The Investigation of the Coal Ignition Temperature in Oxygen-Enriched Atmosphere by TGA

The oxygen-enriched Circulating fluidized bed (CFB) combustion technology is a new method to reduce CO₂ emissions. The coal ignition temperature, T_i, in an oxygen-enriched CFB boiler is an important parameter for designing the startup burner and for choosing the operating strategy during the startup process. Comparing with the complicated operation in real oxygen-enriched CFB boiler or in a laboratory scale fluidized bed (FBR), thermo gravimetric analyzer is a more simple and convenient method to determine the T_i, because the TGA results would be related in some way with the field results. Thermo gravimetric analyses of seven different types of coal were operated in air and oxygen-enriched atmosphere (O₂ 40%, CO₂ as balance gas), with three different heating rate (10, 20, and 30 K/min). It was found that the T_i, determined by the DTGA, decreased with the O₂ concentration increasing. The coal with the higher volatile content had a lower ignition temperature. The influence of the heating rate on the T_i was relatively significant. With 40% O₂, the coal ignition temperatures firstly increased and then decreased with the increasing heating rate. Compared with the tests results obtained in a laboratory scale FB, the results obtained by these two methods have the same tendencies, and there must be a way to make the TGA results relative to the real coal ignition temperatures in the oxygen-enriched CFB boilers.