US2550677A - Method of and apparatus for dry distillation - Google Patents

Description

May 1, 1951 D. DALIN ET AL METHOD OF AND APPARATUS FOR DRY DISTILLATION Filed June 24, 1946 2 Sheets-Sheet l -wzs 2: 5-Z9 5 39 13 7 l zszvun Cmvnae'n q {22 5M Davzd Dalm' Clays Ju 52 2 02 I Arvzu Wilhelm Juhanssan o 0 o .4 Tare Jahannes Hgdbaak Patented May 1, 195i zssaw METHOD OF AND APPARATUS FOR DRY DISTILLATION David Dalin, Stenkullen 'Ronninge, Tore Johannes Hedback, Sodertalje, and Claes Joel Gejrot and Arvid Wilhelm J ohansson, Oreloro,

Sweden Application June 24, 1946, Serial No. 678,766 i In Sweden March 31, 1944 15 basis. (01. 202-12) 7 1 1 This invention relates to the dry distillation of solid fuel in-ovens of the type discussed in the pending application of David Dalin and Claes Joel Gejrot, Serial No. 581,700, filed March 8, 1945.

In apparatus of this type solid fuel such as oil'bearing shale, coal, or wood is fed in pieces of convenient size through anupright distillation retort in 'a'furnace for discharge from the open bottom of the retort onto a fuel bed where the residue coke is burned. Thehot combustion gases emanating from the fuel bed and continuously withdrawn from the furnaceare utilized'to heat the fuel traveling through the retort to effect preheating followed by degassing of the fuel and distillation of the gases. Distillation gases produced in the retort are continuously withdrawn by means of a duct havin its mouth opening to the interior of the retort in'the zone at which distillation takes place but near the bottom of the distillation zone.

1 Hence, the speed with which the distillation process can be carried out dependsupon the degree of heat developed by burning of the fueland applied to the retort to effect degassing and distillation of the fuel therein. h

This would seem to indicate that high combustion rates would produce correspondingly high rates of distillation of the fuel and this is true except for the fact that most fuels suitable for dry distilling sinter at relatively low temperatures and high temperatures must, therefore, be

avoided to preclude waste of the fuel and even complete stoppage of the distillationprocess. To preclude sinterin it has been customary in the past to control the temperature of the fuel bed by forcing excess quantitiesof air through the fuel'bed from beneath or to inject large quantities'of steam or inert gas onto the fuel bed all forth'e purpose of maintaining the fuel bed beneath'sintering temperatures.

While it was possible to cool the fuel as and avoid s'intering by these past expe'dients, distillation was not speeded but was, in fact, retarded. This follows from the fact that the produced combustion gas was low in carbon dioxide (CO2) conh J In the drydistillation of fuel, it is, of course,

necessary to draw off the cornbustion'and dis tillationgase's separately without allowing ad mixture thereof. This was to some extentac complished in the process of the aforementioned application, Serial No. 581,700, by vertical ad- 'justmentof the mouth of the distillation gas withdrawal duct within the retort-to locate the same a distance above a zone of substantialbal ance between the pressures of the combustion and distillation gases, and thus definitely above the area of zero pressure difi'erential therebetween. The location of the zero pressure differential area within the retort is capable of wide variation, however, since it is a function of the size of the fuel pieces being processed, and the relationship between the sub-atmospheric pressuresof the distillation and combustion gases.

Hence, it was frequently necessary to adjust the position of the withdrawal duct lengthwise of the retort in accordance with change in the location of the area of substantially zero pressure differential therein so as to avoid admixture of combustion gases with the distillation gases being withdrawn from the retort, and the retorts had to be of substantial height to enable such adjustment without interfering with preheating, de-

gassing, and distillation of the fuel therein prior to its passage out of the distillation zone and before reaching said area of substantiallyzero pressure differential. It will also be seen that the location ofsaid area of zero pressure differential within the retorts, of past distilling apparatus depended to a certain extent upon the rate of combustion of the fuel as controlled by excess quantities of air, steam, orinert gas.

