FIREPLACE AND METHOD FOR CLEANING COMBUSTION GASES FROM A FIREPLACE

The present invention relates to a fireplace according to the preamble of claim 1. The invention also relates to a method for cleaning combustion gases from a fireplace as according to the preamble of claim 10.

The use of fireplaces for heating purposes has been known since antiquity. In the present-day application of fireplaces for heating purposes it is possible to envisage gas- fired fireplaces and solid fuel devices (such as for instance wood-fired fireplaces) of very diverse types. Fireplaces include, non limitatively: open hearths, gas-permeable shielded fireplaces, fireplaces closed with glass, stove heaters and so forth. A drawback of existing fireplaces is that they can have an environmental impact in densely populated areas because of the contamination of the combustion gases with dust particles. Furthermore, the energy efficiency of fireplaces is generally low (open fireplaces normally have an efficiency in the order of magnitude of -5 to 15% and built- in/insert fireplaces and freestanding stoves have an efficiency in the order of magnitude of 70 - 85%). It is therefore official government policy to discourage the use of open fireplaces. Examples are therefore already known where the emission values of a fireplace may not exceed determined norms.

The European patent application EP 1 353 125 describes a method and device for treating flue gases of fireplaces with solid fuels, such as are for instance released when wood is burned in a domestic environment Described herein is a filter element embodied as a ceramic netting, manufactured for instance from ceramic foam. The filter element can be incorporated into/above the fireplace and the flue gases flow therethrough. The outlet of the fireplace can be fully covered by the filter element.

The present invention has for its object to provide a fireplace and a method corresponding to the type described in EP 1 353 125 with which the emission of dust from a fireplace can be reduced still further in an efficient manner.

The invention provides for this purpose a fireplace as according to claim 1. The ceramic foam material can function as filter material during the combustion of both fossil fuels and non-fossil fuels. The advantage of a releasable ceramic foam passage is that it

hereby becomes possible to replace or clean the ceramic foam if there is a need to do so. It may well be for instance that, despite the high temperatures to which the ceramic foam is heated, not all captured contamination is burned and/or that non-combustible material contaminates the ceramic foam. After a period of use it is then desirable to be able to release the ceramic foam from the fireplace, for instance for the purpose of external cleaning thereof or replacement thereof by another, less contaminated ceramic foam. Another reason for taking out ceramic foam is that it has been damaged as a consequence of use. The ceramic foam can for instance crack or crumble as a result of temperature (change). The ceramic foam can also be damaged as a result of mechanical loads.

Yet another possibility is, depending on the conditions of use (such as for instance the type of fuel), to opt for an associated ceramic foam element. Dimension and/or composition of the ceramic foam and possible additives thereto can here be optimized for specific conditions. The action of the ceramic foam in the fireplace can be optimized by these measures, this resulting in increased efficiency of the fireplace and/or reduced emission of undesired elements. In order to obtain sufficient heating of the ceramic foam material so as to achieve the above stated results, the ceramic foam material is desirably oriented toward the grate, whereby it is heated by direct irradiation from the fuel bed.

The releasable coupling can be realized such that plates of ceramic foam material can be taken out by removing a locking element. Another possibility is to mount the ceramic foam material in a partial or full frame or framework which can be manufactured from metal. Such a frame can facilitate simple replacement of the ceramic foam material and also forms a mechanical protection for the relatively vulnerable ceramic foam material. The frame can be embodied such that it can be coupled releasably to the housing in simple manner with coupling means (for instance by providing the frame with passage openings through which bolts can be placed).

The ceramic foam passage must desirably be oriented toward the grate such that it is irradiated by the fire present there, and for this purpose the ceramic foam material must adjoin the grate without interposing of other objects, such as for instance a flame baffle plate or other fireplace part, or in other words forms part of the housing at least partially

enclosing the grate. It is further noted that the ceramic foam filter material can be applied in fireplaces of varying power, for instance in wood-fired and ambiance heating fireplaces up to 25 kW, but also in biomass-fired fireplaces with a power of as much as SOO kW. The captured dust particles are caught in the ceramic foam material and, provided the ceramic foam material is sufficiently heated as a result of the oriented placing of the material, can burn once again so that combustion gases remain that are much cleaner than if these measures are not taken. At the same time, owing to the good combustion of the captured dust particles, contamination of the ceramic foam material is prevented or at least limited. In addition to filtering of the combustion gases, another significant advantage of the ceramic foam material in the application according to the present invention is that, after heating, it will begin to function as a source of radiant heat, with the result that the combustion efficiency can increase; this is because the fireplace will radiate more heat than if the flue gases enter the outlet directly. It is also advantageous here for the ceramic foam material to be oriented at least partially toward the grate; the radiant heat will thus be radiated in the direction of the grate, which can result in an even better (more complete) combustion and the radiant heat can moreover be guided out of the fireplace via the usual path. The fireplace according to the invention has the advantage of combining an increased efficiency with a reduced emission of (fine) dust particles compared to a prior art fireplace.

