GB2147525A

GB2147525A - Equipment for removal of dusts from industrial gases

Info

Publication number: GB2147525A
Application number: GB08420768A
Authority: GB
Inventors: Theodor Niess; Kong Seng Tjoa; Albert Brinkmann
Original assignee: Gottfried Bischoff Bau Kompl Gasreinigungs und Wasserrueckkehlanlagen GmbH and Co KG
Current assignee: Gottfried Bischoff Bau Kompl Gasreinigungs und Wasserrueckkehlanlagen GmbH and Co KG
Priority date: 1983-08-17
Filing date: 1984-08-15
Publication date: 1985-05-15
Also published as: JPS60106552A; CA1249529A; GB8420768D0; GB2147525B; ES535238A0; ES8504490A1; DE3329638A1; DE3329638C2; JPH0317547B2

Abstract

Equipment for the removal of dusts from industrial gases by treatment with a scrubbing fluid consisting mainly of water, has a scrubbing tower (1), at least one spray nozzle (2) for the scrubbing fluid on the scrubbing tower axes (3), and a corona electrode unit (4) disposed above the spray nozzle, a dirty gas inlet (5) at the top, and a clean gas outlet (6) at the bottom, the scrubbing tower cross-section being designed for a dirty gas stream velocity of 5 to 30 m/s, preferably 5 to 15 m/s, more particularly about 10 m/s, the corona electrode unit (4) having corona electrodes (7) with surrounding polarisation electrodes (8) which have a length of 15 to 40 cm, preferably 15 to 20 cm, more particularly 15 cm, in the direction of dirty gas flow; separation takes place in the otherwise insert-free scrubbing tower around and below the spray nozzle, or in an annular- gas scrubber (see Fig. 4) downstream thereof.

Description

SPECIFICATION Equipment for removal of dusts from industrial gases This invention relates to equipment for the removal of dusts from industrial gases by treatment with a scrubbing fluid consisting mainly of water and having a scrubbing tower, at least one spray nozzle for the scrubbing fluid on the scrubbing tower axis, and a corona electrode unit disposed above the spray nozzle, in which the scrubbing tower has a dirty gas inlet at the top, a clean gas outlet at the bottom and a wet scrubbing space. In the context of the invention, a scrubbing tower is a substantially vertically disposed flow channel in which a stream of gas is purified by scrubbing. The scrubbing tower axis can be provided with a plurality of single spray nozzles or sets of two or more spray nozzles, arranged one above another.

The wet scrubbing space includes the scrubbing space in the vicinity of the spray nozzles and the lower space for separation of the wetted dust. It is self-evident that the scrubbing fluid can also absorb gaseous components. The scrubbing tower can also incorporate an annular-gap scrubber. The term "corona electrode" is known in the technology of electrostatic precipitators (cf. Lueger, "Lexikon der Verfahrenstechnik", vol. 16, 1970, p 119).

In principle, an electrostatic precipitator consists of a cylindrical or plate capacitor. A d.c. voltage of about 20,000 to 70,000 V or more, approaching the breakdown voltage as closely as possible, is applied across the field electrodes; it is usually taken from a two- or three-phase a.c. mains net-work, using highvoltage transformers and rectifiers. The negative pole of the rectifier output is connected to the corona electrodes, which have the smallest possible radius of curvature and from which electrodes protrude. The corona electrodes usually consist of a relatively slender wire, which may be rectangular in cross-section and in many cases may carry spikes. The positive pole of the d.c. voltage source is usually earthed and so is the preciptiation electrode. However, the opposite polarity is equally possible.The invention also embraces the arrangement whereby the corona electrodes are connected as usual to the negative side of the rectifier output while the surrounding electrodes are earthed. It also embraces the arrangement with the polarities reversed.

The electrical processes in an electrostatic precipitator correspond to those taking place in spontaneous discharges, when an electrical current flows from the corona electrodes to the electrodes of opposite polarity. The stream of dirty gas is directed between the electrodes. The entrained dust particles or fine dust-like liquid droplets acquire a charge, negative on by far the majority, and in a conventional corona unit they migrate to the precipitation electrode, where they give up their charges and are precipitated.

In known equipment of this type, the corona electrode unit forms part of an electrostatic precipitator. The unit as a whole has sufficient length for the dust first to pick up its charge and then separate out at the precipitation electrodes. To this extent, the equipment is a combination of two dust removal devices.

