Abstract: This invention pertains to methods for removal of pollution from the exhaust gas stream of combustion sources. More particularly, the invention relates to an improved method of elimination of particulate matte, sulfur dioxide (SO.sub.2) and volatile toxic materials from the flue gas of coal fired boilers, especially in large electric generating plants.

Abstract: An apparatus and method for reducing back corona effects while charging high resistivity dust or the like in a corona field, includes a corona discharge electrode, a passive electrode and a screen electrode, the screen electrode being positioned between the discharge electrode and the passive electrode. The screen electrode is positioned more closely to the passive electrode than the discharge electrode and is supplied with an electrical potential which is of the same polarity as and a fraction of the magnitude of the discharge electrode relative to the passive electrode. Gas having entrained therein the particulate material, which is to be removed, flows between the screen and discharge electrode and thence to a particulate material collection stage. The space between the screen and corona discharge electrode remains essentially a unipolar ion field, while ions of the opposite polarity originating at passive electrode due to back corona are collected by the screen electrode.