US2416462A

US2416462A - Method of and apparatus for recovering heat and chemicals

Info

Publication number: US2416462A
Application number: US465384A
Authority: US
Inventors: Leslie S Wilcoxson
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1942-11-12
Filing date: 1942-11-12
Publication date: 1947-02-25
Anticipated expiration: 1964-02-25
Also published as: GB569951A

Description

Feb. 25, 1947. s. wmcoxsou I 2,416,462 A METHOD OF AND APPARATUS FOR RECOVERING HEAT AND CHEMICALS Filed Nov. 12, 1942 7 sh ets-sheet 1 INVENTOR.

Fig! 7 Les/2e S m/coxsoh ATTORNEY Feb. 25, 1947. 1.. s. WILCOXSON 2,416,462 METHOD OF AND APPARATUS FOR RECOVERING HEAT AND CHEMICALS Filed Nov. 12 1942 7 Sheets-Sheet 2 Fig.2 Q

INVENTOR.

Les/[e Wi/coxson Y W Attorney I Feb. 25, 1947. I s, w coxso 2,416,462

' METi-IOD OF AND APPARATUS FOR RECOVERING HEAT AND CHEMICALS Filed Nov. 12', 1942 '7 Sheets-Sheet 4 57 u n q i i 9 v u u u u 58 1 2 57v 21 fig.

' A I INVENTOR.

' Leslie Wilcoxson BY ATTORNEY Feb. 25, 1947. 5 w o 2,416,462 METHOD OF AND APPARATUS FOR RECOVERING HEAT AND CHEMICALS File d Nov. 12, 1942 7 Sheets-Sheet 5 INVENTOR. v

Leslie 5 Wi/coxson ATTORNEY Feb. 25, 1947. s. w|| coxsoN METHOD OF AND APPARATUS FOR RECOVERING HEAT AND CHEMICALS INVENTOR. Les/ieS WF/coxson '7 Sheets-Sheet 6 Filed NOV. 12,- 1942 A TTORNE Y L. s. WILCQXSONY 2,416,462 METHOD OF AND APPARATUS FOR RECOVERING'HEAT AND CHEMICALS Fi led Nov. ,12, 1942 7 Sheets-Sheet 7 Feb. 25, 1947;. r

INVENTOR. Les/1' e S Wilcoxson ATTORNEY -i-----i-i iitL Patented Feb. 25,1947

UNITED STATES PATENT OFFICE,"

METHOD OF AND APPARATUS FOR RE- COVERING HEAT AND CHEMICALS L'eslie S. Wilcoxson, Ridgewood, N. J 'assignor to The Babcock'& Wilcox Company, Jersey City,

, N. J -a corporation of New Jersey Application November 12,1942, SerialNo. 16 5,384

' 11 Claims. (Cl. 23-48) The present invention relates in general to the recovery of chemicals and/or heat from waste liquor containing inorganic chemicals and combustible organic matter, and more particularly, to the recovery of chemicals and heat from the pulp digester residual liquor in the sulphate and soda processes of manufacturing pulp;

In the treatment of residual or black liquor from the pulp digesters used in the sulphate or kraft pulp industry, for example, the weak liquor from the digesters is usually concentrated to a solid concentration of 50-65% before delivery to the chemical recovery furnace. The inorganic chemical content of the liquor is mainly sodium carbonate (NazCOa) and sodium sulphate (Na2SO4) together with traces of sodium sulphide (NazS) and other salts in various complex combinations with the ligneous matter. The heat values in the liquor are due to the presence of organic combustible matter or lignins released from the wood in the digesters.

The main functions of such recovery units are to recover the sodium salts in the form of smelt, reduce the sodium sulphate to sodium sulphide, and recover a high percentage of the heat values of the liquor in the'form of steam." Such apparatus is well known and shown, for example, in my joint patent with G. H. Tomlinson No. 2,161,110. The reduction of the sulphate to sulphide is essential to permit its immediate reuse in the preparation of fresh cooking liquor for the digesters. This reducing action is usually represented as Na2SO4+4C- NazS+fi'CO. With normal operation of 'such recovery units, about 92% of the available sulphate is reduced to the sulphide, and seldom more than 95%. It is believed that this reaction does not go to completion because some of the sulphide is reoxidized in the unit to sulphate.

A considerable amount of the chemical is evaporated, volatilized or sublimed under normal furnace temperature conditions, and even though subsequently solidified may be carried out of the unit with the products of combustion. The chemical losses due to unrecovered chemical may run from 50 to 150. pounds per ton of pulp. A' large percentage of the volatile material is believed to be sodium sulphate formed by the union of vola tilizedsodium' oxide with carbon dioxide, sulphur dioxide and oxygen in the heating gases in successive stages:

2 It is also believed that there is a critical temperature of about 2100 F. above which volatilization of such chemicals increases rapidly.

