A

PROJECT REPORT

ON

COKE OVEN AND BY-PRODUCT PLANT

Prepared By: Checked By: Approved By:

Saurabh Vashishtha Mr. Siladitya Mukherjee Mr. Satyabrata

(GET-2014) (Project Facilitator) Chowdhury

(Section Head)

LARSEN & TOUBRO Ltd.

MMH-IC, EDRC- KOLKATA

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Acknowledgement

I have taken efforts in this project. However, it would not have been

possible without the kind support and help of many individuals and

organizations. I would like to extend my sincere thanks to all of them.

I would like to express my gratitude to Mr. Satyabrata Chowdhury,

Section Head & Mr. Siladitya Mukherjee, project facilitator of the project, for

guiding and correcting various documents of mine. I am highly indebted to

L&T for their guidance and constant supervision as well as for providing

necessary information regarding the project & also for their support in

completing the project.

I would also like to thank my colleagues for helping me in developing

this document and helping me during this training.

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TABLE OF CONTENTS

Acknowledgement...................................................................................................................ii

Table of contents.....................................................................................................................iii

List of figures...........................................................................................................................iv

Introduction..............................................................................................................................1

Chapter-1 Coke oven battery.....................................................................................................2

1.1 Coke.........................................................................................................................2

1.2 Classification of coke oven plant.............................................................................3

1.3 Coke making process...............................................................................................4

1.4 Charging gas collection..........................................................................................10

1.5 Wet quenching........................................................................................................11

1.6 Coke dry quenching...............................................................................................13

Chapter-2 By-Product plant.....................................................................................................15

2.1 Functions of a by-product plant.............................................................................15

2.2 Processing of liquid condensate stream.................................................................15

2.3 Processing of gas stream........................................................................................17

Current projects.....................................................................................................................21

Conclusion...............................................................................................................................21

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LIST OF FIGURES

Fig:1.1 Coke in steel making process.......................................................................................2

Fig:1.2 Top charging coke oven...............................................................................................4

Fig:1.3 Burning coke inside the oven.......................................................................................5

Fig:1.4 General layout of coke oven plant...............................................................................5

Fig:1.5 Coal tower....................................................................................................................6

Fig:1.6 PFD of coke oven battery............................................................................................7

Fig:1.7 PFD of coke oven plant...............................................................................................9

Fig:1.8 Gas collection system................................................................................................10

Fig:1.9 Gooseneck pipe..........................................................................................................11

Fig:1.10 Wet quenching tower.................................................................................................12

Fig:1.11 Spray system..............................................................................................................12

Fig:1.12 Coke dry quenching...................................................................................................13

Fig:2.1 By-product plant.........................................................................................................16

Fig:2.2 PFD of by-product plant.............................................................................................20

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INTRODUCTION

Coke is an important raw material in steel making process. For obtaining quality steel

from blast furnace, high quality raw material should be used. A high quality coke will result

in little degradation of blast furnace burden and provide the lowest amount of impurities,

highest thermal energy, highest metal reduction, and optimum permeability for the flow of

gaseous and molten products. Introduction of high quality coke to a blast furnace will result

in lower coke rate, higher productivity and lower hot metal cost.

This report is the study of Coke oven battery and by-product plant based on the

works undertaken by L&T. The study is part of the training schedule at EDRC Kolkata in

Larsen and Toubro ECC division for Graduate Engineer Trainee (GET). This report deals

only with Mechanical works of the plants.

Coke being an important part in the steel making process has its own

interesting production information. The coking process, historical sources say dates to the

4th century in ancient China. Since that time the process has undergone lot of changes. Coke

making simply is the process of heating special grade of coal in absence of air. Co first melts

into plastic form, re-solidifies and then stabilizes to form coke. Coke oven plant not only

has coke making as its important operation but also to take care of the charging gases

produced. Here comes by-product plant into picture which helps to clean the coke oven

gas and at the same time extracting by products which are used in some or the other form.

These plants also consist of some specialized equipments such as CGT car, quenching car etc

which are mentioned in the report ahead.

The report is divided in three chapters. The first chapter deals with the coke oven

battery. Process and equipment information related to plant is reported. In the second

chapter the subsequent by-product plant is seen with its process description and information

about various sub-plants as well as equipments are mentioned. Third and the final chapter is

conclusion of the complete training in the coke oven and by-product plant.

