DK173944B1 - Method for filtering particles from exhaust gas, an exhaust gas filter and a vehicle - Google Patents

Description

in DK 173944 B1

The present invention relates to the filtration of flue gas particles generated by fossil fuel combustion such as coal, fuel oil or diesel fuel. A particular application of the invention will be filtration of exhaust gas particles from an internal combustion engine, in particular a diesel engine which may be an engine in a vehicle eg a truck, a locomotive, an airplane, a ship or constitute a working engine in a power plant. Alternatively or further, the present invention may apply to flue gas emitted from power plants and waste incinerators.

It is well known in the art to filter particles or soot from exhaust or 10 flue gases generated by combustion of combustible material such as coal or oil, especially fuel oil or diesel oil. Exhaust or exhaust gas filters for diesel engines aim to filter the soot from the exhaust or exhaust gas from diesel engines. The emission of soot from diesel engines is not desirable as the surface of the soot particles contains small amounts of absorbed substances, which soot particles and which substances are considered harmful.

15

Some filters for filtering soot from exhaust and flue gas generated by diesel engines are made of a monolith of porous ceramic material, which consists of thin-walled ducts. The ducts are parallel to each other and all lie the entire length in the direction the exhaust or flue gas flows. The channels are closed alternately at the top or bottom and are often open and closed alternately as in a checkerboard pattern. Thus, each channel has an open and a closed end. In an alternative embodiment, the filter may be twisted into a shape like a spiral and form a gas-permeable package as a piece of corrugated cardboard. In this way, the coverage of the individual channels resembles not only a chessboard, but also a spiral.

25 When exhaust from a diesel engine is passed through the aforementioned filter type, the exhaust or flue gas flows into the channels open on the Inlet side. The exhaust or flue gas is then forced to flow sideways through the porous duct walls into the adjacent ducts which are open on the exit side. In this case, the soot particles will collect in the channels open on the entrance side as they cannot pass through the channel walls. The soot collected will burn when a certain temperature is reached and when a sufficient concentration of oxygen is present in the exhaust or flue gas and the filter will then be regenerated. Between two such processes, there is a significant increase in exhaust or flue gas pressure, which means an increased strain on the filter. In some cases, the burning of soot becomes extremely intense. Thus, if the filter has reached a high temperature as the engine is operating and as high exhaust or low oxygen flue gas has been passed through the filter and if the exhaust or flue gas stream is then reduced to low flow with high oxygen content, the soot is burned. In this burning, due to low gas flow, the energy generated by the burning is collected in the filter, resulting in an extreme increase in the temperature of the filter, which can result in the melting point of the ceramic being exceeded and the filter being destroyed.

The above problem is described in U.S. Pat. Patent No. 4,667,469 according to whose teachings a particular structure of the ceramic gas filter is claimed to solve the above problem. However, it has been found that gas filters constructed in accordance with the aforementioned U.S. Pat. patent teachings, are still subject to destruction during the burning of the sod.

U.S. Patents Nos. 4,436,538 and 4,604,869 disclose alternative ceramic gas filter structures. Common to the known gas filters based on ceramic materials is the fact that the gas filters are very prone to destruction by burning the soot collected in the gas filters. Furthermore, the known gas filters based on ceramic materials have an extremely low mechanical strength. Thus, it has been found that a Corning gas filter disc, which is a component of the gas filter described in U.S. Patent 4,667,469, is very brittle and has a very low tensile strength.

JP-A-57110311, JP-A-58143817 and US-A-4813231 also disclose different types of SiC filters. JP 58143817 relates in particular to a honeycomb primer and describes the known use of extremely fine silicon carbide particles. The active pore structure of the finished filter is provided by a "pore forming agent", for example graphite particles having a diameter of 25 μηη.

JP 55 137 022 discloses a filter formed by forming quartz sand or silicon carbide particles of specially arranged particle size into a 20 bottom porous cylinder by means of a refractory binder, for example water glass. By the principle described in JP 55 137 022, in the case of silicon carbide particles, a heterogeneous material is formed in which the binder phase, according to later experiences, creates problems by, for example, crystallizing, creating volume changes, reacting and giving tension and cracking, and also due to deviating thermal expansion provide tension and cracking.

25

An object of this invention is to provide a method for filtering flue gas gas particles and a flue gas filter by means of which the aforementioned combustion problems are solved.

An advantage of the present invention, compared to the known ceramic gas filter structures which are currently very expensive, is the fact that the smoke or gas filter according to the invention can be made of fairly inexpensive materials and, as a result, sold to a low cost using very simple manufacturing processes well known as such.

