US3163495A - In the recovery of chemicals from the incineration of waste black liquor, the method f eliminating noxious compounds entrained in the combustion gas - Google Patents

Description

Dec 29 1964 J. E. GREENAWALT 3,163,495

N THE RECOVERY OF CHEMICALS FROM THE INCINERTION OF WASTE BLACK LIQUOR, THE METHOD OF' ELIMINATING NOXIUS COMPOUNDS ENTRAINED 1N THE coMusToN GAS 3 Sheets-Sheet l Filed May 2, 1962 mm 9.505 amazon man Dec. 29, 1964 J. E. GREENAWAL'I IN THE RECOVERY OF' CHEMICALS FROM THE INCINERATION BLACK LIQUOR, THE METHOD OF' ELIMINATING NOXIOU COMPOUNDS ENTRAINED IN THE COMBUSTION GAS Filed May 2, 1962 Dec 29, 1954 J. E. GREENAWALT 3,163,495

IN THE RECOVERY OF CHEMICALS FROM THE INCINERATION OF' WASTE BLACK LIQuoR, THE METHOD oF ELIMINATING Noxous COMPOUNDS ENTRAINED IN THE COMBUSTION GAS Filed May 2,. 1962 y 5 Shees-Shee?l 3 las-fi FIG. 3

United States Patent IN RECOVERY F CHEh/HCALS FROM THE INCINERATIGN 0F WASTE BLACK LIQUR,

THE METHOD @it ELllMlNATlNG NXGUS COMPUNDS ENTRAINED IN THE COMBUS- 'rroN GAS John Eckert Greenawalt, Bronxville, N.Y. (13S E. 42nd i St., New York, N.Y.); .Icy S. Greenawalt, executrix of said .lohn E. Greenawalt, deceased Filed May 2, 1962, Ser. No. 191,871

3 Claims. (Cl. 2.3.-43)

This invention relates generally to a method of and apparatus for the recovery of chemicals from waste black liquor, a by-product obtained in the production of pulp from wood; and more particularly to a method of and apparatus for not only recovering the chemicals by ka burning or combustion operation but' also for utilizing the caloric value of the black liquor for producing steam, all in a manner which eliminates objectional odors yin the residual Vgaseous products which, after passing through the apparatus, are discharged into the atmosphere and dissipated.

In the prevailing methods of burning the black liquor, it is burned in a furnace in a manner to burn out the combustible organic matter in the black liquor and so that the incornbustible chemical part may be collected. The hot gaseous products of the combustion of this burning operation are passed into contact with the tubes of steam boilers wherein steam in useful quantities is generated. Ultimately the residual products of the combustion are discharged through a stack to be dissipated in the atmosphere. In those conventional methods the odor from the escaping gases, i.e., the residual gases discharged into the atmosphere, is sutiiciently unpleasant, noxious or oifensive, and intense that pollution of the atmosphere in the neighborhood of the black liquor burning plant, in many instances, constitutes a public nuisance.

Among other things, this invention provides method and means whereby the malodorous or noxious products existing in or produced as a result of the burning of the black liquor are eliminated so that the residual combustion gases discharged to the atmosphere are not ofensive. According to this invention, the products accounting for the bad smells are destroyed at a high temperature in a highly oxidizing atmosphere before the combustion products reach or come in contact with a cooled surface; i.e., before the combustion gases reach the steam boiler unit where the gases are subjected to cooling when they come into contact with the boiler tubes. Consequently, when the residual combustion gases are discharged from the plant throughthe stack to be dissipated into the atmosphere they have been freed from malodorous constituents. Furthermore, substantially all of the chemicals in the black liquor are recovered for reuse; so the nuisance ofv stream and waterways pollution is also eliminated. It is typical that in the manufacture of paper pulp from Wood that onlyV about 50% of the wood entering the process is cellulose-which is the desired ingredient in the wood available for the cellulose ibers for pulp. Typically, or by way of example, the remainder consists of about 30% lignin, about 16% carbohydrates, about 3.3% rosin and fats', all of which` are ldissolved by the chemical solution during the cooking process..

