US2316381A - Furnace with reflex arch - Google Patents

Description

April 13, 1943. "P, WRIGHT 2,316,381

FURNACE WITH REFLEX ARCH Filed Oef. 16, 1939 3 Sheets-Sheet l April 13, 1943. P, wRlGHT 2,315,381

y FURNACE WITH REFLEX ARCH Filed oct. 16, 1959 s sheets-sheet s Patented Apr. 13, 1943 geistig UNITED STATES ATENT OFFICE 2,316,331 FURNACE WITH REFLEX Anon raul Wright, Birmingham, Als. Application October 16, 1939, Serial No. .299,665

(ci. 11o- 72) v 11 Claims.

This invention relates to furnaces, and particularly such boiler and industrial furnaces as utilize the various forms of wood fuels, refuse and other adaptable fuels.

The general object of my inventionis to provide, as a substitute for the customary dutch oven furnace, an improved furnace effecting a reflex movement of the furnace gases over fuel therein moving progressively; a furnace attaining higher furnace temperatures with attendant hastening of fuel burning; a furnace having an improved regulation and proportioning of combustion air through the fuel and over the fuel.

A further object is to provide such furnaces with protection of thel grates and related parts against'heat; to facilitate the removal `of ash and cinder; to provide improvements infurnace enclosures to retain and utilize heat and reducel maintenance costs.

Another object is to provide a furnace that utilizes a reflex arch that is exposed to furnace heat on both sides, whereby intense heat can be reflected below and above said arch within the furnace.

One feature of the invention is the provision for gravitational placement of fuel to transversely cover the grate uniformly and repose in greater thickness upon a lower adjoining hearth in comf bination.

Another feature of the invention is the provision for a steam generator, of a wood refuse burning furnace capable of sustaining high performance ratings, without employing supplementary fuels like oil or gas.

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

Of the drawings:

Fig. l is a longitudinal section illustrating one embodiment of my invention.

Fig. 42 is a transverse vertical section taken at line 2--2 as shown on Fig. 1.

Fig. 3 shows by enlarged view, the gas passages indicated at section 3-3 in Fig. 1.

Fig. 4 is a longitudinal section illustrating a modification embodying the invention.

Fig. 5 is a. transverse vertical section on line 5--5 of Fig. 4.

Fig. 6 is an enlarged view of the uppermost grate rest.

Fig. 7 illustrates the application of the reflex arch and imperforate hearth, to the type of dutch oven furnace shown.

Fig. 8 furnishes an enlarged sectional View of the huid cooled tubes as taken at 8 8 in Fig. 7.

In the furnace embodying my invention illustrated by Figs. 1 and 2, a front wall I closes the portion forward of the grates, and an upward continuation 2 and 3 provides a front wall portion, along which entering fuel is fed into the furnace. Fuelv is delivered thru an opening 4, preferably across the entire furnace width; or there may be a series of openings ll locatedtransversely as shown. One form of roof enclosure comprises a shape bounded by portions 5, 6 and 1 as illustrated in Figs. 1 and 4. A wall 8 on each side extends upward from the foundations 9, on which the structure rests.

As the illustration of Figs. 1 and 2 shows the relation of the furnace to a steam generator, I designate the lowermost water chamber I0, from which water is conveyed thru pipes II, I2 and I3 to a tube header I 4 at the upper front. A plurality of spaced tubes I5 extend from header I4, to a steam and water chamber I6. The assembly of pipes and tubes in combination with the steam generator forms a path of flow of water from chamber I0 to chamber I 6. The spaced tubes I5 may be incased along portions 5 and 6, with blocks and spacers similar to the constructions covered by my patent application Serial 294,568 of 1935 series; or otherwise the space about tubes I5 is closed with refractory between same.

A front row of tubes I I support an upper front baffle I8 thru which spaced openings I9 pass furnace gases between tubes v2i) and 2| beyond, whereby upper stratification of gases is relieved. Baffie I8 constitutes a downward continuation of the furnace roof 6, as defining the uppermost rear closure of the furnace of Fig. l. The primary heating surface lof the steam generator is comprised of tubes I1, 20 and 2l.