35

A further advantage of the present invention, compared to the known ceramic gas filter structures which have very low mechanical strength, is the fact that the flue gas filter, according to the invention, has a high mechanical strength, which makes it possible to produce filter joints which are larger than filter assemblies made from known ceramic 40 filter structures. Known ceramic structures or ceramic filter assemblies are thus difficult to manufacture with a volume greater than 2.5 liters, since larger structures become too brittle and can be destroyed by exposure to vibrations such as vibrations generated in a vehicle. In contrast to these known filter assemblies, the gas filter of the invention can be used in assemblies of at least 20-30 liters in size. The invention thus makes it possible to produce large assembly units.

Another advantage of the invention, compared to the known ceramic gas filter structures which have very low thermal conductivity and very low heat exchange coefficients, is the fact that, unlike the known ceramic gas filter structures which require a sophisticated package, the flue gas filter according to the invention can be easily is packed in, for example, a low alloy stainless steel box or wrapper or in another can or wrapped in another suitable metallic material.

10

According to the invention, the above and other objects, features and advantages of a process for the preparation of a porous filter body are obtained in which SiC particles are mixed with a particle size of 75-170 µπη, a "green" or volatile binder, a plasticity or viscosity regulating agent and a solvent for making a plastic paste, extrudes the paste to form an extruded "green" body and sinters the extruded body to produce a filter body, thereby forming a permanent or ceramic binder, which filter body has a maximum pore size p 100 μΓη, a thermal conductivity of at least 5 W / (m2K) and a porosity of 30-60%.

The basis of the technical solution to the above problem is the understanding that the accumulation of energy through the burning of particles collected in the porous filament can be eliminated or reduced by producing the porous filter blank of a material with a high thermal conductivity to conduct or disperse the heat generated locally by the burning of particles, collected in the porous filter blank, through the porous filter blank 25 to reduce the local temperature rise caused by the porous filter blank by burning, and consequently to reduce the thermal stresses that the porous filter blank is subjected locally to such a degree that elimination of the porous filter blank is eliminated.

A particular aspect of the invention relates to a regeneration technique. According to a preferred embodiment of the method according to the invention, the burning of the particles is carried out by heating the porous filter blank to such a temperature that the particles are burnt.

Thus, the porous filter blank may conduct heat from an external heat source or may conduct an electric current which heats the filter blank to cause heating of the filter blank. The temperature at which carbon is oxidized in the atmosphere to carbon monoxide is approx. 500 ° C, while the temperature at which coal particles, contained in exhaust or flue gas from, for example, a diesel engine, is oxidized is about 500-550 ° C. As a consequence, the porous filter blank according to the invention should be of a material that can withstand heating to a temperature of at least 550 ° C or more, such as 600 ° C, unless the oxidation temperature is reduced by using a carbonation catalyst, e.g., vanadium pentoxide.

Fe 2 O 3, other ferrous oxides or copper oxides, at which the carbon oxidation temperature DK 173944 B1 4 is reduced to approx. 350-450 ° C. Accordingly, the temperature, provided that a carbon oxidation catalyst is used, to which the filter blank is heated, in accordance with the regeneration aspect of the process of the invention, is about 300-600 ° C, preferably 300-450 ° C.

5

The above-mentioned regeneration of the filter according to the invention, by heating the porous filter blank to such a temperature that particles collected in the porous filter blank can be incinerated, which is preferred, periodically, and it is also preferred that the above-mentioned act of conducting the flue gas through the filter is periodically arranged so that at least two porous filter blanks are used, one of which is used to filter flue gas particles by passing the flue gas through it, while the other porous filter blank is regenerated by heating it to a temperature which causes the burning of particles collected therein. After a period of time constituting an operating cycle, the first porous filter blank is regenerated and the second porous filter blank is used to filter particles from the flue gas by passing the flue gas through it.

However, it should be emphasized that the periodic regeneration of the porous filter blanks according to the method of the invention is not limited to a set of porous filter blanks comprising at least two porous filter blanks, since a single porous filter blank 20 can be periodically heated to a temperature at which particles are collected herein is incinerated while the flue gas is still being passed through the porous filter blank or while the porous filter blank is not in operation (the particle-generating engine or plant whose exhaust or flue gas is passed through the porous filter blank is not operating). Furthermore, during the regeneration of the porous filter blank according to the process of the invention, oxygen can be introduced into the porous filter blank to accelerate the combustion of the particles collected therein, or a chemical component which promotes or catalyzes the combustion of the particles can be used further. preheated air is introduced into the porous filter blank to cause burning of the particles collected in the porous filter blank, which, in accordance with the alternative method of the invention and in accordance with the teachings of the invention, serves the purpose of directing the heat generated locally by burning the particles through the porous filter blank to eliminate the risk of damaging the porous filter blank through a local excessive exposure to extremely high temperatures.

In accordance with a further embodiment of the method according to the invention, the porous filter blank is regenerated or purified by passing a purifying air stream in the opposite direction to the direction in which the flue gas is passed, so that most of the particles collected in the porous filter blank are blown back into a return current.

