US2010985A - Furnace - Google Patents

Description

H. P} FORD Aug. 13, 1935.

FURNACE Filed April 24, 1950 5 Sheets-Sheet l.

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INVENTOR fi ra/a/ P fZraf TTORNEY Aug. 13, 1935.

H. P FORD F-URNACE Filed April 24, 1950 5 Sheets-Sheet 2 Nun."

if! TTORNEY Aug. 13, 1935. R FORD 2,010,985

FURNACE Filed April 24, 1930 5 Sheets-Sheet 3 INVENTOR Harv/a I- O/"d ATTORN EY H. P. FORD Aug. 13, 1935.

FURNACE Filed April 24, 1930 5 Sheets-Sheet 4 INVENTOR BY Ham/d P Fara.

A TORNEY H. P. FORD 2,010,985

FURNACE Filed April 24, 1930 5 Sheets-Sheet 5 Aug. 13, 1935 Q E 5?? 08 Go 8o 00 o C 00000 000 oo womvo 0000 000 000000 00000000 000000 0000000 000000 00000000 0000 00 0000 000000 0000 0000000 000000 oooooooo oooooo oo 00 000 00 0000 00000000 000000 0000 000 000000 00000000 000000 000000 00 0000 f I i N\\ \&

INVENTOR BY Ham/0 Pfara ATTORNEY Patented Aug. 13, 1935' UNITED i S TAT ES FURNACE 7 Harold P. Ford, Seattle, Wash. 7 Application April 24. 1930', Serial-No. 447,024

8 Claims.

My invention relates to furnaces and the general object of my invention is to provide a furnace of improved construction which will pro duce a more complete and'efficient combustion of the fuel and which will utilize a maximum amount of the heat derived from the fuel combustion.

In furnaces of the type now in common use it is common practice to allow the gases produced by combustion of the fuel to escape up the chimney in a partially burned and a relatively hot condition. This is undesirable and results in low efficiency, because the availableheat in the gases has not all been liberated by complete combustion, and because the heat which has been liberated has not, all been used, and because the partly burned gases carry with them much soot and smoke which tend to foul the passageways in. the furnace and chimney and which are a nuisance and a source of dirt when released in the atmosphere. Other objections to the usual types of furnace are that large volumes of cold air are often drawn through the open furnace door or through cold spots of the fuel bed into the furnace and brought into contact with and chilling the heat absorbing devices, and that the heat absorbing or pick up devices are often placed within the hottest, portion of the combustion chamber, thus tending to re.- duce the temperature within the combustion chamber to too low a degree for'completecombustion.

My invention overcomes the objectionable features hereinbefore set forth by providing for a re-circulation of thefuel gases through the fuel bed and combustion chamber and past heat absorbing means'until substantially all of the combustible matter is burned andsubstantially all of the heat is absorbed out of these gases before they are allowed to discharge through the chimney. To accomplish this, I use? what I term a recirculation principle in which the gases resulting from combustion are re-circulated through the fire box and combustion chamber until substantially all of the volatile matters are burned or oxidized.- In carrying out this re-circulation principle, I provide a refractory fire box in which a very hot bed of coals either large or small may be maintained and provide a refractory combustion chamber in direct connection with this fire box which is maintained at a high temperature and which is not cooled by the presence therein, or close proximity of heat take off means. The fire box and combustion chamber, together with th space im d at y b low the fire box constitute what I term the hot leg of a recirculation system in which the gases rise or flow upwardly and in which said gases and preheated air are brought into intimate contact with the fuel and are retained in highly heated chambers long enough to effect substantially perfect combustion. The heat pick up means constitutes the coldleg of this re-circulation system and is arranged to receive the highly heated gases after they leave the combustion chamber and extract the heat from said gases; The general direction of flow of the gases in the hot leg of the circuit is upward and their velocity will varywith the temperature and may be influenced by introduction of fresh air under pressure. The general direction of flowof the gases in the cold leg of the circuit is down to a point below" the fire box and thence up again'through the hot leg of the circuit. A portion of these gases is allowedto pass off constantly into a vent which leads to a chimney, the location v liere these gases are taken off being the lowest part of the circuit or the location at which the gases pass from the cold leg into the hot leg of said circuit. Fresh air, preferably preheated, may be admitted at various parts of the. recirculation circuit but is preferably introduced from a blast chamber or admission, chamber through the zone where initial and hottest burning of the fuel takes place, and thence mixing with'the recirculation gases. A forced air admission may be used but such is not essential to the operation of the furnace as the gravity circulation in the hot and cold legs of the furnace is ample to overcome all internal friction and the resistance of the fire bed, and the external chimney need only serve as a vent stack to elevate the waste gases to a point of discharge. The closed circuit through which the gases travel brings said gases into effective. contact with the lowest as well as the highest portion of the heat pick up means. When the fire box is chilled as by leaving open the fire box door, the gravity circulation is retarded or stopped, thus preventing said heat pick up means from being subjected to cold blasts or drafts of air. Checking of the draft does not hinder the flow of 're-circulation gases in the closed circuit but may reduce the amount of gas discharged through the chimney. The high state of combustion of the fuel tends to prevent fouling of the surfaces with which the burned gases come into contact andthe downward movement of the gases in the cold leg of I the circuit tends to cause any small particles of ash or solid matter insaid gases to be deposited in the ash pit. Fire hazard is greatly reduced by having the gases comparatively cool before they discharge into the chimney.

