WO2004037389A1

WO2004037389A1 - Treatment of fluids

Info

Publication number: WO2004037389A1
Application number: PCT/GB2003/004561
Authority: WO
Inventors: Allan Douglas Clark; Christopher Withers
Original assignee: Metallic Dust Processing Ltd
Priority date: 2002-10-22
Filing date: 2003-10-22
Publication date: 2004-05-06
Also published as: GB2409655A; GB0508610D0; AU2003274359A1; GB0224481D0; GB2409655B

Abstract

Apparatus for use in the treatment of fluids, in particular hot gases comprises a filter element (9) and a displacement arrangement (16). The invention, the displacement arrangement (16) is spaced from the filter element (9) so as to allow a build up of particulate material on the surface of the filter element (9). The layer of particulate material serves to protect the filter element (9), and to help avoid fluctuations in the operating pressures of the system. This system also allows for a layer of activated or other treatment material to be present on the surface of the filter element (9).

Description

TREATMENT OF FLUIDS

The present invention relates to treatment of fluids, and in particular to treatment of hot liquids or gases (particularly hot gases) by filtering, cleaning or separation of particulate, liquid or gaseous constituents.

During for example pyrolysis process treatment of organic materials, the organic materials are heated up either in the absence of oxygen or by hot inert gases. Organic materials are pyrolysed and carbon is produced in a fine particulate form and also fine particles of other materials may be produced from the materials being pyrolysed.

The hot raw gases being evolved in such pyrolysation processes are typically drawn out of the pyrolyser at temperatures varying from 200°C to 1000°C. These are then used as sources of energy for many processes since they are mainly hydrocarbons.

If the gases are condensed, oils may be produced and these oils are normally valuable as transportable energy products. However, since the gases are dirty leaving the pyrolyser once they are condensed the dust carried over in the gases will contaminate the oils and render them less valuable.

Similarly, if the gases are combusted, any particles in the gas will contaminate the products of combustion produced and thus filtration of these will be necessary and costly because the volume of the products of combustion produced will be many times that of the pyrolysed gases.

It is known technology to clean gases at elevated temperatures above 250 °C by use of ceramic filter systems. The cleaning mechanism for these filters is typically compressed air or gas forced down the inside of the filter element, causing a shock wave which disturbs the material attached to the outside wall of the filter medium. In the pyrolysis process, the process has to operate between the stringent pressure constraints to ensure that (a) none of the pyrolysis gas escapes the seals, and (b) that no ambient air is sucked into the system. During conventional cleaning of the filter elements the shock wave of the compressed gas disturbs the pressure system in the pyrolyser and pushes gases out of the seals.

Moreover, the prior art methods of cleaning filters used in pyrolysis are inefficient and thus limit the size of the filter that can be used.

Filters are used for treating fluids in many other fields, and means of cleaning such filters are known. However, these would not be suitable for use with filters for treating hot gases.

DE 43 41 515 discloses a filter for removing particles from highly viscous liquids or pastes. A wiper is provided to remove particles from the outside of the filter. This filter could not be used for treating gases produced by pyrolysis for several reasons. This filter provides a compact arrangement, whereas the treatment of gases produced by pyrolysis requires a large filter surface area for the large volumes of gas that are generated. Morevover there is no allowance for the expansion that would inevitably occur at the temperatures generated during the treatment of hot gases. The different components of the system would expand at different rates, the piston would expand and buckle and the wiper would jam. In addition there is no spacing for provision of a layer of material permitted to adhere to the filter.

US 6, 187, 177 discloses a filter unit for filtering pressurised liquid carrying solid contaminants. A wiper unit rotates about the filter element to remove filtered out accumulated solids. The scraper mechanism is very complex, which limits the possible length of the filter element. Such a complex cleaning mechanism could not work at the temperatures generated during pyrolysis. Preferred aspects of the present invention seek to provide an improved apparatus and method for cleaning filters for filtering fluids, especially hot gases, and which overcome one or more of the above problems.

According to a first aspect, the present invention provides apparatus for treating hot gases comprising: a filter element; a displacement arrangement movable relative to the filter element so as to displace material adhering to the filter element.

The present invention enables cleaning of the filter element by mechanical means and does not require the reversal of pressure (pressure shock) which is a feature of prior art techniques. The mechanical means (the displacement arrangement) may be operated continuously or intermittently depending upon circumstances. The removal of filter element adhering material is more controlled than with prior art techniques.

The displacement arrangement preferably comprises a scraper arranged to scrape the surface of the filter element or material adhering to the surface of the filter element.

