GB2419544A

GB2419544A - Improvements in and relating to apparatus for removing pollutants from a gas stream

Info

Publication number: GB2419544A
Application number: GB0423915A
Authority: GB
Inventors: Peter Kukla
Original assignee: Per Tec Ltd
Current assignee: Per Tec Ltd
Priority date: 2004-10-28
Filing date: 2004-10-28
Publication date: 2006-05-03
Also published as: GB0423915D0

Abstract

The present invention provides an apparatus 1 for removing pollutants from a gas stream. An apparatus 1 according to the invention has a first flow path providing fluid communication between an inlet 5 of the apparatus 1 and an outlet 7 of the apparatus 1, the first flow path comprising treatment means 9 including a chargeable electrode arranged, in use, to impart a charge to pollutant material and a pollutant collector 11 through which gas is arranged to pass, and wherein the apparatus 1 comprises separator means arranged to cause a primary gas stream to split into a first, pollutant particle rich, gas stream for travelling along the first flow path and a second, cleaner, gas stream for travelling along a divert flow path, the divert flow path having an inlet 73 (divert inlet) from the first flow path and being in fluid communication with an outlet of the apparatus, and wherein the separator means is located downstream of the chargeable electrode and upstream of the pollutant collector 11 and comprises a constriction in the first flow path upstream of the divert inlet 73 to reduce the cross-sectional area of the first flow path such that an inlet 99 (expansion inlet) is provided to an expansion chamber 101 in which the divert inlet 73 is located.

Description

1 2419544

IMPROVEMENTS IN AND RELATING TO APPARATUS FOR REMOVING

POLLUTANTS FROM A GAS STREAM

Field of the Invention

The present invention relates to apparatus for removing pollutants from a gas stream.

Background to the Invention

The presence of pollutants in gas streams from industrial processes and vehicle exhausts and their impact upon the environment are a matter of concern. Accordingly, attempts have been made to provide apparatus instream for removing such pollutants. Applicants have for example worked upon apparatus for removing pollutants as disclosed in WO 03/074846 which can advantageously reduce the quantity of pollutants released to the environment. Such apparatus may comprise a flow path passing through a filter and an alternative flow path avoiding the filter such that should the filter become blocked gas may still exist the apparatus thus alleviating the build up of back- pressure.

However, with such apparatus a gas stream comprising a greater level of pollutants than is desirable may follow the alternative flow path, thus avoiding the filter.

There thus remains a need for apparatus which can remove pollutants with high efficiency and avoid back-pressure, especially for vehicle exhaust applications.

It is an aim of preferred embodiments of the present invention to obviate or overcome a disadvantage of the prior art, whether referred to herein or otherwise.

Summary of the Invention

According to the present invention in a first aspect there is provided an apparatus for removing pollutants from a gas stream, the apparatus having a first flow path providing fluid communication between an inlet of the apparatus and an outlet of the apparatus, the first flow path comprising treatment means including a chargeable electrode arranged, in use, to impart a charge to pollutant material and a pollutant collector through which gas is arranged to pass, and wherein the apparatus comprises separator means arranged to cause a primary gas stream to split into a first, pollutant particle rich, gas stream for travelling along the first flow path and a second, cleaner, gas stream for travelling along a divert flow path, the divert flow path having an inlet (divert inlet) from the first flow path and being in fluid communication with an outlet of the apparatus, and wherein the separator means is located downstream of the chargeable electrode and upstream of the pollutant collector and comprises a constriction in the first flow path upstream of the divert inlet to reduce the cross- sectional area of the first flow path such that an inlet (expansion inlet) is provided to an expansion chamber in which the divert inlet is located.

Suitably, the chargeable electrode is for at least partially ionising the gas. Suitably, the electrode is for imparting a charge to pollutant particles in the gas.

The charge may be positive. Alternatively the charge may be negative.

Suitably, the electrode is mounted at one end only.

Suitably, the electrode is mounted in a substantially non- conductive electrode mount. Suitably, the mount is at least partly covered by a substantially non-conductive hood.

Suitably, the treatment means comprises a field tube arranged to substantially surround the electrode to define a treatment chamber.

Suitably, the separator means is located within the field tube. Suitably, the divert inlet is located within the

field tube.

Suitably, the pollutant collector comprises a filter.

Suitably, the filter is a regenerative filter. Suitably, the filter is electrically regenerative.

