Coke Oven By-Product Plant.doc

8/14/2019 Coke Oven By-Product Plant.doc

http://slidepdf.com/reader/full/coke-oven-by-product-plantdoc 1/9

The Coke Oven By-Product Plant

Contributed by Mick Platts,

ThyssenKrupp EnCoke US

Table o! Contents

• What is it and what does it do?

• Coke oven / by-product plant interface

• Composition of coke oven gas

• Duties of the by-product plant

• The by-product plant gas train

• Primary cooler

• Tar precipitators

• !hauster

• "mmonia removal

• #inal cooler

• $aphthalene removal

• %ight oil removal

• Coke oven gas desulfuri&ation

• Tar and %i'uor Plant

• Conclusion

W("T )* )T "$D W("T D+* )T D+?

The coke oven by-product plant is an

integral part of the by-productcokemaking process, )n the process

of converting coal into coke using theby-product coke oven the volatile

matter in the coal is vapori&ed anddriven off, This volatile matter leavesthe coke oven chambers as hot rawcoke oven gas, "fter leaving the cokeoven chambers the raw coke oven gas is cooled which results in ali'uid condensate stream and a gas stream, The functions of the by-

product plant are to take these two streams from the coke ovens toprocess them to recover by-product coal chemicals and to condition the

gas so that it can be used as a fuel gas, (istorically the by-product

http://www.tkencoke.com/

http://www.steel.org/learning/howmade/byproducts.htm#1%231

































http://www.tkencoke.com/



chemicals were of high value in agriculture and in the chemical

industry and the profits made from their sale were often of greaterimportance than the coke produced, $owadays however most of these

same products can be more economically manufactured using othertechnologies such as those of the oil industry, Therefore with somee!ceptions depending on local economics the main emphasis of amodern coke by-product plant is to treat the coke oven gas sufficientlyso that it can be used as a clean environmentally friendly fuel,

Top

Coke oven / by-product plant interface

)n a by-product coke oven the evolved coke oven gas leaves the cokeoven chambers at high temperatures approaching .0101#, This hotgas is immediately 'uenched by direct contact with a spray of a'ueousli'uor 0flushing li'uor1, The resulting cooled gas is water saturated andhas a temperature of 2340101#, This gas is collected in the coke ovenbattery gas collecting main, #rom the gas collecting main the raw cokeoven gas flows into the suction main, The amount of flushing li'uor

sprayed into the hot gas leaving the oven chambers is far more than isre'uired for cooling and the remaining unevaporated flushing li'uor

provides a li'uid stream in the gas collecting main that serves to flushaway condensed tar and other compounds, This stream of flushing

li'uor flows under gravity into the suction main along with the raw cokeoven gas, The raw coke oven gas and the flushing li'uor are separatedusing a drain pot 0the downcomer1 in the suction main, The flushingli'uor and the raw coke oven gas then flow separately to the by-

product plant for treatment,

http://www.steel.org/learning/howmade/byproducts.htm#top%23top




Top

Composition of coke oven gas

Raw coke oven gas coming from the coke oven battery has the following

typical composition:

"rybasis

ctual co#position$%ater saturated at&'()*+

Water vapor - 536

(ydrogen 776 .86

9ethane .76 2:6

$itrogen 26 76

Carbon 9ono!ide 46 :6

Carbon Dio!ide :6 .6

(ydrocarbons0ethane propaneetc,1

.6 26

;aw coke oven gas also contains various contaminants which givecoke oven gas its uni'ue characteristics, These consist of<

• Tar vapors

• %ight oil vapors 0aromatics1 consisting mainly of ben&ene

toluene and !ylene 0=T>1

• $aphthalene vapor

• "mmonia gas

• (ydrogen sulfide gas

• (ydrogen cyanide gas

Top

Duties of the by-product plant

)n order to make raw coke oven gas suitable for use as a fuel gas atthe 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

• ;emove tar aerosols to prevent gas line/e'uipment fouling







• ;emove ammonia to prevent gas line corrosion

• ;emove naphthalene to prevent gas line fouling by

condensation+ther duties may include<

• ;emove light oil for recovery and sale of ben&ene toluene and

!ylene

• ;emove hydrogen sulfide to meet local emissions regulations

governing the combustion of coke oven gas,

)n addition to treating the coke oven gas the by-product plant mustalso condition the flushing li'uor that is returned to the coke ovenbattery and treat the waste water that is generated by the cokemaking process,

Top

The by-product plant gas train

The gas treatment processes in the by-product plant typically consist ofthe following plant items arranged in the order in which they aredescribed,

Top

Primary cooler

The first step in the

treatment of rawcoke oven gas is tocool it to removewater vapor and sogreatly reduce itsvolume, This is donein the PrimaryCooler, There are

two basic types thespray type cooler

and the hori&ontaltube type, )n aspray type coolerthe coke oven gas iscooled by directcontact with arecirculated waterspray with the

contact cooling water being itself cooled e!ternally in heat e!changers,)n the tubular type the coke oven gas is cooled indirectly by flowing

across hori&ontally mounted tubes through which cooling water ispumped, )n this case the cooling water does not come into contactwith the coke oven gas and so it can be cooled in a cooling tower for







e!ample,

"s the coke oven gas is cooled water tar and naphthalene condenseout, The condensate collects in the primary cooler system and is

discharged to the tar li'uor plant,

Top

Tar precipitators

"s the raw coke oven gas is cooled tar vaporcondenses and forms

aerosols which are carried along with the gas flow, These tar particleswould contaminate and foul downstream processes and would foul gas

lines and burner no&&les if allowed to continue in the gas stream, Thetar precipitators typically use high voltage electrodes to charge the tarparticles and then collect them from the gas by means of electrostaticattraction, The tar precipitators can be installed before or after thee!hauster, The usual practice in $orth "merica is to place themimmediately after the e!hauster,