Normal combustion depends upon the quantity of air supplied-from beneath the fuel bed, the characteristics of the fuelbeing burned,and the resistance which a bed of such fuel offersto the flow of air for combustion 'therethrough. The use of relatively small size fuel pieces would seem des'irable'from the standpoint of speeding distillation by reason of their ability to burn at a faster rate than larger pieces, but they have the disadvantage of causing more rapid sintering of the fuel and offering increased resistance to the flow of air through a bed of such'f'u'el making it difficult to cool the fire bed by excesses of air in the conventional manner.

Hence, relatively small size fuel pieces were avoided in past distillation processes and apparatus, and the rate at which distillation was car'- ried out was limited not only for this-reason but also becaus 01 the use of steam, air, or inert gases to prevent sintering of the fuel as hereinbefore brought out.

The main object of the present invention resides in the provision of a dry distillation process of the character described by which distillation is eifectd'in considerably less time than was heretofore possible so as to enable greatly increased production.

More specifically it is an object of this inven-v tion to provide a process for dry distilling relatively small size fuel pieces which are capable of being burned faster to speed distillation, and to provide for removal of sufficient heat from a burning bed of such fuel pieces as to effectively prevent sintering of the fuel without incurring all of the objections inherent in theuse of ex cess air, steam or inert gas for this purpose.

It is another object of this invention to provide a distillation process of the character deseribed in which the differential in pressure above 51 bene th merge bed is maintained at a which prqdi ces the maximum rate of combpstiq ndmakes pgssijb utilization to the fullheat energy'available in the een t a a mea u of con o pf the, temperature of the fuel bed to' prevent sintering has been obtained by flowing considt u h which a heat absorbing fluid is r fled to be circulated to carry off sufficient heatfrorn the interior. of the fuel bed to prevent .sim 'rieanf the f el a d. thu 'wmb l at maximum rates.

Z 9q,. uQ I1 2 e d makes on of th excess heat absorbed from .d or use u isamf par fi las excess. hea qw c hel wcr o n of the retort was subjected in the past has necessitated the useof costly heat resisting alloys in the eonstructien of the retort. In this respect it nother object of this invention to provide for QQQ ing i. ha owsr e mr i n f h retort lib gt d t he n ense .h a o he ur in fue directlyjthere bgneath by fluid. cooled ducts in se wi h. he wal c rt s. w r vent. bver eat ee thereo n o allow h reto :EQab m de. om. dina y nd less xp n v metals I 333? di ii lat a mm of h? i l' described it is essential that the distillation gas produced within the retort of the furnace be withdrawn. from above a neutral zone separating .2. .1? div, i l anad c mbu c Q-n s and w t I h is anarea where the differential in press re. be en the dis l t o n u ti n e grcesses of air through the fuel bed, or by .1 a i .slesq brdw thl s afisd ils iss a ngducts extending through the fuel :9}. =9. Prevent sem na s of QQ W" great height have been employed in the past to thereby lengthen the processing zone and allow the location of the area of zero pressure differential t e vary. Optimum results as regards the production rate and combustion conditions have,

however, notv been attained or even approached by these past methods because they entailed the maintenance of temperatures low enough to prevent disruption of the distillation and degassing processesand sintering of the fuel being burned. Only by slow combustion, an excess of air, steam .0 in t g s s for or ss p pos s nd siq an iuma es qr r a height ha it ee n ssi l to process this type of fuel.

Itis another object of this invention, therefore, to provide an improved distillation apparatus of considerably lessheight than was heretofore possible o as i ve th s ur e t s a t e je t of thisinvention to provide a distillation apparat o he. cha acter scribed in whiqh th combustion and distillation gas pressures are n nu us m a ed and alanced a ain t se en the t t l time in ai i r a of. zero pr ssure d eren l a a. fixeiiv ti n ace b n a t e dis i t qn, Zone and, abq e h rma be but referabl @05 hers q as t pe mi r duct on. in he. Overall h i ht 0 the apparatus.

'By .c n r llin he diflere tia o th c mbu tion and distillation gas pressures in this ma nner and, by ol the uslbed n na y in. the mannerst ed 9 as t amid e bj ct onab e consequences of using excess air for this purpose, it is possible to reach distillation efficiencies heretofore unattainable.

