DE29600681U1 - Soot filter system - Google Patents

Description

Hug Engineering Ag HUG960101GDE

CH-8484 Weisslingen 16.01.1996

Soot filter system

The invention relates to a soot filter system for separating non-volatile substances from an exhaust gas stream, in particular soot particles from diesel engines, which soot filter system has interior spaces connected via filter media in a housing with gas supply and gas discharge nozzles, wherein the filter media comprise a plurality of axially spaced, upstream closed and downstream open filter cartridges with a dimensionally stable, perforated inner casing and an outer casing made of a heat-resistant material, in particular an organic fiber material, which is permeable to gas with low resistance.

In combustion systems, particularly in stationary or mobile diesel engines, incomplete combustion produces harmful gaseous components as well as non-volatile substances, primarily soot particles. So-called polycyclic hydrocarbons accumulate on this amorphous form of pure carbon when the exhaust gas cools down. Both these polycyclic hydrocarbons and the soot particles themselves are considered carcinogenic.

Soot particles from diesel engines are mostly very small, they can be submicron in size, which is why they are absorbed with the air we breathe and can penetrate deep into the lungs. Several institutes from different countries

3 found a carcinogenic effect in the lungs in animal experiments at diesel soot concentrations of around 2.2 mg/m. In the context of increasing ecological awareness and corresponding legal restrictions, it is therefore essential to remove not only the harmful gas components but also the soot particles from the exhaust gases of all types of diesel engines.

EP, Al 0558452 describes a method and a device for removing gaseous pollutants from exhaust gases of combustion plants, including diesel and gas-diesel plants. This economical system has a high level of efficiency in terms of removing gaseous pollutants, but is not specifically designed for removing soot particles when used for diesel engines; a suitable diesel soot filter must be installed upstream.

A large number of different diesel soot filters are known, which basically use an open-pored foam or a fiber material as a filter medium.

Of central importance is the detailed design of the filter medium, which on the one hand must remove the soot particles from the exhaust gas flow with high efficiency, but on the other hand must not generate too high a back pressure that reduces the efficiency of the engine. In the following, only the filter media made of fiber material of the generic type used in the present invention will be considered. Fibrous filter media are disclosed, for example, in WO 93/23657 with cross-shaped filter layers, in DE, Al 4125686 with support bodies statistically distributed in the fiber material and in EP, Bl 0334910 with filter material formed at least partially or completely from a circular knitted fabric.

EP, Al 0515776 describes a filter cartridge, called a soot filter candle, which is exposed to exhaust gas from the outside. The soot is deposited on the outer wall, which consists of a structure of temperature-resistant fibers and is designed as a woven, knitted, warp-knitted, wound and/or felt. The fibers consist of ceramic and/or metal, both preferably sintered.

During operation of a diesel soot filter, the particles, which consist almost exclusively of soot, are separated mechanically and by adhesion forces in the fiber material, loading the filter. The filter media must therefore be regenerated from time to time, whereby the soot is burned practically without residue. Various regeneration processes are known:

- A combustion chamber is installed in front of a soot filter and a free space is created inside (DE, Al 4909478). It is also known to use a burner sector by sector {WO 87/073424).

- A hot gas generator is installed upstream of a diesel soot filter, which can be detachably connected (DE, Al 4226 901).

- An electrical resistance heating device is installed in the diesel soot filter.

The present invention is based on the object of creating a soot filter system of the type mentioned above, which, with a durable, robust construction, allows a simple recycling concept and is universally usable.

The object is achieved according to the invention in that the soot filter system comprises at least one removable soot filter insert or removable soot filter modules, whereby these are equipped with filter cartridges detachably attached at both ends. Special and further embodiments of the device according to the invention are the subject of dependent claims.

During operation of the soot filter system, residue-free combustible soot particles are continuously deposited on the filter medium of the filter cartridges and in very small quantities

Mass non-combustible deposits are deposited. During regeneration, i.e. when the soot is burned off, the non-combustible deposits remain in the filter medium. If the properties of the filter medium are no longer sufficient as a result of these non-combustible deposits, the soot filter insert or the soot filter module in question is removed, one or more filter cartridges are removed and the filter medium is cleaned or replaced. Even when the filter medium is replaced, the inner casing of filter cartridges, also known as perforated tubes, can be used several times. This saves valuable resources and increases efficiency.

