EP3353470B1 - Device and method for treating exhaust gases in single-chamber combustion systems - Google Patents

Description

Field of application of the invention

The invention relates to the field of combustion technology and relates to a device and a method for treating exhaust gases in single-room firing systems, which can be used, for example, for the combustion of wood or coal in the domestic sector.

State of the art

Single room firing systems are fireplaces that are used to heat rooms and / or provide hot water, are operated with solid fuels and, together with the exhaust system, form the combustion system. This definition is part of the combustion ordinances of the federal states and the Federal Immission Control Ordinance. According to the decision of the European Commission (Official Journal EG L 184 of 17.07.1999), individual room heating systems are "room heating systems that burn solid (...) fuels for use in buildings".
Single room firing systems are nationally and European standardized. They are included as building products in the building regulations list A part 1 and 2 of the German Institute for Building Technology.

Solid fuels are biogenic or fossil solid fuels. The biogenic solid fuels essentially include natural lumpy or non-lumpy wood and pellets made of natural wood. Fossil solid fuels are hard and lignite coke as well as hard and lignite briquettes.

• Leistungsbereich bis 50 kW
• Abgastemperaturen bis 400 °C
• erforderliche Mindestabgasförderdrücke 8 bis 20 Pa
• Abgasmassenströme bis 60 g/s.

Individual room firing systems are essentially characterized by the following parameters:

• Power range up to 50 kW
• Flue gas temperatures up to 400 ° C
• required minimum exhaust gas pressure 8 to 20 Pa
• Exhaust gas mass flows up to 60 g / s.

The individual room firing systems are connected to exhaust systems.

Single room firing systems for burning solid fuels such as wood are increasingly used. In particular, the emission of undesirable gaseous pollutants is a problem that has not yet been adequately resolved.

For the treatment of exhaust gas flows from single-room firing systems with low heat outputs, filters have been developed in recent years in which solid pollutant particles and aerosols are retained and burned when sufficiently high temperatures are reached.
On the other hand, solutions for treating gaseous pollutants have not yet been widely used.

Gaseous pollutants are primarily understood to mean carbon monoxide (CO) and hydrocarbons (HC), which are created when wood is incompletely burned or other fuels used in domestic single-room heating systems. The hydrocarbons include a number of compounds that are solid or liquid at room temperature, but become gaseous at elevated temperatures such as those in flue gas. If these hydrocarbons and CO are released into the environment untreated, they cause harmful and undesirable effects, e.g. health, toxic damage to humans and animals or even odor nuisance effects.

The gaseous pollutants in the exhaust gas from individual room heating systems can be converted into harmless compounds through chemical reactions. As a rule, these are oxidation reactions in which the harmless compounds carbon dioxide and water are formed. For these reactions, the presence of oxygen is necessary, which is contained in the combustion gas supplied to the fireplace, which is mostly air and gets into the fireplace through primary, secondary and other feeds. Furthermore, these reactions require the necessary activation energy, which usually has to be supplied thermally. This means that the reactions require a certain minimum temperature, with the higher the temperatures being, the faster and more complete they are. A necessary reaction time is still required for the most complete possible conversion of the pollutants.

The breakdown and conversion of gaseous pollutants in or after the fireplace depend, in addition to the concentration of the pollutants, above all on the temperature and the residence time of the exhaust gases at these temperatures. The higher the temperature and the longer the residence time, the better the degradation. The temperature in a fireplace differs at different points and usually decreases continuously from the place of combustion to the exhaust gas discharge into the exhaust system. While temperatures of around 1000 ° C or higher can prevail in the vicinity of the flame, smoke gas temperatures of 200 ° C to 300 ° C occur at the flue gas nozzle, where the flue gas escapes into the flue gas system. With a constant temperature in the combustion zone, a certain temperature distribution of the components of the fireplace is established, which depends on the structural design of the fireplace and the materials used and which in turn influences the temperature distribution of the exhaust gas flow.

