Method for dry filtration of a gas stream carrying foreign matter and filtration device for purifying raw gas carrying foreign matter - Patents.com

Abstract

The present invention relates to a method and apparatus for dry filtering of a gas stream carrying foreign matter, particularly in a filtering device for purifying exhaust gases generated in additive manufacturing techniques, in which a raw gas stream (44) containing foreign matter is introduced into a raw gas space (15) of a filter unit (12) having at least one filter surface separating the raw gas side from the purified gas side, and an oxidant is supplied downstream of the filter surface to a reaction zone (24) on the raw gas side of the filter surface, whereby materials dropped from the filter surface and / or foreign matter contained in the raw gas stream react with the oxidant in the reaction zone (24) to form oxide-containing foreign matter.

Description

[Technical Field]

[0001] The present invention relates to a method for dry filtration of a gas stream carrying contaminants, and to a filtration device for purifying raw gas carrying contaminants. [Background technology]

[0002] When cleaning gases carrying highly flammable foreign particles or substances, such as occurs in systems for additive manufacturing of workpieces made of metal (e.g., in the laser sintering of workpieces made of titanium or aluminum alloys), there is a risk of uncontrolled combustion of the exhaust gas. This risk is particularly great when such highly flammable foreign particles are deposited on the filter surface and accumulate during the process. Attempts have been made to neutralize these risks by pre-coating the filter surface with an inert filter aid such as CaCO3, as in the configuration shown in Patent Document 1, or by adding such auxiliary substances to the raw gas to be cleaned. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2012 / 032003A1 Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to prevent or suppress raw gas combustion by means of a dry filter when filtering raw gases containing combustible foreign matter, in particular when filtering exhaust gases produced in additive manufacturing techniques. [Means for solving the problem]

[0005] In a method for dry filtering a gas stream carrying foreign matter, particularly in a filtering device for purifying exhaust or waste gases generated in additive manufacturing techniques, according to the present invention, a raw gas stream containing foreign matter is supplied to a raw gas space of a filter unit having at least one filter surface separating the raw gas side from the purified gas side. Furthermore, an oxidizing agent is supplied downstream of the filter surface to a reaction zone located on the raw gas side of the filter surface. The oxidizing agent is supplied so that the foreign matter contained in the raw gas stream and / or in the material removed (cleaned) from the filter surface reacts with the oxidizing agent in the reaction zone to form oxide-containing foreign matter.

[0006] The present invention proposes a method and correspondingly designed filtering device for specifically inducing spontaneous oxidation of highly reactive or even highly reactive foreign particles in exhaust gases, such as metal-containing particles in the exhaust gases of additive manufacturing machines, such as laser sintering machines. The high reactivity of such foreign particles with oxidizing agents, such as oxygen or air—the reason why dry filtration of such exhaust gases is problematic in practice—is targetedly utilized to induce a spontaneous reaction between the foreign particles and the oxidizing agent. Surprisingly, this spontaneous reaction can be initiated targetedly by appropriate control of the supply and / or discharge of the oxidizing agent, and by other means, if necessary, and its course can be maintained under control so that uncontrolled reactions between the foreign particles and the oxidizing agent can be avoided. The proposed approach effectively dissipates the heat generated during the reaction, eliminating the risk of uncontrolled combustion or explosion.

[0007] The basic idea of ​​the present invention is not to inert easily combustible foreign substances contained in the raw gas, but rather to render them harmless by deliberately initiating and carrying out a controlled conversion (i.e., chemical reaction) of these combustible foreign substances into an oxidized structure, in which they are generally less reactive or inert, are no longer flammable, and further handling of these foreign substances no longer requires special precautions.

[0008] However, care must be taken to ensure that the spontaneous oxidation reaction proceeds in a controlled manner. This can be achieved by appropriately supplying the oxidizing agent to a predetermined reaction zone containing material shed from the filter surface and thus containing the foreign matter, and / or by other means of removing the oxidizing agent from the reaction zone. It has been found that the course of the normally highly exothermic oxidation reaction can be better controlled if the oxidizing agent is not only supplied to the reaction zone, but also flows through the reaction zone. In this case, the oxidizing agent is supplied to the reaction zone at a first location or zone (inlet) and flows through the reaction zone until it re-exits the reaction zone at another location or zone (outlet), unless the oxidizing agent is consumed by reaction with the foreign matter-containing material during its flow through the reaction zone. This makes it possible to supply an excess of oxidizing agent to the reaction zone in a targeted manner, as is necessary to spontaneously initiate or maintain a controlled level of the desired reaction for the formation of oxide-containing foreign matter. The flow of oxidizing agent through the reaction zone allows for precise control of the course of the oxidation reaction. Once the oxidant flow is initiated, it proceeds naturally but in a controlled manner and can be well controlled by adjusting the intensity of the oxidant flow and, in some cases, by adjusting the composition of the oxidant flow.

[0009] In the case of spontaneous oxidation, the desired reaction to form oxide-containing inclusions essentially occurs without the supply of activation energy from an energy source such as an ignition source or a heat source. Oxidation can already be initiated when the oxidizing agent comes into contact with materials that fall off the filter surface during cleaning, are present in the reaction zone, or enter the reaction zone.

[0010] The oxidant may be air or an oxygen-containing gas. Other substances, such as inert gases such as nitrogen or noble gases, may be mixed with the oxidant to form the oxidant stream. For example, air can be used to form the oxidant stream, or an oxygen-depleted mixture having an oxygen content of 5 to 21 volume percent can be used. The concentration of oxidant in the oxidant or oxidant stream is selected to be sufficiently high to allow spontaneous reaction of the foreign material-containing material in the reaction zone to form oxide-containing foreign material.

[0011] The expression "downstream of the filter surface on the raw gas side of the filter surface" is intended to indicate that the reaction zone is downstream of the raw gas space with respect to the transport of foreign matter accumulated on the filter surface and dislodged from the filter surface during the cleaning cycle (e.g., by applying a pressure pulse to the filter surface). Thus, the material dislodged from the filter surface is transported to the reaction zone. In particular, the reaction zone should be separated from the raw gas space, and in particular downstream of the raw gas space. If an oxidizing agent is first supplied to the downstream reaction zone but not to the raw gas space or to the area upstream of the raw gas space, these areas remain oxidizing agent-free, so that the oxidation of the dislodged foreign matter-containing material does not affect the process environment in which the actual filtering of the raw gas is performed by the introduction of the oxidizing agent. In particular, the filtering process or the working process in which the exhaust gas to be filtered is produced is largely carried out under inert conditions and is not disturbed by the oxidation process. Maintaining an inert environment in the raw gas space can further be ensured by temporarily separating the reaction zone from the raw gas space during the supply of the oxidizing agent, in particular by separating it gas-tightly.

[0012] As explained above, when the material removed from the filter surface reacts with the oxidizing agent, it is advantageous to actively remove unused oxidizing agent from the reaction zone. In this way, an appropriate surplus of oxidizing agent can be provided, and thus a controlled progression of the oxidation reaction can be achieved. This means that the objective is not necessarily to remove only the reaction products, especially oxide-containing foreign substances formed during the reaction, and possibly unconverted or incompletely converted removed material, from the reaction zone after a more or less complete chemical conversion has occurred. Rather, the oxidizing agent not consumed during the reaction should be removed during the course of the oxidation reaction, usually to the same extent as new oxidizing agent is added. In this way, the oxidation reaction in the reaction zone can proceed essentially under constant ambient conditions, especially at a constant oxidizing agent concentration.

[0013] It is intended that the oxidation reaction is stopped at least in the partial region belonging to the reaction region as soon as a sufficient proportion of the foreign matter-containing material has been converted into oxide-containing foreign matter in the reaction region or at least in the partial region belonging to the reaction region and / or a sufficiently large amount of the foreign matter-containing material has been removed from the reaction region or at least from the partial region belonging to the reaction region. In this case, the supply of further oxidizing agent to the reaction region or to the partial region belonging to the reaction region is stopped. Then, the reaction products or reaction residues are generally removed from the reaction region or the partial region belonging to the reaction region. It is often intended that substantially all of the reaction products or reaction residues are removed from the reaction region or the partial region belonging to the reaction region. It may also be sufficient to remove only a portion of the reaction products or reaction residues. The reaction products or reaction residues remaining in the reaction region or the partial region belonging to the reaction region can then be further oxidized together with new material entering the reaction region or the partial region belonging to the reaction region, if necessary after the addition of further oxidizing agent. After removal of the oxidant still remaining in the reaction zone or in a partial zone belonging to the reaction zone after the reaction has been stopped or has taken place, the reaction zone or in a partial zone belonging to the reaction zone can be fluidly connected to the raw gas space without risk of the oxidant entering the raw gas space.

[0014] In particular, the oxidizing agent can be sucked or drawn out of the reaction zone or a subzone belonging to the reaction zone. For this purpose, the reaction zone may be subjected to a negative pressure in order to suck out the oxidizing agent still present in the reaction zone from the reaction zone. Reaction products or other reaction residues can also be sucked out of the reaction zone by applying a negative pressure to the reaction zone. The application of a negative pressure to the reaction zone can take place during and / or after (subsequent to) the reaction of the oxidizing agent with the material that has fallen off the filter surface.

[0015] An oxidant inlet may be provided for supplying oxidant to the reaction zone or to a subzone belonging to the reaction zone. An oxidant outlet may be provided for removing oxidant from the reaction zone or from a subzone belonging to the reaction zone. In the simplest case, the oxidant inlet may simultaneously function as the oxidant outlet. In principle, however, it is contemplated that the oxidant outlet may differ from the oxidant inlet, in particular so that an oxidant flow that crosses as large a portion of the reaction zone or a subzone belonging to the reaction zone is formed between the oxidant inlet and the oxidant outlet.

[0016] The oxidant outlet may be an outlet specially provided for discharging gas, especially oxidant. However, it is also possible that unconsumed oxidant is discharged through the same oxidant outlet, as are oxide-containing foreign materials formed during the reaction and, in some cases, as unreacted, dropped foreign materials. In this case, the oxidant outlet is designed to discharge both gaseous materials and solid-containing materials.

[0017] It is conceivable, but not necessary, that all reaction of the foreign material-containing material with the oxidant occurs in the area upstream of the oxidant outlet. The oxidant or a mixture of oxidant and further (e.g., inert) fluid discharged via the oxidant outlet is then not used for further oxidation, apart from the possible recirculation of the oxidant stream to the oxidant inlet. However, the reaction zone may comprise multiple areas located downstream of the oxidant outlet, in particular conduits or lines, conveying means and / or containers located downstream of the oxidant outlet. This is particularly worth considering if the unconsumed oxidant is discharged through the same oxidant outlet as the foreign material-containing material formed during the reaction and possibly the foreign material that has not yet been converted or reacted.

