US2840047A - Fuel burning apparatus - Google Patents

Description

June 24, 1958 o, LOTZ 2,840,047

A FUEL BURNING APPARATUS Original Filed May 31. 1952 OHo LoTz BY ATTORNEY United States Patent() FUEL BURNING APPARATUS Otto Lotz, Oberhausen, Germany, assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Original application May 31, 1952, Serial No. 290,876.

Divided and 'this application March 29, 1956,V Serial zo claims. (ci. 122-235) combustible ash residue from `each cyclone Afurnace asV liquid slag.` The cyclone furnaces are suitably formed about horizontally extending axes and furthermore are arranged to discharge into a secondary furnacc'chamber `in a generally horizontal direction, thereby constituting the source of heat for an associated fluid heating unit.

v The instant application is a division of my copending application for Fuel Burning Apparatus, Serial No. 290,-

y 876, filed May 3l, 1952.`

The'granular fuels normally used in such cyclone furnaceshave particle sizes of SAV and under, kandcontain .as a result of the fuel crushing operation a proportion of dustlike particles, known .as fines The fuel and air mixture is introduced in the furnace chamber through a tangential inlet arranged to effect a whirling motion of the fuel and air mixture in a helical path axiallyof and toward the opposite end'of the furnace. In operation the entering fuel and air stream is rapidly ignited and the centrifugal eiect'of-.the whirling stream causes the ash particles released from the burning fuel particles to deposit in a molten condition on the furnace wall and form a film or layer ofV molten slag thereon on which the larger fuel particles are caught fand burned.

In prior embodiments of lhorizontally arranged cyclone furnaces, the gases of combustion `are caused to enter a lower part of the secondaryfurnace chamber .at one side of .a steeply inclined dividing or intermediate wall or arch by which the. gases are'deected downwardly toward the floor of the secondary furnace chamber, the ilow of gases continuing'in an upward direction at'the downstrearn side ofthe arch and thence into a radiation chamber where the heat of the gases is transferred to uid conducting elements disposed "at elevations beyond the arch. Due tothe bilateral heating, `this intermediate wall is subject to a high degree of vwear which is difficult to detect by observation. Y It also obstructsy all free observation of the openings through which thefurnace gases and the slag pass from the v'cyclone furnace chamber into the secondary furnace chamber.y

In the normal operation of a cyclone furnace of the character described, there is elected within the furnace a high degree of separation of suspended slag particles from Vthe'gas'es in order to permit gases relatively .free `from slag particles to be discharged through the central gas -outlet'while the collected slag isy separately discharged througha separate, lower outlet. Owing toythis, the slag outlet is heated onlyby a partial gas current which is furtherdecreased as the slaglevel rises -therebypre- `senting some d ifliculty in maintaining slag fluidity `at the 2,840,047 Patented June 2,4, 1958 Z t slag outlet. It has also been customary to position the cyclone furnace laterally adjacent and opening' to the secondary furnace chamber, with the major axis of the cyclone furnace arranged substantially horizontal and the entire axial length of the cyclone furnace disposed outside the secondary furnace chamber. While satisfactory operation has been obtained with the cyclone furnace so arranged, some difficulty has been encountered in providing for effective fluid circulation inthe tubes defining the cyclone furnace walls.