40

It is known in the art of plastic materials to use rigid metal filters to filter a mass of plastic material. Within this technical field, a variety of rigid metal filters has been developed, which serves to provide a filter capable of withstanding a high pressure gradient through a built-in high mechanical strength in the rigid metal filter. Thus, in the U.S. patents Nos. 3,620,690, 3,788,486 and 3,940,269, a sintered austenitic-ferritic chromium-nickel alloy, a rigid filter for filtering a molten thermoplastic resin, in addition to a process for mixing powdered austenitic chromium-nickel steel. According to the techniques described in these U.S. Pat. patents, low density products can be manufactured which are claimed to be particularly useful as filter elements. However, it should be noted that the filters described in these U.S. Pat. patents take little or no account of the thermal conductivity of the metal filter elements, and further do not take into account the aforementioned burning problem.

Advantageously, the porous filter blank from the flue gas filter according to the invention can be used in accordance with known techniques in the art as such, such as the techniques described in the aforementioned U.S. Pat. patents Nos. 3,620,690, 3,940,269 and 3,788,486 and further in accordance with the techniques described in numerous references such as the following U.S. Patent Nos. patents Nos. 2,792,302, 2,709,651, 2,902,363, 2,593,943, 3,223,523, 3,836,302 and 3,919,384.

Thus, according to these techniques, porous filter blanks can be made of powdered metal or metal-like materials by various processes including the well known cold compaction process with or without a volatile pore forming component 20 such as fibers or spheres of plastic material such as organic polymeric materials, e.g. silicon compositions, polypropylene or polystyrene, and subsequent sintering and the so-called no-pressure sintering method. Alternatively, the porous filter blank may be made by a molding process, for example, an injection molding process in which a form of plastic material or wax is used. After the mold is filled with the particulate metal or metal-like material, the plastic material or wax is melted or burned away. The material may be poured into the mold in liquid form containing a volatile liquid and / or a liquid or solid binder. Further, the porous filter blank may be prepared by an extrusion process, e.g., in accordance with the techniques described in the aforementioned U.S. Pat. patents Nos. 3,836,302 and 3,919,384. It is also known to mix metal powder with a binder, either mildly solidifying the mixture and / or linearly pressing the mixture isostatically and sintering the mixture and in this sintering process removing or solidifying the binder so that the metal powder is bonded together. In the above-mentioned U.S. patents refer to numerous materials and binders. These methods find use in the preparation of particulate porous articles, and the selection of the optimum process parameters, etc. for an application depends on the size of the item to be manufactured, its contours, dimensions, porosity and / or permeability, mechanical strength and thermal conductivity.

In a report "Technical and Economic Evaluation of a Cold Isostatic Pressing Technique and 40 Examination of the Pre-Green Specimen Process" published by the Institute of Technology,

The Department of Industrial Metallurgy Technological Institute, Tåstrup, Denmark, dated February, 1987, discusses aspects of a process for producing samples or products based on powder materials. The report is mainly aimed at products of high compactness, but the technique described In said report, by simply reducing the static pressure to a very low pressure value, the production of a high porous filter blank in a flue gas filter according to the invention can be adapted .

In German Patent Nos. 34 40 202 and in published German patent applications Nos 32 32 5 729 and 34 38 217, interesting carbon monoxide catalysts are mentioned, namely zirconia (ZrOCl 2), lithium oxide (Li 2 O) and vanadium pentoxide (V 2 O 5). Thus, the catalyst can be a component of the filter blank or a coating on the blank. Thus, it is believed that the porous filter concept of the invention makes it possible to select carbon dioxide catalysts which are different from the carbon dioxide catalysts used so far in flue gas filters made of ceramic materials, since the catalysts compatible with a SiC blank are different. from the catalysts which are compatible with or can be used in conjunction with known ceramic filters.

The filter of the invention can be made in numerous sizes and structures, such as the structures 15 described in the above references. In the preferred embodiment of the filter according to the invention, the porous filter blank has a flue gas inlet surface and an oppositely directed flue gas outlet surface, a first set of a large number of blind filtration sinks extending from the Inlet surface and generally perpendicular thereto, and a second set of a plurality of blind filtration holes extending from the exit surface and generally 20 perpendicular thereto into the blank, and the first and second sets of filter holes extending side by side and separated from each other.

Alternatively or further, the porous filter blank in the filter of the invention may have partitions of structure as a honeycomb pattern, or the porous filter blank may have a tubular structure. In accordance with a further or alternative embodiment of the flue gas filter according to the invention, the porous filter blank consists of a circular plate of a thickness which is much smaller, several factors of ten, than the diameter of the plate. The above described embodiments of the filter blank are highly advantageous embodiments for filtering particulate matter or soot from exhaust gas from diesel engines, such as diesel diesel engines on vehicles.

