Sulfur fate during bituminous coal combustion in an oxy-fired circulating fluidized bed combustor

To clarify the sulfur transformation behavior during oxy-fired circulating fluidized bed (CFB) combustion, experiments on SO₂ emission characteristics were carried out in a 50 kWth CFB combustor. Results show that SO₂ emission is quite dependent on the bed temperature in different atmospheres without limestone injection. With Ca/S=2.5, SO₂ emission in 21%O₂/79%CO₂ atmosphere is smaller than that in air atmosphere, but SO₂ emission decreases with the increase of O₂ concentration. The calcium forms in the ash prove the combination of calcination/carbonation and direct sulfation mechanism of limestone under oxy-combustion conditions. And the desulfurization efficiency of limestone (as deducting the self-retention efficiency from the total sulfur removal efficiency) increases from 40% to 52% as the O₂ concentration increases from 21% to 40%.