GB2419543A

GB2419543A - Apparatus for removing pollutants from a gas stream

Info

Publication number: GB2419543A
Application number: GB0423914A
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: GB2419543B; GB0423914D0

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, and a second flow path, providing fluid communication between an inlet 5 of the apparatus 1 and an outlet 7 of the apparatus 1, wherein each flow path comprises treatment means 9, 13 each treatment means 9, 13 comprising a pollutant collector 11, 15 and wherein the treatment means 9 in the first flow path (first treatment means) is arranged, in use, to impart a positive charge to pollutant material and the treatment means 13 in the second flow path (second treatment means) is arranged, in use, to impart a negative charge to pollutant material.

Description

IMPROVEMENTS IN AND RELATING TO APPARATUS FOR REMOVING

POLLUTANTS FROM A GAS STREAH

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.

However, it has been noted that when such apparatus is used in vehicle applications pollutants which are not removed from the gas stream may deposit on the vehicle body in the region of the exhaust.

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, and a second flow path, providing fluid communication between an inlet of the apparatus and an outlet of the apparatus, wherein each flow path comprises treatment means, each treatment means comprising a pollutant collector and wherein the treatment means in the first flow path (first treatment means) is arranged, in use, to impart a positive charge to pollutant material and the treatment means in the second flow path (second treatment means) is arranged, in use, to impart a negative charge to pollutant material.

Suitably, the apparatus is arranged to combine the first and second gas streams such that a combined gas stream is released by the apparatus.

Suitably, the first and second flow path are in communication with a common outlet. Suitably, the apparatus is arranged such that a combined gas stream exits from the common outlet.

Suitably, the first and second gas streams are combined downstream of the pollutant collectors.

Suitably, the first and second gas streams are combined such that particles from each stream may transfer charge with those from the other stream. The gas stream released from the apparatus as a combined stream may contain less charged particles and/or particles having a lower charge (i.e. a positive or negative charge closer to neutral) than would be the case if the gas stream released from the apparatus comprised distinct first and second gas streams.

Suitably, the first and second flow path are in communication with a common inlet.

Suitably, the apparatus comprises an inlet arranged to receive a primary gas stream.

Suitably, the apparatus is arranged to split the primary gas stream to provide a first gas stream for travelling through the first flow path and a second gas stream for is travelling through the second flow path.

Suitably, the primary gas stream is split upstream of the pollutant collectors.

Suitably, the pollutant collector of each treatment means comprises a filter. Suitably, each filter is a regenerative filter. Suitably, each filter is electrically regenerative.

Suitably, the filters are spaced from one another by between 2 and 20mm, for example by between 6 and 10mm.

Suitably, the first 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 positive charge to pollutant particles in the gas.

Suitably, the second 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 negative charge to pollutant particles in the gas.

Suitably, each electrode is mounted at one end only.

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

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

Suitably, each field tube has an outer diameter of between and 130mm, for example around 110mm.

Surprisingly, it has been found that an apparatus having two treatment means having oppositely charged treatment chambers may be more effective at removing pollutants than one having only one treatment chamber or one having two treatment chambers of the same charge.

It may be that the use of two treatment means having oppositely charged treatment chambers may enable higher potential differences to be obtained between charged pollutant particulate and the field tubes than would be the case in an apparatus having only one treatment means or two treatment means having chambers of the same charge.

Suitably, the inlet of the apparatus is into a first chamber. Suitably, the first chamber has openings into the first and second flow paths. Suitably, the first chamber has openings into the first and second treatment chambers.

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

Suitably the primary gas stream is divided into first and second gas streams as it enters the treatment chambers.

Suitably, the apparatus comprises a third chamber downstream of the second chamber and in which the pollutant collectors are located.

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

Suitably, the first and second gas streams are combined in the third chamber after passing through the pollutant collectors.

Suitably, the apparatus comprises by-pass means to allow gas to exit the apparatus without passing through a filter of a pollutant collector. Thus, in the event of the filter becoming 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 apparatus is arranged such that the major part of a gas stream passes through a filter of the collector unless the filter is substantially obstructed.

