Patent Publication Number: US-2015075510-A1

Title: Catalytic unit for solid fuel burning stoves

Description:
FIELD OF THE INVENTION 
     The present invention relates to a solid fuel burning stove comprising a catalytic unit. 
     BACKGROUND OF THE INVENTION 
     Wood and coal burning stoves are employed for home heating and purposes such as cooking. However, especially the burning of wood often results in incomplete combustion and exhaust comprising a high amount of particles, volatile organic compounds and carbon monoxide, all of which are a hazard to the environment. 
     Furthermore, the incomplete combustion results in a loss of overall combustion efficiency. 
     In order to increase the combustion efficiency and minimize the pollution from the wood burning stove, the combustion temperature in the combustion chamber has been increased, and catalytic converters introduced into the stove. 
     EP0037281 describes a wood burning stove with a combustion chamber and a flue, where a catalytic converter is located either in said combustion chamber or in the flue. The catalytic converter comprises a plurality of catalytic cells with a length oriented in the direction of the flow. The catalytic converter is a honeycomb structure with a plurality of mutually parallel cells extending through the structure. 
     EP0354674 discloses a wood burning stove with a catalytic cell for reducing exhaust emissions from the stove. The catalytic cell forms a secondary combustion chamber within the stove communicating with the primary combustion chamber. Hereby the exhaust from the primary combustion chamber is catalytically combusted in the secondary combustion chamber. 
     WO85/02455 discloses an insulated secondary combustion chamber where a mixture of exhaust gasses from the primary combustion chamber is burned. The secondary combustion chamber can be retrofitted on existing wood burning stoves. The retrofitted apparatus is formed as a heat exchanger with a first and second passageway, where the heat exchanger has an undulating shape for better heat exchange. Insulating material is provided along one side of the first and second passageway, respectively. A perforated catalytic igniter is provided in the lower portion. 
     However, in order to achieve the most powerful reduction of pollutants from stoves, it is important to optimise the catalytic unit with regard to temperature and catalytic power. 
     Additionally, the catalytic unit is to be designed in a manner which results in a minimal pressure drop when the exhaust passes through the catalytic unit. If the pressure drop is too large, the combustion in the combustion chamber will be insufficient and result for example in a large amount of particles. 
     OBJECT OF THE INVENTION 
     It is the object of the present invention to provide a stove having an alternative catalytic unit for effectively minimising the exhaust of particles, carbon monoxide (CO) and volatile organic compounds (VOC), hereby increasing the overall combustion efficiency and decreasing the negative effects on human health and the environment. 
     DESCRIPTION OF THE INVENTION 
     This object is achieved by a stove comprising
         a combustion chamber and a flue for removing exhaust from said combustion chamber, where said combustion chamber and said flue are connected via a passageway;   said combustion chamber comprising a top and a bottom, where said top and said bottom are connected by one or more sides;   a catalytic unit arranged between said combustion chamber and said flue in said passageway;   said catalytic unit provides a guide way for the exhaust, where said catalytic unit comprises at least two isolating members and at least one catalytic member,   said catalytic member comprising a first wave-like structure, said first wave-like structure being provided on at least one catalytic surface of said catalytic member and, in use, at least partly being in contact with the exhaust and, where, in use, the direction of the exhaust is substantially transverse to the waves of said first wave-like structure.       

     In one embodiment, the stove is a solid fuel burning stove. The solid fuel burning stove is to be understood as a stove capable of burning for example wood and coal. The wood and coal are burned in a combustion chamber releasing exhaust, which is transported to the outside of a building by a flue. The exhaust is transported via a passageway from the combustion chamber to the flue. 
     The passageway can be either just a connection or a secondary chamber for heat exchange and/or secondary combustion of the particles present in the exhaust. The passageway may also be a combination of both a connection and a secondary chamber. 
     By “heat exchange” is meant that the heat from the exhaust is transmitted to the surroundings, whereby the temperature of the exhaust from the fuel is decreased. 
     The combustion chamber comprises a top and a bottom, which are connected via one or more sides. Solid fuel is arranged at the bottom of the combustion chamber for burning. The exhaust obtained during burning exits the combustion chamber through an opening in the combustion chamber, preferable in the top or next to the top of the combustion chamber. 
