Effect of CO₂ and H₂O on Char Properties. Part 3: Semi-Char from Continuous Sampling in a Microfluidized Bed

Abstract

Oxy-steam coal combustion is performed in an atmosphere with a mixture of O 2 , CO 2 , and H 2 O. In this case, both CO 2 and H 2 O in the cyclic flue gas may have an influence on coal char properties in either pyrolysis or combustion. In a traditional combustion reactor, coal char reactivity is usually measured from a whole reaction view, where we could not identify the behavior of the semi-char during the combustion itself. This study reported a microfluidized bed reactor, which combines a solid char particle online sampling system. Semi-char was continuously sampled out from the reactor. The effect of CO 2 /H 2 O on semi-char properties and reactivity was investigated. The results show that the activation energy of the semi-char increases during oxy-steam combustion. In the early combustion stage, the reactivity of the semi-char is higher than that of the original coal char and increases with the sampling time, which is due to the increase of the disordered carbon. While the CO 2 partial pressure has little influence on the reaction index R s of the semi-char, the H 2 O partial pressure has a positive effect on R s . Compared to CO 2 , H 2 O has a greater influence on semi-char reactivity.