Note: Descriptions are shown in the official language in which they were submitted.
Case 2h56
3L~9~
I~lPROVE~ENTS IN THE RECOVERY O~ HEA~ AND
CHEMICAL VAL~JES FROM SPENT PULPIMG LIQUORS
¦ BACKGROUND OF TH~ INVENTION
I. ~
The present invention relates to the art of converting
liynocellulosic materials, such as wood, into pulp, more
specifically to those processes employing at least some chemicals
to convert the lignocellulosic materials into the desired pulp.
The commercially valuable processes for the chemical
pulping of lignocellulosic materials, commonly wood chips, are
slormally referred to as the kraft process, the soda process and
the sulfite process. There are also pulping processes which
employ a combination of chemical and mechanical pulping steps and
these processes are sometimes referred to as semi-chemical or
chemi-mechanical pulping processes These processes use some of
the same chemicals as the kraft, soda and sulfite processes.
For a number of reasons, the preferred chemical pulping
¦ process is the kraft process which involves cooking or pulping
¦¦ appropriately comminuted prices of lignocellulosic material, e.g.
¦ wood chips, in an aqueous alkaline solution of sodium hydroxide,
1 sodium carbonate, and sodium sulfide. Normally the process is
carried out in a pressure vessel called a digester in which the
contents are heated to temperatures of about 160 to 180C, for
about one to three hours. Following the cooking or pulping stage
the cooking liquor is separated from and to a greater or lesser
extent washed out of the pulp and is then subjected to a recovery
treatment to recover the chemical and energy values. Because of
its dark color the pulping liquor is known as kraft black liquor.
5~L c a s e 265fi
The sulfi~e proce~ COmpriseS cooking or pulping
appropriately comminuted lignocellulosic material in an acidic
aqueous solution of sulfur dioxide together with chemicals
providing calcium, magnesium, sodium, or ammonium ionsO The
aqueous solution, thus, contains sulfurous acid, sulfite and
bisulfite ions. The cooking period requires from about six to
about eight hours during which time the temperature rises to
about 140C. In a variation of this process the cooking liquor
may be made neutral or mildly alkaline. Recovery of the spent
pulping liquors has been accomplished by a number of techniques.
In general/ recovery of chemical values from spent liquors of the
sulfite process has proven more difficult than recovery of
chemiczl values from the black liquors of the kraft process.
This is a significant reason for the predominance of the kraft
process over the sulfite process for pulping lignocellu~osic
material.
The traditional recovery process for kraft black liquor
has employed the so-called Tomlinson kraft recovery boiler. In
this boiler, concentrated black liquor serves as fuel to provide
heat for general process use. The combustion process produces,
in addition to the heat generated from the combustion of organic
matter ~resent, a smelt or molten body of inorganic chemical
which comprises sodium carbonate and sodium sulfide. The furnace
process essentially consists of two stages, an initial combustion
stage ~-herein the inorganic salt residue comprises sodium
carbonate and sodium sulfate and a second reduction stage wherein
sulfate is reduced to sulfide. The molten smelt from the
reduction stage is dissolved in water to produce so-called green
liquor which is then treated with lime to convert some sodium
carbonate to sodium hydroxide thus converting the solution into
-2-
~g~s~
white liquor after separation of calcium carbonate. The white
liquor may then be employed as a kraft cooking or pulping liquor
useable in future pulping operations after replenishment of any
depleted components.
The Tomlinson recovery furnace is less than an ideal
solution to the problem of kraft black liquor energy and chem-
ical recovery for several reasons. These are briefly, an op~
portunity for serious explosions if water inadvertently con-
tacts molten inorganic salts, recovery of en~rgy values is re-
duced and independent control of the physical and chemical ac-
tions present in the process is not possible since both oxida-
tion and reduction steps are being carried out in a single ves-
sel within close proximity and emission of reduced sulfur com-
pounds to the atmosphere requires extensive odor control.