The 'liquor resulting from the cooking processis commonly known as waste black liquor. As a typical examt ple, it will contain about 30% ofthe wood entering the process; including that part of the wood having the highest fuel value.

This black liquor is produced in large quantities in the alkaline pulp making processes and asit comes from the digesters it contains the spent but valuable soda compounds, which were contained in the cooking liquor` ini- Y marras Patented Dec. 29, 1964 tially charged to the digesters and necessary for carrying out the cooking or digesting process. The black liquor, after the cooking process, will contain, in a typical example, about l6%-l7% solid matter, 83%-84% Water and will have a density of about 11 Baume at 601 F.

In order to use this black liquor in the burning process for the recovery ofthe chemicals, it is subjected to varying degrees of concentration before it is introduced into the furnace wherein it is burned; this burning step being an important step in the process of recovering the valuable soda compounds contained in the black liquor. In the process of this invention the black liquor should preferably be concentrated so that it will contain about 60% solids. The black liquor will contain, in spent condition, sodium compounds such as sodium carbonate, sulfur' compounds such as sulfates'and organic sulfur compounds and organic complexes of one kind or another. It has been common practice to burn the concentrated spent black liquor in a reducing atmosphere with the object of converting the sodium sulfate (NazSOl) present to sulfide form (NazS), the sodium sulfide being the form that is wanted in making up the cooking liquor for the kraft process. In some instances the sodium sulfide may be further processed to produce sodium sulflte for use in the semi-chemical process-another well known pulp producing system. In any event, the black liquor is burned to recover the spent chemicals in the concentrated black liquor and the chemical sulfur product recovered is primarily in sodium sulfide form.

In accordance with the process of this invention the waste black liquor, after concentration to a solids content suitable for burning, is burned in a furnace with air under conditions which maintain a desirable reducing atmosphere in the furnace at a temperature above the melting point of the incombustible chemical part of the liquor, usually a temperature in the neighborhood of 1950n F. is satisfactory. The incombustible chemical part produced by the burning of Vthe black liquor is collected and drawn off as a molten product containing predominately sodium sulde and sodium carbonate, and caustic soda if it has been used in the causticizing of the cooking liquor. In the initial burning step, some of the incombustible or chemical part of the black liquor is not immediately collected in that step because a part of it passes along with the products of the combustion either as a vapor or as entrained particles. By reason of the reducing atmosphere under which the initial burning step is conducted with insufficient air to completely oxidize it, there is a material amount of the chemicals carried along with the stream of combustion gases and these entrained and unoxidized particles, in large part, contain bad smelling compounds, such as H28 and some of which are probably in the form of organic sulfur compounds of complex nature. If these bad smelling and often noxious products, carried along in the stream of gases, are cooled before'they are changed or eliminated they persist and continue with the residual combustion gases which are discharged into the atmosphereto be dissipated, with the result of contaminating the ambient atmosphere with offensive odors. This will happen if, for example, the offensive ingredients in the combustion gases from.A the initial burning step in a reducing atmospherel are not eliminated before the hot combastion gasesare contacted with the relatively cooler boiler tubes which are heated by the hot combustion gases.

According to the process of this invention, the combustion gases produced in the initial burning step in a first combustion chamber under reducing atmosphere vconditions are then subjected in a second step to a burning operation under oxidizing conditions by the addition of air in a second chamber (herein called an oxidation chamber) in sufficient amount to produce anY oxidizing t reaction with the compounds entrained in the combus- 3 tion gas stream to completely oxidize them, with the result that all of the compounds which account for the noxious odors or fumes, which otherwise would persist, are changed to a form in which the malodors are com pletely destroyed and eliminated in the combustion gas stream before the combustion gases strike or come into contact with the relatively cooler tubes of the steam boiler unit. The compounds which account for the noxious odors or fumes, having been eliminated by complete oxidation, the hot combustion gases are then passed through the boiler unit tube chamber Ito heat the Water in the tubes to form steam and then through such heat exchangers and scrubbers as may be desirable before discharging the combustion gases into the atmosphere to be dissipated. The noxious or malodorous compounds having been eliminated from the combustion gas stream are then not present in the discharged residual gases to contaminate the ambient atmosphere with noxious or badsmelling odors.

