Improving Rapping System Performance
All precipitator rapping systems allow adjustment of rapping frequency, normally starting with the highest frequency (the least time between raps), progressing to the lowest frequency. The times that are actually available may be limited. Rapping systems with pneumatic or electric actuators allow variations of the rapping intensity. Pneumatic or electric vibrators allow adjustments of the rapping time. State-of-the-art rapper controls allow selection of rapping sequences, selection of individual rappers, and provide anti-coincidence schemes which allow only one rapper to operate at a given time.
Rapping systems can be optimized for top precipitator performance using precipitator power input and stack opacity as criteria. Optimization of the rapping system starts with the discharge electrode rapping system operating on its own time schedule, for example with repeat times of 2 – 4 minutes. The rapping system for the gas distribution screens in the inlet and outlet of the precipitator should then be operated with repeat times of 2-3 minutes for the inlet and 2 – 3 hours for the outlet screens.
The only rapping system requiring optimization is the collecting plate rapping system. The optimization should start with the Collecting Plate Rapping Schedule determined above. Next, the rapping frequency of the inlet field should be increased or decreased until the electrical power input of the inlet field remains constant. Next, the rapping frequency of the other fields should be adjusted in sequence until their electrical power inputs remain constant. If the stack opacity trace shows rapping spikes, the rapping intensity should be reduced while observing the electrical power input of the precipitator.
The adjustment of the rapping system for optimum precipitator performance is a slow process. It requires a substantial amount of time for stabilization after each adjustment.