2,161,110 5 oil, and heated to arelatively high temperature before introducing the black liquor. The black liquor together with the salt cake added Is the delivered to the spray nozzle . and discharged against the side and rear walls to form the siiccessive layers of char, thereon. The lumps of char - sep arating from the walls drop into the lower section of the furnace onto the hearth where the coml)itstible organic content i:s@burned 10 and the inorganic solids fused. -The products of combustion from the lower section ascend in the furnace past and in contact with.the deposited char and through the spray stream. Iii the upper section, the secondary alrIntroduced ef15 fects the combustion of any unburned gases in the iiseending stream including any combustible voiatiles distilled from the char on the walls. The products of combustion at a temperature normally around 17000 P. pass out of the upper 20 end of the recovery furnace into the associated steam boiler. As shown In Fig. 1, the steam boiler illustrated is of the Babcock & Wilcox type having a horizontally inclined tube bank 100, the 16wer rows 25 100,@ of which and the tubes therein are suitably spaced to form,a slag screen for the remaining @r ows. Headers 101 are arranged at 'opposite ends of the tube bank and connected by eirciflators to a steam and water drum 102.: Baffie@s 30 103 and 104 are positioned to provide a multipass flow of the gases across the tube bank. A steam superheater 105 may lie Installed above the tube bank, as conventionally, Illustrated. &.dust hopper 106 is located below the second and third 35 passes of the boiler. Lancing doors 107 are formed in opposlite side waus of the boiler adJacent the tube bank to facihtate cleaning of the tubes therein. An outlet 'conduit 108 forms a gas connection between the boiler third pass and 40 the spray tower 3. The spray tower 3 is formed by a steel casing .II 0, Ofrectangular form lined at its inner side with vitrified brick I I 1. 'A transverse metal baffle 112 extends downwardly from the top of 45 the spray tower to a point short of the bottom and divides the spray tow6r into a relatively narrow downflow pass. 1 13 and a relatively wide upflow pags 114. A series of vertically spaced spray nozzles If 5,are located in the downflow pass 50 113 and arranged to deliver sprays of weak black liquor across,the flow area of the pass. The boiler gases pass downwardly through the pass I f 3 in intimate contact witl@ the successive spray streams @ whereby dust particles in suspension 56 are washed-out and the weak Rquor absorbs sufflcient heat from the gases to effect the evaporation of large amounts of moistur6 and thereby increase the density of the weak liquor. The gases i@ass downwardly around the lower end of .oo the baffle 112 aAd enter the low velocity up-paSS 114, the abrupt change in direction and ihe substilntial decrease in velocity at this point due to the substai@tial drop in temperature of the gases and increased flow area of the passage tending 65 to further separate Hquor and dust In suspension. The bottom of the spray tower Is formed by a steel plate I 16 Across wmeh the liquor flows to an outlet pipe 117, advantageously located at the. rear end of the spray tower and extending slightTO ly above the bottom plate@ i 16 to provide a thin layer of liquor on the bottom plate for niinimleing @ corrosion thereof. The outlet pipe I 1 7 is connected to ' one or more evaporators (not shown), preferably of the. multiple effect type 75 utilizing steam generated in the boiler, and inwhich the weak liquor is@further concentrated to the desired density and subsequently delivered to the recovery fumace. The gases leave the spray tower through an outlet conhection 119 controlled by a @series of a dampers 120 at the upper end of the pass 114 and leacung to an induced draft fan 12 1. The fan discharges through an outlet conduit 122 Into a stack connection 123 Under certain conditions of operation it may jo be necessary br desirable to close off the spray tower and pass the gases, directly to the stack connecti on 123 under natural draft ' For such condition s a by-pass conduit 124 is provided between the outlet conduit 108 and the stack con- 15 nection 123. Cut-off dampers. 125 and 126 at th6 inlet end of the spray tower and outi6t end of the fan discharge conduit 122 respectively can be ciosed to close off the spray tower. V,7hen the by-pass 124 is to he used cut-off dampers I"-27 20 at the inlet end of the by-pass are opened. Combustioii air may be admltted dirertly to the wind box through the doors 77 when the forced draft fan 60 is out of service. ]In Flg. 17 we have illustrated a modifted ar- 25 rangeme nt oi th6 spray provisions for a recovery furnace of the character described in whidh two spray nozzles 130 are employed and mounted in the side wallg 7 and 8 at opposite ends thereof. The nozzles 130 are formed and arranged to 30 discharg e flat coarse sprays mainly through the crosssecti6nal areas indicated by the broken lines against the opposite, side wall. The spz-ay nozzle., 130. are preferably mounted to i)ermit only vertical oscillations thereof, the nozzle mounting 35 and operating mechanism being similar to that shown for fhe same purpose in Mgs. 8-12. V@bil e in accordance with the provisions of the statutes we have Illustrated and described herein the best forms of our invention now known 40 to us, those skilled In the art will understand that changes zhay be made in the process and in the form of the apparitus disclosed without departIng from the spirit of the invention covered by our claims, and that certain features of our ln- 46 ventioii may sonietimes be used to advantage witliout a corresponding us6 of other. features. We @laim: 1. A process of recovering chefiiicals and heat in a vertical recovery furnace from Hquor con- 50 taining inorganle chenucals and combustible organic matter which comprises introducing the liquor in a relatively flat spray directed across the. furnace and of a character such that a major portion of the spray particles impact on and ad- sa here to a vertical arrcistin67 surface exposed to the temperatu,re conditions In the fumace after passing throueh and bein,g heated by an ascending stream of high temperature gases sufficiently to pUt the spray particles when impacting in a 60 sticky condition, and continuously oscillating the spray verticall@, to deposit the spray particles in successive layers on the arresting,surface. 2. A process of recovering chemicals and heat in a vertical recovery furnace from liquor con- 65 taining inorganic chemicals and combustible organic matter which comprises introducing the liquor in a relatively flat spray directed aciross the furnace sknd of a character such that a major portion of the spray particles impact on and ad- 70 here to a vertical arresting surface exposed to tiie temperature cond@tions in the furnace after -passing through and being lieated by an ascending stream of high temperature gases sufficiently to put the spray partic.les when impactin4@ In a Tg

