CA1091428A - Method for substantially complete removal of hydrogen sulfide from sulfur bearing industrial gases - Google Patents

Abstract

METHOD FOR SUBSTANTIALLY COMPLETE REMOVAL
OF HYDROGEN SULFIDE FROM SULFUR BEARING
INDUSTRIAL GASES

Abstract of the Invention Hydrogen sulfide is substantially completely removed from a sulfur bearing industrial gas stream by absorbing the H2S into a liquid absorbent, stripping the absorbent of absorbed H2S and reacting it with SO2 in a ratio of H2S/SO2 greater than the stoichiometric ratio of 2.0:1.0 to produce elemental sulfur and water, leaving a tall gas containing an excess of hydrogen sulfide but no sulfur dioxide. At least the last stage of the reaction is carried out in a liquid reaction medium at a temperature not i greater than 160° C. The excess H2S assures complete reduction at these temperatures of all SO2 to elemental sulfur. The remaining excess H2S is then recycled in the tall gas back into the original industrial gas stream prior to the point of contact of the industrial gas stream with the liquid absorbing solution.

Description

1~91428 Background of the InYention This invention relates to the alleviation of industrial air and water pollution and particularly to the removal of sulfur pollutants from industrial exhaust gases.
Industrial gases such as coke oven gas, natural gas and various artificially-produced fuel gases are used either by industrial plants to make useful products or burned in suitable combustion apparatus to produce heat. These gases are composed of varying mixtures of hydrogen, carbon monoxide, various aliphatic and aromatic hydrocarbons, hydrogen sulfide, hydrogen cyanide, carbonyl sulfide and other combustibles. The presence of sulfur compounds in such industrial gases is particularly undesirable because of possible corrosion of intermediate gas transmission lines and other apparatus by the gases, possible contamination of chemical substances made from the gases, and possible discharge of undesirable concentrations of sulfur oxides to the atmosphere during combustion of the gases.
In the past such industrial gases have often been treated by passing them through absorption-desorption processes of various types.
These absorption-desorption processes give off so-called foul gases which are treated to recover the sulfur present in the gas and thus prevent its discharge to the atmosphere.

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` 1091428 Typlcal ab30r~tlon-desorptlon processes are the hot potas3ium car~onate process, the vacuum carbonate process, the amSne processes, especlally tho~e using mono-, dl-, and trlethanolamlne, and various other processes using organlo solvents. ~he alkanolamine processe~ and particularly the dlethanolamlne and monoethanolamlne processes have pro~en to be especlally attractSve ~ro~ an lndustrlal ~tand-polnt due to thelr attractlve economics and relatively trouble-rree operatlon. The monoethanolamine proce~ses ln parttcular have proven to be very convenlent and effl¢lent ln re~ovlng hydrogen sulrlde and other sulrur compounds rrom sulrur-containlng ~as streams. Monoethanolamlne ~olution~
can ea~lly re~ove substantlally the entire aulrur content trom lndu~trlal gase~ 80 that the ga8 leavSng the mono-ethanolam~ne absorber contalns no more than 10 ~rains o~~ulrur per 100 standard cublc ~eet o~ gas exhausted, a very ~mall amount.
The~e ab~orptlon-desorptSon type processes, whlle i er~ectlve to reduce the sulrur contcnt Or treated industrlal gas to a very low level, do recover the a¢id gases ln a more con¢ontrated ~orm. The recovered "roul" gase~ have to be treated Sn turn to remove their ~ulrur ¢ontent in so~e ~atls~actory manner. ~ery rrequently the ~oul gases ~rom the ab~orptlon step have been used to produce elemental sul~ur by some varlatlon o~ the so-called Claus process. In thls process a portlon Or the sul~ur removed, usually ln the ~orm o~ hydrogen ~ulrlde, 18 oxldlzed to sulrur dloxlde and the sul~ur dloxlde and remalnlng hydrogen sulrlde are then rea¢ted ln a ¢atalyti¢ converter to rOr~ elemental sul~ur 3 and water.

.. . ,1 1 ~here are a number o~ ~ndustrial varlatlon~ o~ the baslc Claus proce~s ln which either an inltlal portlon o~
tbe hydroEsen sul~lde 18 oxldlzed to 8Ul~Ur dioxlde or a portlon Or the rlnal elemental ~ulrur product ls ~ubse~uently 5 oxidized to 8ul~ur dlox~de ~or use ln the Clau~ reactlon.
The Claus reactlon may be conducted elther in the gas phase by mlxlng the two ga~es ln approprlate apparatus, ln wblcb case tho process 1~ usually rererred to elther a~ the Claus prôce~s or a gas phase ~ul~ur recorery proce~ or the reactlon may be conducted ln the llquid phase. The llquld phase proce~s is conducted by dlssolvln~ onc or both Or the component sulrur base reac~ant compound~ ln a llquld and the~ either passlng tho other reactant ¢ompound through the llquld or brln~ln~ together two parts Or liquld ln wh~ch the roactantJ aro dlssolved. Such llquld reactlon medlu~
proce~e~, whlah are ~requently re~erred to as llquld phase ~ulrur recovery pro¢e~se~, are usually run at lo~er te~pera-turoJ than the moro u~ual Claus type proce~se~ and have cortain other ad~anta8e~ a~ ~ell.
The Claus process and the other related processes ~or the recovery o~ elemental sul~ur such a~ the llquid reactlon medlum procosseJ are ~alrly err~clent but have the dl~advanta~e that there 18 lnvarlably a re~lduo Or gas known a~ the tall 8a~ ln whlch elther ~ul~ur d~o~lde or hydrogen sulrlde or rrequently both remaln. Thl~ tall ga~ must be dl~posed Or 1~ some msnner and 18 usually at thl~ polnt di~char ed to th- at~o~pher-.

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`. l~gl4Z8 ``~1 Whlle the total amount or re~idual sulrur compound~
contained ln the tall ~as and dlschar~ed to the atmo3phere 18 much reduced rrom the concentratlons Or 9ulrur in the l orl~lnal gas treated, there 18 otlll, due to lnherent ln-5 ¦ e~rlclencleJ o~ the ~yJtem, a re~idual amount of ~ulrur ln ¦ the romalnlng tall gas whi¢h may be obJectlonable. The ¦ amount Or this remalning su~ur can be decreased by ~ub-¦ sequent proce~sing, ror e~ample, by the use of several Claus ¦ type reactor~ in serles, but due to the ~mall amount Or 10 ¦ remalnin~ sul~ur component~ ln the rinal tail 6as any ¦ rurther processing becomes more and more lnerrlcient and ¦ e~pen~ive and there is a rlnal mlnimum Or ~ulfur whlch i5 ¦ lmpo~slble to remove.
¦ One ralrly simple exped~ent ror rlnal treatment 15 ¦ ha~ been to oxldize all the remalning sulrur compound~ to ¦ ~ul~ur dloxide and then waJh the ~ul~ur dloxide out Or the ga~ ~lth a ~lmple water wa~h syJtem. The wa~h water ¢an then be dlJcarded, or used i~ it i~ concentrated enough to ¦ make ~ul~uric acid. Ho~ever, the amount o~ sulrur dloxide 20 ¦ diJJolved in the water 18 insu~ricient rOr really errective ; ~ ¦ use as a source Or sulrur, yet it is undeslrable to waste ¦ the ~ulrur value~ by di~carding the wash water.
¦ The Clau~ process in particular oxhibltJ a ~alrly ¦ poor recovery Or sulrur ba~ed upon the amount o~ sulrur ln ¦ the original ga~ and it 1~ customary to use three or even ¦ ~our Claus reactors ln serles in ordor to errect recovery Or ¦ more than a5 to 95% or occasionallg as much a~ 97% Or the aulrur e~oved rrom the orl61nal ~sa.

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~`` 109~4Z8 ¦ Some Or the ~any li~ul~ reactlon pha~e processes are, on the other hand, ~ignl~icantly more e~riclent 80 ~ar a3 the per¢entage of the orlginal 8Ul~Ur content which 18 I re~oved rrO~ the 6a~ as elemental sulrur ~ concerned.
5 ¦ Ho~ever, there i8 alway~ some small amount o~ sul~ur lert in the ~lnal tall ~as whlch lt 1~ ~ubatantlallg imposs~ble to ¦ romo~e. One Or the dl~rl¢ult~es 1~ t~at even ~lth the be~t ¦ control and mixing o~ the two ~ase~ H2S and S02, it ~s ¦ lnevltable that one or tho other Or the t~o reactant gases lO I ~ill be present ln ~ome de8ree Or ex¢ess and ~u¢h exce~s ¦ wlll pass unrea¢ted through the pro¢es~. It 18 3imply ¦ impo~slblo under induatrial condltlona to exactly meter the ¦ t~o Base~ together ln an exact ~tolchlometr~o relationshlp.
¦ Uauallg, Or cour3e, other rea¢tin~ ¢onditions will also not 15 ¦ be ¢omplctelg ravorablo ~or co~pletlon o~ the rea¢tlon ~o that a ~uantlty Or one ga~ or the other, and very o~ten both, i~ le~t unroacted. Sometime~ lt i~ declded berorehand ¦ ~hlch 8aa 18 mo~t de~lrable or leaat detri~ental to have ln ¦ exceas and thls gas is then dellberately supplled in a 20 ¦ sllght ex¢ea~ ln order to assure that sub~tantially none or ; ¦ the other gas remain~ at tho end Or the pro¢eas. Usuall~
¦ S2 wlll be pre~erred ln the tall 8as rather than ~2S
¦ be¢au~e S02 1~ less obJectlonable to the aense~ than H2S ln I similar ¢on¢entratlon~.
; 25 ¦ Tho relatlve amount~ Or hydrogen ~ulrlde, carbon ¦ dloxlde, wst-r vapor and extraneou~ hydrocarbons Sn thc roul ¦ or a¢ld ga~ ~ed to ClauJ reactor~ have a pronoun¢ed ln~luen¢e ¦ on the recovery erflclency ror a gSven number Or reactor~.
¦ A~ polnted out above there 18 a llmlt to the number or I