Despite the capital investment in existing recovery
systems, it is therefore not surprising that the paper indus-
try has and is investigating alterna-tive recovery possibilities.
One such alternative is a multiple solids fluidized bed recov-
ery system described in U.S. Patent No. 4,303,469. The present
invention provides an alternative technique for the opera-tion
of the apparatus and of the processes described and claimed
therein. In the recovery system of the patent and the appli-
cation, concentrated spent pulping liquor is combusted in a
fluidized bed reactor, employing multiple inert solid compo-
nents, one of which may be referred to as being of fine parti-
cles and the other of coarse particles. The spent liquor is
introduced at the bottom of an initial fluidized bed reactor
which also contains the plurality of inert solid particle co:m-
ponents and is
~g~s~
Case 2656
subjected to the introduction of sufficient air to support a
substantial combustion of most, but not all, of the organic
matter contained in the concentrated spent pulping liquor.
Desirably, only about 80 to 90 percentr based on carbon content
of the organic material is com~usted in the initial fluidized
bed. The plurality of inert particulate solid components, more
¦ particularly, the finer fraction of said particulate solids, as
¦ well as the combustion gases and uncombusted material from the
¦ initial fluidized bed reactor, are removed from the top of the
I fluidized bed reactor and subjected to a separation of most of
the inert solids from the mix'ure of gases and, if necessary,
from uncombusted solids from the combusted spent liquor.
Thereafter in the system the separated inert solids may
optionally be fed to a unit which may be referred to as a
gasifier which is another fluidized bed reactor in which the
inert solids present are only the finer inert particulate solids
from the initial fluidized bed reactor. More spent liquor having
an organic matter content, such as additional kraft black liquor
is introduced in the gasifier unit. Under the thermal conditions
present and in the absence of oxygen, the organic matter is
decomposed to provide reducing gases for later in the process.
I When providing for incomplete combustion in the initial
fluidized bed reactor, as described above, so as to provide for
the formation of uncombusted carbonaceous material, the gasifier
may optionally be eliminated from the process. The uncombusted
carbonaceous material or the reducing yases from the gasifier are
intended to provide a reductant for the conversion of sulfate,
formed in the initial combustion of the spent liquor, to sulfide.
5~ c a s e 265~
.i
The separated inert solids which may optionally pass
through the ~asifier are then transmitted to one or more
fluidized beds acting as external boilers. This unit or units
may preferably contain immersed heat exchange tubes and hiyh
pressure steam may be generated from the sensible heat released
by the solids. The external boiler or boilers remove rnost of the
residucl heat value produced in combustion in the initial
fluidized bed reactor and contained in the finer inert sGlids.
These riner inert solids, with much of their heat value
recovered, are returned to the bottom of the initial fluidized
bed reactor where they are contacted with the air and
concentrated spent liquor and refluidized.
The employment of the plural-stage fluidized bed
reactors, the initial stage of which employs two sizes of solid
particulate components, performs the role of absorbing heat of
combustion and as distinguished from conventional fluidized bed
reactors some of the solids, as well as the gaseous components
are re oved at the top of the reactor, instead of the bottom. In
this wzy, combustion is carried out efficiently at high gas
veloci=y without the need of internal heat removal surfaces in
the in-tial fluidized bed reactor. Conventional fluidized bed
reacto~s remove heat via tubes embedded in the reactor and these,
depending on the operating conditions, may hinder the
fluidization process. The plurality of solid particulate
components employed in the initial fluidized bed reactor are
inert znd perform the roles primarily of recovering heat from the
combus.ion process and providing excellent mixing of air and
concentrated spent pulping li~uor.
¦~ Case ~656
9~S~
A suitable multiple solid fluidized bed reactor for use
in the present invention is disclosed in Nack, et al., U. S~
Patent No. 4,0$4,5~5. Suitable multiple inert solid components
are disclosed in the aforementioned U. S. Patent No. ~,303,469 as
are typical operating conditions.
