US2511307A

US2511307A - Method for the utilization of impure coke-oven gas and waste pickle liquor in the manufacture of ammonium sulfate

Info

Publication number: US2511307A
Application number: US672896A
Authority: US
Inventors: Tiddy William; Franklin D Cooper
Original assignee: Allied Chemical and Dye Corp
Current assignee: Allied Corp
Priority date: 1946-05-28
Filing date: 1946-05-28
Publication date: 1950-06-13
Anticipated expiration: 1967-06-13

Description

June 13, 1950 w. TIDDY E-r Ax. 2,511,307

METHOD FOR THE UTILIZATION 0F IMPURE COKE OVEN GAS AND WASTE PICKLE LIQUOR IN THE MANUFACTURE oF AMMONIUM suLFATE Filed May 28, 1946 Patented June 13, 1950 UNITED STATES PATENT OFFICE METHOD FOR THE UTILIZATION OF IMPURE COKE-OVEN GAS AND WASTE PICKL'E LIQUOR IN THEl MANUFACTURE OF AM- MONIUM SULFATE William Tiddy, Manhasset, N. Y., and Franklin D.

Cooper,

Ashland, Ky., assignors to Allied Chemical & Dye Corporation, a corporation of' New York Application-May 28, 1946,' ySerial No. 672,896

(Cl. .2B-119) 16 Claims.

coke oven gas and .the recovery of iron values from' pickle liquor. Copendng. application Serial .Number 672,895,-.iiledfMay 2.8, 1946, relates to a similar process.

In-the manufacture andr processing of steel,r a serious wasteproblem existsindisposing of the pickleA liquor -produced in` the Vcleaning of steel with sulfuric acid. Thef annual kproductionof Wastepickle` liquor amounts to .about 800,000,000 'gailonsz Even if itcannot-be vutilizedin the production of useful iproducts,` the Ypickle liquor, .con-

taining as it docs free sulfuric-acid,y presents a seriousproblem of: disposal. In fact, many communities prohibit the disposal;` ofv this liquor in streams or rivers unless ithas been `previously neutralized. VAtthepresenttime a great portion oven gas contains ammonia, and processes have Vbeen-suggested for utilizing the ammonia inthe cokeoven gas .forneutralizing the ferrous sulfate and residual sulfuricacid in the pickle liquor. Sinceecoke oven'v gas contains in addition other Vimpurities suchA as cyanides and' suldes which also lreact with the fferroussulfate in-pickleliquor, oneisuch proposed:methodfinvolvesinitiallyfseparating theY ammonia `from the other constituents of the coke oven gas and then reacting the resulting ammonia with thepickle liquor. This procedure, however; involves operatingy difculties which'- render it impractical for commercial practice'and further involves an additionalrelativelyfexpensivestep; `Many similariprocesses for the util-ization of pickleliquorandcoke oven` gas which have f been proposed arenoteconomically feasible,- andmany steel manufacturersdispose ofthe pickle liquor Without' utilizing. it.V for conversion intofuseful products.

In accordancewvith this invention, a cyclic vpl :-::ess is providedwhich is economical inoperationand whichremoves both thesulfate and iron values from the pickle liquor and: ammonia and `otherconstituents=fromLunpuriiied.coke oven gas.

not. infrequently adjacentthecoke ovens which recover ammonia in the coke-ovenfgaswith purchased sulfuric acid. Forsuch situations, in addition to utilizing both the pickle'liquor'and the ammonia in the coke gas for the production of a useful product, this process reduces the hazards of pickle liquor waste disposal.

An object of this invention is to remove substantially completely or materially reduce the ammonia contained in unpurified coke oven gas.

Another object of this invention is to utilize unpuried coke oven gas for the recovery of iron values from waste pickling solution and simultaneously to remove ammonia and other consti'- tuents from coke oven gas.

Another object of this invention is to provide an economic cyclic process for the production of ammonium sulfate by the utilization of unpuriiisd coke oven gas and pickling liquor whereby the ammonia is removed substantially completely from the coke oven gas and iron values are recovered from the'pickling liquor.

Another object of this invention is to increase markedly the ease of removal of the precipitated iron compounds produced by the reaction of waste pickleliquor and coke oven gas.

In the process of this invention, unpuried coke oven gas is contacted intimately with a feed liquor comprising pickle liquor containing free sulfuric acid and ferrous sulfate and a liquor containing ammonium sulfate. The unpuried coke oven gas contains ammonia, cyanide and hydrogen sulfide and is ordinarily utilized without any prior removalof the ammonia, cyanide or hydrogen sulfide, although some partial removal of one or all of these constituents may have been prior to contact with the feed liquor. In the contact between the unpuriiied coke oven gas and the feed liquor, soluble ammonium sulfate and insoluble ferrous hydroxide, ferrous sulfide and ammonium ferroferrocyanide are formed. The insoluble ferrous hydroxide, ferrous sulfide andiammonium ferroferrocyanide are separated from the liquor by any suitable means, such as ltration, decantaton or centrifugation. After separation of the insoluble materials, a portion of the liquor is recycledwith additional pickle liquor toecntaet the unpurifled coke ovengas. Desirably, from to 90%, and preferably fromY '70 to of the liquor is recycled to form the feed liquor in the process. The remaining portion of the separated liquor is oxidized by aeration, for example, to remove any residual ferrous sulfate in that portion of the clear liquor. The free ammonia contentof this vportieri of the liquor should be in excess of that necessary to react with the sulfate radicalspresent to form ammonium sul-.-

fate. For this purpose, the ammonia content of this portion of the liquor is adjusted, if necessary, by addition of ammonia to the liquor prior to oxidation; thus the free ammonia content of the liquor should be at least 0.5 gram per liter, and when the ferrous sulfate content of the liquor is 2 to e grams per liter, the free ammonia content of the liquor should be about 0.8 gram per liter or higher. The resulting iron hydrate formed in the oxidation step is removed by any suitable means, such as decantation, filtration or centrifugation, and the ammonium sulfate, after such separation, is recovered from the clear liquor by any conventional means.