With the abovev and otherobjects in view which w l a a as. th d scr i proce d m s en iqnf e ide n e ov l. ap lica ion of h met od n re edi n in t e. n u ti ccmbin on and arrangeme t 9 Pa t AbS aIA- tially ashereinafter described and more particularl d n d. by he app de a ms, it being understood that such changes in the precise emh diment of. th .he e ndi clcses nven m y be madeas come within the scope of the claims.

The accompanying drawings illustrate several cpmp ete san pl s i he .nhy i al mbdd men of .t-h n entip qnst in. c erd nc wit thebe m des f dlfld or h rafi ce ppli a i n f e. rinqip ss here t and which;

.isa d e sm@ ati l udina cros ecti na view th ou h dr s illation appaa e f is nventi n;

ur 2 i a cross e ional View. h u h h furnace of. Figure 1 taken on the plaiiQpf the ne 4 Figure 3- is a plan view of a dry distilling installation employing batteries of furnaees connected with common combustion and distillation gas withdrawal ducts;

Figure 1; is a fragmentary cross sectional view illustrating a modified furnace. construction employed when the units are to be arranged in batteries l Figure 5 is a fragmentary detail perspective through a furnace illustrating the retort provided with means to improve heat transfer from 'wallsto the fuel pieces'passing through the terior of the retort; and

Figure 8 is a detail view of a portion of the distillation gas withdrawal duct.

Referring now more particularly to the ac in I companying drawings in which like numerals wood or oil bearing shale broken up intorelatively small particles is fed into the furnace through one or more upright distillation retorts J4 extending down into the furnace toward the grate structure l2'but with their bottom ends Opening to the interior of the furnace at a point: spaced above the grates to define the depth of,

the fuel bed whichextends between the bottom ends of the retorts and the grate structure.

The upper ends of the retorts project upwardly in through a seal l5 of refractory material at the 7 top of the furnace to be provided with a receiving hopper H5 in which the solid fuel pieces to be dry distilled are charged for. travel through the retort.

The distillation process depends upon subjection of the fuel pieces in the retorts to sufiicient heat to effect preheating, degassing and distillationduring their travel through the retorts and before passing out of a, distillation zone spaced a distance above the bottom of each retort, and

consequently before reaching the fuel bed. Such heat is supplied by burning the residue coke on the bed !3. f i

, The combustion gases emanating from the fuel bed are withdrawn from the top of the furnace" through one or more outlet ports I1 communi-- eating with. the combustion gas discharge duct [8 exteriorly of the furnace which usually leads to a stack or any other suitable draft producing means capable of drawing the combustion gases out of the shaft l l. The combustion gas comes into intimate contact with the exterior walls of the retorts as the gases pass upwardly in the substantially restricted passages between the walls of the retorts and the inside walls of the furnace to eifectheating of the retorts and the fuel therein to the temperatures necessary to produce degassing and distillation.

The distillation gas produced within the retorts is drawn off through ducts l9 extending centrally down through the retorts from their open tops vandhaving their mouths 23 opening to the in- .terior. of the retorts at ;a fixeddistance above -thecombustion zone definedby the upper portionsbfthe fuel bed, and in'the distillation zones nearthe bottom thereof. These ducts lead to a distillation gas collecting duct 2| maintained under a constant sub-atmospheric pressure as by means of a suction pump (not shown) Air for supporting combustion of the residue coke is fed through the fuel bed from below and to assure an adequateair supply for combustion,

: the ash pit indicatedby the numeral 22 is prefthe'hot combustion gases flowing over itsexterior erably maintained 1 at an above atmospheric pressure so as to constitutes, plenum chamber. Obviously, the plenum chamber 22 may constitute the entire basement room in which the ash pit is located, but in either event, it is important that the pressure of the air be so adjusted with relation to the size of the fuel pieces being treated and the resistance which a bed of such fuel offers to the flow of air therethrough under constant stack draft conditions as to avoid excesses of air which lead to incomplete combustion and cooling of the fuel bed.

Positive assurance against such excesses of air which were found so objectionable in the past is had in the present invention by the maintenance .of a constant differential in pressure above and below the fuel bed, which differential may be adjusted with fuel beds of different character to always cause the correct supply of air through the bed for optimum combustion conditions.

