What is Pyrolysis?
Pyrolysis is the process of heating organic material at high temperatures in the absence of oxygen. Since no oxygen is present, the organic material does not combust. Instead, the chemical compounds (i.e. cellulose, hemicellulose and lignin) that make up the material decompose into combustible gases and charcoal.
Pyrolysis of biomass produces three products – a liquid, a gas and a solid:
- Bio-oil: comes from the combustible gases of the process, which are condensed, into a liquid. Bio-oil can be used as a low grade diesel oil.
- Bio-char: is the solid material that is created in the process. Biochar is being promoted for its potential to improve soil properties and fertility as well as sequester carbon.
- Syngas: are the permanent gases (CO2, CO, H2, light hydrocarbons) that remain after the pyrolysis process is complete. Syngas can be used in place of natural gas or converted with catalysts to ethanol.
There are two types of Pyrolysis systems. Fast Pyrolysis optimizes bio-oil production by increasing the rate of pyrolysis temperature to 1000°C/second. This process yields approximately 60-70% bio-oil, 15-25% bio-char, and 10-15% syngas. In contrast, Slow Pyrolysis uses slower heating rates and bio-char is the major end product. In both process, the system is self-sustaining by harnessing the syngas to drive the reaction.
Pyrolysis has been used since ancient times to turn wood into charcoal. Today pyrolysis is being developed as a waste to energy technology to convert biomass and plastic waste into liquid fuels[refernce number =1].
Liquid fuels are projected to increase in demand and remain the most consumed fuel type for the next 30 years. The transportation sector relies heavily on petroleum based liquid fuels, which emit a significant amount of greenhouse gases. Pyrolysis presents an opportunity to manufacture low-carbon liquid fuels and decrease the emissions of the industry. In fact, Pyrolysis can be carbon negative if the bio-char produced is buried into the soil and used for crop enhancement instead of combustion2.
The fuels produced are considered second generation fuels since the feed stocks are from renewable sources, like waste and biomass. As a result, they are less carbon-intensive than fossil fuels.
These fuels are also compatible with our existing transportation infrastructure which eliminates the need to introduce costly new infrastructure.
Pyrolysis does have higher costs associated with the machinery and heating and is dependent on a supply of cheap biomass3. The quality of the bio-oil is also low grade and cannot be used in all applications where fossil fuels are used.
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