpful if were ventured by the Govt. in this regard.
Finally in chapter 6, we have mentioned the conclusive remarks about the total study. We also mentioned here our shortcomings and the problems we had to face during the study, the contribution of this dissertation and the scope of future work.
We have also included a list of references and an appendix with our work. Interested readers may consult these references in case of any obscurity and verification.
Rice Husk and Different Aspects
To understand the uses and applications of rice husk in power generation discussed in later chapters, we need a clear perception of different aspects of rice husk. Accordingly, we are now going to give some basic information about rice husk, its types, chemical component analysis and its application in different fields.
We have also included a brief description of paddy, the source of husk and current situation of paddy production in Bangladesh as usable amount of husk largely depends upon it. Also a brief overview of the rice mills all over the country is included here along with their paddy processing capacity and operations.
To get along with the topics, we visited an automatic rice mill where husk is produced. In this chapter we have included our findings from the visit which will be helpful to be familiar with the topics.
2.2 Rice Husk
Rice, a cereal food plant, Oryza sativa, of the grass family Gramineae, is extensively cultivated in warm climates, especially in East Asia, producing seeds that are cooked and used as food . About 40 percent of the world’s population derives most of their calories from rice. Almost 90 percent of the population of Bangladesh, Myanmar, Sri Lanka, Vietnam and Kampuchea are rice eaters. Rice husk is the main by product of rice production. In this section an introduction to rice husk is included.
2.2.1 What is Rice Husk?
The rice husk is the hard, protective shell on the grain . To protect the seed during the growing season, the husk is made of hard materials, including opaline silica and lignin. The husk is mostly indigestible to humans. During the milling process, the husks are removed from the grain to create white rice. The very high content in amorphous silica of the husk confer to them and to their ash (SiO2 ~ 20 wt. %) after combustion very valuable properties .
2.2.2 Types of Rice Husk
During rice milling process three types of rice husk are produced. They are -
Pure ground rice husk: It is a coarse component and larger than bran. It is produced separately in automatic rice mills and used as the source of thermal energy needed both for parboiling and drying. The average production of pure rice husk is about 206 kg/ton of paddy and on average 92.7kg/ton is consumed for parboiling and 100 kg/ton is used for drying. The rest amount of husk is sold at a price about 2.78tk/kg .
Pure bran:It can be produced separately from engleberg huller mill with simple modification and mainly sold for pet food at high price .
Mixed:In engleberg huller mills, a mix of ground rice husk and bran is produced. The average production of this type of mixed byproduct is about 290kg/ton of paddy from which 131kg/ton is consumed for steam production and rest amount is mainly sold for poultry feed and fish farm at about 3.54tk/kg .
2.2.3 Byproducts of Paddy
By–products from the growing and processing of rice create many valuable new products. Rice husks, rice stubble, rice bran, broken rice and rice straw are used as common ingredients in horticultural, livestock, industrial, household, building and food product.
Rice stubble is the stalks and roots of the rice plant left in the ground after it has been harvested. Rice stubble is very thick and difficult to deal with. Livestock graze on recently harvested paddocks and eat some of the rice stubble. A portion of the remaining stubble is usually burnt off and a winter cereal crop, such as wheat, is planted. On some rice farms, rice stubble is left to break down naturally and is incorporated into the soil, to improve the soil structure .
Rice bran is the outer layer of the brown rice grain. The rice bran is removed during the milling process if white rice is to be produced. Stabilized rice bran is sold as a health food in supermarkets and health food shops, or to food manufacturers who use it as an ingredient in foods such as crisp breads and breakfast cereals . Unsterilized rice bran is used in stock feed and for other animal and industrial products.
Broken rice grains:
Unfortunately, during the rice milling processes some of the rice grains break. They are removed from the milling process. The larger broken rice grains are used in pet foods and stock feed, or breakfast cereals. The smaller broken rice grains are ground into rice flour which is used in baby foods, snack foods, including muesli bars, or as a baking ingredient. Ground broken rice grains are also used in manufactured foods, such as sausages and milk powder drinks.
Rice straw is the stalks left over after the grains of rice have all been removed in the milling process. Rice straw is used as a building material because it is easy to work with, inexpensive and good for the environment. Some dairy farmers use rice straw as fiber for grain–fed stock. It can also be used to make paper .
2.2.4 Components Analysis of Rice Husk
To know about the gases that are produced as the result of burning rice husk, a complete analysis of rice husk is necessary. In the following figure we have shown the main components of husk that is calculated by chemical analysis . For the full chart we refer the reader to have a look at the Table A.1 and A.2 in appendix.
Figure 2.1: Component analysis of rice husk sample
From the Figure, we see that rice husk mainly contains carbon and oxygen. Methane gas is produced during combustion and separated for power generation . The sulphur content in rice husk is very small and the small amount sulphur is emitted as SO2.
2.2.5 Uses of Rice Husk
Rice husks are mainly used in the following sectors-
Building material: Rice husk is a popular building material  because of its excellent insulation property. It is difficult to burn and protects moisture and mold to propagate through it. It is mainly used to build mud house in Chittagong region.
Fertilizer: Rice husk are low cost material and available for farmers. It can be composted by vermicomposting techniques . Earthworm is used for the process because its high lignin contents can make the process slower.
Industry: Rice husk, as a low cost material, contains silicon carbide which can be used to reinforce ceramic cutting tools, increasing their strength tenfold. Cement industry can use rice husk to add silica in the product itself because rice husk content high silica .
Fuel: Methane gas can be extracted by gasification process which can be used to run gas engines for power generation. It is also used as a fuel in road construction nearly about 40% .
Briquette: Rice husk made briquette is widely used for cooking in urban area where gas is not available. Efficiency is enhanced than normal use in this process.
Poultry bed: It is also used to prepare poultry bed to protect chickens from moisture which is used as fish feed later.
2.3 Source of Rice Husk
Paddy is the only source of rice husk. As a cereal grain, rice is the most important staple food for a large part of the world’s human population, especially in tropical Latin America, the West Indies, East, South and Southeast Asia. Rice is our main food and different kind of rice is cultivated in our country but mainly there types are named.
Different kinds of Paddy
Rice is cultivated in Bangladesh throughout the year as 
· Aman: (i) Transplanted
· Boro: (i) High yielding
About 40 percent of the world’s population derives most of their calories from rice. Almost 90 percent of the population of Bangladesh, Myanmar, Sri Lanka, Vietnam and Kampuchea are rice eaters .
Different Aspects of Paddy
In Table 2.1, the relative per cent age of land occupied by different kinds of paddy along with their period of cultivation & harvesting time is pointed out . With the help of this table we can easily calculate the time during when most amount of husk is produced in Bangladesh.
Table 2.1: Land occupation & Cultivation time of Different kinds of Paddy 
|Paddy||Land occupied by this kind (%))||Planting period||Harvesting period||Cultivation Area|
|Aush||17.59||April-May||July- August||Scattered in most of the districts|
|Aman (Transplanted)||46.30||August-September||November-December||Throughout Bangladesh|
|Aman (Broadcast)||9.26||August-September||November- January||South & Sothern East part of Bangladesh|
|26.85||(a ) December- February||(a ) May -June||In various districts of Bangladesh specially in low-lying lands|
|(b)Local Boro||(b) December- February||(b) April-May|
From the above data, we observe that about 50% of the cultivating land is occupied by the ‘Aman’ as it grows throughout Bangladesh. Also Aman is regarded as the high quality paddy. Though Boro covers almost 25% of the total production, it is actually of low quality .
Gross production of rice from year to year basis
Rice husk production can be estimated from rice production for a country. So to find out available quantity of rice husk first we have to consider rice production quantity of our country. Rice production data are provided in Table B.2 in appendix.
Figure 2.2: Rice production in Bangladesh
2.4 Rice Mills and Operation
2.4.1 Rice milling processes
Three types of rice milling processes  are found
1. Puffed rice processing
2. Parboiled rice processing
3. Un-parboiled rice processing.
In first two processes supply of steam is needed. On the other hand there is no need of steam in the last process. In this processes two steps are followed and those are,
Step one (Removal of the outer hard protective layer)
The rice husk is the protective layer surrounding the grain. Once removed, the rice grain can be packaged, sold and eaten as brown rice. Brown rice still contains the rice germ and outer bran layers . If the rice is to be sold as white rice, the grain continues through further milling in Step Two.
Step two (Removal of the germ and brown layers)
The germ and bran layers from the rice grain are then removed to expose a white starch centre. This polished white starch centre is what is known as white rice .
2.4.2 Types of rice mills
There are two types of rice mills .
Steel shaft huller mill (Engleberg):
This is a traditional rice mill of low capacity
about 1-13 metric ton per day. In these mills mixed type rice husk is produced and extra machineries are needed to separate husk and bran. Here sun drying is followed so huge space and time is needed for a single cycle .
Automatic rubber roll mill with stone publisher:
This is a modern rice mill and are being popular for high capacity, 11.3-48metric ton per day, and high speed of operation.Here Louisiana State University type modern mechanical drying is followed for time and cost optimization .
2.4.3 Rice Mill Clusters in Bangladesh
According to directorate of food there are 25600 number of rice mills in our country which are located in different cluster. Size and location of a rice mill cluster depends on rice production and transportation condition of that area. There are some major clusters in the survey made by the GTZ.
The rice mills of small capacities were found in the BSCIC area at Pulhat. About 300 rice mills are situated in the cluster within 2km radius. There are about 50 automatic large rice mills in this district .
About 775 rice mills are situated in three different sub-clusters which are Naogaon sadar, Mohadebpur and Raninagar. All rice mills in a cluster are situated within 2km radius .
It is spitted into two sub-clusters are named as Sherpur and Santahar. Distance between these sub-clusters is 55km.There is about 110 rice mills in these cluster .
In this cluster rice mills are larger in capacity and situated separately in a group. There are about 16 large capacity rice mills few of those have more than one unit .
Rice mills are situated in a line at a road side and distributed within 2km radius. There are about 50 rice mills in this cluster .
Other major clusters are Jamalpur, Mymensingh, Ashugonj, Kustia, Chuadanga, Jessore, Khulna, Sylhet and Chittagong. A details map of Bangladesh is shown in Appendix C.
2.4.4 Paddy Processing Capacity of Rice Mills
To know the available quantity of rice husk in a cluster we have to know the cluster size as well as paddy processing capacity of rice mills in that cluster. We have mentioned few major clusters and their size in previous subsection and now average capacity of the mills of different clusters are tabulated as follow.
Table 2.2: Total amount of paddy processed (MT/year) in different cluster 
|Cluster||Annual paddy processed
|Number of rice mills (surveyed)||Average paddy processed (MT)||Total number of rice mills||Total amount of paddy MT/year|
Here we find out average paddy processed in metric ton by a mill from surveyed data and from this estimate the total amount of paddy processed in each cluster. Quantity of rice husk is assumed as 20% of the amount of paddy and so annual husk production of these clusters would be like this, (Refer to Table A.3 in appendix)
Figure 2.3: Available rice husks for commercial processing in different cluster
2.4.5 Parboiling and Drying Operations of Paddy
Amount of rice husk consumption during parboiling process shows a great variation due to use of traditional parboiling system with low efficiency. This variation indicates that there is a scope of saving husk if improved and efficient boiler could be used. Most of the mills consume from 100~150kg of rice husk per ton of paddy parboiling. On average, we assume 125kg of rice husk is used for per ton of paddy parboiling .
There are two types of drying methods which are sun drying and mechanical drying. For mechanical drying LSU type dryers are normally used in our country. Most of the mechanical dryer at rice mills use 80-115 kg husks per ton of paddy drying. On average we can assume 97kg husk is required for per ton paddy drying. We found that almost all (100%) rice mills in Naogaon and Ishwardi use sun drying . On the other hand 54%, 3% and 99% rice mills use mechanical drying in Dinajpur, Bogra, and Nawabganj respectively .
For mechanical drying thermal energy is produced in a furnace fired by rice husk. So amount of surplus rice husk after parboiling and drying can be calculated as follow.
