Application of Different Combustion Models for Simulating the Co-combustion of Sludge with Coal in a 100 MW Tangentially Coal-Fired Utility Boiler

摘要

Co-combustion of sludge with coal is a promising sludge disposal approach. In this study, three different combustion models, including different turbulent gas-phase combustion and char surface combustion sub-models, were employed to simulate the combustion and emission characteristics of co-combusting sludge with coal in a 100 MW tangentially coal-fired utility boiler. By comparison of the numerical results from different combustion models to a set of full-scale coal-sludge co-combustion field experiments, a precise and suitable computational fluid dynamic (CFD) model was finally developed. The comparison result demonstrated that the finite-rate/eddy-dissipation model together with the multiple-surface-reaction model, which have carefully considered the effect of high moisture content on the fuel ignition and char combustion processes, were competent in modeling the characteristics of coal sludge co-combustion. On the basis of the developed numerical model, the ignition, char burnout, and NO, emission characteristics of co-firing different mass contents of sludge were further investigated. The result demonstrated that co-firing sludge with coal would cause a slight delay on the fuel ignition and a decline on the char burnout. The high moisture and high nitrogen in sludge had a dual promotion effect on NO formation, leading to an increase of NO, emission after co-firing sludge.