The volatilized or sublimed chemicals tend to solidify on the heat absorbing. surface of the unit as the temperature of the gases is reduced by heat absorption therefrom. Chemical particles are also present in the gases due to the suspension burning of spray particles. The deposited chemical is usually found in substantially different conditions in the different parts of the unit, ranging from running smelt in the furnace to dry talc-like deposits in the boiler tube bank, depending upon the temperature conditions in the different portions of the unit. 'The chemicals tend to adhere tightly to any surface on which they may deposit. When the surface on which the chemicals deposit are normally spaced convection heated steam boiler tubes, the depositing chemicals tend to bridge over the intertube spaces and rapidly reduce the available gas flow area in that section with consequent disadvantageous results in the operation of the unit. 7

The general object of my invention is the provision'of an improved method'of and apparatus for recovering chemicals and/or heat from waste liquors of the general character described. Further and more specific objects are the provision of an improved method of and apparatus for incinerating pulp residual liquor in a selfvsustaining manner and in which the percentage cfreduction of the sodium sulphate to sulphide is increased, the volatilizationand sublimation of. the included chemicals is reduced, and the deposition of chemicals in a fused or semi-fused condition is confined to the furnace section of the unit. A further specific object is an improved construction and arrangement of the heat absorbing surface in apparatus of the character described whichprovide a rapid solidification of any volatilized or sublimed chemicals in the furnace gases, which minimizes the deposition of chemicals and is readily cleaned by standard cleaning devic's, and which facilitates thesep -jl aration and recovery. ofchemicals in suspension.

in the heating gases generated. I

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification; For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described a preferred embodiment.

a of Fig. 1; a Fig. 3 is a horizontal section taken on the line 3-3 of Fig.2;

Fig. 4 is an enlarged view of the lower portion of Fig. 1 and taken on the line 4-4 of Fig. 5; Fig. 5 is a vertical section taken on the line 5-5 of Fig. fl;

Fig. 6 is a plan view partly in section of'one of the superheater tube supports;

Fig. 7 is an elevation partly insection on the line 11 of Fig. 6;

Fig. 8 is a view similar to Fig. 6 of a support at the opposite end of the superheater;

Fig. 9 is an elevation partly in section of the a structure shown in Fig. 8;

Fig. 10 is an enlarged horizontal section taken I on the line l0-l o of Fig. 2;

V Fig. 11 is a front view of the structure shown a in. Fig. 10; r

. Fig. 12 is an enlarged view of the rear wall primary and secondary air connections;

Fig. 13 is a horizontal section showing the wind-box arrangement for the primary and secondary air systems; and

Fig. 14 is a side view of the wind-boxes shown 1 in Fig. 13.

The chemical recovery unit illustrated in the The apparatus shown has a vertically elongated setting of substantially rectangular horizontal cross-section throughout and divided into a primary furnace section I 0,a secondary furnace section II, a steam superheating section I2, and a steam generating section [3, which are serially connected in the order named. The primary furnace section is defined by a front wall l5, a rear :wall it, side walls I? and I8, and a rearwardly Qinclined bottom l9 forming a furnace chamber 7 of substantially rectangular horizontal and vertical cross-section. All of the boundary walls are fiuid cooled by rows of water tubes wholly or partly covered by refractory material, the front wall having a row of tubes extending upwardly from a bottom header 2!, the bottom and rear walls having a row of tubes 22 extending from the header 2! along the furnace bottom and thence upwardly along the rear wall, and the side walls I! and I8 having

tube rows

23 and 24 extending vertically from

bottom headers

25 and 26 respectively. All of the described tubes are supplied with water through large diameter pipes 21 at opposite sides of the unit and pipe connections 28 leading therefrom to the headers 2|, 25; and 26. The furnace bottom and lower sections 'ofthe' rear and side walls are of the full studded type, i. e.'

these tubes are provided Withmetallic studs and the studs and tube surfaces completely'covered with refractory to a level above the secondary air ports hereinafter described. providing a high percentage of refractory surface surrounding the fuel bed space. The front wall and upper portionsof the side'and rear walls are of the partial particles in a sticky condition when impacting on a vertical arresting surface formed by the side and. rear walls, on which a major portion of the sprayed particles deposit. With this arrangement a mass of partly dried spray particles accumulates on the side and rear walls, as indi cated in Figs. 4 and 5, and remains thereon until dried substantially completely bythe rising gas stream passing over the surface. thereof, forming a porous readily combustible char. The dried char falls in lumps from the walls onto the fuel bed in the furnace bottom, maintaining a fuel bed of substantial depth having the contours sub-- stantially as indicated in Figs.'4 and 5. One or more smelt outlets 3| are arranged in the, front wall I5 at the lower end of the bottom |9..

