GB2260278A

GB2260278A - A method of and apparatus for treating flue gases

Info

Publication number: GB2260278A
Application number: GB9221225A
Authority: GB
Inventors: Gerald Wilson Don
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-10-10
Filing date: 1992-10-09
Publication date: 1993-04-14
Anticipated expiration: 2012-10-09
Also published as: GB9221225D0; GB9121521D0; GB2260278B

Abstract

Spray heads (5, 6, 17) are fitted at intervals within a chimney (1) and are mostly arranged to direct water mist downwardly, against the gas flow. The pipes (7, 8) leading to the spray heads may be of insulating material, the metal heads being charged positively and/or negatively through leads (11, 12) from a control unit (13). Alternatively the pipes themselves may be conductive and charged to impart charge to the water droplets. More than one spray head (14, 15, 16) may be provided at any one level and provision (3, 4) is made at the base of the chimney (1) for removing the contaminated spray water. <IMAGE>

Description

A Method of and Apparatus for treating Flue Gases This invention relates to a method of and apparatus for treating flue gases.

The substantial reduction of pollution from flue gases is now of worldwide concern. It is accepted that the burning of fossil fuels, in particular, is very damaging to the environment, causing "acid rain" and other harmful effects.

However, it is equally accepted that it is not practical to abandon the burning of fossil fuels and to transfer to "clean" sources overnight. Therefore, the search is on for measures that will eradicate as much as possible of the harmful substances from flue gases before they reach the atmosphere.

It is known to use a water spray in a chimney or flue, and to direct the spray on to electrically charged plates in the passage. The droplets thereby acquire a charge, which make them better equipped to capture the impurities in the gases. To a certain extent, this duplicates the electrochemical reaction which normally takes place in the upper atmosphere.

However, this is not entirely satisfactory. Although bombarded with spray, the plates do become coated and therefore need cleaning from time to time to maintain efficiency. Of course, they also offer quite a substantial obstruction to the gas flow.

According to one aspect of the present invention there is provided apparatus for treating flue gases comprising a spray head for installation in the flue, a water conduit thereto, and means for electrically charging water delivered to the spray head before or at the spray head.

There may be two or more spray heads in sequence along the flue, and the electrical charge may be positive on the downstream spray heads and negative on the upstream spray heads, for reasons explained below. For large installations there may be two or more spray heads distributed substantially evenly across the flue. Generally the majority at least of the spray heads will be arranged to direct the spray upstream, lengthwise of the flue.

According to another aspect of the present invention there is provided a method for treating flue gases comprising spraying electrically charged water into the flue.

The flue can be assumed to be vertical, but with a sump at the base to collect the contaminated spray water. It can then go to drain or be taken to a further treatment plant.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic vertical section through a flue for exhaust combustion gases, and Figure 2 shows cross-sections through a flue with different spray head arrangements.

The flue is provided by a vertical chimney 1 with a lateral entry duct 2 near its base. This leaves a sump 3 at the bottom of the chimney, from which leads a drain 4.

At intervals along and centrally within the chimney 1 there are spray heads 5 and 6. In this example there are two and they point downwards. Just one would produce results but preferably there will be more, and they may be differently directed. Also, as indicated in broken lines, another spray head could be disposed in the entry duct 2 and point towards the chimney 1, that is in the downstream direction. These spray heads are at the ends of branch pipes 7 and 8 from a main water supply 9 which preferably goes through a purifying unit 10. The pipes 7 and 8 are of electrically insulating material but each spray head is of a metal that can take an electric charge via leads 11 and 12 from a control unit 13. Water passing through them will acquire this charge and the mist droplets will be negative or positive accordingly.

Instead of using the insulating pipes 7 and 8 to support the spray heads 5 and 6, they may be independently suspended through insulators, while the pipes may be conductive back to near the control unit 11. The charge can then be applied to them. Obviously, there would be insulation between the pipes and the chimney at the points where they pass through.

The droplets will absorb impurities in the gases, particularly sulphur dioxide and oxides of nitrogen, and to a slightly lesser extent carbon dioxide. The contaminated water will gravitate to the sump 3, whence it can be removed.

The charge applied to the spray heads may be negative or positive, as suggested by the diagrammatically illustrated control unit 13. It is believed that it would be best to apply a high negative charge to the upstream spray head 6, since the molecules in hot flue gases tend to lose electrons and therefore to have a net positive charge. Mains water is often slightly positive, and its droplets would be repelled rather than attracted. At the downstream spray head 5, however, the water droplets will beneficially be positively charged to be attracted to the now negative flue gas.

However, this is the subject of experiments and tests and other arrangements may prove advantageous.

It may be better in some circumstances to have more than one spray head at any one level and to direct one or more of the sprays across or aslant the chimney, or even upwards in the opposite direction to that shown. Referring to Figure 2, certain of these alternative spray arrangements are illustrated.

In Figure 2(a) there is a group of four spray heads 14 at one level, symmetrically arranged about the axis of the chimney 1. This may be advisable when the chimney is of large cross-sectional area: a single spray head might not be able to spread its mist over the whole of that area.

In Figure 2(b), the group of spray heads 15 is reduced to three, again symmetrically arranged, for a slightly smaller chimney than that of Figure 2(a).

In Figure 2(c) there are three equi-spaced spray heads 16 mounted on the inside wall of the chimney, throwing their mist inwards.

In Figure 2(d) the spray head 17 takes the form of a tubular ring with fine apertures distributed evenly around it. This is concentric with the chimney and the spray mist is cast substantially uniformly over the whole crosssectional area of the chimney.

The impurities captured by this technique will pass in solution out of the chimney 1 via the drain 4. This may lead to a holding tank and, particularly for the benefit of the carbon dioxide, this will have an alkali such as calcium hydroxide added and maintained to prevent the decomposition of the carbonate. Otherwise carbon dioxide might be released back into the atmosphere.

The system can quite easily be applied to existing plant.

Claims

CLAINS

1. Apparatus for treating flue gases comprising a spray head for installation in the flue, a water conduit thereto and means for electrically charging water delivered to the spray head before or at the spray head.

2. Apparatus as claimed in Claim 1, wherein there are two or more spray heads in sequence along the flue.

3. Apparatus as claimed in Claim 2, wherein the electrical charge is positive on downstream spray heads and negative on upstream spray heads.

4. Apparatus as claimed in Claim 1, 2 or 3, wherein there are two or more spray heads distributed substantially evenly across the flue.

5. Apparatus as claimed in any preceding Claim, wherein the majority at least of spray heads are directed upstream, lengthwise of the flue.

6. Apparatus for treating flue gases substantially as hereinbefore described with reference to the accompanying drawing.

7. A method of treating flue gases comprising spraying electrically charged water into the flue.

8. A method of treating flue gases substantially as hereinbefore described with reference to the accompanying drawing.