US-20260124568-A1 - METHOD FOR THE DRY FILTRATION OF A GAS FLOW CARRYING FOREIGN OBJECTS, AND FILTER DEVICE FOR CLEANING RAW GAS CARRYING FOREIGN OBJECTS

US20260124568A1US 20260124568 A1US20260124568 A1US 20260124568A1US-20260124568-A1

Abstract

A method and a filter device for the dry filtration of a gas flow carrying foreign objects in a filter device for purifying waste gas produced in additive manufacturing technologies, conducting a raw gas flow containing foreign objects into a raw gas space of a filter unit having at least one filter surface separating a raw gas side from a clean gas side, feeding oxidant to a reaction region located on the raw gas side of the filter surface downstream of the filter surface, such that foreign objects contained in material cleaned off from the filter surface and/or in the raw gas flow react with the oxidant in the reaction region to form foreign objects containing oxides.

Inventors

Walter Herding
Urs Herding
Sebastian Dandorfer
Stefan Hajek
Dino Bethke
Klaus Rabenstein
Maximilian Rösch
Thomas Sehr
Franz Weiss

Assignees

HERDING GMBH FILTERTECHNIK

Dates

Publication Date: 20260507
Application Date: 20251219
Priority Date: 20200128

Claims (20)

1 . A method for the dry filtration of a gas flow carrying foreign objects, comprising: conducting a raw gas flow containing foreign objects into a raw gas space of a filter unit which has at least one filter surface separating a raw gas side from a clean gas side; cleaning-off foreign objects that have accumulated at the at least one filter surface in a cleaning-off cycle and transporting the cleaned-off foreign objects to a downstream reaction region, wherein the reaction region is downstream of the raw gas space with respect to the transport of foreign objects that have accumulated on the filter surface and have been cleaned off from the filter surface during a cleaning-off cycle; feeding oxidant to the reaction region by a pneumatic conveyor; such that foreign objects contained in material cleaned off from the filter surface and/or in the raw gas flow react in the reaction region with the oxidant to form oxide-containing foreign objects.
2 . The method according to claim 1 , wherein the pneumatic conveyor operates as a solids injector or jet pump.
3 . The method according to claim 1 , wherein oxidant is supplied to the reaction region via an oxidant inlet and removed via an oxidant outlet, wherein the oxidant outlet is connected to the pneumatic conveyor.
4 . The method according to claim 1 , wherein the oxidant outlet is different from the oxidant inlet and/or wherein oxidant not consumed during the reaction of material cleaned off from the filter surface with oxidant is removed from the reaction region, wherein not consumed oxidant is discharged through the same oxidant outlet as oxide-containing foreign objects formed during the reaction and, if applicable, foreign objects not yet reacted.
5 . The method according to claim 4 , wherein the reaction region comprises regions located downstream of the oxidant outlet.
6 . The method according to claim 1 , wherein the reaction region has a negative pressure applied thereto.
7 . The method according to claim 6 , wherein the application of negative pressure to the reaction region takes place during and/or following the reaction of material cleaned off from the filter surface with the oxidant; and/or wherein, during reaction of material cleaned off from the filter surface with the oxidant, oxidant that has not been consumed is withdrawn from the reaction region by the pneumatic conveyor.
8 . The method according to claims 1 , wherein the reaction region is supplied by an inert fluid or inert gas; and/or wherein the reaction of material cleaned off from the filter surface with the oxidant takes place in reaction phases and, following a respective reaction phase, the reaction region is supplied by inert fluid without addition of oxidant; and/or wherein inert fluid is fed into the reaction region via a further fluid inlet different from the oxidant inlet; and/or wherein inert fluid and/or oxidant is discharged from the reaction region through a further outlet provided in addition to the oxidant outlet; and/or wherein the reaction region has a heat transfer fluid flown therethrough for removing heat generated during the reaction of material cleaned off from the filter surface with the oxidant.
9 . The method according to claim 1 , wherein the reaction region includes an agglomerate collection region configured to receive material cleaned off from the filter surface, wherein foreign objects or agglomerates containing foreign objects, which have accumulated on the filter surface, are cleaned off and collected and stored in the agglomerate collection region; and/or wherein a first closure means having a first shut-off member is associated with the agglomerate collection region, which closure means is designed such that it enables material falling from the filter surface during cleaning off to be collected in the agglomerate collection region and, after collecting the cleaned-off material in the agglomerate collection region, closes off the reaction region with respect to the raw gas space at least until the concentration of oxidant in the reaction region and/or in the agglomerate collection region has dropped to a sufficient extent.