More specific objects of my invention are to provide a furnace of neat and attractive appearance, which is compact in construction, low in first cost and upkeep and occupies a relatively small floor space; to provide a furnace which will not be liable to be damaged by overheating or unequal expansionstrains; to provide a force feed furnace having an improved form of grate which will burn low grade, cheap and fine coal efficiently, which will not drop the fine coal and which will keep the bed of burning coal broken up and evenly distributed over the grate at all times thus preventing the formation in the bed of coal of dead spots and air channels through which large volumes of air can pass without coming into intimate contact with the coal. Another specific object is to provide a furnace in which the re-circulation air is caused to pass through the ash pit whereby it may pick up the heat of the discharging ashes.

In certain types of furnaces now in use, fans, injectors and other mechanical means have been used to re-circulate a portion of the chimney gases through the fire bed or fire zone for the purpose of a more complete combustion of the products from the fuel. This necessitates a more expensive and complicated installation.

As ordinarily employed, this return or recirculation of the gases by means other than by gravity is not well suited to the varying conditions of temperature and combustion within the furnace or fire zone, and does not permit satis factory operation and control.

The gravity re-circulation principle returns the gases in a quantity in proportion to the temperature within the fire zone. In other words, with high firebox temperatures, a greater portion of return is automatically produced, and with low firing rate and low temperature in the fire box, a smaller portion of return gases is produced, which is satisfactory for practical operation of the furnace. If fan or other mechanical means, as differentiated from gravity, be employed to return or re-circulate a portion of the chimney gases, this desired ratio is not maintained.

The above mentioned general objects of my invention, together with others inherent in the same, are attained by the device illustrated in the following drawings, the same being preferred exemplary forms of embodiment of my invention, throughout which drawings like reference numerals indicate like parts:

Figure 1 is a vertical sectional view substantially on a broken line I--l of Fig. 2 of a domestic hot air furnace constructed in accordance with my invention;

Fig. 2 is a vertical section of the same substantially on broken line Z-2 of Fig. 1;

Fig. 3 is a cross section substantially on broken line 3-3 of Fig. 1;

Fig. 4 is a vertical mid-section on a broken line 44 of Fig. 5 of a hot water furnace constructed in accordance with my invention;

Fig. 5 is a cross section substantially on broken line 5-5 of Fig. 4;

constructed in accordance with my invention,

said furnace being substantially identical with the hot water furnace shown in Figs. 4 to 7 except that a steam drum is provided in connection therewith;

Fig. 9 is a front elevation of said steam furnace;

Fig. 10 is a side elevation of said steam furnace;

Fig. 11 is a fragmentary sectional view on a larger scale illustrating wall and door construction embodied in my furnace;

Fig. 12 is a fragmentary-plan view on a larger scale of a portion of the grate or tuyere used in the bottom of my fire box;

Fig. 13 is a fragmentary sectional view substantially on broken line l3-l3 of Fig. 12;

Fig. 14 is a detached view partly in elevation and partly in section of one form of automatic fuel feed device which may be used in connection with my invention;

Fig. 15 is a View partly in end elevation and partly in section substantially on broken line [5-45 of Fig. 14 of said automatic fuel feed device;

Fig. 16 is a vertical sectional view showing my invention embodied in a relatively large steam boiler;