Although the novel features which are believed to be characteristic of the invention will be pointed out in the annexed claims, the invention itself as to its objects and advantages and the manner in which -it may be carried out may be better understood by reference to the following more detailed description taken in connection with the accompanying drawings forming a part hereof, in which FIG. 1 is a ow plan in diagrammatic form to illustrate the process of `the invention;

FIG. 2 is a view Ain elevation, partly in cross section, and partially diagrammatic, showing apparatus in which the process may be carried out;

FIG. 4 is a view on line 4-4 of FIG. 3.

Referring now to the drawings in which like reference characters indicate like parts throughout the several views, the apparatus, in general, comprises a reduction furnace A in which the concentrated black liquor is initially burned in a reducing atmosphere, an oxidizing furnace B connected to furnace A in which the combustible particles entrained in the combustion gas stream from furnace A are burned with additional air to completely oxidize the oxidizable components in the combustion gas stream; a steam boiler unit C, connected to furnace B, through which the hot combustion gas stream passes in contact with the boiler tubes; an air heater unit D connected to the boiler unit in which air is heated for lintroduction into the combustion chamber of furnace A and the oxidation chamber of furnace B; an aqueous solution scrubber unit E connected to the air heater in which residual water soluble components not previously removed from the combustion gas stream are removed; and a suction fan F connected to the scrubber unit for drawing the combustion gases through the apparatus and forcing the residual combustion gases through a stack (not shown) for discharging the combustion gases into the atmosphere where they are dissipated.

After the cooking process the black liquor may contain, as a typical example, about 16 to 17% solid matter and about 83 to 84% water and will test about 11 B. at 60 F Before burning, it is concentrated to about 60% sol-ids and will contain liquid carbohydrates, rosin and fats which are combustible in addition'to the non-burnable chemical soda compounds.

Referring first to the flow diagram of FIG. 1 the waste black liquor from the digesters, after having been yconcentrated to the desired solids content is introduced through conduit l0, through a burner 11. Heated air is introduced through hot air conduit 12 through the burner 11 into the combustion chamber 13 of furnace A. The hot air is taken from air heater unit D through hot air conduit 14v which connects with air conduit 12.

The concentrated black liquor which, in a typical example, will contain about'60% solids -is burned in the combustion chamber 13 with insufficient air to completely oxidize the combustible parts of the liquor so that a reducing atmosphere is maintained in chamber 13 at a temperature in the neighborhood of 1950" F. In this first or initial burning step the ligneous matter and other combustible organic material is burned out of the black liquid and forms a combustion gas stream. The unburnable chemicals are collected in the bottom of furnace A. At the temperature maintained therein the unburned chemicals will form a molten product which may be drawn off through a suitable draw-olf conduit 15. If additional fuel is needed to maintain proper burning it may be introduced into the furnace chamber 13. For example, fuel oil may be passed through fuel conduit 16a, through the burner 11; such fuel being also burned for preheating the plant when starting up. Inasmuch as a reducing atmosphere is maintained in combustion chamber 13, the molten product which ows to the bottom of the chamber is drawn off at 15, will contain sodium sulfide NazS produced by reducing sodium sulphate contained in the spent black liquor, sodium carbonate and other condensed sulfur compounds in small amounts, such as sodium sulte (NaZSOg), sodium thiosulfate (Na2S2O3), sodium sulfate Na2SO4, sodium carbonate, sodium hydroxide, possibly minor amounts of other sulfur complexes and a small amount of insoluble material. The following Table A shows typical analyses of dry chemical which may be drawn off from the combustion chamber 13 in different typical runs, after the burning operation and before any water is added for making up a cooking liquor.

