DE102020102034A1 - Process for the dry filtration of a gas stream carrying foreign bodies, use of an inorganic material based on silicon dioxide as a filtration aid, and filter device for cleaning raw gas carrying foreign bodies - Google Patents

Abstract

A method for dry filtration of a gas stream (44) that carries foreign bodies, in particular in a filter device for cleaning off exhaust air resulting from additive manufacturing technologies, comprising: supplying a crude gas stream (44) containing foreign bodies into a crude gas space (15) of a filter unit which has at least one filter surface from filtration aid to the raw gas stream (44) and / or to the filter surface; wherein the filtration aid is configured in such a way that it suppresses a reaction of foreign bodies with oxidizing agents, in particular with oxygen; wherein the filtration aid is an inorganic material based on silicon dioxide.

Description

The invention relates to a method for dry filtration of a gas stream carrying foreign bodies, as well as the use of an inorganic material based on silicon dioxide as a filtration aid, and a filter device for cleaning raw gas carrying foreign bodies.

The WO 2012/032003 A1 shows a method for dry filtration of gases that carry foreign bodies, eg exhaust air from a paint shop, in which the filter surfaces are coated with limestone powder (CaCO ₃ ) as a filtration aid before being charged with raw gas containing foreign bodies. In this way, pores of the filter can be suppressed from being closed by sticky foreign matter. This coating of filter surfaces with limestone powder before they come into contact with foreign bodies is known as precoating. Precoating is typically used to clean exhaust air from wet painting systems.

The object of the invention is to avoid or suppress raw gas fires when filtering raw gases containing inflammable foreign bodies by means of a dry filter, in particular at high operating temperatures.

In the method according to the invention for dry filtration of a gas flow carrying foreign bodies, in particular in a filter device for cleaning off exhaust air resulting from additive manufacturing technologies, a raw gas flow containing foreign bodies is fed into a raw gas space of a filter unit which has at least one filter surface. Filtration aid is supplied to the raw gas stream and / or the filter surface, the filtration aid being designed in such a way that it suppresses a reaction of foreign bodies with oxidizing agents, in particular with oxygen. The filtration aid is a silica based inorganic material.

It has been found that the addition of limestone powder by means of precoating has some disadvantages if high temperatures prevail or arise during dry filtering, such as when filtering raw gases loaded with highly flammable foreign bodies. The formation of agglomerates from limestone powder and foreign bodies does not seem to be sufficient in such cases to achieve sufficient inertization of the foreign bodies. More detailed investigations have shown that limestone powder at high temperatures, in particular above the calcination point of 650 ° C., at which CaCO ₃ breaks down to CaO and CO ₂ , tends to split off oxygen. The resulting connections promote the development of a fire instead of preventing it.

The invention proposes to modify the precoating process in such a way that instead of limestone powder, a substance is added as a filtration aid that is selected with a view to suppressing a reaction of spontaneously inflammable foreign bodies with oxidizing agents, in particular with oxygen, during the filtration. This ensures that fires do not arise or that, after ignition, the further spread of flames is effectively hindered. The filtration aid proposed here is easy to dose. In particular, the proposed filtration aid is suitable for forming agglomerates containing foreign bodies. The addition of the filtration aid does not interfere with the functioning of the filter in normal operation (i.e. without fire). This includes, in particular, that the filtration aid, after contact with the gas flow contained in the foreign body, forms a well-adhering filter cake on filter surfaces that is also easily detachable by means of compressed air pulses.

The raw gas is an uncleaned gas that carries foreign bodies and has not yet passed through a filter device. For example, the raw gas can be a gas (aerosol) or smoke that carries metal particles. The term smoke is intended to denote an aerosol made up of dust particles and / or liquid droplets in finely divided form that is carried in an air or gas flow. In the case of smoke, the particle diameter is usually 800 nm or smaller. In the case of a raw gas carrying combustible foreign bodies, provision can be made for an inert gas to be provided as the carrier gas, ie for the proportion of oxygen and other components that can act as oxidizing agents in the carrier gas to be kept below a predetermined threshold. In such a case, the filtration of the raw gas also takes place under inert conditions, ie the proportion of oxygen and other components that can act as oxidizing agents also remains below a predetermined threshold in the raw gas space. Foreign bodies only come into contact with oxidizing agents such as oxygen when material is discharged from the raw gas space.
An inorganic material is in particular a material which mainly consists of carbon-free compounds, in particular is free of organic chemical compounds of carbon. Certain carbon compounds such as carbon monoxide, carbon dioxide, carbon disulfide, carbonic acid, carbonates, carbides, ionic cyanides, cyanates and thiocyanates are also to be considered as inorganic materials. The inorganic materials include, in particular, silicon dioxide.

Based on silicon dioxide (SiO ₂ ) or based on silicon dioxide im means In connection with the present invention, that the filtration aid has silicon dioxide or a silicon dioxide compound as the main component. The filtration aid can also contain other materials which are present in lower mass fractions than silicon dioxide.

The raw gas space is part of the filter device into which the raw gas is introduced. Agglomerates containing foreign bodies are formed by the accumulation of foreign bodies on the filtration aid. Such agglomerates can be formed in the raw gas flow or raw gas space, but in particular when foreign bodies from the raw gas flow accumulate on filter surfaces when the raw gas flow passes through the filter surface of the filter unit into a clean gas space.

The addition of filtration aid based on SiO ₂ is particularly helpful if the raw gas to be filtered contains foreign bodies that are self-igniting or combustible. Such foreign bodies or foreign particles tend to ignite spontaneously. This ignition can often take place without additional input of heat energy from the outside. If foreign bodies have a small particle size, the foreign bodies have a relatively large surface area in relation to their volume, as a result of which the foreign bodies can ignite particularly easily. It can be sufficient for the foreign bodies to rub against one another as a result of the movement in the raw gas flow. Often the foreign bodies are also charged electrostatically when they rub against each other, which leads to an additional ignition source through electrical discharges. The addition according to the invention of filtration aids based on silicon dioxide reliably suppresses such self-ignition in the raw gas.