The present invention is concernedv with the provision of an improved construction of a fluid heating unit comprising upwardly extending walls including lluid cooled tubes defining a secondary furnace chamber receiving the products of combustion directly from a, ,Cyclone type furnace, the axis of which is preferably arranged substantially horizontal and the axial length of which is disposed within the secondary furnace chamber, with some of the fluid cooled tubes of the secondary furnace chamber walls having intermediate portions forming the vfurnace chamber of the cyclone furnace. An outlet is arranged tangentially of the circumferential wall of the cyclone furnace for the discharge of both molten slag and high velocity gases including slag particles in suspension. The outer vertical Wall zof the lower portion of the secondary furnace chamber is positioned opposite the cyclone furnace gas and slagoutlet at a distance suicient to insure' that the gases and suspended slag particles discharging from the gas and slag outlet will impact on the outer wall at a velocity sucient to cause most of the suspended `slag particlesin a molten or sticky condition to adhere to the Vouter wall and thence ilow downwardly to a slag pit. With this arrangement continuous Vdischarge of slag lin a molten condition through the cyclone furnace gas and slag outlet is assured.- Further, the wall tubes forming the combustion chamber of the cyclone furnace are exposed to the heat of the gases on one side along a substantial portion of their length, while a portion of said tubes .are subject to the yheat of the gases on both sides, thus promoting continuous and effective circulation in theseV wall tubes. Moreover, a self-cleaning slag deposition area is provided bythe Outer wall of the secondary furnace chamber for effectively removing .the vslag particles carried out of the cyclone furnace in suspension in the heatingV gases discharged, and the outer wall is less exposed to wear than the intermediate gas directing arch or baille wall heretofore employed because -of the unilateral heating by gases llowing thereover.

The various features of novelty which characterize lmy y invention are pointed out with particularity in the-claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained byV its use, reference should be had tothe accompanying drawings and descriptive matter in which .I have illustrated and4 described a specific embodiment of my invention.

`Of the drawings: 4

Fig. 1 is a vertical sectional View of a cyclone yfurnace vfired fluid heating unit constructed in accordance with my invention;

Fig. 2 is a partial vertical section taken along therline 2-2 of Fig. l; and Y A Fig. 3 is a ydiagrammatic vertical section of a modified form of the `cyclone furnace vshown in Figsfl and 2.

While various kinds of liquidand gas fuels can be burned in the cyclone furnace construction illustrated, the constructions illustrated .and hereinafter described are specifically designed and particularly adapted `for' burning coarsely pulverized or granulated bituminous or semibituminous coal. l

The main portions ofthe unit .illustratedin Figs. l

and 2 include a fuel-firing section consisting ofa pair of cyclone furnaces and 12 arranged to burn a solid fuel` directed upwardly within the secondary furnace 14,`then owthrough fa slag collecting screen 16 into a vertically elongated radiant heat transfer chamber 18 of horizontal rectangular cross-section, and thenceto a convection heat- :ing section, not shown. Y

vT he secondary furnace chamberV 14 isof horizontal vrectaittgula'r cross-section, being defined by a water-cooled rear or ictarget wall 20, front wall 22 and opposite side walls 24, and partitioned from theeyclone furnaces 10, -12 by portions of the circumferential wall of each cyclone furnace` chamber. The `'secondary furnacechamiber 14 opens upwardly into the radiant chamber 18,v which is formed by vertical'extensions of the front, rear and side boundaries ofthe chamber- 14.fTl1e lower end of the secondary furnace chamber includes `inclined floor portions-26 converging downwardly` toward a rectangular Vthroat` passage `28 for dischargingmolten slag into a slag tank, only a portion ofwhich is shown, positioned therebelow. c i n 'Ihe cyclone furnaces 10 and 12 are `of horizontally elongated substantially `circular cross-section, the furnace cham'ber ofceach 'being formed by closely spaced studded `tubes `covered by a layer of suitable refractory material and having its entire axial length disposed within the secondary furnace 14. Each furnace chamber includes a circumferential wallV 30, a portionof which is also commonto the front wall boundary of the secondary furnace chamber 14, and an end wa'H 32, which is also common tothe plane of its corresponding secondary furnace chamber side wall boundary. The cyclone furnaces 10 and 12 are combined in"endtoend relation, to form a single furnace unit 34 having'a lower outlet 36 opening tangentially Vtoward one side thereof, adjacent the bottom, for

the combined discharge ofV all gases and slag into the secondary furnace 14. `The cyclone furnace chambers are formed `about longitudinalaxesV inclined downwardly toward thecenter of the secondary furnace 14 in a common vertical plane so `that the rotating fuel and air streams traveling along the circumferential wall of eac'h 'furnacechamben from axially opposite directions, willY not leave a dead space-in anupper part Vof the chamber. A whirling stream of primary air and fuel is introduced into each of the cyclone furnaces 10, 12 through a primary burner or head 38 which opens axially thereof through the walls 24 and 32, the two streams whirling in oppositedirections, as `viewed from the respectiveenda "but providing a common direction of rotation within the furnace unit 34 as viewed from a single end. Thus, as seen in Fig. l, with the common outlet 36 positioned as shown, the direction of fuel-air rotation is counterclockwise. Secondary air is introduced tangentially into the furnace unit 34 in the same direction of Vrotation as the streams of fuel laden air through two `sets of ports 40 .located adjacent opposite ends.