Table A Example I II III 24. 0 20.23 01 6 0. 01 1.3 1.36 Sodium Sulfate (NanSO4) 1. 56 10.3 1.60 Sodium Carbonate (N agGOaL" 74. 92 57.6 72. 65 Sodium Hydroxide (NaOH) 1. 24 -0. 9 .40 Insoluble Material 1.77 6.0 1. 89

Total as present, percent 100. 00 98. 9 98.14

In commercial operations, the combustion gases which pass from the combustion chamber 13, through flue 16 still contain chemical compounds either in solid, vapor or gaseous forms which are carried along with the combustion gas stream. Some of these compounds are valuable recoverable chemicals and also contained in the combustion gas stream are malodorous compounds which, in accordance with the process of the invention, may be eliminated by further burning in an oxidizing atmosphere.

The combustion gases are then passed upwardly through flue 17 into the oxidizing chamber 18. At the upper end of combustion furnace unit B there is provided air introducing ports 19 through which additional hot air may be introduced through hot air conduit 20, which is connected to hot air conduit 14. Introduction of additional hot air into the mixing zone 21 of the oxidizing furnace B provides an excess of oxygen in the combustion gas stream and the chemical compounds carried along in the combustion gas stream from the reducing furnace A are burned and further oxidized as they pass downwardly through the oxidizing combustion chamber 18. The oxidizing chamber isl packed with refractory brick 22 laid up in checkered form so as to expose as large a hot surface as possible to the stream of combustion gases to which has been added an excess of oxygenby introducing hot air through ports 19. Brick known to the trade as chrome brick are preferred because they act in the nature of a catalyst to accelerate the desired oxidizing reaction and, of course, the b ricklaid up in checker fashion provide a large hot refractory surface which enhances the oxidizing reaction that is desired. Any suitable means may be provided to provide a large hot surface area but it is preferred to use a material which provides a catalytic effect to enhance the oxidation of the oxidizable Constituents that are carried in the combustion gases discharged from the reducing chamber 13.

The temperature of the combustion gas stream is raised in the oxidizing chamber 13 by reason of the oxidizing reaction which is exothermic and the temperature is considerably higher than the melting point of the chemicals so that if any chemical product drops out of the combustion gases as the combustion gases pass through flue 25 into the first section 24 of boiler tube chamber 26 of the steam boiler unit C, the product is sufficiently hot to be molten and may be drawn off in molten condition through draw-off conduit 27 in the bottom of the oxidation chamber. Inasmuch as the atmosphere in chamber 18 is oxidizing, H28 carried into it is burned to H2O and SO2 or oxidized to the sulfate form and also any other oxidiza'ole compounds are oxidized and this oxidation will convert entrained bad odor compounds to other compounds in which the bad odor does not exist, whereas otherwise the ill smelling sulfur compounds and ill smelling complexes would persist and be carried along with the combustion gas stream.

The hot combustion gas stream from the oxidation chamber 18 which may be in the neighborhood of 2200 F. cornes into contact with the boiler tubes in the steam boiler unit and gives up heat by heat interchange with the water in the boiler tubes. It will be observed that the boiler tube chamber 26 is provided with a vertical baffle 30 which terminates short of the top of the boiler tube chamber so the combustion gas stream passes through flue 25 then upwardly into the rst section 24 of the boiler tube chamber thence over the top of baille 39; thence downwardly through the second section 31 of the tube chamber, andthen through Hue 32. In some instances it may be desirable to introduce additional fuel in addition to air into the oxidizing chamber 21, if it is desired to produce hotter combustion gases to the boiler tube chamber 26. 'This may be done by passing fuel, such as fuel oil, through pipe 23 through a suitable burner at port 19.

The hot combustion gases which pass through the first section 24 of the boiler tube chamber are rapidly cooled because of their contact with the relatively cooler boiler tubes 28 and as the combustion gas stream passes over the baille 30 and thence downwardly in section 31 of the boiler tube chamber they give up, further Vheat through the tubes to the water in them. In this section 31 the gases are suiciently cooled so that any chemical products that drop out of the combustion gas stream will be in powder form as distinguished from molten, and Vmay be removed from time to time through a suitable removal port 33. The chemical products which are recovered from oxidation4 chamber 18 and from the boiler tube chamber may be added to the black liquor which is introduced to the first burning step or to such other make-up solutions as best suited to the overall operation-#but in any case they are returned to the cycle and hence ultimately recovered.

