Method and device for preventing fine dust from wood heating and pellet heating systems

Abstract

The invention relates to a device (10) for treating and in particular for cleaning gases (1) arising during the combustion of biomass, the device (10) comprising a line (2) for conducting the gases (1), through which line the gases (1) can be conducted in a flow direction, and the line (2) comprising a supply section (2a) via which the gases (1) can be supplied to the line (2), as well as a discharge section (2b) through which the gases can be discharged from the line 2, characterized in that a heating device (4) is arranged between the supply section (2a) and the discharge section (2b), which is suitable for heating gases passing through this heating device (4) in the flow direction.

Description

[0001] Method and device for preventing fine dust from wood and pellet heating systems

[0002] Description

[0003] The present invention relates to a method and a device for preventing fine dust and aerosols (in the form of smoke) during the combustion of wood, or in general of biomass and other solid materials in various forms, such as pellets, logs, wood chips and the like.

[0004] The flue gases produced during complete combustion consist only of carbon dioxide (CO2) and water vapor (H2O) and are therefore transparent, or rather invisible. If the flue gas temperature is below the water vapor dew point, white clouds form due to condensation.

[0005] If combustion is incomplete, gray smoke is produced, indicating the presence of various gaseous and / or aerosol hydrocarbons. These reduce combustion efficiency and are also harmful to the environment, particularly in the form of particulate matter and aerosols, which are lung-permeable and often carcinogenic.

[0006] Incomplete combustion is caused by a lack of oxygen and / or excessively low temperatures in the combustion zone. This is particularly the case during the ignition phase, even in modern furnaces that otherwise guarantee complete and clean combustion during nominal operation. In addition to smoke, a strong odor is also produced, which is a further indication of the aromatic hydrocarbons being emitted.

[0007] DE 40 12 119 A1 describes a device for purifying polluted air through catalytic combustion. This document discloses a device in which polluted air is fed into the device via a fan. This air is heated by a heater and then conveyed to an oxidation reactor consisting of at least three catalysts. The heater upstream of the oxidation reactor can be an electric heater.

[0008] DE 102005 049 096 A1 discloses an exhaust gas purification device for fuel-generating units. This device comprises a filter chamber into which exhaust gases are fed via an inlet opening, as well as an outlet opening. A particulate filter is provided within this chamber to filter out particles.

[0009] EP 0 585 047 A2 describes a purification system for exhaust emissions from internal combustion engines. Exhaust gases are introduced via a feed device and then electrically discharged by a plasma field generated by electrodes. The discharged exhaust gases are then purified in a zone made of catalytic material.

[0010] EP 0630 681 A1 discloses a method for removing unwanted impurities from a gas.

[0011] The present invention is therefore based on the object of improving the cleanliness of the gases produced during combustion. This is achieved according to the invention by the subject matter of the independent patent claims. Advantageous embodiments and further developments are the subject matter of the dependent claims.

[0012] A device according to the invention for treating gases produced during the combustion of biomass comprises a line and, in particular, a pipeline (for conducting the gases), which is therefore suitable and intended for conducting the gases. The gases can be guided through this line in a flow direction. Furthermore, the line has a feed section, via which the gases can be fed to the line, and a discharge section through which the gases can be discharged from the line. According to the invention, a heating device is arranged between the feed section and the discharge section, which heating device is suitable and intended for heating the gases passing through this heating device in the flow direction.

[0013] Preferably, the biomass is taken from a group of biomasses which includes wood, wood chips, pellets, straw and the like.

[0014] Preferably, the heating device is designed such that it does not reduce, or does not significantly reduce, the flow cross-section of the gases flowing through the line. A non-significant reduction is understood to mean a reduction of less than 50%, preferably less than 30%, preferably less than 25%, preferably less than 20%, preferably less than 15%, preferably less than 10%, and particularly preferably less than 5%.

[0015] Preferably, the heating device is suitable and intended to ignite and / or burn the gases passing through it at least temporarily and / or at least locally.