Combustion under near ideal conditions is only had, therefore, when certain above atmospheric pressure conditions exist in the plenum chamber 22, and certain conditions Of less or sub-atmospheric pressures exist within the furnace shaft .II to establish a predetermined constant differential in pressure above and beneath the fuel bed for any one size or type of fuel employed. Ob

to reach the top of the fuel bed where combustion of the degassed fuel, or residue coke, begins.

A balance between the low or sub-atmospheric pressures ofthe combustion gases in the shaft and the distillation gases within the draw-01f equipment therefor must be maintained within this neutral zone 24. In other words, the mouth 23 of each of the withdrawal ducts l9 must be located in the distillation zone of its retort, but a distance above the zone 24 of pressure balance so as to assure separate withdrawal of the combustion and distillation gases from the furnace without admixture ofeither with the other.

The elevation of the actual area of zero pressure differential in the zone 24 above the fuel bed is determined for the most part by the magnitude of the pressures of the combustion and distillation gases, and for this reason was subject towide variation in elevation in past processes brought about especially by change in the combustion gas pressure in the shaft. 7

In past distillation apparatus, it was necessary,

therefore, to have retorts and furnaces of great height or to provide for longitudinal adjustment of the distillation-gas withdrawal ducts in their within the neutral zones 2 of the retorts.

retorts to enable: positioning of the mouths. of, the,

One of the objectsoi'. the present invention,

however, is to. maintain the areasv of zero pressure differential spaced from; and at substantially fixedelevations between the distillation zones and. the fuel, bed so as to obviate the no: cessity for frequent. adjustments of the withdrawalducts and to enableforeshortening ofthe retorts and reduction in overall height of, the apparatus.

This is accomplished by means of continuously comparing and balancingcombustion and distillation gas pressures, detected at locations outside. of; theneutral zonesv 24 andwhichmay be remote from these neutral zones, through the medium of a pressure sensitive element}?! and a valve-like, damper 28 in they exhaust gas, duct i3 controlled by the pressure sensitive elementid,

The combustion gas pressure obtaining, within the shaft, H at an elevation spaced a, distance above the, fuel bed is impressed on one side of the-pressure sensitive element 25. through atube 21, while the pressure of the distillation gas within the header 2H. is impressed on the: opposite side of the pressure sensitive element 25 through a. tube 28. Hence, any sustained, fluctuation in combustion gas pressure within the shaft l lpr'oducedby changing stack draft conditions and which tends to cause shifting, of the, areas, of

zero pressurediiferential up or down within the neutral zones 24is-reflected-in the pressure sensitive element 25, to result in the transmission of electrical pulsations thereby through wiring 29 to, a: reversing motor tfl of known type. drivingly connected with the damperlt so as to, effect an adjustment of the position thereof in the discharge duct, l3- in. a direction and to a degree such as to return the combustion gas pressure to its desired value.

It is desired to emphasize, therefore, that the pressure sensitive element. 25 enables maintenance of the areas of zero pressure differential within the medial portions of the neutral zones 24' and hence at substantially fixed elevations above the fuel bed, and in addition serves to maintain the desired differential in pressure above and below the fuel bed despite changing stack draft conditions which tend to alter the combuse tion gas pressure within the shaft H. Thus, air for combustion of the fuel under optimum conditions is assured together with substantial fixation of the areas of zero pressure differential These conditions, it will be noted, are maintained despite fluctuations in pressures of either the combustion or distillation gases.

As will be readily apparent, the desired differential in pressure above and below the fuel bed may also be maintained by varying the above atmospheric pressure of the air supply'at the dictation of the pressure sensitive element. Zfito offset any changes in sub-atmospheric combustion gas pressure which might tend to shift the zero pressure differential areas within the zones 24.

The location of the zero pressure differential areas within the zones 24 enables substantial reduction in the height of the apparatus, while the maintenance of optimum conditions of combustion to utilize all of the heat energy available in the fuel being burned assures preheating, degassing, and distillationof the materials being treated in such retorts'of less height. v

As stated, speeding the distillation process by the application of additional heat to the fuel bein treated was impossible with past dry distillation apparatus because of the excesses of air, steam, or inert gas employed to cool the fuel bed below the sintering temperature of, the fuel. When, thefuel bed is cooled in this manner, prevention of sintering is accomplished at the expense of the loss of considerable heat energy.