The fuel support comprises a lowermost transverse grate support 22 upon which in close contact, is placed rest bar 23 as shown by Fig. 1.`

This construction supports the lower ends of grates 26, and resists the downward thrust caused by the weight of grates and fuel thereon. The masonry structure 3| beneath is an added safeguard to resist deflection of the beam 22. Said masonry structure also functions as a furnace hearth in combination with said grates adjoining same. The hearth slopes as shown or it can be level.

An intermediate transverse grate support 22a with grate rest bar 24, is used to hold up the grate ends that abut. An uppermost transverse grate rest 25 is also illustrated by an enlarged view Fig. 6. which shows how air passage is arranged and provision made for the upper grate ends to slide due to expansion or contraction.

The upper structural front 28 holds wall 2 and 3, supports header I4 slidably and fastens to upper rest bar 25 as shown. Access to grates for advantageously cleaning, while the furnace is in operation, is afforded by openings 29 whereby a steam lance can be used to blow thru the grate openings or, in cases of excessive accumulation of ash or fused matter, a slice bar can readily be used. Upper grates 21 or upper parts of grates 2B generally have a minimum of clinker.

Natural draft air admission to the furnace setting beneath grates, may be thru draft doorways 3S, that also serve for ash removal.

As an extension for supporting the fuel beyond the lowermost ends of grates 26,1 provide a hearth 3| made preferably of refractory having arched passages 32 beneath as shown by Figs. 1 and 2. The number and location of ash doorways 3D is arranged to suit passages 32 for easy ash removal. Forward of passages 32, I provide one or more draft gates 33 that are raised or lowered by chain 3d which passes thru front wall I. Keeping the chains taut will hold the gates 33 from leaning. however gate guides may be used. To effect a complete closure downward from lower grate support 22, I employ a partit-ion 36 that extends transversely and fastens at the lower side to guides 35. Thus with gates 33 raised, air thru the front side may pass thru passages 32 or thru grates above or thru both, depending on conditions of fuel bed effecting resistance to air flow. 'This partition 36 may be sloped to shed ashes from grates 2S to the floor forward of gates 33.

For introducing forced draft beneath grate-.s only, with gates 33 down or closed, I provide a passage 31, preferably thru the side wall 8 and forward of partition 33; however, if gates 33 be raised, this forced draft may also pass thru passages 32. I have found that the height that gates 33 are open, will somewhat tend to proportion the air how between grates and arched passages 32 but not with adequate control. I therefore have embodied in my invention, another source of forced draft thru opening 38 which is rearward of the partition 3B. This arrangement of air inlets thru passages 33, 31 and 38 provides several combinations of air supply beneath the fuel thru grates and over the fuel from passages 32 below, in an improved distribution.

In prior furnace constructions of the general character described and with either flat or inclined fuel supports, the furnace gases ow away from the fuel bed in the most direct route to the furnace chambers exit. Thus in the case of moderately wet bogged wood fuel, the moisture and volatiles gasify and rise toward the furnace roof and pass outward before air thru the fuel bed can reach or mix with same.

Hogged fuel is usually made from wood that is waste such as scraps, trimmings, edgings with bark; and these are chipped, macerated and reduced in size thru a machine called a hog whence the terni. Wood refuse fuel often comprises varied mixtures of hogged fuel with saw dust, shavings, bark waste and the like, which pass by conveyor to a fuel storage.

asiassi Heretofore endeavor has been made to retard the gas ow under such circumstances, with the intended purpose to accomplish most of the combustion in the primary furnace. This retarding has not been practically accomplished especially at forced rates of firing. Furthermore, the late addition of needed air for combustion at a zone beyond the primary chambers exit, does not promote as good combustion as is accomplished by earlier distributing air in the gas distillation zone and under high temperature conditions. And still further, the admission of air thru the roof of the 'furnace and at the fuel entrances has a chilling effect, reducing the roofs useful radiation effect, and air thru the roof is not as desirable as supplying air lower down close to the fuel bed. Various arrangements have been tried or introducing air thru the bridge wall on its forward side and such openings invariably clog or close by slagging. affording only temporary inlets and thus it is difficult to avoid undesirable air variations.

Air passing thru the bridge wall at high velocity towards the fuel, tends to wait light fuel to settle beyond unburned, unless burned in transit. Also admitting air thru the rear of bridge wall results in lanning of gases and insufficient mixing, whereby combustion is not completed.

