Note: Descriptions are shown in the official language in which they were submitted.
` 7~2 ~lZ~3
~LOWING MELT ~AYER PROCESS FOR PRODUC~ION OF 5ULFIDES
Background of the Invention
1. leld of the Invention
The present invention relates to a process for the
production of alkali metal sulfides by reduction of the
corresponding oxysulfur compounds, that is, compounds
containing alkali metal, oxygen and sulfur, such as alkali
metal sulfites or sulfates, using a solid carbonaceous
reducing agent. In one of its more particular aspects, this
invention relates to such a process in which there is formed
a melt which is caused to flow in a layer along the periphery
of a reaction zone into which the reactants are lntroduced.
2. Prior Art
The produc~ion of alkali metal sulfides has been of
significant interest for some time. Alkali metal sulfides
as industrial chemicals have a wide variety of end uses.
They are also used as intermediates in flue gas
desulfurization processes in which sulfur values are
recovered from gases produced in burning sulfur-containing
fuels and in other industrial processes.
Various processes are known for producing alkali metal
sulfides, particularly by the reduction of oxysulfur
compounds. U.S. Pat. No. 125,275 describes a process in
which molten sodium sulfate is percolated through a heated
carbon bed to produce sodium sulfide.
U.S. Pat. No. 1,212,702 describes a process for
reducing sodium sulfate or sodium bisulfate to sodium
sulfide in a shaft furnace in which a reducing atmosphere is
maintained by feeding a controlled amount of air to burn
large pieces of carbonaceous matter, such as coal or coke.
The sulfate or bisulfate salt is mixed with an excess of
coal, charged into the reducing atmosphere of the furnace,
and the salt melted and reduced over the heated carbonaceous
matter at a temperature of about 1000C.
U.S. Pat. No. 3,867,251 discloses a process for
producing alkali metal carbonates and alkali metal sulfides
from evaporated alkaline cooking liquor obtained from pulp
b` , ~
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production which utilizes a horizontal combustion cyclone to
produce turbulence within a reaction chamber. The cooking
liquor is pyrolyzed to alkali metal carbonate/ carbon and
hydrogen sulfide in a first zone, into which a hot oxygen-
containing gas is introduced tangentially at a temperatureof about 700C. In a second zone, into which hot flue gases
are injected tangen~ially, alkali metal carbona~e in the
form of a smelt reacts with hydrogen sulfide to form alkali
metal sulfide at a ~emperature of about 900C. In a third
zone~ combustion gases are oxidized by means of tangentially
injected oxvgen-containing gas at a temperature of about
1100 to 1200C.
U.S. Pat. No. 4,198,385 discloses a two-stage process
for the reduction of sodium sulfate accumulated in spinning
baths during viscose fiber manufacture. In the first stage
a reducing atmosphere is provided at a temperature greater
than the melting point of sodium sulfide, so that molten
sodium sulfide plus ~mreacted sodium sulfate collects in a
melt at the bottom of a combustion chamber. In ~he second
stage, a separately applied reducing agent and inert exhaust
gases are introduced into the melt to agitate the melt and
to produce additional sodium sulfide from unreacted sodium
sulfate. The sodium sulfide can then be reacted with inc
oxide to produce sodium hydroxide for use in the spinning
baths.
The conversion of oxysulfur compounds to sulfides is
particularly important in plants which are designed to
remove sulfur oxides from the flue gases of power plants
generating electricity by the combustion of fossil fuels.
In the molten carbonate process described in U.S. Pat~
No. 3,438,728, sulfur oxide impurities are removed from a
hot combustion gas by contacting the gas at a temperature of
at least about 350C. with a molten salt mixture containing
alkali metal carbonates as the active absorbent. The molten
absorbent solution containing the absorbed sulfur values,
principally as alkali metal sulfites, is treated with a
reductant gas rnixture containing hydrogen, carbon monoxide,
or a mixture thereof, at a temperature of at least about
75~2 ~ 2
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400C., under reaction conditions favoring formation of
sulfides, to convert the absorbed sulfur values to alkali
metal sulfides. Thereafter, the molten salt containing the
alkali metal sulfides is treated with a gaseous mixture
containing steam ~nd carhon dioxide at a temperature below
about 450C., to regenerate the alkali metal carbonates and
convert the alkali metal sulfides to hydrogen sulfide gas
which can be converted to sulfur or sulfuric acid.