[0018] In one possible embodiment, the oxidant outlet is connected to a pneumatic conveying means. In particular, this pneumatic conveying means may be a conveying means operating as a solid injector or a jet pump. Alternatively, a suction blower is conceivable. The pneumatic conveying means may be connected to the oxidant outlet by a conveying connection and thus may exert a suction effect on the reaction zone or a subzone of the reaction zone. The suction effect causes the oxidant or a mixture of oxidant and a further (e.g. inert) fluid introduced into the reaction zone or subzone of the reaction zone to flow as an oxidant flow towards the oxidant outlet, thereby passing through the reaction zone or subzone of the reaction zone and causing the oxidant to react with the foreign matter-containing material to form oxide-containing foreign matter.

[0019] Oxide-containing foreign matter formed during the reaction, and possibly also unreacted foreign matter, can be discharged via a pneumatic conveying means, particularly a conveying means operating as an airless injector or jet pump. The pneumatic conveying means can further transport such solid-containing material, for example, via a line to a collection container or a waste container. The transported solid-containing material can include oxide-containing foreign matter resulting from the reaction with the oxidizing agent, as well as unreacted, dropped material. This pneumatic conveying means can be specifically designed to remove solid-containing material from a reaction zone or a partial region of the reaction zone. However, it is also conceivable that the pneumatic conveying means can be designed to discharge solid-containing material from a reaction zone or a partial region of the reaction zone, discharge gaseous material from a reaction zone or a partial region of the reaction zone, and / or add an oxidizing agent to the transported solid-containing material. For example, in an airless injector, an oxidizer-containing fluid such as air or an oxygen-containing gas mixture can be used as the transport fluid. In this way, the desired oxidation reaction efficiently occurs due to the mixture being transported through the transport line downstream of the airless injector.

[0020] By controlling the pneumatic conveying means, it is possible to adjust the suction strength acting on the material in the reaction zone or in a sub-zone of the reaction zone. At lower suction strengths, (at least substantially) only gaseous material is discharged from the reaction zone or a sub-zone of the reaction zone, whereby the opening (suction opening) connected to the conveying connection of the pneumatic conveying means forms the oxidant outlet. At higher suction strengths, both solid-containing material and gaseous material are discharged from the reaction zone or a sub-zone of the reaction zone. In this case, the suction opening forms an outlet for further conveying the solid-containing material in the reaction zone or a sub-zone of the reaction zone, and at the same time, an oxidant outlet and / or a device for supplying oxidant to the further conveyed solid-containing material. This is done, for example, by mixing the solid-containing material with an oxidant-containing conveying fluid in an airless injector.

[0021] The reaction zone or a sub-zone of the reaction zone can further be acted upon by an inert fluid, in particular an inert gas. For example, by mixing an inert gas, the concentration of the oxidant in the oxidant flow can be appropriately adjusted, and if necessary, the progress of the oxidation reaction can be accelerated or slowed down. Acting an inert fluid on the reaction zone or a sub-zone of the reaction zone without an oxidant serves, for example, to stop further reaction of the oxidant with the dropped material in the reaction zone or in the sub-zone of the reaction zone. The inert fluid can also serve to drive out any remaining oxidant in the reaction zone or in the sub-zone of the reaction zone, to create a sufficiently inert atmosphere in the reaction zone or in the sub-zone of the reaction zone, and to establish fluid contact between the reaction zone or in the sub-zone of the reaction zone and the raw gas space. Stopping the reaction can be intended, for example, after a certain amount of the dropped material has reacted with the oxidant or after a certain percentage of the dropped material has reacted with the oxidant.

[0022] For example, it is contemplated that the reaction of the material dropped from the filter surface with an oxidizing agent proceeds in a reaction phase, the application of oxidizing agent to the reaction zone or a subzone of the reaction zone occurs during and following each reaction phase, and the reaction zone or subzone of the reaction zone is acted upon by an inert fluid without the addition of an oxidizing agent. In this way, the course of the reaction can be managed in a very controlled manner, since the reaction stops after the supply of oxidizing agent is switched off, and any solid or gaseous material in the reaction zone or subzone of the reaction zone can then be removed from the reaction zone or subzone of the reaction zone. By simultaneously flushing the reaction zone or subzone of the reaction zone with an inert fluid, the concentration of the oxidizing agent can be reduced to such an extent that fluid contact between the reaction zone or subzone of the reaction zone and the raw gas space becomes possible again without the risk of the oxidizing agent entering the raw gas space. The reaction zone or subzone of the reaction zone is then ready to receive a further charge of material dropped from the filter surface.

[0023] The introduction of the inert gas into the reaction zone or into a sub-zone of the reaction zone can be achieved simply, for example, via a purge port of an airless injector supplied with an inert fluid.

[0024] In support of the above-mentioned measures, it may be provided that the inert fluid is supplied to the reaction zone or to a sub-zone of the reaction zone via a further fluid inlet different from the oxidant inlet. For example, such a further fluid inlet may be provided near an opening connecting the reaction zone or a sub-zone of the reaction zone to the raw gas space, allowing for selective (targeted) flushing of the oxidant from the vicinity of this opening. It is also conceivable to provide multiple such further fluid inlets.

[0025] It is advantageous if the inert fluid and / or the oxidant is discharged from the reaction zone or a subzone of the reaction zone through one or more further outlets provided in addition to the oxidant outlet. For example, it may be envisaged to arrange a plurality of oxidant outlets distributed over the housing surrounding the reaction zone or a subzone of the reaction zone, so that a widely distributed oxidant flow that covers the volume of the reaction zone well occurs in the reaction zone or a subzone of the reaction zone. In order to particularly efficiently flush the oxidant from certain areas of the reaction zone or a subzone of the reaction zone, it may also be envisaged to arrange several outlets for the inert fluid in relation to each assigned inlet opening for the inert fluid.

[0026] While the reaction of the oxidant with the material removed from the filter surface is occurring, application of the inert fluid to the reaction zone or a portion of the reaction zone may already have begun. In particular, the inert fluid may also serve to remove heat. This often occurs, for example, when the oxidant stream is a mixture of an inert gas (e.g., nitrogen) and an oxidant (e.g., oxygen) containing only a small amount of oxidant.

[0027] The reaction zone or a sub-zone of the reaction zone can be traversed by a heat transfer fluid to remove heat generated during the reaction of the oxidant with the material dropped from the filter surface. In some cases, the heat transfer fluid flow can flow through the reaction zone or a sub-zone of the reaction zone together with the oxidant flow. It is also possible for the oxidant itself to function as the heat transfer fluid, especially when the oxidant only partially reacts because it was added in excess to accelerate the reaction. The heat transfer fluid can also function as an inert fluid to flush any oxidant still present from the reaction zone or a sub-zone of the reaction zone after the reaction is complete. It is then advantageous to use the inert fluid as the heat transfer fluid without adding an oxidant.

[0028] The reaction zone may include an agglomerate collection zone adapted to receive material that has fallen off the filter surface, and foreign matter or agglomerates (agglomerates) that have accumulated on the filter surface are cleaned, collected, and stored in the agglomerate collection zone. The agglomerate collection zone thus constitutes a subzone of the reaction zone described above. The agglomerate collection zone may be designed so that material that has fallen off the filter surface falls directly from the raw gas space into the agglomerate collection zone without being previously collected at a location between the filter element and the agglomerate collection zone (e.g., in the bottom area of ​​the filter housing surrounding the raw gas space).

[0029] The agglomerate collection area may be assigned a first closing device having a first blocking member, which may be designed to allow material that has fallen off the filter surface during cleaning to be collected in the agglomerate collection area, in particular for a short period of time, and to close the reaction area to the raw gas space (in particular to seal it off gas-tightly) after collecting the material that has fallen in the agglomerate collection area, at least until the concentration of oxidant in the reaction area has been sufficiently reduced.

[0030] "Sufficiently reduced" means, in particular, until the concentration of oxidant in the reaction zone can be assumed to fall below a predetermined threshold. This may be the case when the reaction to form oxidant-containing inclusions has occurred so completely that the oxidant is largely consumed and / or all material is removed from the reaction zone or agglomerate collection zone. In practice, this state may be achieved by waiting a predetermined time after the oxidation reaction has started, if the rate at which the reaction proceeds is sufficiently well known (e.g., from testing). However, in general, this state will in any case be achieved when the oxidant has been removed from the reaction zone or agglomerate collection zone after the reaction has been completed, in particular by suction and / or evacuation with an inert fluid.

[0031] In particular, the first shutoff element can be designed so that when it is open, the collection of material that has fallen off the filter surface in the agglomerate collection area is not significantly hindered. In particular, the first shutoff element should be open during and / or immediately following the cleaning of the filter element, and should remain open until material that has fallen off the filter surface on the raw gas side during cleaning has largely collected in the agglomerate collection area. In particular, the first shutoff element can be reopened after the reaction for the formation of oxidant-containing foreign matter in the reaction area is completed, as soon as the concentration of oxidant in the reaction area has decreased sufficiently so that there is no longer any reason to fear that process conditions under which the oxidant would spread from the reaction area to the raw gas space would be hindered.

[0032] The material that falls off the filter surface can be transported from the agglomerate collection region to a downstream discharge region. The discharge region can be located downstream (after) the reaction region, in the sense that further oxidation of the foreign matter does not occur in the discharge region itself. However, it is conceivable and entirely preferred that the reaction region still at least partially include the discharge region, and that the foreign matter still be oxidized in the discharge region depending on the presence of an oxidizing agent. In such cases, the oxidizing agent can be supplied not only to the agglomerate collection region, but also to the discharge region, or only to the discharge region.

[0033] The discharge zone may have a second closing device with a blocking element capable of sealing the discharge zone from downstream zones, particularly sealing it airtight. This second closing device is not necessary, especially if the goal is to achieve a substantial complete conversion of combustible contaminants into oxide-containing contaminants before the material introduced into the discharge zone reaches the downstream end of the discharge zone. Without a second closing device or when the second closing device is open, the desired oxidation reaction in the discharge zone can be carried out very efficiently by the rapid forward transport of the transported material. When a second closing device is provided, the associated blocking element may be designed to form an airtight barrier in its closed position. However, this feature is not necessarily required. In many cases, a simple blocking function for particles above a certain size is sufficient. In particular, a reaction zone may be located between the first and second closing devices. The discharge zone may further have a collection container in which solid-containing materials, particularly oxide-containing products, from the oxidation of materials that have fallen off the filter surface are collected and ultimately disposed of.

