Fertilizer Production: TSP COMPLEX LIMITED, CHITTAGONG (AN ENTERPRISE OF BCIC)

View with images and charts

Fertilizer Production

TSP COMPLEX LIMITED, CHITTAGONG (AN ENTERPRISE OF BCIC)

INTRODUCTION

Triple Super Phosphate Complex Limited (TSPCL) is a Public Sector enterprise

registered as a Private Limited Co. Situated at Patenga, Chittagong having its registered office at BCIC Bhaban, 30-31. Dilkusha C/Area, Dhaka-1000, It is under the administrative control of Bangladesh Chemical Industries Corporation (6C1C), one of the Largest public sector corporation of the country having big and medium sized Industries covering at present Nitrogenous and Phosphatic Fertilizer, Paper Cement Chemical. Sanitary Ware-etc.

TSP Complex was established with the objective of producing TSP Fertilizer. Accordingly 2 (Two) units viz TSP-I and TSP-II-1,20,000 MT respectively). Among the units TSP-II was commissioned earlier. TSP-I unit went into commercial production in April 1977 and TSP-II in September, 1974. TSP Complex is the only Phosphatic Fertilizer Factory of the country. Initially the factory started with production of TSP. Later on since 1990 manufacturing of SSP Fertilizer was started and his already established itself as a major fertilizer of the country. On account of technical problem in TSP-I unit, the Phosphoric Acid (PA) Plant of the unit was abandoned and closed. Due to increasing demand of SSP Fertilizer in the country, the facilities of TSP-I were then converted to produce SSP. In TSP-II Unit, necessary TSP-I and TSP-II plants are now known as Unit-I and Unit-II respectively. Production of this factory is increasing day by day and in 2002-2003 total production of 2,00,528 MT Phosphatic Fertilizer was achieved. The basic raw materials are Phosphate Rock (PR) and Element Sulphur (S) which are imported.

Basic Data About the location of the projects and raw materials of TSPCL:

01. Location of the Project:

It is located on the bank of the river Karnaphuli at Patenga which is about 4 km from Chittagong Airport an 1km to the south of Chittagong City. This location is in Patenga Industrial Area having communication facilities by rail, road and river.

02. Product Name:

a) Main Product: Triple Super Phosphate (TSP) Fertilizer, Single Super Phosphate (SSP) Fertilizer and Mixed Fertilizer (NPKS).

b) Intermediate Product: Sulphuric Acid, Phosphoric Acid.

c) By-Product: Gypsum.

03. Plant Capacity Unit-I Unit-II

a) Sulphuric Acid Present-100MTD Installed-400MTD

Present-60 MTD Present-320 MTD

b) Phosphoric Acid Dismantled & Closed Installed-270MTD

(50% P₂O₅) Present- 135 MTD

c) TSP/SSP 50,000MTY(SSP) 500MTD (1,50,000MTY)

Capacity Basis: On 300 Stream (TSP 70,000 MT and

Days per year SSP 80,000 MT)

04. Design/Erection Technical Enterprise Hitachi Zosen (Japan)

Incorporation (USA)

05. Type of Contract FOB Contract Turn Key Contract

06. Com. Production April, 1977 September, 1974

07. Capital Investment Tk. 274 Lac Tk. 2374 Lacs

Additional for Fertilizer Industries Rehabilitation Project of Tk. 5562.72 Lacs (1980-87). Part MBRE Tk. 972.43 lacs (as on 30-06-98 TSP-I & TSP-II combined).

08. Plant Process:

a) Sulphuric Acid Monsanto Contact Process Monsanto contact process

b) Phosphoric Acid Nissan (Hemi Di-Hydrate)

c) Reaction Den Process Den Proecess

d) Granulation Stami Carbon

09. Auxiliary/Ancillary/Special facilities:

a) Jetty for raw material unloading facility having maximum length of ship 535 ft. Mooring to Mooring 665 ft. and draft 8 meters.

(Unloading Capacity-2,500 MTD)

d) Raw material storage capacity

– Rock Phosphate : 50,000 MT

– Rock Sulphur : 23,000 MT

– Phosphoric Acid : 10,000 MT

– Sulphuric Acid : 7,000 MT

c) 300 MT per hour capacity Water Treatment Plant with tow Demineralization Units each having capacity 35 MT per hour

d) 3 tracks Railway siding for dispatch of products.

e) Polythne Bag Manufacturing plant (10,000 pcs. per day).

f) Bagging Machine (2) units for TSP-I and 3 units for TSP-II).

g) 2 Nos. Weighing Bridge Scale having capacity of 20 MT. and 30 MT.

10. Factory Area (Acre)

a) Plant Site : 37.25

b) Gypsum filed : 11.98

c) Housing area : 16.69

d) Jetty & adjoining area : 9.90

e) Others : 4.69

Total : 80.50

11. Main Raw Materials and Source:

a) Rock Sulphur from : Iraq, Iran, Canada, Morocco, Saudi Arabia, Poland,

b) Rock Phosphate from : Jordan, Morocco, Egypt, China, Algeria, Syria.

c) Phosphoric Acid from : Tunisia, Poland, Iran, Morocco, India.

RESEARCH AND DEVELOPMENT

The factory is equipped with a modern laboratory and testing facilities for controlling quality of raw materials, finished products as well as control of pollution. Continuous research & development is conducted in its laboratory for the purpose of process improvement and product diversification including search for new source of Phosphate Rock at lower cost.