The ferrous sulfate content of the feed liquor after contact with the coke oven gas may fluctuate from to 10 grams per liter; the contact of the coke oven gas with the feed liquor is regulated so that the liquor after contact contains not more than grams of ferrous sulfate per liter and is preferably regulated so that the ferrous sulfate content of the liquor after contact with the gas is ordinarily within the range of 2 to 4.. grams per liter. A concentration of at least 2 grams per liter of ferrous sulfate insures substantially that the insoluble ammonium ferroferrocyanide formed is not converted to soluble ammonium ferrocyanide. When the ferrous sulfate content of the liquor after contact with the gas is substantially 0 gram per liter, the free ammonia content of the liquor should not exceed 1.5 grams per liter in order to avoid formation of soluble ammonium ferrocyanide. The amount of ammonium sulfate in the feed liquor prior to contact with the gas is at least 100 grams per liter and is preferably at least 200 grams per liter. The

vammonium sulfate content of the liquor increases during contact with the gas, the increase ordi.- narily being 35 to 40 grams per liter. Within limits, the concentration of the ammonium sulfate in the solution after contact with the unpuried coke oven gas may be controlled by regulating the proportion of recycled liquor to the pickle liquor forming the feed liquor. With a .pickle liquor of known concentration of ferrous sulfate and sulfuric acid, this proportion can readily be determined.

The practice of the cyclic process of this invention involves material economic and engineering advantages. The recyclingr of ammonium sulfate solution provides a flexible means of controlling the volume of feed liquor relative to the gas, the dilution of the ferrous sulfate and sulfuric acid to be reacted with the unpuriiled coke oven gas and the concentration of the ammonium sulfate in the feed liquor. The addition of large quantities of ammonium sulfate solutions to pickle liquor promotes more eicient contact between the liquor and gas, whereby greater reactivity is achieved with the unpurified cone oven gas, by virtue of the increased volume of liquor' aifording more intimate contact with the gas as well as a greater dispersion of precipitate in the liquor, thereby minimizing entrapment of unreacted ferrous sulfate and sulfuric acid in agglomerates of precipitate. Further, the dilution of the liquor with respect to iron precipitated and the concentration of the ammonium sulfate is controlled by means of recycling liquor separated from the precipitate so that the absorption and reactor units operate without plugging and with minimum back pressure, producing a concentrated ammonium sulfate solution which can be economically evaporated for the production of ammonium sulfate. Another advantage of the dilution of the pickle liquor with ammonium sulfate solution is that a smaller quantity of precipitate is formed per unit volume of liquor treated whereby separation of such precipitate is facilitated. And, as will be described in detail later, the resulting precipitate may be separated by filtration markedly more effectively than the precipitate formed when pickle liquor is treated with purified coke oven gas. In addition, only a portion of the total iron in the pickle liquor is oxidized. In fact, it has been found in the practice of one specific embodiment of this invention that about 8 to 10% of the ferrous sulfate content of the original pickle liquor was oxidized, the other 90 to 92% having been removed as a result of contact with the unpuried coke oven gas.

Desirably in the practice of this invention, the unpurified coke oven gas is contacted with the feed liquor in a plurality of chambers, such as by passing the coke oven gas through two chambers in sequence and contacting the coke oven gas passing through these chambers countercurrently with the feed liquor. If two chambers are employed, the coke oven gas flows from a iirst chamber to a second chamber, While the feed liquor flows in countercurrent direction from the second chamber to the first chamber. In the second chamber in which the feed liquor is first introduced, the ammonia in the coke oven gas reacts primarily with the free sulfuric acid to remove the ammonia substantially completely. The feed to the second chamber is desirably adjusted so that complete removal of the ammonia from the coke oven gas is effected. In the rst chamber in which the feed liquor is directed after passage through the second chamber and in which the coke oven gas is first introduced, the reactions which take place are primarily among the ammonia, hydrogen sulfide and cyanides of the coke oven gas and the iron sulfate contained in the feed liquor. Desirably the liquor after contact in the second chamber contains from 0 to 10 and preferably from 2 to 4 grams of ferrous sulfate per liter. The precipitated iron compounds in the feed liquor, after passage through the rst chamber, may be removed by any suitable means such as decantation, filtration or centrifugation. After the liquor has been separated from the solid material, from 60 to 90% of the liquor, for example about is recycled with raw pickle liquor, which is introduced into the second chamber to provide continuous operation. The remainder of the separated liquor, for example about 20%, is contacted with air or oxygen to oxidize the ferrous sulfate dissolved in this portion of the liquor. Prior to contact with the air or oxygen, sufficient ammonia is introduced into the liquor to convert substantially completely the ferrie sulfate produced in the oxidation step to ferric hydrate. A minimum of 0.5 gram per liter of ammonia has been found satisfactory for this purpose when the ferrous sulfate content of the liquor is 2-3 grams per liter. Any unused ammonia in this oxidation step is absorbed by fresh pickle liquor; and the liquor, after reacting with the unused ammonia, may be used as a component of the feed liquor introduced into the second chamber for contact with the coke oven gas. The ferrie hydrate precipitated in the oxidation step is separated from the liquor and the ammonium sulfate recovered in the usual manner from the resulting liquor. Conventional concentrators or evaporators may be used for this purpose.