All lboundaries of the `secondary furnace and `radiant chambers '14 and 18 are uid cooled by means of fluid conducting `tubes associated with the respective walls. The-rear wall 20 is `lined by tubes 42 having their lower ends connected to a header 44. The circumferential wall of each furnace chamber includes oppositely curved rows of `fluid cooled tubes 46 and 4,8, the formerextending between lower headers' 50 and upper headers 52v and the latter having their upper portions extending upwardly along the `frontgwall 22 and their lower ends connected to headers 54. The `slag screen 16 arranged across the outlet from the secondary furnace chamber 14 isfformed by tubes 56 connected at oppositeendstoheaders 58 and..60 and `having intermediate portions extending along a portion of the circumferentialwall of the corresponding furnace chamber. It is to Vbe understood that the portions of the fluid circulation system described are suitably connected into the circulation system of the unit. For example, the upper ends of tube rows 42 and 48 may be connected to a steam and water drum and the headers 44 and 54 may `be supplied with water from the water space of said drum. The rear wall 20, being Aan outer wall, and thus freely accessible from the outside, may be provided with' a closable port, opposite the gas and slag outlet 36, and thereby enable inspection to be made of furnace operating conditions.

In the operation of the cyclone furnace 10, 12, the slag which is deposited on the walls is continuously contacted by the whirling stream of burning fuel and gases and thereby brushed through the common outlet 36 into the slag discharge opening 28 of the secondary furnace chamber 14.1Y .The gases discharging through the outlet 36 contain little, if any, combustible matter, combustion being substantially completed in the furnace unit 34. Fly ash and molten particles present in suspension in the outgoing gases a're largely removed in the secondary furnace chamber 14. The rear vor target wall 20 is positioned opposite the outlet 36 at` a distance therefrom short enough to insure that the gases and suspended ash and molten particles will impact on the target wall at a velocity sufficient to cause most of the suspended ash and slag particles in apmolten or sticky condition to adhere to the target, wall, while` large enough `that the discharging gases will not flow upwardly through the lower portion of the secondary furnace chamber 14 at a velocity which would cause the'` slag deposited on the target wall to be picked up by the gases and carried into the convectionheating `section of the unit. In general a distance between the outlet 36 and the target wall 20 of not greater than `one cyclone furnace diameter has been found to be satisfactory. With the target wall so arranged, the products of combustion from the furnace unit 34 dischargeinto the lower portion of the secondary furnace chamber 14 and due to the proximity of the wall 20 the gas stream impacts thereon and is Yforced to move upwardly. The adhesive property of the vslag particlesand this relatively abrupt change in direction of movement of the gas stream results in most of the remaining ash and slag particles in suspension being deposited on the wall 20 and from there drained downwardly to the slag tank. The gases then flow upwardly through the slag screen 16` into the radiant chamber 18, and thence to the convection heating section of the unit. 1

Fig. 3 is a modification diagrammatically` illustrating an arrangement of two cyclone furnaces 62, 64 in which the increasing radial dimension from opposite ends facilitates the passage of slag into an outlet 66. In other respects, this form of furnace may be constructed in the manner of the furnace unit 34 and may be substituted thirefor in the furnace arrangement shown in Figs. l an 2. .While in accordance with the provisions of the statutes I have illustrated and described herein a specific form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit` of the invention covered by my claims, and that certain features of the invention may sometimes be used Vto advantage without a corresponding use of.other feacooled tubes -of said secondary furnace chamber-walls, means forming a gas outlet at one end of said furnace chamber opening to said secondary furnace chamber, means for introducing a combustible mixture into said furnace chamber for discharge through said gas outlet into said secondary furnace chamber, some of the fluid `cooled tubes' of said circumferential Wall absorbing heat from the hot gases therein and from the gases flowing ythrough said secondary furnace chamber, and means connecting said fluid cooled tubes into said fluid circulation system.