The foreign bodies can, for example, contain metals or be metals and have a granular, in particular chip-like, powdery or smoky configuration. The foreign bodies can in particular have a configuration that is not completely or even not at all oxidized. In particular, the foreign bodies can be titanium powder or titanium shavings. The foreign bodies can be metallic foreign bodies that are not or not completely oxidized. Such foreign bodies arise, for example, in the additive manufacturing of metallic workpieces, through the use of powdery metallic materials when building up workpieces in layers from a powder bed. Typical metals that are used in such processes and which can lead to combustible foreign bodies in the exhaust air are titanium, aluminum, magnesium and their alloys, as well as many steels such as structural steel, heat-treated steel, high-alloy stainless steels. The proposed addition of a filtration aid based on SiO ₂ in additive manufacturing processes in which titanium and / or aluminum-magnesium alloys are used has proven particularly suitable for suppressing raw gas fires. The laser sintering process is known, for example, as an additive manufacturing process that produces exhaust gases that tend to self-ignite.

When added, the filtration aid can have a granular, in particular powdery, configuration. This allows precise dosing of the filtration aid into the raw gas stream and / or into the filter device, in particular for covering filter surfaces (precoating). In addition, a corresponding filtration aid enables the use of a simple feed mechanism, such as a flap or a compressed air supply. The finer-grained the filtration aid is when added, the more efficient the formation of ignition-retarding agglomerates.

The filtration aid can be configured in such a way that it binds metal-containing foreign bodies with a granular configuration in agglomerates, in particular at temperatures of 600 ° C. or more, in particular at temperatures of 650 ° C. or more, in particular at temperatures of 700 ° C. or more, in particular at Temperatures of 750 ° C or more, especially at temperatures of 800 ° C or more. Depending on the filtration aid, temperatures of up to 1000 ° C., in particular up to 1250 ° C., in particular up to 1500 ° C., can be reached without excessively inhibiting the formation of agglomerates and / or causing the decomposition or disintegration of agglomerates to an undesirably large extent . The agglomerates formed are not or only with difficulty inflammable in the temperature ranges mentioned, so that greater operational reliability compared to conventional filter devices is possible as a result. Numerous SiO ₂ glasses begin to soften at temperatures above 600 ° C and can then form agglomerates with foreign bodies. Depending on the configuration of the SiO ₂ material, for example by adding additives or forming it as a glass foam, the temperature at which softening begins can be varied in a suitable manner.

When heated strongly, the agglomerates can change into a flowable configuration that resembles a glass melt and, after cooling below the glass transition point, change into a glass-like configuration. The filtration aids melt and thereby enclose the foreign bodies in the melt, so that an inertization already takes place in this state. After the melt has solidified, a glass-like configuration is formed. To form a flowable configuration, it can be used in particular after heating to temperatures of 600 ° C. or more, in particular of 650 ° C. or more, in particular of 700 ° C. or more more, in particular from 750 ° C. or more, in particular from 800 ° C. or more. The agglomerates can have a glass-like configuration after cooling below the glass transition temperature. In this way, contact of the oxidizing agent with the metal-containing foreign body can be avoided.

The filtration aid can in particular be a material which has a glass-like configuration or which can be converted into a glass-like configuration under the action of heat.

Materials based on silicon dioxide with a vitreous configuration are made from a solid 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 from silicon dioxide. This includes so-called silicate glasses in particular. The silicate base glass can be present in its pure form, for example as silica glass. Quartz glass is also conceivable if higher softening temperatures are desired. In addition to the silicate base glass, additional components can also be present, for example phosphate, borate, and the like.

The main component of the filtration aid can be at least one of the following materials: expanded glass spheres, glass powder, silicon dioxide particles (SiO ₂ particles), quartz powder or a mixture of at least two of these materials.

In particular, well-suited glass materials are those made from recycled waste glass (recycled glass), such as expanded glass or foam glass. Expanded glass is produced by grinding old glass shards and adding binding and / or expanding agents to them. This results in roughly round grains with small, gas-filled pores. Expanded glass can be produced in grain sizes from 0.04 to 16 mm. The granulate has a closed pore structure. Foam glass, especially foam glass crushed stone, is made in a similar manner. Expanded glass or foam glass can be produced in such a way that the lower limit for the temperature at which the softening range begins and / or the glass transition temperature assumes a value between 600 ° C and 750 ° C.

In the event of a fire, the initially formed still powdery or granular agglomerates of filtration aid and metal powder soften or melt under the action of heat. The flowable glass melt surrounds the metal-containing foreign bodies and makes them inert. After the melt has solidified, a glass-like structure is formed, with metal-containing foreign bodies being permanently enclosed in the filtration aid or being enclosed by the filtration aid. As soon as the flowable configuration is created, the individual self-igniting particles of the metal are bound (vitrified) by the filtration aid. A reaction with oxidizing agents, in particular with oxygen (02), is difficult or impossible in the vitrified state. A vitrification process of the type described occurs in particular at those points where agglomerates of filtration aid accumulate. In particular, a filter cake that has formed on the raw gas side on a filter surface and which also consists entirely or at least largely of agglomerates of filtration aids can, when heat develops (e.g. in the event of a fire), such a phase transition from a powdery or granular configuration to a flowable one and finally show vitreous configuration. Such a vitrification process can also take place on the surfaces of the cone of material which have formed in an agglomerate collecting area during operation and lead to an efficient inertization of the material stored in the agglomerate collecting area. This vitrification process can be supported by covering the surface of the bulk material cone forming in the agglomerate collecting area with a layer of filtration aid from time to time.

In the event of fire, i.e. in the presence of an oxidizing agent (normally oxygen), the agglomerates formed can remain chemically stable at temperatures of up to 650 ° C., in particular at temperatures of up to 750 ° C., in particular at temperatures of up to 850 ° C., in particular at temperatures of up to 1000.degree. C., in particular at temperatures of up to 1250.degree. C., in particular at temperatures of up to 1500.degree.

