VACATIONAL TRAINING PROJECT

PROJECT TITLE:

TO STUDYTHE PROPERTIES AND PERFORMANCE EFFECTIVENESS OF CLASS CATALYST

SUBMITTED BY: GUIDED BY: Narendra Kumar Mr. Rakesh Kumar Verma

VT B.E, IIIrd YEAR

CHEMICAL ENGINEERING SIT, TUMKUR

KARNATAKA

1

ACKNOWLEDGMENT

I would like to thank TATA Steel for giving me such a great opportunity

to use its resources and work at industrial platform.

The guidance shown to me by the various people working in this

organization has acted as a stimulant and provided me strength to

complete this project in the present form.

The time, which we spent in TATA STEEL (Jamshedpur) during the

training, was a wonderful experience in itself. We would like to thank all

those who directly or indirectly assisted in successful completion of this

project.

I would like to express my profound gratitude towards:

1. Mr. Rakesh Kumar Verma (Project Guide ,Sr. Manager)

2. Staff members of NBPP

Their support & guidance helped me convert my concepts into

visualization & and also for the guidance throughout the project. Last but

not the least we would like to thank all the staff members of TISCO,

without their corporation this training would not have been possible.

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Certificate

This is to certify that the project on “TO STUDYTHE PROPERTIES AND PERFORMANCE

EFFECTIVENESS OF CLASS CATALYST” is a bonafied and original work carried out by Mr. Narendra Kumar

under my supervision and guidanceHe has been sincere and an avid learner throughout the 4 weeks

of internship programme .

DATE: 31.6.2016

Rakesh Kumar Verma

Sr.Manager (New- BPP)

Tata Steel Limited

Jamshedpur, Jharkhand

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Index Page

4

Introduction 5

Chapter 1 Overview1.1 Carbonisation 6

1.2 Gas Purification 9

Chapter 2 Major Units2.1 Tar Recovery 12

2.2 Primary Gas Cooler 14

2.3 Electrostatic Tar Precipitator 17

2.4 Exhauster 19

Chapter 3 Removal Of Ammonia & Hydrogen Sulfide From COG

Through Scrubbing Process

3.1 Principle 20

3.2 Scrubbing of NH3 & H2S from COG through scrubber 26

3.3 Ammonia Stripping And De-Acidifying Unit 33

Chapter 4 Processes After Ammonia & Hydrogen Sulfide Removal4.1 Claus Process of Sulphur Recovery 34

4.2 Naphthalene Removal ; Naphthalene Distillation Plant 43

4.3 Booster 44

4.4 Waste Water Treatment 46

4.5 Utility Devices 47

Conclusion 48

References 49

INTRODUCTION

5

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. Historically, the

by-product chemicals were of high value in agriculture and in the

chemical industry, and the profits made from their sale were often of

greater importance than the coke produced. Nowadays however most of

these same products can be more economically manufactured using other

technologies such as those of the oil industry. Therefore, with some

exceptions depending on local economics, the main emphasis of a

modern coke by-product plant is to treat the coke oven gas sufficiently so

that it can be used as a clean, environmentally friendly fuel.

The report focuses on the by-products obtained from the Coke plant in

By-Products Plant. The report gives the overview of the Carbonization

process and the chief emissions from the coking process. Further the

project mentions different kinds of process involved in purifying the

Coke Ovens gas evolved in coke plant, focusing mainly on the NH3

removal from ammonia scrubber.

Chapter 1

6

Overview

1.1 CARBONIZATION

The destructive distillation of bituminous coal, done in the absence of air

in order to obtain coke and other fractions having a greater percentage of

carbon than the original material .The volatile constituents of the coal,

including water, coal-gas and coal-tar, are driven off by baking in an

airless oven at temperatures as high as 1,000 degrees Celsius so that the

fixed carbon and residual ash are fused together.

Most coke in modern times is produced in "by-product" coke ovens, and

the resultant coke is used as the main fuel in iron making blast furnaces.

Today, the hydrocarbons are considered the by-products of modern coke

making facilities (though they are usually captured and used to produce

valuable products).

Coke oven operation is a continuous production process and to ensure the

normal operation, the key is the stability of the charged coal cake. The

bulk density of the coal cake to be required is normally ranged from 1.05

– 1.1 MT/m3 (wet). Hence, for above reason, besides improving the

performance the separated into intervals, i.e. each carbonization coking

process is considered an interval while the process as a whole is

continuous.

Difficult to crush coal

Battery Details:

Total batteries running 7Stamp charge 6Top charge 1

7

Main unblended Pre crushing Coal mixing room Grinding

Coke Oven Coal Tower Mixing room

Battery 10&11 details:Ovens 88Ovens in each block 44Volume of oven 36.5m3

Width 524mmHeight 5 mLength 16mDry coal charge per oven 36.5 ton

Mechanical equipment of Coke –oven

Types of machine 4SCP(Stamp charging and pushing machine) 3 CGC 3Loco 3 Cgt 3

1.2 Gas Purification

8

Fig : Layout of Coke By Product Plant

After the charging coal being high-temperature dry distilled in the coke oven

coking chamber, there are about 75 % of coal turned into coke, and the

remaining 25 per cent turned into chemical products and gas. There are

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impurities in the coke oven gases (i.e. raw gas) such as aqueous, coal tar,

naphthalene, hydrogen sulphide, cyanide and ammonia, so we need to send

the raw gas to the coke oven gas purification plant to remove the impurities of

the raw gas and get pure gas to the user. The coke oven gas purification plant

is the matching equipment of the coke oven with one battery able to produce

approx. 330 M3 of raw gas per ton of coal. The major products designed are

pure gas, crude tar, sulphur.

