Patent GB-1167904-A (GB)
Title: Electrostatic Precipitation of Dust from Dust Laden Gas.
IPC: B03C3/74
Filed: 1966-10-17
Abstract: 1,167,904. Electrostatic precipitators. BAND MINES Ltd. and CHAMBER OF MINES SERVICES (PROPRIETARY) Ltd. 17 Oct.. 1966 [19 Oct., 1965], No. 46334/66. Heading B2J. Dust-Jaden gas is dry de-dusted by dividing a flow of the gas into a number of separate streams, passing each stream through an electrical precipitator, intermittently rapping the electrodes of each precipitator in turn to detach adherent dust therefrom and causing a stream of air to flow through the respective precipitator in a direction opposite to the normal direction of gas flow through that precipitator in order to assist in the removal of the deposited dust detached by rapping. A main duct through which the dust-laden gas flows has a number of branches each leading to a precipitator unit, Fig. 1 (not shown). Each precipitator unit comprises a cylindrical shell 20, Fig. 2, provided with an inlet 32 for dust-laden gas and with electrodes consisting of wires 22 each shielded in a tube 24 and mounted between grids 26 and 28, the grid 28 being stabilized by an insulated post 30. The clean gas leaving the bank of electrodes flows, through a chamber 34 and a venturi duct 36, into a chamber 38 which constitutes an inlet for a fan contained within a casing 40, the fan discharging into a stack 44. A normally open outlet damper 42, Fig. 3, is arranged between the fan and the stack and is operatively coupled by means of a linkage 68 to a normally closed by-pass damper 46 located between the chamber 38 and a louvered box 48 in communication with the atmosphere, the dampers being operated by an actuator 64 so that when one is open the other is closed. The electrodes are rapped by means of vibrators 58, 60, 62 which are operated by compressed air supplied through flexible tubings 80, 81, 82, Fig. 4, connected to a common conduit 83. One end of conduit 83 is constantly connected to a source of compressed air 69 through a bleed conduit 71 which supplies bleed air through an orifice plate 78 to the tubings 81, 82 to keep them dry, and thereby minimize the possibility of electric leakage, as well as to cool them. The other end of conduit 83 is connected to the air supply 69 through a conduit 70 incorporating a normally closed valve 72 which is opened by a relay operated by a limit switch 74 when the outlet damper 42 is closed and the by-pass damper 46 is open. In operation, the fans are set in motion and with the actuators 64 in retracted position and the damper 46 of each precipitator unit closed and the damper 42 open, the gas to be treated is drawn through the main duct and via the branches to each precipitator unit. After deposition of dust on the electrodes 22 the cleaned gas is drawn by the fan 38 and discharged through the open damper 42 up the stack 44. After a certain time, a time-switch 84 operates and energizes the actuator 64 of one of the precipitator units so that the damper 42 is closed and the damper 46 opened. At the same time the valve 72 is opened through the action of the limit switch 74 so that the vibrators 58, 60, 62 are caused to operate to effect rapping of the electrodes to dislodge accumulated dust therefrom. With the damper 46 open, air is drawn, by the suction created by the fans of the other precipitator units, through the louvered box 48 via 38, 36, 34, the tubes 24 and into the tank 10, thereby encouraging detachment of dust from the electrodes. After a suitable period of time, the timer 84 de-energizes the actuator 64 of the respective precipitator unit causing the dampers to return to their normal position and the valve 72 to close. The actuator 64 of another unit is subsequently operated so that all units are cleaned in turn. Instead of using a timer 84, the operation of the actuators 64 may be manually controlled. An access door 88 is provided for manual cleaning of a unit where desired.