30

The particles filtered from flue gas from diesel engines mainly comprise coal, but further include, as indicated above, additives arising from additives to the diesel oil, additives from lubricants and materials or particles arising from engine wear.

The origin of the particles is not known with certainty, but a spectroscopic analysis of 35 particles from a diesel engine reveals that the particles contain, inter alia: Li, B, C, F, Na, Mg, Al,

Si, P, S, CI, K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn. The particles from a diesel engine are extremely small, so more than 50% of all particles are less than 0.5 microns and have a density of 0.05-0.1 g / cm 3. A further analysis of the particles reveals that the soluble organic content of the particles is 5-20% by volume, in some cases even up to 90%, 40 the hydrogen content is 0-2%, the carbon content is 70-90% and the content of ash is 0.2%.

The shape of the particles is irregular and defines a very large surface area. Thus, the particles are very porous and have a soft surface.

7 DK 173944 B1

From the above it can be seen that the particles filtered from the exhaust gas from a diesel engine are not only carbon particles which can be oxidized to carbon monoxide and further, for example, by means of a platinum catalyst, as is well known in the art, can be oxidized to carbon dioxide. However, some of the contents of the particles remain in the filter blank and result in clogging of the filter blank. Therefore, it is believed that a filter according to the invention has a limited service life of approx. 3000-4000 hours corresponding to 100,000-150,000 km driven by a vehicle with a diesel engine.

As indicated above, it is envisaged that the flue gas filter of the invention is applicable in the field of filtration of flue gas particles generated in power plants, waste incinerators, etc. through combustion of combustible material such as fossil fuel, e.g. coal, fuel oil or diesel fuel or waste. At present, flue gas generated in power plants is filtered by means of electrostatic filters, bag filters or textile filters comprising membranes made of plastic material, such as 15 fiberglass resin, teflon, dralon, etc., which, however, cannot withstand temperatures in excess of approx. 200 ° C and so-called multi-cyclone filters. In contrast to these known filters, the filter of the invention is considered to be an effective means for filtering flue gas particles generated in power plants or waste incinerators. In this application, one should prefer a version of the filter in which the porous filter blank is of a tubular structure through which the outer wall of the flue gas is passed. It is preferred that several tubular filter elements be used in a filter composition in a flue gas filter used in a work of the above type.

The SiC material can be directly bonded together, e.g. using pressure or heat, e.g.

25 generated by an electric current, or simply by heating the material, or alternatively or further, the material may be bonded together by a binder. In the above references, a variety of binders are mentioned and as the binder to be used in connection with the particulate material bonded together in the porous filter blank of the flue gas filter according to the invention, a binder which is activated at high temperature effect is preferably preferred. an effect of a temperature of 1000-2000 ° C, preferably 1400-1900 ° C, or a heat volatile binder such as a heat activated glue. Examples of such binders are elastomeric, thermoplastic or synthetic polymeric materials or well-known resin-based binders. Alternatively, the binder may be a metal such as molybdenum, tin, or a metal obtained by reduction of a metal salt, the material being bonded together in the porous filter blank. Alternatively or further, the binder may be a silicate such as clay or hydrated aluminum silicate (Al 2 O 3 * 2 SiO 2 2H 2 O) or another metal silicate composition, e.g. potassium or sodium silicate, which is a binder well known in the art, e.g. described and discussed in the above article published by the Institute of Technology / Department of Industrial Metallurgy and 40 additional In the above-mentioned U.S. patent no. 4604869. Furthermore, a silicic acid ester is believed to be an advantageous binder.

As indicated above, in accordance with the techniques described in the above references, the particulate SiC can be bonded together in a sintering process. In the high-temperature sintering process, sintering is preferably carried out in an atmosphere of N2 or an inert atmosphere such as He or Ar or in the atmosphere. Furthermore, the particulate SiC can be compacted prior to the sintering process by subjecting the material to pressure in a so-called isostatic compression, in which process the material can be further exposed to heat.

5

The invention will now be further described with reference to the drawings, in which

FIG. 1 is a perspective view of a partially cut-away embodiment of the flue gas filter according to the invention, comprising a first embodiment of a porous filter blank housed in a container.

FIG. 2 is a perspective view of a schematic view of another embodiment of a porous filter blank.

FIG. 3 is a general schematic illustration of a set of flue gas filters connected to an exhaust or flue gas output line from a diesel engine, showing the operation cycle and regeneration cycle concept of the invention.

FIG. 4 is a perspective view of a partially cut-away third embodiment of a porous filter blank according to the invention.

FIG. 5 is a perspective view of a portion of the porous filter blank shown in FIG. 4th

FIG. 6 is a perspective view of a partially cut-away view of an alternative fourth embodiment of a flue gas filter according to the invention; and

FIG. 7 is a schematic view of a truck comprising a flue gas filter according to the invention.