The yields of different products are :

Coke 70 to 80 %Pure coke oven gas 15 to 19 %Tar 3 to 4 %Combined water 2 to 4 %Ammonia 0.25 to 0.30 %Others 0.90 to 1.10 %

Purified coke oven gas:

a) Pressure (97,000 Nm3/h at battery limit): 3.5kPa (min.)

b) Gas composition (volume %):

CO2 3~4

CnHm 2~2.6

O2 0.6

CO 6~9

H2

52~56

CH4 24~26

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N2 balance

H2S 0.5 g/Nm3

NH3 0.04 g/Nm3

C10H8 0.12 g/Nm3

Tar 0.02 g/Nm3

c) Temperature: ~28˚C .

d) Content of impurities (the figures are valid for gas flow 88,000Nm3/h)

The calorific value of the gas after purification is 4200 to 4400 kcal/m3,

and specific gravity is 0.48 kg/m3.

From carbonization of coal, coke ovens gas is produced which is a

Volatile Organic Gas comprising CO, H2 (having fuel value), H2S, NH3,

Naphthalene, tar, BTX, Suspended particulate matters as its primary

constituents.

Since it has a high calorific value, it is utilised as a fuel in Blast furnace,

in heating of ovens of Coke Ovens Battery. Before recirculating the gas

into the system, the gas is cleaned from H2S, NH3, Naphthalene, tar, BTX

as these cause corrosion and blockage in the in the passage.

Gas along with tar, coming out of the battery is at a temperature of 8000C

and it has to be cooled down to lower temperature for further treatment

else it will corrode the pipe and equipment, being at a very high

temperature.

Just before the Primary Gas collector, the crude gas along with tar is

mixed with Ammonia liquor which acts as a coolant and reduces the

temperature of the gas to 820C. The liquor has affinity for Tar and forms

a solution of Ammonia liquor and Tar. Thus the output contains gas

along with solution of Ammonia liquor and tar. The volumetric flow rate 11

is almost 1/4th of the volumetric flow rate of the whole effluent. 820C

crude gas from coke oven enters together with tar and ammonia liquor

into the down-comer along gas suction main. Here two phases gets

separated by gravity. Crude gas goes out of the down-comer and

ammonia liquor and tar solution being heavy, enters into the down-

comer.

Chapter 2

12

MAJOR UNITS

2.1 TAR RECOVERY

82℃ crude gas from coke oven enters together with tar and ammonia

liquor into the down-comer along gas suction main. After the separation

of liquid and gas, the crude gas goes out of the down-comer and enters

into a cross tube type primary cooler where gas is cooled in 2 stages. In

the upper stage, 34℃ circulating water is used for cooling and in the

lower stage 14℃ low temperature water is used for cooling crude gas

down to 21℃. The gas discharged from the bottom of cross tube primary

coolers goes into the electric tar precipitator to remove the tar entrained

in gas, and then is boosted to the H2S/NH3 scrubber by gas exhausters.

In order to ensure the cooling effects of coolers, the mixed liquor of tar

and ammonia liquor is used to continuously spray at the upper and lower

stages. Top of the coolers is washed regularly with hot ammonia liquor to

remove tar and naphthalene etc. deposited on tube walls.

The condensate from the upper stage of the primary cooler flows into the

condensate tank for upper stage via the water seal pot, from which it is

sent to the process gas cooler by the upper stage condensate pump.

The condensate discharged from lower stage of the primary coolers flows

into lower stage condensate tank via water seal pot, and then the tar and

ammonia liquor mixture is added into it according to a certain proportion

and delivered by the lower stage condensate pump to the lower stage of

the primary coolers for lower stage spray. The excess condensate flows

by gravity into the condensate tank for upper stage via the bypass pipe.

First, tar and ammonia liquor separated from the decanter enters into the

pre-separator of tar residue where the separation of tar, ammonia liquor

and tar residue are accomplished and a screen is installed at its outlet.

Solids bigger than 8 mm will remain in the pre-separator and settle in the

conical bottom and withdrawn by tar press pump. Solids are crushed in

the tar press pump and sent back to the top of pre-separator of tar residue. 13

The tar and ammonia liquor separated from pre-separator of tar residue

enters into the mechanical ammonia liquor decanter, where ammonia

liquor, tar and tar residue are separated. Conical plate is installed at the

bottom of the mechanical ammonia liquor decanter, by means of the

difference of temperature and gravity, the tar is settled to the bottom

where it is withdrawn by tar intermediate pump to supper class centrifuge

for further dewatering. After dewatering and residue removal, the treated

tar flows by itself to the tar tank where it is delivered to oil depot by tar

pump. Tar residue is sent to the tar residue tank and to the tar residue

adding system of the coal preparation plant. The upper ammonia liquor

of the mechanical ammonia liquor decanter flows into the lower

intermediate tank for flushing liquor and then is sent by the flushing

liquor pump into the gas collecting main to spray and cool coke oven gas.

One part of ammonia liquor at the outlet of flushing liquor pump is

pressurized by a high pressure ammonia liquor pump and sent to the coke

oven for smokeless charging. The coal water goes out from the upper part

of the tar and ammonia liquor decanter. It flows into No.1 coal water tank

to precipitate and separate light oil and heavy oil first and into No. 2 coal

water tank. Then coal water is delivered to H2S/NH3 scrubber by the coal

water pump.

Tar and ammonia emulsion are taken out from the interface of the

decanter. The tar and ammonia emulsion containing 30~50% tar are sent

to the upper part of the cross tube primary cooler by spraying pump and

used as spraying liquor for gas scrubbing.

2.2 PRIMARY GAS COOLER

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Purpose of cooling:

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Gas inlet temp (820c)

Outlet gastemp (210c)

Cooling water inlettemp(340c)

Cooling water outlettemp(450c)

Chilled water inlet(140C)

Chilled water outlet (220c)

Lower condensate tankUpper condensate tank

Common Condensatetank

Emulsion

To reduce temperature of Coke oven gas as absorption is

favourable at low temperature as well as gas volume is also

reduces according to gas law so pumping cost will be less.

