DECLARATION

I hereby declare that this thesis work entitled "A study report on COAL CHEMICALS "is my work, carried out under the guidance of my faculty guide Miss CH.NAGAMANI and company guide Sri. G.VENKATA RAO, asst general Manager (O) of Visakhapatnam Steel Plant this report neither full nor in part has ever been submitted for award of any other degree of either this university or any other university.

PLACE: VisakhapatnamGSANJEEV SK.MOULALI ROHINI KUMAR.ODATE:

ACKNOWLEDGEMENT:

This project is a result of the hard work & sincere effort put by many hands. We would like to thank SRI G.VENKATA RAO, asst general Manager (O), Visakhapatnam Steel Plant, for his valuable guidance and timely advice during the study period for the successful completion of the Project work. We wish to render my sincere gratitude to the staff & Officers of Plant Personnel section, Visakhapatnam Steel Plant for their support in providing all relevant data, help and guidance in completing this project. Finally we thank the management of Visakhapatnam Steel Plant for permitting me to take up this Project.

Place: VisakhapatnamDate:G.SANJEEVSK.MOULALI ROHINI KUMAR

INDEX

Introduction of VSP Coke Ovens &Coal Chemical Plant Coal Preparation Plant Coke Oven Batteries Coal Chemical Plant Primary Gas Coolers Ammonium Sulphate Plant Final Gas Coolers M.B.C Tar Distillation P.C.L.A Naphthalene Fraction Crystallization Benzol Recovery Hydro Refining Extractive Distillation Unit

INTRODUCTION

The role of ferrous metals in general and of steel in particular in national economy is enormous. One cannot name an economic branch where ferrous metals find no applications. The economic power of country is determined by its output of steel, since it determines the progress in the principle economic branches, be it mining, transport, manufacture engineering or agriculture implements is unthinkable without steel.

An additional impetus for increasing the scope of steel manufacturers had been the vigorous progress in chemical engineering. It has turned out that steel can be very profitable combined with certain novel materials for instance plastic combined with stainless steel are excellent materials fore making furniture, decorating automobiles internal lining of houses and building purposes. As a result the manufacture of stainless steel has been appreciably increased in order to cover these new demands in recent years. The world for the steel rises continuously and is expected to reach the level of thousand million tons per year by the end of this century. The steel will obviously remains the principle structural material in for seeable.

To meet the above requirements the following iron and steel companies were established: Tata iron and steel company is the first ever-integrated steel plant in India in 1908 at Jamshedpur. TISCO in Bihar IISCO in Burnapur Bhadravathi steel in Karnataka Hindustan steel plant at Bhilai, Roerkela and Durgapur Visakhapatnam steel plant at Visakhapatnam

VISAKHAPATNAM STEEL PLANT

In order to increase the steel production reasonably high in the nation and remove the regional imbalances in industrial developments, the government of India took a great step in setting up the coastal-based steel plant of India is Visakhapatnam steel plant in Andhra Pradesh. This plant is located 16km south west of the city limits. A great emphasis has been made on total automation, seamless integration and efficient up gradiation at Visakhapatnam steel plant.This has resulted in a great demand for Visakhapatnam steel plant product in India and abroad which are having international standards. Visakhapatnam steel plant is considered to be the first integrated steel plant in India to become fully ISO-9002 certified company. This certificate covers quality systems of training and marketing functions over four regional marketing functions and 22 stock yards located allover the country. The decision of the government of India to set up an integrated steel plant at Visakhapatnam was announced by the Prime Minister Smt.Indira Gandhi. The plant was inaugurated formally on 20th January 1971 by the prime minister.

The project was estimated to the cost of rupees 3,897.28 crores based on process on 4th quarter of 1981 but during the implementation of VSP is has been on served that the project cost as increased substantially over the sanctioned coast mainly due to this and the approved concept were studied in 1986 the rationalization has basically been from the point of view of obtaining maximum output from the equipment already installed paneled for procurement, achieving the higher level of operation efficiency and procurement over what was envisaged earlier under the rationalized concept.3.1 million tons of liquid steel is to be produced in a year and the project is estimated to cost 5,822 crores based on 4th quarter of 1987.

VSPS FRUITFUL ACHIVEMENTS:

Ithascrossedmanymilestonesinthefieldsofproduction, productivity and exports. Coke rate at an order of 543kg/tonn hot metal Average converter life of 649 heats. An average of 11.5 heats per sequence in continuous bloom caster.

Specific energy consumption of 7.51 Kcal/ton of liquid steel. Specific refractory consumption of 15.2kg. A labor productivity of 192-ton/man yr.

COKE OVENS&COAL CHEMICAL PLANT

ORIGIN OF COAL:Coal originated from the arrested decay of the remains of trees, bushes, mosses, vines and other forms of plant life, which flourished in huge swamps and bogs millions of years ago, during prolonged periods of humid, tropical climate and abundant rainfall. Streams into the swamps and lake basins to form the coal beds carried an enormous amount of vegetations. Owing to pressure, the streams have generally been crushed to an elliptical section and formed coal.

