Patent GB-850275-A (GB)
Title: Electrostatic precipitators
IPC: B03C3/40
Filed: 1956-10-08
Abstract: 850,275. Electrostatic precipitation. LUEDER, H. Oct. 8, 1956 [Oct. 17, 1955], No. 30558/56. Class 39(1). An electrostatic precipitator comprises two groups of electrodes which are maintained at different potentials, each, or each but one, electrode surface being closed upon itself and inclined with respect to an axis, all, or all but one, of the electrodes being open at both ends so as to have an outer, and an inner edge, the electrodes being stacked one within the other with electrodes from one group alternating with electrodes from the other group, each electrode being spaced from an adjacent electrode of opposite polarity by a single uninterrupted passage through which gas can flow, and at least the majority of the electrodes being supported by one edge only. The electrode surfaces are formed according to a given definition. Frusto circular or elliptical conical surfaces, part spherical or ellipsoidal surfaces, and irregular surfaces are referred to. The electrode surfaces may be true surfaces of revolution, and the generating line of each surface may be formed of a number of straight lines whose inclinations in relation to the axis of revolution are different. Each electrode can be of frusto-conical form provided at least at one end with a bent-over edge. In the construction shown in Fig. 1 frustoconical electrodes 1, 2, 3, 4 and 5 of a first group alternate with frusto-conical electrodes 6, 7, 8 and 9 of a second group, the electrodes 1 and 5 being made of thicker material to protect the separator chamber. The electrodes 1-5 of the first group are supported at their bent outer edges, the electrode 1 being provided with a cylindrical skirt 1 forming a housing in which the other electrodes are stacked with distance pieces 10 between them. The distance pieces are preferably of annular shape and can be of insulating material or of conducting material such as metal. The electrodes 6, 7 and 8 of the second group are supported at their bent inner edges between plane annular discs 12, groups of distance pieces 13, of insulating or conducting material, being distributed uniformly around the periphery of the inner edges of the electrodes. The unsupported edges of the electrodes of both groups are bent and the electrodes are arranged in such relation to one another that the extremity of each bent edge is at a greater minimum distance from the neighbouring electrode or electrodes than is the major part of the remainder of the electrode surface. Insulation between the two groups of electrodes is effected by spacing rings 14 and 15 which are disposed only at the gas outlet end of the precipitator and are provided with electrical heating elements 16 to prevent the formation of conductive coatings thereon. The spacing rings may be made of moisture-repellent material at least on their external surfaces. The heating elements 16 are fed by a high voltage transformer 17 in a chamber 19 which may be swept by purified gas. The gas is led through openings 21 in the electrodes of the first group and leaves through spaces 22 between the distance pieces 13 and openings 23 in the cap 24. In the construction shown in Fig. 2 supporting devices 28 for the first electrode group 32 of frusto-conical form and supporting devices 29 for the second electrode group 33 of frusto-conical form are distributed uniformly around the periphery of the insulating base plate 27, distance pieces 30 and 31 being provided for spacing the outer edges of the electrodes. The gas is ionised by bands 34 mounted on the electrodes, the free edges of the bands, which are of knife-edge form, causing a corona discharge. The bands 34 preferably consist of semi-conducting material and are cut in the form of spirals out of flat discs. There may be introduced into the gas to be purified finely atomised liquid which, after being electrically charged, is separated out on to the electrodes and washes away the separated particles of dust. The precipitator shown in Fig. 3 serves to purify gases which are under pressure, the strength of the field between the electrodes being maintained at a value greater than the breakdown value of the field strength as described in Specification 843,782. The gas enters through a pipe 38 and leaves through a pipe 39. The frusto-conical electrodes 40 of the first group are supported only at their outer edges between distance pieces 41. The frusto-conical electrodes 42 of the second group are supported only at their inner edges between plane annular discs 43 separated by distance rings 45 provided with apertures 44. The two electrode groups are supported by insulating rings 47 and 48. The first electrode group is connected through earth to the secondary winding of the transformer 52, and the second electrode group is connected to the secondary winding through a rectifier tube 53. A glow lamp 56 is connected through a high ohmic resistance 57 to the high voltage electrode group. A pressure-sensitive switch 54 connects the primary winding of the transformer 52 to a low voltage source through a cable 55. A wave ring 58 carrying a radioactive preparation serves as ioniser and is connected through the wire 59 to one of the electrodes 42 of the second group. Any liquid separated from the gas runs down the electrodes, through the apertures 60 and collects in the lower cap 35 whence it can be discharged through a drain-cock 62. Packings 64 ensure the sealing of the pressure vessel and packings 65 prevent unpurified gas from penetrating into the path of the purified gas.