[0034] The oxidant not consumed in the reaction zone and possibly additional fluids produced after leaving the reaction zone, especially as excess fluid or waste liquid (especially in the case of gaseous fluids, as waste gas) upon reaching downstream portions of the discharge zone, can be advantageously returned to the reaction zone in whole or in part. For example, the waste liquid outlet or waste gas outlet can be assigned to a collection container, and the fluid flow leaving the waste liquid outlet can be returned or recirculated in whole or in part to the reaction zone. Fluid recirculation of the type described here can significantly limit the amount of fluid consumed, in particular as oxidant, heat transfer fluid, purge fluid, and / or transport fluid. In particular, inert fluids are generally not consumed during transport through the reaction zone and can be maintained substantially permanently in the circuit thus created. If necessary, fresh oxidant can be added to the recirculated fluid flow to compensate for oxidant consumption in the reaction zone.

[0035] If fluid recirculation is provided, a control / regulation system may be provided that is designed in particular so that the fluid pressure in the circuit, in particular in the reaction zone, does not exceed and / or fall below a predetermined value, in particular so that it remains within a predetermined range. As a control variable for controlling the fluid pressure, it may be intended, for example, that only a portion of the fluid flow accumulated as waste is returned to the reaction zone, and another portion is discharged to the environment or to an external waste disposal system, whereby the returned fluid flow is constantly regulated so that the fluid pressure in the circuit, in particular in the reaction zone, remains constant, in particular does not exceed a predetermined value and / or does not fall below another predetermined value, in particular so that it remains within a predetermined range.

[0036] The reaction zone may be provided with a conveying member for conveying the material dropped from the filter surface. Preferably, the conveying member may be a conveying fluid. For example, when an airless injector is provided to convey the material from the agglomerate collection container to the discharge line, a fluid that functions to create a negative pressure or vacuum in the conveying portion of the airless injector may function as a conveying fluid for further conveying the material conveyed from the agglomerate collection container downstream of the airless injector. The conveying member may be used to further convey the solid-containing material quickly and efficiently. In addition, the conveying member may improve the mixing or loosening of the solid-containing material so that such material comes into contact with the oxidizing agent more quickly. Alternatively or additionally, the conveying member may include a screw conveyor, a rotary valve, a gradient or slope, and / or a fluidizer. In particular, the conveying member may be designed so that the conveying direction of the material dropped from the filter surface can be reversed.

[0037] Further embodiments of the above-mentioned methods and of the filtration device described in more detail below are described below.

[0038] The reaction zone may have a collection container, and the collection container may be provided with at least one element for transferring the material that falls off the filter surface, in particular a screw conveyor, a fluidizer, a swivel for the collection container and / or a mixer.

[0039] The reaction zone may be designed to be temperature-controlled, in particular to be heated and / or cooled. Deviating from the above, designs are conceivable in which an ignition device and / or a heating device is assigned to the reaction zone in order to actively initiate the reaction between the foreign material and the oxidizing agent. The conversion of the dropped material to form oxide-containing foreign material then does not depend on the initiation of spontaneous oxidation. In all other respects, the preceding and following statements also apply to this alternative embodiment of the invention. The applicant reserves the right to directly claim such alternative embodiments, for example by divisional application.

[0040] The foreign matter may, for example, contain or be metal and may have a granular, particularly scrap-like, powder-like, or smoke-like structure. In particular, the foreign matter may have a structure that is not fully oxidized or not oxidized at all. In particular, the foreign matter may be titanium powder or titanium scrap. The foreign matter may also be a metallic foreign matter that is not oxidized or not fully oxidized. Such foreign matter is created during the additive manufacturing of metal workpieces, for example, by using powdered metallic material when building up the workpiece layer by layer from a powder bed. Typical metals used in such methods and that may result in combustible foreign matter in the exhaust are titanium, aluminum, magnesium and their alloys, as well as many steels, such as structural steels, hardened and tempered steels, and high-alloy stainless steels.

[0041] The method may include adding a filter aid to the raw gas stream, the filter surface, the reaction zone, and / or the discharge zone. The filter aid may be configured to inhibit reaction of foreign matter and / or material shed from the filter surface with oxidizing agents, particularly oxygen. If necessary, a flame-retardant additive may be added to the exhaust gas to form agglomerates of foreign matter and filter aid. The addition of a SiO2-based filter aid has been found to be suitable for inhibiting raw gas ignition in additive manufacturing processes using titanium and / or aluminum-magnesium alloys. For example, laser sintering is known as an additive manufacturing process that generates exhaust gases prone to self-ignition.

[0042] The filter aid may be, for example, an inorganic material, in particular an inorganic material based on silicon oxide or calcium carbonate, which may be used as the filter aid. In particular, the filter aid may ensure that the oxidation occurring in the reaction zone does not become uncontrollable.

[0043] When added, the filter aid may have a granular, particularly powder-like, structure. This allows for precise metering of the filter aid into the raw gas stream and / or into the filtration device, particularly for coating the filter surface (pre-coating). In addition, suitable filter aids allow for the use of simple feed mechanisms such as flaps (valves) or pressurized gas feeds. The finer the filter aid when added, the more efficient the formation of ignition-retardant agglomerates.

[0044] The filter aid may be configured to mix metal-containing foreign matter into a granular structure, particularly at temperatures above 600°C, particularly above 650°C, particularly above 1220°C, particularly above 750°C, particularly above 1320°C. Depending on the filter aid, temperatures up to 1000°C, particularly up to 1250°C, and particularly up to 1500°C may be reached without excessively suppressing agglomerate formation and / or causing agglomerate decomposition or disintegration to an unnecessarily large extent. The agglomerates formed are not flammable or only flame-retardant in the aforementioned temperature ranges, thus enabling increased operational safety compared to conventional filtration devices. Many SiO2 glasses (quartz glass) begin to soften at temperatures above 600°C and may therefore form agglomerates with foreign matter. Depending on the structure of the SiO2 material, the temperature at which softening begins can be appropriately adjusted, for example, by adding additives or forming it as a glass foam.

[0045] When the agglomerate mixed with the filter aid is heated strongly, it can change into a fluid structure similar to a glass melt, and can change into a glassy structure after cooling below the glass transition temperature. The filter aid melts, thereby trapping the foreign matter in the melt, thereby causing inactivation already in this state. Once the melt solidifies, a glassy or vitreous structure is formed. The formation of a fluid structure can occur particularly after heating to temperatures above 600°C, particularly above 650°C, particularly above 1220°C, particularly above 750°C, particularly above 1320°C. In this process, the agglomerate can have a glassy structure after cooling below the glass transition temperature. This can prevent the oxidizing agent from coming into contact with the metal-containing foreign matter.

[0046] In particular, the filter aid may be a material that has a glassy structure or that may be converted to a glassy structure under the influence of heat.

[0047] Silicon dioxide-based materials with a glassy structure are produced from solids and have an amorphous or at least partially crystalline structure. Such glasses have silicon dioxide as their main component, and their network is mainly formed by silicon dioxide. These include, in particular, so-called silicate glasses. Silicate-based glasses can exist in pure form, for example, as silica glass (quartz glass). If a higher softening temperature is desired, quartz glass (quartz glass) is also conceivable. In addition to silicate-based glasses, additional components, such as phosphates, borates, etc., may also be present.

[0048] The filter aid may have at least one of the following materials as its main component: expanded glass beads, glass powder, silicon dioxide particles (SiO2 particles), quartz powder, or a mixture of at least two of these materials. Particularly suitable glass materials are those made from recycled waste glass (recycled glass), such as expanded glass or foamed glass. Foamed glass is made by crushing waste glass cullet and adding a binder and / or a foaming agent. This produces roughly rounded particles with small gas-filled pores. Expanded glass can be produced with a particle size of 0.04 to 16 mm. The granules have a closed pore structure. Foamed glass, especially foamed glass ballast, can be produced in a similar manner. Expanded glass or foamed glass can be produced so that the onset of the softening range and / or the lower limit of the glass transition temperature are between 600°C and 750°C.

[0049] In the event of fire, the initially formed, still powdery or granular agglomerates of filter aid and metal powder soften or melt under the action of heat. The flowable glass melt surrounds the metal-containing inclusions, rendering them inert. After solidification of the melt, a glass-like structure is formed, in which the metal-containing inclusions are permanently surrounded by or surrounded by the filter aid. As soon as the flowable structure is formed, the individual autoignition particles of metal are bound by the filter aid (vitrified). Reaction with oxidizing agents, especially oxygen (O), is only possible with difficulty in the vitrified state, or is no longer possible. The aforementioned type of vitrification process occurs particularly where filter aid agglomerates accumulate. In particular, filter cakes formed on the raw gas side of the filter and consisting entirely or at any rate largely of filter aid agglomerates may undergo a phase transition from a powdery or granular structure to a flowable and ultimately glassy structure upon the generation of heat (e.g., in the event of fire). Such a vitrification process may also occur at the bulk conical surface that forms in the agglomerate collection region during operation, resulting in efficient inactivation of the material contained in the agglomerate collection region. This vitrification process may be facilitated or assisted by occasionally coating the conical surface of the bulk material formed in the agglomerate collection region with a layer of filter aid.

[0050] The agglomerates formed may remain chemically stable in the event of ignition, i.e. in the presence of an oxidizing agent (usually oxygen), at temperatures up to 650°C, in particular up to 750°C, in particular up to 850°C, in particular up to 1000°C, in particular up to 1250°C, in particular up to 1500°C.

[0051] The filter aid may also have a gaseous structure, in which case the filter aid may further be used as a heat transfer fluid after oxidation of materials and / or foreign matter shed from the filter surface has occurred.

[0052] After the filter element has been cleaned and material dislodged from the filter surface has been deposited in the agglomerate collection area and / or discharge area and / or reaction area, the agglomerate collection area and / or discharge area and / or reaction area may be acted upon by a filter aid and / or an oxidizing agent.

[0053] The application of the oxidizing agent to the agglomerate collection area and / or discharge area and / or reaction area may be carried out in a timed relationship with the application of the filter aid to the agglomerate collection area and / or discharge area, and in particular may be carried out prior to the application of the filter aid to the agglomerate collection area and / or discharge area and / or reaction area, or subsequent to the application of the filter aid to the agglomerate collection area and / or discharge area and / or reaction area.