01. RS/BMR Executed:

In TSP Complex during 1974-79, the capacity utilization had been very poor, maximum 40%. The main reason for low production had been teething problems, electrical/mechanical breakdown, power failure and shortage of raw materials. An improvement Program under the name of Fertilizer Industries Rehabilitation Program (FIRP) was taken up and the scheme was started in July 1980. The scheme envisaged setting up a granulation plant of 1,50,000 MT/yr, facilities for use of imported phosphoric acid and replacement and modification in different sections to improve the operating capacity, setting up of a power generator of 5 MW capacity. The FIRP was completed in June, 1987 at a cost of Tk. 55.62 crore. After completion of the program, TSPCL’s production capacity was restored at 1,50,000 MT TSP per year (1,00,000 MT/yr. by own Phosphoric Acid and 50,000 MT/yr. by imported phosphoric Acid).

02. BMR Project:

Another BMRE program of Tk. 972.43 Lacs Undertaken in may, 95 was completed in June 98 for enhancing production capacity from 1,52,000 MT to 2,00,000 MT (TSP 70,000 MT + SSP 1,30,000 MT),

ORGANOGRAM :

Manpower :

Total	Labour	Staff	Officer
604	294	165	145

NAME & DESIGNATION OF THE DEPARTMENTAL HEADS

Dept.	Depastmental Heads Name	Designation
1. Administration	Md. Saquee Hussain	Manager (Administration) Head of Administration
2. Accounts	Md. Abul Kashem	Deputy Chief Accountant Head of Accounts
3. Commercial	Md. Golam Rasul Khan	General Manager (Commercial)
4. Maintenance & Technical Services (MTS)	A.U.M Zubair	Genaral Manager (MTS)
5.Technical Division	Md. Hossain	Additional Chief Chemist Acting General Manager
6. Opposition	Md. Zulfiquar Ali	Additional Chief Chemist Acting General Manager

1. Sulphuric Acid Plant:

Sulphuric acid required for manufacture of phosphoric acid is produced by Monsanto Contact Process in both the units.

In this process, rock sulphur is melted in a melter and burnt in a furnace in presence of dried air where sulphur is oxidized to sulphur dioxide (SO₂) gas. This gas is then converted into sulphur trioxide (SO₃) gas in a converter in presence of catalyst, V₂O₅ under optimum conditions. SO₃ gas is then absorbed in 98.5% H₂SO₄ in an Absorbing Tower. Strength of the absorbing acid is thereby raised which in turn is diluted by adding demineralised water to maintain the desired strength. The quantity of acid in Absorbing Tower is thus continuously increased and the increased portion is sent to the storage tanks as 98.5% H₂SO₄.

Reactions: S + O₂ = SO₂, SO₂ + ½ O₂ = SO₃, SO₃ + H₂O = H₂SO₄

2. Phosphoric Acid Plant:

Phosphoric Acid required for production of TSP is manufactured by Hemihydrate- Dihydrate process.

In this process, rock phosphate ground to the fineness of 70% passing through 200 Tyler mesh is mixed thoroughly with Sulphuric Acid (70%) and dilute Phosphoric Acid (19-21%) in a tank to acidulate. The reacted slurry is passed into a series of tanks successively to effect decomposition of rock, crystallization of Gypsum and completion of reaction. Slurry in each reacting vessel is constantly agitated with agitators. Temperature and solid-liquid ratio and acid concentration are kept at standard levels designed for the process. From the last reacting vessel, the slurry is pumped into a Vacuum Filter to separate the acid form the Gypsum. The first filtrate is the product acid of 30% P₂O₅. The residue is the filter cake (Gypsum) which is sent to Gypsum Yard after final washing with hot water. This residue is the by-product Gypsum (CaSO₄, 2H₂O).

Reaction:

Ca₃ (PO4)₂ + 3H₂SO₄ + 6H₂O = 2H₃PO₄ + 3CaSO₄.2H₂O

The product acid of 30% P₂O₅ is then concentrated to 50% P₂O₅ acid in a concentrator (Calendria) by heating the material with steam under forced vacuum circulation system as 50% P₂O₅ acid is required to manufacture TSP of 46% P₂O₅.

3. TSP Plant:

Triple Super Phosphate is manufactured by decomposition of rock phosphate ground to the fineness of 80% pass through 200 Tyler mesh in an air swept Ball Mill, with phosphoric acid (50%) P₂O₅ in a Reaction Den under standard conditions of temperature and flow are. The Den product is koown as Green TSP. Green TSP is fed in a Granulator through conveying system, where granules are formed through the principle of agglomeration with steam and process water. Granular TSP is then dried with hot air generated by combustion of natural gas and then bagged to get finished product of granular TSP.

Reaction: Ca₃ (PO₄)₂ + 4H₃PO₄ + 3H₂O=3CaH₄ (PO₄)2.H₂O

4. SSP Plant:

SSP is manufactured by acidulating finely ground phosphate rock with 70-75% sulphuric acid in Reaction Den under standard conditions of temperature and flow rate. The outlet Den product known as Green SSP is kept in a curing house for about three weeks for completion of the reactions. The cured SSP is then dried by natural air and bagged to get finished product of powder SSP.

Production of SSP in powder form started since 1988 in Unit No. 1. But with the rising trend of use of SSP in agriculture, arrangement was made to produce SSP through Unit No. 2 also.

