Oxy-fuel heat transfer characteristics and impacts on boiler design

An outline of the basis of radiative transfer which dominates furnace heat transfer for coal-fired oxy-fuel furnaces is presented and illustrated by comparisons of the significance of the radiating species influencing heat transfer, and also differences between air-fired and oxy-fuel fired furnaces. Heat balances and heat transfer for three different oxy-fuel furnaces of 1.2 MWt, 30 and 420 MWe are given by a simple well-stirred reactor model and also comprehensive computational fluid dynamics models. It is concluded that oxy-fuel combustion can be operated at the same heat transfer rate as air-firing, but results in operational changes -lower volumetric gas flow rate, lower adiabatic flame temperature and lower flue exit gas temperature - associated with the higher gas emissivity of oxy-fuel firing and different heat capacity of the flue gas