NO750053L - - Google Patents

Description

The present invention relates to a fluid treatment structure, more specifically a fluid treatment structure which is suitable for use as a filter and/or catalytic reactor.

Loose fibers used for filtration or as catalyst carriers can be entrained by the fluid flow. and become compressed during use, leading to fiber tag in the first case and to high resistance to the fluid flow in the second case.. The use of binders helps to overcome fiber loss - problem, but makes the problem of flow resistance even bigger. When inorganic

fibers are used to withstand high temperatures, for example tempera-

trips that are taken during the treatment of exhaust gases from engines, the problem is even greater, as inorganic fibers are tame

tend to be brittle and tend to break when compressed. Binding of inorganic fibers using inorganic binders

is proposed to prevent compaction, but this leads to even greater brittleness and failure during use.

It has now been found that high pressure drop in the fiber filter or reactor due to compression of fibers and the resulting high flow resistance can be reduced by using a bent corrugated or corrugated metal screen in combination with the fibers. This combination is particularly advantageous when it comes to inorganic fibres, as the need for bonding is avoided, and as the fibers are provided with a structural support.

The invention thus provides a fluid processing structure comprising at least one layer of bent, corrugated or wavy (eng. "concoluted" hereinafter referred to as "corrugated") metal mesh in laminar assembly with at least one layer of organic or inorganic fibers.

Structures according to the invention can be used

such as filters, absorption devices or reactors and are particularly

useful for separation processes of solids and gases, for example for the removal of soot and lead from engine or exhaust gases. The fluid flow is normally preferably parallel to the laminar layers.

For filtration or catalytic applications where

temperatures of over 150°C are used, the fibers are preferably inorganic fibers, for example of asbestos, glass or aluminosilicate, but for applications where temperatures of over 1000°C occur, or aggressive conditions, it is preferred to use polycrystalline, refractory metal oxide fibres, for example zirconium oxide or alumina fibres. Particularly suitable fibers for the invention are sold under the trademark "Saffil". Although loose, irregular fibers can be used, it is preferred that the fiber layers are in the form of a laminated mat, so that the fibers offer minimal resistance to the flow of the fluid to be treated. The fibers can be used in woven or non-woven form. Moist felt materials formed from dispersions of loose fibers have better adjustable density and thickness than loose fiber materials and are preferred. Sewn, non-woven materials are particularly advantageous as they are easy to handle and the fibers are held together without compression. The mass density of the fibers can have a vicTt] range of values. and are chosen to suit each particular use.

For "Saffil", the bulk density is preferably 0.06 to 0.24 kg/dm 3

for example approx. 0.15 kg/dm 3 . Below 0.06 kg/dm 3 the fibers move too easily during use, and above 0.24 kg/dm<3> the pressure drop is too high for many applications.

Fibers with an average diameter between 0.5 and

50 micron is generally suitable for the invention. The metal sieve can

suitably be a woven or knitted wire mesh or may be of the type normally known as expanded metal mesh. The metal sieve is chosen to suit the conditions below

which structure to use. Stainless steel or nickel alloys (for example Incaloy DS or Inconel X750) pre-

is drawn for most embodiments of the invention. Nickel/iron alloys are particularly good for use under high-temperature oxidizing conditions in the presence of carbon, for example soot, as the problems associated with carbonization of steel are thereby avoided.

The screen is formed into its particular shape preferably by crimping, crimping or corrugating it in any suitable manner, for example by passing a knitted screen between interlocking rolls and provided with teeth. The corrugations do not have to be uniform, although for most applications a more or less regular corrugation pattern is preferred. Corrugation or corrugation can also be carried out by folding the sight into waves of suitable amplitude and length, which will depend on the use for which the structure is intended. For example, for a filter,

the amplitude and length will be selected in accordance with the Set pressure drop that can be allowed in the filter. For most embodiments, the waves have approx. 3 to 6 mm amplitude and length. Corrugations or waves of less than 3 mm are rather difficult to produce, and above 6 mm the structure is too open for effective filtering.