In addition, the temperature distribution in individual room firing systems is subject to highly dynamic changes, as the temperatures in the combustion zone can fluctuate very strongly. Such fluctuations can be the result of different fuel quality and quantity, fuel application cycles influenced by the user or the manually operated supply air control. It is typical, for example, that after the fireplace has been lit, the fuel burns up until embers form, on which new fuel is then placed again after a while. This creates a lot strong cyclical temperature changes in the fireplace and the flue gas. The pollutant content in the exhaust gas also fluctuates significantly. When lighting the fireplace, when it burns out and shortly after adding fuel to the embers, there are high emission peaks. A high level of pollutants can also arise with very small editions and low temperatures, as well as with little air supply.

The dwell time of the exhaust gas components at a certain temperature is determined by the specific exhaust gas routing in the fireplace, which, in addition to the structural design of the fireplace, also depends on the exhaust gas volume flow and the exhaust gas feed pressure (negative pressure) of the connected exhaust system. If the temperature of the exhaust gas is very low and the dwell time is too short, not enough gaseous pollutants are broken down, so that the concentration of pollutants escaping into the environment is high.

An improvement in pollutant emissions into the environment can be achieved through the use of catalysts.

A catalyst or a catalytically active material is understood to mean a substance that increases the reaction rate of a chemical reaction by lowering the activation energy without being consumed itself. It accelerates the back and forth reaction equally and thus changes the kinetics of the chemical reactions, but not their thermodynamics. A catalyst takes part in the reaction, but is not consumed by it, but can go through these reactions several times.

Depending on the type of catalyst and reactants, they can be divided into homogeneous and heterogeneous catalysts. A heterogeneous catalysis is the reaction of gaseous pollutants on a solid catalyst.

The use of catalysts in single-room heating systems enables a better reaction of the gaseous pollutants, which is achieved by the fact that chemical reactions take place at lower temperatures than in single-room heating systems without the use of catalysts. Has Each catalyst has a specific working window in relation to the respective chemical reaction, which among other things depends on the prevailing temperature. If the temperature is too low, the catalyst will not cause any noteworthy chemical reactions. If the temperature is too high, the catalyst can possibly be damaged by decomposition and / or coarsening of the specific surface ("thermal aging"). It is therefore important to set the catalyst to an optimal working temperature for the respective reaction and to keep it at this working temperature in order to achieve optimal conversion rates of chemical reactions and a breakdown or conversion of gaseous pollutants.

A characteristic of the catalytic converter is the working temperature. The T50 temperature for a chemical reaction is the temperature at which 50% of the conversion, eg of a hydrocarbon, takes place. Likewise, the T10 value describes the temperature at which 10% are converted. At the T90 temperature, 90% of the hydrocarbon, for example, is converted.
The light-off temperature of the catalytic converter is the temperature at which a first measurable chemical reaction takes place. Typically, the course of the reaction is examined comparatively without the use of a catalyst and then the conversion temperatures of the chemical reaction with and without a catalyst are compared.

In addition, the aging of a catalytic converter is investigated by comparing a chemically and / or thermally aged catalytic converter with an unused catalytic converter in the range of the T50 temperature.

For the respective chemical reactions, the working window of the catalytic converter essentially depends on the material composition and the specific surface area of the catalytic converter. The specific surface is described by the surface of the catalyst available for the chemical reactions. Different catalysts can be used for the same chemical reactions, which in turn can each have different working windows. Conversely, in the case of a large number of pollutants in the exhaust gas, it is necessary that the catalytic converter (s) be in a wide range of chemical reactions act with different working windows. In the case of technically complex industrial equipment for exhaust gas aftertreatment, for example, the catalytic converter is brought to the optimum working temperature and kept there by a special heating and cooling device. If the temperature of the exhaust gas fluctuates, this temperature is measured with sensors and the exhaust gas is brought to and maintained at the optimum working temperature by this device. Such devices are not used for single-room firing systems for reasons of cost or because of the technical complexity of such devices.

For the treatment of gaseous pollutants when using single-room firing systems, solutions are already known in which part of the exhaust gas or all of the exhaust gas is passed over or through a catalytic converter. Post-combustion of carbon monoxide and hydrocarbons is usually implemented by installing ceramic or metallic components with catalytic properties in the exhaust system or in the fireplace. This can be, for example, cladding of the furnace walls, baffle and baffle plates, perforated plates, open-cellular foam ceramics or molded bodies such as honeycombs up to beds of regularly or irregularly shaped molded parts such as spheres. These are either made up of materials that themselves have catalytic properties or they are provided with catalytically active materials on the surface.