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COKE OVEN BATTERY CHAPTER-1

1.1 COKE:

Coke is the solid carbonaceous material derived from destructive distillation of low-

ash, low-sulphur bituminous coal. Cokes from coal are grey, hard, and porous. Coke is

created by combustion of Coal in a Coke Oven in the absence of air. It is a highly effective

fuel, essentially producing double the heat content of the Coal required to create it.

Coke making is the process of converting, through a series of operation, coking coal

to metallurgical coke by heating in the absence of oxygen. Coke forms an important part of

steel making process. It is used as a fuel as well as a reducing agent to obtain raw iron from

the fed ore. This is very well shown in the figure below where we see coke being made from

coal and eventually is used in the preparation of burden which is fed to the blast furnace.

FIG:1.1 COKE IN STEEL MAKING PROCESS

1.1.1 ADVANTAGES OF COKE:

There are various advantages of using coke instead of coal directly in the blast

furnace. Some of which are-

∑ Calorific value of coke is very much higher than that of coal.

∑ Coke forms a support to the burden inside the blast furnace.

∑ Coke produces lesser amount of ash and smoke and has low moisture content.

∑ It is the most important raw material of steel making process.

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1.1.2 DISADVANTAGES OF COKE/COAL:

In spite of many of the advantages coke/coal usage have some disadvantages also-

∑ Coke/Coal is non renewable hence depleting with a very fast rate.

∑ Coke dust is extremely hazardous hence transportation must be carried out with

extensive precautions.

∑ Burning coke/coal releases carbon dioxide contributing to the global warming.

∑ It leaves behind harmful by-products upon combustion (both airborne and in solid

waste form), thereby causing a lot of pollution. Very expensive scrubbers must be

installed to remove a significant amount of it. Even then, a significant amount escapes

into the air.

1.2 CLASSIFICATION OF COKE OVEN PLANT:

Classification of any coke oven plant can be done on two basis:

1.2.1 By-Product Recovery:

a) Recovery type-

∑ High capital outlay

∑ Crude gas is the most important by-product.

∑ Solid/liquid/gaseous waste generation.

b) Non recovery type-

∑ Heat recovery ovens.

∑ Self sustaining.

∑ WHB based power.

1.2.2 Type of charging:

a) Top charging-

∑ Lesser cost.

∑ quality coal.

b) Stamp charging-

∑ high cost

∑ lesser pollution

∑ mixed quality coal.

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1.3 COKE MAKING PROCESS (BATTERY):

The coking process consists of heating coking coal to around 1000-1200ºC in the

absence of oxygen to drive off the volatile compounds (pyrolysis). The physical properties of

coking coal cause the coal to soften, liquefy and then re-solidify into hard but porous lumps

when heated in the absence of air. Not all types of coal are suitable for coke making. Coking

coals are classified as prime Coking Coal (PCC) and Medium Coking Coal (MCC). The coal

must also have low sulphur and phosphorous contents.

Coal is extracted from the coal mines and processed in washeries to lower the ash

content and make it fit for the process ahead in the coke oven plant called as coke battery.

The battery is composed of many coke ovens stacked in continuous rows into which coal

is charged. The coking process takes place over long periods of time between 12-36 hours in

the coke ovens. Once pushed out of the vessel the hot coke is either wet or dry quenched to

cool it before storage or transfer directly to the blast furnace for use in iron making. Given

below is a schematic of a coke oven. Prime components of the plant are coal tower, coke

oven batteries with intermediate and end benches for operation, chimney, SCP machine,

guide car, CGT car, quenching car, quenching tower and coke wharf.

FIG:1.2 A TOP CHARGING COKE OVEN

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FIG:1.3 BURNING COKE INSIDE THE OVEN

FIG:1.4 GENERAL LAYOUT OF A COKE OVEN PLANT

Before coke making process, coal is first blended and prepared in a coal preparation

plant. Blended coal is then stored in a coal tower.

Then according to the coke oven type coal is fed into it. The above figure 1.3 shows a top

charging oven in which coal from the coal tower is charged in the carbonization chamber

through charging holes on the top of the oven with the help of coal charging cars.

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Whereas in stamp charge type stamping charging and pushing machine known as SCP

Machine retrieves coal from coal tower as per the schedule. In SCP Machine the coal is

stamped by a hammer and formed into cakes. Coal cakes are then charged into coke ovens by

the charging arm of the machine. The SCP machine is provided with a door manipulator for

opening and closing of the coke oven door. After charging of coal into the oven, the machine

closes the door and puts on the latch.

In the coke oven, the coal is heated in the absence of air at about 1100 ◦C. In one

coking cycle coal is carbonized to coke and crude gas. The coal-to-coke transformation takes

place as follows:

∑ The heat is transferred from the heated brick walls into the coal charge. From about

375°C to 475°C, the coal decomposes to form plastic layers near each wall.

