Fuel nitrogen release during black liquor pyrolysis; Part 1: Laboratory measurements at different conditions

Fuel nitrogen release during black liquor pyrolysis is high. There is only minor release during the drying stage. Ammonia is the main fixed nitrogen species formed. The rate of fixed nitrogen release increases with increasing temperature. The level of fixed nitrogen released by birch liquor is almost twice the level for pine liquor. Assuming complete conversion to NO, fixed nitrogen yields gave NO concentrations near typically measured values for flue gases in full scale recovery boilers. The purpose of this work was to gain more detailed information about the behavior of the fuel nitrogen in black liquor combustion. The work focused on the pyrolysis or devolatilization of the combustion process. Devolatilization is the stage at which the majority (typically 50--80%) of the liquor organics release from a fuel particle or droplet as gaseous species due to the rapid destruction of the organic macromolecules in the liquor. In this paper, the authors use the terms devolatilization and pyrolysis interchangeably with no difference in their meaning.