Patent ID: 8550810

Claim:
A method of controlling a boiler plant during a switchover period from an air-combustion mode to an oxygen-combustion mode, the method comprising the steps of: (a) feeding fuel into a furnace of the boiler plant at a rate determined by a fuel feeding scheme; (b) feeding air into the furnace at a rate determined by a descending air feeding scheme; (c) feeding substantially pure oxygen into the furnace at a rate determined by an ascending oxygen feeding scheme; and (d) recirculating flue gas into the furnace at a rate determined by an ascending flue gas recirculating scheme, wherein (i) the fuel feeding scheme, the air feeding scheme, and the oxygen feeding scheme are such that the fuel is combusted and flue gas containing residual oxygen is produced, (ii) the fuel feeding scheme, the air feeding scheme, and the oxygen feeding scheme are such that the content of the residual oxygen in the flue gas is, during at least a portion of the switchover period, greater than during any of the air-combustion mode and the oxygen-combustion mode, and (iii) the amount of the residual oxygen is, during at least a portion of the switchover period, at least 100% greater than during any one of the air-combustion mode and the oxygen-combustion mode.