Table 2.3: Use of rice husk for parboiling and drying 
|Cluster||Available rice husk (MT/year)||Total number of rice mills||Kg husk/ton paddy for parboiling||Kg husk/ton paddy for drying||Rice mills use mechanical drying (%)|
Amount of surplus rice husk= A – B×C – B×D×E/100.
Here A is total rice husk output from rice mills. But rice mills use rice husk for own parboiling and drying purpose which should be deducted. Amount of rice husk for parboiling is calculated by multiply total number of rice mills with average amount of rice husk required for parboiling (refer to Table A.4 in appendix). For drying requirement use of mechanical drying percentage should be consider.
By this equation the amount of surplus rice husks are shown in Figure 2.4
Figure 2.4: Surplus rice husk or rice husk avilable for sell.
2.5 Case Study: Visit to an Automatic Rice Mill
We visited an auto rice mill to get practical knowledge about the milling procedure, different equipments and machineries used in the procedure, different kinds of husk and also the stages of production of rice.
The rice mill that we visited is situated at a river bank near Muktarpur in Munshiganj district. In Muktarpur there is a small rice mill cluster which consists of 5 auto rice mills and a number of traditional rice mills.
Branches of Rice Processing Mill:
Dry raw paddy (Figure 2.4) is supplied by farmers of mainly the neighboring areas. This raw paddy consists of impurities and undesired wastes like grass, stubble, soil etc which have to be separated in the first step. The machine for this process is like a filter and uses simple techniques. This machine is shown in Figure 2.6.
Paddy is boiled and dried out by steam produces from the huge boiler (Figure 2.7). Rice husk is used to fire the furnace (Figure 2.8) (The included photo figures were taken by the writers) which is carried to the boiler room from the mill site by a conveyor belt. Husk consumption can be reduced if efficient furnace is employed. New paddy contains more wet so more steam is required for parboiling process. Required quantity of steam is reduced for older paddy.
Figure 2.5: Raw paddy from the farmers Figure 2.6: Paddy Cleaner Machine
By products of Paddy and different stages of processing
Clean paddy is stored in a large reservoir then small cylinders under the reservoir are filled through a duct. Steam and water are supplied to the cylinders when those are filled with clean paddy.
Lower portion of cylinders are shown in Figure 2.9. On the other hand, upper portion (Figure 2.10) of cylinders is connected with water and steam supply pipe where pressure gauge and water level indicator are employed to monitor pressure and water level respectively. Parboiled paddy are stored in new medium size reservoir then rotated
Figure 2.7: Boiler used in the rice mill Figure 2.8: Furnace of the boiler
Respectively. Parboiled paddy are stored in new medium size reservoir then rotated between upper and lower reservoir and dried out by steam with high pressure at the flowing path.
Figure 2.9: Lower portion of cylinders Figure 2.10: Upper portion of cylinders
The whole process needs ten hours so consistent power supply is mandatory after the process is began. This mill uses diesel engine generator. Diesel cost is a great headache for the owners so they appreciated the plan of power generation from rice husk to fulfill their own demand.
Rice husk (Figure 2.11) and rice bran (Figure 2.12) are produced separately in automatic rice mill. Initially those are in mixed form (Figure 2.11). Rice husk is conveyed to the boiler room and rice bran is packed up for sell. In the following pages we include the photos of the husk, bran and mixed husk that was just produced by the mill.
Figure 2.11: Rice husk
Figure 2.12: Rice bran
Figure 2.13: Mixed form of rice husk
After separating the mixed rice husk from the rice we get coarse rice which is full of dirt and impurity. In this stage produced rice is brownish and large.
Figure 2.14: Rice after first step (Coarse rice)
This coarse rice is then passed to the next stage for polishing. In the polisher machine, outside layers of rice are cut down to make it smooth and small. The polished rice looks like the following figure.
Figure 2.15: Rice after second step
This rice is passed to again to another polisher and same process is applied. The rice that we get from this stage is fine rice that is ready for sale.
Figure 2.16: Rice after third step
Vitamin density is higher in those layers so the process reduces food value of the rice. Waste of the process contains outside layers of rice which are sold at high price to biscuit companies.
From the visit, we came to know that about 30-40% of the produced husk is used by the rice mill itself as a fuel for the boiler that is used for parboiling. The rest of the total husks were sold at a low price by them which according to them were bought by Indian buyers who take husk to India to produce oil.
We also found out that the rice mill had to pay about BDT 0.1 to 0.11 million per month for the electric bill. The load shedding condition was really severe in the area and to operate during load shedding they had to spend about BDT 80,000 to 90,000 apart from their electric bill for the cost of diesel to run the generator.
Power Generation from Rice Husk
Now that we have the basic information about rice husk and current situation of husk production in Bangladesh, we can proceed to the process of its use as fuel in power generation process in details. In this chapter, we have first discussed the necessary considerable factors for power station siting and layout in brief to have a perception which will help us determine the condition of different locations in Bangladesh in the next chapter. After this technological procedures of generation process have been described step by step. Then a segment showing current technologies used for Power Generation has been included.
The first husk based dual-fuel plant in South Asia has been recently established in Bangladesh. For the thesis purpose, we visited the plant and collected information about it. We have given a long and short of our findings about this visit hereby.
3.2 Factors for Power Station Siting and Site Layout
It is important to identify and investigate a number of potential sites for constructing a power plant. The following considerations  can be made in this regard:
Whether the existing stations capable of further improvements.
Pieces of land already purchased by the Government for future development and pieces of land not owned by the Government, but identified as potential sites.
In this section we have described the important factors considered for the power station siting and layout.
(i) Transmission of Energy
It Energy transmission the plant area should be very easy. We have to consider several points  in this regard. They are-
Source of energy supply must be in the close proximity to the load centre.
We must consider the cost of copper and aluminium wires and make sure that total cost of transmission structure is reduced.
Long transmission line incurs large line drop. Hence high Voltage transmission might be required. So large insulation may be necessary.
(ii) Supply of Raw Material
The raw material from which electricity is made (in this case mainly rice husk) must be available in the region of the site.
The near the plant to the source of fuel, the less cost will be incurred.
In case of rice husk cogeneration plant the best sites are the places around the rice mills.
(iii) Land Requirements
Sufficient land will be required not only for the station when it is in operation, but also to provide adequate areas during its construction period. Areas should be provided for adequate working and storage areas for the contractors and for the construction car and bus parks. In addition, areas will be required for topsoil removed during excavations. Subsoil investigation , permeability test and groundwater tests are often performed to design proper cooling system.
(iv) Access to a Power Station
Access to a power station is required for construction materials and plant, fuel supplies and employees. Good road is essential for construction, and rail and sea facilities are useful advantages. Direct access to a main trunk road to bring in heavy loads is desirable. Road traffic can be reduced by delivering the loads through the sea .
While a power station is being built, traffic is greatly increased and so local roads adjacent to the site are often reconstructed and re-routed to avoid undue inconvenience or risk to other road users. The site must also be conveniently situated either close to a main railway line to accept rail-borne fuel or in areas remote from coal fields or refinery, on an estuary or the sea coast to enable it to take fuel from the colliers or tankers .
(v) Water Supplies
Water supply must be provided from a suitable source like a treatment plant or from a river or borehole. Where water for firefighting is to be taken from the town mains, allowance should be made either to duplicate the supply or to provide adequate storage capacity to ensure 100% availability; this is the most important factor during the commissioning period of a boiler  when the demands on the supply are heavy. During the construction period, water consumption depends on the size of the labor force, the nature of the civil engineering works e.g. aggregate washing, water jetting of piles, concreting etc and plant testing.
(vi) Safety Considerations
Historical data are used to assess and identify the fault location on the earth surface. Proper care must be taken while constructing a nuclear plant so that it is not located on the fault line.
Other Natural Hazards:
Studies are carried out to investigate the weather pattern of the site. If there is any possibility of cyclone or tidal wave or anything like that is investigated.
The industrial or manmade hazards are also important to deal with. Stations must not be positioned where there is regular traveling route of fuel or flammable liquid carrying transports.
Sites should not be constructed in the area where there is a dense population so that it doesn’t cause any major damage in case of any incident .
(vii) Other factors
Site and Station Levels:
A site should be reasonable level, not liable to flooding and not so high above the source of cooling water that excessive pumping power is required to supply water for cooling purposes.
Ash and Dust Disposal:
When selecting site for a rice husk cogeneration power plant, very careful consideration must be given to the provision of suitable economic ash disposal, either on low-lying ground or worked out mineral workings which can be filled by the creation of landscaped hills, or by the sale of pulverized fuel ash to the construction industry .
Labor Force Supplies:
For successful and efficient operation and construction process of a power plant, adequate size of labor force is required. Not only the size matters, but also the quality and efficiency of the labor force are a matter of significant concern.
3.3 Technological Procedures of Generation Process
3.3.1 Layout Area and Expected Capacity of Power Station
The power station is expected to be built on the area where rice husk are available which also depend on the production of paddy. In Bangladesh, the main production areas are mentioned in the previous chapter. We also consider the area near river side because transportation and collection of rice husks from neighboring rice mills will be easy by water way. The capacity of the plant will be variable depending on the coverage of the area. We will try to cover the rice mill and around the mill in plant located area.
3.3.2 Base for Selection of Technology for Cogeneration
The selection of rice husk combustion technology for producing energy (heat and power) is based on the following criteria  –
1. Production cost
2. Recovery of capital and financial benefit
3. Rice husk availability and fuel characteristics
4. Overall efficiency of the cycle (cogeneration plant)
5. Equipment manufacturing and supplying capability
6. Environmental impacts and measures for mitigation.
Some worldwide proven technologies are described below for analyzing and selecting the most appropriates to small-scale rice mills which are popular.
The existing six main biomass conversion technologies are:
1. Direct Combustion
At present, the most common technologies are direct combustion and gasification from rice husk to produce electricity . An analysis of these two technologies is carried out below in order to select the more appropriate in terms of capacity and practical application. Before selecting the technology, an analysis of fuel characteristics is needed.
Moisture content of biomass fuel is one of its important characteristics because after collection from the field it is not homogeneous. Thus, a careful consideration should be made in selecting the suitable mode for fuel feeding and combustion technology . The presence of water in biomass fuel will reduce the portion of combustible substances. Biomass having high moisture content should be dried naturally under the sun or in a dryer before being used as fuel.
On the other hand, too high moisture content always needs more time for heating biomass up to fire setting temperature. Now-a-days, new existing technologies and techniques allow burning the fuels having high moisture content up to 60% . Thus, we have to consider and choose the moisture content in a range suitable to the technology.
Heating Value of Fuel
It is the amount of heat liberated from the complete combustion of 1 unit of fuel. This is a basic feature, which will be used for calculating the parameters of combustion chamber like heat volume, surface of grates as well as combustion and mass/heat transfer processes in the furnace. In the technical documents on combustion of biomass in furnace / boiler from abroad, it was proved that the heat value of biomass having moisture content at 50% should be not less than 1850 kcal/kg .
Homogeneity of Fuel
If the homogeneity of fuel in terms of size and type is not ensured, the combustion process in the furnace could not be stable. It needs to select an appropriate combustion technology.
From the above analysis, ash content has important effects on fuel properties: reducing heating value, causing dust and corroding the material of boiler, leading to decreased heat transfer intensity. For biomass fuel, ash content is very low and the ratio between fly ash and slag depends a lot on the shape and size of fuel as well as selected combustion technology, size and form of boiler / furnace. For conventional combustion on grate, this ratio is of 60/40 and even 80/20 . During combustion process, the ash is usually entrained in the smoke stream due to suction effect of the fan. Consequently, in order to keep on the environmental allowable parameters it needs to use the ash traps, flue gas filters (dry, wet or bag).
