GB2419545A

GB2419545A - Apparatus for removing pollutants from a gas stream

Info

Publication number: GB2419545A
Application number: GB0423917A
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
Anticipated expiration: 2024-10-28
Also published as: GB2419545B; GB0423917D0

Abstract

The present invention provides 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 flow path comprising treatment means 9 including a pollutant collector 11 through which gas is arranged to pass, and wherein the apparatus 1 comprises by-pass means arranged to provide an alternative flow path to the outlet 7 should the flow path through the pollutant collector 11 become obstructed, the by-pass means having an inlet 73 (by-pass inlet) in communication with the first flow path and wherein the by-pass inlet 73 is orientated to face a direction ranging from substantially the same direction as that in which a gas stream flows along the first flow path in normal use and a direction substantially perpendicular thereto.

Description

1 2419545

IMPROVEMES 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.

çjground 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 in-stream 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 greater level of pollutants, than is desirable may follow the alternative flow path, thus avoiding the filter, even when the filter is working effectively. 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 flow path comprising treatment means including a pollutant collector through which gas is arranged to pass, and wherein the apparatus comprises by-pass means arranged to provide an alternative flow path to the outlet should the flow path through the pollutant collector become obstructed, the by- pass means having an inlet (by-pass inlet) in communication with the first flow path and wherein the by- pass inlet is orientated to face a direction ranging from substantially the same direction as that in which a gas stream flows along the first flow path in normal use and a direction substantially perpendicular thereto.

Suitably, the by-pass inlet is arranged such that pollutant particles will substantially not enter the by- pass inlet and travel along the alternate flow path unless the pollutant collector becomes substantially obstructed.

By "normal use" it is meant the condition when the pollutant collector is substantially unobstructed and gas may pass therethrough.

The axis of the by-pass inlet may be arranged to extend substantially antiparallel to the direction in which a gas stream flows along the first flow path in normal use. The by-pass inlet may thus be orientated to face substantially the same direction as that in which a gas stream flows along the first flow path in normal use. Alternatively, the axis of the by-pass inlet may be arranged to extend substantially Perpendicularly to the direction in which a gas stream flows along the first flow path in normal use.

The by-pass inlet may thus be orientated to face substantially Perpendicularly to the direction in which a gas stream flows along the first flow path in normal use.

The gas stream may thus have to substantially change, for example reverse, its direction in order to enter the by- pass inlet.

Suitably, the by-pass inlet is arranged to lie within a central region of the first flow path. The by-pass inlet may be arranged to lie within 5cm of the axis of the first flow path.

Suitably, the pollutant collector comprises a filter.

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

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 MC25, 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 normal 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 by-pass means is arranged to allow gas to exit the apparatus 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 and particles carried thereby may still have a route through the apparatus. The creation of a back-pressure may thus be substantially avoided.

Suitably, the apparatus is arranged such the majority of a gas stream travelling through the apparatus passes through a filter of the collector unless the filter is substantially obstructed. Suitably, at least 50%, preferably at least 70% of gas travelling through the apparatus passes through a filter of the collector unless the filter is substantially obstructed.

Suitably, the by-pass means is arranged such that unless the filter is substantially obstructed no more than 70% of the pollutants from a gas stream travelling through the apparatus travel to the outlet via the alternative flow path. Preferably, the level is significantly less than 70%, for example, 50% or less, preferably 40% or less, more preferably 30% or less, still more preferably 20% or less, for example 10% or less.

Suitably, the by-pass means is arranged such that unless the filter is substantially obstructed no more than 20% of the gas from a gas stream travelling through the apparatus travels to the outlet via the alternative flow path.

Suitably, the treatment means is arranged, in use, to impart a charge to pollutant material.

Suitably, the treatment means comprises a chargeable electrode upstream of the pollutant collector. 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 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, the outlet of the apparatus is from the third chamber.

Suitably, the apparatus comprises a fourth chamber in communication with the by-pass means and the third chamber.

Suitably, the by-pass means comprises a catalyst.

Suitably, the catalyst is located at the by-pass inlet.

The catalyst may comprise 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 by-pass inlet is located at a point removed from the outlet of the apparatus.