The filter cartridges are closed upstream and must in this case be open downstream. They are screwed on the gas inlet side with a filter cartridge holder that is open in the area between the cartridges, on the gas outlet side with a filter cartridge holder that is open in the area of the cartridges. Particular attention must be paid to the seal; no gas streams may creep past the filter medium, instead the entire exhaust gas stream must be guided through the filter medium.

A detachable mechanical connection, e.g. screwing, of the individual parts creates solid soot filter inserts or soot filter modules that are stable in themselves. The seal can be achieved by a preferably multi-part clamping piece which is arranged on the inside next to the downstream filter cartridge holder and acts on the rigid inner casing of the filter cartridges via a seal.

The holding and support parts of the soot filter system are preferably made of stainless steel, which largely prevents scaling of the metal parts and ensures a very long service life. Special attention is paid to the design of the dimensionally stable inner casing of

·

Filter cartridges are given as a gift. The porosity is usually achieved by forming round and/or elongated holes in a sheet metal casing. A cylindrical surface with the necessary mechanical strength can also be achieved with a wire or ribbon grid.

The dimensionally stable inner casing must support the outer casing of the filter cartridges, which separates the soot particles. The heat-resistant, inorganic fiber material consists of high-temperature filaments or yarns with high adsorption capacity, whereby the yarns can be designed in a conventional manner as multifilament yarn or fiber yarn, twisted or untwisted. The filaments or yarns, collectively referred to as fibers, are preferably applied as at least a single-layer braid. The outer casing can, however, also be applied as a single- or multi-layer knitted fabric, warp-knitted fabric, fleece or the like.

The high adsorption capacity of the high-temperature fibers, in physical terms the high van der Waals forces, is ensured by the formation of a high specific surface. The high-temperature fibers used are preferably made of glass or ceramic.

In order to burn the soot separated during filter operation, a regeneration temperature of about 600 ^° C must be exceeded in a known manner, e.g. according to a variant described above, then the soot burns without residue.

According to a particularly preferred embodiment of the present invention, the soot ignition temperature can be reduced to about 300 - 400°C if the filtering fiber material is coated with a catalytically active material. This consists, for example, of vanadium oxide (VO ₁ -), also with a noble metal component, eg platinum (Pt).

For a very good efficiency of the soot filter system, it is also important that no leaks can occur between the individual soot filter inserts or soot filter modules, which would result in uncleaned creeping gas flows. Soot filter modules in particular are preferably effectively sealed against each other with an elastic glass fabric seal.

Of particular advantage is the use of a soot filter system according to the invention or of soot filter modules of a soot filter system according to the invention in an exhaust gas purification system in combination with a downstream selective reduction catalyst or a downstream selective reduction and oxidation catalyst. Preferably, each soot filter insert or each soot filter module has at least one catalyst arranged downstream, e.g. flanged, wherein the cross-sectional dimensioning and the number of elements are matched to the exhaust gas volume flow.

A soot filter system with soot filter inserts or soot filter modules and downstream catalysts can be conveniently installed in an exhaust gas purification system according to EP, Al 0558452. A system of this type for producing electrical power described below as an example has a diesel engine of 6000 kW. At 100% load, the gas temperature is in the range of up to about 550 ⁰ C, with a

Exhaust gas volume flow of 100,000 m3 /h is generated. Low-sulphur (approx. 0.05% S) diesel fuel is used as fuel and ash-free or synthetic lubricating oil is used as engine lubricating oil. With the engine optimally adjusted, an exhaust gas back pressure of approx. 12 mbar is generated, the raw gas

3
Dust content is about 120 mg/Nm .

In this plant, 176 soot filter modules with a downstream selective reduction and oxidation catalyst are used, with each soot filter module having a capacity of 150 x 150 x

1000 mm comprises nine filter cartridges with a diameter of 47 mm and a length of about 1000 mm. The exhaust gas pollution

3
per module is about 570 m /h.

At normal load, a soot separation efficiency of at least about 90% has been measured, usually at least about 95%.

