Patent GB-411033-A (GB)
Title: Electrical systems and methods for treating gaseous fluids
IPC: B03C3/66
Filed: 1933-11-16
Abstract: In electrical precipitating plants comprising a number of treater units energized from a common source of high tension current, energy directing means are provided whereby each unit is intermittently energized in rotation, the full voltage of the supply being applied, and electrical fields of the same polarity being produced in each unit when energized.  The arrangement is stated to improve the efficiency of the plant, since each unit is uninfluenced by other units which may possess different electrical characteristics owing to <PICT:0411033/III/1> <PICT:0411033/III/2> <PICT:0411033/III/3> <PICT:0411033/III/4> differences in the nature of the gases treated and their dust content.  Fig. 1 shows two pipe-type precipitators P1 and P2 of which the discharge electrodes 17 are connected to each side of the secondary of a step-up transformer T and also to shoes 5 and 6 of a switch 10 rotated in synchronism with the alternating current supply.  The collecting electrodes 18 are earthed and also connected to shoe 8 of the switch.  This switch alternately connects each side of the transformer secondary to earth and thus alternately short-circuits each precipitator, the discharge electrode of the unit in action being supplied with current of the same polarity, due to the reversal of polarity of the transformer. The rotary switch may be replaced by two thermionic rectifiers, each in parallel with one end of the secondary and the earthed collecting electrodes, and resistances may be inserted in each discharge electrode circuit to alter the voltages applied to a given precipitating unit.  Instead of short-circuiting each unit in turn, they may be isolated from the supply during the cycle and the discharge electrode retains its potential, thus increasing the operating efficiency, since the unit acts as a non-ionising separator.  This may be done by interposing thermionic rectifiers 33 and 34 in series with the discharge electrodes as shown in Fig. 3.  In this circuit, when point A is negative, current flows from point A to discharge electrode 5, the thermionic rectifier in parallel with the electrodes of unit P5 being non-conductive. When point A is positive, the rectifier in parallel short-circuits the point A and the collecting electrode of unit P5, and the rectifier 33 is non-conductive and allows the discharge electrode 35 to retain its charge.  Spark-gaps may be used in place of the thermionic rectifiers 33 and 34.  Rotary switch rectifiers may be used to obtain the same results, as shown in Fig. 4.  As illustrated, if point B is negative, the unit P8 is energised and functions in a normal manner, and the discharge electrode 43 of unit P7 is isolated and retains its charge from the previous cycle.  In the arrangement shown in Fig. 7, four precipitator units P9--P12 are energized from a single transformer by means of three rotary switches 40, 43 and 44.  Switch 40 causes the current in conductors 41 and 42 to be of a chosen polarity at all times. Switch 43, making one complete revolution for every two cycles of the supply, connects units P9 and P10 to the respective half cycles of the correct polarity and switch 44 performs the same function for units P11 and P12.