2. A fluid heating unit having a fluid circulation vsystem and comprising upwardly extending walls including fluid cooled tubes defining a secondary furnace chamber, a cyclone furnace having a furnace chamber of substanltially circular cross-section extending into said secondary furnace chamber and arranged with its major axis `substantially horizontal, said furnace chamber being defiend in part by a circumferential wall including intermediate .portions of some of `thefluid cooled tubes of said secondary furnace chamber walls, means forming a gas outlet `at one end of said furnace chamber opening to said secondary furnace chamber, vmeans for introducing a .combustible mixture into said furnace chamber for discharge through said gas outlet into said secondary furnace chamber, some of the fluid cooled tubes of said circumferential wall absorbing heat from the hot gases'therein and from Ithe gases flowing throughsaid secondary .furynace chamber, and means connecting said fluid cooled tubes into said `fluid circulation system.

3. A fluid heating unit having a fluid circulation -system and comprising upwardly extending walls including .fluid cooled tubes defining a secondary furnace chamber, a cyclone furnace having a furnace chamber of substantially circular cross-section arranged with its major axis substantially horizontal and defined by walls including intermediate portions of some of the fluid cooled tubes of said secondary furnace chamber walls, said furnace chamber having its entire axial length disposed in said secondary furnace chamber, means forming a gas outlet at one `end of said furnace chamber opening to said -secondary` furnace chamber, means for introducing ra combustible mixture into said furnace ,chamber for discharge -fthroughsaid gas .outlet into said secondary furnace chamber, some of the fluid cooled tubes of said furnace cham- -ber absorbing heat from the hot gases therein and from ythe gases flowing ythrough said secondaryfurnace chamber, and means connecting said fluid cooled tubes yinto said -fluid circulation system.

4. A fluid heating unit having a fluid'circulation system and comprising upwardly extending walls including fluid cooled tubes defining a secondary furnace chamber, a cyclone furnace having a ,furnace chamber ofsubstantiallyvcircular 'cross-section arranged with its .major axis substantially horizontal and defined by walls including intermediate 'portions of some of the fluidV cooled tubes of `said secondary furnacefchamber walls, said furnace chamber .having its entire axial length disposed in said secondary furnace chamber, means forming a gas outlet at one end of said furnace chamber openingl to said secondary furnace chamber, part of the fluid cooled circumferential wall of said furnace chamber being common with a wall of said secondary furnace chamber, means .for introducing a combustible mixture Yinto said furnace chamber for discharge through said gas outlet into said secondary `furnace chamber, some of the fluid cooled tubes ofsaid furnace ychamber absorbing heat lfrom the `hot gasestherein and from the gases flowing through said secondary furnace chamber, andy means connecting said fluid cooled tubes into said fluid circulation system.

y 5. Alfluid heating unit having a fluid circulation system Aand comprising upwardly extending walls including fluid cooled tubes defining a ,secondary furnace chamber, a ycyclone furnace having-a furnace chamber of substantially 'circular cross-section extending into saidsecondary furnace chamber Aand denedby walls including intermediate portions of some of the fluid cooled tubes of said secondary furnace chamber walls, mcans'for burning a slag-forming solid fuel in said furnace chamber under a mean furnace chamber temperature above the fuel ash fusion temperature, means forming an outlet at Lone Vend of said furnace chamber extending through and arranged tangentially to the circumferential wallof said furnace chamber Ifor the discharge of molten slag and heating gases carrying .slag particles in suspension into said secondary furnace chamber, some of the fluid cooled tubes of said furnace charnber absorbing heat from the hot gases ktherein and from the gases flowing throughl said secondary furnace chamber, and means connecting said fluid cooled tubes into said fluid circulation system.

