Experimental and modeling study of pinewood char gasification with CO2

Abstract

The objective of this study is to measure apparent rate parameters for pinewood char gasification with CO2 using large particles with relevance to practical gasifiers. The novel features of this work include: (1) char gasification for CO2 recycling, which is studied less in the past than char gasification in other environments, (2) independent measurements involving gravimetric analyses and product gas composition gas chromatography, (3) detailed uncertainty analyses of both methods to report resulting uncertainties in kinetic rate constants, and (4) investigation of the char structure development and its role in gasification. A fixed-bed reactor providing a slip-velocity of 0.12m/s gasifier and control of the bed temperature to within ±10K at 1000–1170K is used. A low-ash (<0.01wt.%) pinewood char is selected to minimize the catalytic effects of ash on mass-loss rates. The char is prepared by heating pinewood sawdust in an electrical furnace to a temperature of 1100K. Gravimetric and product gas composition data are interpreted using the volumetric, non-reactive core and random pore models. The results show that the activation energies corresponding to these models are 217±6, 186±13, 125±30kJ/mol respectively. The random pore model shows the closest agreement with the experimental data, despite the uncertainties in the measured activation energies. The estimated random pore model structure parameter Ψ increases from 0 to 16.5 with increases in the gasification temperature. Measurements of BET surface area show significant increase with char conversion. The results of this study show that the apparent gasification rate parameters for relatively large particles of practical relevance are comparable to those obtained from laboratory studies with much smaller particles.