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Abstract

A method and apparatus for controlling the combustion of multiple fuels, especially fuels having diverse combustion air requirements. A heating rate demand signal indicative of the heating rate desired is generated and is compared with a fuel based fuel heating rate signal. The larger of the two signals is selected to be an air demand signal that serves as set point for a combustion air controller. The flow rates of each of the fuels being burned is monitored and the resulting signals are scaled and summed to produce the heating rate signal. The fuel signals are also scaled by factors reflecting the combustion air requirements of the fuels. The signals are summed and combined with the fuel heating rate signal to produce a feedforward signal which in turn is combined with a signal reflecting the measured combustion air flow to produce an equivalent air heating rate signal. This latter signal is communicated to the combustion air controller and if different than the air demand signal causes an adjustment of the combustion air controller. The equivalent air signal is also compared with the heat demand signal and the lower of these two signals is communicated to a fuel heating demand subsystem which controls the metering of the fuels. An 0.sub.2 set point generator modifies the feedforward signal should a deviation occur between the 0.sub.2 set point and the measured 0.sub.2 content of flue gas exhausted by the combustion process.

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First Claim