reactor~ which can practlcally be used to reduce tho sutrur ¢ompound~ in t~e tail gas. ~here 1~ also a llmit to the prealsene~s ~lth whlch an operatlon can be run ln order to keep the reaction exa¢tly ln balance and prevent decreases ln the ¢onver~lon o~ the sulfur compound gases to elemental ~ul~ur due to variatlons rrom prcclse stolchlometrlc ratio~
o~ tho rea¢tlng gase~. Tho re~er~lble reactlon 2H2S + S02 ~ ' 3S ~ 2H2 (1) o~ the Clau~ proce~a cannot, rurthermore, be completed to tho rl~ht or the equatlon becauoe Or limltatlons or the thormodynamlc oqulllbrlum at temperatures above 250 C at whlch tho Clau~ reactlon 18 run. Surrlclent water and ~UlrUr YapOr i8 always present to ltmtt the desired reactlon.
Carbon d1oxlde and additlonal wator vapor ln the reed ga~
ro also dlluont~ ~hlch ahirt tho oqulllbrium at~or~ely.
Exaot alr/acld 8a~ ratlo control i8 al~o never contlnuou~ly ;~ chl~vod even wlth the mo~t sophl~tlcated lnstrumentatlon, b-c-u~o Or uncontrollablo Yarlation~ in the ~eed rato and c~ol~po~ltlon Or tho ~a~e~. Hydrocarbons ln the ~oed al~o ~ZO ~arrect th- plant erriciency by increasing undeslrable ~ide ~roactlon product~ ~uch a8 C08 and CS2, which are dirrl¢ult to convert to elemental ~ul~ur. The tall eas ~rom a ~lnglo auJ re~a¢tor may ao a re~ult contain a~ much a~ 10% o~ tho -ulfur orlglnally remo~ed by the ab~orptlon ~ystem ~rom the 25~ ruel ga~.
A number o~ proce~e~ haYe been proposed as "cle~an-uD" proce~e~ ~or ~urther treatment Or Clau~ unlt tall ~a~. Se~eral Or these depond upon treatment o~ the tail gas 80 that the restdual sulrur values occur as hydrogen ~ulrlde whlch ls then converted to sul~ur in a so-called Stret~ord unit. ~here are a nwmber o~ other propoaals ~or l~pro~ed clean-up of the tail gas ~ncluding the use Or lmproved catalyst~ ln the Claus reactor, w~t scrubblng, reactlon w~th am~on~a, hl~h temperature sul~ur dioxide removal, con¢entration o~ sul~ur dlo~lde by abaorptlon, catalytic ~ulrurlc ac~d productlon, absorptlon on ¢arbon and ab~orptlon-desorptlon type chemlcal reLoYal. So~e or these proposals are applied to the ta~l gas a~ter ~nc~neratlon to chan8e all the sulrur VQ lue~ to sul~ur dloxlde. Whlle some are ralrly er~lclont, at least in the labor~tory, ln removlng the sulrur ¢o~ponent~, many have pro~ed lmpractlcal under Sndustrlal condltSon~ and nono i~ completely e~1¢1ent ln removing ~ulrur compound~.
j 15 ¦ Ono notable yet ralrly typlcal example or a Clau~-type proce~ in ~hlch re~ldual H2S Ss oxldlzed to S02 1 ~hown in U. S. Patent 1,915,364 Ss~ued June 27, 1933 to J. W. ~arrcl. Harrel separate~ a gaa havin~ a hi~h content Or H2S into two portlons. One portion i8 sent to a burner or rurnace where lt 18 burned wlth 2 to S02. The S02 18 absorbed into a water solutlon whlch i~ then passed con-currently or countercurrently to the re~alnder o~ the ~2S
6a~ ln a reaction tower where thc Clau~ reactlon converts H2~ and S02 to olemental ~ulrur and water. In order to elimlnate ~lde reaction~ and po~sible 1088 Or 8ul~ur an oxce~s Or H2S 1~ malntalned ln tho reactor. Thls excess results ln resldual ~2S 6as leavlng the reactor wlth t~e solutlon, whlch H2S 1~ then ~eparated rrom the solutlon and returned or recycled back to the burner or furnace where it ¦ la burne or o~ial~-d ~lth o~yEen to or~ add~tlonal S02 required ror the Claus reaction. Some Or thls S02 eventually e wapeJ through a vent on the top o~ the absorber where the S2 i~ absorbed by water, but no H2S leaves the apparatus and pollution Or the alr wlth H2S i~ thus sa~d to be com-pletely liminated. The elemental sulrur ~ormed ln the ¦ Claus rea¢tion 1~ separated rrOm the water suspenslon by any ~uttable méthod ~uch a~ rllterlng or the llke.
Harrel i8 ralrly typl¢al Or prlor processes in lO ¦ whlch excess H2S 18 ox~dlzed aubsequent to the Claus reactlon.
Many later pro¢esse~ have, ho~ever, attempted arter oxidizlng the H2$ to removo the re~ultlng S02 ~rom the tall gas by the u~e Or addltional re~oval apparatus, none Or whlch ha~
proved to be really practlcal or e~lclent under lndustrlal condltlon~. A number Or proce~ao~ rOr tho treatment Or tall ga~ rrom ~ulrur recovery plants ror the mlnimlzatlon o~
~ul~ur emls~lon~ are Jummarlzed in the rollowlng articles.
~a) "Reduco Claus Sulrur ~mlsslons" by C. B. 8arry drocarbon Proces~ln~ Aprll 1572 pages t02-106 tb) "Productlon o~ Clean Energy and Sulfur Recovery" by Mlkio Harima Chemical Economy and En~lneerln~ Review, Vol. 6 No. 8 (No. 76), August 1974, pages 13-21 et 8eq.
Reoycllng per ~e ln connoctlon with 3ulrur recover~
processo~ i~, Or course, not in it~el~ new as illustra~ed by tho Harrel patent noted above, and a large number o~ pro¢esses have been developed whlch specl~lcally make use Or the broad princlple Or recycllng $n order to increase the recovery Or the sul~ur compounds rrom a gas. For example, normal Claus !1-' " l ~ ~0914Z8 rea¢tor tail gas contalnln~ both H2S and S02 has been o~ldlzed to ¢onvert all res~dual HzS to S02 and the S02 ha~ then been recycled back to the Claus reactor to replace a portlon Or the S02 used ln th~ reactor. In some propo~als ~he S02 has been ab~orbed ~rom the ta~l ~as lnto l~me or the like and then re8enerated ~rom the llme and recycled into the Claus reactor.
Se~eral processe~ havo been developed ln which ~2 snd S02 are reacted together in a liquld reaction medlum Or some sultable composltion. ~he llquld reactlon med~um may bc renewed at lntervals by strlpping gases and volatllizable components lncludlng, ~or e~ample, H2S whlch 18 then recycled to the primary reactor. Occaslonally an ammonlum salt solution ~u¢h a~ an ammonium sulrite ~olution has been used ¦ 15 a~ the reactlon or ab~orptlon solutlon and ln these casea exces~ ~25 or S02 pa~slng ~rom the solutlon may be recycled ba¢k to re¢onstitute the absorption solution. It has also i been propo~ed to recy¢le the entlre tail ~as ~tream con-talnins both S02 and ~2S rrom a Claus rea¢tor back to an original co~e oven gas stream to react wlth the ammonla in the coke ga~. More re¢ently it has al~o been proposed to use a so-called ~olecular sleve to rever~bly adsorb H2S
~rom a tall gas der~ved rrom a Claus reactcr and recycle it back to an absorptlon step.
Whlle prlor worker~ have, there~ore, u~ed the prlnciple Or rec~cllng 1n varlous ~ays in connectlon wlth sul~ur remo~al ystems ~or the desul~urtza~lon Or lndustrial ga~, ~uch prlor systems have not been completely success~ul in eliminating exhaust of sulfur components to the environ-ment and have in many cases been expensive to build or uneconomical to operate. Furthermore, while a great many prior workers have made use of the basec principle of recycling various sulfur compounds back to various parts of the processes for retreatment in order to increase the recovery of the sulfur compounds, none has conceived or used the novel arrangement developed by the present inventors.
Summary of the Invention The foregoing problems and difficulties associated with the prior art methods of removing minor amounts of hydrogen sulfide remaining in industrial gases after con-version of the major amount of hydrogen sulfide to elemental sulfur have now been obviated by the present invention. In accordance with the invention a reaction loop is established which includes an absorption-desorption process zone or unit and a liquid phase sulfur reaction zone or unit. The tail gas from the liquid phade reaction process is recycled back to the gas entering the absorption-desorption apparatus. An excess of H2S is maintained in the liquid phase sulfur reaction apparatus to insure that no SO2 is recycled. Since the absorption-desorption system is extremely efficient in removing H2S from the ags stream, substantially all of the sulfur values in the original gas can be removed. Less than 0.2288 grams of sulfur values per standard cubic meter, i.e.
10 grains per 100 standard cubic feet of gas, remain in the gas stream exhausted from the absorber. This is a very small amount. The process can be combined with a Claus type process wherein the foul gas derived from the absorption-desorption system initially passes through one or more Claus type reaction units prior to passage through the liquid phase sulfur reaction unit.
According to the present invention there is provided a method of substantially completely removing H2S and recovering the sulfur values as elemental sulfur from an industrial gas stream without exhaust into the environment of a tail gas, a bleed-off or a vent stream containing sulfur pollutants other than the desulfurized industrial gas comprising:
(a) absorbing substantially all H2S from an H2S containing industrial gas in an absorption zone by contacting said gas stream with an alkanolamine absorbent solution in said absorption zone at a rate such that not more than 3 moles of C2 per mole of absorbed H2S is absorbed from the gas stream to form an H2S-rich absorbent solution and a substantially desulfurized industrial gas, ~b) stripping the H2S-rich absorbent solution to recover the H2S, : (c) combining the recovered H2S with S02 in a ratio of H2S to S2 from 2.1:1 to 2.5:1 in a low temperature reaction zone operated at a temperature not greater than 160C within a liquid-phase reaction medium to form elemental sulfur and H20 with an excess of unreacted H2S remaining sufficient to ensure that there is essentially complete reaction of all S02 in said reaction zone with H2S, ~d) removing sulfur from the liquid phase reaction medium in the low temperature reaction zone in the form of elemental sulfur and excess unreacted H2S contained in a tail gas from said reaction zone, ~e) recycling the tail gas containing the excess H2S from the liquid phase reaction medium in the low temperature reaction zone of step ~c) to the absorption zone of step ~a), and ~f) passing the tail gas with the sulfur containing industrial gas through the absorption zone wherein H2S contained in the tail gas is absorbed into the alkanolamine absorbent solution while the remaining gases of the tail gas become part of the desulfuri~ed industrial gas.
It is in~portant in the invention that the principal amount of the H2S content of a gas stream is initially removed by passing the gas through an absorption type acid gas removal apparatus which has a good selectivity and efficiency in the removal of H2S from a gas stream. It is also important to continuously maintain a molar ratio of H2S to S02 of greater than the stoichiometric ratio of 2 and preferably less than 2.5 in order to form elemental sulfur from a reaction of all of the S02 with the H2S present, leaving an excess of H2S sufficient to assure that there is in fact complete reaction of the S02. More preferably the ratio of H2S to S02 should be maintained between about 2.1 and 2.5 or even more preferably between about

2.1 and 2.3. At least the last stage of the raaction of the H2S with S02 must be accomplished in a low temperature reaction zone in which the temperature is maintained at not greater than 160C. The low temperature reaction is run preferably in a liquid phase sulfur reactor. The hydrogen sulfide-containing tail gas is then recycled back to the original gas stream, usually just prior to its contact with the absorption medium.
Absorption with alkanolamines and equivalent absorption solutions is very efficient in removing substantially all the H2S content from the gas stream. Thus - 12a -B

-` 10914Z8 ¦ any recycled H2S which 18 returned to the reed 8as stream ¦ ~lth the reoy¢led tail ~as 18 lmmedlately removed rrom the ¦ ~as ~tream agaln and returncd to the react~on zone ~or ¦ reaction wlth the So2 acc~dlng to t~e basic Clau~ Reactlon 1 5 I abo~e. Thls reactlon 1~ not a~ e~rlclent in re~o~ing the ~ul~ur component~ Or the ~as by rormatlon o~ element~l ¦ ~ul~ur as the roregolng ab~orption proce~es are ln removlng the H2S ~rom the orlglnal gas ~tream. The provlslon or an o~co~ or H2~, howe~er, and the use Or a rlnal low-temperature ~0 ¦ liquld phase rea¢tlon zone a~ures that ~ub~tantlally all o~
¦ the S02, which 18 not a~ errtclently removcd by the alkanol-¦ amlne or other ~ultable ~b~orptlon ~y~tem as H2S~ wlll ~e react~d to rOrm elemontal ~ul~ur, ~h~le the rema~nlng H2S
¦ can be recycl~d to tho main gaa ~tream and retreated in tho 15 ¦ ab~orption ~y~tem ~hore lt 1~ vory e~riciently romoved.
¦ Practlcally all Or the recycled H2S can be absorbed rrom the ¦ ga~ otroam by the ab~orption ~y~tom 80 that ror all lntent~
~ I and pur~o~e~ none rea¢hes the atmo~phere. The sulrur removal ¦ ~ I ~-y~tem thus ¢an, Sn accordance wlth the instant ~nventlon, 20 ¦ be msde into an o~roctlvely clo~ed ~y~tem to prevent escape ~or any ga~ou~ sul~ur component at all rrom the desul~ur-lzation and ~ul~ur-recovery sy~tom.
Only elemental ~ul~ur ln llquld or ~olld ~orm 18 removod rrom the ~ul~ur-removal system. The onlg gaseous ¦ ~ul~ur compound~ whlch can e~cape rrom tho sy~tem are tho~e ¦ very a~all amount~ whlch are not lnltlally absorbed by the absorb~ng medlum and whlch pass ~rom the abaorber wlth the desul~urlzed gas. Thu~ the ~ulrur e~tlng rrom the ~ulrur I
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remo~al system can be reduced to a level well below 0.22B8 grams Or H2S per one standard cublc meter~ Or ga~, i.e. 10 gralns Or H2S per one hundred ~tandard cubic ~eet o~ 6as.
In order to prevent the occurrence o~ any SG2 in the recycled tall gas, whlch S02 would not be a~ er~ectlvely removed by or a~sorbed ~nto the absorblng ~olutlon, at least the la~t stage o~ the Claus-type rea¢tion, l.e. the reactlon o~ H2S wlth S~2, should be conducted at a temperature below about 160 C, and prerersblg 140 C or lower, ln a llquld-pha~e rea¢tor. Thls wlll result ln the emlsslon Or a tallga~ contalnlng ~ome H2S and C02 and posslbly some other gase~, but, ror all e~rectlve purposes, no rree S02. Con-~-quently, i~ this gas ~tream 18 thon recycled back to the proceJ~ prlor to the lnitlal H2S absorblng step, there i9 ~ub~tantlally no po~iblllty Or any sul~ur escap~n~ rrom the ~ulrur romovlng procos~ o~ the lnventlon in a ga8eou8 rOrm.
Normally where the Clau~ type sul~ur roaction 18 to be run at le8~ than 160 C lt wlll be carrled out ln a ~lqu~d-phsse roaotor.
It 18 posslb~e ~or there to be several sta8es u~ed in the ~ul~ur romo~al operatlon as 18 customary ln the normal Clau~ reactlon. The lnltlal stages can comprl~e hlgh temperature ga~-phase rea¢tor~, but at leaat the la~t ~tage mu~t b- a lo~-temperature reactor such a~ a llquid-phase ~ulrur reactor. Thi~ 1~ becau~e no S02 must remaln ln the tall ga~ rrom the rea¢tor and lt ls characterl~tlc ror a ~mall amount Or unreacted S02 to remaln ln the tall gas rrom a hlgh-temperature ga~-pha~e reaction because the thermo-; dynamlc equlllbrlum 18 not conduci~e to complete reaction of the SO2. Naturally the entire sulfur removal reaction may be run in theliquid phase with very effective results.
Brief Description of the Drawings Figure 1 is a block diagram type flow sheet, and Figure 2 appearing on the second sheet of drawings, is a schematic type diagram, of an apparatus arrangement for the practice of one version of the process of the invention for removing hydrogen sulfide from industrial gas streams.
Figure 3,appearing on the first sheet of drawings, is a block diagram type flow sheet, and Figure 4 is a schematic type diagram, of an apparatus arrangement for the practice of an alternative embodiment of the process of the invention.
Figure 5 is a block diagram type flow sheet of another embodiment of the invention applied to the desulfurization of coke oven gas.
Figure 6 is a block diagram type flow sheet of still another simplified embodiment of the invention which includes for reference designations of gas flows and compositions attained with the invention.
Figure 6A, appearing on the fifth sheet of drawings, and Figures 6B, 6C and 6D appearing on the sixth sheet of drawings are tables setting forth the compositions of gases at various points designated in the apparatus shown in Figure 6.
Figure 7, appearing on the fifth sheet of drawings, is a block diagram flow sheet of yet another simplified embodiment of the invention for treating an H2S and HCN containing gas stream which includes for reference designations of gas flows and compositions attained with the invention.

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FIGURES 7A, 7~, 7C and 7D are table~ setting ~orth the composltlons o~ gases at ~arlous points de~nated ln the apparatus shown ln FIGURE 7.