.A more: comnrehensive. understanding: of lthis inventionisbtainedmy reference toithezaccom- :panying z drawing.

11nl Ythe drawing, .pickle -liquor .(whichfordinarily from 1.0 to 2.2% .of;ferrous"su1fate, butfwhichmay containmorenr less-of these components) is. col y-lected in a .Suitable .tank :I and Alis kpumped through pump 2 .from the tank `I .throughaconduits orpipes and 4 '.tofaeed tank'5. As de` scribed 'in detail later, thepickle 'liquor is unteri mixedzizn the-feed tank 5 with -;partial1y-neutral izedpick-le vliquor from an -ammonia`-necov ery .tank .38 and recyclediliquon obtained raftergcon- .tact with runpuriedv coke-:oven igas. ;Erom :the :feedtank 5 fthe v:feed liquor which' comprises :the recycledliquor, the fresh pickle liquor :and -the :p artially; neutralized :pickle liquori flows through conduits 6 and'l t0 zanrgabsorber 8. Fromtheabl sorber' 8 l the vieed liquor isopumpedzthrough..;a conduit 9 by a .pump IIJ throughfconduits ,Iflqfand I 2 to a reactor i3. The absorber and reactor-may 33e .any suitable equipment for 'effecting "intimate f contact between ithe :cokeoven ngas-and 1feed1-liqiuor. Thus,-for exampleythese elements may :be v-substantially empty shells equippedv'at ithe :top with'adistributorffor liquor -and at the baserwith Ia distributor for the j gas, .or either A-orgloothvmay :be towers packed with anyisuitable packing, eng.

. refractorytile. `From..the;reactor :t3 athe"'feed liquor is :pumped throughaconduit I .4 ,byfapump :I5 through Aconduits AIgandxll .to a` decanter I8 which operates :in a conventional .manner vato separate fsupernatant .liquor :from precipitated material. The clarifiedliquorowszthroughucom duit 45 intoltrate tank '20. .lf.desir ed,V a'ffilter IS into which liquor from conduit .46"1enters, ,-may. also be lp-rovidedgfor effecting a umore-.complete fseparation of the. liquor :from the-precipi-A Vtatedmaterial. The clear liquor :is stored in --a 'filtrate tank 120.. Erom theg'ltratetankthe .c1ear liquor is pumped @by a :pump 2 I\ .through` a .confduit 22. Aportion; for example about 8.0%, :of .the total volume of 'the liquorwpassing-fthrough 'the conduit: 22, is .recycled through thefabsorber -and reactor through `a .conduit 23, theioutletqof .the conduit 23 being directedzinto vthe'feed 'tank 5. The remaining r-portion, for 4exan'lple:about 2.0%, of lthe total volume `oif theliquor-passing through the conduit .22 is ypassed'ithroughza.cony.duit 29 `to an-oxidizer '30.

Unpuried coke ovenfgasiis passed-3 in countercurrent relationl :with thexflow of the :feed .liquor through the reactor I3 andithenbsorber. Pref- :erably, the 1unpurifled :coke oven gas is processed initially by. passage through a'Cottrella orptar-removal unit 24. The `nnpuried 4'coke oven gas news from ;the Cottrell unit 24 throughaconduit 25 'tothe reactor .I3 The outletzof-.the conduit 125 in .the :reactor I3 islocated desirablymeafr .the bottom thereof Vto ,ensure the countercurrentrelationship between theicokeoven-gas;and;the:feed liquor. The wcoke oven gas flows :upwardly through the Y.reactor :through a conduit '26 =t o ythe absorber 8. The .conduit 2 6 may be .provided with a preheater '21'.to raise the .temperature of the gas .prior to introduction into thev absorber. 4I'n'the absorber the;r esidual Aammonia in .the 1coke oven gasis reacted `with the feed liquor which `iiows countercurrently to the coke oyen ggas. rEhe coke :oven gas -with substantiallyA all AAof the ammonia removed therefrom passes through zan '.outlet 28 in thefabsorber 8. 'The feedliquor--is repeatedly recycled v.by vpumpl 0 :through the ab- -;sor-ber 8. and conduits l :and .9 and ihyiinunp I 5 fthroughzreactor lnaandsconduits L2 and :Listo maintainithe ;necessary" rates mi fziiow==uffliquor f V through '-thefreactor and absorber-to effect 4the desired intimate contact fbetween the gas-fand liquor. Liquoris fed from the; absorber;throush vconduit i;l `tothe :recycling system for the reactor and; from' the reactorthrough conduit I 'I-r-.to

ocean-ter I8 at substantially thefgratef-:at @which 'liquor :s/fed .through conduit 6 to theabsorber. As -gheretofore describedia'portion of theliquor f. from theconduit .22, for example about;20 of .with ls uiiicientair, Yeither fcontinuouslyzor s intermittently to remove substantially completely -anyferrous sulfatefr ernaining in theliquor and to convert lthe ironvalues .containedftherein f to insolubleferric hydrate. After :treatmentinthe oxidizer,Y 'the' liquor containing the vprecipitated y gferrichydrategis passed through 'aconduit 33:1to

.a;dec anter 34 or lter '-.to remove :the fer-.ricky- .dra-te therefrom. Thedecanted liquor is =then collected in V`a suitable :collecting tank 35, VAfrom V;vvhich itgmaybe removed byrmeains-ofa'pump ito `a 4lconduit 31 -connected to any @Suitable :apparatus for the *recovery yof ammonium sulfate in lcrystalline f orm.