     A catalytic unit is arranged in the passageway for boosting the oxidation of compounds in the exhaust from the combustion chamber. Hereby, the amount of particles, volatile organic compounds (VOCs) and carbon monoxide (CO) is decreased in the exhaust. 
     In one embodiment, the catalytic unit is arranged just after the combustion chamber, i.e. when the exhaust leaves the combustion chamber, it enters the catalytic unit. When the exhaust leaves the catalytic unit, it enters into the secondary chamber for maximal exploitation of the heat generated in both the combustion chamber and during the secondary combustion in the catalytic unit. From the secondary chamber, the exhaust is directed to the flue. Thus, the catalytic unit provides a guide way for the exhaust on its way from the combustion chamber to the flue. 
     In one embodiment, the catalytic unit is arranged in the secondary chamber of the stove. A secondary chamber is commonly present in multiple solid burning stoves, and the catalytic unit can be fitted into existing stoves without the necessity of redesigning presently known stoves. 
     In a further embodiment, the catalytic unit forms the secondary chamber of the stove. 
     In one embodiment, the catalytic unit can be retrofitted onto existing stoves. 
     In another embodiment, the catalytic unit is installed in newly produced stoves. In one embodiment, the catalytic unit comprises a catalytic member and at least two isolating members. 
     The catalytic member preferably operates at temperatures up to 1050° C. More preferably, the catalytic member operates at temperatures between 200° C. to 900° C. In another preferred embodiment, the catalytic member operates at temperatures between 200 and 350° C. 
     In order to maintain the temperature of the exhaust after exiting the combustion chamber, the catalytic unit further comprises at least one isolating member. Hereby, the temperature is kept in a range between 200 and 900° C. 
     By “at least one isolating member” is to be understood that the number of isolating members enclosing the catalytic member can be one, two, three, four, five, six etc members. 
     More than one isolating member can be engaged with one another in order to secure a high temperature close to the catalytic member and to form a catalytic unit, which forms a guide way for the exhaust. 
     In one embodiment, the guide way through the catalytic unit is a closed space except for an inlet opening and an outlet opening. 
     At least an inlet opening and an outlet opening is present in the catalytic unit for allowing the passage of exhaust into the catalytic unit and out of the catalytic unit. Hereby, the exhaust is able to come into contact with the catalytic surface of the catalytic member. Advantageously, the exhaust is able to come into contact with all catalytic surfaces of the catalytic member. 
     In one embodiment, the inlet opening and the outlet opening is one opening. 
     In one embodiment, the inlet opening is of a width similar to the width of the passageway. In a further embodiment, the outlet opening is of a width similar to the width of the passageway. In a further embodiment, the inlet opening and the outlet opening are of a width similar to the width of the passageway. 
     Isolating the catalytic unit along the flow direction of the exhaust by isolating members results in a minimal temperature loss over the catalytic unit. Thus, an optimal reaction temperature with regard to the catalytic process can be maintained i.e. between 200° C. and 900° C. Furthermore, a large pressure loss is prevented. Therefore, the exhaust easily exits the flue though the amount of particles, VOC and CO is diminished. 
     The catalytic member is provided with a first wave-like structure on at least one catalytic surface of the catalytic member. 
     As an example, the first wave-like structure can be a sinus-shaped curve having 5 cm between the first waves and a first wave-height of 1 cm. 
     In one embodiment, the distance between the first waves differs along the catalytic unit. In a further embodiment, the height of the first waves differs along the catalytic unit. In a still further embodiment, both the distance between the first waves and the height of the first waves differ along the catalytic unit. 
     The first wave-like structure is arranged in a manner, whereby the intended travel direction of the exhaust is directed substantially transverse to the first waves. Hereby, turbulence is induced in the exhaust flow and the exhaust flow is continuously mixed, whereby the entire flow comes into contact with the catalytic member. Furthermore, the catalytic area is increased. 
     The intended travel direction of the exhaust is to be understood as the primary travel direction of the exhaust. 
     The design of the catalytic unit minimises the pressure drop between the air intake of the combustion chamber and the end of the flue. Preferably, the pressure drop over the catalytic unit is no different from the pressure drop over the secondary combustion chamber not including a catalytic unit. 
     In one embodiment, the catalytic unit is designed in a manner which allows a pressure drop between the combustion chamber and the end of the flue to be at a maximum of 12 Pa (static pressure) according to European standards (EN13240). 
