A study of high pressure pinewood char gasification with CO2

Abstract

This work involves CO2 gasification of a pinewood char at temperatures between 1140K (867°C) and 1260K (987°C). Novel features of this work include: (1) measurements of char conversion for large (∼3mm×1mm×1mm) char particles at pressures up to 10±0.1atm, (2) Thiele analysis of the char conversion data to quantify the influence of internal heat-and-mass diffusion on apparent reaction rates, and (3) an assessment of the nth order and the Langmuir–Hinshelwood kinetics rate models for elevated pressures. Pinewood sawdust with low ash content (<0.01 wt.%) is pyrolyzed at 1100K to produce char particles. The dry char particles are gasified to CO with 99.9% purity CO2 in a fixed-bed reactor. Product gas composition analysis enabled by gas chromatography is used to track char conversion with time. The results show that conversion rates for the char particles are limited by diffusion of gases through the pores. The results also show that the surface CO concentrations during the gasification process exceed the bulk CO concentrations by as much as an order of magnitude. Therefore, internal mass transfer resistance and CO inhibition must be considered in calculations of apparent char conversion rates.