The reduction of alkali metal oxysulfur compounds to
the corresponding sulfide is also a part of the regenerative
sodium-based flue gas desulfuriza~ion process described
in "A 100-~IW Second Generation SO2 Removal Demonstration
Plant for .lew York State Utilities" by Robert G. Aldrich
and Richard D~ Oldenkamp, "Proceedin~s of the ~merican
Power Conference, 1977, Vol. 39, p. 319. In this process an
aqueous solution of sodium carbonate is used to absorb
sulfur dioxide from flue gas. During the absorption step,
the solution is converted to a dry spent salt containing
unreacted sodium carbonate plus the two oxysulfur compounds,
~0 sodium sulfite and sodium sulfate. In order to regenerate
the absorbent, it is necessary to reduce the oxysulfur
compounds to sodium sulfide, then react the sodium sulfide
with water and carbon dioxide to produce hydrogen sulfide
gas and sodium carbonate solution.
According to this reference, the reduction step is
accomplished in a large pool-type reactor held at about
1000C. The spent salt is fed into the reactor together
with a solid carbonaceous reducing agent such as petroleum
coke or coal. Air is also fed into the reactor through feed
nozzles located below the surface of the melt. The air
serves primarily as a source of oxygen which reacts with a
portion of the reducing agent exothermally to provide heat
for the system. This reaction generates typical combustion
gases such as carbon monoxide, carbon dioxide and water
vapor, which bubble through the molten salt pool together
with the nitrogen from the air feed. Gases which are
produced by the chemical reduction reaction join the
combustion product gases, and the mixed gas stream leaves
" 75A2
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the reactor as product gas. Oxysulfur compounds in the
spent sal~ feed are largely reduced to sulfide by the carbon
present in the pool. Molten salt containing the sodium
sulfide product, sodium carbonate from the original feed
plus small amo-mts of unreacted carbon and oxysulfur
compounds is withdrawn from the molten pool by an overflow
system. Gases leave the vessel via a discharge port near
the top.
While the process described in this reference provides
an effective route to sulfur dioxide removal from flue gases
and has many advan~ages over the prior art cited above, it
is not witAout its disadvantages. The major problem with
this reducer design is that it is ~uite large and therefore
expensive. The large size results from the requirement to
bubble air and product gases through the pool of liquid
without entraining excessive amounts of liquid in the
ef1uent gas or creating a hydraulically unstable pool of
meltD For practical purposes, a superficial gas velocity of
about 2 feet per second has been found to be the maximum
allowable for this type of reducer, and this low velocity
establishes the required vessel diameter for a given reducer
capacity.
A second problem with this kind of reactor design is
the difficulty in maintaining constant melt-discharge rate.
For example: A slight increase in air rate will cause the
melt level to increase because of the increased number of
bubbles within it. This causes a great increase in the
instantaneous melt overflow rate which, in turn, can
represent a safety as well as operational problem for the
melt quench step which follows.
Objects of the Invention
It is an object of the present invention to provide a
process for producing alkali metal sulfides in high yields
from corresponding oxysulfur compounds.
Another object of this invention is to provide a
process in which a mixture of alkali metal sulfites and
sulfates produced in a flue gas desulfurization process is
reduced to alkali metal sulfides.
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Another object o this invention is to provide a
process capable of essentially completely reducing alkali
metal sulfites to sulfides.
Another object of this invention is to provide a
reduction process utilizing molten salts which does not
require the molten salt pools of the prior art.
Yet another object of this invention is to provide such
a process whlch can be conducted ln a relatlvely simple
apparatus.
Other objects and advantages of the present inventlon
will be apparer~t in the course of the following detailed
description.
Summarv of the Inventlon
In accordance with the broad aspects of the present
invention, an alkali metal oxysulfur compound is converted
into the corresponding alkali metal sulflde by a process
which comprises introducing an alkali metal oxysulfur
compound and a solid carbonaceous reducing agent lnto a
reaction zone; subjecting the oxysulfur compound and
reducing agent to centrifugal force; heating the reaction
zone to melt the oxysulfur compound and to cause the
oxysulfur compound and reducing agent to rPact to produce an
alkali metal sulfide; flowing a melt containing the alkali
metal sulfide thereby produced, unreacted oxysulfur compound
and unreacted reducing agent through the reaction zone and
along the periphery thereof, to cause the unreacted
oxysulfur compound and the unreacted xeducing agent to react
to produce additional alkali metal sulfide; and recovering
alkali metal sulfide from melt exiting the reaction zone.
