GB2089969A - Solid-fuel stoves - Google Patents

Abstract

A stove, particularly for burning wood, has a grate formed by a plate 18 formed with slots which are normally out of register with further slots in a plate (25, Fig. 4) beneath the plate 18. For riddling the stove, the plate (25) can be reciprocated by means of a lever (33) to bring the slots in the two plates into and out of register, some wood ash always being left on the plate 18. An air inlet duct 48 meanders over the upper part of the stove and thereby delivers preheated air (up to 300 DEG C) to the fuel on the grate. <IMAGE>

Description

SPECIFICATION Solid-fuel stoves The present invention relates to stoves for burning solid fuel, more particularly but not exclusively wood.

According to one aspect of the present invention, a stove for burning solid fuel defines a substantially closed space, the bottom of which forms a bed for supporting burning fuel, and an air inlet passage for supplying air for combustion of the fuel, the air inlet passage being in heat exchange communication with the upper part of the space within the stove, the arrangement being such that, in use, air entering the inlet passage is preheated by heat exchange with combustion gases proceeding from the fuel to an outlet flue.

Typically, the preheating of the inlet air is such that it enters the combustion temperatures at up to or exceeding 3000C and is thus more effective in burning volatile components of the fuel, thereby increasing efficiency. The inlet passageway preferably meanders in the upper part of the combustion space of the stove before reaching a downwardly directed discharge section arranged to discharge the inlet air into the combustion space above the fuel bed.

A further air inlet may be provided leading into an outlet adjacent the fuel bed to provide air at least for assisting the lighting-up of the stove.

According to another aspect of the invention a stove for burning solid fuel has a base for its fuel bed formed by a plate formed with apertures beneath which is a further, movable plate having apertures which, by movement of the second plate relative to the first plate, can be brought into and out of register with the apertures in the first plate.

With this construction, a riddling action can be effected by reciprocating the second plate relative to the first plate to reduce the amount of ash on the first plate, but some ash will always remain on the portions of the first plate between the apertures. When burning wood, the space beneath the plates will be effectively sealed and by normally leaving the second plate with its apertures out of register with those of the first plate, air will be prevented from passing upwards into the fuel bed.

Advantageously, the ash and riddlings drop into an ash pan in the said space which then has a door through which the ash pan can be removed for emptying. By waiting for a short period, if necessary after riddling, to allow any dust in the ash to settle, the ash pan with its contents can be removed without causing dust or mess near the stove.

When burning coal in the stove, a flow of air may be passed in to the fuel bed by leaving the movable plate in a position in which its openings are at least partly in register with the openings in the other plate and by arranging an inlet opening into the chamber beneath the plates.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a front elevational view of a wood burning stove; Fig. 2 is a horizontal section through the stove on the line Il-Il of Figure 1; Fig. 3 is a horizontal section on the line Ill-Ill of Figure 1; Fig. 4 is a vertical section on the line IV--IV of Figures 2 and 3 with the doors of the stove removed; and Fig. 5 is a vertical cross-section on line V-V of Figure 4.

The stove shown in the drawings is assembled from castings and fabrications which fit together, so far as possible without nuts and bolts so as to facilitate assembly and disassembly for cleaning.

The stove stands on a base 1 having four stub legs 2. On the base 1 sits a bottom casting 3, defining an ash space and supporting sheet metal side walls 4 bent at right angles to a back wall 5.

The lower edges of the walls 4 and 5 are inwardly flanged at 6 to seat on the top of the bottom casting 3 and their top edges are flanged at 7 to support a top casting 8 having a central raised rectangular dome 9.

A pair of doors 10 and 11 are mounted on hinges 12 welded to the side walls 4 and having their hinge pins 13 proud of the side walls 4 so that the doors 10 and 11 can be folded back almost flat against the side walls 4. The doors 10 and 11 have large windows which are closed by strips 14 of heat-resistant glass. A catch for holding the doors closed is operated by a handle 15.

An outlet flue collar 16 is carried by the upper part of the back wall 5 to form a flue outlet for connection to a flue (not shown) by means of a connector 1 7.

A fuel bed is defined by a plate 18 located ina rebate 1 9 in the top of the bottom casting 3.

Around the back and side edges of the plate 1 8 are stood refractory blocks 20 and 21. If desired, the back block 20 may be replaced by a back boiler (not shown). At the front edge of the plate 1 8 is mounted a fire bar assembly 22 fabricated from square section bars welded together, the two end vertical bars 22A being extended downwards to engage in apertures 23 in the plate 18. The plate 1 8 (Fig. 3) is formed with a set of riddling slots 24 which are spaced apart by a distance greater than their width. Slidably mounted below the plate 1 8 is a riddling plate 25 having a further set of riddling apertures 26 similar to, but normally out of register with, the apertures 24. A riddling shaft 27 extends through the rear part of the bottom casting 3 and is journalled therein at 28 and 29.A shaft 27 carries two upwardly extending arms 30 engaged in elongated holes 31 in the riddling plate 25. By oscillating an external riddling lever 33 carried by the shaft 27, the riddling plate 25 can be reciprocated fore and aft to bring its apertures 26 into and out of register with the apertures 24 in the bed plate 1 8 so as to reduce the amount of ash reposing on the plate 1 8. Some ash will however always remain on the lands between and around the slots 24 to ensure that there is at least a minimal ash bed which is necessary when burning wood.

Beneath the riddling plate 25 is an ash pan 34 which is removable through an aperture in the front of the base casting. The centre portion of the back wall of the ash pan is cut away to clear an air inlet passage 35 leading from an opening in the back wall of the bottom casting 3, this opening .being controlled by a damper (not shown) the air inlet duct 35 extending forwards to the front of the bed plate 18 where it turns upwards to reach a discharge outlet 36 directing air rearwardly through the fire bars 22.