Reaction: Ca₃ (PO4)₂ + 2H₂SO₄+5H₂O = 2CaSO₄.2H₂O + CaH₄(PO₄)₂.H₂O

5. Gypsum:

Gypsum (CaSO₄.2H₂O) a by-product of Phosphoric acid manufacturing process has use as a supplementary fertilizer for soil treatment. It is generally used in sulphur deficient areas.

6. Mixed fertilizer (NPKS):

From the year 2002, TSPC is experimentally producing one grade of mixed fertilizer for paddy grade as per recommendation of Bangladesh Agricultural Research Council (BARC). Marketing of this fertilizer has already been started for use at farmer’s end. We are also working for production of NPKS suitable for tea production. This fertilizer will increase the fertility of land and also production. The basic raw materials are TSP, SSP, Ammonium Sulfate (AS), Di-ammonium Phosphate (DAP) and Murate of Potash (MOP).

Raw materials for sulphuric acid production :-

1. Rock Sulphur

2. Air (O₂)

3. Deme Water (H₂O)

Raw materials for Phosphoric acid production:

1.Higher grade rock Phosphate

2.Sulphuric acid

Raw materials for TSP plant:

1.Low grade rock phosphate

2.Phosphoric acid

Raw materials for SSP plant:

1. Low grade rock phosphate

2. Sulphuric acid

Rock Sulphur

Source : Iran, Canada, USA, Soudi Arabia

Chemical Ingredients:

i. Sulphure Content : 99.50% (Min) w/w

ii. Moisture : 0.5% (Max) w/w

iii. Organic Matter : 0.10% (Max) w/w

iv. Ash Content : 0.06% (Max) w/w

v. Water Soluble Chloride : 10 PPM (Max) w/w

vi. Acidity as H₂SO₄ : 0.025% (Max) w/w

vii. Colour : Yellow

viii. AST (Arsenic Salemium : Nil

Tellarium

ix. Particle Size : 30-50 mm 10% Max.

Above 0.2 mm and below

30 mm 89% Min.

Below 0-0.2 mm 1% Max.

ROCK PHOSPHATE

low grade rock phosphate:

Source :

Jordan,Morocco,Egypt,China,Algeria

Specification of lower grade rock phosphate (65.5% BPL Min.)

A. Chemical Ingredients

i. Moisture 2.00 (Max) % w/w

ii. Total Phosphate (P₂O₅) 30(Min) % w/w

iii. Calcium Oxide (CaO) 45-52 % w/w

iv. Sulphate (SO₃) 0.5 – 2.0 % w/w

v. Silica (SiO₂) 5 – 8 % w/w

vi. Carbon-di-Oxide (CO₂) 5 – 6 % w/w

vii. Cluoride (F) 4 (Max) % w/w

viii. Iron (Fe₂O₃) 1.0 (Max) % w/w

ix. Iron and Aluminum (R₂O₃) 2.0 (Max) % w/w

x. Water Soluble Chloride (Cl) 0.2 (Max) % w/w

xi. Sodium Oxide (Na₂O) 0.8 (Max) % w/w

xii. Potassium Oxide (K₂O) 0.3 (Max) % w/w

xiii. Magnesium Oxide (MgO) 0.5 (Max) % w/w

xiv. Organic Matter with 2.4 (Max) % w/w

Crystalline Water

xv. BPL 65.5 % Min.

B. Physical Ingredients

i. Fluidity Free Flowing

ii. Particle size distribution

a. + 4 mesh (4.75 mm) 0 – 2 % w/w

d. -4+100mesh (4.75mm-0.15mm) 65-80% w/w

c. -100 +200mesh (0.15mm-0.075mm) 15-25 % w/w

d. -200 + 270mesh (0.075 mm- 0.053mm) 1-3 % w/w

e. -270mesh (0.53mm) 2-3 % w/w

C. Colour : Whitish /Off – White (Blackish not acceptable)

HIGHER GRADE ROCK PHOSPHATE

Source:

Jordan, Morocco, China (Wong-fu mine)

Specification of Higher Grade Rock Phosphate (72% BPL min.)

A. Chemical Ingredients

i. Moisture 2.00 (Max) % w/w

ii. Total Phosphate (P₂O₅) 32.95(Min) % w/w

iii. Calcium Oxide (CaO) 48-52 % w/w

iv. Sulphate (SO₃) 0.7-1.9 % w/w

v. Silica (SiO₂) 2.5-5 % w/w

vi. Carrbon-di-Oxide (CO₂) 5 (Max) % w/w

vii. Cluoride (F) 4 (Max) % w/w

viii. Iron (Fe₂O₃) 1.0 (Max) % w/w

ix. Iron and Aluminum (R₂O₃) 2.0 (Max) % w/w

x. Water Soluble Chloride (Cl) 0.04 (Max) % w/w

xi. Sodium Oxide (Na₂O) 0.2-0.8 (Max) % w/w

xii. Potassium Oxide (K₂O) 0.1-0.3 (Max) % w/w

xiii. Magnesium Oxide (MgO) 0.5 (Max) % w/w

xiv. Organic Matter with 2.4 (Max) % w/w

Crystalline Water

xv. BPL 72 % Min.