3.3.3 Analysis and Selection of Technology Biomass Gasification
Biomass gasification is a process of converting solid biomass into a combustible gas by combustion with insufficient oxygen supply. There are 3 modes of biomass gasification , they are:
2. Updraft and
3. Gross draft.
The composition of produced gas (mainly volatile matter) depends on the factors like temperature, pressure, heat transfer process and type of gasifier. In gaseous mixture, beside combustible gases, there exist also other substances such as steam, and tar. This gaseous mixture should be cleaned (for removing tar and particles) and cooled before coming to the combusting appliance / furnace. For internal combustion engines, the content of tar in combustible gas should not be more than 50 ppm (part per million) while for gas turbine this feature should be well lower .
(i) In the case of down -draft gasifier, producer gas has to pass a zone with higher temperature so its temperature is rarely high, at 600-800° C
(ii) In the case of updraft gasifier, producer gas should pass a bed of raw biomass fuel, which has very low temperature. That’s why its outlet temperature is low, ranging from 100 to 300oC.
When using this type of gasifier for internal combustion engines (also for gas turbine), the produced gas needs to be cleaned due to higher content of tar. The up-draft gasifiers are suitable only for fuels having high moisture content. Both types of gasifier are designed with a “throat” to form a high temperature zone for cracking tar. However, this throat will restrict the biomass flow, especially for the biomass having very low bulk density (kg/m3).
In current development trends, Fluidized Bed Combustion (FBC) technology is used for combustion of solid fuels, including biomass, and particularly rice husk. FBC combustion is chosen when fuel particle size is less than 6 mm . The bed consists of inert particles, and commonly, sand is used. Two types of FBC, which could be used for combustion of rice husk fuel are Bubbling Fluidized Bed Combustion (BFBC) and Circulating Fluidized Bed Combustion (CFBC). They are described below:
(i) Bubbling Fluidized Bed Combustion (BFBC)
· Reducing NOx emission.
· High heat transfer effect due to the increment of contact surface when the fuel particles are sunk in the “boiling layer”.
It is important to note that biomass fuel has high volatile content (V ~ 70%); the heat liberated in the fire box is much higher than that on the grate as the volatile matter released from biomass fuel will burn in the space of combustion chamber . Based on this, FBC would be affected in the furnace with two combustion chambers. In the first chamber, fuel burns at low temperature. The generated volatile and unburned fuel particles are led to the second chamber, to which the secondary air is supplied sufficiently for complete combustion.
(ii) Circulating Fluidized Bed Combustion (CFBC)
A typical feature of FBC is the great quantity of fly ash, which contains a considerable amount of unburned carbon (only volatile matter was burnt out). Fly ash recycle system should be used for improving the furnace efficiency. Fly ash, after being separated from flue gas precipitators (cyclone type), is returned back to furnace.
Combustion on Grates
Based on the required capacity, the type of furnace and various fuels feeding mode van is selected. The main factors for this selection are:
• Fuel characteristics
• Plant’s capacity
For on-grate combustion furnace, there are some types of grate which might be chosen: fixed, flat grate, inclined step grate, moving grate (shocker grate) but only the inclined moving grates are in common use. The furnace may be divided into two separate parts: combusting and heating (pre – furnace) or direct . Fuel feeding could be done from the bottom or from the top, continuously or in batch. To facilitate the selection, two modes of fuel feeding are analyzed.
Selection of Technology
Based on the above analysis, a conclusion is made on the possibility of using one of the following technological schemes for power generation from rice husk :
1. Rice husk → downdraft gasifier → internal combustion engine or small scale gas turbine → generator
2. Rice husk → Combined cycle (gas – steam) → gas and steam turbines → alternator
3. Rice husk → furnace / boiler → steam turbine → alternator
Cleaned produced gas of biomass is preheated and led to gas turbine/I.C engine for combustion. Low investment cost and simple operation (few of facilities required) are the advantages of this scheme. However, it can be used for small scale power generation (up to 1000 kW) and it need tar removing process  since along with operation, the dust / tar will accumulate on heat exchange surfaces.
Rice husk is gasified in a gasifier. Produced gas is led to gas turbine for combustion and power generation. The temperature of gas exhausted from gas turbine is still high enough to produce steam. This superheated steam will be led to the steam turbine to drive the generator producing electricity . This scheme has some advantages like high overall efficiency and high electric capacity.
Biomass is burnt in a furnace (fluidized bed / grate type) for preheating water and producing steam, which will be used in a steam turbine for driving the generator. This scheme has higher efficiency compared to the first one and easy to apply for cogeneration . It requires, therefore, higher investment cost and skilled operators.
Conclusions on selection of technology
Cogeneration plant consists of rice husk storehouse, conveying and automatic boiler feeding systems, and furnace/boiler. The boiler is equipped with automatic ash removal system, heat exchangers and turbo-generator. The turbine used here is a backpressure.
3.4 Current Technologies used for Power Generation
3.4.1 TORBED process reactor technology
Rice husk is currently being used for energy production through direct combustion or gasification in many areas of the world. Unfortunately, in almost all of these installations, the ash produced is not suitable for use as a silica fume substitute . Generally there are two shortcomings in the ash by-product from current rice husk to energy technology: first, they can contain unacceptably high concentrations of residual carbon; and second a portion of the amorphous silica has been transformed into crystalline silica, cristobalite. The second of these two problems is the more serious; cristobalite does not have the same pozzolanic (cementitious) properties, as the amorphous form , and in the particle size range at which it would be used in concrete, it is recognized as a potential human carcinogen. The transformation to the crystalline state takes place if the ash is exposed to high temperatures and becomes even more likely if it is exposed to these high temperatures for extended time periods. Most of the current energy generation technologies do not control temperatures well and most allow the ash to remain at high temperatures for a relatively long residence time .
TORBED Process Reactors applied to rice husk combustion and gasification technology utilize a unique reactor configuration that completes the combustion or gasification of husk in a short residence time at precisely controlled temperatures . It has been shown that, using the TORBED reactor technology, an ash can be produced at a moderate temperature that has zero or at most trace quantities of cristobalite and a residual carbon content of 1-4%. The first commercial TORBED rice husk combustor was installed and successfully started up in India during September and October 2003 .
Because of the moderate temperatures used in the TORBED reactor there is a slight reduction in the usable energy that can be recovered from a TORBED reactor used as a rice husk combustor. However, in some instances this may be compensated for by achieving a much more complete combustion of the available fuel. The TORBED reactor can be designed into a new facility to combust rice husk for energy production, or this combustor can be retrofitted into an existing facility to replace a current combustor that is producing an unusable ash waste.
Figure 3.1: A typical TORBED reactor
The capital investment in a replacement combustor will generate an attractive Return On Investment (‘ROI’) based on the benefits of turning a waste disposal cost into a by-product credit. Similarly, installation of new plant for energy generation will produce an attractive ROI based on both energy and ash values .
3.4.2 Firing Process
(i) Process Description
First of all, the system boundary of the study is set as shown in Figure 3.2, for doing the environmental assessment using the Life Cycle approach. Raw material, electricity and resource consumption, electricity generated, waste and emissions generated have been considered within the boundary . This figure also shows list of all flows – water, flue gas, steam, electricity and ash. The process started at, water from Shi River is treated before using for steam production. Particulates and ions in water must be removed to protect erosion of boiler. This is accomplished by coagulation by PACl. Sludge is removed as solid waste and is sent to the landfill .
Figure 3.2: System boundary for power generation scheme.
Then water is passed through filter tank and demineralization tank to remove ions by ion exchange resin. After that, water is heated in the economizer using the waste energy from the hot flue gas released after steam production in the boiler . The heated water is then sent to the boiler. Rice husk is the fuel source for boiler and is ignited by burning paper during startup. Steam is produced at 300°C and is further heated by super heater to produce higher energy steam at approximately 400°C . This superheated steam is then used for steam turbine for generating electricity. The exhaust steam is then condensed to water by the cooling tower.
(ii) Emissions and Waste Generation/ Treatment
Wastewater was produced from water pretreatment before using in boiler part. After coagulation, wet sludge is separated and the water removed. Dry sludge is sent to the landfill. This sludge contains the particulate in raw water. Regeneration of resin in demineralization part requires 35% hydrochloric acid and 50% sodium hydroxide . The blow down water has high turbidity and conductivity, and a pH 9.6–10.5. Water blow down from cooling tower is also considered as wastewater. The water has pH in the range of 8–9 and also some hardness and turbidity. Wastewater treatment steps are pH balance, coagulation and ion removal . Water discharge after the treatment has a pH value of 7– 7.5, 0.6 kg/MWh of total suspended solid, turbidity and conductivity lesser than before treatment. The ash production from the power plant is bottom ash 0.017 kg/MWh and fly ash 0.1 kg/MWh. The solid residues are sent to the landfill .
3.4.3 Biomass Gasification Power Generation System
Power generation by biomass fuels gasification and its comprehensive utilization is a rising industry. Research and design newly type complete set of equipment of biomass gasification power generation in order to reduce the fuel cost for the users and improve the efficiency of energy exchange are highly practiced.
In this process a gasifier is used to conduct the combustion procedure. The biomass gasification system produces a valuable gas named producer gas -“Syngas” (Synthetic gas). Among few types of gasifier fluidized-bed gasifier is mostly used for low carbon ignition property. A small water cooling system is needed to control temperature. The water used in the cooling system of this process can be recycled after undergoing a simple treatment and thereby having no harmful effects to the ecological system and the environment. Then a gas enrichment process dissolves impurities of H2S and CO2. Water Scrubber (WS) and Zeolite Molecular Sieves (ZMS) are two popular types of gas enrichment technology. Then different steps of filters are used to as purification process. Coarse filter, Passive filter and Safety filter are most commonly used filters for gas purification. Blowers are used at different stage to control gas pressure and flow rate. After purification the cleaned CH4 gas is supplied to a gas engine for power generation. This is the most efficient power generation process from rice husk. The production of 1 KW of power requires only 1.55-1.85kg of rice husks if efficient system is involved. In this process thermal loss is low. The power station requires a small land area to operate. It is environmental-friendly, simple to install.
Figure 3.3: Biomass Gasification Power Generation System
There is no mechanical loss because gas engine is used rather than steam or gas turbine. So the technology of producing power by gasification of biomass is easy to operate, simple and economical in maintenances and service, has no high pressure steam, no turbines and is easy to start up and run the standard combustion generator.
3.5 Case Study: ‘Dreams Power Private Ltd’
To get the complete picture of Husk Based generation system, we visited ‘Dreams Power Ltd’, a rice husk based duel fuel plant. Dreams Power Private Ltd. (DPPL) a local sponsor has developed this project. The Plant is the first ever its kind in Bangladesh. The project was funded by IDCOL. IDCOL provided concessionary loans and grants, sourced from IDA and Global Environmental Facility to this project.
Union: Giaspur, Thana- Kapasia, District- Gazipur
Start of Operation:
The project started commercial operation in October 2007 .
Figure 3.4: Flow Diagram of Dreams Power Ltd
The technical equipments include mainly the following
(i) Gasifier Unit
(ii) Gas purification unit
(iii) Generator Unit: Duel-fuel Engine
The specification of (i) and (iii) is included in the Table A.5 and A.6 in the Appendix.
(ii) Gas Purification unit
Following gas purification stages and filter element have been used in each stage of this rice husk based power plant:
Stage 1: Coarse Filter: uses rice husk char as filter element to partly clean the gas.
Stage 2: Fine Filters: sawdust is used as filter element to trap all the particulate and
Figure 3.5: Reservoir of the plant Figure 3.6: Hopper used in the Plant
Figure 3.7: Passive Filter Figure 3.8: Safety Filter
Figure 3.9: Generator Unit Figure 3.10: Safety measures in the plant
Figure 3.11: Outside view of the Plant
Stage 3: Safety Filter (‘SF’): a special fabric (5 micron particulate size) is used as filter Element.