     In one embodiment, the stove further comprises a blower in order to force convection. In this embodiment, the design of the catalytic unit can be more complex and hereby introduce a significant pressure drop. 
     The catalytic member can be arranged with regard to the isolating members by either resting the catalytic member against the surface of one of the isolating members or by small attaching means, where the attaching means are attached to both the catalytic member and to one or more isolating members. By using the small attaching means, a given distance between the isolating members and catalytic member can be maintained. 
     In an advantageous embodiment, said catalytic member is integrated in an exposed isolating surface of at least one isolating member. Hereby, is to be understood, that the catalytic member is part of at least one of the isolating members and that the oxidative boosting takes place at a surface of the isolating member, where the surface is exposed to the exhaust passing through the catalytic unit. 
     The catalytic member can be integrated only partly on the exposed surfaces of the isolating members. Hereby is to be understood that only parts of the exposed surface can be provided with the catalytic member. 
     By exposed isolating surface is to be understood the surface of the isolating member which faces the guide way for the exhaust and hereby is exposed at least partly to the exhaust passing through the catalytic unit. 
     In another embodiment, the catalytic member is only integrated with some of the exposed surfaces i.e. if the catalytic unit comprises two isolating members and two exposed isolating surfaces, the catalytic member is provided only on one of the exposed surfaces or if the catalytic unit comprises four isolating members and four exposed isolating surfaces, the catalytic member is provided only on one, two or three of the exposed surfaces. 
     In another embodiment, the catalytic member is integrated with all of the exposed isolating surfaces i.e. if the catalytic unit comprises two isolating members and two exposed isolating surfaces, the catalytic member is provided on both of the exposed isolating surfaces or if the catalytic unit comprises four isolating members and four exposed isolating surfaces, the catalytic member is provided on four exposed isolating surfaces. 
     In one embodiment, the catalytic member is formed by adding a metallic layer onto the exposed surface of the isolating member. 
     In an alternative embodiment, the exposed isolating surface is formed by providing the surface with a ceramic layer and a catalytic metal layer. Hereby, the catalytic surface area is increased due to the porous structure of the ceramic layer. 
     In a further advantageous embodiment, said catalytic unit comprises said catalytic member being surrounded by one isolating member. 
     In this embodiment, the isolating member is formed as a pipe or a tube, where the catalytic member can be arranged inside the tube. Since the isolating member is not to be assembled from more members the catalytic member is easily installed in the stove. Furthermore, no assemblies will be present and thus, the temperature of the catalytic unit can be kept at a high level to obtain optimal reduction of particles, VOC and CO. 
     Alternatively, the catalytic member can be an integrated part of the exposed surface of the isolating member. 
     In an advantageous embodiment, said exposed isolating surface of at least one isolating member facing said catalytic member comprises a second wave-like structure, where, in use, the direction of the exhaust is substantially transverse to the waves of said second wave-like structure. 
     The at least one isolating member comprises at least one isolating surface. One of the isolating surfaces faces the catalytic member and is thus, an exposed isolating surface. Between this exposed isolating surface and the surface of the catalytic member, the flow of exhaust moves. 
     The exposed isolating surface can comprise a second wave-like structure. 
     In one embodiment, the exposed isolating surface at least partly comprises a second wave-like structure. 
     As an example, the second wave-like structure can be a sinus-shaped curve having 5 cm between the second waves and a second wave-height of 1 cm. 
     In one embodiment, the distance between the second waves differs along the catalytic unit. In a further embodiment, the height of the second waves differs along the catalytic unit. In a still further embodiment, both the distance between the second waves and the height of the second waves differs along the catalytic unit. 
     The second wave-like structure is arranged in a manner, whereby the intended travel direction of the exhaust is directed substantially transverse to the second waves. Hereby, further turbulence is induced in the exhaust flow. 
     An increased number of collisions between CO, VOC, particles and oxygen at the surface of the catalytic member at a temperature between 200 and 900° C. in combination with only a minor pressure drop over the catalytic unit are obtained by providing the catalytic unit with both first and second wave-like structures. The concentration of the polluting components CO, VOC and particles are hereby efficiently decreased. 