To condense the most easily condensable (high boiling point)

components like tar, naphthalene and water vapour also.

Technical process:

After the separation of liquid and gas, the crude gas goes out of the

down-comer and enters into a cross tube type primary gas cooler

where gas is cooled in 2 stages. First cooling water at 340C is used

to cool down the gas in the upper stage from 820C to 400C and

chilled water at 140C is used in the lower stage to further cool it

down to 210C. We don’t directly cool gas with chilled water

because deposition tar and naphthalene will bloke PCDC.

The cooling process is an indirect contact type heat exchanging

process where cooling water and chilled water is flown inside

pipes and gas is flown continuously from the top .The cooling

process also causes some tar in the air to condense and is taken out

from the bottom.

In order to ensure cooling effects of primary gas coolers, the mixed

liquor of tar and ammonia liquor is used to continuously spray at

the upper and lower stages. Top of the primary gas coolers is

washed regularly with hot ammonia liquor to remove tar and

naphthalene, etc. deposited on tube walls.

The gas discharged from the bottom of cross tube primary gas

coolers goes into the electric tar precipitators to remove the tar

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entrained in gas, and then is boosted to the H2S/NH3 scrubber by

gas exhausters.

The condensate from the upper stage of the primary gas cooler

flows into the upper condensate tank for upper stage via the upper

seal pot, from which it is sent to the process gas cooler by the

upper condensate pump.

The condensate discharged from lower stage of the primary gas

coolers flows into the lower condensate tank via the lower seal pot,

and then the tar and ammonia liquor mixture is added into it

according to a certain proportion and delivered by the lower

condensate pump to the lower stage of the primary gas coolers for

lower stage spray. The excess condensate flows by gravity into the

upper condensate tank via the by-pass pipe.

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GAS FROM PDC

SOLID AND TAR MIST DEPOSIT

CERAMIC INSULATOR IS FILLED WITH NITROGEN FOR PROTECTION

SEAL POT

SLOPE TANK

efficient honeycomb type electric tar precipitators

800C COG TO EXHAUSTER

Heater

2.3 ELECTROSTATIC TAR PRECIPITATOR:

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This is used mainly to remove tar mist particles. As the raw coke oven gas

is cooled, tar vapor condenses out and forms aerosols (minute mist

particles) which are carried along with the gas flow. These aerosols would

contaminate and foul downstream processes and would damage gas lines

and burner nozzles if is not controlled. The tar precipitator is installed

before exhauster.

Gas enters into electric tar precipitator from its bottom, via the gas

distribution plate gas is uniformly distributed onto the whole section, then

flows through high voltage electric field of the honeycomb upward to

leave electric tar precipitator and enters into the exhauster unit. When gas

passes through electric tar precipitator, solid and tar mist droplet in gas is

deposited on surface of honeycomb, the tar flows via the tar outlet at the

bottom into water seal pot, from which it flows into underground slop

tank. To enable electric tar precipitator in normal operation, the hot

ammonia liquor spraying device is provided on the top of electric tar

precipitator. Water seal pot is connected with the pressure equalizing

system.

Process feature- High efficient honeycomb type electric tar precipitators

is adopted, tar content in the treated gas can be controlled <50mg/m3, so

as to be favorable for normal operation of the downstream equipment. The

power supply of electric tar precipitator is a constant power supply that

can keep stable electric field. The ceramic insulator is filled with nitrogen

for protection so as to reduce repair amount and extend its service life.

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2.4 EXHAUSTER:

Fig – block diagram of Exhauster

The task of the unit is to boost crude gas from coke oven to the

downstream gas purification system, for this purpose three electrically

driven gas exhausters are installed, two in operations and one as standby.

The gas exhauster is located after electric tar precipitator and before H2S

scrubber. In order to stabilize the pressure of the gas suction main before

primary gas cooler, the gas pressure regulation before primary cooler is

realized by means of regulating speed of exhauster through VVVF.

The condensate deposited in gas pipe at inlet and outlet of gas exhauster

flows via water seal pot into the slop tank from which it is sent to the

decanter VIA COMMON CODENSATE TANK OF PGC AREA.

Water seal pot and slop tank are connected with the pressure equalizing

system.

.

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CO GAS FROM ETP CO GAS TO H₂S/NH₃

SCRUBBER

SLOP TANK

SEAL POT

Chapter 3

REMOVAL OF NH3 & H2S FROM

COG THROUGH SCRUBBING

PROCESS

3.1 Principle: Ammonia gas is highly soluble in water. The absorption of ammonia (or any gas) in a liquid is guided mainly by Henry’s law and Raoult’s law. Henry’s law says that the partial vapour pressure of the solute is proportional to its mole fraction in the gas. Raoult’s law states that the solubility of a solute will depend upon the concentration of solute in the solution. From these two simplified statements, it can be concluded that the solubility of ammonia in water will increase if(a) The temperature of solution is kept low(b) Partial pressure of ammonia is kept much below equilibrium(c) Concentration of ammonia in the solution is not allowed to rise

muchMoreover, absorption being a mass transfer phenomena, is heavily favoured if the area of contact between the gas and liquid is increased.

H2S / NH3 scrubber:

H2S, NH3 and Combi scrubber help in the removal of H2S / NH3 from coke oven gas. Properties of gas before and after purification:Content of impurities in crude coke oven gas (excluding tail gas, charging gas and Respiration gas):

Temperature: 82˚C.

