CA1046734A - Apparatus and method for removing sulfur from sulfur-bearing gases - Google Patents
Apparatus and method for removing sulfur from sulfur-bearing gasesInfo
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- CA1046734A CA1046734A CA210,619A CA210619A CA1046734A CA 1046734 A CA1046734 A CA 1046734A CA 210619 A CA210619 A CA 210619A CA 1046734 A CA1046734 A CA 1046734A
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Abstract
ABSTRACT OF THE DISCLOSURE
Sulfur bearing gases are contacted with metal oxide bearing prepared solids containing iron, and reacted in an absorption procedure to produce both gases that are suitable for discharge to the atmosphere as "pollution free" effluents, and solids that contain either metal sulfates or metal sulfides that can be oxidize to metal sulfates The metal sulfate baring solids are contacted with reducing gases under controlled condition- in a decomposition procedure, the sulfates are converted to metal oxides that are suitable for use as sorbents, and the oxide bearing solids are recycled to the absorber The product gas from the decomposition procedure, which contains sulfur dioxide at high concentration, is utilized as feed gas for the production of sulfuric acid and/or elemental sulfur by conventional processes.
Sulfur bearing gases are contacted with metal oxide bearing prepared solids containing iron, and reacted in an absorption procedure to produce both gases that are suitable for discharge to the atmosphere as "pollution free" effluents, and solids that contain either metal sulfates or metal sulfides that can be oxidize to metal sulfates The metal sulfate baring solids are contacted with reducing gases under controlled condition- in a decomposition procedure, the sulfates are converted to metal oxides that are suitable for use as sorbents, and the oxide bearing solids are recycled to the absorber The product gas from the decomposition procedure, which contains sulfur dioxide at high concentration, is utilized as feed gas for the production of sulfuric acid and/or elemental sulfur by conventional processes.
Description
BACKGROUND OF THE INV~NTION
This applica~ion pertains to the art of gas purification, and more particularly to removal of sulfur from sulfur-bearing gas. The sulfur~bearing gas may be either a reducing gas or an oxidizing gas. The application is particularly applicable to production of commercial quality elemental sulfur, sulfuric acid and iron oxide from industrial waste materials.
Many industrial operations produce iron sulfate, sulfur-bearing gases, or combinations of both, as waste materials.
Such waste materials are c~mmonly produced from mining and industrial operations involving the production of non-ferrous metals, coal, steel, titanium pigments, sulfuric acid, elemental sulfur, electric power and similar products. Discharge of these waste material~ result in undesirable pollution of air and water.
United States Patent No. 3,053,651 discloses a process for conversion of iron in sulfide minerals, mineral waste materials, or combinations of both, to a calcined product containing acid soluble iron. The calcined product may also be reacted with dilute solutions of industrial wastes containing sulfuric acid and impurities to obtain purified neutral solutions having a high content of iron sulfate~
It would be desirable to have the capability of obtain-ing commercial quality iron and sulfur products from industrial wastes bearing iron sulfate and sulfur dioxide.
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 irritating 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 very corrosive.
At the present time, the largest amount of industrial sulfur oxide emissions results from the combustion of certain types of coal and oil which contain appreciable amounts of ~ulfur.
Waste gas streams containing sulfur dioxide similarly are produced by other industrial processes such as in the smelting of sulfur-bearing minerals, the refining of sulfur containing crude oils, the syntheses of sulfuric acid, the sulfonation of hydrocarbons, the production of coke, the production of sulfur in a Claus process, the production of paper by way of a wood-pulping process, and similar industrial processes.
Furthermore, the discharge of these gas streams contain-ing sulfur dioxide into the atmosphere constitutes a waste of a valuable mineral because the sulfur contained therein is an industri-al commodity. Currently, tens of millions of tons of sulfur oxides are released into the atmosphere over populated regions of the United States each year. Thus, the recovery of some of this sulfur dioxide either as such or in another form could result in the accumulation of a supply of useful chemicals of definite value.
Many processes have been proposed for removal of sulfur dioxide from these gas streams. Most of the proposed removal procedure~ which have been suggested utilize liquid sorption in which the sulfur dioxide containing gases are intimately contacted with an aqueous sorbent which typically contains chemicals in solution or in slurry which will react with the sulfur dioxide and absorb ~he same into the liquid solution. Examples of such sorbents include the oxides, hydroxides and carbonates of ammonia,
This applica~ion pertains to the art of gas purification, and more particularly to removal of sulfur from sulfur-bearing gas. The sulfur~bearing gas may be either a reducing gas or an oxidizing gas. The application is particularly applicable to production of commercial quality elemental sulfur, sulfuric acid and iron oxide from industrial waste materials.
Many industrial operations produce iron sulfate, sulfur-bearing gases, or combinations of both, as waste materials.
Such waste materials are c~mmonly produced from mining and industrial operations involving the production of non-ferrous metals, coal, steel, titanium pigments, sulfuric acid, elemental sulfur, electric power and similar products. Discharge of these waste material~ result in undesirable pollution of air and water.
United States Patent No. 3,053,651 discloses a process for conversion of iron in sulfide minerals, mineral waste materials, or combinations of both, to a calcined product containing acid soluble iron. The calcined product may also be reacted with dilute solutions of industrial wastes containing sulfuric acid and impurities to obtain purified neutral solutions having a high content of iron sulfate~
It would be desirable to have the capability of obtain-ing commercial quality iron and sulfur products from industrial wastes bearing iron sulfate and sulfur dioxide.
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 irritating 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 very corrosive.
At the present time, the largest amount of industrial sulfur oxide emissions results from the combustion of certain types of coal and oil which contain appreciable amounts of ~ulfur.
Waste gas streams containing sulfur dioxide similarly are produced by other industrial processes such as in the smelting of sulfur-bearing minerals, the refining of sulfur containing crude oils, the syntheses of sulfuric acid, the sulfonation of hydrocarbons, the production of coke, the production of sulfur in a Claus process, the production of paper by way of a wood-pulping process, and similar industrial processes.
Furthermore, the discharge of these gas streams contain-ing sulfur dioxide into the atmosphere constitutes a waste of a valuable mineral because the sulfur contained therein is an industri-al commodity. Currently, tens of millions of tons of sulfur oxides are released into the atmosphere over populated regions of the United States each year. Thus, the recovery of some of this sulfur dioxide either as such or in another form could result in the accumulation of a supply of useful chemicals of definite value.
Many processes have been proposed for removal of sulfur dioxide from these gas streams. Most of the proposed removal procedure~ which have been suggested utilize liquid sorption in which the sulfur dioxide containing gases are intimately contacted with an aqueous sorbent which typically contains chemicals in solution or in slurry which will react with the sulfur dioxide and absorb ~he same into the liquid solution. Examples of such sorbents include the oxides, hydroxides and carbonates of ammonia,
-2-10~6734 the alkali metals, and the alkaline earth metals.
One disadvantage of the wet sorption process is that the sorption of the sulfur dioxide must occur at a rather low temperature. This results in cooling of the gases which are ultimately discharged to the atmosphere. Such cool gases will remain near ground level thus causing pollution of the ambient air at ground level which may be as serious as that presented by the untreated flue gas.
Other methods have been suggested for removing sulfur oxides from flue gases. Attempts to desulfurize fuels prior to combustion have been costly and not always effective. For so~e fuels, such as coal, many processes investigated to date do not economically desulfurize fuel.
Additive processes have been suggested wherein materials having the ability to combine with sulfur oxides are added either to the fuel or to the com~ustion gases. Additives which have been employed include soda, limestone, magnesia and magnesite, but such additives generally are costly.
Dry adsorption also has been suggested. Sulfur dioxide can be adsorbed at low temperature by materials such as aluminum oxide, activated carbon, and silica gel. A disadvantage of such adsorption processes is that they also require relatively low temperatures and have similar drawbacks to those of the wet absorption process described above.
Solid acceptors which absorb sulfur oxides also have been reported. Examples of such acceptors include alkalized alumina which 1s converted to the aluminum sulfate and mixtures of alkali metal oxides and iron oxide which are also converted to the corresponding sulfates. One important advantage of these solid absorption processes is that they can ~e operated at elevated ~46734 temperatures, and the gas which ultimately is discharged to the atmosphere is at an elevated temperature and is readily dissipated to the atmosphere.
Reducing gases generated from the partial combustion of coal and fuel oil also contain sulfur and the rem~val of this sulfur from the gas is desirable. These gases behave differently from the oxidizing gaseq described above with re~pect to sorbents.
There continues to be a need, therefore, for effective solid acceptors which are regenerative and economically acceptable in commercial scale sorption processes.
S~MMARY OF THE DISCLOSURE
Thi~ invention involves the treatment of sulfur and oxygen bearing gases in an absorber xeactor in contact with metal oxide bearing prepared solids that contain iron, to produce both gases that are suitable for discharge to the atmosphere as pollution free effluents, and solids that contain both metal sulfates and metal oxides. The metal sulfate bearing solids from the absorber are contacted with both reducing gas and air under controlled conditions in a decomposition reactor, to produce both a sul~ur dioxide bearing gas, and metal oxide bearing solids that are suitable for use as sorbents.
The metal oxide bearing solids from the decomposition reactor are recycled to the absorber reactor, while the sulfur dioxide bearing gas is utilized as feed gas for the production of either sulfuric acid and/or elemental sulfur by conventional processas.
This invention also provides for the desulfurization of hot reducing gases from the partial combustion of commercial fuels. The reducing gases are processed in contact~ith the metal oxide bearing solids from the decomposition reactor of the 10~6734 combined process, and the sulfur i8 extracted as metal ~ulfide compounds in the sorbent. The metal sulfides are oxidized to metal sulfates in the absorber reactor of the combined process and the sulfur is recovered in theform of either sulfuric acid and~or elemental sulfur, as described above.
This invention also involves the treatment of iron sulfate from industrial wastes, and provides for recovery of both the iron and the sulfur content of the iron sulfate as industr~al products of commercial quality by the procedures of the combinsd process.
In one preferred arrangement, ferrous sulfate and iron oxide are simultaneously fed to an agglomerator where the ferrous sulfate and iron oxide are mixed or formed into agglomerates.
The agglomerates are fed to a sizer. Oversized agglomerates and particles are fed to a mechanical crusher which recycles to the sizer. Undersized particle~ are fed to a fluidized bed drier, dried and sized. The dried sorbent agglomerates and particles of iron oxide, iron sulfate, or mixture thereof, are fed to an absorber. Oxygen and sulfur-bearing gas passes through the absorber and the sulfur and oxygen in the gas react with the sorbent to form ferric sulfate.
The spent sorbent is then fed to a unit which decomposes the ferric sulfate at low temperatures to form a concentrated sulfur dioxide gas and solids that contain magnetite as a major component. The magnetite from the decomposition unit either is recycled to the absorber or fed to a sulfur stripper where it is contacted by air to drive off any remaining sulfur as sulfur dioxide. Iron oxide from the sulfur stripper is of commercial quality and may be marketed for production of steel. The sulfur dioxide gas from the decomposition unit may be converted into elemRntal sulfur or sulfuric acid of commercial quality.
