Black liquor is generated in paper and pulp mills as a by-product of the kraft pulping process. Nearly all of the black liquor generated is currently used to produce the heat, steam, and electricity used to run the mill. Excess electricity is sold in the electricity markets and constitutes the largest component of existing bioenergy production.
The demand for wood at U.S. paper and pulp mills in 2010 is projected to be 218.6 million green tons, increasing to 304.4 million green tons in 2050. Black liquor yields are equal to 40-50% of the wood used in bleached pulping processes and 50-65% of the wood used in unbleached processes. The average moisture content of black liquor is 25-35% water.