Pure oxy-fuel circulating fluidized bed combustion by controlling adiabatic flame temperature using fuel staging

Abstract

In the present study, a new method is proposed for temperature controlling by combustion staging. Two combustion stages can be used with two stages of fuel feeding. A high stoichiometric ratio (SR) λ > 1 is used at the first stage to mitigate adiabatic flame temperature (AFT) in case of high O2% in the oxidant. For validation, a series of experiments are conducted using mini-CFB (circulating fluidized bed), and an oxidant of 100% O2 concentration is used with three SR ratios, i.e. λ = 1.25, 2.0 and 3.0. The resulting average temperatures along the riser for biomass are 1031°C, 950°C and 798°C; and for coal 1129°C, 1051°C and 961°C respectively. The controlling of AFT with pure oxy-fuel combustion eliminates the recycled flue gas in oxy-fuel CFB combustion and flue gas recirculation section; this simplifies design, fabrication and installing-operating costs of the power plants. Familiarizing this concept can accelerate adapting oxy-fuel combustion in CFB power plants for carbon capturing and sequestration. This study can help commercialize the third generation of oxy-fuel CFB combustion with zero RFG. Finally, the concept of controlling AFT by SR is validated experimentally.