GB2157418A - Solid fuel combustion appliances - Google Patents

Abstract

A solid fuel combustion appliance for domestic use employs an underfeed stoker (14) the retort (12) of which is disposed within the body (2) of the appliance. A profiled arch having faces 43 arranged at an angle to each other extends partly over the retort (12) and in use induces the spread of flames issuing from the firebed (28). <IMAGE>

Description

SPECIFICATION Improvements in or relating to solid fuel combustion appliances This invention concerns improvements in or relating to a solid fuel combustion appliance.

In particular, the invention has reference to such an appliance for use in a domestic or quasi-domestic environment in which the ap pliance can assume a central feature. There are many different types of such an appliance currently available commercially, but most, if not all, include a grate on which fuel is burnt in up-draught or down-draught conditions, the fuel being introduced on to the top of the grate either directly from above or through an opening in the front of the appliance.

It it known in the industrial field to employ underfed stokers in which fuel is burnt within a retort in an ascending fire bed to which raw fuel is fed from below by a screw conveyor, the combustion air being provided through tuyere assemblies super-mounting the retort and also surrounding the upper part of the fire bed. The off gases from the fire bed rise to exhaust through an appropriate flue arrangement. It is usual for the retort itself to be contained within a closed housing in order to ensure that the off gases do not escape into the relevant environment and to maintain good thermal insulation.

It is an object of the present invention to adapt such an underfeed stoker as a solid fuel combustion appliance for use in a domestic or quasi domestic environment whereby it can be employed as a feature fire either as an open fire or closed roomheater possessing, in operation, aesthetic qualities with regard to the visibility of the combustion process.

Accordingly the invention provides a solid fuel combustion appliance including a body having an exhaust gas outlet therein, a combustion zone defined within the body, an underfeed stoker, a retort of the underfeed stoker being located in said combustion zone, and an arch located at least partly over and in spaced relation to the retort, the arch being profiled such as in use to induce a spread of flames issuing from a firebed in the retort.

The profile of this arch may in section be a shallow chevron, but may be convex or concave.

The underfeed stoker advantageously includes the retort together with a tuyere assembly mounted thereon for introducing, in use, air into the firebed contained within the retort and also the assembly. A screw feeder is connected at one end to the base of the retort and at or towards the other end to the base of a hopper for solid fuel, a suitable drive mechanism for the feeder being provided. Means may conveniently be provided for the introduction of overfire air.

The body may have an opening in the front thereof. There may be provided means for introducing air in use at least one margin of the opening to provide an air curtain at least partially thereacross.

The means for introducing air to provide the air curtain may be so constructed as to allow the flow of overfire air to pass directly on to the top of the fire bed in the retort.

The tuyere assembly may be provided with external ports at least partly therearound to enable air to exhaust in use into a region circumjacent the assembly whereby any unburnt fuel in this region discharged from the retort may continue to undergo combustion. A suitable support for such discharged fuel and ash is conveniently provided around the top of the retort and tuyere assembly and may be constructed by the upper wall of an air plenum chamber. The support may in one embodiment by an imperforate plate and in an alternative embodiment of perforate form. In the latter case, the support may be a grate capable of retaining incandescent fuel for the purpose of continued burning outside the retort, an air supply arrangement being provided for introducing an upward flow of air through the grate. The provision of such a support enhances this visual effect of burning fuel.

Conveniently the rear of the combustion zone may be defined by a refractory member which may have a part thereof protruding over the retort to form the arch. The provision of the arch not only effects a spread in flame but also enhances combustion intensity by virtue of heat reflection, stabilieses the firebed and assists in deflecting any particulates entrained in the off gases from the firebed.

Water containment spaces may be provided in the body of the appliance to give it a boiler capability.

By way of example only, one embodiment of solid fuel combustion appliance according to the invention is described below with reference to the accompanying drawings in which: Figure 1 is a cut-away perspective view; Figure 2 is a diagrammatic side sectional view; and Figure 3 is a diagrammatic plan view of part of the appliance.

Referring to the drawings, a solid fuel combustion appliance 1 includes a body 2 set against a wall 4 and having an opening 6 in the front 8, a flue (not shown) being provided for the body. A combustion zone 10 is defined within the body 2 and disposed therein is a retort 1 2 of an underfeed stoker 14, a feed tube 1 6 of the stoker 14 extending from the base of the retort through the wall 4 to a hopper 1 8 and a drive unit 20. The unit 20 serves as a drive for a conveyor screw (not shown) housed within the tube 16, the hopper 1 8 being located intermediate unit 20 and wall 4.