An oxidizing agent can be applied to the agglomerate collecting area in a targeted manner or oxidizing agent can be introduced into the agglomerate collecting area. The introduction of oxidizing agent can take place automatically, in particular in accordance with a control system or software. Alternatively or additionally, manual introduction of oxidizing agent can also be provided. Particularly suitable oxidizing agents are gases or gas mixtures with a sufficiently high proportion of oxygen. In the simplest case, the oxidizing agent introduced can be air. The introduction of oxidizing agent into the agglomerate collecting area has the effect that material stored in the agglomerate collecting area can react with the oxidizing agent. This specifically initiates the reaction that actually needs to be suppressed or at least controlled. The heat of reaction generated during the oxidation is absorbed by the filtration aid and leads to an increase in temperature. If the temperature is the If the vitrification temperature of the filtration aid is reached or even exceeds it, the filtration aid changes into a flowable glass-like phase and includes the already oxidized and possibly still non-oxidized agglomerates. The phase change of the filtration aid that is brought about in this way causes the material to be vitrified in the agglomerate collecting area and thus makes this material insensitive to further oxidation processes and thus harmless. After vitrification has taken place, the risk of uncontrolled ignition of material stored in the agglomerate collecting area when the agglomerate collecting area is removed from the filter device can thus be avoided. This measure allows the material held in the agglomerate collecting area to be transferred in a targeted and controllable manner from a reactive configuration to an inert configuration. The amount of filtration aids and / or oxidizing agent added in each case can be used to control or control how much material stored in the agglomerate collecting area is allowed to react with the oxidizing agent. This increases the safety of personnel when handling the agglomerate collecting area, in particular when changing from containers to receiving cleaned material.

The agglomerate collecting area can be acted upon with oxidizing agent in temporal connection with the agglomerate collecting area being acted upon with filtration aid. In particular, the agglomerate collecting area can be acted upon with the oxidizing agent after the filtration aid has been applied to the pouring cone or to the material stored in the agglomerate collecting area. In particular, the agglomerate collecting area can be exposed to the oxidizing agent before an agglomerate collecting container assigned to the agglomerate collecting area is detached from its holder and removed. If, after removing the agglomerate collecting container, the material in the agglomerate collecting container comes into contact with atmospheric oxygen, the combustible substances or mixtures are rendered harmless by vitrification or conversion into an inertly oxidized configuration, so that there is a risk of uncontrolled oxidation or a The fire no longer exists.

After the action of heat, the agglomerates formed from the filtration aid and foreign bodies have a shell enclosing foreign bodies with a vitreous configuration, so that no foreign bodies or foreign bodies come into contact with the oxidizing agent. This reliably prevents a fire in the raw gas space, in a raw gas supply line upstream of the raw gas space of the filter device and / or in an area downstream of the filter device, in particular in an agglomerate collecting area or a line leading to an agglomerate collecting area.

A chemically resistant substance can form from the filtration aid, which can hermetically seal the self-igniting foreign bodies before they can ignite. The chemically resistant substance formed from the filtration aid can even become flowable under the action of heat and thus suffocate flames after foreign bodies have ignited. Silicon dioxide glasses in particular remain chemically stable as a melt up to high temperatures and do not decompose under the action of oxygen or other oxidizing agents. In particular, silicon dioxide glasses do not split off any oxygen-containing functional groups, even at high temperatures.

The filtration aid can be designed such that when heated to temperatures of 600 ° C or more, in particular at temperatures of 650 ° C or more, in particular at temperatures of 700 ° C or more, in particular to temperatures of 750 ° C or more, in particular at temperatures of 800 ° C. or more, no elements or compounds which can act as oxidizing agents are split off. In particular, the filtration aid can be designed in such a way that it remains chemically stable up to temperatures of 1000 ° C., in particular up to temperatures of 1250 ° C., in particular up to temperatures of 1500 ° C., and in particular does not split off any elements or compounds that act as oxidizing agents can work.

The filtration aid can have an average particle size of 10 to 30 μm, preferably between 15 and 25 μm. The mean particle size is understood to mean that the majority of the particles of the filtration aid have a diameter that is between 10 and 30 μm. All information relates to the X50 value, i.e. 50% of the particles have diameters in the specified range.

Depending on the raw gas to be filtered, the filtration aid can have a softening point or a glass transition temperature of 600 ° C or more, in particular 650 ° C or more, in particular 700 ° C or more, in particular 750 ° C or more, in particular 800 ° C or more, and up to 1000 ° C, in particular up to 1250 ° C, in particular up to 1500 ° C. In the event of a fire, this allows a phase change of the filtration aid, i.e. transition of the filtration aid into a flowable state, and thus a vitrification of the foreign bodies. A fire can thus be reliably avoided or stopped.

The method can further distribute or atomize the filtration aid in the Have raw gas space, in particular a uniform distribution on components arranged in the raw gas space, such as filter elements and raw gas space walls of the filter device.

In the process, agglomerates containing foreign bodies deposited on the filter surface can be cleaned off and collected and stored in an agglomerate collecting area. It can be provided that the agglomerate collecting area is acted upon with filtration aid.

The agglomerate collecting area can be acted upon when the agglomerate collecting area holds a predetermined amount of agglomerates. This prevents the amount of agglomerates lying against one another from exceeding a certain amount in order to reduce the risk of the agglomerates igniting.

Before removing an agglomerate collection container assigned to the agglomerate collection area, filtration aid can be applied to the agglomerate collection area in such a way that the agglomerates containing foreign bodies collected in the agglomerate collection area or in the agglomerate collection container are covered with a layer of filtration aid. After the agglomerate collecting area has been charged with filtration aid, the agglomerate collecting area can also be charged with an oxidizing agent, in particular after filtration aid has been applied to material stored in the agglomerate collecting area and before the agglomerate collecting container is removed.

The agglomerate collecting container can in particular be a disposable container intended for single use only. After the agglomerate collecting area has been charged with filtration aid and oxidizing agent, the agglomerate collecting container can be removed and disposed of. Since, after the addition of oxidizing agent, the cleaned material has already been vitrified in the agglomerate collection container before it was removed from its holder, it is ensured that all material is bound in the agglomerate collection container and that it can be safely disposed of in the usual way.

• - Vorrichtung zur Absaugung von Abgasen, die bei additiver Fertigung von Werkstücken aus pulverförmigen metallischen Ausgangswerkstoffen entstehen;
• - Vorrichtung zur Beseitigung von Rauchgasen, die beim Herstellen von Werkstücken mittels Laser-Sinter-Verfahren erzeugt werden;
• - Vorrichtung zur Beseitigung von Luftverunreinigungen in einer Laserstrahlschweißanlage oder einer sonstigen Schweißrauchabsaugungsanlage,
• - Vorrichtung zur Beseitigung von Verunreinigungen in Rauchgasen, insbesondere in Rauchgasen, die bei additiver Fertigung oder in thermischen Prozessen anfallen.