     In a further advantageous embodiment, the mutual distance perpendicular to the intended travel direction of the exhaust is constant between said first and said second wave-like structures. Hereby, the flow of exhaust experiences turbulence and an increased surface area of the catalytic member along the flow path, but the pressure drop over the catalytic unit will only be minimal allowing an efficient flow of the exhaust through the catalytic unit and out the flue. 
     Arranging the catalytic member in the middle of the passageway will constantly force the exhaust through the catalytic member. Hereby the number of collisions and the reduction of emissions will be increased by only a minimal loss of pressure. 
     In a further advantageous embodiment, at least one isolating member forms at least a part of the top of the combustion chamber. 
     One of the isolating members or a part of one of the isolating members can be a part of the general insulation of the combustion chamber especially when the catalytic unit is arranged in direct connection to the combustion chamber. Hereby, less material is to be used for optimal insulation and combustion in the stove. 
     Furthermore, using an isolating member both as part of the combustion chamber as well as for the catalytic unit is less space demanding, which is advantageous especially for small stoves. 
     In a further advantageous embodiment, said stove further comprises an additional member, said additional member is arranged in said passageway, where said additional member extends said guide way for the exhaust and said additional member preferably is an additional isolating member. 
     Hereby, the travelling direction of the exhaust can be further rearranged in the passageway and an extended guide way through the passageway is formed. Thus, the duration of the exhaust being in the passageway is increased and hence the amount of particles, VOC and CO decreased. 
     In one embodiment, the additional member is made from isolating material. The isolating material can be the same as described below for the isolating members of the catalytic unit. Hereby, the high temperature between 200° C. and 900° C. of the exhaust is maintained and the combustion of the particles, VOC and CO is increased. 
     In a further embodiment, the material of the additional member is the same as for the isolating members. 
     In a further embodiment, said additional member is a plate-like member. 
     In a still further embodiment, the additional member is arranged in a first inclined position in the passageway in relation to the bottom of the combustion chamber maintaining the exhaust in the passageway for a longer time either forcing the exhaust downwards or just modifying the natural upwards movement of the exhaust. 
     The additional member can be arranged either before or after the catalytic unit in the passageway with regard to the travel direction of the exhaust. 
     In one embodiment, the additional member is a part of the catalytic unit. 
     In a further advantageous embodiment, said at least one isolating member comprises at least one end at at least one opening of the catalytic unit, where, in use, said exhaust enters and/or exits said catalytic unit and that at least one of said isolating member comprises a bent edge where the bent edge is formed at least partly along said at least one end of said isolating member. 
     To allow the inlet and outlet of the exhaust the catalytic unit is provided with at least one opening for the exhaust to enter into and out of the catalytic unit, the inlet and outlet opening, respectively. 
     In this embodiment, the at least one opening is provided at the end of the catalytic unit and thus, at the end of the at least one isolating member. 
     In one embodiment, the opening is both an inlet and an outlet opening for the exhaust. 
     In one embodiment, the bent edge is shaped to direct the flow of the exhaust towards the catalytic member and is thus formed at the inlet opening of the catalytic unit. 
     In one embodiment, the bent edge is arranged on the isolated member opposite of the isolating member facing the combustion chamber, and the bent edge is arranged next to the inlet of the catalytic unit. Thus, the bent edge prevents the exhaust from not entering the guide way through the catalytic unit. Hence, the connection between the catalytic unit and the combustion chamber is automatically generated by the bent edge. 
     Alternatively, the bent edge is formed at the outlet opening of the catalytic unit to direct the exhaust properly towards the flue. 
     The bent edge can be formed along the entire end of the isolating member or one or more bent edges can be formed along the end of the isolating member i.e. each bent edge only arranged along part of the end. 
     In a further advantageous embodiment, said catalytic member is a plate. 
     In a still further advantageous embodiment, the plate is arranged between by at least two isolating members, where at least one isolating member is arranged on either side of the catalytic member. Hereby, a thin catalytic unit can be achieved, which takes up only a minimal amount of space and still is provided with a large surface area. 
     Furthermore, a plate only introduces a minimal pressure drop across the catalytic unit. 
     In one embodiment, the thickness of the plate is preferably between 0.1 to 3 cm. In a further embodiment, the thickness of the plate is preferably between 0.5 and 2 cm. In a still further embodiment, the thickness of the plate is approximately 1 cm. In a still further embodiment, the thickness of the plate is preferably between 0.01 and 3 cm. In a still further embodiment, the thickness of the plate is preferably between 0.05 and 1 cm. In a still further embodiment, the thickness of the plate is preferably between 0.1 and 0.2 cm. 
