GB1090728A - Pyrolysis of coal - Google Patents

Abstract

Coal is distilled at low pressure, i.e. at up to 500 p.s.i.g., in at least three fludized bed stages in succession, the beds being at successively higher temperatures. In the first stage the coal is heated at a temperature below its fusion temperature, e.g. at 600 DEG to 650 DEG F., until 1 to 10% b.w. of the dry coal has been removed as volatiles, in the absence of added O2 and of oily vapours from the coal in the succeeding beds; in the second stage, which may comprise two beds in series at different temperatures (see Figs. 1, 2 (not shown)), the coal is heated at a temperature below its fusion temperature (a total range of 700 DEG to 1050 DEG F. is mentioned) in the absence of added O2 for a time sufficient to remove nearly all volatiles condensible to oily liquids; and in the final stage, the coal is substantially devolatilized e.g. at 1500 DEG to 1800 DEG F., air or O2 being supplied to fluidize and partially combust the coal. The first stage is fluidized by hot inert (e.g. flue) gas, which heats the coal, but the second stage may be fluidized by distillation gases from stage 3 or by an inert gas. External heating may be applied to both stages. Some recycling of the char from the later sub-stages of sta to the earlier sub-stages may be carried out (see Fig. 2) to prevent agglomeration, and the vapours from the top of stage 2 and from stage 1 are delivered to a condenser. Residence time in all the stages and sub-stages may be 1 to 30 minutes. Three specific examples are described.