Fig. 17 is a fragmentary sectional view substantially on broken line l'l--ll of Fig. 16; and

Figs. 18 and 19 are fragmentary cross sectional views substantially on brokenlines l8-l8 and l9i9 of Fig. 16. 7

Referring first to the hot air furnace, as disclosed in Figs. 1 to- 3 inclusive, I show a furnace of a type suitable for domestic use embodying an outer metal housing 2 having a convergent top end 3 arranged to be connected with a plurality of heat distribution pipes i which may extend to the rooms or other areas to be heated. The cold air is admitted through an opening 4 to a compartment 5 in the lower rear portion of the furnace and flows upwardly as indicated by arrows A, in a manner hereinafter described.

The side of the furnace shown at the left in Fig. l and hereinafter termed the front side, is provided with an upper removable wall section B and with a fire pot door 1 and with an ash pit door 8. The wall section 6 is preferably in the nature of a slab of refractory material cast into a metal casing 9 which extends over the outer surface and over the edges thereof, said edges preferably being inclined, as shown, to prevent displacement of the refractory slab. The door 1, which is more clearly shown in Fig. 11, is a slab of refractory material cast in a similar manner in a metal casing and said door is secured as by bolts ID to a metal door plate H which is connected by hinges l2 to a wall i3. The bolts 56 extend through enlarged holes M in the door plate H whereby the position of the door slab l on the plate H may always be adjusted to fit snugly within the door opening, the nuts on said bolts being on the outside where they are readily accessible for the purpose of adjustment and serv- 'ing to clamp the door slab firmly to the door plate in any desired position. All of the doors and wall sections in all forms of my invention herein disclosed are preferably of substantially the same 'form of construction. The refractory slabs are preferably secured to the metal casings within which they are placed by anchor bolts !5 having conical heads 56 seated within the metal plates and having large flat nuts H which are embedded within the refractory slabs all as more clearly is shown in Fig. 11. All sections forming the outer .wallsof the furnace are preferably flanged outfire box and the grate being positioned toward form the ends of the fire box. From the abovedethe front. The grate l9 may be formed of overlapping spaced apart angle bars extending crosswise of the fire boo: and stepped or inclined downwardly from rear toward the front. A dump plate 2| is provided at the front edge of the fire box to catch the ashes which pass over the grate l9. This dump gate is preferably connected with a weight or spring, not shown, and is arranged'to dump automatically when sufficient weight of ashes has accumulated thereon. It may also be dumped by hand. The blast box, which is shown on a larger scale in Figs. 12 and 13, may be of varied size and shape, and is capable of preheating the air which passes through it and of keeping the fuel broken up enough to allow the air to pass freely through said fuel. A preferred form of blast box, as shown in the drawings may be constructed with an air tight bottom wall 22,

7 an upwardly inclined front portion 23 and a rear portion 24 which extends upright for a short distance and is thence inclined forwardly" for a short distance sothat the incoming fuel may first pass over this inclined portion and then over a plurality of tuyere members 25. The tuyres 25 may be transversely disposed overlapped, spaced apart, angle bars with their openings di rected forwardly as shown, or'said tuyeres may be of a different form of construction so long as their openings are turned away from the direction of movement of the fuel whereby they will not be liable to become clogged by the fuel. Air is admitted to the blast box through a plurality of nozzles 5! which are connected with an air inlet pipe 52. Either a gravity or forced circulation of air may be used. This air is preheated in the blast box before iii-discharges from the tuyeres. The front portion 23 of the blast box terminates at a substantial distance above the grate I3 and forms a lip so that there will be a cascading or falling of the fuel where it passesonto the grate. In addition to this, spurs 28 may extend above the edge of the lip portion 23 to break up the partly burned fuel at this location and permit the air to pass freely through thefuel and come into intimate contact with said fuel at this point. The more intense burning of the fuel is done as it passes over the blast box and the final and less intense burning is done as the fuel passes over the grates IS. The angle or pitch of the grates l9 from rear to front, may be varied to suit different requirements and different kinds of fuel. The spacing of the grate bars and of the tuyre members may be varied to suit different requirements.

The rear side of the fire box may be formed by a slab 21 of refractory material and the top rear wall of said fire box above the blast box, is formed by another slab 28 of refractory material which is. inclined upwardly from rear to front, as shown Two refractory end slabs 29 scription it will be seen. that the fire box. is substantially triangular in cross section and is lined throughout the greater portion of its area'with refractory material which helps to maintain a high temperature within said fire box.