The present invention provides an alternative operating
mode for said multiple solids fluidized bed recovery system. In
this alternatîve mode in addition to or instead of a carbonaceous
residue provided by incomplete combustion of black liquor solids,
carbonaceous residue is provided by incomplete combustion of a
hydrocarbon fuel, such as coal, petroleum or petroleum coke,
added to the initial fluidized bed combustor.
CITATION OF OTHER ~RT
In addition to the above discussed patents and
applications which applicant considers to be the most pertinent
to this invention, an independent search in the Patent and
Trademark Office has revealed the following patents:
U. S. Patent No. 1,565,300 discloses the use of
charcoal and other carbonaceous material to reduce sulfate in the
ash remaining from combustion of kraft process black liquor. The
charcoal or other carbonaceous material is added to the ash not
prior to or during the combustion step.
U. S. Patent No. 11801,945 discloses the addition of
carbon, as a reductant for sulfate, to the residue from a black
liquor recovery system which remains after a combustion step.
¦¦ Case 2656
~L~9~5~
. S. Patent No. 3,309,262 discloses the optional use
of supplementary carbonaceous fuel in a fluidized bed black
liquor combustor. In column 7 at lines 60 to 63 thereof it is
stated that combustion is complete and negligible carbvn remains
uncombusted.
U. S. Patent No. 3,322,492 discloses the optional use
of a hydrocarbon fuel as a heat supplement in both the drying and
the reducing fluidized bed stages of a black liquor recovery
syste~. The initial drying stage is apparently not intended to
perform any substantial combustion of the black liquor and there
is no suggestion that residues of incompletely combusted
hydrocarbon fuel should be carried over to the second stage
reductor to provide additional reducing agent. In any case the
recovery process being carried out differs in many important
technical aspects from that of this invention.
U. S. Patent No. 3,414,468 discloses a process for
reclaiming limemud by roasting a mixture of limemud and
uncombusted black liquor in a fluidized bed. A supplemental
hydrocarbon fuel is added to provide the heat reguired for
1 calcination until ignitio`n temperature is reached and then the
organic matter in the black liquor provldes the necessary fuel.
U. S. Patent No. 4,224,289 discloses burning black
liquor rrom a soda pulping process in a fluidized bed to recover
alkali.
The present invention differs substantially from the
teachings of all the cited references either singly or when taken
together.
9~S~-~ case 2656
C~lMM~l~V 1~ lF TN~/Fl\~'rTO~;I
The invention provides an integrated process for the
recovery of energy and chemical values from spent pulping liquors
comprising an initial stage of subjecting concentrated spent
pulping liquor and a carbonaceous fuel to combustion with air in
a fluidi~ed bed reaction chamber provided with a plurality of
inert solid particulate materials, at least one of which is of
finer particle size than another, followed by at least one
further step of treating the finer particulate size inert
particulate material in an external fluidized bed unit to recover
the heat values, wherein-at least a portion of said inert finer
particle size solid particulate material is separated from the
gaseous and solid combusion products produced by said combustion
with air and wherein the portion of said solid combustion
products which consists essentially of inorganic salts is
subjected to the reducing action of another portion of said solid
combustion products which consists of uncombusted carhonaceous
material.
Special mention is made of particular embodiments of
the invention wherein the spent pulping liquor is kraEt black
liquor, wherein the carbonaceous fuel is coal, wherein the
carbonaceous fuel is petroleum, wherein the carbonaceous fuel is
petroleum coke those wherein a gasifier is employed, those
wherein effluent gases from the reducer are exhausted into the
initial fluidized bed combustor, and those wherein the solid
combustion products comprise the finer particle size solid
particulate material.
--8--
4S4 case 2656
BRIEF DESCRIPTION OF THE DRAWING
The Figure is a sche~atic representation of an
apparatus and process for the recovery of the heat and chemical
values of kraft black liquor.
