A gas separation apparatus using electrostatic precipitators and mechanical rappers is enhanced by the addition of an opposite polarity refreshing power supply and a switching arrangement. The switching components selectively disconnect the primary power supply and connect the refreshing power supply to the electrostatic precipitator, causing an electrical impulse in the precipitator sufficient to dislodge precipitate from the collector plates. In one embodiment, an RC filter is further provided to control the impulse and reduce the burden that would otherwise be placed upon the refreshing power supply. In a second embodiment, a pair of SCR strings serve as the switches. Cleaning power is delivered from a capacitor through one of the SCR strings using a resonant circuit, the resonance which causes the SCR string to commutate off after the impulse has been delivered. The capacitor is charged to a pre-calculated potential, dependent upon a measured potential just prior to delivery of the cleaning power, to ensure that the cleaning voltage stays below a corona onset voltage. The novel separation apparatus and technique offer particular synergy when applied to the effluent stream from a coal-fired electric power plant or other similar gas streams.