B. Physical Ingredients

i. Fluidity Free Flowing

ii. Particle size distribution

a. + 4 mesh (4.75 mm) 0 – 2 % w/w

d. -4+100mesh (4.75mm-0.15mm) 65-80% w/w

c. -100 +200mesh (0.15mm-0.075mm) 15-25 % w/w

d. -200 + 270mesh (0.075 mm- 0.053mm) 1-3 % w/w

e. -270mesh (0.53mm) 2-3 % w/w

SULPHURIC ACID

CHEMICAL FORMULA : H₂SO₄

ANNUAL PRODUCTION : 62704 MT (uni-1 in 2007-2008)

SPECIFICATION : Specific gravity (at 20^oC) : 1.830

H₂SO₄ : 98.5%

Iron (Fe ++) : 0.004%

SO₂ : 0.0001%

Ignition reside : 0.005%

Color : Turbid White

USES :

sulfuric acid is an intermediate product. It is mainly used for manufacturing SSP and for production of phosphoric Acid, required for manufacturing TSP, Sulphuric acid is an essential item for all kinds of chemical factory small or big in size. About 5000-6000 MT Sulphuric acid per year is sold to the Industrial organization of the country. This Sulphuric acid plays an important role towards country’s industrial development.

PHOSPHORIC ACID

Chemical formula : H₃PO₄

Production capacity : 17884MT (2007-08)

Product specification:

Specific gravity (at 20^oC) : 1.830

H₂SO₄ : 98.5%

Iron (Fe ⁺⁺) : 0.004%

SO₂ : 0.0001%

Ignition residue : 0.005%

Colour : Turbid White

Use & application:

it is an intermediate product and used for manufacture of TSP.Entire qantity of phosphoric acid produced,is used in the process.

By-product : Gypsum

TRIPLE SUPER PHOSPHATE (TSP)

Chemical formula : 3CaH₄ (PO₄)₂.H₂O

SPECIFICATION OF TSP:

Moisture : 5% (Max)

Total P₂O₅ : 46% (Min)

Water soluble P₂O₅ : 40% (Min)

Free P₂O₅ : 3% (Max)

Physical appearance : Granular

Size : 85% (Between 6& 16 mesh)

i.e. Between 3.3 mm & 1 mm).

SINGLE SUPER PHOSPHATE (SSP) PLANT:

Chemical Formula : CaH₄(PO₄)₂H₂O

Annual production: 55,014 MT (2007-2008)

Specification :

Moisture : 8% (Max)

Total P₂O₅ : 18-20%

Available P₂O₅ : 16% (Min)

Free P₂O₅ : 3% (Max)

Sulphur : 10% (Min)

Calcium : 18% (Min)

Physical appearance : Powder.

Use & application :

Single Super phosphate commonly known as SSP contains (a) phosphorus, (b) Sulphur and (c) Calcium nutrients and as such it is called mixed fertilizer. Sulphur has been established as the fourth primary plant nutrient and is necessary for all kinds of crops. It is also proved that without correction Sulphur deficiency of the land, the remaining three nutrients (NPK) can only be utilizer by the plants to a limited extent and hence the product quantity but also improves the product quality in helping to add more vitamin and protein value. To provide both phosphorus and Sulphur nutrients to the lands, use of SSP is rapidly increasing. As pre Govt/s instruction SSP is produced in powder form.

GYPSUM (a by product)

Chemical formula : CaSO₄. 2H₂O

Uses of Application:

Gypsum is obtained as a by product during phosphoric acid manufacturing. For a long time, use of gypsum except in Cement factories as retarder was not known. Ultimately with the help of BARC this Sulphur enriched gypsum has been established as a fertilizer. About 70-80% of the country’s soils are deficient in Sulphur which causes significant yield reduction. As such gypsum is being used at large quantities in Bangladesh to Compensate the deficiencies of Sulphur specially in the northern districts.

This gypsum contains 18% Sulphur and 30% calcium, So, for 20kg Sulphur for a land of one hectre 112kg gypsum is to be applied.

Annual Production: 41,575 MT (2007-2008)

Analytical report on a Particular sample:

– Total P₂O₅ : 0.47%

– Water Soluble P₂O₅ : 0.15%

– CaO : 31.69%

– Total SO₃ : 45.32%

– Total SiO₂ : 0.70%

– Fe₂O₃ : 0.011%

-Al₂O₃ : 0.007%

– Fluorine : 0.32%

– Moisture : 15-20%

– Water of Crystallization : 19.29%

– Acidity as CO₂ : 0.26%

-Organic matter : 0.02%

– Water soluble chloride : 0.13%

Packing: Lose delivery through Track/ wagon as arranged by the Customers.

Process Outline:

Gypsum (CaSO₄.2H₂O) a by- product of phosphoric acid manufacturing process has use as a supplementary fertilizer for soil treatment. It is generally used is Sulphur deficient areas.

Comparative Specification of Products

Specification of Products : TSP SSP

1. Total P₂O₅ : 46% (Min) 18-20%

2. Free P₂O₅ : 03% (Max) 3% (Max)

3. Sulphure : – 10% (Min)

4. Available P₂O₅ : 43-44% 16-17%

5. Moisture : 05% (Max) 08% (Max)

6. Physical Character : Granular Powder

WATER TREATMENT PLANT

1.1 AIM of the Plant:

This plant has been planed to supply process water to the chemical complex of chittagong (Bangladesh Chemical Industries Corporation.)

1.2 Characteristics of Raw Water:

The water to be treated is river water.