∑ At about 475°C to 600°C, there is a marked evolution of tar, and aromatic

hydrocarbon compounds, followed by re-solidification of the plastic mass into semi-

coke.

∑ At 600°C to 1100°C, the coke stabilization phase begins. This is characterized by

contraction of coke mass, structural development of coke and final hydrogen

evolution.

FIG:1.5 COAL TOWER

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∑ During the plastic stage, the plastic layers move from each wall towards the centre of

the oven trapping the liberated gas and creating in gas pressure build up which is

transferred to the heating wall.

∑ Once, the plastic layers have met at the centre of the oven, the entire mass has been

carbonized (fig:1.3).

The red hot coke mass at about 1000°C is pushed out from the oven by SCP machine, and is

guided into the quenching car by coke guide. An electric locomotive hauls the quenching car

into the quenching tower. In quenching tower water from the overhead tank is sprayed though

the quenching system from the top. The quenching car then unloads the cooled coke in the

coke wharf region. The process flow diagram of a coke oven battery is shown below.

FIG:1.6 PFD OF COKE OVEN BATTERY

Crude coke oven gas generated during the coking process is collected in a collecting

main via a standpipe and gooseneck. The figure below shows the gas handling system. To

bring the temperature of crude gas from 800-850°C to 82°C flushing liquor is sprayed at

high pressure in the gooseneck. This also creates sufficient suction for the gas to

circulate ahead. Liquor and tar are taken care of in Tar decanter plant and the gas is treated

further in the By Product Plant (BPP). The coke oven gas after cleaning is used for heating

the coke ovens.

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The waste gases generated due to fuel combustion are discharged into the

atmosphere via chimney but before that their heat is recovered using checker bricks in

regenerators. This extracted heat is used for heating the fresh air coming to the combustion

chamber.

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FIG:1.7 PFD OF COKE OVEN PLANT

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1.4 CHARGING GAS COLLECTION:

The major components of gas collection system are standpipe, gooseneck, water

sealing valve, water sealing lid, gas collection main, high and low pressure ammonia

liquor spraying nozzle, emergency water system. The figure below illustrates theses parts-

FIG:1.8 GAS COLLECTION SYSTEM

Standpipes are provided with fireclay brick lining and heat insulating material to

keep the external surface temperature lower. Standpipe is connected to the coke oven via

a cast iron seat. A stainless steel water sealing lid at the top of standpipe connects to the

gooseneck.

Gooseneck is provided with flushing liquor spray nozzles. The suction created

due to flushing action enables smooth flow of the gases. A gooseneck is shown in the

figure below.

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FIG:1.9 GOOSENECK PIPE

The gas collecting main stores the gas before it is passed on to the down-

comer for separation from tar and liquor. It has a provision for automatic liquor cleaning

device. To control the pressure in the gas collecting main a butterfly damper is provided with

the suction main ahead.

1.5 WET QUENCHING:

In order to transport and store the coke it is very important to cool it upto the

room temperature. For this purpose coke oven plants deploy quenching system which can be

either wet type which is the conventional one or the dry type which has recently come into

practice.

A complete wet quenching system consists of coke quenching car, quenching

tower, quenching pump house, overhead tank, dust capturing device, settling pond, clear

water tank, dewatering table for coke fine and a scraper.

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The red hot coke from the oven is carried by a coke quenching car which is pushed

by an electric locomotive to the quenching tower. Generally the quenching time is

controlled to be within 70-90 seconds.

FIG:1.10 WET QUENCHING TOWER

Water sprays are directed at the static quenched car. The figure below shows the spray

system used in quenching tower. These can be vertically pouring as well as angled quench

water sprays.

FIG:1.11 SPRAY SYSTEM

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A water mist catching system is present to catch the emissions generated during

quenching. These emissions rise along with the steam and tend to a form a misty layer.

This steam is purified using a scrubber and cooled before releasing to the atmosphere. A

certain part of water carries with it the dust grains and coke particles and is collected

in the breeze pond having a scraper. Coke fines after removing the water is transported by

truck and water is recirculated for use. Breeze pond of a coke oven plant is shown in

figure below. The moisture content of the coke is maintained to about 3-4% and is

transported and unloaded by quenching car in the coke wharf region.