(iii) Generator Unit: Duel-fuel Engine
Electricity is generated by a 300 kW capacity duel-fuel generator . In this rice husk based power plant, to run the generator certain amount of diesel is required. Because, the producer gas has relatively lower heating value and needs to be supplemented by diesel to get the necessary power output. That’s why the IC engine has been converted into duel fuel mode, i.e. it can run both on producer gas and diesel. Here, the producer gas to diesel ratio is. 70:30. During the start up of the plant, main generator is started first on diesel and then changed over to duel fuel mode when the producer gas is available for charging to the engine .
Power distribution Network
A mini grid has been constructed to sell the power to the adjacent area. The plant is able to deliver power to at least 200 households and over 100 commercial entities of that area.
Environmental Impact of the Plant
Generally 4 types of effluent are generated from the gasification process; ash, char, tar, and waste water. Ash is collected in wet condition. Around 20% of rice husk is made up of ash and the ash coming from the gasifier contains 10 to 15% carbon by weight . The ash-laden water can be used as organic fertilizer or land filling purpose. The plant has on site storage facility for ash. Char can be transformed into charcoal which is used as a domestic fuel for cooking and heating. Tar can be either recycled or burnt in the gasifier or used as black paint for the wooden materials like boat, wooden structures and construction of roads. The plant has onsite storage facility to deposit waste water which needs to be changed in every three month.
Total cost of the project was around Tk. 2.5 crore. Financed by grant from
World Bank – 60%
IDCOL – 20%
DPPL – 20%.
Production Cost: 4.3 BDT/KW 
Achievements of the Plant
At present about 38% of population in Bangladesh has access to electricity , and Bangladesh is still way behind in this regard. Expanding rural electrification is the key to the prosperity of rural areas. While growth in electricity consumption is directly related to economic growth, electrification is also required to attain Millennium Development Goals. Electricity also opens new avenues for job creation and thus increases income.
As stated earlier, Dreams Power is the first endeavor in its field in Bangladesh. The first always faces the biggest challenges. Dreams Power is the one who overcame all those challenges to become first. And hence she has laid down a path for others to follow and create opportunities to be replicated.
The lessons learnt from installing this plant could be effectively used while preparing other biomass plants. This will certainly reduce the challenges for the next entrants and can attract new entrepreneurs to install biomass power plants in rural Bangladesh to meet the electricity demand. This will also create employment opportunities in rural Bangladesh.
Problems faced by the Users:
Failures of the project
From our visit to the plant, we came to know about some of the severe problems suffered by the customers of Dream Powers Ltd. We talked with the local people to know about the practical situation down there.
We found out that though the plant supplied electricity for almost 16 to 18 hours per day when it started operation in 2007. But after only a few months it started to narrow down the supply time. At the moment when we visited the plant, it was only supplying electricity for hardly 5 to 6 hours.
The main problem we found out is the load shedding throughout the whole day time and the inhabitants did not get electricity even at peak moments of business. The schools and colleges did not get electricity to operate and the students had to suffer a lot in the scorching heat. The businessmen suffered a lot as they need power at day hours and as a result they were at a loss as people had to run to the nearby unions to fulfill any necessity.
The authority of Dreams Power Ltd was not listening to the people’s demand of electricity. And the locals said that Dreams Power showed documents to the GOB and the World Bank that they were meeting the energy demand of the whole union. As a result the inhabitants could not get power from any other option like Rural Electrification Board as they were supposed to be the customers of Dream Powers only.
Dreams Power supplied power from about 6 pm to 11 pm. But even at this small duration it could not operate at full load.
We found out that though the plant was supposed to be operated as a duel fuel plant, it was probably operating mainly on diesel, because we did not find a large collection of rice husk which is a must for a husk base power plant.
Findings from the Visit
Though the plant seemed to have a lot of problems still it is a praise-worthy initiative in the sense it has started a new era. The probable reason of their failure is that they were trying to meet the demand of a whole union of more than 6000 inhabitants. This is actually not possible for a small plant like this. By studying the problems of this plant, new husk based plants can be successfully set up.
Feasibility Study in Respect of Bangladesh
In the previous chapter, we got familiar with the technology of the power generation from rice husk. Being an agricultural country, it is believed that Bangladesh has a potential to emerge as one of the most successful users of biomass for power generation in the form of rice husk.
In this chapter we have made an attempt to find out whether it is just a mere common belief or really we have a possibility to succeed if rice husk is used as fuel for power generation. We have made an estimation of power that could be generated from husk cogeneration plants. Then we pointed out the feasibility of location selection along with its problems. We tried to analyze the financial and economic perspective of the project and its environmental impact on our countryside.
We also mentioned the benefits of this project and the problems that might stand in the way of success and then suggested the necessary steps to overcome them.
4.2 Estimation of Generation and Demand
4.2.1 Amount of Surplus Rice Husk Estimation
Available rice husk estimation is necessary if we want to predict amount of power generation. We got the total rice production data from the Statistical Year Book of Bangladesh Bureau of Statistics (BBS).
To estimate the available husk amount, first we convert rice production data to amount of produced paddy. Rice is approximately 67% in weight of total paddy. The blue line in Figure 4.1 indicates total rice production which is divided by 0.67 (Ahiduzzaman) to get amount of paddy production. The amount of paddy per year is indicated by the red line in the same figure.
According to the studies, (Ahiduzzaman) total amount of paddy is not available for milling process, 30% paddies are processed by the farmers themselves with the help of rural old technology. So according to this data we estimate available paddy for milling process by taking 70% of the total gross paddy indicated by the green line in the figure. Amount of husk is 20% in paddy. So we get the available husk from previous data indicated by the violet line in Figure 4.1. For the data used in Fig 4.1 and 4.2 the reader is requested to refer to the Table B.1 in appendix.
Figure 4.1: Production of Total Rice, Gross Paddy, Milled Paddy, Rice Husk
This husk is mainly used in parboiling and drying for milling process. 67% husks are used in parboiling and 5% are used in drying process. 20% of it goes to briquette production and the rest goes for poultry and pet feeding as shown in Table 4.1.
Figure 4.2: Production of Rice Husk & husk for parboiling (including approximation)
In Figure 4.2 the total amount of rice husk is shown (indicated by the blue line) with the utilizable amount for cogeneration considering only the parboiled amount to be used (red line). In this case, a question arises that how the parboiling is to be done if husk is used for generation. The solution to this is very simple. The heat of the exhaust gas from the power plant is enough to serve the purpose of parboiling. So actually we are increasing the total efficiency of the whole system.
In Figure 4.2 we also include a forecast by using mathematical calculation and simple interpolation techniques. With the help of advanced statistical methods considering various forecast techniques this approximation can be improved to a substantial amount.
4.2.2 Calculation of Probable Generation
From the previous section we have got an idea about the surplus husk amount in our country. By increasing boiler efficiency, the amount of surplus husk can be increased. Now probable generation from husk is calculated for a 500 KW power plant in the following table.
Table 4.1: Husk consumption of a 500 KW plant
|Milled paddy / gross paddy ratio||%||70|
|Rice husk / milled paddy ratio||%||20|
|Husk for parboiling / total husk ratio||%||67|
|Husk consumption||Kg / KWh||2|
|Operating time||Hours / year||6000|
|Total Husk consumption||tons / year||6000|
Considering the above data and the amount of surplus rice husk in the year 2003-04, we mention here the calculation of the total generation possible in the following table as a sample to give the reader an idea of the process followed later.
Table 4.2: Total potential generation of power from rice husk (2003-04)
|Total Husk consumption for per KW||tons / year||12|
|Available total rice husk
(using data from Table A in appendix )
|Million tons / year||5.473|
|Husk for parboiling (usable)||Million tons / year||3.667|
|Probable generation of power||MW||305.583|
|Possible no of 500 KW plant||units||610|
Based on the above calculation we show here a graph in Fig 4.2 of probable power generation from the year 2000 to until now along with the estimation till 2014.
Figure 4.3: Generation of Power in present & improved condition (inc. approximation)
In Fig 4.2 we see two graphs where first one is showing the probable generation of power in the prevailing condition in Bangladesh indicated by the blue line. Now we already mentioned that 70% of total paddy is taken to the mills (30% is processed in the households) and we considered only 67% of the total husk for use in power generation. If the amount of milled paddy can be increased to 80% and by using improved techniques boiler efficiency can be increased to use 75% of the total husk can be utilized, then we would be able to increase the amount of total generation by 28% and in the improved condition the generation is shown by the red line Fig 4.3. In both cases of present and improved condition we show here the estimation till 2014. For the data of the figures the reader is referred to the Table B.3 in appendix.
4.2.3 Electrical Load in Rice Mills
Rice mills can use their own husk to generate power if they can afford to build a small power plant within their capability. Before establishing cogeneration plants with the rice mills a study is necessary to be made on the electrical loads. The load drawn by the mills is dissipated in different segments like parboiling, drying, milling etc.
Electrical Load for Parboiling
Most of the rice mills have no electrical load for parboiling except the lighting load. However, in some rice mills Naogaon and Bogra cluster, mechanical blowers are used for rice husk fuel feeding. The motor capacity of the fuel feeding system ranged from 0.746 to 1.5 KW .
Electrical Load for Drying System
The average electrical load for mechanical drying of paddy varies from 22KW to 40 KW and it is mostly required by a LSU type dryer .
Electrical Load for Milling System
The modern rice mills consume more electrical energy, therefore, the electrical load for modern machines is high and it is ranged from 55 KW to 250 KW, whereas, in engleberg rice mills the electrical load varied from 20 to 50 KW .
Electrical Load for Lighting and other Purposes
The highest electrical energy used for lighting and other purposes is about 10 KW in the automatic rice mills in the Dinajpur cluster. The most of rice mills use less than 1.0 KW electrical load for these purposes .
4.2.4 A Study on Power source in Rice Mills
Source of Grid
At present the rice mills are receiving power from two sources mainly-
Bangladesh Power Development board (PDB)
Bangladesh Rural electrification Board (REB)
For example, 100% of the rice mills in bogra and Nawabgonj clusters utilize PDB source whereas Naogaon, Dinajpur, Ishwardi clusters use both PDB and REB sources at the range of about 40% to 60% respectively.
The connected load distribution of Rajshahi division’s major rice mill clusters has been studied by Ahiduzzaman, Baqui, Mahmud, Khair during a project work accomplished under GTZ. The report says that 20 to 30 KW load is connected to 35%, 98/5 and 79% of rice mills of Dinajpur, Naogaon and Bogra cluster . Hpwever, 85% of rice mills of Ishwardi cluster use 31to 50 KW and 101-150 KW is used at 58% of rice mills at Nawabgonj clusters. In Fig 4.4 we show the comparative analysis of the five districts in the graph. The corresponding data used is included in Table A.5 in appendix.
Emergency Power System
The report says that emergency generator was found in 12 automatic rice mills. The capacity of the generator varied from 130 KVA to
Figure 4.4: Distribution of connected load from national grid at Dinajpur, Naogaon, Bogra,
Nawabganj, Ishwardi Cluster
460 KVA. The diesel consumption of the generator varied from 600 litre/month to 24480 litre/month. The average diesel consumption of these generators is 6437 litre/month. There are some small generators ranging from 2 KW to 12 KW for emergency lighting purposes .
4.3 Feasibility Study of Locations in Bangladesh
Bangladesh is an agricultural country with a lot of potential for establishing rice husk base cogeneration plant. Before setting up plants, a number of things have to be considered. In spite of having huge number of rice mills and surplus rice husk, there are some constraints for choosing a proper location. Also Bangladesh Govt. has a policy for setting up a new power plant.
4.3.1 Considerations made for a Power Plant
The construction of a major new power plant takes typically about 5/6 years from the decision to build the station to the commissioning of the first unit. So, planning, study and investigations must be made 7/8 years prior to start a new plant . There are many factors essential to consider while constructing a new power plant. Such as: capacity considerations, economic considerations, future requirement predictions etc.
Forecasting and Determination of Required Capacity
Forecasting is to be made about the demand of electric power in the near future. It is necessitated that a proper forecasting should be made as it is required that the power station is equipped with a considerable extent of generation capacity. This is usually tackled by the concerned authority of the Government of the country. The forecasting comprises of different types of data handling .
