Evaluation of process configurations to produce hydrogen from black liquor

Black liquor is the residue from the kraft paper pulp process and consists, mainly, of water, lignin, organic residues from cellulose and hemicelluloses and inorganic matter (mostly sodium, potassium and sulfur). Before any combustion or gasification, the dry content of the black liquor is increased, typically from 14-18% to 75-80%, to permit autogenous combustion and high conversion efficiency of the fuel value to superheated steam. The main reason to produce hydrogen or other energy carriers in a pulp mill is that there is a surplus of energy and fuel available, from wood waste and spent pulping liquor, in modern, stand-alone pulp mills. The reason to use black liquor to produce hydrogen is that it is easier to process black liquor, a pumpable liquid, and an extremely reactive fuel, in a pressurized gasifier than it is to process solid biomass.