Electrostatic precipitor

Abstract

An electrostatic precipitator for removing particulates from boiler fine gas is provided. The electrostatic precipitator comprises discharge electrodes and collecting electrodes fitted in a gas passage, the electrodes being arranged in at least two electrical fields that are placed successively in relation to gas flow, and the electrical field establishing at least one electrical unit in transversal direction of said gas passage. The at least one electrical unit has the ability to be de-energised independently, separately from the other electrical units of the electrostatic precipitator. The first electrical field of the at least two electrical fields is also arranged first in the gas flow, and the first electrical field comprises more electrical units than a second field following the first field.

Claims

1. An electrostatic precipitator for removing particulates from boiler flue gas, the electrostatic precipitator comprising a number of first electrical units in a passage that receives boiler flue gas flow, each first electrical unit comprising at least one discharge electrode and at least one collecting electrode for forming an electric field inside said first electrical unit, the first electrical units being first in the boiler flue gas flow, a number of second electrical units arranged after the first electrical units in relation to the boiler flue gas flow, each second electrical unit comprising at least one discharge electrode and at least one collecting electrode for forming an electric field inside said second electrical unit, each electrical unit constituting a portion of the electrostatic precipitator having ability to be de-energised independently, separately from the other electrical units of the electrostatic precipitator, and the number of the first electrical units being greater than the number of the second electrical units.

2. The electrostatic precipitator as claimed in claim 1, wherein the number of the first electrical units is two and the number of the second electrical units is one.

3. The electrostatic precipitator as claimed in claim 1, wherein following the second electrical unit there is arranged a number of additional successive electrical units, each of the additional successive electrical units comprising an equal number of units with the second electrical units.

4. The electrostatic precipitator as claimed in claim 3, wherein the number of the additional successive electrical units is 2 to 8.

5. The electrostatic precipitator as claimed in claim 1, comprising at least two parallel and independently operating gas passages separated by a gas-tight division wall.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Some embodiments illustrating the present disclosure are described in more detail in the attached drawings, in which

(2) FIG. 1a is a schematic side view of a prior art solution of an electrostatic precipitator from above,

(3) FIG. 1b is a schematic perspective view of the electrostatic precipitator shown in FIG. 1a,

(4) FIG. 2a is a schematic top view of an electrostatic precipitator,

(5) FIG. 2b a schematic perspective view of the electrostatic precipitator shown in FIG. 2a,

(6) FIG. 3a is a schematic top view of another electrostatic precipitator, and

(7) FIG. 3b a schematic perspective view of the electrostatic precipitator shown in FIG. 3a.

(8) In the figures, some embodiments are shown simplified for the sake of clarity. Similar parts are marked with the same reference numbers in the figures.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

(9) FIG. 1 is a schematic side view of a prior art solution of an electrostatic precipitator from above, and FIG. 1b is a schematic perspective view of the electrostatic precipitator shown in FIG. 1a.

(10) The electrostatic precipitator 100 comprises discharge electrodes 1 and collecting electrodes 2 fitted in a gas passage 3. The electrodes 1, 2 are arranged in three electrical fields 4a, 4b, 4c that are placed successively in relation to gas flow G.

(11) Each of the electrical fields 4a, 4b, 4c establishes two electrical units 5a, 5b arranged in transversal direction of the gas passage 3.

(12) The electrical unit 5a, 5b constitutes a portion of the electrostatic precipitator 100 that has ability to be de-energised independently, separately from the other electrical units 5a, 5b of said electrostatic precipitator 100.

(13) FIG. 2a is a schematic top view of an electrostatic precipitator according to the invention, and FIG. 2b a schematic perspective view of the electrostatic precipitator shown in FIG. 2a.

(14) The electrostatic precipitator 100 comprises discharge electrodes 1 and collecting electrodes 2 arranged in at least two electrical fields that are placed successively in relation to gas flow G in a gas passage 3. The embodiment shown here comprises three electrical fields 4a, 4b, 4c. It is to be noted, however, that the number of the electrical fields may vary from two to eight, or even to higher numbers.

