Note: Descriptions are shown in the official language in which they were submitted.
1046734
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
1046734
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.
1046734
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 ,~
-- 6 --
1046734
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 -
6734
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
--7--
1046734
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:
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
-8-
~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_
1046734
fuel with air in chemical reactions such as the following
reactions:
4 2 2 2
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:
--10--
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:
3 4 2 2 3
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
1046734
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
-12-
1046734
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
2 2 2 2
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
-13-
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.
1046734
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
-15-
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.
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~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
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1046734
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.
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~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.
1046734
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
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1046734
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.
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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
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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.
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