GB2577709A - A fuel-burning stove - Google Patents

Abstract

A fuel-burning stove 100 with a base 101, top 116, and a wall 105 defining a fire chamber 114, with the outlet 102 being near the top of the chamber. Extending across the chamber is a baffle 103 having at least one catalyst surface for performing exothermic reactions with combustion products in the flow path. The baffle may be coated with catalyst or feature an integral catalyst element, the catalyst may also consist of multiple compounds. The baffle may direct radiation produced by exothermic reactions in a desired direction to perform environmental heating or to equalise temperature in the chamber. To achieve this, the baffle may be flat or curved and may be adjustable in its mounting, there may also be a secondary baffle to further extend the flow path. The catalyst may possess a property for indicating its condition, this may be a heat erosion element to expose an indicative surface.

Description

A Fuel-Burning Stove The present invention relates to a fuel-burning stove, particularly, though not exclusively, to a natural wood fuel-burning stove having improved heat efficiency.

Fire and heating systems have been an essential element of human home life for more years than has been recorded. The core process remains the same: that fuel is burned and releases heat, radiating a portion of the heat and transferring a portion of the heat into the surrounding air and waste gases, causing them to rise. While there are no simpler or more-convenient heat sources, the present environmental climate discourages the use of open fires to provide heat. However, there is still commercial demand for stoves to provide heat and, in present changing times the demand has changed for less-polluting and more-efficient stoves.

Most current wood-burning systems rely on the natural draw of the chimney to pull oxygen over the fuel. Incoming air is directed into the combustion chamber at various levels, forcing the flame to the back or front of the combustion chamber and the heated air escapes out the chimney.

It is known in the art that, to obtain good or near-complete combustion of fuel, three conditions are required: 1. Thorough mixing of oxygen and the fuel.

2. Time for the mixing to continue and the reaction to complete.

3. A high combustion chamber temperature in which the combustion takes place.

Figure 1 is a diagram showing a cross-section of a typical modern stove 100 as is known in the art. A typical modern stove 100 has a base 101, a top 116, sides (not shown in the cross-sectional view of Figure 1), and a back wall 105, such construction enclosing a chamber 114. The typical modern stove 100 also has an air outlet 102/102ALT, a chimney 115, (which can be top, side or rear of the stove) a baffle panel 103, and a front wall 117 comprising a lower air inlet 108, a glass door 109, and an upper air inlet 110 which provides an air wash to the glass door 109 and reduces the amount of soot deposited on the glass door 109, and some stoves have an extra rear air inlet 106. Fuel 111 is placed on the base 101 or on a grill 112 and is set alight. The fuel 111 burns with air from the upper air inlet 110, the lower air inlet 108 and the rear air inlet 106. As the fuel 111 burns, the flames 113 rise and hot gases are conveyed by convection upward and out of the chimney 115, drawing unburned air in through the upper air inlet 110, the lower air inlet 108 and the rear air inlet 106. The hot gases above the flames 113 pass over the baffle panel 103 and transfers heat to the baffle panel 103.

The baffle panel 103 is mounted so as to extend into the chamber and is spaced from but across the air outlet 102 in order to provide a path for gases between the centre of the chamber and the outlet 102. The baffle panel 103 therefore extends the combustion path length of the escaping gases in order to increase the combustion time.

Such a typical modern stove 100 has problems with respect to efficiency and presentation of environmental heat about the stove.

The present invention therefore seeks to provide a fuel-burning stove which overcomes, or at least reduces the above-mentioned problems of the prior art.

Accordingly in a first aspect, the invention provides a fuel-burning stove, comprising a base, wall or walls and a top together defining a combustion chamber, an outlet provided at or near the top of the chamber, the chamber including a baffle extending across the chamber in a combustion flow path, the baffle including at least one catalyst surface with an exothermic catalytic action to combustion products in the combustion flow path Other aspects of the present invention are defined in claims dependent upon claim 1 below.

The invention will now be more fully described, by way of example, with reference to the drawings, of which: Figure 1 is a diagram showing a cross sectional view of a typical wood-burning or multi-fuel stove, as known in the art; Figure 2 is a diagram showing a cross sectional view of a first stove illustrating typical prior use of catalysts at the point of exhaust for removal of noxious gases from combustion products; Figure 3 is a diagram showing a cross sectional view of a first stove illustrating aspects of the present invention; and, Figure 4 is a diagram showing a cross sectional view of a second stove according to a second embodiment of the present invention.

There is shown in Figure 2 in accordance with prior use of catalysts in the exhaust or chimney 115 to remove noxious gases in the combustion products. The rear air inlet 106 may be made from any suitable material so for example metals such as stainless steel or other conductive material. It should be clear to someone skilled in the art that a variety of other suitable materials may be used. (1) Stoves can include a number of other air inlets 106, 108, 120 to achieve better combustion efficiency but perfect stochiometric is not readily achievable in practical stoves. In such circumstances achieving best collection and presentation of environmental heat is desirable.