6. VA fluid heating unit having a fluid circulation system and comprising upwardly extending Walls including fluid cooled tubes defining a secondary furnace chamber, a cyclone furnace having a furnace chamber of substantially .circular cross-section extending into said secondary furnace chamber and arranged with its major axis substantially horizontal, said furnace chamber being defined by walls'including intermediate portions of some .of the fluid cooled tubes of said secondary furnace chamber Walls, means for burning a slag-forming solid fuel in said furnace chamber under a mean furnace chamber temperature above the fuel ash fusion temperature, means ,forming an outlet at one end of said furnace chamber extending through and arranged tangentially to the circumferential wall of said furnace chamber ,for the .discharge `of mol-ten slag and heatinggases carrying slag particles in suspension into said secondary furnace\chamber,.some of the fluid cooled tubes of said furnace chamber absorbing heat from the hot gases therein and from'the gases flowingV through said secondary furnace chamber, and means connecting said :fluid ycooled :tubes into said fluid circulation system.

7. A fluid heating unit having a fluid -crculatiousys- Vtem and comprising upwardly extending walls including fluid cooled tubes defining a secondary furnace chamber, t

a cyclone furnace having a furnace chamber of substantially circular cross-section arranged with its major jaxis n substantially horizontal and defined by walls including intermediate portions of some of the kfluid cooled tubes of v said secondary furnace chamber walls, said furnace vcham- `ber having its `entire axial length disposedin said secondary furnace chamber, means for burning a slag-forming solid fuel in said furnace chamber under a mean furnace chamber temperature above the fuel ash fusion temperature, means forming an outlet at one end of said furnace chamber extending through and arranged tangentially -to the circumferential wall of ksaid furnace chamber for the ldischarge of molten slag and heating gases carrying slag particles in suspensioninto said secondary furnace chamber, some of the -fluid cooled tubes ofsaid furnace chamber absorbing heat from theV hot gases therein and ,from the gases flowing through said secondary furnace chamber, and .means connecting said'fluid cooledtubes .into'said fluid circulation system. l

S. A fluid heatingunit having a fluid circulation system and comprising upwardly extending Walls including uid cooled tubes dening a lsecondary furnace chamber, a cyclone furnace having a furnace chamber of substantially circular cross-section extending into said secondary furnace chamber and arranged with its major axis substantially horizontal, said furnace chamber being defined by walls including fluid cooled tubes, means for burning: a

slag-forming solid fuel in said furnace chamber under a mean furnace chamber 4temperature. above -the fuelzash fusion temperature, means forming an outlet at roneend of said furnace chamber'for the discharge ofmolten slag and heating gases carrying slag particles in suspension into said secondary furnace chamber, said secondary furnace chamber including Va lower Isection :having avertically arranged louter wall :opposite said gas and slag :outlet Vcooled tubes of said `furnace'chamber absorbing heat from'the hot gases, therein and from the gases flowing through said secondary furnace chamber, and means connecting said fluid cooled tubes into said fluid circulation system. i t o t 9. A fluid heatingunit having a fluid circulation syso tem and comprising upwardly extending walls including fluid cooled tubes defining a secondary furnace chamber, Aa cyclone furnace having a furnace chamberof substantially circular cross-section extending into said secondary N furnace chamber and arrangedtwith its major axis substantially horizontal, said `furnace chamber being defined by walls including intermediate portions of some of the fluid cooled tubes o'f said secondary furnace chamber walls, means for burning a slag-forming solid fuel in said furnace chamber under a mean furnace chamber temperature above `the fuel ash fusion temperature, means forming an outlet at vone end of said furnace chamber extending through and arranged tangentially to the circumferential wall `of said furnace chamber for the discharge of molten slag `and heating gases carrying slag particles in suspension into 4said secondary furnace chamber, said secondary furnace `chamberincluding a lower section having a vertically arranged outer wall, opposite said gas "and `slag outlet andspaced horizontally therefrom a distance notgreater thanv the diameter'of said cyclone furvnace to receive the impact of Ta major portion of the slag particles in suspension inthe` dischargedr heating gases, some of the fluid cooled-tubes of said furnace chamber labsorbing heat from the hot gases therein and from the gases, flowing through said secondary furnace chamber, and meansconnecting `,saicluidfcooled tubes into said fluid circulation system. Y