For some embodiments, it is preferred to place a layer of non-corrugated metal screen between the corrugated screen and the fibers. This is advantageous for further lowering the pressure drop when the structure is used as a filter, by increasing the unconstricted area of the gas paths. A stainless steel woven wire cloth with 2 mm meshes and 29 standard wire gauge (swg) is suitable for this purpose.

In some embodiments, it is necessary to attach corrugated metal screens therein to a suitable anchoring point which can form a jdjel of the structure. For example, the sieve may be connected to a container or a suitable support part, for example an axial rod.

In some embodiments, for example when it is desired to carry out catalytic reactions at high temperatures, the structures and/or the fluid can be heated using any suitable means. If it is desired to burn solid material, for example soot filtered out of the fluid by means of the structure, it may be necessary to inject air into the structure at a suitable point as well as to supply iviaarm to provide combustion.

An advantageous way to add heat to the structure

on consists in connecting the metal sieve with a source of electrical energy, so that it can act as an electrical heating element.

Catalysts can, if desired, be deposited on the fibers and/or on the metal sieve, for example in embodiments where the structure is used as a reactor for catalytic treatment of exhaust gases that require the removal of harmful components, for example

pel gases from pipes and exhaust gases from cars.

The metal sieve or the fibers in the structure according to the invention can advantageously be treated with a material that protects them from the environment in which they are to be used, for example from high temperature or oxidizing conditions, for example in engine exhaust gases. A suitable coating is a refractory inorganic compound,

for example a metal oxide, especially aluminum oxide1 or a metal phosphate.

Coating the metal screen or fibers may be advantageous in providing a further component of the structure according to the invention which improves the filtering or absorption capacity of the structure. For example, a be-

deposit aluminum oxide on the metal sieve a beneficial component that facilitates the removal of unwanted materials in exhaust gases, for example odors in Diesel exhaust gases or lead in exhaust gases from internal combustion engines. Particularly advantageous is a structure where a stainless steel screen coated with aluminum oxide is used in conjunction with aluminum oxide fibers. Such a combination is very effective for removing lead from the exhaust gases of petrol-powered engines.

Alumina can conveniently be deposited as

coating the metal screen or fibers by contacting them with a solution of soluble aluminate, such as sodium or potassium aluminate. It is best to make the contact by

high temperature, for example 60 - 100°C. After contact (for example by soaking) of the screen pg/or fibers with the solution/H5Tir the excess of the solution is washed away, the screen and/or fibers dried (for example by heating) and the coating calcined, for example at 400°C to 1000° C.

Catalysts can be introduced in or on the coatings described here, particularly for embodiments where the structure is used as a reactor for catalytic treatment of exhaust gases from cars. Thus, chromium compounds or phosphates can be used to remove lead, or oxidation catalysts, especially platinum or palladium, can be used in oxidative processes for treating gases.

Structures according to the invention can: comprise a plurality of corrugated metal sieves and a plurality of fiber layers in which, for example, sieves alternate with fiber layers. The particular combination of fiber layer, corrugated metal screen and non-corrugated screen (if used) will depend on the particular application the structure is to be used for. The fiber layers and the sieve can be flat or curved. It is usually most advantageous that the structures are formed from spirally wound or concentric layers as shown below.

As mentioned earlier, the fluid flow is normally preferably parallel to the layers. The fluid is preferably introduced into the structure in such a way that it flows in the direction along the waves of the corrugated screen. In most embodiments, there are spaces in the corrugations between the fiber layer and the sieve that immediately supports the fiber layer, so that at least some fluid can flow within the structure relatively undisturbed and thereby keep the pressure drop to a minimum. However, this part of the fluid does not pass through the structure completely untreated or unfiltered, as it repeatedly comes into contact with the surface of the fibers.