H2S 5~6.5g/Nm3

NH3 10~11 g/Nm3

BTX 30~35 g/Nm3

Tar 35~45 g/Nm3

C10H8(naphthalene) 6~10 g/Nm3

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HCN 1~1.5 g/Nm3

Purified coke oven gas:a) Pressure (97,000 Nm3/h at battery limit) 3.5kPa (min.)

b) Gas composition (volume %):

CO2 3~4 CnHm 2~2.6O2 0.6CO 6~9H2 52~56CH4 24~26N2 balanceH2S 0.5 g/Nm3

NH3 0.04 g/Nm3

C10H8 0.12 g/Nm3

Tar 0.02 g/Nm

c) Temperature: ~28˚C.

d) Content of impurities (the figures are valid for gas flow 88,000Nm3/h)

Here Combi (Stand by) scrubber can act as both H2S and NH3 scrubber

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3.2 Scrubbing of NH3 & H2S from COG through scrubber

H2S scrubbing unit:

The coke oven gas from exhauster is first fed into H2S scrubber . Gas flows upward along H2S scrubber. Gas goes through the cooling stage at the lower part of H2S scrubber. The heat of superheating in gas is absorbed by the cooling water. After the heated circulating water is cooled by the cooler for circulating water . At the upper part of H2S scrubber , H2S in gas is scrubbed with the lean solution from deacidifier and enriched ammonia liquor from ammonia scrubber . At the same time of H2S removal in H2S scrubber, also CO2, HCN and NH3 are absorbed. Because the absorption process of H2S, CO2, HCN and NH3 is the exothermic process, therefore both upper stage and lower stage of H2S scrubber are provided with the coolers and for H2S scrubbing solution respectively in order to prevent that the heat released heats gas. A part of cooling water of each cooler is drawn and after it is cooled, it is sent back to H2S scrubber.

Fig- Block Diagram of H2S Scrubber

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H2SScrubber

CO gas out

Rich ammonia liquor

Lean liquor

CO gas in

Enrich liquor

NH3 Scrubbing unit:

In ammonia scrubber, ammonia in gas is washed with soft water and the stripped water from deacidifier and ammonia stripping unit. In addition to these, coal water from coal water filtering system is added to the bottom of ammonia scrubber after cooling in coal water cooler to enhance ammonia scrubbing effect. If the concentration of free ammonia in coal water is very high, part of or all coal water is directly sent to ammonia stripper. Rich ammonia liquor out of the sump of ammonia scrubber is first cooled with ammonia liquor cooler and then sent to the top of H2S scrubber.

The upper stage of ammonia scrubber is provided with soda washing stage, where the diluted soda lye, can be added for further absorbing H2S and HCN in gas. Soda lye out of ammonia scrubber flows to soda lye tank in deacidifier and ammonia stripping unit.

Soft water is used for ammonia scrubbing on top stage of ammonia scrubber. Ammonia content in purified gas is 0.04 g/Nm3.

Except soda lye, all scrubbing solutions are finally gathered at the sump of H2S scrubber, from which they are pumped to enriched solution tank in deacidifier and ammonia stripping unit.

Fig- Block diagram of ammonia scrubber

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NH3

Scrubber

Ammonical liqour

Strip Water

Coal Water

Soda lye

CO gas in

Soft Water

CO gas out

NAOH

In order to keep continuous running and high efficiency of H2S/NH3 removal, H2S/NH3 scrubber is provided as standby, that is there are three scrubbers:

o H2S scrubber (Height=46m)o H2S/NH3 scrubber (Combi-Scrubber) Height=61mo Ammonia scrubber (47m).

In normal operation, any two scrubbers out of three present operate in series. This purification guarantees the desired gas parameters have been achieved.

After NH3 scrubber COG goes into Naphthalene scrubber for naphthalene removal.

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Fig- Packing material inside scrubbers

Fig: Block diagram of deacidifier and stripper

3.3 DEACIDIFIER AND AMMONIA STRIPPING UNIT:26

DEACIDIFIER

SOUR GASES

LEANLIQUOR

STEAM

ENRICH LIQUOR

NH3 STRIPPER

NH3

VAPOUR

STRIPPED WATER

NAOH

STEAMWASTE WATER

BODPLANT

In order to remove the H2S & NH3 compounds from the enriched

scrubbing liquor, coming from the H2S & NH3 scrubbers, a

distillation plant, consisting of deacidifier and ammonia strippers

is installed. The vapours leaving the distillation plant mainly

consisting of H2S, NH3 , HCN and CO2.

The deacidifier and ammonia stripping unit is provided with one

enriched solution tank, one lean solution tank and one stripped

water tank.

Two de-acidifiers and two ammonia strippers are provided in the

unit with one in operation and one as standby for continuous

running operation. The solution in enriched solution tank is

pumped to lean solution/enriched solution heat exchanger for heat

exchange with lean solution from the sump of de-acidifier and then

sent to the top of de-acidifier where enriched solution is stripped

with ammonia containing vapour out of ammonia stripper, most of

H2S, HCN,CO2 in solution are stripped out.

The lean solution out of deacidifier is pumped out with the lean

solution pump, part of it is heat exchanged in lean/enriched

solution heat exchanger with enriched solution, then cooled in the

lean solution cooler and sent to H2S scrubber in H2S/NH3

scrubbing unit. The rest is directly sent to ammonia stripper.

At the upper stages of ammonia stripper, free ammonia in lean

solution from deacidifier is further stripped out, and part of

stripped water is taken after free ammonia stripped out, the

stripped water is first cooled with the cooler and then sent to

ammonia scrubber in H2S/NH3 scrubbing unit for absorbing

ammonia in gas. The rest liquor is reached to the lower stage of

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ammonia stripper, where soda lye is added for decomposition of

fixed ammonia

Ammonia-containing vapour out of ammonia stripper enters into

deacidifier for stripping of the enriched solution. The stripped

water out of the sump of ammonia stripper is pumped to the cooler

for stripped water for cooling. After that, it is pumped and a small

part of it is used for diluting soda lye. The rest, namely waste

water is sent to bio-chemical waste water treatment plant.

The mixed vapour contained with NH3, H2S, HCN and CO2

discharged from the top of deacidifier is first partially condensed

using enrich liquor coming from H2S scrubber to remove water

vapour that is entrained with these sour gases and then sent to the

separator to remove remaining water vapour and then send to

Claus kiln.