FIG. 8 shows a comparative test between a filter according to the invention and a known filter type.

In FIG. 1 shows a porous filter blank 10 comprising SiC and having a preferred porosity of approx. at least 70% and a maximum pore size of approx. 35 pm. The blank 10 preferably has a thermal conductivity of more than 5 W / mK, such as a thermal conductivity of 5-100 W / mK, preferably about 5-40 W / mK. The blank 10 is basically of circular, cylindrical shape and has a circular inlet side surface 12 from which a plurality of blind filtration holes extend perpendicularly to the blank 10. From the surface at the opposite side or end of the blank 10, the side surface of which forms a output end not shown in FIG. 1, a further variety of blind filtration channels extends perpendicularly to blank 10. At the above outlet end of blank 10, blank 10 is provided with a peripheral thickening 16 which fits into an outer enclosure 18. Thickness 16 serves the purpose of guiding blank 10 within the enclosure 18 to allow mounting and removal of the blank 10 relative to the enclosure 18, even if the blank 10 has been more easily deformed by being subjected to thermal stresses or high temperatures.

In FIG. Figure 2 shows another embodiment of a filter blank or, rather, an embodiment of a filter blank assembly comprising a plurality of circular porous metal filter plates made of particulate SiC, whose plates 20 are provided with central openings 22.

In FIG. 3, two sets of circular, porous filter plates 20 are arranged in a first flue gas filter assembly 24 and a second flue gas filter assembly 26.1. 32, 34, 36 and 38 are connected to an electrical control block 40 which in turn is connected to an electric heater or heating element 28 mounted inside the assembly 24 which extends through the central circular openings 22 of the plates 20 1 of the assembly 24. Also an electric heater or heating element 30 mounted in the flue gas filter 26. As will be apparent from the description and further shown in FIG. 3, the joints 24 and 26 are identical.

The joints 24 and 26 are mounted in exhaust or exhaust gas lines connected to an exhaust duct 43 from a diesel engine 54. The engine 54 may constitute an engine in a bus, tram, truck, locomotive or other vehicle. The exhaust or flue gas generated 20 by the engine 54 and ejected through the exhaust duct 43 is guided by conductive member 49 to a first input duct 44 which is connected to an input of the assembly 24 or alternatively, as shown in FIG. 3, is directed to a second input channel 46 which is connected to an input of the assembly 26. A first output channel 45 is connected to an output of the assembly 24, and a second output channel 47 is connected to an output of the assembly 26, which output channels 45 and 47 are connected to a common output channel 48.1 The exhaust channel 43 from the motor 54 is mounted a temperature sensor and a pressure sensor, which is connected to the control block 40 through the lines 50 and 52, respectively. On an output shaft In the motor 54 is mounted a pulley 56 which is connected with a pulley on an electric generator shaft 62 by a belt. The electrical generator 62 is connected to the control block 40. The block 40 may further or alternatively be connected to the electricity grid through electricity terminals 63 and 64 to receive electricity from the electricity grid such as a 380 V, 50 Hz electric current.

When the exhaust or flue gas cleaning or filtration system shown in FIG. 3, Initial, 35, the filtration of the exhaust or flue gas is periodically changed from one of the joints 24 and 26 to the other. The shift may be time controlled so that, after a specific period of time, the control block 40 elicits a shift from filtering by means of assembly 24 to filtering by means of assembly 26 or vice versa. Alternatively, the time for a shift from one assembly to another may be controlled by the control block 40 determined through the pressure detector connected to the control block 40 through a conduit 52 such that an excessive increase in pressure from the exhaust duct 43 results in a shift from the filter assembly that is in use for filtering exhaust or flue gas for the second filter assembly. Alternative operational routines will be obvious to a person with ordinary insight in the field.

10 DK 173944 B1

While the filter assembly 26 is used to filter out exhaust or flue or particulate additives generated by the engine 54 by means of the plates 20, the first filter assembly 24 is regenerated or purified at a time, while the filter assembly 26 is in use, by burning particles which mainly comprise coal, which is collected on the plates 20 in the filter assembly. The burning of coal particles is initiated by the application of heat to the filter assembly 24 or more precisely, in the embodiment shown in FIG. 3, upon supply of heat to the plates 20 of the filter assembly 24, a heat generated by the electric heater 28 which receives electric current from the generator 62 or alternatively from the electricity grid through the terminals 63 and 64. The electric generator serves that purpose in any of the 10 trap providing electric power to a battery pack on control block 40, which in turn supplies the electronic and electrical control means on block 40 with electrical power. Alternatively, the control block 40 may be selected to control the electrical generator 62 and to alternate the electric generator 62 between a first and a second operation state.

