CA1087830A - Process for the production of sorbent solids for use in the desulfurization of gases - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This disclosure describes a process for the prepara-tion of iron-bearing and calcium-bearing sorbent solids for use in the desulfurization of gases. The process involves mechani-cal procedures for generating porous agglomerated solids that are high in surface area and uniquely suitable in both particle size and mechanical properties for processing in gas-solids contacting equipment of conventional design. The process also involves the use of water in the agglomeration procedures in quantities controlled to react both chemically and mechanically with solid components of the feed materials and to generate ad-hesive cement between finely divided solids in porous agglomer-ated particles of the sorbent product. All components of the solid feed to the sorbent preparation process may be obtained from both finely divided new solids and solids obtained by re-cycle of regenerated solids from other sections of the combined process. The selection of either iron-bearing or calcium-bearing solids for use in the process generally depends on the type of gas that is to be desulfurized, and on both the total demand and the net cost of the new solids required by the com-bined process, Iron-bearing sorbents are significantly less costly to regenerate than calcium-bearing sorbents, and gene-rally are preferred for most industrial uses. When iron-bear-ing sorbents are utilized in the desulfurization of fuel gases at temperatures above 750°C, magnesium and/or aluminum bearing diluent materials are employed as components of the new feed to the sorbent preparation process. These diluents, when con-verted to refractory oxides in agglomerated particles of the sorbent solids by procedures of the combined process, eliminate the tendency of these solids otherwise to fuse, to agglomerate, and to defluidize in contact with the hot gases in desulfuriza-tion absorber equipment.

Description

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ACKGROUND OF THE_INVENTION
This invention relates to a method of preparing im-proved sorbents for the removal of sulfur compounds from sul-fur-bearing gases.
Air pollution with sulfur dioxide is a major problem in the United States today. Sulfur dioxide is objectionable principally because above relatively low concentrations, it .
~-' is toxic to human beings and animals and is destructive to " , .
vegetation. Sulfur dioxide and its oxidation products, sulfur trioxide and sulfuric acid, are a major source of acidity in . ... . .
` rain and fog which in turn can be corrosive.

` Industrial plants that utilize sulfur-bearing commer-... . .
cial fuels such as coal or residual oil in the production of r glass, lime, cement, ceramics, metals, and/or electric power, etc., are major sources of sulfur dioxide emissions to the ' atmosphere. Moreover, plants that utilize these raw fuels ~- as feed materials in the production of refined fuels or ~1 ~
1 chemicals such as coke, ammonia, methanol, formaldehyde, ~1 methane, and industrial gases also involve the production of , .,"~ .
reducing gases co~taining hydrogen carbon monoxide and hydro-gen sulfide.
~- Objectionable sulfur dioxide-bearing gases also are generated as waste gases in the smelting of sulfur-bearing : . :
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minerals, the refining of sulfur-containing crude oils, the synthesis of sulfuric acid, the sulfonation of hydrocarbons, the production of sulfur by the Claus process, the production ~,~ of paper by way of a wood-pulping process, and similar industrial processes.
~ ` Furthermore, ~he discharge of gas streams containing `5- `~ sulfur dioxide into the atmosphere constitutes a waste of a useful material because the sulfur content thereof is a poten~
-~ tiall~ useful industrial commodity. Currentl~, tens of millions ~- 10 of tons of sulfur oxides are released into the atmosphere over ~ ~ populated regions of the United States each year. Thus, the '~ s recover~ of some of this sulfur either as such or in another ~ form could result in ~b~e accumulation of a supply o~ useful ,i chemicals of significant value.
, Many pxocesses are`available and/ox have been proposed both for the removal of sulfur dioxide from oxygen bearing com-vl bustion gases and/or for the removal o~ hydrogen sulfide from ~`' reducing gasea. Most of these processes involve scrubbing the gases in~contact with organic or a~ueous solutions of alkaline chemicals to extract the acid sulfur compounds by ~: either physical and/or chemical reactions between components ` ~ o~ the gases and liquids. The reactive chemicals utilized in ,~ ; .
these proceSses include ammonia, organic amines, and oxidesr ,';' ,'`, carbonates and sulfites of alkali and alkaline earth metals.
Wet processes of the type discussed above, however, generate sulfur-bearing solutions and/or slurries that must be ~ i either regenerated or discarded as waste. Moreover, the com~
! ~ ~' bLned treatment~ and regeneration processes are expensive in -~:
~oth capital and operating costs, and the sulfur-bearing effluents, ~hen discarded, frequently generate alternate water pol}ut;on problems.

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2 -r~ 33~) The scrubbing of gases in contact with solutions also involves cooling the ga~es to temperatures near to or below the boiling point of the scrubbing liquor. We~ processes, therefore, have the disadvantage of both operating at low tem-peratures and of generating product gases that are saturated with water vapor. Moreover, if ~hese cold gases are released to the atmosphere they will remain near ground level, and ~re-quently will pollute the local ambient air more seriously than ~ i would the untreated but hot flue gas.
The wet processes are particularly disadvantageous when utilized in the treatment of hot gases. Moreover, when ~
utilized in the desulfurization of gases such as the hot reducing gases from the partial combustion of sulfur-bearing coal or fuel oil, etc., these processes are unusually costly in heat transfer equipment and wasteful in energy consumption.
Other processes that have been either utilized or proposed for use in the desulfurization of either combustion ~ gases containing sulfur and oxygen, and/or reducing ~ases con-; taining hydrogen sulfide, involve contacting the gases with dry solid sorbents. Processes of this t~pe may be sub-divided into general classification as follows:
(a) Processes that utilize the ph~sical properties of ~orbents such as activated alumina, activated ;~ carbon, and silica gel, and operate at low ~ , temperatures; and (b) Processes that utilize minerals and chemicals ~j such as dolomite, magne~ite, calcite, siderite, `~ magnetite, hematite, bauxite, lime, soda ash ;` and/ox ma~nesia, etc., as solid sorbents con taining components that react chemically with ,, :