To :remove the small amount Yof ammonia `evolved from the -oxidizer, thegair Vafter Vpassage through -the 'oxidizer is L'brought in contact throughazeonduit ;or pipe -42 vwith v pickle .liquor in an ammoniarecovery vessel 38, the-pickle liqucr-being supplied to the vessel 38 frcm thereonduit ..3 through a conduit 5.39. .After .the :pickle liquor has contactedthe :airontaining theammonja, :in the ammonia recovery .tank 38, 'it is .pumped by v'means of a .pump 4 0 .through-:acon- The precipitated. product zobtained irom...;the :lter i;9 or :the decanter 1.8 andwhich vcontains primarily iron hydrate and Liron suldermavrif zdesired, be converted .substantially completelyto iron :oxide `From ithe idecanter or Ffilter .the precipitate :maybe pumperitoa continuous vacuvzum filter in which itis washed free-ironicamvfmoriiuzn :sulfate and subsequently delivered-:t0: a

-drier or heat treating-oven '43. Inzthe ovenfthe ilter cake may be heated in 'the 'presence :of4 air. l)Thefresulting precipitate .contains liromei to 69% of zironfdepending upon the. amount of -t-iron 'hydroxide or iron oxidewpresent The presence .of Airon .suliide in thefprecipitate :materially/'gas- I `sists l.in reducing :the heat required .to .dry v01"..heat

treat the. precipitate.

vThe advantage of @utilizing .nnpuried Acoke oven:A gas, .containing as it does :hydrogen Asull-ide and resulting in thefinclusion ofiron suliidein the precipitate, Was demor1strated.by a.com- .70

-parison .of the :filtration ara-tes of thepl'ecipitate obtained V`from the neutralization ofi pickle` liquor in .the-.apparatus showninthedrawing with puri- :ned `and vunpuriiied .;cokezoven -gas coke oven-gas was substantially fr eedof cyanides and sulfides, but containedv 'ammoniaY prior :to

Theppuriied through conduit position whether neutralized with the purilied or unpuriiled Coke oven gas and contained l Agrains per liter of ferrous sulfate and 2 grams per liter of sulfuric acid. When purified gas was employed for the neutralization of the feed liquor, the rate of ltration of the precipitate contained in the liquor passing from the reactor i3 through the conduit I4 was 7.2 pounds of dry filtration cake per hour, per square foot of filter surface, whereas when unpuriiled coke oven gas was used, the filtration rate under the same conditions was sil pounds of dry cake per hour per square vfoot of filter surface. With the purified :coke oven gas, the `iilter cake was 1/8 inch in thickness, and the composition of the cake substantially all ferrous hydrate; While with the unpurified coke oven gas the thickness of the cake was 3/4 and the composition about 86% ferrous sulfide the remainder ferrous hydrate and some insoluble ammonium ferroferrocyanide. Accordingly, a substantial increase in efficiency in the removal of the precipitate was achieved by utilizing unpurified instead of purified coke oven gas. When unpuriiied coke oven gas is .used in accordance with this invention in the apparatus shown in the drawing, the composition of the Wet filter cake from a 100% ammonia remov-al or a ammonia removal from the vcoke `oven gas is a mixture primarily of iron sulfide,

iron hydrate and insoluble ammonium ferroferrocyanide. rThe iron sulcle content of the lter cake (dry basis) may vary from 35 to 95% and preferably should be between 'T5 and 95%,

#depending upon the proportions of hydrogen sulfide, ammonia and cyanides in the gas treated.

In the pre tice of the process of this invention in the apparatus illustrated in the drawing, ythe unpurined coke oven gas leaving the conventional Cottrell precipitator and reheater apparatus 2e and 2t hows upwardly through the reactor i3 and absorber 8 and then to suitable recovery apparatus through the conduit 28.

to 'temperatures conventionally employed in recovery of ammonia from coke oven gas. If desired, the gas may be heated between the reactor and absorber by preheater 2l', for example to avoid naphthalene deposits in the equipment.

Addition of hee-.t to the system may be accomplished by heatin@r the feed liquor solution before entering the absorber to a temperature such that the 'temperature of the coke oven gas leaving the absorber S is maintained at or above the temperature of the gas entering the reactor i3, instead of by adding heat to the gas by means -of reheaters 2li and 2l.

The feed liquor leaving the tank 5 through the conduit 6 is a blend of pickle liquor supplied partially neutralized pickle `liquor supplied through conduit 4I and recycled liquor supplied through conduit 23. This mixture of recycled liquor and pickle liquor, which may contain a maximum of 100 grams per liter of ferrous sulfate and 5G grams per liter of sulfuric acid, and preferably contains at least 2i) grams of ferrous sulfate and at least .2 gram of sulfuric acid per liter, passes first through Athe absorber 3 and then through the reactor YIt. rThe composition of the feed liquor is so controlled that the amount of sulfate radicals in the feed liquor is approximately equivalent vtothe. desired amount of sulfate radicalsin the Re-.. be utilized to reheat the gas the reactor I3.

f recycledliquor and the feed liquor is ordinarily so controlled that it contains sulfate radicals equivalent to more than 100, preferably more than 200, grams of ammonium sulfate per liter of recycled liquor. The flow of the feed liquor through the absorber and reactor is countercurrent to that of the coke oven gas passing apparatus. It is possible to design the equipment to incorporate the two units in one, but it has been found that better control is obtained when the reactor is separated from the absorber.

