Question

Assuming that electricity will be produced, compare the use of a pyrolysis or gasification system to a conventional mass burn combustion system. Under what conditions would a pyrolysis or gasification system be used?

Answer 1

Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere. Pyrolysis is most commonly used to the treatment of organic materials. It is one of the processes involved in charring wood. The phenomenon involves exceeding the decomposition temperature of the material. pyrolysis occurs at temperatures in the range of 400 to 800ºC. With the addition of heat the biomass breaks down to condensable vapours, non-condensable gases (pyrolysis gas), and charcoal. In some cases a limited amount of air, not enough for gasification, may be admitted to promote the process by heat generation. The pyrolysis gas contains carbon monoxide, carbon dioxide, hydrogen, methane and higher hydrocarbons. The condensable vapours form a liquid known as bio-oil or pyrolysis liquid, which contains a wide range of oxygenated chemicals and water. All products are combustible. Which can be burned to generate electricity. Gasification  process is the conversion by partial oxidation (i.e. more oxidizing agent than for pyrolysis but less than for complete combustion) at high temperature (>800°C) of biomass into a gas. This gas, commonly called "producer gas" if the oxidizing agent is air and "syngas". Steam can be added with the oxidant to promote gasification or used as an oxidant by itself. Gasification is used both on fossil and no fossil fuels. Gases generated are combustible and used in electricity generation. We have seen how in pyrolysis we get fuel in all 3 forms liquid gas and solid but in gasification everything is being converted to gas.