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~ ~3-31) sulfur compounds in the gas, and operate at relatively high temperatures.
Processes o~ the type described in (a) abov~, which operate at low temperatures, have disadvantages similar to those of the wet processes described previously. Moreover, ; .
~- ; sorbents that utilize the physical properties of solids to ~- separate components of gases, are generally low in capacity, -~-~
low in operating life, and costly both to produce and to regen~
erate.
lQ Processes o~ the type described in (b) above, which utilize dry minerals and/or chemicals as active sor~ents for su~fur from gases, have been proposed for use, and some have ; been used commercially in the desulfurization of both combustion ,s~ gases containing oxygen and oxides of sulfur, and reducing gases ~i, ~`~ containing carbon monoxide, hydrogen, and hydrogen sulfide.
Some of these processes have involved addition of the sorbents to the combustion fuel, and discard of the reacted products with the ash or residue from the combustion furnace. Other similar processes have involved partial oxidation of the fuel 2a wi~h air or oxygen and steam, desulfurization of the reducing gas products in contact with the solid sorbents, and discard ;
of the spent sorbent as solid waste.
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t;~ .'' The minerals or chemicals utilized in the above type ~ of processes, such as limestone, lime, dolomite or soda ash, ;~
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etc., generally are employed at a ratio higher than stoichio-, metric to sulfur in the fuel, and the finely divided fraction t , o~ the reacted solids are difficult to separate from the gas.
;3 Moreo~er, the large quantities of sor~ent used in these pro~
i cesses are costly to ohtain, and the spent sorbents are costly ;( .,~ . . ~:
~ 3Q to discard as solid ~aste, and after discard are a potential s~ æaurce of ~atex pollution.
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1~8~830 When commercial fuels such as coal or residual oil ~ are utilized as raw materials in the production of ammonia, ; methanol, methane, fuel gas, or combined cycle electric power,~ ~ etc., an early step of the conversion process generally in~olves .~ partial combustion of these fuels with air or oxygen and steam, , , , ~;- to produce hot reducing gases containing hydrogen and aar~on monoxide. Moreover, when the available fuels contain sulfur, the hot reducing gases are contaminated with hydrogen sulfide and car~on~l sulfide, etc., and generally must be desulfurized for use in the synthesis or conversion processes.
;`` Conventional processes for the desulfurization of hot reducin~ gases of the above ~ype, generall~ involve cooling the hot gas, desulfurizing the cooled ~as in contact with aqueous solutions of alkaline chemicals, and reheating ~he desulfurized ` gas for use in the conversion processes. Processes of this , :
~; type generally utilize heat exchange equipment of alloy construc-s~ tion, and generall~ are costly in capital investment and waste~
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ul in energy consumption.
~; Alternative processes for the desulfurization of 2a reduoing gases in contact with minerals or chemicals at high :~ temperatures have been proposed, and some of these processes have been test operated in pilot plant equipment. Most o~
these procesSes involve the use of limestone or dolomite as a sorbent f~r sulfur, and involve chemical reactïons between ~, calcium in the minerals and sulfur in the gas to produce calcium sulfide and/or calcium sulfate in the reacted solids.
! Processes of the above type, ho~ever, utilize calcium ~;
~; at a hi~h ratio to- sulfur on a stoichiometric basis, consume large ~uantities of sorbents, and generate large quantities of solid waste. Moreover, both the calcium sul~ide and sulfate .. .:
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compon~nts of the spent sorbent are both highly 3table and unusually costly to regenerate for reuse as 30rbents in the process.
In view of the increasing demand for energy~ the decreasing supply of low sulfur fuels, and the large known `~
` reserves of ~ul~ur-bearing coal, thera is an increasing demand for a low cost process for the desulfurization of sulfur-bearing gases.
SUMMARY OF THE DISCLOSURE
This disclosure describes a process ~or the prepara-tion of dry solids that are both suitable for contacting with gases in gas-solids contacting e~uipment, and have unusual properties for use in the desulfurization of sulfur-~earing ~ :
:;i gases. The preferred solid sorbent products are the iron- ~
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~ bearin~ and the calcium-bearing solids, and both of these are ~
., capable of desulfurizing either oxygen-bearing combustion gases, or h~drogen-bearing reducing gases. Moxeover, both also are ~'l effective ~ith either type of gases ~hen conta~ted at various .;~
temperatures bet~een 150 and 1800C, The iron-~earin~ pre-~ ;
2~ pared sorhentsj ~hen utilized in the desulfurization of oxygen-bearLng g~ses at temperature of contact helo~ a~out 55~C.~
;' prefexably are ~repared from iron-bearing solids containing ~`
:, either ferrous sul~ate or iron oxides generated from iron sulfates `~
at tem~eratures belo~ about 75aC., and these salids generally ... .. .
contain both iron oxides and iron sulates.
This disclosure describes procedures for utilization `
of ~he Lmpro~ed sorbent solids in the desulfurization of either ~; o ~he i~bove t~pes of gases. It also descrihes procedures ~: ` !
. ~f for regeneratin~ the spent sorbents rom the desulfurization ~i 30 of either t~pe o~ ~ases in contact ~ith the iron-bearing `'i .
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~ ~ ! 6 ~ ~01~ 33al sorbents. The calcium-bearin~ sorbents are either dîscarded as solid waste, or are regenerated by processes other than those described in this disclosure.
This disclosure also describes procedures ~or ge~-erating refractory solids for use as diluent materials in the iron-bearing sorbents, and procedures ~or utilizing these sorbents in the de~ulfurization of reducing gases at tempera-; ~-~ tures ahove 750C.
,, :
All desulfurization processes that are utilized for the purpose of air pollution control are essentially negative ;~ in economic impact, and most conventional processes are un~
usually costly in operating economy. The features of the process of this invention that signi~icantly improve economy and efficiency of operation and simultaneously distinguish it ~rom all known alternative processes, are summarized as follows:
(1) The combination of mechanical and chemical pro-cedures utilized in accordance with the invention in preparation ., ~
of the sorbent solids and their use in the desulfurization of gases, are unusually high in performance and low in both capital and operating costs, in comparison with the procedures of all known conventional alternative processes.
(2j The procedures of the new process enable the repeated recycle, regeneration, and reuse of sorbent solids and, in comparison with all known alternative processes, the demands ~or new solid ~eed to khe sorbent preparation process, and thus the cost of raw materials in the desulfurization of -gases are unusually low.

(3) The novel procedures for the preparation and ~; use o~ solid sorbents in the process of this invention, enable 3Q the utilization o~ either iron or calcium compounds as ~oth ,-~
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~ : the major and the chemically effectîve components o~ the ; ~ prepared sorbents. Moreover, both of these compounds normally are commercially available as major components o~ industrial minerals, chemicals, and/or waste materials at aosts that are attractively low. ~
.: (4) The sor~ent preparation procedures of this ~.. ' ,~ invention provide dry sorbent solids that are highly effective in the desulfurization of either oxy~en-bearing combustion '~
,~ ~
'. gases, or hydrogen-bearing fuel gases. These solids are ~ ' ,~ 10 non-corrosive to process equipment ~nder most operatin~ con~
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,,,. dition~ and, when utilized for the desulurization of combustio~
., ,l gases at po~er generating facilities, can ~e processed in ~-'.' equipment fabxicated ~rom low cost structural materials. In ,' comparison with the "wet scrubber" desulfurization processes utilized in conventional power plants, the desulfurization ., " ! processes utiliæin~ the material of this invention have capital ' ,~::^ and maintenance costs that are unusuall~ low. , -::3 ;-~
': (5~ The sorbent preparation and re~enerati~n pro- ', ,!,',1 cedures. of this invention, when utilized in power generating ;
~",,~, 20plants as described in (.4) above, have impoxtant economic ,.~
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advantages deriYin~ from lo~ demands ~or operating supplies .
and from minimum requirements or the disposal of wastes. In .~
,~ addition,,there axe advantages to ~e dexived ~rom the production ,'.' ,:~ o marketable gulfur and ~rom increased output o~ marketable ,~.',~ powex ~rom the primary ~uel supply. ~et power generatin~ costs can thua be si~ni~icantly xeduced, in comparison to the con- ' ventional. I!
(6) The processes of this invention, w.hen utilized ' ~ in conjunction ~ith power ~eneratin~ facilities as described 1--3Q in items (.4~ and ~5~ ab,ove,,further enable the utilization ~: i '::`'.';`' :
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of lower quality, higher sulfur fuels (of which there are large known reserves) at significant ~avings in the cost of the fuel.
; (7) The process o~ this invention, when utilized in conjunction with the desulfurization of reducing gases at , low gas-solids contacting temperatures (below a~out 350C.), and compared with certain commercially available alternative ~ processes, is at least marginally attractive in economic 'i ~ impact. However, when utilized in coniunction with the desul-furization of reducing gases at temperatures between 350 and 750 C., the procedures of the invention become increas-. -, ~ ` ingly attracti~e in operating economy with increasing tempera- ~
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tures of the available gases.
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5 .~ ~8) When iron-bearing sorbents are prepared in ~, :.1 .
the ahove process, and are intended to be contacted with reducing gases at temperatures above about 750 C., magnesium ~;~ and/or aluminum bearing diluent materials are utilized as 5 ~ ~` i part of the new ~ee material. ~hese components, after conver-sion to their inert oxides by procedures of the process, 2Q eliminate certa~n mechanical problems in the gas-solids - c~ntacting e~ui~me~t, and permit the sorbents to be utilized s Ln the regenerati~e desulfurization of these gases. In comparison ~th all known alternative processes for the de- `
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~i~ sulfurization of reducing gases obtained ~rom the partial .
combustion o~ ~uels at temperatures above 75Q C., this process is esaentially uni~ue in currently available technology.
When such sorbent~ are utilized in combined c~cle power ~; 1 generation ~rom coal, and in other industrial applications that utilize gasi~ication processes in the treatment of sulfur-;1 30 ~earing fuels, it provides for increased recovery o~ energy ~,.'." :

