TABLE OF CONTENTS Combustion efficiency, defined as the ratio of heat released by the fuel to the heat input by the fuel, is generally high in FBC systems. The combustion efficiency is typically higher than stoker-fired systems and is comparable to pulverized coal-fired systems. It is generally higher in a CFB boiler than in a BFB boiler because of the use of finer particles, more turbulent environment, and a high solids recycle rate [14]. Similarly, PCFBC boilers achieve higher efficiencies due to smaller and more frequent bubbles, which result in better gas-solid contact.
Combustion efficiency is affected by fuel type, bed temperature, gas velocity, and excess air levels. Combustion efficiency increases with fuel volatile matter content and bed temperature. Combustion efficiency decreases with increasing superficial gas velocity. Combustion efficiency initially increases with increasing excess air level and then decreases. This is believed to be due to an increase in CO and hydrocarbon emissions as the excess air level increases to higher levels [14].