According to the invention, it is proposed to use an inorganic material based on silicon dioxide as a filtration aid in the dry filtering of a flow of crude gas carrying foreign bodies in order to suppress or at least control reactions of foreign bodies with oxidizing agents, in particular with oxygen, in particular when cleaning foreign bodies from a gas flow in a filter device, in particular in a device of one of the following types:

• - Device for the suction of exhaust gases that arise during additive manufacturing of workpieces from powdered metallic starting materials;
• - Device for removing smoke gases that are generated during the manufacture of workpieces by means of laser-sintering processes;
• - Device for removing air pollution in a laser beam welding system or other welding fume extraction system,
• - Device for removing impurities in flue gases, especially in flue gases that occur in additive manufacturing or in thermal processes.

The filtration aid and / or the dry filtering can have at least one of the features disclosed above in relation to the filtration aid and / or dry filtering.

A filter device according to the invention for cleaning crude gas carrying foreign bodies comprises at least one filter element with at least one filter surface in a crude gas space, to which a crude gas stream containing foreign matter can be fed, and a filtration aid feed arrangement with an upstream and / or downstream into the crude gas space and / or into the crude gas stream Filtration aid feed line opening into the raw gas space for supplying filtration aid. The filtration aid is configured in such a way that it suppresses a reaction of foreign bodies with oxidizing agents, in particular with oxygen. The filtration aid is an inorganic material based on silicon dioxide.

The filtration aid can be fed to the raw gas stream upstream of the raw gas space, the raw gas space, the filter surface and / or a collecting area for material cleaned from the filter surface (hereinafter also called agglomerate collecting area).

The filtration aid inlet arrangement can be designed in such a way that the filtration aid forms a glass-like protective layer on the filter surfaces facing the crude gas space and / or on the crude gas space walls under the influence of heat and / or can be distributed in the crude gas stream in such a way that it is in the crude gas stream upstream and / or downstream from the filter surface or on Form glass-like agglomerates of filtration aid and foreign bodies on the filter surface under the action of heat.

The filter device can furthermore have an agglomerate collection container assigned to the agglomerate collection container, which is arranged on an underside of the filter device, the agglomerate collection container having a filtration aid access opening through which the filtration aid can be fed into the agglomerate collection container. The agglomerate collecting container can form the agglomerate collecting area.

The filter device can have a first line through which filtration aid can be delivered from a filtration aid storage reservoir into the raw gas space and / or into a raw gas line opening into the raw gas space, and in particular a second line through which filtration aid can be delivered from the filtration aid storage reservoir into the agglomerate collecting container. The second line can optionally also be provided to conduct an oxidizing agent, in particular air or an oxygen-containing gas mixture, into the agglomerate collecting container in order to apply oxidizing agent to material located in the agglomerate collecting container. If desired, the introduction of oxidizing agent can also take place via a third line different from the second line.

The filter device can have a material switch that connects the second line to the first line. This enables the filtration aid to be introduced selectively both into the raw gas space and into the agglomerate collecting container. This increases the safety for operating personnel when operating filter devices according to the invention.

The material switch can be controlled in such a way that a flow of filtration aid can be guided selectively through the first line and / or through the second line. An automatic control device can preferably be used for this purpose. Alternatively, the material switch can also be operated by operating personnel who manually manipulate the material switch and thus introduce the flow of auxiliary filtration into the first line and / or the second line.

The agglomerate collecting container can have an oxidizing agent access opening through which oxidizing agent, in particular air or an oxygen-containing gas mixture, can be introduced into the agglomerate collecting container. By adding oxidizing agent, oxidizable material stored in the agglomerate collecting container can be activated in a targeted manner in order to render the oxidizable material harmless by glazing with a filtration aid and / or converting the oxidizable material into inert oxidized material. This increases the safety of service personnel when replacing the agglomerate collecting container.

The filter device can furthermore have an oxidizing agent line which opens into the oxidizing agent access opening of the agglomerate collecting container. The oxidizing agent line can be used to deliver the oxidizing agent automatically or manually to the agglomerate collecting container in a targeted manner. Automatic is understood to mean that a controller takes over the supply of oxidizing agent. In the case of manual feeding, this is done by the service staff by operating a switch or lever to introduce the oxidizing agent into the agglomerate collecting container. In certain embodiments, the second line can serve as an oxidizing agent line at the same time. For example, the introduction of filtration aid into the agglomerate collecting container can take place at the same time as the material in the agglomerate collecting container is charged with oxidizing agent. It is also possible to introduce the filtration aid into the agglomerate collecting container and to apply oxidizing agent to the material located in the agglomerate collecting container one after the other, for example by means of additional valves in the second line.

The filter device can also have a metering device designed to set a predetermined amount of filtration aids. This allows a precise delivery of filtration aids into the filter device and thus an increase in the operational reliability of the filter device.

The aforementioned embodiments and advantages of the method according to the invention also apply to the use according to the invention and the filter device according to the invention.

• 1 zeigt in einer Seitenansicht eine erfindungsgemäße Filtervorrichtung.
• 2 zeigt die Filtervorrichtung aus 1 in einer gegenüber der Ansicht aus 1 um 90 Grad gedrehten Seitenansicht.
• 3 zeigt eine detaillierte Darstellung einer Dosiereinheit für die Filtervorrichtung aus den 1 und 2.
• 4 zeigt eine detaillierte Darstellung eines Endes der Filtervorrichtung aus 1.
• 5 zeigt ein schematisches Ablaufdiagramm eines erfindungsgemäßen Verfahrens.

The invention and special embodiments of the invention are explained in more detail below using exemplary embodiments.

• 1 shows a filter device according to the invention in a side view.
• 2 shows the filter device 1 in an opposite the view from 1 90 degree rotated side view.
• 3 shows a detailed representation of a metering unit for the filter device from FIG 1 and 2 .
• 4th FIG. 4 shows a detailed illustration of one end of the filter device from FIG 1 .
• 5 shows a schematic flow diagram of a method according to the invention.