DE:SCRIPTI(~l n~ ~ ~n FMRrlnTM~T
The manner of practicing the process of the invention
will now be illustrated with reference to the drawing and to a
specific embodiment namely the recovery of kraft black liquor.
Kraft black liquor, as it is removed as an effluent in
the pulping of wood in a paper making plant, is normally of
relatively low solids conc,entration, containing usually
approximately 14 percent by weight of solids. In the practice of
the process of t.he invention, this liquor is desirably
concentrated to a total solids content of at least about 50
percent and desirably between about 50 and 100 percent by weight
of solids, preferably about 60 to 85 percent by weight. This may
be accomplished by treating the kraft black liquor as it leaves
the pulping operation in multiple~effect evaporators (1) to
remove a large proportion of the water and increase the total
solids content.
In normal operation, the effluent from the multiple
effect evaporators (1) has a total solids content of about 65
percent by weight and has had its temperature increased to about
150 to 200F, desirably about 180F, where it is passed through
conduit (2) into initial fluidiæed bed reactor (3), near the
~ '
_y _
lower end of the reactor. In accordance with one embodiment of
the invention, the fluidized bed reactor is a multiple solids
fluidized bed reactor of the type disclosed in Nack, et al.,
U.S~ Patent, 4,084,545, granted April 18, 1978.
The multiple solids fluidized bed reactor 13~ is op-
erated with a plurality of solids present. The finer and en-
trainable solid may be Speculite, sand or some other inert
material of particles of -16+140 mesh U.S. sizes; that is, the
partieles will pass through a 16 mesh screen but not through
a 140 mesh screen, and the coarse, non-entrainable particles
may be an equal amount by weight of Speculite or other dense
inert material of about -12+16 U.S. mesh size.
Into the fluidized bed reactor (3) there is also in-
troduced air at ambient or elevated temperature through the
bottom of the reaetor as shown at (4), along with carbonaceous
fuel, for example, at or near the bottom of the reactor as
shown at (5), together with the concentrated black liquor which
also enters the reaetor near -the bottom as shown at (2) and op-
tionally recycled gases from a reducer (20) conveyed through a
eonduit (25) and introduced at or near the bottom of the reac-
tor at 126). The amounts of air, reeycled redueer gases, if
any, concentrated black ]iquor and carbonaceous fuel are ad--
justed to provide combustion of about 80 to 90 percent based
on carbon content of the black liquor and carbonaceous fuel,
while yet suspending all solids present. The gaseous products
of the combustion process comprise primarily carbon dioxide,
nitrogen, and water vapor. The inorganic or mineral content
of the black liquor is converted
--10--
* Trade Mark
99 45 4L c a s e 2656
~o sulfate and carbonate salts, normally sodium sulfate and
sodium carbonate. Because the combustion of organic material in
the combination of black liquor and hydrocarbon fuel is intended
to be incomplete, carbonaceous materials, including carbon, are
produced. Desirably, sufficient combusion takes place to
generate a temperature within the fluidized bed rector ~3) of
between about 1100 and 1400F,-preferably about 1300~F. At this
temperature range the non-gaseous combustion products are solids~
The superficial velocity of the air and recycled
reducer gases introduced is adjusted t~ about 30 feet per second
so as to permit entrainment of most of the solids produced by
combustion in the reactor (3) along wi~h much of the entrained
fine particle solid. Desirably, a weight ratio of air to
optionally recycled reduce,-r gases of about 5 to 100 is employed.
These solids escape out the top (6) of the fluidized bed reactor
(3). The combined entrained solids are transferred through
conduit (7~ into cyclone separator (8) which separates most of
the inert solid-content from the mixture of combustion residue
solids and gases. The gaseous materials, comprising primarily
carbon dioxide, nitrogen and water vapor, are removed from the
top of the cyclone separator (8) through conduit (9) along with a
major portion of the combustion product inorganic solids,
comprising sulfate and carbonate, and uncombusted carbonaceous
materials. The major portion of the inert solids, consisting of
the fine particle size inert solid and unseparated inorganic
sulfate, carbonate-and uncombusted carbonaceous materials is
removed from cyclone separator (8) through conduit (10~. The
solids transferred from the cyclone separator (8) through conduit
~ 4 3 ~ Case 2656
(10) are desirably at a temperat~lre of between about 1100 and
1400F, preferably about 1250F. They are passed into gasifier
~11) into which a small proportion of additional concentrated
black liquor is introduced at (12).