[0054] A filter device according to the present invention for purifying a contaminant-carrying raw gas includes at least one filter element having at least one filter surface in a raw gas space to which a contaminant-containing raw gas stream can be supplied. Further, an oxidant supply means is provided, configured to supply an oxidant to a reaction zone located downstream of the filter surface on the raw gas side of the filter surface. The oxidant supply means is designed so that contaminants contained in materials removed from the filter surface and / or in the raw gas stream react with the oxidant in the reaction zone to form oxide-containing contaminants.

[0055] The explanations given above with regard to the method according to the invention apply equally to the filtration device according to the invention, and explicit reference is made to the preceding explanations to avoid repetition.

[0056] In particular, the oxidant may be air or an oxygen-containing gas. In particular, the reaction zone may be located downstream of the raw gas space. In particular, the reaction zone may be configured to be closed off from the raw gas space when the oxidant is supplied. These measures contribute to ensuring that the raw gas space remains largely free of oxidant.

[0057] The filtration device can be designed so that during the reaction of the oxidant with the material that has fallen off the filter surface, any unconsumed oxidant can be removed from the reaction zone, which can provide particularly good control of the reaction that occurs in the reaction zone.

[0058] The filtering device has an oxidant inlet configured to supply oxidant to the reaction zone or a sub-zone of the reaction zone, and an oxidant outlet configured to remove oxidant from the reaction zone or a sub-zone of the reaction zone, in particular the oxidant outlet is different from the oxidant inlet.

[0059] The filtering device may further be designed to discharge, in particular to suck, unconsumed oxidant through the same oxidant outlet as oxide-containing foreign matter formed during the reaction and possibly as unreacted foreign matter.

[0060] The reaction zone may include multiple zones located downstream of the oxidant outlet, in particular downstream lines, conveying means and / or containers.

[0061] It is particularly elegant if the oxidant outlet is connected to a pneumatic conveying means, in particular a conveying means operating as an airless injector or jet pump, or to a suction blower. The filtering device may further comprise a pneumatic conveying means, in particular a conveying means operating as an airless injector or jet pump, intended for removing oxide-containing foreign matter formed during the reaction and possibly unreacted foreign matter. This pneumatic conveying means may also serve to remove oxidant or other gaseous substances from the reaction zone or from a subzone of the reaction zone.

[0062] The filtering device may be configured to apply a negative pressure to the reaction zone or a sub-zone of the reaction zone during and / or after the reaction of the oxidant with the material that has fallen off the filter surface. Additionally or alternatively, the filtering device may be configured to apply an inert fluid, in particular a noble gas, to the reaction zone or a sub-zone of the reaction zone.

[0063] The filtration device further has a control system adjusted so that the reaction of the material dropped from the filter surface with the oxidizing agent occurs in a reaction phase, with application of the oxidizing agent to the reaction zone or a subzone of the reaction zone occurring during the reaction phase, and / or application of an inert fluid occurring subsequent to each reaction phase without addition of the oxidizing agent to the reaction zone or a subzone of the reaction zone.

[0064] The filtration device may have a further fluid inlet into the reaction zone or into a sub-zone of the reaction zone, different from the oxidant inlet, for introducing an inert fluid.

[0065] The filtering device may have further outlets in addition to the oxidant outlet for discharging the inert fluid and / or the oxidant from the reaction zone and / or from subzones of the reaction zone.

[0066] In any case, the reaction zone or a sub-zone of the reaction zone can be acted upon by an inert fluid, in particular an inert gas, and / or by negative pressure after the reaction of the oxidant with the material dropped from the filter surface has occurred. In this case, the inert fluid displaces the oxidant from the reaction zone or sub-zone of the reaction zone, so that uncontrolled oxidation can no longer occur. This effect can also be achieved by applying negative pressure to the reaction zone or sub-zone of the reaction zone, i.e., the oxidant is sucked or drawn out of the reaction zone or sub-zone of the reaction zone. Both measures can also be combined and can support each other in this respect.

[0067] The filtering device may further have an oxidant inlet through which an oxidant can be supplied to the reaction zone or a sub-zone of the reaction zone. The oxidant inlet may be equipped with a shut-off device to allow the oxidant to be controllably admitted to the reaction zone or a sub-zone of the reaction zone. The filtering device may also have an oxidant outlet, in particular different from the oxidant inlet, through which the oxidant still present in the reaction zone or a sub-zone of the reaction zone after reaction of the oxidant with the material dropped from the filter surface can be discharged.

[0068] The oxidant inlet may preferably be located at the head end of the reaction zone or sub-zone, the head end being located on the side of the reaction zone or sub-zone facing the raw gas space. In particular, the outlet may be located at the foot end of the reaction zone or sub-zone, the foot end being located on the side of the reaction zone or sub-zone facing away from the raw gas space. This arrangement ensures that the oxidant is efficiently and reliably supplied to the reaction zone, and that materials that fall off the filter surface are emptied from the reaction zone or sub-zone by the oxidant flow through the outlet.

[0069] The filter device may have a common outlet through which residues of the reaction between the oxidant and the material that has fallen off the filter surface, in particular the oxide-containing foreign matter that has formed, the completely or partially unreacted material, and excess oxidant, can be removed from the reaction zone or from a subzone of the reaction zone. This results in a simple construction for the filter device, in particular for the reaction zone. The reaction zone or a subzone of the reaction zone may have a heat transfer fluid flowing therethrough to remove the heat generated during the reaction.

[0070] The reaction zone may also include an agglomerate collection area designed to receive material that has fallen off the filter surface, in which foreign matter or agglomerates containing foreign matter that have accumulated on the filter surface following cleaning can be collected and received, the agglomerate collection area thus constituting in particular a sub-area of ​​the reaction zone mentioned above.

[0071] The agglomerate collection area may be assigned a first closing device having a first blocking member, which allows the material falling off the filter surface during purification to be collected in the agglomerate collection area, particularly for a short period of time only, and is designed to close the reaction area to the raw gas space after collecting the fallen material in the agglomerate collection area, at least until the concentration of the oxidant in the reaction area has decreased to a sufficient extent.

[0072] Furthermore, the filtration device may further comprise a discharge area located downstream of the agglomerate collection area, into which the material that has fallen off the filter surface can be conveyed, in particular the discharge area comprising at least a part of the reaction area, in particular the oxidant can be supplied to the agglomerate collection area and / or to the discharge area.

[0073] The discharge area may have a second closure device, in particular the reaction area being arranged between the first and second closure devices.

[0074] The reaction zone may be provided with a transport member configured to transport the material that has fallen off the filter surface, the transport member particularly comprising a transport fluid. For example, when an airless injector is provided to discharge the material from the agglomerate collection container to the discharge line, the fluid that functions to generate negative pressure at the transport port of the airless injector may function as a transport fluid to transport the material that has been transported from the agglomerate collection container further downstream of the airless injector.

[0075] For the advantages and benefits of the individual features, please refer to the description of the method and further features according to the invention.

[0076] The oxidizing agent may be air or an oxygen-containing gas, in particular having an oxygen content of 1 to 21 volume percent. The oxidizing agent allows spontaneous reaction of foreign particles and / or substances shed from the filter surface in a reaction zone, which may be located downstream of the raw gas space.

[0077] The filtration device may be intended as a device for supplying a heat transfer fluid to the reaction zone and for discharging the heat transfer fluid after flowing through the reaction zone or part of the reaction zone in order to remove the heat generated during oxidation along with oxide-containing contaminants and excess oxidant.

[0078] Conveying elements for conveying the material dropped from the filter surface, in particular screw conveyors, rotary valves, gradients or slopes, and / or fluidizers, can be installed in the reaction zone. The conveying elements can be specifically designed so that the conveying direction of the material dropped from the filter surface is reversible. In particular, the conveying elements can be pneumatic conveying means such as airless injectors.

[0079] The discharge area may include an exhaust outlet area through which fluid materials produced after undergoing the process can be discharged. When the oxidation treatment of materials removed from the filter surface described herein is performed with a gaseous fluid, particularly a gaseous oxidant, heat transfer fluid, purge fluid, and / or carrier fluid, the gaseous exhaust (exhaust gas) is primarily produced in the exhaust outlet area. For simplicity, the terms "exhaust gas" and "exhaust gas outlet area" are also used herein, regardless of whether the fluids accumulating at the end of the process are primarily in a gaseous or liquid state. The exhaust outlet area may include a filter unit with at least one filter element and an exhaust gas outlet. The exhaust outlet area may include, in particular, a pressurized gas purifying device. The pressurized gas purifying device may be configured to apply pressure pulses to the at least one filter element. Alternatively, the filter unit may include at least one filter element with multiple storage filters. The exhaust outlet area may be designed so that a mixture of residues and excess oxidant formed during the reaction is filtered there and discharged from the filter device through the exhaust gas outlet.

[0080] The filtration device may in particular have a fluid recirculation unit designed so that the oxidant not consumed in the reaction zone and possibly further fluids that accumulate as waste liquid or exhaust gas after leaving the reaction zone are returned completely or partially to the reaction zone. In particular, a control system / regulation system may be provided so that the fluid pressure in the circuit thus created, in particular in the reaction zone, does not exceed a predetermined upper limit and / or does not fall below a predetermined lower limit, in particular remains within a predetermined range.

[0081] The discharge area may have a collection container for solid-containing material, in which solid-containing material, in particular oxide-containing foreign matter, can be collected. Once full, the collection container can be removed by the operator and replaced with an empty collection container. In particular, the discharge area may have a collection container for separating solid-containing material, the collection container having an outlet (exhaust gas outlet) for fluid material, in particular gaseous material. In this case, a filter unit for cleaning the fluid material from foreign matter of the aforementioned type may be assigned to the outlet. Furthermore, a fluid recirculation unit of the aforementioned type may be assigned to the outlet.

[0082] In particular, devices for temperature control, for heating and / or cooling the reaction zone or parts of the reaction zone, may be assigned to the reaction zone or parts of the reaction zone. In an alternative embodiment, the reaction zone or parts of the reaction zone may include an ignition device and / or a heating device that actively initiates the reaction of the foreign substance with the oxidant.

[0083] The filter device may further comprise a filter aid supply device having a filter aid supply line leading to the raw gas space, to the raw gas flow upstream and / or downstream of the raw gas space and / or to the reaction zone and / or to the discharge zone, in particular to a collection container, for supplying a filter aid. The filter aid may then be configured to inhibit further reaction of the foreign matter with the oxidizing agent, in particular oxygen, as soon as initial oxidation of the material that has fallen off the filter surface has occurred.