Noticeably dutch oven furnaces operating at high ratings with refuse materials as fuel, often employ supplementary combustion chambers in which other fuels such as oil, gas or powdered coal are relied on to produce high temperature radiant exposures that will aid in consuming the carry-over of unburned fuel, as previously described.

To facilitate improvements in fuel burning, as compared with the dutch oven operations just described, I have invented a furnace construction embodying a reiiex arch as illustrated in part by Fig. 1, Fig. 4 and Fig. '7. The furnace may also comprise in part, a transverse ash pit 39 spaced beyond the refractory hearth structure 3| and closed on the rear by a transverse bridge wall 4c. Refractory lined doorways 4| in either or both side walls 8 afford access for raking out or for inspection. Adjoining the transverse wall t5 above and inclining over the pit 39 and hearth 3 l. there is extended a reflex fluid cooled arch 62 which spans the furnace between side walls 8. This reex arch 132 inclines somewhat parallel to the grate surface but not necessarily.

In the case of wide furnaces it is optional to provide a furnace partition wall 43 as shown in Figs. 1 and 7. This wall 43 is not illustrated in Fig. 4. The partition wall 3 is arranged across the pit 39 and hearth 3| so as to extend upward to the arch 42 and is usually located midway between the side walls 8. Wall d3 is advantageous to absorb heat, which can be radiated when wet fuel enters the furnace or when the grates 26 are cleaned, with fire retained on hearth 3|. Side access doorways 46 are placed in side walls 8 also just above the top of hearth 3|, there are provided appropriate doorways 45 for slicing clinker off hearth 3| into pit 39 below.

For further facilitating ash or clinlcer removal in combination with raising gates 33, I provide a transverse trench 45 which is covered by removable plates 41 whereby with plates 47 in place, the rakeout is over same thru doors 30 or with plates 41 removed, ash is deposited in trench 155, to be moved away, and thereafter plates 41 are replaced to cover 46.

Referring particularly to Fig. 4, I have shown an approximate upper contour of the fuel when Asingle source without the burning wet hogged southern pine; also from my observations made in practice, I have shown the travel of combustion flames and gases. In like manner in Fig. 1, by means of arrows I show the direction of flow of air and gases thru the furnace and beyond. In Fig. 4, I illustrate the preferred placement of fuel on the grates 26 and hearth 3|, whereby the thicknessof the fuel bed gradually increases to a maximum thickness over the hearth 3| and beneath arch 42. The fuel uniformly can cover the grate transversely of the furnace, which facilitates a controllable passage of air thru the fuel without blowing holes thru the re bed.

It is practical to operate 'the illustrated embodiments of my invention by providing natural draft alone thru doors 3U; natural draft thru doors 30 along with forced draft thru passages 32 from inlet 38 with gates 33 closed or down; forced draft from inlet 3' I and doors 30 closed, thru gates alone with gates 33 closed or thru grates and passages 32 with gates 33 lifted, as desired. Another useful method of air supply is to supply forced draft thru openings 31 and 38 with gates 33 closed, and being supplied from a furnace or from separate individual sources as may be desired. Damper controls on ducts to 31 and 38 from the same source of air supply will separately vary the flow thru gates and over fuel under the reflex arch. Again, separate sources of air supply thru openings 31 and 38 permit variations in air quantity and pressures beneath the fuel and over the fuel. Y

Heretofore grates in many wood burning furnaces have given trouble due to overheating and clinkering; various forms of pusher bars have been tried to advance fuel and move clinker; also disposal of ash and clinker repairs and shut-downs. Further record of such operating difliculties with pusher grates, is the trial usage of these in combination with watercooled tubes; however such means does' not eliminate the causes of depositing slag or cinder on said grates. My invention improves upon these conditions as will be understood from my specification and illustrations of this invention, as pertains to these features.

In the present construction, instead of using dump grates or the equivalent, to dispose of clinker that may-collect at the lower section of the grates, I employ an inclined hearth in combination with a reflex arch above, whereby the heat is so intense as to melt and collect and runoi the clinker as illustrated in Fig. 4 at top of hearth 3 I. Spilled fuel in the rear of pit 39 burns intensely with air thru passage 32 and bridge wall 40 reflects heat against a thick mass of charred fuel in the region or elevation of door 44. Thus ash, sandy matter and the like, settle to the bottom of the fuel on hearth 3 I, lndicatedj clinker gathers on lower ends of grates at 1c. If A 26, it will generally melt and run downward to the hearth; yet while it is soft, it can be sliced from doors 29 if it adheres to the grates. Use of a steam lance at necessary intervalswill remove from the grates such ash, sand and substances that make clinker, before they become sticky 0r viscous. When the furnace is operating at lower than average temperatures, the doors may be used to slice hardened clinker off the hearth and a cleavage betweenthe hearth and clinker is assisted by utilizing the cooling section, employing tube 55 as shown.