Its main characteristics are as follow:

Physical -chemical analysis (contractual analysis)

• Turbidity ………………………………………….. 150⁰ kaolin
• p^H ……………………………………………………… 7.4
• Total hardness (ppm CaCO₃) ……………….. 128.41
• Calcium hardness (ppm CaCO₃) …………… 38.52
• magnesium hardness (ppm CaCO₃) ………. 89.89
• m-alkalinity (ppm CaCO₃) ……………….. 43.66
• Strong acid salts (ppm CaCO₃) …………..
• Sulphate (ppm CaCO₃) ……………………..
• Chloride (ppm CaCO₃) …………………….. 39.18
• Iron …………………………………………………0.25 mg/l
• Silica ……………………………………………… 40 mg/l
• Nitrite ……………………………………………. None
• Nitrate …………………………………………… traces

Table : showing approximate calculation of ion content

Cations	meq/l	mg/l	Anions	meq/l	mg/l
Ca++	0.769	15.40	HCO3–	0.873	43.66
Mg++	1.774	21.57	CO3—	0	–
Na+	6.13	141.00	SO4—	0.816	39.18
K+	0.180	7.05	NO3–	–	–
Na+ + K+	6.21	148.05	Cl–	7.102	251.80
Fe+++	0.012	0.23	SiO3–	0.67	40.00

1.3 Treated water Characteristics

1.3.1 Filtered water before demineralization

• • Turbidity …………………………………… max. 2⁰ (kaolin)
  • Free chlorine …………………………….. max. 0.2 mg/l

1.3.2 Dematerialized water

o Conductivity ………………………. max. 10 micromhos/cmat 25⁰

o Silica residual ……………………. max. 0.2 mg/l

1.4. Plant Flow Rate

o Clarified water ………………………. 300 m³/hour

o Filtered water ……………………….. 55 m³/hour

o Demineralized water …………….. 40 m³/hour

1.5 Treatment Principle

1.5.1 Pretreatment

Coagulation – Flocculation – Settling

Water contains very fine, colloidal or pseudocolloidal suspended solids which must be gathered into a bulky and heavy floc to allow settling and help retention in the filters.

The interfaces of colloids are electrically charged, which prevents nearby particles from coming close together.

The action takes place in three steps:

Þ Coagulation, which destabilizes the colloids to give rise to a precipitate.

Þ Flocculation, which destabilizes the colloids to give rise to a precipitate,

Þ Flocculation, which is intended to increase the volume and cohesion of the floc formed by coagulation,

Þ Settling, which is intended to permit particles to settle out.

A/Coagulation

Use is made of a metal salt such as aluminum sulphate.

Þ It is determined at plant start-up after jar tests have been conducted.

Þ The greater a water’s colloid content, particularly matter of vegetable origin, the higher the amount of reagent required for clarification,

Þ The nature of organic matter has an influence on coagulation.

Þ The p^H of the medium is of paramount importance in coagulation and in the dosage of chemical.

The hydrolysis, and thus the efficiency, of aluminum sulphate is maximum when the p^H is close to 6.1 and organic matter removal is maximum when the p^H is between 6 and 7. Therefore, the p^H must range within these limits. However, aluminum sulphate is a strong acid salt and causes the p^H to decrease, which may render the water aggressive.

Neutralization is applied before treatment so as to adjust the flocculation p^H to its optimum value.

B/ Flocculation

Flocculation is promoted by constant speed, slow mechanical stirring which increases likelihood of collision between destabilized colloidal particles without breaking the floc.

Flocculation is further improved by the addition of a flocculant aid (a polyelectrolyte which will not always be necessary).

C/ Settling

Settling is designed to allow the particles in suspension in the water to settle, under the effect of gravity, to improve water quality.

To ensure that settling takes place, the settling rate of the particles must be higher than the water’s rising velocity, V_a, in the units:

These particles exist in the raw water and are precipitated into larger (and thus heavier) floccules by adding chemical agents during flocculation.

OPERATING PRINCIPLE

Pretreatment :

The pretreatment is carried out in three steps : injection and mixing of reagents, flocculation, settling.

Reagent Injection :

It takes place in the mixing chamber in the following order : caustic soda and aluminium sulphate. When it is used, the polyelectrolyte is added at the outlet from the mixing chamber.

Mixing is achieved by a stirrer at a speed of 70 rpm.

Flocculation :

The flocculator is a tank which provides a significant contact time between the water and the flocculation reagents (30 min).

The unit is equipped with a mixing device with vertical paddles with a specially designed propeller which rotates relatively slowly, but rapidly enough to prevent sedimentation on the bottom of the flocculator.

The rotation speed is slow in order not to break up the floc. There will be a large weir so that the flocculated water flows slowly into the following treatment unit with no sudden surges which could result in floc break up.

Settling:

The static settling tank is a rectangular basin in which water is continually.

The bottom of this settling tank is sloped for maximum sludge concentration in the low point of the static settling tank will be emptied periodically in order to eliminate settled sludge.

This system must operate in a regular manner. Variations in flow rate cause stirring which lifts the sludge to the surface.

DEMINERALIZATION:

Demineralization is designed to remove dissolved salts from the raw water. These salts are essentially bicarbonanates, sulphates, chlorides and silica.

Two types of ion exchangers are available :

1. Cation exchangers, featured by the presence of acid, sulphonic functional radicals in the molecule.

They exchange their cations (H⁺ or any other cation) bound with the active radicals for the cations in the liquid with which they are in contact (Ca, Mg, Na, etc.), and this in a reversible menner.

They are regenerated with an acid solution.

