US2149184A - Method of and apparatus for feeding fuel - Google Patents

Description

Feb. 28, 1939 C. E. RICHARDSON ET AL METHOD OF AND APPARATUS FOR FEEDING FUEL Filed NOV. 1, 1934 CHARLES E. RICHARDSON.

JOHN CARROLL. lNVE TOR A TORNEY Patented Feb. 28, 1939 UNITED STATES PATENT OFFICE 2,149,184 7 METHOD OF AND- APPARATUS Foa FEEDING FUEL Canada Application November 1, 1934, Serial No. 751,066

1 Claim.

Our invention relates to means for feeding fuel to the firebox of a furnace, boiler or the like, and to a method of promoting combustion of the fuel within the firebox. More particularly our invention relates to a motor driven means of the type commonly referred to in the art as a mechanical stoker, which may be thermostatically controlled, and which is adapted to feed a solid fuel such as coal to the firebox of a domestic furnace or the like, and to a method of supplying combustion air thereto by a combination of forced and natural draft.

In devices of this nature heretofore put forward it is a known expedient to employ a motor,

driven screw acting within a pipe of relatively large diameter for transferring a solid fuel from a suitable hopper or bin to the firebox of the furnace. It has also been the practice to supply combustion air under pressure from a suitable motor driven fan or blower to the bottom of the firebox in order to promote combustion of the fuel within the furnace. So far as we are aware, in installations where combustion air is forced through the firebox from the section of the furnace immediately thereunder (hereinafter termed the ashpit) it has heretofore been necessary to seal this section of the furnace to prevent the escape of air under pressure from the ashpit other than through the firebox. The necessity of a sealed ashpit is a factor in determining the cost of a mechanical stoker installation and presents other disadvantages as well; leaks inevitably develop, which not only allow the escape of air from the ashpit, but also allow the escape of dust, which in the case of domestic installations is particularly objectionable; the sealed ashpit involves the elimination of the ashpit door from which it follows that ash other than in the form of clinkers may not readily be removed; the sealed ashpit further involves an entire dependence for combustion air on the forced draft provided by the fan or blower, an interruption in the power supplied to the fan or blower consequently placing the user in the position of having no fire; and the sealed ashpit still further involves the entire elimination of natural draft for supplying combustion air to the fire and consequently necessitates a greater number of rates of fuel feed to meet varying weather conditions.

In certain installations, and particularly in domestic installations used for house heating purposes, a mechanical stoker must be adapted to supply fuel and combustion air to the firebox of the furnace, boiler or the like at widely varying rates in order to take care of widely varying weather conditions. For example in the type of mechanical stoker relying entirely on forced draft and wherein a single motor serves to drive both the screw and the fan it has been shown that the fuel feeding means operates under thermostatic control more often and for longer periods than is necessary to maintain the desired temperature during mild weather conditions. This is due in part at least to the fact that during the idle periods of the fan or blower, the fire dies very rapidly owing to the lack of combustion air. In order to overcome this difficulty in devices of the prior art it has been proposed to provide a multi-speed gear reduction between the driving motor and the fuel feeding means in order to provide a number of varying rates of fuel feed to meet varying weather conditions, at the same time allowing for longer periods of operation of the fan or blower. The provision of a m-ulti-speed gear reduction not only adds complexity to the operation of the stoker as a whole but also tends to increase the cost of the unit and consequently is decidedly objectionable.

It is an object of our invention to provide a mechanical stoker particularly designed for domestic installation which will overcome all of the above referred to objectionable features of similar devices of the prior art.

It is a further object of our invention to pro-- vide a mechanical stoker for a furnace, boiler 01; the like fired with solid fuel which will employ a combination of natural and forced draft for supporting combustion within the firebox.

A further object of our invention is to provide a mechanical stoker for solid fuels, which, when added to furnaces, boilers or the like already installed, will necessitate a minimum of disturbance to the existing installation.

A still further object of our invention is to provide a device of the character hereinbefore referred to wherein the escape of dust and combustion air from the hopper and ashpit is substantially prevented, without the necessity of sealing the ashpit against air leaks.