Description of the Preferred Embodiments In FIGURE 1 there is shown a ~low dlagram Or one embodlment of the lnventlon whereln a reed ga~ containing hydrogen sulrlde (H25) and carbon dioside (C02) a~ lmpur~ties enters the apparatus at 11. This ~as may be deri~ed ~rom ~arious sources such as natural ~a~ product~on racllitles or metallurgical process~s. Where the reed gas also contalns hydro~en cyanide (~ICN), such as in coke oven gas, it 18 prererably treated accordlng to another embodlment or the ~nventlon as shown ln ~IaU~E 5. The reed ~as pa~se~ ~ia line 11 to a co~mercial ~12S absorptlon-d~sorption proce~s unit Or the alkanolamlne type, ln this ca~e shown a~ a monoethanolamlne, or MEA, proce~s apparatus 13. In the monoethanolamine process sub~tantlally all of the H2S
pre~ent in the gaa i8 removed as the gas t g contacted ln any ~ultable apparatu~ wlth an aqueous monoethanolamlne ~olutlon.
The absorption apparatus ~ay be Or several dlrrerent klnds, rOr e~ample, a packed tower apparatu~, ~pray contact apparatus and the li~e. ~he ~2S will react almost ~nstantaneou~ly wlth the aqueou~ monoethanola~lne solutlon to rorm mono-ethanolamlne ~ul~ide or hydrosulrlde which mQy then be decomposed by the appllcatlon Or heat to the solutlon prlor to or slmultsneou~ wlth the 8trlpping Or the ~2~ rrom the solution, ror example by the use Or stea~. The monoethanol-amlne solutlon 18 e~tremely e~flcient ln absorblng practlcally ~(191428 all o~ the H2S from the ~as 80 that the ~a~ whlch pas~es rrom the absorber 18 ~ubstantlal~y ~ree o~ H~S and contatns at the most le88 than 0.2288 gra~ o~ H2S per one standard cubl¢ meter, l.e. 10 gralns Or ~25 or equl~alent per 100 ~tandard cub~¢ reet Or gas.
Carbon dloxlde, on the other hand, takes a ~ignlflcant ~inite time to react with the water ln the monoethanolamlne solut~on to rorm carbonlc acld accordin6 to the well-kno~n oqulllbrium reactlon prlor to reacting wlth the ~onoothanolamlne to rorm a monoethanolamlne carbonate or blcarbonate. Thu~
the C02 doe~ not tend to be taken up by the monoethanola~lne solution as readtly, and 1J ¢onsequently not r¢moved rrom . the ga~ stream a~ qui¢kly, as the H2S. In general lt may be ~impll~tlcally Jtated that the molar ratlo Or C0z to H2S
ab~orbed in the absorbing ~olutlon wlll depend prlnolpally upon tho g88 llquid contact area and the gas resldence tlme ln the ab~orber, By controlllng the throughput Or the gas to the abJorber 80 that only a portion Or the C02 has tlme to be ab~orbed, the relative amount o~ C02 and H2S taken up by the ab~orbing solutlon can be ¢ontrolled 80 that ~ub-~tantlally all o~ the H2S ¢ontent o~ the ~as iB ab80rbed, ~hile pre~erably le~ than 3 moles Or C02 ls absorbed into thc monoethanolamlne ror e~ory mol o~ orlglnal H2S ab~orbed plu~ any H2S which may be produced by reactlonJ o~ any carbonyl ~ul~lde (COS) ant carbon dlsulrlde (CS2) whlch may be present ln the gas. The remalnlng C02 leaves the absorbing apparatus vla outlet llne 15 along wlth any other gases which may be present and Nhl¢h are not absorbed lnto the ab~orbent solutlon.

So long a~ the throughput of the ~as to the absorber 1~ nlrlcantly ~aster than the tlme required to absorb all o~ the C02 lnto the solutlon the ratio o~ C02 and H2S absorbed wlll tend to remaln ~ub~tantlally constant.
Whlle the C02 passed to the absorber will lncrease because o~ the recycle, the amount Or C02 ln the ~ystem wlll soon com~ to an e~uillbrium and the amount of C02 in the reed 8as and tho de~ul~urlzed gas ~111 then remaln the ~ame wltb no rurther bulldup ln the recy¢le loop and an equal amount o~
C02 ln the ~oed gaJ stream and the de~ul~ur~zed ~as ~tream.
Stnce any C02 ab~orbed in th~ ab30rblng solution in er~ect takcs up absorpt~on cApaaity ~hlch i8 deslred to be used ror thc ab~orption o~ H2S, it 18 de~irable ror economlc reasons and e~rlclen¢y to keep the absorption Or C02 as low as po~ible. For practlcal reason~ the molar ratio Or C02 absorbed to H25 absorbed ~hould be malntalned at not more than 3 to 1. Prererably this ratio ~hould be malntalned evon lower, ror example, at le88 than 2 to 1 or even 1.4 to 1. A eood ratlo may be consldered to be between 1.4 to 1 and 2 to 1.
T~e monoethanola~ine absorpt~on medlum, whlch i8 usually ln the rorm o~ a 10 to 25S aqueous solut~on, can be broadly replaced with any other llquid absorptlon-de30rptlon medlum whl¢h wlll remo~e sub~tantially all o~ the H2S rrom th~ ~as whlch i8 to be desul~urlzed. Such liquld medla are dlethanol~mlne and trlethanolamine solutions and vacuum ¢arbonate solutlons such as aqueous sodlum or potasslum carbonate solutions, aqueous ammonia, or polyhydroxyl alcohols such as propylene carbonate or glycerol triacetate or other equivalent absorbents. The advantages of the present invention are obtained only where the abbsorption solution has a selectivity such that it will remove sub-stantially all of the H2S from the industrial gas which is being desulfurized, but will not remove the entire content of any other gas which does not take part in the reaction in the sulfur reactor. Since there are many, many possible absorption-desorption mediums for H2S, alternative systems couled be worked out within the confines of the basic concept of the invention. Various possible absorption solutions have been mentioned above and as a further example of the diversity of possible absorbing solutions for removal of H2S
from gas streams reference may be had to the following patents: U. S. Patent 3,767,766 to G. H. Tjoa et al and U. S. Patent 3,856,921 to A. L. Shrier et al. Applicants have found, however, that their invention can be rendered particularly effective for and applicable to the removal of H2S from industrial gas streams by the use of alkanolamine type absorption-desorption systems.
More specifically, since monoethanolamine is the only known absorption medium which is effective to remove substantially all organic sulfur commpounds, in many cases quantitatively, such as carbonyl sulfide or carbon disulfide from a gas stream, if the maximum removal and recovery of sulfur compounds is to be effected from the gas stream, it is important to use a monoethanolamine solution as the absorption medium if organic sulfur compounds are present.
Since the process of the invention is designed, therefore, 10914Z~I

to remove the ultlmate amount o~ sulrur compounds of whatever klnd ~rom the ga~ ~tream and prevent ~uch compound~ ~rom ~alnlng access to t~le envlronment~ ir the ~ 5 ~tream contain~
any algni~lcant amount of organic ~ulrur co~npounds lt ~s much prererred to use a monoethanolamlne solutlon or some other absorptlon medlum havlng an equal ablllty to absorb such compounds.
Arter the abaorbed gases are strlpped rrom the monoethanolamine solutlon ln the strlppln~ apparatus - which ls not separately shown ln PI~URE 1 - the strlpped gas or "~oul gas" 18 dlrected ~la llne 17 to a reactor whlch ln thls case i8 shown as a block labeled as a llquld phase sulrur reactor 19. A sultable rea¢tor deslgn i8 shown generally ln U. S. Patent~ 2,881,047 and 3,170,766 to 15 F. M. Town~end whlch dlsclose the well-known Townsend pro-aes~. Another acceptable process ls the co~merclally practlced "cltrate ~rocessl', whlch uses a sodium cltrate-cltrlc acld solutlon as a reactlon medlum. The pH Or the solutlon 18 controlled. A small part Or the sulrur product 20 18 oxldl~ed ln thls process to sul~ate lons and must be o¢aa~lonally or contlnuously removed by crystalllzatlon as ~lauber salt. The removed ~odlum lons are replaced by addin~ NaO~I to the solutlon med~um. Thus onlg a solid by-produ¢t contalning 80me Bul~ur values must be disposed or.
The cltrate pro¢ess 18 typl¢al Or aqueous reactlon ~edlum proces~es. There are a conslderable number o~ other aqueous reaction medium processes, suah as the process o~ U. S.
Patent 2,563,437 the reactlon medlum o~ whlch contalns alumlnum sulrate and sulrurlc acld. These aqueous processe~

operate at pH value~ rangln& ~rom sll~htly to stron~sly acidic. Any resslble ltquid pha~e sul~ur recovery process can be u~ed a~ sulrur reactor 19. The apparatus o~ the _ llquid-p~ase sul~ur removal apparatus 19 ls al~o shown ln addltlonal detail in FI5URE 2 herelna~ter descrlbed.
Apparatus 19 1~ specir~c to the Townsend proce8~ . The aqueouJ reactlon medlum proce~se~, such a~ the c~tra~e proces~, do not need a solvent dlstlllatlon unit. In~tead they require other ~aclltie~ ~uch a~ a glauber salt cryatal-lizatlon and removal unlt In tho liquid-pha~e sulrur removal apparatu~ 19 the H2~ contalned ln the roul gas received ~rom the absorption-de~portion apparatus v~a the line 17 18 rea¢ted ln the well known Clau~ type roactlon:

2H28 ~ S02 er 3S + 2~20 ~ herein Mol-ratlo H2S/~02 > 2.0) to ~orm elomental ~ul~ur and wator. The elemental ~ul~ur preclpltato~ trom the reactlon medium and 19 collected at the bottom o~ the reactor while the water 18 dlspo~ed o~ by passage ~rom the reactor vla line 21 and dlrected to a ~trlppin6 column or apparatu~ 23 where dls~olved ~2S 13 ~trlpped rrom the ~ater by the ~team. The H2S i8 then re-turned a~ sho~n ln PIOURE 1 through llne 25 dlrectly ba¢k to the llquld-pha~e reactor 19. Excess H20 rormed ln the reaction and rrom whlch the 8a~e~ have been removed 18 pa~sed through llne 26 to dlsposal or to ~ome approprtate use.
Thc S02 ror the reactlon ~n reactor 19 is obtained by burnln~ some o~ the elemental ~ulrur product which i~

_ 1(~914Z8 wlthdrawn rrO~ the reactor 19 ln a molten condltlon through ¦ llne 27 to 5torage, usually also as ll~uid sulrur, or to use ln variou~ manners a~o not shown. The portion o~ the ¦ elemental sulrur product which ~ s to be b~ned i~ tapped orr 5 ¦ llne 27 through branch llne 29 to ~ulrur burner 31 where the : I sul~ur 1~ burned wlth alr, ox~gen-enrl¢hed alr, or pure ; ¦ oxygen recel~ed through line 33 to ~orm S02 ~htch ls then ¦ passed ~la llne 35 back to the rea¢tor 19. Only suf~l¢lent ¦ ele~ontal ~ulrur product i8 burned to provlde le8s than one 10 ¦ mol Or S02 ~or every two moles o~ H2S ~ed to the reactor ¦ through the llne 17. It wlll be understood that the necessary ¦ S2 8a~ could be pro~lded in other ~ultable manners, not ~ ,"., ,-- I
.. I illustrated, ~uch as from somo external source or by inltlsl ¦ partlal combu~tlon Or some Or the ~oul gas pas~ed throu~h 15 ¦ the llne 17 elther by ~pllttln~ the Bas stream lnto two ¦ partJ snd burnln~ only one part or by supplilng only surrlcient oxygen.to the 6as stream 80 that only a portion o~ the H2S
content i9 oxidlzed to S02. It wlll Se understood that ln l all cases no more sulrur, whether orlglnally ln t~e rorm o~
20 ¦ elemental sulrur or ln the ~orm Or H2S, wlll be oxldlzed, or at lea~t ~ill be passed to tho reactor 19, than wlll con-stltute 1008 than the stol¢hlometrlc ratlo o~ S02 neces~ary ¦ to react ~lth the amount o~ H2S passed to the reacto~ ln the I ~oul gaJ in llne 17. Prorerably the ratlo Or ~2S to S02 : 25 ¦ wlll be malntained between 2 and 2.5, or more prererably 2.1 ¦ and 2.5, or e~on more pre~erably bet~een 2.1 and 2.3.
Whlle it 18 theoretlcall~ po~sible ror the ~2S gas I to be oxid1zed to pro~lde S02, lt i8 as a practlcal matter ¦ necessary rOr the S02 to be generated b~ the burning o~ a ~ 1~1914Z~