28

29

Steam

NH3 SCRUBBERH2S SCRUBBER

Waste Water

BOD Plant

NAOH

NEPTHALENE SCRUBBER

DEACIDIFIR NH3 STRIPPER

Lean liquor Tank

Ammonia Vapour

NH3 and H2S VapourTO CLAUS KILN

T=850C

T=960CT=1150C

T=1000C

PFD of scrubbers, stripper & deacidifier

To network

Enrich liquor Tank

Soft WaterCoal water

Water

Strip water

Strip Water

COG

T=450C

T=240C

T=220C

REACTION INVOLVED:

In ammonia scrubber Ammonia is highly soluble in water than other gases, so it

forms ammonium hydroxide with water as shown below:-

NH3 + H20 NH4OH + ∆H (Ammonical liquor)

This ammonical liquor is used as scrubbing agent in H2S scrubber.

In H2S scrubber

NH4OH + H2S (NH4)2S + ∆H (Enrich liquor)This enrich liquor is stored in enrich tank, from there it is send to deacidifier.

In ammonia stripper

Ammonia present in two forms:-1. Free ammonia2. Fixed ammonia

1) Free ammonia can be present in following forms:-a) Ammonium carbonateb) Ammonium bicarbonatec) Ammonium sulfided) Ammonium cyanide

2) Fixed ammonia are present in forms :-a) Ammonium chlorideb) Ammonium thiocyanatec) Ammonium ferrocyanided) Ammonium thiosulfatee) Ammonium sulfate

30

Free ammonia can be directly stripped out using steam as :-

(NH4)2S + 2H2O + ∆T H2S + 2NH4OH

(Steam)

NH4OH + ∆T NH3 + H2O

For fixed ammonia stripping we use caustic soda as :-

Frist convert fixed ammonia into ammonium hydroxide then

ammonia is stripped out from ammonium hydroxide.

NH4SCN + NaOH NH4OH + NaSCN

NH4Cl + NaOH NH4OH + NaCl

(NH4)2 SO4 + NaOH (NH4)2OH + Na2SO4

NH4OH + ∆T NH3 + H2O

(Vapour)

In deacidifier

(NH4)2S + 2H2O + ∆T H2S + 2NH4OH (Vapour)

Na2S+2 H2O + ∆T H2S + 2NaOH (Vapour)

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List of main equipment:

NO Name and Specification QTY

1 Standard equipment

2 Pump for enriched liquor 2

3 Pump for H2S wash water 2

4 Pump for H2S wash water 2

5 Pump for ammonia water 4

6 Pump for soft water 2

7 Coal water pump 2

8 H2S scrubber DN4400 1

9 NH3 scrubber DN5200 1

10 H2S/NH3 scrubber DN4800 1

11 Coal water tank 1

12 Soft water tank 1

13 Seal pot 1

14 Cooler for recycled water 3

15 Cooler for coal water 2

16 Coal water first cooler 2

17 Cooler for H2S wash water 2

18 Cooler for H2S wash water 2

19 Cooler for ammonia water 2

20 Cooler for soft water 2

Redistribution trays are provided between individual stages of packing in

scrubbers to enable full contact between scrubbing solution and gas and

increase scrubbing effect.

Both H2S scrubber and H2S/NH3 scrubber are provided with the

circulating cooling stage to ensure the H2S absorbing efficiency.

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Composition and Quality Parameter

Stripped waste water Properties:

Total ammonia content : 150 mg/l

Quantity : 105 m3/hr.

Temperature : 400C

Coal water contents (per Lt of coal water):

H2S : 1 gm/L

NH3 : 3 gm/L

HCN : .15 gm/L

CO2 : 2 gm/L

Enrich liquor contents (per m3 of enrich liquor):

H2S : 3.6 gm/m3

NH3 : 14 gm/m3

HCN : .58 gm/m3

CO2 : 7.26 gm/m3

Lean liquor contents (per m3 of lean liqour):

H2S : 2.5 gm/m3

NH3 : 20 gm/m3

HCN : .58 gm/m3

CO2 : 7.26 gm/m3

33

Waste water contents (per Lt of waste water):

Ph = 8-10

Phenol : 800 mg/L

Cyanide : 20 mg/L

Ammonia : 150 mg/L

COD : 3500-5500 mg/L

BOD : 950 mg/L

Thiocynide : 300 mg/L

Emulsion liquor properties:

Tar % : 20-40%

34

Chapter 4

Processes After Ammonia & Hydrogen Sulfide Removal

4.1 CLAUS process for Sulphur recovery:

Hydrogen sulphide (H2S) is a smelly (with its signature "rotten egg" smell) , corrosive, highly toxic gas. Besides its other harmful effects, it also deactivates industrial catalysts. As H2S is such an obnoxious substance, it is converted to non-toxic and useful elemental sulphur through the Claus Sulphur Recovery process.

The Claus process is a catalytic chemical process. The process is commonly referred to as a sulphur recovery unit (SRU) and is very widely used to produce sulfur from the hydrogen sulphide found in raw natural gas and from the by-product sour gases containing hydrogen sulphide derived from refining petroleum crude oil and other industrial facilities.

There are many hundreds of Claus sulphur recovery units in operation worldwide. In fact, the vast majority of the 66,000,000 metric tons of sulphur produced worldwide in 2006 was by-product sulphur from petroleum refining and natural gas processing plants.

The Claus process is nothing but an improved CYCLASULF PROCESS mentioned earlier.

