The effect of internal geometry, electrode type, and operating conditions on the performance of a coal electro static precipitator (ESP) has been analyzed by means of an extensive parametric testing program. rests under different conditions of plate spacing, discharge electrodes, gas velocity, and energization waveform have been performed using two extreme coal types, with very high and low resistivity ashes, respectively. The study was made by means of a Pilot installation operating with a flue gas slipstream drawn upstream of a powerplant ESP. The experimental includes a specifically designed pilot ESP, able to admit an internal modification of plate spacing and electrode type. The ESP is equipped with a microprocessor controlled power supply which can generate both continuous and intermittent rectified current. The measured sensitivity of the precipitation process to the dust properties, filter configuration, electrode type, al td energization method is presented, covering both the ESP efficiency evolution and the associated power consumption. The results of this work allow to extract practical conclusions about specification of ESP design and size for a given application, and assess the conditions In which use of wide plate spacing, new electrode geometries, or intermittent current are actually advantageous.