Investigation of Combustion Characteristics in a Vortexing Fluidized-bed Combustor with a Contraction Chamber

Abstract

This investigation was undertaken to obtain information on the effects of a contraction chamber and secondary air ratio (() on combustion temperature distribution, gas emissions of rice husk combustion and flow behaviours in a vortexing fluidized-bed combustor with a contracted chamber (VFBCC).The combustor chamber was modified by reducing the diameter chamber size (contraction) near the top part of the chamber to create a large central recirculation zone. In the experiment, the effects of secondary air ratio (() of 0.0, 0.25 and 0.4, and the equivalent ratio, (() of 0.2, 0.25, 0.3 on combustion characteristics and temperature distribution were examined. The results indicated that the temperature profile inside the combustor between a typical vortexing fluidized-bed combustor (VFBC) and VFBCC was slightly different.The emission of VFBCC was lower than in the original VFBC. At the equivalent ratio of 0.3 and secondary air ratio of 0.4, the average concentrations of O₂, CO₂, CO and NO_x of the flue gases from the original VFBC were 10.5%, 6.7%, 717 ppm and 287 ppm, respectively while those from the modified VFBCC were 9.7%, 6.3%, 357 ppm, and 250 ppm, respectively. In addition, flow visualization results showed the presence of a contracted part led to the recirculation formation in the top chamber.