1 and 2 show a filter device in side views rotated by 90 degrees to one another 10 for cleaning of foreign bodies entrained raw gas according to one embodiment. The filter device 10 includes a filter unit 12th (in 1 not shown in 2 is one of the filter elements 14th the filter unit 12th indicated). The filter unit 12th is above a raw gas inflow opening 16 in an upper part of a housing, which is partially omitted for the sake of clarity 18th appropriate. The filter unit 12th comprises several filter elements designed as rigid body filters or dry filters 14th , which are attached to a common bracket and parallel to each other in the vertical direction, as in 2 is indicated schematically, the one of the filter elements 14th shows at its installation position. Each of the filter elements 14th has at least one filter surface to which the raw gas acts. In 1 the filter surface exposed to the raw gas is on the outside of a respective one of the filter elements 14th .

In the in 1 and 2 pictured lower part of the housing 18th , which has a raw gas space 15th encloses are next to the raw gas inflow opening 16 another filter aid feed opening 20th as well as a raw gas space opening 22nd educated. These openings 16 , 20th , 22nd are essentially at the same level in an upper area 18a of the lower part of the housing 18th . As an alternative or in addition, the filter aid feed opening can be used 20th in the direction of flow of the raw gas in the raw gas space 15th after or next to the raw gas inflow opening 16 be arranged so that the raw gas mixes with the filtration aid before the raw gas reaches the filter elements 14th got. In 1 is such a downstream or adjoining filtration aid feed opening 20 ' above the raw gas inflow opening 16 , i.e. in the direction of the filter unit 12th shown. In one below this area 18a adjoining area 18b takes the case 18th the shape of a funnel with downwardly tapering side walls. The housing closes at the bottom 18th a catchment area 24 which foreign bodies are collected before it passes through to the deepest point of the collection area 24 arranged disposal opening 26th and a disposal funnel 28 into a vacuum conveyor 30th is directed and disposed of, see the arrow 32 in 1 .

Since the raw gas carries with it combustible foreign bodies, it can be provided that an inert gas is provided as the carrier gas for the raw gas, ie that the proportion of oxygen and other substances that can act as oxidizing agents in the carrier gas remains below a predetermined threshold. Therefore it also remains in the raw gas space 15th the proportion of oxygen and other substances that can act as oxidizing agents below a predetermined threshold. Filtration of the raw gas carrying combustible foreign bodies thus takes place under inert conditions, ie only when material is being discharged from the raw gas space 15th foreign bodies come into contact with oxidizing agents such as oxygen.

The disposal funnel 28 can through a valve 34 be closed at its deepest point, which is only opened briefly when foreign bodies come out of the catchment area 24 should be discharged. To dispose of the waste in the collection area 24 collected foreign bodies, which are usually easily self-igniting without filtration aids, is located in the collection area 24 an inclined fluidizing floor 36 who has a connection 38 is supplied with air. At the port 38 a fan, only schematically designated 40, is connected via the pressurized air or inert gas into the fluidizing floor 36 is directed. The one in the fan 40 generated air flow is adjusted so that although that in the catchment area 24 The collected material is loosened up to such an extent that it can flow freely and thus easily through the disposal opening 26th is removable, but that this material on the other hand not again from the collection area 24 in the housing 18th or in the raw gas space 15th can arrive.

The one with the arrow 44 designated raw gas flow, which carries foreign bodies with it, with the device 10 are to be deposited, occurs via a raw gas supply line 54 through the raw gas inflow opening 16 in the from the housing 18th enclosed raw gas space 15th one that is on its top from the raw gas side of the filter unit 12th is limited. The raw gas flow 44 is after entry into the raw gas space 15th to the filter unit 12th transported. On the raw gas inflow opening 16 opposite side of the case 18th the filter aid feed opening is located 20th , through which filtration aids from a storage container 72 in the raw gas space 15th can be directed. The filtration aids can be in the raw gas space 15th be initiated before this with the raw gas flow 44 is charged. The introduced filtration aids are then deposited in particular on the filter surfaces of the filter elements 14th and / or on the walls of the raw gas space 15th and each form a layer of filtration aid (precoat layer) there. The one through the filtration aid supply port 20th in the raw gas space 15th incoming flow of filtration aids is in 1 with an arrow 45 designated.

Alternatively or additionally, a filter aid feed opening can be used 52 in the raw gas supply line 54 be arranged. The raw gas supply line 54 is with the raw gas inflow opening 16 connected. This allows the filtration aid into the Raw gas flow 44 to be introduced before this in the raw gas space 15th the filter device 10 entry. This results in an advantageous mixing of in the raw gas stream 44 Contained foreign bodies and the filtration aid in order to raise the self-ignition threshold of the raw gas. Optionally, a baffle plate or a distributor plate can be used 56 so near the filtration aid supply port 52 be arranged so that the filtration aid is evenly in the raw gas flow 44 distributed. For this purpose, the flow of filtration aid is applied to the distributor plate 56 directed, thereby removing particles of the filtration aid from the manifold 56 "Chaotically", that is, in non-specified paths, bounce off and get caught in the raw gas flow 44 to distribute. A corresponding distributor plate can also be used in the raw gas space 15th at the filtration aid feed opening 20th or 20 ' be arranged, which ensures a uniform distribution of the filtration aid, in particular on a filter surface of the filter elements 14th enables. In this way, the distributor plate can be attached to the filter aid feed opening 20th be arranged so that particles of the filtration aid bouncing off it in the direction of the filter element 14th are conducted and on the filter surface of the filter elements 14th cling to.

In a lower area of the funnel-shaped housing area 18b there is a connection 48 that with a horizontally through the housing 18b running ring main 46 communicates. The ring line 46 is located above the catchment area 24 and especially always above that in the catchment area 24 collected material. With the connection 48 is another blower 50 connected that in 2 is also only indicated schematically. The blower 50 can, for example, as is the case with the fan 40 , include a side channel blower. In a preferred embodiment, the fan 50 during operation of the filter device 10 operated continuously. The connection 48 and the ring line 46 are optional features for the filter device 10 . In the event that an inert gas is provided as the carrier gas for the raw gas, the ring line should also be used 46 an inert gas in the raw gas space 15th reach.

The filter unit 12th is assigned a compressed air cleaning unit, not shown in the figures, which is located on the clean gas side of the filter unit 12th above the filter elements 14th is located. The compressed air cleaning unit acts on a respective filter element at certain time intervals 14th so that it experiences a pressure surge from its clean gas side. The pressure surge leads to that on the raw gas side of the respective filter element 14th Foreign bodies deposited on the filter surface, such as filtration aids and easily ignitable foreign bodies, move away from the filter element 14th peel off and fall down as a result of their gravity.