¦ portlon of the elemental sulrur product lf there i8 any ¦ signi~icant amount Or carbon compounds ln the roul gas enterlng the reactor 19 through the roul gas llne 17. This ¦ ls because if a portlon Or the roul gas ls oxldized side 5 ¦ reactlons will for~ ¢ontaminating compounds of sulrur and carbon such as CS2 and C05 along wlth the S02. These con-taminatlng compounds, usually rormed ln equlllbri~m quantitles ¦ at any given temperature, pa~s through the reactor and, upon l recycle, sho~ up in the ab~orptlon-desorptlon atep with 10 ¦ detrimental e~rects u~on both the absorbent solutlon and the errlcl~ncy o~ the process in removing sulrur compounds rrom the lndustrlal ga~ stream. Speclrically, carbonyl sul~ide, COS, 1~ absorbed by the monoethanolamlno solutlon and ls hydrolyzed to ~2S and C02 by a complex m'echanl~m. Carbon dlJulrlde, CS2, ~8 only partlally absor~ed. However, the ab~orbed~portion produces one molecule Or H2S and one, molecule Or a thlourea-ty~e compound that con,sumes one ~ole o~ ~onoethanolamine. The thlourea compound i8 eYentUally re¢o~ered as a ~olld sludge ~rom the "reclslmer" Or the absorptlon-desorptlon type desulrurizer, not shown. The non-ab~orbed portlon o~ the CS2 rlnds its way to the desulrurlzed gas and thus decrease~ the overall sul~ur removal e~l¢lency o~ the procoss. ~he sul~ur values converted to COS and CS2 ~n a Clau~-type reactlon are roughly equal. All the co~pounds S02, CS2, COS and even elemental sulrur ltselr are hl~hly corroJlYe snd hlghly reactl~e in the tall ga~ and it is ver~
desirable that a tall gas contalnlng such compounds ~hall 10914Z~8 not be reclrculated to additlonal apparatus. Thu3, slthoueh the use o~ the pre~erred monoethanolamlne absorbent ln the absorber wlll remove substantlally all organlc 3ulrur compounds elther partlally or completely ~rom the ~as ~tream belng treated, lt ls desirable to mlnlmlze the productlon or organic sulrur ln the system. When the elemental ~ulrur produ¢t itselr 1~ burned to produce S02 only a m~nute amount Or sulrur-carbon ¢ompound~ are ~ormed derived ~rom the rclatlvely dilute C02 ln the air 1~ air ls used as the oxldlzlng ga~.
In the pro¢es~ shown ln FIGURE l, the H2S-ab~orptlon-desorptlon ~tep 13 produces a ~oul gas ~tream 17 thàt contain3 sub~tantially no COS and no CS2~; Slnce the ~ul~ur-burner 31 ' and the llquld phase sul~ur reactor 19 also produ¢e no COS
and CS2, the tail 6as ln the re¢y¢le llne 37 contains sub-stantlally nono, and the overall,pro¢ess Or FIGURE 1 can be Jald to be con~ertln6 most Or the COS and CS2 which may o¢cur ln tho ~eod ~as stream il,to,other products and to produce no ne~ COS and CS2.
Tho overall sul~ur recovery erflclency o~ the pro¢e~s depends upon tho ther~odyna~lc equill~riu~ ln the last ~ta8e o~ the step ln which the Reactlon 1 ~ allowed to proceed. Even wlth a surplu~ Or unrea¢ted ~2S, lt ls lmposslble to ellmlnate all S02 ~rom the tall ~as as along as the last ~ta&e ls allowed to proceed ln vapor phase above160 C, be¢ause the thermodynamlc equillbrlum does not drive the reactlon rar enough to the right. Only ln li~uld-phase or equlvalent reactlons, operating prererably well below 16Q C, wlth the mas~ action Or a sl&n~ricant surplus o~

¦ unre~cted H2S, and wlth the ~electlve S02 retentlon o~
¦ various liquid-pha~e reactlon medla, 18 it po~s~ble to ¦ vlrtually ellm~nate S02 ~rom the tal~ gas. Since S02 i8 ln ¦ general more ~oluble ln ~any llquids than H2S, lt tends to 5 ¦ bo retalned ~n ~olutlon ~n the llquld react~on medium untll it r~acts wlth the e~ce~s H2S pas~ln~ throu~h the liquid.
Thus lt is de~lrable to uJe a rea¢tion liquid whlch has ~
airly hlgh oolubillty wlth re~pect to S02. Varlous aqueous I roactlon solutlons ~n ~eneral con~orm to the requlre~ent.
10 ¦ ~o~ever, any other l~quid reactlon medlums in which S02 1 ~gniri¢antly ~ore soluble than H2S ~ill be ~atl~a¢tory.
~t 1~ rQr this reason that lt ha~ been tound ¦ nece~sary ~hen only,a sin~le- tage ~ul~ur remo~al step i8 .
¦ u~od as 1n FIGURE 1, that ~uch a step ¢on~titute a liquid- , ,~ , 15 ¦ pha~e typo proce~ such as tho ~o-called Townsend proc-ss.
'~' ¦ Al~o~ a8 ~ b- explalned ln ~ore detail later, lt is I ~ ' ¦ nQ¢cs~ary in'tho pre~ent inventlon, 1~ a Clau~ type rea¢tor l~, "" , ¦ 1~ to be,u~ed, l.e. a rea¢tor in ~hl,ch the reactLon~ occur ¦ in tho ~a~ pha~e at ~ore than 160 C, rOr t~ere to be at 20 ¦ ~ l-ast two stage~ ~or ~ul~ur recovery. The lnltlal stage~
can~constitut- Clau~-type burner~ and~or reactor~, but at . l-a8t the ~lnal stage must bc a li~uld-phase type proces~
; ~u¢h ns tho Town~end proces~ operstlng at le~ than 160 C, and'pre~crably not 8reater thQn 140 C or le~a. In thls 2S casQ the bulk Or the sulrur values are converted ln the lnlttal Claus reactors and the S02 content o~ the tall gas i~ then decrea~ed to e~entlally zero in the rlnal liquld--~ phaae stage. However, the sulrur recovery selectlvlty Or '.

thl~ type o~ multlple ~tage proces~ 18 ~ar ~rom ldeal. Thl~
¦ i8 beC~Use whlle the ~oul gas ~rom th¢ absorber-de~orber 18 ~ree o~ COS and CS2, the lnltial Cau~ reactlon 3tage or ~tages (commonly~ the Claus ther~al reactor) produce the 5 1 usual quantlties Or cos and CS2 whl¢h then pa88 unreacted through the ~lnal llquld-phase staee and are totally recycled I to the H2S absorption-desorptlon step. In the absorption-¦ de~orptlon sta~e the COS 18 practlcally totally converted to l H2S and C02, and CS2 i~ conYerted to one mole o~ H2S and one 10¦ mole Or ~hlourea-type compound that con~umes monoethanol-¦ amlno. The Jul~ur remo~al erriclency Or the process Or FIGURE 1 i~ thus slightly decreased, na~ely by the sllghtly ¦ hlg~er amount o~ C82 lcft 1n the de~ulfurlzer 6as. However, ¦ no sulrUr ~alues are di~charged rrom the process lnto the 151 atmo~phere nor into any water ~tream~.
; ~ince tho Clau~ resction 2H2S ~ S02 3S ~ 2I~20 and also the prelimlnary reactlon Or ~2S with oxy~en accordin6 to the reactlon ~ 20¦ 2H2S ~ 32 ~ 2S02 ~ 2H20 (2) i~ ¦ (wh-re thls reactlon is used to rorm S02 ~or uoe ln the ~ub-¦ ~equent Clau~ reactlon rather than usln~ the combustlon Or ¦ a portion Or the elomental ~ulrur deri~ed ~rom the Clau3 I rea¢tion) both re~ult ln the rormatlon o~ water as a reaction 251 product~ a rair amount Or H2S is dl~solved ln the water ~enerated. ~hi~ water must eventually be dlsposed o~ ln some manner. Ir thls water was r¢mo~ed rrom the process wlthout remoYing the dissol~ed H2S, the pro¢ess would 1 0~ 1 4 const~tute a 1088 or sulrur rrOm the ~y~tem. Thu~
the dl8801~ed H2S 18 pre~erably separated rrom the water by means o~ heat de~orptt on or the like and 13 recycled e~ ther to the liquld phase ~ulrur removal 3tep, or to a Claus pro¢ess step, or less pre~erably ~ay be comblned wlth the H2S-contalnlng tall gas whlch 18 returned to the absorptlon step.
In FIGURE 1 the tail gas from the llquld-pha~e reactor 19 i~ recycled ~la recycl~ llne 37 back to the llne 11 whlch conducts the H2S containing reed 6as to the 8 absorption-desorption apparatus 13. The recycle llne carrles a ralrly large amount o~ C02 whlch has passed through the reactor 19 unchanged and a ~mall amount o~ ~2S
whlch ha~ pas~ed through reactor 19 unchanged. Thls ga8 19 comblned tn the llne 11 ~ith the H2S and C02 entering the sg-tem and pa~ses lnto the ab~orptlon-desorptlon apparatus 13 whero conditlons ha~e been predetermlned to be su¢h that ~ubJtantlally all o~ the H2S i~ absorbed rrom the gas leaving le~ than 0.2288 ~rams o~ H2S per standard cublc meter, l.e. le88 than 10 grains o~ H2S per 100 ~tandard cubla ~eet Or Ra~. Some additlonal H2S may be produced by the reactlon o~ any C08 and CS2 contained in the eas in the MEA ab~orblng solution.
Becsuse acid gasos 8UCh as C02 dilute the H2S ln the llquld-pha~e ~ulrur reactor 19 and mlght thereby adver3elg a~rect the e~ectlveness o~ sulrur recovery, it 13 very desirable to limit the absorptlon Or lar~e amounts Or these a¢ld Base~ ~n the ab~orption-desorptlon step 13. In the 1()914Z8 pre~ent state o~ the art lt 18 posslble to design and operate MEA-process absorpt~on-de~orptlon unlts wlth an H2S-~electl~lty such that no more than about 1.4 to 2.o volumes Or Co2 are ab~orbed ~or each volume o~ H2S. Once thl3 rat~o ls rixed, ln the recy¢le 8y~tem or FIGURE 1, the C02 content ln the desul~urlzed ga3 14ne 15 ~ the ~ame a~ the C02 content ~n the reed eas line 11. The C02/H2S ab~orption ratlo tn step 13 ~mply determlne~ the C02 content Or the recgcle stream 37. A hi~h C02/H2S absorptlon ratio wlll cau~e the absorption stêp 13 to become overloaded unnecessarlly wlth C02 and makes the step e~penJlve to bulld and to operate.
Thu~ lt Ss ~ery deJlrable to use a low C02/H2S absorptlon ratlo ln the pro¢os~ Or thls ln~entlon. Ang con~entional method o~ operat~on ~h~ch limSts the C02 plckup may be uaed.
1 15 Ordinarilg the ga~ ~tream ~111 3~mply be driven or p-~sed rapldly through the absorptlon zono, allowlng only a short re~ld-nce tlme ~or 8as-contact ~ith the alkanolamlne ab~orbent. The rate Or H2S ab~orptlon 19 oon81derably ~a~ter than the rate Or C02 ab~orptlon and by allowln~ only a limlted re~ldence tlme rOr ~as-llquld ¢ontact, lt 18 ; ~ pos-lbl- to selectlvely absorb H2S in tho presence Or larger amount~ Or C02. Thl~ te¢~nique 1~ errectlve wlth all alkallne ab~orbents Or acld ga~eo ln ~arlous de~ree~. It 1 ¦ ~ also errectlve wlth monoethanolamlne ~olutlons. Thu~, ln a recy¢le ~g~tem con~l~tlng Or an ab~orptlon-desorptlon type de~ulrurlzer~ and a Claus reactlon type Julrur plant, lt 18 posslble to selectlvely ab~orb ~ub~tantlally all o~ the ~2S
ln the de~ulrurlzer whlle leaving a large ~ractlon o~ the .

Il......... ... ............................................-`.

C2 ln the ~as, 80 that, when the absorbed ~ractlon Or C02 18 eventually recycled ~rom the sul~ur removal apparatu~ it does not become unde~irably concentrated ln the recycle ga~
: stream ~ut rema~ns ln~tead l~rgely ln the desul~urlzed ga~.
What ha~ been sald o~ the C02/H2S absorption ratlo and lts e~ect~ on the process 18 al~o largely true rOr the ~CN~H2S absorption ratio where the ~eed 8as also contaln~
~CN. Howcver, there ~9 one dlrr~rence. Whtle ~he C02/~2S
: abJorption ratlo c~n be ln~luenced by de~ign and operatlon measures, there 1~ not much, ~hort Or water washlng or : chemlcal treat~ent, that can be done to ar~ect the HCN/H2S
ratlo, because the absorptlon rate~ Or ~2S and ~CN are not : a~ dlr~erent as those ot H2S and C02. In the process ot ~I~URE l 1~ th- lndu~trlal gao strcam contalns ~CN ln add~.tlon to H2S and C02, such a~ in coke oven gas, the HCrJ
. . ¦ cannot simply b¢ lgnored but should pre~erably be remo~ed ,: . ~rom the ~oul gas be~ore the toul ~aa enters the llquid I . pha~e sul~ur reactor. Any NCN present in the ~oul ga8 ~tream la aboorbed into the ltquid reactlon medlum as cyanlde ion~ (CN ) Nhlch react wlth tho elemental sulrur al~o present rOrminB thtocyanates (SCN ). ~hls ~de reactlon in the ;~ llquld pha~e ~ulrur rea¢tor con~umes sulfur Yalue~. Slnce i~ the thlocyanatea do not readlly deco~po~e, they cannot be expelled rrom the rcactor solution and thu3 accumulate ln the llquld reaction medlum. Over a ~ery short perlod the HCN can be ignored because the concentratlon o~ th~ocyanate ln the llquld reaction ~edlum wlll be low enough to not 10~14Z8 arrect the proces~. For a continuou~ process the thiocyanate wlll qulckly accumulate to the point where the reactlon medlum beco~es inerrectlYe. This probl~m can be allevlated by cont~nually bleedlng Or~ a portlon Or the llquld reaction medlum and replacin~ with ~resh medlum. ~hlle the process la now a contlnuou~ operatlon, there i5 stlll a d~sposal problem Or the deterlorated liquld reaction medlum that has been bled Orr and a 1088 Or sulrur values. Currently, there doe~ not exlt a llquid r~actlon medlum ror the llquld phase ~ulrur reactor that i8 lnert to HCN 80 that the pre~ence of HC~ ln a teod gas ¢an be l~nored without cau~ln~ a hlgh con¢entratlon o~ thiocyanates ln the ~ystem. Accordin~ly, where HCN 1~ pre~ent ~n the ~eed ~as, the pre~erred embodl-ment Or tho ~-n~ention 18 that dl~closed ln FIGURE 5 ror treatlng coko o~en gas and 1~ doocrlbed ln detall herolna~ter.
~ he C02 ~hich pa~e~ through the absorblng 801u-tion, plus ~2 and other ~nert or non-acld gases whlch pas~
throu~n the solutlon, leave the ab~orber ln the de~ulfurlzed - ga~ in llne 15 whlch wlll occasionall~ con~t1tute an exhau~t llne to the atmosphere, but will u~uallg be a line to some rurther treatment or use o~ the de~ul~urlzed ~as. The ga8 ln line 15 wlll contain le~s than 0.228a ~rama o~ hydro~en Julr~de per standard cublc meter Or gas, l.e. 10 gralns or S per every 100 standard cubi¢ reet Or ~as. Under good operating conditlon~ ¢onslderably less sul~ur ¢ompounds e~en than this may re~ain ln the ~inal desulrurized ga~. It will be noted that there 18 no other di~charge o~ gase~ rrom the ~ystem ~o that the sy~tem 1~ ~erg clean wlth respect to the ~ulrur compound content o~ the dischar~ed ~a~e~.