The previously known solutions cause problems in the design of single-room heating systems with low thermal output, as are now required in modern residential construction due to the significantly improved thermal insulation properties of the building. Small combustion chambers with low fuel requirements, on the other hand, lead to high emissions. The same applies to conventional devices, provided that they are operated in partial load operation due to the low heat requirement.

From the DE 37 05 793 A1 a filter device for gas cleaning, preferably for flue gas cleaning with a dust filter in the raw gas space of the dust filter is known, in which as a dust filter in the filter device elements from an open-pore Foam ceramics are arranged, which are optionally coated with metals, metal oxides or other metal compounds.

It is also known from the DE 102 15 734 A1 a device for the treatment of exhaust gases from solid-fuel fireplaces, in which a ceramic network is installed, through which the exhaust gas flow flows completely or predominantly.

In addition, from the DE 10 2010 007 253 A1 a device for treating exhaust gases from a small combustion system is known which has a catalytically active material, which is a ceramic, and the ceramic has a plurality of openings through which exhaust gases can flow.

From the DE 20 2010 007 246 U1 an apparatus for treating exhaust gas from a small combustion system is known, which consists of a housing with a base and cover and at least two devices arranged in the housing between the base and cover. These each contain a catalytic converter device which has a catalytically active material, the catalytically active material being a ceramic with which an oxidation of the exhaust gases can be catalyzed, and the catalytic converter device has a plurality of openings through which the exhaust gases can flow. The bottom of the apparatus has an opening through which exhaust gas from the small combustion system can be fed into the apparatus. The lid of the apparatus has an opening through which the treated exhaust gas can be discharged.

Known from the DE 20 2008 012 668 U1 is a device for reducing emissions for solid fuel fireplaces, which comprises at least one catalyst element and at least one filter element.

From the DE 10 2013 210 985 A1 Built-in components in small combustion systems are known which mix combustible exhaust gas components with combustion air and have a heat capacity which prevents the temperature from falling below a desired minimum temperature due to a temporarily reduced combustion output.

Known from the DE 196 27 028 A1 is a flue gas filter system for small firings, especially small firings for the combustion of wood, with an exhaust air chimney which has a particle separator which is designed as a regenerable filter with a flue gas fan and which is followed by a regenerable device for chemical reduction of the gaseous pollutants in the flue gas.

In addition, from the DE 10 2006 021 133 A1 a method for cleaning polluted exhaust gas streams is known in which the exhaust gas stream is catalytically cleaned in a reactor with a bed of metal chips contained therein and in which the doped metal chips are heated to a starting temperature before use. Before, with or after the catalytic cleaning, the magnetizable particles of the exhaust gas flow are dedusted in a magnetic field.

The disadvantage is that the known solutions for treating exhaust gases in single-room firing systems are technically complex and cost-intensive and continuous exhaust gas treatment is not possible with regard to the discontinuous mode of operation of the individual-room firing system.

Presentation of the invention

The object of the present invention is to provide a device for treating exhaust gases in single-room firing systems which is technically simple and inexpensive and with which an essentially continuous exhaust gas treatment is implemented with regard to the discontinuous mode of operation of the individual-room firing system.

The object is achieved by the invention specified in the claims. Advantageous embodiments are the subject matter of the subclaims, the invention also including combinations of the individual dependent claims in the sense of an and link, as long as they are not mutually exclusive.

The solution according to the invention consists of a device for treating exhaust gases in single-room firing systems, in which at least one component is arranged in the exhaust gas flow, which consists entirely or partially of a catalytically active material, and in which furthermore in the exhaust gas flow in the direction of flow after the component there is a catalytically active component Material at least one component is arranged, which consists of a material with a higher volumetric heat capacity than the component of a catalytically active material.

According to the invention, the absolute heat capacities resulting from the volume of the components and their specific volumetric heat capacity are in a ratio of component made of catalytically active material: component with higher volumetric heat capacity = 1: 5 to 1:20.