USE OF COAL IN VSP:Coal is used in the form of coke to serve the purpose of iron ore reduction in blast furnace. It also serves as a heat source.

TYPES OF COAL:

There are 2 types of coal:(1) Coking Coal.(2) Non-Coking Coal. The different coking coals used in VSP are:1) M.C.C-Medium coking coal-BENGAL, BIHAR

2)I.C.C-Imported coking coal-AUSTRALIA

3)I.S.S.A.C-Imported coking coal-AUSTRALIA

4)SOFT-Imported coking coal-AUSTRALIA

In VSP coking coal is used for producing metallurgical coke where as non- coking coal is used for producing thermal power (in boilers).

TYPES OF COAL AND PROPERTIES:

S.NO.TYPE OF COAL%% ASHMEAN

MOISTUREMAXIMUM REFLUTANCE

1.M.C.C25-2817-220.9

2.I.C.C24-268-101.10-1.3

3.I.S.S.A.C23-258-101.16-1.3

4.SOFT30-348-100.9-1.0

COKE:

It is a strong porous hard mass that is obtained by heating of the coal in the absence of air at high temperature. It is a reactive fuel and satisfies the need for blast furnace.

FUNCTIONS OF COKE:

1. It acts as heat producer in blast furnace2. It acts as reducing agent by carbon reduction in blast furnace with oxygen reaction.3. It gives a permeable bed and also as a slag carrier. CARBONIZATION OF COAL:Heating of coal in the absence of air at high temperatures to produce residue coke, coke oven gas is called CARBONISATION OF COAL or DESTRUCTIVE DISTILLATION. Its main purpose is to produce coke and the by-product known as coke oven gas from which various products are obtained and this is used as fuel of high calorific value.

NEED FOR MANUFACTURE OF COKE FROM COAL:1. Natural coal is too dense and fragile to be used as a fuel in the furnace.2. Coal is not strong enough to withstand nearly 25 mts of burden lying on it inside the furnace.3. Coal is nearly VOLATILE MATTER FREE so it does not create problems of hot shortness and coal shortness.4. As compared to coal coke is of high quality and is highly reactive.5. Coke is highly porous mass and it equalizes the blast coming from the bottom of the charge.6. As coke is a rigid hard mass it does not create the problems of dust nuscence.7. The ASH CONTENT in coke is very low i.e.) around 10%. So it does not arise problems of striking on the grates.

The coke oven and coal chemical plant is mainly divided into the following department:1. Coal Preparation Plant(C.P.P)2. Coke Oven Batteries3. Coal Chemical Plant(C.C.P)

COAL PREPARATION PLANTPURPOSE OF COAL PREPARATION PLANT:

The main purpose of this plant is to prepare the coal by removing the foreign matter and bringing to the size suitable for carbonization or coking process.

COAL BLEND COMPOSITION:

1. M.C.C-15%2. I.C.C-40%3. I.S.S.A.C.C -35%4. SOFT-10% PROPERTIES: VOLATILE MATTER:It is the matter which is unstable at high temperature and converts itself into gaseous state like tar, benzene compounds etc. it is around 20-25%. MEAN MAXIMUM REFLUCTANCE:It is a coal ranking. It decides the properties of coal. It is around 1.12-1.14. CRUSING INDEX:% of -3mm size particles which should be around 70% - 75% FIXED CARBON:The carbon left behind after the removal of the volatile matter is fixed carbon. ASH CONTENT:The % of ash present in coal. It can known by testing in the laboratory. It is around 17-22 in Indian coking coal & 8-10 in imported coking coal. TOTAL MOISTURE:The amount of total moisture present in coal. There lies some internal moisture also.

CONTENTS IN 1 TON OF COAL:

1. Coke-746 kgs2. Crude Tar-32kgs3. Crude Benzol-6.9 kgs4. Ammonia-4.1 kgs5. CO Gas-150 kgs6. Losses-61kgs

COALPREPARATIONPLANTCONSISTSOFFOLLOWING SECTIONS:

Foreign material separation section Selective crushing sections.

FOREIGN MATERIAL SEPERATION SECTION:

The coking coal is taken from coal yard by using bucket elevators on the conveyors. Then it is sent to foreign material separation section.

In foreign material separation section the following equipment exists:

1. 2 Cylindrical screens.2. 2 Suspended iron separators.3. 2Selfunloadingsuspendedironseparatorsforseparatingthe magnetic particles in the coal.PROCESS:

First the suspended iron separators separate the iron particles in the coal. After it is demagnetized, the separated coal falls on self-unloading suspended separators. it works for 19 seconds. After that coal is separated into +150 mm & -150 mm sized particles in rotary screens. +150 mm sized particles fall in the chute and are sent back for crushing. Where as -150 mm particles are transferred to reversible conveyors. There are further connected

to shuttle conveyors for filling the bins. There are a total of 16 bins, equally divided into 2 rows. All the odds like 1, 3, 5, 7, 9, 11, 13, 15 & the evens 2,4, 6, 8, 10, 12, 14, 16. The capacity of each bin being 800 T and a height of20 mts.

