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Pyrolysis of some western Canadian coals in a spouted bed reactor Jarallah, Adnan Mohammed


Coal pyrolysis has been studied in a 12.8 cm diameter continuous spouted bed reactor with the aim of determining conditions for maximum liquid yields from Western Canadian coals. Coals studied included two British Columbia bituminous coals and one Alberta sub-bituminous coal. The basic characteristics of the spouted bed pyrolyzer were determined by carrying out experiments over a range of spouting gas velocities and composition, coal feed rates and particle size, reactor temperatures, and bed heights. The process was assessed by measuring the yields and compositions of the tar, char, and gas. Nitrogen and nitrogen/carbon dioxide mixtures and coal of size - 3.36 + 1.19 mm were fed at atmospheric pressure to an electrically heated reactor containing sand. The tar yield was determined by sampling the outlet gas through a series of cooled impingers. The spouted bed pyrolyzer behaves in a manner similar to a fluidized bed unit, and shows a maximum tar yield with temperature at a fixed feed rate. At a given pyrolyzer temperature, the tar yield was inversely proportional to the coal feed rate over the range 0.4 to 7.6 kg/h. This effect is attributed to the detrimental effect on tar yield of the increasing amounts of char present in the reactor as coal feed rate increases. Coal type strongly influenced the liquid yields as expected. Sukunka bituminous coal from the Peace River coal field gave a maximum tar yield at 600°C of 31% wt/wt MAF coal. The corresponding gas yield was 3.6%, and the char yield was 64%. The maximum tar yield from Balmer bituminous coal from Crowsnest coal field was 19.4% wt/wt MAF coal at 580°C while that from a high-ash Balmer bituminous coal was 12.1% at 620°C. Forestburg sub-bituminous coal from the Edmonton formation gave a maximum tar yield of 21% at 530°C and significantly higher gas yields of 20% versus 6% for the bituminous coals due to higher C02 production. With Sukunka coal, a steady increase in tar yield from 20.4 to 26.7% wt/wt MAF coal at 580°C was found as the average coal particle size was reduced from 2.28 to 0.65 mm. No significant effects on tar yield were found for variations in spouted bed depth, or vapour residence time over the range 0.68 -1.15 s. No serious problems were encountered with agglomeration. Composition of gas, tar and char are presented for conditions of maximum tar yield for the various coals tested. The H/C atomic ratio of the tars was as high as twice that of the parent coal. Oxygen, sulphur and nitrogen together represent up to 10 wt% of the bituminous coal tars, which suggests considerable upgrading will be necessary to produce liquids of quality comparable to petroleum oils. The total volatiles yield data were well represented by a first order kinetic model. An activation energy of 4.71 kcal/mole was obtained for the sub-bituminous coal while that for the bituminous coals was 14.1 kcal/mole.

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