When available gases must be desulfurized at high temperatures, calcium oxide is utilized as a substitute for part of the iron in the prepared sorbent. The calcium oxide is converted to calcium sulfate in contact with sulfur and oxygen bearing gases in the absorber reactor. Moreover, when co-precipitated iron also is present in the sorbent, the sulfur is released at low temperatures by the decomposition procedures of the process of this invention.
When reducing gases are desulfurized by the process of this invention, calcium oxide in the sorbent is converted to calcium 9ulfide. Calcium sulfide is converted to calcium sulfate in the absorber reactor, and the sulfur is recovered by the normal procedures of this process as described above.
The invention relates to a process for removing sulfur from gases containing sulfur and oxygen.
The invention also relates to a regenerative process for the desulfurization of gases that contain both oxygen and oxides of sulphur.
In another aspect the invention relates to a regenerative process for the desulfurization of reducing gases.
The processes of the invention comprise contacting the gases with porous or sorbent solid material comprising iron bearing compounds, for example, ferrous sulfate, iron oxide and mixtures thereof. The solid material is contacted with the sulphur-containing gas at a temperature of about 250C,to 550C. to produce oxidized solids and a product gas essentially free of sulphur. The oxidized solids are contacted with a reducing gas to generate iron oxides and sulfur dioxide, in particular the reducing gas is suitably at a temperature of about 300C. to about 700C. and the iron oxides comprises magnetite. The generated iron oxides or at least a portion of them are suitably recycled to form part of the solid material B ,~
in the first stage of the process, Conveniently the solid material contains metal oxides in excess of the sulfur content of the gas on a stoichiometric basis.
The invention also relates to an apparatus for removing sulfur from a sulfur and oxygen-bearing gas which utilizes a solid sorbent convertible to ferric sulfate when contacted with said gas comprising:
sorber means for receiving the sorbent, sorbent feed means for feeding the sorbent to the sorber means, gas feed means for feeding the gas to the sorber means, reductive decomposition means for collecting and decomposing the used sorbent from the sorber means in a reducing atmosphere to regenerate the sorbent and form a sulfur dioxide gas, agglomerating means for agglomerating the regenerated sorbent product of the reductive decomposition means into agglomerates, and - recycling means for recycling at least a portion of the agglomerates to the sorbent feed means.
~ - 6a -1C~46734 The invention may take form in certain parts and arrange-ments of parts, preferred embodiments of which will be described in detail in this specification and illustrated in the accom-panying drawings which form a part thereof.
Fig. 1 is a flow diagram showing an operation of the process of the invention utilizing iron oxide and~or ferrous sulfate;
Fig. 2 is a flow diagram showing a more detailed modification of the operating arrangement for generating ele-mental sulfur from the sulfur, dioxide gas from the decompositionof iron sulfate in accordance with the process of the invention;
Fig. 3 is a flow diagram showing one modification of the improved process of the present invention for producing high purity iron oxides and elemental sulphur;
Fig. 4 is a flow diagram showing a modification operating arrangement of the improved process of the present invention for B
- 6b -producing high purity iron oxides and sulfuric acid: ana Fig. 5 is a flow diagram of the process for desulfur-izing both reducing and oxidizing gases with a calcium and iron bearing sorbent.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to the drawings, wherein the showings are for purposes of illustrating preferred embodiments of the invention only and not for purposes of limiting same, Fig.
illustrates the general arrangement of the process of the invention wherein both iron oxide and ferrous sulfate comprise the sorbent.
The process also may be used with either of the sorbents used alone, e~pecially, for example, when the iron sulfate is available in large quantities as an industrial waste material.
Solid iron sulfate is fed into absorber E as indicated by arrow 100. Iron oxide is fed into absorber E as either fresh iron oxide, as indicated by arrow 103, or recovered iron oxide from decomposer F, as indicated by arrow 112. The solids in absorber E are contacted with a sulfur and oxygen-bearing gas entering the absorber as indicated by arrow 102. The operating temperature of absorber E may be between 250 and 550C. and is preferably between 325 and 450C.
When ferrous sulfate and particularly hydrated ferrous sulfate is contacted by gas which bears sulfur an`d oxygen in the described range of temperatures, a reaction occurs between the components of the gas and the sorbent material to generate principally ferric sulfate. We assume that the theoretical basis for the absorption may proceed by a combination of the steps which may include reactions such as the following:
1) FeSO4-xH2O + Heat - FeSO4 + xH2O
One disadvantage of the wet sorption process is that the sorption of the sulfur dioxide must occur at a rather low temperature. This results in cooling of the gases which are ultimately discharged to the atmosphere. Such cool gases will remain near ground level thus causing pollution of the ambient air at ground level which may be as serious as that presented by the untreated flue gas.
Other methods have been suggested for removing sulfur oxides from flue gases. Attempts to desulfurize fuels prior to combustion have been costly and not always effective. For so~e fuels, such as coal, many processes investigated to date do not economically desulfurize fuel.
Additive processes have been suggested wherein materials having the ability to combine with sulfur oxides are added either to the fuel or to the com~ustion gases. Additives which have been employed include soda, limestone, magnesia and magnesite, but such additives generally are costly.
Dry adsorption also has been suggested. Sulfur dioxide can be adsorbed at low temperature by materials such as aluminum oxide, activated carbon, and silica gel. A disadvantage of such adsorption processes is that they also require relatively low temperatures and have similar drawbacks to those of the wet absorption process described above.
Solid acceptors which absorb sulfur oxides also have been reported. Examples of such acceptors include alkalized alumina which 1s converted to the aluminum sulfate and mixtures of alkali metal oxides and iron oxide which are also converted to the corresponding sulfates. One important advantage of these solid absorption processes is that they can ~e operated at elevated ~46734 temperatures, and the gas which ultimately is discharged to the atmosphere is at an elevated temperature and is readily dissipated to the atmosphere.
Reducing gases generated from the partial combustion of coal and fuel oil also contain sulfur and the rem~val of this sulfur from the gas is desirable. These gases behave differently from the oxidizing gaseq described above with re~pect to sorbents.
There continues to be a need, therefore, for effective solid acceptors which are regenerative and economically acceptable in commercial scale sorption processes.
S~MMARY OF THE DISCLOSURE
Thi~ invention involves the treatment of sulfur and oxygen bearing gases in an absorber xeactor in contact with metal oxide bearing prepared solids that contain iron, to produce both gases that are suitable for discharge to the atmosphere as pollution free effluents, and solids that contain both metal sulfates and metal oxides. The metal sulfate bearing solids from the absorber are contacted with both reducing gas and air under controlled conditions in a decomposition reactor, to produce both a sul~ur dioxide bearing gas, and metal oxide bearing solids that are suitable for use as sorbents.
The metal oxide bearing solids from the decomposition reactor are recycled to the absorber reactor, while the sulfur dioxide bearing gas is utilized as feed gas for the production of either sulfuric acid and/or elemental sulfur by conventional processas.
This invention also provides for the desulfurization of hot reducing gases from the partial combustion of commercial fuels. The reducing gases are processed in contact~ith the metal oxide bearing solids from the decomposition reactor of the 10~6734 combined process, and the sulfur i8 extracted as metal ~ulfide compounds in the sorbent. The metal sulfides are oxidized to metal sulfates in the absorber reactor of the combined process and the sulfur is recovered in theform of either sulfuric acid and~or elemental sulfur, as described above.
This invention also involves the treatment of iron sulfate from industrial wastes, and provides for recovery of both the iron and the sulfur content of the iron sulfate as industr~al products of commercial quality by the procedures of the combinsd process.
In one preferred arrangement, ferrous sulfate and iron oxide are simultaneously fed to an agglomerator where the ferrous sulfate and iron oxide are mixed or formed into agglomerates.
The agglomerates are fed to a sizer. Oversized agglomerates and particles are fed to a mechanical crusher which recycles to the sizer. Undersized particle~ are fed to a fluidized bed drier, dried and sized. The dried sorbent agglomerates and particles of iron oxide, iron sulfate, or mixture thereof, are fed to an absorber. Oxygen and sulfur-bearing gas passes through the absorber and the sulfur and oxygen in the gas react with the sorbent to form ferric sulfate.
The spent sorbent is then fed to a unit which decomposes the ferric sulfate at low temperatures to form a concentrated sulfur dioxide gas and solids that contain magnetite as a major component. The magnetite from the decomposition unit either is recycled to the absorber or fed to a sulfur stripper where it is contacted by air to drive off any remaining sulfur as sulfur dioxide. Iron oxide from the sulfur stripper is of commercial quality and may be marketed for production of steel. The sulfur dioxide gas from the decomposition unit may be converted into elemRntal sulfur or sulfuric acid of commercial quality.
When available gases must be desulfurized at high temperatures, calcium oxide is utilized as a substitute for part of the iron in the prepared sorbent. The calcium oxide is converted to calcium sulfate in contact with sulfur and oxygen bearing gases in the absorber reactor. Moreover, when co-precipitated iron also is present in the sorbent, the sulfur is released at low temperatures by the decomposition procedures of the process of this invention.
When reducing gases are desulfurized by the process of this invention, calcium oxide in the sorbent is converted to calcium 9ulfide. Calcium sulfide is converted to calcium sulfate in the absorber reactor, and the sulfur is recovered by the normal procedures of this process as described above.
The invention relates to a process for removing sulfur from gases containing sulfur and oxygen.
The invention also relates to a regenerative process for the desulfurization of gases that contain both oxygen and oxides of sulphur.
In another aspect the invention relates to a regenerative process for the desulfurization of reducing gases.
The processes of the invention comprise contacting the gases with porous or sorbent solid material comprising iron bearing compounds, for example, ferrous sulfate, iron oxide and mixtures thereof. The solid material is contacted with the sulphur-containing gas at a temperature of about 250C,to 550C. to produce oxidized solids and a product gas essentially free of sulphur. The oxidized solids are contacted with a reducing gas to generate iron oxides and sulfur dioxide, in particular the reducing gas is suitably at a temperature of about 300C. to about 700C. and the iron oxides comprises magnetite. The generated iron oxides or at least a portion of them are suitably recycled to form part of the solid material B ,~
in the first stage of the process, Conveniently the solid material contains metal oxides in excess of the sulfur content of the gas on a stoichiometric basis.
The invention also relates to an apparatus for removing sulfur from a sulfur and oxygen-bearing gas which utilizes a solid sorbent convertible to ferric sulfate when contacted with said gas comprising:
sorber means for receiving the sorbent, sorbent feed means for feeding the sorbent to the sorber means, gas feed means for feeding the gas to the sorber means, reductive decomposition means for collecting and decomposing the used sorbent from the sorber means in a reducing atmosphere to regenerate the sorbent and form a sulfur dioxide gas, agglomerating means for agglomerating the regenerated sorbent product of the reductive decomposition means into agglomerates, and - recycling means for recycling at least a portion of the agglomerates to the sorbent feed means.