Desirably, the rate of flow of feed liquor to the absorber 8 is adjusted so that substantially complete removal of ammonia from the coke oven gas is effected. If the removal of a lesser quantity of ammonia from the coke oven gas is desired, for example a ammonia removal, the rate of now of the feed liquor and coke oven gas to the reactor i3 and absorber 8 is regulated to eiect this requirement. This regulation can be obtained by any suitable means such as valves (not shown) in the conduit 'l and 25. The free sulfuric acid content of the liquor leaving the absorber is ordinarily below .3 gram per liter of sulfuric acid although it may attain a maximum of 2 grams per liter or higher of free sulfuric acid.

After the feed liquor has passed through the absorber 8, it is Vcontacted with the coke oven gas in the reactor i3. The primary function of the reactor I3 is to precipitate the greater amount of the ferrous sulfate from the feed liquor solution alter it has left the absorber, and the contact time of the liquor with the gas is controlled so that the solution withdrawn from the reactor i3 through the conduit I4 has no soluble ammonium ferrocyanides and from 2 to l0 and preferably from .S to 4 grams of ferrous sulfate per liter. One method of controlling the contact time of the gas and liquor in the reactor I3 is by regulating, for example by means of Valves (not shown) in conduits E or I2, the amount of liquor and gas passing through the absorber 8 and reactor I3.

The principal reactions which take place in the reactor I3 are among the ammonia, hydrogen sulfide and cyanides in the gas and the ferrous sulfate in the feed liquor. The ferrous sulfate reacts with the sulfide and ammonia in the gas to produce respectively iron sulde, ferrous hydroXide and ammonium sulfate. Some of the ferrous sulfate reacts with the cyanides in the gas to produce insoluble ammonium ferroferrocyanide. In the use of the apparatus shown in the drawing, it has been found that no soluble ammonium ferrocyanide is formed in operating -under conditions such that the solution leaving y the pickle liquor, a considerable amount of soluble ammonium ferrocyanide maybe formed when acrimed the free ammonia content of." the solution leaving thefreactor I3 is in excess of 1.5 grams per liter.

The solution leaving the reactor at normal gas temperatures is pumped by means of a pump I5 to the" decant'erv i8, and the solution may be filtered through the filter l to assure substantially complete removal of the precipitated ir'on compounds. The supernatant liquor from the filtration is stored inthe filter tank 2b and is recycled and blended with raw pickle liquor in the feed tank 5 to produce a feed liquor of such concentrations that (l) the resulting feed liquor contains at least 100 grams of ammonium sulfate per liter and preferably at least 200 grams of ammonium sulfate per liter and (2) the volume and consistency'of the' precipitated iron hydrate and iron sulfide is controlled so that no blocking' or high pressure differential exists in the absorber 3 or reactor I3.

The liquid withdrawn from the tank'2 which is not recycled and' which ordinarily comprises a minor portion, for example about of the liquor, is subjected to' oxidation conditions to convert' the remaining ferrous sulfate tor insoluble iron hydrate by passage'through the oXidizer 30. The ammonia content of the solution leaving the absorber 8 or the reactor I3 desirably varies from 0.1 to'1.0 gram per liter. If'necessary, therefore, prior to passage through' the oxidizer 351', the ammonium content of the'supernatant liquid is increased to' contain at least 0.5 gram per liter' of' free-v ammonia. The' primary purpose of the oxidizer is to eliminate the remaining ferrous sulfate in the solution'v leaving the reactor I3' s'o that' ammonium sulfate substantially free from iron' can be obtained'in the crystallization step. The reaction which takes places is among' free ammonia, oxygen and ferrous sulfate at atmospheric temperatures. The ferrous sulfate is oxidiced and the' ammonia' precipitates as ferrie hydroxide. While the sulfate radical'is converted to ammonium sulfate'. Substantially' complete removal of the ferrous sulfate effected when the ammonia in the feed liquor contains or is strengthened to 0.8' gram per liter and the original solution fed to the oxidizer containsf'rom' 3 to 4 grams per liter of'ferrous sulfate'. The solution in'the oxidizer is blown' with air, after'which substantially no ferrous'sulfat'e exists in' the solution and all' of the iron' has been converted to insoluble iron hydrate. The liquor containing the precipitated iron hydrate is transferred'to a decanter 34 and the iron hydrate removed from the liquor. The clear liquor is then collected in a-tank 35 from which the ammonium sulfate may be recovered by any Well known means. lf desired,A a filter may be installed between the oxidizer 3i) and the decanter 3ft or between the` decanter 34 and collector tank 35 to remove any suspended iron hydrate carried in the supernatant liquor.

To recover the' small amount of unused` ammonia from the oxidize'rt, the air released from the oxidizer is contacted with fresh pickle liquor in the ammonia recovery tank 33, and the freeV sulfuric acid in the pickle liquor readily absorbs this ammonia. The pickle liquor, after absorption of the ammonia, passes through conduit il to the feed tank 5.

