Tata Steel Project

TO STUDY ABOUT SAFETY INTERLOCKS OF COG EXHAUSTERS AND BOOSTERS [Report Subtitle]

Shubham Pandey | [Course Title] | [Date]

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INTRODUCTION TO TATA STEEL SADSAD DSD SDFDSF DSFDSF DG DFGFDGDF SGDF GDFGDF GFSD G DFSGFD G FDG DFG DF GD FG DF G SDG FGSGDSF DFSGDFSG dgDFGDSGFDGDGDSG DG DFGDF

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G

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COKE PLANT

Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. In the coke ovens, naturally found coal is converted into coke which is suitable for use in blast furnaces. The coke oven by-product plant is an integral part of the by-product coke making process. In the process of converting coal into coke using the by-product coke oven, the Coke Oven Gas, tar, ammonia, naphthalene, etc. are produced as by product. Sections of Coke Plant are: 1) 2) 3) 4)

Coal Handling Batteries Coke handling By Product Plant

1) Coal Handling:Coal is brought from Jharia, Jamadoba, West Bokaro and imported from Australia. This coal is normally unloaded by wagon tipplers. To prepare coal blend suitable for carbonization, various steps involved are unloading and storage of coal, blending of coal of various grade, coal crushing and transport to coal storage tower. 2) Batteries:Coking is a process of heating the coal, resulting in a solid, porous, and carbonized residue, together  with the evolution of a certain number of volatile products that escape the coking chamber. The process of carbonization takes place in batteries. There are batteries in operation. Battery# battery# Battery# Battery# Battery#

The batteries have employed new technology for charging the raw coal into ovens namely Stamp Charging using SCP machines (stamping, charging and pushing) in order to obtain high output of coke and of improved quality. The role of SCP ( Stamping charging pushing ) machines is pivotal in COKE PRODUCTION unit .

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3) Coke handling:Coke handling involves crushing and sorting of coke to suitable size for use in blast furnace. The steps involved are coke pushing, coke quenching, coke crushing/ screening. As per requirement, the various sizes of coal required are as follows: BLAST FURNACE COKE

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NUT COKE PEARL COKE COKE BREEZE

4) By Product Plant:The coke oven by-product plant is an integral part of the by-product coke making process. In the process of converting coal into coke using the by-product coke oven, the volatile matter in the coal is vaporized and driven off. This volatile matter leaves the coke oven chambers as hot, raw coke oven gas. After leaving the coke oven chambers, the raw coke oven gas is cooled which results in a liquid condensate stream and a gas stream. The functions of the by-product plant are to take these two streams from the coke ovens, to process them to recover by-product coal chemicals and to condition the gas so that it can be used as a fuel gas. COAL RECEIVED FROM WAGON TIPPLERS

BLAST FURNACE

GAS CLEANING BY NH3 & NAPTHALENE SCRUBBER 

COAL BLENDING

COAL CRUSHING(PRIMA  RY AND SECONDARY)

SERVICE BUNKER 

COKE OVENS

SCP MACHINES • STAMPING • CHARGING • PUSHING

COKE QUENCHING

GAS EXHAUSTER 

ELECTROSTA  TIC TAR PRECIPITATO R 

PCDC

BOOSTER 

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BY PRODUCT PLANT

In order to make raw coke oven gas suitable for use as a fuel gas at the coke oven battery and elsewhere in the steelmaking facility the by-product plant must:      

Cool the coke oven gas to condense out water vapor and contaminants Remove tar aerosols to prevent gas line/equipment fouling Remove ammonia to prevent gas line corrosion Remove naphthalene to prevent gas line fouling by condensation To supply clean gas at desired pressure to all consumers like gas grid  Water treatment of byproducts before releasing to atmosphere according to government norms

CHILLED WATER

FROM BATTERIES

PCDC

ETP EXHAUSTER HOUSE

NAPTHALENE SCRUBBER

NH3 SCRUBBER

BOOSTER HOUSE

TO GAS MILLS, GAS GRID, ETC.

GAS HOLDER

SCHEMATIC LAYOUT OF BY PRODUCT PLANT

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OVERVIEW OF BY PRODUCT PLANT:-

During carbonization, coal is converted to coke in coke oven batteries. The exhauster coke oven gas produced is laden with impurities which makes it difficult to use as a fuel. Raw gas has to subject to a process of cleaning before it can be put into st eel plant’s gas grid. Coal tar, naphthalene and ammonia are the three impurities which are removed in coke oven gas processing plant. Besides these chemicals, moisture, hydrogen cyanide and hydrogen are removed. The gas cleaning process at our byproduct plant is designed to handle on average of 1, 11,000 Nm 3 /hr. of coke oven gas. The exhauster, primary cum deep cooler and scrubbers can process coke oven gas peaks up to 1, 35,000 Nm 3 /hr. The crude gas coming out from the ovens at 850°C is cooled to 80 °C by spraying flushing liquor. The temperature of this gas is a very important controlling factor for the processes downstream. This is to be monitored and controlled very rigidly. The gases through foul main goes to the primary-cum-deep coolers (PCDC’s) where temp. drops from 80°C to 22°C. The main objectives of cooling the gas are: 1) Reducing the volume of the gas and thus decreasing load on downstream units. 2) Separating impurities by condensing them. 3) Facilitate the subsequent leaning of the gas through scrubbers (Absorption and adsorption of gases are favored at low temperature 1) PRIMARY CUM DEEP COOLERS:The first step in the treatment of raw coke oven gas is to cool it to remove water vapor and so greatly reduce its volume. This is done in the Primary Cooler. The lowering in temperature is caused by indirect cooling by water. Due to lowering in gas temperature from 80°C to 22°C. 98% of total tar is separated out of the gases 8.0-9096 of total naphthalene also condenses in PCDC’s.  A PCDC looks like a vertical box with rectangular cross-section. As the name suggests, this box is divided into two zones-namely the primary cooling zone and the deep cooling zone. We have thin tubes fixed horizontally all along the height of the PCDC through which water flows. The gases coming into the PCDC enter from the top of this rectangular box. These gases come indirectly into the contact with the gases flowing in thin tubes, thus causing heat transfer from gas to water, resulting in a temperature decrease in gas. The gas pressure at the top of PCDC’s is about -120 to -130 mm of WC. There is a pressure drop of about 70 mm of WC across the PCDC’s.  As indicated before, a PCDC is divided into two zones. The two zones are primary cooling zone and the deep cooling zone. There is no physical difference between the designs of these two zones. The only difference is that in the primary cooling zone, the gas cooling is achieved by service water,  whereas in the deep cooling zone, the gas cooling is achieved by refrigerated water. The purpose