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. rom the ~uel, and signiicant saving in the production cost of clean fuel gases.
(9) When the sorbent materials ~f the invention are utilized in the regenerative desulfurization of either ;~
~ oxygen-bearing combustion yases or hydrogen-~eari~g fuel gases, '~ both magnetite-bearing solids, and hot gases high in concen- `~
tration of sulfur dioxide and favorable for use as ee in the Y '` ~, production of either acid and/or sulfur, are o~tained as ~I products of the process.
.l, ~ . .
o 10 BRIEF DESCRIPTION OF THE_DRAWINGS
~` Figure 1 is a flow diagram showing one operation for ``
providing agglomerated sorbent materials according to the in~
vention.
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`~!.'"., Figure 2 is a flow diagram illustratiny the prepara-tion and regenerative utilization o~ agglomerated sorbent materials in conjunction with the desulfurization of an oxidizing ~,!
~'"J, gas.
, Figure 3 is a flow diayram illustrating the prepa-~;, ration and Xegenerative utilization of agglomerated sorbent ~-materials and ln conjunction with the desulfurization of a reducing gas and an oxidizing yas.-DESCRIPTION OF THE PRE'iFERRED EMBODIM_~TS
This invention provides a process for preparing dry, soxbent solids thak are suitable in both particle size and ', ph~sical and mechanical properties æor contacting with gases ' in gas-solids contacting e~uipment. These solids also have ~-~
unusual proeerties for use as sorbents for sulfur compounds rom dilute sul~ur-bearing gases. The sorbent products are uni~uely suitable for use in the desulfuriz~tion of eithex oxygen-bearing co~ustion gases or hydrogen-bearing reducing ~ ~ A

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gases. Moreover, both are eEfective at various ranges of gas-solids contacting temperatures between the practical limits of 150 and 1800C.
The general process for preparing dry sorbent solids according to the invention involves the following steps:
;- ~a) Finely divided solids, containing suitable sorbent materials, are mixed with water, ~-; sulfuric acid, or aqueous mîxtures containing ~`- sul~uric acid. The mixed liquids and solids . ar~ b~ended at temperatures below 100C.
and at ratios suficient to generate moist -~ agglomerated solids which contain water ; .......................................................................... :
~-~ soluble or reversibly hydratable compounds .. of such solids. The agglomerated solids are ~:. essentially free of particles smaller than ' 'î:
. ten microns in size.
; ~b) The moist agglomerated solids are sized, to ~: separate particles larger than one-~uarter ~
inch in diameter; the smaller particles are ~:
2Q collected as a product o~ the sizing procedure.
.~ (c) The moist product so-ids coll~cted in the .. - ~ . I
sizing procedure are contacted in a reactor with gases at temperatures between 80 and `-~.
3aooc. to evaporate water from the interior o~ particles, and thus to generate p~rous agglomerated dry solids. These solids are high in both mechanical strength and in aggre-gate surface area.
~! (d~ The drx solids are then clas~ified to remove 3Q ~axticles smaller than 2~Q microns in diameter.
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~e) qZhe classiied solias are collec~ed as the ~ ~ primar~ product of the sorbent preparation 3 ~ process.
In a preferred emhodi~e~t of the invention, the classification o~ particles in step (d) is carried out in and simultaneously with contacting step (c) by operating the reactor at a gas flow rate that elutriates from the bed of t , ,~ j the reactor, the available particles smaller than 200 microns in diameter.
; 10 In other embodiments, the prccess may involve the ~- addition of one or all of the following procedural steps:
) The o~ersize solids from the sizing step may ` be crushed and recycled as part of the feed ,, i . ;:, .
~i to the sizing step. ;~
(g) The solids elutriated rom the bed of the ~;l reactor may be separated ~rom the gas in gas ~ cleaning equipment, and the clean gas discharged ; ~ to the atmosphere as an efluent of acceptable ~ualit~.
'' 2Q (h) The solids collected at the gas cleaner may ,......................................................................... .. ~
;~, be rec~cled for use as part of the recycled feed to the mixing and agglomeration procedures.
Sorhent solids prepared in accordance with the process of this invention include those solids whioh are i, ~ ;.
suitable for absorption of sulfur from gases containing the same. In general, ~he sorbents are reactive with sulfur and ahsorh sul~ur by forming a new chemical compound as will be descrikZed more fully below.
Examples o~ solid sorbe~ts ~hich can ~Ze prepared in accordance with the process o~ the invention include the oxides , .~
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and hydroxides or iron, calcium, sodium, ma~nei~ium, manganese, copper, etc. Iron is ~ particularly preferred sorbent solid ; prepared by the process vf the invention and it is utilized as iron oxide, ferrous sulfate or mixtures thereof. Although . .
the foregoing are known sorbents for sulfur, the sorbent pre-paration process of this invention significan~ly improves ~he capacity and useulness of the sorbents for the desulfurization ` ` of gases in commercial scale operations.
When iron-bearing sorbents are the desired product from . 1 ~; 10 the sorbent preparation process, finely divided iron-bearing minerals or industrial materials such as limonite, hematite, ~- ~
`- magnetite, ~iderite, pyrrhotite, iron oxides, sulfates or sulfides may be utilized as the feed materials to the mixing , step, and the aqueous mixture generally will contain iron sulfate or iron carbonate. Iron sulfates in the feed materials are utilized as the active components of the cement in the agglomeration procedure of the sorbent preparation process.
When the iron bearing sorbent products from the prepa-- ration process are utilized in the desulfurization of oxygen-bearing c~mbustion gases containing, for example, S02 or S03, the prepared sorbents must contain either ferrous sulfate or ,:~ ....................................................................... . .
active iron oxides such as those generated from iron sulfates at temperatures below 750C., and preferably below 650C. ~ctive :
iron oxides of the desired type can be generated from iron sulfate-bearing solids by regeneration procedures described ~i in U.S. Patent No. 4,008,169 issued February 15, 1977 to ''l Patrick John McGauley~ ~Moreover, the dry solid feed to the sorbent preparation process normally will contain this type of iron oxide as a major component. ~-~
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~he iron oxide-containing sorbent products, pre-~ pared according to the invention, are used in the desulfuriza-;~ tion of oxygen-bearing gas at contacting temperature below 550C. and preferably below 450C. This desulfurization process normally generates a product gas of reduced sulfur , ~
content which is accep~able for discharge to the atmosphere, from oxygen-bearing feed gases generated by the combustion of sulfur-bearing ~uels. The resulting product solids genera~ly are high in content of ferric sulfate, and this product may ,~ 10 be formed by chemical reactions such as the following:
~, 1. 2FeS04 + S02 + 2 = Fe2(S4)3 ~, 2. 2Fe304 + 9S02 + 52 2 4 3 , 3. 2Fe203 ~ 32 + 5S2 ~ 2Fe2(S04)3 ..~
-' 4. 2Fe304 + 402 + 7S2 + 2S03 = 3Fe2(S04)3 5. 2FeS04 H20 + 2 + S2 = Fe2(S4)3 2 ~^, The iron-bearing product solids from the sorbent '~ I preparation process also may be used to reduce the sulfur ~;, content of reducing gases. The sulfur in these gases may be ' present in the following forms: H2S, C05, R5H, R2S, or RSSR -,~ 20 wherein R is an organic radical~ ;
hen the iron-bearing product solids ~rom the sorbent preparation process are used in the desulfurization of such ~' xeducing gases at contacting temperatures belo~ about 750C,, , the sorbents are prepared as described above. The desulfuriza-tion of reducing gases by this process generates product gases that are acceptable for ind~strial use as a desulfurized fuel.
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The resultin~ product solids generall~ are high in content '1 of iron sulfides which may be formed b~ chemical reactions . `
i such as the follo~in~:
~'', 30 6. Fe2Q3 ~ 2H2S + H2 =,2FeS ~ 3H20 , .. ~,;
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~ 14-)8';'1~30 7. Fe3O4 + 3H2S -~ H2 ~ 3FeS ~ 4~2 v~ ~ 8. Fe2Q3 ~ 2E~2S ~ CO -- 2~ei~ ~ 2H20 + C2 ;
9. Fe3O4 + 3COS ~ CO = 3FeS ~ 4CO2 10. Fe3~ ~ 4H2 = 3Fe 11. Fe + H2S - FeS ~ EI2 .,~ .

