The present invention relates to a method for improving the performance of particulate collection devices in coal fired steam generating plants. More specifically the invention relates to the control of the temperature of the flue gas flowing from the air preheater to an electrostatic precipitator or baghouse filter.
Coal fired steam generating plants employ air preheaters to transfer heat from the flue gas to the incoming combustion air and many employ electrostatic precipitators or baghouse filters downstream from the air preheater to remove the particulate fly ash from the flue gas prior to discharge. Depending upon the particular coal being used and the resulting nature of the fly ash produced including the sulfur content, the temperature of the flue gas entering the electrostatic precipitator or baghouse can have a significant impact on the collection efficiency. For example, the so-called back corona in the electrostatic precipitator can be a major source of increased particulate emissions for high resistivity fly ash and the flue gas temperature can significantly impact the back corona effect. Likewise, the flue gas temperature can significantly affect the caking properties of the fly ash in baghouse fabric filters.
For the reasons stated above, it is desirable to be able to control the temperature of the flue gas entering the precipitator or baghouse. On the other hand, the requirements for the quantity and temperature of the primary and secondary combustion air and the design of the air preheater have a basic effect on the flue gas temperature leaving the air preheater. Also, the temperature of the flue gas leaving the air preheater cold end needs to be controlled to avoid condensation and plugging.