The filtration aid can in particular be a material which has a glass-like configuration or which can be converted into a glass-like configuration under the action of heat. Materials based on silicon dioxide with a vitreous configuration are made from a solid 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 from silicon dioxide. This includes so-called silicate glasses in particular. The silicate base glass can be present in pure form, for example as quartz glass or silica glass. In addition to the silicate base glass, additional components can also be present, for example phosphate, borate, and the like.

3 shows a dosing unit 70 for feeding the filtration aid into the filter device 10 or the raw gas flow 44 . The dosing unit 70 has a storage container 72 on, which has a filling opening 74 can be filled with the filtration aid. The reservoir 72 has an outlet at its lower end 76 on, from which the filtration aid is taken if necessary. The outlet 76 is preferably arranged in such a way that the filtration aid reaches the outlet as far as possible by gravity alone 76 is promoted. The reservoir 72 is in a holder 78 attached. The bracket 78 can use one or more weight sensors 79 be provided, with which a fill level of the storage container 72 can be determined. A controller can use this fill level 110 Determine quickly and precisely how much filtration aid is in the raw gas space 15th was fed.

At the outlet 76 is a solid fuel injector 80 arranged, which is controllable so that the filtration aid via a connecting line 82 from the solids injector 80 to a valve 84 and thereafter to one or more of the filtration aid feed openings 20th , 20 ' and 52 is transported. The solid injector 80 can be operated pneumatically, so that the filtration aid is fed through the connecting line by means of compressed air 82 is transported. In 3 includes the connecting line 82 optionally a material switch 86 , which allows a flow of filtration aid into a feed line 88 initiate. This feed line 88 is with a feed opening 90 in a docking plate 98 connected, whereby the filtration aid in one of the agglomerate collecting area 24 assigned agglomerate collecting container 92 can be transported. Another valve 94 is in the feed line 88 near the feed opening 90 arranged to provide a filtration aid feed to the agglomerate sump 92 to control.

The valves 84 , 94 can preferably be designed as a flap or as a disk valve. Alternatively, the agglomerate collection container 92 themselves have a feed opening, not shown, which connects to the feed line 88 and the valve 94 connected is. Alternatively, the feed line 88 also directly with the storage container 72 be connected by a further solid injector, not shown. In that case, the filtration aid could be at different pressures and at the same time both in the raw gas flow 44 as well as in the agglomerate collecting container 92 be initiated. This allows more efficient control of the filter device and further increases the safety during the operation of the filter device 10 .

4th shows a further embodiment of the filter device 10 , in which instead of the disposal funnel 28 and the vacuum conveyor connected to it 30th the agglomerate collecting container 92 on the lower housing part 18b is arranged. Between the lower part of the housing 18b and the agglomerate collection container 92 is a discharge flap 96 and the docking plate 98 arranged through the foreign bodies from the raw gas space 15th into the agglomerate collecting container 92 be carried out. The docking plate 98 enables a gas-tight connection of the agglomerate collecting container 92 to the discharge flap 96 . The agglomerate collection container 92 has a level sensor 100 with which the fill level of the agglomerate collecting container 92 is checked. For example, the level sensor 100 trigger a signal to indicate that the agglomerate collection container 92 must be emptied, or data from the level sensor can be used 100 to be used via the controller 110 the solid fuel injector 80 , the material switch 86 and the valve 94 to be controlled so that the filtration aid in the agglomerate collecting tank 92 is introduced to a barrier layer of filtration aid on the in the agglomerate collection container 92 to build up the particles. This creates a tendency for the particles in the agglomerate collecting container to self-ignite 92 reduced or completely suppressed. It is also possible to periodically add filtration aid to the agglomerate collection container several times 92 to be introduced so that layers of foreign bodies and filtration aid alternate.

An oxidizing agent line also opens 114 into an oxidizer access port 118 of the agglomerate collecting container 92 . Via the oxidizing agent line 114 can the agglomerate collecting container 92 with an in 4th oxidizing agent, for example air or an oxygen-containing gas, which is schematically designated as 112. The oxidant access port 118 has a valve 116 on, reducing the supply of oxidizing agent 112 into the agglomerate collecting container 92 can be controlled or regulated. The valve 116 can for example be designed as a flap or a disc valve.

In particular, the agglomerate collecting container can be provided 92 temporally related to the introduction of filtration aid into the agglomerate collecting container 92 with oxidizing agent 112 to apply. In particular, the agglomerate collecting container can be provided 92 to be charged with oxidizing agent after previously filter aid in the agglomerate collecting tank 92 was initiated. The agglomerate collecting container can also be provided 92 to apply oxidizing agent before the agglomerate collecting tank 92 from the docking plate 98 is removed, for example around a full agglomerate collecting container 92 to be replaced by a new agglomerate collecting container. By pressurizing the agglomerate collecting container 92 with oxidizing agent, an oxidation of the agglomerate collecting tank is targeted 92 located material promoted. This causes, on the one hand, some of the in the agglomerate collecting container 92 Any combustible foreign matter located there are converted into an inert, oxidized form and, on the other hand, due to the heat generated during the oxidation, the filtration aid changes into a glass-like phase while still in the agglomerate collecting container 92 Enclosed material - whether combustible or not - in a vitreous coating. This glazing prevents the flammable foreign bodies still present from further contact with the oxidizing agent and thus transfers the material to the agglomerate collecting container 92 into a harmless chemically inert configuration.

Alternatively or in addition, it is also possible to use oxidizing agents 112 via the feed line 88 into the agglomerate collecting container 92 initiate, for example with the help of a corresponding branch in the supply line 88 upstream of the agglomerate collection tank 92 . Then there may not be a dedicated oxidizing agent access opening 118 in the agglomerate collecting container 92 required.

With the supply of oxidizing agents 112 can target an oxidation of filtered foreign bodies in the agglomerate collecting container 92 to be triggered. The intensity of this specifically triggered oxidation reaction can be determined by the amount and composition of the added oxidizing agent 112 steer well. In addition, the filtration aid, which can be added in large quantities if necessary, absorbs excess thermal energy and vitrifies the reactive material present in the agglomerate collecting container 92 . In this way, an effective and easily controllable way of converting combustible material into Inactive and harmless material in the agglomerate collecting container 92 to reach. This increases the safety when operating the filter device.