~ - 6a -1C~46734 The invention may take form in certain parts and arrange-ments of parts, preferred embodiments of which will be described in detail in this specification and illustrated in the accom-panying drawings which form a part thereof.
Fig. 1 is a flow diagram showing an operation of the process of the invention utilizing iron oxide and~or ferrous sulfate;
Fig. 2 is a flow diagram showing a more detailed modification of the operating arrangement for generating ele-mental sulfur from the sulfur, dioxide gas from the decompositionof iron sulfate in accordance with the process of the invention;
Fig. 3 is a flow diagram showing one modification of the improved process of the present invention for producing high purity iron oxides and elemental sulphur;
Fig. 4 is a flow diagram showing a modification operating arrangement of the improved process of the present invention for B
- 6b -producing high purity iron oxides and sulfuric acid: ana Fig. 5 is a flow diagram of the process for desulfur-izing both reducing and oxidizing gases with a calcium and iron bearing sorbent.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to the drawings, wherein the showings are for purposes of illustrating preferred embodiments of the invention only and not for purposes of limiting same, Fig.
illustrates the general arrangement of the process of the invention wherein both iron oxide and ferrous sulfate comprise the sorbent.
The process also may be used with either of the sorbents used alone, e~pecially, for example, when the iron sulfate is available in large quantities as an industrial waste material.
Solid iron sulfate is fed into absorber E as indicated by arrow 100. Iron oxide is fed into absorber E as either fresh iron oxide, as indicated by arrow 103, or recovered iron oxide from decomposer F, as indicated by arrow 112. The solids in absorber E are contacted with a sulfur and oxygen-bearing gas entering the absorber as indicated by arrow 102. The operating temperature of absorber E may be between 250 and 550C. and is preferably between 325 and 450C.
When ferrous sulfate and particularly hydrated ferrous sulfate is contacted by gas which bears sulfur an`d oxygen in the described range of temperatures, a reaction occurs between the components of the gas and the sorbent material to generate principally ferric sulfate. We assume that the theoretical basis for the absorption may proceed by a combination of the steps which may include reactions such as the following:
1) FeSO4-xH2O + Heat - FeSO4 + xH2O
3~ 2) 2FeSO4-XH2O + 2 + S2 = Fe2(SO4)3 + 2xH2O
3) 2FeSO4 + 2 + S2 = Fe2(SO4)3
3) 2FeSO4 + 2 + S2 = Fe2(SO4)3
4) 4FeS04 + 2 + 2S03 = 2Fe2(S04)3 Alternatively, the ferrous sulfate may absorb the oxides of sulfur by the series of reactions outlined below as S and 6:
5) 6FeS04 + 3/2 2 = 2Fe2(S04)3 + Fe23
6) Fe23 + 3S02 + 3/2 2 = Fe2(so4)3 The mechanism of corptlon may be different to some extent from that postulated above since there is evidence (X-ray diffraction) that the final bed after absorption of S02 contains some Fe2S209-xH20 and FeS04 in addition to the Fe2(S04)3. The X-ray diffraction does not indicate the presence of a significant amount of iron oxides.
The iron oxide sorbent in absorber unit E can react with sulfur and oxygen in the gas by reactions such as the following:
The iron oxide sorbent in absorber unit E can react with sulfur and oxygen in the gas by reactions such as the following:
7) 2Fe203 + 32 + 6S02 = 2Fe2(S04)3
8) 2Fe304 ~ 52 + 9S2 3Fe2( 4 3 ) 3 4 2 2 3 2 4 3 It has been found that the use of magnetite generated from iron sulfate as described below and particularly that generated at low temperatures and oxidized either simultaneously with or prior to being subjected to the sulfur an~ oxygen-bearing gas is highly effective in the absorber unit. On the basis of equal weights of iron oxide and iron sulfate, the capacity of such iron oxide to absorb oxides of sulfur from the hot sulfur-bearing gas i8 much higher than for iron sulfate. The absorber unit utilized in this invention may comprise one or more beds of the sorbent described above. The beds may be of the fixed, moving, fluidized or countercurrent type.
The sulfur and oxygen-bearing gases pass through absorber E and the sulfur and oxygen react with the iron oxides and ferrous sulfate to form principally ferric sulfate. The ~046734 product gas from the absorber i~ essentially free of sulfur and is suitable for discharge into the atmosphere as a pollution-free effluent as indicated by arrow 104.
~he spent sorbent from absorber E is fed to de~omposer F as indicated by arrow 106. The spent sorbent in decomposer F
is contacted with hot reducing gases containing CO and ~2 fed into the decomposer as indicated by arrow 105. Because magnetite is the desired decomposition product, the temperature of the decomposition and concentration of the reducing gas utilized are interrelated as will be described below. The temperature of the decomposition may vary from between about 300C. to about 800C. although temperatures from about 400C. to about 700C.
are preferred. Any equipment in which contact can be effected between a gas and a solid may be used for the decomposition. For example, fixed bed, moving bed and fluid bed techniques may be utilized. It has been observed that decomposition accomplished at lower temperatures results in a more active oxide product.
The hot reducing gases utilized in the decomposition process normally contain both CO and H as e~sential components, and normally are generated by the partial combustion of commer-cial fuels with air, and/or with preheated air. These gases normally are generated at high temperatures, and are used in the decompo~ition process at much lower temperature~. They normally provide both heat and chemical reagents for use in the reactions of the decomposition proce~s. Moreover, they normally are generated in separate equipment attached to the decomposition reactor, but when certain types of commercial fuel are available for use in the process, the gas generation may be accompli~hed in the decompo~ition reactor.
The hot reducing gases utilized in the process of the invention may be generated by partial combustion of commercial _g_ fuel with air in chemical reactions such as the following reactions:
11) CH4 + 2 ~CO ~2 2 12) 2C ~ 2 = 2CO
) 2 CO2 H2 In the low temperature decomposition process of this invention, the hot gas product from the above gasification reactions is processed in contact with sulfate-bearing solids in decomposer F. The gas is utilized both a~ a source of reducing agent and a source of heat for the decomposition process. More-over, the composition and temperature of the gas in the reaction zone of the process determines the composition and many of the properties of both the gas and solid products from the process.
For example, the sulfur sorbent property of the oxides obtained by the low temperature decomposition process of the invention is significantly improved.
When the product gases from the reaction zone of the decompo~ition process are held between limits of composition and temperature that generate magnetite as a major component of the iron-bearing product, the decomposition reactions can be carried out both at temperatures and with ratios of fuel and air that are unusually low. This results in the generation of a product gas which is concentrated in sulfur dioxide. The concentration of reducing agent~ in the feed gases utilized should be quch that the product gas is in equilibrium composition with the magnetite at these temperatures.
The magnetite-bearing product obtained by the above-described low temperature decomposition reaction is assumed to be produced by reactions such as the following:
10467;~4 14) 3FeS04 + 2H2 = Fe34 + 2H2 2 15) 3FeS04 ~ 2co = Fe304 + 2Co2 + 3So 4~3 1OH2 = 2Fe304 + 1H2 + 9S0 17) 3Fe (S0 ) + lOC0 = 2Fe 0 1 lOC0 + 9S0 18) 3Fe203 I H2 = 2Fe O + H20 19) 3Fe203 + Co = 2Fe30 + Co The magnetite obtained by decomposition of the sulfates in decomposer F can be recycled to absorber E as indicated by arrow 112 or advanced to sulfur stripper G as indicated by arrow 110. Air or oxygen i~ supplied to sulfur stripper G in controlled quantities as indicated by arrow 107, and the magnetite i~
oxidized to pro~iae heat for re val of any sulfur present by reactions such as the fotlowing:
2(S04)3 ~ Heat = Fe203 + 3S0 22) 2Fe304 ~ S03 - 2Fe23 2 High purity commercial quality iron oxide is withdrawn from sulfur .. ~tripper G as indicated by arrow 121. The re val of the objectionable sulfur generally does not require complete conversion of the magnetite to hematite, and the purified product generally will contain both magnetite and hematite.
A hot sulfur-bearing gas is discharged from sulfur stripper G and may be recycled to absorber E as indicated by arrow 122.
The sulfur dioxide containing gas produced in decomposer F is discharged therefrom as indicated by line 108 and fed as indicated by line 114 to a Claus plant or as indicated by line 116 to an acid plant. In Claus plant J, the sulfur dioxide can be contacte~ with reducing agent~ and the hydrogen sulfide-bearing product gas contacted with a catalyst to produce water and elemental sulfur. The elemental sulfur is discharged from the Claus plant as indicated by line 118. The elemental sulfur produced in the Claus plant is of commercial quality.
A~ mentioned previously, the product gas exiting from S decomposer F contains sulfur dioxide in high concentrations. In order to effectively utilize this gas mixture in a sulfuric acid plant, the product gas from decomposer F is reacted with air in quantities that will both oxidize the reducing agents present and provide excess oxygen. This oxygen-bearing product gas is utilized as the feed gas in the acid plant.
The magnetite obtained by the decomposition of the sulfates in decomposer F and recycled to absorber E can be made more active toward the oxides of sulfur by subjecting the magnetite to a low temperature oxidation treatment (not shown in Fig. 1). When the magnetite is oxidi~ed at a temperature below about 450C., it is converted to a product (principally hematite) which i~ highly reactive towaras absorption of the oxides of sulfur. It is not known preci~ely why this low temperature pre-oxidation produces a more reactive iron oxide. At higher oxida-tion temperatures,the effectiveness of the product as a ~orbentis minim~zed.
The oxidation of the magnetite-bearing solids can al80 occur in absorber E since the gas entering the absorber contain oxygen as well as sulfur. The magnetite-bearing solid obtained from the decomposition zone is advanced directly to the absorber as indicated by line 112 where it is contacted with a gaseous mixture containing sulfur and oxygen. The oxygen converts the magnetite to an active hematite sorbent which then reacts with S2 in the gas.
Figure 2 shows another arrangement of an improved process of the present invention for producing commercial quality iron oxides and elemental sulfur. Like parts have been given the same numerals and letters as those in Figure 1. This example illustrates the process wherein both iron oxide and ferrous sulfate comprise the sorbent bu~ the process also may be used with either of the sorbents used alone.
The S02 gas from decomposer F is advanced to cyclone separator T as indicated by arrow 130. Entrained solids are removed from the hot gas in the cyclone separator and withdrawn as indicated by arrow 132. The sulfur dioxide gas after removal of the entrained solids in cyclone separator T is advanced to reduction furnace R as indicated by arrow 134. Reducing gases are fed into reducing furnace R as indicated by arrow 136. This reducing gas can be of the same composition as the reducing gas utilized in decomposer F of the process illustrated in Figure 1.