In accordance with my invention air is supplied to the primary furnace chamber at three eleva-i tions therein in separately controllable primary, secondary and tertiary air streams. The provi; sions for supplying preheated primary and sec ondary air comprise a forced draft fan 32 having outlet control dampers 33 and a flue 34 incorporating a steam heated air heater 35. .The flue 34 opens into a line 36 extending along the rear side of the furnace, the flue 36 in turn being con-i nected to wind boxes 31 along the side and rear walls. Each wind-box 3'! is divided by a horizon tal partition 38 into an upper section 39 and-a lower section 49. The lower section 40 of each wind-box is subdivided by vertical partitions 4i and inclined horizontal partitions 42 to form a series of primary air compartments 4!! with the air admission to each compartment 4!) controlled by an externally operable inclined damper 43 positioned in a corresponding opening in the partition 42. Each compartment 40' opens to the primary furnace chamber l0 through vertically elongated rectangular primary air inlet ports 44 positioned in the side and rear walls between adjacent water tubes thereof and outwardly in clined. Y The air ports .4 are preferably arranged in a horizontal line along the rear wall andin rearwardly stepped groups along each of the side walls at a level relative to said walls at which the primary air ports will normally be submerged in the fuel bed. A supplementary control of each primary air port is supplied by an adjustable filler plate 45 at the outer end of each port and ar ranged to control the air velocity therethrough without changing the level of the bottom of the corresponding air stream. I

The upper section 39 serves as a secondary air supply chamber extending the full length of each wind-box- The chambers 39 receive their air supply from the duct 36 through branch conduits 47 at the rear corners of the furnace controlled by aseries of secondary air dampers 48. The secondary air is delivered to the furnace chamber at a level slightly above the normal fuel bed level through a series of substantially horizontally arranged secondary air inlet ports 50. The ports 50 are in vertical alignment with some of the primary air ports 42 and of similar flow area but only approximately half the number or primary air ports. Control of the individual secondary port areas is obtained by adjustable filler plates 5| adjustable to raise the effective bottom of the correspondingsecondary air ports without chang ing the level of the top of the air stream therefrom.

The provisions for the tertiary air supply consist of an independently controlled fan 55 and discharge duct 56 leading to a rectangular windbox extending completely around the furnace chamber and opening thereto at a level above the upper char level through tertiary air inlet ports 58 in the front, rear and side walls similar in cross-section to the primary'and secondary air ports and in alignment with alternate secondary air ports in the same wall. The ports 58 in the side walls [1, I8 are horizontally arranged and relatively staggered while those in the front and rear walls are on the same level but outwardly inclined and relatively staggered. Observation doors 59 are provided in the corresponding windboxes opposite each of the

air ports

44, 50 and 58.

The secondary furnace section II forms a ver tical continuation of the primary furnace chamber with its front and side walls defined by continuations of the walls l5, l1, and I8 respectively, and its rear side defined by a forwardly inclined partition or baffle 60 forming a continuation of the primary furnace rear wall I8 and arranged to progressively reduce the efiective flow area of the lower part of the secondary furnace chamber. The baffle 60 is continued vertically to a point short of the rearwardly inclined roof SI of the setting to form a rectangularopening 62 above the upper end of the baflie 68, while the tubes 22 extending a o the furnace side of the baffle continue in a staggered arrangement across the opening 62 to a horizontal roof header $3. The front wall tubes 20 are continued along the roof 8| to the header 63, while'the

side wall tubes

23 and 24 continue upwardly to corresponding headers 64. The headers 64 are connected by tubes 65 to the steam space of the steam and water drum hereinafter described, and the header 63 by roof tubes 66. The portions of the front and side walls and roof in the secondary furnace chamber and the vertical section of the baffle 60 are preferably constructed to provide a greater amount of metallic heat absorption area than the wall por tions in the primary furnace chamber, and in this section the tube studs are replaced by stud plates 66' lining the exposed intertube areas, as shown in Figs. 6 and 'I.