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of deep cooling is to remove bulk of naphthalene from gas and remaining uncondensed tar and liquor. The rate of reversal of naphthalene into solid phase directly from vapour phase is very significant below 35°C. 2) ELECTROSTATIC TAR PRECIPITATOR: As the raw coke oven gas is cooled, tar vapor condenses and forms aerosols which are carried along  with the gas flow. These tar particles would contaminate and foul downstream processes and would foul gas lines and burner nozzles if allowed to continue in the gas stream. Each ETP is equipped with tubes or honey comb for the passage of gas. Within each cell of honey comb, wires are suspended through the insulated system from the top. Each wire has weigh attached to the bottom end to keep the wire taut. The wires in the tar precipitators typically use high voltage electrodes to charge the tar particles and then collect them from the gas by means of electrostatic attraction. The tar precipitators can be installed before, or after the exhauster. 3) EXHAUSTERS:The exhauster is a large blower that provides the motive force to induce the coke oven gas to flow from the coke oven battery and through the by-product plant. They suck the gas from the batteries and boost it to a higher pressure. An exhauster is a high speed centrifugal machine which is coupled  with a steam driven turbine. The exhauster is of prime importance to the operation of the coke oven battery. It allows the close control of the gas pressure in the collecting main, which in turn affects the degree of emissions from the battery. A failure of the exhauster will immediately result in venting to atmosphere, through the battery flares, of all of the raw coke oven gas produced. The speed of the exhauster is controlled by PG-PL governor which can be controlled manually or pneumatically by the governor. At TATA STEEL, usually 3 exhausters are run at a time while 1 runs idle. The governor which is not on load is not stopped. Instead, it is made to run at idle speed of 1000 R.P.M., to avoid any tar deposition and blockage of impellers. PARAMETERS TO BE CONTINUOUSLY MEASURED ARE:

Suction pressure before PCDC R.P.M. Steam pressure to the turbine Delivery pressure after exhauster

-120 to -130 mm of WC 3000 to 4000 R.P.M. 12-15 kg/cm2

The coke oven gas sent by exhauster comes to scrubbing unit for cleaning purpose. Pre scrubbing  would help in reducing the gas temperature also. It is done by flushing liquor.

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4)  AMMONIA SCRUBBING:Because of the corrosive nature of ammonia, its removal is a priority in coke oven by-product plants. The gas is scrubbed in a series of hollow cylindrical columns, where we spray stripped liquor on the gas directly in a stage wise fashion. There are 3 such scrubbers, each divided into 4 stages. Thus, there are total 12 stages of scrubbing, resulting in the final concentration of ammonia in the gas below 4g/100 Nm3. The resulting rich liquor solution is pumped to an ammonia still where steam is used to strip out the ammonia. The resulting vapor released from ammonia still is incinerated in ammonia incinerator. 5) NAPHTHALENE SCRUBBING:The temperature of the gas goes down after it comes from the ammonia scrubbers. Naphthalene being a highly sublime substance starts condensing directly in solid form as the temperature of the gas further goes down. After PCDC and ETP, this level goes down to 80-100 g/Nm 3. If naphthalene is not removed. It will cause unwanted deposition and choking of downstream gas for uninterrupted operation of the plant. Naphthalene is removed from coke oven gas using wash oil in a gas scrubbing vessel. The coke oven gas is passed through a series of naphthalene scrubbers, in which the gas rises from bottom to top facing wash oil being sprayed from a number of nozzles at the top. The vessel may be packed or it may be the "void" type in which the wash oil is sprayed into the gas in several stages. The wash oil is regenerated by stripping out the naphthalene from the wash oil using steam in a still. After 3 stages, we have pure CO gas with naphthalene below 12 g/Nm3. 6) BOOSTER OPERATION:The objective of booster operation is to send the coke oven gas to consuming ends like mills by boosting up its pressure. It is also a high speed centrifugal machine similar to an exhauster machine,  which boosts the pressure of coke oven gas, which is a main fuel in the reheating furnaces of most of the mills. The major difference between an exhauster and booster machine is the suction and delivery side pressures. The exhauster has a negative suction pressure and positive delivery pressure whereas, the booster has positive suction and delivery pressures. The pressure of gas after last naphthalene scrubber is 300 mm of WC, and is not sufficient for gas to reach the different consuming ends. Thus, we boost the gas pressure to about 1000-1200 mm of  WC, so that it can reach different mills situated at distant locations. There are 3 boosters, out of  which 2 run at a time while 1 runs idle. Thus cleaned gas passes through booster and gas holder in the circuit ensures stable pressure of coke oven gas in the gas circuit.

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COKE OVEN GAS EXHAUSTERS AND BOOSTERS

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