The combustion gas stream which passes from the steam boiler unit C through flue 32 still contains a considerable amount of heat. The heat then in the combustion gases is utilized to heat the air which is used to burn the black liquor in reducing chamber 13 and the air which is introduced into oxidation unit 1S. The air heater D comprises a heat exchange unit having headers 34, 35 into which air heater tubes 36 are secured. Atmospheric air is passed through port 3'7y and then passes through the tubes in heat interchange relation with the hot combustion gases. The heated air then passes through the discharge end 3S of the air heater into conduit 14 which carries the hot air to the units A and B. If any chemical` in powder form collects in the air heater it may be removed from time to time through a suitable port 40.

The combustion gas stream which leaves the air heater is now cooled to a temperature approaching the temnerature of `the ambient atmosphere introduced into the Vair heater. The gas stream is then passed in to the scrubb er unit E, which is provided with a suitable packing 41 such as ceramic brick or tileto increase contact surface. The combustion gases are then scrubbed with water or an aqueous solution. The scrubber solution is sprayed into the top portion of the scrubber unit and and comes into contact with the combustion gases to dissolve or absorb any residual chemicals that may still be carried along with the gas stream. Of course, and H28 that was initially present in the combustion gas stream will have been burned out in the oxidation chamber 22. If SO2 or other .soluble gases or entrained particles are present they are removed with the scrubber solution. In practice it is desirable to circulate the aqueous solution through the scrubber. The solution may be collected in a collector chamber 42 and returned to the scrubber through suitable piping 43. When the solution is sufficiently concentrated it may be used as make-up for cooking solution or returned to the recovery cycle, as desired. Make-up water for the scrubber solution may be introduced through line 44. If desired, sodium carbonate may be added to the circulating scrubber solution to absorb SO2.

Residual combustion gases stripped of the recoverable chemicals and undesirable bad smellingA or noxious fumes are then drawn through flue 45 and forced by fan 45 through its discharge Vconduit 47 into a stack (not shown) from which the residual gas stream is dissipated into the atmosphere.

FIGS. 2, 3 and 4 illustrate a plant for practicing the process of this invention onV a commercial scale. The black liquor burning furnace A is preferably of the Greenawalt down draft type which is shown and described in detail in U.S. Patent No. 2,673,787. In general, it comprises a cylindrically shapedV steel shell 151 lined With a refractory liner and having a top vwall 153 and sloping bottom 154. The inner surfaces of the furnace chamber 113 are lined with pipe coils 155 as described in further detail in said U.S. Patent No. 2,673,787. A centrifugal burner 111 is mounted in the upper end of the furnace chamber into which is introduced concentratedblack liquor to be'burned through a pipe 110 together with hot air through pipe 112, thence through distributor 156 into centrifugal burner 111. A fuel pipe 116a is provided forburning fuel oilV for preheating the plant for starting up. In some instances fuel oil is introduced through pipe 116er when burning black liquor in c order to maintain sutlicient heat in the burning chamber and the desired reducing atmosphere wherein the CO in the combustion chamber is positively controlled to produce the maximum amount of NaZSin the molten product drawn od fromthisfurnace. By introducing fuel oil into the burner in addition to the black liquor and air the temperature in the combustion chamber 113 is intensied and the reducing effect of the reducing atmosphere is also intensified. A water cooled center post 157 serves as a support and as a cooling means to prevent overheating of the centrifugal burner 111.

It will be understood that the Vvarious units of the plant are supported by a suitable steel framework, designated j various units and ilues hereinafter mentioned are con` structed of suitable materials such as brick. And inasmuch as the chambers vand flues of the various units are subjected to hot combustion gases, they arelined with suitable refractory brick to withstand the heat.V

The black liquor burning Vfurnace A has a discharge flue 115 leading from combustion chamber 113 into a vertical flue 161. The vertical wall of the oxidizing unitB terminates short of the roof 163 of the oxidizing unit B. `In the upper end portion of vertical wall 164 of the oxidizing unit B are a plurality of air ports 119 through which air may be introduced to be mixed with the stream4 of combustion gases passing upwardly through ue 161. As explained hereinbefore, hot air is used in combustion chamber 113 and also in the mixing chamber 121 of the oxidizing unit B.