The separator means may be located upstream of all or part of the pollutant collector. The separator means may be located upstream of all or part of the filter. Suitably, the separator means is located upstream of the entirety of the filter.

The pollutant collector may comprise a catalyst. The pollutant collector may comprise a filter having a catalytic coating. The catalytic coating may comprise a diesel formulation catalytic coating. The catalytic coating may comprise an industry diesel application related catalyst. For example, a suitable catalyst is Johnson Matthey MC2S, code 4760.

Suitably, the pollutant collector comprises an elongate hollow body having first and second ends. Suitably, a first end of the pollutant collector comprises an inlet (collector inlet) for receiving a gas stream travelling along the first flow path. Suitably, the ends of the body are interposed by a tubular wall comprising a filter.

In use, a gas stream may enter the pollutant collector via the inlet and then pass through the collector and exit via the filter wall.

Suitably, the divert flow path is arranged to allow gas to exit the apparatus from the pollutant collector without passing through a filter of the pollutant collector.

Thus, in the event of the filter becoming substantially obstructed, for example by the heavy build up of collected pollutants, gas may still have a route through the apparatus. The creation of a back-pressure may thus be substantially avoided.

Suitably, the flow path has a cross-section at the constricted part (ie at the expansion inlet) which is less than 70% of that immediately upstream of the constriction, preferably less than 50%, for example less than 30%.

Suitably, the flow path has a cross-section at the constricted part (ie at the expansion inlet) which is less than 70% of that immediately downstream of the constriction, preferably less than 50%, for example less than 30%.

Suitably, the expansion inlet has a cross-section which is at least 50% of that of the inlet of the apparatus, preferably at least 70%, for example at least 90%. The creation of back pressure may thus be substantially avoided.

Suitably, the constriction is provided by a constriction member. Suitably, the constriction member is arranged to lie in an off-set position in the first flow path.

Suitably, the constriction member comprises a planar face arranged to face upstream.

Suitably, the constriction member comprises a disc. The disc may be circular. Suitably, the constriction member comprises a peripheral wall arranged to extend from the disc in a downstream direction.

The divert inlet may be located within 10cm downstream of the constriction, for example within 5cm.

Suitably, the divert inlet is located behind the constriction member. Thus, the divert inlet may not lie directly in the path of a gas stream passing through the expansion inlet. Gas and particles may thus have to turn and travel substantially perpendicularly to the direction of the first flow path to travel from the expansion inlet to the divert inlet.

Suitably, the divert inlet is orientated to substantially face a direction other than that from which a gas stream travels along the first flow path. The divert inlet may be orientated to face substantially perpendicularly to the direction in which a gas stream travels along the first flow path. Alternatively, the divert inlet may be orientated to face substantially the same direction as that in which a gas stream flows along the first flow path. The gas stream may thus have to substantially change its direction in order to enter the diverter inlet.

Suitably, the divert inlet is orientated to face substantially perpendicularly to the expansion inlet. The gas stream entering the expansion inlet may thus have to turn substantially through 90 degrees to enter the diverter inlet. It will be appreciated that it may be easier for gas to turn through such an angle than it is for particles which have greater momentum. Thus the majority of pollutant particles carried by a gas stream may flow via the first flow path.

Suitably, at least 50% of pollutant particles in a gas stream which enters the apparatus may travel through the first flow path to the filter of the pollutant collector.

Suitably, no more than 50% of pollutant particles in a gas stream which enters the apparatus may travel to the outlet via the divert flow path. Preferably, no more than 30%, more preferably no more than 20%, for example no more than 10% of particles travel to the outlet via the divert flow path. Most preferably, no more than 5% of particles travel to the outlet via the divert flow path, for example only 1% of particles may travel to the outlet via the divert flow path.

Suitably, the apparatus comprises a divert tube which comprises the divert inlet and defines a part of the divert flow path. Suitably, the divert tube comprises the divert inlet at an end thereof.

Suitably, the divert tube extends into the field tube.

Suitably, the divert tube extends into the field tube through a side wall thereof. Suitably, the divert tube extends into the field tube Perpendicularly to the first flow path. The divert tube may extend into the field tube by between 0.5 and 5cm.

Suitably, the divert flow path comprises a catalyst.

Suitably, the catalyst is located at the divert inlet.

Suitably, the catalyst comprises a diesel formulation catalytic coating. The catalyst may comprise an industry diesel application related catalyst. For example, a suitable catalyst is Johnson Matthey MC2S, code 4760.