As example, peak demand of local consumers, peak demands of heavy, medium and small industries, peak demand in winter and summer, demand in daytime or nighttime etc. By virtue of these forecasted data, the required capacity of the generating plant is estimated and it is the first step of planning .
Detailed Site Investigation
Before detailed site investigations are started, the bodies previously consulted have to be notified; the owners and occupiers are to be approached and the announcements are to be made in national and local newspapers. It can take over two years to carry out the necessary detailed studies to prove the viability and determine the optimum capacity of each of the alternative sites being considered . During this period, consultations must take place with the authorities concerned with planning, environmental protection, transport, water supply, flood protection, fisheries, safety and other relevant subjects.
Preliminary station layout
Preliminary layout design includes the disposition of major plant or group of plants in the main station buildings, leading to the determination of the shape and size of the buildings, and external plant items to produce a coordinated system design which achieves the lowest capital cost, ease of construction and efficient operation and maintenance of power station . The preliminary layout enables the on-site geological works to proceed and assessments to be carried out on the proposed site level, disposition of construction contractors’ plant and storage areas and environmental aspects.
Authority to build a new power station
· Each system planning study is begun with the two following studies:
· Examination of system load flow
· Identification of future generation and transmission needs.
The facility and capacity of the existing plants are studied, any scope for further improvement is found out. Along with this, the feasibility for the new sites under consideration is studied. Site environment, technical factors, capital cost and other costs are estimated. Finally, a selection of sites is arranged according to the choice of preference. And the way of detailed siting studies is paved .
After the aforementioned steps, a formal application is sent to the government to sanction the necessary requirements for the power station. In the course of bureaucratic communication different local authorities are also consulted. Local authorities like water supply authority, environment and safety department etc are consulted in this regard. The station development particulars also contain a technical section dealing with transmission connection and parameters of the main plant, particularly the generator transformer, so that they are properly matched to the transmission system. The details cover matters such as power factor, synchronous impedance, frequency regulation, the dynamic response of unit to change in load demand and guidelines on the electrical auxiliary system to ensure a reliable network.
4.3.2 Constraints and Problems in Selection of Location
The common problems faced by the investors in the selection of a particular location for power plant are as follows-
Lack of Fuel Availability
· A location might have all the necessary qualities, but it may suffer from the problem of lack of fuel availability due to some reasons:
· Paddy is a seasonal product. So during the remaining seasons of the year, the supply of rice husk may be low
· Due to change in climatic condition or natural disasters the areas around the plant location may not be able to grow enough paddy in a particular season or all the crops may be washed away. As a result that site would suffer for want of fuel.
Poor Environmental Management
In Bangladesh, the environmental management is actually very poor all over the country. For this reason, in spite of a having all the qualities a location may not be suitable for a power plant. If the site is very densely populated, then safety considerations become an important issue. Also if the flue gas and ash disposal system is not well enough, it might cause troubles to environment and hence the local people.
Too many Plants in the same area
We already mentioned that the rice mills are situated in a cluster throughout the country. That means in a particular location we will find too many mills. Now if we set up a number of plants in the same area, then it may be rather harmful as the pollution made by all of them would create a mess for that location and it would be unlivable for the local habitats. In this case proper planning is necessary before setting up plants.
4.3.3 Govt. Policy in Bangladesh
At present, the major barrier is the absence of energy policy and institutional framework strong enough to promote the exploitation and use of renewable energy, especially for power generation in the areas where the rural electrification and grid connection is least-cost. Lack of financial mechanism for establishing and operating the trading enterprises on renewable energy, for instance, technology market, investment, policy on credit and loan has negatively affected and restricted the renewable energy development in Bangladesh for years.
There exist some policies, which have positive effects on promoting the development and application of renewable energy technologies in Bangladesh. Being market oriented, the policy on rural electrification will be a good base encouraging the investors in development of renewable electricity in order to meet the onsite energy requirements (own use) or providing to the grid through private utilities, cooperatives or other owners. These units will invest in small power stations. Recently, the diverse modes of investment have brought in the encouraging effects.
The financial policies of the GOB for Private Power Organizations at present are as follows-
· BOO projects may involve limited recourse financing and the funds for the projects will be raised without any direct sovereign guarantee of repayment. Instead, the investors and lenders to the project sponsors must look to the revenues earned by the sale of electricity for their returns on equity and debt servicing.
· Minimum requirement for equity investment will be 20 percent.
· The Government of Bangladesh may establish a Private Sector Infrastructure Development Fund (PSIDF), with the assistance of World Bank and or other aid agencies, which may provide part of the capital cost of the project as subordinated debt. The debt would be available on market based interest rates and carry extended maturity periods.
The fiscal policy and incentives offered by the GOB is described here-
· The private power companies shall be exempt from corporate income tax for a period of 15 years.
· The companies will be allowed to import plant and equipment spare parts upto a maximum of ten percent (10%) of the original value of total plant equipment within a period of twelve (12) years of Commercial Operation without payment of customs duties, VAT(Value Added Tax) and any other surcharges as well as import permit fee except for indigenously produced equipment manufactured according to international standards.
· Repatriation of equity along with dividends will be allowed freely.
· Exemption from income tax in Bangladesh for foreign lenders to such companies.
4.4 Financial Analysis
For the sake of the study of feasibility of any project, appropriate financial analysis is a must, because if the project is not financially feasible on the first place for the investors or the Govt. then it should not be tried. Here we are going to try to show a model financial analysis based on the statistics of the costs incurred by the other countries around the world and the factors on which this analysis depends on in brief and try to estimate whether this could be viable for our country or not.
General Techno-economic Assumptions
Cogeneration plant consists of a rice husk storehouse, conveying and automatic boiler feeding system, a furnace/boiler producing 9 tons of steam per hour at 32-bar pressure (Institute of Energy, Viet Nam). The boiler is equipped with automatic ash removal system, heat exchangers and turbo-generator of 0.5 MW (Institute of Energy, Viet Nam). The turbine used here is a backpressure. Rice mill will operate 6000 hours annually. The milling period will be longer than usual due to the installation of power station, which will operate for the same period of time.
The following economic parameters should be taken into account in the analysis.
Rice husk disposal cost saving:
It consists of savings from not having to dispose rice husk, as it will be used for power generation for the whole year. Since the power plant and rice mill will run simultaneously, rice husk does not need to be stored, except for very short periods of time (Institute of Energy, Viet Nam). This will lead to lessening rice husk storage and handling costs.
Electricity cost savings:
It is gained due to
- Not using mined coal for paddy drying
- Not purchasing grid electricity during the milling season.
Surplus power sale revenue from the auto produced electricity in excess of the mill requirement and the excess amount is sold to the power grid or neighboring consumers.
Surplus thermal sale:
This revenue from the auto produced thermal energy in excess of the requirement for paddy drying and the excess amount is used to dry for other mills around the area.
Ash is a by-product from rice husk combustion in the boiler. At present, European boiler manufacturers are able to develop incineration systems to produce rice husk ash of consistent quality . Rice husk of such quality can be considered as a valuable additional material in some industries such as glass and brick manufacturing, in the steel industry and more recently, in semi-conductor industry. Thus, investment in equipment, which could produce good quality ash, will increase the additional revenue for end-users through the sale of ash. Whenever the equipment can produce ash of good quality, the additional income from ash sale is possible. This attractiveness, therefore, should be taken into account in the evaluation. It is assumed that the above revenues will be generated only from the second year and the first year is the construction period .
Capital investment cost<href=”#_ftn1″ name=”_ftnref1″ title=”">
Based on statistical data collected by PREGA National Technical Experts from Institute of Energy, Viet Nam, an equipment unit cost of 1570 US$/KW is used for the rice husk-fired power plant. This cost consists of investment cost of a boiler, a turbo-generator and other costs. Civil works and equipment import duties are also considered when analyzing. Annual operating costs of the cogeneration plant consist of maintenance costs and labor costs. In this study, the production should not only cover the need of rice mill itself (paddy drying and cooling cells for rice storage) but it also should meet the other electricity requirement of the mill and administrative buildings.
A Study of cost
At this point here we include a tentative analysis of cost that may be incurred if this kind of power plant is ventured.
Table 4.3: Estimation of cost for a husk base power plant
Equipment unit cost
Other costs (transmission etc)
Annual maintenance cost
Other annual operating costs
% of equipment cost
4.5 Economic Analysis
In this section we focus on the factors on which a rice husk cogeneration project’s
Economical feasibility depends. Expenditure flow and income flow from a plant is also
Described in brief.
Poverty Alleviation Effect
The economic features bringing in the social profit like labor involvement, job opportunity creation and other benefits gained by the various sectors from the project will contribute in increasing the economy and create good conditions for agricultural and rural development towards direction of modernization and industrialization. Realization of this project will promote the development of rice industry with a competitive advantage through reducing the post-harvest losses and improving quality of goods, mainly rice for export .
Expenditure Flow and Income Flow
Economic Analysis is aimed to evaluate feasibility of the project to national economy, to calculate and compare economic indicators for selecting solution and the best way of implementation.
Economic analysis is to analyze social efficiency of the project to national economy. Economic indicators bring social benefits such as creating new jobs, making the development of other economic sectors, contributing to development of country. Therefore, it is necessary to consider social- economic benefits when defining economic electricity selling price and reduce labor cost and taxes in initial investment cost.
Economic analysis also considers costs of damages by project impacts to other sectors, to environment and to national economy. Contents in economic analysis include cash flow table and economic indicators with each of technology and construction plans .
Investment costs in economic analysis: This is investment cost without labor costs and taxes (benefits for society, brought jobs for society). This eliminated potion is estimated of about 10% of total investment cost of the project .
Operation and maintenance cost (O&M cost) and other costs as in financial analysis.
Turnover from electricity sales
Turnover from thermal energy sales (using for drying rice for other customers around plant area)
Turnover from selling ash
Other benefits gained from the project: reduction of negative impacts on economy, environmental protection, benefits from not purchasing coal for drying rice.
4.6 Environmental Assessment
The environmental profile of the energy production must be assessed to ensure reduced environmental damage. So the raw materials consumed and environmental emissions of energy production from rice husk have to be determined.
4.6.1 Material Balance and Energy Balance
According to the conservation law, matter and energy cannot be created or destroyed . Hence, material/energy inputs must be equal to material/energy outputs. The balances are listed from material flow and energy flow. For example we give here a classic example of the material and Energy Balance by the following flow charts 
Figure 4.5: Material balance of rice husk energy production
Figure 4.6: Energy balance of rice husk energy production
The calculation of material balance is represented by Eq. (1) and Eq. (2), and energy balance is Eq. (3) .
MRH + MA = MFA + MBA + MFG, (4.1)
MRW = MWE + MWD, (4.2)
ERH = EFA + EBA + EFG + EWE + EWD + ER&Ub + EST + EElec (4.3)
MRH = Mass flow rate of rice husk, MA = Mass flow rate of air inlet
MFA = Mass flow rate of fly ash MBA = Mass flow rate of bottom ash
MRW = Mass flow rate of raw water MWE = Mass flow rate of water evaporation
MWD = Mass flow rate of water discharge ERH = Energy in rice husk
EFA = Energy in fly ash EBA = Energy in fly ash
EFG = Energy in flue gas EWE = Energy in water evaporation
EWD = Energy in water discharge EST = Loss at steam turbine
EElec = Electricity
ER&Ub = Radiation and unaccounted loss at boiler
The difference in material input and output works out to 3.58 ton/h, which is about 4.4 % of the total material input. This may be due to averaging of measurement. The difference in water and steam input and output is 0.04 ton/hr or 0.68% . From Fig. 2, the difference in input and output energy is about 6.06 % which may be due to loss in pipes and tubes.
4.6.2 GHG Emission and Other Pollutions
The emission of CO2 from combustion of rice husk are considered zero since they do not contribute to global warming. CO and dust emissions are slightly higher than conventional power production pointing to need for improving the combustion efficiency of the rice husk power plant.