sticky condition, and continuously oscillating the spray about its a)ds of dlscharge to deposit the spray particles on the arresting surface over a substantial area. 5 3. A process of recovering chemicals and heat in a vertical recovery fumace from liquor containing inbrganic chemicals and combustible organic matter which comprises introducing the liquor in a relatively flat spray directed across 10 the fumace and formed of spray particles of a size and at a velocity such that a major p4?rtion of the spray particles Impact on and adhere to a vertical arresting surface exposed to the temperature conditions in the furnace after pass15 ing through and being heated by an ascending stream of high temperature gases sufficiently to put the spray particles when impacting in a sticky condition, and continuously oscillating the spray vertically and about its axis of discharge 20 to deposit the spray particles on the arresting SUrface in successive layeis. 4. A process of recovering chemicals and heat in a vertical recovery furnace from liquor containing inorganic chemicals and combustible or25 ganic mattek which comprises introduring the liquor in a spray directed across the upper section of the fumace and formed of @pray particles of a size and at a velocity such that a major portion of I the spray particles iinpact on a vertical So arresting surface exposed to the temperature conditions In the upper section of the furnace after passing through and being heated by an ascending stream of high temperature gaseg sufficiently to put the spray particles when impact85 ing in a sticky condition. continuously varying the direction of the spray to deposit the spray particles on the arresting surface in an adhering mass of successive layers from which portions separate by gravity, collecting the separated ma40 terial in the lower section of the furnace, sUPplying air to the fumace for the combustion Of the combustible portion of the separated material, utilizing a portion of the heat generated in the lower section of the furnace for the lique45 faction therein of the Included cheniicals, and utilizing the high temperature gases of combustion from the lower section of the furnace for treating liquor subsequently introduced into the udper section of the fumace. 50. 5. A process of recovering chemicals and heat in a vertical recover3@ furnace from liquor containing inorganic chemicals and combustible organic matter which comprises introducing the liquor in a relatively flat spray direrted across 55 substantially the entire cross-sectional area of the upper section of ihe furnace and formed of spray particles of a size and at a velocit@ such that major portion of the spray particles impact on vertical arresting surface exposed to the tem60 perature conditions in the upper section of the furnace after passing through and being heated by an ascendiiig stream of high temperature gases sufficiently to put the spray particles when impacting in a sticky condition, continuously oscil65 lating the spray vertically and about its axis of discharge to deposit the spray particles on the arresting surface in an adhering mass of sucdessive layers from which lumps of substantially dry porous mat.erial separate by gravity, collectTo' ing the lumps of separated material in th-e lower section of the furnace, supplying air mainly to the lower section of the fumace for the combustion of the combustible port.ilon of the material collected therein without the addition of au:@Aliary 75 fuel, utilizing a portion of the heat _gencrated iri 'the lower section of th-e fumace for the liquefaction therein of the included chemicals, utilizing the high temperature gases of combustion from the lower section of the furnace for treating liquor subsequently introduced into the upper see- r) tion of the furnace, withdrawing the high temperature gases from the upper section of the furnace above the'level of the spray, and withdrawing the included chemicals in a liquefied condition from the lower section of the furnace. 10 6. A process of recdvering chemi-Cals and h-eat in a vertical recovery furnace from- liquor containing inorganic chemicals and combustible organic matter which comprises introducing the liquor in a spray directed across the upper section 15 of the furnace and formed of spray particles of a size and at a velocity such that spray particles impact on a substantially vertical arresting surface exposed to the temperature conditions in the upper section of the furnace after passing 20 through- and being heated by an ascending stream of high temperature gases suffleiently to put the spray particles when impacting in condition to coalesce on the arresting surface in an adhering mass and be retained thereon until in a substan- 25 tially dehydrated porous condition, collecting the material separating from said mass by gravity in the lower section of the furnace, supplying primary air to the lower section of th-e furnace for the combustion of the combustible portion of the 80 material collected therein, utilizing a portion of the heat generated in the lower section of the furnace for the liquefaction therein of the inciuded chemicals, utilizing th-e gaseous products of combustion from the lower section of the fur- 35 nace for treating liquor subsequently introduced into the upper section,of the furnace, supplying seco'ndary air to the upper section of the, furnace above the spray level therein for the combustion of combustible gases in the upper section, with- 40 drawing the products of combustion from the upper section of the furnace above the level of the spray, and withdrawing lnclud@--d chemicals in a liquefled condition from the lower section of the furnace. 45 7. A self-sustaining process of recovering chemicals and heat in a vertical recovery furnace from sjdp'hiite paper puly) liquor contairiing inorgat-iic chemicals and combustible organic matter which- comprises Introducing the liquor in a 50 relatively flat spray directed across the upper section of the furnace and formed of sdray particles of a size and at a velocity such that a major portion of the spra,y particles impact on a 55 substantially vertical arrestirig surface exposed to the temperature con,diti-ons in the 'upper.section of the fu-rnace after passmg through and being heated by an ascending stream of high- temperature gases sufficiently to put the spiay particles (10 when impacting in condition to coalesce on the arresting surface in an adhering mass and be retained thereon until in a substantially dehydrated porous condition but without substantial change in its Initial organic eqntent, collectin@ the mate- 6r) rial si@parating from said mass by gravity in the lower section of the furnace, supplying primary air to th, e lower section of the furnace f or the combustion of the combustible portion of the material collected therein without the addition to 7o the furnace of otherecimbustible matter, utilizing a portion of the heat generated in the lower -section of the furnace for the.liquefaction and reduction therein of th-e included chemicals, utilizing the gaseous products of combustion fro,m the 75.