In a preferred embodiment, the displacement arrangement is spaced from the filter element so as to act to remove material adhering to the filter element but permitting a predetermined thickness of material to remain adhered to the filter element. It has been found that optimum filtration/cleaning is achieved by permitting the contaminant present on the filter element to remain at an optimum thickness. A balance is struck between enough adhering material remaining on the filter surface of the filter element to provide a most effective filter and the filter becoming blocked to an extent where the pressure gradient across the filter becomes adverse. An object of the invention is, as far as practicable and possible, to minimise the variation from constant pressure drop across the apparatus. The displacement arrangement may be adjustable relative to the filter element so as to enable alteration of the spacing between the filter element and the displacement arrangement. This allows simple alteration of the predetermined thickness of material permitted to adhere to the filter element according to the different applications for which the apparatus is used.

In a further preferred embodiment the predetermined thickness of material remaining adhered to the filter element comprises a layer of active or other treatment material. Presence of such an active or other treatment material acts not only to protect the filter element but also to remove substances from the gas being treated.

Preferably the active or other treatment material is activated carbon or lime.

In preferred embodiments the thickness of material permitted to remain adhered to the filter element is between 1 mm and 12 mm.

Preferably the filter element is elongate in form, and the displacement arrangement is arranged longitudinally with respect to the filter element.

Preferably the displacement arrangement includes at least one scraper collar or ring extending about at least a portion of the filter surface of the filter element. This provides for a simple arrangement suitable for use at high temperatures. The displacement arrangement is beneficially moved such that the scraper collars or rings move over the filter surface of the filter element to displace the material adhering to the filter element. The degree of spacing of the working portion of the arrangement (for example the scraper collars or rings) determines the degree of material removed from the filter element. At one extreme, the spacing can be a clearance tolerance only ensuring complete removal of the adhering material from the filter element. Toward the other end of the scale a relatively thick layer of adhering material may remain following operation of the displacement arrangement. Beneficially, relatively small movement of the displacement arrangement ensures the filter element is refreshed over a major portion of the filter element. In one embodiment this may be achieved by a reciprocating scraper arrangement having a series of spaced scraper collars or rings along the length of a elongate filter element.

The displacement arrangement may, in one embodiment, be movable in a reciprocating manner to displace the material adhering to the filter element. The reciprocating movement direction is preferably substantially the same as the longitudinal direction of the filter element.

The apparatus is preferably for treating gases at a temperature between 200 °C and 1000°C.

The filter element beneficially comprises a substantially rigid filter element and may comprise a ceramic filter element.

The apparatus preferably includes a fluid upstream zone and a fluid downstream zone. The fluid upstream zone preferably receives contaminated fluid for filtration or cleaning and the fluid downstream zone beneficially carries cleaned or filtered fluid.

The filter element may comprise a tube or cage having a longitudinally running outer filter surface and a closed end, an open and being provided opposed to the closed end preferably communicating with the fluid downstream zones.

The filter element beneficially includes a filter wall provided with apertures or pores for filtering or cleaning the contaminated fluid media.

The apparatus preferably includes: a housing having a gas upstream zone and a gas downstream zone; the gas upstream zone and the gas downstream zone being sealed from one another other than via the filter element; an inlet portion for contaminated gas communicating with the gas upstream zone, the gas upstream zone including the contaminated side of the filter element; and an outlet portion for treated gas communicating with the gas downstream zone.

The apparatus beneficially includes extraction means for extracting contaminant material removed from the filter element. The apparatus may include a gravity fed outlet or hopper for this purpose.

According to a further aspect, the present invention provides a displacement arrangement for use in the apparatus for treating hot gases. Preferably the displacement arrangement is movable relative to the filter element to displace material adhering to the filter element.

A further aspect of the present invention provides a method of refreshing a filter element during treatment of a hot gas comprising moving a displacement arrangement to displace material adhering to the filter element.

According to a further aspect, the present invention provides a method for treatment of a hot gas comprising: passing the hot gas through a filter element; and removing at least part of the material adhering to the filter element by means of movement of a displacement arrangement relative to the filter element.

Preferably a predetermined thickness of material is permitted to remain adhered to the filter element.

In a preferred embodiment the method further comprises the step of adjusting the spacing of the displacement arrangement relative to the filter element. Preferably the movement of the displacement arrangement is reciprocal in nature and is substantially longitudinal with respect to the filter element.

The present invention is particularly suitable for cleaning of hot contaminated gases, the gases may be at a temperature of between 200 °C and 1000°C, or may have been produced by pyrolysis of organic materials.