Here we give a classic example of the amount of emission of gas from a rice husk power plant in Thailand, an agricultural country like Bangladesh.
Table 4.4: Land Estimation Data from the Study Site 
|Fly Ash||1560 kg/h||1560|
|Bottom Ash||323 kg/h||323|
The value of SOx is not measured as the sulphur contebt in rice husk is very small.
The expected impacts of the power plant are as follows:
Bran dusts are emitted during operation of rice mill. In this case, the mill will be located in a convenient place, far from the center of inhabitants.
Additionally, surrounding the mill, the trees have to be planted for collecting dust. Inside the mill, vacuum cleaners and draft fans must be installed to improve the air in working area.
The mill and polishing machine should be located far from the road and inhabitant center so that the noise does not disturb the people living in surrounding.
The issue of resettlement is not impacted.
4.6.3 Water Environment
Water slurry is used to take the ash from the power plant to the ash pond for disposal. The water may contain harmful heavy metals like boron, which have a tendency to leach out over a period of time. Due to this the ground water gets polluted and becomes unsuitable for domestic use. The second factor affecting the water environment is the release of ash pond decant into the local water bodies. This is harmful to the fisheries and other aquatic biota in the water body .
4.6.4 Impact Assessment
Based on the emission data and the priorities in the country, the environmental impact categories selected for this study are global warming, acidification, photo-oxidant formation, nutrient enrichment and solid waste. To assess the environmental impact potential by LCA methodology all emissions have to be calculated by Eq. (4.4) 
Where EP(j)i is the emission’s potential contribution to the environmental impact category (j), Qi is the magnitude of emission of substance (i) and EF(j) is the substance’s equivalency factor for the environmental impact category (j).
In Table 4.4, a comparison of environmental impact potentials between rice husk power plant and Thailand’s fossil fuels power plants is shown for example
Table 4.5: Environmental Impact Potential from Rice Husk & Fossil Fuels Power Production 
|Impact Category||Rice Husk||Fossil Fuels|
(kg CO2 – eq/MWh)
(kg SO2 – eq/MWh)
(kg C2H4– eq/MWh)
(kg N– eq/MWh)
(kg ash– eq/MWh)
The impact assessment results show that the impact of global warming potential of rice husk energy is far less than fossil fuels plants because CO2 from biomass is considered as Green house gas neutral. Sulphur and nitrogen contents in rice husk are small. In addition, the combustion temperature of rice husk is lower than 900°C, preventing the formation of thermal NOx. Hence, acidification and neutralization potential of rice husk energy are lesser than fossil fuels plants even though fossil fuels plants have NOX and SOX removal equipment installed .
Photo-oxidant formation is from CO emissions of rice husk which are higher than fossil fuels plants. This may be due to the low combustion efficiency of the rice husk power plant and moisture content in rice husk.
For solid waste potential only the data from rice husk power plant is available. Hence the comparison cannot be made. The results present that most environmental impacts potentials from rice husk are lesser than the fossil fuels plants.
4.7 Benefits of Rice Husk Co-Generation Plant
Now-a-days scarcity of electricity is probably the most burning issue in the overall economy of our country. To solve this problem, rice husk cogeneration plants can be of great help to us. Though it is still a new technology it has already been proven to have certain benefits.
(i) Introduction of New Electricity Generation Technology
Power generation using rice husk as the fuel is a very new technology. Only a very few number of countries in the world are effectively using this technology to produce power. Researchers are still going on in this regard. For developing and underdeveloped countries this technology can be a boon as most of these countries economy are basically dependent on agriculture. Paddy is grown all over the world and Bangladesh. So there is a good amount of rice husk left unused. Establishment of rice husk cogeneration plants will ensure the proper use of this unused or nor properly used rice husk and thus increase the efficiency.
(ii) Meeting the Present Energy Demand Challenge
The huge shortage of electricity is hurting Bangladesh quite hard in each and every development sector. At present electricity coverage in Bangladesh is only 42% and per capita electricity consumption is about 140 kWh which is one of the lowest in the World . Our main objectives should be to bring the entire country under electricity under 2020, making the power sector financially viable, increase the sector’s efficiency and improve the reliability and quality of electricity supply. Establishment of rice husk cogeneration plants in our country can help to minimize the amount of demand to a certain amount by supplying electricity in a number of sites throughout the country.
(iii) Direct Employment Generation
Unemployment problem is a very severe problem in our country. A large percentage of skilled and unskilled people are unemployed here. This huge manpower can be used in the establishment and operation of rice husk cogeneration plants.
During the establishment of a plant, a large number of workers would be needed which will create job opportunities for local labors.
For the continuous and safe operation a number of permanent engineers, workers and labors are must.
(iv) Supply Electricity and Thermal Energy for Own use of Rice Mill
It is estimated that there are about 25,600 rice mills in Bangladesh . At practical situation this figure would be more because a huge number of rice mills have not been count in the in the list prepared by Directorate of Food, Bangladesh.
In large automatic rice mills, pure husk and pure bran are produced separately. The husk is used as the source of thermal energy needed both for parboiling and drying. The average production of pure rice husk is about 206 kg per ton of paddy in automatic rice mills. The average consumption of rice husk for parboiling and drying are 92.7 kg and 100 kg per ton, respectively . The rest amount of rice husk can be used by the mills themselves to generate power.
(v) Creating New Options for Local IPPs
There are a number of IPPs in Bangladesh. Most of them are gas based power plant, rest are steam, combined cycle, diesel plants. Rice husk can be a new source of fuel for the progressive IPPs now. As a fuel rice husk is very cheap now and amount of surplus rice husk is increasing day by day. So it is now a new option for the IPPs to go for the option of rice husk.
Mills and factories in the vicinity of rice mills can also set up small plants to generate power and operate independently using the surplus rice husk and thus save their electricity bills.
(vi) Socio-Economic Benefits
The cogeneration plant enables the operation of the rice mill at its peak capacity. The competitive advantage of the plant is definitely enhanced as it gets reliable and steady power and steam supply from the cogeneration plant. With the latter, the management can solve the rice husk disposal problem. Moreover, it replaces the current supply of electricity from the grid and current supply of steam using diesel-fired boilers.
(vii) Overall Effectiveness
In Bangladesh, gas is the main source of power. Gas is also used in various mills and industries. But it is a matter of great concern that due to its bulk use in power generation, its amount and reserve is decreasing at a very high rate. So we have to search for other sources of power immediately. Rice husk is a probable solution to this problem. Though the amount of rice husk is not the same all the year round, by using dual-fuel technology we might be able to meet a good portion of the demand.
(viii) Scope of Future Development
As this is a new technology, it is actually still in the research stage in many countries of the world. The developed countries are searching for new options and technologies to incorporate with a husk based cogeneration system. So invention of new techniques and methodologies is eminent in this regard and thus the efficiency of this system can be expected to increase a lot.
In our country, already ‘Dream Power’ is in operation. If new husk based plants are set up here, they can be benefited by studying the techniques incorporated by Dream Power, their fields of success and problems thoroughly.
4.8 Problems behind the Scenario
We have to deal with some practical problems while establishing a rice husk cogeneration plant. Now these problems might become severe if we don’t have proper idea about them. In this section we are going to discuss the problems behind the scenario.
(i) Increase in cost of Rice Husk
Rice husk is actually the main fuel in a husk cogeneration plant. In an agricultural country like Bangladesh, paddy grows in plenty. As a result at present rice husk is available at a very cheap rate.
Another reason behind the present cheap rate is that now we don’t use husk appropriately and the most of it is left as the cattle food without any proper treatment. But if rice husk cogeneration plants are established, then there will be a high competition in the market and then the price of husk will surely go up. Now if the price goes up beyond limit, it would be a serious problem for the investors.
(ii) Possibility of Artificial Crisis of Husk during Peak Time of Year
In Bangladesh, it is a common practice to create artificial crisis of goods or services during the period when people need it most. This is done by some corrupted but powerful businessmen throughout the country. If rice husk is used as the fuel for plants, then the price of it will grow up. So the above mentioned corrupted group might use rice husk as a weapon to earn an extra amount. They might buy the entire husk from the market to create an apparent scarcity of husk and thus force the investors to buy at a very high rate from them.
(iii) Problems for Poultry & Pet Feeding
At present, Rice husk is an inexpensive byproduct of human food processing, serving as a source of fiber that is considered a filler ingredient in cheap pet foods. But if we start using as a fuel for power generation plant, apparent raise in its price will force the poor farmers to leave it as pet food and sell all the extra husk that they could effort previously for their pets. They would have to look for other options for other expensive poultry & pet feeding. As a result the cost incurred by this poor group of the society increases which in turns make them poorer.
(iv) Problems for Briquette Production
At present briquette production is the most important use of rice husk as 20% of it goes to briquette production. The main reason for this is that firewood has been reducing alarmingly and briquette is smokeless and provides higher temperature more quickly than that of coal and wood . Also a good number of people is engaged with the job of briquette production. So we will face mainly two problems in this side.
The use of briquette as a source of energy may decrease a lot with the increase in the bulk use of husk in plants.
If the briquette production company incurs loss for this reason, surely there will be a number of lay-offs which will increase the unemployment problem.
(v) Electrical Problems
In every type of Power Plants a number of Electrical problems have been observed. Rice Husk Cogeneration Plant is not an exception. In such a plant we naturally see load variation problem. As mentioned above, the electrical load is different for parboiling system, drying system, milling system, lighting and other purposes . So it is likely that the demand varies from time to time during different hours of the day. As a result, there could be problems during the switching of loads and the frequency might vary causing electrical problems.
(vi) Meeting the Set up Cost and Running Cost
From real life examples we have observed that the set up cost of any kind of power plant is huge. To meet the demand of the whole country we still need several thousands of MW power plants. But the main hindrance in the way of this is that it needs a large sum of money that our Govt. cannot afford. In case of rice husk cogenerating plants also, the set up cost is very high. So it would not be easy for us to carry the expenditure of the set up cost and running cost of this kind of plants.
In the previous chapter we saw that Bangladesh could be potentially benefited if rice husk cogeneration plants are set up in our country. But it is not an easy job to say the least. To manipulate the condition in our favor, the Govt. of Bangladesh needs to take some strong measures.
In this chapter, we have tried to recommend a number of necessary steps that could help the Govt. to take the right decision at the right time. We mentioned a suitable procedure of generation and suggested the probable location of power stations. We also mentioned the restrictions that should be followed about the user groups to utilize the power without any hazard. Finally we pointed out a list of must-do steps to encourage the investors that should be undertaken by the Govt.
5.2 Site Recommendation
Power plant location is probably the first consideration that should be made and it should fulfill some requirements. Rice husk availability is the main criteria for these types of power plant. Then size of power plant and process for power generation should be kept in mind.
Surveying the whole country was not possible in this level of thesis. So we have used a smart trick to solve the problem. It is well known that Rajshahi division provides a major part of total national production and so we used data of the 5 main districts of Rajshahi division which are popular for rice production . Sufficient analyses about those clusters are provided in chapter two.
According to Figure 2.4 we see that Dinajpur district provides the most rice husk after considering parboiling and drying process consumption. Naogaon is in second position. So after the analysis we see that Dinajpur and Naogaon lead the total production of our country. Now let us concentrate on the locations for our recommended power plants.
Rice mills in Dinajpur district are separated in two different clusters. Pulhat cluster consists 300 rice mills and another one consists only 50 rice mills. It should be noted that rice mills of Pulhat cluster are within a circle of 2km radius. So Pulhat is the most suitable place for rice husk based power plants.
On the hand there are about 775 rice mills in Naogaon district which are situated in three different clusters named as Naogaon sadar, Mahadebpur and Raninagar. Following the same methodology, we can say that in about all the rich production zone of rice husk base cogeneration plants can be set up depending on the other conditions that were mentioned in section 3.1 and section 4.2.
