BASIC STUDIES ON BLACK-LIQUOR PYROLYSIS AND CHAR GASIFICATION

Pressurized gasification of black liquor is a promising alternative for increasing the electrical-energy production in chemical pulp mills. Design constraints include gasification equilibria and kinetics and constraints imposed by the sodium-sulfur chemistry in the recovery of pulping chemicals. Complete gasification of the organic fraction of black liquor is thermodynamically possible with air ratios exceeding 0.3. The theoretical temperature limit for complete gasification decreases with increasing air ratio and decreasing pressure. Conversion of the organic fraction to gases during pyrolysis is kinetically controlled and increases with increasing pyrolysis temperature. Significant sodium-fume formation, in the order of 20% of the sodium in black liquor, is found during pyrolysis at high heating rates.