Specifications of cylindrical screen: Inclined angle-8Feed end length-1.5 m Discharge end length-0.8 m Mesh size-150 mm

1. SELECTIVE CRUSHING SECTION:

Blended coal is send to selective crushing section for crushing of coal from -150 mm to -3mm size. In selective crushing section there are 3 primary crushers and 2 secondary crushers for crushing the coal. First coal is crushed in primary crushers. Then crushers are connected from6.6 KV motors via variable speed coupling and gear box. Speed of motor is controlled from 1000 rpm to 400 rpm by variable speed coupling in order to avoid the breakage of crushers and sudden stoppage of crushers. In primary crushers there are 88 hammers in 12 rows of universal crushing.Total no. of crushers- 5Primary crushers- 3Secondary crushers- 2Cap. of primary crusher-400 T/hr Cap. of secondary crusher-600 T/hr No. of hammers-88(12 rows)Wt of each hammer-19.7 kgsWt of arm-6.0 kgsLength of arm-45.0 kgsMaterial of construction-Nickel Chromium Steel Rotations of hammer-400 rpm

COKE OVEN BATTERIES

Coal is converted into coke by high temperature carbonization in the ovens of the battery. There are 3 batteries working and the Battery 4 is being constructed for more production of hot metal.

RAW MATERIAL-Coal blend.PRODUCT-Coke with 1-3% volatile matter. BY-PRODUCT-Raw coke oven gas.

CONSTRUCTION:

The total length of the battery is 100 mts. It consists of rectangular chambers of length 16 mts, 7 mts high and 0.14 mts width with removal door ends. Coke oven battery is a combination of ovens and heating chambers in alternatively. There are 67 ovens and 68 heating chambers in a battery. These ovens are OTTO-HOFFOMENS by-product oven type. On the roof there are metal lids for the sake of charging purpose. The width of the coke discharge side is slightly more than the pusher side for easy transport of coke outside. Heating flues are arranged in the walls between the ovens. There are regenerators underneath the battery. The oven walls are lined with silica bricks of high thermal conductivity. There is no shrinkage in the refractory walls. These bricks ensure long life. All doors are sealed with refractory clay and water mixture.Battery has 4 machines:1) Pusher car2) Charging car3) Door extractor car4) Loco car PROCESS:Coal is transported from coal preparation plant to coal tower above the battery. a charging car travels on the battery and under the coal tower. 32 T of coal is charged in each oven up to a height of 6.7 mts out of 7 mts by charging position in each oven. Since the coal drops by gravity, it should be leveled which is done by a leveling bar fixed to the pusher car. After leveling all lids and doors are replaced and coking process is continued until most of the volatile matter is removed. This process takes a coking period of 17-18 hrs by indirect heating with coke oven gas or mixed gas (CO gas + BF gas) in absence of air at 1150c.

After complete carbonization, coke oven gas is collected by hydraulic main that is connected to the ovens, which are sent to recovery plant for

cleaning of gas. Later it is sent to recovery plant for cleaning of gas. After cleaning CO gas is recycled back to the battery for heating purpose. The product is 1-3% moisture contained coke. Yield of coke by HIGH TEMPERATURE CARBONIZATION at 900c - 1200c is 65-75%.

Calori3fi3c value of di3fferent gasses used for heating purpose: CV of Coke oven gas-4200 K Cal /Nm3 CV of Blast furnace gas-750K Cal /Nm CV of Mixed gas-1000K Cal /Nm3

The walls start after 5 m level. Until 5 m level it is called the regenerator. The regenerators serve the purpose of recovering heat by heat exchange between hot flue gasses and bricks. The air coming in. thus air gets preheated in the regeneration section takes this heat. In the first cycle fuel gas flows through one set of flues and flue gas goes out through other set of flues. There are 136 waste heat boxes through which air is supplied form one section and flue gas leaves through other section.

As hot air is of low density and by the density difference suction is created by which flue gas rises up out of the chimney. Checker bricks made of silica are placed in the regeneration section so that the contact area and time for regeneration increases and maximum heat is recovered.

SPECIFICATION:Total no of Batteries-4

No of ovens in each Battery-67

Heating wallsHeight of each oven Length of each ovenWidth of each oven(P/S,C/S) Heating wall thicknessCoal charging in each oven Output coke from oven No of vertical flues-68 7 mts 16 mts-38.5 / 43.5 mm-0.105 mts 34 tons 25 tons-32

No of waste heat boxesHeating gas used in Battery 1&2 Heating gas used in Battery 3-136 CO gas CO+BFgas

in1:9

ratios.

Coking period Coke temperatureCoke fluidity temperature-17-18 hrs-1050c-400-500c

Capacity of battery-97 pushing/Battery/day Coking Period Determination (C.P.D)

hrs

No of ovens x 2467 X 24C.P.D=------------------------- =------------=1608No of pushings per day100COKE DRY COOLING PLANT

After pushing the coke from the Battery with a temperature of 1050c, it is transferred into C.D.C.P for cooling purpose. The C.D.C.P technology is adopted only in VISAKHAPANAM STEEL PLANT only because in wet cooling the strength of the coke is reduced.