In the first mode of operation, the generator 62 supplies only the aforementioned battery pack with power. In the second mode of operation, the electric generator supplies one of the electric heaters 28 and 30 with power for regenerating the filter assemblies 24 and 26, respectively.

The heat emitted by, for example, the electric heater 28 to the porous plates 20 1 20 the assembly 24 is conducted by the plates 20 to the particles collected by these plates and the particles are burned at a specific temperature. In the burning of coal and other combustible contents of the particles, such as certain nitrogen and hydrocarbon compounds, additional heat is generated which further heat is passed through the plates 20 and thence to the enclosure about the filter assembly 24 and on to the surroundings. The sudden rise in temperature 25 due to the burning of the combustible particles is detected by the temperature sensors in the joints, such as the temperature detectors 32 and 34 of the assembly 24. Upon detection of the temperature rise, the control block 40 extinguishes the heating element, the heating element 28 in the assembly 24 or alternatively the heating element 30 in the assembly. 26, depending on which heating element is used to regenerate the particular filter assembly.

30

It is pointed out that the above-mentioned regeneration process described with reference to FIG. 3 can be performed with any embodiment of the flue gas filter according to the invention and any embodiment of the porous filter blank characteristic of the invention, such as the first version shown in FIG. 1, and alternative versions described below with reference 35 to FIG. 4-6.

In FIG. 4 shows a third embodiment of a porous filter blank according to the invention, which in its entirety is given the reference number 70. The porous filter blank 70 is basically a honeycomb structure made by an extrusion process described in more detail below in Example 1. The porous filter blank 70 has an outer wall 86 in the form of a circular cylindrical outer wall. In its longitudinal direction, a plurality of through-channels extend from one end, shown in FIG. 4, to the opposite end of the circular cylindrical blank 70, one of which channels is given the reference number 72. The channel 72 is open at the end shown in FIG. 4 and blocked by a plate 11 at the opposite end not shown in FIG. 4. The channels adjacent to channel 72, opposite channel 72, are blocked by the plates 74 at the ends shown in FIG. 4. However, these adjacent channels are open at their opposite ends, which are not shown in FIG. 4. A porous partition extending longitudinally within the porous filter blank 70 is given reference number 76. The plates 74 may be porous or non-porous sheets.

In FIG. 5, a portion of the porous honeycomb filter blank structure 70 shown in FIG. 4, on an enlarged scale. The channel 72 is thus shown in FIG. 5 defined by opposite partitions 76 and 78 and blocked at its lower end by the filter plate 74. 5, it is further seen that the channels 10 adjacent to the channel 72 are blocked at their upper ends by the filter plates 74. J FIG. 5, the upper end of the vertical passageways constitutes a flue gas inlet end through which particle-containing flue gas is passed, as shown by an arrow 80. The arrow 80 illustrates the direction along which the flue gas is conducted or introduced into the porous filter blank. The particles passed into the porous filter blank are illustrated by dots, one of which is given the reference number 15 82. The particles are trapped by the partitions 76 and 78 and further by the filter plates 74 as the flue gas flow is forced through the partitions 76 and 78 in the porous filter blank as indicated by the arrows, one of which is given the reference number 84.

After being forced through partitions 76 and 78, the flue gas does not substantially contain particles or soot.

In FIG. 6 shows a fourth embodiment of a porous filter blank contained in a flue gas filter with reference number 90. The flue gas filter comprises an outer enclosure or housing which is partially cut away and terminates in a pipe-like component 92 for connection to an exhaust pipe. Inside the enclosure is a plurality of hollow tube-like porous filter elements constituting a fourth embodiment of the porous filter blank according to the invention, one of which has been given the reference number 94. Each element 94 is at its upper end, shown in FIG. 6, blocked by a circular plate 96. The plates 96 are supported by a grid structure 100. A wall section 98 of the element 94 is shown on an enlarged scale at 99, where the porous structure of the element is seen. The ends of the tube-like porous filter elements, opposite the ends shown in Figs. 6, are not blocked and constitute inputs or outputs through which flue gas is conducted. As the upper ends, shown in FIG. 6, is blocked, during the operation the flue gas is forced through the porous tube-like walls into the hollow tube-like porous filter elements. A ceramic fiber coil trap of a structure similar to the flue gas filter 90 shown in FIG. 6, is mentioned in the SAE (Society of Automotive Engineers) journal No. 870011 35 entitled "Urban Bus Application of a Ceramic Fiber Coil Particulate Trap", by Η.O.

Hardenberg, Daimler-Benz AG, Stuttgart, Germany.

In FIG. 7 shows a vehicle with reference number 120 in its entirety. The vehicle 120 comprises a frame 122 on which the front and rear wheels, 124 and 126, respectively, rest. A driver's cab 128 40 further rests on the frame 122, which also carries a diesel engine 130, from which an exhaust pipe 132 extends and is connected to a combustion gas or flue gas filter 134 according to the invention. The combustion gas filter 134 may be constructed according to any of the principles described above, however preferably as a porous filter blank structure of the honeycomb type shown in FIG. 4 and 5.