In a preferred embodiment, the centrifugal force to which
the oxysulfur compound and reducing agent are subjected is
produced by tangential injection of at least one of the
oxysulfur compound and the solid carbonaceous reducing
agent entrained in a gaseous stream.
Brief Description of the Drawing
FIG. 1 is a schematic diagram, partly in cross section,
of one embodiment of apparatus which can be used in carrying
out the process of the present invention, wherein product
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gas and product melt are discharged together through a
single nozzle directly into a quench tank containing an
aqueous solution.
FIG. 2 is a schematic diagram, partly in cross section,
of another embodiment of apparatus suitable for use in this
invention, wherein a major portion of the product gas is
withdrawn by way of a centrally located discharge port near
the top of the reactor, and product melt is discharged into
a quench tank through a nozzle near the bottom of the
reactor.
FIG. 3 is a schematic diagram, partly in cross section,
of a third embodiment of apparatus which can be used in the
present invention, wherein product melt and product gas are
discharged into a cooling zone designed to solidify the
product melt into a granular product.
FIG. 4 is a section taken along lines 4-4 of FIG. 3.
Des~cription of the Preferred Embodiments
The present invention provides a continuous process for
the reduction of oxysulfur cornpounds which uses a simple
reactor of compact design with a low-cost solid carbonaceous
material such as coal or petroleum coke as the reducing
agent.
The reduction reactions occurring in the process of the
present invention may be typified in the following
equations:
M2S04 ~ 2C M2 + 2Co2 (l)
M2S04 + 4C M2S ~ 4CO (2)
2M2So3 + 3C = 2M2S ~ 3C2 (3)
M2S3 + 3C M2 + 3CO (4)
M2S04 + 8H M2S ~ 4H20 (5)
M2S03 + 6H M2 + 3H20 (6)
4M2S03 3 2S04 M2S (7)
where M is an alkali metal. Equations l r 2, 3, and 4
illustrate possible routes to the reduction of some of the
most common oxysulfur compounds encountered in practicing
the process of the present invention. Equations 5 and 6
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depict reduction by the hydrogen combined with carbon in the
solid carbonaceous reducing agent. Equation 7 illustrates
the disproportionation reaction which results in the
formation of additional alkali metal sulfate when the alkali
metal sulfite in the reactant stream disproportionates
rather than being reduced in accordance with one of
Equations 3, 4, or 6 shown above. In the event of
disproportionation occurring, the alkali metal sulfate which
forms can be reduced to alkali metal sulfide in accordance
1~ with Equation 1, 2, or 5.
In order to conduct the desired reduction reactions,
use is made of a simple reactor in which the reactions
illustrated above are caused to take place at least partly
in a melt layer which flows down the inside walls of the
reactor. The reactor is heated and the mixture of heated
reactants subjected to centrifugal force to cause the
formation of a melt layer upon the walls of the reactor. In
a preferred embodiment of the invention, the heated
reactants are subjected to cen'rifugal force by injecting at
least a part of the reactants tangentially into a reactor of
circular cross section. In this manner, the heated
oxysulfur compounds are melted and follow a spiral path
downwards in the reactor and under the influence of
centrifugal force become deposited along the walls of the
reactor together with unreacted particles of carbonaceous
reducing agent. The resulting melt layer moves downward
along the walls during the time that the reaction between
the oxysulfur compound and the solid carbonaceous reducing
agent is proceeding. The flowing melt layer exits the
reactor at the bottom thereof and is cooled by contact with
cool gases or by being introduced into an aqueous quench
solution. The reduced oxysulfur compounds are soluble in
the aqueous quench solution and may be recovered therefrom.
For example, the aqueous solution con~aining the quenched
melt may be removed and further processed to recover the
desired alkali metal sulfides from the solution. In addition,
if desired, the recovered sulfides may be further processed
to regenerate alkali metal carbonates or bicarbonates which
7 5A2 ~2~i2~3
--8 -
can be introduced into the reactor along with the oxysulfur
compounds to be reduced. Where such salts are used in
addition to the oxysulfur compounds, the temperatures
utiliæed in the reactor may be lower than those wherein the
salt mixture contains mer~ly sulfates or sulfites.