As shown in Figs. 2 and 3, the secondary furnace chamber contains a series of laterally spaced vertical tube platens, each formed by spaced parallel tubes 61 extending inwardly from vertical headers 68 beyond the front wall l5, and thence vertically the entire height of the secondary fur na-ce chamber. Their upper ends are connected to corresponding horizontal headers 69 which are also connected to the steam space of the boiler drum'by tubes 55. Four of such tube platens are shown. in symmetrical arrangement relative to the center line of the secondary furnace chamber and provide a substantial amount of radiant and convection heated heat absorption area with a relatively low resistance to gas flow. The headers 68 are supplied by pipe-connections from the downcomer pipes 21.

The steam boiler section I3 constitutes the main convection heated steam generating section of the unit, and is located in the upper part 01' the setting rearwardly of and above the. primary furnace rear'wall l8. 'The boiler section is o1 the two-drum vertical tube bank type and comprises an upper steam and water drum 1 I, a lower drum 12, a front tube bank 13, and a spaced rear tube bank 14. A tube bafiie 15, formed by studtubes and. refractory as shown in Figs. 8 and 9, extends downwardly along the first row of boiler tubes from the drum 1| to a point short of the lower drum 12, the space below the lower end of the baifie serving as a gas entranceto the space occupied by the tube bank 13. "A second vertical baffle 16 extends upwardly from the drum 12 along the rear rows of the tube bank 13 to a point short of the upper drum II, the space thereabove serving as a gas entrance into the space occupied by the tube bank 14. With this arrangement the heating gases delivered to the boiler section enter the lower end of the space occupied by the tube bank 13 and flow upwardly therethrough between the baiiles 15 and 16 and over the upper end of the bafile 16 and downwardly along the tube bank 14 to the gas outlet flue 11 connected to the bottom of the setting. An economizer may be advantageously arranged in the gas outlet flue for the recovery of additional heat from the gases which can then be passed through a spray tower or disc evaporator to an induced draft fan and stack connection.

The steam superheater section 12 occupies the setting space between the baflle 60 and the boiler tube bank 13 with the upper end of the space opening to the screen passage 82 and its lower portion to the lower end of the tube bank'space 13. The portion of that space immediately below the upper end of the baffle 68 is occupied by the steam superheating surface of the unit con- SiSting of vertically spaced groups of superheater tubes and 8| with corresponding tubes in each group serially connected. Each tube has vertically spaced horizontal leg portions connected by vertical loops which are exp-ansibly supported on the tube baiiles 50 and 15, as shown in Figs. 6-9; Each-loop at one end carries a hollow hook-, shaped lug 83 which extends over and rests on. a pair of brackets 84 welded to adjacent tubes 22. At the opposite end each loop carries a hookshaped lu-g85' which fits over a pair of short bars 86 welded on the baiiie tubes 13. Each superheater tube is positioned opposite to the intertube spaces of the corresponding supporting

tubes

22 and 13, and the tube loops adjacent the battle tubes 13 are'arranged to project into the spaces between these tubes, the studs and refractory closing these intertube spaces to form the bafile 15 being arranged between the rear halves oi the tubes. 7

Each superheater tube is connected to the steam space of the drum H by a riser tube' 88 extending upwardly along the baffle E5 to the drum H. The riser tubes 88 are positioned for most of their length between the adjacent tubes 73 so as to have their exposed faces substantially flush with the exposed faces of the tubes 13 and are held in that position by overlapping guide lugs 89 and 93 welded on the

tubes

88 and 13 respectively, as shown inFigs. 10 and 11. This construction provides a relatively smooth surface along this portion of the bafile 75 which minimizes chemical deposits thereon and facilitates cleaning'of the same while permitting relative expansion and contraction of the tubes 88 and T3. t

The lowermost leg of the superheater tubes 8|: is continued downwardly along the bafile l5 and across the entrance to the .tube bank 13 to a hon-f:

. point of use.

7 izontal'header 92 adjacent the drum l2 and from which the superheated steam is delivered to the The superheater tubes '80 and 8| occupy only a relatively small portion ofthe superheater section I2, leaving a substantial cavity therein ,both above and below the superheater tubes. The upper unoccupied space serves as a gas turning space for the gases passing-through the screened opening 62, while the lower cavity afiords a substantial space for the separation of dry chemical solids in suspension in the gases, while facilitating the turning of the gases into the tube bank space 13. The inclined smooth rear side of the baffle 60 forms the front wall of a hopper 93 at the bottom of the superheater section and receives the solids separating in the superheater section and also from the tube bank space 13. The opposite side of the hopper is formed by a wall 94 extending downwardly at an angle from the drum 12 across the header .92 to a point in alignment with the rear wall it. The wall 94 is continued downwardly and rearwardly from that point to form an outlet 95 for the hopper which is connected to one or more pipes 96 leading to suitable mechanical injectors 91 for discharging the collected solids through the rear wall of the primary furnace section onto the fuel bed. a r