(15) The electrical fields 4a, 4b, 4c establish at least one electrical unit in transversal direction of the gas passage 3. In the embodiment shown in FIGS. 2a, 2b, the first electrical field 4a comprises two electrical units 5a, 5b, whereas each of second and third fields 4b, 4c following said first field comprises one electrical unit 5 only. In other words, in the first electrical field 4a the cross section of the gas passage 3 has divided in two electrical units 5a, 5b, but there is no such division in the second and third electrical fields 4b, 4c. Thus, the gas flow G flowing through the first electrical field 4a flows through the two electrical units 5a, 5b, and then through one electrical unit 5 in the second electrical field 4b and finally through one electrical unit 5 in the third electrical field 4c.

(16) In the electrical unit 5, 5a, 5b there is maintained an intense electric field between high-voltage discharge electrodes, typically wires, bars or rigid frames, and grounded collecting electrodes, typically parallel plates arranged vertically.

(17) The gas flow G flows through the through a gap between the discharge electrode and the collecting electrode, whereby the gas is ionized by the voltage potential. Particulates contained by the gas are charged and collected on the collecting electrode to remove the particulates from the gas.

(18) In another embodiment, it is arranged three electrical units (5a, 5b, 5c), or even more electrodes, in the first electrical field 4a, and only one electrical unit 5 in each of the second electrical field 4b and further electrical field(s), if any.

(19) Generally speaking, if the number of the electrical units in the first electrical field 4a is marked as X, then the maximum number of the electrical units in the second electrical field 4b is X1 (X subtracted by 1).

(20) Sparks between electrodes create a current path that disrupts an otherwise even distribution of current in the electric field between electrodes. Sparking can damage internal the electrodes and other components of an electrostatic precipitator.

(21) The first electrical field 4a receives the gas flow G, and thus at least practically all the particles contained by the gas, while the second electrical field 4b, and further electrical fields, if any, receive gas flow that has passed the first electrical filed 4a and comprises thus substantially lowered particle content. Therefore, sparkling takes place most frequently in the first electrical field 4a. According to an experiment made by the inventor, the sparkling rate, i.e. number of sparks per minute (spm) was 200-300 spm in the first electrical field 4a, 0-10 spm in the second electrical field 4b, 0 spm in the third electrical field 4c. Thus the second electrical field 4b and further electrical fields, if any, can be structured to include less electrical units 5 than the first electrical field 4a without jeopardizing the effectiveness of the filtering process carried out by the electrostatic precipitator 100. An advantage of this kind of electrostatic precipitator 100 is that the construct of the precipitator 100 is to set two power supplier with control units for 5a and 5b. By doing this way amount of spm per control unit is only half than in the traditional solution. That is why control units can reach higher performance level than the traditional solution.

(22) FIG. 3a is a schematic top view of another electrostatic precipitator according to the invention, and FIG. 3b a schematic perspective view of the electrostatic precipitator shown in FIG. 3a. It is to be noted here that dimensions of the electrostatic precipitator 100 may vary from those shown in Figures.

(23) The structure of the electrostatic precipitator 100 is basically same as in FIGS. 2a, 2b. However, the electrostatic precipitator 100 shown in FIGS. 3a, 3b comprises two parallel structures 6a, 6b separated by a gas-tight division wall 7. The electrostatic precipitator 100 is thus divided into two independently working gas passages 3a, 3b. Each of the passages 3a, 3b comprises similar structure of electrical fields and electrical units as discussed above in connection with FIGS. 2a, 2b.

(24) The embodiment shown in FIGS. 3a, 3b is especially useful in electrostatic precipitators 100 having very large dimensions.

(25) It is to be noted, that the electrostatic precipitator 100 may be divided to three, or even more, parallel structures.

(26) The electrostatic precipitators 100 according to the invention may be applied to variety of purification tasks. In an embodiment, the electrostatic precipitator 100 is used for removing particulates from flue gas of a kraft recovery boiler. In an embodiment, the electrostatic precipitator 100 is used for removing particulates from flue gas of a chemical recovery boiler.

(27) The invention is not limited solely to the embodiments described above, but instead many variations are possible within the scope of the inventive concept defined by the claims below. Within the scope of the inventive concept the attributes of different embodiments and applications can be used in conjunction with or replace the attributes of another embodiment or application.

(28) The drawings and the related description are only intended to illustrate the idea of the invention. The invention may vary in detail within the scope of the inventive idea defined in the following claims.

REFERENCE SYMBOLS

(29) 1 discharge electrode 2 collecting electrode 3, 3a, b gas passage 4a, b, c electrical field 5, 5a, b electrical unit 6a, 6b parallel structure 7 division wall 100 electrostatic precipitator G gas flow