Suitably, the by-pass inlet is located within the pollutant collector. Suitably, the by-pass inlet is located toward the first end of the pollutant collector.

Suitably, the by-pass inlet is coaxial with the collector inlet. Suitably, the by-pass inlet lies substantially on the axis of pollutant collector.

Suitably, the by-pass inlet is orientated to face substantially the same direction as the collector inlet.

The gas stream entering the collector inlet may thus have to turn substantially through 180 degrees to enter the by- pass inlet. It will be appreciated that this may be unlikely to occur in normal use when there is a more efficient and direct flow path through the pollutant collector to the outlet. Thus only a minor portion of the gas stream may flow via the by-pass means in normal use of the apparatus. it will be appreciated that, in normal use, it may be Particularly unlikely that pollutant particles carried by the gas stream will turn through 180 degrees owing to their momentum as they enter from the collector inlet. Thus, only a minor portion of pollutant particles may travel through the alternative flow path in normal use.

Suitably, the by-pass means comprises a by-pass tube which suitably comprises the by-pass inlet. Suitably, the by- pass tube comprises the by-pass inlet at an end thereof.

Suitably, the by-pass inlet lies substantially on the axis of the by-pass tube.

Suitably, the by-pass tube extends into the pollutant collector. Suitably, the by-pass tube extends into the pollutant collector from a first end thereof. The by-pass tube may extend into the pollutant collector by between 0.5 and 10cm.

Suitably, the by-pass means is in communication with the outlet. Thus whether gas follows the first flow path or the alternate flow path it may be exhausted from the apparatus via the outlet.

Suitably, the pollutant collector is housed within a chamber (third chamber) and the gas stream is arranged in normal use to pass through the collector and into said chamber. Suitably, the third chamber comprises the outlet of the apparatus.

The by-pass means is suitably in communication with the third chamber. The by-pass means may have an outlet into a fourth chamber which in turn has an outlet to a third chamber. Thus, should the pollutant collector become obstructed the gas stream may still be conveyed into the third chamber. Suitably, if the pollutant collector is obstructed the gas stream enters the collector but rather than passing through the collector it travels around within the collector until it finds the by-pass inlet.

According to the present invention in a second 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 flow path comprising treatment means including a pollutant collector through which gas is arranged to pass, and wherein the pollutant collector comprises a filter having a catalytic coating.

Suitably, the catalytic coating comprises diesel formulation catalytic coating. The catalytic coating may comprise an industry diesel application related catalyst.

For example a suitable catalyst Johnson Matthey MC25, code 4760.

The filter may be such that it does not require electrical regeneration.

The apparatus may comprise any feature as described in the first aspect.

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

Brief Description of the Drawi

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 third angle projection of an apparatus for removing pollutants from a gas stream; and Figure 2 is a cut-away perspective view of a part of an alternative embodiment of an apparatus for removing pollutants from a gas stream.

Description of the Preferred Embodiment

As illustrated by Figure 1 of the drawings that follow, there is shown an apparatus i 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. L0

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 i 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 by-pass means 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 (not shown) 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 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 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 3 0mm.

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 TLJHB/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 (not shown) of treatment means 9 is mounted. 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 fourth 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 (not shown) 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 35 thus defines a treatment chamber.

The gas 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 by-pass means comprising a by-pass tube 71 extending into the collector 11. The by-pass tube 71 has an inlet (by-pass inlet) 73 orientated in the same direction as the inlet 75 of the collector 11. Thus gas flowing along the first flow path may only enter the by- pass tube 71 by substantially reversing it's direction.

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

The by-pass tube 71 thus ensures that should the filter 51 become obstructed, for example if the filter 51 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.

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 (not shown) of the treatment means 9 imparts a positive charge to pollutant particles. The gas stream, including the charged particles, travels to the collector 11. The walls of the collector ii 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 ii then travels to outlet 7 where it exits the apparatus.

Should the filter 51 become obstructed then some or all of the gas may exit the collector via the by-pass means depending on the level of obstruction.