In ~IGUR~ 2 there i8 shown apparatu3 ~ultable generally ror the practi¢e Or the process illustrated ln FIGURE 1 wlth some m~nor modt~icat~ons. ln F~URE 2 the gas to be desulrurlzed whlch may, ~or e~ample, be natural ~as or other H2S contalning ga~ rlrst enters a monoethanolamlne absorber 51 ~ia reed llne 53. Where HCN 18 present ln the reed gaJ, such as in coke oven gas, the HC~ may conventionally already have been removed borore lt enters the absorption apparatus as may ammonia whlch 1~ cu~tomarlly found ln coke oven ga~. Alternatively and prererably, the ~CN can be removed rrom the roul ga~ emanating rrom the absorptlon~
~esorptlon ~ystem prlor to entering the ~ulrur recovery unit as ~eplcted in FIGURE 5. The absorber 51 may take the rorm Or a spray tower, a packed tower or other conventlonal countercurrent type 8as liquid contact apparatus. The gas a K er nterlng the tower will ascend wlthin the tower to the top ~here the remaining ga~ or unabsorbed gas will pass rro~
the sbsorber through }ine 55 as desul~ur$zed gas. Thls ga3 ~ill contain the original C02 quantity ln the ga3 plu~ other ga~eous co~ponents including combustlble components. ~he deoul~urlzed ga8 may be utillzed as a gaseous ruel in a combustion proce~s and the waste gas rrom said combustlon dlscarded to the atmosphere as a substantially non-pollutln~
ga~ or may be used ~or some other purpose.
The MEA ~olution whlch entcrs the top Or ~he absorber a~ shown vla llne 57 and the ll~uld dl~trlbutor 59 18 collected in the botto~ o~ the ab~orber and 18 then pu~ped ~la llne 61 and ~ump 63 through a heat exchangei 65 to a llquid dl~tributor 67 ln a strlpper 69. In the stripper the ~olution 18 trickled downwardly through rlslng steam ~apor which ri~e~ ~n the strlpper. The solution coliects in the bottom of the strlpptng tower and is passed throu6h line 71 to reboller 73 where the MEA solution is heated by steam c0118 75. Arter bein~ heated in the reboiler the solution 1~ dl~charged again ~ia l~ne 77 into the botto~ Or the strlpper where lt ~lashes partly lnto a hOt vapor which then ~as~es up through the descendlng trickle o~ absorber li~ui~. ~he ga~es stripped ~rom the solution rlnally pass rrOm tho top Or the strlpper tower vla llne 79 and are ¢ondu¢ted ln line 79 to a sparger 81 in the bottom or a sulrur rea¢tor 83.
. Line 85 leads ~rom the botto~ o~ the strlpper 69 : 15 vla pump 87 to heat e~changer ~5 where so~e Or the heat Or the hot solution rrom the bottom Or the stripper 69 18 tran~rerred to the cooler solution pas8in~ through line 61 rom absorber 51 to the ~trlpper 69. The ¢ooled and strlpped MEA solutlon then pas~es throu~h a heat e~chanFer or coolln~
de~lce 89 be~ore passlng through llne 57 to.the llquld distrlbutor 59 ln the top Or absorber 51.
The H2~ and C02 whlch pass ~rom the llne 79 lnto the ~par~er 81 bubble up ln a ll~uid-continuous, ~a~-dl~perse pha~e through the reactlon medlum ln the sul~ur reactor 83 countercurrently to a descendlng rlow Or reaction medium ~rom a llquld dl~tributor 91 in the top Or the sulrur reactor 83.

109142El Meanwhile S02 ~as whlch i8 ~ormed ln a sulrur burner 93 by burning elemental sulrur rrom llne ~5 wlth oxygon or air ~rom llne 97 1~ lnitially pa~sed through a boll~r 99 in ~hlch the hot S02 8as heats boller ~eed water ; 5 whi¢h enter~ ~e boller through l~ne 101 ~rom 80~e external sourco an~ rrOm ~hich boller ~toQm, which may be used in the plant and ln the Yarlous rebollor~ in tbe process, leaves by line 103 The hot S02 ga~, no~ partially ¢ooled, passes n ~t into a heat cschanger or coolor 105 wher~ the hot ea~
i- coolod to a temperaturo appropr~ate rOr pas~a~e via line 107 lnto the ~parger 109 in the bottom Or the rea¢tor 83 ~rom which tho 802 i~ bubbled into *he llquid roaction l medlum in the bottom o~ the rea¢tor ~n the rorm Or dlscroto 1;~ bubblo~
~ Fre~h, ~trlpped~ or dl~tillcd rcQction medlu~
nter~ the liQuid di~trlbutor 91 ~rom a llne 111 The i~ r-a¢tion mealum may b- one Or the or~anl¢ llquld~ listed ln column 3 Or To~nsend~patcnts 2,881,047 or 3J170,766 or ture- Or~t-o or mort o- the~e organl¢ llqulds, or al~er-20 ~nati~ely an queous roaction liquid having an lonlzable ~alt ~dl~ol~cd ln lt a~ used ln the proce~s descr~be~ in U S
Pat-nt 2,563,437 or ot~er llk~ ~rocc~se~
Liquld reaction medium which haa pa~sed do~n the ~ulrur roaotor 83 ~rom the ll~uld dlstrlbutor 91 oollects In the bottom Or rcactor 83 The ~ulrur partlcle~ in the ~lquid settlc in th- botto~ Or tho rc-¢tor ln tho ~or~ or a UlrUr 81Urry ~hlch 18 con~lnuou~ly passed by gravity reed lnto tb- lrur Gelt-r 113 aa a aulrur alurry ~be ~ulrur ~:
~ -33-` 1091428 melter 113 take~ the ~orm o~ a large ~hallow tank haYln~ a ¦ welr 11~ at one ~lde. ~he melter 113 18 held under a ~llght pre~sure, usually about 3 atmo3pheres 1~ the reactlon medium ¦ 18 an a~ueous solution, in order to pre~ent bolllng Or the 51 reactlon medlum as the sul~ur 1s melted. It wlll be under-¦ stood, however, that dl~erent pres~ure~ may be nece~ary dependln~ upon the bo1lin6 te~perature Or the particular uld reactlon medlum whl¢h 18 w ed.
¦ The ~ùlrur ~lurry enters the sulrur meltln~ tank 10 ¦ 113 at one end or slde. The slurry collect 3 behlnd the welr ¦ 115 and the sul~ur particles are melted by lndlrect heat ¦ coll 114. Th¢ melted particles o~ sulrur slnk to the bottom o~ the tank 113 and ~orm a lower layer Or melted ¦ ~ulrur overlaln by a layer o~ slurry and a superlmposed 15¦ layer Or clear llquld reactlon medlum. ~he ll~uld sul~ur I layer at thc bottom Or the sul~ur melter mag be perlodlcally ¦ or continuou~ly wlthdrawn ~rom the melter tank 113 and pumped to the sul~ur burner vla ~alve 117, line 119 and pump ~; ¦ 121. E~ce~s llquld sulrur product may be pas~ed through 201 lln- 123 to ~ome ~urther process or storage.
In ~ome cases lt may be deslrable to operate the 8Ul~Ur rea¢tor at a tomperature above the meltlng polnt Or ~ulrur, l.e. about 130 to 140 C, particularly lr the reactor i~ a packed column type reactor. In this case the reactton medium wlll be comprlsed Or a llquld whlch has a botling polnt hlgher than the meltlng temperature o~ 3ul~ur, or example, glycol or the llke. The molten partlcles Or sulfur, unllke solld partlcle~, wlll not then plu4 up the 09~Z8 Il ~¦ packlng o~er a perlod, and thc sulrur melter may con~oquontly eon~tituto merely a ~ettler or colleetor o~ molton ~ulrur.
Howe~er, the l~qul~-phaJo r-actor ~hould be op~rated at a Il te~p~ratur- not oxceedlnt 160 C, ana prererably b~lO~
5 l 140 C, in order to a~old handl~n~ ~ery v~cou~ liquld cul~ur and al~o ln order to attaln a r~a¢tion eQullibriu~
hen an oSCe8~ or H2S i~ pro~ent ln ~hich no ~ub~tantial or detcatable 802 remaln~ unrea¢to~. ~ho r~sction medium ~1 ~oloetod may ~ome~me~ conYenl~ntly havo a boll~ng tempera-I ture about that o~ the doJir~d operatln~ temperature ~o that ll vaporlzation or th~ m~dium ~tll ald In ma~ntatntng th~ ~
Il eorrect t~sperature ~n thi~ ea~- a eonden~r ~111 usu~llg l~ b~ required to ¢onden~ and roturn th- ~apor~ ~rom tho i, roaetor Altornat~v-ly the tomperature at ~hlch tho roaatlon 15 l¦ 1~ eondu~t~d may b- eontrolled by mean~ o~ eooling ¢oilJ
po~lt~on~d ln th- reaction ~eetion Or the roaotor ~ ho llquld portion or the roa¢tlon ~edlu~ ~hleh 1 d-eant-d rrO~ the ~lurry overrlo~lng over tho w~lr 115 in ~ ltin~ tsn~ 113 1~ pa~d vla ~alvo 124 and l~no 125 to a 20 j ~tlll eolu~n 129 ~n ~tlll 129 the llqu~ re~ctlon mealum~
~hloh ha~ be~n dllut~d b~ tho reaetlon ~at~r derlve~ ~rom ! Reaetlon 1, 1~ di~t~lled to ~vaporate ~ald roaetion ~later~
tlll 129 1~ provlded l-ith th- u~ual re~oller 133 near ~ the bottom and dophl~mator coolor 137 on top. In caJo tho 25 l~ reaction modlu~ con~i~ts o~ aqueow ~alt ~olutlon~, the i dophlo~ator can be dol-ted. For proce~es ln ~hich an aqueou~ ro~ation m~ium 1~ u~od and ln ~ ch th~ ~at-r , ll ~¦ ~erves 88 a catalyst, surrlclent aat~ly~ic wat~r ~ lert ~n tho liquld roaction mediu~ to malntaln ~he concentration con~tant.
I~ ~he acld ga~ vapor~ and water p8~ through the 5 l~ l~ne 135 to th~ to~ o~ a ~tripping colu~n 141 where the water Yapor and ~S snd other acid ~a~ sr~ ~epsra~ed rro~
I oach othor. At tho bottom Or tho ~tripper 141 1~ a rebollor

3 in ~h~ch the H20 i~ heated to drive o~ dt~solved H2S.
1~ Tbl~ 6a~ pa~ rrom th~ top Or the ~tr~pp~r 141 through 10 ~ ne 14~ and into the lino 79 wh-re it i~ co~bincd ~ith the S an~ C02 ln lln~ 79 and pa~od, or ~n err~ct r~cycled, to the ~pargor 81 ln t~e bottom o~ reacOor 83. Meanwhtle ~he e~ce~ ~2 ~ ~a~ed ~rom tho bottom o~ th- ~tr~ppor 141 ~ia ne 147 to ~ny con~onlont ~lspo~al.
15 Il Tho bottom~ or llqul~ ~ortloa ln the stlll 129 1J
~asscd ~rom tho atlll 129 vla lino 149 and 1~ then pump~d ~la pump 151 through coolin6 apparat w 152 and llno 111 back ¦ ln'co tho eop Or tho rcaotor 8~ ~ia llquld dl~tr~butor 91 ,I The coolinB app~ratua 152 ser~e~ to ¢ool th~ reactlon m~dlum 20 I~ ~u~lcl~ntly ~o th~t tho te~peratur~ in tho reactlon zono Or tho r~actor 1~ ~alntalned at a tcmp~rature Or not greator tl~n 140 C.
~I The tall gaa rrom the top Or the reactor 83, ~hlch ~ tall gaJ oontaln~ ~rlnclpally C02 and X2~ ls pa~sed ~
25 Il rocycl- l~no 153 into the r~ed ga~ lln~ 53 ~hor- the recyoled ~I
ga~ and tho ne r reod g4~ are comlnglod and passed lnto t~e absorber 51 bhere ~ub~tantlally all o~ tho r~cyaled X2~ snd ., , - ~ore than one halr Or the rocy¢lcd C02 1~ ab~orbed.

' .