Likewise advantageously, the volume of the component with a higher specific volumetric heat capacity compared to the volume of the component with a catalytically active material has a deviation by a factor of 2.

It is advantageous if the at least one component with a higher volumetric heat capacity has a plate-shaped and / or irregular geometry.

Likewise advantageously, the at least one component with a higher volumetric heat capacity consists of fireclay, mullite, cordierite, vermiculite, aluminum oxide and / or silicon carbide ceramic.

According to the invention, the side of the component with a higher volumetric heat capacity that faces away from the component made of a catalytically active material has a heat-insulating layer. It is advantageous if the heat-insulating layer is made of ceramic fiber insulating material, porous light-weight fire brick and / or vermiculite.

A further advantageous embodiment of the device according to the invention is when the material of the side of the component with a higher volumetric heat capacity, which faces a component made of a catalytically active material, has a region with a higher thermal conductivity than the material of the side of the component with a higher volumetric heat capacity, which faces away from the component made of a catalytically active material.

The side of the component with a higher volumetric heat capacity, which faces the at least one component made of a catalytically active material, advantageously has an emission coefficient> 0.8.

It is also advantageous if the at least one component with a higher volumetric heat capacity has a catalytically active coating.

The at least one component with a higher volumetric heat capacity is advantageously composed of a catalytically active material. It is advantageous if the at least one component made of a catalytically active material has a plate-shaped and / or irregular geometry.

The at least one component made of a catalytically active material is advantageously an open-cell foam ceramic, a ceramic network molded from textile structures, a bed, a plate and / or a plate coated with a catalytically active material.

Furthermore, the at least one component made of a catalytically active material advantageously has a specific volumetric heat capacity of 200 kJ / (K * m ³ ) to 1000 kJ / (K * m ³ ).

The catalytically active material is also advantageously iron, platinum and / or palladium or mixtures of iron, platinum and / or palladium.

The geometry of the at least one component advantageously has a higher volumetric heat capacity compared to the geometry of the at least one component made of a catalytically active material has a deviation by a factor of ≤ 1.5.

And it is also advantageous if, in the device, the at least one component with a higher volumetric heat capacity and the at least one component made of a catalytically active material have essentially the same geometry.

It is also advantageous if the at least one component with a higher volumetric heat capacity and / or the at least one component made from a catalytically active material has a locally different thickness or a continuous change in thickness.

The at least one component with a higher volumetric heat capacity and the at least one component made of a catalytically active material are particularly advantageously arranged parallel to one another. And in particular it is advantageous if the at least one component made of a catalytically active material is arranged at a distance of 3 mm to 50 mm from the at least one component with a higher volumetric heat capacity.

The at least one component with a higher volumetric heat capacity advantageously has a specific volumetric heat capacity of 1200 kJ / (K * m ³ ) to 3500 kJ / (K * m ³ ).

According to the invention, the at least one component with the catalytically active material and the at least one component with the higher volumetric heat capacity are arranged in the exhaust gas duct after a filter component.

In the method according to the invention for treating exhaust gases from single-room firing systems, the exhaust gas flow is passed through a filter component and then at least one component which consists entirely or partially of a material that has a catalytic effect on components of the exhaust gas flow, guided and directly following to a component which consists of a material with a higher volumetric heat capacity than the component made of a catalytically active material and the side of this component that faces away from the component made of a catalytically active material has a heat-insulating layer, and the Exhaust gas flow at and / or around and / or at most partially passed through this component with the higher volumetric heat capacity along in the direction of the exhaust gas outlet.

According to the invention, a single-room combustion system is provided for the first time, which comprises a device for treating exhaust gases, which is characterized by a cost-effective and technically simple structure and with which an essentially continuous exhaust gas treatment is implemented with regard to the discontinuous operation of the individual room combustion system.

With the single-room firing system according to the invention, it is possible, in particular through better utilization of the functionality of a component with a catalytically active material, to significantly reduce pollutant emissions to the environment when solid materials burn off in a single-room firing system.

According to the invention, continuous operation of a component with a catalytically active material is achieved. A catalytically active material is to be understood in the context of the invention as a material which has a catalytic effect on at least one of the constituents of the exhaust gas flow.