The described apparatus is particularly eifective for treating sulphate pulp residual waste liquor in accordance with my improved process of incineration. According to my invention in normal operation the weak black liquor from" the pulp digesters is concentrated in multiple effect evaporators to a concentration of approximately 50% solids. The liquor concentration is subsequently increased in a spray tower or disc evaporator to about 60-62% solids. Following this point the make-up chemical or salt cake is mixed with the liquor in a mixing tank and the liquor subsequently heated to a temperature of approxi-' mately 220 F. The concentrated liquor is then pumped to the spray nozzle 30 whereby it is sprayed onto the side and rear walls of the primary furnace as previously described. The sprayed liquor is partly dried and some of the volatile constituents distilled off during its passage across the furnace chamber in intimate contact with the uprising gas stream. The par-- ticles after being deposited on the walls are almost completely dried and most of the remaining volatiles distilled off, by contact with the rising gas stream, thus forming a porous char which falls to the fuel bed from time to time in irregular lumps. The combustible organic contentof the char is burned on the furnace bottomeunder a controlled reducing atmosphere, some of the heat generated being utilized in the smelting of the chemicals and the reduction of the sodium sulphate to sodium sulphide before the discharge of the smelt through the smelt outlet 3| to a suitable dissolving tank.

In the operation" of known recovery units of i i this general type a total combustion air supply of approximately 125% of the theoretical amount 1 of air required for complete, combustion of the heat values of the liquor is divided between verf tically spaced sets of primary and secondary air f ports with the primary air. ports above a relat-ively shallow fuel bed and arranged to discharge high velocity air streams sweeping over the fuel bed surface at spaced points. This impingement l of the primary air streams tends to produce localized temperatures in the adjacent parts of the fuel bed considerably above thecritical volatilization temperature of 21009 increasing volatilization'and sublimation of chemicals i'n'thes'e portions of the fuel'bed, 'In accordance with my invention the localize combustion of exposed portions of a relatively shallow fuel bed is replaced to a large extent by a submerged combustion over a substantial part of a relatively deep fuel bed, such as is used in gas producers. The more uniform and lower combustion temperatures resulting in the bed advantageouslyreduce the amount of chemicals volatilized or sublimed therein. The amount of. primary air supplied for this purpose is'reduced and distributed more widely in the fuel bed. The

primary air velocity is made as low as possible 7 to minimize the amount of solids carriedupwardly into the gas space of the furnace chamber by the gaseous products of combustion, yet is maintained sufiicient to secure the desired penetration of the fuel bed and to keep the primary air ports clear of char and smelt. By way" of example and not of limitation, between and of the theoretical amount of combustion air required can be supplied to the primary air ports at a static pressure of 4 to 5 in. H2O, providing a velocity at the air inlet ports of 8-10.000 feet per minute. Due-to the submergence and num ber of the primary air ports the primary air is brought intimately in contact with a large portion of the fuel bed. This distributed and sub- 'merged arrangement of the primary air ports provides combustion of the fuel bed over a large area and maintenance of the smelted chemicals under reducing conditions until discharged, so that little or none of the sulphide produced 15 reoxidized to the sulphate. The amount of chemicals passing upwardly into the gas space of theunit. is; also reduced due to the substantial filter action of the superjacent portions of the fuel bed The secondary air supply is regulated to provide combustion of the combustible volatiles distilled from the bed and carbon monoxide produced to produce sufiicient heat to dry the. char on the walls and partly dry the sprayed liquor traveling across the furnace chamber, From 10-15% of the theoretical air requirements is supplied through the secondary air ports. The static pressure maintained at the secondary air ports can be less than that at the primary air ports, as for example, of the order of 1-2 :in. H2O resulting in a secondary air entrance velocity of 13,000 feet per minute. The primary and secondary air are preferably preheated'to a temperature of 280-350 F. to promote ignition in the fuel bed and high temperature conditions around the center portion of the bed.