[0016] In a further advantageous embodiment, the heating device is arranged and / or configured such that it does not, or only slightly, influence the flow velocity of the gases passing through it. A non-significant influence is understood to mean that the flow velocity of the gases passing through the heating device is changed and in particular reduced by less than 20%, preferably changed and in particular reduced by less than 15%, preferably changed and in particular reduced by less than 10%, and particularly preferably changed and in particular reduced by less than 5%.

[0017] Particularly preferably, this heating device is suitable and intended to heat the gases to a temperature of more than 400 °C, preferably more than 600 °C and preferably more than 800 °C.

[0018] This heating preferably occurs by convection. Particularly preferably, the heating occurs in such a way that the gases ignite. Preferably, at least two, and preferably several, local ignitions of the gases occur. These ignitions can combust other residues contained in the gases, such as, in particular, but not exclusively,

[0019] Particularly preferably, the heating device is suitable and intended to heat the gases flowing through it locally, i.e., in specific sections. Preferably, the gases are heated throughout the entire flow cross-section.

[0020] In a further preferred embodiment, the heating device is an electrically operated heating device. It is possible to provide one or more heating wires, which effect the heating of the gases flowing past them or passing through them.

[0021] It would also be possible for these heating wires to be designed in such a way that the gases heat up locally in a specific way. For example, heating wires could be provided that have coils in certain areas where locally stronger heating occurs.

[0022] In addition, however, it would be conceivable for the heating device to have a fuel-operated heater or heating system.

[0023] The heating device described is installed in particular in areas where flue gases occur, for example downstream of an incineration plant or in connection with biomass utilization plants.

[0024] Particularly preferably, the heating device is arranged at least in sections within the line.

[0025] Particularly preferably, the heating device comprises at least one heating wire which extends at least partially through an interior space of the line. Particularly preferably, this heating wire extends at least in a direction which is transverse and in particular perpendicular to the flow direction of the gases. Particularly preferably, this heating wire extends transversely and in particular perpendicular to a flow direction of the gases. In a further preferred embodiment, the heating device comprises a plurality of heating wires which preferably extend through an interior space of the line. These heating wires are preferably arranged parallel to one another. Thus, the heating wires as a whole can form a type of grid through which the gases pass.

[0026] Particularly preferably, several wires are arranged in series. The spacing of these wires perpendicular to their direction of extension is preferably greater than 2 mm, preferably greater than 3 mm, and particularly preferably greater than 4 mm. This spacing is preferably less than 50 mm, preferably less than 40 mm, preferably less than 30 mm, and particularly preferably less than 20 mm.

[0027] More preferably, this heating wire is made of a material selected from a group of materials including stainless steel, tungsten, Kanthai, mixtures of these materials, and the like.

[0028] Preferably, at least one heating wire has a cross-section that is smaller than 4mm 2 , preferably smaller than 3mm 2 and especially preferably smaller than 2mm 2 .

[0029] Preferably, at least one heating wire has a cross-section that is greater than 0.005mm 2 , preferably larger than 0.007mm2 and particularly preferably greater than 0.01 mm 2 .

[0030] The choice of these cross-sections depends primarily on the applied voltage and the required power. The number of wires used can also be a criterion.

[0031] Preferably, the energy source for heating the heating wire may be an energy source selected from a group including direct current energy sources or alternating current energy sources.

[0032] In a further advantageous embodiment, a heat exchanger device and / or a heat storage device is arranged in the line, wherein this heat exchanger device and / or heat storage device is preferably arranged downstream of the heating device in the direction of gas flow. In the following, the term "heat exchanger device" is used instead of "heat exchanger device" and / or "heat storage device."

[0033] This heat exchanger device is preferably designed such that it at least temporarily heats the gas passing through it. This heat exchanger device is preferably designed such that it at least temporarily ignites the gas passing through it. This heat exchanger device is preferably designed such that it at least temporarily ignites the gas passing through it locally, in particular by means of at least one and preferably a plurality of locally generated flames.

[0034] Preferably, this heat exchanger device is therefore designed such that the gas flowing in the line can pass through it. Preferably, this heat exchanger device is designed such that, above a certain temperature, flames can form on or in it, which further combust the passing gas.

[0035] Particularly preferably, the heat exchanger device is an at least partially porous element, whereby the gases can pass through this heat exchanger device. Particularly preferably, this heat exchanger device is made of a material selected from a group of materials including porcelain, alumina, mullite, and ceramic.