The service life of the soot filter modules depends on the inert, i.e. non-combustible solid particles in the engine exhaust. This ash consists of compounds of the following elements :

Calcium >30% w/w
Zinc 10 to 30 wt.%
^; Phosphorus 3 to 10 wt.%

The remainder consists of compounds of aluminium, iron, magnesium, lead and silicon, each containing about 1 to 3% by weight.
20

The amount of these compounds depends on the consumption of fuel and lubricating oil, and of course also on their composition. A single soot filter module for an operating

3
A volume flow of around 600 m3 /h can be loaded with a maximum of around 80 g of ash. Over time, some of the ash seeps inwards through the filter medium. When the ash on the inside of the filter medium reaches the exhaust gas flow, it is carried along. Thanks to the seepage of the ash, the cleaning intervals become longer.

If the properties of the filter medium are no longer sufficient due to excessive non-combustible deposits, the filter cartridge in question is dismantled and the filter medium cleaned or replaced. The inner casing of the filter cartridge can be used several times, thus saving valuable resources.

A soot filter system according to the invention has a simple basic concept, is flexible in use and economical in production and operation thanks to the replaceable soot filter inserts or soot filter modules with individually replaceable filter cartridges. With a small number of elements, the most diverse soot filter systems can be built, and in addition to the cost-effective large series, there is low storage, which further improves economic efficiency. A preferred, specially designed clamping piece can absorb temperature stresses and vibrations at the downstream end.

The invention is explained in more detail using embodiments shown in the drawing, which are also the subject of dependent claims. They show schematically:

- Fig. 1 a partially cutaway side view

a soot filter module of a stationary soot filter system,
20

- Fig. 2 a front view of the module from the exhaust inlet

tread side,

- Fig. 3 a front view of the module from the exhaust outlet side,

- Fig. 4 is a partially cutaway view of a

filter cartridge,

- Fig. 5 a partially detailed view of the inner casing of the filter cartridge,

-Fig. 6 a view of a multi-part clamping piece,

- Fig. 7 a cutaway view of a mobile soot

filter system with a soot filter insert,

- Fig. 8 a radial section at VIII - VIII in Fig. 7,

-Fig. 9 a soot filter insert for Fig. 7, 5

- Fig. 10 the upstream filter cartridge holder of

Fig.9 ,

- Fig. 11 the downstream filter cartridge holder of Fig. 9,

- Fig. 12 a clamping piece of the soot filter insert according to Fig.

9 and

- Fig. 13 an axial section through a filter cartridge in

Area of the exit side.

A soot filter module 10 of a stationary soot filter system according to Fig. 1 to 3 is essentially cuboid-shaped, it has a cross section of about 150 x 150 mm and a length of about 1000 mm. A module comprises nine filter cartridges 12 with a dimensionally stable inner casing 14 with a diameter of 34 mm and an outer casing 16 made of a braided inorganic fiber material, which is pulled over the inner casing 14 in the shape of a stocking.

The filter cartridges 12 are provided with a closure cap 20 upstream of an exhaust gas flow 18. The exhaust gas 18 flows through openings in the filter cartridge holder 24 into the interior 26 between the filter cartridges 12. The exhaust gas 18 reaches the interior 28 of the filter cartridges 12 via the fibrous outer casing 16 and the porous inner casing 14, whereby the soot particles are separated in the fiber mesh of the outer casing 16. The exhaust gas flow 18, freed of solid particles, exits unhindered from the filter cartridges 12, which are open downstream. A coaxial flange sleeve 30 is attached to this outlet end via a clamping bracket 34. The

·

Sleeve 30 passes through appropriately dimensioned openings 36 in the downstream filter cartridge holder 38. Closure cap 20 and flange sleeve 30 are connected to the inner casing by spot welding, so they are not gas-tight. Sealing is achieved by a front clamp 34, which is placed on the outer casing 16 and tightened in the area of closure cap 20 and flange sleeve 30. The non-gas-tight transitions closure cap 20 - inner casing 14 - flange sleeve 30 are therefore in the clean gas area.

On the inside, a multi-part clamping piece 40, 42, which is shown in detail in Fig. 6, is screwed to the filter cartridge holder 38, the screw connection is designated 56. This clamping piece serves to seal the outlet side of the interior 26 around the filter cartridges 12 and thus to prevent leakage currents. The seals are designated 44, 46.

Upstream, the closure cap 20 of the filter cartridges 12 is attached to the filter cartridge holder 24 via a threaded bolt 48 and a corresponding screw nut 50. Finally, the dimensional stability of the soot filter module 10 is further improved by the filter cartridge holder 24 having an inwardly folded edge 52 and the filter cartridge holder 38 having a folded edge 54. When modules 10 are stacked, the folded edges 52, 54 form the support surfaces.