The oxidizing chamber 118 of unit B is packed with chrome brick 122 laid up in so-called checker brick form, this checker brick being supported on a suitable brick arch 165 constructed in known fashion for passage of gases downwardly therethrough. The black liquor introduced through the centrifugal burner together with hot air from the air heater D is thrown outwardly by centrifugal force in a flat ring and the organic combustible part is burned out in the space between center post 157 and the cylindrical side wall 152. The unburned chemical particles thrown by centrifugal force, strike the water cooled walls of the combustion furnace and are coalesced and run down the side walls 152 and sloping bottom wall 154 into draw-off trough 115 as a molten product. This recovered molten product contains a predominant amount of NaZS and Na2CO3 together with small amounts of other sulfur compounds. A reducing atmosphere and a temperature in the neighborhood of 1950 F. is maintained in the combustion chamber 113. The reducing atmosphere is produced and maintained by incomplete combustion of the organic matter in the black liquor passing through the burner with a reduced amount of air. This incomplete combustion causes and produces malodorous gases and complexes. However, practically all of the unburnable material in the black liquor is recovered in this part of the apparatus in the form of a highly heated molten stream which ows from the furnace through draw-off trough 115. And due to the reducing atmosphere the recovered soda product is in the desirable form of sodium sulfide (NazS) together with Na2CO3 and in this form is used to make up the cooking solution, except in the semi-chemical process in which case the sodium sulfide is first converted to sodium sulte. The reducing atmosphere reduces sodium sulfate in the black liquor to the desired sodium suliide form.

The mixture of hot air introduced through ports 119 and the combustion gases passing through flue 161 and over the upper end 162 of wall 150 is brought into contact with the hot surfaces of the refractory checker brick 122 in oxidizing chamber 118. In this chamber the oxidizing atmosphere oxidizes the oxidizable products carried in the combustion gas stream and converts bad smelling products such as HZS and the organic complexes and converts them into products Which are not offensive. The exothermic oxidizing reaction in chamber 118 raises the temperature of the gas stream which then passes through ue 125 and thence upwardly into the rst section 124 of the boiler tube chamber 126.

The steam boiler unit C comprises upper drum 170 and a pair of lower drums 171, 172 connected by water tubes 128 all mounted within suitable walls. It is important to space the water tubes suiiiciently far apart to permit ready liow of the combustion gases through the chamber and to avoid clogging up of the in-between spaces with chemical products that might be deposited out of the combustion gas stream when the hot gases are quickly reduced in temperature by reason of contacting the relatively much cooler water tubes. Chemical products dropping out of the gas stream in the oxidizing chamber 118 and boiler chamber section 124 will flow as molten product to the bottom wall and may be removed through draw-off trough 127; it being noted that the bottom walls 173 are sloping.

A baiiie 130 separates the boiler tube chamber into the first section 124 and the second section 131. Hence the combustion gas stream iiows upwardly, then over the top edge of the baiiie and downwardly .through section 131 where the heat of the combustion gases is passed through the tubes to heat the water in the boiler. Since the gases become progressively cooler further chemical product may be deposited out of .the stream and since the gas stream is much cooler in section 131 the particles will not coalesce but will fall as a powder and may be removed through a trough 133.

The combustion gas stream, still containing considerable heat, passes through flue 132 and upwardly through the air heater unit D, comprising headers 134 and 135 in which are secured air heater tubes 136. Air from the atmosphere is passed through entrance port 137 and heated air passes out the discharge port 138. Suitable conduits (not shown) in FIGS. 2, 3, and 4, carry the hot air to the burner 111 and to the oxidizing unit through ports 119. Any chemical product dropping out of the gas stream in air heater D may be removed from time to time through a port 140.

The combustion gas stream then passes downwardly through scrubber chamber E which is loosely packed with ceramic pieces 141, such as brick to increase contact surfaces. Water is sprayed through spray nozzles 174 which falls through the scrubber chamber and absorbs any soluble matter still in the combustion gas stream. The aqueous solution -is collected in collector chamber 142 and recirculated through piping (not shown) in FIGS. 2, 3, 4 until a desirable concentration of dissolved chemical product is obtained `after which the concentrated solution may be returned to the recovery cycle as make-up solution.

