Three-dimensional kraft recovery furnace model: implementation and results of improved black liquor combustion models

A three-dimensional mathematical model of a kraft recovery furnace was improved by developing better models of black-liquor combustion. These new models - which describe combustion of black-liquor drops and black-liquor deposits on the furnace walls and char bed - include mechanisms for sodium sulfate reduction and carbon removal by CO 2 and H 2 O gasification. Black-liquor combustion is fully coupled to the solution for gas-phase combustion and turbulent flow in the furnace. Predicted black-liquor combustion patterns are presented for a commercial-scale recovery furnace, including chemical species distributions, temperature maps, and component reaction rates for char burning and smelt reduction. Carbon removal rates for gasification, oxidation, and sulfate reduction are compared and evaluated for entrained particles, furnace walls, and the char bed. Predicted smelt-reduction efficiencies are compared with commercial performance. Application : better models of black-liquor combustion provide more realistic simulations of the kraft recovery furnace.