Numerical simulation and verification of combustion optimization of 600 MW tangentially coal-fired boiler after flexibility retrofit
After completing the flexibility retrofit of a 600 MW tangentially coal-fired boiler,several issues arose during high load operation,including large flue gas temperature deviations at the furnace outlet and difficulties in controlling NOx emissions.To address these challenges and deter-mine the optimal operating parameters of the boiler,a three-dimensional model of combustion,flow and heat transfer in the furnace was constructe dusing the computational fluid dynamics software.The established model employed the standard k-ɛ model to describe fluid flow,the two-step competition model to simulate the release of volatile matter in coal,the dynamic/diffusion control model to explain the coke combustion reaction,the Lagrangian stochastic trajectory models to consider the two-phase flow process of pulverized coal particles and flue gas,the P1 radiation model to calculate the radiation heat transfer in the furnace,the finite rate/eddy dissipation model to simulate the gas phase combus-tion,and NOx mass concentration in flue gas was calculated based on the simulated combustion field in a post-processing way.The effects of excess air coefficient α,primary air rate β and secondary air angle θ on furnace tangential combustion and NOx emission at the outlet were analyzed in the condition of 100%BMCR.The numerical results show that the optimal operating parameters are α=1.1,β=30%and θ=0° to achieve both good tangential combustion and low NOx emission.The simulation results were validated by a boiler combustion adjustment test.The test results demonstrate that under the optimal operation parameters,NOx mass concentration at the economizer outlet of the boiler is reduced by 9.96%,exhaust gas temperature is reduced by 2.66%,flue gas temperature deviation is reduced by 2.26%,and the boiler efficiency is improved by 0.28%.
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