We accomplish the above and other objects in accordance with our invention, by supplying fuel and combustion air under pressure through concentrically located passages to a double walled retort having tuyeres in its inner wall, and located centrally of the bottom of the firebox of the furnace, the remainder of the bottom of the firebox being, closed by a suitable grate. The retort and grate are supported within the furnace by a double walled elbow casting to the central passage of which fuel isfed by a motor driven screw from a suitable hopper or bin and to the outer passage of which air under pressure is supplied from a suitable fan or blower.

A better understanding of our invention will be obtained from a consideration of the following particular description of a specific embodiment thereof and by reference to the drawing attached thereto, and the scope of our invention will be pointed out in the claim appended thereto.

In the drawing:

Fig. 1 is a side elevation of a device of our invention with certain portions broken away to show members otherwise hidden;

Fig. 2 is a rear elevation; and

Fig. 3 is a longitudinal section of a portion of the device of our invention. Throughout all figures of the drawing like reference numerals refer to the same members.

In the drawing we have illustrated at I a hop per or bin provided with a cover 2 and. mounted on a base indicated generally at 3. The hopper is made of sheet metal and is generally of rectangular horizontal section decreasing in area from top to bottom. The base 3 comprises front and rear plates 4 and 5 respectively and a bottom plate 6. The front and rear plates 4 and 5 extend downwardly below the lowest portion of the bottom plate 6 and are turned outwardly to form feet I and 8 which serve to support the hopper assembly on the floor 9. The bottom plate 6 is bent into a V-shape with a rounded apex as shown by the dotted lines in Fig. 2 and forms the bottom of the hopper I. The front wall 4 of. the hopper base is apertured at I and an end of the fuel pipe II is secured within the opening I!) by screw threaded engagement with a ring member I2 supported by bolts I3 on the plate 4. The other end of the fuel pipe II is in screw threaded engagement with the inner wall I4 of a double walled elbow casting I5. A second pipe I6 is located concentrically with respect to first pipe II and is substantially coextensive therewith, forming at one end a tight sliding fit over a conical surface I! provided on the ring member I2 and at the other end forming a second sliding fit with the outer wall I8 of the elbow casting I5, which is preferably also formed into a conical surface Hat.

The casting I5, of metal such as cast iron, is formed with the two walls I4 and I8 defining inner and outer passages. The inner passage as defined by the inner wall I4 makes a bend through substantially 90 and forms in general a bent funnel through which the fuel is adapted to be fed in an upward direction. The passage defined by the walls I4 and I8 is substantially annular in cross section and is adapted to convey combustion air under pressure to the retort described hereinafter. For purposes of removing dust from the outer passage defined by the walls I4 and I8, this passage is somewhat enlarged below the bend in the casting I and the wall I8 has a large opening therethrough at I9, closed by the dust flap 2!]. The dust flap 23 is self aligning, being tiltably mounted on the central support 2I in the end of a weighted lever 22 pivoted at 23 to a lug 24 on the outer surface of the casting I5. The weighted lever 22 is so adjusted that the dust flap is maintained closed against the air pressure Within the outer passage of casting I 5, but permits ready removal of any dust that gathers therein.

The outer wall I8 of the casting is further pro vided with a flange 25 about the upwardly extending opening. Mounted on the flange 25 and secured thereto by suitable means such as the bolts 26 is a retort 21 which is preferably made of metal such as cast iron. The retort 21 comprises outer and inner, concentric, substantially cylindrical walls 28 and 29 respectively, forming therebetween an annular passage which is closed at its upper end by the end wall 33. The inner wall 29 0f the retort is provided with a plurality of tuyeres or openings 3I through which air may pass and the outer wall 28 is provided with a suitable outwardly turned portion 32 adapted to cooperate with the flange 25 on casting I5. Thus the retort 21 is mounted on and is secured to the casting I5 and the inner and outer passages defined by the walls of the retort 2'I register with the inner and outer passages respectively of the casting I5.

