NUMERICAL SIMULATION ON THE COMBUSTION PROCESS IN THE FURNACE OF A LIGNITE-FIRED USC BOILER

摘要

The Computational Fluid Dynamics (CFD) code PHOENICS and reasonable mathematical model were applied to investigate the combustion process in the furnace of 1000 MW lignite-fired ultra supercritical unit with a single furnace and double-tangential firing system. The influence of different primary air ratios (35% and 42%) on the flow, mixing characteristics of the gas-solid two-phase flow, the combustion process in the furnace was focused on. The results indicate that in the furnace with double tangential firing, the flow field shows two well-symmetrical ellipses at different primary air ratios. The surface temperatures of the burners at which, the long axis of the ellipses pointed, are much higher than those in the other four corners. Thus the phenomenon of ‘Hot corners’ and ‘Cold corners’ arises. In practical operating, the flow erodes the walls in the hot corner which may lead to high temperature corrosion and slagging. The NOx distributions are similar at different primary air ratios. By the comparison of the parameters such as NOx emission and char burnout, the situation with the 35% primary is preferable. The results of this paper have value because of the support they lend to the design of USC lignite-fired boilers.