     In a further advantageous embodiment, said catalytic member is a grid. Hereby, the total surface area of the catalytic member is enlarged, and thereby the capacity of the catalytic member for promoting reduction of particles, VOC and CO. 
     The first wave-like structure of the catalytic member introduces turbulence. Hence, the flow of exhaust is, besides continuously mixing the exhaust, also able to pass through the openings of the grid, and e.g. particles are thus capable of being transported by the exhaust on both sides of the catalytic member as well as from one side to the other side. Efficient contact is therefore established between the components of the exhausts and all surfaces of the grid. 
     Furthermore, introducing a grid as the catalytic member lowers the pressure drop across the catalytic unit. 
     In one embodiment, the grid is a plate. 
     Potentially the passage through the grid can be clogged up due to the particles in the exhaust. However, having both the first and second wave-like structures increases the turbulence of the exhaust to a degree, which reduces the risk of the grid being clogged up. Thus, the catalytic effect of the catalytic member can be exploited continuously without the risk of the grid clogging up whereby the catalytic effect would decrease or the guide way clog up whereby the exhaust would not be able to exit the combustion chamber. 
     In a further advantageous embodiment, said catalytic member is arranged between two isolating members. Hereby, is to be understood that the catalytic unit comprises two isolating members and one catalytic member, where the catalytic member is arranged between the two isolating members. In one embodiment, the isolating members are plate-like members, where the plate-like members comprises two ends each at the inlet and outlet opening of the catalytic unit, respectively. The isolating members further comprise two sides each, connecting the ends of the isolating members. Each of the plate-like members is arranged on either side of a catalytic member in the form of a plate i.e. the catalytic member is sandwiched between the two isolating members. 
     Advantageously, the catalytic member is a plate and a grid. 
     In a further advantageous embodiment, said exposed isolating surface on said at least one isolating member comprises at least one protruding portion. 
     By providing at least one protruding portion on the exposed isolating surface, a guide way is automatically created between isolating members. The size of the guide way can easily be changed by changing the size of the protruding portions. In one embodiment, the catalytic member is arranged in the guide way. 
     The top of the at least one protruding portion rests against the exposed isolating surface of the opposite arranged isolating member. Alternatively, the top of the at least one protruding portion arranged at a first isolating member can rest against the top of another protruding portion arranged at a second isolating member. 
     In a still further advantageous embodiment, said at least one isolating member comprises at least two ends at at least an inlet and an outlet opening of said catalytic unit, where, in use, said exhaust enters and exits said catalytic unit, said at least two ends is connected by at least two sides and where said at least one protruding portion is arranged along at least one of said sides of said isolating member. 
     To allow the inlet and outlet of the exhaust the catalytic unit is provided with an inlet and an outlet opening, respectively. In this embodiment, the at least one opening is provided at the end of the catalytic unit and thus, at the end of the at least one isolating member. The ends of the isolating members are connected by isolating sides to form the isolating member. Along at least part of the sides protruding portions can be provided. 
     A space will be formed between the isolating members when an isolating member engages with another isolating member for forming a catalytic unit if at least one side of one of the isolating members is provided with protruding portions. The exhaust travels through this space which forms a guide way for the exhaust. 
     In one embodiment, the catalytic unit comprises two isolating members where both members comprise protruding portions. The protruding portion of the first isolating member and the protruding portion of the second isolating member engage during the formation of a catalytic unit. Hereby, a space between the exposed isolating surfaces is created. 
     In one embodiment, the catalytic member can be retained between isolating members by being arranged between the protruding portions and hereby being retained in position within the catalytic unit. 
     In a further embodiment, the catalytic member is retained between the isolating members by being arranged between the protruding portions of one of the isolating members and the surface of the other isolating member where the two isolating members engage. 
     In a further embodiment, the catalytic member is arranged in a recess formed along the sides of at least one of the isolating members. Hereby, the engagement between the isolating members is not influenced by the fact that part of the catalytic member is present where the isolating members engage. Furthermore, the catalytic member is kept in place by engaging with the recess of the member. 
     In a further embodiment, the recess is provided in the at least one protruding portion in at least one of the isolating members. 