The combustion gas'stream, now stripped of all recoverable chemicals and stripped of offensive-smelling fumes, passes throughV a ue 145; the suction-blower 146 drawing the gases through the treating apparatus and forcing the clean residual gases through ue 147 and through a suitable stack (not shown) to the atmosphere to be dissipated.

It will be seen from the foregoing description that the process eliminates the offensive-smelling and noxious products resulting from the burning of the black liquor, before the hot combustion gases strike or come into contact with a cooler surface, such as the boiler tubes. The oxidation of the malodorous products in the very hot oxidizing chamber eliminates them. Hence, they are eliminated before they ever reach the steam boiler unit and therefore do not persist with the gas stream which ultimately is discharged into the atmosphere.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

l. A process for recovering chemicals from black liquor containing sulphur in the form of a metallic sulfate together with other chemical compounds used in producing paper pulp which comprises, as a first step, burning the black liquor in a combustion chamber with air in an amount that produces a reducing atmosphere in said combustion chamber and thereby converting the metallic sulphate to sulphide form while maintaining the temperature and atmospheric conditions in said combustion chamber such as to burn out the organic combustible matter and to produce the unburned chemical matter in a molten condition, collecting the molten chemical product containing metallic sulfide thus produced and removing it together with said other chemical compounds in molten form from said combustion chamber, then, as a second step, passing the combustion gas stream produced in said combustion chamber and additional air through an oxidizing chamber in contact with highly heated refractory surfaces while maintaining an oxidizing atmosphere in the said oxidizing chamber at a temperature substantially higher than the temperature maintained in said combustion chamber and under oxidizing conditions which con- Vvert any metallic sulphur compounds entrained in said stream to metallic sulfate form and simultaneously destroying obnoxious fumes in said combustion gases by completely oxidizing the oxidizable constituents carried in said combustion gas stream from said combustion chamber while producing chemical product which Was entrained in said gas stream in molten oxidized form, collecting said oxidized chemical product produced in said oxidizing chamber as a molten product, then passing said combustion gas stream through a steam boiler unit and therein utilizing the heat of said combustion gases to generate steam, and thereafter scrubbing the combustion gases with an aqueous solution and then dissipating the combustion gases stripped of noxious fumes into the arnbient atmosphere.

2. A process according to claim 1 in which a hydrocarbon fuel is introduced into the combustion chamber along with the black liquor and air to intensify the tempe-rature and reducing effect of the reducing atmosphere maintained therein.

3. A process according to claim 1 in which the refractory surfaces in said oxidizing chamber are of a material which serves as a catalyst to enhance the oxidizing reac` tion therein. Y l

4. A process according to claim 3 in which the refractory surfaces are provided by checkered chrome brick.

5. A process according to claim 1 in which a hydrocarbon fuel is introduced into said oxidizing chamber along with said combustion gas stream.

`6. A process according to claim 5 in which the combustion gas stream after passing through said steam boiler i unitis passed in heat interchange relationship with the air introduced into said combustion and oxidizing chambers.

7. A process for recovering chemicals from black liquor containing non-burnable sodium sulfate, non-burn able sodium carbonate and burnable organic matter which comprises burning the black liquor in a combustion charnber With air in an amount Whichprovides a reducing atmosphere in said combustion chamber and burning out the burnable combustible organic part of said liquor in said K combustion chamber and reducing sodium sulfate contained in said black liquor to sodium sullide while simultaneously maintaining the temperature in said combustion chamber suiciently high to maintain the unburned chemical part of said black liquor in molten condition, collecting the unburned chemical part of said black liquor in said combustion furnace as a mixture of sodium sulfide and sodium carbonate in molten condition, passing the combustion gas stream produced in said combustion chamber together with additional air into Contact with highly heated refractory surfaces in an oxidizing chamber maintained at a temperature substantially higher than the temperature maintained in said combustion chamber and under atmospheric conditions such that any entrained sodium sulfide carried in said combustion gas stream is oxidized to sodium sulfate and thereby simultaneously destroying noxious fumes contained in said combustion gas stream, collecting in said oxidizing chamber as a molten mixture the oxidized sodium sulfate and sodium carbonate which is entrained and carried with said gas stream into said oxidizing chamber, passing said combustion gas stream from said oxidizing chamber into contact With the Water tubes of a steam boiler unit to generate steam, thereafter passing the combustion gas stream through an aqueous solution scrubber and dissipating the gas stream stripped of noxious fumes into the ambient atmosphere.