` Heretofore in dutch ovens, an inclined step has caused costly grate arranged with a. dump grate at the lower part has been used. and endeavor has been made to control the thickness of fuel bed by a width of throat at the fuel entrance whereby 4the fuel would burn out bythe time it progressed to the dump grate, thus intending to providev a thin re at the bottom enabling ash and clinker to be dumped; but experiences show such dump grates are not satisfactory because the fuel at times avalanches over same and against an adjacent bridge wall and results in clinkering and burning of the lower grates.

This burning is due to intense heat vabove and air passages being partly stopped by slagging on l the dump. Again, step grates have been used without a dump grate 4where the fuel regularly avalanches onto a shelf, to pile up against the adjacent bridge wall and at an elevation below the ends of said grates. Here also a. deficiency of air neededover the fire occurs, as air does not suitably pass thru this piled fuel where ash and cinder accumulate on the said shelf.

An improvement wanted in fuel burning, is accomplished with my new combination of a fuel support having a lower hearth adjoining an ash pit open to the furnace'and a reflex archdirecting the gases of combustion, allin the manner described and as shown by the drawings.

With further referencevto ,the specification of the reflex iiuid cooled arch ,'42, shown by Fig. l, it comprises various blocks supported by single tubes 55 and doubletubes 55 extending across the furnace and resting on s lde walls 8. The tube 'acts as a beam andma preferred material would be seamless steel tubing of a size and strength calculated to resist the weight of fuel and the blocks forming the arch.

As a means of practically constructing my reflex arch in extendedwidths, another preferred form of support comprises two tubes 56 as illustrated in Figs.y 1 and 7.. The double tubes 56 are incas'ed with blocks and spacers as shown and furnish a stronger and vstiffer beam than the same size single tubes 55 shown.

In the wall 40 of Fig. 7 where tubes 55 appear, a means of -Afacilitating the erecting of tubes is shown by Fig'. 8 which isa partial section at 8 8 where tubes 55 pass thru wall 8. A clearance space 64 above each tube 55 in wall 8 is provided and this may be packed with removable mineral'wool for example. Thereby the' tubes are free to slightly move with the inner arch or wall which expands more than the outer part of wall 8which is` exposed to atmosphere.

Thel use of tubes 55 as utilized in the wall bounding refractory hearth 3 I, serves to strengthen the construction v by bridging the upper parts of arches over, passages 32.

From the foregoing descriptiverspecication of the reflex arch construction, it willbe apparent that theinclination of the arch 42 can be suited to the upper contour of. thfe'fuel bed) in a manner to direct combustionair from pit 39 so as to be in intimate contact with the fuel as shown by Fig. 4f The extent of coverage of the'reex arch over the fuel bed is not limited by structural features of Support.

In Fig. 7. I show how this dutch oven furnace was improved by providing the hearth 3|, ash and slag pit 39in combination with' wall 40 and arch 42b. Alsothepartition wall 43a is retained, .the forward lower side of which was, aligned with a bridge wall that was removed.

Heated air and gases from the fuel bed and pit below, pass far enough forward by means of thereflex arch, to aid in heating and gasifying the entering fuel on the upper fuel support.V

Heretofore furnaces have been adapted to retain a thin bed of fuel in an inclined position with a forwardly sloping wall spaced therefrom to for-m a combustion chamber between, said wall extending upwardly to the level of the upper grate; but such constructions fail to provide my improvements utilizing the thick lower fuel bed, spaced close to my reflex arch for intensifying burning. with air admitted over the fuel from low down passages.

The reflex arch favors burning a thick fuel bed at the lower part of the fuel support whereby refuse in larger sized pieces can be burned under its intense reflected heat, yet the lower grates are protectedby the thick fuel as well. Also the thick fuel bed enables carrying a banked fire not practical with a thin fuel bed.