4' ~ 12. FeS + H2S = FeS2 ~ H2 The particles of iron sulfide-bearing spent sorbent are relatively low in melting temperature, and when processed ~ -~
in desulfurization equipment at gas-solids contracting tem-peratures above about 750C., these solids have a tendency -~
to become adhesive and to obstruct the mechanical performance of the e~uipment. We have found that finely divided magnesium ` and~or aluminum~compounds, and/or certain types o~ fly ash, when utilized as diluent components o~ the new iron-bearing feed to the sorbent preparation process, have permitted mechanical operation o the gas-solids contacting equipment at temperatures up to at least 1200C.
~e have found that finely divided minerals and/or chemicals such as magnesite, high magnesia dolomitej magnesium carbonate, oxide,~and~or hydroxide etc., and bauxite, aluminum ~'':'! oxide, and/or hydroxide etc., and hi~h magnesia and~or alumina-bearing fly ash etc., are e~ective diluent components ; of the new iron-~earing feed to the soxhent preparation pxocess. M~reover, we have ound that the magnesium and aluminum components o the above diluent materiails in the ~eed,~are conYerted to the chemically ~ert oxides of mag-~
nesium and aluminum by procedures o~ the process, and that ~; th~se oxides do not participate si~nificantly in the chemical reactions o~ the desul~urization and regeneration procedures.
The r~genexation pxocess ~hich m~ be utîlized in ~;
this invention to prepare active iron oxides for use in the ; ............................... : ,. ~' 15- `

108~7~

~orbent preparation process, involves the production of Fe304-bearing solids from iron ~ulfate-bearing feed materials under controlled condition~ of temperature and gas composi-tion. This process, which is described more fully in U.S.
Patent No. 4,000,169 involves contacting the iron ~ulfate-bearing spent sorbents from the desulfurlzation of oxygen-bearing gases, with both reducing agents and air in gas-,, , solids contacting aquipment. The reducing agents may be `~ either solid, liquid, or gaseous carbonaceou~ fuels of commar-~.
cial quality, and preferably are hydrogen-bearing reducing gases generated fram one or more of the commercial fuels. The reducing agents may include iron sulfide-bearing minerals ;s and/or iron sulfide-bearing solids. Thus, an active iron '~! oxide sorbent may be regenerated from a mixture of iron sulfate and iron sulfide.
The regeneration of iron oxide also involves supplying ~ each component of the total combined solid, liquid, and gaseous ;~ feed to the reaction zone of the regenerator at ratios that provide both oxygen and reducing agents (or fuel) both in quan-' 20 tities and at stoichiometric ratios in the reaction zone, that .~., .. :
satisfy the following conditions~

~;, (a) Provide exothermic heat ~ufficient in quantity to , ., ~,t maintain the temperature of the reaction zone bet- ~
~.,.

~;~ ween the limits of 400 and 750C,, and preferably between about 550 and 650C., ~ 1 ~`~ (b) Generate product gases containing both sulfur dioxide and reducing agents at ratios that ~;~ approach the equilibrium composition of gases in contact with Fe304 at the operating temperature of the reaction zone, and ' `1 ~^,; ' vl -16-:~0~3~783~
.
(c) Generate reactive Fe304 as a major component of the iron oxiae-~earing product from the - reaction zone of the process.
The product gas from the reaction 20ne of the regenerator is high in content of sulfur dioxide and essentially -~
free of oxygen. The product solids are high in content of ~ Fe304 which may be generated by chemical reactions such as y ;~ the followLng:
. ~
13. 3FeS04 ~ 2H2 ~ Fe34 + 2H2 ~ 3S0 ~ 10 14. 3FeS04 ~ 2C0 a Fe304 ~ 2C02 + 3S2 - 3Fe2(So4)3 ~ loH2 = 2Fe304 ~ lOH2o + gS0 16. 3Fe2(S04)3 ~ lOC0 = 2Fe304 ~ lOC02 ~ 9S2 ~ 17. Fe2(S4)3 + ~eS = Fe304 + 4S02 v,i 18. 2FeS0~ + Fe~ ~ 2 ~ Heat = Fe304 ~ 3S0 ,- i .
~ 19. 3FeS ~ 502 = Fe304 -~ 3S02 -~ Heat ; The regeneration of Fe304 from the iron sulfide-bearing spent soxbents from the desulfurization of reducing gases in contact with iron-bearing prepared sorbents is accomplished .,i b~ oxidation of the spent sorbent. Moreover, when both iron sulfate and iron sulfide-bearing spent sorbents ~re available, ~ ;~
` these sorbents are mixed, and the iron sulfide is utilized as both fuel and reducing a~ent, as indicated by the chemical ~I reactions of equations 17-19 above.
f~ hen the available supply of iron sulfate-bearing spent sorbent is insufficient in quantit~ to cool the reaction zone hy the endothermic reactions for generating iron oxides from iron sulfates, t~e excess heat is removed by the genera-tion o~ steam in hea~ exchange equipment. Moreover, when the regenerated Fe3Q4 bearing product from this process is to i`! 30 be used as sorbent in the desulfurizat~on o~ reducing gases at :.; ,...
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.' ' . ' .. . . .. . . ...

temperatures above 750c., the temperature o the reaction ~; zone ma~ exceed the maximum al}owahle temperature for the regeneration of iron sulfate-bearing spent sorbents, as i.
described previously.
The above process for the regeneration of iron-bearing spent sorbents from the desulfurization of gases, when combined with the prLmary sorbent preparation process o~
the invention, provides a uniquely advantageous combined process. As will be apparent ~rom the previous description and discussion, this regeneratiYe combined pxoc~s~ is highly flexible and generally is suitable for use in conjunction with-the desulfurization o~ either oxygen-bearing ef~luent gases from the c~mbustion of sulfur-bearing fuels, or sulfur-bearing reducing gases generated from these fuels.
When significant quantities of iron sulfates are available from industrial wastes, the combined process of the invention is capable, in conjunction with its use in the desulfurization of gases, of also geneXatiny ~oth iron and sulfur products of saleable commercial qualit~, from the iron and sulfur content of the iron sulfates. This application of the process involves use of the available iron sul~ate as new feed to the sorbent preparation process, and recovery of this coml~onent of the feed as part of the prepared sorbent product rom this process. When this prepared pxoduct is contacted ~ith gases containing bo~h oxygen and oxides of sulfur, ~errous ulfate from the ne~ ~eed is capable of extracting oxides ,: ',Z
~- of suifur from the dilute gas, as indicated b~ equations 1 p and 5, producing ~erric sulfate. ~;
hen the ferric sulfate-bearing product~ from the 3a de~ul~urization process are used as feed to the regenerator, ~ :