The object of the invention is to provide equipment in which the corona electrode unit and the wet scrubbing space combine functionally to purify the gas, thereby improving the dust removal efficiency, the particle size limit and the overall degree of dust removal.

According to the present invention, the scrubbing tower cross-section is designed for a dirty gas stream velocity, after allowing for the inserts referred to, of 5 to 30 m/s, preferably 5 to 15 m/s, and the corona electrode unit has surrounding polarisation electrodes with a polarisation electrode length of 15 to 40 cm, preferably 15 to 20 cm, in the direction of dirty gas glow, separation taking place in the otherwise insert-free scrubbing tower around and below the spray nozzle.

Preferably, the scrubbing tower cross-section and the installation as a whole are designed for a dirty gas stream velocity of about 10 m/s, while the polarisation electrode length is preferably 15 cm. It is also within the scope of the invention to operate the corona electrodes at a corona-forming voltage of 20,000 to 70,000 V, preferably about 45,000 V.

There are several possibilities in detail for further modifying and adapting the equipment within the scope of the invention. The corona electrode unit preferably consists of a plurality of tube lengths set in close array, for example as a honeycomb array of lengths of hexagonal tubing disposed in the direction of dirty gas flow and connected up as polarisation electrodes, the corona electrodes being set axially in the tube lengths. According to another proposal of the invention, of special significance because of the high separation efficiency, the arrangement is such that the tube lengths are made from metallic material and participate as precipitation electrodes.The spray nozzle featured in the invention is preferably of the type known as a spinning cup nozzle, having a cylindrical nozzle housing with a tangential inlet for the scrubbing fluid and producing spray by its spinning action. If the scrubbing tower incorporates an annulargap scrubber, the corona electrode unit is preferably mounted upstream of the annulargap scrubber. In this connection, the corona electrode unit is preferably mounted downstream of at least one spray nozzle, so that the gas entering the corona electrode unit and the annular-gap scrubber is already saturated with water vapour. The corona electrode unit can be mounted adjustably in relation to the annular-gap scrubber.

The invention arises from the realisation that it is not essential to design the corona electrode unit in such a manner that it provides an electrostatic precipitation action and dust precipitation on precipitation electrodes.

Accordingly, the components surrounding the corona electrodes are simply the polarisation electrodes that must be provided for electrostatic reasons. These polarisation electrodes may indeed contribute towards dust precipitation, but most of the charged dust is still charged when it enters the wet scrubbing space, where the normal scrubbing process takes place. It is a surprising fact that under these conditions there are major overall improvements in the dust removal efficiency, the particle size limit and the overall degree of dust removal.

Two embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a longitudinal section through equipment in accordance with the invention; Figure 2 shows the portion A of Fig. 1 on a larger scale; Figure 3 is a cross-section, taken on the line A-A of Fig. 2; and Figure 4 is a view similar to Fig. 1 of another embodiment of equipment in accordance with the invention.

The equipment illustrated in Figs. 1 to 3 is designed for the removal of dusts from industrial gases by treatment with a scrubbing fluid consisting mainly of water and consists of a scrubbing tower 1, a plurality of spray nozzles 2 for the scrubbing fluid on the scrubbing tower axis 3, and a corona electrode unit 4 disposed above the spray nozzles 2. The scrubbing tower 1 has a dirty gas inlet 5 at the top and a clean gas outlet 6 at the bottom, i.e., the gas stream to be purified flows through it from the top downwards.

The scrubbing tower cross-section is designed for a dirty gas stream velocity-after allowing for the inserts referred to-of 5 to 15 m/s. The preferred stream velocity is about 10 m/s. The corona electrode unit 4 has polarisation electrodes 8 in the vicinity of and surrounding the corona electrodes 7 with a polarisation electrode length L of 15 to 20 cm, preferably 15 cm, in the direction of dirty gas flow. The scrubbing tower 1 is otherwise insert-free. In the embodiment shown, the negative lead 9 from a d.c. source is connected to the corona electrodes 7, while the positive lead 10 is earthed and connected to the polarisation electrodes 8. The corona electrodes 7 are operated at a corona-forming voltage of 20,000 to 70,000 V, preferably about 45,000 V.Fig. 3 shows that the corona electrode unit 4 is constructed from a plurality of hexagonal tube lengths 8 set in close honeycomb array as polarisation electrodes.