When burning solid fuels, fuel exposure-related fluctuations in the exhaust gas temperature occur. These temperature fluctuations in the exhaust gas flow are compensated for by the material-dependent thermal radiation of the at least one component with a higher volumetric thermal capacity. As a result, an essentially constant working temperature of the at least one component with a catalytically active material is achieved and a better mode of operation of this component and of the entire individual room combustion system is achieved.

The compensation of the temperature fluctuations and an essentially constant working temperature are thus achieved over the entire performance range of the individual room combustion system and in particular also during partial load operation of the individual room combustion system.

The at least one component with a catalytically active material can be a highly porous carrier or a cellular structure or a bed which consists of a catalytically active material and / or is coated with this. The component according to the invention made of a catalytically active material is arranged in the exhaust gas flow after a filter component. With such a filter component, solid particles, such as soot, for example, are filtered from the exhaust gas flow.

The component arranged after the filter element made of a catalytically active material can be made up of individual components through which the exhaust gas flows. Typically, the at least one component made of a catalytically active material has a plate-shaped geometry with a large area perpendicular to the direction of the exhaust gas flow and a small expansion in the direction of the exhaust gas flow. However, irregularly shaped components with different thicknesses can also be used. It is also possible that the components deviating from the plate shape are curved and pleated plates, hemispherical shells or cylinder jackets.

According to the invention, the at least one component with a catalytically active material has a low specific volumetric heat capacity of ≤ 1000 kJ / (K * m ³ ), preferably of <500 kJ / (K * m ³ ), particularly preferably from 200 to 400 kJ / ( K * m ³ ). According to the invention, a component with a higher volumetric heat capacity is arranged immediately adjacent to and in the exhaust gas flow after the at least one component with a catalytically active material. This component has a specific volumetric heat capacity of> 1200 kJ / (K * m ³ ), preferably from 1500 to 3500 kJ / (K * m ³ ). In the context of the invention, adjacent is intended to mean the distance between the two sides of the at least one component with a catalytically active material and the at least one component a higher volumetric heat capacity can be understood. This distance can be between 3 mm and 50 mm, in a preferred embodiment the distance is between 5 and 20 mm.

The specific volumetric heat capacity (also called heat storage number) is the volume-related heat capacity of a material and results from the specific, i.e. mass-related heat capacity of a material, multiplied by its density. The unit is kJ / (K * m ³ ). Since the heat capacity in particular is a temperature-dependent value, the values mentioned are based on values at room temperature. Although the heat capacity at the higher operating temperatures is the correct physical quantity for the application according to the invention, since the known temperature dependencies of the heat capacities of most materials are similar, reference is made to the room temperature values for the sake of simplicity.

The specific volumetric heat capacity of a component is calculated from the heat capacity and density of the materials forming the component, based on the total volume of the component. The total volume is defined by the outer delimiting geometry of the component. If the building element is made up of different components and materials, the specific volumetric heat capacity results from the sum of the heat capacities of the individual components and materials, based on the total volume of the building element. The specific volumetric heat capacity of many solid substances is in the range from 1500 to 4500 kJ / (K * m ³ ), which essentially depends on the molar mass and the density of the atomic packing. Low specific volumetric heat capacities below 1500 kJ / (K * m ³ ) can be achieved through porosity or through a cellular structure of the materials, since the gas (mostly air) contained in the pores has a negligibly low volumetric heat capacity. In this respect, the reduction in density as a result of the porosity or cellularity of a material has a very strong effect on the reduction in the specific volumetric heat capacity of a material.

Additional heat absorption and release is realized when the materials contain substances that show a phase change at a certain temperature (so-called PCM = phase change materials), e.g. melt, solidify and / or crystallize. Additional thermal effects can also occur through adsorption / desorption.

The at least one component with a higher volumetric heat capacity is arranged, starting from the direction of the exhaust gas flow, behind the component made of a catalytically active material, advantageously in parallel. This ensures that the entire or at least the major part of the hot exhaust gas first flows through the at least one component with a catalytically active material and only then the at least one component with a higher volumetric heat capacity on and / or around and / or at most partially flows through.