A top wall for the combustion chamber 37 above the fuel bed is formed by a plate 38 resting on lugs 39 and carried by the side walls 4. As can be seen from Fig. 4 and 5, the plate 38 slopes slightly downwards from front to rear where it abutts the rear wall. At the front, it is spaced from the doors 10 and 11 so that the combustion gases can pass upwards into the space above the baffle 38. The latter supports two further baffles 40 and 41 which are located hy pegs 42 fixed to the top surface of the baffle 38. The top edge of the front baffle 40 is spaced from the under surface of the dome 9 to provide a passage 43 for the flue gases.

The top edge of the rear baffle 41 conforms to the underside of the dome 9 but its left hand end is spaced from the left hand wall 4 to leave a passage 44.

An inlet 45 in the rear wall 5 is controlled by a damper (not shown; normally operated by a thermostat) and admits air to a tubular duct 46 which meanders around the rear baffle 41, passing through the passage 44 and continues through a cut out 47 in the front baffle 40 to turn downwards at the centre of the front of the stove at 48 and register with a rectangular-section duct 49 defined by flanges on the doors 10 and 11, the duct 49 terminating at its lower end in a discharge nozzle 50 angled to deliver air into the combustion chamber 37 in a region adjacent the upper edges of the blocks 20 and 21 and just above the position of the bed of burning fuel.

A convector duct is formed at the back of the stove by a sheet metal wall 51 which has its two edges 52 bent inwards to form spacing walls and then flanged outwards at their extreme edges at 53 to be secured to the rear wall 5 by screws 54.

The bottom and top of the convection duct are open so that air within the duct is warmed and rises within the duct to provide a flow of warm air for the space to be heated by the stove.

In operation, with the doors 10 and 11 open, paper, kindling and wood are laid on the bed plate 18 in the normal manner and the fire is lit. The doors 10 and 11 are closed and air is admitted through the inlet passage 35 to establish the fire.

Once the stove and its flue have become warmed, further air combustion is drawn in through the inlet 45 and duct 46. During its passage through the long duct 46, this air is heated by counterflow heat exchange with the combustion gases leaving the combustion chamber 37 around the front edge of the baffle 39 and travelling to the flue outlet 1 7.

Preferably, the air is heated in the duct system 47,48 to a temperature of at least 2000C and typically 3000C before being discharged through the nozzle 50, but this temperature will of course depend on the rate of air flow through the duct and the temperature around the duct.

Once the steady state has been reached, it may be found that the inlet to the air passage 35 may be completely closed, all air for combustion being supplied by the inlet 45 and being preheated. The rate of combustion is then determined by the setting of the control damper for the inlet 45.

Since the air from the duct 46 has to travel downwards to reach the combustion zone, the ,combustion tends to be self-regulating and avoids surges. By feeding the air from the nozzle 50 into the centre of the front of the combustion area, the flames tend to fan out sideways and transmit heat more evenly throughout the hole in the stove and thus keep the windows in the doors cleaner.

To add fuel to the stove when in normal operation, a by-pass damper 55 in the rear of the baffle 38 is first opened to allow the combustion gases to flow directly to the flue connection 1 7.

The doors can then be opened. Preferably, an interlock (not shown) is arranged to ensure that the doors cannot be opened until after the damper 55 has been opened.

The units of the stove can be assembled without spanners. Further, the stove can be taken to pieces for transport or maintenance by lifting of the top 8, then lifting out the duct 46, baffles 40, 41 and 38, lifting off the doors 10,11, taking out the fire bricks, lifting off the side and back wall assembly 4,5 lifting off the grate components and separating the bottom casting 3 from the base 1.

In this way, a purchaser can take the components home from the point of sale in his car.

In a modification (not shown), the undergrate air inlet passage 35 is replaced by air inlet slots formed through the bottom rails of the doors to provide lighting up air. These slots are then closable by slides.

If an "open fire" is required at any time, the damper 55 is opened and the doors 10 and 11 are swung back against the sides of the stove.

Claims (8)

1. A stove for burning solid fuel, the stove defining a substantially closed space, the bottom of which forms a bed for supporting burning fuel, and an air inlet passage for supplying air for combustion of the fuel, the air inlet passage being in heat exchange communication with the upper part of the space within the stove, the arrangement being such that, in use, air entering the inlet passage is preheated by heat exchange with combustion gases proceeding from the fuel to an outlet flue.

2. A stove according to claim 1 wherein, in use, the preheating of the inlet air is such that it enters the combustion temperatures at about 3000 C.

3. A stove according to claim 1 or 2 wherein the inlet passageway meanders in the upper part of the combustion space of the stove before reaching a downwardly directed discharge section arranged to discharge the inlet air into the combustion space above the fuel bed.

4. A stove according to any of the preceding claims having a further air inlet leading into an outlet adjacent the fuel bed to provide air at least for assisting the lighting-up of the stove.

5. A stove for burning solid fuel in which a base for its fuel bed is formed by a plate formed with apertures beneath which is a further, movable plate having apertures which, by movement of the second plate relative to the first plate, can be brought into and out of register with the apertures in the first plate.

6. A stove according to claim 5, wherein an ash pan is disposed in a closed space beneath the plates, having a door through which the ash pan can be removed for emptying.

7. A stove according to any of claims 1 to 4 and according to claim 5 or 6.

8. A stove for burning solid fuel, substantially as described with reference to the drawings.