Fuel is supplied to the rear of the fire box througha feed tube 3| having a. feed screw 3i therein. 3 i An upright combustion chamber 32 preferably formed of a refractory member 33 of rectangular cross-section is provided directly above the front'endofthe'fire boxand adjacent to the front. wall 6 of the furnace. This refractory member 33 may be of one piece construction as shown, or it maybe of multiple piece construction. The purpose of this combustion chamber is to provide additional space through which the gases from the fire box may flow while a high temperature is maintained and i where a more complete combustion of'the gases may be obtained, additional time for this'combustion being afforded in this highly heated refractory com bustion chamber. This combustion chamber together with the fire box and ash pit provide what I term an internal chimney or the hotter leg of a re-circulationsystem for the gases.

At the top end of the combustion chamber 32, I provide a curved deflector plate 33' for directing the hot gasesrearwardly to the heat absorbing means. Thisheat absorbing means in the hot air furnace, is preferably in the nature of spaced apart plates 34 of heat transmitting metal, as thin steel, connected at their edges by similar strips of metal 35 'sothat they present a deeply corrugated appearance, when seen in cross section, as in Fig. 3,and so that they form one series orgroup of spaces 36 through which the heated gases may pass downwardly and another series of spaces 31 through which the air that is being heated may pass upwardly. This gives a very large heat transmitting area where the ases may give up their heat and the air may pick up this heat. The plates 34 may be upright or substantially upright and substantially parallel, and are preferably smooth on the side where they pick up the heat and roughened on the side where they give up the heat to increase their heat transmitting capacity.

The air transmission spaces 31 are open at their rear edges and communicated with a space 38 within the furnace housing 2 and the front edges of said spaces 31 are closed by the walls 35, which are spaced far enough from the wall of the combustion chamber 32 to afford room for a coil 39 of hot water tubes, and which are inclined rearwardly toward the bottom and above the inclined refractory fire box wall 28 to afford room for a soot blower tube 40 through which a blast of sand and air may be discharged into the heated gas passageways 35 to keep the plates 34 free from carbon and soot and thus prevent reduction of their heat transmitting capacity. The soot blower tube 4!) is mounted so that it may be rotated .from the exterior of the furnace through part of one revolution to clean all parts of the plates 34. The sand discharged from the soot blower discharges into the ash pit.

After passing down through the heat pick up passageways 38, the gases descend through a passageway 4| into a chamber 42 in the ash pit 43. In its travel through the passageway 4| the still warm gases come in contact with the fuel inlet tube 30 and preheat the fuel before it enters the fire box. In the chamber 42 a portion of the ases passes through a slot 44 into a smoke pipe 45 and discharge and the remainder of said gases passes upwardly once more through the grate I 9 and the fuel bed and mix with the freshly introduced air and re-circulate in themanner heretofore described."

The ash pit 43 is preferably depressed below the fioor on which the furnace rests to afford suflicient depth for the reception of a relatively large ash can 46 which may be removed through the door 8 and through thespace afforded by the removal of a horizontal door 8' thus making possible the removal of the ashes without shoveling. A hopper 53 is provided for the reception of an adequate supply of fuel.

The air which is to be heated is admitted through the opening l into the compartment 5. Thence it may pass over a humidifying device in the nature of a plurality of shallow overflow pans 4'! having water therein. Said air then passes upwardly through a passageway 48 and through the heat pick up spaces 31 and is conveyed by the pipes l to the rooms or area to be heated. Water for the humidifier pans 41 may be admitted through a pipe 49 and receptacle 49' and any excess or overflow water may discharge into a receptacle 5B which is provided with a suitable outlet. The fuel inlet tube 30, where it extends through the fresh air passageway 48, is preferably enclosed within a jacket 38 to preclude any possibility of contamination of the fresh air by smoke and gases, and, for the same reason, all parts separating the gas and combustion chambers from the air passageways are of gas tight construction. Suitable check drafts and dampers are necessarily provided in the smoke pipe 45 outside of the furnace.