A further aspect of the present invention provides a displacement arrangement for use in a method of refreshing a filter element during treatment of a hot gas or in a method for treatment of a hot gas.

A further aspect of the present invention provides apparatus for treating fluids comprising: a filter element; and a displacement arrangement movable relative to the filter element so as to displace material adhering to the filter element, wherein the displacement arrangement is spaced from the filter element so as to act to remove material adhering to the filter element but permitting a predetermined thickness of material to remain adhered to the filter element.

Preferably the displacement arrangement is adjustable relative to the filter element so as to enable alteration of the spacing between the filter element and the displacement arrangement.

Preferred embodiments of the present invention are described below, by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of apparatus in accordance with the invention; Figure 2 is a schematic view of a further embodiment of apparatus in accordance with the invention; and

Figure 3 is a schematic view of a further embodiment of apparatus in accordance with the invention.

Referring to the drawings, and initially to Figure 1, there is shown gas treatment apparatus 1 comprising a housing 2 defining a clean gas outlet plenum 3 communicating with an outlet conduit 4. The clean gas outlet plenum 3 is sealed to a cylindrical mid- housing portion 5 at a flanged connection 6 which is provided with tube plate seal 7.

Tube plate seal 7 is provided with a central aperture which locates a collar 8 of a tubular ceramic filter 9. Ceramic filter 9 has a circumferential filter surface having apertures or pores (not shown) dimensioned to permit a desired gas to pass through the filter from an upstream gas zone 10 defined in the chamber bounded by housing 5. A gas inlet 15 provides for gas entering through mid-housing 5 into the upstream gas zone 10.

The lower portion of mid-housing 5 is connected at a flanged connection 11 to a material hopper 12, the purpose of which will be explained below. A gravity fed outlet 13 is provided with a seal device 14.

A displacement scraper arrangement 16 comprises an elongate carrier rod 17 carrying, at 15 cm spaced intervals, a series of scraper rings 18 over a co-extensive length of the tubular ceramic filter 9. The scraper rings 18 are dimensioned to be spaced from the surface of filter 9 by a predetermined spacing (h) (typically h = 5 mm). The carrier rod 17 extends through the housing 2 (via hopper 12) and is driven in a reciprocating motion in a direction corresponding to the longitudinal direction of the tubular ceramic filter 9.

In operation gas (or a mixture of gases) to be cleaned possibly containing contaminating particulate material is fed through the apparatus, entering the housing 2 via inlet 15. The apparatus may be vacuum driven, for example. The gas passes through the tubular filter 9 and cleaned or filtered gas leaves the apparatus via outlet 4. Where contaminating particulate material (such as carbonaceous material carried in hot gases resultant for example from pyrolysis) is present in the gas to be treated, it collects on the outer circumferential surface of the tubular ceramic filter tube 9. It is advantageous to aid the filtering process by maintaining a covering of filtered particulate on the surface of the filter tube 9. It is however, important that the build up of particulate is maintained below a level where the filter becomes clogged. If this were to happen, the pressure drop across the apparatus becomes too large and the treatment process inefficient.

The displacement arrangement 16 is actuated via a piston mechanism (not shown) and moves reciprocally in a longitudinal direction with respect to the filter element 9. In this embodiment, the movement in each direction is around 7.5 cm. This allows the layer of adhered material to be scraped to a uniform thickness along its full length by the scraper rings 18.

Following actuation of the displacement arrangement 16 to refresh the ceramic filter tube 9, the removed particulate material drops into hopper 12 where it may be periodically removed via outlet 13 when seal device 14 is removed.

There are various advantages of the above-described arrangement.

Ceramic filter elements enable gas streams at temperatures of up to 1000°C to be treated. Depending on the specific application, this apparatus could be used to treat gases at any temperature above the "dew point" of the gas up to 1000°C.

In known hot gas treatment apparatus, the vacuum pressure may be periodically reversed to dislodge particulate clogging the filter. The pressure reversal (pressure shock) is disadvantageous to the overall pressure regime in operation and also results in uncontrolled refreshing of the filter 9. In accordance with the present invention, periodical, cyclical or continuous operation of the reciprocating displacement arrangement 16 to dislodge or displace the material adhering to the ceramic filter 9 results in refreshing of the filter 9 to a controlled degree without the requirement (or minimal requirement) to reverse the pressure regime of the system. The spacing (h) of the spacer rings 18 relative to the surface of the filter 9 scrapes the adhering material to a required degree to remove a predetermined depth of coating. This means of refreshing the filter 9 is more controlled than prior art techniques.