     In a further advantageous embodiment, said catalytic member is coated with at least one layer of metal; said metal is located on the surface of said catalytic member for reacting with particles in said exhaust. In a still further advantageous embodiment, said metal is palladium, platinum, cerium, rhodium, zinc, cupper or a mixture hereof. 
     Hereby is to be understood that the catalytic member can comprise one, two, three, four etc. layers of metal. 
     In one embodiment, the layer of metal fully coats the catalytic member. 
     In a further embodiment, the layer of metal partly coats the catalytic member. 
     By coating the entire surface of the catalytic member with at least one metal layer, the catalysing compound will be distributed over the entire surface of the catalytic member and will be as effective as possible. 
     The metal can be provided in combination with a ceramic monolith layer. The ceramic monolith is porous. Therefore, the ceramic monolith has a high surface area pr. volume upon which surface the metal can be coated. Hence, a large catalytic area can be obtained. Thus, using both ceramic monolith and metal increases the catalytic activity of the catalytic member. 
     In one embodiment, the catalytic member has a steel core, preferably of stainless steel, where the steel core is coated with a ceramic monolith layer comprising Al 2 O 3  or SiO 2  and a metal layer. 
     In another embodiment, the catalytic member has a core of a ceramic monolith layer comprising Al 2 O 3  or SiO 2 . 
     As a catalytic material can be used precious metals such as platinum, palladium, rhodium or metal oxides of one or more of the following metals: chromium, iron, molybdenum, wolfram, manganese, cobalt, copper, nickel, zinc. 
     In a further advantageous embodiment, said catalytic unit is inclined relative to said bottom of the combustion chamber. Thus, the catalytic unit is arranged in a second inclined position in the passageway maintaining the exhaust in the catalytic unit for a longer time, either forcing the exhaust downwards or just modifying the natural upwards movement of the exhaust. The catalytic unit is inclined with a given angle relative to the bottom of the combustion chamber. 
     In a first embodiment, the angle is between 0-70°. In a second embodiment, the angle is between 0-60°. In a third embodiment, the angle is between 0-45°. In a fourth embodiment, the angle is between 1-70°. In a fifth embodiment, the angle is between 1-60°. In a sixth embodiment, the angle is between 1-45°. In a seventh embodiment, the angle is between 15-70°. In an eight embodiment, the angle is between 25-60°. In a ninth embodiment, the angle is between 35-45°. 
     In a further advantageous embodiment, said catalytic unit is downwardly inclined for forcing a downwardly movement of the exhaust. The free movement of the exhaust is upwards due to the temperature of the exhaust among other things. By forcing the direction of the exhaust to be downwards in an inclined angle, the exhaust is forced to flow in a direction different from the free movement. Thus, the exhaust will maintain in the catalytic unit for a longer time period whereby the secondary combustion will be increased and fewer particles, VOC and CO will be directed to the environment. 
     In one embodiment, the catalytic unit and the additional member are inclined relative to the bottom of the combustion chamber having a substantially similarly angle. Thus, the isolating members and the additional member are substantially parallel. 
     In a further advantageous embodiment, said isolating members are made of vermiculite. Vermiculite is a natural mineral that expands with the application of heat. Vermiculite is formed by weathering or hydrothermal alteration of biotite or phlogopite. 
     Vermiculite is a fire resistant material which can cope with high temperatures without being damaged and which in addition shows high isolating properties and non-reactivity against contents in the exhaust from solid fuel burning stoves. 
     Alternatively, Calcium Silicate, Perlite and moler earth (diatomaceous earth) can be used for the isolating members. All of which are fire resistant material which can cope with high temperatures as described for Vermiculite. Furthermore, these materials along with Vermiculite are of an insulating nature resulting in the isolating member being an insulating member as well. This further has the advantage that the exhaust travelling through the catalytic unit can be maintained in the high end of the temperature range. This results in combustion automatically along with combustion due to the catalytic member and the system is kept adiabatic. Furthermore, it results in the temperature range between 200° C. and 900° C. can be kept for a longer time period why the catalytic process can be maintained for a longer period of time. Thus, more efficient removal of CO, VOC and particles from the exhaust is achieved. 
