Improvements in and relating to fireboxes

Abstract

 This invention relates to improvements in fireboxes and more particularly to a firebox which is adapted for the combustion of both low and high energy density fuels.
The firebox (1) incorporates a base or floor (2) having an apertured portion (16) which is a smaller proportion of the area of the floor of the firebox, the apertured portion is provided to supply oxygen to high density fuels supported on the floor of the firebox, the restricted area of the apertured portion restrict the flow of oxygen to the fuel and thus at least the maximum combustion heat output of the high density fuels to substantially similar levels to that of a full charge of low density fuel placed into the firebox. In this manner, the construction of the firebox restricts the danger of overheating of the firebox when combusting high density fuels in a firebox of a size to accommodate low density fuels.

Description

[0001] This invention relates to heating apparatus and more particularly to improvements in fireboxes for such heating assemblies.

[0002] Historically, solid fuel heating apparatus have generally been provided either for burning low density fuels such as wood, wood products, wood by-products, briquettes and similar material or alternatively, for burning high density fuels such as coal, coke, coal or coke based products and like fossil fuels. This occurs owing to the need for such heating appliances to be specifically designed to suit the combustion and combustion heat output characteristics of such fuels in a solid fuel heater. High density fuels generally require greater quantities of oxygen for complete combustion and also have a substantially higher heat output for a given volume than that of the lower density fuels. Of itself, this dictates certain firebox design requirements, rendering a solid fuel heater suitable for low density fuels generally almost useless for the efficient burning of high density fuels and vice versa.

[0003] Specific fuel heating appliances are often inconvenient for use in that on occasions high density fuels can be more readily available than lower density fuels; also the opposite can be the case. There is therefore, an advantage if a solid fuel heating appliance can be made to burn both low and high density fuels. In the past, such "dual fuel" units have exhibited tendencies of inefficiency in one or both modes of operation leading to undesirably high exhaust emissions which limit areas in which the heating apparatus can be used and further, in certain instances where for example a high density fuel is loaded excessively into a large firebox intended for low density fuels, there is a significant danger of runaway combustion, overheating and melting down of the firebox as a result of the substantially greater heat output capability of the volume of the fuel in the firebox. This can be very dangerous.

[0004] In the past, some solid fuel heating appliances intended for low density fuels have incorporated a removable grate which is insertable into the firebox when it is intended to burn the high density fuels; these are supported within the grate. The installation and removal of the grate is an extremely difficult and messy operation and can obviously only be carried out when the unit has gone out and cooled down sufficiently for the portions to be handled. Often heating appliances specifically developed for burning high density fuels will not provide sufficient heat when burning low density fuels.

[0005] The modification of existing heating units intended for high density fuels to burn low density fuels and vice versa, in addition to the practical difficulties outlined hereinbefore, also causes inherent disadvantages, costs and the like such as in component manufacture and supply, purchase options and increases the cost and difficulty for manufacturers and sellers of such products.

[0006] It is an object of this invention to come some way in overcoming the abovementioned problems or at least provide the public with a useful choice.

[0007] According to one aspect of this invention there is provided a firebox for a solid fuel heating apparatus, said firebox having a fuel support portion for supporting solid fuel thereon, said fuel support portion having an apertured portion therein able to be fed with oxygen from beneath, said apertured portion of a size smaller than that of the fuel support portion to limit the maximum combustion level of fuel supported thereon.

[0008] Other aspects of this invention which should be considered in all its novel aspects will become apparent from the following description.

[0009] The preferred form of the invention will now be described with reference to the accompanying drawings in which:

Figure 1: is a cross-secti onal plan view of the firebox of a solid fuel heating apparatus according to the invention

Figure 2: is a substantially diagrammatic cross-sectional side view on lines A-A of the heating appliance of Figure 1 showing the heating appliance in a mode suitable for burning low density fuels such as legs of wood

Figure 3: is a substantially diagrammatic cross-sectional view on lines A-A of the apparatus of Figure 1 showing the apparatus in a mode suitable for burning high density fuel such as coke, coal and like fossil fuels

[0010] Referring to the drawings, the firebox assembly of this invention as generally indicated by arrow 1 is preferably formed in suitable material for example relatively high temperature resistant robust material such as mild steel plate and the like however, the invention is not limited to these materials and alternative materials having the necessary properties of inherent strength, robustness and resistence to temperature can be utilised.

[0011] The firebox 1 is formed as a substantially enclosed firebox having a floor 2, side walls 3 and a roof 4 and preferably, although not essentially incorporating a baffle 5 to create a labyrinth to a flue 6 for exhaustion of the products of combustion.

[0012] Preferably a side wall 3a defining the front of the firebox incorporates a door 7 which is openable to expose an opening for access to the interior of the firebox 1 such as for the installation of fuel and tending the fire or the products of combustion.