The advantages of DRY COOLING are:1) Waste heat recovery (by producing steam)2) Pollution control (done by closed circuit)3) Better Coke strength (there is no thermal shock as in wet cooling) PROCESS:Coke form Battery falls into loco on the coke side, which is brought into C.D.C.P. The loco is lifted up and coke is charged into the cooling chambers. Later the chambers are closed by lid and N2 gas is passed inside through a temperature of 55c by a mill fan. The hot coke is cooled from 1050c to 180c-200c. There occurs no chemical reaction, as N2 is an inert gas. The heated gas is utilized for producing steam in boilers. These boilers are water tube boilers, which are of capacity 25 T/hr. the temperature and pressure of the steam, are 440c and 40 Kg/cm2. Cooled coke i3s convey6ed to C.S.P and the steam is used to run back pressure turbine station for producing power of 15 MW.

SPECIFICATIONS OF C.D.C.P:

No of C.D.C.P-4/4 Batteries

No of chambers-4 Chambers/each C.D.C.P

Capacity of each C.D.C.P-50-52 T/hr

Coke temp before cooling-1050c

Coke temp after cooling-180c-200c

Coolant used-N2 gas

Dry coolant temperature-55c

COKE SORTING PLANT

Coke from C.D.C.P enters the C.S.P section. Here coke is crushed, screened and later conveyed to different consumers.

PROCESS:

In C.S.P dust will be removed from the coke with the help of dedusting fans. After that coke is sent to crushing section to crush into 80mm size particles. There B.F coke (25-80mm) is separated through 14- roll screen and sent to Blast Furnace. The remaining 0-25 mm fractions will be sent to vibrating screen. Here 0-10 mm particles called BREEZE COKE is conveyed to Sinter Plant and 10-25 mm called NUT COKE to Blast Furnace.

COAL CHEMICAL PLANTMany by products are extracted from the coke oven gas at this department. It consists of the following sections:

Exhauster house.

Ammonium sulphate plant.

M.B.C plant.

Tar distillation plant.

P.C.L.A

Naphthalene fraction crystallization.

Benzol plant. Benzol distillation plant. Hydro refining. Extractive distillation.

PRIMARYGASCOOLERThe coke oven gas from the separator is fed to the PGC from the top. The cooler consists of three zones. This is a shell and tube heat exchanger in which the CO gas exchanges with service water in the top two zones and with chilled water in the bottom zone the tubes are inclined in all the zones. The inclination is maintained at 15c with the horizontal. This provides any naphthalene condensate to drain easily. The main purpose of PGC is to cool the gas from 90c to 30c.During this cooling process the naphthalene and traces of tar present in the gas condense and this is collected at the bottom of the PGC. The liquid collected at the bottom is sent to the seal pot by gravity. The level in the seal pot should be maintained constant as this acts as a seal to the gas in the cooler.Tar at a temperature of 90c is flushed from the top of the cooler to remove the condensed naphthalene on the tubes. The tar is then collected at the bottom in the seal pot. Tar and naphthalene from the seal pot is fed to the storage tank of the CPH. The CO gas from the bottom of the PGC is fed to the electrostatic precipitator.

Gas temperature before PGC80-95cGas temperature after PGC27-30cService water inlet temperature32-33cService water outlet temperature43cGas condensate flow to each PGC10-15 Nm3/hrChilled water inlet temperature11-12cChilled water outlet temperature20cTotal number of tubes409ELECTROSTATIC PRECIPITATOR:

The CO gas enters the ESP from the bottom. Electrostatic precipitators are cylindrical vessels with a conical bottom. Each ESP is provided with a seal pot. A round disk having electrodes in suspended state is present inside the precipitator. Electrodes are nothing but SS metal rods. Three are present at the top of precipitator, which supplies the necessary power to each ESP. high voltage of about 50,000 volts is supplied to each electrode. Due to high voltage the fine and foggy tar get sticked to the walls of the electrodes and they fall down due to gravity. The liquid thus collected at the bottom is fed to the seal pot. Each electrode is covered to prevent the connection between any two electrodes.

Capacity30,000 Nm3/hrVoltage70KVNumber of electrodes148ESP insulator boxes temperature80C EXHAUSTERS:These are centrifugal fans necessary to drive the gas from the batteries itself to various plants like ASP. Benzene recovery and finally to the main header of the coke oven gas. Exhauster sucks the CO gas from the batteries. The pressure at the suction side of the exhauster is -350mm WC and the discharge side is +2500mm WC. Due to increase in the pressure the temperature is increased to 55-60c.

The flow of gas is controlled by Askania valve, which is a butterfly valve. The function of this valve is to control the flow of gas to the exhauster. When the quantity of gas is low then the valve is closed and when the gas quantity is high valve is opened. If any condensate is collected and when the gas lines and sent to the storage tank of the condensate pump house.