2,161,110 7 lower section of @the furn ace for treating liquor subsequently introduced 'mto the upper section of the furnace, supplying secondary air to the upper section of the furnace above th6 spray level therein for the combustion of combustible gases in the upper section, withdrawing th-e products of combustion from the upper section of the furnace above the level of the spray, and withdrawing included chemicals in a liquefled condition from io the lower section of the furnace. 8. Apparatus for'recovering chemicals and heat from liquor containing inorganic ch6micals and combustible organic matter comprising vertical walls forming a vertical recovery furnace sub15 stantially rectangular in horizontal cross-section, a spray nozzle adjacent one of said walls and constructed and arranged for spraying th-e liquor substantially horizontally across substantially the entire cross-sectional area of the upper section 20 of the furnace in a single relatively flat spray having spray particles of a size and at, a velocity such that a major portion of the spray particles 'impact on aIl of the remaining vertical wa-Ils of the furnace and coalesce thereori In an adhering 25 mkcs a hearth receiving material separating from said @dhering mass, ineans for sui)plying air to the lower section of said furnace for the combustion of the combustible organic matt ;er therein, said walls being arranged to direct the gaseous 30 products of combustion'from the lower section of the furnace into the upper section of the fumace, and an outlet for the gaseous products of combustion from the upper sectlon of the furnace above the spray level therein. 35 @ 9. Apparatus for recovering chemicals and heat from liquor containing lnorgaiiie chemicals and combustible organic matter comprising vertical walls forining a vertical recovery furnace substantially, rectangular In horizontal cross40 section, means constructed and arranged to spray the liquor through one of said walls across the upper section of the furnace In arelatively flat spray having spray partteles of a size and at a veiocity such that spray particles impietct on 45 at least one of the remaining vertical walls and coalesce thereon In an adhering mass, means for varying the direction of 'said spray to deposit thie spray particles In successive layers on said remaining side wall, a he' arth receiving m 50 terial sepiirating from said adhering mass, means for supplying air to said furnace for the combustion of the combustible organic matter therein, said walls being arranked to direct the gaseous products of combustion from th6 lower section 56 of the furnace Into the upper section of the furnace, an outlet for the gaseous products of combustion from the upper section of the f-urnace above the spray. level therein, and an outlet for the withdrawal of included chemicals in a lique-@ 60 fled condition from the lower section of, the furnac& 10. Apparatus for recovering chemicsLIs and heat from Hquor contgining inorganic chemi- cals and combustible organic matter comprising 65 vertical walls fonning the sides of a vertical recovery furnace, means constructed and arranged to spray the liquor across the upper sec- . tion of the furn@Lce in intimate contact with gaseous pioducts of combustion from the lower sec70 tion of the furnace and in a spray having spray particles of a size aixd at a velocity such that spray particles impact on at least one of said walls vlnd coalesce thereon in an adhering mass, means for continuously oscillating said spray 75 means vertic6lly to deposit the spray particle@, In successive layers on said wall, a hearth i-eceiving material separating from said adhering mass, primary air ports bpening -to the lower section of the fumace for the combustion of the combustible portion of the material collected on 5 the hearth, said waus being arrang@d to direct the gaseous products of combustion from the lower section of the furnace Into the upper, section of the fumace, secondary air pbrts opening to the upper section of the furnace above 10 the spray level, and an outlet for the gaseous PrOducts of combustioh from the upper section of the furnace above the spray level therein. 11. Apparatus fbr recovering chemicals and heat from liquor containing inorganic chemicals 1,5 and combustible organic matter comprising walls forming a vertical recovery furnace, means constructed and arranged to,spray the liquor across the UPPer section of the furnace in intimate contact with the gaseous products of combustion 20 from the lower section of the furnace and in a spray having spmy particles of a si,ze and at a velocity such that spray particles Impact on at least one of said walls and coalesce thereon in an adhering mass, means for continuously oscil- @5 lating said spray means about its axis of discharge tQ deposit the spray Particles in successive layers on said wall, a hearth receiving ma7 terial separating from said adhering mass, primary -air ports opening to the lower section of @0 the furnace for the combustion of the combustible portion of the material collected on the hearth, said walls being arranged to direct the g@seous products of combustion from the lower se,tion of the fumace into the upper section Of 35 the furnace, secondary air ports opening to the upper - section of the furnace above the spray level, and an outlet for the gaseous products of comb I ustion from the upper section of the furnace above the spray level therein. @ 40 12. Apparatus for recovering chemicals and heat from liquor containing inorganic chemickls and combustible oi-ganic matter comprising walls forming a vertical recovery furnace, means adJacent one of said walls constructed and arranged 45 to spiay the liquor across the upper section of the furnace in intimate contact with gaseous Products of combustion from the lower section ?f the furnac6 and In a relative] . y. flat spray having spray particles of a size and at a velocity such 50 that spray particles Impact on the remaining side walls and coalesce thereon in an adhering mass, mearis for continuqusly oscillating said spray means vertically and about its akis of discharge to deposit the spray particles in succes-- 55 sive layers on said remaining side walls, a hearth receiving material separating from s'aid. adhering mass, primary air ports -opening to the lower section of the furnace for the com,bustion of the combustible,p ortion of the material collected on, 60 the hearth, said walls being arranged to direct the gaseoiis prodticts of c6mbustion from the lower section of the furnace into the upper section of the furnace, secondary air ports opening to the upper. section of the. furnace above the 65 spray level, an outlet foi the gaseotis produ.cts of combustion'from the- upper section of the furnace above the spray level therein, and an. outlet for the withdrawal of included ch&micais in a liquefled condition from the lower section 70 of the furnace. 13. Apparatus -;'for recovering chemica'18 - and heat from liquor containing,inorganic chemicals and combustible orgir@c matter ccim prising vertical wall@ forming'a vertical reco-ver3@ furnace 75

subst@ntially rectangular in horizontal ebrosssection, means for spraying the liqugr through one of said walls acrosg the upper, section of the furnace in intimate contact wi-th gaseous products of combustion from the lower section of the furnaceand in a relatively flat spray having spray particles of a size and at a velocity such that a major portion of the spray particles impact on the remaining @side walls land coalesce 10 thereoh In an adhering mass, means for continuousl@ osciuating the spray means vertically and about its axis of discharge to deposit the spray particles In successive layers on said remaining side walls, a hearth receiving material 15 separating from said idhering mass, primary air ports opening to the lower section of the furnace for the conibustion of the combustible portion of the material collected on the hearth, said walls being arranged to direct the gaseous products 20 of combustion from the lower section of the furnace into the upper section of the furnace, seeondary air ports opening to the upper section o ' f the furnace above the spray level, an outlet for the gaseous products of combustion from 25 the upper section of the fumace above the spray level therein, and an outlet, for the withdrawal of incluo@d chemicals In a. liquehed conditign from the lower section of the furnace. 