Abstract: A process reduces SOx emissions in a flue gas stream by adding a wet collector plate section to an existing electrostatic precipitator (ESP) or by converting the last field of an existing ESP to wet operation. To achieve the conversion, the last field or fields of an existing dry ESP are removed and replaced with components made from materials suitable for operation in a wet environment. After the ESP contains wet operation, ammonia is added to the flue gas stream while it is progressing through the collection plates in the ESP.

Abstract: A flue gas purification system comprising in the flue gas stream an electrostatic precipitator, mercury sorbent injection and a two-stage electrostatic separator, and wherein the mercury sorbent injection is positioned between the electrostatic precipitator and the two-stage electrostatic separator.

Abstract: 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.

Abstract: A gas separation apparatus which uses electrostatic precipitators and a DC power supply is controlled to optimally remove moderate to high resistivity ash. The DC power supply is pulse width modulated to maximize the product of the peak electric field and the average electric field. The method used to optimize operation includes selecting initial on and off times for the power supply, operating the power supply using the initial off and on times, and progressively decreasing the off time. A determination is made whether the off time may be further decreased. Ultimately, the on and off time intervals that produce the highest peak and average voltage are determined, and the system is operated using these parameters. A procedure may be periodically repeated to monitor the process and detect if there has been a change in the system that would require new time intervals.

Abstract: A method is provided for improving the electrostatic precipitation of particulates, i.e., from combustion gases by withdrawing part of the flue gases, catalytically converting the SO.sub.2 to SO.sub.3 and reinjecting it into the main flue stream.