GB2048725A - Wire-in-tube Electrostatic Precipitator - Google Patents

Abstract

A vertical wire-in-tube precipitator for removing dust from waste gases includes a dust removing set composed of separate units 6, 6a mounted closely adjacent one another and each comprising a plurality of tubular collecting electrodes. Each unit is supported by its own central supporting column 9 and comprises six electrodes of hexagonal or circular cross section disposed around the associated column 9 and rigidly fastened together. Each unit is furnished either with its own liquid washing system 17 to wash away dust deposits or with an impact device 21 to shake off the deposits. In one dry precipitator embodiment, the bottom part of the collecting electrode unit 6a forms a heat exchanger and is made from helical tubes 25. Gas entering the electrodes flows through a distributing grid 14. <IMAGE>

Description

SPECIFICATION Wire-in-tube Precipitators The present invention relates to a vertical wirein-tube electrical precipitator for removing dust and other contaminants from contaminated gases, such as waste gases from chemical and metallurgical processes and power plants and, particularly, from sulphuric acid production.

Wire-in-tube electrical precipitators of both wet and dry types and well-known and commonly used for electrostatic dust removal from hot or cold gas at the temperatures ranging from OOC to 4800C. The collecting electrodes of such precipitators are either vertically hanging circular tubes supported from holes in a top sheet of hexagonal tubes joined together along adjacent sides and forming one solid honeycomb set suspended at the top from a supporting grid. The precipitators which collect dust from hot gas at temperatures ranging from 1 500C to 4800C are fitted with a mechanical system for shaking deposited or precipitated dust from the collecting and corona electrodes and are called dry precipitators. The precipitators operating below 1 000C have a liquid system for washing the collecting and corona electrodes and are called wet precipitators.In such wet wire-in-tube precipitators, water spraying nozzles are installed above the supporting frame for the corona electrodes in order to wash out periodically the deposits from the precipitator.

A disadvantage of presently known precipitators is the necessity of providing a top supporting component -- either a sheet or a grid which is loaded with the depending set of collecting electrodes. Because of the limited strength of this supporting component, in such a design, the precipitator diameter is practically restricted to 5 m which consequently restricts also the gas flow through the precipitator. The solid tubular set, particularly of the honeycomb design, make it difficult or even impossible to replace or repair individual collecting electrodes.

Another disadvantage of presently known wet wire-in-tube precipitators is the unsatisfactory arrangement for washing the collecting and corona electrodes. The water-spraying nozzles, which are located above the top frame of the depending corona electrodes, do not ensure uniform washing of deposits from the electrodes.

The duration of the washing step is thus prolonged which reduces the overall efficiency of dust removal.

In dry wire-in-tube precipitators, the dust is removed by mechanical impacts applied to the collecting electrodes and this requires these electrodes to be hung so as to allow vibrations to be freely propagated throughout each electrode without any damping. Hence, the collecting electrodes set should be divided into separately - vibrating, light -- weight groups having either vertical or horizontal freedom of movement.

This condition in not met by hitherto known designs of dry wire-in-tube precipitators, since a solid and heavy set of collecting electrodes makes free vibrations impossible. Therefore, dust removal from the collecting electrodes by generating mechanical impacts which are then applied to the collecting electrodes is also impossible.

The present invention consists in a wire-intube electrical precipitator for removing dust and other contaminants from contaminated gas, including tubular collecting electrodes, washing or shaking devices for removing deposited contaminants, and a distributing grid for the contaminated gas, wherein the collecting electrodes are arranged in units of a plurality, which units are located closely adjacent each other, each unit being supported on its own central supporting column.

Each unit of collecting electrodes may comprise hexagonal or circular tubes, preferably located about the associated supporting column and connected together in closely adjacent or adjoining relation. Each unit may have it own individual liquid washing system for cleaning deposited contaminants or may have a known impacting device to shake-off the deposits.

The distributing grid for the contaminated gas to be treated may be furnished with helical inserts. Corona pointed electrodes may have annular grooves uniformly spaced along the electrodes, the spacing being approximatelv eaual to the radius of a collecting electrode.

In another design of dry precipitator, the bottom portion of each collecting electrode unit may comprise a heat exchanger made of helically wound tubes.

In a multi-section precipitator, the bottom portion may include a bottom gas chamber for the incoming, contaminated gas, which chamber is common to all section, whilst the top gas chamber for the treated gas may be divided by means of fluid-tight vertical baffles which separate the section from one another.

An advantage of the invention is that it results in a considerably simplified design which is achieved by eliminating the top supporting components hitherto used for the collecting electrodes. The separate self-supporting collecting electrode units of the invention allow the construction of precipitators of an unrestricted diameter, as well as easy electrode replacement, e.g. during repair and the use of hexagonal tubes as collecting electrodes enables utilization of both sides of the tube walls to collect dust.