10 . The method according to claim 9 , wherein material cleaned off from the filter surface is conveyed from the agglomerate collection region into a downstream discharge region, wherein the discharge region comprises at least a part of the reaction region, and oxidant is supplied to at least one of the agglomerate collection region and the discharge region; wherein the discharge region comprises a second closure means, wherein the reaction region is located between the first closure means and the second closure means; and/or wherein the discharge region comprises a collecting container for solids-containing material.
11 . The method according to claim 1 , wherein oxidant not consumed in the reaction region and, if applicable, further fluid accumulating as excess fluid after leaving the reaction region, is completely or partially recirculated to the reaction region; and/or wherein a control/regulation unit is provided which is arranged such that a fluid pressure within the reaction region does not exceed a predetermined upper limit value or remains within a predetermined pressure range.
12 . A filter device for cleaning raw gas carrying foreign objects, comprising: at least one filter element having at least one filter surface separating a raw gas side from a clean gas side in a raw gas space, to which a raw gas flow containing foreign objects can be supplied; a cleaning-off device adapted to clean-off foreign objects, that have accumulated at the at least one filter surface, in a cleaning-off cycle and transporting the cleaned-off foreign objects to a downstream reaction region; wherein the reaction region is downstream of the raw gas space with respect to the transport of foreign objects that have accumulated on the filter surface and have been cleaned off from the filter surface during a cleaning-off cycle; an oxidant supply means adapted to supply an oxidant to the reaction region by a pneumatic conveyor; such that foreign objects contained in material cleaned off from the filter surface and/or the raw gas flow react with the oxidant in the reaction region to form oxide-containing foreign objects.
13 . The filter device according to claim 12 , wherein the pneumatic conveyor operates as a solids injector or jet pump.
14 . The filter device according to claim 12 , comprising an oxidant inlet arranged to supply oxidant into the reaction region and an oxidant outlet arranged to remove oxidant from the reaction region, wherein the oxidant outlet is connected to the pneumatic conveyor.
15 . The filter device according to claim 14 , wherein, during the reaction of material cleaned off from the filter surface with the oxidant, oxidant not consumed can be removed from the reaction region; wherein the oxidant outlet is different from the oxidant inlet; wherein the filter device is designed to discharge unconsumed oxidant through the same oxidant outlet as oxide-containing foreign objects formed during the reaction and, if applicable, foreign objects that have not yet been reacted.
16 . The filter device according to claim 15 , wherein the reaction region comprises regions located downstream of the oxidant outlet.
17 . The filter device according to claim 16 , which is arranged to apply a negative pressure to the reaction region during and/or following the reaction of material cleaned off from the filter surface with the oxidant; and/or is arranged to supply an inert fluid to the reaction region such as an inert gas; and/or wherein the filter device comprises a controller programmed such that the reaction of material cleaned off from the filter surface with the oxidant takes place in reaction phases, wherein an application of inert fluid to the reaction region without addition of oxidant is provided following a respective reaction phase.
18 . The filter device according to claim 17 , further comprising an additional fluid inlet into the reaction region, which is different from the oxidant inlet, for introducing inert fluid and/or heat transfer fluid; and/or further comprising an additional outlet for discharging inert fluid and/or oxidant, which is provided in addition to the oxidant outlet.
19 . The filter device according to claim 12 , wherein the reaction region includes an agglomerate collection region arranged to receive material cleaned off from the filter surface, wherein foreign objects or agglomerates containing foreign objects, which have accumulated on the filter surface, can be collected and stored in the agglomerate collection region after cleaning off thereof; wherein the agglomerate collection region has a first closure means associated therewith which has a first shut-off member and which is designed such that it enables material falling from the filter surface during cleaning off to be collected in the agglomerate collection region and, after collection of the cleaned-off material in the agglomerate collection region, closes off the reaction region with respect to the raw gas space at least until the concentration of oxidant in the reaction region has dropped to a sufficient extent; wherein the filter device further comprises a discharge region which is located downstream of the agglomerate collection region and into which material cleaned off from the filter surface can be conveyed, wherein the discharge region comprises at least a part of the reaction region, and oxidant can be supplied to the at least one of the agglomerate collection region and the discharge region.
