Effect of Thermal Flux

The products resulting from the thermal destruction of hy-drocarbonaceous solids depend upon the maximum temperature of pyrolysis and the time needed to bring the feed to this temperature. The products formed during slow heating are far different than the products obtained during rapid heating. At very slow heating rates to low temperatures, the molecule has sufficient time to break at the weakest level and reorganize itself into a more thermally stable solid that becomes increasingly hard to destroy. On rapid heating to a high temperature, the molecule explodes and forms a range of smaller organic molecules.

For the cellulose molecule, slow heating forms high char yields and low gas and liquid yields. The gas is composed primarily of CO, H2O, and CO2 and has a low heating value. For rapid heating rates and high temperature, the gas yield increases and the liquid is smaller. The gas is composed primarily of CO2, CO, H2, CH4, C2H2, and C2H4 and has a reasonable heating value. For intermediate heating rates and temperatures, high liquid yields are obtained. The gas produced is composed of many C1, C2, C3, and C4 compounds and has a high heating value.

Table 10.12.1 shows some values obtained for pyrolysis gas obtained at 1300 and 1600°F at a slow heating rate in a retort. For comparison the table also shows 1450°F pyrolysis at a high heating rate in a fluidized bed. Both systems pyrolyzed MSW.

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