This filter enables a constant pressure in the system to be maintained while constantly cleaning the filter and processing gas through a predetermined thickness of material permitted to remain adhered to the filter to remove residual traces of non-particulate impurities. In prior art systems all material is removed during the filter cleaning operation. This loading and removing of adhered material causes fluctuations in the operating pressure of the filtration system. In some operations, such as pyrolysis, it is very important to maintain a constant very low positive pressure.

Ceramic filters for high temperatures are extremely delicate and expensive. The filter media is not exposed to the gas stream directly as it is protected by the predetermined thickness of material permitted to remain adhered to the filter and does not wear away due to scraping. The filter media will not be subjected to mechanical shock from conventional type cleaning methods and thus will last much longer than in conventional filtration processes.

Another advantage of the displacement arrangement of the present invention is that it could be retro-fitted to a typical gas filter if, for instance, a continuous pre-coat operation were required to meet more stringent emission standards.

There are various modifications that can be made to the above-described embodiment. The displacement arrangement 16 may be positioned such that the scraping rings 18 are in scraping contact with the surface of filter element 9 so as to scrape the filter 9 surface clean (i.e. where h=0). However, in this case there is a danger of the damage to filter element 9 caused by scraping. Furthermore, the displacement arrangement 16 may be adjustable relative to the filter element 9 so that the spacing h may be changed.

The spacing h may be any convenient distance. It depends on what is being filtered and for what particular application. Typically h will be in the ranges of 0.5 mm to 12 mm, 1 mm to 12 mm, or 2 mm to 10 mm.

The rings may be spaced at any convenient distance, with reciprocal motion of a corresponding distance in each direction. In this embodiment, it is preferred that movement of the displacement arrangement cause the scraper rings to scrape the entirety of the length of the filter or the material adhered to the filter.

Movement of the displacement arrangement could be rotational rather than longitudinal, in which case it may also be continuous rather than reciprocal. However, the cost of such a mechanism would be prohibitive.

Filtration could occur from the inside of the filter element to the outside, with the displacement arrangement being located inside the filter element. However, as this puts limitations on the cleaning mechanism, it is preferred that it be located outside the filter element.

The filter need not be cylindrical in shape. Other cross-sections are possible, for example square instead of circular. This gives a greater filter surface area per unit of filter size.

A layer of active or other treatment material may be present on the surface of the filter tube 9. For example, a layer (typically 4 mm to 12 mm) of activated carbon may be present to remove materials such as dioxins from a gas or mixture of gases being treated. Lime as a particulate layer (typically 1 mm to 4 mm) on the filter tube 9 would also be effective in collecting/filtering chlorine gas or sulphur. In such cases, the displacement arrangement 16 acts to present a fresh surface of the active or other treatment material adhering to the surface of the filter element during or following operation of the process.

A second embodiment of the invention is shown in Figure 2. The apparatus shown is generally similar to the apparatus of Figure 1 (with like parts identified by like reference numerals) but orientated in a horizontal configuration rather than the vertical orientation of the apparatus of Figure 1. The filter 9 and displacement arrangement 16 are housed within a tube 2 of diameter 150 mm and length 1450 mm. Flanged connection 6 is positioned 150 mm from the outlet end of housing 2. Leg supports 21 support the housing 5 horizontally above ground level such that the centre of the filter 9 is 640 mm from the floor and filter supports 22 support the ceramic filter tube 9 horizontally in housing 5. Adhering material removed from filter tube 9 by the displacement arrangement 16 falls onto the horizontal floor surface of housing 5 for subsequent cleaning and removal. The gas inlet 15 and outlet 4 are arranged in-line. The inlet 15 comprises a 5 cm OD pipe with a BSP thread. The outlet 4 comprises a 2 cm threaded pipe. The inlet and outlet each extend 150 mm from the housing 2.

In a third embodiment of the invention shown in Figure 3, a longer ceramic filter element 9 is used. This could be useful where a filter of larger surface area is required. Filter elements that are beyond a certain size require mechanical support, in this embodiment, by means of one or more clamps 31. In this embodiment, the scraper rings are spaced such that the reciprocating motion of the displacement arrangement 16 does not interfere with the clamp 31. For example, instead of the scraper rings being spaced at regular 15 cm intervals (with 7.5 cm movement in each direction), the rings positioned either side of the clamp are spaced at 20 cm (but still with 7.5 cm movement in each direction). This would allow a 5 cm space for a support clamp, which would thus not interfere with the cleaning mechanism. In this embodiment a portion of the filter element 9 (that to which the clamp 31 is attached) will not be scraped by the scraper rings 18.

