Several types of equipment are available for the pyrolysis of waste. The general types include retorts, rotary kilns, shaft kilns, and fluidized beds. The type of equipment and the manner of contacting have a significant effect on the pyrolysis product yield.
The retort has the longest application history and has been used extensively to make wood charcoal and naval stores. It is a batch system where the retort is charged, sealed, and heated externally. The heating cycle is long (often over twenty-four hours). The products are complex. They are normally solid char and a pyroligneous acid plus the gas produced which is used as the energy source for indirect heating. The process is limited by the rate of heat addition; a typical analysis for demolition lumber shows a yield of 35% char, 30% water, 12% wood tar, 5% acetic acid, 3% methanol, and 15% gas with a heating value of 300 Btu/cu ft.
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