8. A process according to claim 7 in which hydrocarbon fuel is introduced into the oxidizing chamber along with the gas stream from said combustion chamber.

References Cited bythe Examiner UNITED STATES PATENTS MAURICE A. BRNDS, Primary Examiner.

Claims (1)

1. A PROCESS FOR RECOVERING CHEMICALS FROM BLACK LIQUOR CONTAINING SULPHUR IN THE FORM OF A METALLIC SULFATE TOGETHER WITH OTHER CHEMICAL COMPOUNDS USED IN PRODUCING PAPER PULP WHICH COMPRISES, AS A FIRST STEP, BURNING THE BLACK LIQUOR IN A COMBUSTION CHAMBER WITH AIR IN AN AMOUNT THAT PRODUCES A REDUCING ATMOSPHERE IN SAID COMBUSTION CHAMBER AND THEREBY CONVERTING THE METALLIC SULPHATE TO SULPHIDE FORM WHILE MAINTAINING THE TEMPERATURE AND ATMOSPHERIC CONDITIONS IN SAID COMBUSTION CHAMBER SUCH AS TO BURN OUT THE ORGANIC COMBUSTIBLE MATTER AND TO PRODUCE THE UNBURNED CHEMICAL MATTER IN A MOLTEN CONDITION, COLLECTING THE MOLTEN CHEMICAL PRODUCT CONTAINING METALLIC SULFIDE THUS PRODUCED AND REMOVING IT TOGETHER WITH SAID OTHER CHEMICAL COMPOUNDS IN MOLTEN FORM FROM SAID COMBUSTION CHAMBER, THEN, AS A SECOND STEP, PASSING THE COMBUSTION GAS STREAM PRODUCED IN SAID COMBUSTION CHAMBER AND ADDITIONAL AIR THROUGH AN OXIDIZING CHAMBER IN CONTACT WITH HIGHLY HEATED REFRACTORY SURFACES WHILE MAINTAINING AN OXIDIZING ATMOSPHERE IN THE SAID OXIDIZING CHAMBER AT A TEMPERATURE SUBSTANTIALLY HIGHER THAN THE TEMPERATURE MAINTAINED IN SAID COMBUSTION CHAMBER AND UNDER OXIDIZING CONDITIONS WHICH CONVERT ANY METALLIC SULPHUR COMPOUNDS ENTRAINED IN SAID STREAM TO METALLIC SULFATE FORM AND SIMULTANEOUSLY DESTROYING OBNOXIOUS FUMES IN SAID COMBUSTION GASES BY COMPLETELY OXIDIZING THE OXIDIZABLE CONSTITUENTS CARRIED IN SAID COMBUSTION GAS STREAM FROM SAID COMBUSTION CHAMBER WHILE PRODUCING CHEMICAL PRODUCT WHICH WAS ENTRAINED IN SAID GAS STREAM IN MOLTEN OXIDIZED FORM, COLLECTING SAID OXIDIZED CHEMICAL PRODUCT PRODUCED IN SAID OXIDIZING CHAMBER AS AMOLTEN PRODUCT, THEN PASSING SAID COMBUSTION GAS STREAM THROUGH A STEAM BOILER UNIT AND THEREIN UTILIZING THE HEAT OF SAID COMBUSIONT GASES TO GENERATE STEAM, AND THEREAFTER SCRUBBING THE COMBUSTION GASES WITH AN AQUEOUS SOLUTION AND THEN DISSIPATING THE COMBUSTION GASES STRIPPED NOXIOUS FUMES INTO THE AMBIENT ATMOSPHERE.

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