The gasifier ~11), which is optionalr is operated
without the addition of any oxygen whereby the black liquor
provides a reducing gas composition unoer the relatively high
temperature non-oxygen atmosphere and in the presence of the
solids. This gaseous reducing composition is removed through
line (13), where the gases now have a temperature of about 1050
to 1350F, preferably about 1250F. The contents of line ~13)
are reducing gases consisting mainly of carbon monoxide and
hydrogen along with hydrogen sulfide and methane, as well as
carbon dioxide, nitrogen, and water vapor.
The inert solid component is passed from gasifier (11)
through line (14) into heat exchanger (15) whereby a portion of
the heat of the remaining solids is exchanged into a coil (16)
containing water, producing steam. The heat exchanger (15) is a
conventional unit emF~loyed in combination with 2 conventional
fluidized bed reactor whereby the coil (16~ provides the role of
a heat removal component. The solids, having surrendered a good
portion of their heat are removcd from the heat exchanger (15)
through conduit (17) and returned into the bottom of multiple
solids fluidized bed reactor (3) to be recycled therethrough.
The gaseous component removed from the cyclone
separator (8) through conduit (9) containing the combustion gases
from reactor (3), sulfate and carbonate solids and uncombusted
carbonaceous material are passe~ through a second cyclone
1~--
r-~
~ Case 2656
separator (1~) ~here additional separation is made of retained
solidsr namely, the uncombusted organics and inorganic salts of
sulfate and carbonate ions, such as sodium and potassium sulfate
and carbonate, which are removed from the bottom of cyclone
separator (18) through conduit (19) into reducer (20). In the
normal operation of the process, the qaseous effluent froln
cyclone separator (18), passing out of the top thereof and
through conduit (21), contains substantially no reducing gases,
particularly those containing sulfur in oxidation states below
the +4 formal valence state, and is composed mostly of carbon
dioxide, nitrogen, moisture, and traces of sulfur dioxide. These
gases having been almost completely separated from the solids and
passed through conduit (?1~ are transmitted into heat exchanger
(22) which is a standard heat exchanger capable of removing heat
from the gases before they are vented from the system through
conduit (23), by which time the temperature of the flue gases has
been substantially reduced to a temperature compatible with the
environment, such as about 400F. At this stage, the gases
~ leaving the system contain no pollutants, except perhaps mere
1I traces of sulfur dioxide which may be removed by conventional
¦ means before release of the remaining gases to the atmosphere.
The solids, including the uncombusted carbonaceous
material, are introduced through conduit (19) into reducer (20)
and mingled with air introduced through inlet (24~. The reducer
(20) is a standard furnace or reactor. The purpose of the
introduction of air into the reducer (20) is to combust
sufficient amounts of uncombusted carbonaceous material, reducing
gas optionally provided from gasifier (11) through conduit (13)
- -13-
11 119~99s54 case 2656
~nd anv othe~ ~nreacted redocing gases, soch as carbon mono~ide,
hydrogen, methane, and hydrogen sulfide to provide the heat
required for reduction of sulfate to sulfide, an endothermic
reaction. The remaining uncombusted carbonaceous material and
uncombusted reducing gases are employed in the reduction.
Complete combustion and reaction of all such components is not a
realistic expectation and some obnoxious gases especially
hydrogen sulfide and other volatile compounds containing sulfur
in a negative or reduced formal valence state, may remain. To
avoid the necessity for provision of other means of removal of
the obnoxious gases, conduit (25) may transmit these gases to
initial fluidized bed reactor (3) at (26). The reducer is
desirably operated at a temperature of about 1650F. The reducer
contains a molten mixture of about two to three parts by weight
of sodium carbonate and about one part by weight of sodium
sulfate in which a substantial amount of the chemical reduction
takes ~lace, and which is provided with a means of agitation.