The tube lengths 8 are disposed in the direction of dirty gas flow. The corona electrodes 7, which are formed as spiked electrodes, are set axially in the tube lengths 8, which are preferably made from metallic material, so as to be used and connected up to act as precipitation electrodes. The spray nozzles 2 are of the spinning cup type.

In the embodiment shown in Fig. 4, the scrubbing tower 1 is constructed differently.

On the scrubbing tower axis 3 there are spray nozzles 2 for a scrubbing fluid consisting mainly of water. Downstream of the spray nozzles 2 there is an annular-gap scrubber 11 with an adjustable core 12. Upstream of the annular-gap scrubber there is the corona electrode unit 4. As already described, the corona electrode unit 4 can be connected to a highvoltage source.

The scrubbing tower cross-section is designed for a gas stream velocity of 5 to 15 mjs, preferably about 10 m/s. The corona electrode unit 4 also has polarisation electrodes 8 surrounding the corona electrodes 7 with a polarisation electrode length L of 15 to 20 cm, preferably 15 cm, in the direction of gas flow. Separation takes place in the annular-gap scrubber 11, which is mounted in the normal manner and thereby earthed. The corona electrode unit 4 is disposed downstream of the two spray nozzles 2. These are so disposed that the dust-laden gas entering the corona electrode unit 4 and the annular-gap scrubber 11 is saturated with water vapour.

At least one additional spray nozzle 13 can be mounted downstream of the corona electrode unit 4.

Claims

1. Equipment for the removal of dusts from industrial gases by treatment with a scrubbing fluid consisting mainly of water, having a scrubbing tower, at least one spray nozzle for the scrubbing fluid on the scrubbing tower axis, and a corona electrode unit disposed above the spray nozzle, in which the scrubbing tower has a dirty gas inlet at the top, a clean gas outlet at the bottom and a wet scrubbing space, the scrubbing tower cross-section is designed for a dirty gas stream velocity of 5 to 30 cm/s, and the corona electrode unit has surrounding polarisation electrodes with a polarisation length of 15 to 40 cm in the direction of dirty gas flow, separation taking place in the otherwise insertfree scrubbing tower around and below the spray nozzle.

2. Equipment as in Claim 1, wherein the scrubbing tower cross-section is designed for a dirty gas stream velocity of about 5 to 15 m/s.

3. Equipment as in Claim 2, wherein the scrubbing tower cross-section is designed for a dirty gas stream velocity of about 10 m/s.

4. Equipment as in any one of Claims 1 to 3, wherein the corona electrode unit has a polarisation electrode length of 15 to 20 cm.

5. Equipment as in Claim 4, wherein the corona electrode unit has a polarisation electrode length of 15 cm.

6. Equipment as in any one of Claims 1 to 5, wherein the corona electrodes can be operated at a corona-forming voltage of 20,000 to 70,000 V.

7. Equipment as in Claim 6, wherein the corona electrodes can be operated at a corona-forming voltage of about 45,000 V.

8. Equipment as in any one of Claims 1 to 7, wherein the corona electrode unit consists of a plurality of tube lengths set in close array disposed in the direction of dirty gas flow and connected up as polarisation electrodes, the corona electrodes being set axially in the tube lengths.

9. Equipment as in Claim 8, wherein the corona electrode unit consists of a honeycomb array of lengths of hexagonal tubing.

10. Equipment as in Claim 8 or Claim 9, wherein the tube lengths are made from metallic material and additionally used and connected up as precipitation electrodes.

11. Equipment as in any of Claims 1 to 10, wherein the spray nozzles are of the spinning cup type.

12. Equipment as in any one of Claims 1 to 11 or independent thereof, having at least one annular-gap scrubber with an adjustable core disposed downstream of the spray nozzle, the corona electrode unit being mounted upstream of the annular-gap scrubber.

13. Equipment as in Claim 12, wherein the corona electrode unit is mounted downstream of at least one spray nozzle so that the gas entering the corona electrode unit and the annular-gap scrubber is already saturated with water vapour.

14. Equipment as in either of Claims 12 and 13, wherein the corona electrode unit is mounted adjustably in relation to the annulargap scrubber.

15. Equipment for the removal of dusts from industrial gases substantially as hereinbefore described with reference to Figs. 1 to 3 of the accompanying drawings.

16. Equipment for the removal of dusts from industrial gases substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.