About 12% excess air is supplied'through the tertiary air ports at a high velocity, windbox staggered and angularly spaced arangernent described promote mixing and turbulence in the rising gases and insure intimate contact of the air and combustible constituents of the furnace gases as to insure rapid and complete combus tion. Elimination of solids from the gases is also facilitated by the large gas flow area and consequently low gas velocities in the primary furnace section. v

The rising gases thenenter the high heat ab of convection, heating surface. chemicals in suspension are ordinarily in a solid sorptlonzone formed by the completely-water cooled secondary furnace chamber. The progressive reduction of the effective flow area in this section offsets the cooling of the gasesand increases the convection heating effect on the,

tubeplatens. solidification of the chemicals in tions. The heating gases continue their upward now. and turn through the screened Opening 62,

the screen tubes providing a substantial amount The remaining the gases is rapidly effected in the secondary fur- ,nace section and a substantial amount of chemicals collect on the furnace walls and tube platens and are returned to the primary furnace section ,by gravity alone or the periodic cleaning operav -spray level for the combustion after passing through and being heated by an ascending stream of high temperature gases sufficondition on entering, the superheater section;

Ihe substantial increase in gas flow area in the superheater, section duegto the cavities therein and the two major changes in directionof gas flow therein are effective in separating most .of the remaining solids in the gases. The separated solidscollect inthe hopper 93 and arereturned to the primary furnace chamber by the injector. The vertical arran ement of the boiler tubes and the parallel-flow of the heatinggasesrelative thereto minimize the collection of chemicals on the tube surfaces and permit'the same to be readily cleaned with mechanical soot blowers. l e While in accordance with the provisions .of

' the statutes I have illustrated and described herein-th'e best form of my invention now known to me, those skilled. in the art will understand that changes may be made in the form of the apparatus and operation of the process disclosed without departing from the spirit of the invention covered by my claims, and that certain heat from liquor containing inorganic chemicals and combustible matter which comprises spray- .ing the liquor into a vertical furnace chamber in intimate contact with an ascending stream of high temperature gases, collecting dehydrated combustible material to form a fuel bed of substantial depth in. the bottom of the furnace chamber, and supplying combustion air to said furnace chamber so as to minimize chemical carryover therefrom comprising supplying a major portion of the total air supply but less than the theoretical air requirements as primary combus- -tion air in a series of spaced streams directly to submerged portions of the fuel bed for self-sustaining combustionof the combustible material and smelting of, the included inorganic chemicals therein under reducing conditions, supplying secondary combustion air in an amount not more than the balance of the theoretical combustion air requirements and in a series of spaced streams *directlyto the space between the fuel bed and the spray levelfor the combustion of combustible gases rising from the fuel bed, in-

dependently controlling the amount and'velocity of the primary and secondary air streams to maintain "a maximum temperature in the fuel bed suificient .to smelt the included inorganic chemicals therein but normally below 2100 F. and supplying the remaining air as tertiary combustion air in a series of spaced streams directly to the' portion ofthe furnace chamber above the ciently to put the spray particles when impacting in a sticky condition, maintaining the sticky particles in an adhering mass on the arresting surface until sufficiently dehydrated to separate and form a fuel bed of combustible material of substantial depth in the bottom of the furnace chamber, and supplying combustion air to said furnace chamber so as to minimize chemical carryover therefrom comprising supplying a major portion of the total air supplybut less than the theoretical air requirementsas primary combustion air ,directly'to submerged portions of the fuel bed for the combustion of the combustible material and smelting of theincluded inorganic chemicals therein under reducing conditions, supplying secondary combustion air directly to the space between the fuel bed andthe spray level for the combustion of combustible gases rising from the fuel bed, and supplying tertiary combustion air directly to the portion of the furnace chamber above the spray level for the combustion of combustible gases present above the spray level.

3. The process of recovering chemicals and heat from liquor containing inorganic chemicals and combustible matter which comprises introducing the liquor at a solid concentration in the peratur'e gases sufficiently to put the spray particles when impacting in' a sticky condition,

maintaining the sticky particles in anadhering mass on the arresting surface until sufliciently dehydrated to separate'and form a fuel bed of combustible material of substantial depth in'the bottom of the furnace chamber, and supplying combustion air to said furnace chamber soasto minimize chemical carryover therefrom comprising supplying a major portion of the total air supply but less than the theoretical air require merits as primary combustion'air'in a series of spaced streams directly to submerged portions of the fuel bed for the combustion of thecombustible-material and smelting of the included inorZ- ganic chemicals therein under reducing conditions, controlling the amount of and velocity of the primary combustion air to maintain a maximum temperature in' the fuel bed sufficient to smelt the included inorganic chemicals therein but normally below 2100 F., supplying secondary combustion air in a series of'spaced streams directly to the space between the fuel bed and the spray level for the combustion of combustible gases risingfrom the fuel bed-and supplying tertiary'combustion air in aseries of spaced streams directly to the portion of the furnace chamber bustible gases present above the spray level.

combustion of combustible the-spray level.

