Reduction of Caking Propensity in Large (Millimeter-Sized) South African Coal Particles with Potassium Carbonate Impregnation To Expand Fixed- and Fluidized-Bed Gasification Feedstock Suitability

Abstract

The caking propensity of coal causes challenges in combustion, gasification, and fluidized-bed applications, where this property limits coal selection. Certain gasifiers are fitted with mitigation technologies such as stirrers to overcome operational problems associated with caking. However, additive addition is a possible alternative method with benefits such as reduction of caking and swelling and increased reaction rates. It is known that select additives alter the coal’s thermoplastic behavior, where studies have predominantly focused on powdered coal. Here, large coal particles (5, 10, and 20 mm) suitable for select fluidized-bed and gasification applications, from three South African coal fields, were examined. The coals have different thermal swelling characteristics: Highveld (TWD) (FSI 0), Grootegeluk (GG) (FSI 5.5–6.5), and Tshikondeni (TSH) (FSI 9) (where FSI is the free swelling index). Digital photography, SEM, and X-ray computed tomography were used to evaluate the caking propensity during d...