Numerical Simulation Study on Thermal Performance of Tubular Boiler after Surface Combustion Modification
The use of surface burners is currently the mainstream technology in the low nitrogen transformation of tubular boilers.Based on the ANSYS software and taking the actual running boiler as the research object,conducts numerical simulation research on the flow characteris-tics,temperature characteristics,heat transfer characteristics and emission characteristics of the fuel and air mixture after the surface combus-tion transformation of the cross-flow boiler,and obtains the flow velocity characteristics of the cold and hot fuel and air mixture and flue gas,the hot flue gas flow field distribution,the temperature field and CH4 distribution in the furnace,and the concentration distribution of CO2 and NOx,The water pipe wall temperature distribution,etc.Through simulation,it is found that the flow direction of the flue gas changes when it passes through the first return exit,and due to the reduction of the flow section of the flue gas,the flue gas velocity increases as it gets closer to the first return exit,and the maximum velocity exists in the channel formed by the inner tube and the outer tube.The calculation of radiant heat load on the heating surface shows that the radiant heat load is significantly reduced after the surface combustion transformation compared with the original design of the boiler with the diffused burner.The outer water pipe at the first return of the flue gas is vertically washed by the high temperature flue gas without sufficient heat exchange at high speed,resulting in high temperature of part of the outer water pipe,and the repeated action of overheating and thermal fatigue stress makes the water pipe easy to produce dense cracks.From the point of view of heat transfer,it is concluded that the water pipe at the outlet of the first return passage after surface combustion transformation of cross-flow boiler is prone to crack due to overheat fatigue.
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