[0084] The invention and specific embodiments of the invention are explained in more detail below using exemplary embodiments. [Brief explanation of the drawings]

[0085] [Figure 1] FIG. 1 shows a side view of a filtration device according to the present invention. [Figure 2] 2 shows the filtration device of FIG. 1 in a side view rotated 90° with respect to the view of FIG. 1. [Figure 3] FIG. 1 shows a schematic depiction for an embodiment of a reaction region. [Figure 4]FIG. 10 shows a schematic depiction for a further embodiment of a reaction region. [Figure 5] FIG. 10 shows a schematic depiction for a further embodiment of a reaction region. [Figure 6] 1 shows a schematic representation of an exemplary discharge area, in particular a collection container for solid-containing material; DETAILED DESCRIPTION OF THE INVENTION

[0086] 1 and 2 show, in side views rotated 90° relative to each other, a filtration device 10 for purifying raw gas carrying foreign matter according to an embodiment of the present invention. The filtration device 10 includes a filter unit 12 with at least one filter element 14 (not shown in FIG. 1; one of the filter elements 14 of the filter unit 12 is shown in FIG. 2). The filter unit 12 is installed above a raw gas inlet opening 16 in the upper part of a housing 18, which is partially removed for clarity. The filter unit 12 includes multiple filter elements 14 in the form of dry filters, each of which is configured as a rigid filter. This term is intended to indicate that the walls of the filter element 14 are sufficiently rigid to hold the filter element 14 upright without the aid of additional support structures. In this sense, the filter elements 14 are inherently stable. The filter elements 14 are suspended from a horizontally extending common holder and extend vertically parallel to one another. This is shown diagrammatically in FIG. 2, which shows one of the filter elements 14 approximately in its installed position. It should be noted that different mountings of the filter elements 14 in the housing 18 are also possible, such as horizontal mounting, in which the filter elements extend horizontally and are mounted in a vertical holder. Each of the filter elements 14 has at least one filter surface that is acted upon by the raw gas. In Figures 1 and 2, the filter surface acted upon by the raw gas is located on the outer side (the raw gas side) of one of the filter elements 14. After passing through the wall of the filter element 14, the purified gas passes from the raw gas side to the clean gas side, which faces the interior space enclosed by the wall of the filter element 14. The filter element 14 is open toward the top, so that the purified gas space 17 extends from the interior space to the area above the filter unit 12.

[0087] In the lower region 18b shown in FIGS. 1 and 2, the housing 18 has the shape of a funnel with downwardly tapering sidewalls. Adjacent to the lower region 18b is a reaction region 24, into which foreign matter-containing material accumulated on the filter elements on the raw gas side falls after cleaning each one of the filter elements 14 (e.g., by applying pressure pulses to each filter element 14; see the pressurized gas cleaning unit 58, shown diagrammatically in FIG. 2). In particular, the material entering the reaction region 24 includes foreign matter-containing material from the raw gas flow and / or from material that falls off the filter surface. The reaction region 24 is located downstream of the housing 18 and is connected via a passage 28 to the lower region 18b of the housing 18, which surrounds the raw gas space 20. A first closing device having a first shutoff member 30 is arranged in the passage 28. The shutoff member 30 can be designed as a shutoff valve, a flap, a disc valve, or a pinch valve, similar to the other shutoff members described herein.

[0088] In the illustrated example, the reaction zone 24 has a funnel-shaped container 32 that forms an agglomerate collection area 33. In the illustrated example, the container 32 has sidewalls that taper downwardly away from the raw gas space 20. The container 32 could have other shapes, such as a cylindrical or rectangular shape. At its head end 34, i.e., the end of the container 32 facing the raw gas space 20, the container 32 has an optional further fluid inlet 38 and a further fluid outlet 40 through which excess fluid, such as excess oxidant, excess purge fluid, a heat transfer fluid for removing heat generated during the reaction, or a mixture of the aforementioned fluids, can exit the container 32. It should be noted that multiple additional fluid inlets 38 and multiple additional fluid outlets 40 can be provided as needed, and that the placement of these further inlets and further outlets on the container 32 can be selected as desired.

[0089] The container 32 has an oxidant inlet 36 in its lower region or at its base end 42, i.e., at the end of the container 32 remote from the raw gas space 15. The oxidant inlet 36 is configured to allow an oxidant flow to be introduced into the agglomerate collection area 33. In addition to an oxidant such as oxygen, other fluids, for example, inert fluids, particularly inert gases such as nitrogen, can be introduced into the container 32 surrounding the agglomerate collection area 33 via the oxidant inlet 36. The mixture of the additional fluid and the oxidant serves to adjust the appropriate concentration of the oxidant for purging purposes and / or for heat removal. If the additional fluid functions as a heat transfer fluid and / or a purge fluid, the additional fluid can alternatively or additionally be introduced into the container 32 via one or more inlets, such as the aforementioned additional inlet 38. In particular, the oxidant inlet 36 may be configured as a fluidizer, for example, with a fluidization tray, so that, upon introduction of the oxidant flow, loosening or fluidization of the solid-containing material in the agglomerate collection area 33 is also achieved.

[0090] The container 42 further has an outlet 39 for discharging solid-containing material, which in the illustrated embodiment is located in the lower region 42 of the container 32. Such solid-containing material preferably includes oxide-containing foreign matter generated during oxidation. However, it is not necessary that all foreign matter and / or material that has fallen off the filter surface and entered the agglomerate collection region 33 be fully oxidized by the time it is carried away from the container 32 via the outlet 39. It is also possible that oxidation of easily oxidizable foreign matter nevertheless occurs downstream of the outlet 39.

[0091] The process environment in additive manufacturing processes that produce easily oxidizable or flammable residues should usually be inert and not change, or at least not change excessively. This also applies to the treatment of the exhaust gases generated in the process, especially if the discarded exhaust gases are recycled to the process as a loop or circuit. While flammable contaminants in the exhaust gases can be removed by dry filters, an inert mixture of inert carrier gas and particulate contaminants usually enters the raw gas space. In the raw gas space, the proportion of oxygen and other substances that can act as oxidizers is below a predetermined threshold. Therefore, the filtration of raw gases carrying flammable contaminants is carried out under inert conditions, and the addition of oxygen or other substances with oxidizing properties is undesirable. This complicates the possibility of rendering the solid-containing materials accumulated on the filter surface harmless by oxidation.

[0092] A raw gas flow carrying contaminants to be separated by the device 10, as indicated diagrammatically in FIG. 1 by arrow 44, passes through a raw gas supply line 54 and a raw gas inlet opening 16 into the raw gas space 15 enclosed by the housing 18. After entering the raw gas space 15, the raw gas flow 44 is transported to the filter unit 12. The side of the housing 18 opposite the raw gas inlet opening 16 has a filter aid supply opening 20, through which a filter aid, such as a solid with flame-retardant properties such as CaCO or an SiO-based solid, can be supplied from a storage container to the raw gas space 15. Before the raw gas space 15 is filled with the raw gas flow 44, the filter aid can be introduced into the raw gas space 15. The introduced filter aid then accumulates, in particular on the filter surface of the filter element 14 and / or on the walls of the raw gas space 15, where it forms a filter aid layer (precoat layer). The flow of filter aid through filter aid feed opening 20 and into raw gas space 15 is indicated by arrows 45 in FIG.

[0093] Alternatively or additionally, a filter aid feed opening 52 may be disposed in the raw gas feed line 54. The raw gas feed line 54 is connected to the raw gas inlet opening 16. This allows the filter aid to be introduced into the raw gas stream 44 before it enters the raw gas space 15 of the filtration device 10. This results in favorable mixing of the filter aid with contaminants contained in the raw gas stream 44, increasing the autoignition threshold of the raw gas. Optionally, a baffle plate or distribution plate 56 may be disposed near the filter aid feed opening 52 to ensure that the filter aid is uniformly distributed in the raw gas stream 44.

[0094] Associated with the filter unit 12 is a pressurized gas purification unit 58, shown diagrammatically in FIG. 2 , which is located in the purified gas space 17 of the filter unit 12 above the filter elements 14. At certain time intervals, the pressurized gas purification unit 58 pressurizes each filter element 14, causing it to experience a pressure increase in the purified gas space 17. The pressure increase dislodges foreign matter, such as readily self-igniting foreign matter, and possibly filter aid accumulated on the raw gas-side filter surface of each filter element 14, from the filter element 14 and fall downward as a result of their gravity. This material, together with the foreign matter and also the filter aid, then falls through the passage 28 into the agglomerate collection area 33 in the reaction area 24.

[0095] The first barrier member 30 is normally open, so that there is fluid communication between the raw gas space 15 and the reaction zone 24. This is particularly true at the beginning and during the cleaning-off cycle for the filter element 14. In this way, material that falls off the filter surface during cleaning can fall unimpeded, or at least largely unimpeded, into the agglomerate collection zone 33 of the reaction zone 24 and does not significantly accumulate on the floor or walls of the housing 18 surrounding the raw gas space 15. As soon as cleaning is performed and the oxidation cycle is initiated in the reaction zone 24, the first barrier member 30 is closed, so that the agglomerate collection zone 33 of the reaction zone 24 is fluid-tightly separated from the raw gas space 15, at least during the period when an oxidant-containing atmosphere prevails within the agglomerate collection zone 33. An oxidant is then introduced into the agglomerate collection zone 33 via the oxidant inlet 36 to cause spontaneous oxidation of material entering the agglomerate collection zone 33. The oxidizer inlet 36 is designed so that the oxidizer flows through or mixes with the solid-containing material in the agglomerate collection area 33, especially with easily oxidizable material that has fallen from the filter surface, thereby initiating oxidation of this material spontaneously, i.e., without additional energy input via a heating device, ignition device, etc. The oxide-containing, now inert foreign matter, excess oxidizer, and other materials formed by oxidation can then be transported via outlet 39 along discharge line 60 to a discharge area 62 downstream of the agglomerate collection area 33. After completion of this discharge process, the first shutoff member 30 can be reopened as soon as the concentration of oxidizer in the agglomerate collection area 33 has dropped to such an extent that contamination of the raw gas space 15 is no longer a concern. To assist in the discharge of the oxidizer from the container 32 surrounding the agglomerate collection area 33, a purge fluid in the form of nitrogen, a noble gas, or another inert gas can be introduced into the container 32 via an optional further inlet 38. This allows residual oxidant still present in the container 32 to be removed from the container 32 via the further fluid outlet 40 and thus from the agglomerate collection area 33, creating an inert atmosphere in the container 32 or in the agglomerate collection area 33. When the blocking member 30 is open, foreign matter from the raw gas space 15 and material that has fallen off the filter surface again enters the reaction area 24 without intermediate storage.By not collecting foreign matter in the lower region 18b of the housing 18, dust bridges are effectively avoided, which would otherwise greatly exacerbate the subsequent sliding of foreign matter into the reaction region 24.