14. Apparatus for recovering chemicals and.: 30 heat from liquor containing inorgante chemicalg Eind combustible organic matter comprising vertical wallg forming a veitical recovery ftqnace, means forming an inwardly projecting ledge at the furnace side of and intermediate the height sr) of one of said vertical walls, means for spraying, the liquor across the upper section of the furnace in intimate r-ontact with gaseous products of combustion from the lower section of the furnace and in a spray having spray particles of a size and at 40 a velocity such that spmy particles impact on at least said last mentioned vertical wall above said ledge and coalesee thereon in an adhering mass, a hearth receiving material separating from said adhering mass, means for supplying air to said 45 furnace for the combustion of the combustible organic matter therein, said walls being arranged to direct the gaseous products of combustion from the lower -section of the furnace into the upper section oftlie.fumace, and an outlet foi, the gaser ,,o ous products of combustion from the upper section of the furne@ce above the spray level therein. 15. Apparatus for recovering chemicals and heat from liquor containing inorganic chemicals and combustible organic matter domprising re55 fractory faced vertical side walls forming a vertical recovery furnace, means constructed and arranged to spray the liquor across the upper section of the fumace in intimate contact with gaseous products of combustion from the lower 6o I section of the furnace and in a spray having spray particles of I a size and at a velocity such that spray particles impact on at least one of the side walls of the furnace and coalesce thereon in an adhering mass, a hearth receiving material sepaS5 rating from said adhering mass, a row of wall cooling tubes extending upwardly from said, hearth to a level. above said spray means and in cooling relation with the portion of -the side waH receiving the spray Impact, air ports for supply@. To ing air to said iurnacel for the combustion of the combustible organic matter therein, said side Wa@lls being armnged to direct the gaseous products of combustion from thi@ low6r secti6n of the furnace into the upper section of the fumace, an outlet for the gasous produdts of combustion from the upper section of the furnace above the spray level therein, and an outlet for the withdrawal of included chemicals in a liquefied condition from the lower section of the furnace. 16. Apparatus for recovering chemicals and heat from liquor containing inorganic chemicals and combustible organic matter comprising refractory faced vertical side wails forming a vertical recovery furnace, means for spraying the liquor across the upper section of the furnace in ]0 a spray having spray particles of a size and at a velocity such that spray particles impact on at least one of the side walls of the furnace and coalesce thereon in an adhering mass, a hearth receiving substantially- dry material separating 15 from said adhering mass, wall cooling tubes extendirig upwardly from said hearth to a level above said spray means and in cooling relation v@ith said side walls, projections on said cooling tubes arranged to support refractory material at 20 the inner side thereof, air ports between said cooling tubes for supplying air to said fumace for the conibustion of the combustible organic matter therein, said side walls being arranged to direct the gaseolis products of combustion from 25 the lower section of the fumace into the upper section of the furnace, an outlet for the gaseous products of combustion from the upper section of the furnace above the spray level therein, a steam boiler receiving the produr-ts of combus- 30 tion from said outlet, conduits connecting said wall cooling tubes into t boiler c cula System, and an outlet between said cooling tubes for the withdrawal of included chemicals in a liquefled condition from the lower section of the 35 furnace. 17. A process of treating paper pulp residual liquor which comprises introducing the liquor into a vertical recovery furnace in a spray directed apross the upper section of the furnace and de- 40 positing in an adhering mass on a vertically disposed wall surface after passing through and being heated by an ascending stream of high temperature gases, varying the direction of the spray to cause the spray particles to deposit on 45 the wall surface over an extended area, supplying air to the furnace for the combustion.of dehydrated material separating from said mass and collecting in the Iower section of the fumace, and withdrawing the high temperature gases gener-@ 50 ated from the upper section of the furnade after. contacting with liquor being sprayed across the upper section of the fumace. 18. A process of treating paper pulp residual liquor which comprises introoucing the liquor 55 into a vertical recovery furnace in a spray directed across the upper section of the furnace and deposifing in an adhering mass 6n a vertically disposed wall sur face after passing through and being heated by an ascending stream of high 60 temperature ga@es, varying the direction of - the spray to cause the spray particles to deposit on the waH surface in successive layers and from which mass dehsrdrated portions separate and collect in the lower section of the furnace, sup- 65 plying air to the furnace for the combustion of the separated material, and withdrawing the high temperature gases generated from the upper section to the fumace after contacting with liquor being sprayed across the upper section of the 70 furnace. 19. A process of treating pappr pulp residual, liquor which com@rises ' introdiacing' the liquor into -a vertical recovery furnace@. iri a spray directed across the upper section of the fumace and 75

.2,101 110 formed of spray particles of a size and at a velocity such that a major portion of the spray particles Impact on a verticauy disposed wall surface of the fumace after passing through and r, b@ing heated by an ascending stream of high temperature gases sufficiently to put the spray particles when Impacting in a sticky condition, varying the directing of the spray to cause the spray particles to deposit In an adhering mass .,Io over an extended wall area and from which mass dehydrated portions separate and c6llect in the low@r section of the fumace, supplying air t46 the furnace for the combustion of , the separated mateilal, and withdrawing the high t@emPer6,iure 15 gases generated from the upper section of the furnace after contacting with liquor being sprayed across the upper section of the fumace. 20. A process of treating paper pulp residual liquor which comprises Introducing the liquor go into a vprtical recover@, furnace In a spray directed across the upper section of the fumace and formed of, sprey particles of a size and at a velocity such that-a-major portion of the spray par26 face in the upper section of the furnace after passing, through and being heated by an aseehding stream. of high temperature gases sufficiently to put the spray particles when Impacting in a sticky condition, continuously varying the direc30 tion of the spray to cause the spray particles to -deposit on the wall surface over an extended area, in an adhering mass of successive layers and from which mass dehydrated portions separate and fall Into the lower section of the fumace, supplying 35 air to the lbwer section of the fumace f6r the combustion therein of the combustible portion of the sdparated material, and withdrawing the high temperature gapes generated in the lower section of the fumace from the upper section of the fur40 nace after contacting *Ith liquor being sprayed across the ui?per section of the furnace. 21. A furnace comprising walls. forming a verticauy elongated chamber, nozzle means constructed and arranged'to spray a combustible 45 liqiior aeross the upper section of said chamber in a relatively flat spmy towards a vertically disPosed waH surface and so as to deposit thereon in an adhering mass, mechanism for varying the Position of said nozzle means to shfft the area 5o of iinpact of said spmy on said wa I U surface, a kefractory hearth forniing the bottom of said chamber and arranged to receive by gmvity dehydrat6& combustible material separating from said wall surface, primary air ports op@ning to the 55 lower section of said chamber, said chamb@-rforming wars being arranged to direct any high temperature gases generated.in the lower section@ through the spray In the upper smtion of said chamber, secondary air ports opening to the upp6r section of said chamber adjacent the spray level therein, and a gas outlet in the upper section of add ebamber above the spmy level therein. 