[0036] Ceramic is a particularly suitable material because it is heat-resistant up to very high temperatures and can therefore also withstand high temperatures of gases.

[0037] In a further advantageous embodiment, the device comprises a supply temperature detection device which is suitable and intended for detecting a temperature of the gas in the direction of gas flow, in particular upstream of the heating device. In particular, this supply temperature detection device is suitable for detecting a temperature of a gas flowing past it.

[0038] It would also be possible to provide several first supply temperature detection devices, which are arranged, in particular, at different areas in the cross-section of the line. In this way, an average temperature of the gas can also be detected (before it reaches the heating device).

[0039] In a further advantageous embodiment, the device comprises a discharge temperature detection device which is suitable and intended to detect a temperature of the gas in the flow direction of the gas downstream of the heating device and preferably also downstream of the heat exchanger device.

[0040] Here, too, several temperature detection devices can be provided, which can be distributed over a cross-section of the line in order to also detect local temperatures and / or an average temperature.

[0041] In a further preferred embodiment, the device comprises a further temperature detection device, which is particularly suitable and intended for detecting the temperature of the gas between the heating device and the heat exchanger device. Here, too, several further temperature detection devices can be provided, which enable local detection of the temperature and / or the determination of an average temperature.

[0042] In a further preferred embodiment, the device comprises at least one sensor device suitable and intended for determining the moisture content of the gas flowing through the line. This sensor device is preferably arranged upstream of the heating device in the direction of gas flow. This embodiment is based on the idea that the moisture content of the gas also affects the combustion temperature. In addition, one or more sensor or analysis devices can also be provided, which are suitable and intended for analyzing the composition of the gases flowing through.

[0043] Preferably, a sensor device is provided which is suitable and intended to determine a moisture content of the fuel.

[0044] In a preferred embodiment, the device comprises a control device that controls the heating device based on a measured value detected by the supply temperature detection device and / or based on a measured value detected by the discharge temperature detection device. This control device could, for example, activate the heating device if it is determined that the temperature of a supplied gas is too low, for example, below 800°C.

[0045] The discharge temperature detection device can determine whether the gas has a sufficiently high temperature, particularly after passing through the heat exchanger, and / or is igniting. If this is the case, it can be concluded that the heat exchanger is already causing combustion of the fuel gases. In this case, the heating device can be shut down.

[0046] Particularly preferably, the heat exchanger device is also suitable and intended to cause ignition and / or combustion of gases passing through it. It is possible that spontaneous combustion may occur once the heat exchanger device and / or the gases have reached a certain minimum temperature.

[0047] In a further preferred embodiment, the heat exchanger device has a solid-state structure and is particularly designed as a ceramic and / or porous body. This heat exchanger device is particularly preferably arranged entirely within the line. It is particularly preferred that all gas is conducted through the heat exchanger device. The porosity of this solid-state structure is preferably at least 50%, preferably more than 70%.

[0048] In a further preferred embodiment, the heat exchanger device comprises a catalyst. In a further preferred embodiment, the heat exchanger device comprises a solid-state structure with a coating. This coating, in particular, acts as a catalyst.

[0049] Particularly preferably, the heat exchanger device has a length in the direction of extension of the line and / or in the flow direction of the gases which lies between 5 mm... and 50 mm.

[0050] Particularly preferably, the heating device also has a length in a flow direction of the gases that lies between 5 mm and 50 mm. In a further preferred embodiment, a structure of the heat exchanger device is selected from a group of structures that includes honeycomb structures, foam-like structures, beds, combinations thereof, and the like.

[0051] Particularly preferably, the heat exchanger device has a porosity of between 40% and 90%.

[0052] In a further advantageous embodiment, the device comprises a second heat exchanger device, which is particularly preferably arranged downstream of the first heat exchanger device. This can be, for example, a gas-liquid heat exchanger device. This second heat exchanger device can be used to utilize the high temperature of the now purified flue gases, for example, to heat water.

[0053] The present invention is further directed to a method for treating gases produced during combustion of biomass, wherein the gases are guided and / or transported through a line and the gases are fed through a feed section of the line and are discharged from the line via a discharge section.