5.3 User Group and Connection System
The power generation capability of a husk cogeneration plant varies a lot depending on its size. For our country, the standard for generation may be between 200-500 KW. We should keep in mind that the cost increases a lot for a very big power plant and along with it increases the need for fuel. If a very large power plant is set up without considering whether it can be provided with the sufficient amount of fuel throughout the year, then it will be a new burden to us. In fact, all around the world, the number of small rice husk plants are a lot more than those producing more than 2 to 3 MW.
Now as the expected size and capability of a power plant is smaller, its user group should be small as well. If the user group is large in number, then the power plant cannot operate on full load and thus will not be able to fulfill the requirements. As already mentioned, the only husk based power plant in Bangladesh, ‘Dreams Power Private Ltd.’ has been assigned to carry a load of a whole union of a district of about 12000 people, it is not operating satisfactorily causing a lot of troubles.
That is why we recommend here to the Govt. to keep the facility of this power plant confined to a small group. In this case, if the plant is cogeneration based set up beside an automatic rice mill, and then the mill labors, staffs, mills’ internal demand and a small group of selected users should be the users of the power produced. Also if the plant is produced by a IPP or some other organization, then they should sell this power to the local factories or a local hospital or a manufacturer company, not a whole village or union. If this restriction is maintained then power supply would be smooth to the customers.
As the amount of production of husk varies a lot in different seasons of the year, we can not expect to get sufficient amount of husk all the year round. Also the husk production can be hampered by natural calamities and disasters and its supply may be reduced by a big margin. If the plant goes out of operation at that time, then the customers will suffer a lot as a result.
That is why we recommend grid connected system. This system allows the customer to feed its own load utilizing the available energy from the cogeneration plant and the surplus energy can be injected into the grid under the energy buy-back scheme to reduce the payback period. Grid connected system can become a part of the utility system. The contribution of husk bas system depends on the size of the system and the load curve of the house. When this system is integrated with the utility grid, a two way power flow is established. The utility will absorb the excess power from the plant and will feed the house of the customers at instants when the power from the plant is inadequate.
5.4 Suggested Power generation Process
Biomass gasification is viewed today as an alternative to conventional fuel. Biomass gasification is the process of converting solid fuels (rice husk, wood/ wood-waste, agricultural residues etc.) into a combustible gas mixture usually called the “Producer Gas” i.e. biomass materials are gasified to produce “Producer Gas”. The technology can be used for both thermal applications and power generation.
It ensures efficient usage of traditional biomass products by converting it into a high quality, combustible gaseous fuel. We can reduce the parboiling husk consumption by using this technology. Biomass gasification technology is environment friendly which significantly reduces environmental pollution caused by traditional usage of biomass products. Reasonable cost of energy/ power production to operate as a commercially viable entity. Rice husk based power plants are two types, one is 100% gas based system and second one is duel-fuel system. Initial investment of 100% gas based system is slightly higher than dual-fuel system. According to our technological limitation and scarcity of well trained persons dual-fuel system is preferable for our country.
|W: Water Scrubber C: Coarse filter P: Passive filter S: Safety filter R: Reservoir F: 4-way connector V: Valve|
Figure 5.1: Recommended Technology for Power generation
Now we can focus on types of gasifier. The gasifier is essentially a chemical reactor where various complex physical and chemical processes take place i.e. drying of fuel, pyrolysis, combustion and reduction. There are mainly two types of gasifier:
In updraft technology, the produced gas is drawn from the top of the gasifier while in down draft technology; the gas is drawn from the bottom of the gasifier. The gasifier is separated in two part hopper and reactor. The tar production is the minimum in the fluidized process which eases its disposal and increases the life of the engine. Fluidized based gasifier provides high gasification efficiency, clean biomass gas with higher energy value and low fuel consumption. So fluidized-gasifiers are suitable for our country. The principle is simple. The rice husk is gasified in a fluidized-bed reactor to yield “Producer Gas”, which comprises primarily of a mix of combustible gases – Carbon Monoxide (CO), Hydrogen (H2) and Methane (CH4).
Biomass Enrichment System
The combustible are cleaned, cooled, filtered to store in a buffer gas reservoir, from where it is fed to Producer Gas Engines. This process is known as biomass enrichment system. Water Scrubber type (WS) system and Zeolite Molecular Sieves (ZMS) type systems are two popular enrichment systems. In WS system, water & gas scrub against each other in opposite direction at moderate pressure. Impurities of H2S & CO2 are dissolved in water during the scrubbing process. 90% content of CH4 achieved through water scrubbing and balance CO2. It is a low investment, low power consumption & low maintenance system. It is user friendly & ideal for use in rural areas. In ZMS impurities of H2S & CO2 are adsorbed & vented. 95 – 97% content of CH4 are assured with balanced quantity of CO2. In this process no water are required and power consumption is negligible. PLC based semi-automatic operations system can be involved. In Figure 5.3 W is a water scrubber biomass enrichment system which is selected for its low technology requirement
Pressure and Flow Control system
Clean and wet gases are collected by a blower to store in a reservoir (R). The reservoir is connected to a 4-way connector (F). Water can be extracted by blower to clean the reservoir. In this step solid particles are totally separated and gases are sent to purification unit. Pressure and flow of gases are controlled and monitored in this system.
Gas purification system
Gas cleaning and cooling system is less complicated in downdraft gasification system. Three types of filters are used for gas purification system. These types of filters are selected for low cost materials and availability of materials. Coarse filter (C) is the first step of purification system. Rice husk char are used as filter element in this filter. Only one coarse filter is enough for medium size power plant. Water level indicator and pressure gauge are used to monitor water level and pressure. Rice husk char are replaced weekly for better performance. Fine filters (P) are the second stage of gas purification system. It is also known as passive filter. A series of passive filters are used to improve gas quality. In fine filters sawdust is used as filter element to trap all the particulate and ash particles. This kind of gas purification system is recommended for its low cost and less effort of operation. Safety filter (S) is the third stage of the system. A special kind of fabric (rated for 5 micron particulate size) is used as filter element in this filter. Pressure and flow are monitored in this step. An emergency exhaust bypass is employed for safety in this step.
In this type of rice husk based power plant, to run the generator certain amount of diesel is required. Because, the producer gas has relatively lower heating value and needs to be supplemented by diesel to get the necessary power output. That’s why the IC engine will have to be converted into duel fuel mode, i.e. it can run both on producer gas and diesel. Using this technology Producer gas to diesel ratio is. 70:30. During start up of this type of plant, main generator is started first on diesel and then changed over to duel fuel mode when the producer gas is available for charging to the engine. Valves (V) are used to select the generator which one will be used. This is conducted from a generator selection panel.
The described method is highly suitable for our country. In this process we get rice husk ash as waste which can be used for silica production. So silica would be a byproduct of the system. Silica precipitation technique is described in the following section.
5.5 Suggestions to Solve the Underlying Problems
To solve the above mentioned problems, we hereby include some suggestions that we believed to be helpful in this regard.
(i) Assuring Stability of Cost of Rice Husk
Cost of Rice Husk is an important issue for plant set up. The Govt. and the people concerned should be careful of this fact. There should be a monitoring committee which might work to ensure that the market price of the husk is stable. In reality, it is sure that the price is to go up if bulk portion of husk is used as fuel, but the committee has to make sure that it is not over the limit or beyond the scope of the budget for fuel cost of the investors. This cannot be accomplished single handed by the Govt. only, public concern is also very important in this regard.
(ii) Govt. Intervention to Stop Artificial Crisis of Husk
To prevent the activities of corrupt groups, the investors and the Govt. should keep a close eye on the market. The monitoring committee should always keep an eye on the listed businessmen. People should be made aware about the market policy of the Govt. about the buying and selling of rice husk very clearly. We should also make sure that no single person or business organization is buying out a lot of husk without selling them. The punishment for breaking the rule should be exemplary.
(iii) Control over Poultry Food Price
With the increasing use of husk as fuel, less portion of it will be used as the poultry or pet food. So the farmers will have to look for other food options. Now there is a possibility that poultry and pet food manufacturers may try to manipulate this condition by increasing the price of their products. To prevent this, the Govt. has to take strong measures and the monitoring committee has to also provide a section of its work force in this regard.
(iv) Recruiting Briquette Production Workers in Power Plants
Increase of the use of husk as a fuel in cogeneration plants will hamper the briquette production industry. As a result, a number of workers in these industries is likely to lose job opportunity. To fight this problem, we might use this work force in the husk base cogeneration plants. As this power plant will need skilled and unskilled labor force for continuous and safe operation, it should not be much of a problem to recruit them.
(v) Use of Technology to solve Electrical Problems
To solve the electrical problems like switching load or load variation problems, recent developed technologies have to be used. In recent times, for the safe operation of a power plant, it has to maintain so many rules and regulations. The engineers and workers engaged with the load management system in the plant should have appropriate knowledge of these regulations for the safe operation. To prevent electrical hazard, the use of recent technologies is a must and also continuous monitoring of the total technological operation has to be ensured by the investors.
(vi) Financial Help from Govt. and Welfare Organizations
To establish and run a rice husk cogeneration plant an investor group needs a lot of liquid cash. Apart from the huge set up cost, there are other costs like land acquisition cost, labor cost, fixed deposit cost, insurance cost, equipments cost etc. So it might be hard for a single company or individual to carry the expense single handed. That is why help from the Govt. and other organizations like the World Bank, IDCOL, IMF etc is necessary. In this regard, the loan terms should be easy for the entrepreneurs to carry the load.
5.6 Using Existing Power Plants
In a third world country like Bangladesh, bearing the cost of a number of fully new operating power plant will be a huge burden on the Govt. So if the existing power plants can be used in this regard, it would be really helpful to the Govt.
Among the existing power plants some are located near or in the rice production clusters already mentioned. Presently they are operated by other fuels. But if they could be operated also using the husk as fuel too, then the total contribution of them would increase. In this regard, the Govt. should make surveys and search for newer improved technologies that can be used fruitfully to make this a success.
There are two advantages of using the existing power plants. They are:
Increase of Efficiency
· Use of this scheme is going to increase the total efficiency of the total system as the cost is not increased by much followed by a considerable increase in production of power.
· Saving Initial Cost of Power Plant
· This scheme would save the huge cost of setting up new power plant and also the running cost is saved as the number of workers needed in this case is not much.
5.7 Ash utilization
5.7.1 Chemical Composition of Rice Husk Ash.
Ash, the waste of power generation process, can be utilized by further processing. Rice husk has a high silica content varying from 18-20%. Silica is the major constituent of rice husk ash and the following table gives the chemical composition of rice husk ash. With such large silica content in the ash it becomes economical to extract silica from the ash, which has wide market and also takes care of ash disposal.
Table 5.1: Chemical composition of rice husk ash
|Element||Mass Fraction %|
|Titanium dioxide||Very low|
5.7.2 Uses of Silica
· Precipitated silica can be used in industrial purpose as like as follows,
· Rubber industry- as a reinforcing agent.
· Cosmetic industry
· Toothpaste industry- as cleaning agent.
· Food industry- as a anti caking agent.
· Semiconductor industry
5.7.3 Silica Precipitation Technology
The silica precipitation technology developed at CGPL, Indian Institute of Science, Bangalore is a novel method for silica precipitation where the chemicals used are regenerated making it a closed loop operation
The following gives the brief description of the process.
Digestion: This involves the digestion of the rice husk ash with caustic at specific conditions. In this process the silica in the ash is gets extracted with caustic to form sodium silicate solution. Then the solution is filtered for the residual undigested ash present in the solution. The clear filtrate is taken for precipitation.
SiO2 + 2NaOH = Na2SiO3 + H2O
Figure 5.2: Flowchart of Silica precipitation technology.