In the operation of this furnace a large propor tion of the combustion gases is constantly recirculated and a small amount of these gases is taken off constantly through thesmoke pipe $5. This re-circulation of the combustion gases under the conditions described, insures a maximum eificiency in combustion of the fuel and prevents an obnoxious discharge of soot and heavy smokeinto the atmosphere.' The ash pit chamber 42 together with the fire box i8 and the combustion chamber 32 constitute the hot leg or ascending internal chimney and the spaces 36 and passageway constitute the cold leg or descending section of my re-circulation system.

The hot water furnace shown in Figs. 4 to '7 in clusive is the same as the previously described hot air furnace so far as the ash pit, grates and blast box, fuel feed, fire box and combustion chamber are concerned and the same reference numerals and descriptive matter are applied to these parts. This hot water furnace differs from the hot air furnace essentially in the fact that hot water tubes 5% are provided in the heat pick up space at the rear of the combustion chamber and are connected with an upper header or receptacle 55 and a lower header 56. The circulation of the heated gases in this type of furnace will be the sameas previously described in connection with the hot air furnace. The gravity circulation. of the water will be into the lower header 56 through a conduit 56 thence through the pipes 54 in the direction indicated by the arrows to the upper header 55, thence out to any suitable device to which the hot water is to be delivered through outlet conduit 55. In this form of construction the soot blower pipe 40' is located at the common center of the pipes and is arranged to deliver sand and air for keeping said pipes clean. The headers 55 and 56 are preferably insulated by refractory material as at- 5'! to help conserve heat and extra slabs of insulating material are provided at the sides of the heat pick up chamber, as indicated at 58in Figs. 5 and 6, and at the top of said heat pick up chamber as indicated at 59 in Fig.4; A block 60 of'refractory material replaces the plate 33 shown in Fig. l.

The operation of this form of the invention is the same as the operation of the form shown in Fig. 1 except that water instead of air is heated 1 by the hot gases from the combustion chamber.

In Figs. 8, 9 and 10, I show a steam drum 6| mounted above the furnace and connected by pipes 62 with the return conduits 56' and by pipes 63 with the outlet conduits 55. When the steam drum is thus provided steam will collect in said drum BI and the'device may be used in a steam heating system.

Figs. 8, 9 and 10 also show a forced circulation means for supplying air to the soot blower pipe 40 or ll) and to'the pipe 52 which furnishes air to the blast box, said air being supplied through pipes 64 and 65 which are connected with a fan or blower 66. A split damper til is provided at the junction of the pipes (i l and 65 for selectively directing any desired proportion of the air which is delivered by the fan into either one of said pipes; The pipe 65 also has an opening to the. atmosphere which is arranged to be regulated by a damper Bl whereby when said damper iii is opened a gravity circulation may be maintained through the blast box pipe 52 in the event the blower 66 is not operating. When a force draft is to be used continuously the blower 56 will ordinarily be driven by a motor, not shown, but when no continuous source of power is available said blower may be operated by hand to start, or speed up the fire or to deliver a blast to the soot blower, and the operation of the draft portion of the furnace may otherwise be by gravity. It will be understood that this draft and blower system may be used on the hot air furnace shown in Figs. 1 to 3.

