Black liquor (BL), a by-product of the papermaking process, is an important liquid fuel in the pulp and paper industry. It consists of the remaining substances after the digestive process where the cellulose fibres have been cooked out from the wood. This report is aimed to provide a comparison of the recovery boiler with a pressurised gasifier for black liquor. Fundamentals concerning the conversion of black liquor, some details about the two recovery technologies and differences between these two will be presented.
In industrial chemistry, black liquor is the waste product from the kraft process when digesting pulpwood into paper pulp removing lignin, hemicelluloses and other extractives from the wood to free the cellulose fibers.The equivalent material in the sulfite process is usually called brown liquor, but the terms red liquor, thick liquor and sulfite liquor are also used.