The reducing gases react with the cleaned S02 ga~ from the cyclone separator T to generate a hot product ga~ that contains elemental sulfur, hydrogen sulfide, sulfur dioxide, and other compounds which involve chemical reactions such a~ the following:
23) CH4 + 2S02 = 2Sx* + C02 + 2H20 24) CH + S0 = H2S + C0 + H
25) CH + S0 = COS + H 0 + H
26) C H + 2S02 = 2H2S + 2C0 + H2 28) 2H2 + S2 = S + 2H20 29) 3C0 ~ S02 = COS + 2C02 30) 2C0 + S0~ = S + 2C02 31) 2H2S + S02 = 3Sx + 2H20 32) 2COS + S02 = 3S + 2C02 33) COS + H20 = H2S + C2 34) C0 + H20 = H2 + C2 1~46734 * Where Sx = Sl on the basis of stoichiometry, but the actual sulfur may be present in the product gas in the form of S2, S4, S6, etc.
The reducing gases used in reduction furnace R generally will contain CO and/or H2, and generally will be obtained from the partial combustion of commercial fuels with air. We have found, however, that raw hydrocarbon reducing agents, such as methane, ethane, etc., can be utilized in the reduction as illustrated above in equations 23-26 when the temperature of the reaction zone in the reduction furnace is higher than about 1100C. Up to about 40% or more of the sulur content of the sulfur dioxide product gas from the decomposer can be converted to elemental sulfur in reduction furnace R. This elemental sulfur is recovered as liquid sulfur by advancing the product gas from reduction furnace R to condenser U as indicated by arrow 138 and cooling the product gas therein to temperatures below the dew point of the sulfur. Liquid sulfur is recovered from con-denser U as indicated by arrow 140.
The amount of reducing gas supplied to reduction furnace R is adjusted to provide a reducing agent concentration equal in quantity to that required by the stoichiometry of the reactions.
When this control i9 maintained, the cooled gas exiting from the condenser U will contain H2S and SO2 in the ratio of 2:1. This ratio is desirable ~ince it is the ratio required to recover the remaining sulfur by the catalytic reactions of the conventional Claus process as indicated by equation 31 above. This cooled gas from condenser U is fed to a conventional Claus plant J as indicated by arrow 142 where the usual catalytic reactions can be effected to produce additional sulfur as indicated by arrow 144.
The remaining small quantities of entrained solids are carried through the process and are in the product gas from condenser U. Because any entrained solids will be entrapped in the interstices of the catalys~ and this obstructs the further passage of the gas, they must be removed from the gas stream.
We have found that partially cooling and scrubbing the product gas, and condensing the sulfur vapor in contact with liquid sulfur in equipment such as Venturi scrubbers (not shown in Fig. 2), will remove the remaining solids and enable operation of the Claus plant in the conventional manner. Solids such as silicates and sulfates which may be present in the liquid sulfur product can be removed by contacting the liquid sulfur with super-heated water which effects an extraction of the solids from the sulfur into the water phase. Alternatively, filtration of liquid sulfur can be utilized to remove any solids present.
The embodiment in Figure 3 includes the u~e of optional and generally preferred agglomerator and sizing unit~ although these are not essential elements of the process of this invention.
The agglomerating and sizing units illustrated in Figure 3 result in the formation of iron-bearing solids that are suitable in both particle size and mechanical properties for contacting with the gases containing the oxides of sulfur in fixed bed, fluid bed and/or transport reactors. In processes that involve the contacting of solids with gases, finely divided solids such as those smaller than 10 microns are difficult to separate from the gases. Moreover, finely divided solids that lV~6734 contain sulfate compounds are known to agglomerate into lumps of unmanageable size and/or to accumulate on the walls of the equipment under certain process conditions. secause these accumulations frequently interfere with the mechanical performance of the equipment, the process of this invention provides for separation of the finely divided solids and for the production of sized and classified solids that are eqsentially free of troublesome particles of both oversize and undersize solids.
Ferrous sulfate, in the form of a dry solid, solution, slurry or wet crystals, or combinations of theqe, is fed to an agglomerator A as indicated by arrow 12. Agglomerator A may be any of the well-known type of mixers wherein wet and dry materials are agglomerated during mixing. Dry iron oxide is also fed to agglomerator A as indicated by arrow 14 or by arrow 48 when the iron oxide is recycled from decomposer F. obvi the quantities of sulfate and dry iron oxide are proportioned in order that agglomeration will occur. Water and/or sulfuric acid may be added.
Agglomerates of iron sulfate and iron oxide are dis-charged from agglomerator A to sizer B as indicated by arrow 16.
Sizer B may be any of the known mechanical sizing systems con-taining equipment such as screens, pneumatic sizers, etc. Over-sized agglomerates are fed to a mechanical crusher C as indicated by arrow 18. Oversize agglomerates are reduced in size to maximum size particles generally that are between 4 and 40 mesh and preferably betweén about 10 and 20 mesh and recycled as indicated by arrow 20 to sizer B. Undersized particles are fed as indicated by arrow 24 to a fluidized bed drier D.
104f~734 Hot gases essentially free of sulfur are fed to drier D as indicated by arrow 26. Although Figure 3 shows the hot gases originating in absorber E and/or cyclone separator S, the hot gases obviously can be derived from other sources not shown.
The fluid bed drier is operated at a temperature between 80 and 250C., and preferably between 120 and 180C. ~he hot gases pass through drier D, contact the iron sulfate and iron oxide, and evaporate water to a stoichiometric ratio of water-to-iron . sulfate in the product that is between 0.1 and 4.5, and preferably between 0.3 and 3Ø This dried product of desired particle size is fed as indicated by arrow 28 to absorber E.
The flow rate of the hot gases through the fluid bed drier D is regulated to remove essentially all of the finely divided solids which are carried into the drier from the sizer.
The solid fines such as those less than 10 microns are separated from the gas exiting from the drier as indicated by arrow 25 in cyclone separator S, and the fines are recycled to the agglomerator as indicated by arrow 29.
The agglomerated particles of hydrated iron sulfate and iron oxide are contacted in absorber E by a high temperature gas entering absorber E as indicated by arrow 30. The high temperature gas entering absorber E contains oxygen and sulfur.
The operating temperature of absorber E may be between 2504 and 440C., and preferably between 325 and 450C. The hot gases entering absorber E are waste gases fed into incinerator I as indicated by arrow 70.
The spent sorbent from absorber E is fed to decomposer F as indicated by arrow 32 where it is contacted with hot re-ducing gases. In Figure 3, the reducing gas is generated in situ by a partial combustion of process fuel and air fed into decomposer i~46734 F as indicated by arrows 34 and 38, respectively. The process air passes through air preheater H as indicated by arrow 40. The reactions between a process fuel and the proceæs air generating the hot reducing gas utilized in decomposer F have been described above as reactions 10-13.
The magnetite from decomposer F can be recycled either to absorber E as indicated by arrow 46, to agglomerator ~ as indicated by arrow 48, and/or fed to the sulfur stripper G as indicated by arrow 44. The magnetite which is recycled to absorber E can be oxidized at a low temperature prior to being fed to absorber E although this embodiment is not shown in Figure 3.
Sulur stripper G is supplied with air as indicated by arrow 52. This air is supplied in controlled quantities and the magnetite is oxidized to provide heat for removal of sulfur by reactions in the sulfur stripper such as described with respect to the embodiment of Figure 1. High purity commercial quality iron oxide, principally a mixture of magnetite and hematite, is withdrawn from sulfur stripper G as indicated by arrow 54.
A hot sulfur-bearing gas is discharged from sulfur stripper G as indicated by line 58 which can be recycled to absorber E directly as indicated by arrow 62 or the gas discharged from ~ulfur stripper G can be passed through air preheater H as indicated by arrow 60 and then recycled to absorber E as indicated by arrows 66 and 62. The hot sulfur-bearing gas fed to air pre-heater H as indicated by arrow 60 is used to heat combustion air flowing to air preheater H as indicated by arrow 40. The hot sulfur-bearing gas is not mixed with the combustion air but is simply used to transfer heat to the decomposition reactions.
~046734 ; Sulfur-bearing waste gas from an industrial operation is fed to incinerator I as indicated by line 70. This sulfur-bearing waste gas can be mixed and fired with the air and fuel entering incinerator I às indicated by arrows 72 and 74, respectively. The amount of air and fuel supplied to incinerator I is adjus~ed depending upon the temperature of the sulfur-bearing waste gases entering through line 70, and depending upon the desired temperature of the feed gas to absorber E. Sulfur-bearing hot gases are discharged from incinerator I as indicated by line 76. Some or all of these gases may be discharged as indicated by arrow 78 into line 62 for feeding directly to absorber E. Some or all of these hot gases may also be fed as indicated by line 80 into air preheater H for use in preheating combustion air. These sulfur-bearing gases are also discharged from air pre-heater H as indicated by arrow 66. Air heated within air pre-heater H is fed to decomposition device F as indicated by arrow 38. The line represented by numeral 38 may also be connected directly with process air line 40, but in thi~ instance cold air and additional fuel will be used in the decomposition reactions.
Sulfur dioxide gas produced in decomposition unit F
is discharged therefrom as indicated by arrow 84 to Claus plant J. When it is available, hydrogen sulfide gas may be fed to the Claus plant J as indicated by line 86. Hydrogen sulfide and sulfur dioxide when contacted with the catalyst of the Claus plant will react to produce water and elemental sulfur.
The elemental sulfur produced within Claus plant J isdischarged as indicated by line 90. The elemental sulfur i~ of commercial quality. Tail gas from Claus plant J is discharged as indicated by arrow 92 and fed to incinerator I where it is fired with air and fuel.
The arrangement of Fig. 4 i5 for the production of sulfuric acid rather than elemental sulfur. Like parts have been given like numerals and letters as in Fig. 3. In the arrangement of Fig. 4, instead of feeding sulfur dioxide gas from decomposer F to a Claus plant, all or a portion of such gas is fed as indicated by arrow 102 to air preheater H. Alternatively, all or a portion of the sulfur dioxide gas may be fed directly as indicated by arrow 104 to an acid plant K. In this instance, however, gas will be cooled and cleaned in the acid plant. Sulfur dioxide gas used in air preheater H to heat process air going to decompos~er F is simply discharged to the acid plant K as indicated by arrow 106. Instead of feeding hot sulfur-bearing gas from sulfur ~tripper G to air preheater H as in Fig. 3, the arrangement of Fig. 4 provide~ for feeding of such hot sulfur-gearing gas to gas heater I. All or a portion of the sulfur-bearing gas from the sulfur stripper G as required for acid production may be fed as indicated by line 108 over to line 104 to acid plant K. All or the remaining portion of the sulfur-bearing gas from the sulfur stripper G may be fed through line 62 to absorber E. Alternatively, all or any desired fraction of the sulfur-bearing gas from sulfur stripper G may be directed through the gas heater as indicated by arrow 112.
~046734 The sulfur dioxide fed to acid plant K will be cleaned and converted into sulfuric acid by a conventional process.
Prior to conversion to sulfuric acid, however, the hot sulfur dioxide-bearing gaseC must be treated to remove any reducing gases therein. Air in excess of that required to oxidize all of the remaining combustible material in the product ga~es from decomposer F is mixed with said product gases and reacted to form a hot product gas that contains both sulfur dioxide and oxygen. This hot gas iæ then subjected to a further cleaning operation in conventional equipment such as a cyclone separator, cooled and converted to sulfuric acid in acid plant K. A
sulfur-bearing tail gas i8 recovered from acid plant K as shown by arrow 118. ~his tail gas is recycled to absorber E as indicated by arrow 30. The sulfuric acid product from acid plant K is recovered as a commercial product as indicated by arrow 116.