EXAMPLE 1 65% SiC powder, quality SIKA III with a purity of 99.4% and with grain size in the interval 75-170 pm produced by Ahrendal in Norway, and 2% by weight of very fine-grained Alfa SiC with a grain size pi 0.1-10 pm, quality A 10-20 or B 10-20 from Herman C.

Starck was blended dry in a mixer with 8% by weight MH 300 methyl cellulose from Hoechst. After 15 minutes of mixing time, a powder was obtained, then 10% by weight of water and 15% by weight of ethanol were added and the mixture was further mixed for 15 minutes.

The homogeneous mass obtained was characterized by high rigidity and viscosity, and it was comminuted in chunks of approx. 10-50 grams and was not sticky. The powder composition provided maximum packaging of the material without obstructing plastic molding.

15 extrusion.

On a Handle 80 mm vacuum extruder equipped with a purpose-made extruder head with approx. 500 channels and connected holes, a continuous rod of a so-called circular honeycomb blank was pressed out at an extruder pressure of 10-25 bar.

The diameter of the workpiece was 85 mm and the piece was cut with a length p in approx. 200 mm. The duct cross section was 2.5x2.5 mm and the wall thicknesses were all approx. 1.0 mm.

The prepared "green" blank was dried over 3 days by blowing 5-15 liters of atmospheric air per minute at a temperature of 20 ° C.

25

The filter blank, which had a high mechanical strength after drying, was straightened at both ends with a rotating or cutting tool. Since all channels were to be blinded, every other channel was blocked with a plug 5 mm in length of the plastic material. Then the filter was flipped and the other half of the channels were blocked to obtain a WFF (Wall Flow Filter) filter blank.

The channels can be blocked manually or hydraulically by blocking half of the channels at one time through a mask.

The sintering took place by placing the "green" item in a tightly sealed container made of graphite, which was then placed in a suitable chamber oven. The furnace was emptied of atmospheric air to obtain 99.999% vacuum after which the furnace was filled with argon so that the content of oxygen atoms was extremely limited. The oven was heated at a rate of 5-10 ° C / min to about 350 ° C where the organic binder in the green blank 40 was pyrolyzed and converted to pure carbon over 10-20 minutes. The oven was then heated at a speed of 25 ° C / min to approx. 2500 ° C where the workpiece was sintered for 60 minutes after which the oven was cooled to room temperature and the workpiece was taken out.

13 DK 173944 B1

The item with dimensions of 0 85 L 200 mm was wrapped in a ceramic mat sold under the name INTERAM by the company 3M. This had to hold the workpiece in a steel container fitted with flanges for mounting in an exhaust system on a diesel engine. The mat had to accommodate expansion differences between filter blank material and 5 container material (steel).

For the test, a Golf 1.5 liter 4 cylinder diesel engine was installed in a SuperFlow computer controlled engine dynamometer at Stobbe Engineering A / S in Gentofte. Exhaust backpressure data was measured and collected between the engine and the filter, temperature in the exhaust and various locations within the filter itself. Follow. Figure 8 shows the total test run of the SiC filter. The fully drawn line describes the temperature of the filter. It is seen that the temperature of the filter increased during the first 60 minutes when the engine was operating at 2500 rpm. per minute and a load of 30 Nm. Pi the dashed line describing the back pressure in the filter, i. the pressure between the engine and the filter that this pressure increased as a function of time. This means that particles were collected in the filter during these first 60 minutes. After 60 minutes of driving, the engine was set at 3000 rpm. per minute and the load set up to 53 Nm. This prevented the collected particles from oxidizing as the exhaust gas now contained less oxygen (about 6-8%). After 5 minutes, within a few seconds, the engine was put at 18% idle, increasing the oxygen content of the 20 exhaust gas. Now the temperature in the filter was up to approx. 680 ° C where it is generally known that soot particles oxidize.

An uncontrolled burning of the soot particles collected now occurred immediately. Other experiments have shown that the amount of soot particles collected is about 10 grams. The energy contained in the 25 soot particles was now released in less than 30 seconds, simply because the oxygen concentration was so high and the engine constantly pumped more oxygen through the filter.

Two NICrAI thermometers with a thickness of 2 mm were used to measure the temperature in the filter. After compensating for the inertia of the probes, it is seen that the temperature rise in the filter was of a very limited size: approx. 100 ° C. This increase and the temperatures reached by the filter would not affect the filter at any time or shorten its service life. A SiC WFF surface filter with relatively thick walls has an extremely high thermal conductivity which ensures that no local "hot spots" occur.