Suitably, the inlet of the apparatus is into a first chamber. Suitably, the first chamber has an opening into the treatment chamber.

Suitably, the apparatus comprises a second chamber, downstream of the first chamber and in which the treatment chamber is located.

Suitably, the apparatus comprises a third chamber downstream of the second chamber and in which the pollutant collector is located. Suitably, gas can pass through the collector into the third chamber.

Suitably, the outlet of the apparatus is from the third chamber.

Suitably, the apparatus comprises a fourth chamber in communication with the diverter means and the third chamber, suitably, the treatment chamber is located within this as well as the second chamber.

The divert tube is suitably in communication with the third chamber. The divert tube may have an outlet into the fourth chamber which in turn has an outlet to the third chamber.

Suitably, the first flow path and divert flow path are in communication with a common outlet. Suitably, the apparatus is arranged such that first and second gas streams are combined in the third chamber Thus, whether gas follows the first flow path or the alternate flow path it may be exhausted from the apparatus via the same outlet.

According to the present invention in a second aspect there is provided a vehicle comprising an apparatus for removing pollutants from a gas stream according to the first aspect.

Brief Description of the Drawings

The present invention will now be described by way of example only, with reference to the drawings that follow, in which: Figure 1 is a cross sectional view of an apparatus for removing pollutants from a gas stream; and Figure 2 is a section along line C-C of Figure 1.

Description of the Preferred Embodiment

As illustrated by Figure 1 of the drawings that follow, there is shown an apparatus 1 for removing pollutants from a gas stream. it should be noted that while it is an aim of the apparatus i to remove as much of the pollutant as possible from a gas stream, it is not a requirement for it to remove all or even a substantial part thereof.

The apparatus i is encased in a tubular metal casing indicated by dashed line 3 in Figure 1, but which is excluded generally for ease of illustration and explanation. The apparatus 1 comprises a gas stream inlet 5 and a gas stream outlet 7 with a path of fluid communication between the gas inlet 5 and outlet 7 as described below. The inlet and outlet are in communication via a first flow path illustrated generally by arrows A. A divert flow path provides an alternate flow path illustrated generally by arrows B branching from the first flow path.

The first flow path includes a treatment means 9 comprising an electrode (shown schematically as E) for imparting a negative charge to pollutants in a gas stream and a collector 11 downstream thereof for removing pollutants from the gas stream. The collector 11 comprises a tubular wall comprising a filter 51 through which gas is arranged to pass.

The electrode is carried centrally in an electrode mount (not shown) having an electrode hood.

Both the electrode mount and circular tubular electrode hood are formed from a ceramic high purity alumina material, sold under the trade mark SINTOX FF which is believed to have a dielectric strength of between 30 and 40 ky/mm.

The electrode mount comprises a first ceramic mounting portion and a second ceramic mounting portion mounted in a bore. The second ceramic mounting portion is of a reduced external diameter compared with the first ceramic mounting portion. The electrode mount can be formed from a single ceramic. Thus the electrode mount has a portion of a first diameter and a portion of a lesser diameter towards the distal end (from which the electrode projects) thereof. The second portion of second diameter extends a substantial distance beyond the hood typically at least 30mm.

The hood protects a substantial part of the electrode (mounted in central bore) from the inflow of pollutants containing gas thus minimising the risk of shorting.

However, it is believed that at least a 30mm length of the electrode needs to project beyond the hood.

The electrode mount and hood can be glazed to reduce pitting of the surface and hence the build up of particulates thereon. The glaze acts as a means for smoothing the surface of the electrode mount.

The hood helps prevent build up of often carbon based deposits on the electrode.

The alumina content of hood and mount is typically at least 80%, normally at least 90%, preferably more than 95%, more preferably more than 97% and most preferably more than 99%.

The electrode is connected to a direct current power source for charging the electrode to l8kV-40kV negative polarity.

An electrically resistive organic barrier coating may be provided over any (typically metallic) surface downstream of the beginning of the electrode. The coating is TLHB/02 available from Camcoat Performance Coatings on 127 Hoyle Street, Bewsey Industrial Estate, Warrington, WA5 5LR, United Kingdom. it is believed that by reducing the discharge rate of the agglomerated particulates along the tube by providing the coating, the particulates are more likely to stay in the vicinity of the tube.