A baffle 103 greatly lengthens the distance or combustion path that combusted gases must travel to exit the chamber 114, thus delaying the path of air exiting from the stove. The additional distance travelled provides the advantages of lengthening the time in which the air may mix with the flames 113 to combust and ensuring that more energy is released from combustion while in the chamber 114 rather than in the chimney 115. Fuel 111 is generally placed on a grate such that once ignited the flames extend upwards.

The baffle 103 is normally a panel made of a heat-conducting material, preferably formed with a high ratio of surface area to volume, stainless steel or vermiculite board (among other suitable materials). It should be clear to someone skilled in the art that further baffle panels could be included to further delay the air from exiting the chamber.

Baffle 103 provides an extension of the combustion path of the gases that flow between the centre of the chamber 114 and the air outlet 102. Further, due to the combination of the baffle 103 with other baffles, respectively made of heat conducting material and heat insulating materials, the space in-between the baffles effectively forms an additional combustion chamber inside of which further combustion is able to occur at higher temperatures than in the main chamber of the stove. The baffles and the combustion path are defined such that an additional chamber may be located above the flames 113, or at the back or on a side of the stove 100.

It will be appreciated that the combustion process continues from the flames through the chamber 114 along the combustion path to the outlet 102 and hence on to the chimney. Whilst the baffle 103 might promote and aid combustion with a mesh any combustion process is not complete or perfect.

With previous teaching as depicted in figure 2 catalysts 301, 302, 303, again normally in the form of matrix components (3) such as plate, mesh or honeycombe with a surface covered with catalyst material, are located at or about the outlet 102 to remove, by conversion, noxious gases such as NOx as combustion gases pass through them. The catalytic processes are generally exothermic once 'ignited' or the catalyst has reached an activation temperature. The catalyst components are generally expensive and/or rare earth metals so as indicated are presented in a mesh or other similar form to maximise surface contact with the combustion gases. It will also be understood that the catalyst in terms of position most take account of the possibility of soot, ash or other contaminants obscuring contact between the catalyst and the combustion gases. The main consideration is removal of noxious gases and the exothermic heat of such catalytic action is generally a nuisance with potential issues with regard to the heat of the catalyst at the outlet 102 and/or chimney causing distortions at joints and possibly aiding secondary ignition in the chimney etc. It will also be understood that any exothermic heat due to the catalytic action is lost to the chimney and not into the room for at least environmental heating.

Aspects of the present invention are illustrated with reference to the two embodiments illustrated in figure 3 and figure 4. A catalyst surface is provided within a fire chamber 114 upon a baffle which extends into the chamber 114. The catalyst surface is normally upon an edge where the combustion path turns generally through a tight angle towards the outlet 102. Such a turn in the combustion path means the combustion product and gas flows are exposed to the catalyst. The combustion products and gas flow over a normal solid surface with a catalyst surface or through a catalyst matrix to move in the direction B. The surface can be stippled or ribbed or otherwise shaped.

In particular, Figure 3 shows a cross-section of a stove 100 having features as described previously including a baffle 103 extending into a fire chamber 114. At or about an edge 300 of the baffle 103 a catalyst surface or catalytic matrix 310 is provided such that catalytic conversion of combustion gases is provided in a stream of combustion gases over the surface 310 or through the matrix in the direction of arrowhead A towards the outlet 102. The catalyst surface 310 act on the combustion products and particularly the noxious gases within the stream on both the flame 113 side and the opposite side of the baffle 103. The same formulation of catalyst materials or compounds can be provided on both sides of the baffle 103 or different catalysts on either side reflecting possibly different condition and/or combustion gas composition on the fire side of the baffle compared to the other side.

Figure 4 again shows a cross-section of a stove 100 having features as described previously including a baffle 103 extending into a fire chamber 114. A secondary baffle 315 is provided which again spans and extends into the fire chamber 114. The baffles 103, 315 provide a combustion path from the flame 113 side to the outlet 102 so again extending that combustion path to maximise combustion with appropriate air inlets to achieve that combustion. In accordance with these aspects of the present invention the baffle 315 has a catalyst surface 320 towards and end 325 to again engage with a combustion gas flow in the direction of arrowheads B. It will be noted that the catalyst surface 320 is directed inwards and towards the rear of the fire chamber 114 as compared to the forward and front positioning of the catalyst surface 310 in figure 3. These differing orientations will provide different responses as described below with different configurations of air inlets and stove style. It will also be understood that catalyst surfaces can be provided on both baffles and there may be more than two baffles to render a labyrinth nature to the combustion path in a stove.

