Numerical Simulation And Optimization Of The Gas Temperature Deviation In A 660MW Supercritical Wall-tangentially Fired Boiler

In China, the tangentially fired boiler has been widely applied to coal fired power plants for many advantages. Its main feature of tangentially fired furnace is the rotation of airflow, forming the low-pressure rotation center to entrain high temperature flue gas,to make the airflow fully mixed. And the good fire condition and stable combustion environment are formed. Moreover, the particles stay for a long time in furnace, which helps to burn out. However, due to the limited height of the furnace, the residual airflow rotation in the outlet still persists, resulting in the flue gas temperature deviation and speed deviation at the left and right side of the horizontal flue, which makes the screen of superheater and reheater uneven heated. Then thermal deviation phenomenon occurs;especially, over-temperature tube rupture of heating surface may happen. Therefore, it is of great significance to study the flue gas temperature deviation of the furnace exit to improve the safety, reliability and economic efficiency of boiler.In this paper, a 660 MW wall tangentially supercritical boiler was numerically simulated about the optimization of flue gas temperature deviation. Under the benchmark conditions, the simulation results and experimental results about the furnace outlet parameters were compared. The simulation results were consistent with the experimental,confirming the feasibility of the simulation. It showed that, a good tangential combustion with low emissions of NOx was formed, and coal particles had a long residence time,which helped to burn. Before entering the bottom of separate screen the furnace temperature distribution and flow velocity distribution were symmetrical. However, due to the formation of a counter-clockwise flow in furnace, a residual rotary airflow occurred in the outlet, and obvious flue gas temperature deviation appeared in the furnace exit. High temperature region concentrated on the bottom right corner. The furnace temperature distribution and flow velocity distribution showed a left-low and right-high trend, in the furnace exit cross-section.Based on the baseline conditions, simulation and experimental work were both done by sequentially adjusting horizontal swing angle of separate over-fire air, secondary air and separate over-fire air damper opening. And we analyzed the impact of three changing conditions on the furnace exit flue gas velocity and flue gas temperature deviation. The results showed that, with horizontal swing angle of separate over-fire air swinging a counterclockwise angle, the rotary furnace airflow weakened, flue gas temperature deviation decreased, and the horizontal velocity and inscribed circle diameter of outlet section were reduced. With the secondary air damper opening increasing, the rotary furnace airflow increased, and the inscribed circle diameter and horizontal velocity component increased. However, with separate over-fire air damper opening increasing,the results were contrast with the secondary air. It was effective to reduce the flue gas temperature deviation of the left and right sides of the furnace exit, via adjusting three variable conditions.