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Fig: Simplified Diagram of Sulphur Recovery Unit

REACTION INVOLVED:-

For vapour burner (Claus kiln):H2S + 3/2 O2 SO2 + H2O2NH3 + 3/2 O2 N2 + 3H202HCN + 5/2 O2 N2 + 2CO2 + H20

For cracking reactor:2NH3 N2 + 3H2

HCN + H2O ½ N2 + 3/2 H2 + CO

For Claus reactor:2H2S + SO2 3S + 2H2O

1.  The composite gas sent from de-acidifier is fed into the burner

of Claus furnace. Under the proportion ratio of air, part of

composite gas is burnt and SO2 and H2O are formed. The

optimum proportion of H2S and SO2 is 2:1. The temperature of

process gas in the furnace is kept in the range from about

1050℃ to about 1150℃. Under the condition that the

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temperature cannot be kept by the combustion of H2S, small

amount of gas can be introduced to control the temperature of the

furnace. H2S and SO2 in process gas react in the furnace as

follows

2. Before leaving the furnace, 60% of H2S entering into the furnace

has been converted into mono sulphur. According to the main

balance state in the furnace, there are COS and CS2 formed in

the furnace. Air and gas needed for gas combustion are sent by

an air blower and gas booster to burner. The burner is equipped

with an automatic igniter.

3. The block valves which are used as cutoff valves are also

installed on gas pipe and ignition pipe and used as safety cutoff

devices. During normal operation, temperature is controlled by

the control of the amount of gas sent into the furnace. Air

amount is determined according to the gas flow rate and

composite gas flow rate sent into the furnace. After process gas

goes through the catalyst layer of the furnace, it enters into

process gas cooler and carries out heat exchange with

demineralized water to generate steam with a pressure of

0.3MPa. During cooling process, part of liquid sulphur is

condensed and it goes into sulphur intermediate vessel via

sulphur inspection box.

4.   The temperature of the process gas going out of the waste heat

boiler is controlled by a method of regulating its “screw plug” of

central pipe. The steam drum and bottom of the waste heat boiler

are equipped with the blow-down outlets for blow-down. After

process gas goes out of the waste heat boiler it enters into the

bottom of the first stage of Claus furnace. Reactor is filled with

catalyst. Under the condition of inlet temperature of 250~300℃ S2 is converted mainly into S6 and S8. The released heat in

the reaction under normal condition can make the temperature of

process gas rise 20~30℃. After the high temperature process 37

gas from the outlet of the reaction of Claus furnace goes through

process gas pre-heater, it enters into the first stage of sulphur

condenser.

5. The process gas goes again through indirect cooling to cool and

condense part of sulphur process gas. The cooled process gas

goes through a sulphur separator to separate sulphur liquid drop

and process gas. Liquid sulphur goes into sulphur intermediate

vessel via sulphur inspection box. Then the separated process

gas goes through the pre-heater again, after the heat exchange

with high temperature process gas and its temperature goes up by

about 220℃, it enters into the second stage of Claus reactor to

carry out catalyst reaction. The low temperature process gas

after reaction goes through the second stage of sulphur condenser

for further separation.

6. After tail gas out of Claus reactor is cooled, it enters into a

negative pressure gas pipeline. The tail gas pipe has jacket

thermal insulation to prevent the consolidation of liquid sulphur

droplet in tail gas. With the help of the analyzer, the contents of

H2S and SO2 in tail gas can be kept close, but not less than 4:1.

The water needed by process gas cooler is pre-treated and

preheated. The liquid sulphur in the intermediate vessel or

storage vessel is delivered to the liquid sulphur filtering system

before a sulphur granulator by liquid sulphur pump.

7. The filtered liquid sulphur is then sent into the sulphur

granulator for liquid sulphur spraying and granulation. The

cooling water is sprayed by steel strip to condense liquid sulphur

to carry out granulation, then conduct the weighing, bag sewing,

packing and so on.

Sulphur Purity – 99.5%Colour – Bright Yellow

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4.1.a Catalyst for sulphur recovery

Why titanium dioxide?

TiO2 is used in the Claus Process to aid in the hydrolysis of carbonyl

sulfide (COS) and carbon disulfide (CS2) into hydrogen sulfide (H2S),

which can then be converted in elemental sulfur; this allows much higher

quantities of sulfur to be recovered and lowers the quantity of COS and

CS2 from going to flare.

Alumina Claus Catalyst: This Alumina Catalyst is a hard working

product that offers a high Surface Area for the conversion of H2S and

O2 to form elemental sulfur and water.

Promoted Alumina Catalyst for Claus Process: The addition of a

promoter to an Activated Alumina Catalyst increases the hydrolysis of

CS2 and COS into H2S, adds resistance to Thermal Aging, lower

operating temperatures in the first Claus Reactor

Blended Titania Alumina Catalyst for Claus Reaction: This Catalyst

is a blend of Activated Alumina Catalyst and Titania Catalyst. Titania

Catalyst is added to the Alumina Catalyst  to improve the hydrolyzation

of CS2 and COS to reform HS2, which can be converted into elemental

sulfur. This product has a high resistance to Thermal Aging, lower

operating temperatures in the first Claus Reactor, an increased level of

activity during the hydrolysis of carbonyl sulfide (COS) and carbon

disulfide (CS2), and increased Working Capacity during life span.  The

improved rate of hydrolysis of CS2 and COS creates a more efficient

process, which recovers more sulfur than the standard Alumina Catalyst.

Super titanium dioxide (TiO2) Titania based Super Claus Catalyst

for Sulfur Recovery: This product contains the highest composition of

titanium dioxide of all Claus Catalyst products. Titania Catalysts are

often used in the first reactor to increase the hydrolyzation of CS2 and 39

COS to reform HS2, which can be converted into elemental sulfur. Super

claus catalyst is the highest quality product for Sulfur Recovery and

offers the highest levels of efficiency and recovered sulfur.  This catalyst

offers a high resistance to Thermal Aging, allows lower operating

temperatures in the first Claus Reactor, high levels of activity during the

hydrolysis of carbonyl sulfide and carbon disulfide, and an increased life

span.