:'5.'Th'e process of heat from liquor containing'inorganic chemicals ducing the liquor-at'a solid-concentration in the and combustible matter 'wl'iich-comprises'intro range of approximately 50-65% solids into a vertical furnace chamber in "a spray directed across -6. Thepro'cess of recovering chemicals and heat from liquorcon-taining inorganic chemicals and combustible organic matter which "comprises introducing the liquor at a solid'con'centration in the furnace chamber andformed of spray particles of a size and at a velocitysuch that a major portion of the spray particles impact'on an arresting surface after passing through and beingheated by an ascending stream of high temperature gases sufiiciently to put the spray particles when'impacting in asticky condition, maintaining the sticky particles in anfadhering mass on fthe arresting surface until sumciently dehydrated to separate and form afuel bed of combustible material of substantial depth in the 'bottomloi the furnace chamber; and supplyingcombustion "air to said furnace chamber so as to minimize "chemical, carryover therefrom comprising sup plying 'a major portion of the total air supply but less than the theoretical air requirements as pri- "mary combustionair in a series of horizontally spaced streams directly'to submerged 'portionsof the; fuel bed for the combustion of the combusjtible material and smelting of the included inorganic'chemi'cals therein under reducing conditions, controlling the amcunt'of and velocity of 7 primary combustion air to mainta'in a maximum temperature in the fuel bed suificient to smelt the includedinorganic chemicals therein but normal1y below 2100" R, supplying secondary combustion air in an amount approximating the balance of the theoretical air requirements and in a series of horizontally spaced streams directly to the space between the, fuel bed and the'spray V ,level for the combustion of combustible gases rising from the fuel bed, and supplying the remaining air as tertiary combustion air in a series ofhorizontally spaced streams at ajvelocity subondary'air at a relatively low velocity directlyto 2 the range of approximately 50 65% solid's'into a verticalfurnace chamber in a spray directed into the furnace chamber, introducing primary air in a series of distributed streams directly to submerged portions of the fuel bed, introducing sec- 5 the space between thefuel bed and the spray'ilevel,

introducing tertiary air'in a'ser-ies of streams and at a velocity substantially higher than the primary'air 'velocityfdirectly' to the portion of the furnace chamber'above the spray level; passing the heating gases generated-upwardly through a zone of high heat absorption at an increased velocity toreduce the gas temperature sufficiently to solidify sublimed chemicals therein, directing V the heating gases downwardly at a low velocity through a solid separating and steam superheating zone, returning the chemical solids separated in the separating zone to the fuellbed, and then directing the heating gases vertically through a steam'generating zone." Y r '7. Apparatus for recovering cchemicalszand 7 heat from liquor containing chemicals and comstantially; higher than the velocity of the vprimary air streams directly tothe portion of the (furnace chamber above the spray level for the gases present above recovering chemicals and and combustible organic matter which comprises introducing the liquor at a solid concentration in the range of approximately -65% solids intoa across the furnace chamber and formed of spray rvertical furnace chamber in a spray directed particles of a size and ata, velocity such that a major portion of the spray particles impact onan arresting surface after passing through andbeing heated byan ascending. stream of high temperature ases Sufficiently to put the ,spray particles when impacting inasticky condition, maintaining'thesticky .particlesrin an adhering mass .on the arresting surface untilsufficiently dehydrated to separate and form a fuelbed of combustible material of substantial depth in, the bottom of g the furnace, introducing primary airdirectly to submerged portions of the, fuel bed, introducing secondary air directly to the space between the fuel bed and the spray level, introducing tertiary air directly to the portion of the furnace chamber above thespraylevehpassing the heating'gases generated upwardlythrough a zone ofhigh heat absorption at an increased velocity to reduce the gastemperature sufiiciently to solidifylsublimed chemicals therein, directing the. heating gases downwardly at a low velocity through a solid separating ZOl'ldyEtYld returning the chemicalsolids tially rectangular horizontal cross-section having an upper section and a communicatinglow er sec,-

tion, spray means in said front wall for introducing liquor so arranged thatthe liquor is directed in an expanding spray substantially horizontally across said upper section so that the sprays impact against at least one of the remaining vertical walls over an extended area, a'hearth at the bottom of saidlowersection arranged to receive substantially dry material falling from said last mentioned wall to form afuel bed therein, means for supplying air to said furnace chamber including a series of primary air inlet ports in said lower'section'side walls opening to said furnace chamber at a level below thenormal upper level of 'said'fuel bed,'a series of secondary air inlet ports ;in said lower section side walls opening to said furnace chamber at alevel between the normal j: upper level ofj said fuel bed and said spray level, 'anda series of tertiary air inlet ports in said upper section side walls opening to said furnace chamber-above said spray level, a gas outlet from said-upper section wholly above the spray level, andan outlet in saidlower section for the incombustible residue.