10914~Z~
~he de~ulrurizlng sy~tem shown ln FI~URE 2 thus ¦ operates substantially as shown broadly ln outllne ln URE 1 by lnltlally a~orbing all the H2S ln a ~eed ga3 ¦ alon~ wlth varlous portlon~ Or other acld gases lnto an 5 ¦ absorbinK solutlon whlch i~ then thermally regenerated. The I ga~ 18 then passed to a sul~ur reactor where the concentrated ¦ X2S content 18 reacted with a stolchlome~rlc derlclency Or ¦ S2 to rorm elemental ~ulrur and water. The excess H2S
¦ remalnlng ln the resultlng tall gas 18 then reclrQulated 10 ¦ ba¢k to the reed tas stream prlor to the absorber. The ¦ reactlon medium in the sulrur reactor 15 re~enerated in a ¦ Jtill and tho dlssolved H2S and other acld gase~ are ~trlpped ¦ rrom the re¢overed reaction wster in a ~eparate stripper and ¦ are recycled back to the concentrated H2S ln the roul gas lS ¦ whlch pa~JeJ ~rom the absorber Jtrtpper to the sulrur reactor.
¦ It is o~s~ntlal ~or the er~ectl~e operatlon or the recyclo system that the 8Ul~Ur reactor be a liquid reactlon medlum type sulrur reactor operating at no ~reater than 160 C and prererably not ~reater than 140 C or less, below 20 ¦ whlch temperature lt 18 po~slble to es~entlally ellminate ¦ S2 ~rom the tall 8as and no COS and CS2 are rormed. It i8 prererable, ~urthermore, that the amount o~ C02 or other acld ga~e~ whlch are to ~e dlscharged ~rom the ~y8tem shall ¦ not be ab~orbed ln the absorber ln an amount greater ~han 3 25 l moles Or C02 ~or ever~ mol Or H2S ln such ~eed 6as.
In FICURE 3 there 18 shown ln rlow dlagra~ rorm an alternatt~e embodlment Or the present ln~ent;lon ln whlch a ¦ two ~tage sulrur remo~al proces~ 18 u~ed. The ~lr~t ~tage Or the ~ulrur process 1~ a convent~onal Clau~ type 3ul~ur reactor or the like ln whlch the reactlons are carrled out ln a &aa phase whlle ~he ~econd ~tage i8 a llquid reactlon medlum reactor ln ~hich the rea¢tlons are carried out ln llquld-pha~e.
In FIGURE 3 the gas to be treated enters the apparatus or ~ystem through the llno i61 and 1~ passed to an ab~orptlon-desorptlon type apparatu~ 163 Or the thermal regeneration type. ln the ab~orption-desorption apparatu~
a¢ld ga~ components o~ the gas and partl¢ularly the H2S
contont Or the gas are absorbed and removed rrom the gas stream whlch then exlts rrOm the abiorber ~la the llne 167 wlth le~,than 0.2288 grams o~ hydrogen sul~lde per Jtandard cublc meter, ~.e. lcsa than lO gralns o~ H2S ln every lOO
~tandard ¢ublc ~eet Or gas. As ln the embod~ments Or the inventlon Jhown ~n FIGURES 1 and 2 lt wlll be noted that there 19 no other discharge o~ sul~ur containln~ gas ~rom thc oy~te~ as there 18 no tall gas at all discharged rrom the sub~e~uent reactors into the surroundlng envlronment,.
2Q Arter thermal reeeneratlon o~ the absorbln~
solutlon in the ab~orptlon-desorptlon unlt 163, the regenerated roul 8as. whlch wlll ha~e a relatl~ely hlgher content Or H2S
than the orlglnal gas, 1~ passed throu~h the llne 165 lnto a partlal oxldatlon unlt 169 assoclated wlth a Claus-type sulrur rea¢tor unlt 179. A boller 171 13 al~o a~soclated wlth the oxldatlon unlt 169. Oxygen or alr enters the oxldatlon unlt 16g through a llne 173 and comblne~ wlth the H2S and other combustlble Bas passln~ lnto the oxldat~on -~8-~ 1428 ¦ un~t ~rom the line 165. Only su~rlcient o~ygen or air 18 ¦ pro~lded to oxldlze a portlon Or the ~2S to S02 ln order to malntain the mol ratlo o~ H2S to S02 ln the ga3 greater than ¦ the stolchlometrlc reactlon ratlo of 2. Con~lderable heat 51 18 glYen Orr by the partial oxldatlon Or the ga~ stream and ¦ thls heat ls used ln boller 171 to heat water provlded through llne 17~ and make ~team whlch leaves the boller throueh line 177. Thls stea~ may be used ln the plant I genorally or may be used to provide heat to the reboiler lO ¦ associated wlth the thermal re~enerator o~ the absorptlon-desorption apparatus.
¦ Thc partlall~ oxldlzed gas now contalning S02 a3 ¦ ~oll as H2S and C02 and also 3mall but ~igniricant amounts ¦ Or COS and CS2 rormed durlng the partlal oxldatlon condltlons l~ ¦ alon~ ~lth small amounts o~ elemental ~ulfur now enters the l Clau~-type reactor 179 where lt i8 catalytically reacted to ¦ ~orm more elemental sulrur and water ~n accordance with the ¦ Reactlon l. Some Or the COS and CS2 al~o react wlth water ¦ vapor to rorm addltlonal elemental sulrur. The ele~ental 20 ¦ ~ulrur e~lts through llne 181 while the unreacted H2SJ SO2, ¦ C2 and other remalnlng gases such as N2, COS and CS2 exlt ¦ throu~h the line 183 which leads into a llquld-phaoe type ¦ ~ulrur reactor 185. In this reactor 185 the remalnlng S02 ¦ rcact~ with the ~2S pre~ent to ~orm addltlonal elemental 25 ¦ sulrur product and ~ater. The reactlon ln thls reactor is I run at low temperatures Or less than 160 C and the reactlon ¦ Or S02 wlth H2S, unllke the reactlon ln the Claus reactor, 18 sub~tantlally complete. In addlt~on the llquld-phase proces~ does not result in the rormatlon Or any COS or CS2 ~ he additional elemental 8Ul~Ur ~ormed in the low temperature llquld phase reactor 185 i8 passed rrom the reactor 185 through llne 187 whlch connect~ ~lth the sulrur product llne 1~1 through whlch the comblned elemental ~ul~ur product then leaves the system. The ex¢e~s water ~ormed ln both reactors 179 and 185 leaves the reactor 185 vla line 191 ~hich pa~ses to strlpper 193 where the aqueous ~olution i8 heated to drive Or~ any H2S dt~solved ln the water. The strlpped ~aseo may be returned to the inlet to the llquld-phase reactor 185 ~la llne 195 and line 183 ~hlle the exce~
~2 1~ removed rrom the system through line 197. Thl~
e~cess water may be dl~carded or may be used ~or some other purposc ~n the plant. Alternatively the strlpped H2S may be roturnod to the lnlet to the'Clau~ reactor by pa~lng lt ~nto ~oul ~as llne 165. The ~mall remalnlng amount o~ H2Sln tho tall ga~ ~hlch passes rrom the llquld phase sulrur reactor 18 recycled vla llne 199 to the orlglnal reed ga~ ' stream pr~or to lts entrance lnto the absorber-desorber 163 i and i8 completely reab~orbed 1n the ab~orber. As a ¢on-sequencc, no H2S at all escapes ~rom the ly~tem e~cept rOr tho ~mall amount whl¢h pa~ses out the llne 167 with the de~ulrurized gas. There ~8 thu~ no tall Ba~ at all whlch f e~cspes rrOm th¢ sy~tem as a whole.
~IaURE 4 shows ln more detail a desul~urlzer ~y~tem wlthout a tall gas discharge such as shown ln FIGURE
3. The lnltlal abaorber-desorber arrangement has been shown ~or ~l~pll¢lty' 8 ~ake a8 almost identlczl and the ~lnal ': .

1C~J1 4Z~3 llquld pha~e de~ulfurizer arrangement has been lllustrated as ~ubJtantlally 3imilar to the arrangement ~hown ln FIGURE
2. rho central portlon Or the ~y~tem shown ln F~GURE 4, which portlon constltute8 essen~lally the Claus type reac~or portlon or the system, 18 substantially difr~rent, however.
~he same numbers as used ln FIOURE 2 have been used to ldentl~y ldentical apparatus and tho~e portlons o~ the apparatu~ ~hich are ldentlcal to ~I~URE 2 have been des¢ribed only brle~ly ror the sake o~ ¢ontlnulty. For a more ¢omplete descrlptlon rererence may b~ made to the descrlptlon o~
FIGURE 2.
' In ~I~URE 4 hydrogen ~ulrlde-contalnlng ga~ passes . through ~ced llne 53 to the bottom Or ab30rber 51. Absorbent ; ' ~ solution enter~ the ab~orber 51 through llne 57 and llquid d,i~tributor 59. Almost ¢ompletoly dosulrurlzed ~as lea~es the sy~te~ ln the line 55. Thi~ gas ~111 be de~ulrurlzed to ha~e le~s than 0.2288 8ram~ o~ hydrogen ~ul~lde per standard .
¢ublc moter o~ Bas. Used aboorblng solutlon 18 passed vla llne 61 and pump 63 through heat exchan~er 65 to llquld dlstrlbutor 67 in the top Or strlpping column 69. H2S and : CQ2 and other acid ga~es absorbed or held ln the ab~orbent in loo~- ¢hcmlcal as~ociatlon 1~ ~recd ~rom the absorbent I solutlon ln the ~trlppin~ colu~n and passes rrom the top Or the ~tripplng column throu~h the roul ga~ llne 79.
The ~tr~pped absorbent solutton collects ln the bottom or the strlpping colu~n 69 where lt 18 contlnuously pumped ~la llne 71 to reboiler 73, whlch is heated by heatin8 c0118 75, and through return llne 77 bac~ to the ~trlpplng column 69. The absorbent :solutlon is also pumped vla line 85 and pump 87 throu~h the heat exchan~er 65, where lt glve~ Up some Or its heat to the absorbent ~olutlon ; pas~lng ~rom the absorber 51 to the strippln~ ¢olumn 6g~ and 5 thence through a heat e~changer or coolln~ coll 89, wher~
the abJorbent 1~ eooled, and thon baek through llne 57 to the top ot the ab~orber 51.
The ~2S or C02-contain~ ng roul gas ~rom the stripper 69 pasoe~ throu~h the line 79 to a burner 239 wh~re the ~2S-eontaln ng roul 8as 18 partlally o~idize~ by oxygen or alr ~hleh enter~ the burner 239 through line 241. Assoe1ated ~ith the burner 239 18 a thermal roactor 242 and a boilor 243 whlch makeJ U80 Or the hoat or combust~on and also the hoat o~ roaetlon Or the H2~ and S02 ln the thermal reaetor 242 to ~orm ~toam rrom boiler water whleh entors the boiler through line 245. Steam ~rom tho boil¢r ~xlts through line 247. ~h runetlon or tho thermal reaetor 242 ln tho Jystem lS 08~0ntlally to allow ~urrieiont r~idenee time ror the reaetlon gases to rea¢h their thermodgnamlc equlllbrlum 20 ~polnt and to thoroughlg lntermix. -- Tho a~ount Or o~y~en admltted to the burner 239 18 ; ln~ur~lolent to eompletely oxldize tho H2S eontent or the g-~ and i~ kept limited 80 that the ratlo o~ H2S to S02 in ~tho oxidized ~as la more than 2, or, ln other words, greater ; 25 than the stoi¢hlometrle ratlo. Prererably thls ratlo wlll be maintained bet~een 2.1 and 2.5 or ~ore pre~erably 2.1 to 2.3. Somo o~ the S02 lmmedlately rea¢ts wlth the H2S ln the thermal reactor 242 to rorm elemental sulrur. Th1~