The oxidation step may be omitted, if the presence of a small amount of iron in the ammonium sulfate recovered by the method is not objectionable. In that procedure, the separated liquor passing'through' the' pipe 29vis directly processed conventional means, such-aslevaporationi- Howiever,v substantiallyI iron-freeammonium sulfate is ordinarily required, andi the metho'df-desirably 1'st Run 2nd Run* Gas rateiol' coke ov'enfgas; ou. ft. per l1'rl0, 000 10,000 NH3 content of gas; Lb. perr10,000fcu. ft 6 6f- Pickle liquor used :l

Composition- MS04, percent; i i--- 18,88 16.7 H2504, per cent....I Y 2. 64 8.5

Volume'per hour, Percent o feed 'r or reactor (Remainin 78-'80Aperceiit is re'cyf* Y l cled liquor) 20-22 23. 6 Feed to absorber:

5o. o., 4910 4, 7 25.0 52,. v 36.8 I* eed to reactor, Gal per hour 52 36.8 Feed to thickeneror decanter, -Gal.1per'hour 52' 36.8 Volume of filtrateA plus claried-liquor-romdecant'er or thickener 'plus'water Washin 'of' cake, Gal. perlhoulz 551 .3 Volume returned to system-for blend Y fresh pickle liquor, Gal.' p'er h'our 41' 2232'1y Volume tooxidizer, Gal. per hour 121.A I 11. 2V Volume to collector tank for ammonium-sulate recovcry'unit, Gal. p'er'hour 14 11,;2,` Composition, G. p. l.- (NHDSOi 220i' 300.1 Filter cake produced from ltratio Y.

enedslurry from'decanter, Pounds 4811' 33:'2' Composition of wet Washed'cake(dry b'a'si's) Fei-percent.v 89 89 f insoluble' ammonium ie oferro e,

percent; 7.' 7' hIron hydrate, percent-- 4V 4 Molsture content of lter cake, percent. 65' 35" Weight'ioicake dried at'lO5'C.-, Pounds 1327' 9.'5 Ammonia recovery, percent (approx.) 100'` It will'be obvious'fromz the" above descriptionY that various. changes may belmadelwithoutdee parting from-thescopezof thednvention.- Thus;- ior example, while fortheipurposeof' economy.

we prefer to blend recycled.4 liquor containing ammonium sulfate with the pickle-liquor'toform the feed liquor employed in the procesa. the

pickle liquor may be blendedwith ammonium. sulfate solution from other sources'to 'form the feed liquor. Further, the: liquor.' fromr the-` reactor (afterseparation ofi precipitate) may' bef continuousiy introduced both into the` feedtank"v andoxidizer; crmay be alternately fe'dtorthe` ence'ofthe coke. ovenv gas, for example,.by separately spraying the liquors into the topi ofithe` Ammonia fromany desired source;vr

absorber. e. g. theconventional ammonia still, maybe 'utilized at anyl point in the process, for example;Y

such ammonia may be-'mixed With thecokefoven: gas before'it entersthereactor or'the absorberr or maybe introduced into the'feed tankL to neutralize partially the pickle liquori before. entry.V

of thelliquor into` the absorber.

Further, itisunnecessary to passithecoke ove'nly gas through the absorber in contact with pickle:

iiquor. Thus, pickle liquor may beblend'e'd with recycled liquor to obtain` feed liquor' containing" preferably notvmore than 25 grams of r'ee sulfuric acid per liter and this feed liquor may 'be-- introduced directly into the reactor or the equivalent. In order toiobtain feed liquor of desired-' low free sulfuric acid contentfor introduction; directly into the' reactor, it may be desirable to' neutralize partially' the' picklefliquor'before' :ln--

il troduction into the reactor with extraneous ammonia or scrap iron before or after blending the pickle liquor with the recycled ammonium sulfate solution. When the feed liquor is introduced directly into the reactor, it is desirable to remove residual ammonia from the gas leaving the reactor by reaction with a mineral acid, e. g. in a saturator or scrubber,

As hereinabove described, contact between the coke oven gas and the liquor is preferably effected in countercurrent manner in suitable towers. However, the gas may be intimately contacted with the liquor in other types of apparatus, for example, the gas may be passed through saturator-type chambers containing bodies of pickle liquor diluted with recycled liquor containing ammonium sulfate While maintaining the precipitate suspended in the liquor by agitation. Recycled liquor and pickle liquor may be added to the saturatcrs as required and reacted liquor drawn 01T and filtered or decanted for oxidation and recycling to the chambers.

In carrying out the invention, it is important that the coke oven gas contain hydrogen sulfide and ammonia, but it is not essential that other constituents which are capable of being removed by conventional coke oven gas purification processes be present in the gas. Further, other inert gases containing ammonia and hydrogen sulde may be utilized in accordance with the invention. The invention may be carried out at temperatures ordinarily employed in conventional processes for recovery of ammonia from coke oven gas, for example from 35 to 70 C.

The terms and expressions which we have employed are used as terms of description and not of limitation, and we have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

What is claimed is:

l. A cyclic process for producing ammonium sulfate comprising contacting unpuried coke oven gas with a feed liquor comprising pickle liquor containing ferrous sulfate and free sulfuric acid and a recycled liquor containing ammonium sulfate, separating liquor from the resulting precipitate formed, recycling a portion of the separated liquor for blending with the pickle liquor to form said feed liquor for contact with the unpuried coke oven gas and oxidizing the remaining portion of the separated liquor.

2. A cyclic process for producing ammonium sulfate comprising contacting unpuriiied coke oven gas with a feed liquor comprising pickle liquor containing ferrous sulfate and free sulfuric acid and a recycled liquor containing ammonium sulfate, separating liquor from the resulting precipitate formed, recycling from 60 to 90% of the separated liquor for blending with pickle liquor to form said feed liquor for contact with the unpuried coke oven gas and oxidizing the remaining 40 to 10% of the separated liquor.