Strong acid cation exchangers (sulphonic function) can take up all cations. Including those in equilibhrium with strong anions : sulphates, chlorides, nitrates.

2. Anion exchangers, featurd by the presence of basic functional radicals in the molecule.

They exchange their anions (OH or any other anion) bound with the active radicals for the anions in the liquid with which they are in contact (Cl^–, SO₄ ^—, NO₃^–, SiO₂), and this in a reversible menner.

They are regenerated with an a alkaline solution.

Weak-base anion exchangers can only take up the anions from strong acids (HCl, HNO₃, H₂SO₄).

Strong-base anion exchangers can take up the anions from strong acids and the anions from weak acids such as carnbonic acid and silica.

The feed water successively passes through one H⁺ cycle cation exchanger and two OH^– cycle anion exchangers.

After passing through the strong acid cation exchanger, all the cations in the water are replaced by the hydrogen ion, H, of the resin; then, the treated water only contains the acids of the initial salts.

The decationized water next passes through the weak-base anion exchanger and the strong-base anion exchanger. All of its anions are replaced by the hydroxyl ion, OH^–; then, the demineralized water only contains traces of caustic soda corresponding to the cation leakage.

The treated water is highly pure and has a constant quality at a pH close to neutral.

SULPHURIC ACID PLANTS

(SA- 1 & SA- 2)

There are two sulphuric plants namely SA-1 (Capacity: 100 NT/Day) and SA-2 (Capacity: 400 MT/Day). In both the plants, sulphuric acid is manufactured by the Monsa to designed single contact single absorption process with Rock sulphur imported at 99.5% (Min) purity.

SA-1 was commissioned in 1967 and SA 2 in 1974.

The manufacturing process of sulphuric acid consists of the following principal steps :

1. Melting of sulphur.
2. Production of sullphur dioxide (SO₂)
3. Conversion of sulphur dioxide to sulphur Trioxide (SO₃)
4. Cooling of SO₃ gas and absorption of SO₃ in water to produce 98.5% sulphuric acid.

SA-1 PLANT

PROCESS OUTLINE :

1. MELTING OF SULPHUR :-

Rock sulphur is charged into the charging chamber of a melter and melted by steam coils installed in it. Steam is supplied to the steam coil to maintain the temperature at 132-135⁰C. The molten to the flows out to the settling chamber of the melter where the heavy impurities settle at the bottom and the light impurities rises on the upper layer as scum. The charging chamber and the settling chamber are provided with agitators to make a satisfactory contact between sulphur and steam coil. The molten sulphur from the settling chamber is pumped to the pumping chamber of the melter through a pre-coated sulphur filter which separates the impurities present in molten sulphur.

2. PRODUCTION OF SULPHUR DIOXIDE :-

The clear molten sulphur from the pumping chamber of the molten is pumped through the sulphur burners into a sulphur which as preheated to a temperature of about 800⁰C by the combustion of natural gas. In the sulphur Furnace, Sulphur starts to burn with oxygen from dried air that has passed through the Drying Tower and produces sulphur dioxide as per following reaction :-

S + O₂ = SO₂

A steady supply of dry air is made available to the burner. Atmospheric air is sucked and pressurized by Blower, passed through Drying Tower to eliminate moisture and forced into the burner. The burning of sulphur evolves a large amount of heat which rises the temperature of the burner gas at around 1000⁰C where strength of 2% SO₂ is maintained. The exit temperature of the Furnace should never be allowed to exceed 1025⁰C in order to ensure long life of brick lining. The hot combustion gas (i.e.SO2) coming out of the sulphur furnace at around 1000⁰C is cooled down to a temperature of 420-430⁰C suitable for conversation reaction in the converter, by passing through state host boiler waste heat boiler generates steam which is mainly used in the boiler melter and phosphoric acid plant. From the waste heat boiler, the gases (SO₂ +O₂ + other) pass to a hot gas filter where impurities like ash, dust, etc are filtered out by graded layers of crushed bricks. This protects the catalyst of the converter from contamination and prevents build up of A pressure across the catalyst beds of the converter.

3. CONVRSION OF SULPHUR DIOXIDE TO SULPHUR TRTOXIDE :-

The purified SO₂ gas leaving the hot gas filter is passed into converter containing V₂O₅ catalyst. 4 (four) beds of catalysts are placed inside the converter at different positions. SO₂ gas is allowed to pass through each bed of the converter and optimum conditions (of temperature/ pressure/ flow rate/ air supply) are maintained to favor the conversion of SO₂ to SO₃ in the converter. As conversion of SO₂ to SO₃ is exothermic reaction, temperature rises in each bed and is controlled by supplying dry air in the 1^st bed and 2^nd bed and by circulating the gases of the 3^rd bed through a air cooled heat exchanger.

The reaction that takes place in the converter in presence of catalyst is represented below :-

SO₂ + ½-O₂ = SO₃

1. COOLING OF SO₃ AND ABSORPTION OF SO₃

IN WATER TO PRODUCE SULPURIC ACID :-

After converter, the temperature of SO₃ gas is around 430⁰C, heat of which is made available for the following purpose in order to get the SO₃ gas at a suitable temperature for absorption in 98.5% sulphuric acid.

a) To preheat a part of the dried air leaving the Drying Tower required for combustion of molten sulphur in the sulphur furnace. This type of equipment is called SO₃ cooler and is installed in SA-1 Plant.

b) To heat the deaerated dematerialized boiler feed water, which has a temperature of 100-150⁰C. This type of equipment is called Economizer and is installed in SA-2 plant.