A tuyere assembly 24 is mounted on the retort 1 2 and has air ports 26 for directing air in use into a firebed 28 therewithin. Additional ports 27 (Fig. 3) are formed in the rear half of the assembly 24 to direct air externally of the assembly. An air plenum chamber 29 is formed at the base of the body 2, the relatively upper margin thereof being formed by a plate 30 through which the retort 1 2 and tuyere assembly 24 protrude. A fan (not shown) in use feeds air to the chamber 29 and thus to the assembly 24. The lower part 31 of the front of the body 2 is of hollow construction and communicates with the chamber 29.Apertures 32, only one of which is shown in Fig. 1, are formed in the part 31 and so orientated as to direct air, in use, issuing therefrom upwardly to provide an air curtain 34 (Fig. 2) extending at least partially across the opening 6. Further apertures 33 (Fig. 2) are also provided in the part 31 at a lower level than apertures 32 and are disposed so that in use air passing there through flows downwardly towards the firebed 28.

A refractory wall 40 defines the rear of the combustion zone 10 and is formed with an arch 41 which extends at least partly over the retort 1 2 and thus in use the fire bed 28. The lower part of the arch 41 is provided with two flat faces 43 which in cross-section assume the form of a shallow chevron.

In operation, solid fuel, e.g. coal, is fed from the hopper 18 by the conveyor screw through the tube 1 6 to the base of the retort 12 wherein it is ignited initally, by, for example, a hot air, air for combustion being passed via the chamber 29 to the parts 26.

The firebed 28 is formed and continually rises through the retort 1 2 and tuyere assembly 24, fresh fuel ascending from the base of the retort. Air also issues from apertures 32 to provide the curtain 34, as referred to above, thereby preventing the emission of combustion products into the ambient environment in which the appliance is located, for example a domestic room, and to encourage the flames of the firebed 28 to impinge on arch 41. The impingement of the flames on faces 43 of arch 41 causes a spread of the flames thereby enhancing the visual appearance of the fire.

Apertures 33 provide overfire air which acts as secondary air to promote the combustion of volatiles given off from the firebed 28 and to assist the combustion of coke trees.

As the incandescent fuel and ash reach the top of the tuyere assembly 24, they overflow and are deposited on the top of the plenum chamber 29 whereon any still unburnt fuel is combusted in the presence of air emerging from ports 27 at the rear of the assembly 24.

The provision of the arch 41 assists in enhancing combustion intensity by reflecting heat back into the bed 28, and into any fuel overlying the top of the plenum chamber 29.

By the provision of the air curtain 34, the environment is protected from firebed emissions which are thus kept within the body 2, this air also assisting in directing firebed flames towards the arch 41 thereby effecting a visual appearance similar to that of a conventional domestic fire.

In alternative embodiments (not shown), a side grate may be provided around or to one side of the retort whereby overflowing unburnt fuel may be deposited thereon for complete combustion and subsequently removed automatically for disposal.

Claims (12)

1. A solid fuel combustion appliance including a body having an exhaust gas outlet therein, a combustion zone defined within the body, an underfeed stoker, a retort of the underfeed stoker being located in the combustion zone, and an arch located at least partly over and in spaced relation to the retort, the arch being profiled such as in use to induce a spread of flames issuing from a firebed in the retort.

2. An appliance according to claim 1 in which the profile of the arch is in section a shallow chevron, presenting two flat faces to the retort.

3. An appliance according to claim 1 in which the arch is concave or convex in profile.

4. An appliance according to any one of the preceding claims in which the body has an opening in the front thereof.

5. An appliance according to claim 4 in which means are provided for introducing air in use at least one margin of the opening to provide an air curtain at least partially thereacross.

6. An appliance according to any one of the preceding claims in which a tuyere assembly is mounted on the retort and is provided with internal ports and external ports.

7. An appliance according to claim 6 in which the external ports are arranged at least partly around the periphery of the tuyere assembly.

8. An appliance according to any one of the preceding claims 5 to 8 which a lower part of the front of the body defining the margin of the opening is of hollow construction and has formed therein the means for introducing air.

9. An appliance according to claim 8 in which the means for introducing air includes apertures arranged in a first level adjacent the top of said lower part.

1 0. An appliance according to claim 9 in which the means for introducing air includes further apertures arranged at a second level beneath the first level.

11. An appliance according to any one of the preceding claims 6 as dependent upon claims 5, 7 to 10, in which a plenum chamber is provided in the base of the body for feeding air to the tuyere assembly and the means for introducing air.

12. An appliance according to any one of the preceding claims in which a refractory wall defines the rear of the combustion zone and includes a part thereof protruding over the retort to form the arch.

1 3. A solid fuel combustion appliance substantially as hereinbefore described with reference to Figs. 1, 2 and 3 of the accompanying drawings.