It will be recognized that the iron oxide used in the process may be obtained from the process of the invention by the conversion of ferric sulfate to iron oxide and sulfur dioxide gas, and this iron oxide is more absorbent. In addition, it will be recognized that iron oxide of sufficient purity is produced to enable sale of commercial quality iron oxide for use in manu-facturing ~teel or the like. In addition, the improved process of the present invention removes the troublesome fraction of the sulfur from sulfur-bearing gas to provide an effluent of acceptable quality.
When the feed material to the process of the invention is ferrous sulfate from industrial wastes, both the sul~ur content from the waste gases and the sulfur and iron content of the ferrous sulfate will be recovered by the process as products of commercial quality. The sulfur can be recovered as either elemental sulfur or sulfuric acid, and the iron ig recovered as iron oxide. Rather than recycle the iron oxide obtained, it is sold as a u~eful product of the process and additional waste ferrous sulfate is fed to the process. The invention, therefore, provides a useful method for disposing of waste ferrous sulfate.
Although the above description of the process with respect to Figures 1 to 4 inclusive has involved the use of sorbents that contain iron as the only metal component, we have found that metals such as calcium and/or magnesium can be used in substitution for part of the iron in the sorbent. Moreover, when one or more of these alternative metals is utilized in combination with iron, and is blended intimately by procedures such as co-precipitation with iron during preparation of the sorbent, we have found that certain desirable properties of the alternative metals are acquired by the sorbent.
The above findings have enabled the preparation of metal oxide bearing mixtures that both contain iron and when used as sorbents in the basic procedures of this invention, are capable o~ desulfurizing gases under a wider variety of conditions. Moreover, these mixed sorbents enable both desulfur-ization of gases that contain either oxygen or reducing agents, and both recovery of the sulfur and regeneration of the sorbent by the combined procedures of this invention.
~046~34 soth the use of lime (CaO) as a sorbent, and the desulfurization of both a gas that contains reducing agents and a gas containing oxygen, are illustrated on the flow diagram of Figure 5. Details of the combined process will be discussea with reference to Figure 5 as follows .
A sulfur bearing reducing gas generated frsm the partial combustion of coal with air and steam atabout 800C., and which contains hydrogen and carbon monoxiae~ is fed to desulfurizer N as indicated by arrow 300. The gas is processed in contact with a solid sorbent ~hat contains both iron and lime, contains lime as a major component, and is prepared by t~e co-precipitation, agglomeration, and sizing procedures of this invention.
The above sorbent solids are supplied to the desulfur-izer as indicated by arrow 339 at a weight ratio that provides lime and iron oxide in excess of the sulfur content of the gas on a stoichiometric basis, and provides for the removal of sulfur from the gas by reactions such as the following:
35) CaO + H2S = CaS + H2O
) CaFe2o4 ~ 3H2S + H2 = CaS + 2FeS + 4H2O
The desulfurized reducing gas is removed from the desulfurizer as indicated by arrow 304, is available for combustion as a fuel for power production, and is suitable for discharge to the atmosphere as a "pollution free" effluent product from the process of this invention.
The spent sorbent from the desulfurizer still containingunreacted CaO is charged to absorber E as indicated by arrow 306 and contacted with gases containing excess oxygen to generate calcium sulfate by reactions such as the following:
37) CaS + 202 = cas04 38) 4FeS ~ 702 = 2Fe o + 4so2 39~ 2CaO + 2SO2 + 2 = 2CaS04 ) e2 3 CaFe2O4 The oxidizing gas supplied to the absor~er as indicated by arrow 316 is a tail gas from sulfuric acid plant K and/or process air as indicated by arrow 334. AS indicated by arrow 302, additional sulfur and oxygen-bearing gas can be ~upplied to the absorber from an outside source such as a flue gas. The product gas from the absorber (arrow 320), containing oxygen but essentially free of sulfur, is available for power production, and is suitable for discharge to the atmosphere as a pollution free effluent. The product solids from the absorber containing iron compounds and both CaO and CaSO4, is charged to decomposer F, as indicated by arrow 322, and reacted at a temperature within the range of from 600 to 1000C. with both reducing gas and air fed to the decomposer as indicated by arrows 332 and 335, to produce lime and sulfur dioxide by reactions such as the following:
Al) CaSO + CO = CaO + So2 + CO2 42) CaSO4 + H2 = CaO + SO + H2O
43) 2CO + 2 = 2CO2 + Heat 44) 2H + O = 2H O + Heat The product gas from the decomposer containing sulfur dioxide i8 charg~d as indicated by arrow 340 to a conventional sulfuric acid plant K. The product solids from the decomposer, containing CaO as a major component and iron compounds as a minor component, is recycled to the desulfurizer, as indicated by arrow 339.
104~734 The sulfur dioxide bearing feed gas to the sulfuric : acid plant, as indicated by arrow 340, is cooled, cleaned~
combined with process air, and a major fraction of the sulfur content is converted to ~ulfuric acid of commercial quality.
The sulfuric acid is recovered as a product of the process, as indicated by arrow 346.
The tail gas from the acid plant, containing oxygen and traces of oxides of sulfur, is recycled as indicated by arrow 316 to the absorber both for rem~val of the objectionable remaining sulfur and for uYe as both a cooling agent and a source of oxygen for the exothermic reactions of the absorber process.
As indicated by arrow 326, a stream of solid8 also is removed from the absorber and charged to sorbent preparer M where these solids are reacted with water for the purpose of "slaking"
the lime to disintegrate the densified particles, to produce Ca(OH)2 for use as cement between particles in the agglomeration process, and to regenerate the sorbent and maintain its activity at a level that is acceptable for use in the desulfurization reactions.
As indicated by arrows 310 and 312, streams containing both limestone, iron and water are imported for use in the sorbent preparation procedures of the combined process. The iron is either imported as iron sulfate or reacted with recycled sulfuric acid and water to generate a solution of iron sulfate as part of the sorbent preparation process. The solution of iron sulfate is reacted with limestone to generate wet solids containing co-precipitated iron and calcium hydroxides, sulfates and/or carbonates for use in preparation of the sorbent solids by the 1~)46734 agglomeration, sizing, drying and classification procedures of this invention, as previously described. A stream of solids in addition to that described above is removed from the decomposer as indicated by arrow 338 and discarded as waste. Both the calcium and iron in this stream must be replaced by calcium and iron from imported feed materials. In this process, the size of this stream a~d the demand for imported feed materials may be determined by the quantity of silica that is present in the reducing gases in the form of fly ash and reacts with lime to produce inert calcium silicates in the sorbent.
Although the invention has been shown and described with respect to certain preferred embodiments, equivalent altera-tions and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the claims.
The above descriptions have illustrated the process of the invention with regard to the extraction of ~ulfur from a gas containing sulfur and oxygen and from gase~ containing sulfur and reducing agents. As mentioned previously, the procedure can be utilized for removing the oxides of sulfur from waste gas streams and various industrial processes such as the smelting of sulfur-bearing minerals, the refining of sulfur containing ~rude oils, and from stack gases of industrial plants such as power generating stations.
The sulfur and oxygen-bearing gases pass through absorber E and the sulfur and oxygen react with the iron oxides and ferrous sulfate to form principally ferric sulfate. The ~046734 product gas from the absorber i~ essentially free of sulfur and is suitable for discharge into the atmosphere as a pollution-free effluent as indicated by arrow 104.
~he spent sorbent from absorber E is fed to de~omposer F as indicated by arrow 106. The spent sorbent in decomposer F
is contacted with hot reducing gases containing CO and ~2 fed into the decomposer as indicated by arrow 105. Because magnetite is the desired decomposition product, the temperature of the decomposition and concentration of the reducing gas utilized are interrelated as will be described below. The temperature of the decomposition may vary from between about 300C. to about 800C. although temperatures from about 400C. to about 700C.
are preferred. Any equipment in which contact can be effected between a gas and a solid may be used for the decomposition. For example, fixed bed, moving bed and fluid bed techniques may be utilized. It has been observed that decomposition accomplished at lower temperatures results in a more active oxide product.
The hot reducing gases utilized in the decomposition process normally contain both CO and H as e~sential components, and normally are generated by the partial combustion of commer-cial fuels with air, and/or with preheated air. These gases normally are generated at high temperatures, and are used in the decompo~ition process at much lower temperature~. They normally provide both heat and chemical reagents for use in the reactions of the decomposition proce~s. Moreover, they normally are generated in separate equipment attached to the decomposition reactor, but when certain types of commercial fuel are available for use in the process, the gas generation may be accompli~hed in the decompo~ition reactor.
The hot reducing gases utilized in the process of the invention may be generated by partial combustion of commercial _g_ fuel with air in chemical reactions such as the following reactions:
11) CH4 + 2 ~CO ~2 2 12) 2C ~ 2 = 2CO
) 2 CO2 H2 In the low temperature decomposition process of this invention, the hot gas product from the above gasification reactions is processed in contact with sulfate-bearing solids in decomposer F. The gas is utilized both a~ a source of reducing agent and a source of heat for the decomposition process. More-over, the composition and temperature of the gas in the reaction zone of the process determines the composition and many of the properties of both the gas and solid products from the process.
For example, the sulfur sorbent property of the oxides obtained by the low temperature decomposition process of the invention is significantly improved.
When the product gases from the reaction zone of the decompo~ition process are held between limits of composition and temperature that generate magnetite as a major component of the iron-bearing product, the decomposition reactions can be carried out both at temperatures and with ratios of fuel and air that are unusually low. This results in the generation of a product gas which is concentrated in sulfur dioxide. The concentration of reducing agent~ in the feed gases utilized should be quch that the product gas is in equilibrium composition with the magnetite at these temperatures.
The magnetite-bearing product obtained by the above-described low temperature decomposition reaction is assumed to be produced by reactions such as the following:
10467;~4 14) 3FeS04 + 2H2 = Fe34 + 2H2 2 15) 3FeS04 ~ 2co = Fe304 + 2Co2 + 3So 4~3 1OH2 = 2Fe304 + 1H2 + 9S0 17) 3Fe (S0 ) + lOC0 = 2Fe 0 1 lOC0 + 9S0 18) 3Fe203 I H2 = 2Fe O + H20 19) 3Fe203 + Co = 2Fe30 + Co The magnetite obtained by decomposition of the sulfates in decomposer F can be recycled to absorber E as indicated by arrow 112 or advanced to sulfur stripper G as indicated by arrow 110. Air or oxygen i~ supplied to sulfur stripper G in controlled quantities as indicated by arrow 107, and the magnetite i~
oxidized to pro~iae heat for re val of any sulfur present by reactions such as the fotlowing:
2(S04)3 ~ Heat = Fe203 + 3S0 22) 2Fe304 ~ S03 - 2Fe23 2 High purity commercial quality iron oxide is withdrawn from sulfur .. ~tripper G as indicated by arrow 121. The re val of the objectionable sulfur generally does not require complete conversion of the magnetite to hematite, and the purified product generally will contain both magnetite and hematite.