Since ceramic filters are brittle, the prior art methods of cleaning ceramic filters at high temperature by reverse flow or pulse of compressed air of gas limit the size of filter elements that can be used. The size of filter elements that can be used in such systems is also limited by the efficiency of the filter cleaning methods. The present method provides a better cleaning efficiency, which in turn means that the size of the filter is not so limited. The method using the above-described apparatus allows for mechanical support of the filter elements, thereby allowing much larger filter elements to be used, as the length of the filter element is not limited by its structural strength.

The features of the various embodiments may be interchanged and/or combined as appropriate.

The invention has been defined in specific embodiments by way of example and the skilled addressee will understand that various items of the proposed embodiments may be varied or exchanged without departing from the scope of the invention. In particular, whilst particularly suitable for use in hot gas situations, the invention is perceived to have application for other gases, liquids and fluids in general.

Claims

1. Apparatus for treating hot gases comprising: a filter element 9; a displacement arrangement 16 movable relative to the filter element so as to displace material adhering to the filter element.

2. Apparatus as claimed in claim 1 wherein the displacement arrangement is spaced from the filter element so as to act to remove material adhering to the filter element but permitting a predetermined thickness of material to remain adhered to the filter element.

3. Apparatus as claimed in claim 2 wherein the displacement arrangement is adjustable relative to the filter element so as to enable alteration of the spacing between the filter element and the displacement arrangement.

4. Apparatus as claimed in 2 or 3 wherein the predetermined thickness of material remaining adhered to the filter element comprises a layer of active or other treatment material.

5. Apparatus as claimed in claim 4 wherein the active or other treatment material is activated carbon or lime.

6. Apparatus as claimed in claim 5 wherein the thickness of material permitted to remain adhered to the filter element is between 1 mm and 12 mm.

7. Apparatus as claimed in any preceding claim wherein the filter element is elongate in form, and the displacement arrangement is arranged longitudinally with respect to the filter element.

8. Apparatus as claimed in any preceding claim wherein the displacement arrangement includes at least one scraper collar or ring extending about at least a portion of the filter surface of the filter element.

9. Apparatus as claimed in any preceding claim wherein the displacement arrangement is movable in a reciprocating manner to displace the material adhering to the filter element.

10. Apparatus as claimed in any preceding claim wherein the displacement arrangement is movable substantially longitudinally with respect to the filter element.

11. Apparatus as claimed in any preceding claim for treating gases at a temperature between 200°C and 1000°C.

12. Apparatus as claimed in any preceding claim wherein the filter element is a ceramic filter element.

13. Apparatus as claimed in any preceding claim further including: a housing having a gas upstream zone and a gas downstream zone; the gas upstream zone and the gas downstream zone being sealed from one another other than via the filter element; an inlet portion for contaminated gas communicating with the gas upstream zone, the gas upstream zone including the contaminated side of the filter element; and an outlet portion for treated gas communicating with the gas downstream zone.

14. A displacement arrangement for use in the apparatus as claimed in any preceding claim.

15. A method for refreshing a filter element 9 during treatment of a hot gas comprising moving a displacement arrangement 16 to displace material adhering to the filter element.

16. A method for treatment of a hot gas comprising: passing the hot gas through a filter element 9; and removing at least part of the material adhering to the filter element by means of movement of a displacement arrangement 16 relative to the filter element.

17. A method as claimed in claim 15 or 16 wherein a predetermined thickness of material is permitted to remain adhered to the filter element.

18. A method as claimed in claim 15, 16 or 17 further comprising the step of adjusting the spacing of the displacement arrangement relative to the filter element.

19. A method as claimed in any of claims 15 to 18 wherein the movement of the displacement arrangement is reciprocal in nature.

20. A method as claimed in claim 19 wherein the reciprocal movement of the displacement arrangement is substantially longitudinal with respect to the filter element.

21. A method as claimed in any of claims 15 to 20 wherein the gas being treated is at a temperature of between 200°C and 1000°C.

22. A method as claimed in any of claims 15 to 21 for use in the treatment of gas produced by pyrolysis.

23. A displacement arrangement for use in a method as claimed in any of claims 15 to 22.

24. Apparatus for treating fluids comprising: a filter element 9; and a displacement arrangement 16 movable relative to the filter element so as to displace material adhering to the filter element, wherein the displacement arrangement is spaced from the filter element so as to act to remove material adhering to the filter element but permitting a predetermined thickness of material to remain adhered to the filter element.

25. Apparatus as claimed in claim 24 wherein the displacement arrangement is adjustable relative to the filter element so as to enable alteration of the spacing between the filter element and the displacement arrangement.