Suitably, each collector is provided with by-pass means.

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 perspective view of an apparatus according to the present invention.

Figure 2 is a detailed perspective view of a part of the apparatus of Figure 1.

Figure 3 is a perspective view of an alternative embodiment of the apparatus according to the present invention.

Figure 4 is a plan view of the apparatus of Figure 3.

Description of the Preferred Embodiment

As best 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 1 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 1 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 S and outlet 7 as described below. The inlet and outlet are in communication via first and second parallel flow paths.

The first flow path includes a first treatment means 9 comprising an electrode (not shown) for imparting a positive charge to pollutants in a gas stream and a collector 11 downstream thereof for removing pollutants from the gas stream. The second flow path includes a second treatment means 13 comprising an electrode (not shown) for imparting a negative charge to pollutants in a gas stream and a collector 15 downstream thereof for removing pollutants from the gas stream.

Each 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 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 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%.

Each electrode is connected to a direct current power source for charging the electrode to l8kV-4OkV negative or positive polarity depending on the respective treatment means 9, 13.

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 mounting apertures 19, 21 through which the electrodes (not shown) of the first and second treatment means 9, 13 are 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 and a second dividing wall 27 which define a number of chambers therebetween. 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.

The collectors 11, 15 are located within the third chamber 33. The electrodes (not shown) extend into the second chamber 31 and are surrounded by first and second field tubes 35, 37. The field tubes 35, 37 have openings 39, 41 into the first chamber and extend the length of the second chamber and are in communication with the collectors 11, respectively. The first and second field tubes 35, 37 thus define first and second treatment chambers respectively.

The first dividing wall 25 further comprises an aperture 44 to provide communication between the part of second chamber 31 lying outside the field tubes 35, 37 and the first chamber 29.

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.

As illustrated by Figure 2 the end of each collector 11, adjacent the second end wall 23 of the apparatus comprises a by-pass means comprising an apertured wall 45.

The apertured wall 45 is provided by a first tube 47 which locates within a second tube 49, which comprises a filter 51, and protrudes beyond the end thereof such that the apertures open directly into the third chamber. The apertured wall 45 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 collector. This may reduce the creation of back-pressure within the apparatus. The first tube 47 is moveable relative to the second tube 49 such that the capacity of the by-pass means can be adjusted. This may allow the apparatus to be set to best suit a given application to ensure optimum removal of pollutant whilst minimising the risk of back-pressure creation.

In use, a primary gas stream (the 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 primary gas stream passes through the first chamber 29 and is divided to provide a first gas stream which travels along the first flow path and a second gas stream which travels along the second flow path. This separation is provided by the inlets 39, 41 to

the field tubes 35, 37.

The electrodes of the first and second treatment means 9, 13, are charged to substantially equal but opposite voltages. That of the first treatment means 9 is given a voltage of around l8kV-40kv negative polarity and that of the second treatment means a voltage of around l8kV- 4OkV positive polarity.

As gas travels along the first flow path the electrode (not shown) of the first 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 11 comprise a filter material Sla through which the gas passes and which collects pollutant particles. Some particles may though exit from the collector with the gas stream.

As gas travels along the second flow path the electrode (not shown) of the second treatment means 13 imparts a positive charge to pollutant particles. The gas stream, including the charged particles, travels to the collector 15. The walls of the collector 15 comprise a filter material 51b through which the gas passes and which collects pollutant particles. Some particles may though exit from the collector with the gas stream.

Should either filter become obstructed then gas may exit the respective collector via the by-pass means. In normal use some of the gas stream, including pollutants, may exit via the by-pass means but owing to the bypass location the majority of the gas stream, will exit the collector via the filter which will thus remove pollutants from the gas stream.

The cleaner gas streams which exit the first and second collectors 11, 15 mix within the third chamber 33 and then travel to outlet 7 where they exit as a combined gas stream. It is believed that this mixing allows the charges of those particles which have passed through the collectors 11, 15 to cancel one another out. The gas released from the apparatus may thus contain less charged particles than would be the case had the first and second gas streams not being combined.