When cleaning the filter elements 14th there is a compressed air input into the filter elements directed against the flow direction of the raw gas flow 14th , eliminating foreign matter from the filter element 14th be blasted off by means of the pressure surge and over the lower housing part 18b into the agglomerate collecting container 92 fall. As soon as the level sensor 100 indicates that the agglomerate collection container 92 has reached a specified maximum level, the discharge flap 96 closed. Then it is done manually or by means of the controller 110 the valve 94 open, the material switch 86 actuated and the solid fuel injector 80 activated so that the filtration aid from the reservoir 72 via the connecting line 82 , the material switch 86 , the feed line 88 , the valve 94 and the docking plate 98 into the agglomerate collecting container 92 is transported. A filtration aid feed to the agglomerate sump 92 takes place until over one by the weight sensors in the holder 78 determined weight loss of the storage container 72 a predetermined amount of filtration aids in the agglomerate collecting tank 92 was entered. The amount preferably corresponds to a barrier layer made of filtration aid with a predetermined thickness, for example an approximately 2 cm high barrier layer made of filtration aid, in the agglomerate collecting container 92 . Then the valve 94 closed. After that, an oxidizing agent can be used 112 via an oxidizing agent line 114 and an oxidizer access port 118 into the agglomerate collecting container 92 be initiated. When combustible foreign bodies react with the oxidizing agent 112 the filtration aid is heated in such a way that it vitrifies the foreign bodies and thus prevents any further reaction of the foreign bodies. The agglomerate collection container 92 can from the filter device 10 can be removed without the foreign bodies in the agglomerate collecting container 92 self-ignite. The barrier layer made of filtration aid ensures that the foreign bodies are kept in the agglomerate collecting container 92 does not ignite by itself. This is particularly true when the barrier layer has assumed a glass-like configuration, for example after exposure to heat in the event of a fire. The agglomerate collection container 92 can be lifted and lowered using a lifting and lowering device 99 from the filter device 10 be lowered.

The control 110 is in particular with the weight sensors via data lines or control lines 79 , the solid fuel injector 80 , the valves 84 , 94 , the material switch 86 , and the discharge flap 96 connected to operate or manipulate them.

5 shows schematically a process sequence for dry filtration of a gas flow or raw gas flow carrying foreign bodies in the filter device 10 . The filter device 10 is used in particular to purify exhaust air that is produced in additive manufacturing technologies, with the exhaust air forming the raw gas. This is done in step 102 the raw gas flow 44 the one in the filter device 10 arranged filter unit 12th via the raw gas inflow opening 16 and the raw gas space 15th fed. The raw gas flow 44 in this case contains spontaneously inflammable foreign bodies, such as powdery or chip-like metal dusts, which tend to spontaneously ignite on contact with oxygen or under the action of mechanical energy. In step 104 becomes the raw gas flow 44 and / or the filter element 14th via at least one of the filtration aid feed openings 20th , 20 ' and 52 the filtration aid is supplied, which deals with the foreign bodies in the raw gas stream 44 mixed and thereby reduced the tendency to self-ignition. The softening point of the filter aid is 500 ° C or more. After the softening point has been exceeded, the filtration aid changes to a glass-like configuration and vitrifies the foreign bodies through the associated phase change from an agglomerate of loosely attached solids to a uniform solid with a vitreous configuration. In other words, the filtration aid encloses the foreign bodies with a layer of glass, so that agglomerates of filtration aid and foreign bodies are formed. A supply of oxidizing agent to the foreign body or to the foreign bodies is thus effectively prevented.

QUOTES INCLUDED IN THE DESCRIPTION

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Patent literature cited

• WO 2012/032003 A1 [0002]

Claims (30)

