Studies on Gasification of Coal under Pressure

Abstract

Rapid pyrolysis of Taiheiyo coal was studied at 900°C and argon pressure-50atm. An increase in argon pressure to 50atm caused the secondary decomposition of tarry materials in the interspace among coal particles, which led to an agglomeration of coal particles as well as an increase in char yield.It was suggested that the overall pyrolysis of coal proceeded with the following reaction sequence.Decomposition of coal → fast decomposition of volatile → slow reactions between product gases(primary decomposition) (secondary reactions)Compared with slow heating at 3.3°C/min, rapid heating of coal enhanced the yield of unsaturated gaseous hydrocarbons such as ethylene and propylene. The unsaturated hydrocarbons were converted to methane when the secondary reactions were forced to proceed by elevating the pressure or prolonging the residence time of product gases.Effect of pressure and product-gas residence time on the distribution of gaseous hydrocarbons were quantitatively well expressed by a reaction model which was concerned only in the last step in the above sequence.