A hot sulfur-bearing gas is discharged from sulfur stripper G and may be recycled to absorber E as indicated by arrow 122.
The sulfur dioxide containing gas produced in decomposer F is discharged therefrom as indicated by line 108 and fed as indicated by line 114 to a Claus plant or as indicated by line 116 to an acid plant. In Claus plant J, the sulfur dioxide can be contacte~ with reducing agent~ and the hydrogen sulfide-bearing product gas contacted with a catalyst to produce water and elemental sulfur. The elemental sulfur is discharged from the Claus plant as indicated by line 118. The elemental sulfur produced in the Claus plant is of commercial quality.
A~ mentioned previously, the product gas exiting from S decomposer F contains sulfur dioxide in high concentrations. In order to effectively utilize this gas mixture in a sulfuric acid plant, the product gas from decomposer F is reacted with air in quantities that will both oxidize the reducing agents present and provide excess oxygen. This oxygen-bearing product gas is utilized as the feed gas in the acid plant.
The magnetite obtained by the decomposition of the sulfates in decomposer F and recycled to absorber E can be made more active toward the oxides of sulfur by subjecting the magnetite to a low temperature oxidation treatment (not shown in Fig. 1). When the magnetite is oxidi~ed at a temperature below about 450C., it is converted to a product (principally hematite) which i~ highly reactive towaras absorption of the oxides of sulfur. It is not known preci~ely why this low temperature pre-oxidation produces a more reactive iron oxide. At higher oxida-tion temperatures,the effectiveness of the product as a ~orbentis minim~zed.
The oxidation of the magnetite-bearing solids can al80 occur in absorber E since the gas entering the absorber contain oxygen as well as sulfur. The magnetite-bearing solid obtained from the decomposition zone is advanced directly to the absorber as indicated by line 112 where it is contacted with a gaseous mixture containing sulfur and oxygen. The oxygen converts the magnetite to an active hematite sorbent which then reacts with S2 in the gas.
Figure 2 shows another arrangement of an improved process of the present invention for producing commercial quality iron oxides and elemental sulfur. Like parts have been given the same numerals and letters as those in Figure 1. This example illustrates the process wherein both iron oxide and ferrous sulfate comprise the sorbent bu~ the process also may be used with either of the sorbents used alone.
The S02 gas from decomposer F is advanced to cyclone separator T as indicated by arrow 130. Entrained solids are removed from the hot gas in the cyclone separator and withdrawn as indicated by arrow 132. The sulfur dioxide gas after removal of the entrained solids in cyclone separator T is advanced to reduction furnace R as indicated by arrow 134. Reducing gases are fed into reducing furnace R as indicated by arrow 136. This reducing gas can be of the same composition as the reducing gas utilized in decomposer F of the process illustrated in Figure 1.
The reducing gases react with the cleaned S02 ga~ from the cyclone separator T to generate a hot product ga~ that contains elemental sulfur, hydrogen sulfide, sulfur dioxide, and other compounds which involve chemical reactions such a~ the following:
23) CH4 + 2S02 = 2Sx* + C02 + 2H20 24) CH + S0 = H2S + C0 + H
25) CH + S0 = COS + H 0 + H
26) C H + 2S02 = 2H2S + 2C0 + H2 28) 2H2 + S2 = S + 2H20 29) 3C0 ~ S02 = COS + 2C02 30) 2C0 + S0~ = S + 2C02 31) 2H2S + S02 = 3Sx + 2H20 32) 2COS + S02 = 3S + 2C02 33) COS + H20 = H2S + C2 34) C0 + H20 = H2 + C2 1~46734 * Where Sx = Sl on the basis of stoichiometry, but the actual sulfur may be present in the product gas in the form of S2, S4, S6, etc.
The reducing gases used in reduction furnace R generally will contain CO and/or H2, and generally will be obtained from the partial combustion of commercial fuels with air. We have found, however, that raw hydrocarbon reducing agents, such as methane, ethane, etc., can be utilized in the reduction as illustrated above in equations 23-26 when the temperature of the reaction zone in the reduction furnace is higher than about 1100C. Up to about 40% or more of the sulur content of the sulfur dioxide product gas from the decomposer can be converted to elemental sulfur in reduction furnace R. This elemental sulfur is recovered as liquid sulfur by advancing the product gas from reduction furnace R to condenser U as indicated by arrow 138 and cooling the product gas therein to temperatures below the dew point of the sulfur. Liquid sulfur is recovered from con-denser U as indicated by arrow 140.
The amount of reducing gas supplied to reduction furnace R is adjusted to provide a reducing agent concentration equal in quantity to that required by the stoichiometry of the reactions.
When this control i9 maintained, the cooled gas exiting from the condenser U will contain H2S and SO2 in the ratio of 2:1. This ratio is desirable ~ince it is the ratio required to recover the remaining sulfur by the catalytic reactions of the conventional Claus process as indicated by equation 31 above. This cooled gas from condenser U is fed to a conventional Claus plant J as indicated by arrow 142 where the usual catalytic reactions can be effected to produce additional sulfur as indicated by arrow 144.
The remaining small quantities of entrained solids are carried through the process and are in the product gas from condenser U. Because any entrained solids will be entrapped in the interstices of the catalys~ and this obstructs the further passage of the gas, they must be removed from the gas stream.
We have found that partially cooling and scrubbing the product gas, and condensing the sulfur vapor in contact with liquid sulfur in equipment such as Venturi scrubbers (not shown in Fig. 2), will remove the remaining solids and enable operation of the Claus plant in the conventional manner. Solids such as silicates and sulfates which may be present in the liquid sulfur product can be removed by contacting the liquid sulfur with super-heated water which effects an extraction of the solids from the sulfur into the water phase. Alternatively, filtration of liquid sulfur can be utilized to remove any solids present.
The embodiment in Figure 3 includes the u~e of optional and generally preferred agglomerator and sizing unit~ although these are not essential elements of the process of this invention.
The agglomerating and sizing units illustrated in Figure 3 result in the formation of iron-bearing solids that are suitable in both particle size and mechanical properties for contacting with the gases containing the oxides of sulfur in fixed bed, fluid bed and/or transport reactors. In processes that involve the contacting of solids with gases, finely divided solids such as those smaller than 10 microns are difficult to separate from the gases. Moreover, finely divided solids that lV~6734 contain sulfate compounds are known to agglomerate into lumps of unmanageable size and/or to accumulate on the walls of the equipment under certain process conditions. secause these accumulations frequently interfere with the mechanical performance of the equipment, the process of this invention provides for separation of the finely divided solids and for the production of sized and classified solids that are eqsentially free of troublesome particles of both oversize and undersize solids.
Ferrous sulfate, in the form of a dry solid, solution, slurry or wet crystals, or combinations of theqe, is fed to an agglomerator A as indicated by arrow 12. Agglomerator A may be any of the well-known type of mixers wherein wet and dry materials are agglomerated during mixing. Dry iron oxide is also fed to agglomerator A as indicated by arrow 14 or by arrow 48 when the iron oxide is recycled from decomposer F. obvi the quantities of sulfate and dry iron oxide are proportioned in order that agglomeration will occur. Water and/or sulfuric acid may be added.
Agglomerates of iron sulfate and iron oxide are dis-charged from agglomerator A to sizer B as indicated by arrow 16.
Sizer B may be any of the known mechanical sizing systems con-taining equipment such as screens, pneumatic sizers, etc. Over-sized agglomerates are fed to a mechanical crusher C as indicated by arrow 18. Oversize agglomerates are reduced in size to maximum size particles generally that are between 4 and 40 mesh and preferably betweén about 10 and 20 mesh and recycled as indicated by arrow 20 to sizer B. Undersized particles are fed as indicated by arrow 24 to a fluidized bed drier D.
104f~734 Hot gases essentially free of sulfur are fed to drier D as indicated by arrow 26. Although Figure 3 shows the hot gases originating in absorber E and/or cyclone separator S, the hot gases obviously can be derived from other sources not shown.
The fluid bed drier is operated at a temperature between 80 and 250C., and preferably between 120 and 180C. ~he hot gases pass through drier D, contact the iron sulfate and iron oxide, and evaporate water to a stoichiometric ratio of water-to-iron . sulfate in the product that is between 0.1 and 4.5, and preferably between 0.3 and 3Ø This dried product of desired particle size is fed as indicated by arrow 28 to absorber E.
The flow rate of the hot gases through the fluid bed drier D is regulated to remove essentially all of the finely divided solids which are carried into the drier from the sizer.
The solid fines such as those less than 10 microns are separated from the gas exiting from the drier as indicated by arrow 25 in cyclone separator S, and the fines are recycled to the agglomerator as indicated by arrow 29.
The agglomerated particles of hydrated iron sulfate and iron oxide are contacted in absorber E by a high temperature gas entering absorber E as indicated by arrow 30. The high temperature gas entering absorber E contains oxygen and sulfur.
The operating temperature of absorber E may be between 2504 and 440C., and preferably between 325 and 450C. The hot gases entering absorber E are waste gases fed into incinerator I as indicated by arrow 70.
The spent sorbent from absorber E is fed to decomposer F as indicated by arrow 32 where it is contacted with hot re-ducing gases. In Figure 3, the reducing gas is generated in situ by a partial combustion of process fuel and air fed into decomposer i~46734 F as indicated by arrows 34 and 38, respectively. The process air passes through air preheater H as indicated by arrow 40. The reactions between a process fuel and the proceæs air generating the hot reducing gas utilized in decomposer F have been described above as reactions 10-13.
The magnetite from decomposer F can be recycled either to absorber E as indicated by arrow 46, to agglomerator ~ as indicated by arrow 48, and/or fed to the sulfur stripper G as indicated by arrow 44. The magnetite which is recycled to absorber E can be oxidized at a low temperature prior to being fed to absorber E although this embodiment is not shown in Figure 3.
Sulur stripper G is supplied with air as indicated by arrow 52. This air is supplied in controlled quantities and the magnetite is oxidized to provide heat for removal of sulfur by reactions in the sulfur stripper such as described with respect to the embodiment of Figure 1. High purity commercial quality iron oxide, principally a mixture of magnetite and hematite, is withdrawn from sulfur stripper G as indicated by arrow 54.
A hot sulfur-bearing gas is discharged from sulfur stripper G as indicated by line 58 which can be recycled to absorber E directly as indicated by arrow 62 or the gas discharged from ~ulfur stripper G can be passed through air preheater H as indicated by arrow 60 and then recycled to absorber E as indicated by arrows 66 and 62. The hot sulfur-bearing gas fed to air pre-heater H as indicated by arrow 60 is used to heat combustion air flowing to air preheater H as indicated by arrow 40. The hot sulfur-bearing gas is not mixed with the combustion air but is simply used to transfer heat to the decomposition reactions.