According to the invention, the geometry of the at least one component with a higher specific volumetric heat capacity is essentially the same as the geometry of the at least one component with a catalytically active material, it being possible for the geometric dimensions of the two components to deviate by a factor of ≤15, for example, that a component can have a length and / or width and / or thickness that is up to 1.5 times greater.
The volume of the component with a higher specific volumetric heat capacity can be essentially equal to, greater than or also smaller than the volume of the at least one component with a catalytically active material, with a deviation in the volume of the two components by a factor of ≤2 may be present. The absolute heat capacities (in J / K) resulting from the volume of the components and their specific volumetric heat capacity are in a ratio of 1: 5 to 1:20 (component with a catalytically active material: component with higher volumetric heat capacity). With values above 1: 5 = 0.2, the compensating effect of the components on the temperature distribution is too small. With values below 1:20 = 0.05, the thermal inertia influences the heating of the two Components disadvantageous, so that the working temperature of the catalytic converter is only reached very late.

According to the invention, the treatment of exhaust gases from individual room firing systems is realized in that when the individual room firing system is put into operation, the exhaust gas flow is first passed through a filter component and then through the at least one component with a catalytically active material. When the hot exhaust gas flow is passed through the at least one component with a catalytically active material, the required working temperature of this component is reached quickly due to its very low volumetric heat capacity. After the exhaust gas flow has passed through the at least one component with a catalytically active material, the exhaust gas flow is guided directly to the component arranged downstream with a higher volumetric heat capacity. Due to the high heat capacity of the component with the higher volumetric heat capacity, this component is slowly heated, the function of the catalytic converter element not being influenced by this. As time goes on, the temperatures of the neighboring components are adjusted.

If, on the other hand, the component with a catalytically active material has a high volumetric heat capacity, either alone or in combination with the component with a higher volumetric heat capacity, this leads to a very slow heating of the component with a catalytically active material, so that the working temperature is very late , or, for example, at part load, is not reached at all.

With the individual room combustion system according to the invention and the method it is achieved that when the solid fuel burns up in the individual room combustion system and the associated drop in the exhaust gas temperature due to the heat radiation of the component with a higher heat capacity to the neighboring component with a catalytically active material, the temperature of the component with a catalytic acting material remains at a higher temperature level despite a drop in the exhaust gas temperature. This effect is completely without the supply of further auxiliary energy, for example by an electrical one Heater and achieved without the use of special control and regulation elements, in particular over a period of time that bridges the time span until the next solid fuel application.

Another positive effect of the invention is that if the individual room heating system is overloaded, as can occur due to incorrect operation by the user, e.g. due to excessive fuel consumption, the high heat capacity of the component with the higher volumetric heat capacity also prevents the catalytically active component from overheating too much protects, whereby thermal damage to the catalytically active material is avoided.

The at least one component with a catalytically active material and the at least one component with a higher volumetric heat capacity are arranged in the exhaust gas duct so that when the solid fuel burns, a working temperature for the component with the catalytically active material of 250 ° C to 600 ° C Available.

The at least one component with a higher volumetric heat capacity can be made from different materials and accordingly have different physical and thermal properties. The exact selection and design of the materials, their geometry and arrangement depends on the respective constellation of the individual room combustion system, in particular the size of the combustion chamber and the nominal output, as well as the geometry and lining of the exhaust gas duct. After the selection of the components according to the invention according to their specific volumetric heat capacity, the person skilled in the art can carry out further coordination by designing the volumes and the spacings. Further influencing variables on the effect to be achieved according to the invention consist in the heat transfer coefficient and the thermal conductivity of the materials. It has been shown, however, that the main influencing factor lies in the heat capacities of the two components and their relationship to one another. These in turn depend on the volume of the components and the specific volumetric heat capacities of the materials used.

A first selection of the materials required to achieve the inventive effect of the thermal compensation effect of temperature fluctuations caused by conditions in order to maintain an optimal working window for the catalytically active material can be made in a manner analogous to the relevant design of storage fireplaces, as described, for example, in: H. Hofbauer, T. Schiffert, D. Vogl, Design of Ceramic Storage, Series of publications by the Austrian Tiled Stove Association, Vienna 2002, ISBN 3-901680-07-1 . A person skilled in the art can carry out a more precise coordination with a few experimental measurements of the temperatures on the catalytically active material and / or the CO and HC emissions.