20 . The filter device according to claim 19 , wherein the discharge region comprises a second closure means, wherein the reaction region is located between the first closure means and the second closure means; wherein the discharge region comprises a collecting container for separating solids-containing material, wherein the collecting container has an outlet for fluid or gaseous material, wherein a filter unit for cleaning the fluid material from foreign objects is associated with the outlet; and wherein the filter device further comprises a fluid recirculation unit which is arranged such that oxidant not consumed in the reaction region and, if applicable, further fluid accumulating as excess fluid after leaving the reaction region, is completely or partially recirculated into the reaction region, wherein a control/regulation unit is provided which is arranged such that a fluid pressure within the reaction region does not exceed a predetermined value or remains within a predetermined range.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a divisional of U.S. application Ser. No. 17/796,095, filed Jul. 28, 2022 and is incorporated by reference herein. BACKGROUND The invention relates to a method for the dry filtration of a gas flow carrying foreign objects, and to a filter device for cleaning raw gas carrying foreign objects. When purifying gases carrying highly flammable foreign bodies or objects, such as occur in systems for additive manufacturing of workpieces made of metal (e.g. in laser sintering of workpieces made of titanium or aluminum alloys), there is a danger of uncontrolled fires in the waste gas. This danger is particularly great when such highly flammable foreign objects are deposited on filter surfaces and accumulate in the process. Attempts have been made to counter these dangers by precoating the filter surfaces with inerting filtration aids such as CaCo3 or adding such aids to the raw gas to be purified, similar to the design shown in WO 2012/032003 A1. SUMMARY It is an object of the invention to prevent or suppress raw gas fires when filtering raw gases containing flammable foreign objects, such as in particular when filtering waste gases produced in additive manufacturing technologies, by means of a dry filter. In the method for the dry filtration of a gas flow carrying foreign objects, according to the invention, in particular in a filter device for cleaning off exhaust air or waste gas produced in additive manufacturing technologies, a raw gas flow containing foreign objects is fed into a raw gas space of a filter unit which has at least one filter surface separating a raw gas side from a clean gas side. Furthermore, an oxidant is fed to a reaction region located on the raw gas side of the filter surface downstream of the filter surface. The oxidant is fed such that foreign objects contained in material cleaned-off from the filter surface and/or in the raw gas flow react with the oxidant in the reaction region to form oxide-containing foreign objects. The present invention proposes a method and provides a correspondingly designed filter device in which spontaneous oxidation of reactive or even highly reactive foreign objects in waste gases, such as metal-containing particles in the waste gas from additive manufacturing equipment such as laser sintering devices, is specifically brought about. The high reactivity of such foreign objects with oxidants such as oxygen or air-actually the reason why dry filtration of such waste gases is problematic-is thereby specifically exploited to trigger a spontaneous reaction of the foreign objects with oxidant. Surprisingly, it is possible to specifically initiate this spontaneous reaction by appropriate control of the supply and/or discharge of oxidant and, if necessary, other measures, and to keep its course well under control, so that an uncontrolled reaction of the foreign objects with the oxidant can be avoided. With the procedure proposed herein, the heat generated during the reaction can be well dissipated, so that there is no need to fear uncontrollable fires or explosions. A basic idea of the present invention is not to render inert readily combustible foreign objects contained in the raw gas, but rather to render them harmless by purposefully initiating and carrying out a controlled transfer of these combustible foreign objects into an oxidized configuration (i.e. by chemical reaction). In the oxidized configuration, these foreign objects are generally poorly reactive or inert and no longer combustible, so that further handling of these oxidized foreign objects no longer requires any special precautions. However, care must be taken to ensure that the spontaneous oxidation reaction proceeds in a controlled manner. This can be achieved by suitable supply of oxidant to a predetermined reaction region containing material cleaned off from the filter surface and thus containing foreign objects, and/or by further measures to remove oxidant from the reaction region. It has been found that the course of the usually strongly exothermic oxidation reaction can be well controlled if the oxidant is not only supplied to the reaction region, but rather flows through the reaction region. The oxidant is then supplied to the reaction region at a first location or in a first region (inlet) and flows through the reaction region until it leaves the reaction region again at a further location or a further region (outlet), in any case provided it has not been consumed by reaction with material containing foreign objects while flowing through the reaction region. In this way, it is possible to specifically provide an excess of oxidant in the reaction region, as it is necessary to spontaneously initiate the desired reaction for the formation of oxide-containing foreign objects or to maintain the same to a controlled extent. The flow of oxidant flowing through the reaction region allows precise control of the course of the oxidation reaction.