~046734 ; Sulfur-bearing waste gas from an industrial operation is fed to incinerator I as indicated by line 70. This sulfur-bearing waste gas can be mixed and fired with the air and fuel entering incinerator I às indicated by arrows 72 and 74, respectively. The amount of air and fuel supplied to incinerator I is adjus~ed depending upon the temperature of the sulfur-bearing waste gases entering through line 70, and depending upon the desired temperature of the feed gas to absorber E. Sulfur-bearing hot gases are discharged from incinerator I as indicated by line 76. Some or all of these gases may be discharged as indicated by arrow 78 into line 62 for feeding directly to absorber E. Some or all of these hot gases may also be fed as indicated by line 80 into air preheater H for use in preheating combustion air. These sulfur-bearing gases are also discharged from air pre-heater H as indicated by arrow 66. Air heated within air pre-heater H is fed to decomposition device F as indicated by arrow 38. The line represented by numeral 38 may also be connected directly with process air line 40, but in thi~ instance cold air and additional fuel will be used in the decomposition reactions.
Sulfur dioxide gas produced in decomposition unit F
is discharged therefrom as indicated by arrow 84 to Claus plant J. When it is available, hydrogen sulfide gas may be fed to the Claus plant J as indicated by line 86. Hydrogen sulfide and sulfur dioxide when contacted with the catalyst of the Claus plant will react to produce water and elemental sulfur.
The elemental sulfur produced within Claus plant J isdischarged as indicated by line 90. The elemental sulfur i~ of commercial quality. Tail gas from Claus plant J is discharged as indicated by arrow 92 and fed to incinerator I where it is fired with air and fuel.
The arrangement of Fig. 4 i5 for the production of sulfuric acid rather than elemental sulfur. Like parts have been given like numerals and letters as in Fig. 3. In the arrangement of Fig. 4, instead of feeding sulfur dioxide gas from decomposer F to a Claus plant, all or a portion of such gas is fed as indicated by arrow 102 to air preheater H. Alternatively, all or a portion of the sulfur dioxide gas may be fed directly as indicated by arrow 104 to an acid plant K. In this instance, however, gas will be cooled and cleaned in the acid plant. Sulfur dioxide gas used in air preheater H to heat process air going to decompos~er F is simply discharged to the acid plant K as indicated by arrow 106. Instead of feeding hot sulfur-bearing gas from sulfur ~tripper G to air preheater H as in Fig. 3, the arrangement of Fig. 4 provide~ for feeding of such hot sulfur-gearing gas to gas heater I. All or a portion of the sulfur-bearing gas from the sulfur stripper G as required for acid production may be fed as indicated by line 108 over to line 104 to acid plant K. All or the remaining portion of the sulfur-bearing gas from the sulfur stripper G may be fed through line 62 to absorber E. Alternatively, all or any desired fraction of the sulfur-bearing gas from sulfur stripper G may be directed through the gas heater as indicated by arrow 112.
~046734 The sulfur dioxide fed to acid plant K will be cleaned and converted into sulfuric acid by a conventional process.
Prior to conversion to sulfuric acid, however, the hot sulfur dioxide-bearing gaseC must be treated to remove any reducing gases therein. Air in excess of that required to oxidize all of the remaining combustible material in the product ga~es from decomposer F is mixed with said product gases and reacted to form a hot product gas that contains both sulfur dioxide and oxygen. This hot gas iæ then subjected to a further cleaning operation in conventional equipment such as a cyclone separator, cooled and converted to sulfuric acid in acid plant K. A
sulfur-bearing tail gas i8 recovered from acid plant K as shown by arrow 118. ~his tail gas is recycled to absorber E as indicated by arrow 30. The sulfuric acid product from acid plant K is recovered as a commercial product as indicated by arrow 116.
It will be recognized that the iron oxide used in the process may be obtained from the process of the invention by the conversion of ferric sulfate to iron oxide and sulfur dioxide gas, and this iron oxide is more absorbent. In addition, it will be recognized that iron oxide of sufficient purity is produced to enable sale of commercial quality iron oxide for use in manu-facturing ~teel or the like. In addition, the improved process of the present invention removes the troublesome fraction of the sulfur from sulfur-bearing gas to provide an effluent of acceptable quality.
When the feed material to the process of the invention is ferrous sulfate from industrial wastes, both the sul~ur content from the waste gases and the sulfur and iron content of the ferrous sulfate will be recovered by the process as products of commercial quality. The sulfur can be recovered as either elemental sulfur or sulfuric acid, and the iron ig recovered as iron oxide. Rather than recycle the iron oxide obtained, it is sold as a u~eful product of the process and additional waste ferrous sulfate is fed to the process. The invention, therefore, provides a useful method for disposing of waste ferrous sulfate.
Although the above description of the process with respect to Figures 1 to 4 inclusive has involved the use of sorbents that contain iron as the only metal component, we have found that metals such as calcium and/or magnesium can be used in substitution for part of the iron in the sorbent. Moreover, when one or more of these alternative metals is utilized in combination with iron, and is blended intimately by procedures such as co-precipitation with iron during preparation of the sorbent, we have found that certain desirable properties of the alternative metals are acquired by the sorbent.
The above findings have enabled the preparation of metal oxide bearing mixtures that both contain iron and when used as sorbents in the basic procedures of this invention, are capable o~ desulfurizing gases under a wider variety of conditions. Moreover, these mixed sorbents enable both desulfur-ization of gases that contain either oxygen or reducing agents, and both recovery of the sulfur and regeneration of the sorbent by the combined procedures of this invention.
~046~34 soth the use of lime (CaO) as a sorbent, and the desulfurization of both a gas that contains reducing agents and a gas containing oxygen, are illustrated on the flow diagram of Figure 5. Details of the combined process will be discussea with reference to Figure 5 as follows .
A sulfur bearing reducing gas generated frsm the partial combustion of coal with air and steam atabout 800C., and which contains hydrogen and carbon monoxiae~ is fed to desulfurizer N as indicated by arrow 300. The gas is processed in contact with a solid sorbent ~hat contains both iron and lime, contains lime as a major component, and is prepared by t~e co-precipitation, agglomeration, and sizing procedures of this invention.
The above sorbent solids are supplied to the desulfur-izer as indicated by arrow 339 at a weight ratio that provides lime and iron oxide in excess of the sulfur content of the gas on a stoichiometric basis, and provides for the removal of sulfur from the gas by reactions such as the following:
35) CaO + H2S = CaS + H2O
) CaFe2o4 ~ 3H2S + H2 = CaS + 2FeS + 4H2O
The desulfurized reducing gas is removed from the desulfurizer as indicated by arrow 304, is available for combustion as a fuel for power production, and is suitable for discharge to the atmosphere as a "pollution free" effluent product from the process of this invention.
The spent sorbent from the desulfurizer still containingunreacted CaO is charged to absorber E as indicated by arrow 306 and contacted with gases containing excess oxygen to generate calcium sulfate by reactions such as the following:
37) CaS + 202 = cas04 38) 4FeS ~ 702 = 2Fe o + 4so2 39~ 2CaO + 2SO2 + 2 = 2CaS04 ) e2 3 CaFe2O4 The oxidizing gas supplied to the absor~er as indicated by arrow 316 is a tail gas from sulfuric acid plant K and/or process air as indicated by arrow 334. AS indicated by arrow 302, additional sulfur and oxygen-bearing gas can be ~upplied to the absorber from an outside source such as a flue gas. The product gas from the absorber (arrow 320), containing oxygen but essentially free of sulfur, is available for power production, and is suitable for discharge to the atmosphere as a pollution free effluent. The product solids from the absorber containing iron compounds and both CaO and CaSO4, is charged to decomposer F, as indicated by arrow 322, and reacted at a temperature within the range of from 600 to 1000C. with both reducing gas and air fed to the decomposer as indicated by arrows 332 and 335, to produce lime and sulfur dioxide by reactions such as the following:
Al) CaSO + CO = CaO + So2 + CO2 42) CaSO4 + H2 = CaO + SO + H2O
43) 2CO + 2 = 2CO2 + Heat 44) 2H + O = 2H O + Heat The product gas from the decomposer containing sulfur dioxide i8 charg~d as indicated by arrow 340 to a conventional sulfuric acid plant K. The product solids from the decomposer, containing CaO as a major component and iron compounds as a minor component, is recycled to the desulfurizer, as indicated by arrow 339.
104~734 The sulfur dioxide bearing feed gas to the sulfuric : acid plant, as indicated by arrow 340, is cooled, cleaned~
combined with process air, and a major fraction of the sulfur content is converted to ~ulfuric acid of commercial quality.
The sulfuric acid is recovered as a product of the process, as indicated by arrow 346.
The tail gas from the acid plant, containing oxygen and traces of oxides of sulfur, is recycled as indicated by arrow 316 to the absorber both for rem~val of the objectionable remaining sulfur and for uYe as both a cooling agent and a source of oxygen for the exothermic reactions of the absorber process.
As indicated by arrow 326, a stream of solid8 also is removed from the absorber and charged to sorbent preparer M where these solids are reacted with water for the purpose of "slaking"
the lime to disintegrate the densified particles, to produce Ca(OH)2 for use as cement between particles in the agglomeration process, and to regenerate the sorbent and maintain its activity at a level that is acceptable for use in the desulfurization reactions.
As indicated by arrows 310 and 312, streams containing both limestone, iron and water are imported for use in the sorbent preparation procedures of the combined process. The iron is either imported as iron sulfate or reacted with recycled sulfuric acid and water to generate a solution of iron sulfate as part of the sorbent preparation process. The solution of iron sulfate is reacted with limestone to generate wet solids containing co-precipitated iron and calcium hydroxides, sulfates and/or carbonates for use in preparation of the sorbent solids by the 1~)46734 agglomeration, sizing, drying and classification procedures of this invention, as previously described. A stream of solids in addition to that described above is removed from the decomposer as indicated by arrow 338 and discarded as waste. Both the calcium and iron in this stream must be replaced by calcium and iron from imported feed materials. In this process, the size of this stream a~d the demand for imported feed materials may be determined by the quantity of silica that is present in the reducing gases in the form of fly ash and reacts with lime to produce inert calcium silicates in the sorbent.
Although the invention has been shown and described with respect to certain preferred embodiments, equivalent altera-tions and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the claims.
The above descriptions have illustrated the process of the invention with regard to the extraction of ~ulfur from a gas containing sulfur and oxygen and from gase~ containing sulfur and reducing agents. As mentioned previously, the procedure can be utilized for removing the oxides of sulfur from waste gas streams and various industrial processes such as the smelting of sulfur-bearing minerals, the refining of sulfur containing ~rude oils, and from stack gases of industrial plants such as power generating stations.
