Method of and means for electrically purifying gases

Abstract

Abstract <PICT:0404635/III/1> In the process described in the parent Specification for the separation of suspended particles in gases by means of potential impulses of short duration, the duration of the individual impulses is kept so short that the negative ions proceeding from the discharge electrode can only just reach the surface of the collecting electrodes or points immediately in front of them. Preferably a sufficient time interval is allowed after each impulse to allow the surface charge which accumulates on the dust layer of the collecting electrode to disperse before the arrival of the next impulse, thus preventing the formation of positive brush discharges on the collecting electrode. The duration of the impulse discharge is related to the velocity of the ions in the gas and the distance between the electrodes, e.g. if the distance between the discharge and collecting electrodes is 6 cm. and air containing dust in which the velocity of negative ions is 60 metres per second is passed between them, each voltage impulse must last not longer than 10-<3> seconds. The time interval between impulses depends upon the resistance of the dust layer and may be for example one hundredth or one fiftieth second or even longer. The velocity of negative ions is stated to be about 280 metres per second in hydrogen, about 36 metres per second in carbon dioxide and about 16 metres per second in sulphur dioxide. The increase of the voltage impulse is preferably made so sudden that the voltage increase from zero to maximum occurs in about 10-<6> seconds, and preferably with a steep wave front, thus allowing the use of potentials which are approximately 30--100 per cent above the highest potential possible when using continuous direct current. During the intervals between the impulses, the potential applied to the discharge electrodes is preferably kept below the discharge limit. According to the arrangement shown, the discharge electrode 2 is supplied with impulse potentials by means of a spark-gap 5 and earthed condenser 10 interposed in the supply from transformer 8 and rectifier 6. Chokes 11 and 12 and condenser 14 are provided to prevent transference of high frequency oscillations through the supply line. Disruptive discharges are prevented by means of an auxiliary spark-gap 16 and condenser 17 connected in parallel with the electro-filter, the spark-gap 16 functioning by means of an igniting electrode 19 connected to the discharge electrode 2 through a condenser 20 and resistance 21 before a disruptive discharge occurs. The condenser 17 discharges through a resistance 18 leaving a sufficient charge on the electrodes of the filter to ensure the separation of the dust particles. The process may also be employed for the production of chemical reactions in gases.

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