~ , ~ 18-7133() the iron content of the iron sulfate i~ Xecoverea as part of the active Fe304-~earing .iron oxide product from this pro-cess. Tllis product ge~nerall~ ~ntains sulfur in excess o~
the allo~able sulfur content of iron oxide products of commercial ~ualit~. When significank ~uantities of iron sulfates are used in the new ~eed to the combined process, product from the regen~rator containing iron equivalent to the iron conte~t of the iron sulfate feedr is removed for ` furth~r desul~urization.
la The above fraction of ~he Fe304-bearing product from ~he regenerator is contacted with air in gas-solids contacti~g i~` "stripper'l equipment. A fraction of the Fe304 in the feed ...
to this "sulfur stripper" is converted to Fe203 in the product.
Heat from the oxidation reactions increases the temperature of the reaction zone to a level ~enerally above 750C., and high enou~h to remove the remainin~ undesirable sulfur, b~
, .
chemical reactions such as the following:
~ 20. 4Fe304 -~ 2 = 6Fe23 ~ Heat ;~ 2 2 3 2 ~ ;
22. 2Fe2(So4)3 + Heat = Fe23 + 3S03 ,: . j . .
` 1~ 23- 2Fe304 ~ S03 = 3Fe203 ~ S02 ~ Heat When calcium-bearing soxbents are desired ~or use ~s in the desulfurization processl ~inely divided raw materials i such as limestone or dolomite, and/or calcined limestone or dolomite are utilized as the new solid feed to the sorbent `~?
preparation process, and the aqueous mixtures ma~ contain cal-cium compQ~nds. Ei~her gypsum and/or calcium h~droxide in . ~ , the feed materials is utilized as the active components of the cement in the ag~lomeration procedure of the sorbent preparation proce~
. .:.i. ~
. ',t''' ' '., ' '7~3~
..
The calcium-bearing product solids ~rom the sorbent preparation process are suitable for use in the desulfurization ~,' of either oxidizing or reducing gases. Although these sorbents are effective at temperatures between theoretical limits of about 2aoo and 18~0C., they generally are used at contacting ~ ' temperatuxes bet~een 300 and lQ00C. The operating procedures ', ~ of the sorbent preparation process enable the production of . :
'~ sox~ent products suitable for use in an~ desired type of gas- ;~
solids contacting equipment. The equipment selected ~or use ~' '' 10 in the desulfurization process generally will he determined .. .
,~ by properties of the available gas.
',,; When calcium-bearing sorbents are utilized in the ~: ','t desulfurization of o~ygen-bearing gases J the spent sor~ents ' ~'~
are high in content of calcium sulfate and/ox calcium sulfite.
. ~ .
',~, `, These components may be formed by chemical reactions such as the following: ;
~, 24- CaC03 + S02 = CaS03 + CA2 ", 25. 2CaC03 ~ 2S2 + 2 =,2CaS04 + 2C02 ' .:~
~ 26. CaO ~ S02 = CaS03 -~, 2a 27. CaO + S03 = Ca504 '~ ( )2 3 4 2 ,, 2~. Ca(OH)2 ~ S02 =,CaS03 ~ ~2 ,;~ 3~. 2Ca(,OH)2 + S2 ~ 2 = 2CaS04 ~ 2~120 hen the calcium-bearing sorbents are utilized in ~,l the desulfurization of reducing gases/ the spent sorbents ' ,,l are high in content of calcium sulfide. This component may ~ he ~ormed h~ chemical reactions such as the following:
$~ 31- CaC03 + H2S =,CaS + C02 + H20 32- CaO + ~I2S = CaS + H20 3Q 33. CaO ~ COS = CaS + C02 ;

,. ..
~:"''' ~
,. .~.
," ~
~: i -20-l~B~830 34~ CaC03 ~ C05 = CaS ~ 2Co~
35~ Ca(OH)2 + H2S = CaS ~ 2H2V ~
The finely divided solids ~enerated in the gas ~`-contacting e~uipment used in either of the above desulfuriza-tion proceases are separated from the product gases. A major fr~ction of these solids generally are rec~cled for use as part of the recycled feed to the mixing and a~lomeration procedures of the sorbent preparation proce~s.
When the spent sorbent products from the abo~e ~ , desulfurization processes are regenerated b~ any available ~;~
~ process that utilizes gas-solids contacting equipment, the ;~ finely divided solids elutriated from this e~uipment generally ~f are recovered from the product gas. A major fraction of -~ these elutriated solids generally i5 recycled for use as feed . ., ~ to the mixing and agglomeration procedures of the sorbent i .; .
preparation process. Moreover, an additional ~raction of the sorhent solids from the regeneration process generally ~ !
. .
are pulverized and recycled for use as part o~ the feed to ~;
~ I the agglomeration procedures of the sorbent process. These ;~ r; 20 solids generall~ contain densified particles that have become s7 : inert to ch~mical reactions with ~ases, presumahly because the lo~ surface area of the solids does not provide sufficient ~, surface fox contact wi~h the ~ases~
i The den~i~ied and inert solids diacus~ed a~ove ~re~uently are ~ound as components of sorbents that have been 7 ' subjected to repeated changes in temperature when contacted ~,~ ~ith di~fexent ~ases in re~enerati~e processes- inYolving chemical reaction~ bet~een ~ases and solids. ~hen the above type o~ densified inert solids are pulverized and utilized : j .
~1 30 as part of the feed to the sorbent preparation ~rocess of this ~
": ~:

~ ,. .
~' "' ' ~. ~ .
: . ~ , ~ 21-3~ :
invention, ~le original sorbent propertie~ of the inert components are regenerated. Moreover, the combinad products ; from the preparation process are not significantly different in sorbent properties khan products generated ~rom feed materials thak are essentially ~ree o~ densi~ied and inert components.
The sorhent prepara*ion process of ~his invention, as applied to the production of iron-bearing sorbents suitable for use in the desulfurization of combustion ~ases, is illus-; 10 trated on the ~1QW diagram o~ Figure 1, and is described in detail with re~erence to this figure, as follows:
,~ ., The available dry feed materials utilized in the preparation of the sor~ents generally include both new and .
~ rec~cled iron oxide and/or sulfate-bearin~ solids. These , ~ "
solids may ~e combined with reactive Fe304 (magnetite~ bearing ~i solids o~tained from the decomposition of iron sulfates and~or iron sulfide from the absorption processes previously described, ~.
and are fed either to the Pulverizer as indicated by line ....
~ 01 ~ or when su~iciently finely divided, are fed directly ``
. ".
to the A~glomerator as indicated ~ line 103.
The ~inely divided products ~r~m ~oth the Pulverizer - and the Gas Cleaner also are fed to the ~glomerator as `i^"'i indicated by lines 102 and 104, respectively.
~ ater, sul~uric acid, and~or a~ueous mixtures of ~3 solutions containing iron and sul~ur compounds are fed to . ~ . .
; the Agglo~erator as indicated by line ln5, and mixed and ~ . .
~ lended with th~ dry solids in the A~glomerator at ratios ...
that generate "green" pellets or a~lomerates ox porous moist solids that are essentially free of particles smaller .:. , ~ ~ 3a than ten micr~ns in diameter~ ~
~: ,i .

'. :, 1ClB'7830 , ~ ~ ~he "green" pellets or agglomerates are fed rom : - the A~glomerator to a Sizer as indicated ~y line 106. Par- .
.' ticles l~rger than one-quarter inch (and pre~erably larger ~;
thii~n one-ei~ht inch) in diameter are considered oversize ., :
' and are separated from the product and fed to the Crusher ," as indicated by line 109. In the Crusher, the large particles are reducea in size iim~ recycled to the Sizer as Lnaicated ..
~,' by line llQ. The smaller product rom ~he Sizer is fed to the Drier-Classifier as indicated by line 111.
lQ In alternative embodimen~s, the wet solids produced ~:~ in the ~gglomerator ma~ he fed directly to the Crusher,'as ' indicated by broken line 107. Alternatively, the moist green .,, .,., ., ~,.
solids from the A~lomerator may be fed di~ectly to the Drier~
. Classifier, as indicated hy lines lQ8 and 111.
In the Driar-Classifier, the green a~glomerates ~ .' are charged to a moving bed reactor such as a flui.d bed reactor 37~ `, and contacted ~ith a stream of sulfur-free gas fed as indi~
,' .'l cated by line 112. Water is evaporated, surface area is created by expulsion of the water from the interior of the , ~ 2Q particles, the partially water soluble cement (iron sulfate) het~een finel~ di.Yiaed ~iolids in the agglomerated pi~rticle ':. is "cured", and the moist soft eed is converted t~ hardened '.
l;:; a~gl~merated particles of dry porous solids th.at are high.
,, "
in b.oth surface area and mechanical strength, and ~h.en con~
tacted ~ith sulfur-bearing gases, are suitahle as sorbents , :¢;i, for sulfur compounds. ~.-.
The hot sulfur-free gas utilized in the Drier-.' Classifier is controlled in temperature to remove the desired uantit~ ~f ~ater from the solids, and in ~low rate to remove ~' 1. 30 unders~zed ~rticles of solids from the pr~duct b~ elutri.ation :~