The product gases may be removed from the reactor and
likewise further processed in order to recover valuable
byproducts. For instance, the carbon monoxide content may
be burned to provide heat and form additional carbon dioxide
and the carbon dioxide content may be used to drive hydrogen
sulfide from sulfide solutions in accordance with the
following reactions:
M2S + 2C02 + 2H20 = 2MHCO3 ~ H2S ~)
M2S + CO2 ~ H2O = M2CO3 ~ H2S (g)
Hydrogen sulfide may be sepaxated and converted to sulfur in
a Claus plant or utilized in the manufacture of sulfuric
acid. The product gases may be removed from the top of the
xeactor or they may be removed from the bottom of the
reactor along with the melt, as desired.
Heat for the reduction reaction may be produced by
means of a suitable burner incorporated with the reactor or
may be produced by oxidation of a portion of the
carbonaceous reducing agent.
The reduction reaction is suitably carried out at an
elevated melt temperature, usually in the range of about
900 to 1400C., and preferably in the range of about 950
to 1150C.
One of the principal advantages of the present
invention is that external heating of the reactor is not
required. Rather, heating to produce the required melt
temperature is accomplished in situ by the combustion of a
fuel by a moving stream of an oxidizing gas. The oxidizing
gas serves two purposes, namely, causing combustion of the
fuel used to heat the reaction zone and propelling particles
of reactants in a spiralling path within the reaction zone
in a way such that the particles melt and the resulting melt
75A2 ~z~ 3
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flows in a layer at the outer periphery of the reaction
zone. The thus-produced flowing melt layer enables ~he
reactants to be in contact for a longer period of time than
if the reactants reacted only directly in the stream of
oxidizing gas without forming such a flowing melt layer.
The process of the instant invention can be used to
convert a wide variety of oxysulfur compounds to the
corresponding alkali metal sulfides. Some of the moxe
common oxysulfur compounds include lithium sulfite, sodium
sulfite, potassiwn sulfite, lithium sulfate, sodium sulfate,
and potassium sulfate as well as other alkali metal sulfites
and sulfates. Bisulfates, bisulfites, thiosulfates, and
sulfonates can also be converted- to- sulfides in accordance
with the process of this invention.
As reducing agents, any of a wide number of solid
carbonaceous materials are satisfactory. Coal or petroleum
coke is preferred. Other forms of carbonaceous materials
are also suitable. For example, asphalt, peat, lignite, or
wood may be used.
In addition to the oxysulfur compound and carbonaceous
material, it is sometimes desirable to add another salt in
order to lower the melting point of the salt mixture in the
reactor, thereby reducing the amount of heat which must be
produced in the reactor in order to form the required melt.
For this purpose, compounds such as alkali metal halides,
for example, sodium chloride or alkali metal carbonates or
bicarbonates, such as sodium carbonate and sodium
bicarbonate have been found particularly satisfactory. They
may be used in an amount of up to about 50~ of the oxysulfur
compound.
The carrier gas used to introduce reactants into the
reactor can be an oxidizing gas, such as oxygen or air, or
it may be an inert gas such as nitrogen or flue gas. It is
used, in general, in an amount sufficient to entrain the
reactants, principally the alkali metal oxysulfur compound
and finely divided solid carbonaceous reducing agent. If an
oxidizing gas is used, it will function both as an oxidizer
and as a carrier and must be added in sufficient quantity to
75A2 ~ Zi3L2 ~3
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provide both functions. An oxidizer is desirable in order
to oxidize a portion of the carbonaceous material which is
used as the reducing agent in the reaction. Oxidation of
the carbonaceous material results in the release of a large
amount of heat, since such a reaction is highly exothermic.
Heat is required not only for melting the oxysulfur compound
and for keeping the product sulfides in the molten state,
but also for the carrying out o~ the endothermic reduction
reactions which are carried out in the reactor. However, it
is not desirable to utilize an oxidizing gas in excess of
the amount required to provide the requisite heat to the
reactor, since an excess of oxidizing gas may result in
oxidizing part of the sulfides produced in the reactor,
thereby decreasing the overall yield of sulfide.
In some instances it may be desirable to provide the
requisite heat by means of a separate burner which may be
oriented tangentially or axially with respect to the
reactor. However, the use of such an auxiliary burner i5
not deemed essential, since ade~uate heat can be furnished
by oxidation of a part of the carbonaceous reducing agent ln
the reactor.
In other instances it may be desirable to use a
separate burner to provide part of the heat required and to
use an oxidizing gas, such as air or oxygen, as the carrier
gas to furnish part of the heat by oxidation of a portion of
the carbonaceous material entrained in the oxidizing gas.