To increase the fluid flow path within the structure and thereby improve the efficiency of the filtration or reaction, the corrugated metal screen can be shaped in such a way that the windings follow one of a number of different paths through the structure. This can conveniently be achieved by superimposing a zigzag, curved, stepped or other similar pattern in view of the original windings, as shown below.

The structures according to the invention are suitable for a wide range of fluid flow velocities, and as the pressure drop in the structures is usually low, high gas velocities, for example up to 8 metres/sec., can easily be used.

In addition to being used for separating solids and gases, the structures can be used to separate solids and liquids. They are thus used in the removal of solid deposits from machine oil.

In use, the structures of the invention are placed in any suitable container, for example when used to treat exhaust gases from engines, they can be placed in a metal chamber similar to a conventional exhaust muffler.

Three embodiments of the invention are shown in Figures 1-3. It will be understood that the invention is not limited to these embodiments.

Figure 1 is a partial section of a rectangular device or stack within an external container 4 to which the metal sieves 1 and 3 are attached. Screen 1 consists of woven stainless steel wire in crimped form (9017/2 x 33 swg/corrug. 3 ex Knitmesh Limited). Each layer of screen 1 is assembled with screen 3 which is a non-corrugated woven stainless steel wire cloth (2 mm, 29 swg).

Between the underside of each screen 3 and the top side of the supporting screen 1 is inserted a cloth 2 of "Saffil" aluminum oxide fibers which has an average bulk density of approx. 0.1 kg/dm 3.

Gases to be filtered by the structure must be made to pass into the openings 5 formed by shrinking or crimping the screen 1.

A preferred embodiment of the invention is illustrated in figure 2 which is a partial section of a structure used for filtering soot from diesel exhaust gases.

A corrugated screen 1 of stainless steel woven wire cloth (9017/2 x 33 swg/corrug. 3 ex Knitmesh Limited) is attached along one edge to a stainless steel rod 4 and is designed as a spiral roll coaxial with the rod 4. A cloth 2 of "Saffil" zirconium oxide fibers with an average bulk density of approx.

15 kg/dm 3 also in the form of a spiral roll which is coaxial with the rod 4, is placed within the spirals in the screen 1. A woven wire cloth 3

of stainless steel (2 mm, 29 swg) is inserted between the screen 1 and the fiber cloth 2 in front of the spiral and attached to the rod 4.

In use, the Diesel exhaust gases flow axially through the spiral by means of the openings 5 formed by the corrugation in the sieve 1 and are thereby filtered. '

In an alternative application, for example-to remove lead from exhaust gases fr al. ib 11 is, the fiber cloth 2 is replaced with a cloth of "Saffil" aluminum oxide fibers.

Figure 3 shows a structure analogous to fig. 1, but where the layers are arranged coaxially to form a cylindrical structure. The layers are arranged concentrically around a central rod 4 in the following order: the fiber cloth 2, non-corrugated cotton screen 3,

corrugated screen 1, when starting from rod 4. The fiber cloth and metal screens are similar to those described in the embodiment shown in figure 1, and again the corrugation forms spaces 5 for the passage of gas or other materials, for example when the structure used for filtering.

Several structures can be used to provide the filtration surface necessary to achieve the desired degree of filtration compatible with the exhaust gas flow rate. Figures 4 to 7 schematically show alternative paths that the waves in the corrugated sieve can take in the structure in relation to the direction of the fluid flow. Figure 8 schematically shows the shape of the corrugation after a section 'A'-'A' in each of figures 4 to 7. Figures 9 to 12 schematically show four different combinations of corrugated metallic (1), fiber layer, (2) and non-corrugated metal sieve (3).

The use of the structure according to the invention is illustrated by means of the following examples.

The following two examples of soot in Diesel engine exhaust gases using a fluid treatment structure according to the invention.