8. Apparatusfor recovering chemicals and heat from liquor conta ining chemicals and combus'tl-- ble organic matter comprising vertical walls defining a stationary furnace chamber of theverti- I cal shaft type having anuppersection and a communicating lower section, spray means in one of said vertical walls forintroducing liquor so arranged thatithe liquoris directed in an expanding 3 spray across said upper section so that the spray;

13 to said furnace chamber including a series of horizontally spaced primary air inlet ports in said lower section walls opening to said furnace chamber at a level below the normal upper level of said fuel bed, a series of horizontally spaced secondary air inlet ports in said lower section walls opening to said furnace chamber at a level between the normal upper level of said fuel bed and said spray level, said secondary air inlet ports being substantially less in number and more widely spaced apart than said primary air inlet ports, and a series of horizontally spaced tertiary air inlet ports in said upper section walls opening to said furnace chamber above said spray level, said tertiary air inlet ports being substantially less in number and more Widely spaced apart than said secondary air inlet ports, a gas outlet from said upper section wholly above the spray level, and an outlet in said lower section for the incombustible residue. I

9. Apparatus for recovering chemicals and heat from liquor containing inorganic chemicals and combustible organic matter comprising vertical walls forming a setting including a Vertical furnace chamber, spray nozzle means extending through one of said vertical walls and constructed and arranged to spray liquor, in an expanding spray, into said furnace chamber, a hearth at the bottom of said furnace chamber arranged to receivecombustible residue to form a fuel bed on said hearth, means for supplying air to said furnace chamber, a vertically extending partition wall arranged to divide the upper part of said setting into a vertical gas upfiow pass forming a continuation of said furnace chamber and an adjoining vertical downflow pass, laterally spaced vertically extending platens of steam generating tubes arranged in said upfiow pass, steam superheater tubes extending across said downflow pass, anda steam generating tube bank positioned at one side of and arranged to receive heating gases from said downflow pass.

10. Apparatus for recovering chemicals and heat from liquor containing inorganic chemicals and combustible organic matter comprising vertical walls forming a setting including a vertical furnace chamber, spray nozzle means extending through one of said vertical walls and constructed and arranged to spray liquor, in. an expanding spray, into said furnace chamber, a hearth at the bottom of said furnace chamber'arranged to receive combustible residue to form a fuel bed on said hearth, means for supplying air to said furnace chamber including a series of primary air inlet ports in said vertical walls opening to said furnace chamber at a level below the normal upper level of said fuel bed, a series of secondary air ports in said vertical .walls opening to said furnace chamber at a level between the normal upper level of said fuel bed and the level of said spray nozzle means, a series of tertiary air inlet'ports in said vertical walls opening to said furnace chamber at a level above the level of said spray nozzle means, a vertically extending partition wall arranged to divide the upper part of said setting into a vertical gas upfiow pass forming a continuation of said furnace chamber flow pass.

and an adjoining vertical gas downflow pass,

steam superheater tubes extending across said downflow pass and arranged transversely of the gas flow therein, anda steam generating tube bank positioned at one side of and arranged to receive heating gases from said downflow pass.

11. Apparatus for recovering chemicals and heat from liquor containing inorganic chemicals and combustible organic matter comprising vertical Walls forming a setting including a vertical furnace chamber, spray nozzle means extending through one of said vertical walls and constructed and arranged to spray liquor, in an expanding spray, into said furnace chamber, a hearth at the bottom of said furnace chamber arranged to receive combustible residue to form a fuel bed on said hearth, means for supplying air to said furnace chamber including a series of primary air inlet ports in said vertical walls opening to said furnace chamber at a level below the normal upper level of said fuel bed, a series of secondary air ports in said vertical walls opening to said furnace chamber at a level between the normal upper level of said fuel bed and the level of said spray nozzle means, a series of tertiary air inlet ports in said vertical walls opening to said furnace chamber at a level above the level of said spray nozzle means, a vertically extending partition wall arranged to divide the upper part of said setting into a vertical gas upfiow pass forming a continuation of said furnace chamber of reduced flow area and an adjoining vertical gas downflow pass, laterally spaced vertically extending platens of steam generating tubes symmetrically arranged in said upfiow pass, steam superheater tubes extending across said downflow pass, a hopper forming the bottom of said downflow pass, means for returning material collecting in said hopper to said fuel bed, and a steam generating tube bank positioned at one side of and arranged to receive heating gases from said down- LESLIE S. WILCOXSON.

" REFERENCES CITED The following references are of record in the file of this patent:

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