In Figs. 14 and 15, I have shown, in detail, one form of hydraulic motor which may be used to operate the fuel feed of my furnace, it being understood that any other desired form of power actuated mechanism may be used for this purpose. When this device is thus utilized I provide a ratchet wheel 88 on the shaft 3| of the worm 3!, see Fig. 4, and'preferably provide two pawls 69 and 10 for rotating said ratchet wheel in the direction indicated by the arrow in Fig. 14. These pawls are totally independent of each other in their operation, one of said pawls 69 being pivotally mounted on a hand lever H which may be reciprocated by hand for speeding up the delivery of the fuelinto the fire box and the other pawl '75 being-pivotally mounted on a power lever 12 which is connected by a slot and pin connection 13- with-a piston rod M. A hydraulic piston 15 on one end of the rod '58 is reciprocably disposed within a-cylinder 1B; A compression spring "H is provided on the other end of the rod kl between a cross pin and washer l8 on the rod and a rigid frame bracket '19. The cylinder l5 and frame bracket iii are both rigidly mounted on the same frame piece 88, the arrangement being such as to allow the piston to move the rod l to the left from the position shown in Fig. 14 and the spring to return said rod by moving it to the right when fiuid pressure behind the piston is released. Water under pressure for moving the piston 15 is admitted to the end of cylinder it through a pipe 8| having a three way valve 82 therein. When the valve member is in the position shown in Fig. 14 water under pressure is free to enter through a supply pipe 81' but when the valve member is moved clockwise througha substantial angle, as bymoving the lower end of a crank arm 533, which is connected with said valve, from point E to point F, then the port of the supply pipe 8lf will be closed and pipe 81 will be connected with a discharge or exhaust pipe -84. The lower end of the crank arm 83 is pivotally-connected by a link 85 with one end ofa reciprocable member 8S5 which is slidably mounted in brackets 87 and adapted to be moved by a flat spring 88 which is secured to the lever 12. A stud bolt 89 issecured to the frame piece 8-0 in the path of movement of the end of the spring 88 and is preferably adjustable in a direction crosswise of the frame piece 80 to vary the distance which the arm 12 will have to move past center in order to snap over the stud bolt 89, strike the member, 86 and throw the valve. Fig. 14 shows the several parts in the position they would occupythe instant after the spring 88 had snapped over the stud pin 35 and opened the valve 82 .to intake as the lever 72 moved toward the right. As soon as this opening movemen-t of the valve occurs the water pressure begins to move: the piston 75 to the leftcarrying with it the lever J 2 and rotating the ratchet wheel clockwise. When the lever arm 12 is substantially vertical the end of the spring 88 strikes against the stud pin 8-9 but the arm 12 continues to move on to the left until the spring 88 has flexed enough to slip over the top of. the stud pin, strike the member 86 and move said member to the left thus closing the valve '82 to intake and opening the same to exhaust, whereupon the spring I7 begins to move the piston 15, and parts connected there with back toward the position shown in Fig. 14. By adjusting the position of the stud pin 89 vertically, the length of stroke may be increased or decreased and by governing the rate of flow through either or all of the pipes 81, 81', 82, the speed of movement of the piston '15 and connected parts may be varied. The levers H and 72 may be forked or may be in duplicate on both sides of the ratchet wheel 53 as shown in Fig. 15. The application of the hydraulic feed means shown in Figs. 14 and 15 is indicated diagrammatically in Fig. 9. This hydraulic means forms a relatively cheap, simple efficient and reliable device for operating the automatic fuel feed but it will be understood that other power operated means may be used for this purpose.

In Figs. 16, 1'7, 18 and 19, I have shown my invention as embodied in a relatively large steam boiler or heating plant. In this installation I provide a furnace housing 90 of refractory material which may be divided by partitions 90 to form a plurality of separate fire boxes SI and combustion chambers 92. The grates l8 and blast boxes 20 in each of these compartments are similar to the corresponding parts hereinbefore described both in construction and mode of operation. A power operated traveling ash discharge conveyor 93 may replace the ash can 46 thus automatically taking care of the ashes and reducing the necessity for a large ash pit. The heat pick up devices are located in the same relative position as previously described and comprise a multiplicity of upright or slightly inclined water tubes 96 connected at their upper end with a steam drum 95 and at their lower end with. a water drum 96 and a mud drum Scot blower nozzles Ml are provided for keeping the water tubes clean and feed screws 3| are provided for delivering fuel into the rear end of each fire box. Fresh air, preferably from a blower, not shown, enters through a common chamber 98, thence passes through pipes 99 and 99 to the blast boxes 20'. The pipes 99 extend through the exhaust vent Hill which may be connected with a chimney not shown, and the pipes 99 extend through the passageway by which the re-circulation gases return to the chamber below the grate. In this way the fresh air is preheated before it reaches the blast box. The re-circulation gases are split by a damper HH and any desired proportion of. said gases are allowed to passoutwardly through the vent I00. The operation of the furnace shown in Figs. 17 to 20 is substantially the same as the operation of the previously described furnaces, in so far as the principle .of re-circulation of the gases and combustion of the fuel is concerned.

By employing this principle of re-circulation of the gases and of maintaining a high temperature in the fire box and combustion chamber, I am able to produce a furnace in which the combustion of the fuel is substantially complete and the heating efficiency is greatly increased, and undesirable smoke and soot are substantially done away with.

Obviously, changes may be made in the form, dimensions and arrangement of the parts of my invention, without departing from the principle thereof, the above setting forth only a preferred form of embodiment.

