Effect of oxygen concentration on combustion behavior of single coal pellets from three different ranks in a concentrating photothermal reactor.

Comparative combustion studies were performed in a concentrating photothermal platform (room temperature chamber type experimental bench with less volumetric reactions) on coal pellets (>6mm) from three different ranks: bituminous coal, sub-bituminous coal, and lignite. The combustion of single coal pellet in 21 ~ 50% oxygen concentration was observed with IR pyrometry and high-speed cinematography to obtain temperature–time–size histories. Based on the combined mass measurement and gaseous product analysis, a comprehensive understanding of the effects of oxygen concentration on single coal pellet combustion behaviours was developed. Distinctive three-stage processes were proposed with characteristical temperature and cinematography variations. No obvious flame duration was detected in 21% or 30% O 2 while transient but luminous flames were clearly observed in 40% and 50% O 2 and formed notable temperature peaks in the second stage during combustion of all the three ranks coal pellets. Volume and density both changed non-linearly during combustion and such processes were accelerated with the increase of oxygen concentration. High concentrations of CO and CH 4 were detected due to the suppression of volumetric reactions. CO accounted for about 9.3% of the gaseous products and consistently exhibited two peaks with the first peak independent from oxygen concentration. Three-stage combustion process was further validated by CO 2 /CO ratio and the effective reaction orders of oxygen concentration were 1.91 (bituminous coal), 1.81 (sub-bituminous coal) and 1.26 (lignite). [ABSTRACT FROM AUTHOR]