According to the invention, the side of the component with a higher volumetric heat capacity that faces away from the component with a catalytically active material has a thermally insulating material. It is also advantageous if the thermal conductivity of the material on the side facing the component with a catalytically active material is as high as possible. It is also advantageous if the side of the component with a higher volumetric heat capacity that faces the at least one component made of a catalytically active material has a high emission coefficient> 0.8. This can be achieved, for example, by a special coating on the side of the component with a higher volumetric heat capacity. This ensures that the heat stored in the component with a higher volumetric heat capacity is mainly given off only in the direction of the component with a catalytically active material.

It is also possible for the at least one component with the higher volumetric heat capacity to have a catalytically active coating. This can be realized by a surface layer made of catalytically active materials on the surface facing the component with a catalytically active material. It is also possible that the component with a higher volumetric heat capacity is itself a catalytically active component. Iron, platinum or palladium and / or mixtures thereof can be used as catalytically active materials.

Embodiment

The invention is explained in more detail below using an exemplary embodiment.

A wood-fired wood-burning stove as a single-room heating system has a nominal heat output of 7 kW, the exhaust gas temperature being 230 ° C, the exhaust gas delivery pressure 12 Pa and the exhaust gas mass flow 9.7 g / s. The combustion chamber of the stove has a cross-section of 200 x 350 mm. A filter material is installed between the combustion chamber and the flue gas collector. The filter material is an open-cell foam ceramic made of cordierite with a cell size of 10 ppi with the dimensions 200 x 300 x 25 mm and is fixed in a frame. Above the filter in the exhaust gas flow in the direction of flow, a component made of a catalytically active material is installed parallel at a distance of 60 mm. The component made of a catalytically active material is an open-cell foam ceramic made of cordierite with a cell width of 10 ppi with the dimensions 200 x 300 x 20 mm, which is coated with a Pt-Pd catalyst. The catalyst has a T50 conversion temperature for CO of 150 ° C and for HC (measured as propane) of 300 ° C.
A working temperature of 400 ° C is aimed for as high a pollutant breakdown as possible of> 90%. Thermal damage to the catalyst sets in at temperatures above 800 ° C.
The specific volumetric heat capacity of the component with the catalytically active material at room temperature is 350 kJ / (K * m ³ ), the absolute heat capacity 420 J / K. Above the exhaust gas flow in the direction of flow of the component with the catalytically active material, another component in the form of a plate with dimensions of 180 x 280 x 40 mm is installed parallel to this at a distance of 20 mm. The component has a higher volumetric heat capacity than the component with the catalytically active material and consists of silicon carbide ceramic with a specific volumetric heat capacity at room temperature of 1300 kJ / (K * m ³ ). The absolute heat capacity of this component is 2600 J / K. The side of this component facing away from the combustion chamber is coated with a 3 mm thick layer of ceramic fiber insulation. The side of this component facing the combustion chamber has an emission coefficient of 0.85 on. The ratio of the absolute heat capacities of the component with the catalytically active material and the further component is 420: 2600 = 1: 6.2 = 0.16.
When operating the single-room firing system under nominal load, the working temperature of the component with the catalytically active material of 400 ° C is reached after 10 minutes when the solid fuel is applied for the first time. After a further 20 minutes, the burning has taken place, so that further layers of logs are made at intervals of 30 minutes. During the application cycles, the temperature of the component with the catalytically active material fluctuates only between 350 ° C and 450 ° C.
As a result, an essentially continuous exhaust gas treatment is achieved in the single-room combustion system.