, :i ~,-..'i,

5.
~ 23- :~

~ 71~;30 from the fluid ~ed.
The dr~ solids that remain in the ~ed of the ~luid bed Drier-Classifier are withdrawn as the prepared sorbent ;
product of the process, as indicated by line 113, and are available for use in the gas treatment processes descri~ed above. The gas-solids mixture from the Drier-Classifier is fed to the Gas Cleaner as indicated by line 114 where the elutriated solids are separated from the gas, a~d the clean ~. gas is discharged to the atmosphere as indicated by line 115.
`i 10 The solids removed from the gas in the Gas Cleaner are recycled to the Agglomerator as indicated by line 104.
- When the sorbent preparation process described above , ~ is to be utilized for the desulfurization of oxygen and sul-`~ fur-bearing combustion gases, recycled iron ~ulfate product, -~
and iron oxides obtained from the low temperature decomposition of iron sulfates, are employed as major components o the feed. Moreovex, the recycled feed materials generally will ;:, ` contain, as a major component, activated magnetite (Fe3O4) j, ~earing solids. Water soluble components such as iron sulfates ;~ 20 generally will be used as cement between particles of finely ~, divided solids in the a~glomeration procedure, and the re-c~cled feed ~aterials ~enerally will contain iron sulfa~es.
The utility o the iron-bearing sorbent solids o~
.; 1 , this invention for desulfurizing oxygen-bearing combustion i I gases and for generating both e~luent gases accepta~le for discharge to the atmosphere, and both iron and sulfur products ~!
o~ commexcial ~uality from objectlona~l~ industrial effluents, is illustr~ted in Figure 2, and is de~cribed in detail with reference to this ~i~ure, as follows:
~, 30 A~aila~le new iron sulfate, iron o~ide and~or iron-~ .^1, ,, ~earing solids rec~cled from the gas treatment process includins .:.. . .
.~ , ~ . ~.. . . . . . . ..

~' :
the iron oxi.de-bearing solids ob~ained from the decomposi-tion regenerator and/or th.e iron oxide Puri~ier illustrated in Figure 2, are fed to the Sorbent Preparation systemr as ..
indicated by line 201. Additional undersized solids reclaimed from Gas Cleaners A, B, and C also are fed to the sor~ent preparation process, as indicated by line 2Q2. The Sorbent .: Preparation system of Figure 2 comprises procedures such as .` illustrated in Figure 1. AS an alternatlve in Figure 2, the prepared sorbent fed to the Absorber, as indicated by line lQ 2Q3 in Figure 2, may be replaced by line 113 representing the . prepared sor~ent removed from the Drier-Classifier in Fi~ure `~
1 . 1 thereb~ incorporating the flow sheet of Figure 1 into ~ Figure 2. In addition to the prepared sorhent fed to the ~
;~- Absorber as Lndicated by line 203, recycled solids containing : :
` . highly active magnetite (Fe3O4) from the Decomposition Regen-;.~
` ` erator are fed to a gas-solids contacting reactor system within the Absorber as indicated by line 2~4.
.~ .; .
Both new and recycled dilute sulfur dioxide (.less .:
than 2~ 52~ and oxygen-bearing combustion gases also are ~~ 20 fed to the Absorber, as indicated by lines 205 and 2a6, .;
.. ~ res~pectivel~ The gas is reacted ~ith the solids at tempera- ~.
. tures bet~een about 25Q and 550C.~ and prefer~ly between ;~
, , .
~ .~ 325 and 450~C. to generate, as products of the Absorber, :::
.3 both ferric sul~ate-~earing solids, and a combustion gas reduced in suLfur content. The spent sorbent solids from the Absorber are charged to a gas-solids contactin~ Decomposition Regeneratorj~as indicated by line 2Q8. Fuel yas and air aLso ; ~ are added to the feed mate.xials, as indicated ~y Lines 2~
and 21a,. respectively. The feed rates o~ b.oth.gases and solids ,G; 3~ to the Decomposition Regenerator are reguLated in quantity ., ,~,,~,, . ''.

i: `'' .
.

,:

x:i.:::, ,, : :::: .:. . . .

~ 3'783~
, to generate temperatures between ahout 30Q and 750C. and preferably between SQ0 and 650C. in the reaction zone of . the decomposition e~uipment. Moreover, the ratio of the solid and gaseous ~eed materials to the reactï.on æone of the Decom- ;
position Reyenerator provide oxidizing and reducing agents at stoichiometric ratios that promote thQ formation of iron oxides, and generate chemically reactive Fe3O4 as a major ~:~
component of the iron oxide bearing product of tha decomposi-. tion reactor. In addition to the chemically reacti.ve Fe3O4, . 10 the decomposition regenerator also produce~ a gas high.in content of sulfur dioxide.
, . .. .
:` When ne~ iron sulfate is utilized as a feed to the `; sorbent preparation process, for example, when there is an . abundant source of iron sulfate available to the process from other sources, at least a fraction of the ma~neti.te-~earins ! `
~, product from the decomposition regenerator is fed to gas-.. ~ solid~ contacting reactor of the iron oxi.de Purifi.er, as ~ :.
~;~ indicated by line 211. Process air also is fed to this Purifier,as indicatea b~ line 212, and said air is reacted with the 2~ magnetite in ~uantities sufficient to remove the remaining sulfur from the iron oxide product~ The essentially sulfur-~ree iron oxide product from the Puri~ier is discharged as product ~rom the proce~s, as indicated by line 214.
. .
The remaining fraction of the magnetite-bearing .`
;. product from the decomposition regenerator i5 rec~cled to :
I~rj the absorberj a~ indicated by line 204. Althou~h not indicated .:~; in Figure 2, whan the magnetite-bearing product from the ;~ decomposition regenerator becomes deactivated ~y densification :1 and 1055 of $urface area, a fraction o~ this; product i.s re-.j 3Q cycled to the sor~ent preparation process rather than to the .

~/ ~

,, . . :-, ~ :

~Q~'7133~
absorber. The process steps o~ the sor~ent preparation process described in Figure 1 axe gUCCQ85~ul in reducing the ~ density of the solid product and increasing sur~ace area, thereb~ regeneratlng the reactive properties o~ these solids.
: Also exiting from the Absorber in Figure 2 is a gas reduced in sulfur rontent that contains fine solids .
; elutriated from the bed of the Absor~er b~ the gas. The solids-bearing, but essentially sulfur-free pxoduct ~as ~rom . the Absorber, is fed to Gas Cleaner A as indicated ~y line 297. The contained solids are separated from the gas and ~ .
.
recycled to the sor~ent preparation process, as indicated by; ~ ;
lines 216 and 2Q2. The clean gas is discharged to the atmos~
~ phere, as indicated by line 215.
;...................... The concentrated sulfur dioxide and solids-bearing ......
~ product ~as from th.e Decomposition Regenerator is ~ed to : :
,.~ Gas Cleaner B as indicated by line 215. Th.e solids are ~ .
separated ~rom the gas and recycled to the Sorbent Preparation .~ ~
~;~ procesfi, as indicated by lines 217 and 202. The sulur .. ~ .
`,1 .. .:
~:~ dioxide-bearing clean gas from Gas Cleaner B i~ used as feed:. , 20 gas to either the Claus Plant and/or to the Acid Plant, ;~
as indicated b~ lines 218 and 221. In the Claus Plant, the sul~ur dio~îde ~as from Gas-Cleaner B. is reacted with fuel ~.
1 ~as $ed to the Claus Plant as indicated h~ axrow 222, to -~ produce elemental sul~ur. In the Acid Plant, the sul~ur :~
dioxide gas reacts ~ith air supplied, as indicated b~ line 223, to produce sul$uric acid of commercial qualit~. The acid is . -,`.1 - ~ discharged as a product of the pxocess as indicated b~ line .
226. The sul$ur-bearing tail gases $rom bot~ the Claus Plant and the ~c~d Plant are rec~cled to the A~.sor~er as indicated ~-;
~; 30:~ ~y lines 225, 227 and 2~6.
,-,.~, .'.`.' '~
j, ., ,:
,., : .
. ~','.'. :
-27- :