On the inflow side of the soot filter module 10 shown in Fig. 2, the bowl-shaped filter cartridge holder 24 is provided with essentially square recesses. The filter cartridges, which are screwed on at the front via the closure caps 20, leave an interior space 26 free upstream, through which the exhaust gas to be cleaned can flow without any problems thanks to the openings 22.

In the downstream filter cartridge holder 38 according to Fig. 3 in addition to the openings 36 for the inner casing of the filter cartridge,

•11

The screw connections 56 for the clamping piece 40, 42 are visible.

The inner casing 14 of a filter cartridge 12 (Fig. 1), shown in abbreviated form in Fig. 4, comprises the closure cap 20 with a welding bolt 48, which is designed as a threaded rod, at the upstream end. A flange sleeve 30, also called a collar, is fitted onto the downstream end of the inner casing 14 and spot-welded to the inner casing.

Fig. 5 shows the expanded inner casing 14, also shown in abbreviated form, according to Fig. 4. The porosity consists of regularly arranged round holes 58, which are distributed over the entire inner casing 14. In this case, the round holes 58 have a diameter of 5 mm and a distance d of 7 mm on all sides. The hexagonal perforation thus ensures sufficient mechanical stability to support the fibrous outer casing 16 (Fig. 1).

The multi-part clamping piece, of which an end and middle piece 40, 42 are shown, has, according to Fig. 6, essentially semicircular recesses 60, which in total correspond to the number of filter cartridges to be accommodated. The recesses 60 have a radius approximately 1 mm larger than the flange sleeve 30. Screw holes 62 are also provided, which serve to attach to the downstream filter cartridge holder 38 (Fig. 1, 3).

Fig. 7, 8 show a mobile soot filter system 66 with a removable soot filter insert 70 and a downstream catalyst 64 for removing harmful gaseous components by means of selective reduction or selective reduction and oxidation. A stationary soot filter system in the sense of Fig. 7, 8 can contain any number of soot filter modules according to Fig. 1 instead of a soot filter insert 70. In this case, the catalyst has

expediently a corresponding number of equally dimensioned catalytic converter modules, also called honeycombs. To form the filter catalyst, a catalyst housing 72 is expediently flanged to a soot filter housing 68. The screw connection 74 is embedded in an insulation layer 76 surrounding both housings.

The exhaust gas flow 18 to be cleaned flows via a flanged gas supply nozzle 78 into the soot filter housing 68, then through the openings of the filter cartridge holder 24 into the area of the soot filter insert 70, which is shown in detail in Fig. 9. The housings 68, 72 are flanged together with a sealing ring 80 in between. A peripherally running swelling mat 82 is inserted inside the catalyst housing 72 and a swelling mat ring 84 is inserted on both sides of the front. In the direction of the longitudinal axis L, these paddings are limited by an inserted spacer 86 and an annular constriction 88 in the catalyst housing 72. Downstream, a gas discharge nozzle 90 is flanged to the catalyst housing 72.

Adjacent to the gas supply nozzle 78, a pipe 92 with a cable sheath passes through the insulation layer 76 and the soot filter housing 68. It is used to insert a measuring probe and is closed when not in use.

Fig. 8 shows a radial section VII-VII according to Fig. 7. The soot filter insert 70 comprises nineteen filter cartridges 12 with inner casing 14 and outer casing 16. The soot filter housing 68 with the insulation layer 76 is surrounded by a clamping ring 94, which can be secured with a screw connection 96.

The soot filter insert 70 shown in Fig. 9 corresponds essentially to a soot filter module 10 according to Fig. 1. With a hexagonal design of the filter cartridge holders 24, 38 forming the outer circumference or of their folded edges

52, 54 (Fig. 1), the soot filter insert 70 becomes the soot filter module 10 with nineteen filter cartridges 12. The frontmost filter cartridge 12 of the middle level is visible in full size, the others are partially covered.
5

If the exhaust gas volume flow is larger, the soot filter insert 70 can be enlarged by adding additional rings of filter cartridges. For mechanical and static reasons, a limit for the number of filter cartridges must be set for a soot filter insert; the soot filter insert is replaced by several soot filter modules.