The starting materials utilized in this inv ntion
containing the oxysulfur compound and which may also
contain, for example, alkali metal carbonate and other
alkali metal salts as well, can be obtained from various
industrial processes. For example, a convenient source of
oxysulfur compounds can be the spent absorbent from
processes used to desulfurize flue ga~es from plants burning
fossil fuels, spent sulfite "black liquor" from paper mills
or spent "seed" from magnetohydro~ynamic (MHD) power plants.
In the last mentioned case, the principal oxysulfur compound
produced is potassium sulfate which is generated when
potassium carbonate, added to high temperature combustion
75A2
23 ~
gases to increase electrical conductivity, also absorbs
sulfur compounds in the gases. Thus, the oxysulfur compound
can be derived from a number of process streams. In the
case where the oxysulfur compound is formed in the aqueous
carbonate process (ACP), it may be desirable'to form a
premixed oxysulfur compound - carbonaceous material feed for
use in the process of the present invention. This is
accomplished by mixing the carbonaceous material with the
carbonate which is used to absorb sulfur dioxide from the
flue gases treated in the aqueous carbonate process. Adding
the carbonaceous material to the carbonate while it is in
aqueous solution permits a very intimate mixture of dry
reducing agent and dry spent absorbent to be obtained. The
presence of reducing agent in each droplet of sodium
carbonate solution while it is absorbing sulfur dioxide and
being dried also acts to inhibit the oxidation of sulfite to
sulfate. Adding the reducing agent prior to drying permits
use of an aqueous slurry of reducing agent. For example,
sewage sludge or a coal slurry may be used. The mixture of
sodium carbonate e reducing agent and water is then sprayed
into a hot sulfur dioxide-containing gas in the usual
manner, whereby efficient contact between liquid d-oplets
and gas is obtained and a dry powder containing both sodium
sulfite and reducing agent is obtained as the product of the
sulfur dioxide absorption - drying step in the ACP process.
This technique obviates the need for mixing reactants in the
reactor.
The amounts of solid carbonaceous material, burner
fuel, and oxidizing gas required to produce a given amount
of alkali metal sulfide will depend upon the nature of the
oxysulfur compound feed, the percent conversion desired, the
reactor design, and other factors. For example, if the
carbonaceous material is carbon and the oxysulfur compound
is pure sodium sulfate, at least 2 moles of carbon are
required per mole of feed salt for the reduction alone. In
addition, fuel and oxidizing gas are required in sufficient
amounts that their combustion will provide all of the heat
necessary to melt the feed salt, provide the heat for
75A2 ~2~ 3
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endothermic reducti~n reactions, raise the temperature of
all products to their discharge temperatures, and provide
for any heat losses from the system. All or a portion of
the required fuel may be in the form of the solid
carbonaceous material. The total amount of reactive carbon
and hydrogen in both the solid carbonaceous reducing agent
and the combusion fuel must be in excess of the
stoichiometric amount required to convert all of the oxygen
in the oxysulfur compounds and the oxidizing gas to carbon
lQ dioxide and water.
The reactants can be introduced into the reactor in a
number of different ways depending upon the result sought
and the type of starting materials which are used. The most
desira~le configurations are those in which the combustion
mixture and the mixture of oxysulfur compounds, reducing
agent, and carrier gas are introduced through separate
ports. In particular, it is desired to introduce a mixture
of, for example, oxysulfur compound, carbonaceous material
and a caxrier gas tangentially while at the same time
introducing fuel, which may be the same carbonaceous
material, and oxidizing gas through a specially d signed
burner port, such as a "vortex" burner located at the center
top of the reactor. This combination of gas streams results
in producing the desired spiral path for the reactants and
also realizing optimal heating conditions for the reactant
stream.
In an especially preferred embodiment of the present
invention, air is used as both the carrier gas and the
oxidant, coal is used as the carbonaceous material
functioning as both the reducing agent and the oxidizable
fuel and a mixture of sodium sulfite, sodium sulfate and
sodium carbonate is the salt mixture. In this embodiment,
coal and approximately one-half of the air is introduced
axially to the reactor through a burner which imparts a
swirling ~low to the combustion products, while a mixture of
salts, coal and the remainder of the air is introduced
tangentially. This arrangement results in producing the
desired cyclone action in the reactor so that the reactants
` 75A~ ~Z~2~
are propelled through the reactor in a spiral path, the
desired melt formation takes place in the tr~versal of the
spiral path through the reactor and the melt is deposited
upon the wall of the reactor and flows down the wall as the
reaction proceeds.