It will be understood from what has been said hereinbefore that the diameter of the retort 21 is substantially less than the diameter of the furnace or boiler in which it is used. In the space between the retort and the furnace walls there is provided the natural draft grates 33 having a down turned rim or flange 34 which rests on the flange 32 of the retort 21. Thus the space within the furnace above the retort 2'! and grates 33 constitutes the firebox and the space below the grates 33 constitutes the ashpit, and in order to adjust the grates 33 and retort 21 to the proper level within the furnace there is provided the adjustable leg 53 mounted on the casting I5.

Fuel is transferred from the hopper I to the casting l5 and retort 21 through the fuel pipe II by means of the screw or worm 35 which extends through the hopper base 3 from the rear wall 5 thereof through the aperture I3 in the front wall 4 thereof, and through pipe I I into the inner passage of casting I5. The screw 35 is given a small clearance within the pipe II and, when rotated in one direction serves to drive the fuel forwardly through pipe II toward casting I5, as is well known in the art.

Combustion air under pressure is delivered through the pipe connection 36 to the air pipe I6 which connects with the outer passages in casting I5 and retort 21, by a fan or blower 31 of the well known centrifugal type mounted by means of a suitable bracket (not shown) adjacent the side of the hopper base 3. The intake to the fan may be controlled by means of the swinging disk 38 mounted on the set screw 39. During operation of the screw 35 driving fuel into and through the pipe II a certain amount of dust is created within the hopper I and hopper base 3. In order to prevent the escape of this dust from the hopper I there is provided an additional intake conduit to the fan 3'! in the form of the pipe connection 43 through which air is delivered from within the hopper I to the intake of the fan.

A single electric motor 4| serves to drive both the blower 31 and the fuel screw 35. A gear reduction mechanism 42 is mounted on the rear wall 4 of hopper base 3 and has a projection on its output shaft extending through a suitable aperture in the wall 4 and engaging in a socket in a boss 43 on the end of the screw 35, as is shown in Fig. 3. The gear reduction mechanism shown generally at 42 may be of any suitable type, but we prefer to use a ratchet gear mechanism such as is shown and claimed in a copending application of D. D. Panabaker, now Patent No. 2,121,405, dated June 21, 1938. The gear reduction unit disclosed in the above identified copending application comprises a pair of ratchet discs alternately operating upon a ratchet wheel to impart thereto and to the output shaft of the unit an intermittent rotary motion. Not only does the unit of the above identified application form a simple and economical means for driving the fuel screw 35 but by reason of intermittent motion transferred to the fuel screw, it has certain advantageous features to be more fully disclosed hereinafter. The input shaft 44 of the gear reduction mechanism is provided with a suitable pulley 45, and the drive shaft of the blower 31 is provided with a suitable pulley 46, each of which is engaged by a belt 41 driven by a suitable pulley 48 mounted on the shaft of motor 4|. It will be understood of course that motor 4| may be controlled in any manner, either manually or by any of the Well known thermostatic control systems.

In describing the installation of the mechanical stoker of our invention it will be assumed that the furnace or boiler construction is already installed except for the grates defining the bottom of the firebox. The hopper end of the unit of our invention will first be assembled, that is, the hopper I will be mounted on the base 3 and the blower 31 will be secured thereto, with the auxiliary pipe connection 40 made between the hopper I and intake of blower 31. An aperture will then be cut in the wall of the ashpit of the furnace, and the casting I5 will be mounted at the proper height within the ashpit and one end of the fuel pipe I I will be screw threaded therein. One end of the air pipe IE will also be placed in position on the conical surface I1a on the outer wall of casting I5 and the two pipes will be secured in concentric relation by screwing the ring member I2 on the other end of fuel pipe II, the other end of pipe I6 making a tight fit over the conical surface I1. The hopper assembly and pipe assembly will be connected together merely by securing the ring member I2 to the front wall 4 of the hopper base by means of the bolts I4. The fuel screw 35 may then be inserted through the opening in the rear wall 5 of hopper base 3, the opening being closed and the screw 35 being supported by the gear reduction unit 42 which is then mounted on the outside of the wall 5. Motor 4| may then be mounted on the top of the gear reduction unit 42 and the belt connection 41 made to drive blower 31 and unit 42. The retort 21 and natural draft grates 33 will then be mounted within the furnace on the casting I5 and will be secured thereto by the bolts 26. Thus the complete assembly is made with the minimum disturbance to the furnace construction. The ashpit need not be sealed against air leaks for the reason that air under pressure is conveyed directly to the fire by means of the pipe I6 and the outer passages in casting I5 and retort 21. Furthermore a natural draft through the ashpit is desirable for reasons which will be explained hereinafter. Attention is also directed to the fact that the stoker may be installed from any side of the furnace, as desired, by reason of its unitary means for conveying fuel and air under pressure to the firebox.

