an electrostatic precipitator with at least one pair of spaced , flat - plate grounded dust collecting electrodes and a floating , insulated dust collecting flat - plate electrode arranged in the center of each space between the grounded dust collecting electrodes parallel to the gas flow and provided at its edges at fixed intervals with sets of needle - shaped discharge electrodes . the needles are fabricated along an outer longitudinal edge of a channel bracket member by welding or the like at precise equal spacings . plural bracket members are riveted along the respective leading and trailing edges of each floating flat electrode plate in such a fashion that the tips of the needles are aligned vertically in the precipitator chamber . the diameter of the needle - shaped discharge electrodes is smaller than approximately 5 mm and the tips of the needle - shaped electrodes have a maximum radius of approximately 0 . 5 mm while the intervals between the needle - shaped discharge electrodes is smaller than the distance between the grounded dust collecting electrodes and the floating dust collecting electrodes .