l0.` A fluid jheating unit having a fluid circulation system'nd comprising upwardlyfextending walls including fluid `co'oled tubes vdefining a secondary furnace chamber, a cyclone furnace having a furnace chamber of substantially circular cross-'section `arranged with its major axis substantially" horizontal A,and defined bywalls including intermediate ,portionsof somek of the fluid cooled tubes of said secondary lfurnace `chamber walls, said furnace "chamber having its entire axial length disposed in said secondary furnace chamber, means for burning a slagformingsolid fuelV jin said furnace chamber Aunder a mean furnace chamber `temperature above the fuel ash fusion; temperature, means forming an outlet at one 'end of said furnace chamber extending through and arranged tangentiallyto the'circumferential wall of said furnace chamber forthe discharge of molten slag andtheating gases carrying vslagparticles in suspension into said secondary furnace chamber, said secondary furnace chamber including a lowersection having a vertically arranged outerl wallopposite'said gas and slag outlet and spaced horizontally therefrom-a distance not greater than the diameter vof said cyclone furnace to receive the Aimpact of a major portion of the slag particles in suspension in the discharged heating gases; some of the fluid cooled ltubes of said furnace chamber absorbing heat from the hot gases therein andfrom the gases flowing through 'said'secondary fuma'ce chamber, and means connecting said fluid cooled tubes into said fluid circulation system. I 11.` A fluid heating unit having a fluid circulation system and comprising upwardly extending walls including fluid cooled tubes defining ,ar secondary furnace. chamber,4 a ipairof cyclone furnaces each having a furnace chamber V'of substantially circularcross-section extending into said secondary `furnace chamber and defined by walls includ- .ing intermediate.- portions of some of the fluidcooled `tubes of said secondary furnace chamber walls, said -cycloneifrnaces `being arranged in separate walls ofsaid ,scondarylfurnace chamber and havingtheir furnace `chambers in communicating relationship, means forming l2. A fluid heating unit having a fluid circulation system Vand comprising `upwardly extending walls including fluid "cooled tubes. defining a secondary furnace chamber, a

pair of cyclonjefurnaceseach having a furnace chamber of substantially circular cross-section extending' into said secondary furnace chamber and arranged with its major 'axis substantially horizontal, each of said furnace chambers being defined by walls including intermediate portions of` some of the fluidcooled tubes of said secondary furnace chamber/walls, said cyclone furnaces being arranged in separate walls of said secondary furnace chamber and having their furnacechambers in communicating relationship, means'forming a gas outlet common to said furnace chambers opening to said secondary furnace chamber, means for introducing a combustible mixture into each'furna'ee chamber for discharge through said gas outlet into said secondary furnace chamber, some of the fluidcooled-tubesy of each furnace chamber absorbing heat concurrently from the hot gases therein and from the gases `flowing through said secondary furnace chamber,

4and means connecting said fluid cooled tubes into said fluid circulation system. r o

