NUMERICAL SIMULATION OF THE OPTIMAL RECYCLING RATIO IN THE BOILER WITH FLUE GAS RECYCLING

摘要

Pointed to the 420t/h comer tangential boiler with flue gas recycling, the combustion process and NOx emission characteristics were simulated in a power station. Integrated with the direct flow burner and flue gas recycle techniques, the flue gas recycle ratio was adjusted to reduce the NOx emission as much as possible. Simultaneously, the combustion stability and operation economy and security were ensured. The software Fluent was used for the calculation and k-ε model was used in the turbulent flow. Discrete random walk model was used for pulverized coal. Non-premixed combustion model was used for combustion. The simplified PDF model was used to calculate the reaction and element transfer. On the other hand, NOx was calculated by the post-processing method. The calculation results showed that the average and highest temperature distributed in the boiler with the flue gas recycling was decreased obviously. At the same time, the NOx emission concentration was decreased sharply, which was consistent with the test results. There existed an optimal recycling ratio. In view of the effect of furnace temperature on ignition and fully combustion, the optimal flue gas recycling ratio was achieved , which was between 15% and 20%.