99/00638 The effect of coal particle size on pyrolysis equilibrium

Abstract

This chapter discusses the effect of heating rate on normal and catalytic fixed-bed hydropyrolysis on a UK bituminous coal, the Wyodak Argonne Premium Coal Sample, and the high sulfursulfursulfur Mequinenza lignite at a pressure of 150 bar. The tar yields and the conversions increased markedly by 5–20% daf coal as the heating rate is decreased from 300 to 5°C min-1, both with and without a sulphided molybdenum catalyst, demonstrating the value of slow heating in analytical applications of hydropyrolysis that include the determination of organic sulfursulfursulfur forms in coals. Pyrolysis processes are associated with much lower yields of liquid products than vehicle solvent liquefaction processes. A sulphided Mo or other suitable dispersed catalyst is required as tar yields without catalyst are typically no more than 35%. For low-rank coals, catalysts are less effective at high pressure, increasing tar yields typically by less than 10% daf coal, but without a catalyst, the tar yields of 40–50% are appreciably higher than for bituminous coals. Rapid heating is used in process situations; slow heating is being applied in the analytical applications of hydropyrolysis to specify organic sulfursulfursulfur forms in coals and to release covalently bound biomarkers. The conversions approaching 100% could be obtained at 600°C for low-rank coals with slow heating.