3. A cyclic process for producing ammonium sulfate comprising contacting unpuried coke oven gas with a feed liquor comprising pickle liquor containing ferrous sulfate and free sulfuric acid and a recycled liquor containing ammonium sulfate, regulating the Contact of the gas with the feed liquor so that the liquor, after contact, contains not more than l grams per liter of ferrous sulfate, separating liquor from the resulting precipitate formed, recycling a pori tion of the resulting clear liquor for blending with pickle liquor to form said feed liquor for contact with unpuried coke oven gas, adjusting the ammonia content of the remaining portion of said clear liquor to at least 0.5 gram of free ammonia per liter and oxidizing said remaining portion.

4. A cyclic process for producing ammonium sulfate comprising passing unpurified coke oven gas through a plurality of chambers in sequence, passing through said chambers afeed liquor comprising pickle liquor and recycled liquor containing ammoniimi sulfate, in countercurrent relation to the coke oven gas whereby the ammonia in the coke oven gas initially reacts primarily with the iron salts in the feed liquor, and the residual ammonia in the coke oven gas after the initial reaction is removed substantially corni pletely by reaction primarily with the sulfuric acid of the feed liquor, separating the liquor from the precipitated iron compounds formed, recycling a portion of the resulting clear liquor for blending with the pickle liquor to form said feed liquor and oxidizing the remaining portion of the resulting clear liquor.

5. A cyclic process for producing ammonium sulfate comprising passing unpuried coke oven gas through a rst chamber and a second chamber in sequence, passing a feed liquor comprising a blend of pickle liquor and recycled liquor containing ammonium sulfate through said second chamber and said rst chamber in sequence, in countercurrent relation to the flow of the coke oven gas for contact therewith, separating the liquor from the precipitated compounds formed in the feed liquor after passage through said chambers, recycling a sufcient portion of the separated liquor for blending with pickle liquor to form said feed liquor so that the feed liquor prior to contact with the coke oven gas contains at least grams of ammonium sulfate per liter and oxidizing the remaining portion of said separated liquor to convert the residual ferrous salts to the ferric compounds.

6. A process for removing ammonia from unpuried coke oven gas and recovering iron values from waste pickle liquor comprising intimately contacting unpurified coke oven gas with pickle liquor, separating the liquor from the precipitated product formed, contacting a portion of the resulting separated liquor with unpuried coke oven gas, oxidizing the remaining portion of said separated liquor and separating the precipitated product therefrom.

7. In the process of removing ammonia from unpuriiied coke oven gas and recovering iron values from pickle liquor, the steps comprising substantially completely removing the sulfuric acid from the pickle liquor and reducing the ferrous sulfate content thereof to between 2 and l0 grams per liter, separating the precipitated iron compounds formed, adjusting the ammonia content of the resulting clear liquor to at least 0.50 gram per liter of ammonia and passing air. through the liquor to precipitate substantially completely the residual iron salts in said liquor.

8. In the process of removing ammonia from unpuried coke oven gas and recovering iron Values from waste pickle liquor, the steps comprising substantially completely removing the sulfuric acid from a pickle liquor and reducing the ferrous sulfate content thereof to between 2 and 10 grams per liter, separating the precipitated iron compounds formed, adjusting the antimonia,-

aim-511,311?? content of theresulting-clear liquor to at least .50 gram per liter of ammonia, passing air through the liquor to precipitate substantially completely the residual iron salts in said liquor and recovering the excess ammonia-in the air after passage through said liquor by contacting with ,pickle liquor.

In `the process ofremovingv4 ammonian from coke oven gas and recovering. 'iron'7 values-from waste pickle liquor, the st'eps which comprise'co'ntacting countercurrently coke oven gas with waste pickle liquor at a rate suii'icient to remove substantially completely the sulfuric acid content thereof and reduce the iron sulfate content to 2 to grams per liter, separating the precipitated iron compounds, adjusting the ammonia content of the resulting clear liquor to greater than 0.5 gram per liter, and aerating the clear liquor.

10. A process for removing ammonia from coke oven gas and recovering iron values from pickle liquor comprising passing coke oven gas successively through a first and a second chamber, passing a feed liquor comprising a pickle liquor and a recycled liquor containing ammonium sulfate successively through said second chamber and said first chamber, contacting countercurrently in said iirst chamber and said second chamber the coke oven gas with the feed liquor passing therethrough, the rate of iiow of the coke oven gas through said rst chamber and said second chamber being regulated so that the ammonia in the coke oven gas is substantially completely removed after passage through said second chamber and the amount of ferrous sulfate in the feed liquor after passage through said first chamber contains not less than 2.0 grams per liter, separating the resulting precipitate from the feed liquor after passage through said rst chamber, recycling a portion of the resulting clear feed liquor successively through said second chamber and said iirst chamber, increasing the ammonia content of the remaining portion of said clear feed liquor to contain at least .50 gram of ammonia per liter, oxidizing said remaining portion, separating the precipitated product, contacting any unused ammonia obtained from the oxidation step with pickle liquor and adding the resulting partially neutralized pickle liquor to the feed liquor for contact with coke oven gas in said second and said first charnber.

1'1. A process for the recovery of ammonia as ammonium sulfate from gases containing ammonia and hydogen sulde, which compises intimately contacting the gas with pickle liquor containing free sulfuric acid and iron sulfate, whereby the major portion of the iron in the pickle liquor is precipitated and the ammonia in tne gas reacts with the sulfate radicals of the liquor to form ammonium sulfate, withdrawing liquor from the zone of contact, separating withdrawn liquor containing dissolved ammonium sulfate and ferrous sulfate from the precipitate, and oxidizing separated liquor with al1` in the presence of free ammonia to form additional ammonium sulfate.