In the process of the present invention the oxysulfur
compounds fed to the reactor are reduced to the
corresponding sulfides. For example, where the feed
consists of sodium sulfite and sodium sulfate, sodium
; 10 sulfide is produced. Since the reaction takes place in a
flowing layer of melt, the product sulfide is recovered as a
melt.
Melt residence time within the reactor may vary within
a wide range depending upon the velocity of the reactant
stream within the reactor, the temperature and pressure of
the reactor and the length of the reaction zone within the
reactor. In general, melt residence times less than about
2 minutes and preferably about 5 to 60 seconds are used.
The residence time is adjusted to be long enough to insure
that at ieast about 80% of the oxysulfur compound introduced
into the reactor is reduced to sulfide~
The product melt exiting the reactor must be cooled in
order to enable recovery of the sulfide for its use in
further processing. For this purpose it is convenient to
contact it with water or cool gas, although other methods
may be used if desired. In the case of the water contact,
the melt flows into a water bath or is contacted by a spray
of liquid water. Alternatively, an aqueous solution
containing previously dissolved melt or other process salts
may be used. Provision is made for the removal of the
gaseous products of the reaction as well as the products
present in the melt. The aqueous solution containing the
quenched melt may be drawn off from the quench tank and
subjected to further processing including recovering
relatively pure alkali metal sulfide from the solution, in
accordance with known procedures.
If it is desired to recover the alkali metal sulfide in
solid form, instead of an aqueous quench, a gas-contacting
75A2
Z~
device such as a prilling tower is utilized. The melt
containing the sul~ide product is blown throuyh a discharge
nozzle at the bottom of the reactor by the gases formed
during the reactions taking place within the reactor and is
formed into small droplets. These droplets harden into fine
shot-like beads or prills as a result of contacting
relatively cool gas in the prilling tower. Gas is
continuously removed from the prilling tower, cooled and
reinjected to provide the means ~`or cooling and soli~ifying
the prills. The prills, containing alkali metal sulfide,
fall to the bottom of the prilling tower and are collected
in a bed either in the tower or in a separate vessel as
desired. Gas containing carbon dioxide and water vapor is
passed through the bed at a temperature below the melting
point of the salts and preferably in the range of about 250
to 650C. The alkali metal sulfide is thereby converted to
alkali met~l bicarbonate or carbonate in accordance with ~ations 8 or 9.
Preferably all or a portion of the gas produced in the
reduction is used as the source of carbon dioxide for these
reactions. This gas, as pointed out above, contains an
adequate supply of carbon dioxide and can be enriched in
water vapor, if necessary, by the injection of liquid water
or steam. Because of their special shape, the prills form a
porous high surface area packed bed which is permeable to
the flow of gas and does not hang up or plug in the contact
zoneO
The use of the prilling tower for recovering solid
alkali metal sulfide from the reduction reactor can also be
taken advantage of in MHD feed regeneration and the
regenerated prills recycled directly ~o the ~D combustor.
~sh compounds which were in the original seed or were added
with coal in the reducer will be decomposed by the high
temperature in the MHD combustor and redistributed
downstream of the MHD channel so that only a small portion
reappears in the spent seed. In this way the ash in the
seed can be recycled to extinction with all of this
eventually leaviny via the main discharge point for coal ash
which passes through the channel.
7 5A2
-15- ~2~1Z~3
When used for the regeneration of spent salt for flue
gas desulfurization, it is desirable to remo~e ash and
produce the regenerated carbonate in the form of an aqueous
solution. To accomplish this, the prills are ~issolved in
5 water which is filtered or otherwise separated to produce a
solution of sodium carbonate and an insoluble ash cake.
The prilling tower recovery process described above is
yiven as one example of a gas/particle contact process.
Similar results can be obtained by use of a fluidized bed
rotar~ kiln or other gas/solids contactor.
The products of the process of this invention include
not only the melt referred to above, which is a source of
the alkali metal sul~ide, but also gases which are produced
in the various reac,ions occurring in the reactor. These
gases include carbon monoxide, carbon dioxide and water
vapor. The production of a gaseous product having a CO2:CO
ratio of at least about 1:1 is desirable. With this ratio
being realized, the carbonaceous material is substantially
used up in the reactor. The app.reciable quantity of carbon
dioxide present in the gaseous product can be used for
carbonate regeneration if desired.
