CA1199454A - Recovery of heat and chemical values from spent pulping liquors - Google Patents

Abstract

IMPROVEMENTS IN THE RECOVERY OF HEAT AND CHEMICAL VALUES FROM SPENT PULPING LIQUORS ABSTRACT OF THE DISCLOSURE Introduction of a carbonaceous fuel such as coal or petroleum into the combustion stage of a multiple solids fluidized bed reactor system for pulping liquor combustion and chemical regeneration provides an alternative source of unburned carbonaceous solids which may be transferred along with pulping liquor solid combustion residues to a reduction stage providing a carbon source for the reduction of sulfate to sulfide.

Description

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.

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 * 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) 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.

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 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 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.

Claims (10)

The subject matter which applicant regards as his invention is particularly pointed out and distinctly claimed as follows:

1. 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 fluidized 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 material in an external fluidized bed unit to recover heat values, wherein at least a portion of said inert finer particle size solid particulate material is separated from the gaseous and solid combustion 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 carbonaceous material.

2. A process as defined in claim 1 wherein the spent pulping liquor is kraft black liquor.

3. A process as defined in claims 1 or 2 wherein the carbonaceous fuel is coal.

4. A process as defined in claims 1 or 2 wherein the carbonaceous fuel is petroleum.

5. A process as defined in claims 1 or 2 wherein a chemically reduced product of subjecting the inorganic salts to the reducing action of uncombusted carbonaceous material is dissolved in water.

6. A process as defined in claims 1 or 2 wherein the carbonaceous fuel is coal and wherein a chemically re-duced product of subjecting the inorganic salts to the re-ducing action of uncombusted carbonaceous material is dis-solved in water.

7. A process as defined in claims 1 or 2 wherein the carbonaceous fuel is petroleum and wherein a chemically reduced product of subjecting the inorganic salts to the re-ducing action of uncombusted carbonaceous material is dis-solved in water.

8. A process as defined in claims 1 or 2 wherein the carbonaceous fuel is petroleum coke.

9. A process as defined in claims 1 or 2 wherein the carbonaceous fuel is petroleum coke and wherein a chemi-cally reduced product of subjecting the inorganic salts to the reducing action of uncombusted carbonaceous material is dis-solved in water.

10. A process as defined in claims 1 or 2 wherein the inert finer particle size solid particulate material is a portion of the solid combustion products comprising inor-ganic salts.