Fundamental study on fuel-staged oxy-fuel fluidized bed combustion

Abstract

The concept of a fuel-staged oxy-CFB (oxy-fuel circulating fluidized bed) combustion technology is proposed by this article to extend the operation range of an existing air-fired CFB boiler retrofitted for oxy-fuel operation. Experiments were designed to study the combustion behavior of a single coal particle at different locations of the furnace (dense bed and freeboard), which should differ largely from those in the conventional feeding to dense bed. Three different kinds of coal under various atmospheres were studied in a visualized fluidized bed combustor, by on-line monitoring the temperature of fuel particle and volatile flame simultaneously. As expected, shorter ignition delay time (td) was observed in the dense bed due to the stronger heat transfer than that in the freeboard. However, surprisingly, shorter devolatilization time (tv), higher peak temperature (Tpeak) and shorter burnout time (tb) were observed in the freeboard of the furnace, which were probably due to higher mass transfer rate of oxygen from gas phase to the reacting particle. When N2 was replaced by CO2, both the td and tb increased while the flame and particle temperature decreased significantly.