[0054] Preferably, a heating device is arranged between the supply section and the discharge section, which heating device at least temporarily heats the gases passing through this heating device in the flow direction.

[0055] This heating device is particularly preferably designed such that it at least temporarily ignites these gases. Particularly preferably, this causes local ignition of the gases (relative to the cross-section of the line). This heating device is preferably designed such that it enables or carries out heating of the gases passing through it to over 800°C.

[0056] Particularly preferably, a heat exchanger device further heats the gases at least temporarily. Preferably, the heat exchanger device combusts the gases at least temporarily. In another preferred method, a temperature of the gases is determined, in particular before they reach the heating device. Particularly preferably, a temperature of the gases is determined after they have passed through the heat exchanger device.

[0057] Preferably, the temperature of the gases is determined after they have passed through the heating device and before they reach the heat exchanger device. In this way, the temperature can be measured at three points, and these temperature values ​​can be used to control the heating device.

[0058] Preferably, the heating device is controlled and / or regulated with regard to its performance.

[0059] Preferably, the heat exchanger device is a passive device that is not itself heated or electrically operated. Heating of this heat exchanger device occurs primarily due to the gases passing through it. However, the heating is so high that the heat exchanger device is also capable of igniting the gases, at least temporarily, even if the heating device is no longer activated at that time.

[0060] The present invention thus relates to a method and a device that solves the above-mentioned problems through a system consisting of an electrically heated wire and a ceramic porous solid structure. During an ignition phase, the electric heater is activated, heating the wire to approximately 800°C. The escaping flue gases contain a sufficient amount of oxygen and a calorific value sufficient for a stable flame.

[0061] This preferably reaches a temperature, or rather, an ignition source, that is preferably present with the hot wire. This ignites the flue gases, creating a flame that results in almost complete combustion of hydrocarbons. It is also possible that no flame forms, but rather a flameless thermal oxidation of the exhaust gases takes place. Above the heated wire, or further in the direction of flow, is the solid-state structure (referred to above as the heat exchanger device), which preferentially accumulates the generated heat. Once the accumulated heat and the temperature are sufficiently high, the electric heater can be switched off.

[0062] The ignition of the flue gases now takes place in the solid-state structure, i.e., the heat exchanger device described above. In both cases, the flue gases, after passing through the solid-state structure, are clean, fully combusted, free of aerosols or particulate matter, and odorless. They can also be further used for heat dissipation.

[0063] Once the ignition phase is complete, the flue gases may have already been completely combusted before reaching the wire, eliminating the need for further electric heating. The hot flue gases continue to flow through the solid structure, maintaining a high temperature. The stored heat allows for shorter combustion interruptions, which would otherwise produce unburned carbon, to be eliminated without reactivating the electric heating.

[0064] The heating device or electric heater described above can be provided using commercially available heating wires, heating rods, or similar devices. Direct current or alternating current can be used. The heating time is preferably very short, especially no longer than 5 minutes, so that power consumption is minimal.

[0065] It is advantageous that this heating system does not require heating the entire flue gas to, for example, 800°C. The heating system is preferably used only to generate the hot spots, which then serve as ignition sources. The remaining energy required to heat the flue gases to 800°C comes primarily from the flue gases themselves, particularly from the chemical energy of the hydrocarbons they contain.

[0066] The present invention preferably also includes a solid-state structure, and in particular the heat exchanger device described above. This serves to store the generated heat and act as an ignition source itself, thus minimizing the required heating time and the electrical energy consumed. A structure made of honeycomb, solid foam, loose fill, or a combination thereof can be used for the heat exchanger device. All heat-resistant materials are suitable, especially various ceramic materials, but also various metals or natural materials. This solid-state structure can also serve as a support for heating elements.

[0067] The pressure loss due to the solid structure should preferably be low to enable trouble-free operation even in furnaces with natural draft. The pressure loss is preferably less than 30%, preferably less than 25%, preferably less than 20%, and particularly preferably less than 15%, and particularly preferably less than 10% (compared to a pressure loss without the solid structure).