     In a further advantageous embodiment, iron and iron alloys including steel, nickel, chromium, cobalt, molybdenum, titanium, wolfram, vanadium and other temperature resistant metals can be used for the isolating members as well as alloys comprising one or more of these metals. The advantages of these metals and the alloys to be used are that they can cope with high temperatures as well as they are relative easily shaped. 
    
    
     
       DESCRIPTION OF THE DRAWING 
         FIG. 1  illustrates a first embodiment of a catalytic unit; 
         FIG. 2  illustrates a solid fuel burning stove comprising a first embodiment of a catalytic unit; 
         FIG. 3  illustrates a close-up of the first embodiment of the catalytic unit as illustrated in  FIG. 2 ; 
         FIG. 4  illustrates a solid fuel burning stove comprising a second embodiment of a catalytic unit; 
         FIG. 5  illustrates a close-up of the second embodiment of the catalytic unit as illustrated in  FIG. 4A ; 
         FIG. 6  illustrates a solid fuel burning stove comprising a third embodiment of a catalytic unit; 
         FIG. 7  illustrates a fourth embodiment of a catalytic unit; 
         FIG. 8  illustrates a fifth embodiment of a catalytic unit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a first embodiment of a catalytic unit  101  comprising a catalytic member  103  and two isolating members  105 . 
     The catalytic member  103  is shaped as a plate and comprises a first wave-like structure  107 . 
     The two isolating members  105   a,b  are plate-like members and are arranged on either side of the catalytic member  103 . The surface  104   a,b  of the isolating members  105   a,b  facing the catalytic member is provided with a second wave-like structure  109   a,b.  The two isolating members each comprise two ends  110   a,b,c,d  and two sides  108   a,b,c,d.    
     Furthermore, one of the isolating members  105   b  comprises a bent edge  111  along the end of the isolating member  105   b.  The bent edge  111  secures the direction of the exhaust from the combustion chamber and into the space  113  between the two isolating members  105   a,b  as illustrated in  FIG. 2 . This isolating member  105   b  further comprises protruding portions  106 , which rests against the other isolating member  105   a,  when the isolating members  105   a,b  are assembled to form a catalytic unit  101 . 
       FIG. 2  illustrates a cross-section of a solid fuel burning stove  115  comprising a first embodiment of a catalytic unit  101 . The catalytic unit  101  is arranged in the passageway  118  between the combustion chamber  117  and the flue  119 . In this illustration, the intended travel direction of the exhaust  121  is shown for illustration purposes alone as a white band moving in the direction of the arrow. The exhaust  121  enters the catalytic unit  101  through the inlet opening  112  and exits through the outlet opening  114 . For illustration purposes and in order to illustrate the inlet opening  112  the right side of the stove is removed in this figure. 
     The combustion chamber  117  comprises a top  123  and a bottom  122  connected by sides  124 . 
     The exhaust  121  travels from the combustion chamber  117  to the catalytic unit  101 , where the bent edge  111  of the catalytic unit  101  prevents the exhaust  121  from moving further up and directs the exhaust  121  in between the isolating members  105   a,b  for contact with the catalytic member before the exhaust  121  exits the catalytic unit  101  and travels towards the flue  119 . 
     In this embodiment, one of the isolating members  105   a  forms the top  123  of the combustion chamber  117 , as well as being an isolating member  105   a  of the catalytic unit  101 . 
     A close-up of the first embodiment of the catalytic unit  101  in use is illustrated in  FIG. 3  which is a close-up of the region defined by the circle A defined in  FIG. 2 . 
     In this close-up, it is illustrated how the catalytic member  103  is arranged between the two isolating members  105   a,b,  with the mutual distance  125  being constant between the first wave-like structure  107  and the second wave-like structure  109   a,b  i.e. that the top of the first waves correlates with the top of the second waves. 
     Furthermore, it is illustrated how the two isolating members  105   a,b  engage with one another at the sides of the catalytic unit  101  due to the protruding portion  106  of one of the isolating members  105   b.    
     The close-up, furthermore, illustrates how the exhaust  121  is able to pass between the catalytic member  103  and the isolating members  105   a,b  on both sides of the catalytic member  10  i.e. both between the first isolating member  105   a  and the catalytic member  103  as well as between the second isolating member  105   b  and the catalytic member  103 . In addition, the exhaust  121  is able to pass through the catalytic member  103 . The catalytic member  103  can for example be a grid. 