35

This SiC filter was compared to a Corier EX 66 Cordierite filter with the same volume. The temperature gradient in this filter is described in step 8 of the dotted line when running a 100% equivalent test. It is seen that the temperature during burning of the soot particles in this filter reaches approx. 1100 ° C which is quite close to the Cordierite 40 melting point (about 1200 ° C), and thus it is not without reason that the Cordierite filter is known for, under adverse, adverse or uncontrolled circumstances, to melt locally.

The consequence of a melt is that the system must be replaced.

EXAMPLE 2 14 DK 173944 B1

Porous filter blanks made of the metal-like material SiC, with different embodiments, were produced at Stobbe Engineering A / S's laboratory in Gentofte,

Denmark and at the Institute of Mineral Industry, Denmark's Technical College. The porous 5 SiC filter blanks were prepared using the extrusion and injection molding techniques, which created an extrusion and injection pressure of about 5-15 bar.

The porous SiC filter blanks were made from SiC grains having a size of 75-170 µm. A "green" or volatile binder and a permanent or ceramic binder were used. The following permanent or ceramic binders were used: glass mullite and silicon nitride. The following volatile or "green" binders were used: methylceilulose, clay and carbon black with a total weight percent of 5-15. The following plastic and viscosity control agents with a weight percent of up to 0.2 were used: glycerol and alcohol. In addition, 15 alcohol and water were used as solvents with a weight percent of 20-25.

All of the above components constituted a paste from which "green" blanks were prepared and dried. The "green" blanks were then heated to a temperature of 1500-1900 ° C to generate the permanent or ceramic binder and sintered the blanks together. The glass mullite was generated from the clay blend, provided that the sintering process was carried out in the atmosphere and silicon nitride was generated as the permanent or ceramic binder provided that the sintering process was carried out in an N 2 atmosphere. By sintering the "green" blanks containing clay as the volatile or "green" binder, in an N 2 atmosphere, additional Al 2 O 3 was generated as a permanent binder.

The porous SiC filter blanks prepared in this way were tested and had the following properties: the porosity was about 30-60%, the total density was about 1.0-1.7 g / cm 3, resulting in a geometric total density of the filter blanks of about 0.5-0.8 g / cm 3. It turned out that the pore size of the porous SiC filter blanks could be adapted to certain requirements depending on the original size of the SiC granules.

It is believed that the following components can be used in conjunction with porous SiC-35 filter blanks: permanent binder: microcrystalline silicon carbide instead of glass / mullite or silicon nitride, 40 green or volatile binder: wax, silicon alkoxides, polycarbosilane instead of or together with methylceilulose , clay and carbon black.

It is further believed that the sintering process can be carried out 1 atmospheres different from the atmosphere and the N2 atmosphere, e.g. in an atmosphere of argon or helium.

DK 173944 B1

The porous filter blank of SiC is highly resistant to corrosion and has a high thermal conductivity (100 W / mK). Resistance to corrosion is especially important in connection with filtration of exhaust gas from diesel engines, as these exhaust gases are known to be extremely corrosive. The porous SiC filter blank according to the invention has a further high melting point which ensures that the porous filter blank is not melted down under any circumstances.

Apart from the ability to withstand thermal stresses generated by the firing of 10 particles trapped in the porous filter blank, the porous filter blank concept of the invention has distinct advantages over the prior ceramic flue gas filter structures. The flue gas filter according to the invention provides an almost optimal connection between space and filtration surface, which is of the utmost importance in the case of automobiles, vehicles, locomotives, etc., where the flue gas filter must be of maximum compactness to fill a minimum space and still provide sufficient large filtration surface area.

A further important aspect of the invention relates to the ease of encapsulation of the porous filter blank, for example, in a low alloy stainless steel container or enclosure which is simply welded or soldered to the porous metal filter blank. As discussed above, the porous filter blank according to the invention can be equipped with a catalyst to catalyze the burning of soot collected in the porous filter blank. However, this catalyst may alternatively occur in the container or enclosed, for example, as an inner coating thereon.

It is further believed that the teachings of the invention may apply to other technical fields where gases or liquids are to be filtered, by which filtration process particles are collected in the filter, whereupon the particles are burned, and in which case the drainage of the subject is subjected to high temperatures to be controlled or reduced. or even eliminated to exclude the risk of damaging the filter blank.

Claims (1)

A process for preparing a porous filter body / characterized by mixing SiC particles with a particle size of 5 75-170 µΐπ, a "green" or volatile binder, a plasticity or viscosity regulating agent and a solvent for preparing a plastic paste, extrudes the paste to form an extruded "green" body and sinters the extruded body to produce a filter body, thereby forming a permanent or ceramic binder, which filter body has a maximum pore size of 10-100 μηι, a thermal conductivity 10 of at least 5 W / (m2K) and a porosity of 30-60%.