1.6 COKE DRY QUENCHING:

In the coke oven, due to carburization of coal coke temperature reaches to

approximately 1100 to 1350 0C. The volatile matter vaporizes and decomposes, becoming

gas. After escaping from the coke surface the gas is collected through a pipe located in the

upper section of the carburization chambers. The coke from the battery is charged from top in

the chambers. While it descends through the chambers it is cooled with circulating gas blown

from the bottom of the chamber. After it has cooled to approximately 200 0C the coke is

ejected from the bottom of the chambers and as the circulating gas is heated up to 800 0C or

high is used in a boiler to generate steam. after this gas is purified by the dust collector and

then sent back to the chambers for recycling. the generated steam in the boiler is used to

generate power.

The whole process could be understood by referring the diagram below-

FIG:1.12 COKE DRY QUENCHING

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1.6.1 FEATURES OF CDQ PROCESS:

∑ CDQ is a gradual coke quenching process and it improves coke strength and

coke size distribution. Improved blending ratio reduces cost for raw material

in coke dry quenching.

∑ CDQ coke has lower moisture content (0.1-0.3%) than CWQ coke (2-5%)

hence the coke ratio of blast furnace can be reduced.

∑ Steam generation of 500-700 Kg/t-coke and power generation of 140-185

kWh/t-coke can be obtained according to CDQ operation and steam

conditions.

∑ Such excellent features realize the payback period of initial investment within

three to five years.

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BY-PRODUCT PLANT CHAPTER-2

This is extension of the coke oven battery. Some of the coke oven plants do not opt

for by-product plant are called as non-recovery type and other type known as recovery

type have a by-product plant with them. The purpose of by-product plant is to carry clean

the COG for further use (coke oven) and also separate out different useful by-products

having market value.

Liquid condensate stream and gas stream from the gas collecting main is separated in

the down-comer and sent to BPP. The functions of BPP are to take these two streams, to

process them to recover by-product coal chemicals and to condition the gas so that it can be

used as a fuel gas. The recovery and separation involves these following elements:

∑ Ammonia

∑ Sulphur compounds such as H2S

∑ Naphthalene

∑ BTX (Benzene Toluene Xylene)

∑ Tar and related compounds

Composition of these by-products in raw coke oven gas is as below-

Composition Raw COG Units

H2S 5-6.5 g/m3

NH3 10-11 g/m3

B.T.X. 30-35 g/m3

Naphthalene 0.15-0.2 g/m3

Tar 0.02 g/m3

CO2 3-4 % v/v

HCN 0.5 % v/v

2.1 FUNCTIONS OF A 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.

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∑ Remove ammonia to prevent gas line corrosion.

∑ Remove naphthalene to prevent gas line fouling by condensation.

∑ Remove light oil for recovery and sale of benzene, toluene and Xylene.

∑ Remove hydrogen sulfide to meet local emissions regulations governing the

combustion of coke oven gas.

In addition to treating the coke oven gas, the by-product plant must also condition the

flushing liquor that is returned to the coke oven battery, and treat the waste water that is

generated by the coke making process.

FIG:2.1 BY-PRODUCT PLANT

2.2 PROCESSSING OF LIQUID CONDENSATE STREAM:

Liquid condensate stream generally consists of tar particles which flows down from

the down-comer and goes to the tar separating unit.

2.2.1. Heavy tar pre-separator: The tar and flushing liquor flows into the heavy tar pre-

separator where heavy tar are scrapped out by a scrapper and collected in tar sludge.

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2.2.2. Tar decanters: The condensate further flows down to tar decanters where tar is

separated by gravity separation process. Heavier tar particles settle at the bottom and finer

tar particles along with flushing liquor is at the top. The finer tar particles along with

flushing liquor are pumped to coal water gravel filters and to ammonia stripping unit.

2.2.3. Tar centrifuges: The tar settled at the bottom of tar decanters enters into tar

centrifuges where further separation of tar is done by effect of centrifugal force and are

collected in tar sludge box which is then send to tar storage.

2.3 PROCESSING OF GAS STREAM:

Gas stream from the down-comer is sent for further purification and extraction of chemicals.

The process is as follows:

2.3.1. Primary coolers: Primary coolers are basically heat exchangers. The gas stream

enters the primary coolers where cooling takes place in two stages. In the upper part of

heat exchanger the water circulates at about 35°C thus by bringing down the temperature

of gas from 82°C. Lower part has chillers in which water circulates at about 15°C thus,

further reducing the temperature of gas. The water vapour in the gas is completely

condensed and is separated from the gas. Cooled gas freed from water vapour is send to

electrostatic detarrers.

2.3.2. Electrostatic detarrers: 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. 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.