Top

!hauster

The e!hauster is a large blower that provides the motive force toinduce the coke oven gas to flow from the coke oven battery andthrough the by-product plant, The e!hauster is of prime importance tothe operation of the coke oven battery, )t allows the close control ofthe gas pressure in the collecting main which in turn affects the

degree of emissions for e!ample door emissions from the battery, "failure of the e!hauster will immediately result in venting to

atmosphere through the battery flares of all of the raw coke oven gasproduced,

Top

"mmonia removal

=ecause of the corrosive nature of ammonia its removal is a priority in

coke oven by-product plants, (istorically the removal of ammonia fromcoke oven gas has yielded one of the more profitable by-products that

of ammonium sulfate, The ammonium sulfate process can take variousforms but all basically involve contacting the coke oven gas with asolution of sulfuric acid, @ariations include the use of an absorber inwhich the sulfuric acid solution is sprayed into the gas or the use of asaturator in which the gas is bubbled through a bath of sulfuric acidsolution, The sulfuric acid reacts readily with the ammonia in the coke

oven gas to form ammonium sulfate, This is then crystalli&ed outremoved from the solution and dried for sale typically as a fertili&er,

$owadays the cost to produce ammonium sulfate often outweighs therevenue from the product however there are still very many cokeplants around the world producing ammonium sulfate,











$aphthalene removal

$aphthalene is removed from coke oven gas using wash oil in a gas

scrubbing vessel, The vessel may be packed or it may be the BvoidBtype 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, )n many plants naphthalene removal isintegrated with the similar process of light oil removal, Thenaphthalene is typically recovered as a heavier oil stream that is thenoften mi!ed with the tar that is produced in the by-product plant,

Top

%ight oil removal

%ight oil is a general term for a mi!ture of similar chemicals consistingmainly of ben&ene toluene and !ylene, The removal of light oil fromcoke oven gas uses wash oil in a similar process to that described fornaphthalene removal, The light oil is stripped from the wash oil in a stilland is then condensed to form crude light oil, This can be sold forfurther refining offsite or it can be refined in the by-product plant usingseveral distillation steps in the light oil plant, The light oil can actually

be left in the coke oven gas where it increases the calorific value, )tsremoval has historically been e!tremely cost effective as ben&ene

toluene and !ylene from coke oven gas were once vital raw materialsfor the developing chemical industry, (owever these materials cannowadays be obtained at lower cost and in greater 'uantities from

other sources

Top

Coke oven gas desulfuri&ation

There are several different processes for removal of hydrogen sulfidefrom coke oven gas, The specific process determines where in the gas

train it is installed, The main desulfuri&ation processes in use are

@acuumCarbonate

Process

(ydrogen *ulfide is absorbed from the

coke oven gas using a solution ofPotassium Carbonate then stripped

out in a still

"mmonia

WashProcess

(ydrogen sulfide is absorbed from thecoke oven gas using a solution of

ammonia then stripped out in a still -this process is often combined with theammonia removal system

*ulfibanProcess

(ydrogen sulfide is absorbed from thecoke oven gas using a solution of9onoethanolamine 09"1 thenstripped out in a still







The hydrogen sulfide is converted into elemental sulfur using the Claus

process or it can be used for the production of sulfuric acid,

Top

Tar and %i'uor Plant

The tar andli'uor planthandles the

flushingli'uor that

circulatesbetweenthe by-productplant andthe cokeovenbattery, )t

alsoprocesses the waste water that is generated by the cokemaking

process and which results from coal moisture and chemically boundwater in the coal, The flushing li'uor flows into tar decanters where the

tar separates out from the water and is pumped to storage for latersale, (eavier solid particles separate out from the tar layer and theseare removed as tar decanter sludge 0TD*1, The a'ueous li'uor is thenpumped back to the battery with a portion bled off from the circuit

which is the coke plant Be!cess li'uorB or waste water, This containsammonia and after the further removal of tar particles it is steam

stripped in a still, "n alkali such as sodium hydro!ide is added in thestill to decompose ammonia compounds dissolved in the li'uor, The

ammonia vapor from the still is then either fed into the coke oven gasupstream of the ammonia removal system or the still itself is often

integrated into the ammonia removal system, ither way the ultimatefate of the ammonia removed from both the coke oven gas and thewaste water is the same, The stripped still effluent is either dischargedto a municipal sewer or it can be treated in an on-site biologicaleffluent treatment plant to remove residual ammonia phenol andcyanides,

Top

Conclusion

The above describes the main features of the maority of coke ovenbyproducts plants around the world, The resultant main output streamsare shown in the table below, The 'uantities shown are intended to beindicative only and relate to a typical facility producing 2 million tonsper year of blast furnace coke, Coal properties and plant design andoperation influence the actual 'uantities,







Strea# "estination Typical

uantities,based on &

#illion tonsper yearcoke

Coke +ven as Ased as fuelgas at thecoke ovenbattery andsteel works

7 millionstd,cu,ft,/day

#lushing %i'uor ;ecirculatedback to thecoke oven

battery

@aries withplant design

Waste Water Discharged totreatmentplant

@aries withplant design

Tar *old asproduct

.8gallons/day

"mmonia/"mmonium*ulfate

*old asproduct

2. tons/day0as ammonia1

%ight +il 0ifrecovered1

*old asproduct

2.7gallons/day

*ulfur/*ulfuric "cid 0ifgas is desulfuri&ed1

*old asproduct

@aries withcoal propertiesand localre'uirements

Top



Documents

Coke Oven By-Product Plant.doc