Numerical Modeling Of Unsymmetrical Burning In 1000MW Dual Circle Tangential Firing Boiler

Currently,thermal power generation is the major power supply in China.The boiler,a key component of a plant,crucially influences the safety and efficiency of a power generation process.Unsymmetrical burning of boiler caused by the inlet flow deviation may change the distribution of heat flux and lead to overheating of local steam and cracking of water wall tubes.The model of a 1000MW dual circle tangential firing single furnace ultra-supercritical boiler was established in FLUENT.Numerical simulations under the boiler rated load(BRL)condition were conducted to investigate the unsymmetrical burning.After the simplification of the geometrical symmetry of the boiler,simulations of the inlet deviations at nozzle No.1 or No.2 were carried out.The conditions of the deviations of the secondary air and the coal flux at different heights were studied in this work.To evaluate the risk of unsymmetrical burning,the heat flux distributions of water wall in each unsymmetrical burning case were compared to those under the BRL condition.Under the secondary deviation conditions,the results show that the deviation of the heat flux distributions is much more on the left part than that on the right part of the boiler.For the one nozzle air flow deviation of 10%increase,air deviation at No.1 nozzle causes more obvious change in the flux than that at No.2 nozzle.The middle layer of the secondary air at either nozzle No.1 or No.2 has most impact on heat flux.Additionally,heat flux decreases on left wall,but increases on the left part of font and rear wall.For the two nozzles air flow deviation of 10%increase on three layers including low,middle and high layers of the secondary air,the heat flux distributions on side,rear and front are impacted most evidently by the air deviations on these three layers respectively.Furthermore,the heat flux increases on left wall but slightly decreases on right wall in above conditions.However,the variation of heat flux on front and rear wall shows similar but more obvious trends compared with one-nozzle deviation cases.For the two nozzles air flow deviation from 10%to 30%increase on middle layer of the secondary air,30%increase causes the most significant variation of heat flux distribution on left and front wall,however,a peak of heat flux variation on rear wall appeared when air flow increases 20%.For the two coal nozzles conditions with 10%coal flow increase at three different heights,the coal flux deviation of the nozzles at higher results in more distinct deviation of heat flux.In addition,coal flow deviation leads to a heat flux increase on left wall but a converse and slighter change on right wall.Meanwhile,similar changes of heat flux happens on the left part and right part of both front and rear wall,but particularly,the lowest level on which coal flux deviation occurs impacted rear wall most.When two coal nozzles flux deviate from +10%to +30%at third layer,the condition of 20%coal deviation caused the most significant horizontal transfer of heat flux.In particular,the direction of coal deviation on middle nozzle showed consistency with heat transfer.