I claim:

1. A furnace embodying a fire box; an ash pit chamber below said fire box; a combustion chamber-communicating with the upper portion of said fire box; a heat pick up chamber communicating withthe upper portion of said combustion chamber and with said ash pit chamber andcooperating with said fire box and said combustion chamber and said ash pit chamber to .form a closed circuit for the re-circulation of heated gases resulting from combustion; walls of heat insulating refractory material separating said heat pick up chamber from said fire box and said combustion chamber whereby coolingof the gases in said fire box and said combustion chamber is prevented; means for admitting fresh air at the lower portion of said fire box and means within said ash pit chamber for withdrawing a portion of said re-circulated gases.

2. A furnace embodying a fire box; a combustion chamber communicating with the upper portion of said fire box; an ash pit chamber below said fire box; a heat pick up chamber at one side of said combustion chamber, said heat pick up chamber communicating with said ash pit chamber and with the upper end of said combustion chamber and cooperating with said combustion chamber and said fire box and said ash pit chamher to form a closed circuit for the re-circulation of gases, walls of heat insulating refractory material separating said heat pick up chamber from said fire box and said combustion chamber whereby cooling of the gases in said fire box and said combustion chamber is prevented and a difference in temperature in said two chambers sufficient to produce a gravity circulation of gases upward in said combustion chamber anddownward in said heat pick up chamber is obtained, heat pick up means in said heat pick up chamber, flue means in said ash pit chamber for withdrawing a portion of said re-circulation gases; and means in said ash pit chamber for admitting fresh air to said fire box.

3. A furnace embodying a fire box; a grate forming the bottom of said fire box; a blast box forming a tuyere in said grate; a tubular chimney-like member forming a combustion chamber above said fire box and communicating with said fire box, said fire box and said combustion chamher constituting an internal chimney through which heated gases may ascend; means forming a heat pick up chamber communicating with the upper end of said combustion chamber and with the space below said grate, whereby said gases may descend through said heat pick up chamber and again pass upwardly through said fire box and said combustion chamber; fiue means for withdrawing a portion of said gases from the space below said grate; means for feeding fuel into said fire box over said blast box; and means fdr delivering fresh air into said blast box.

4. A furnace embodying a fire box; an inclined grate forming the bottom of said fire box: a blast box at the side of said grate, said blast box having tuyre openings therein; force feed means for delivering fuel into said fire box onto said blast box; means for delivering fresh air to said blast box; means forming a combustion chamber above said fire box and communicating with the same; means forming a heat pick up chamber at the side of said combustion chamber for receiving heated gases from the top of said combustion chamber and passing said gases downwardly to the space below said grate whereby a portion of said gases may re-circulate upwardly through said grate; and vent means below said grate for withdrawing a portion of said gases.

5. The apparatus as claimed in claim 4 in which said fire box has an inclined top wall of refractory heat insulating material extending over said blast box and forming a banking roof above said blast box.

6. The apparatus as claimed in claim 4 in which the inclined grate is formed of a plurality of overlapping spaced apart plates for preventing the passage of fine fuel therethrough and in which a dump plate is yieldingly supported for swinging movement at the lowermost forward edge of said grate to dump by gravityin response to the pres ence of a load of ashes thereon.

a blast box at the rear side of said grate; means forming tuyere openings in the top of said blast box; an upwardly extending lip at the forward edge of said blast box over which fuel may drop downwardly onto said grate; spurs on said lip for breaking up said fuel; power operated feed means for forcing fuel into the rear of said fire box and moving said fuel over said blast box; means for delivering fresh air to said blast box; means forming a combustion chamber above said fire box and communicating with the same; means forming a heat pick up chamber at the side of said combustion chamber for receiving heated gases from the top of said combustion chamber and passing said gases downwardly to the space below said grate whereby a portion of said gases may recirculate upwardly through said grate; and vent means for withdrawing a portion of said gases below said grate.

8. A furnace embodying a fire box; a grate in the bottom of said fire box; a feed chute entering one side of said fire box; means for feeding fuel through said chute into said fire box; means forming a combustion chamber above said fire box and communicating therewith; means forming a heat pick up chamber communicating with the space below said grate and with the upper portion of said combustion chamber whereby heated gases may pass downwardly through said heat pick up chamber and be returned to said fire box, said feed chute passing through said heat pick up chamber whereby fuel therein will be preheated before entering said fire box; and vent means below said grate for withdrawing a portion of said gas.

HAROLD P. FORD.

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