Fluidized Bed Combustion of High Ash Chars

Abstract

The behavior of the fluidized bed combustion of high ash chars is analyzed by applying the two-phase theory, the gas (lowing in plug flow both in the emulsion and bubble phases. The ash is assumed to remain attached to the char particle and therefore the shrinking core model is considered.

Combustion efficiency increases with bed temperature, excess air and ash content of char, as well as when the char mass flow rate and particle diameter decrease. The effect of excess air on the exit concentration is found to be related to the interphase mass transfer coefficient.

The carbon monoxide concentration is reduced in the freeboard by two orders of magnitude due to its oxidation to carbon dioxide. These emissions are further reduced when preheated secondary air is introduced.