In. past distillationprocesses the large percentage of excess air contained in the combustion gases results in inefficient combustion, excessive power consumption to remove the excessively large quantity of combustiongas and a substantially slow distillation.

Moreover, the solid fuelswhich are suitablefor dry distillation usually have low sintering temperatures, and high, combustion rates are out of the question. The present invention provides for cooling of the fuel bed to effectively prevent sintering of the fuelin a manner, enabling optimum conditions of combustion to be maintained inthe apparatus so as to speed the distillation process. Optimum conditions of combustion and high speed distillation is made possible by ducts 3i extending inside the fuelv bed, and provided with a number of branches 32 extending vertically down into the fuel bedtowards the grate structure l2 and upwardly into the open bottoms of the retorts. The ducts 3! lead outwardl of the furnace as illustrated to be connected with a source of a fluid heat absorbin medium such as water, steam or a combination of both adapted to be circulated therethrough.

When substantially uniformly distributed throughout the fuel bed the ducts 3| exert a cooling influence throughout the entire bed to cool the samebeneath the sintering temperature of the fuel. Obviously, the extent to which the fuel bed is cooled may be readily determined by regulatingthe amount and temperature of the heat absorbing medium circulated through the ducts.

Since the cooling ducts and their branches in nowise interfere with proper and efficient combustion ,of the fuel, it will be apparent that the fuel may be efficiently and completely burned,

without sintering, at a maximum rate to produce combustion gases of maximum temperature for degassing and distillation of the fuel at higher sufficient coolin effect of the steam, air or inert gas used for prevention of sintering.

The upwardly extending branches 32 of the .fluid cooled ducts extend into the open bottoms .of the retorts so as to effectively cool the lower portions of the retorts to reduce the risk of cracking. and the formation of encrustations. Further assurance against, cracking of the distillation gases and. the formation of encrustations is had through. the provision of jackets 35 surrounding the,l"ower portion of the distillation gas with- .drawal. ducts l9, as, indicated in Figure 8, and

through which a fluid heat absorbing medium is adapted to be circulated. The distillation gases, therefore, come into contact with wall surfaces of the. distillation gas withdrawal ducts that have been cooled at their portions closest to the combustion zone and which become excessively heatedthereby. A covering of insulating material 36 encircling thejackets prevents coolin of the .fuel

pieces passing through i of fiuid through the ducts.

the retort in a manner which might retard the distillation process.

It will be noted that the lower end portions of the retorts l4 are'directly above the fuel bed and close to the combustion zone.

avoid the frequent replacement encountered when ordinary and inexpensive materials were used.

The present invention enables the retorts to be made of inexpensive ordinary metals inasmuch as protection for the lower end portions thereof is afforded by means of fluid cooled ducts 3B and 39 encircling the lower endportions of the retorts in contact with the walls thereof to prevent overheating of the same.-

Thercooling of the fuel bed and the retorts and their withdrawal tubes by ducts through which a heat absorbingmedium such'as water .is circulated is highly advantageous for another reason aside from speeding distillation. These ducts enable the excess heat removed from the apparatus to be used for useful steam generatin purposes, while in the past the excess heat was largely wasted.

Ordinarily the temperature of the fuel bed may be controlled to effectively prevent sintering of the fuel by regulation of the circulation In. some instances, however, it maybe desirable to avoid direct contact of the fuel with the cooled walls of the ducts in a manner which might result in undesirable cooling of the fuel pieces closest to the ductsto below the temperature required for combustion.

' In such instances the branches 32 of the ducts may be surrounded by shells 40 of metal or insulating material,as shown in Figure 5, which reach temperatures between that of the fuel bed itself and the temperature of the fluid-heat 'absorbing medium circulated through the ducts so as to prevent excessive cooling of the fuel pieces in contact therewith. Preferably, the shells 40 are spaced from the branches 32 as shown so as to provide an air space between the inner walls of the shells and the exteriors of the branches.

When desired, more uniform cooling of the fuel bed may be obtained by providin the branches 32 of the ducts with vertical vanes 4| extending substantially radially from the branches, as shown in Figure 6.