Among the principal advantages of the present
invention, in addition to those already mentioned, is the
fact that, since the carbonaceous material is used up in the
reactor, there is very little carbon contaminating the
product sulfide. Another advantage lies in the realization
of very much higher gas velocities than in conventional
molten pool reducers, which permits the use of smaller
vessels and results in major cost savings. Further, the
elimination of the need to inject a.ir and feed materials
beneath the surface of a high temperature pool of melt
obviates the problem of plugging of nozæles. Another
advantage is the reduction of ash-melt interaction. That
is, the ash-melt interaction to form insoluble silicates
does not have sufficient time to reach equilibrium because
of the short residence time in the reactor. Sodium loss and
processing problems downstream of the reducer attributable
to silicate contamination are therefore virtually
75A2
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eliminated. Another advantage is that liquid level control
of very hot corrosive highly agitated pools of molten salt
lS unnecessary.
Referring now to FIG. 1 of the drawings, a reactor 10
is a vessel of circular cross section lined with a corrosion
resistant refractory 12, such as fusion cast alumina blocks
within a metal containment 14. Reactor 10 has a tangential
entry nozzle 16 located near the top of the reactor and a
discharge nozzle 18 located at the bottom of the reactor.
mixture of salts containing oxysulfur compounds and
pulverized solid carbonaceous reducing agent, such as coal,
is introduced into reactor 10 through tangential entry
nozzle 16 via a line 20. Air is supplied via a line 22 to
entrain the salt-coal mixture. The top of reactor 10 is
provlded with a burner 24, which includes a tangential entry
nozzle 26 and an axial entry nozzle 28. Air is supplied
through tangential entry nozzle 26 via a line 30, and
combustion coal is supplied to axial entry nozzle 28 via a
line 32. A flame 34 is shown exiting burner 24 and
occupying the top part of reactor 10. A spiral path 36
represents the course followed by the mixture of salt and
reductant coal, which is introduced together with a carrier
air stream through tangential entry nozzle 16. A melt 38,
shown along an inside wall 40 of reactor 10, is foxmed as
molten salt particles and associated particles of reducing
agent are thrown to wall 40 by the action of centrifugal
force. Melt 38 proceeds downwardly ln a moving layer along
the inside wall 40 of reactor 10 and exits reactor 10
through discharge nozzle 18, together with product gases.
The mixture of melt and product gases enters a quench
tank 42, containing an aqueous quench solution 44. Quench
tank 42 is equipped with an exit nozzle 46, through which
the off-gases are removed via a line 48. The product salts
can be recovered from quench solution 44 and further
3~ processed as desired.
The embodiment of FIG. 2 differs from that of FIG. 1
primarily in the manner of removing product gas. In this
embodiment, a reactor 100 i5 of circular cross section and
75A2
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lined with a corrosion-resistant refractory 102 within a
metal containment 104. Tangential entry nozzles 106 are
positioned near the top of reactor 100. At the top of
reactor 100 and centrally located is a gas discharge
nozæle 108, coated with a refractory 110. Gas discharge
nozzle 108 is configured to minimize the discharge of
particulate matter with the gas. This embodiment permits
the product gases to be removed at a high tempexature, so
that heat recovery can be realized, ~hereby improving the
overall thermal efficiency of the process. The melt is
discharged through a discharge nozæle 112 at the bottom of
reactor 100 into a quench tank 114, containing an aqueous
quench solution 116 and an agitator 118. High pressure
water or steam is injected through nozæles 120 to break up
the str~am of melt falling from discharge nozzle 112 before
it contac~s quench solution 116. Quench ~ank 114 is
equipped with an aqueous solution feed nozzle 122, through
which the aqueous quench solution is fed to quench tank 114
via a line 124; a quenched melt discharge nozzle 126,
through which aqueous solution containing the quenched melt
is discharged via a line 128; and gas discharge nozzle 130,
through which product gases from quench tank 114 are
discharged via a line 132.