The catalyst surfaces 310, 320 in accordance with aspect of the present invention may be a coating applied to an underlying substrate such as a metal, ceramic or insulating plate to present the catalytic material to the combustion gas flow. The catalyst surfaces could also be integral or attached components or elements secured to parts of the baffles presented in the fire chambers. As indicated above the catalyst surface will provides some conversion of combustion gases and particularly noxious combustion gases for exhaust purposes but mainly in accordance with aspects of the present invention the catalyst surfaces will act with the baffles to radiate heat, from the exothermic catalytic action, environmentally about the stove and/or to provide so prior heating of secondary air flows through air inlets for greater combustion efficiency.

In order to direct heat from the catalytic exothermic reaction the baffles will generally be heat conducting and shaped for radiation of heat. The baffles can be flat plates as illustrated but also may be curved if appropriate to radiate and/or direct heat appropriately within and about the chamber 114. Similarly, the underlying baffles or catalyst surface(s) may include undulations, ribbing and/or bulbous features particularly at the edges for engagement with combustion gas flows within the fire chamber towards the outlet. The catalyst surface in accordance with aspects of the present is forward in the combustion path as compared to near prior exhaust/chimney location.

The combustion gases pass through the matrix using readily and widely available materials to limit additional costs of stoves in accordance with aspects of the present invention.

It will be appreciated that the catalytic surface in accordance with aspects of the present invention need not be highly efficient and so use less expensive catalytic materials to the presented combustion gases. The aim is to provide some exothermic reaction so heat gain which can then be directed and/or radiated for better overall thermal efficiency of the stove. In such circumstances the catalyst surface may be detachable from the baffle for replacement when exhausted and/or too covered by a sleeve for contact between the combustion gases and the catalysis. It will also be understood that the baffles and/or the catalyst surface will be accessible with the stove (when cold) so replacement may be possible.

Stoves in accordance with aspects of the present invention will generally be used with wood as the fuel but it will also be understood that stoves can use coal and coke. It will also be understood that wood itself can be from different tree variety, be variously seasoned, be in log or chipped form and may be combined with other material such as compressed cardboard/paper etc. The shaping and particularly the catalyst nature of the catalyst surface can be chosen and/or changed depended upon the fuel type used. Such variation also may include altering the length and/or width of the catalyst surface. The catalyst surface may be presented in a displaceable sleeve to vary the length of the catalyst surface exposed.

As indicated above an important aspect of the present invention relates to 'recovery' of heat so the orientation of the baffle and/or catalyst surface can define the direction and/or radiation of heat from the baffle environmentally to heat about the stove as well as otherwise. In such circumstances the baffle(s) may be presented upon a mounting or a series of different mountings each to arrange for presentation at respective angles for projection of heat in a direction and appropriate radiation. It will be understood that the mountings may also themselves allow some rotation about a pivot to be fixed at a desired angle but the high temperatures might make such rotary mountings difficult.

As indicated above temperatures and conditions with a stove may be harsh. Thus, the catalyst surface might become worn and/or exhausted and/or damaged or in some way inhibited in terms of its performance. In such circumstances as also indicated above the catalyst surface itself or as part of its baffle might be replaced. In order to determine when such replacement or repair or maintenance is needed the catalyst surface or baffle might include a tell-tale feature. This tell-tale feature might be a colour change so the catalyst surface wears or evaporates away to reveal an underlaying substrate of the baffle or surface e.g. silver stainless steel or an aperture/edge formation exposed by wear.

Aspects of the present invention provided advantages as follows 1. Simpler operation: When used in any of the positions shown in Figure 2, a mechanical bypass system has to be added, for starting and reloading the stove to allow for the restriction in flow caused by the catalyst 301, 302, 303 matrix. A bypass flap is needed to allow the products of combustion straight to the flue/chimney to warm the flue/chimney and the catalyst 301, 302, 303 matrix.

2. Water/condensation coming down the flue/chimney damages catalysts put in positions as show in figure 2 this is not a problem in catalyst positions as shown in figure 3 and figure 4.

3. With a catalyst surface in positions as shown in figure 3 and figure 4. The catalyst surface heats up quicker and clears soot and tar from the surface very quickly. With prior flue catalysts as illustrated in figure if the by-pass flap is miss operated, it is difficult and slow to get the catalyst is hot enough to clean it.

4. Catalyst surfaces at positions shown in figure 3 and figures 4 run hotter and more effectively than prior arrangements.

5. With the catalyst surfaces as shown in positions as show in figure 3 and figure 4 the energy from the exothermic reaction is released in to the stove and not into the chimney increasing the efficiency of the stove.

It will be appreciated that although only one particular embodiment of the invention has been described in detail, various modifications and improvements can be made by a person skilled in the art without departing from the scope of the present invention.