Longitudinal fins 42 both exteriorlyand interiorly of the retorts l4 may be provided, as illustrated in Figure 7, to increase the surface 'area of the retort so as to enable the same to spaced distillation gas withdrawal ducts. 46 dis posed therein with the combustion gases withdrawn through the substantially rectangular space if surrounding the retorts and through substantially rectangular. passages 43] disposed between adjacent pairs of withdrawalducts 46.

A number of such retorts located in substantially cellular rectangular shafts or furnace units are arranged in rows to provide groups or batteries 49 and a number of such batteries 49'may be positioned in rows at opposite sidesof a common distillation gas withdrawalductfill leading to the inlet of a suction pump 5|. Each battery of distillation units has its distillation gas withdrawal ducts connected with the common conduit 50 by means of a header 52and each of the individual furnaces is connected with a combustion gas header 53 having a valve-like damper 26 situated therein for withdrawing the combustion gases and controlling the rate of their withdrawal respectively.

Pressure sensitive elements 25 responding to the pressures of the distillation gases in the headers 52 and to the combustion gases in the individual furnaces are likewise employed to automatically maintain the areas of substantially zero pressure differential in the retorts at fixed elevations but spaced above the combustion. zone and below the mouths of the distillation gas withdrawal ducts as previously explained. v

Each row of batteries has its combustion gas .discharge duct '53 leading to amain smoke-gas duct 55 which in turn is adapted to be connected with a stack or suction pump to effect withdrawal of the combustion gases from the individual furnaces.

From the foregoing description taken in connection with the accompanying drawings it will be readily apparent to those skilled in the art that this invention provides an improved process for dry distilling solid fuel at rates higher than hitherto possible, and which enables, the overall height of the apparatus for carrying out the process to be materially reduced to effect not only a saving in space but cost as well.

What we claim as our invention is:

1. In a dry distillation apparatusjof the character described wherein solid fuel is fed through a retort heated exteriorly by hot "combustion gases emanating from a fuel bed upon which degassed fuel discharging from the retort is deposited and burned. and wherein the rate and and depends upon-the differential in pressure between combustion gas above the fuel bed and combustion air fed to the fuel bed from below:

duct means for withdrawing combustion gases from the furnace after passage of the combustion gases over the retort to degas and distill fuel therein, said duct means being connected with a source of suction whereby sub-atmospheric pressure conditions obtain within the furnace above the fuel bed and within the discharge end of the retort; means providing a supply of combustion air below the fuel bed at a pressurev of such'magnitude with respect to -the sub-atmospheric pressure obtaining above the fuel bed as to establish a predetermined differential between the pressures obtaining above and below the fuel bed at which combustion air is fed through the fuel bed at a rate to support combustion under optimum conditions; other duct means having its mouth opening to the interior of the retort near the discharge end thereof for withdrawingdistillation gases from .the retort. said other duct means being connected with a source of sub-atmospheric pressure- 0f a magnitude so related to the sub-atmospheric pressure in the furnace as'to create a zone :of balance between the pressures of combustion v and distila sso cvv ill tween and spaced from the mouth of the distillation gas withdrawal duct and the discharge end said location'and also maintain substantially said predetermined differential in pressure above and below the fuel bed to assure burning of the fuel under optimum conditions of combustion.

- 2. A distillation furnace as set forth in "claim 1 including fluid cooled duct means entering the "furnace to be embedded in thebed of burning "fuel adapted to circulate sufficient coolant :through said fuel, in heat exchange .relation'ibut out of contact therewith, "for carrying away enough heat therefrom to preclude sintering of the fuel and thereby permit burning of the fuel under optimum conditions of combustion.

A distillation furnace as set forth in claim 1 including a fluid cooled jacket on -the :duct

.means for the distillation :gas for precluding heating of the distillation gas passing :therethrough to excessively high temperatures.

4. A distillation furnace as set forth in claim ,1 including a fluid cooled jacket on the duct means for .the distillation gas for precluding heating of the distillation gas passing therethrough to ex cessively high temperatures; andheat insulation interposed between the fluid'cooled jacket on the 'duct means for distillation gas and the fuel in "the retortto prevent undesirable cooling of the "fuelprocessed in the retort.

5. A distillation furnace as set forth in'claim 1 including fluid cooled means on the discharge end of the retort which issubjected to .theintense heat of the burning fuel bed for cooling said discharge end of'the retort to thereby enable the retort U0 be constructed from inexpensive materials ordinarily damaged by intense heat.