Utilization of a unit formed from collecting electrodes which are partially wound from tubes, through which heating fluid is circulated, permits simultaneous use of the precipitator as a heat exchanger for gas cooling and steam generation.

This arrangement may be adopted for direct cooling and dust removal from furnace gases.

Due to the swirling of the gas, which is to be decontaminated in the distributing grid, the deposition velocity of the dust particles in the bottom section of the collecting electrodes is considerably increased, and in certain part, the precipitator operates on a cyclone and electrostatic field principle.

Examples of the invention are illustrated in the accompanying drawings, in which: Fig. 1 shows a half-section through an acidresistant wet wire-in-tube precipitator according to the invention; Fig. 2 shows a half-section through a dry wirein-tube precipitator according to the invention; Fig. 3 respectively illustrates quarter-sections along the lines A-A and C-C of Fig. 1, and lines B-B and D-D of Fig. 2; Fig. 4 is a top view of a distributing grid; Fig. 5 is a fragmentary vertical section through the passages in the distributing grid; Fig. 6 is a side view of a corona pointed electrode; Fig. 7 is a cross section through the corona pointed electrode; Fig. 8 illustrates a collecting electrode unit of a wet precipitator, half in section and half in elevation;; Fig. 9 is an end view of a collecting electrode unit, in the direction of the arrow E in Fig 8; Fig. 10 illustrates a collecting electrode unit for a dry precipitator, half in section and half in elevation; and Fig. 11 is a cross section along the line F-F in Fig. 10.

As shown in the drawings, the precipitator includes a vertical body 1 which is mounted on a horizontal bottom 2 (in the wet precipitator) or on the ridge bottom 3 for each section (in multisectional dry precipitator). The body 1 is covered by a roof 4 and is internally coated with an acid resistance lining 5. In the body 1, is disposed the dust-removing set consisting of closely adjacent separate units 6 of collecting electrode 7 and corona electrodes 8, which are positioned on the vertical axis of the electrodes 7.

Each unit 6 consists of six wire-in-tube collecting electrodes 7, which are circular or hexagonal in cross-section and are uniformly disposed about a central pipe 9 which also serves as a supporting column for the unit. The tubular collecting electrodes 7 are rigidly inter-connected, e.g. by welding, and are mounted on the pipe 9 by means of plates 10.

The corona electrodes 8 are suspended from a top frame 11 and are loaded or tensioned by a bottom frame 1 2.The electrodes 8 are either pointed or smooth. Pointed electrodes have annular grooves 13, the distance between these grooves being substantially equal to the radius of each collecting tube 7. This ensures the stability of the electron corona about the corona electrodes 8, as well as an increase on the uniformity of the electric field.

Below the bottom frame 12, there is a distributing grid 14 whose purpose is to equalize the velocity field of the gas entering the collecting electrodes 7. The grid 14 has helical inserts 1 5 which accelerate the gas and give it a swirling motion. The grid 14 is mounted on the pipes 9.

Each collecting electrode unit 6 in the wet precipitator has a pipe connection 1 6 for the supply of washing liquid, e.g. water to nozzles 17 which are radially spaced at the top end of the pipe 9. The pipe connections 1 6 of each unit 6 are connected to a water system 1 8. In the lower section of the body 1, there is a pipe connection 19 for draining liquid, e.g. washing water.

In the dry precipitator, the pipes 9 are supported on spring cushions 20 and at their top or bottom are provided with known impact shaking devices 21 which periodically give the units 6a of collecting electrodes 7a a vertical vibrating movement. Conveyors 22, e.g. screw conveyors, all provided to discharge precipitated dust, the conveyors being disposed in nozzles 23 which are inserted into the body 1. The conveyors 22 are operated by drive means 24.

In a further embodiment also illustrated in Fig.

2 the dry precipitator serves at the same time as a heat exchanger to generate high-pressure steam.

In this case, the units 6a of the collecting electrodes 7a are used, and the lower sections of these units comprise helical tubes 25 connected to the supporting pipe 9. Owing to the baffles 26 and 27 installed in the pipe 9, this also acts as an inlet header for the heating fluid, e.g. water, which is supplied through the pipe connection 28, as well as an outlet header for the vapour or heated fluid which is discharge through a conduit inserted into the pipe 9. The heater system is connected to the pipe connection 28 and the conduit 29.

The unit 6a of the collecting electrodes 7a is mounted on the supporting pipe 9 by means of fins 31 which are welded to the tubes 7a and to the pipe 9. The top end of the pipe 9 is closed by a cover plate 32, while the top ends of the tubes 7a are formed into hexagonal end portions.

