GB808522A - Improvements in or relating to gas generating plant including electrical precipitation equipment - Google Patents

Abstract

808,522. Automatic control systems for electrostatic precipitators. STANDARD TELEPHONES & CABLES Ltd. July 4, 1956, No. 20700/56. Class 38 (4). An electrical precipitation plant for cleaning gas generated by a cyclic process is provided with automatically operating means for varying the high-tension voltage applied to the discharge electrodes in direct accordance with normal variations of the electrical resistance of the gas due to the variation in the rate of flow of the gas through the precipitation equipment. In this way compensation is effected for the increase in interelectrode resistance which takes place with an increase of gas flow, and efficiency is improved by reducing the standing current to a minimum during the quiescent portion of the cycle. The curve (a), Fig. 2, shows the fluctuations in gas flow which occur during one operating cycle of a gas generator. From O to A and D to O there is no gas production and at A there is a sharp rise in production followed by a fall to D. The curve (b) shows the corresponding precipitator current in the absence of external control, and the chaindotted line curve (c) shows the discharge current when compensation is effected to maintain it at one or other of two predetermined values. The apparatus comprises an auto-transformer AT connected via terminals H or L of a contactor CTR to a transformer and rectifier unit T-R providing the high-tension supply to the precipitator P. One output terminal of T-R is earthed via an ammeter A and marginal relays VS1, VS2, the relay VS1 being set to operate only at high values of current and VS2 to release at a predetermined low value. The contactor coil is supplied with D.C. via terminals 3, 4. During the time interval O to A, VS2 is operated, VS1 is not operated, and CTR is operated and held over contacts A. At A the discharge current starts to fall and VS2 releases to release CTR and so apply a higher voltage to the precipitator. VS2 re-operates, and at C, VS1 operates to energize CTR and cause a lower voltage to be applied to the precipitator. When CTR operates, VS1 releases, and the cycle is repeated. Specification 724,068 is referred to.