Effective heating of the ceramic foam material takes place in that the ceramic foam material is heated by the transfer of heat from the flue gases as well as by the direct radiation from the grate toward the ceramic foam material. The heating by irradiation from the grate is possible because the ceramic foam passage is oriented toward the grate, i.e. is directly adjacent to the grate without interposing of other objects. It is otherwise noted here that the term "fireplace" is understood in the context of this invention to mean an optionally fully enclosed grate, in particular fireplaces applied for heating purposes.

Examples of ceramic foam material according to the present invention are ceramic foam materials provided with aluminium and oxygen (A12O3) and/or zirconium oxide (ZrO2); optionally in combination with other oxides such as calcium and oxygen (CaO) and silicon and nitrogen (Si3N4). Also advantageous in the context of the invention is the application of SiC and/or cordierite (a magnesium-aluminium-silicate with the

chemical formula Mg2A14Si5018) in a fireplace according to the present invention. Advantages of these material choices are that these materials, in addition to having the desired properties in respect of temperature resistance, can also be readily processed and are relatively inexpensive. They are typically of crystalline structure and are generally hard, brittle, heat-resistant and corrosion-resistant. These types of ceramic foam material are commercially available and are applied in the filtering of, among other materials, liquid metals. The definition of a ceramic foam material in the context of this invention is: "an inorganic compound of a metal and a non-metal which is formed under the influence of heat". Another important advantage of the fireplace according to the present invention is that, using the ceramic foam material (provided there is a good, i.e. preferably gas-tight seal of the ceramic foam material onto the outlet), a higher gas pressure can occur in the fireplace than on the discharge side of the ceramic. As a result the residence time of the combustion gases in the fireplace is longer than if the ceramic foam material were not present. A longer residence time of the combustion gases in the fireplace will result in a better mixing of the combustion gases and the supplied air.

The active area of the ceramic foam passage is preferably 0.8 to 5 times the throughflow area of the outlet for flue gases. The specific size of the active area of the ceramic foam passage can be chosen subject to, among other factors, the height at which the ceramic foam material is located relative to the grate. It is further the case that fireplaces usually taper toward the top, whereby the ceramic foam material, when placed is a higher position, will have a smaller active area. The size of the throughflow area of the ceramic foam material will of course influence the resistance encountered by the flue gases (combustion gases). The path which the flue gases must cover through the ceramic foam material is desirably 2 to 5 centimetres long.

In another preferred embodiment of the fireplace the ceramic foam passage is provided with a profiled surface on the side toward the grate. A surface can be envisaged here which is provided with for instance protruding parts, such as for instance elongate protruding material strips, chamfered surfaces enclosing mutual angles, and so forth. The size of the protruding parts is here in the order of several centimetres in height. The radiation pattern with such a profiled ceramic foam material can be influenced in both form and intensity so that the radiation pattern can also be further optimized. The

filtering action of the ceramic foam material with profiled surface can also be influenced.

The fireplace is preferably provided with a construction such that the housing at least partially enclosing the grate is provided on the top side and at least one of the side walls with a releasable ceramic foam passage. The discharge of the flue gases/combustion gases via one or more side walls and the top side results in an advantageous combustion process with a higher efficiency than a combustion process with extraction only on the top side. Multilateral discharge of the combustion gases by means of ceramic foam passages results in a more homogenous temperature level in the combustion space, and thereby a better quality of combustion. The homogeneity of the temperature is achieved, among other reasons, because the ceramic foam passages accumulate heat and, by generating radiation toward the combustion space (the burner bed), also holds the temperature level at a relatively stable level at the beginning and end phases of a charge. The beginning and end phases of a charge (in a so-called batch firing method) are precisely those phases which provide for relatively high emissions. The multilateral discharge of combustion gases/flue gases will result in reduced emission.

In a preferred embodiment the ceramic foam passage is formed from at least one ceramic foam plate. It is possible to envisage the ceramic foam passage being formed by a single plate, although it is also possible to envisage this passage being defined by a plurality of plate which for instance lie connecting to each other in a plane, which enclose mutual angles or which wholly or partially overlap each other. A suitable solution can thus be selected depending on the geometry of the fireplace and the obtainable ceramic foam material.

When choosing the ceramic foam material, material must be applied which is sufficiently porous to allow passage of the flue gases without too much resistance. Ceramic foam material with a porosity of between 5 - 50 PPI is found in practice to produce good results. Ceramic foam material with a porosity of 10, 20 and 30 PPI has been found particularly advantageous. The possibility also results here of building up the ceramic foam material from multiple layers of mutually differing porosity. Three connecting layers of differing porosity are for instance envisaged here, such as for instance a thinner layer of 30 PPI, a first supporting layer of 20 PPI and a second

supporting layer of 10 PPI. The material with the finer porosity of 30 PPI, which can be given a relatively thin form, here has good properties as radiation surface, while the less fine layers provide strength and provide for a subsequent filtering of the first finer ceramic foam layer. The layer of the ceramic foam material closest to the grate thus has the smallest cells. For the sake of clarity: the ceramic foam material having the smallest cells is understood to mean the finer ceramic foam material producing the greatest resistance to throughflow. The particles (fine dust) to be captured have in wood-fired fireplaces a size of about 0.1 μm to about 10 μm.