6. In a-dry distillation apparatus of the c'haracter described whereinsolid fuel is fed through a retort heated exteriorly by hot combustion gases emanating from a fuel bed upon which degassed fuel discharging from the retort is deposited and burned, and wherein the rate and distillation gases from "the retort, said withdrawal duct being connected with a source of substan- :-tially uniform sub-atmospheric pressure of a magnitude so related to the sub-atmospheric pressureobtaining in the furnace as to create a zone of balance between said sub-atmospheric pressures of the combustion and distillation gases so as to preclude-withdrawal of combustion gases with the distillation gases and vice versa, said zone of balanced pressure within the retort being subject to shiftingupon change'in the sub-atmospheric pressure obtaining within the furnace; and a pressure sensitive element for comparing the pressures of combustion and distillation gases measured at points remote from said zone of balanced pressure and operable upon change in "the relation-of said pressures to effect adjustment of the regulator in .said duct means to maintain said zone of pressure balance at a' location between and spaced from tthennouth "of'the distillation igas withdrawal duct and the atmospheric pressure conditions obtain within the furnace above the fuel bed and within the "discharge end of the retort; means providing a .supply of combustion air below the'fuel .bed at a substantially uniform pressure; a regulator in; i

said duct means for adjusting the sub-atmos- 'pheric pressure obtaining within the furnace and by which a differential in pressure above and below the fuel bed of predetermined magnitude may be establishedat which combustionair flows through the fuel bed in quantities assuring burnsingv of the fuel underoptimumconditionsof combustion; a distillation gas withdrawal duct hav ingits mouthopenin to the interiorof the retort near :the discharge. end thereof "for withdrawing discharge .end of therretor't.

7. A distillation furnace as'settforth in claim '6' including .fiuid cooled duct :means enterin the furna'ce'to beiembedded in'the .bed' of burning fuel and adapted'to have enough fluid coolant'circw latingtherethrough for carrying away sufficient heat to preclude sintering of :the fuel and there= by permit burning of the fuel under optimum conditions of combustion.

8. A distillation 'furnace'as-setforth in claim 1 including fluid cooled duct means entering the furnace to be embedded within and distributed throughout "the bed of burning fuel for absorbing sufficient heat therefrom to preclude sintering of the fuel and to thereby enable burning of the fuel under optimum conditions of "combustion; and heat insulating means for said fluid cooled duct means to prevent excessive cooling of the fuel nearest the fluid'cooled-duct means.

9. A distillationfurnace as-set forthinclaim 1 including heat-absorbing'surfaces on'the exterior of the'retort for improving heat transfer between heating thereof.

11. A distillation furnace as set fol-thin claim 1 including fluid cooled duct means entering thefurnace to be embedded within and distributed throughout the bed'of burning fuel for absorb- ;ing *sufficientheat therefrom to preclude sintering of the fuel and to thereby enable burning of the fuel under "optimum conditions of combustion; and means encircling portions'of the fluid :cooled duct :means in spaced relation thereto to provide an air space between .the encircled portions of the fluid cooled duct means'and the'directly adjacent fuel pieces to preclude excessive cooling thereof.

12. A 'distillationfurnace as set forth in claim 1 including fluid cooled duct means entering the furnace to be embedded Within the bed of burning fuel for absorbing sufficient heat therefrom to preclude sintering of the fuel and to thereby enable burning-ofthc-fuel under optimum conditions 'of "combustion; and .fins on portions of said fluid cooled-duct mean-s extending "3 a; outwardly therefrom into the fuel bed to absorb heat from areas thereof spaced from said portions of the fluid cooled duct means so that cooling of the fuel bed is not restricted to areas immediately adjacent to said portions of the fluid cooled duct means whereby the fuel bed is substantially uniformly cooled by said finned portions of the fluid cooled duct means.