13. A fluid heating unit having a fluid circulation Ysystem and comprising upwardly extending walls including fluid cooled tubes definingl a secondaryvfurnace chamber, a pair of cyclone" furnaces each having a furnace chamber of substantially-circular cross-section arranged with its majorvaxis substantially horizontal and defined by walls including intermediate portions of some of the fluid Icooled VVtubes-of said secondary furnace chamber walls, each of saidfurnace chambers having its entire axial length extendinginto said secondary furnace chamber, said cyclone furnaces being arranged in separatevwalls `of `said secondary furnace chamber and having their furnace chambers in` communicating relationship, means forming a gas outlet common to said furnace chambers opening tosaid secondary furnace chamber, means for introducing a` combustible mixture Vinto each furnace chamber for discharge through said gas'outlet into said secondary furnace chamber, some of Vthe fluid cooled tubes of each furnace chamberabsorbing heat concurrently from the yhot gases therein and from'the gases flowingfthrough said secondary furnace chamber, and means :connecting said fluid cooled tubes intov said fluid circula- 14. A fluid heating unit having a fluid circulation system and comprising upwardly extending walls including fluid cooled tubes defining a secondary furnace chamber, a pair of..cyclone furnaces each having a furnace chamber of` substantially'circular cross-section extending into said secondary furnace chamber and arranged with its major axis substantially horizontal, each of said furnace chambers being defined by walls including intermediate portions of someof the fluid cooled tubes of said secondary'furnace chamber walls, said cyclone furnaces being ,arranged in opposite walls 'of 'said secondary furnace chamber and having theirfurnace chambers in coaxial 'and :communicating relationship, means forming a `gas opening .to said secondary furnace chambers, means for introducing a combustible mixture into each furnace chamber for discharge through said gas outlet into said secondary furnace chamber, some of the uid cooled tu-bes of each furnace chamber absorbing heat concurrently fromA the hot'igasesftherein and from 'the4 gases flowing through-'said secondary-furnace chambenand sauna? means connecting said fluid cooled tubes 1into said iluid circulation system.

15. A lluid heating unit having a fluid circulation system and comprising upwardly extending walls including lluid cooled tubes defining a secondary furnace chamber, a pair of cyclone furnaces each having a furnace chamber of substantially circular cross-section extending into said secondary furnace chamber and defined by walls including intermediate portions of some of the fluid cooled tubes of said secondary furnace chamber walls, said cyclone furnaces being arranged in separate walls of said secondary furnace chamber and having their furnace chambers in communicating relationship, means for burning a slagforming solid fuel in each of said furnace chambers under a mean furnace chamber temperature above the fuel ash fusion temperature, means forming a gas outlet common to said furnace chambers opening to said secondary furnace chamber, some of the lluid cooled tubes of each furnace chamber absorbing heat concurrently from the hot gases therein and from the gases owing through said secondary furnace chamber, and means connecting said lluid cooled tubes into said iluid circulation system.

16. A fluid heating unit having a luid circulation system and comprising upwardly extending walls including fluid cooled tubes defining a secondary furnace chamber, a, pair of cyclone furnaces each having a furnace charnber of substantially circular cross-section extending into said secondary furnace chamber and arranged with its major axis substantially horizontal, each of said furnace chambers being defined by walls including intermediate portions of some of the fluid cooled tubes of said secondary furnace chamber walls, said cyclone furnaces being arranged in separate walls of said secondary furnace chamber and having their furnace chambers in communicating relationship, means for burning a slag-forming solid fuel in each of said furnace chambers under a mean furnace chamber temperature above the fuel ash fusion temperature, means forming a gas outlet common to said furnace chambers opening to said secondary furnace chamber, some of the fluidrcooled tubes of each furnace chamber absorbing heat concurrently from the hot gases therein and from the gases flowing through said secondary furnace chamber, and means connecting said iluid cooled tubes into said lluid circulation system.

17. A fluid heating unit having a iluid circulation system and comprising upwardly extending walls including tluid cooled tubes defining a secondary furnace chamber, a pair of cyclone furnaces each having a furnace chamber of substantially circular cross-section extending into said secondary furnace chamber and arrangedvwith its major axis substantially horizontal, each of said furnace chambers being defined by walls including intermediate portions of some of the iluid cooled tubes of said secondary furnace chamber walls, said cyclone furnaces being arranged in opposite walls of said secondary furnace chamber and having their furnace chambers in coaxial and communicating relationship, means for burning a slag-forming solid fuel in each of said furnace charnbers under a mean furnace chamber temperature above the fuel ash fusion temperature, means forming an outlet common to said furnace chambers extending through and arranged tangentially to the circumferential walls of said furnace chambers for the discharge of molten slag and heating gases carrying slag particles in suspension into said secondary furnace chamber, some of the fluid cooled tubes of each furnace chamber absorbing heat concurrently from the hot gases therein and from the gases flowing through said secondary furnace chamber, and means connecting said iluid cooled tubes into said fluid circulation system.