The filter cartridge holder 24 according to Fig. 10 on the inlet side corresponds essentially to Fig. 2. Due to the hexagonal structure of the soot filter insert 70, the openings 22 are, however, triangular in shape. The nineteen holes 98 serve to accommodate threaded bolts 48 (Fig. 4) for fastening the filter cartridges (not shown). Similarly, the filter cartridge holder 38 according to Fig. 11 corresponds to the above Fig. 3. The numerous holes 100 serve to fasten a multi-part clamping piece. On the periphery further screw holes 102 are provided for flanging a catalyst housing 72 (Fig. 7).

A clamping piece according to Fig. 12 assigned to the filter cartridge holder 38 on the outlet side is made up of five parts. The two terminal clamping pieces 40 have three essentially semicircular recesses 60 on their straight long sides, which have a radius approximately 1 mm larger than the flange sleeves 30 (Fig. 4). The four middle clamping pieces 41 have three to five corresponding semicircular recesses 60 on their long sides. Between the clamping pieces 40 ₇ 41 there is a slot 104 approximately 1 mm wide. The arrangement of the holes 100 for the screw connections 56 (Fig. 1,9) corresponds exactly to that of the filter cartridge holder 38 arranged downstream.

Fig. 13 shows a variant of the sealing of the interior 26 (Fig. 1,2) outside the filter cartridges in a soot filter module or soot filter insert. Adjacent to the front side, the inner casing 14 has a spot-welded flange sleeve 30. A clamping piece 40, 42 resting against the front side of this flange sleeve presses the flange sleeve 30 against the seal 44 and the filter cartridge holder 38 when the screws 56 (Fig. 1,9) are tightened. The filter cartridges 12 therefore do not have to be held in the filter cartridge holder 38 with a seal.

Claims (9)

Expectations 1. Soot filter system (66) for separating non-volatile substances from an exhaust gas flow (18), in particular soot particles from diesel engines, which soot filter system has interior spaces in a housing (68) with gas supply (78) and gas discharge nozzles (90) connected via filter media, wherein the filter media comprises several axially spaced filter cartridges (12) which are closed upstream and open downstream and have a dimensionally stable, perforated inner casing (14) and an outer casing (16) made of a heat-resistant material and which is permeable to gas with low resistance, characterized in that the soot filter system (66) comprises at least one removable soot filter insert (70) or removable soot filter modules (10), which are equipped with filter cartridges (12) detachably attached at both ends. 2. Soot filter system (66) according to claim 1, characterized in that the upstream closed filter cartridges (12) are screwed on the gas inlet side to a filter cartridge holder (24) that is open in the area between the cartridges, and are held on the gas outlet side in a filter cartridge holder (38) that is open in the area of the cartridges or are screwed to it. 3. Soot filter system (66) according to claim 1 or 2, characterized in that the filter cartridges (12) are enclosed downstream with play by a preferably multi-part clamping piece (40, 42), which acts on a seal (44) inserted between the clamping piece (40, 42) and the filter cartridge holder (38) and seals the interior (26) outside the filter cartridges (12). "16 4. Soot filter system (66) according to claim 3, characterized in that the clamping piece (40, 42) is strip-shaped, with essentially semicircular recesses (60) for the filter cartridges (12). 5. Soot filter system (66) according to one of claims 1 to 4, characterized in that a closure cap (20) placed upstream over the inner casing (14) of the filter cartridges (12) and a flange sleeve (30) downstream serve to fasten the filter cartridges (12), wherein the closure cap (20) and flange sleeve (30) are preferably connected to the inner casing (14) by spot welding. 6. Soot filter system (66) according to claim 5, characterized in that the outer casing (16) is attached to the closure cap (20) and the flange sleeve (30) in a gas-tight manner by means of clamping brackets (34). 7. Soot filter system (66) according to one of claims 1 to 6, characterized in that the outer casing (16) of the filter cartridges (12) consists of inorganic fiber material, in particular of high-temperature filaments or yarns with high adsorption capacity, which are preferably applied as at least one-layer mesh. 8. Soot filter system (66) according to claim 7, characterized in that the high-temperature fibers, which are made of glass or ceramic with a high specific surface, are catalytically active coated, preferably with vanadium oxide, also with a noble metal component, in particular platinum. 9. Soot filter system (66) according to one of claims 1 to 8, characterized in that the soot filter modules (10) are sealed against each other with an elastic glass fabric seal.