13. The method of dry distilling solid fuel which involves feeding the fuel to a distillation zone defined by an upright duct open at its bottom and contained within a shaft, distilling the fuel in said zone, feeding degassed fuel through a neutral zone in the lower portion of the upright duct to a combustion zone in the lower portion of the shaft surrounding the duct and in open communication with the distillation zone through said neutral zone,- burning the degassed fuel in a bed in said combustion zone, and passing the hot combustion gases resulting from such burning of the degassed fuel upwardly through the shaft in indirect heat exchange relation wit the fuel in the duct to effect distillation of said fuel, which method is characterized by the steps of: withdrawing the distillation gases from the distillation zone; exhausting the combustion gases after the, same have been passed in indirect heat exchange relation with the fuel in the distillation zone; supplying primary combustion air to the fuel in the combustion zone; detecting the pressure of the combustion gases leaving the combustion zone, at a point outside the neutral zone; detecting the pressure of the distillation gases leaving the distillation zone, at a point outside the neutral zone; automatically comparing these W pressures; and regulating the pressure at the combustion zone in accordance with the differential between said two detected pressures to at all times maintain a zero differential between the pressure of the gases in said neutral zone in an area thereof as close as possible to the medial portion of the neutral zone to preclude combustion gases being withdrawn with the distillation gases and vice versa.

14. The method defined in claim 13 further tends to fluctuate back and forth between the distillation and combustion zones in consequence to changes in pressure in the combustion and distillation zones; detecting the pressure of the gases leaving the combustion zone, at a point outside the neutral zone; detecting the pressure of the distillation gases leaving the distillation zone, at a point outside the neutral zone; automatically comparing these two pressures; and regulating the pressure at the combustion zone proportionately to the degree of deviation from the pressure differential indicated by said comparison when the area of zero pressure differential is adequately spaced from the distillation and combustion zones, to restore said differential and thereby maintain said area of zero pressure differential adequately spaced from the distillation and combustion zones.

15. The method of dry distilling solid fuel which involves feeding the fuel into the top of a distillation zone defined by an-upright duct open .at its bottom, distilling the fuel in said zone, feeding degassed fuel through a neutral zone in the bottom portion of the upright duct to a combustion zone in the bottom of a shaft surrounding the duct'and in open communication with the distillation zone through the neutral zone, burning the degassed fuel in a bed in said combustion zone, and passing the hot combustion gases resulting from such burning of the degassed fuel upwardly through the shaft in indirect heat exchange relation with the fuel in the duct to effect distillation of the fuel therein, which method is characterized by the steps of Withdrawing the distillation gases from near the bottom of the duct which defines the distillation zone; exhausting the combustion gases from the shaft after the same have been passed in indirect heat exchange relation with the fuel in the distillation zone; supplying primary combustion air to the burning fuel in the combustion zone at a pressure higher than that of the combustion gases leaving the combustion zone; measuring the pressure of the combustion gases leaving the combustion zone at a point outside the neutral zone; measuring the pressure of the distillation gases leaving the distillation zone, at a point outside the neutral zone; automatically comparing these two pressures; regulating the pressure at the combustion zone in accordance with the differential between said two measured pressures to establish an area of zero pressure differential within said neutral zone to restrict said area of zero pressure differential to a relatively small range of fluctuation in the medial portion of the neutral zone so as to preclude combustion gases being withdrawn with the distillation gases and vice versa, and to also maintain a predetermined differential in pressure across the combustion Zone which induces combustion of the fuel in said zone at a rate greater than that which causes sintering of the fuel; and cooling the fuel in the combustion zone by passing a heat absorbing and dissipating medium in indirect heat exchange relation with all portions of the fuel in the combustion zone and in quantities sufficient to permit combustion of the fuel at said greater rate without danger of sintering.

DAVID DALIN.

JOHANNES HEIDBACK.

CLAES JOEL GEJROT.

ARVID WILI-IELM JOHANSSON.

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

UNITED STATES PATENTS Number Name Date 1,176,432 Chrisman Mar. 21, 1916 1,618,566 Bergh Feb. 22, 1927 1,780,653 McDevitt Nov. 4, 1930 1,838,622 Herrick Dec. 29, 1931 1,922,321 Parker Aug, 15, 1933 FOREIGN PATENTS Number Country Date 354,588 Germany June 13, 1922 228,897 Great Britain Dec. 3, 1924 240,497 Great Britain June 17, 1921 419,370 Great Britain Nov. 12, 1934 116,963 Switzerland Oct. 1, 1926

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