Capacity67,000-76,000Nm3/hrPower1250KWMaximum suction at inlet500mm WC g Maximum pressure at delivery2700mm WC g

CONDENSATE PUMP HOUSE:

Flushing liquor separated from the separators is fed to the condensate pump house. This consists of decanters and storage tanks. The tar and flushing liquor collected from the exhauster house is stored in the storage tanks.

DECANTERS:

Decanters are used to settle the flushing liquor by gravity. These are mechanical decanters provided with scraper mechanism. This scraper is a chain like arrangement provided at the bottom. The flushing liquor is fed at the middle of the decanter. In decanters due to density difference, flushing liquor, tar & sludge form as three layers from top, and the flushing liquor is then sent to the storage tanks.

A telescopic valve provided to the decanter removes the tar settled in the middle layer. The valve works on the principle of U tube manometer. Sludge removed by scraper mechanism provided at the bottom of the decanter. The scraper then dumps the sludge into a bunker provided at the end of the scraper. A motor provided with a gearbox runs the scraper. The sludge from the bunker is removed periodically.

Tar collected from the flushing liquor decanter is stored in the tar storage tanks. Then it is pumped to tar decanters. The tar from the tar decanters contains less moisture and sludge. Flushing liquor from the decanter is stored in the storage tank and again pumped to batteries. If the flushing liquor is excess then 60% is sent to excess flushing liquor tanks.

AMMONIUM SULPHATE PLANTCoke oven gas with a pressure of 2500mm WC from exhauster is fed to the ASP. Ammonia present in the CO gas is recovered in ASP as ammonium sulphate fertilizer.

PROCESS:

The CO gas from the exhauster is fed to the pre-heater to preheat the gas to 60-70c. But according to our atmospheric temperature, this temperature is obtained after the exhauster. So the gas is directly fed to the saturator.

SATURATOR:

Saturator is a cylindrical vessel with conical bottom. It is provided with a bubbler hood, which is duct prolonged to the middle of the saturator. The duct has a hood at the bottom provided with vanes like arrangement. Another ring like structure with small openings is provided at the conical portion, which is used for nitrogen feeding. Hot water rings are provided at the top of the saturator. Saturator is always maintained with acid bath called mother liquor, which contains 4-5% of sulphuric acid.The CO gas enters through the bubbler hood which is dipped in the bath. The gas rises through the mother liquor. During this period, the ammonia present in the gas reacts with the sulphuric acid in the liquor.

NH3+H2SO4NH4 (HSO4) NH4 (HSO4)+NH3(NH4)2SO4

Ammonium sulphate thus formed settles at the bottom of the saturator. Pure nitrogen is purged into the saturator through N2 rings at 4-5 kg/cm2. N2 purging increases the crystal growth. Pure sulphuric acid (98%) is fed to the saturator to maintain the acidity in the saturator. The gas collected at the top of the saturator is fed to the acid trap. As the gas rises up, some of the crystals may be carried with the gas and they get stacked to the walls of the saturator at the top. Then the hot water is sprayed to the rings provided. The crystals attached to the walls of the saturator are washed away. When hot water is sprayed the concentration of the liquor decreases. So inlet acid concentration increases to 6-7% at that period. After the reaction mother liquor is continuously drawn to the circulating tank provided at the side of the saturator. This acts as a seal for the saturator. From the circulating tank, mother liquor is fed to the mother liquor tank. The crystals collected at the bottom are fed to the crystal receiver tank by using pump.

ACID TRAP:

The outlet gas of the saturator carries some acid mist. In order to remove the acid mist, the gas is sent to the acid trap. It is a hollow cylindrical vessel. The coke oven gas from saturator enters tangentially to the trap. Due to the centrifugal motion, the acid mist gets separated. The acid collected a the bottom is fed to the circulating tank. The CO gas is fed to the Benzol recovery.

CRYSTAL RECIEVER TANK:

Ammonium slurry from the bottom of the saturator is pumped to the crystal receiver tank with conical bottom. The ammonium sulphate crystal settled at the conical portion of the tank, which is wet with liquor. The mother liquor from the top of the receiver is fed to the saturator. The slurry from the bottom is fed to the centrifuge.

CENTRIFUGE:

Centrifuge is a horizontal cylindrical structure having two drums inside it. One drum moves with rotary motion and the other in reciprocating

motion. The feed enters at the center of the rotation drum through pipe known as cone pipe. Crystals present in the slurry are separated by the centrifugal force of the rum. Hot water is sprayed into the centrifuge to wash of the free acidity that is the acid layer on the crystal.The cleaned crystal is discharged into the outer drum which is reciprocating. The reciprocating drum pushes the material into the discharge chute. The liquor seper4ated is then sent to the saturator. The discharge chute of crystals opens onto a conveyor.

