Combustion Behavior of High Ash Bituminous Coal in a Pilot Scale Circulating Fluidized Bed Rig

In contrast to pulverized coal combustion systems, fluidized bed technologies offer significant advantages such as a low temperature environment and lower NOx, SOx emissions. Another advantage is the potential utilization of a wide range solid fuels such as biomass and low rank coals with high ash content. In this study, a bituminous coal from the northern part of Kazakhstan with ash content of around 40% was tested in a pilot-scale circulating fluidized bed rig under air environment. The pilot-scale circulating fluidized bed has a thermal output of 200 kW, a riser height of 7000 mm and inner diameter of 150 mm. The combustion and fluidization behavior of coal were determined by measuring the pressure drop profiles along the height of the rig and flue gas measurements with FTIR system. The coal and bed material are introduced from separate silos equipped with an electrical motor connected to the feed screw to achieve a controlled feeding rate. The rig is also equipped with primary and secondary air supply as well as solid separation cyclones. Part of the exit stream of flue gas is directed to a FTIR for gas analysis system (Gasmet dx4000). The level of bottom ash in the dense zone of CFB rig was controlled with a bottom ash screw removal system. Typically, roughly 40% of feed coal was converted to the ash, hence tests were also performed using the ash as the bed material. In addition to combustion tests, the chemical composition of the fly ash and bottom ash were examined by X-ray fluorescence and the results are presented in the paper.