The apparatus comprises a first end wall 17 having a mounting apertures (not shown) through which the electrode of treatment means 9 is mounted (mounting not shown) . The apparatus has a second end wall 23 having an aperture providing the outlet 7.

The first and second end walls 17, 23 are interposed by a first dividing wall 25, a second dividing wall 27 and a third dividing wall 28 which define a number of chambers there between. The inlet 5 opens into a first chamber 29 downstream of which is a second chamber 31 and downstream of the second chamber 31 is a third chamber 33 which is in communication with the outlet 7. Between the second and third chamber is a fourth chamber 34.

The collector 11 is located within the third chamber 33.

The electrode (shown schematically as E) extends into the second chamber 31 and is surrounded by field tube 35. The field tube 35 has an opening 39 into the first chamber and extends the length of the second and fourth chambers and is in communication with the collector 11. The field tube thus defines a treatment chamber.

The inlet 5 comprises an aperture in the casing 3 which is in communication with an inlet tube 43 from which pollutant laden gas can flow into the first chamber 29.

The apparatus comprises separating means for splitting a primary gas stream into a first, pollutant particle rich gas stream for following the first flow path and a second, cleaner, gas stream for following the divert flow path.

The separating means comprises a constriction in the first flow path formed by constricting member 91.

The constricting member 91 comprises a circular disc 93 having a substantially planar face 95 arranged to face upstream. A peripheral wall 97 extends from the disc 93 in a downstream direction. The constricting member and wall 36 of the field tube define an opening between them which provides an inlet (expansion inlet) 99 into an expansion chamber ioi formed downstream of the constriction.

The apparatus comprises a divert tube 71 extending into the field tube 35 in the expansion chamber 101. Figure 2 illustrates the arrangement of the constricting member 91 within field tube 35 and also shows in dotted lines an inlet (divert inlet) 71 provided by divert tube 73.

The inlet divert inlet 73 of the divert tube 71 is orientated to face perpendicularly to the inlet 99 of the expansion chamber 101. Thus gas and particulates flowing along the first flow path may only enter the divert tube 71 by substantially reversing their direction. Further, divert inlet 73 is located behind the constricting member 91 such that gas and particulates must travel substantially perpendicular to the direction of the first flow path in order to reach the divert inlet 73.

The divert tube 71 has an outlet 77 into the fourth chamber 34. The fourth chamber in turn has an outlet to the third chamber 33.

In use, a gas stream (pollutant laden gas), for example from a vehicle exhaust, typically a diesel engine exhaust, is introduced into the first chamber 29 through inlet 5.

The gas stream passes through the first chamber 29 and along the first flow path.

The electrode of the treatment means 9 is charged to a voltage of l8kV4OkV negative polarity.

As gas travels along the first flow path the electrode of the treatment means 9 imparts a positive charge to pollutant particles. The gas stream (primary stream), including the charged particles, travels toward the collector 11.

The primary gas stream then reaches the constriction of the separating means provided by constricting member 91.

The gas stream passes through the expansion inlet 99 into expansion chamber 101. As it does so it is divided into first and second gas streams, the first then following the first flow path and the second the divert path.

To enter the divert inlet 73 into divert tube 71 and follow the divert flow path the gas stream must turn whereas to follow the first it can travel substantially linearly. Particulates which have greater momentum than gas may make this turn less easily and accordingly more follow the first flow path than the divert flow path. Gas may make the turn more readily and thus the separator may act as a "momentum filter" such that the gas stream following the first flow path comprises a higher level of pollutant particles after the separating means than before.

The first gas stream following the first flow path then travels into the pollutant collector 11. The walls of the collector 11 comprise a filter 51 through which the gas passes and which collects pollutant particles. Some particles may though exit from the collector with the gas stream. The cleaner gas stream which exits the collector 11 then enters third chamber 33.

Should the filter 51 become obstructed then some or all of the gas may exit the collector via the divert flow path depending on the level of obstruction.

The second gas stream following the divert flow path is conveyed by divert tube 71 into fourth chamber 34 from which it travels to the third chamber 33.

The first and second gas streams combine in the third chamber 33 and exit the apparatus via outlet 7.

The provision of separating means and a divert flow path for cleaner gas may result in an apparatus which is surprisingly effective in the removal of pollutants from a gas stream following the first flow path. The separating means may cause pollutant particles to agglomerate reducing the number of fine particles which might otherwise pass through the collector. This may be the result of an increased potential at the expansion inlet created by the constriction. Also, the collector may be better able to remove pollutants from the gas stream when the flow rate through it is lower as a result of the relief provided by the divert flow path.

