Control of staged combustion, low NOx firing systems with single or multiple levels of overfire air

摘要

A control system for a fuel-fired furnace and more specifically the control of the stoichiometric ratio of the combustion process occurring within the furnace of a steam generating power plant. The control system, when so employed, is capable of regulating the distribution of air flow to the combustion process such that the formation of oxides of nitrogen are maintained at acceptable levels. The control system includes in general a stoichiometric subsystem that determines the mass flow rate of air required to maintain the stoichiometric ratio within the combustion process; an override protection subsystem which ensures control precedence of the windbox-to-furnace pressure differential over the stoichiometry subsystem; and an overfire air subsystem that acts to apportion air flow amongst the various levels of overfire air within the boiler.