Gas treatment

A method of removing pollutants from high temperature gases prior to their introduction in to a heat exchanger of a steam generating boiler within a power generation system, the method comprising:

• placing a filter system in the hot gas flow path upstream of a waste-heat boiler, said filter system comprising at least two banks of substantially hollow elongate filters, each filter configured to filter particles from the gas flow as it flows from an external surface thereof to an internal surface thereof and valve means to enable each bank of filters to be isolated from the hot gas flow path;
• passing hot exhaust gases through said filters to remove pollutants therefrom;
• periodically isolating at least one bank of filters while passing hot gases through at least another of said banks of filters;
• cleaning said isolated bank of filters;
• and, after cleaning the filters, injecting lime into the flow path such that it coats the outer surface of the filters to produce a loose lime coating thereon, and further including:
• introducing particles of lime into the hot gas flow upstream of the filter system;
• and
• sensing the acidity of the gas downstream of said filter system,
• creating a signal indicative of the acidity of the gas downstream of said filter system;
• and
• controlling the injection of said lime particles in response to said signal to substantially neutralize all of the acid within said exhaust gas;
• and
• removing the lime particles with said filter system.