Combustion of hydrocarbon fuels in a bubbling fluidized bed

A laboratory size quartz reactor has been used to burn methane, LPG (liquid petroleum gas) and aromatic hydrocarbon vapors in a bubbling fluidized bed. Most measurements and observations were made for lean mixtures of fuel and air with quartz sand in the bed, but in some experiments NO, NO2, or CCl4 were introduced with the fuel, the stoichiometry was varied or the bed material changed. The quantities monitored were the bed temperature at two levels and the freeboard concentrations of O-2, CO2, CO, NO, NO2, and in some runs, of hydrocarbons. An attempt was made to relate the measurements to the sound level and to visual observations. The results obtained suggest that with the air excess, lambda, constant at 1.4 and with the bed at above similar to850degreesC, the fuel can be fully oxidized and [CO] very low. [NO] is also low and does not increase even if the temperature is raised by another 150 to 200degreesC. However, such a stable combustion process can be perturbed by adding a chemical inhibitor. With a suitable bed material it is possible to lower [CO] and [NO] in the freeboard to similar to1 ppm. At lower temperatures, with [CO] high, the conversion of NO to NO, takes place. Most of the observations are consistent with the dominance of gas-phase reactions in the bubbles, but some effects can only be accounted for by the participation of heterogeneous chemical reactions. (C) 2002 by The Combustion Institute.