SiBiochar is the carbon-rich product obtained by heating biomass in a closed system under limited supply of oxygen. Currently, there are several thermochemical technologies such as pyrolysis, gasification, and hydrothermal conversion to produce biochar. Pyrolysisinvolves
the heating of organic materials in the absence of oxygen to yield a series of bioproducts: biochar, bio-oil, and syngas. Pyrolysis is a simple and inexpensive process which has been used to produce charcoal for thousands of years. However, traditional earthen and brick kilns used to produce charcoal usually vent a large amount of volatiles to the atmosphere, which causes air pollution. Modern pyrolyzers are designed to capture the volatiles for the production of bio-oil and syngas. Gasification is a thermochemical process where biomass is heated with a small amount of air to produce a main product-syngas and a byproduct-biochar. Hydrothermal conversion primarily focuses on using wet biomass to generate biooil. Biochar is a byproduct of that process as well.
Biochar can be used directly as a replacement for pulverized coal as a fuel. But one of major distinctions between biochar and charcoal (or char) is that the former is produced with the intent to be added to a soil as a means of sequestering carbon and enhancing soil quality. When used as a soil amendment, biochar has been reported to boost soil fertility and improve soil quality by raising soil pH, increasing moisture holding capacity, attracting more beneficial fungi and microbes, improving cation exchange capacity (CEC), and retaining nutrients in soil. Another major benefit associated with the use of biochar as a soil amendment is its ability to sequester carbon from the atmosphere-biosphere pool and transfer it to soil, moreover also may decrease emissions of other more potent greenhouse gases such as N2O and CH4.