2.3.3. Exhausters: Exhauster is a large blower that increases the pressure of the gas in

order to make the gas flow through the scrubbers and the rest of the by-product plant. It is

of greater importance to the plant operation.

2.3.4. H2S Scrubber: H2S scrubbers consist of various layers of plates with raschig ring

packing. Raschig ring increases the surface area for the absorption. Ammonia and water

solution is sprayed from the top which absorbs hydrogen sulphide. The absorption

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process is exothermic in nature. In order to control the temperature in the scrubber, the

pump around coolers are installed outside the scrubbers. H2S and NH3 liquor solution is

sent to de-acidifier and rest of the gas enters ammonia scrubber.

2.3.5. Ammonia scrubber: The gas then passes from the ammonia scrubber in which

water is sprayed from top. The water dissolves ammonia and the alkaline solution is fed

to the H2S scrubber as an absorbent.

2.3.6. Combi scrubber: There is a combi scrubber which contains both H2S and

NH3scrubber but it is only operative when H2S or ammonia scrubber is not working. It is

used as a backup scrubber unit.

2.3.7. BTX/Naphthalene scrubber: Naphthalene is removed from coke oven gas using

wash oil in a gas scrubbing vessel. In the vessel lean wash oil is sprayed into the gas in

several stages. The enriched wash oil leaves the scrubber at the bottom via seal pot under

gravity and is collected in buffer tank. The enriched wash oil is then pumped to the BTX-

recovery unit. Wash oil losses are compensated by dosing fresh wash oil from fresh oil

tank into buffer tank.

2.3.8. Wash oil regeneration unit: Rich wash oil from the BTX-scrubber which was

stored in the buffer tank is pumped to the BTX stripper where it is steam stripped.

Naphthalene and BTX are extracted at the top of the distillation column which is operated

under atmospheric pressure. The BTX and naphthalene vapours are cooled in a condenser

and cooler and are divided from water in a benzol/water separator. The naphthalene oil in

water is then stripped by scrubber which is collected at the bottom and stored. After

stripping the regenerated or lean oil is sent back to the BTX/Naphthalene scrubber

2.3.9. Ammonia cracking/Sulphur recovery unit: The H2S and NH3liquor enters the

de-acidifier where, steam is passed from bottom in still. H2S/ammonia vapour mixture is

produced and is fed to the burner system of the cracking reactor. In this combustion takes

place to reach a proper temperature for cracking reactor. Only a small portion of H2S is

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converted to SO2. After combustion the gas, it then enters the catalyst bed of the

Catalytic Oven Reactor, where, nitrogen components are cracked on a catalytic basis. It is

then sent to the Claus reactor where reaction between SO2 and H2S takes place to

produce elementary sulphur S + H2O. The sulphur passes through condensers and is

processed and later collected.

2.3.10. Ammonia stripping columns: There are 2 ammonia stripping columns. Upper

one is for removal of free ammonia and lower for the removal of fixed ammonia. Each

column of free ammonia stripper receives the hot de-acidified water and the pre-heated

steam of coal water. The strippers are so designed to strip off all the components so that

free ammonia is obtained. The waste liquor flows into the lower stripping column. In this,

caustic soda is added due to which fixed ammonia components are destroyed and stripped

off. The stripped water as scrubbing liquor is buffered in tank and from there pumped to

the top of ammonia scrubber.

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FIG:2.2 PFD OF BY-PRODUCT PLANT

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CURRENT PROJECTS:

S.No. Project Number of

Ovens

Type of

Charging

Dimensions Technical

Partner

1. BSL,

Angul

1 X 72 TOP H=7.6m

L=20.8m

W=530mm

PWIT

2. TATA

KPO

4 X 44 STAMP H=5m

L=15.98m

W=530mm

ACRE,

CHINA

3. DSP,

COB

2 X 39 TOP H=4.45m

L=13.59m

W=450mm

LUET,

CHINA

CONCLUSION

Training under the coke oven and by-product plant has been very enriching. During

the duration of two weeks basics of coke making process, coke oven plant and by-product

plant were covered. With the aid of previous project details, the study was done. Layout

indicating various segments of coke oven battery, process flow diagrams and the manuals

helped to understand how and where different equipments such as various types of cars come

into use during the coke making process in the plant.

In the by-product plant I was exposed to the plant process and its flow diagrams. All

the by-products and their respective separation methods were covered. Hydrogen sulphide

scrubbing, ammonia scrubbing, various chemical stripping units and tar decantation.

An overview of complete equipments was given in very brief. Some details of

instrument and process automation were also covered.