Lee Enterprises Consulting, Inc.

Lee Enterprises Consulting, Inc.


Pyrolysis refers to the decomposition or transformation of a compound caused by heat. Pyrolysis and gasification are two related process, differing mostly by temperature and process reactants. As discussed in other sections, low temperature pyrolysis can be used to produce various products including torrefied wood, biochar and biocarbon. High temperature pyrolysis is used for converting waste materials, e.g., municipal solid wastes, tires, biomass, etc., into electrical energy or other products. The process is performed in the complete absence of oxygen and generally performed in the 800⁰C range. The process thermally decomposes the organic materials into carbon char, combustible gases (carbon monoxide and hydrogen), and tars.

The gases and tars are often burned in a subsequent step using air as the oxidizer to produce steam for operating a steam turbine powered electric generator. Care must be taken in a pyrolysis system to keep all equipment at high enough temperatures so that the tars do not condense on equipment where they can become a significant maintenance challenge. The carbon char produced is co-mingled with the ash that is dependent on the feedstock material being pyrolyzed. For example, municipal solid waste ash contains an ash fraction in the range of 20% to 25%. This ash-carbon residual is generally disposed in landfills and can have small quantities of hazardous metal constituents. The cost of disposal negatively affects the process economics and can vary widely in different regions.

Public acceptance is an issue in many locations as fear of emissions is perceived with any high temperature process. However, gas cleaning equipment can be used to minimize emissions. Pyrolysis units are treated much like and incinerator for permitting purposes.

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