I ` ~L0~'783~
~,~ The dilute sulfur dioxide and solids-hearing product :~ ; gas from ~he iron oxide Purifier is ~ed to Gas Cleaner C, as ~,i. . indicated by line 213, The solids are separated ~rom the gas and recycled to the sor~ent preparation process, as indicated j by line 219. The dilute sulfur-bearing but solid~-free product ., .~ gas from Gas Cleaner C is recycled to the ~bso.rber, as indicated ,:~
~ ' by lines 22Q and 2Q6. Should ~he combined feed gas to the :
s ~ Absorber be low in content of ox~en, process air is added , ~
' to this gas stxeam as indicated b~ discontinuous line 228.
,. 10 An example of the combined process of this invention ~,, ' utilizin~ the iron oxide sorbent prepared in accordance~with ~:', the process of the invention for desulfurizing separate stream~
", ~
.' of hot reducing gases and oxygen-bearing com~ustion gases is illustrated on the flow diagram of Figure 3 and is described ,~. in detail with reference to this figure as follows:
. ~, A hot reducing as containing hydrQgen, carhon monoxi.de and h~drogen sulfide is fed to a gas-solids contacting desulfurizer, as indicated ~y line 3Ql. Iron oxides from .~
~'~, the Decomposition Regenerator also are fed to tha Desulfurizer '.
2Q as indicated b~ line 30.2. The solLds are reacted with the ~' ~:~ feed ~as to generate product solids containin~ ~ron sulfides ~; and a reducin~ gas containing less sul~ur than the initial . .
~; reducing gas. ~.
' Although not indicated in Fi~ure 3,,a portion or :~
' all o~ the iron oxide-bearing solids ~rom the Decomposition ..
egenerator ~a~ ~e oxidized to hematite (,Fe203) in contact :' " ~ith air at low temperature before the solids are recycled ~.
as indicated ~ line 3a2 to the Desul.~urizer, by line 3~8 to the Sor~ent Preparation system,,and b~ line 313 to the ~, ~, 30 Absor~er. ~;~
s, ~, .

~,, , ;: :

'7~33(~ :
:
When iron-bearing prepared sorbents are to be uti-lized Ln the desulfurization o~ reducing gase~ at gas-solids ' ~ contacting temperatures a~ove 750C., magne~ium and/or aluminum oxide~, hydroxides, car~onates and/or sulfates are used as part of 'dhe new feed to the sorhent preparation procedures of the process. ~oreover, the molecular ratio '` `i of magnesium and/or aluminum to iron in the new eed materials is increased with each increase in ~he operating temperature o~ the gas-solids contacting desul~urization absorber. This ratio may approach or exceed 50% at gas-solids contacting temperatures in excess of 1000C. The t~tal supply of soLids to the sorbent preparation procedures of the process contains r both new feed materials, as indicated by line 306, and pre-viousl~ utilized sorbent solids recovered from the Decomposition Regenerator and/or the gas cleaning equipment, as indicated by lines 3~8 and 307, respectively.
The porous dry agglomerated pxoducts from the Sorbent Preparation system described previously with respect to Figure l are ~ed to the Absorber as indicated by line 309. A fraction .. . .
of the iron sulfide-bearing product from ~he Desulfurizer `' also is fed to the ~as-solids contactin~ Absorber as indicated `~
'~! ;
by line 3Q4. The remaining fraction of the iron sulfide-,j bearin~ solids from the Desulfurizer i5 fed to the Decomposition 1~' 'il ~;l Re~enerator as indicated by line 305. Each of the above ractions o~ the pxoduct from the desulfurizer is utilized as fuel in the Absorber and as fuel and a reductant in the ~: ~ Decomposition ~e~enerator. The quantity of each portion is ' ;~ determ~ned ~X the therlnal re~uirements o each process and the heat ~alance of th~ com~ined process. Sulfur-bearing -~ 30 stack gases containin~ sulfur dioxide and oxyyen are fed to , ~ :,., :', ~ l lns ~3v the Absorber as indicated by line 310. Process air also is used in the Absorber as required by the process and as `~ indicated by lines 312 and 311. The sulfur-bearing gases are reacted with the feed solids in ~he Absorber to generate product solids tha~ contain ferric sulfate and gases of re-i ~ duced sulfur content.
~, ~; The iron sulfate-bearing product from the Absorber is fed to the Decomposition Regeneira~or as indicated by line 330. Process air also is fed to this regenerator as indicated by line 314 and is utilized in quantikies that provide oxygen sufficient to react with the available iron sulfide in the .;
- - solid feed. The products from this process are iron oxide-. ......................................................................... ~, bearing solids high in content of Fe304 and a gas high in - ~ concentration of sulfur dioxide. The sulfur dioxide-bearing product gas from the Decomposition Regenerator is fed to Gas Cleaner C as indicated by line 315. The solids are separated rom the gas and recycled to the sorbent preparation process as indicated by lines 316 and 307. The clean sul~ur dioxide product gas ~rom Gas Cleaner C is fed to either the Claus `;~;
Plant and/or to the Acid Plant, as indicated by lines 317 and 318. Reducing gas ~rom ~as Cleaner A, may be ~ed to the Claus Plant as indicated by line 319, and elemental sulfur may be : ;1 produced ar.d removed as indicated by line 321. Process air is fed to the Acid Plant as indicated by line 320, and the sulfuri~ acid product is removed as indicated b~ line 322.
Su}fur-bearing tail gases recovered from both the Claus Plant y~l and the Acid Plant arQ collected and recycled to the Absorber, as indicated by lines 323, 324 and 311.
The hot reducing gas from the Desulfurizer, which ~; 3a may contain ~inely di~ided solids, is fed to Gas Cleaner A
. ", ;, .. ; ~` :

,~
~ ~30-~ 8715~30 as indicated by line 303~ The solids are separated from the gas and recycled to the sorbent preparation process, as indi-cated by lines 325 and 307. The clean reducing gas product ~`
- from Gas Cleaner A, to the extent it is not used in the Claus Plant, is discharged for industrial use or marketed as a fuel , .
gas as indicated by line 326.
The product gas from the desulfurization absorber, whi~h contains solids but is essentially free of objectionable quantities of sulfur compounds, is fed to the Gas Cleaner B, lQ as indicated by line 3~7. The solids are separated from the . gas and recycled to the sorbent preparation process, as indi-cated by lines 328 and 307. The clean product gas is discharged ~
to the atmosphere as an effluent of acceptable ~uality as ~ ;
~; indicated b~ line 329.
The follo~ing examples illustrate the procedures of this invention. Unless otherwise indicated, all parts and percentages are by weight. ~`
Example 1 Finely divided (-200 mesh) iron-bearing dry solids containing both iron oxides generated from iron sulfate at ~ ~, ~ temperature below 750C., and about 10% by weight of finely ; divided ferrous sulfate are blended to provide a uniform mixture. Water is added to the above mixture in the form of a finely divided spray, and the solids and liquidæ are mixed : in a mechanical blender to generate moist agglomerated solids ~.
that are essentially free of individual particles smaller than ten microns in diameter.
~! The above agglomerated solids are siæed on t~enty mesh screena, the oversize particles are crushed and recycled , ~`r 30 to the screens, and the smaller solids are collected as the .' "~
'"'' , ,~

