Influence of potassium carbonate on the swelling propensity of South African large coal particles

Abstract

The swelling propensity of some coals may restrict their use in fixed- and fluidized-bed gasification operations, and effective reduction of swelling can widen the applicability of these coals. Extensive research has been published on the influence of additives on the swelling of pulverized coal (<500 μm), but limited knowledge exists on the influence of additives on large coal particle swelling behavior. This paper presents an investigation on the influence of K2CO3 on the extent of swelling of 5, 10, and 20 mm particles, which are suitable sizes for fixed- and fluidized-bed operations. Three South African coals were selected: TSH coal (FSI 9), GG coal (FSI 5.5–6.5), and TWD coal (FSI 0). Large coal particles (5, 10, and 20 mm) were impregnated with a 5.0 M K2CO3 solution, and the K-loading increased by a factor 9–33. Maximum K-loadings of 3.3, 3.0, and 1.4 wt % K (coal basis) were obtained for the 5, 10, and 20 mm particles, respectively. The volumetric swelling ratio (SRV) of the 20 mm GG particles was reduced from 3.0 to 1.8, and for the TSH particles from 3.1 to 2.1. The TWD coal particles showed SRV values up to 1.7, in contrast to the nonswelling behavior of the pulverized (−212 μm) coal, and were not influenced by the K2CO3 addition. It was concluded that K2CO3 only influences the volumetric transformation of coals that undergo significant plastic deformation, such as GG and TSH. Comparison of the maximum swelling coefficients showed that K2CO3 impregnation reduces the kA from 0.025 to 0.015 °C–1 for GG and from 0.013 to 0.009 °C–1 for TSH. The results show the viability of using an additive for swelling reduction of large coal particles, and together with further development, may be a suitable method for reducing unwanted swelling in relevant coal utilization processes