22. A fuimace comprising vertically dismsed walls forming a chamber substantially rectangu65 -lar in horizontal cross-xmtion, nozzle means for spmying, a combustible Uquor through one of said walls aera@s the uppet section of said chamber in,. a relatively flat spray directed towards and so as to deposit on at least one of the remaining vertical 70 waus In an adhering mpos, mechanism for vary-. ing the Position of swd@nozzle means to swft the Wa of impact of said spray an add waU, a re.,f@rwtm hearth formiuff the bott4= of sgd cbamber and arranged to receive by gravity dehydrated 75 combustible materisa separating from said rematwng wall, primary air ports opening to the lower secti6ii of said chamber, Wd vertically disi@osed@ waus being arranged t6 direct any high temperature gases generated in the lower section through the spray in the upper section of said 5 chamber, secondary a@r ports opening to the upper section of said chamber above the spray level therein, and a gas outlet in the upper section of said ehamber above the spray level therein. 23. A furna@ce comprising opposite pairs of ver,- 10 tical walls arrangt-d to define a chamber of rectangular horizontal cross-section, a troughshaped inclined refractory hearth forming the bottom of said chamber, means for discharging a combustible liquid intb the upper portion of 15 said,cha mber, an outlet in the upper portion of said chimber for gaseous products of combustion, rows of cooling tubes extending upwardly froxn below the upper and lower ends of said hearth to a level above said liquid discharge 20 means and In cooling relation with the corresponding side walls, transverse ]@eaders,connected to the lower ends of said tube rows, conduit means rows, a header below said hearth,,and arranged In 25 vertical alignment with the lon4itudinal center line thereof, rows of cooling tubes having curved lower ' end portions connected to said last named header extending upwardly to a level above said liquid dischiirge means and in cooling relation .30 with said iiearth and remaining side walls, and conduit means supplying a cogling fluid to said last xiamed header and tube rows 24. A furnace comprising opposite pairs of vqrtical walls arranged to define A chamber of ree, 35 tangular horizontal cross-section, a hearth forming the bottom of said chamber, means for introduc ing a combustible liqwd Into the upp'er portio n. of said chamber, an outlet In the upper portio n of said chamber for gaseous products of 40 comb ustion rows of cooling tubes extending upwardl y fro said hearth in cooling relation with a pair of opposi te side waus, transverse headers conne cted to the lower ends of said tube rows, condid t means supplying a cooling.fluid to said 45. heade rs, a header below saiid h4@arth ajid extendirtg longitudinall thereof in vertical 'aligiment with the longitudinal center line thereof, rows of coolin g tubes having their lower ends connected 50 to said last naineci header and e:ktending upwardly In cooling relation with said hearth and remaining ilde *alls, and conduit means supplying a cooling fluid to said last nar4ed hee@der alid tube rows. 155 25. A process of tkeating paper pulp residual liquor which comprises introduc'mg the liquor into a recovery furnace in a spray directed across the upper section of the fumace and formed of spray particles of a character such that a major So portion of the spray particles impact on an - arresting surface in the upper section of the furnace after passing t . hrough and being heatid by an ascending stream of, high temperature gases sufficiently to put the spray particles when 65, impacting in a- sticky condition and to cause spray particles to deposit.on the arresting surface in an adhering mass from which dehydrated portions separate and are burned in. the lower section of the furnace, withdrawing the high 70 temperature gages generated in the lowe@! section of the furnace from the upper section of the furnace after contacting with liquor being spr@-yed across ihe iipper section of the fumace, and varying the path of travel of the spray across 75 ticles Impact on a vertically disposed wall sur- __;)supplying a coc)ling fluid to said headers Eknd tube

10 the uppei- section of the@furnace to shift the axea of spray deposition on the'arresting surface. 26. Apparatus for recovering chemicals and heit from liquor containing Inorganic chemicals and combustible organic matter comprising a vertical recovery furnace having@ a verticall@ disposed arrestiiig surface in the upper part thereof exposed to the temperature conditions therein, spray nozzle means constructed and arranged to le spray the liquor across the upper paxt of said fur-@ nace towards said arregtirig surface in a sptay of a character su6h that a major por%on of ihe spray particles impact on and adhere to said arresting surface, a hearth arranged to receive de15 hydrated material separating from said arresting surface, means for supplying air to said furnace above said hearth for burning the combustib.le material collecting thereoii, and means for varying the direction of the gpray discharged to shift 20 the area of spray deposition on said arresting surface. 27. Apparatus for recov.ering, chen-dcals and heat from liquor containin6@r.inorganid chemicals and combustible organic matter comprising a 25 vertical recovery furnace havind a substantially vertical arresting surface in the upper part theri@of exposed to the temperature conditions therein, spray nozzle means construcied and arranged to spray the liquor across the upper part of said 30 fuhace. tov@ards said arre@ting surface in a spray having spray particles of a size and at a velocity such that a major portion of the spray particles tnipact on and adhere to said arreiting -surface, a hearth arr6mged to receive, debidrated material separ@Lting from said.arresting SUrfaC4@, --- eans for supplying air to said fumam above said hearth for burning the combustible itiaterial collecting @5 thereon, and means for continuoiisly varying the direction of the spray discharged to deposit, the spray particles In successive layers on said arresting surface. 28. A furbace for the recovery of heat and 10 chemicals comprtsing vertically disposed walls defining a furnace chamber, means opening into the upper 13ortion of said furnace chambe., for Introducing therein material containing inorganic chemice4s and dombustible organic matter, 15 a hearth defining the'bottom of said furnace chamber, means forming an outlet for molten cheadeals collecting on said htatth, means ad@ jacent sa . Id hearth for introdueang air for the combustion of organic metter depodting on said 20 hearth, and said furnace chamber vaus coi4prioIng fluid conduit means having a multiplicity of metallic studs projecting Inwardly from the fiirnace cheimber side thereof, And a-layer of plastic chronie. ore refractory molded around said studs 20 and over the'fumlace cham-ber side of said fluid conduit means . and forming atemperature and alkaline-resistant refractory lining for said furhae@ chamber vmhs. 30 GEORGE H@ TODEinqsoN. IMUIE S. WHMXBON.

