Pore development during gasification of South African inertinite-rich chars evaluated using small angle X-ray scattering

Abstract

Pore development arising from steam and CO2 gasification of a char, prepared from an inertinite-rich Witbank Seam 4 coal, was investigated using small angle X-ray scattering. The char, ∼75 μm, was gasified to specific conversions (10, 25, 35 and 50%) using two gasification reagents, CO2 and steam. A novel ratio analysis technique was developed to study the pore development from experimental data. Differently sized pores grow at different rates with the difference not being simply due to gas accessibility. In particular, the pores between 1 and 40 nm in size showed more pore growth than larger or smaller sizes. Steam gasification created a more porous char with increased pore growth of pore sizes between 1 and 40 nm than CO2 gasification. The pore growth rate of steam was up to a factor 7 times faster than CO2, compared at the highest gasification temperatures. For the smaller pores, <1 nm, it was found that the rate of pore generation was slower compared to larger pores, though pore growth was still evident with the critical cross over pore size for CO2 to be 1 nm compared to 0.6 nm for steam. This may be a direct consequence of CO2's greater kinetic diameter.