The reflex arch effectually lengthens the gas travel from the lower part of fuel to exit of the furnace, by reason of the longer reflex path of passage, as compared with that in the customary dutch oven employing an approximately vertical bridge wall. The invention provides an improvement in the rate and completeness of burning.

The combination of hearth 3| and arch 42 intensifies burning to the extent that grates 26 can be provided with small perforations or without perforations if desired.

The reflex arch being safely and practically held in position by fluid cooled tubular supports, it can withstand re on both exposed sides whereby the upper side can usefully serve to radiate and reflect to the furnace chamber above and gases traversing it. Practice shows fuel does not remain unburned over this arch.

Concerning the dutch oven roof construction as illustrated by Fig. '7, it has been common to suspend refractory tiles to match a desired furnace roof contoiu'. While such roof tiles are replaceable, the heat radiation loss and the maintenance cost is greater, than that of my fluid cooled roof 5, 6 and 1 of Figs. 1 and 4.

By illustrating preferred shapes of furnace roof enclosures and 8 as in Figs. 1 and 4, I desire to show that an enclosure of this type can be suited to various furnace and reflex arch constructions as related to boilers, in a manner to withstand intense furnace temperatures economically and and accommodate reflex movement of the combustion gases as described.

It is practical and desirable to feed fuel across the furnace width thru entrances 4 as shown by Fig. 1 and Fig. 4 and between the spaced tubes l5.

Before the dutch oven of Fig. 'l was remodeled by adding the hearth 3|, pit 39, wall 40 and arch 42h of this invention, it was customary to provide a thin fuel bed at the bottom of grates 26a, also air entered thru dump grates adjoining the lower ends of grates 26a. A fuel bed thick at its lower part similar to that of Fig. 4, would therefore hinder air passage thru the lower grates 26a if employed in the furnace of Fig. 'I not equipped with the above named hearth, pit, wall and arch. Hence the disadvantage of slagging on dump grates is avoided by improving the furnace like Fig. '7 shows. It usually requires more than an hour daily toclean one set of dump grates of slag, and the time and expense saved by my invention' makes it,u seful to facilitate continuous furnace performance.

In the case of burning light comparatively dry wood shavings, it is possible with excessive forced draft and a thick fuel bed, to waft unburned shavings beyond the reflex arch, therefore I provide a drop combustion chamber B6 as shown in Figs. 1 and 4. The ratio of hearth length to grate length can be advantageously increased when burning shavings; and in such case the hearth can be approximately level, since dry shavings make less ash than hogged fuel" which may contain sand. The fuel on the floor at 66 will burn-readily upon admitting air thru doorway 6l, provided the chamber is hot enough to promote combustion. If the chamber is only moderately hot, an improved means for rapidly burning the fuel, only to clear the floor, is had by employing a steam jet thru openings 68 as shown in Fig. 1, and air is admitted thru openings 68 thereby.

In the present construction shown by Figs. l and 4, I employ a bafe 69 that is supported by tubes 20 and 2l, as a means to direct the furnace gases rearward over the reflex arch and thence over the steam generators primary heating surface. A special feature that eliminates a gas pocket in the uppermost furnace chamber adjacent said steam generator at the top of baffle 69, provides for gas passages I9 as shown by Figs. 1 and 3. Similar passages in Fig. 4, are designated at These openings i9 and l9a, serve to shunt upward portions of the combustion gases, which causes floating unburned fuel to rise in a flurry that increases its time in transit and improves burning of same. In Fig. 1, the perforate baille I8 corresponds to a downward extension of the roof 6, to adjoin bale 69, with the openings I9 occurring just above the baille 69.

I have previously stated that my invention utilizes other adaptable fuels. For example, as an overfeed method of firing coal, the novel imperforate hearth functions to reduce slagging of the grates. Furthermore, coalsV that have low temperature fusion of ash properties. will burn in improved manner, since the ash can melt on the hearth and pass to the slag pit.