A method for dry filtration of a gas flow (44) that carries foreign bodies, in particular in a filter device for cleaning off exhaust air produced in additive manufacturing technologies, comprising: Directing a raw gas stream (44) containing foreign bodies into a raw gas space (15) of a filter unit (12) which has at least one filter surface, Supplying filtration aid to the raw gas stream (44) and / or to the filter surface; wherein the filtration aid is configured in such a way that it suppresses a reaction of foreign bodies with oxidizing agents, in particular with oxygen; wherein the filtration aid is an inorganic material based on silicon dioxide. Procedure according to Claim 1 , whereby the foreign bodies are spontaneously flammable. Procedure according to Claim 1 or 2 , wherein the foreign bodies contain metals or are metals and have a granular, in particular chip-like or powdery, configuration, in particular titanium, aluminum, magnesium, alloys of these elements, structural steel, heat-treated steel, and / or high-alloy stainless steel. Method according to one of the preceding claims, wherein the filtration aid has a granular, in particular powdery, configuration when added. Method according to one of the preceding claims, wherein the filtration aid is configured in such a way that it binds metal-containing foreign bodies with a granular configuration in agglomerates, in particular at temperatures of 600 ° C or more, in particular at temperatures of 650 ° C or more, in particular at temperatures of 700 ° C or more, in particular at temperatures of 750 ° C or more, in particular at temperatures of 800 ° C or more, in particular at temperatures up to 1000 ° C, in particular at temperatures up to 1250 ° C, in particular at temperatures up to 1500 ° C. Procedure according to Claim 5 , the agglomerates having a glass-like configuration after being heated to temperatures of at least 600 ° C., in particular of at least 650 ° C., in particular of at least 700 ° C., in particular at temperatures of at least 750 ° C., in particular at temperatures of at least 800 ° C. . Procedure according to Claim 5 or 6th , wherein the agglomerates formed up to temperatures of 650 ° C, in particular up to temperatures of 750 ° C, in particular up to temperatures of 850 ° C, in particular up to temperatures of 1000 ° C, in particular up to temperatures of 1250 ° C, in particular remain chemically stable up to temperatures of 1500 ° C in the event of fire. Method according to one of the Claims 5 to 7th , wherein agglomerates formed from filtration aid have a shell enclosing foreign bodies with a vitreous configuration, such that the shell _{suppresses contact of oxidizing agent, in particular O 2} , with trapped foreign bodies. Method according to one of the preceding claims, wherein the filtration aid is designed such that when heated to temperatures of 600 ° C or more, in particular to temperatures of 650 ° C or more, in particular to temperatures of 700 ° C or more, in particular to temperatures from 750 ° C. or more, in particular to temperatures of 800 ° C. or more, and up to temperatures of, 1000 ° C., in particular up to temperatures of 1250 ° C., in particular up to temperatures of 1500 ° C., no elements or compounds are split off that can act as oxidizing agents. Method according to one of the preceding claims, wherein the filtration aid has an average particle size of 10 to 30 µm, preferably between 15 and 25 µm. Method according to one of the preceding claims, wherein the filtration aid has a softening point of 600 ° C or more, in particular of 650 ° C or more, in particular of 700 ° C or more, in particular of 750 ° C or more, in particular of 800 ° C or more , and up to 1000 ° C, in particular up to 1250 ° C, in particular up to 1500 ° C. Method according to one of the preceding claims, wherein the main component of the filtration aid is one of the following materials: expanded glass spheres, glass powder, silicon dioxide particles, quartz powder or a mixture of at least two of these materials. Method according to one of the preceding claims, further comprising distribution of the filtration aid in the raw gas space (15), in particular uniform distribution on elements such as filter surfaces and walls of the raw gas space (15) arranged in the raw gas space (15). Method according to one of the preceding claims, in which agglomerates containing foreign bodies deposited on the filter surface are cleaned off and collected and held in an agglomerate collecting area (24; 92), wherein the agglomerate collecting area (24; 92) is acted upon with filtration aid. Procedure according to Claim 14 wherein the agglomerate collecting area (24; 92) is charged with filtration aid when there is a predetermined amount of agglomerates in the agglomerate collecting area (24; 92). Procedure according to Claim 14 or 15th , wherein the agglomerate collecting area (24; 92) is acted upon with an oxidizing agent (112). Procedure according to Claim 16 wherein the agglomerate collecting area (24; 92) is charged with the oxidizing agent (112) in temporal connection with the charging of the agglomerate collecting area (24; 92) with filtration aid, in particular when the agglomerate collecting area (24; 92) is charged with filtration aid follows. Procedure according to Claim 16 or 17th wherein the agglomerate collecting area (24, 92) is charged with the oxidizing agent (112) before an agglomerate collecting container (92) assigned to the agglomerate collecting area (24; 92) is removed. Method according to one of the Claims 14 to 18th , wherein prior to the removal of an agglomerate collecting container (92) associated with the agglomerate collecting area (92), filtration aid is applied to the agglomerate collecting area (92) so that agglomerates containing foreign bodies collected in the agglomerate collecting area (92) are coated with a layer of filtration aid are covered, and if necessary, the agglomerate collecting area (24, 92) is exposed to the oxidizing agent (112). Use of an inorganic material based on silicon dioxide as a filtration aid in the dry filtering of a raw gas flow (49) that carries foreign bodies with it to suppress reactions of foreign bodies with oxidizing agents, in particular with oxygen, in particular when cleaning spontaneously ignitable foreign bodies from a gas flow in a filter device, in particular in a Device of one of the following types: - Device for the suction of exhaust gases that arise during additive manufacturing of workpieces from powdered metallic starting materials; - Device for removing smoke gases that are generated during the manufacture of workpieces by means of laser-sintering processes; - Device for removing air pollution in a laser beam welding system or other welding fume extraction system, - Device for removing impurities in flue gases, in particular in flue gases that occur in additive manufacturing or in combustion processes; Use after Claim 20 , wherein the filtration aid and / or the dry filtering at least one of the in the Claims 1 to 19th features mentioned. Filter device (10) for cleaning foreign bodies entrained raw gas, comprising: at least one filter element (14) with at least one filter surface in a raw gas space (15) to which a raw gas stream (44) containing foreign bodies can be fed; a filtration aid inlet arrangement with a filtration aid supply line (82) opening into the crude gas space (15) and / or into the crude gas stream (44) upstream and / or downstream of the crude gas space (15) for supplying filtration aid; wherein the filtration aid is configured in such a way that it suppresses a reaction of foreign bodies with oxidizing agents, in particular with oxygen, wherein the filtration aid is an inorganic material based on silicon dioxide. Filter device (10) after Claim 22 , wherein the filtration aid can be fed to the raw gas stream (44) upstream of the raw gas space (15), the raw gas space (15), the filter surface and / or a collecting area for material cleaned from the filter surface. Filter device (10) after Claim 22 or 23 , the filtration aid inlet arrangement being designed in such a way that the filtration aid forms a glass-like protective layer on the filter surfaces facing the crude gas space (15) and / or on the crude gas space walls under the influence of heat, and / or can be distributed in the crude gas flow (44) in such a way that the raw gas flow (44 ) upstream and / or downstream of the filter surface or on the filter surface under the action of heat, vitreous agglomerates of filtration aid and foreign bodies form. Filter device (10) according to one of the Claims 22 to 24 , further comprising an agglomerate collecting area (24; 92) assigned to an agglomerate collecting container (92), which is arranged on an underside of the filter device (10), the agglomerate collecting container (92) having a filtration aid access opening through which the filtration aid is in the agglomerate collecting container (92) can be fed. Filter device (10) after Claim 25 , comprising a first conduit (82) through which filtration aid from a Filtration aid storage container (72) in the raw gas space (15) and / or in a crude gas line (54) opening into the raw gas space (15), as well as a second line (88) through which filtration aid from the filtration aid storage container (72) into the agglomerate Collection container (92) is available. Filter device (10) after Claim 26 , the second line (88) being connected to the first line (82) via a material switch (86), the material switch (86) being controllable in such a way that the flow of filtration aid selectively through the first line (82) and / or can be guided through the second line (88). Filter device (10) according to one of the Claims 25 to 27 wherein the agglomerate collection container (92) has an oxidizing agent access opening (118) through which an oxidizing agent (112) is deliverable into the agglomerate collection container (92). Filter device (10) after Claim 28 , further comprising an oxidizing agent line (114) which opens into the oxidizing agent access opening (118), oxidizing agent (112) being deliverable to the agglomerate collecting container (92) through the oxidizing agent line (114). Filter device (10) according to one of the Claims 22 to 29 , further comprising a metering device (100, 110) designed to set a predetermined amount of filtration aids.

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