Combustion of high ash Indian coals in a fluidized bed combustor

Abstract

High ash Indian subbituminous coal and coal washery rejects were burned in a 1 m × 1 m fluidized bed combustion (FBC) test facility at the Bharat Heavy Electricals plant in Trichy, India. Freeboard combustion and heat transfer were measured with the aim of improving the design database for large FBC boilers. Observed freeboard combustion levels were 10–15% for overbed feed and 6–10% for underbed feed. The results indicate that, even with high ash Indian coal, it is possible to achieve overall combustion efficiencies of up to 97% if sufficient bed temperature and excess air are utilized. Overall combustion efficiencies of 98% are possible with flyash recycle. The heat transfer coefficient in the bed was in the range 193–300 kcal (h m 2 °C) −1. In the freeboard, the coefficient ranged from 137–168 kcal (h m 2 °C) −1 close to the bed surface and decreased exponentially at the higher elevations.