18. A fluid heating unit having a fluid circulation systern and comprising upwardly extending walls including lluid cooled tubes defining a secondary furnace chamber, a pair of cyclone furnaces each having a furnace cham- -ber yof substantially circular crosssection extending into said secondary furnace chamber and arranged with-its major axis substantially horizontal, each `of said furnace chambers being defined by walls including fluid cooled tubes, said cyclone furnaces being arranged in separate walls of said secondary furnace chamber and having their furnace chambers in communicating relationship, means for burning a slag-forming solid fuel in each of said-furnace chambers under a mean furnace chamber temperature above the fuel ash fusion temperature, means forming an outlet common to said furnace chambers for the discharge of molten slag and heating gases carrying slag particles in suspension into said secondary furnace chamber, said secondary furnace chamber including a lower section having a vertically arranged outer wall opposite said gas and slag outlet and spaced horizontally there-V from a distance not greater than the diameter of said cyclone furnace to receive the impact of a major portion of the slag particles in suspension in the discharged heating gases, some of the lluid cooled tubes of each furnace chamber absorbing heat concurrently from the hot gases therein and from the gases flowing through said secondary furnace chamber, and means connecting said fluid cooled tubes into said fluid circulation system.

19. A fluid heating unit having a lluid circulation system and comprising upwardly extending walls including iluid cooled tubes defining a secondary furnace chamber, a pair of cyclone furnaces each having a furnace chamber of substantially circular cross-section extending into said secondary furnace chamber and arranged with its major axis substantially horizontal, each of said furnace chambers being defined by walls including intermediate portions of some of the fluid cooled tubes of said secondary furnace chamber walls, said cyclone furnaces being arranged in separate walls of said secondary furnace chamber and having their furnace chambersin communicating relationship, means for burning a slag-forming solid fuel in each of said furnace chambers under a mean furnace chamber temperature above the fuel ash fusion temperature, means forming an outlet common to said furnace chambers for the discharge of molten slag and heating gases carrying slag particles in suspension into said sec.- ondary furnace chamber, said secondary furnace chamber including a lower section having a vertically arranged outer wall opposite said gas and slag outlet and spaced horizontally therefrom a distance not greater than the diameter of said cyclone furnace to vreceive the impact of a major portion of the slag particles in suspension in the discharged heating gases, some of the iluid cooled tubes of each furnace chamber absorbing heat concurrently from the hot gases therein and from the gases flowing through said secondary furnace chamber, and means connecting'V said fluid cooled tubes into said lluid circulation system.

20. A fluid heating unit having a fluid circulation system and comprising upwardly extending wallsv including fluid cooled tubes defining a secondary furnace chamber, a pair of cyclone furnaces each having a furnace chamber of substantially circular cross-section arranged with its major axis substantially horizontal and defined by Walls including intermediate portions of some of the lluid cooled tubes of said secondary furnace chamber walls, said cyclone furnaces being arranged in opposite walls of said secondary furnace chamber and having their furnace chambers in ycoaxial and communicating relationship, means for burning a slag-forming solid fuel in each of said furnace chambers under a mean furnace chamber temperature above the fuel ash fusion temperature, means forming an outlet common to said furnace chambers extending through and arranged tangentially to the circumferential walls of said furnace chambers for the discharge of molten slag and heating gases carrying slag particles in suspension into said secondary furnace chamber, said secondary furnace chamber including a lower section having f `greater than the diameter of said cyclone furnace to receivethe impact of a major portion of the slag particles in suspension in the discharged heating gases, someof vthe uid cooled tubesof each furnace chamber absorbing heat concurrently from the hot gases therein and from the gases owing through said secondary furnace chamber, and means'connecting4 said uid cooled tubes into said uid circulation system.

i12 References Cited in the-file 'of this patent UNITED STATES PATENTS 406,659 Mason July 9, 1889 5 `2,594,312 Kerr et al. Apr. 29, 1952 Seidl May 29, 1956,

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