Example 1

The structure shown in Figure 2 was used to filter soot from the exhaust gases of a 4.1 liter static Diesel engine operated at 3000 rpm. minute in a period of 16 hours. The filter (consisting of 1.1 kg of "Saffil" zirconium oxide fibers and 2.1

kg of a 7.6 cm wide rolled up sieve was installed in a cylindrical chamber with a diameter of 33 cm, and a volume of 13 liters. The gas was passed through the filter in an axial direction. During the 16-hour test, the maximum pressure drop was 1.2 kgN/m (90 mm Hg), the maximum temperature was 680°C and a 25% reduction in smoke (based on the Bosch scale) was achieved.

Example 2

A similar filter as used in example 1 was

used for a 3.6 liter Diesel machine driven at 2160 rpm. minute under the conditions that prevail when rolling on the road. The amount of smoke in the exhaust gas was reduced to 0.5 Bosch units from the original 2.2 Bosch units.

The following two examples illustrate the reduction of

lead in exhaust gases from a gasoline powered machine by means of the fluid treatment structure according to the invention.

Example 3

The structure described in Figure 2 was used to reduce the lead content in exhaust gases from a 1,600 c, m 3 petrol-powered engine which operated with a cycle of 4 minutes of idling at 700 rpm. minute, and 16 minutes at 400.0 revolutions per minute corresponding to a marching speed of 112 kg/hour. The gas temperature during the two parts of the cycle was 360° and 670°C respectively.

The filters (consisting of 860g of "Saffil" aluminum oxide fibers and 2.0kg of rolled up screen of 7.6cm width) were placed in a 13 liter cylindrical container with a diameter of 33cm. During the experiment, the maximum pressure drop in the filter was 2 kgN/m. 2and the lead filtration efficiency was 55%.

Example 4

A filter similar to that used in example 3, but with a smaller size, was placed in a 3 liter container with a diameter of 10 cm and examined on the engine described in example 3, which worked at a constant 2750 revolutions per minute. minute, which corresponds to a walking speed of 80 kg/hour. It contained 100 g of "Saffil" aluminum oxide fibers and 430 g of a rolled-up screen of 7.6 cm width. During a 60-hour test, the maximum pressure drop in the filter was 42 kgN/m<2>, the temperature of the gas flowing into the filter was 460°C and the lead filtration efficiency was 4990.

Claims (13)

1. Fludum processing structure, characterized in that it comprises at least one layer of "convoluted" metal screen in laminar assembly with at least one layer of organic or inorganic fibres. 2. Fluid treatment structure as stated in claim 1, characterized in that the fibers are asbestos, glass or aluminosilicate fibres. 3. Fluidumbehaidlings structure as stated in claim 1, characterized in that the fibers are polycrystalline metal oxide fibers. 4. Fluid treatment structure as stated in claim 3, characterized in that the metal oxide is zirconium oxide or aluminum oxide. 5. Fluid treatment structure as set forth in any of the preceding claims, characterized thereby the fibers are in the form of a laminated mat. 6. f] Fluid processing structure as set forth in any one of the preceding claims, characterized in that the corrugated metal screen is a knitted wire screen. 7. Fluid treatment structure as set forth in any of the preceding claims, characterized in that the metal of the corrugated screen is stainless steel or a nickel/iron alloy. ' • 8. Fluid treatment structure as set forth in any one of the preceding claims, characterized in that it comprises a layer of non-corrugated metal screen between the corrugated metal screen and the fibers. 9. Fluid treatment structure as set forth in any of the preceding claims, characterized in that the metal screen or fibers are coated with aluminum oxide, silicon oxide or a metal phosphate. 10. Fluid treatment structure as set forth in any of the preceding claims, characterized in that a catalyst is deposited on the fibers and/or on the metal screen. 11. C) Fluid treatment structure as stated in claim 10, characterized in that the catalyst is a chromium compound. platinum or palladium. 12. Fluid treatment structure as set forth in any of the preceding claims, characterized in that it comprises a plurality of corrugated metal sieves and a plurality of fiber layers in which the sieves alternate with the fiber layers. 13. Fluid treatment structure as stated in 1 which, preferably from the preceding claims, characterized by the fact that the sieve and the fiber layers are in spirally wound or concentric form..