In normal use a proportion of the gas stream, including pollutants, may exit the collector via the alternate flow path provided by the by-pass means. The majority of the gas stream will though exit the collector via the filter which will thus remove pollutants from the gas stream.

Additionally, the arrangement of the by-pass inlet may mean that the part of the gas stream following the alternate flow path comprises less pollutant particles than that which continues along the first flow path. The reason for this may be that it is easier for the gas than the particles to turn to enter the by-pass inlet. Thus pollutant particles may preferentially follow the first flow path to be collected by the filter in normal use.

Figure 2 illustrates a part of an alternative embodiment of an apparatus 1 for removing pollutant from a gas stream. This apparatus comprises two treatment means 9, 13 each of which comprise a collector ii, 15. Otherwise the apparatus is substantially the same as that of the first embodiment and like parts are labelled accordingly.

The treatment means 9, 13 each function in substantially the same manner as that of the first embodiment. Each comprises an electrode (not shown) but one is arranged to impart a positive charge to pollutants and the other to impart a negative charge.

A first flow path is defined by one treatment means 9 and a second flow path by the other treatment means 13. In use, a primary gas stream enters the first chamber 29 via inlet 5. The primary gas stream is split to form first and second gas streams as it enters field tubes 35, 37 in the second chamber 31 which define part of the first and second flow paths. The gas streams are then combined in the third chamber 33 before exiting via the outlet (not shown in Figure 2).

Each collector ii, 15 is provided with by-pass means in the form of a bypass tube 71, 79. Should the filter 51 of either collector become obstructed gas can flow via an alternative flow path through the respective by-pass tube and into the fourth chamber 34. From there it can pass through aperture 81 into the third chamber 33.

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

CLAI MS

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 flow path comprising treatment means including a pollutant collector through which gas is arranged to pass, and wherein the apparatus comprises by-pass means arranged to provide an alternative flow path to the outlet should the flow path through the pollutant collector become obstructed, the by-pass means having an inlet (by-pass inlet) in communication with the first flow path and wherein the by-pass inlet is orientated to face a direction ranging from substantially the same direction as that in which a gas stream flows along the first flow path in normal use and a direction substantially perpendicular thereto.

2. An apparatus according to claim 1, wherein the by-pass inlet is arranged such that pollutant particles will substantially not enter the by-pass inlet and travel along the alternate flow path unless the pollutant collector becomes substantially obstructed.

3. An apparatus according to claim 1 or 2, wherein the axis of the bypass inlet is arranged to extend substantially antiparallel to the direction in which a gas stream flows along the first flow path in normal use.

4. An apparatus according to claim 1 or 2, wherein the axis of the bypass inlet is arranged to extend substantially perpendicularly to the direction in which a gas stream flows along the first flow path in normal use.

5. An apparatus according to any preceding claim, wherein, the pollutant collector comprises a filter.

6. An apparatus according to any preceding claims, wherein the pollutant collector comprises a catalyst.

7. An apparatus according to claim 5 or 6, wherein the by-pass means is arranged to allow gas to exit the apparatus without passing through a filter of the pollutant collector.

8. An apparatus according to any preceding claim, wherein the treatment means is arranged, in use, to impart a charge to pollutant material.

9. An apparatus according to claim 8, wherein the treatment means comprises a chargeable electrode upstream of the pollutant collector.

10. An apparatus according to claim 9, wherein the

treatment means comprises a field tube arranged to

substantially surround the electrode to define a treatment chamber.

11. An apparatus according to any preceding claim, wherein the by-pass means comprises a catalyst.

12. An apparatus according to any preceding claim, wherein the by-pass inlet is located within the pollutant collector.

13. An apparatus according to any preceding claim, wherein the by-pass means comprises a by-pass tube which comprises the by-pass inlet.

14. An apparatus according to claim 13, wherein the by- pass tube extends into the pollutant collector.

15. 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 flow path comprising treatment means including a pollutant collector through which gas is arranged to pass, and wherein the pollutant collector comprises a filter having a catalytic coating.

16. An apparatus for removing pollutants from a gas stream, substantially as herein described with reference to the accompanying drawings.

17. A vehicle comprising an apparatus for removing pollutants from a gas stream according to any preceding claim.