Study of the Effect of Coal Type and Particle Size on Char–CO₂ Gasification via Gas Analysis

Abstract

Char gasification is affected by operating conditions such as reaction temperature, reactant gas partial pressure, total system pressure, and particle size, in addition to the chemical composition and the physical structure of the coal. We characterized the effects of coal type and particle size on the CO 2 gasification of chars prepared from 12 bituminous coals at different reaction temperatures (1050À1400 °C). Each coal sample was devolatilized at 950 °C in a nitrogen atmosphere to become coal char, and it was further heated to reach the desired temperature for gasification with CO 2 under isothermal conditions. Temporal variations of CO and CO 2 concentrations were measured using a real time gas analyzer with a nondispersive infrared (NDIR) CO/CO 2 sensor. The reactivity increased as the volatile matter content and alkali index of the coal increased. In addition, the reactivity increased as the particle size decreased for a given temperature. The shrinking core model (SCM) was better for higher particle sizes, whereas the volume reaction model (VRM) was better for smaller particle sizes.

Effect of operating parameters on coal gasification

“…As the bed temperature increases, the carbon conversion during gasification reaction increases by oxidation, Boudouard and water gas shift reaction which shows almost linear relationship. Results of Xiao et al (2006) are in good agreement with the other authors (Liu et al 2008;Kim et al 2011). Corella et al (2006) have reported that gasification temperature has both the positive effect as well as negative effect on coal gasification reaction.…”

“…In contrast to above results, Miura et al (1989) and Hurt et al (1991) have reported that the pore structure is not a factor which controls the gasification reaction rate of highly reactive char. Jenkins et al (1973), Beamish et al (1998), Messenbock et al (2000), Zhang et al (2006) and Kim et al (2011) have reported that the reactivity of coal char during gasification is dependent on volatile matter content in coal and rank of coal. Reactivity of char is directly proportional to the volatile content of coal, i.e., reactivity of char increases with increase in volatile matter content (Beamish et al 1998;Zhang et al 2006;Kim et al 2011).…”

“…Jenkins et al (1973), Beamish et al (1998), Messenbock et al (2000), Zhang et al (2006) and Kim et al (2011) have reported that the reactivity of coal char during gasification is dependent on volatile matter content in coal and rank of coal. Reactivity of char is directly proportional to the volatile content of coal, i.e., reactivity of char increases with increase in volatile matter content (Beamish et al 1998;Zhang et al 2006;Kim et al 2011). Messenbock et al (2000 reported the variation of volatile content of coal with respect to change in pressure.…”

“…Higher gasification temperature increases the carbon conversion which improves gasification rate. Kim et al (2011) have reported the effect of temperature ranging from 1050 to 1350°C on carbon conversion during gasification. They found that as the gasification temperature increases gasification time required for carbon conversion decreases.…”

Numerical Simulation of Char Particle Gasification

“…A considerable amount of literature is available in which gasification of char is presented. Kim, et al [10] prepared char from 12 different bituminous coals at different reaction temperature for the gasification with CO 2 under isothermal conditions. The concentration of CO and CO 2 measured using online gas analyser.…”