In order to maximize the effect of cleaning and heat recovery, it is desirable for the outlet for flue gases to be shielded gastightly from the grate except for the ceramic foam passage. The flue gases can hereby only enter the outlet by passing through the ceramic foam material. The flue gases are thus fully filtered by the ceramic foam material, and the generation of heat from the flue gases to the ceramic foam material is also maximized

The fireplace can be adapted as desired for the burning of solid fuel (an example hereof is for instance a wood-fired fireplace), although the fireplace can also be adapted to bum gases. An example hereof is a natural gas-fired fireplace. Conversely, it is also possible to envisage the fireplace being adapted for optionally combined firing of different types of fuel.

hi order to enhance the cleaning of the flue gases still further, the ceramic foam material can also carry a catalyst. Envisaged more particularly here is an oxidizing catalyst such as for instance platinum, palladium, rhodium or gold, although other catalysts can advantageously also be applied subject to the conditions of use.

The present invention also provides a method for cleaning combustion gases from a fireplace, comprising the processing steps of: heating the ceramic foam material by at least the direct irradiation of the ceramic foam material by the fire in the fireplace; carrying the combustion gases through a ceramic foam material in order to remove from the combustion gases at least some of the dust particles present therein, and burning at least some of the dust particles captured in the ceramic foam material as a result of the heating of the foam material. Using this method the advantages can be realized as

already described in the foregoing with reference to the fireplace according to the present invention. In particular the combustion gases can be cleaned and a higher heating efficiency can be realized. In order to optimize the desired effect, all flue gases coming from the fireplace must be carried through the ceramic foam material.

The present invention will be further elucidated on the basis of the non-limitative exemplary embodiments shown in the following figures. Herein: figure IA shows a cut-away perspective view of a fireplace according to the present invention; figure 1 B shows a cross-section through a wall part of the fireplace of figure 1 A; figure 1C is a top view of the wall part of the fireplace shown in figures IA and IB; figure 2 A shows atop view of the alternative embodiment variant of a part of a wall part of the fireplace according to the present invention; figure 2B is a top view of the wall part shown in figure 2 A in a situation where it is provided with ceramic foam plates; and figure 3A-3D show cross-sections through different embodiment variants of ceramic foam plates for use in a fireplace according to the present invention.

Figure 1 A shows a fireplace 1 with a grate 2 which is partly enclosed by a housing 3. Connecting to housing 3 is an outlet 4 through which the combustion gases can escape. Situated between grate 2 and outlet 4 is a plate 5 with a central opening 6, this opening 6 being covered by a foam plate 7. Plate 5 functions here both as flame baffle plate, filter (of inter alia soot) and as radiation panel. The combustion gases will flow through foam plate 7 to outlet 4, during which passage some of the dust particles will remain behind in foam plate 7. Foam plate 7 is here also heated, and part of this heat will be irradiated downward such that the heating efficiency of fireplace 1 is hereby improved. Figure 1 B shows a cross-section through plate 5 and foam plate 7. It can also be seen here that foam plate 7 can be built up of stacked layers 8, 9 of ceramic foam material 7 with different properties. Figure 1C shows a front view of plate 5 and ceramic foam material 7.

Figures 2A and 2B show an alternative embodiment variant of a plate 20 which can be compared to plate 5 of the already shown fireplace 1. Plate 20 is provided with a central opening 21, on either side of which angle profiles 22 are arranged between which

ceramic foam plates 23 (only shown in figure 2B) can be inserted. Two stops 24 prevent the ceramic foam plates 23 being pushed through too far and, in order to lock the ceramic foam plates 23 in the inserted position, there is arranged in plate 20 a recess 25 into which a releasable locking pin 26 can be inserted. Ceramic foam plates 23 can be taken out as desired and optionally replaced by other ceramic foam plates (for instance cleaner plates, plates of metal foam, plates made up of a combination of ceramic foam and metal foam and/or foam plates with other properties). The ceramic foam material comprises for instance silicon carbide, magnesium oxide and aluminium oxide. Conversely, the combination with metal foam is also possible. These are foams made from metals, in particular though not exclusively aluminium and aluminium alloys. Ceramic foam plates 23 can for instance have a length of 0.3-0 .75 m and a width between 0.3 and 0.5 m, these being very readily applicable for instance up to fireplace power to a maximum of 500 kW.

Figures 3A-3D show cross-sections through different embodiment variants of ceramic foam plates 30, 31 , 32, 33 for use in a fireplace 5 according to the invention. Ceramic foam plate 30 is made up of a uniform ceramic foam material, while foam plate 31 consists of two different material layers 34, 35, of which the porosity, the material and/or a possible additive such as a catalyst can for instance differ.

In figure 3C the ceramic foam plate 32 is embodied with three different material layers 36, 37, 38, while figure 3D shows that it is also possible for a ceramic foam plate 33 to be embodied with abutting segments 39, 40 of differing ceramic foam materials.