In SA-1, SO₃ gas from the converter is cooled to 230⁰C in the SO₃ cooler and introduced to the Absorption Tower.

In SA-2, SO₃ gas from the converter is cooled to 230⁰C in the 1^st Economizer and further cooled to 170⁰C in the 2^nd Economizer (Formerly, 2^nd Heat Exchanger using air cooling) before the SO₃ gas is entering the Absorption Tower.

The cooled SO₃ gas (along with gaseous components) is passed into Absorbing Tower from the bottom and a stream of sulphuric acid (98.5% strength) is circulated from top and mixed counter currently to effect absorption of SO₃, strength of absorber acid is thereby raised which in turn is diluted by adding water to maintain the desired strength of 98.5%. The quantity of acid in Absorbing Tower is thus, continuously increasing and the increased portion is cooled by passing through irrigation cooler and finally sent to storage. The unabsorbed gas leaving the Absorbing Tower is discharged to atmosphere.

The reaction that takes place in the Absorbing Tower is represented below: SO₃ + H₂O = H₂SO₄

SA-2 PLANT

3. Detailed description of process :

3.1. Sulfur melting

1) Equipment

V -1202 1. Sulfur Pit

E-1202 2. Sulfur Melting Coil

J- 1201 A, B3. Sulfur Pump

M- 1202 A, B4. Agitator

2) Standard of operation

(a) Stamard feed rate of sulfur to melter 5,610 kg/hr.

(b) Standard temperature

Molten sulfur 132-135⁰C

Heating steam 7 kg/cm²G (abt. 169⁰C)

3) Purpose

To melt solid elemental sulfur and pump up molten suflur to the sufur furnace.

4) Description

(a) Sulfur melter

Best results will usually be obtained by maintaining the molten sulfur in the melter at approximately 132-135⁰C. Higher temperature entering the furnace are sometimes beneficial, but never in excess of approximately 149⁰C. Materially higher or lower temperatures than those stated should not be used because of the increased viscosity of molten sulfur. It is necessary to keep the level of molten sulfur at normal level. Sulfur itself is no corrosive. Any corrosive properties result form contaminants, and most corrosion results form sulfurous and sulfuric ac id generated by the reaction of sulfur, moisture, and air. Most corrosion occurs in liquid-handling equipments at sulfur-air interface. On the part of these equipments at the interface, some protectors are provided, then if the liquid level is not kept normally, corrosion occurs in the other part of them having no protectors.

When it becomes necessary to clean sulfur pit, it should first be pumped as low as possible. In order to do this, the pump should be taken out of the melter, for the extension of the inlet piping as required and the pump then installed again. This change in the inlet piping makes it possible for the pump to draw form a greater depth than would otherwise be the case.

After removing as much of the molten sulfur as possible, cleaning may start immediately by adding the small portion of the water at the corner where the work is to be started.

It is advantageous to start cleaning before the mixture of sulfur and dirt has become cold, as the immediate addition of water will often give mixture a “much” c consistency which is readily shoveled. Water should be added however only at the spot where the man is working. Since there are two settling sections, this cleaning can be handled for one setting section while the other is operating.

(b) Sulfur pump

The burner feed pump is mounted in the sulfur pit located near the furnace. When installing a sulfur pump, be sure that it is perfectly plumb and that it turns freely by hand. Piping should be connected, and held firmly, so that no starains are ever put on the pump.

For further information, any instructions about the pump and pump drive should be consulted.

The sulfur pump drive is interlocked with the blower driving unit so that whenever the blower stops, the sulfur pump simultaneously stops. Nevertheless, when evern the blower is stopped the operator should always make sure at once that the sulfur pump has actually stopped. If the sulfur pump should remain in operation while the blower is stopped, the system would soon become filled with sublimed sulfur and much damage may occur to the sulfur furnace and other equipment.

In order to test a sulfur pump while the blower is stopped, provision has been made so that it is possible to operate the pump, even though the blower be stopped. Before testing a pump in this manner, however, the blind flange on the end of the jacketed tee in the discharge piping nearest this pump should be removed and a pail should be placed under the end of the tee. The jacketed valves should be turned so that the pump to be tested will deliver sulfur to the pail instead of the furnace. When starting the pump always be sure that there is at least 3.0 kg/cm² steam pressure in the jacketed discharge line.

It is very clear by Monsanto’s experience that many troubles with sulfur pumps are due to misalignment. It is to be emphasized that spare pumps or pumps out of service for repaid should be properly maintained while in storage or while being handled so that they cannot become sprung or distorted. All parts must b e carefully aligned with one another and also the pump with the drive.

The usual warning to the operator that plugging is occurring at some point is that the furnace temperature, as shown on the temperature recorder, gradually decreases. It has been found that tripping the pump and allowing the sulfur in the discharge line to drain back for a minute or so, often cures the trouble. This procedure often saves the trouble and expense of removing a pump for inspection and repair, when actually no repairs are needed.

It should be emphasized that under any conditions sulfur flow should be in creased by only small steps and the operator should make sure of the result of each change on gas strength before making further adjustment.

(c) Steam-jackted molten sulfur piping.

The sulfur in this line may freeze, if an adequate amount of steam is not supplied to all parts of it, and if condensate is not kept drained. Only rarely, however, will this line become scaled or plugged with foreign matter.