- ~1 10914Z~
~ulrur i~ entralned as sulrur vapor in the hot ¢as whlch leaves tho thermal reactor The hot ga~es and entralned sul~ur vapor are passed throu~h llne 249 to a heat eschange or coollng co~l ?51 ~here the ga~e~ are cooled su~rlclently 5 to conden~e the ~ul~ur ~apor to molten ~ulrur w~lch 18 then ¢ollected ~n ~ulrur collectlng tank 253 a~ the cooled ~a~e~
pa~s through the upper portion~ Or the tan~ and out throu~h ltnc 255 to heat eschang~r 257 where the ga~ 18 reheated berore bo~n~ passod into a catalytla reactor 259 where addltional H2S and SO2 arc reacted together to rorm elemental ~ulrur and ~at~r The ga~ pa~sos rrOm the catalytlc rea¢tor 259 through lln~ 261 to beat eschang~r 257 where it give3 up ~ome Or itJ heat Or reaction to thc gas enterlng the reactor and then passos through th~ coollng coll or conden~er 263 ~here the elem~ntal sul~ur vapor 1~ conden~ed to molten ~ Jul~ur whlch 1~ thon collected ln the bottom Or the ~ul~ur j colloctor tank 265 Thc molten ~ulSur collectod ln the two ~ulrur collector tank~ 253 and 26~ is removed, uBuaily porlodl¢ally, ~rom tbe~o tank~ through llne 271 whlch leads to ~ul~ur ~tora~e or u~e ~acllltle~, not ~hown Th~ tnll gas rrom ~he cataly~lc reactor 259 pa~aeJ
~la th- colloctor tank 265 through llne 267 to a ~parger 272 ~n~tho bottom o~ a llquld phaso ~ul~ur reactor 83 Tho ro-otor 83 contain~ a llquld reactlon medlum ln whlch rcaction ~; ~ Or the remalnlng S02 contalned ~n the tall gas rrom the ¢atalytlc reactor 259 takes placo and Nill remo~e all rlnal traccs o~ S02 rrom tho Ba~ The gas bubble~ up rrom the ~arger 2 throu~b th- reaotor ~edlu~ llquld ln the -~3-¦ reactor 83. The tall ~as~ wlth su~stantlally every last bit ¦ ~ S2 reacted wlth H2S to rorm elemental sul~ur and ~2~
¦ then passes to&ether with the excess H2S contalned ln the ¦ ga3 ~rom the top Or the reactor 83 through the recycle llne ~ ¦ 153 ba¢k to the or~glnal reed llne ~3 which ~eeds gas to ; ¦ the absorber 5}. ~one Or the tail gas thus has any ac¢es~
to the environment external to the system and no sulrur ¦ reaches the onrlronment e~cept as an elemental sul~ur product ¦ or as that very amall amount Or sulrur whlch 1s able to pas3 10 ¦ through the absorber wlth the orl&lnal gas stream.
¦ The liquld reactlon medlum 18 cont~nuously removed ¦ rrom the bottom Or the reactor 83 as ln ~IaURE 2 together ¦ wlth precipitated sulrur partlcles suspended in the ll~uld ¦ and 1~ passed to ~ sulrur melter 113 ~here the sulrur 151 partlcle~ are melted and allowe~ to ~-parate in an upper ¦ solutlon layer, an lntermed1ate ilurry layer and a lower molten sul~ur layer. The llquld sul~ur layer settles beh~nd a ~elr 115 and can then be pumped or removed throu~h llne ¦ 123 and val~e 117 to stora8e. The melter 133 18 malntained 20¦ under sur~lclent preJsure to keep the reactlon medium I oolutlon ~rom bolling at the sulrur meltln~ temperature.
¦ The llquld portion Or the reactlon medium whlch ¦ overrlows over the ~eir 114 passes as ln FIGURE 2 through l tho valve 124 and llne 125 to a solvent dlstlllatlon oolumn 251 129 where the solutlon passes downwardly through hot rlsln~
~apor3 rrom a reboller 133. Dissolved gases are stripped rom the ~olutlon ln the distillatlon colu~n and pas~ out the llne 35 throu~h a dephleemator 137. The oondensate _44_ ¦ ~low back to stlll 129 and the non-condensed ~rapors are ¦ plped lnto an H20 stripplng column 141. ~ree H2S passes ¦ rrOm the top or the H20 ~trlpper column through llne 145 to ¦ the llne 267 whlch conducts the ta~l ~as rrom the catalytic 5 ¦ resctor 259 to liquid pha~e rea¢tor 8~. Water whlch contalns ¦ dt8801ved H2S i8 ~trlpped ln the strlpper 141 by mean~ Or ¦ ~team generated ln a re~oiler 143. Thl8 strlpped ga8 al8o pa88e~ throug~ the llne 145 and re¢ycle llne 267 back to the ¦ reactor 83. The strlpped and e~entlally ~a~-~ree water 10 ¦ then passe~ rrom the ~2 strlpper 141 throuEh line 147 whlch ¦ dlrocts the strlpped water to disposal.
The strlpped reactlon medium ln the bottom o~ the .
¦ solvent distlllation ¢olumn 129 i8 passed rrom the bottom o~
¦ the ¢olumn a~ Jhown ~ia line 149, tnto a cooler 152 and then 15 ¦ contlnue~ vla ~lne 111 lnto th~ top Or the llquld-pha8e ~ulrur reactor 83 whero lt 18 pas~ed lnto the reactor ~rom ¦ the dlatributor 91. The ¢ooler 152 ~erves to reduce the .
¦ temperature o~ the react~on medlum su~riclently to keep the l reactlon zone at not greater than 160 C during reactlon and 201 pre~erably below 140 C.
In FIGURE 5 there is shown a varlation o~ the : I pro¢e~s shown ln PIaURE 3. This 1~ the preferred method Or ¦ treating an H2S and HCN conta~nine ~eed OEas~ part~cularly ¦ coke oven Kas. The deslgnat~ng numbers and descrlption are 251 identical to that associated with FIGURE 3 except ~or the add$tion or three llnes and an XCN removal step or apparatu~.
In FIGURE 5 a coke oven ~a~ to be desulrurized enter~
¦ through l$ne 161 and passes to an ab30rption-desorption 1~t91428 apparatu~ 163 where 3ub~tantially all the H2S and much or the content Or other acid ga~es 1~ ab~orbed and thermally regenerated to provlde a ~oul gas stream ln llne 165. ~he de8ul~urlzed ga8 leaves through llne 167.
Coke oven gas normally ha~ about 0.04-0.1~ o~ HC~
ga~ contained ln it and thls HCN 1~ to a large e~tent absorbed and regenerated ln the absorption-dèsorptlon apparatus 163. Althou~h the Claus burner burns most o~ the HCN whlch pas~es through lt, there is always a surri¢lent amount lert to do COnsiderable damage by corroslon to the sheet steel rro~ which the Claus plant equlpment 18 usually ~ormed ln only a matter o~ a re~ day~. Consequently this ~CN must be ellmlnated ~rom the roul 8as be~ore the gas pas~es to the Claus proce~s.
15¦ In order, there~ore, to de¢rease the a~ount Or HCN
in the ~oul 8as it ~ rirst passed via llne 165 to an HC~7 re val apparatu~ 321 which compri~e~ absorptlon and desorption .
stopo, not oeparately sho~n, u~lng H20 as the ab~orblng solutlon. The HCN is strlpped ~rom the water ln a strlppln~
column uslng a portion o~ the already desulfurlzed gas tapp-d ~rom llne 167 throuKh llno 323. The de~ulrurlzod ga~
18 preheated and pas~ed up~ardly through the H20 ln the ~trlpplng colu~n~ whlch 18 not shown, but whl¢h ~ay be ~ubstantially ll~e the ~2S stripper 69 shown in ~IGURES 2 or 4. The strlpped HCN passes out Or the stripp~ng column along wlth the stripplng gas and pa~ses through llne 325 ba¢k to the coke oven batterles where t~e gas 19 burned under the coke oven batterles as a gaseou~ ruel e~recti~ely 1~914Z8 destroying all of the HCN and forming harmless N2 and C02. The practically HCN-free foul gas after absorption of the HCN is passed through the line 327 to the sulfur burner 169 associated with the Claus reactor 179. The gas passing to the sulfur burner will contain less than 0.1% HCN and will not harm the Claus apparatus. From this point on the operation and numbering of Figure 5 is identical to Figure 3 and a description of the Figure will not be repeated. For an explanation of the remainder of the operation of Figure 5 reference should be had to the description of Figure 3.
As an alternative to the water absorption system illustrated in Figure 5 for the removal and disposal of HCN from the foul gas stream some other HCN destruction or removal system may be used such as an HCN hydrolysis reactor where the HCN is hydrolyzed by heating in the presence of water vapor, usually in the form of steam. Ammonia, water and COg are formed in this reaction and the resulting gas can be processed in a Claus plant, where NH3 may be made to burn harmlessly. A further alternative is the use of a so-called hydrogen cyanide destruct system such as disclosed in United States patent 3,923,957 to O.A. Homberg et al. The HCN conversion by this process produces, besides NH3 and C02, some COS and CS2. However, this does not further increase the COS and CS2 content of the tail gas of the Claus process, since the COS and CS2 contents are determined by the thermo-dynamic equilibrium in the catalytic gas phase reactors, irrespective of the COS and CS2 contents of the foul gas.

.~ - 47 -.__ 1~914Z8 ¦ In FI~URE ~ there i8 shown a schematic 3i~pllrled ¦ block d1agram type rlow ~heet o~ the baslc operation of the ¦ presont invention lncludlng representatlons o~ typlcal ga~
¦ compositlons and gas quantltle~ ln moles per hour passlng 5 ¦ the varlous points. The gas compo~ltions and quantitles ¦ whlch are ~ound at the ~arious po~nts deslgnated by letters ¦ A through P ln FIGURE 6 are show~ under the3e letter deslgnn-¦ tlons ln Tables I, II, III and rv o~ Pigures ~A, 6B, 6C and ¦ 6D respectlvely. Th~ rigure~ in the tables are calculated 10 ¦ ba~ed upon a¢tual experimental data. FIGURES 6A and 6B are ¦ lllustratl~e o~ the treatment Or a reed gas contalnin6 ~2S
¦ but not containSn~ HCN~ in thl~ e~ample natural gas. FIGURES
¦ 6C and 6D are representat~ve Or the treatment Or a reed gas ¦ containlng HCN 4uch a~ coke oven gas~ with the operatlon 15 ¦ being Or a ~hort durat~on in whlch the thlocganate doe~ n~t ¦ accumulate to a concentratlon ~urrlclont to deterlorate the liquid pha~e reaction medlum and ar~ect the proce~s. As I pre~lously stated, a reed ga~ containing H2S and HCN can be ¦ treated by tbe system dep~cted ~y the block dia8ram of 20 1 PIGURE 6 ln a contlnuous oporatlon 1~ a portlon o~ the llquld phase reactlon medium 1~ bled Orr and replaced by rresh rea¢tlon medlum to prevent lts de~eneration by thlo-l c~snate accumulatlon. Prererably such a reed gas 18 treated ¦ by the operatlon Or the present invention ~hown ln the block 25 ¦ dlagra~ type ~low sheet o~ FIaURE 7.
~he ba3i~ taken ln the tables 1~ that 2 832,000 I Nm3 (-lO0 MM standard cu~ic ~eet) per day o~ ~as enter the ¦ reed llne 351 at polnt ~A) ~lth a compo~ltlon a~ ~hown under `~ lO9i428 (A) ln Tables I and I~I ~FIGURES 6A and 6C). A quantlty Or ~a8 ln kg-~ole~ per hour whlch passe~ polnt (A) 18 shown under ~A) ln Table~ II and I~ ~FIGURES 6B and 6D). ~he ga~
Or ¢ompos~tlon ~A) is treated to re~o~e X2S ~elect~vely, i.e. ~o that H2S 1~ removed ~u~tant~ally completely even thou~h other component~ may not be removed completely, in the mono~thanolamine ab~orber-desorber 353. All but 0.015 percent ot the H25 18 ab~orbed, thermally regenerated and pa~sed lnto the ~oul ~as line 355. Thls produ¢es a de~ul-: 10 ~urlzed gas havln~ a co~po~ltion (C) which leaves the.
:: absorber-de~orber 353 through llne 357. Th~ rOUl ~a8 in ~tne 355 ha~ a com~ositlon (D). ~he rou~ 8a~ then passe~
into a ~ul~ur recovory ~y~tem 359 comprl~ed o~ a llquid-pha~e ~ul~ur r~actor in ~hi¢h S02, whl¢h 1~ produced ln,a burner, not shown, by burnln~ a portlon o~ the aultur product . ~Or thc roul 8a~ w~th about 0.5 moles ~ 2 ror o~ery ~ol o~
~; H2S, 1B roaot¢d ~ith the H2S. ~he S02 produced 1~ reacted ln;~the ll~u~d-phase rea¢tor wlth the H2S to torm ele~ental ~ul~ur ha:vlng a ¢ompo~ltlon ~F), ~hl¢h leave~ ln lln~ 361, ZO and~- tall gas havlng a compositlon ~), whlch i~ recycled back in recJclQ line 363 to the reed 8as line 351 ~iving a ¢ombtn-d gas composltlon at point (B) ~u~t prior to the ~absorber-d sorber 353 o~ ¢ompo~ltSon (B).
. In ~I~U~E 7 there 18 shown a sl~pll~led s¢hematlc block dlagram tgpe ~low sheet o~ the operatlon o~ the present : lnventlon to treat a reed ~as conta~nin~ H2S and HCN.
Becau~e o~ t~e nsertton Or an ~CN romoYal system a~ter the Ras de~ulrurlzer an~ be~ore the ~ulrur re¢overy sy~tem, coke ' ~ . ' :

, -49-lQ914Z8 oven gas can be expediently processed. Tables V and VI in Figures 7A and 7B
respectively pertain to an aqueous absorption/desorption HCN removal system and Tables VII and VIII in Figures 7C and 7D respectively pertain to an HCN
destruct and removal system. The general description of Figure 6 and its associated tables applies here as well and will not be repeated. Coke oven gas passes through the feed line 351 at point (A) and enters the MEA gas desulfurizer 353. Foul gas emerges via line 355 and enters the HCN removal system 365. Where the HCN removal system comprises an absorption and desorption step using water as the absorbing solution, the HCN is stripped from the water in a stripping column using a portion of the already desulfurized gas tapped from line 357 through broken line 367. The stripped HCN passes out of the HCN removal system along with the stripping gas and passes through broken line 369 back to the coke oven batteries to be utilized as a fuel. The practically HCN-free foul gas is then passed through line 371 to the sulfur recovery system which in this case can simply be a liquid phase reactor. The gas composition and quantities at various points throughout this embodiment having the aqueous absorption/desorption HCN
removal system are shown in Tables V and VI of Figures 7A and 7B. Alter-natively, where the HCN removal system is an HCN destruct system such as an HCN hydrolysis reactor or the HCN destruct system disclosed in United States patent 3J923,957 to 0. A. Homberg et al, the foul gas containing H2S and HCN enters . ' ,-;

109~4Z8 the reactor o~ the HCN re~oval ~ystem ~65 vla llne 35; and e~lt~ a3 a ga3 containing i~H3 among lt~ componenta in llne 371. Because thl~ resultlng gaa contaln3 ~3, lt must ~o handled ln a ~ulrur recovery system 359 compri~ing ~lrst a Clau~ reactor to burn the NH3 to N2 and ii20 in addltlon to burnlng the H2S to S02 tollowed by a lSquld pha~e 3ul~ur rea¢tor B0 that the NH3 wlll not upaet the pH or the llquld roQ¢tlon medium. The ta~l gas ~rom ~he ~ul~ur reco~ery ay~tem 18 re¢ycled ba¢k in re¢y¢le llne 363 to reed llne 351 prior to the ~EA ab~orber-de~orber 353. L~ne~ 367 and 369 ~ould not be needed rOr no strlpplng or abaorbed KC-J rrom a I aolution ~g a portion Or the dosulrurlzed gas stream la required in thi~ partl¢ular HCN romoval syatem. ~he ~as ¢ompo~itlon~ and qu ntStleJ at the var~ous polnt~ throu~hout the embodiment or FIGURE 7 having an ~CN doatruct syatem o~
U. S. ~atent 3,923,957 s~re ~hown ln Tablos VII and ~ITI o~
PlGURE8 7C and 7D.
By operatlon in a¢cordan¢e wlth the present lnven-tlon a do~ulrurlzatlon pro¢oa~ la pro~ided whlch produces only a very mlnor a~ount o~ H2S contamlnation ln the desul-~urlzod ga~ and which ha~ no tall ga~ o~ any de~cription to ~di~ose Or. All Or the sul~ur whl¢h doe~ not exit with the orlglnal dosulrurlzed ga~ lea~cs tho aystem in the ~orm or ole~ental sul~ur whlch can be u~ed or ~old prorltably upon the commerolal ~arket. Whlle 80me thlourea-type compounds may be rormed ln the de~ulrurlzer portlon Or the system ~rom the reactlon Or CS2, the percentage o~ 8ulrur value~ 50 wasted i9 ~0 8~all a~ to be completely ne~ ble rrom an overall proce~ ~iewpolnt.