Claims (13)

1. Single-chamber combustion installation, comprising a device for the treatment of exhaust gases, in the case of which at least one structural element which is composed entirely or partially of a catalytically active material is arranged in the exhaust-gas flow, and in the case of which, furthermore, at least one structural element which is composed of a material with a higher volumetric heat capacity than the component composed of a catalytically active material is arranged in the exhaust-gas flow downstream, in the flow direction, of the structural element composed of a catalytically active material, characterized in that that side of the structural element with a higher volumetric specific heat capacity which is averted from the structural element composed of a catalytically active material has a heat-insulating layer, and wherein the at least one structural element with the catalytically active material and the at least one structural element with the higher volumetric heat capacity are arranged in the exhaust-gas conduit downstream of a filter structural element, and wherein the absolute heat capacities resulting from the volume of the structural elements and the specific volumetric heat capacity thereof have a ratio of structural element composed of catalytically active material : structural element with higher volumetric heat capacity = 1:5 to 1:20.
2. Single-chamber combustion installation according to Claim 1, in which the volume of the structural element with a higher specific volumetric heat capacity deviates by a factor of ≤ 2 in relation to the volume of the structural element with a catalytically active material.
3. Single-chamber combustion installation according to Claim 1, in which the at least one structural element with a higher volumetric heat capacity has a plate-shaped and/or irregular geometry and/or the at least one structural element with a higher volumetric heat capacity is composed of chamotte, mullite, cordierite ceramic, vermiculite ceramic, aluminium oxide ceramic and/or silicon carbide ceramic.
4. Single-chamber combustion installation according to Claim 1, in which the heat-insulating layer is composed of ceramic fibrous insulation material, porous lightweight refractory brick and/or vermiculite.
5. Single-chamber combustion installation according to Claim 1, in which the material of that side of the structural element with a higher volumetric heat capacity which faces towards a structural element composed of a catalytically active material has a region of higher thermal conductivity than the material of that side of the structural element with a higher volumetric heat capacity which is averted from the structural element composed of a catalytically active material, or that side of the structural element with a higher volumetric heat capacity which faces towards the at least one structural element composed of a catalytically active material has an emission coefficient > 0.8.
6. Single-chamber combustion installation according to Claim 1, in which the at least one structural element with a higher volumetric heat capacity has a catalytically active coating.
7. Single-chamber combustion installation according to Claim 1, in which the at least one structural element with a higher volumetric heat capacity is composed of a catalytically active material.
8. Single-chamber combustion installation according to Claim 1, in which the at least one structural element composed of a catalytically active material has a plate-shaped and/or irregular geometry, or the at least one structural element composed of a catalytically active material is an open-pore foamed ceramic, a ceramic network moulded from textile structures, a bulk material, a plate and/or a plate coated with a catalytically active material.
9. Single-chamber combustion installation according to Claim 1, in which the at least one structural element composed of a catalytically active material has a specific volumetric heat capacity of 200 kJ/(K*m³) to 1000 kJ/(K*m³), or the catalytically active material is iron, platinum and/or palladium or mixtures of iron, platinum and/or palladium.
10. Single-chamber combustion installation according to Claim 1, in which the at least one structural element with a higher volumetric heat capacity and the at least one structural element composed of a catalytically active material have a substantially identical geometry, or the at least one structural element with a higher volumetric heat capacity and/or the at least one structural element composed of a catalytically active material has a locally different thickness or a continuous thickness variation.
11. Single-chamber combustion installation according to Claim 1, in which the at least one structural element with a higher volumetric heat capacity and the at least one structural element composed of a catalytically active material are arranged in parallel with respect to one another, or the at least one structural element composed of a catalytically active material is arranged with a spacing of 3 mm to 50 mm to the at least one structural element with a higher volumetric heat capacity.
12. Single-chamber combustion installation according to Claim 1, in which the at least one structural element with a higher volumetric heat capacity has a specific volumetric heat capacity of 1200 kJ/(K*m³) to 3500 kJ/(K*m³).
13. Method for the treatment of exhaust gases of single-chamber combustion installations, in which method the exhaust-gas flow is conducted through a filter structural element and subsequently at least through a structural element which is composed entirely or partially of a material which has a catalytic action on constituents of the exhaust-gas flow, and directly subsequently to a structural element which is composed of a material with a higher volumetric heat capacity than the structural element composed of a catalytically active material, and that side of said structural element which is averted from the structural element composed of a catalytically active material has a heat-insulating layer, and the exhaust-gas flow is conducted along onto and/or around and/or at most partially through said structural element with the higher volumetric heat capacity in the direction of the exhaust-gas outlet.