Figures 3 and 4 illustrate an alternative embodiment of an apparatus 1 for removing pollutant from a gas stream. The apparatus is substantially the same as that of Figures 1 and 2 and like parts are labelled accordingly. The main distinction relates to the by-pass means though the field tubes 35, 37 are also distinct.

Rather than extending the full length of the second chamber 31 the field tubes 35, 37 extend from the first dividing wall 25 towards but not to the second dividing wall 27. The field tubes thus have outlets 53, 55 into the second chamber 31 and the collectors 11, 15 have inlets 57, 59 opening to the second chamber. The electrodes (not shown) are located within the field tubes.

Each field tube 35, 37 has an opening into a by-pass tube 61, 63 and the bypass tubes are in communication with the third chamber 33. The by-pass tubes project from the side of the field tubes such that in normal use the gas stream substantially travels past the openings and enters the collectors. The collectors comprise filters which the gas stream then passes through such that pollutants can be collected.

The collectors are not, unlike those of the first embodiment, provided with a tube comprising by-pass apertures. Thus, if the filter becomes obstructed the gas stream can not travel through the collector. This will cause the gas stream to back-up and be diverted through a by-pass tube. The diverted gas stream will then enter the third chamber 33 and travel to the outlet 7.

In an alternative embodiment, not illustrated, the apparatus comprises separator means arranged within a field tube of the treatment means having a negatively charged electrode. The separator means is arranged to split the gas stream flowing there through into a pollutant particle rich gas stream for travelling to the collector and a cleaner gas stream for conveying to the third chamber by-passing the pollutant collector. The apparatus is similar to that of the second embodiment and the cleaner gas stream is conveyed from the field tube by a by-pass tube. The main distinction between the embodiments, other than the addition of separating means, is that in the non-illustrated embodiment the by-pass tube performs a significant role even when the filter is substantially unobstructed. Additionally, the field tubes extend the full length of the second chamber. The separator comprises a constricting member located upstream of the by-pass tube inlet such that the by-pass tube is located in an expansion chamber. This construction causes pollutants to preferentially follow the first flow path to the collector such that the apparatus can effectively remove pollutants from a gas stream whilst cleaner gas may have a less impeded flow path.

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

1. An apparatus f or 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, and a second flow path, providing fluid communication between an inlet of the apparatus and an outlet of the apparatus, wherein each flow path comprises treatment means, each treatment means comprising a pollutant collector and wherein the treatment means in the first flow path (first treatment means) is arranged, in use, to impart a positive charge to pollutant material and the treatment means in the second flow path (second treatment means) is arranged, in use, to impart a negative charge to pollutant material.

2. An apparatus according to claim 1, wherein the apparatus is arranged to combine the first and second gas streams such that a combined gas stream is released by the apparatus.

3. An apparatus according to claim 1 or 2, wherein the apparatus comprises an inlet arranged to receive a primary gas stream.

4. An apparatus according to claim 3, wherein the apparatus is arranged to split the primary gas stream to provide a first gas stream for travelling through the first flow path and a second gas stream for travelling through the second flow path.

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

6. An apparatus according to any preceding claim, wherein the first treatment means comprises a chargeable electrode upstream of the pollutant collector and the second treatment means comprises a chargeable electrode upstream of the pollutant collector.

7. An apparatus according to claim 6, wherein the first

treatment means comprises a field tube arranged to

substantially surround the electrode to define a first treatment chamber and the second treatment means comprises a field tube arranged to substantially surround the electrode to define a second treatment chamber.

8. An apparatus according to any preceding claim, wherein the apparatus comprises by-pass means to allow gas to exit the apparatus without passing through a filter of a pollutant collector.

9. An apparatus according to claim 8, wherein the apparatus is arranged such that the major part of a gas stream passes through a filter of a collector unless the filter is substantially obstructed.

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

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