Resumo

BUNT, J.R.; MARX, S.; WAANDERS, F.B.  e  LEOKAOKE, N.T.. Green coal development for application in fixed-bed catalytic gasification. J. S. Afr. Inst. Min. Metall. [online]. 2018, vol.118, n.4, pp.419-429. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2018/v118n4a12.

A novel 'green coal' product formulation has recently been developed and the utilization concept tested at the North-West University coal research laboratories. Hydrothermal liquefaction was used to produce bio-oil and biomass char from sweet sorghum bagasse at operating temperatures ranging between 280 and 300°C, and the resultant char was mixed in various ratios (0, 0.25, 0.50, 0.75, and 1) with fine medium-rank C bituminous discard coal (<212 μm) and CaCO₃ (1-5 wt%). The mixtures were pressed into 12 χ 12 mm pellets using an LRX press at a pressure of 4 bar and gasified using CO2 at atmospheric pressure and temperatures ranging between 800 and 1000°C. Kinetic parameters obtained from the experimental data showed that the reaction rate of the biochar was an order of magnitude higher than that of raw coal, with the blend containing 3 wt% CaCO₃ having the fastest reaction rate. In order to study the effect of temperature and catalyst on the retention of elemental sulphur during combustion of the various pellets, a combustion set-up consisting of a furnace, glass bayonet-type reactor, Liebig cooler, liquid traps, and an SO₂ gas analyser was used, with experiments conducted at temperatures between 500 and 800°C. As expected, sulphur retention was low for the raw coal and biochar blends, but increased significantly to between 56 and 86%, decreasing with increasing temperature, in the runs with added metal catalyst/sorbent. A simulation using FactSageTM predicted that >50% of the pyritic sulphur entering the fixed-bed gasifier would be removed from the gaseous phase as insoluble CaSO4 when operated in a catalytic gasification mode at a temperature of 800°C, which is in good agreement with the experimental findings.

Palavras-chave : Coal briquette; catalytic gasification; reactivity; sulphur retention.

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