Elsevier

Fuel

Volume 60, Issue 9, September 1981, Pages 779-787
Fuel

Comparative investigations of coal pyrolysis under inert gas and H2 at low and high heating rates and pressures up to 10 MPa

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Abstract

Five German hard coals of 6–36 wt% volatile matter yield (maf) were pyrolysed at pressures up to 10 MPa, using two different apparatuses, which mainly differ in the heating rates. One consists of a thermobalance where a coal sample of ≈ 1.5 g is heated at a rate of 3 K min −1 under a gas flow of 3 I min−1. The other apparatus is constructed for rapid heating (102−103 K s−1) of a small sample of ≈10 mg of finely-ground coal distributed as a layer between the folded halfs of a stainless-steel screen, heated by an electric current. The product gas composition was determined by quantitatively analysing for H2, CH4, C2H4, C2H6, CO, CO2 and H2O. The amounts of tar and char were measured by weighing. The heating rate, pressure and gas atmosphere were varied. Under an inert gas atmosphere, high heating rates result in slightly higher yields of liquid products, e.g. tar. The yields of light hydrocarbon gases remain the same. With increasing pressure, the thermal cracking of tar is intensified resulting in high yields of char and light hydrocarbon gases. Under H2, pyrolysis is influenced strongly at elevated pressure. Additional amounts of highly aromatic products are released by hydrogenation of the coal itself, particularly between 500 and 700°C. This reaction is less effective at higher heating rates because of the shorter residence time and diffusion problems of H2. The yield of light gaseous compounds CH4 and C2H6 increases markedly under either heating condition owing to gasification of the reactive char.

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  • Influence and action mechanism of pressure on pyrolysis process of a low rank Naomaohu coal at different temperatures

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    One is the decrease of char yield under pressurized condition, known as the promoting effect. Due to the high volatile and hydrogen content of Naomaohu coal, at low temperature, tar free radicals and coal char undergo hydrogenation reaction, gas products and tar increase, and the char yield decreases [24–26], increasing the pressure within a certain range promotes this process. Furthermore, pressurization enhances the heat transfer rate of coal char and the movement rate of molecules [27], causing an increase in the release rate of volatiles and a decrease in the probability of secondary reactions of tar.

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Presented at the Conference: ‘Industrial Conversion of Coal and Carbon to Gas, Liquid and High-Value Solid Products’ organized by the Industrial Carbon and Graphite Group of the Society of Chemical Industry, and held at the Society of Chemical Industry, 14, Belgrave Square, London SW1X 8PS, UK, 7–9 April 1981.

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