Precipitation: This step involves precipitation of silica from the sodium silicate solution. Carbon dioxide at a specific flow rate is passed through the silicate solution at design conditions. Continuous stirring is employed during the operation. The precipitated silica is filtered, washed with water to remove the soluble salts and dried. The filtrate containing sodium carbonate is taken for regeneration. The chemical reaction is
Na2SiO3 + CO2 = SiO2 + Na2CO3
Regeneration: Regeneration is the step where calcium compound reacts with the sodium carbonate to form calcium carbonate and sodium hydroxide. The resulting solution is filtered to remove the solid calcium carbonate and the aqueous sodium hydroxide is used for digestion again. The calcium carbonate is washed with water and dried. The dried calcium carbonate can be either processed to get calcium oxide, which is reused, for regeneration or the calcium carbonate is sold and fresh calcium hydroxide is used for regeneration which gives an option of one more value addition.
The chemical reaction is
Ca(OH)2 + NaCO3 = CaCO3 + NaOH
In this process NaOH is regenerated upto 90 % and CaCO3 is treated as a byproduct here. No regeneration of calcium carbonate is attempted here.
5.8 Govt. Steps to Encourage Local and Foreign Investors
(i) Change in Structure of Policy and Recognition
From our findings we can say that rice mill sector requires approval for reproduction of the new improved furnace system. It involves a complex structure of policy and regulation through several departments/players. Existing boilers related act is very old and not updated, despite the improvement in technologies and new requirements and standards . So we need a qualitative change in the structure of policy of the Govt. in this regard.
(ii) Growing the Attitude of Reformation
For any reformation or new invention the primary struggle is that there comes a psychological barrier to shift from conventional system to the improved system. A psychological perception on certain concepts of the conventional furnace may take time to change the users. The lack of awareness and low levels of education or technical knowledge is an added factor for shifting to new system . So we must grow an attitude for reformation for taking such huge decision.
(iii) Tangible Financial Arrangements
To facilitate the creature and encouragement of a corporate debt securities market essential for raising local financing for power development projects, the following provisions should be allowed:
· Permission to power generating companies to issue Corporate Bonds both bearer and registered with the consent of the Securities and Exchange Commission (SEC).
· Permission to issue shares at discounted prices upto the limit of 10% of the face value to enable venture capitalists to be provided higher rates of return proportionate to the risks.
· Permission to foreign banks to underwrite the issue of shares and bonds by the private power companies with recognition by SEC of such underwriting.
· Tax facilities for private sectors instruments as available to Non-Banking Financial Institutions.
· Modification of Prudential Regulations to allow 80:20 debt equity ratio, if necessary
(iv) Security Package
· Model Implementation Agreement (IA) Power Purchase Agreement (PPA) and Fuel Supply Agreement (FSA) must be prepared for private power projects to eliminate the need for protracted negotiations between GOB and sponsors.
· The Power Purchase Agreement (if executed by Government Agencies) should be guaranteed by GOB for performance obligations of the concerned utilities.
· In case the fuel is to be supplied by a public sector organization, the performance of the fuel supplier will be guaranteed by the GOB under the term of Fuel Supply Agreement.
For private sector project Government should provide:
· Standard protection against specific force major risk.
· Protection against changes in certain taxes and duties.
(v) Fiscal Incentives
· Power generation has already been declared as an industry and the companies are eligible for all other concessions which are available for industrial projects.
· The companies have to be exempted from the requirements of obtaining insurance/reinsurance only from the National Insurance Companies. Private power companies should be allowed to buy insurance of their choice as per requirements of the lenders and the utilities.
· The Instruments and Deeds required to be registered under local regulation must be exempted from stamp duty payments.
· The private parties should be allowed to raise local and foreign finance in accordance with regulations applicable to industrial projects as defined by the Board of Investors (BOI).
· Local engineering and manufacturing companies should be encouraged to provide indigenously manufactured equipment of international standard to provide power plants.
(vi) Other Facilities
The following facilities and incentives have to be provided to private power producers:
· Tax exemption on royalties and technical assistance fees, and facilities for their repatriation.
· Tax exemption on capital gains from transfers of shares by the investing company.
· Avoidance of double taxation in case of foreign investors on the basis of bilateral agreements.
· Exemption of income tax for upto three years for the expatriate personnel employed under the approved industry.
· No restrictions on issuance of work permits to project related foreign nationals and employees.
· Facilities for repatriation of invested capital, profits and dividends.
· Provisions of transfer of shares held by foreign shareholders to local shareholders/ investors.
· Re-investment of remittable dividend to be treated as new foreign investment.
· Foreign owned companies duly registered in Bangladesh will be on the same footing as locally owned companies with regard to borrowing facilities.
Discussion and Conclusions
This dissertation investigates the practicability of the establishment of rice husk based power generation if produced in bulk quantity by the Govt. in Bangladesh. In the previous chapters we have shown the process involved for power generation from husk in details, tried to find out the feasibility considering various factors and mentioned a number of recommendations.
In this chapter we are going to summarize the result of the total study drawing conclusive remarks. We are going to mention the contribution of this dissertation to the national benefits, discuss the problems we had to face during the thesis work, shortcomings or limitations of the analysis.
6.1 Findings from the Study
Geographical condition of our country is favorable for rice production and currently a lot of rice husk is being used inefficiently whereas the countries like Vietnam, Thailand, China are using this opportunity to generate power at comparatively low cost. To utilize this factor, we have studied the situation thoroughly. The findings of the study are mentioned as follows in a brief-
· The national average connected load of an Engleburg huller mill is about 31.8 KW per rice mill and the connected load of an automatic rice mill is about 170.8 KW in national average . 883.6 MW of peak load is necessary for 25,600 mills in Bangladesh according to the calculation.
· Bangladesh produces almost about 26 to 27 million tons of rice per year presently. 70% of the total paddy goes to the rice mills and the total husk can be approximated to 5.2 to 5.4 million tons per year.
· Considering only 67% of it can be used for power generation, we can produce about 300 to 320 MW power at present.
If the amount of milled rice can be increased to 80% from 70% and 75% of total husk can be utilized by increasing efficiency in the system, then the total generation can be increased to about 28% and 370 to 400 MW power can be produced.
Using simple statistical techniques extrapolation an estimation of probable power generation in future is mentioned. In this approximation by us advanced techniques were not used rather it was an attempt to focus on the potential behind.
6.2 Problems Faced during the Study
During the study work and investigation of the topic, we had to face a number of difficulties that bothered us heavily. Some of them are pointed out at this juncture:
The main problem face during the study was the lack of necessary data about the amount of rice husk. We had to struggle a lot for getting the correct data of the percentage of husk’s uses and also the amount of surplus rice husk.
This technology of using rice husk as fuel is actually a very recent technology and not vey common; that is why we had to work hard a lot to find out authentic information about the technology.
As this technology is only practiced in only a few countries, we got little help in collection of necessary information.
Due to unavailability of necessary and reliable information about Dreams Power Private Ltd. we had to depend on the information provided by the power plants outside the country.
6.3 Limitations of the Study
Naturally all the scientific studies and experiments have some shortcomings. This dissertation is not an exception and has quite a few limitations. They are described as follows
Due to unavailability of proper data and correlation factors, this thesis work has not been able to cover the economic factors clearly. The interdependence of lots of economic variables could not be analyzed.
As we had to use information provided by the plants outside the country, some of them could vary as ours is a different country and the availability of various materials could be different here.
During the calculation of surplus rice husk and probable power generation, we had to assume an ideal situation which might not be the case in every practical situation. Depending on the change of the situation of the calculation may vary as well.
Due to natural disasters or some other reasons the production of rice husk may be affected; accordingly the generation of power may change by a lot of margin. This situation has not been considered in the approximation.
6.4 Contribution of the Study
This dissertation is probably the first of its kind to depict a complete image of the prevailing condition in Bangladesh. It includes about all the primary fields necessary to investigate the feasibility of the husk based power generation.
This dissertation includes the calculation of probable power generation in Bangladesh. Though it has considered the ideal situation, still this can be used as a guideline in any further calculation.
The results of the study will be ever helpful in all kinds of future feasibility study of rice husk base power generation. In fact, the content and methodology in the feasibility study of this dissertation can be used in any kind of feasibility study.
6.5 Future Scope of Work
As this technology has a lot of potentials of success in Bangladesh, there are many scopes to work in future. The scopes are described here in brief
An overall survey should be made to find out the total picture of Bangladesh. With the help of this survey, the number of probable sites can be found out. Also we could clearly identify the feasible locations
Being a very recent technology, husk based power generation has lots of chance to be improved. Continuous research work is necessary to implement this technology to meet our requirement efficiently.
A major scope of work lies in the proper and thorough study of economic factors. Use of advanced statistical analysis in this regard is a must to have a clear view of the economic success of this project.
The disposed ash content is not properly used right now. Ensuring the proper use of this ash content in future may be another contribution from the plant.
Important Data Tables
Table A.1: Component analysis of rice husk sample 
Table A.2: Technological Characteristics of rice husk sample 
Table A.3: Available rice husks for commercial processing in different cluster in Rajshahi 
|Cluster||Total amount of paddy MT/year||Total amount of rice husk MT/year|
Table A.4: Calculation of surplus rice husk 
|Cluster||Available rice husk (MT/year)||Total number of rice mills||Kg husk/ton paddy for parboiling||Kg husk/ton paddy for drying||Rice mills use mechanical drying (%)||Amount of surplus rice husk|
Table A.5: Distribution of connected load from national grid at Dinajpur, Naogaon, Bogra,
Nawabganj, Ishwardi Cluster 
Table A.6: Specification of the Gasifier Unit 
|Capacity||Total 250 KW|
|Rated Gas Flow||625 Nm3 / hr (up to total 250 KW capacity)|
|Average Gas Calorific Value||> 1,050 Kcal / Nm3|
|Rated Biomass Consumption||Up to 300 kg / hr (for total 250 KW capacity)|
|Gasification efficiency||Up to 75%|
|Temperature of Gas at Gasifier Outlet||250 to 400°C|
|Desired operation||Continuous (minimum 300 days / year)|
|Typical Auxiliary Power consumption||Up to 11 KW|
|Typical Gas Composition||CO- 20.62%, H2- 10.62%, CO2- 13.61%, CH4- up to 4%, N2- 52.62%|
Table A.7: Specification of the Generator Unit (Collected during the visit)
|Alternator||MECC ALTE ECP 34 1L|
|Engine||DEUTZ BF6M 1013E|
|Prime Power||136.5 KVA- 109.2 KW|
|Standby Power||142 KVA – 113.6 KW|
|Rated Voltage||400 V|
|Maximum Current||204.97 A|
Data for Calculation of Probable Generation
Table B.1: Production of Total Rice, Gross Paddy, Milled Paddy, Rice Husk
|Year||Husked Rice (mt)||Gross Paddy (mt)||Milled Paddy
Table B.2: Rice Production (in million metric ton) in Bangladesh [3, 4]
|Year||Aus||Aman||Boro||Grand Total||MV %|
|MV||LV||Total||MV %||MV||LV||Total||MV %||MV||LV||Total||MV %|
Table B.3: Generation of Power in present & improved condition (including approximation)
|Year||Husk for parboiling (mt)||Total Generation (MW)||Increased husk
|Improved Generation (MW)|
|Figure C.1: Detailed map of major rice clusters in Bangladesh|
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 Report on “Survey of Major Rice Mill Clusters of Rajshahi Division”, German Development Cooperation (GTZ), Bangladesh,- Ahiduzzaman, Baqui, Mahmud, Khair
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 Thipwimon Chungsangunsit, Shabbir H. Gheewala, and Suthum Patumsawad, “Environmental Profile of Power Generation from Rice Husk in Thailand”, The Joint International Conference on “Sustainable Energy and Environment (SEE)”, 1-3 December 2004, Hua Hin, Thailand
 “Demonstration of Rice Husks-fired Power Plant in An Giang Province”, PREGA National Technical Experts from Institute of Energy, Viet Nam
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International, Oxford, 1991 (3rd Edition)
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<href=”#_ftnref1″ name=”_ftn1″ title=”"> This section used results from “Demonstration of Rice Husks-fired Power Plant in An Giang Province”, PREGA National Technical Experts from Institute of Energy, Viet Nam