. . I

~31 4 28 ¦ When the proce~s Or the lnventlon 1~ used ln con-¦ nectlon with the deoulfur1zat~on Or coke oven gas or ehe ¦ llke lt is partlcularly important that the recycled tall ~as ¦ ~a) be recycled lnto the system ahead o~ the desul~uri2er 5 ¦ ~or absorptlon-desorptlon apparatu~ ) but arter the pri~ary coolers or a~ter any step inrolvln~ 8as contact w~th an alXallne ~olutlon, and (c) that the tail gas contain e~entlally no S02.
¦ FSr~tJ lr the recycle gas 18 added to the main ¦ coke oven g~ ~tream ahead Or the prlmary cooler some o~ the ¦ H2~ wlll be reacted wlth ammonia in the coke oven gaJ to ¦ ~orm (NH4)2~ or NH4~S which will be dl~solved ln the am~onla ; I llquor. In the pr~mary cooler thls ammonla llquor partlally ¦ ab~orb~ o~ygen whlch may have leaked through the coke oven 15 ¦ door~ or entered the coke oven durlng coal charging, or been 1 1 added to the tall gaJ by burning ~ul~ur with an exces~ Or ;~ ¦ alr. As a rosult Or thl~ oxygen absorptlon, the dls~olved ¦ HS lon~ are o~ldlzed to thlo~ul~ate lon~ S203 . Once ¦ rormod, the thio~ulrate ion~ cannot be str~pped ln the ¦ a~monla liquor ~trlppers and ha~c ultSmately to bc dlsposed or, thu~ contrlbutlng to water pollutlon. Even more slgnlrl-, , ~ ~
¢antly ~uch lo~ Or thlo~ulrate~ contributes to a net 108B
or sulrur values ~n the proce~s.
Second, ir the recy¢le ~a~ ¢ontaSnJ S02 ln addltlon 25 ¦ to H2S, tho S02 1~ lmmedSately di~301ved Sn the ammonla i ; I llquor rormlng ~ul~ttes, blsulr~tes and th~o~ulrates, and thlD rurther reduces the reco~ery Or sul~ur values ln the pro¢e-~ and lncrease~ possible ~ater pollutSon problem~.

, I

~ I -52-l Third, 1~ the recycle gas containlng S02 18 added ¦ to the coke oven ~as strea~ arter tbe prlmary cooler~, but ¦ ahe~d Or the ~as desulfurizers, the S02 will be immediately ¦ dl~solved in the alkallne }I2S ab~orbent formlng thio~ulrate 1 5 ¦ whlch 18 nonregenerable. The de~ulrurlzer 301utlon wlll as a ¢onsequence be con~tantly contaminated wlth increa~ln~
¦ quantltltes Or alkall thiosulrate. This contaminat1on (a) ¦ repre~ents a slgnl~lcant loss ln 8ul~ur value~ ~ro~ the ¦ system, (b) increases the heat requlrements Or the desul-lO ¦ ~urizor ltripper, and (c) ~ust be regularly dispo~ed Or by ¦ bleedln~ at least part Or the absorbed ~Qlutlon, thus ¦ croatlng a serious water pollution problem. I~ the desul-¦ ~urlzer absorbont 19 a monoethanolamine solutlon, the ¦ thlosulrate may be dlsposed Or ln the recla~er a~ a solld 15 I waste.
¦ In the pre~ent inventlon, on the other hand, the ¦ tail ~as stream that is recycled to the coke oven ~as ¦ ~troam a~ter the pr~ary coolers but ahead Or the H2S
¦ absorber, does not contaln any S02, thus the recycled H2S is 20¦ totally ab~orbed ln the ~2S absorber without rorming any ¦ tblosulrate. Con~equently substantlally all the sul~ur values ln the coke oven gas may be recovered as elemental ¦ sul~ur, and none are de~raded lnto thiosulrates, 3ul~1~es, I ¦ ~ul~ite~ and sulrate~.
25¦ It 18 thu~ qulte critical ~or the succe~s o~ the proce~s o~ the invention for a su~ricient stolchiometrlc l exces~ Or H2S over 32 to be u~ed in the ~ulrur reactor to ¦ assure that a complete reaction o~ all the S02 enterlng the I ¦ ~ystem i8 errected. An e~cess Or rrom 5% to 20% o~ H2S over 10914Z~
the stolchiometric reactlon ratto has been found to be satistactory, but an excess Or about 5~ to 15S 1~ pre~erred.
Broadly any amount Or H2S beyond a ~tolchlometrlc ratlo o~
2 may be satlsractory ln a giYen system 80 long as the ratio i8 surriclently great, or the excess 1~ sutrlclently large, to drlYe the reactlon to a point ~here substantlally no S02 lea~es the sulrur reactor. It ha~ also been ~ound that ~lnce the hlgh-temperature Clau~ reactlon never completely u~e~ up all the SO2 present due to the unra~orable thermo-dynaml¢ qulllbrlum condltlon~ at loast wlth praotlcal oxces~es Or H2S that lt 1~ e~entlal that at leaat the last sta8e Or the sulrur re~oval ~tep ~hall be accompllshed ln a ltquid-phase type ~ulrur rcmoYal operation or other equlYalent low temperature ~ultur remoYal proce~. An exce~ or H2S ln ~uch a proce~ wlll as~ure that ~ub~tantlally no 8O2 1~
pro~ont ln tho tall gas rrom the reactor and al~o that no now quantltlos Or detrimontal ~ide-reactlon compounds such aJ C0S, and CS2 ~ill be tormed.
It wlll bo recognlzed *rom the rore~oln~ detalled de~crlptlon Or examples Or the proccss Or the lnventlon that a ~-ry oconomlcal yet ~trectlYe system tor subJtantlally complote el~minatlon Or ~ulrur pollutlon ha~ been provlded in the torm of an orrectlYely clo~od sy~tem *rom whlch as a practlcal matter no ~ul*ur values can e~cape. The com-blnatlon ot tbe use ot a low temperature ~ultur removal step in a llquid pba~e reactlon zone whlcb may be the primary zone or may be comblned ln series wlth a Clau~ or ga~ pha~e react on zone u~n~ 3n e~ce3~ Or ~2S wnlch la then rec~cled ` j 10~14Z8 ¦ to an e~i¢lent alkanolamlne or equivalently e~ectlve II2S
¦ absorptlon reaction whl¢h removes practically all the ~2S
¦ content or ~he comblned gas stream 18 both unlque and par-¦ tlcularly efrectlve ln preventlng ~ul~ur pollution and 51 recoverln~ all practical ~ul~ur ~alues. The arran~ement o~
¦ the ln~entlon 18, rurther~ore, not only partlcularly ¦ e~ect~ve, but 18 also relatl~elg slmple and may u~o only ¦ standard lndu~trial equlpment units which are read~ly avallable and econo~ical to use.

. I .

Claims (15)

Claims We claim:

1. A method of substantially completely removing H2S and recovering the sulfur values as elemental sulfur from an industrial gas stream without exhaust into the environment of a tall gas, a bleed-off or a vent stream containing sulfur pollutants other than the desulfurized industrial gas comprising:
(a) absorbing substantially all H2S from an H2S containing industrial gas in an absorption zone by contacting said gas stream with an alkanolamine absorbent solution in said absorption zone at a rate such that not more than 3 moles of CO2 per mole of absorbed H2S is absorbed from the gas stream to form an H2S-rich absorbent solution and a substantially desulfurized industrial gas, (b) stripping the H2S-rich absorbent solution to recover the H2S, (c) combining the recovered H2S with SO2 in a ratio of H2S to SO2 from 2.1:1 to 2.5:1 in a low temperature reaction zone operated at a temperature not greater than 160°C within a liquid-phase reaction medium to form elemental sulfur and H2O
with an excess of unreacted H2S remaining sufficient to ensure that there is essentially complete reaction of all SO2 in said reaction zone with H2S, (d) removing sulfur from the liquid phase reaction medium in the low temperature reaction zone in the form of elemental sulfur and excess unreacted H2S contained in a tall gas from said reaction zone, (e) recycling the tail gas containing the excess H2S from the liquid phase reaction medium in the low temperature reaction zone of step (c) to the absorption zone of step (a), and (f) passing the tall gas with the sulfur containing industrial gas through the absorption zone wherein H2S contained in the tail gas is absorbed into the alkanolamine absorbent solution while the remaining gases of the tail gas become part of the desulfurized industrial gas.

2. A method of removing H2S according to claim 1 wherein the tall gas is recycled into the H2S-containing gas stream of step (a) prior to contact of said gas stream with the absorbent solution in the absorption zone of step (a).

3. A method of removing H2S from a gas stream according to claim 2 wherein the tall gas is recycled into the gas stream prior to contact of said gas stream with said absorbent solution in the absorption zone but subsequent to any prior gas processing step which would remove sulfur values from the gas stream.

4. A method of removing H2S from a gas stream according to claim 3 wherein the low temperature reaction zone 18 operated at a temperature not greater then 140°C.

5. A method of removing H2S from a gas stream according to claim 3 wherein the absorbing of H2S in step (a) is at a rate such that from 1.4 to 2 moles of CO2 per mole or absorbed H2S is absorbed from the gas stream.

6. A method of removing H2S from a gas stream according to claim 1 wherein the ratio of H2S to SO2 in stop (c) 18 from 2.1:1 to 2.3:1.

7. A method of removing H2S from a gas stream according to claim 1 when the industrial gas stream also contains HCN wherein the H2S of stop (b) is recovered as an H2S-rich gas stream additionally comprising removing HCN
from the H2S-rich gas stream by an aqueous absorption/desorption HCN removal stage prior to reaction of said H2S with SO2.

8. A method of removing H2S and recovering the sulfur values as elemental sulfur from an industrial gas stream without exhaust into the environment of a tail gas, a bleed-off or a vent stream containing sulfur pollutants other than the desulfurized industrial gas comprising:
(a) contacting an H2S containing industrial gas stream with an alkanolamine absorbing solution to absorb substantially all H2S
from said gas stream at a rate such that not more than 3 moles of CO2 per mole of absorbed H2S is absorbed and provide a substantially desulfurized industrial gas, (b) stripping the H2S-rich absorbing solution of step (a) to recover H2S, (c) reacting the H2S recovered in step (b) with SO2 in at least two reaction stages comprising (i) a gas-phase reaction stage, and (ii) a final reaction stage operated at a temperature not greater then 160°C within a liquid phase reaction medium, (d) said reaction stages having an operating H2S/SO2 ratio from 2.1:1 to 2.5:1 such that no SO2 passes from the final liquid phase reaction stage of step (c)(ii), (e) removing sulfur from the reaction stages of step (c) in the form of elemental sulfur and from the final liquid phase reaction medium of step (c)(ii) as H2S
contained in a tall gas, (f) recycling the tall gas from the final liquid phase reaction medium of step (c)(ii) into contact with the alkanolamine absorbing solution of step (a), and (g) passing the tall gas with the sulfur containing industrial gas through the absorption zone wherein H2S contained in the tall gas is absorbed into the alkanolamine absorbent solution while the remaining gases of the tall gas become part of the desulfurized industrial gas.

9. A method of removing H2S from a gas stream according to claim 8 wherein the tall gas from the final liquid phase reaction is recycled into the H2S-containing gas stream of step (a) prior to contact of said gas stream with the absorbent solution of step (a).

10. A method of removing H2S from a gas stream according to claim 9 wherein the tail gas from the final reaction stage of step (c)(ii) is recycled into the H2S-containing gas stream passing to the absorbing solution subsequent to contact with any gas treating stage which might remove any sulfur values from the gas stream.

11. A method of removing H2S from a gas stream according to claim 10 wherein the ratio of H2S to SO2 in step (c) is from 2.1:1 to 2.3:1.

12. A method of removing H2S from a gas stream according to claim 10 wherein the final liquid-phase reaction stage of step (c)(ii) is operated at a temperature of not greater than 140°C.

13. A method of removing H2S from a gas stream according to claim 10 wherein the absorbing of H2S in step (a) is at a rate such that from 1.4 to 2 moles of CO2 per mole of absorbed H2S is absorbed from the gas stream.

14. A method of removing H2S from a gas stream according to claim 11 when the industrial gas stream also contains HCN wherein the H2S of step (b) is recovered as an H2S-rich gas stream additionally comprising removing HCN
from the H2S-rich gas stream prior to reaction of said H2S
with SO2.

15. A method of removing H2S from a gas stream according to claim 10 wherein the absorbing solution is a monoethanolamine solution.