INERT ALUMINA CERAMIC BALL

Having stable chemical features and a low rate of water absorption, Inert

Alumina ceramic balls can resist high temperatures

and high pressure. Inert Alumina ceramic balls can

also resist the corrosion of acid, alkali and some other

organic solvents, Inert Alumina ceramic balls are able

to stand the thermal shock (quick change of

temperature) during the manufacturing process. The

main role of these  Inert Alumina ceramic balls is to

increase the distribution spots of gas or liquid, and to

support and protect the activating catalyst of low

strength in the reactors and column/tower.

Applications:

As refractory bed top plugs and supports in order to protect the catalyst

bed from thermal impurities so that the catalyst bed is kept intact in spite

of wide pressure variation. Inert aluminum  Ceramic Ball is widely used

in petrochemical industry, chemical industry, fertilizer industry, natural

gas industry and environment protection, etc.

Stoneware Catalyst Bed Supports are used routinely in the following

specific services: Ammonia plants, Hydrotreaters, Bender treaters, 40

Isomerization units, Chloride absorbers, pretreaters and reactors, Claus

units, Molecular sieve units, Diesel hydrotreaters, Naphtha treaters, Fixed

bed reformers, Reformer pretreaters, Fluidized pollution control, 

Hydrocrackers (1st stage), VGO pretreaters, Hydrogen plants.

Specification:

Inert aluminum Ceramic Balls are available in several specifications.

according  to the alumina content percent: 17%    25%   65%   95%.

Diameter from 3mm to 25mm or bigger on customer request.

Size Density Free  Space Specific Surface area

inches mm lbs/ft3 g/cm3 Percent ft2/ft3 m2/m3

1/8 3 90 1.44 38 350 1150

1/4 6 87 1.4 40 160 520

3/8 10 86 1.38 44 120 390

1/2 13 86 1.38 44 80 260

3/4 19 86 1.37 44 50 160

1 25 84 1.34 46 40 130

Chemical Analysis:

SiO2 ---------------------- 65-76%

Al2O3 ----------------------- >25%

SiO2 + Al2O3------------ >90%

Physical Properties:

Density: ----------------- 2.30-2.45 g/cm3

Bulk Density -----------  1.35-1.44  g/m3

Water absorption: ------- 0.30-0.60%

41

TiO2 --------------------- 0.5-0.6%

Fe2O3 ---------------------- <1.0%

Fe leachable ----------- 0.002%

CaO ------------------------ ~0.3%

MgO -------------------- 0.3-0.5%

K2O --------------------- 1.8-2.5%

Na2O ----------------------- ~0.2%

Porosity: -------------------- 0.60-1.10%

Crush strength: --------- ~400 N/mm2

H2SO4 solubility: ------------- 0.40%

Mohs Hardness: --------------- 7-8

Thermal expansion: --- 5.5 x 10-6 /°C

Catalyst poisons: ------------- none

A958 sulfur recovery catalyst: A958 sulfur recovery catalyst is a new-type sulfur recovery catalyst with

a high Claus activity and deoxidization protection features. It can be

separately used as a Claus catalyst and may also work together with

A918 Al2O3 catalyst for the purpose of deoxidization protection catalysis.

In the same device and the same technical conditions, the total sulfur

conversion rate can be increased by about 1.7%. It is particularly suitable

for sulfur recovery unit with considerable fluctuations in acid gas H2S

content and / or flow. A958 catalyst can work with Al2O3 in any

converter of the sulfur recovery unit or be filled in a tiered manner across

the full bed. During tiered filling and application, A958 catalyst can be

deposited on the upper part of the primary converter bed layer,

accounting for at least 1/3 of the total volume, So as to protect the lower

Al2O3 catalysts from sulfating poisoning by the tiny amount of oxygen

existed during the process, or mitigate the poisoning, thus prolonging the

life of the catalyst. The excellent performances of A958 catalysts have

been proven in industrial applications.

A988 TiO2 sulfur recovery catalyst:

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 The A988 Claus catalyst is TiO2 as main active component catalyst, it

has good ability of resistance to sulfate. It’s the flag-ship of sulphur

recovery catalyst series. The performance is in world leading position.

The main advantages of A988 catalyst are:

(1)Owing to high activity of COS and CS2 hydrolysis and Claus

conversion almost reaches the thermodynamics equilibrium level,

therefore it is one of the best catalyst of sulphur recovery

.

(2) It is non-sensitive to the trace O2 in the acid gas and sulfated poison

doesn’t exist.

(3) Because A988 catalyst only needs 3s of contact time and can be used

in the 1200h-1 GHSV, therefore, the reactor volume can be reduced and in

the condition of same contact time, the acid gas loading can be improved

greatly.

(4) A988 catalyst is specially applicable to cope with the lean acid gas

and Claus tail gas. Considering the excellent performance of A988

catalysts, it is recommended to use it in the first reactor to promote the

full hydrolysis of COS and CS2 and in the second and third reactors to

improve Claus conversion rate. A988 catalysts can replace imported

catalysts in an imported device. It can also be more extensively used in

other domestic sulfur recovery devices.

4.2 NAPHTHALENE SCRUBBING:

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Fig – Naphthalene scrubber

The gas coming from NH3/H2S scrubber which has the temperature of

about 24℃ enters into the naphthalene scrubber which is divided into

two stages. There is no split tray between two stages. The circulating

wash oil sprayed at the top of the first stage of the scrubber contacts with

gas in counter current to absorb the naphthalene in gas. In the second

stage, the mixture of the lean oil sent from the naphthalene distillation

unit and circulating wash oil is used to spray gas in order to absorb the

naphthalene in gas. The gas after naphthalene removal is sent to the user.