Patented June 6, 1939 21161,110 FUNITED STATES PATENT OFFICE 2,161,110 METHOD OF AND APPARATUS FOR BURNING WASTE IJQUOR George H. Tomlinson, Westmount, Quebec,, Canada, and Lesllie S. Wilcoxson, Ridgewood, N. L; said Leslie S. Wilcoxson assignor to The Babcock & Wilcox Company, Newark, N. J., a corporatioir of New Jersey. Ai@plication May 16, 28 Claims.. The present invention relates in general to the recovery of chemice@ls and/or heat from waste liquors containing inorganic cheniicals, and conibustible organic matter, and m6re particularly, to r) the recovery of cheniicals and heat from the pulp digestor residual liquor in the sulphate and soda processes of- manufacturing paper pulp. The present invention is directed to certain improvements in the process of and apparatus for lo recovering cheniicals and heat from liquor of the character described, disclosed and claimed in Patent,#2,070,632 of said Tomlinson. The main obji@ct of the present invention is the provision of a self-sustaining process of recover15 ing chemicals and lieat from liquor of the character described which is characterized by an in-, crease in the amount of. liquor treated per sq. ft. of furnace cross-sectional areb, per day, a highei percentage of recovery of the chemicals and heat 20 in the liquor treated, greater -ease of and more effective coritrol of the xecovery operations, and the maintenance of more uniform and stable op.erating. r,6nditions, than with the process disclosed in said prior application. A further object 25 is the provision of impro,ved apparatus for ca@rrying out our iml)roved process which'is characterized by the high liquor treatirig capacity,,relatively low c , ost of maintenance and operation, and ease of control P-nd repair of the recovery 30 furnace; high. steam generating capacity of the pressure p4rts at relatively low cost; and effective provisions for recovering heat and chemicals in the products of combustion from the steam boiler. 35 The various features of novelty which charac@ terize our invention are pointed out with particularity in the claims aiinexed to and forn-dng a part of this specification. . For a better understanding of the invention, its operating advan40 tages and specific objects attained by its use, reference should be had to the accompanying dr,,Iwings and descriptive matter I in wwch we have Illustrated and described preferred einbodiments of our invention. 15 Of tie drawings: Mg. I is a sectional elevation of a recovery unit constructed in accordance with our inven Mg. 2 is an enlarged view of the recovery furnace shown in Flg. 1; So M@. 3 is a vertical transverse section taken on the line 3-3 of Mg. 2;. Fig. 4 is a horizontal section taken-on the line 4-4 of Flg. 2; Flg. 5 is a sectional elevation of the spray. nozzle 55 taken on the line 5-5 of Mg. 6; 1935, Serial No. 21,836 (Cl. 23-48) Mg s. 6 and 7 are plan and end views of the spray nozzle; Mg. 0 is a vertical section through the front furnac e wall illustrating the mounting of @the spray nozzle; 5 Ogs . 9 and 10 are plan and end views respeetively of the parts shown in Mg. 8;. Mg. 11 is a somewhat diagrammatic elevation of th6 spray nozzle operating iiaechanism; Mg. 12 is a front view of the rrank disc; IC Mg. 13 is a vertical section through one of the ledge blocks; Mg. 14 is a horizontal section through one of the primetry air nozzles; Fig. 15 is a vertical section.through the air 15 nozzle of Flg. 14; Mg. 16 is an outer end view of the smelt spout; and Mg. 17 is a view similar to Mg. 4 illustrating a modffi ed spray arrangement. 2(, In view of the especial. applicability of our inventio n to the paper pulp industry, our improved proce ss will be speciflcally.deseribed as employed for the reboirery of chemicals and heat from the residu al or "black" liquor of pulp dlgestors used 26 in the kraft or sulphate process. In this process, the weak black li(luor fr6zil the digestors and washe rs ordinarily contains from 85%-90% moisture and 10%-15olo solids. The chemical content of the weak black liquor is mainly -sodium car- 30 bonat e (Na2CO3) and sodium sulphate (Na2SO4) togeth er with traces of sodium sulphide (Na2S) and other salts in various complex combinations with the ligneou@ matter. During the recovery process the sulphates -are. reduced as much as 35 possible to sodium sulphide (Na2S) in aebordance with general formula INa2SO4+4C=Na2S+4CO The heat value of the weak bladk liquor is due to 40 the pi7esence of organic combustible matter or lignins released from the wood in the digestors. In acordance with our process the weak black liquor from the digestor pulp is delivered to an evaporat ing d6vic6 in which it is brdught into in- 45 timate contact, with the products of combustion from. @, recovery , furnace and associated heat transfer apparatus, preferably in such a way that any chemicals suspended in the hot gases will be washed out by the weak liquor and eventuauy re- 5o turned to the recovery furnace. The weak liquor absorbs a substantial amount of sensible heat Of the hot gases,, causing the evaporation of a large am6unt of its water content. The weak black liquor with the chemicals washed out or otherwise 55

2 separated in the evaporating device is then subjected to further evaporation until it is concentrated to a density of preferably at least 50% solids. - The concentrated liquor at the desired viscosity and density is then delivered under pressure to a vertical recovery furnace, through which normally ascends a stream of high temperature gases produced by the burning of previously 10 treated black liquor. -The black liquor is preferably introduced into the upper section of the recovery furnace in the forn@ of one or more relatively flat diverging streams of coarse spray particles directed across substantially the entire 15 cross-sbctional area of the furnace in intimate contact with the ascending stream of high temperature gases. The spray particles produced are advantageously of sufficient size and at sufficient velocity that they will not burn during 20 transit but are dried sufficiently to be,in a sticky condition when iinpacting on the fumace walls towards which they are directed. The particles tend to coalesce on the walls in the form of an adhering-r4ass which builds out into the furnace. 25 If the spray particles produced are too flrie in size they tend to be bumed in transit and carried by the ascending gas stream oui of the furnace, causing a loss of chemicals and excessive deposits in the associated heat recovery device. The coSo alesced masses of sprayed material on the walls are in position to receive heat by radiation from the furnace bed and to contact by the ascending high temperature,, gases, causing the gradual evaporation of most ' of the remaining moisture 35 and the distillation of some of the low temperature volatiles, whereby the deposited material assumes a porous character. The material on the walls contains substantiauy all of its original organic content and for convenience is herein40 after referred to as the "char". Each portion of the char continues to adhere to the wall or surrounding mass until the gravity effect thereon Is sufficient to overcome the forces of adhesion or cohesion, whereupon it breaks off in lumps of 45 various size falling into the lower section of the furnace and collecting on the hearth therein. To insure the delivery of the char to the hearth in a substantially dry porous condition with substantially no change in its original organic content and also to substantially increase the liquor treating capacity oi the furnace, the spray particles are discharged so as t6 be distributed in successive thin layers over an extended wall area. Our preferred method of effecting this result in a rectangular furnace is by locating the spray means adjacent an end Wall and oscillating the same both vertically and about its axis of discharge to continuously impact on the remaining walls over a varying area. The vertical oscillations alone would cause the flat spray to be deposited on the opposing wall ovet a substantially rectangular area and over a substantiallytriangular area on the adjacent side walls. By the simultaneous oscillation about the spray axis, the side walls also will receive spray particles impacting over a substantially rectangular area. With this method of introducing the black liqllor into the furnace the char on one portion of the walls will be directly exposed to contact by the furnace gases and flurnace radiation, while the spray particles are impacting on another wall portion. The' char will be thus dried in layers over an extended wall area. The char separating from the wall masses falls on the hearth at the bottom of the furnace in a pile of varying depth, a's indicated in Flgs. 2 and 3. Primary combustion air, preheated if desirable, is supplied in a multiplicity of downwardly diree ted streams against the char on the hearth for the burning of the combustible portion of the r) char collected thereon, and the dry porous condition of the char and presence of substantially all of its original organic content facilitates its ignition and burning. The amount of primary air supplied is desirably no more than sufflcient 10 to make up thd theoretical oxygen requirements for the combustion of the char on the hearth. Under the@e conditions, a reducing atmosphere can be easily maintained throughout most of the bed. Of the heat generated in the lower section, jr, a small percentage is used for the hquefaction of the chemicals inciuded in the char and to support the reducing reaction by which the sgdium sulphate is reduced to sodium sulphide (Na2S). The liquefied chemicals are continuously with- 20 drawn from the hearth and passed into a dissolving tank for return ultimately to the digestors, while the products of combustion flow upwardly into the upper section of the furnace into contact with the char on the walls and the discharg- 2.9 ing spray particles. The relatively flat coarse spray employed provides an effective liquid screen across the furnace for removing dust particles from the ascending gases and returning them eventually to the hearth. A relatively small 30 amount of secondary air, preheated if desirable, is supplied to the u]@per section of the furnace above the spray level to consume any combustible volatiles distilled off from the char masses on the furnace walls and any unburned combus- 35 tible gases escaping from the lower section. The combustibles in the liquor are thus fully utilized and the heat thus generated irfereases the sensible heat in the gases passing out of the upper end of the recovery furnace. 