Claims (20)
1. A process for removing sulfur from gases containing sulfur and oxygen comprising the steps of:
a) providing a solid sorbent material selected from the class consisting of ferrous sulfate, iron oxide, mixtures thereof, b) advancing at least a portion of said absorbing solids to an absorption zone, c) contacting the sulfur and oxygen-bearing gas in the absorption zone with the sorbent at a temperature between 250°C to 550°C, d) reacting sulfur and oxygen in the gas with the solid sorbent to form ferric sulfate and to produce a gas that is reduced in sulfur content, e) recovering the gas from the absorption zone as a sulfur-free product of the process, f) withdrawing a portion of the ferric sulfate-bearing sorbent solids after contact with the sulfur-bearing gas, reacting the ferric sulfate in said withdrawn solids in contact with a hot reducing gas at a temperature of from about 300°C to about 700°C to produce magnetite in the decomposition product, and a product gas that contains sulfur dioxide, and h) recovering the concentrated sulfur dioxide-bearing gas and the magnetite-bearing product.
a) providing a solid sorbent material selected from the class consisting of ferrous sulfate, iron oxide, mixtures thereof, b) advancing at least a portion of said absorbing solids to an absorption zone, c) contacting the sulfur and oxygen-bearing gas in the absorption zone with the sorbent at a temperature between 250°C to 550°C, d) reacting sulfur and oxygen in the gas with the solid sorbent to form ferric sulfate and to produce a gas that is reduced in sulfur content, e) recovering the gas from the absorption zone as a sulfur-free product of the process, f) withdrawing a portion of the ferric sulfate-bearing sorbent solids after contact with the sulfur-bearing gas, reacting the ferric sulfate in said withdrawn solids in contact with a hot reducing gas at a temperature of from about 300°C to about 700°C to produce magnetite in the decomposition product, and a product gas that contains sulfur dioxide, and h) recovering the concentrated sulfur dioxide-bearing gas and the magnetite-bearing product.
2. The process of claim 1 wherein a portion of the recovered magnetite-bearing product is recycled to the absorption zone.
3. The process of claim 1 wherein the sulfur-bearing gas from the decomposition of the sulfates is used in the production of elemental sulfur.
4. The process of claim 1 wherein the sulfur dioxide recovered from the decomposition of the sulfate compounds is converted to sulfuric acid.
5. The process of claim 1 in which iron sulfate is a major component of the imported feed to the process and the magnetite-bearing product from the decomposition reactor is contacted with air in a sulfur stripper to remove residual sulfur from said magnetite.
6. A regenerative process for the desulfurization of gases that contain both oxygen and oxides of sulfur which comprises the steps of:
a) providing porous solids that contain iron-bearing compounds and are suitable in both particle size and chemical and mechanical properties for use as a sorbent for oxides of sulfur when contacted with sulfur and oxygen bearing gases in gas contacting equipment b) contacting the above solids with the sulfur-bearing gases in an absorber at a temperature from 250°C to 550°C, and at a weight ratio that provides metal oxides in the solids in excess of the sulfur content of the gas on a stoichiometric basis, and reacting the solids with the gas to produce both a product gas that is essentially free of sulfur and is suitable for discharge to the atmosphere as a pollution free effluent, and solids that contain both ferric sulfate and iron oxides, c) collecting the gas from the absorber as a product of the process, d) contacting the solids from the absorber with reducing gas and air in a decomposition reactor, e) maintaining both the temperature of the solids in the decomposition reactor between about 300°C and 700°C, and the composition of the gas between limits that generate both sulfur dioxide in the gas and magnetite as a major fraction of the iron in the solids, f) collecting the sulfur dioxide bearing gas as a product of the process, and g) recycling a fraction of the magnetite-bearing solids from the decomposition reactor to the absorber for use as a sorbent in the desulfurization of additional sulfur and oxygen-bearing gas.
a) providing porous solids that contain iron-bearing compounds and are suitable in both particle size and chemical and mechanical properties for use as a sorbent for oxides of sulfur when contacted with sulfur and oxygen bearing gases in gas contacting equipment b) contacting the above solids with the sulfur-bearing gases in an absorber at a temperature from 250°C to 550°C, and at a weight ratio that provides metal oxides in the solids in excess of the sulfur content of the gas on a stoichiometric basis, and reacting the solids with the gas to produce both a product gas that is essentially free of sulfur and is suitable for discharge to the atmosphere as a pollution free effluent, and solids that contain both ferric sulfate and iron oxides, c) collecting the gas from the absorber as a product of the process, d) contacting the solids from the absorber with reducing gas and air in a decomposition reactor, e) maintaining both the temperature of the solids in the decomposition reactor between about 300°C and 700°C, and the composition of the gas between limits that generate both sulfur dioxide in the gas and magnetite as a major fraction of the iron in the solids, f) collecting the sulfur dioxide bearing gas as a product of the process, and g) recycling a fraction of the magnetite-bearing solids from the decomposition reactor to the absorber for use as a sorbent in the desulfurization of additional sulfur and oxygen-bearing gas.
7. The process of claim 6 in which the sulfur dioxide-bearing gas from the decomposition reactor is utilized both as a feed gas and source of sulfur for the production of sulfuric acid, and the tail gas from the acid production process is recycled to the absorber step of the process.
8. The process of claim 6 in which the sulfur dioxide-bearing gas from the decomposition reactor is utilized as feed gas for the production of elemental sulfur, and the tail gas from the sulfur production process is recycled to the absorber step of the process.
9. The process of claim 6 in which a portion of the iron-bearing solids utilized in the preparation process is iron sulfate, and part of the magnetite-bearing product from the decomposition reactor is collected as an iron oxide product of the combined process.
10. The process of claim 9 in which the collected magnetite-bearing solids are contacted with air in a sulfur stripper, and reacted to expell the remaining sulfur as sulfur dioxide, and to produce an iron oxide product of high purity that is suitable for use in the production of steel.
11. The process of claim 6 in which the undersize particles generated in each gas contacting procedure of the combined process are recycled to the sorbent preparation procedures of this process.
12. The process of claim 6 in which the sorbent is prepared by mixing water, sulfuric acid, iron sulfate-bearing aqueous solutions or slurries, or combinations of these components, with dry solids, to generate agglomerated solids that are essentially free of particles smaller than 10 microns.
13. The process of claim 12 in which the agglomerated solids are crushed, dried and sized by mechanical equipment and particles of the desired size are collected as product of the preparation process.
14. A regenerative process for the desulfurization of reducing gases which comprise the steps of:
a) contacting the reducing gas in a desulfurization reactor with a solid material selected from the class consisting of ferrous sulfate, iron oxide and mixtures thereof, that contains a quantity of iron in excess of the sulfur content of the gas on a stoichiometric basis, and reacting the solid material with the gas at a temperature of about 250°C to 550°C to produce both a reducing gas that is essentially free of sulfur and product solids that contain both iron sulfides and iron oxides, b) collecting the sulfur-free reducing gas as a product, c) advancing at least a portion of said product solids from the desulfurizer to an absorption zone, d) contacting said product solids containing iron sulfide with an oxygen-bearing gas to oxidize the iron sulfide and to produce a product that contains both iron-sulfates and iron oxides and a second product gas which is essentially free of sulfur, e) advancing at least a portion of said sulfate-bearing solids from the absorber to a decomposition zone, f) reacting the iron sulfates in the decom-position zone in contact with reducing gas and air under conditions that generate iron oxides as the solid product of the decomposition and a gas containing sulfur dioxide, g) recovering the sulfur dioxide-bearing gas from the decomposer, h) recovering the solid product from the decomposition zone which contains iron oxide as a major component, and i) recycling the recovered solid product to the desulfurization reactor.
a) contacting the reducing gas in a desulfurization reactor with a solid material selected from the class consisting of ferrous sulfate, iron oxide and mixtures thereof, that contains a quantity of iron in excess of the sulfur content of the gas on a stoichiometric basis, and reacting the solid material with the gas at a temperature of about 250°C to 550°C to produce both a reducing gas that is essentially free of sulfur and product solids that contain both iron sulfides and iron oxides, b) collecting the sulfur-free reducing gas as a product, c) advancing at least a portion of said product solids from the desulfurizer to an absorption zone, d) contacting said product solids containing iron sulfide with an oxygen-bearing gas to oxidize the iron sulfide and to produce a product that contains both iron-sulfates and iron oxides and a second product gas which is essentially free of sulfur, e) advancing at least a portion of said sulfate-bearing solids from the absorber to a decomposition zone, f) reacting the iron sulfates in the decom-position zone in contact with reducing gas and air under conditions that generate iron oxides as the solid product of the decomposition and a gas containing sulfur dioxide, g) recovering the sulfur dioxide-bearing gas from the decomposer, h) recovering the solid product from the decomposition zone which contains iron oxide as a major component, and i) recycling the recovered solid product to the desulfurization reactor.
15. Apparatus for removing sulfur from a sulfur and oxygen-bearing gas which utilizes a solid sorbent convertible to ferric sulfate when contacted with said gas comprising:
sorber means for receiving the sorbent, sorbent feed means for feeding the sorbent to the sorber means, gas feed means for feeding the gas to the sorber means, reductive decomposition means for collecting and decomposing the used sorbent from the sorber means in a reducing atmosphere to regenerate the sorbent and form a sulfur dioxide gas, agglomerating means for agglomerating the regenerated sorbent product of the reductive decomposition means into agglomerates, and recycling means for recycling at least a portion of the agglomerates to the sorbent feed means.
sorber means for receiving the sorbent, sorbent feed means for feeding the sorbent to the sorber means, gas feed means for feeding the gas to the sorber means, reductive decomposition means for collecting and decomposing the used sorbent from the sorber means in a reducing atmosphere to regenerate the sorbent and form a sulfur dioxide gas, agglomerating means for agglomerating the regenerated sorbent product of the reductive decomposition means into agglomerates, and recycling means for recycling at least a portion of the agglomerates to the sorbent feed means.
16. The apparatus of claim is further including drying means for drying said agglomerates prior to recycling to the sorber feed means.
17. The apparatus of claim 16 further including sizing and crushing means for sizing said agglomerates prior to drying.
18. The apparatus of claim is further including converter means for converting the sulfur dioxide formed by the decomposition means to elemental sulfur.
19. The apparatus of claim 15 further including converter means for converting the sulfur dioxide formed by the decomposition means to sulfuric acid.
20. The apparatus of claim 16 wherein said drying means is a fluidized bed drier.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US403951A US3917800A (en) | 1973-10-05 | 1973-10-05 | Method for removing oxides of sulfur from sulfur bearing gas |
| US44521174A | 1974-02-25 | 1974-02-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1046734A true CA1046734A (en) | 1979-01-23 |
Family
ID=27018458
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA210,619A Expired CA1046734A (en) | 1973-10-05 | 1974-10-02 | Apparatus and method for removing sulfur from sulfur-bearing gases |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1046734A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112940795A (en) * | 2021-02-23 | 2021-06-11 | 湖北华特尔净化科技股份有限公司 | Iron-based desulfurizer for blast furnace gas and preparation method thereof |
-
1974
- 1974-10-02 CA CA210,619A patent/CA1046734A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112940795A (en) * | 2021-02-23 | 2021-06-11 | 湖北华特尔净化科技股份有限公司 | Iron-based desulfurizer for blast furnace gas and preparation method thereof |
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