[0096] Alternatively, it is conceivable that a continuous flow of an inert fluid, such as nitrogen or a noble gas, passes at least temporarily through container 32 via oxidant inlet 36 and / or via further inlet 38, passes through conglomerate collection area 33 of reaction zone 24, and flows to outlet 39, via which it again leaves container 32. Once filter element 14 or a number of filter elements has been purged and shut-off member 30 is closed, a sufficient amount of oxidant can be added to this fluid flow so that materials located in conglomerate collection area 33 can be reacted or converted by oxidation. Once conversion has occurred to the desired extent, the supply of oxidant to the fluid flow can be stopped, and the oxide-containing foreign matter or reacted foreign matter is carried away by the fluid flow from conglomerate collection area 33 or from container 32 via discharge line 60 to discharge area 62.

[0097] The coordination between the activation of the pressurized gas purification unit 58, the purification of each one or more filter elements 14 from substances adhering to the filter surface, and the opening and closing of the shut-off member 30 is performed by a control unit 59. The control unit 59 can be configured so that the shut-off member 30 is open by default, so that foreign particles in the raw gas that do not reach the filter element 14 or that fall off the filter element when not in a purification cycle fall directly into the agglomerate collection area 33 of the reaction area 24. Even during the purification of the filter element 14, the shut-off member 30 remains open so that the substances that have fallen off the filter surface can be discharged into the reaction area 24 without intermediate storage. As soon as the purification is completed, the control unit 59 closes the shut-off member 30 for a short time, so that the oxidizing agent can be passed into the reaction area 24, now separated from the raw gas space 15, and in particular into the container 32 surrounding the agglomerate collection area 33. It can be assumed that after a predetermined time, the substances that have fallen off the filter surface in the agglomerate collection area 33 are sufficiently oxidized to form oxide-containing foreign particles. Insofar as the added oxidant was not consumed in the reaction, excess oxidant is then removed from the agglomerate collection area 33, so that an inert atmosphere once again prevails in the reaction area 24, i.e., the oxidant concentration is so low that oxidation no longer occurs even if foreign objects or materials that have fallen off the filter surface enter the agglomerate collection area 33. The control unit 59 then reopens the shutoff member 30, allowing foreign objects or materials that have fallen off the filter surface to re-enter the agglomerate collection area 33.

[0098] In some embodiments, it may be contemplated that the container 32 is movable or acted upon by an agitator and / or lapping device to create a corresponding rocking, vibrating, oscillating, etc. movement of the container 32 to encourage subsequent or successive falls of the solid-containing material through the outlet 39. In this way, it may be achieved to empty the agglomerate collection area 33 as completely as possible.

[0099] In addition to the discharge line 60, the discharge area 62 preferably also has a collection container 64 in which oxide-containing foreign matter is collected. Fluid substances, particularly gaseous substances, that reach the collection container 64 via the discharge line 60 are again discharged from the collection container 64 via the exhaust gas outlet 130.

[0100] Optionally, a second closing device with a second blocking element 66 can be installed in the discharge line 60, for example in the region near the collection container 64. The second closing device separates the upstream part of the discharge area 62, which still belongs to the reaction zone 24 and in which oxidation of the foreign-containing material still occurs, from the downstream part, in which such oxidation no longer occurs. However, the installation of a second closing device is not mandatory. It has been found that the desired oxidation reaction can occur entirely in the discharge area 62, in particular in the discharge line 60, and in particular that the desired oxidation reaction can be completed before the material transported via the discharge line 60 reaches the downstream end of the discharge line 60, where the discharge line 60 leads, for example, to the collection container 64.

[0101] The downstream end of the discharge line 60 leads to (converges with) a collection container 64. Upon reaching the collection container 64, solid-containing materials, particularly oxide-containing foreign matter formed during oxidation, fall into the collection container 64 in the discharge area 62 and can thus be disposed of. At the top, an exhaust gas outlet area 120 (see FIG. 6 ) connects to the collection container 64. The exhaust gas outlet area 120 has an exhaust gas outlet 130 through which excess fluid materials, particularly oxidant, purge fluid, carrier fluid, heat transfer fluid, and other fluids, can be discharged from the discharge area 62. If necessary, this excess fluid material (hereinafter simply referred to as exhaust gas) can be discharged to the environment or to an exhaust system via a shut-off valve 78. Alternatively, as shown in FIG. 2 , all or part of this excess fluid material can be returned to the reaction area 24, particularly to the oxidant inlet 36. Again, a shut-off valve 78 can be installed as needed. The apparatus shown in FIG. 2 is described in more detail below.

[0102] FIG. 3 illustrates a further embodiment of a container 32. Only those features that differ from the container 32 of FIGS. 1 and 2 are described in more detail below. For a description of the additional features in FIG. 3, please refer to the descriptions of FIGS. 1 and 2, where identical or corresponding features are designated by the same reference numerals. In the embodiment of FIG. 3, a pneumatic conveying means, in this case an airless injector 80, is provided to convey material from the container 32. In this embodiment, a hollow lance 68 extends from the head end 34 of the container 32 into the interior of the container 32. The tip of the hollow lance 68 extends to a position near the foot or base end 42 of the container 32. The hollow lance 68 includes one or more openings adjacent its tip through which material can be discharged from the container 32 and is connected to a conveying port 74 of the airless injector 80.

[0103] Alternatively or in addition to the airless injector, a suction blower may be provided to convey materials, particularly gaseous materials, from container 32. Like the airless injector, the suction blower may be connected to container 64 via hollow lance 68 and may be provided to draw or suck oxidizer and other gaseous fluids, particularly from agglomerate collection area 33.

[0104] In addition to the delivery port 74, the airless injector 80 has a carrier fluid inlet 70, which can be supplied with a carrier fluid, e.g., air, and a material exhaust port or material discharge portion 76 communicating with the carrier fluid inlet 70 and the delivery port 74. The delivery port 74 connects the hollow lance 68 to a passage connecting the carrier fluid inlet 70 to the material discharge portion 76. The carrier fluid inlet 70 essentially has a shape tapering toward the material discharge portion 76 so that, when acted upon by the carrier fluid, the carrier fluid is accelerated in the passage, thereby creating a negative pressure within the hollow lance 68 and thus drawing solid-containing material from the container 32 via the hollow lance 68. The material discharge portion 76 of the airless injector 80 is connected to the discharge line 60. When the carrier fluid inlet 70 is actuated, the carrier fluid is delivered from the carrier fluid inlet 70 through the material discharge portion 76 to the delivery line 60, thereby generating a negative pressure in the hollow lance 68. As a result of this negative pressure, solid-containing materials present in the container 32, particularly oxide-containing foreign matter formed during the reaction, are sucked together with gaseous materials, particularly unconsumed oxidant, and transported to the material discharge section 76 via the hollow lance 68. In the process, the sucked materials are mixed with the transport fluid and transported to the discharge line 60 of the transport area 62 via the material discharge section 76.

[0105] Depending on the passage of the carrier fluid through the carrier fluid inlet 70, the suction strength of the airless injector 80 can be adjusted, thereby adjusting the respective amounts of solid-containing material and gaseous material conveyed from the container 32, or the mixture ratio of the carrier fluid mixed with the material conveyed from the container 32. Ultimately, this allows for precise control of the oxidation reaction occurring within the container 32 and any oxidation reactions that may still be occurring downstream of the airless injector 80 in the discharge line 60.

[0106] The oxide-containing foreign matter can also be sucked out of the container 32 in another way. For this purpose, a negative pressure can be generated in the discharge area 62, for example by a blower or suction device, so that the oxide-containing foreign matter is sucked into the discharge line 60 of the discharge area 62 via a hollow lance 68. In addition to the oxide-containing foreign matter, for example, excess oxidizer and / or additional substances or fluids can also be sucked out of the container 32. As soon as the extraction is complete, i.e., as soon as no or almost no oxidizer remains in the agglomerate collection area 33, the blocking member 30 can open the passage 28 from the raw gas space 15 to the agglomerate collection area 33. In such a constellation, a carrier fluid inlet 70 is not necessary, but may optionally be provided to assist in the removal of the oxide-containing foreign matter.

[0107] Alternatively or in addition to using negative pressure to aspirate the oxide-containing particles, a carrier fluid, particularly a carrier gas, can be introduced into the container 32 through the purge fluid inlet 38. The carrier fluid is under negative pressure, and thus, in the case of a gas, air pressure pushes the oxide-containing particles through the hollow lance 68 into the discharge line 60 and up to the discharge area 62. To assist, a carrier fluid can be introduced into the transfer line 60 through the carrier fluid inlet 70 to further transport the oxide-containing particles and prevent the formation of dust bridges. The carrier fluid may be an inert fluid, such as nitrogen. The carrier fluid may also contain an oxidizer, such as oxygen. In this way, oxidation reactions can be ensured to continue as the material is transferred from the container 32 to the discharge area 62. For example, if adding an oxidizer to the carrier fluid is desired, it is convenient to use air as the carrier fluid. Furthermore, an inert fluid can be used as the carrier fluid, with an oxidizer optionally being introduced into the container 32 through a separate inlet.

[0108] To safely remove excess oxidant from the agglomerate collection area 33 or container 32 of the reaction zone 24, the excess oxidant may be removed from the interior of the container 32 via fluid outlet 40, preferably by passing an inert fluid, such as nitrogen or a noble gas, through inlet 38 or oxidant inlet 36 following removal of the oxide-containing foreign matter, where the inert fluid displaces (moves) the excess oxidant from the agglomerate collection area 33 or container 32 of the reaction zone 24.

[0109] Furthermore, after the material has been removed from the container 32 by the airless injector 80, an inert fluid, for example an inert gas such as nitrogen, can be supplied to the container 32 by the airless injector 80. The airless injector 80 has an additional port 72 for impinging with a purge fluid to repair a potentially clogged fluid connection between the hollow lance 68 and the material discharge 76. By applying the inert fluid to the purge port 72 and closing the material discharge 76 as needed, the inert fluid can be easily directed into the container 32 to flush or purge any oxidizer still remaining in the agglomerate collection area 33.

[0110] Figure 4 shows another embodiment of the container, in which, similar to Figure 3, pneumatic conveying means configured in this case as an airless injector 80 are provided for conveying material from the container 32. Only those features which differ from the container 32 of Figures 1, 2 and 3 will be described in more detail below. For a description of further features in Figure 4, reference is made to the description of Figures 1 and 2 and in particular to Figure 3, in which the same or corresponding features are provided with the same reference numerals.