~ -31-'78~
~ useable product o~ the agglomeration and sizing procedures ~, .
of the process.
The above collected useable product rom the screens i~ contacted with hot sulfur-free gases at a temperature of about 150C. in the bed of a fluid bed reactor. Water is thereby evaporated from the interior of the particles, and the ~- water soluble and reversibl~ hydratable iron sulfate-bearing ~ cement between the finely divided solids is cured. The gas '~ stream to the fluid bed is controlled in both temperature r~ !j and flow rate to remove both the desired quantity of water from the solids, and to elutriate rom the fluid bed of the ~ reactor, solids smaller than about 200 microns in particle ;~ ''. sizeO
~. :
In use, the above a~glomerated and classi~ied solids , are contacted with a gas containing about 0.5% So2 and about 2.0% oxygen, at a température of about 450C. in the bed of a fluid bed reactor. The product gas from the reactor contains about 200 ppm of total oxides of sulfur, an~ the product solids from the bed contaLn ferric sulfate as a major component.
Examples of Re~eneration Process ~
.~ . .1 - .
E_~@~
~; Approximately 24,000 grams of the ferric sulfate-! bearin~ solids-produced by the procedures of Example 1 and ~
containing particles smaller than 48 mesh in maximum size, ~`
are processed in contact with a stxeam of gas containing ~ , J ~
.', ~A,~ approximate1~ 65% N2, 18.8% CO, 10% C02 and 6.2% H2O in a fluid bed reactox at an operating temperature of approximately 60~C., and over a continuous operating period of approximately six hours.
The average composition of the product gas from the above test is approximately 22.0% So2, 54.0~ N2, 0.0% C0, " ~ ~

: ,.

1(~87~33~
22~0% C02 and 2.0% H20 during the above test period. The average composition of the Fe304-bearing product ~rom ~he bed of the reactor is approximately 69.0% Fe, 1.0~ S and 30 0~ 2 Example 3 The procedures of Example 2 are repeated at an average operating temperature of 550C. in the bed of the reactor.
~; The average composition of the product gas is approx-imatel~ 17.0~ S02, 60.0% N2, 0.1% C0, 20.0~ C02 and 2.9% H20.
The average composition of the Fe304-bearing product from the ; bed of the reactor is ~5.45% Fe, 2.67% S, with the remainder being 2 and miscellaneous impurities.
.,:
Example 4 , ~ i; , .
The ferric sulfate-bearing product from Example 1 is mixed with ferrous sulfide-bearing solids to produce mixed iron-bearing solids in which approximately lO~ of the iron , j , ~ content is present in the form of ferrous sulfide.
~ . .1 Approximately 200 grams of the above mixed solids are heated to a temperature of approximately 600C. in contact '! 2~ with nitrogen for a period of approximately three hours. The product solids from this procedure contain 0.35% sulfur and the remaininy components are iron and oxygen com~ined in the ratio of Fe304.
Although the invention has been shown and described with respect to certain preferred embodiments, equivalent operations and modifications will occur to others skilled in ~;
the art upon the reading and understanding of this specifica-'~ tion. The present invention includes all such e~uivalent ~¦ alterations and modifications and is limited only by the scope ' ; 30 of the claims.
., ~

., ~

, ,, ,. , '

Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A process for the preparation and utilization of sorbent solids having particular utility in reducing the sulfur compound content of combustion gases and reducing gases, which comprises the steps of:
(a) mixing (i) finely divided solids containing a compound, selected from the group consisting of iron and calcium compounds, as an active component, with (ii) a liquid selected from the group consisting of water, sulfuric acid, and solutions containing sulfuric acid to produce agglomerated particles of moist solids that contain water soluble and reversibly hydratable compounds, which solids are essen-tially free of individual particles smaller than ten microns in diameter, (b) drying the above agglomerated moist solids by contact with relatively sulfur-free gases in a fluid bed drier, at temperatures between 80° and 300°C., to remove the water therefrom and thereby to produce porous dry solids con-taining agglomerated particles high in surface area and to cure water soluble and reversibly hydratable compounds and thereby to produce particles high in mechanical strength, (c) modulating the flow rate of gas in contact with the above solids to elutriate from the fluid bed of the drier, a major fraction of the particles smaller than about 200 microns in diameter, (d) collecting a fraction of the classified, porous, agglomerated, dry solids that remain in the bed of the drier, as product of the sorbent preparation procedures of the process, (e) utilizing the collected sorbent solids by contact with sulfur-bearing gases in gas-solids contacting equipment to generate, as products of the process, spent sorbent solids containing sulfur compounds, and a gas reduced in content of sulfur, and (f) repetitively regenerating and reusing at least a major fraction of said spent solids.

2. The process of claim 1 in which, (a) the agglomerated particles of moist solids are separated into at least two fractions on the basis of particle size, (b) the oversize particle fractions are crushed to the desired particle size, and (c) the crushed product is utilized as part of the feed to the drying step.

3. The process of claim 1 in which, (a) finely divided solids in the product gases from gas-solids contacting procedures of the process are separated from the gases, and (b) major fractions of these separated solids are recycled for use as part of the feed to the mixing and agglomerating step.

4. The process of claim 1 in which, (a) a fraction of the sulfur compound-bearing spent sorbent solids from the utilizing step is regenerated in contact with gases, and (b) at least a fraction of the regenerated sorbent is recycled directly as part of the feed to the utilization step.

5. The process of claim 4 in which, (a) a fraction of the regenerated solids is re-cycled as part of the feed to the mixing and agglomerating step.

6. The process of claim 5 in which, (a) a fraction of the regenerated solids is reduced in particle size prior to recycle as part of the feed to the mixing and agglomerating step, to minimize accumulation of densified, inert particles as a function of repetitive regenera-tion and recycling.

7. The process of claim 1 in which, (a) calcium compounds axe the active component of the prepared sorbent, and (b) at least part of the feed to the mixing and agglomerating step comprises finely divided calcium-bearing industrial materials, selected from the group consisting of limestone, lime and dolomite.

8. The process of claim 1 in which, (a) iron compounds are the active component of the prepared sorbent, and (b) at least part of the feed to the mixing and agglomerating step comprises finely divided industrial materials, selected from a group of such materials containing iron sulfates, iron sulfides, iron oxides, iron hydroxides, iron carbonates, and metallic iron as major components.

9. The process of claim 8 in which, (a) at least part of the iron-bearing feed to the utilizing step comprises iron oxides that are generated from iron sulfates at temperatures of generation below 700°C., and under conditions that provide Fe3O4 as a major component of the iron content of the regenerated oxides.

10. The process of claim 9 in which, (a) the feed gas to the utilization step is at temperatures between 250° and 550°C., and contains both oxygen and oxides of sulfur.

11. The process of claim 8 in which, (a) the feed gas to the utilization step is a reducing gas containing hydrogen sulfide, (b) iron sulfide-bearing spent sorbent from the utilization step is regenerated by oxidation in contact with air, to produce iron oxide, and (c) a fraction of the regenerated sorbent solids is recycled for use as part of the iron-bearing feed to the utilization step.

12. The process of claim 11 in which, (a) the iron sulfide-bearing spent sorbent solids are regenerated in contact with both air and solids that contain iron sulfates.

13. The process of claim 12 in which, (a) iron sulfide-bearing spent sorbent solids from the utilization step are regenerated under con-ditions that produce Fe3O4 as a major component of the iron oxide content of the regenerated sorbent.

14. The process of claim 11 in which, (a) the reducing gas is desulfurized at temperatures above 750°C. and in contact with prepared iron-bearing sorbent solids that contain finely divided particles of chemically inert or refrac-tory oxides of magnesium and/or aluminum inti-mately dispersed within particles of porous agglomerated iron-bearing solids.

15. The process of claim 14 in which, (a) the iron-bearing feed materials to the sorbent preparation step contain finely divided industrial materials, selected from the group consisting of materials that contain oxides, hydroxides, carbonates, and sulfates of magnesium and aluminum as major components, and (b) the magnesium and aluminum compounds are con-verted to refractory oxides in agglomerated particles of the sorbent solids.

16. The process of claim 1 in which, (a) a fraction of the product gas from the utiliza-tion step is recycled for use as part of the feed gas to the drying step.