While in accordance with the provisions of the statutes I have illustrated and described herein the best forms 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 my invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

l. In combination with a furnace: side walls, a front wall and a furnace roof, extending between the side walls, and a fuel entrance into said furnace; within the furnace, a transverse imperforate hearth spaced inwardly from said front wall, a transverse fuel support comprised of inclined grates that upwardly adjoin said front wall and downwardly adjoin said imperforate hearth; a lower ash pit inwardly of and adjacent said hearth, said hearth sloping to and terminated by said transverse lower ash pit; a door in the side wall at said pit; a heat reflecting bridge wall adjacent to the hearth but spaced apart by said pit therebetween; a heat reflecting arch joined to said bridge wall and extending over, and spaced apart from, said pit and hearth; said arch being imperforate and extending upwardly toward said roof but spaced apart therefrom, to provide a furnace passage therebetween; the combination being capable of effect- 42. The construction ing the reduction of cumulating the slag on said hearth, from whence it can pass to said pit.

of claim 1, in combination with a door in the side wall and said door situated to enable the operator to slice slag voff said hearth into said pit.

3. In a furnace, fuel burning apparatus-coinprising, a furnace front wall, furnace side walls and inclined perforate said front wall transversely between the side walls; a furnace imperforate roof extending between the side Walls and to said front wall, and a fuel entrance into said. furnace; a level imperforate hearth adjoining the lower transverse edge of said grates; an ash pit arranged at the rearward transverse edge of said hearth and a door in the side wall to said pit; a bridge wall across the furnace and so arranged that said bridge wall and hearth form opposite sides of said pit; a reflex imperforate arch that adjoins said bridge wall and thence extends relatively close to said hearth and grates; said arch extending upwardly toward said roof but spaced apart therefrom, to provide a furnace passage therebetween; an air supply chamber that is partially bounded by the furnace front wall, and said side walls, and by said grates above the chamber; said front wall having air entrance doors therein; means forming passages under said hearth to connect said air chamber to said pit; doors arranged in the front wall of said air chamber, whereby an operator can clean said grates by ejecting residue on to said hearth whence the residue can be passed to said pit.

. 4. In combination with a furnace for burning solid fuel: side walls, a front wall and a furnace roof extending between the side walls, and a fuel entrance into said furnace; within the'furnace, an inclined imperforate hearth, an ash pitlextending transversely of the hearth, a transverse fuel support comprised of an inclined grate surface that upwardly extends to said front wall and downwardly adjoins said imperforate hearth the pitch of said hearth of repose of the fuel to be burned, and less than that of the inclined grate; said hearth sloping 'to and terminated by said ash pit; a heat reflecting bridge wall adjacent to the apart by said pit therebetween; a heat reflecting arch joined to said bridge wall and said arch extended over, and spaced apart from, said pit and hearth; said arch being imperforate and arranged to provide a fuel burning passage between said fuel support and said arch, whereby fuel in large pieces will repose on the fuel support without substantially spilling into said pit, facilitating the burning of said fuel which is subjected to intense reected heat.

5. In combination with a furnace for burning solid fuel: side walls,-a front wall and a furnace roof, extending between the side walls, and a fuel entrance into said furnace; within the furnace an inclined imperforate hearth, an ash pit extending transversely of the hearth, a transverse fuel support comprised of inclined grates that upwardly adjoin said front wall and downwardly adjoln said imperforate hearth the pitch of said hearth being less than the angle of repose of the fuel to be burned, and less than that of the inclined grates; cleanout doors arranged in the side walls, above said grates; said hearth extending to and terminated by said ash pit; a door in each side wall at said pit; a heat reflecting bridge wall slag on said grates by acgrates that extend freni being less than the angle hearth but spaced adjacent to the hearth but spaced apart by said 4 roof but spaced 5 pitvtherebetween; a heat reflecting arch joined to said bridge wall and extending over, and spaced apart from, said pit and hearth; said arch being imperforate and extending upwardly toward said apart therefrom, to provide a furnace passage therebetween; a partition wail arranged under said arch and across said pit and hearth; the combination enabling burning fuel to be held on said hearth, with said grates bare of fuel,thereby permitting said grates to be cleaned while re is retained in said furnace and heat is maintained in said partition wall to aid combustion.