[0111] Unlike the embodiment of Figure 3, the embodiment according to Figure 3 has the airless injector 80 located at the lowest point of the container 32, where in the illustrated variant the side walls of the container 32 converge downwards, where they are closest to one another. An opening communicating with the delivery port 74 of the airless injector 80 is formed in the bottom of the container 32, through which material can be sucked from the container 32. It is understood that a plurality of such openings can also be formed in the bottom of the container 32. In this embodiment, the carrier fluid inlet 36 of the airless injector 80, which can be acted upon by a carrier fluid, e.g., air, also serves as the oxidizer inlet 36 for the container 32 and is therefore designated by the reference numeral 36.

[0112] The material discharge section 76 is in turn connected to the conveying line 60. Typically, the conveying fluid inlet 36 is connected to the material discharge section 76 via a passageway tapering toward the material discharge section 76 to accelerate the conveying fluid within the passageway when the conveying fluid is applied to the conveying fluid inlet 36. When the conveying fluid is applied to the conveying fluid inlet 36, the conveying fluid is directed from the conveying fluid inlet 36 through the material discharge section 76 to the discharge line 60, thereby creating a negative pressure that draws in or draws out solid-containing materials present in the container 32, particularly oxide-containing foreign matter formed during the reaction, along with gaseous materials, particularly unconsumed oxidant, and conveys them to the material discharge section 76. In the process, the drawn-in materials mix with the conveying fluid and are conveyed to the discharge line 60 of the conveying region 62 via the material discharge section 76.

[0113] If only a slight positive pressure is applied to the carrier fluid inlet 36, the acceleration of the carrier fluid within the passageway toward the material discharge 76 is not sufficient to create a significant negative pressure. In this case, the carrier fluid is directed into the container 32 via the carrier port 74. This effect can be further enhanced by closing the material discharge 76. Thus, if the carrier fluid inlet 36 of the airless injector 80 is acted upon with only a slight positive pressure by an oxidizer-containing foreign object such as air, the end effect is that oxidizer is supplied to the container 32 or the agglomerate collection area 33. Otherwise, the operation of the airless injector 80 in FIG. 4 is the same as the operation of the airless injector 80 shown in FIG. 3.

[0114] 4 further includes a port 72 for acting with a purge fluid to repair a potentially clogged fluid connection between the delivery port 74 and the material discharge 76. By applying an inert fluid to the purge port 72 and closing the material discharge 76 as needed, the inert fluid can be easily directed into the container 32 to purge any oxidizer still remaining in the agglomerate collection area 33. By applying an oxidizer-containing inert fluid to the port 72 in this manner, oxidizer can also be introduced into the agglomerate collection area 33 as needed.

[0115] FIG. 5 shows the agglomerate collection area 33 of the reaction zone 24, located within the container 32 with the first blocking member 30 upstream in the direction of the flow of the fallen material. FIG. 5 also shows schematically how material 89 falling from the filter surface falls into the container 32 from the direction of the blocking member 30. As it does so, the falling material cleaned from the filter surface crosses the oxidant flow 90, which flows from the oxidant inlet 92 to the oxidant outlet 94. As the oxidant flow 90 passes, the material falling from the filter surface spontaneously reacts with the oxidant and is thus converted into reaction-inert and / or oxide-containing contaminants 91. The oxide-containing contaminants formed during oxidation are primarily discharged through the oxidant outlet 94 to the discharge area 62 downstream of the container 32 via the discharge line 60 (not shown in FIG. 5 ) and the oxidant outlet 94. Oxidation of contaminants not yet oxidized may also continue in the discharge line 60. Heat generated by the reaction is dissipated along with the oxidant flow 90 via the oxidant outlet 94. Oxidant stream 90 is essentially a mixture of an oxidant, such as oxygen, and an inert component, such as nitrogen or a noble gas.

[0116] FIG. 6 shows an embodiment of an exhaust gas outlet region 120 leading from the collection container 64. The exhaust gas outlet region 120 includes a filter unit 122 mounted on a partition 124. The filter unit 122 may include one or more filter elements. The partition 124 separates the exhaust gas outlet region 120 into a raw gas space 126 and a purified gas space 128. A mixture of solid-containing materials (e.g., oxide-containing particles, non-oxidized particles, possibly filter aid, other solids, and agglomerates of such materials) and fluid-phase, particularly gaseous materials (e.g., excess oxidizer, carrier fluid, purge fluid, coolant, etc.) enters the raw gas space 126. The filter unit 122 is configured to filter the mixture reaching the raw gas space 126 to remove particulate oxide residue and other particulate particles. The filtered mixture in the fluid phase thus exits the purified gas space 128 and is discharged via an exhaust gas outlet 130 located in the purified gas space 128. In particular, the mixture of fluid phases is gaseous and is therefore referred to in the following in simplified form as exhaust gas. This exhaust gas is discharged, for example via a shut-off device 78, to the environment or to an external exhaust gas system. Alternatively, this exhaust gas can be returned to the reaction zone 24, for example to the oxidant inlet 36, as shown in FIG. 6. It is also conceivable to discharge part of the exhaust gas to the environment or to an external exhaust gas system and return another part of the exhaust gas to the reaction zone 24, for example to the oxidant inlet 36. In this case, it is also intended to control the ratio of the exhaust gas flow returned to the reaction zone 24 to the exhaust gas flow released. In particular, this control can be adjusted so that only a very large amount of exhaust gas is returned to the circuit, in particular to the reaction zone 24, at any one time, so that the fluid pressure (in particular the gas pressure) in the circuit system (in particular in the reaction zone 24) does not exceed a predetermined upper limit value and in particular remains within a predetermined range.

[0117] Additionally, a pressurized gas purification unit associated with the filter unit 122 is disposed in the purified gas space 128 and is designed to generate pressure pulses that act on one or more filter elements for purification. The pressure pulses reach the purified gas space 128 from a pressurized gas reservoir 134 through a pressurized gas opening 132 and then reach one or more filter elements of the filter unit 122. The pressurized gas reservoir 134 is preferably filled with pressurized gas via a pressurized gas line 136. The pressurized gas purification serves to purge the filter unit 122 as soon as its filtering performance deteriorates. In this case, pressurized gas is introduced into the purified gas space 128 in the form of pressurized gas pulses, which subject the filter element walls to pressure pulses and clean the filter unit 122 of any foreign particles that have accumulated on the raw gas side of the filter unit 122. These foreign particles then fall from the exhaust gas outlet region 120 through a passage 136 into the collection container 64. A blocking member 140 is optionally disposed in the passage 138 and separates the discharge region 62 from the exhaust gas outlet region 120. It should be noted that it is not necessary to equip the filter unit 122 with a filter element that can be cleaned; for example, a storage filter that must be replaced from time to time can be used in the filter unit 122 as well.

[0118] To realize the recirculation (return) of fluids, in particular the carrier fluid and / or unconsumed oxidant, it may be intended to connect the exhaust gas outlet 130 to the reaction zone 24, in particular the oxidant inlet 36, as an exhaust gas recirculation line 150, as shown schematically in FIG. 2. As shown in FIGS. 2 and 6, the shut-off valve 78 in the exhaust gas recirculation line 150 is optional, and it is understood that an exhaust gas recirculation line 150 without a shut-off valve is also possible. The recirculation creates a closed circuit, whereby the inert fluid added to the process for the dry filtration described above as the carrier fluid and / or purge fluid and / or heat release fluid can be returned to the process again via the exhaust gas recirculation line 150 after passing through the process. In this way, a considerable saving of the required inert fluid can be realized.

[0119] Since the oxidant (particularly oxygen) is consumed as it passes through the above-described process for the oxidation treatment of the filter residue, it is expedient to add oxidant back to the fluid returning from the exhaust gas outlet 130 to the reaction zone 24, particularly to the oxidant inlet 36, to the same extent as it was consumed as it passed through the process. For this purpose, a sensor 142 may be installed in the exhaust gas recirculation line 150, for example between the exhaust gas outlet 130 and the oxidant inlet 36, to determine the oxidant depletion in the fluid stream leaving the exhaust gas outlet 130 versus the desired concentration of oxidant in the oxidant stream entering the container 32 at the oxidant inlet 36. Furthermore, a device 144 may be installed to supply oxidant to the recirculated fluid stream in accordance with the oxidant depletion determined by the sensor 142.

[0120] 2, sensor 142 is located at oxidant inlet 36 and detects the actual concentration of oxidant in the oxidant stream as it enters container 32 or conglomerate collection area 33 of reaction zone 24. A device 144 for supplying oxidant to the recirculated fluid stream joins exhaust gas recirculation line 150 at a location upstream of sensor 142 and is controlled so that the oxidant concentration sensed by sensor 142 remains at a predetermined value or within a predetermined range around that predetermined value.

[0121] For example, the amount of fluid carried in the process can be kept constant by monitoring the fluid pressure in the circulated fluid stream. For example, this can be achieved by sensing and controlling or regulating the pressure at the exhaust gas outlet 136, at the oxidant inlet 36, or in the exhaust gas recirculation line 150. As shown in FIG. 2, for example, a pressure relief valve 146 can be placed in the exhaust gas recirculation line 150 for this purpose. With the aid of the pressure relief valve 146, a predetermined pressure can be set in the exhaust gas recirculation line 150, which ultimately allows the mass flow rate of the fluid phase in the circuit (i.e., the sum of the oxidant and other fluids, such as carrier fluid, purge fluid, heat transfer fluid, etc.) to be kept constant.

[0122] With the above-described type of device, it is possible to easily control or adjust both the mass flow rate of the fluid conveyed in the circuit and the concentration of the oxidizing agent in this circuit, and therefore the intensity of the oxidation reaction occurring during the treatment of the filter residue can be very precisely controlled or adjusted, thereby achieving a sufficiently efficient oxidation of the combustible material without generating too much heat of reaction. [Explanation of symbols]

[0123] 12 Filter unit 15 Raw gas space 24 Reaction Area 36 Oxidant inlet 39,40 Oxidant outlet 44 Raw gas stream

Claims

1. 1. A method for dry filtering of a gas stream carrying foreign matter in a filtering device for cleaning exhaust gases produced in additive manufacturing techniques, comprising: introducing a raw gas stream (44) containing foreign matter into a raw gas space (15) of a filter unit (12) having at least one filter surface separating a raw gas side from a purified gas side; supplying an oxidant to a reaction zone (24) downstream of the filter surface and on the untreated gas side of the filter surface; whereby contaminants contained in the material removed from the filter surface and / or in the raw gas stream react with the oxidizing agent in the reaction zone (24) to form oxide-containing contaminants; The reaction zone (24) is downstream of the raw gas space (15) with respect to the transport of foreign matter accumulated on the filter surface and shed from the filter surface during a cleaning cycle, A method characterized in that oxide-containing foreign matter formed during the reaction and / or foreign matter that has not yet reacted is discharged via pneumatic conveying means (80).