12. A cyclic process for recovering ammonia from unpurifed coke oven gas containing ammonia, hydrogen sulfide and cyanogen compounds and recovery of iron values from pickle liquor containing free sulfuric acid and ferrous sulfate, which comprises blending pickle liquor containing free sulfuric acid and ferrous sulfate with recycled liquor containing ammonium sulfate to produce feed liquor containing from .2

of ammonium sulfate per literof tl'ieifee'dfliquor;` passing'. saldi unpuriiiedi cokef oven: gas through relation to'.' the cokel ovenf gas, wherebyth'ef ammonia, hydrogensuliideandflcyanogen compounds present inlthev` cokeriven igaslinitially Areactl ini the' reactor; chamber primarily with/f thei iron: salti. in thefeedz liquor: to: form.'n ammonium vsul-ratei` and.;

to precipitate'. iromhydrateg: iron? sul'de and fammonium ferroferrocyanide" and .the residual am:- monia present; iii thecoke-oven gas is removed substantially, completely by.' reaction in the absorber chamber primarily with the sulfuric acid of the feed liquor, regulating the flow of feed liquor through said chambers so that the ferrous sulfate content of the liquor leaving said reactor chamber does not exceed 10 grams per liter and the free ammonia content of the liquor leaving the reactor chamber falls within the range of .1 to 1 gram per liter, separating the precipitate from the liquor leaving the reactor chamber, recycling from 60% to 90% of the separated liquor to the absorber chamber with pickle liquor for contact with additional coke oven gas, passing an oxygen-containing gas through the remainder of said separated liquor in the presence of at least .5 gram per liter of fr'ee ammonia, whereby substantially all of the sulfate radical in said oxidized liquor is reacted to form ammonium sulfate and the iron values in the liquor are converted to iron hydrate, and separating the iron hydrate from the resultant ammonium sulfate solution.

13. A process as defined in claim 12 in which the ferrous sulfate content of the liquor leaving the reactor chamber is substantially maintained Within the range of from 2 to 4 grams per liter and the ammonium sulfate content of the liquor introduced into the absorber chamber is at least 200 grams per liter.

14. A process for recovery of ammonia as ammonium sulfate from gases containing ammonia and hydrogen sulde and recovery of iron values from pickle liquor containing ferrous sulfate, which comprises forming a feed liquor containing at least '100 grams of ammonium sulfate, not more than 25 grams of free sulfuric acid, and from 20 to 100 grams of ferrous sulfate per liter, by blending ammonium sulfate solution with pickle liquor containing ferrous sulfate, intimately contacting said feed liquor with said gas, whereby iron values of said liquor are precipitated as iron hydrate and iron sulfide, separating the precipitate from the liquor, recycling a portion of the separated liquor together with pickle liquor into intimate contact with additional gas containing ammonia and hydrogen sulfide, and oxidizing the remainder of said liquor in the presence of free ammonia.

15. A cyclic process for recovery of ammonia as ammonium sulfate from gases containing ammonia and hydrogen sulfide, which comprises intimately contacting the gas With feed liquor comprising pickle liquor containing free sulfuric acid and iron sulfate and recycled liquor containing ammonium sulfate, whereby iron in the feed liquor is precipitated and ammonia in the gas reacts with sulfate radicals of the liquor to form ammonium sulfate, separating liquor containing dissolved ammonium sulfate from the precipitate, recycling a portion of the separated l5 liquor with additional pickle liquor into contact with additional coke oven gas and oxidizing the remaining portion of the separated liquor.

16. A process for removing ammonia from unpuriiied coke oven gas and recovering iron values 5 from waste pickle liquor comprising intimately contacting unpuriiied coke oven gas with a ferrous sulfate liquor derived from pickle liquor, separating the said ferrous sulfate liquor from the precipitated product formed, contacting a lo REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,983,320 Sperr Dec. 4, 1934 1,986,900 Sperr Jan. 8, 1935 2,416,744 Francis Mar. 4,1947

Claims

10. A PROCESS FOR REMOVING AMMONIA FROM COKE OVEN GAS AND RECOVERING IRON VALUES FROM PICKLE LIQUOR COMPRISING PASSING COKE OVEN GAS SUCCESSIVELY THROUGH A FIRST AND A SECOND CHAMBER, PASSING A FEED LIQUOR COMPRISING A PICKLE LIQUOR AND A RECYCLED LIQUOR CONTAINING AMMONIUM SULFATE SUCCESSIVELY THROUGH SAID SECOND CHAMBER AND SAID FIRST CHAMBER, CONTACTING COUNTERCURRENTLY IN SAID FIRST CHAMBER AND SAID SECOND CHAMBER THE COKE OVEN GAS WITH THE FEED LIQUOR PASSING THERETHROUGH, THE RATE OF FLOW OF THE COKE OVEN GAS, THROUGH SAID FIRST CHAMBER AND SAID SECOND CHAMBER BEING REGULATED SO THAT THE AMMONIA IN THE COKE GAS IS SUBSTANTIALLY COMPLETELY REMOVED AFTER PASSAGE THROUGH SAID SECOND CHAMBER AND THE AMOUNT OF FERROUS SULFATE IN THE FEED AFTER PASSAGE THROUGH SAID FIRST CHAMBER CONTAINS NOT LESS THAN 2.0 GRAMS