The ridge bottom 3 of each section in the dry precipitator is terminated by a central funnel 33, in which the dislodged dust is accumulated.

In the roof 4, are installed a gas inlet gas 34 and outlet 35, the latter being connected to the vertical gas header 36. In the space between the inlet 34 and the header 36 rotary throttle valves 37 are installed. Moreover, on the hangers 39 for the top frame 11 of the corona electrodes 8.

The use of six-tube units 6, respectively, permits the constitution of one, three, six or twelve section precipitators.

In a multi section precipitator, the top gas chamber K1 disposed over the dust removing set is divided by fluid-tight vertical baffles 40, which separate the precipitator section from one another. Each section outlet to the gas header 36 is shut-off by the rotating throttle valve 37. The lower gas chamber K2 below the dust removing set is common to all sections.

In the central portion of the precipitator, is disposed the tube 41 which shields the side gas inlet from each section and supplies the dustcontaining gas to below the distributing grid 14.

The tube 41 constitutes an extension of the inlet 34.

In wire-in-tube precipitators, a side inlet part 42 for the dust containing gas (shown in broken lines in Fig 1) may be arranged in the precipitator bottom chamber K2 below the distributing grid 14.

The precipitators described above operate as follows. The dust contaminated gas is supplied through the inlet 34 and through the central tube 41 into the precipitator bottom chamber K2 below the distributing grid 14, where the gas stream is accumulated and equalized as well as partially swirled by the helical inserts 1 5. Then, the gas enters the electric field between the collecting electrodes 7 or 7a and the corona electrodes 8, where owing to ionization of the gas electric charges are accumulated on the dust and liquid particles. The gas flowing in the interelectrode space deposits these electricallycharged particles on the collecting electrodes 7 or 7a so thnt the particles are removed from the gas flow.The particle free gas flows into the precipitator top chamber K1,from where it is discharged through the outlet 35.

In wet precipitators, the deposits on the collecting electrodes 7 and on the corona electrodes 8 are washed out periodically with water which is supplied by the water system 1 8 through the pipe connection 16 to the spray nozzles 1 7. However, in dry precipitators the units 6a are vertically vibrated by the impacting devices 21 , which shake the dust deposits from the electrodes onto the ridge bottom 3 of each section from where it is fed to the central funnel 33 by means of the conveyors 22.

In the dry precipitators design with the heat exchanger (Fig. 2), the dust which is deposited from the gas is additionally accumulated on the helical tubes 25 forming the heat exchanger, and it is periodically removed by the impacting devices as mentioned above. Owing to the heat transfer between the gas flowing around the tubes 25 and the heating fluid e.g. water, which flows in the tubes, high pressure steam is generated whilst the waste gas is cooled.

Claims (9)

Claims

1. Wire-in-tube electrical precipitator for removing dust and other contaminants from contaminated gas, including tubular collecting electrodes, washing or shaking devices for removing deposited contaminants, and a distributing grid for the contaminated gas, wherein the collecting electrodes are arranged in units of a plurality of electrodes, which units are located closely adjacent each other, each unit being supported on its own central supporting column.

2. A precipitator as claimed in claim 1, wherein each unit of the collecting electrodes comprise six tubes disposed around the associated supporting column and connected together in closely adjacent or adjoining relation.

3. A precipitator as claimed in claim 1 or 2, wherein each unit of the collecting electrodes has its own liquid discharge system for washing out contaminant deposits.

4. A precipitator as claimed in claim 1 or 2, wherein each unit of the collecting electrodes has its own device for shaking off the deposits.

5. A precipitator as claimed in claim 1, 2, 3 or 4 wherein the distributing grid for the contaminated gas is furnished with helical inserts.

6. A precipitator as claimed in any one of the preceeding claims, including pointed corona electrodes having annular grooves which are spaced along the electrodes by a distance approximately equal to the radius of a collecting electrode.

7. A wire-in-tube vertical electrical precipitator for removing dust and other contaminants from contaminated gas including tubular collecting electrodes arranged in units comprising a plurality of electrodes washing or shaking devices for removing deposited contaminants, and a distributing grid for the contaminated gas, wherein the bottom section of at least one of the units of collecting electrodes forms a heat exchanger and is made from helical tubes.

8. A precipitator as claimed in any one of the preceeding claims, wherein the lower part of the precipitator, comprises a bottom gas chamber to which contaminated gas is delivered and which is common to all section of the precipitator, whilst a top gas chamber for treated gas is divided by fluid-tight vertical baffles into separate sections.

9. A wire-in-tube electrical precipitator constructed and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.