2. 2. The method of claim 1, wherein the pneumatic conveying means (80) operates as an airless injector or jet pump.

3. 3. The method according to claim 1, wherein during the reaction of the oxidizing agent with the material that has fallen off the filter surface, unconsumed oxidizing agent is sucked from the reaction zone (24).

4. 4. The method according to any one of claims 1 to 3, characterized in that the oxidant not consumed in the reaction zone (24) and possibly further fluids that have accumulated as excess fluids after leaving the reaction zone (24) are recycled in whole or in part to the reaction zone (24).

5. 1. A method for dry filtering of a gas stream carrying foreign matter in a filtering device for cleaning exhaust gases produced in additive manufacturing techniques, comprising: introducing a raw gas stream (44) containing foreign matter into a raw gas space (15) of a filter unit (12) having at least one filter surface separating a raw gas side from a purified gas side; supplying an oxidant to a reaction zone (24) downstream of the filter surface and on the untreated gas side of the filter surface; whereby contaminants contained in the material removed from the filter surface and / or in the raw gas stream react with the oxidizing agent in the reaction zone (24) to form oxide-containing contaminants; The reaction zone (24) is downstream of the raw gas space (15) with respect to the transport of foreign matter accumulated on the filter surface and shed from the filter surface during a cleaning cycle, 2. A process according to claim 1, wherein the oxidant not consumed in the reaction zone (24) and possibly further fluids that have accumulated as excess fluids after leaving the reaction zone (24) are recycled in whole or in part to the reaction zone (24).

6. 6. The method according to claim 4 or 5, characterized in that a control / regulation unit is provided, which regulates the fluid pressure in the reaction zone (24) so ​​that it does not exceed a predetermined upper limit or remains within a predetermined pressure range.

7. 7. The method according to claim 1, wherein the oxidant not consumed during the reaction of the oxidant with the material removed from the filter surface is removed from the reaction zone (24).

8. 8. The method according to any one of claims 1 to 7, characterized in that the reaction area (24) is subjected to a negative pressure.

9. 9. The method according to claim 8, characterized in that the application of negative pressure to the reaction zone (24) is carried out during and / or after the reaction of the oxidizing agent with the material that has fallen off the filter surface.

10. The method of claim 1, wherein an inert fluid is introduced into the reaction zone (24).

11. 11. The method of claim 10, wherein the reaction of the material shed from the filter surface with the oxidizing agent occurs in reaction phases, and following each reaction phase, the inert fluid is introduced into the reaction zone without the addition of oxidizing agent.

12. The method of claim 10 or 11, wherein the inert fluid is supplied to the reaction zone via an inert fluid inlet (38).

13. 13. The method of any one of claims 1 to 12, wherein an oxidant is supplied to the reaction zone (24) via an oxidant inlet (36) and removed via an oxidant outlet (39).

14. 14. The method of claim 13, wherein the oxidant outlet (39) is different from the oxidant inlet (36).

15. 15. The method according to claim 13 or 14, characterized in that the unconsumed oxidant is discharged through the same oxidant outlet (39) as the oxide-containing foreign matter formed during the reaction and possibly as the foreign matter that has not yet reacted.

16. 16. The method according to claim 15, characterized in that the reaction zone (24) comprises a plurality of zones located downstream of the oxidant outlet (39), namely downstream lines (60), conveying means (80) and / or containers (64).

17. 17. The method according to any one of claims 13 to 16, characterized in that the oxidant outlet (39) is connected to a pneumatic conveying means (80).

18. 18. The method according to any one of claims 13 to 17, characterized in that the inert fluid and / or the oxidant is discharged from the reaction zone via a further outlet (40) provided in addition to the oxidant outlet (39).

19. 19. The method of any one of claims 1 to 18, wherein the reaction zone (24) has a heat transfer fluid flowing therethrough to remove heat generated during the reaction of the oxidant with material dropped from the filter surface.

20. 20. The method according to any one of claims 1 to 19, characterized in that the reaction zone (24) comprises an agglomerate collection zone (33) configured to receive material that has fallen off the filter surface, and foreign matter or agglomerates containing foreign matter that have accumulated on the filter surface are cleaned, collected and stored in the agglomerate collection zone (33).

21. a first closure device having a first blocking member (30) associated with said agglomerate collection area (33); 21. The method according to claim 20, characterized in that the closing device is designed to allow the material that falls off the filter surface during cleaning to be collected in the agglomerate collection area (33) and, after collecting the material that falls off in the agglomerate collection area (33), to close the reaction area (24) from the raw gas space (15) at least until the concentration of oxidant in the reaction area (24) and / or in the agglomerate collection area (33) has decreased to a sufficient extent.

22. Material shed from the filter surface is conveyed from the agglomerate collection area (33) to a downstream discharge area (62); the discharge zone (62) comprises at least a portion of the reaction zone (24); and 22. The method of claim 21, wherein an oxidizing agent is supplied to the agglomerate collection area (33) and / or the discharge area (62).

23. The discharge area (62) has a second closing device (66), the reaction zone (24) is located between the first and second closure devices; and / or 23. The method of claim 22, wherein the discharge area (62) comprises a collection container (64) for solid-containing material.

24. A filtering device (10) for purifying raw gas carrying foreign matter, comprising: at least one filter element (14) having at least one filter surface separating a raw gas side from a purified gas side in a raw gas space capable of receiving a raw gas flow (44) containing foreign matter; an oxidant supply means configured to supply an oxidant to a reaction zone (24) downstream of the filter surface and on the untreated gas side of the filter surface; whereby contaminants contained in the material removed from the filter surface and / or in the raw gas stream react with the oxidizing agent in the reaction zone (24) to form oxide-containing contaminants; A filtration device (10) in which the reaction zone (24) is downstream of the raw gas space (15) with respect to the transport of foreign matter accumulated on the filter surface and shed from the filter surface during a cleaning cycle, The filtering device (10) further comprises a pneumatic conveying means (80) for discharging oxide-containing foreign matter formed during the reaction and / or foreign matter that has not yet reacted.

25. 25. The filtering device (10) according to claim 24, characterized in that the pneumatic conveying means (80) operates as an airless injector or jet pump.

26. 26. The filtering device (10) of claim 25, wherein the oxidant not consumed during the reaction of the oxidant with the material dropped from the filter surface can be removed from the reaction zone (24) by the pneumatic conveying means (80).

27. 27. The filtering device (10) of any one of claims 24 to 26, characterized in that it is configured to apply a negative pressure to the reaction zone (24) during and / or after the reaction of the oxidizing agent with the material that has fallen off the filter surface.

28. 28. The filtration device (10) of any one of claims 24 to 27, configured to introduce an inert fluid into the reaction zone (24).

29. a control unit (59) regulated so that the reaction between the material dropped from the filter surface and the oxidizing agent occurs in a reaction phase; 29. The filtering device (10) according to claim 28, characterized in that each reaction phase is followed by the application of an inert fluid to the reaction zone (24) without the addition of an oxidizing agent.

30. 30. The filtering device (10) according to claim 28 or 29, further comprising a further fluid inlet (38) into the reaction zone (24) for introducing an inert fluid and / or a heat transfer fluid.

31. The oxidant supply means has an oxidant inlet (36) configured to supply oxidant to the reaction zone (24) and an oxidant outlet (39) configured to remove oxidant from the reaction zone (24); Filtration device (10) according to any one of claims 24 to 30, characterized in that the oxidant outlet (39) is different from the oxidant inlet (36).

32. 32. The filtering device (10) according to claim 31, characterized in that it is designed to discharge unconsumed oxidant through the same oxidant outlet (39) as oxide-containing foreign matter formed during the reaction and possibly as unreacted foreign matter.

33. 33. The filtration device (10) according to claim 31 or 32, characterized in that the reaction zone (24) comprises a plurality of zones located downstream of the oxidant outlet (39), namely downstream lines (60), conveying means (80) and / or containers (64).

34. 34. The filtering device (10) according to any one of claims 31 to 33, characterized in that the oxidant outlet (39) is connected to the pneumatic conveying means (80).

35. 35. The filtering device (10) according to any one of claims 31 to 34, further comprising an additional outlet (40) provided in addition to the oxidant outlet (39) for discharging the inert fluid and / or the oxidant.

36. 36. The filtration device (10) according to any one of claims 24 to 35, characterized in that the reaction zone (24) includes an agglomerate collection zone (33) configured to receive material that has fallen off the filter surface, and foreign matter or agglomerates containing foreign matter that have accumulated on the filter surface are collected and stored in the agglomerate collection zone (33) after being cleaned.

37. a first closing device having a first blocking member (30) is assigned to said agglomerate collecting area (33); 37. The filtering device (10) according to claim 36, characterized in that the closing device is designed to allow matter that falls off the filter surface during purification to be collected in the agglomerate collection area (33) and, after collecting the matter that falls off in the agglomerate collection area (33), to close the reaction area (24) from the raw gas space (15) at least until the concentration of oxidant in the reaction area (24) has decreased to a sufficient extent.

38. a discharge area (62) located downstream of the agglomerate collection area (33), through which material that has fallen off the filter surface can be conveyed; the discharge zone (62) comprises at least a portion of the reaction zone (24); and 38. The filtering device (10) according to claim 36 or 37, characterized in that an oxidizing agent can be supplied to the agglomerate collection area (33) and / or to the discharge area (62).

39. the discharge area (62) has a second closure device; 39. The filtration device (10) of claim 38, wherein the reaction zone (24) is located between the first closure device and the second closure device.

40. The discharge area (62) has a collection container (64) for separating solid-containing material; The collection container (64) has an outlet for the fluid material; 40. Filtering device (10) according to claim 38 or 39, characterized in that a filter unit (122) is assigned to the outlet for cleaning the fluid substance from foreign bodies.

41. a fluid recirculation unit (150) configured to recirculate, in whole or in part, to the reaction zone (24) any oxidant not consumed in the reaction zone (24) and possibly any further fluid that has accumulated as excess fluid after leaving the reaction zone (24); 41. The filtration device (10) according to any one of claims 24 to 40, further comprising a control / regulation unit for regulating the fluid pressure in the reaction zone (24) so ​​that it does not exceed a predetermined upper limit or remains within a predetermined pressure range.

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