DRIER:

Drier is fluidized bed type. The principle is based on the loose materials property to acquire fluidity in the airflow under a definite air velocity. The crystal from the centrifuge contains some amount of moisture. To remove this moisture crystals are to be dried. The drier is provided with a screen at the bottom, ceramic rings are arranged at the bottom of the screen. The drier is provided with forced draught fan and air, heated in the duct. A spreader at the feed chute of the drier spreads the feed in all directions.Forced draught fan sucks the atmospheric air and feeds to the drier. The discharge chute of the fan is divided into 2 sections. One for hot air and the other for cold air. The hot air duct is provided with a steam heater. The air is heated to 120-150c by using steam and this hot air is fed form the bottom of the screen. The ceramic rings distribute the air in all directions and allow the crystals in fluidized state. The temperature of the air is sufficient the moisture of the crystals. At the discharge end of the drier, cold air is passed which cools the crystals.

When the pressure level of the fluidized bed reaches the set point (300-400 mmWc) an automatic discharge feeder discharge the dry ammonium sulphate to the bucket elevator .The elevator discharges the dry product into the bunker, which in turn feeds the product to the bagging machine. The zone above the fluidized bed is kept under 5-10 mmWc in order to avoid carryover of the ammonium sulphate particles out of the dr4ying unit to the dust catcher.

CYCLONES:

The air form the drier is sucked by the suction fan and fed to the cyclone separators. Cyclone separators separate fine ammonium sulphate crystals in the air and feed to the bunker. The air from the cyclones is fed to the dust collecting tank which contains flushing liquor up to certain level.

The dust laden air is then fed to the bottom of the tank. The crystals then dissolved in the water and the air is vented into the atmosphere.

MOTHER LIQUOR TANK:

The excess liquor from the saturator enters the mother liquor tank. Each saturator is provided with two mother liquor tanks. One is vertical and the other is horizontal. First the liquor enters the horizontal tank. As the liquor has less density than the tar it floats. Then the clear mother liquor from the bottom is fed to the vertical tank. Form the bottom of the vertical tank mother liquor is fed to the saturator through the pumps provided. The concentration of the liquor is maintained 10-12%. If the concentration decreases, the density of the liquor decreases and it may be contaminated. Then crystals may become back.

AMMONIA COLUMN:

During carbonization of coal ammonia gets vaporized and flows along with flushing liquor in gas collecting mains, a little amount of ammonia gets absorbed in flushing liquor. The excess ammonium liquor after separation of tar, containing free and fixed ammonia, phenols, pyridine bases and cyanides, rodents are pumped to the fourth plate of the ammonia column for distillation of free ammonia.The column consists of 24 bubble cap trays. 40% of liquor level is maintained in the column. Steam is injected at the bottom by steam coils. The purpose of steam is to supply the necessary heat required for distillation. As the liquor is distilled, free ammonia present in the flushing liquor evolves and rises tot the top of the column. The distilled liquor from the bottom of the column is fed to the pitch tank. Certain level of the flushing liquor is maintained in the tank and the over flow from the tank is fed to the M.B.C Plant for treatment. The pH of the flushing liquor at the discharge end of the column should be 7-7.5 and the free ammonia should be less than 50 PPM.

(NH4)2S2NH3+H2S

NH4CNNH3+HCN

(NH4)2CO32NH3+CO2+H2O

NH4HCO3NH3+H2O+CO2

NH4HSNH3+H2S

The ammonia vapors collected at the top of the column are fed before primary gas coolers. The gases are not fed to the saturators directly as the temperature of the vapors is high and secondly the vapors contains not only ammonia but also some traces of rhodonides and cyanides.These chemicals should not be present in the ammonium sulphate fertilizer. To remove some content of fixed ammonia in the liquor, dilute NaOH solution is injected at the inlet of the ammonia column. The NaOH reacts with the fixed ammonia compounds and forms as ammonia gas.

Capacity25m3/hrTotal trays24Types of traysBubble capWorking pressure0.5 atmSteam pressure6 atmFlow rate of liquor25m3/hr Ammonia content before column4 g/lit Ammonia content after column50 mg/lit Temperature of vapors at outlet105cLevel in the column40-50%Steam flow rate3-3.5 ton/hrPH of liquor after column7-7.5

FINAL GAS COOLERSCoke oven gas after ammonia recovery consists of 0.8-1.12 mg/lit of naphthalene. These naphthalene particles are removed by spraying tar.

Temperature at the bottom of FGC50-60cNaphthalene in CO gas after FGC0.4 g/Nm3FGC tar temperature80-90cSpecific gravity of FGC tar moisture5% GAS PRE-COOLER:The gas at 30-35c is fed to the pre-cooler, which is indirect contact cooler. The gas is cooled by chilled water (150c), which passes through the tubes. The gas is cooled to 25-27c so that any particles condensed are received in the seal pot.

SCRUBBERS:

Scrubbers are long towers consisting of aluminum packing or wooden sheets provided with three layers. The main draw back of wooden sheets is that it requires large cross-section and more height, while aluminum is efficient. But the condensate should not have muggy materials, which stick to the plates and scrubbing cannot be done efficiently.

The CO gas from the gas pre-coolers is sent to the first benzol scrubber at the bottom. Solar oil or de-benzolised oil is used for scrubbing the gas to recover benzol. Large amount of the benzol is absorbed in the first scrubber. At the bottom of the first scrubber a certain level of benzolised oil is maintained. CO gas from the top of the first scrubber is fed to the bottom of the second scrubber in which it comes to contact with fresh de-benzolised oil, which removes the traces of benzol remaining in the gas. The benzol free CO gas is sent to customers.