The operation of the device of our invention will now be briefly described. A supply of fuel is placed in hopper I sufficient, for example, to last for one days firing. It will be assumed that initially the control for the driving motor is such that the motor operates to drive the screw 35 and the blower 31. Under these conditions fuel will be slowly fed from the hopper base 3 through the pipe I I to casting I5 and from thence to the Zifirebox through the retort 21, and at the same time air under pressure will be supplied by the blower 31 to the pipe I6 and through the outer passage in casting I5 to thefirebox through the tuyeres in the inner wall of retort 21. As the screw 35 continues to force fuel through the casting I5 the fire will gradually spread throughout the whole of the bottom of the firebox and will cover the natural draft grates 33. The forced draft through the retort 21 creates therein a brilliant fire which rapidly generates heat to be absorbed in the heating system.

When the control for the motor 4| changes to interrupt the power supply thereto the screw 35 will no longer feed fuel to the firebox and no further air under pressure is supplied to the retort 21 by the blower 31. However, in contradistinction to devices of this type known in the prior art, the fire does not die to a very low minimum as soon as the blower 31 shuts off, but is maintained at an intermediate rate of combustion by reason of the natural draft through the grates 33 from the unsealed ashpit. This feature is a very advantageous one particularly in mild weather operation of domestic installations for house heating purposes. The presence of a natural draft through the firebox assures substantially complete combustion of the fuel fed thereto by the screw 35 without continued operation of the blower 31, and contributes to the economy of operation of the installation in that less frequent operation of the blower 31 and feed screw 35 is required to maintain a desired temperature.

Under certain conditions of operation it has been found that the gaseous products of combustion have tended to flow from the retort 21 back through the fuel pipe II. Heretofore this objectionable tendency has been overcome by supplying air under a relatively low pressure to the interior of the fuel pipe at a point adjacent its entrance into the furnace, by means of a special air conduit running from the blower. In the device of our invention this tendency to smoke back is readily and economically overcome by drilling a few holes through pipe U adjacent its juncture with the casting I5.

During operation of the stoker a certain amount of fuel is unavoidably pulverized to dust by the action of the screw 35 within pipe II. Some of the fines thus created falls through the tuyeres 3| in retort 21 into the outer passage of casting I5 and lodges in the bend of the casting, thereby restricting this passage and reducing the rate of air feed from blower 31. The opening I9 which is normally closed by the dust flap 20 provides a convenient means for periodically removing the dust or fines accumulated Within the casting I5.

The dust created by the action of screw 35 and which remains in the hopper I, and any gaseous products of combustion which find their way back to hopper I from the firebox are quickly removed from the hopper by means of the pipe connection 40 to the blower 31. By the suitable adjustment of the intake valve on blower 31 comprising the disk 38, a sufficiently lowered pressure is generated within the hopper I to prevent the escape of dust or gaseous products of combustion therefrom to the outside atmosphere.

The use of the ratchet gear reduction unit of the aforementioned Panabaker application is particularly advantageous in that the intermittent rotary motion imparted to screw 35 provides a small amount of agitation to the fuel within the hopper I and pipe II. It has been found that this agitation settles the fuel around the screw 35 in a very solid mass, reduces the grinding noise arising from the fuel being forced into pipe H from hopper l, and further reduces the amount of fines created by the action of screw 35.

While we have disclosed herein, in accordance with the patent statutes, a specific embodiment of our invention, we do not wish to be limited thereto and aim, in the appended claim to cover all such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

In a device of the character described, a hopport said second pipe in concentric relation with respect to said first pipe.

C. E. RICHARDSON. JOHN CARROLL.

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