6. In a furnace, for burning solid fuel, a slagging hearth-inclined grates for supporting fuel and said grates adjoining and extending upwardly from said hearth; an ash and slag pit arranged along the lowermost transverse edge of said hearth; an air chamber arranged beneath and partitioned apart from said grates, means forming passages arranged to connect said air chamber to said pit, which passages extend under a fuel entrance into'said furnace; an imperforate lower transverse edge of a front furnace and as one source of air supply, a grate air chamber arranged under said grates and partially bounded by, said front wall and said side walls. and a gated partition that adjoins the lower transverse edge of said grates at said hearth; access doors in said front wall whereby air enters forward of said partition into said grate chamber; and as another source of air supply, a pit air chamber arranged below said hearth and connected with combination air and ash passages extended under said hearth to said pit; a door in said side wall whereby air enters said pit chamber, rearward of said partition; whereby the combinations of air thus supplied, facilitate the hastening of fuel burning with higher temperatures in the furnace; and said passages advantageously permit removal of ash, thru said gated partition and said front wall access doors.

9. In a furnace utilizing hogged wood as fuel: a front furnace wall, furnace side walls and inclined perforate grates that extend from said iront wall transversely between the side walls; a furnace imperforate roof extending between the side walls and to said front wall, and a fuel entrance into said furnace; a lower imperforate hearth adjoining the lower transverse edge of said grates; an ash pit arranged at the rearward transverse edge of said hearth; a bridge wall across the furnace and so arranged that said bridge wall and hearth form opposite sides of said pit; a reflex imperforate arch that adjoins said bridge wall and thence extends relatively close over said hearth and grates; said arch extending upwardly toward said roof but spaced apart therefrom, to provide a furnace passage therebetween; said hearth having an inclination less than the angle of repose of the fuel and less than that of the grates, so that fuel will repose on the hearth in greater thickness than on said grates and without substantially spilling into said pit; an air chamber that is partially bounded by the furnace front wall and side walls, also by said grates above the chamber; also said chamber bounded further by a gated partition that zones air between said grates and passages that are arranged to connect said air chamber to. said pit, and said passages arranged under said hearth; a door in the side wall for air entering said passagesl as partitioned from said air chamber: whereby air passes to the furnace thus; with the gates of said partition open, air passes from said chamber thru said grates also thru said passages to said pit; furthermore with theV gates of said partition closed, air passes from said chamber thru said grates, and separately air entering thru said door in the side wall as partitioned off, passes via said passages to said ash pit, thereby enabling improved regulation and proportioning of combustion air thru the fuel and over the fuel.

10. In a furnace burning hogged wood as fuel, fuel burning apparatus comprising, a. furnace front wall furnace side walls and inclined step grates that extend from said front wall transversely between the side walls; a furnace imperforate roof extending between the side walls and to said front wall with a fuel entrance into said furnace; a lower imperforate hearth adjoining the lower transverse edge of said grates; an ash pit arranged at the rearward transverse edge of said hearth and a door in the side wall to said pit; a bridge wall across the furnace and so arranged that said bridge wall and hearth form oppositer sides of said pit; a reflex imperforate arch that adjoins said bridge wall and thence extends relatively close over said hearth and grates; said arch extending upwardly toward said roof but spaced apart therefrom, to provide a furnace passage therebetween; an air supply chamber that is partially bounded by the furnace front wall and side walls, also by said grates above the chamber; access doors in said Vfurnace walls whereby air enters said chamber;

passages with gateways, arranged to connect said air chamber to said pit by extending said passages under said hearth; said hearth having an inclination less than the angle or repose of the fuel and less than that of the grates, so4 that bogged fuel will pass over the grates to pile on the hearth without substantially spilling into said pit also the fuel will repose thicker over said hearth than over the upper area of said grates, thereby providing protection of said grates against furnace heat and air of combustion passed beneath said arch in the furnace.

11. A furnace with reflex arch, having in combination: side walls, a front wall and a furnace roof extending between the side walls and a fuel entrance into said furnace: within the furnace, a transverse imperforate hearth spaced inwardly from saidv front wall, a transverse fuel support comprised of inclined grates that upwardly adjoin said front wall and downwardly adjoin said hearth; a lower ash pit inwardly of and adjacent said hearth, said hearth sloping to and terminated by said ash pit; a heat reflecting bridge wall adjacent to the hearth but spaced apart by said pit therebetween; a reflex arch joined to said bridge wall and extending over, and spaced apart from, said pit and hearth; said arch being imperforatef and extending upwardly toward said roof but spaced apart therefrom to provide a reflex` passage of the combustion gases therebetween; and said furnaceV extended rearward over said reflex arch so as to provide a drop combustion chamber rearward of said bridge wall, whereby unburned fuel carried over said arch will burn within the drop combustion chamber.

PAUL WRIGHT.

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