40 On leaving the recovery furnace the sensible heat of the products 6f combustion is further utilized in a heat transfer apparatus, preferably in a steam boiler. On leaving the steam boiler or other heat recovery device, the products of., 4r, combustion are preferably passed to an evaporating device 'wherein much of the remaining sensible heat is used for partly evaporating weak liquor and dust particles in suspension in the gases are washed out and eventually returned to the 50 recovery furnace with the liquor. Ihe gases on leaving the evaporating device will be at a relatively low temperature indicating an effective recovery of the heat in the gases. The chemicals lost during the pulping process and the relatively 55 small amount lost in the recovery process are made up by the addition of salt cake (Na2SO4) tO the black liquor before its entry into the recovery furnace. Thi3 described self-sustaining process has been found to permit the burning of nearly 60 a ton of 55% solids-liquor per day per square foot of furnace cross-sectional area with a chemical recovery of approximately 95% and an overall thermal efficiency of 91.4%. Stable furnace conditions over varying load conditions are easily 65 maiiitained in operation by suitably regulating the liquor and air supplies and the distribution of the char on the fumace walls. In Mgs. 1-16 of the drawings we have illustrated a preferred form of recovery unit for car- 70 rying out the process heretofore described. The main elements of the recovery unit are a vertical recovery furnace 1, a steam boiler 2, and a spray to*er 3, relatively arranged as shown In Fig. 1. 75

The recovery furnace illustrated is defined by vertical b.oundary walls, including a ffont wall 5. rear wall 6, and side walls 7 aiid 8 respectively, each of which is preferably formed with an inner 'layer of plaitic refractory, wall cooling provisions and one or more outer layers of heat insulating material, enclosed by a steel casing and held in position by suitable steel strlictural members, as indicated in the drawings. The bottom of the 10 furnace is formed by a trough-shaped inclined fluid cooled refractory heartli I 0. The upper end of the recover@ furr@ace is open throughout its entite area to provide a gas exit to the superposed steam boiler 2. i5 More specifleally and as shown most clear].Y in- Mgs.. 3, 14 and 15, the side walls 7 and 8 are. each provided with a row of horizontally spaced vertical water tubes I I having a multiplicity of stud projections 12 thereon substantially through20 out their vertical extent for supporting an inner layer of 'Plastic clirome ore refractory 13. The lower ends of both rows of tubes I I are beiit inwardly intermediate the hearth structure and connected to a common. longitudinally extending 25 inlet header 14. The upper ends of each row of tubes I I are bent outwardly and connected to a longitudinally extending.outiet heador IS. The headers 14 and 15 are suitably connected into the boiler circulation system to provide an upward So fluid flow through the tubes II. As shown in Mgs. 2, 8 And 9, the front wall 5 is similarly provided with a row of horizontally spaced vertical refraotorysupporting stud tubes 16 having their lower ena connected to a transverse inlet header 35' 17 below the hearth, and their upper ends bent outwardly into a transverse outlet header I 8, the headers 17 and 18 being also connected into the boiler eirculati(in system. The rear wall 6 is similarly provided with a row of refractory-sup40 porting stud tubes 19 connected to a lower transverse inlet header 20 and an upper transverse outlet header 21, both of which are connected into I the boiler circulation system. 8ome of the tubes 19 are bent laterally to permit the incor45 POration of an access door 22 in the rear wali. A: furnace of rectangular cross-section is thus defined with the side walls of greater length than the front and rear walls. In accordance with our invention, the concenro trated black liquor is spray@d in ' to the furnace from a point adjacent the front wall 5, and the rear wall 6 and side walli 7 and 8 act as arresting surfaces receiving the impact of the spray particies. As shown in Mgs. 5, 6 and 7, the spray ,55 provisions for introducing the black liquor comprise a spray nozzle 24'formed by a nipple 25 through which the black liquor enters, an inclined tubular hood member 26 welded thereto and surrounding a nozzle plug 27 formed with a 60 tapering discharge passage 27a. The lower end of the plug 27 is cut away to form a central projecting nozzle 27b within the hood and through which the liquor discharges against a flat substantiauy oval impact plate 29 arraiiged at a 65 predetermined angle A to the axis of discharge of the nozzle 27b. The angle A will be varied for different furnace proportions and changes in the desired distribution of the hquor. With the furnace shown, an angle A of approximately 481 70 has been foiind to provide a substantially u@niform spray impact per unit area on the rear and side walls. The lower end of the hood 26 is cut away. at 26a, as shown in Fig. 5, to confine the spray discharged to approximately; 1801, so that 75 with the spray nozzle positioned at the front end of the furnace the spray will. be discharged toward and iinpact on the rear wall 6 throughout its width and on the side walls 7 and 8 substantially throughout their length, forming masses of char: thereon of irregular contour, as indicated 5 in Mgs. 2-4, w@ile the front wall will be clear. The spray nozzle 24 is advantageously mounted so as to permit continuous predetermined oscillating movements thereof to shift the area of impact of the spray particles on the'rear and side 10 walls. Suitable provisions for this purpose are illustrate d in Mgs. 8-12, and include a horizontally arranged liquor supply pipe 30 extending through a verticaily elongated port 31 in the front wall 5, and on the inner end of which the spray 1.5 nozzle 24 is mounted. The pipe 30 is rotatably m6unted at its outer end in a sleeve 32 carried by a plate 33 pivotally mounted for movements about a transverse horizontal axis by means of a pivot pin 34 at its inner end journaled in lugs 20 35 carried by adjacent stud tubes 16. The outer end of the pipe 30 is connected to a flexible black liquor supply connection 36. With this form of mounting, the pipe 30 can be oscillated in -a vertical plane about the pivot pin 34 and about 25 its own axi.s. With the pipe 30 horizontal and the.spray nozzle plate 29 algo in a horizontal position, the spray wowd impact on the side walls 7 and 8 along an area increasing and curving downward- 30 ly towards the rear wall, and on the rear wall 61ong a rectangular area corresponding to the limits of the area bf impact at the rear end of the side walls due to the increasing distance the spray particles must tkavel in a furnace of the 35 crosssection illustrated. Most of the spray would be concentrated In transit in a relatively, small height, with a small percentage of generally finer particles traveling at the upper and lower sides thereof. If the spray nozzle were 40 continuo usly maintained in this horizontal position the impact of the spray particles on the rear and side walls along a relatively restricted area would limit the amount of material that