Capacity58,000Nm3/hrOil flow rate150m3/hrBenzol content in gas after benzol scrubber3 g/Nm3 Specific gravity of solar oil0.8428Molecular weight of solar oil230Flash point132cInitial boiling point270c

OIL CYCLE:The DBO from benzol distillation unit is fed to the top of the second scrubber. Benzolised oil from the bottom of the second scrubber is pumped to the top of the first scrubber through the distribution nozzles. The benzolised oil collected at the bottom of the first scrubber is sent to the benzolised oil tank from where it is pumped to the benzol distillation section.

DRY PURIFICATION UNIT:

700-1000 Nm3 /Hr of coke oven gas is sent to dry purification unit when H2S of the gas is required to be removed from 0.6-0.7 gms/ Nm3 to0.02 gms/ Nm3. The H2S free CO gas is sent to laborites and other special consumers like GETS at BF, CO gas is supplied to dry purification unit After the electrostatic precipitators. Synthetic bog is used as a purification mass. Spent purification mass containing 24 to 25 % sulpher is transferred to dump.

COMPRESSOR HOUSE:

Compressor house provided in the recovery plant is used to supply the plant air and instrument air. In this process air from the atmosphere is fed to the suction side of the compressor through filters for removing the dust particles.

COMPRESSOR:

Reciprocating compressors are used to compress the air up to 6 kg/cm2. This is double acting piston type, which consists of low-pressure side and high-pressure side. A motor drives the compressor. An inter cooler is provided between the LP side and the HP side. An after cooler is provided to cool the air.

Air initially fed to the low-pressure side where it is compressed to 2 kg/cm2. Due to compressor the temperature of the air is increases and it is cooled in the inter cooler. This avoids decrease in the compression efficiency on the high-pressure side. Air is compressed up to 6 kg/cm2 in the HP side. The compressed air is fed to the after cooler. The purpose of this cooler is to remove the moisture in the air. The air from the after cooler is fed to air receiving tanks. Air in the receiving tanks contain moisture and oil particles. So this air cannot be used for instruments. This air is used for cooling and other purposes.

In the compression of air the lube oil is used for compressor bearings. In this process, some oil is mixed with air. To remove this oil the air is fed to the oil filter. The air is then fed to the coke filters where coke layers are placed. This removes moisture and dust particles in the air. Then the air is fed to the dryers in which a bed of activated alumina is placed. This eliminates complete moisture and from dryers the air is fed to the candy filters in which very fine particles of moisture and dust is removed. Then the air is again fed to the buffer vessels, which is an intermediate storage. The dried air is supplied to the instruments and its pressure is in the range of 4 kg/cm2.

MECHANICAL BIOLOGICAL AND CHEMICAL TREATMENT PLANTPROCESS:

Toxic effluents generated in various sections of coke oven and by- product plant are collected and pumped to the treatment plant from two pump houses. One at ammonium sulphate section and the other at tar distillation section. Excess flushing after removal of ammonia in ammonium stripping unit is also fed to this treatment plant. The combined effluent contains large amount of tar and oils and toxicants like phenol, cyanide, thiocyanides etc.

The effluent plant is designed to remove tar and oils with the help of mechanical separation methods followed by biological treatment at effluent namely two stage activated sludge process to remove other toxicants.

Phenolic effluent from two phenolic water pump houses located in CO & CCP are directly fed to pre-aerators of tar settling plants. Excess flushing liquor ammonia stripping is also pumped to the same pre-aerators to

the double pipe heat exchangers where it is cooled from 90c with the help of recalculating cooling water. Water inlet temperature is 34c and outlet temperature is 45c. Mixed effluent at a temperature of about 50c is distributed in equal positions in tar settling tanks by gravity. In pre-aerators effluent mixed thoroughly with the help of air. The tar settling tanks are provided with steam heating coil and scrapper mechanism at the conical hopper bottom. Tar collected at the bottom of each tank is pumped out in the tar collecting tanks ones in 3-5 days time. Tar settling tanks are provided for removing tar and oil form the effluents. Oil floated on the surface of water and tar settles down in the conical bottom. Floated oil removed with the help of scrapping device and flows to oil collecting tanks by gravity.

Over flow from the tar settling tank is collected in vertical steel tanks named phenolic water collecting tanks from where it is pumped to the oil flotation tank through pressurized head tank. Air (5% by volume of water) is injected in the suction line of the pumps before it is pumped to the pressures tank. In the flotation tank air bubbles through the water as the water is depressurized and the oil is entrained by air bubbles and floats at the water surface. The entrained oil is skimmed with oil skimmer mechanism of the flotation tanks and collected to the oil discharge to a tank called tar and oil collecting tank. After oil flotation tank, water goes to the second phenolic water collecting tank, with the help of pump collected water is send to second flotation tank to pressurized tank. Tar and oil from the collecting tank are finally pumped to tar acid utilization plant.