[0013] An oxygen inlet 8 is preferably provided in the firebox 1 adjacent the front wall 3a and the inlet 8 communicates with a manifold 9 which preferably extends across an upper front portion and down interior corners of the firebox 1, terminating in communication with a pit 10 situated beneath a front portion of the floor 2 of the firebox 1. In this preferred form of the invention, preferably the manifold 9 is provided with ports 11 and 12 which enable communication between, in the first instance, the interi cr of the firebox 1 above the floor 2 and in the second instance, the pit 10.

[0014] Preferably a movable slide 13 is mounted adjacent the ports 11 and 12, the slide 13 in itself having a slide port 14 which is alignable with either one or the other of the ports 11 and 12 so as to control oxygen flow from the inlet 8 to the firebox either via the port 12 into the pit 10 or alternatively, through both ports 11 and 12.

[0015] Reference to Figures 2 and 3 show the two positions for the slide 13 in this form of the invention, Figure 2 showing the slide 13 in a raised position whereby the slide port 14 substantially aligns with the port 11 and enables communication between the manifold 9 and the interior of the firebox 1 via the exposed port 11 and additionally with the pit 10 via the port 12. In the arrangement of Figure 3, it will be seen that the slide 13 is in the lowered position and the slide port 14 aligns with the port 12 enabling communication between the manifold 9 and pit 10 whereas non-apertured portions of the slide 13 close the port 11. Movement of the slide 13 is via handle means 15 and preferably suitable detents are provided to assist in convenient alignment of the slide port 14 with the ports 11 and 12 as may be required.

[0016] The floor portion 2 of the firebox is provided with an apertured portion as generally indicated by arrow 16. In this form of the invention, the apertured portion 16 is provided in the manner of a grating and is positioned substantially medially above the pit 10 and preferably substantially behind the openable door 7. Preferably a closeable opening 17 is provided in the lower front wall 3a of the firebox 2 so as to enable access to at least mid portions of the pit 10 and for removal of ash and clinker and other by-products of combustion from the pit 10.

[0017] In this form of the invention, preferably the remaining portions of the floor 2 are provided in non-apertured material such as metal plate and the like and these are sloped downwardly from side walls 3 of the firebox 1 toward the apertured portion 16 although this is not essential to the invention and in alternative embodiments of the invention, the remaining floor portions 2 can be provided in a substantially planar or non-sloping manner, however, the preferred form of the invention incorporates sloping floor portions 2.

[0018] In the preferred form of the invention, the area of the apertured portion 16 approximates 30 % of the area of the floor 2 of the firebox. In alternative forms of the invention, the apertured portion 16 is constructed to be approximately 20 to 40 % of the area of the floor 2 of the firebox however, in further alternative forms of the invention, the apertured area does not exceed 60 % of the total area of the floor portion 2, it will be appreciated that the greater the density of the high density fuel to be burnt the smaller the grate area in relation to the remaining area of the floor 2.

[0019] In the preferred form of the invention, riddling means (not shown) is provided the association with the apertured portion 16, this preferably in the form of vibrating or raking means which vibrate or rake between elements of the apertured portion 16 and remove ash therefrom and also from about burning fuel there adjacent. The ash falls into the pit 10 for removal and improves combustion of the fuel adjacent the grate.

[0020] Operation of the invention using low density fuel will now be described with reference to Figures 1 and 2. In this arrangement of the invention, preferably low density fuel such as logs of wood are inserted into the firebox 1 and are rested upon the floor 2. It will be appreciated that a substantially large charge of low density fuel can be placed into the firebox and combustion is controlled by controlling inlet air or oxygen into the firebox and by moving the slide 13 to the upper position whereby oxygen can flow to the fuel both above the floor 2 and the grate via the port 12 and furthermore, through the port 12 and via the pit 10 and apertured portion 16.

[0021] It will be appreciated that a predominant air flow to the fuel will be through the port 11 in view of the less restricted nature of the air flow and perhaps owing to a build up of ash and other by-products of combustion adjacent the area of the apertured portion 16 after initial burning. It is a characteristic of a wood fuel that it will readily burn on being supplied with oxygen from around the fuel at approximately the same level or even from above and therefore, the wood fuel will burn over a relatively large area, the relatively large volume of low density fuel providing the required heat output.