could be treated in a furnace of the proportions 4r, illustrated without the material flowing down the walls in an excessively wet condition. To provide a more extended area of deposit on the side and rear walis whue maintaining the desirable flat coarse spray and rendering the ma- ro terial as deposited more exposed to the furnace temperature conciitions, mechanism is provided' for continuously oscillating the spray nozzle vertically and about the axis of the pipe 30. As shown in Mgs. 8 to 12, the outer end of the pipe 5r) 30 has secured thereon a lever arm 37, to the upper portion of which an operating chain or the like 38 is adjustably connected. As shown iii Fig. 11, the chain 38 is given. a horizontal oscillating movement by passing it around pul- '60 leys 39 and 40 and connecting it to a crank pin 41 mounted on a crank disc 42 rotated by an. electric motor.43. The opposite end of the chain 38 is passed around pulleys 44 and 45 and supports a suitable counterweigbt 46. The angle 65@ of throw of the lever arm 37 may be varied by shifting the point of connection of the chain 38 thereto to thereby change the effective radius of the lever and/or by varying the radius of the crank pin 41 on the disc 42, as indicat6d in Fig. 70 12. The described parts are preferably proportioned so that the spray nozzle plote 29 will be tilted about 451 in both directions, so that when tilted the spray will impact at different levels on the side walls I and 8. 75

4 if th@! pipe 30 were maintallied in the horizontal position and continuously oscillated about its ax's, the spray would cover an area of generally butterfly form on the rear wall, with an excessively wet area at the axis. To provide a more uniform distribution of the spray deposits over a great6r area on the rear wall, the spray nozzle is desirably given an oscillating movement in a vertical plane. The mechanism for this purpose consists of an arm 47 secured to the rear end of the plate 33 and having an opere@ting chain or the like 48 adjustably connected thereto for raising the arm and thereby the plate 33 about the pivot pin 34. As shown in Fig. 11, the chain 48 passes upwardly aroiind pulleys 49 and 50 and is connected at its lower end to a crank pin 51 on the disc 42. The desired range of movement of the arm 47 being less than that of the lever 3 7, the pin 51 is made shorter than 20 the pin 41 and positioned closer to the axis of the disc 42. With this arrangement the arm 47 will be periodically raised to the upper position indicated in Fig. 8, and returned to the lower position by gravity due to the greater weight of 25 parts at the outer side of the pivot pin. The range of vertical oscillations can be varied by shifting the point of connection of the chain 48 to the arm 47 and/or by changing the radius of the crank pin 51 on the disc 42. 30 The movements of the chains 38 and 48 are advantageously synchronized so that the nozzle plate 29 will not be tilted relative to its longitudinal axis when in its extreme upper and lower positions and progressively tilted to its 35 opposite extreme positions when the pipe 30 Is horizontal. This synchronization can be effected simply by connecting the chains to the common driving disc 42 and spacing the crank pins 51 and 41 at a 90' angle thereon, as shown in 40 Fig. 12. The spray nozzle and nozzle oseluating mechanism disclosed herein are being claimed per se and in combination in an application of Leslie S. Wilcoxson and Frederick.G. Ely, Serial No. 23,406, filed May 25, 1935. 45 The side and rear walls of the recovery furnace are provided at their inner sides with, an outwardly inclined ledge 55 adjacent the lower level of the char. The ledge is formed by a continuous series of inclined metallic blocks 56 supported 50 on and held in heat transfer contaci with the wall tubes, as shown in Fig. 13, by tube clamps 54. The upper surface of the blocks 56 is formed with projections 57 to aid in retaining the deposited material in position on the walls. The 55 lower surface of the blocks 56 is provided with studs 58 to hold an extended portion of the wall refractory 13 in -contact with the underside of the blocks. With the descri bed ledge block arrangement, char dropping from the side and rear 60 walls will be deflected inwardly awai from the walls, thus preventing erosion of the wall refractory in the lower section and clogging of the primary air ports hereinafter described. The air required for combustion is preferably (j r) supplied to the recovery furnace it'two levels therein, primary air being introduced through the side and rear walls adjacent the hearth and secondary air through the side walls above the level of the char. Provisions for this purpose 70 consist of a forced draft fan 60 delivering air to a discharge conduit 61, the discharge being controlled by a series of dampers 50. A steam-air tubular heater 62, having a steam supply connection 63 and a drain connection 64, is located in 75 the conduit 61 for preheating the air when desired. The air is delivered to branch conduits 65 leading to opposite portions of a wind box 66 surrounding the rear and sides of the furnace adjacent the hearth. Vertically elongated primary air ports 67 are formed in. the side and 5 rear *aus of the furnace between, the corresponding wall tubes and at a level adjacent to the desired upper level of the bed of char to be normally present on the hearth 10, The ports 67 in the side walls are arranged In a row parallel 10 to the surface of the hearth, as shown in Mgs. I and 2. A downwardly directed primary air nozzle 68 Is mounted in each of the primary air ports with its lower inner end terminating at the center line of the corresponding tube row. 15 The inner ends of air nozzles 68 are held in h@at transfer contact with adjacent wall tubes, as shown In Figs. 14 and 15, by connecting bolts 69 between flanges on the nozzles and lugs secured to the tubes. Each of the air nozzles 68 Is provided with a peep hole a se . para e 20 connected by a condwt 71, controlled by an adjustable oriflce plate 72, to the wind box 66. With this arrangement, the bed of char on the hearth will be penetrated by downwardly impirig- 25 ing streafns of air on three sides, providing suitable condi,tions for rapid corabustion of the combustible portion of the char. Secondary air ports 73 of smaller flow area than the primary ports are formed in the two 30 side walls 7 and 8 shghtly above the upper level of the char and through which secondary air nozzles 74 discharge substantially horizontal streams of air sweeping across the furnace creating turbulent conditions in, that section pro- 35 moting combustion of any combustible gases present. The secon ary a nozz es are separately connected to the wind box 66 by vertical pipes 75 controlled by adjustable orifice piates 76. Doors 77 are provided along the wind box 40 for natural draft operation. In normal operation the chemicals in the char collecting on the hearth will fuse and flow downwardly through the bed in contact with the exceedingly porous and reactive carbonaceous ma- 4,r, terial which effects an endothermic reducing action converting the sodium sulphate to sodium sulphide. The liquefied chemicals flow downwardly along the hea h towards front wall 5. As shown in Figs. , 2 and 16, the front wall 50 is formed with a tap hole 80 between adjacent water tubes 16 and into which extends an outwardly flaring spout 8 1, the inner end of the spout being supported by a saddle 79 and held against the adjacent wall tubes. The spout 81 5r, is formed with horow sides 82 and a V-shaped hollow bottom 83 through which a cooling fluid fiows from an inlet connection 84 to outlet connections 85. The upper side of the spout bottom is provided with studs 86 for supporting a 60 layer of chrome ore iefractory 87. As indicated in Flig.. 1, the smelt discharging through the spout drops through an opening 90 in the floor into a dissolving tank 91 where it is dissolved in weak green liquor enteri ' ng the tank through a 65 pipe 92 and the solution withdrawn at a predetermined concentration or density through a pipe 93. The dissolving tank 91 has a loose cover 94 and an atmospheric vent pipe 95 for the discharge of the stea@m and other gases 70 gererated in the tank by the addil.ion of the molten smelt. With the recovery furnace constructed as shown and- described, the furnace Is started up by employing an auxwary fuel, such as wood and/or- 7r)