The purpose of reducer (20) is to reduce much of the
¦ inorgaric sulfate solids to sulfides, which are necessary
¦¦ components of the kraft pulping solutions.
The uncombusted carbonaceous material performs a dual
role ir the reducer. It acts as a pot~ent chemical reducing agent
to redLce sulfate and any thiosulfate which may be present to
sulfide salts and to supply heat of combustion due to the
combustion of the carbonaceous material with the aid of the air
introduced in inlet (24). The reduction of sulfate to sulfide is
-an endothermic reaction and heat to supoort this reaction is
conveniently supplied by combustion of part of the carbonaceous
matericl or other reducing agen~s present.
--14--
9 ~ c a s e 2 6 5 6
The molten solids are lemoved from reducer (20) through
conduit (27) in which stage the solids are in the form of
inorganic sulfides, carbonates, and some unreduced sulfates of
sodium where they are introduced into vat (28) and quenched and
dissolved by water added through pipe (29~ to form green liquor~
The green liquor is removed through conduit (30) to be converted
to white liquor in accordance with conventional means, which
white liquor is returned to the pulping process.
A portion of the flue gas may be removed from conduit
(21) through conduit (31), compressed in compressor ~32) and
recycled into the bottom of heat exchanger (15) through conduit
(33). Most of the content of this flue gas is carbon dioxide and
nitrogen, which are relatively inert to the solids. The purpose
of this recycle is to return some of the unexpended heat back
into the system and to provide a temperature ~ithin the heat
exchanser (15) of about 900F to 1100F, as well as to provide
fluidizing gas for the external heat exchanger or boiler (15) and
the optional gasifier (11). Some of the ~aseous material is
transmitted-through conduit (34) into gasifier ~11) to impart its ¦
remainlng heat to the system and, as statedr to provide
fluiaizing gas for the solids in gasifier (11).
Thus, by operation of the process, black liquor has had
a substantial portion of its organic matter combusted in
fluidized bed reactor (3) while coal or another carbonaceous
fuel, such as petroleum, has been added to provide additional
heat value and a supplemental source of uncombusted carbonaceous
material for use in the reduction processes of reducer (20).
fter the combastion process, in d sequence of steps, the heat
ase 2656
values are recapt~[ed in tbe f~rm of steam whlch in turn is
employed directly in various plant processes or indirectly to
generate energy in other forms for use in the plant. The mineral
components are recovered to form a conventional green liquor~
processable by known conventional techniques for reuse in the
~ulping operation, and toxic and obn~xious gases are retained
within the system until they are converted to compounds
acceptable for release or handling by more economical pollution
control techniques than would be required for control of the
to~ic and obnoxious gases in their original form. This is
facilitated, of course, in the Process mode wherein effluent
gases fro~ the reducer are recycled through conduit (25) back to
the bottom of initial fluidized bed reactor (3) at (26). As
stated above, the addition of coal, petroleum, or other
carbonaceous fuels in addition to providing additional fuel value
during the combustion process in initial fluidized bed reactor
(3) per.mits combustion to be carried out under a wide range of
conditions while insuring that ample unburned carbonaceous
rnaterial will be provided as a reduction source in the reduction
reaction of reducer (20). Addition of coal, ~etroleum, or most
other carbonaceous fuels directly to reducer (20) as carbon
sources for the reduction reaction therein is not possible
because coal particularly contains residual moisture and both
coal and petroleu~ contain material volatile at the temperatures
encountered in reducer (20) and which, thus, would interfere with
safe and proper operation of the reducer (20). When added to the
process in fluidized bed reactor (3), of course, the moisture is
driven off with the remaining moisture content of the black
-16-
9't5~L c ~ s~ 2656
liquor and volatiles are consumed in the combustion reaction
adding to the heat available for recovery.