[0022] Operation of the heating apparatus using a high density fuel will be described with reference to Figures 1 and 3. In this mode of operation, the slide 13 is moved to the lowered position whereby it will be appreciated supply through the port 11 is shut off and oxygen is supplied via the inlet 8 manifdds 9 port 12 and pit 10 through the apertured portion 16 to the high density fuel charge which is supported on the floor 2 of the firebox and over the grate 16. Upon the fuel being ignited, the heat output at maximum combusticn level is controlled by the amount of fuel exposed to oxygen from through the grate 16. It is a characteristic of a high density fuel such as coal, coke and the like fossil fuels that efficient burning is achieved by supplying oxygen through a bed of the fuel from therebeneath where ash can dislodge from about the fuel as it burns and pass into a pit. It will be appreciated that burning of the fuel will be restricted to over the area where oxygen is supplied through the apertured portion 16. Burning of the fuel adjacent the perimeter area and over the non-apertured area 12 of the firebox is restricted owing to the lack of oxygen. Thus, whilst the higher density fuel has a greater heat output, the restricted size of the apertured portion 15 relative to the overall area of the firebox floor restricts the amount of fuel which can combust at any one time and thus restricts an accidental runaway of the heat output of the heater should too much oxygen be supplied to the charge of fuel in the firebox and combustion occur over the whole charge.

[0023] It will be appreciated that owing to the substantially sloping nature of the floor portions 2 adjacent the apertured portion 16, upon the fuel over the apertured portion 16 being burnt and ash falling away through the apertured portion 16 and into the pit 10, unburnt fuel then can move toward the apertured portion 16 and the combustion cycle can continue. In this way, a relatively large charge of high density fuel can be inserted in the firebox and yet the combustion can be controlled without the danger of an accidental runaway of combustion with the inherent problems.

[0024] The area relationship in the preferred embodiment of the invention of the apertured portion 16 to the floor area of the firebox 2 is in the preferred form of the invention between 20 and 40%. This roughly equates the maximum heat output achieved with a normal charge of low density fuel such as wood logs which substantially and conveniently fill the firebox with that of a charge of high density fuel such as coal or coke or other fossil fuel which is able to burn over the apertured portion 16. Thus, generally equivalent maximum heat outputs are achieved on combustion in the firebox of both low and high density fuels. It will be appreciated that there is no need to modify or alter the actual construction of the firebox when changing from one firing mode to the other, only change the slide 13 of the oxygen supply.

[0025] Thus it will be appreciated that by this invention there is provided an improved firebox for the combustion of fuels of both high and low energy density and whereby the heat output of the firebox in a high density fuel combustion mode restricts the overall maximum heat output of such firebox to roughly equate the output of the firebox when it is in a low density fuel combustion mode.

[0026] Whilst the invention has been described with reference to a preferred form, modifications are envisaged and maybe incorporated without departing from the scope or spirit of the invention. Modifications are envisaged without departing from the scope of the invention as defined in the appended Claims.

Claims

1. A fire box for a solid fuel heating apparatus, said fire box having a fuel support portion for supporting solid fuel for combustion thereon, said fuel support portion having an apertured portion to feed said fuel with oxygen from beneath, an area of said apertured portion being smaller than the area of the fuel support portion such that in use the apertured portion limits the availability of oxygen to a charge of the fuel supported on the fuel support porticn to limit the maximum combustion heat output of said fuel in said firebox.

2. Apparatus as claimed in Claim 1 wherein the area of said apertured portion is restricted relative to the area of the fuel support portion of the firebox such that in use, at least the maximum combustion heat output of a charge of high density fuel supported on said fuel support portion is restricted to be substantially similar to at least the maximum combustion heat output of a lower density fuel combusted on said fuel support portion without said restriction.

3. Apparatus as claimed in anyone of the preceding Claims wherein the fuel support portion is provided as a base or floor of the firebox.

4. Apparatus as claimed in Claim 3 wherein the apertured portion at least partially defines a pit or recess beneath the fuel support portion, the pit or recess being in control communication with oxygen inlet means to control the flow of oxygen to the apertured portion.

5. Apparatus as claimed in Claim 4 wherein the oxygen control means provides means for directing the flow of oxygen to the fuel supported on the fuel support portion either directly to said fuel, above the fuel support portion, to said fuel via said apertured portion or in a combination of the foregoing.

6. Apparatus as claimed in anyone of the preceding Claims wherein the area of the apertured portion is less than 60 % of the area of the fuel support portion.

7. Apparatus as claimed in anyone of the preceding Claims wherein the area of the apertured portion is between 20 and 40 % of the area of the fuel support portion.

8. Apparatus as claimed in anyone of the preceding Claims wherein fuel moving means is provided for influencing the movement of fuel supported on said fuel support portion toward the apertured portion.

9. Apparatus as claimed in Claim 8 wherein the fuel moving means is a slope of said fuel support portion downwardly toward the apertured portion.

10. Apparatus as claimed in Claim 9 wherein oxygen control means is provided for directing the flow of oxygen to the fuel either directly to said fuel above the fuel support portion or to said fuel via said apertured portion or a combination of both.

Drawing