[0068] The porosity is preferably sufficiently high, preferably at least 40%, advantageously over 60%. The free-flowing channels for the gas, or the equivalent diameters, are preferably at least 2 mm, particularly advantageously at least 5 mm.

[0069] This solid structure or heat exchanger can also act as a filter for inorganic dust, especially if a fine-pored foam or fine-grained packing is used. In this case, it is advantageous to provide a means for regular cleaning.

[0070] In a preferred embodiment, the heat exchanger device is removable from the line, particularly for cleaning purposes. However, it would also be conceivable for the device to have a pressurizing device that offers the possibility of applying a cleaning agent to the heat exchanger device, particularly when installed in the line.

[0071] For more precise control of the proposed system, at least two temperature measurements are preferably provided: a first temperature T 1 is preferably measured upstream of the electric heater or heating device (in the direction of flow), and a second temperature T 2 is preferably measured downstream of the solid-state structure or heat exchanger device. If, during an ignition phase, the temperature T 1 is below a predetermined limit (e.g., 800°C), the electric heater is preferably switched on. If the temperature T 2 is above the limit, the heater is preferably switched off again.

[0072] This means that the conditions for complete combustion have been met. The same applies if the temperature T1 has exceeded a threshold. The threshold temperature TG is preferably the minimum temperature at which the flue gases ignite.

[0073] This depends on several factors, such as the concentrations of CO, methane, and other hydrocarbons, excess air, etc. Ultimately, these factors depend on the fuel used and the furnace design, or rather, the furnace control system.

[0074] Preferably, additional sensor devices are used to measure parameters selected from a group of parameters including a concentration of CO, a concentration of methane, a concentration of hydrocarbons, and the like. Particularly preferably, several of these concentrations are measured.

[0075] A value of 800°C is sufficiently high in any case. For some fuels with higher hydrogen content, it can be lower, or significantly lower.

[0076] Further advantages and embodiments are shown in the attached drawings, which show:

[0077] Fig. 1 is a schematic drawing showing all the main components of the system;

[0078] Fig. 2a Formation of local small flames, directly at the heating wire (if T 1 and T2 are smaller than a limit temperature);

[0079] Fig. 2b Formation of the local small flames at the exit of the solid structure (if T 1 is smaller than the limit temperature TG and T2 is larger than TG); and; and

[0080] Fig. 3 shows a comparison of the efficiency of the invention. In Fig. 1, the relatively cold, unburned (flue) gases 1 come from a combustion chamber, which is not shown here. These are fed via a feed section 2a to a line 2, which serves to transport these gases 1.

[0081] The gases flow upwards and come into contact with the glowing heating wire 42, which here serves as an electrical heater or heating device 4 or forms a component of this heating device.

[0082] At this point, the gases ignite and form several small local flames F (see also Fig. 2a). These hot gases 1 continue to flow through the solid-state structure or the heat exchanger device 6, heating it. The completely combusted gases 1a continue to flow toward a heat consumer, which is also not shown here, or through the discharge section 2a out of the line.

[0083] Reference numeral 12 refers to a discharge temperature detection device. If this temperature measuring point 12 measures a temperature T2 above a predetermined limit value TG (e.g., 800°C), this means that the solid-state structure or the heat exchanger device 6 is fully heated and that the electric heater or the heating device 4 is no longer required.

[0084] The small local flames now arise in the solid-state structure or heat exchanger device 6, and particularly at its outlet, as shown in Fig. 2b. These small local flames are generally understood to be oxidizing gases. These can also be understood as flameless thermal oxidation.

[0085] If the supply temperature detection device 8 or temperature measuring point 8 measures a temperature T 1 above the specified limit value TG, combustion was already complete in the combustion chamber, so that no local flames F can develop and the electric heater 2 is unnecessary. In this case, the heating device 4 can be deactivated.

[0086] Fig. 3 shows a representation of a particle concentration (N / cm 3). The upper curve K2 indicates the number of particles without use of the invention, i.e., in particular, without a heating wire. The lower curve K1 shows the particle concentration when using the invention, i.e., when using a heating wire. It can be seen that the particle concentration without use of the invention is sometimes a factor of 5 or more higher than the particle concentration without use of the invention.