Referring to FIG. 3 and FIG. 4, reactor 200 is a
circular cross-section reactor lined with a corrosion-
resistant refractory 202, such as fusion-cast alumina
blocks, surrounded by a thermally insulating castable
refractory 204 within a metal containment 206. Reactor 200
i5 equipped with two tangential feed nozzles 208 in the
upper portion of reactor 200 and a discharge nozzle 210 at
the bottom thereof. A feed hopper 212 is adapted for
controlled feeding of a feed mixture 214 of salts containing
oxysulfur compounds and pulverized solid carbonaceous
reducing agent into a line 216 through which it is conveyed
to at least one of the feed nozzles 208 by a carrier gas
such as air. The carrier gas enters via a feed line 218 and
a blower 220. A separate burner 222 is shown with its own
fuel line 224 and air supply line 226. Discharge nozzle 210
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is designed to increase the velocity of the discharge gas
sufficiently to cause it to produce breakup of the melt
formed in reactor 200. Melt flows downwardly along an
inside wall 228 of reactor 200 and with product gas is
discharged through nozzle 210 into a melt solidiication
chamber 230. Gas is continuously removed from this chamber
via a line 232, cooled in a heat exchanger 234 by means of a
heat recovery fluid and returned to chamber 230 via a
line 236. Gas circulation is forced by a blower 238 and
an amount of product gas equal to the net amount of gas
produced in the reactor is continuously removed from the
system via a line 240. The solid granular product is
removed through a valve 242. Cooling in chamber 230 is
accomplished by simple contact of falling droplets with a
rising stream of cool gas. Alternative cooling techniques
such as fluidized beds or rotary granulators may be employed
within the scope of this invention.
The invention will be better understood by reference to
the following examples which illustrate embodiments of the
process of this invention and should not be construed as
limiting the scope of the invention.
EXAMPLE 1
A unit was constructed having the general configuration
of the reactor and fuel system of FIG. 3. The upper portion
of the reactor was a cylinder 5 in. ID by 7.3 in. in height.
Below this was a conical section 6 in. in height with a
2 in. ID discharge port at the bottom. The unit was
equipped with two tangential feed nozzles near the top of
the cylindrical section. A feed salt having a nominal
composition: Na2CO3-30%, Na2SO3-50%, Na2SO4-20% was fed
through one of the nozzles mixed with powdered petroleum
coke. A natural gas/air burner was fired through the second
nozzle. Product melt and gas were discharged through the
bottom nozzle. Typical results are given in Table I.
~2~12~3
-- 19 --
TA~LE I
Test A Tes~ B
Salt ~eed 13.2 lb/hr 5.2 lb/hr
Coke Feed 2.8 lb~hr 2.2 lb/hr
Natural Gas to Burner 42~00 scfm 43.00 scfm
Total Air Feed 9.39 scfm 9.83 scfm
Product Gas Composition
C2 16.3 vol~% 12.7 vol.%
CO 0.8 vol.% 3.3 vol.%
2 0 0
Internal Reactor Temp. 972C. 1021C.
Reduction to Sulfide 85% g5%
EXAMPLE 2
A test reactor was constructed of simple cylindrical
1~ design in the general shape and configuration of the unit
shown in FIG. 1. The inside diameter was 1 ft. and the
inside height 6 ft. mhe unit ~ad one tangential feed inlet
and a central burner port at the top. Coal was fed as fuel
with air through the central burner. Salt was fed through
the tangential feed no~zle together with pulverized coal,
using air as the transport gas. The nominal composition of
the salt was varied in the two runs~as shown in Table II.
~, Typical test results were as follow~:~
i . ,
~ABLE ~
Test C Test D
Salt Composition
NaCl , 3 4%
Na2C3 15.0% 13.5%
Na2S3 20.0% 0
Na2S4 s 65.0% 83.1%
Coal/Salt Ratio in Feed 0.25 lb/lb 0.38 lb/lb
Feed Rates
Coal-Salt Mixture2~0 lb/hr 414 lb/hr
Coal to Burner80 lb/hr 105 lb/hr
Total Air 150 scfm 214 ~cfm
Product Gas
C2 ~1 vol.% 14 vol.%
CO 12 vol.~ 14 vol.%
Temperature at Exit;1186C.1100 C.
Conversion to Sulfide85% 87%
75A2 ~21~3
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It will, of course, be realized that many variations in
the configuration of reaction zones and other reaction
conditions may be used in the practice of this invention
within the limits of the critical parameters set forth
herein. Thus, while the examples illustrating this
invention have been described with respect to specific
concentrations, feed rates, temperatures, and other reaction
conditions, and what is now considered to represent its best
embodiment has been illustrated and described, the invention
may be otherwise practiced within the scope of the teaching
set forth, as will be readily apparent to those skilled in
this art. Accordingly, this invention is not to be limited
by the illustrati-ve and specific e~bodiments thereof, but
its scope should be determined in accordance with the claims
thereof.
.
