GB403829A - Improvements in or relating to the electrical precipitation of suspended material from gases - Google Patents

Abstract

<PICT:0403829/III/1> <PICT:0403829/III/2> <PICT:0403829/III/3> In a process for the electrical treatment of suspended material in gases, a unidirectional potential approximately equal to the minimum value required for ionisation but below the arcing potential is continually maintained between the electrodes and superimposed thereon are sharp high potential impulses of steep wave front of the same direction as the continually maintained potential, the potential at each impulse being considerably greater, e.g. at least 50 per cent greater, than the unidirectional potential. The duration of each impulse is also only a fraction of the interval between successive impulses. A suitable method of obtaining the potential impulses is by the use of a system of condensers and spark gap means acting as a voltage doubling circuit. According to the arrangement shown in Fig. 1, the electrical precipitation system 1, consisting of discharge and collecting electrodes of known types is supplied with a unidirectional potential by means of a transformer 5 and a mechanical rectifier 7. Chokes 33 and 34 are included in this circuit to prevent high frequency oscillations developed by the impulse generating means from reaching the power supply, and resistance 35 is included to stabilise the load. The impulse generating means comprises two condensers 15 and 16 which are arranged to be charged in parallel from the above supply of unidirectional potential and to be discharged in series through the electrical precipitator when the spark-gap 28 breaks down. Resistances 24 and 26 are connected between the high potential line and condenser 15 and between condenser 16 and earth. When the spark-gap 28 breaks down, the potential impulse generated is of steep wave front, and is prevented by the impedances 24, 26, 33, 34 and 35 from reaching the rectifier and transformer. The resistances 24 and 26 also regulate the rate of charging of the condensers. Each shaft potential impulse produces a copious corona discharge at the discharge electrode 4, but is of sufficiently short duration, e.g. of the order of 10-<5> seconds or less, to prevent continuous arcing. In the arrangement shown in Fig. 2, the source of unidirectional potential is a transformer 37 and rectifier 38 while the impulse generating means comprises a separate transformer 42, and rectifier 43 and condenser 48, spark-gap 46 and impedances 51 and 52, Fig. 3, shows an arrangement similar to Fig. 1 in which three condensers 55, 56 and 57 are charged in parallel and discharged in series through spark-gaps 58 and 59. The impulse potential obtained is approximately three times the potential at which the individual condensers are charged, thus giving a greater ratio of impulse potential to line potential.