The second flow path also ensures that should the filter become obstructed, for example if the filter becomes heavily laden with pollutant, the gas stream still has an exit path from the apparatus. This may reduce the creation of back-pressure within the apparatus.

It will be appreciated that preferred embodiments of the present invention may be effective at removing pollutants from a gas stream whilst avoiding back-pressure problems which may be associated with placing filters in a gas stream.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extends to any novel one, or any novel combination, of the features

disclosed in this specification (including any

accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims 1. An apparatus for removing pollutants from a gas stream, the

apparatus having a first flow path providing fluid communication between an inlet of the apparatus and an outlet of the apparatus, the first flow path comprising treatment means including a chargeable electrode arranged, in use, to impart a charge to pollutant material and a pollutant collector through which gas is arranged to pass, and wherein the apparatus comprises separator means arranged to cause a primary gas stream to split into a first, pollutant particle rich, gas stream for travelling along the first flow path and a second, cleaner, gas stream for travelling along a divert flow path, the divert flow path having an inlet (divert inlet) from the first flow path and being in fluid communication with an outlet of the apparatus, and wherein the separator means is located downstream of the chargeable electrode and upstream of the pollutant collector and comprises a constriction in the first flow path upstream of the divert inlet to reduce the cross-sectional area of the first flow path such that an inlet (expansion inlet) is provided to an expansion chamber in which the divert inlet is located.
2. An apparatus according to claim 1, wherein the

treatment means comprises a field tube arranged to

substantially surround the electrode to define a treatment chamber.
3. An apparatus according to claim 2, wherein the

separator means is located within the field tube.
4. An apparatus according to claim 3, wherein the divert

inlet is located within the field tube.
5. An apparatus according to any preceding claim, wherein the apparatus comprises a divert tube which comprises the divert inlet and defines a part of the divert flow path.
6. An apparatus according to claim 4, wherein the apparatus comprises a divert tube which comprises the divert inlet and defines a part of the divert flow path and wherein the divert tube extends into the field tube.
7. An apparatus according to any preceding claim, wherein the divert flow path comprises a catalyst.
8. An apparatus according to any claims, wherein the first flow path and divert flow path are in communication with a common outlet.
9. An apparatus according to any preceding claim, wherein the pollutant collector comprises a filter.
10. An apparatus according to any preceding claim, wherein the pollutant collector comprises a catalyst.
11. An apparatus according to any claim 9 or 10, wherein the divert flow path is arranged to allow gas to exit the apparatus from the pollutant collector without passing through a filter of the pollutant collector.
12. An apparatus according to any preceding claim, wherein the flow path has a cross-section at the constricted part (ie at the expansion inlet) which is less than 70% of that immediately upstream of the constriction.
13. An apparatus according to any preceding claim, wherein the flow path has a cross-section at the constricted part (ie at the expansion inlet) which is less than 70% of that immediately downstream of the constriction.
14. An apparatus according to any preceding claim, wherein the expansion inlet has a cross-section which is at least 50% of that of the inlet of the apparatus.
15. An apparatus according to any preceding claim, wherein the constriction is provided by a constriction member.
16. An apparatus according to claim 15, wherein the constriction member is arranged to lie in an off-set position in the first flow path.
17. An apparatus according to claim 15 or 16, wherein the constriction member comprises a planar face arranged to face upstream.
18. An apparatus according to any of claims 15 to 17, wherein the constriction member comprises a disc.
19. An apparatus according to claim 18, wherein the constriction member comprises a peripheral wall arranged to extend from the disc in a downstream direction.
20. An apparatus according to any of claims 15 to 19, wherein the divert inlet is located behind the constriction member.
21. An apparatus according to any of the preceding claims, wherein the divert inlet is located within 10cm downstream of the constriction.
22. An apparatus according to any preceding claim, wherein the divert inlet is orientated to substantially face a direction other than that from which a gas stream travels along the first flow path.
23. An apparatus according to any preceding claim, wherein the divert inlet is orientated to face substantially perpendicularly to the expansion inlet.
24. An apparatus for removing pollutants from a gas stream substantially as herein described with reference to the accompanying drawings.
25. A vehicle comprising an apparatus for removing pollutants from a gas stream according to any preceding claim.