The sulfur nozzle at the end of the sulfur inlet pipe of the furnace may rarely become scaled or plugged. It has been found that the scale may be burned off the nozzle and the nozzle reused. It is recommended, there fore, that a few spare nozzles be stocked.

3.2. Sulfur burning.

1) Equipment

D-1201 Sulfur Furnace

D-1202 Sulfur Burner

D-1203 Oil Burner

D-1204 Oil Burning Unit

2) Standard of operation

(a) Standard flow rate

Molten sulfur to furnace 5,610 kg/Hr.

Dry air to furnace 34,987 Nm³/Hr

Generated gas from furnace 34,900 Nm³/Hr

(b) Standard concentration

Generated gas

SO₂ 11 vol %

O₂ 10 vol %

N₂ 79 vol %

Total 100 vol %

3) Purpose

The sulfur furnace is the combustions chamber where molten sulfur from the sulfur pumps is combined with combustion air from blower to form SO₂ gas.

4) Description

Care must be taken to avoid overheating the brickwork adjacent to the burner. There must be a substantial flow of combustion air around the burner at all times to lower the temperature at this point and especially to carry heat to remote parts of the furnace more rapidly. A large volume of combustion gases at a reasonable temperature will achieve the desired results much faster than a small volume at an excessive temperature. Note also that a substantial flow of combustion gases is required to obtain a representative temperature reading on the thermocouple adjacent to the combustion gas outlet.

Frequent observations must be made of the color of the brick in the combustion zone. To avoid damage, the brickwork should not be heated beyond full red heat. Heating the brickwork to a color of orange, yellow, or white must be avoided.

When the furnace is at normal operating temperature there should never be more than a small pool of molten sulfur in the bottom of the furnace, so that when the blower and sulfur pump are stopped simultaneously, there will be substantially no unburned sulfur left in the furnace.

When the blower stops, any sulfur left in the furnace would sublime; if small in amount it would cause no damage, but large amounts would be harmful. When shutting down the plant deliberately, the sulfur pump should be stopped, and the blower a few minutes later so as to eliminate all possibility of any unburned sulfur being left in the furnace.

There is a close correspondence between the furnace outlet temperature and gas strength. Accordingly, with experience the gas strength can be checked approximately from the furnace outlet temperature. The theoretical flame temperature corresponding to various percentages of SO₂ in the burner gas are as follows :

% S02 by Volume		Approx. Theoretical Flame Temperatures
5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0		540C-10100F 6210C-11500F 6990C-12900F 7770C-14300F 8600C-15800F 9430C-17300F 10240C-18750F 11040C-20200F

It should be noted that the above temperatures are not exactly those which will prevail at the stated gas-strengths. Actually, the are increased in proportion to the amount of heat in the combustion air and decreased in proportion to the amount of heat lost form furnace shell by radiation, convection, etc.

The protecting well and thermocouple in the gas outlet should be inspected and checked occasionally to sure that it is in good condition and is giving an accurate reading.

3.3 Heat recovery

1) Equipment

E- 1201 Waste Heat Boiler

Flush Tank

Sampling Cooler

V-1203 Deaerator

J- 1202, A, B Boiler Feed Water Pump

2) Purpose

To recovery of excess heat of combustion gas-

3) Description

a) Boiler food water treatment.

Experience has shown that any troubles whit the waste heat boilers are almost invariably due to internal scaling of the boiler. In many cases such scaling has been due to inadequate attention to the supply and maintenance of suitable treated feed water of uniform Quality. Because of the great variations in the water supplies available in different locations, it is impossible for a standard treatment to be prescribed. Thus, it is most desirable that competent advice be obtained form specialist in this field, and preferably from those with experience of this type of waste heat boiler.

b) Boiler water testing

Acid plant operators, because of their frequent lack of familiarity with boilers, often negalect faithful routine testing of the boiler water and consistent maintenance of boiler water of the proper analysis. These comments apply also to feedwater treating equipment when such comes under the jurisdiction of the acid plant. Both the feed water and the boiler water must be consistently kept of the composition specified by us and within the limits instructed in the boiler manual.

Attention is particularly required while starting the plant as well as immediately after and during a shutdown.

After the method of treatment and a control procedure has been established, the simple routine tests any be run by the operators. The number and nature of the tests depend entirely upon local conditions. Whenever suitable feedwater is provided and the boiler water is carefully kept within prescribed limits of composition, scaling of tubes is rarely encountered.

Boiler water samples for tests should be taken form the continuous blow down at times to be posted by the supervisor. Each sample should consist of 230 g. These samples are to be tested by the operator according to posted instructions. Frequently, an additional sample should be taken and sent to the laboratory.

The procedure for taking a boiler water sample is a follows:

Case 1: When the conductivity indicator (Al-1001) is operated;

The sample is taken form the conductivity indicator outlet pipe.

Case 2. When the conductivity indicator (Al-1001) is not in good condition;

i) Open the cooling water valve of the sampling cooler on the continuous blowdown line.

ii) Do not disturb the setting of the needle valve. Open the sample valve and let the boiler water escape for a few seconds before taking the sample.

The sample must be sufficiently cold as drawn that none of it flashes into steam.

iii) Rinse the sample bottle twice with the boiler water before collecting the sample for test.

iv) Close the sample valve and the sampling cooler cooling water inlet v alve.

c) Boiler water level.

To avoid completely the entrainment of the water from the boiler into the steam lines, it is