[0087] The applicant reserves the right to claim all features disclosed in the application documents as essential to the invention, provided they are novel, individually or in combination, over the prior art. It is further noted that the individual figures also describe features that may be advantageous in and of themselves. The skilled person will immediately recognize that a specific feature described in a figure may be advantageous even without adopting additional features from that figure. Furthermore, the skilled person will recognize that advantages may also arise from a combination of several features shown in individual or different figures.

[0088] It is further noted that the features described above for the device also apply to the method likewise described. Therefore, if a feature has been described with reference to the device, it is simultaneously disclosed that this feature also applies or can apply to the method likewise described. Conversely, for each feature described for the method, it is also disclosed that corresponding devices are available with respect to the device, which are suitable for carrying out the steps required or advantageous for the method.

[0089] List of reference symbols

[0090] 1 Unburned (smoke) gases containing hydrocarbons (aromatics, aerosols, particulate matter) 1a Completely burned (smoke) gases

[0091] 2 lines

[0092] 2a Supply section of line 2

[0093] 2b Discharge section of line 2

[0094] 4 Heating device 6 Heat exchanger device, solid structure

[0095] 8 Feed temperature measuring device

[0096] 12 Discharge temperature measuring device

[0097] F Small local flames caused by the ignition of the flue gas T1 first temperature measured with the first temperature measuring device 8

[0098] T2 second temperature measured with the first temperature measuring device 12

Claims

Patent claims 1. Device (10) for the treatment and in particular for the purification of gases (1) produced during the combustion of biomass, wherein the device (10) has a line (2) for conducting the gases (1), through which the gases (1) can be conducted in a flow direction (S), and the line (2) has a feed section (2a) via which the gases (1) can be fed to the line (2), and a discharge section (2b) through which the gases can be discharged from the line (2), characterized in that a heating device (4) is arranged between the feed section (2a) and the discharge section (2b), which heating device is suitable for heating the gases passing through this heating device (4) in the flow direction.

2. Device according to claim 1, characterized in that the heating device (4) is an electrically operated heating device (4).

3. Device according to at least one of the preceding claims, characterized in that the heating device has at least one heating wire (42) which extends at least partially through an interior space (2a) of the line (2), wherein preferably this at least one heating wire (42) causes a local heating and preferably at least temporarily a local ignition of these gases.

4. Device according to at least one of the preceding claims, characterized in that a heat exchanger device (6) is arranged in the line (2), wherein preferably this heat exchanger device (6) is arranged downstream of the heating device (4) in the flow direction of the gas and wherein this heat exchanger The device is particularly preferably suitable and intended to cause a particularly local ignition of the gases passing through it.

5. Device according to at least one of the preceding claims, characterized in that the device has a supply temperature detection device (8) which is suitable and intended to detect a temperature of the gas in the flow direction of the gas upstream of the heating device (2) and / or the device has a discharge temperature detection device (12) which is suitable and intended to detect a temperature of the gas in the flow direction of the gas downstream of the heating device (2) and preferably downstream of the heat exchanger device (6).

6. Device according to at least one of the preceding claims, characterized in that the heat exchanger device has a catalyst and in particular the heat exchanger device (6) has a solid structure with a coating which acts as a catalyst.

7. Device according to at least one of the preceding claims, characterized in that the device has a control device which controls and in particular regulates the heating device on the basis of a measured value detected by the supply temperature detection device (8) and / or on the basis of a measured value detected by the discharge temperature detection device (12).

8. Device according to at least one of the preceding claims, characterized in that the heat exchanger device (6) has a solid structure and is designed in particular as a ceramic and / or porous body.

9. Device according to at least one of the preceding claims, characterized in that a structure of the heat exchanger device consists of a group of structures. which contains honeycomb structures, foam-like structures, fills, combinations or the like.

10. A method for treating and in particular purifying gases (1) produced during combustion of biomass, wherein the gases (1) are guided through a line, and the gases (1) are fed through a feed section (2a) of the line (2) and are discharged from the line (2) via a discharge section (2b), characterized in that a heating device (4) is arranged between the feed section (2a) and the discharge section (2b), which heating device at least temporarily heats the gases passing through this heating device in the flow direction.

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