Pressurized oxy-fuel combustion characteristics of single coal particle in a visualized fluidized bed combustor

Abstract

Pressurized oxy-fuel combustion (POFC) is recognized as the second generation of oxy-fuel combustion for the reduction of CO2 emissions, which has gradually gained more and more attention recently. In this work, the influence of pressure on the combustion characteristics (i.e., ignition, volatiles combustion, char combustion) of a single lignite particle was investigated in a pressurized visualized fluidized bed combustor under O2/N2 and O2/CO2 atmospheres. The combustion process was recorded by a color video camera, and the temperatures of volatiles flame and char particle were measured by pre-calibrated two-color pyrometry. The results indicated that increasing the overall pressure and increasing the oxygen volume fraction to a same partial pressure of oxygen will affect the ignition delay time (td) differently. td increased with the operating pressure at the same oxygen volume fraction, but decreased with the increase of oxygen volume fraction under atmospheric pressure. Pressurization significantly changes the coal flame shape and the volatiles flame becomes longer and thinner at a higher pressure. At the same oxygen volume fraction, higher flame and char temperatures and shorter burnout time (tb) of coal particle were observed under a higher pressure due to the better mass transfer of oxygen. With the same oxygen partial pressure, particle temperature is lower at high overall pressure than that at high oxygen volume fraction, which is probably a potential advantage of pressurized oxy-fuel combustion to resist agglomeration. Moreover, compared with atmospheric oxygen-combustion, the gasification of char particle in pressurized oxygen-combustion is more remarkable and cannot be neglected.