After removal of tar and oil the effluent is collected in averaging tank. The averaging tank consists of two chambers and each chamber is having one over flow tank.

In this tank adding ortho phosphoric acid and bacteria nutrient. 73% strong ortho phosphoric acid at the rate of 20 g/m3 of water to be purified. From these tanks effluent is pumped to aeration tank of first stage purification through shell and tube heat exchangers to maintain effluent temperature between 35-38c. Cold circulating water is used for this purpose. In this first stage purification is done with the help of phenol destruction bacteria. To maintain their vital activity, compressed air from the air blower is applied to the aeration tank.

Phenolic water after the first stage of purification is collected in a tank from where it is pumped to aeration tank of second stage purification. In second stage of purification rodents and cyanides are destroyed with the help of rodents destructing bacteria. With each aeration tank (both 1 & 2 stage) of purification sludge settling tank regeneration are attached. The over

flow from each tank first goes to the settling tank where sludge settles down and the super latent water overflows to the collecting of first stage purified water collecting tank.

The settled sludge then flows to the attached regeneration from where it is recycled back to the aeration tanks with the help of air lifting pump. Volumetric flow rate of sludge in each tank its about 80% of the volumetric flow rate of water being purified, to treatment unit for further treatment. Inlet to the treatment plant as well as excess sludge is taken from the bottom of the settling tank and taken to sludge disposal facilities having sludge-drying beds. Treatment effluent from the second stage of purification is collected on a tank from where it is pumped to fecal sewage treatment plant for further treatment and dilution. Further culture of bacteria their accumulation two separate bacteria culture tanks requisite facilities are also provided which can be utilized and when required.

Two MS tanks each of capacity 800m3 are provided as balancing tanks. Water can be pumped from any of the equipment, provision is there to take this water back treated water from the collecting tank after second of purification can also be directed to a balancing tanks.

TARDISTILLATIONPLANT

Tar is a viscous fraction obtained by the cooling of coke oven gas with ammonia liquor. During this cooling coke dust particles mixed with liquor and forms coal tar. It consists of large chain aromatic compounds, which can be distilled into light oils, phenols, naphthalene oil, wash oil and pitch. Coal tar in coke oven gas is collected from CPH and final gas a cooler of benzol recovery is transferred to tar and oil storage. From there it is pumped to mechanized decanter in tar distillation plant.

COMPOSITION OF COAL TAR COMING TO TDS:

Light oil0.5%

Phenol fraction1-1.5%

Naphthalene5-6%

Wash oil8-9%

Anthracene oil18-19%

Moistur4e5-6%

Pi3tch55-60%

PROCESS:

The tar from the condensate pump house is fed to the tar and oil storage of the TDP. The tar to the tar distillation section is fed from the tar and oil storage tanks. This tar contains 5% of moisture, which can be removed in the decanters.

DECANTERS:

The tar from the TOS is fed to the decanters. It is provided with a scraper conveyer to remove the sludge collected at the bottom and transferred to a bunker in the decanter small quantities of water and flushing liquor collects at the top of layer which are continuously removed.The tar from the decanters flows through two strainers to remove suspended matter to a common suction header of liquor plunger pumps for first stage. A plunger pump consists of three piston, suction and delivery valves, which pump with high pressure. Tar initially consists chloride salts and acid, which causes corrosion and damages the piping present in the furnace and the plant. To prevent the soda ash solution of 8% concentration is injected at the suction side of the pumps.

2NH4Cl+Na2CO3---------- 2NaCl +2NH3+CO2+H2O

2HCl+Na2CO3---------- 2NaCl +H2O+CO2

The ammonia formed from the above reactions vaporizes along with water vapor and light oils.

FURNACE:

It consists of two zones one is convection zone and the other is radiation zone. Furnace is having four burners where CO gas is used as fuel. Air draught is taken from the bottom of the furnace. The tar from the filter is pumped to convection zone, which is at the top of the furnace. Here the temperature increases to 120-130c. Controlling the airflow can control the flame length more the air longer the flame and vice versa. This arrangement helps in controlling the temperatures of tar in both the zones.

In radiation zone dehydrated tar is circulated which is pumped from second stage plunger pumps. The temperature of the tar is increased to 400c. The temperature of the tar should not increase beyond 400c as this cause the formation of B.F grade pitch.

The flue gas from the furnace is sent to the atmosphere through the chimney. It is provided with a baffle plate in order to assure complete combustion of the gas.

I STAGE EVAPORATOR:

Evaporator is a cylindrical vessel having baffle plates, which change the direction of gases. Evaporator is designed for the evaporation of water and light oils from the crude tar, which are fed at the middle of the evaporator. The temperature of the tar at the inlet is about 120-130c. Due to this temperature, the moisture in the tar is evaporated. These vapors from the top of the evaporator are fed to the twin condensed coolers. From the bottom dehydrated tar having less than 2% moisture is fed to the dehydrator tar tank and pumped to the radiation zone of the furnace.

Pressure in the evaporator0.3 kg/cm2 Temperatures of vapors102-105c Temperature of DTT