The process provides an effective means of solid
separation and recovery. Exiting at the top of reactor ~3) are
flue gzs, a portion of the inert bed solids, and oxidized salts
to be recovered and reused in the pulping operation, along with
the uncombusted carbonaceous material to be employed in the
recovery process. The inert bed solids which are entrained in
reactor (3) are separated in an initial c~clone separation (8)
and subsequently recovered and recycled to the reactor. The flue
gas, salts and uncombusted organics are effectively separated by
cyclones, with the process solids flowing to reducer (20).
The external heat exchanger or boiler ~15) serves the
important role of recovering heat of combustion as stored in the
sensible heat from the separated bed solids, thus, avoiding the
necessity of providir,g heat exchanger tubes directly in fluidized
bed reactor (3). In addition to improved operation of the
fluidized bed combustion zone provided by the absence of heat
exchanger tubes therein, corrosion of the heat exchanger tubes is
¦ also substantially reduced.
Optional gasifier (11) provides reducing gas to assist
in the chemical reduction of some of the inorganic salt ~roducts
formed in the combustion. If this unit operation of the process
is omitted, separated bed solids will pass directly from cyclone
(8) to external heat exchanger (15). With the addition of
carbonaceous fuel to fluidized bed reaction (3) in accordance
with this invention, the inclusion of gasifier (11) in the
apparatus and process of the invention is, under most conditions
-17-
Case 2fi56
of operation, not preferred~ In the presence or absence of the
gasifier an important phase of the chemical reductions and of the
process as a whole is the conversion of sodium sulfate to sodium
sulfide which is an important ingredient in the kraft pulping
process This reduction takes place in reducer (20), as
described~ Reduction takes place in the molten salt portion in
the lower portion of reducer (20). Air is int~oduced into the
reducer (20~ at (24) to combust combustible gases such as
hydrogen and carbon monoxide before they exit the reducer. The
air, of course, also performs the important role of combusting
uncombusted carbonaceous material to provide heat. These
reactions are exothermic and provide the thermal energy necessary
for supporting the reduction reactions occurring in the reducer
which are endothermic. ~-
The particular grade or type of coal, petroleum orother carbonaceous fuel employed in the process is not
particularly critical. Any heavy gr~de fuel oil or even crude
oil may be employed. Similarly any available grade a~thracite,
or bituminous coal petroleum coke or even lignite in particle
sizes compatible with the means employed for introduction into
the reactor may be employed.
When bituminous coal i5 employed as fuel, it may be
employed from 1:5 to l:100 by weight, preferably about 1:20 by
weight ratio to black liquor at 65% by weight solids content.
In addition to Speculite, a hematite ore containing
about 93% Fe2O3 supplied under that trademark by C. E. Minerals~
Inc., King of Prussia, Pennsylvania, other inert materials
suitable for use as the inert bed solids are aluminum oxide,
~ -18-
45~ ~ase 2656
n i c k el , o r n i c k e l ox i d e . S a nd i s s u i t abl e l o r t h e sm a l l e r s i z e
particles. The finer solid bed component may also be limestone
or dolomite.
One of skill in the art will recognize that as used
herein and in the appended claims the term "inert" means that a
material is substantially unaffected chemically in a particular
unit operation and may pass into and be recovered from that
operation with no substantial chemical change even if in another
later unit process, it may be a reactant Thus, the salts
produced by the combustion are suitable inert solids in the
combustion phase unit process and a portion thereof may be
separated from the salts being passed toward the reducer (~0) and
be recycled as the finer solid bed component.
One of skill in the art will recognize that separation
of the two solid particle phases employed in the fluidized bed
combustor may occur because of differences in particle size or in
density or a comblnation thereof. The term finer particle size,
therefore, comprehends particles of relatively lesser density and
the ter~ larger particle size also comprehends relatively denser
particles.
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