Abstract: A the method and apparatus for cleaning of flue gas from a boiler, and the recovery of heat from gas, the flue with the flue gas being led from the boiler through a heat exchanger in such a manner that it still has a temperature above the acid dew point. The flue gas is then led to a scrubber tower and is washed with a scrubber fluid from a sedimentation tank. The pH value of the scrubber fluid is measured with a measuring element and a liquid additive base is introduced from a tank. The sediment in the sedimentation tank is fed into a high-speed reactor, from which a basic fluid is led to one or more collection vessels supplied with clean gas from a chimney via a blower resulting in the formation of CaCO.sub.3 which, not being easily dissolved, is precipitated. The cleaned base is fed to the tank. The high-speed reactor is supplied with lime water through a ring main and a dosing pump from a lime water plant.

Abstract: An apparatus and method for controlling combustion in a furnace is described. The flue gas content is monitored to determine the oxygen and/or carbon dioxide components therein to provide a control signal which is compared with a control signal from a fuel flow sensor to provide an infinitely variable speed control for a blower which supplies combustion air to the furnace being controlled. The speed of the blower is varied in accordance with the flue gas content and the fuel flow rate to provide a continuously variable blower speed to at all times effect optimum combustion efficiency.