The rich oil at the bottom of the scrubber enters into an oil tank. After

residue removal and emulsion breaking, one part of the rich oil is sent to

the top of the first stage of the naphthalene scrubber by a circulating

wash oil pump to spray gas; one part of the rich oil is sent to the top of

the second stage of the naphthalene scrubber and after it is mixed with

the lean oil sent from the naphthalene distillation unit, the mixture is used

to spray gas; one part of the rich oil is sent to the naphthalene distillation

unit and after naphthalene removal, it is delivered to the top of the second

stage of the naphthalene scrubber for circulation use. The gate valves are

44

used at the gas inlet and outlet of the naphthalene scrubber and the

closing and opening are easy.

NAPHTHALENE DISTILLATION:

Fig – Naphthalene distillation plant

The enriched oil delivered from the naphthalene scrubbing unit is

delivered by the circulating wash oil pump and goes in turn through lean

oil/enriched oil heat exchanger and enriched oil pre-heater and is heated

to 180℃ and then enters into naphthalene distillation column, where the

oil vapour from regenerator is used for stripping and distillation. The oil

vapour evolved from the top of the naphthalene distillation column is

cooled via the partial condenser and goes into the oil-water separator.

The separated naphthalene oil flows into reflux tank. Part of naphthalene

oil is sent to the top of the distillation column as reflux and the rest of

naphthalene oil flows into naphthalene oil tank. And then naphthalene is

45

delivered by a naphthalene oil pump to the tar storage tank in the oil

depot unit.

The hot lean oil discharged from the sump of naphthalene distillation

column is pumped with hot lean oil pump to lean-enriched oil heat

exchanger for heat exchange and fed into lean oil tank. After heat

exchange it is pumped with lean oil pump to naphthalene scrubber via

lean oil cooler after it is cooled to 27℃~29℃.

In order to ensure the wash oil quality, 5% hot lean oil is pumped and

sent into a regenerator. The medium pressure superheated steam is used

for stripping and regeneration. The oil vapour at the top of regenerator

enters into the naphthalene distillation column. Regenerated residue is

discharged into an oil residue tank and pumped into the tar storage tank

in the oil depot unit.

The water separated in the oil-water separator flows into the separated

water tank, from which it is pumped to the deacidifier and ammonia

stripping unit.

4.3 BOOSTER:Boosters are used after naphthalene scrubber for boosting the purified coke oven gas to the network i.e. mills or blast furnace where the gas is used as fuel. Boosters also maintain the pressure of COG line.

4.4 WASTE WATER TREATMENT:

Wastewater generated during the process of cleaning coke oven gases is

toxic in nature due to presence of high phenol, ammonia, thiocyanate and

cyanide. This wastewater is commonly treated using biological methods

of treatment, these treatment plants are known as Biochemical Oxidation

and Dephenolisation Plants (BOD Plants) which have two or three stage

biological treatment units. However, functioning of these BOD plants is

often affected due to high inlet concentrations, biodegradability and

46

improper operational control. The overall efficiency of biological

treatment of coke oven wastewater, even after employing well

acclimatized microorganisms, is constrained due to its resistance to

biodegradability and inhibition.

4.5 UTILITY DEVICES

COOLING TOWER (RCPH)As in primary gas cooler cooled water is used to reduce the temperature

of the gas. The water coming out of the PGC (from upper stage) is sent to

the cooling tower mainly induced draft where it is cooled and recycled

again.

CHILLER PLANTChiller plant maintains the temperature of water at 140 C which is used in

primary gas cooler at lower stage of cooling. Warmed outlet water from

lower stage from PGC is sent to hot water tank, near to the Chiller plant.

Primary pump(centrifugal type) sucked out it and sent to the VAM

(vapour absorption machine),where it’s temperature is reduced to inlet

water temperature .This cooled water is stored in chilled water tank, from

there it is sucked out by secondary pump and pumped to lower part of

PGC.This whole process is repeated continuously .

FILTERS

They are used to filter the flushing liquor and the water used in

rcph(recirculating water pump house).The coal water used in scrubber or

the water used in PGC are generally passed through the filter so that it

does not block the nozzles and pipes .

SOFTENING PLANT

Softening plant generally remove the hardness of water so that it can be

used in ammonia scrubber and also calcium and magnesium salts ,present 47

in hard water get deposited on the pipes and cause scaling. So for this

reason hardness of the water is removed.

Make up water is passed through filter to remove TSP (Total Suspended

Solid) after that brine solution is added to filtered water, this whole

solution is sent to softener tank in which resin are used which retained

calcium and magnesium ions .Brine solution acts as regenerator of resin.

Soft water from there is pumped to soft water tank.

Conclusion:

48

Because of its hydrogen sulphide (H2S) content (up to 9 g/Nm3)

unpurified coke oven gas is unsuited for use in many industrial

applications. When the gas has been desulphurised, however, its use

for a variety of applications becomes potentially viable. TATA STEEL

coke plants meanwhile sell sulfur pellets after desulphurisation at a

profit. Desulphurisation for commercial reasons coincides with the

need to protect the environment from the effect of acid rain, because

desulphurised coke oven gas decreases emissions of SO2 at the site of

coke oven gas combustion.Sulfur Recovery Units are installed to meet

mandated air pollution requirements.

sulphur recovery unit (SRU) operating environment, greater emphasis

must be placed on operating reliability than ever before. Most

environmental agencies are very reluctant to grant operating variances

for conditions that would result in emission levels greater than

permitted. Overall SRU reliability can be increased by increasing the

efficiency of catalyst. And it can be done by improving the property of

catalyst by doping 2 or more metal. The problem with using bare

catalyst for sulphur removal was; the active site on catalyst got

decreased ,also its life duration was very less. So, considering all these

parameter SRU has used catalyst of different composition for better

result.

The catalyst are:

A988 TiO2 sulfur recovery catalyst,

A958 sulfur recovery catalyst

Inert Alumina Ceramic Ball

References

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Presentations and Flow diagrams from our Guide Wikipedia Online Presentations Other Internet Encyclopaedias

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