       FIG. 4  illustrates a cross-section of a solid fuel burning stove  215  comprising a second embodiment of a catalytic unit  201 . The catalytic unit  201  is arranged between the combustion chamber  217  and the flue  219 . In this illustration, the intended travel direction of the exhaust  221  is shown for illustration purposes alone as a white band moving in the direction of the arrow. For illustration purposes and in order to illustrate the inlet opening the right side of the stove is removed in this figure. 
     The exhaust  221  travels from the combustion chamber  217  to the catalytic unit  201 , where the bent edge  211  of the catalytic unit  201  prevents the exhaust  221  from moving further up and directs the exhaust  221  in between the isolating members  205   a,b  for contact with the catalytic member  203 . 
     In this embodiment, an additional member  227  is arranged after the catalytic unit  201  with regard to the travel direction of the exhaust forcing the exhaust  221  to travel in a space between the additional member  227  and one of the isolating members  205   b  before the exhaust  221  travels towards the flue  219 . 
     Advantageously, the additional member  227  is an additional isolating member, in order to maintain a high temperature of the exhaust  221 . Increasing the travelling path of the exhaust  221  through the catalytic unit  201  reduces the amount of particles CO and VOCs in the final exhaust  221  leaving the stove  215 . 
     In this embodiment, one of the isolating members  205   a  forms the top  223  of the combustion chamber  217 , as well as being an isolating member  205   a  of the catalytic unit  201 . 
     A close-up of the second embodiment of the catalytic unit  201  in use is illustrated in  FIG. 5  which is a close-up of the region defined by the circle B defined in  FIG. 4 . 
     In this close-up, it is illustrated how the catalytic member  203  is arranged between the two isolating members  205   a,b,  with the mutual distance  225  being constant between the first wave-like structure  207  and the second wave-like structure  209   a,b,  i.e. that the top of the first waves correlates with the top of the second waves. 
     The close-up illustrates how the exhaust  221  passes between the catalytic member  203  and the isolating members  205   a,b.  Furthermore, it is illustrated how the direction of the exhaust  221  is changed by the additional member  227  in the passageway  218 . Hereby, the time spent by the exhaust  221  in the passageway  218  before it enters the flue is increased. Thus, the amount of particles VOC and CO in the exhaust  221  is reduced further before it exits the stove via the flue. 
       FIG. 6  illustrates a cross-section of a solid fuel burning stove  315  comprising a third embodiment of a catalytic unit  301 . The catalytic unit  301  is arranged between the combustion chamber  317  and the flue  319 . In this illustration, the intended travel direction of the exhaust  321  is shown for illustration purposes alone as a white band moving in the direction of the arrow. 
     In this embodiment, an additional member  327  is arranged in the passageway  318 , where the additional member  327  is part of the top  323  of the combustion chamber  317 . The exhaust  321  is forced downwards from the combustion chamber  317  between the additional member  327  and one of the isolating members  305   b,  before it interacts with the catalytic member  303  between the two isolating members  305   a,b  of the catalytic unit  301  and enters into the flue  319 . 
     One of the isolating members  305   b  comprises a bent end  311 . In this embodiment, the bent end  311  directs the exhaust  321  out of the catalytic unit  301  and towards the flue  319 . 
       FIG. 7  illustrates a fourth embodiment of a catalytic unit  401  comprising a catalytic member  403  and two isolating members  405   a,b.    
     The catalytic member  403  is integrated with the exposed isolating surface  404   a  of one of the isolating members  405   a  and comprises a first wave-like structure. 
     In a further embodiment, a catalytic member  403  can be provided on the exposed isolating surface  404   b  of the other isolating member  405   b  as well. 
     Furthermore, one of the isolating members  405   b  comprises a bent edge  411  along the end of the isolating member  405   b.  The isolating member  405   b  further comprises protruding portions  406 , which rests against the other isolating member  405   a,  when the isolating members  405   a,b  are assembled to form a catalytic unit  401 . 
       FIG. 8  illustrates a fifth embodiment of a catalytic unit  501  comprising a catalytic member  503  and one isolating member  505 . 
     The catalytic member  503  is shaped as a plate and comprises a first wave-like structure. The isolating member  505  surrounds the catalytic member  503  but leaves an outlet and an inlet opening for the exhaust to enter and exit the catalytic unit  501 .