Experimental Study And Numerical Simulation On A Low-NO_x Semi-anthracite Coal Swirl Burner

Low grade coal,such as semi-anthracite,have higher ignition temperature,higher carbon burnout of fly ash and higher NOX emission due to low volatile content.To be retrofitting to the ultra low pollution emission,low NOX burner is the preferred low-cost NOX control technology.Thus,it has attracted more interests in the low NOX combustion research for semi-anthracite.To address the problem of low burnout,higher NOX emission(approximately 750mg/Nm3)in a 600 MWe thermal power plant,a method combined computation fluid dynamics(CFD)with pilot-,factory scale experiments were adopted in this paper,and then the pulverized-coal swirl burner was studied and optimized.The results of cold modeling experiments and CFD for an original swirl burner showed that there exits annular recirculation zone while smaller center recirculation flow out of the burner.To further excavate the gas-solid phase motion and the ignition and combustion of coal particles out of the burner,a CFD model was developed and verified by the pilot-scale experiments in a 30 MW combustor in Harbin boiler research center,and the chemical dynamics of semi-anthracite was investigated in a flat burner at Tsinghua University.The results showed that there has no recirculation flow zone near the burner nozzle,which cause higher flame temperature and lower burnout,and the NO_x emission reaches at 932 mg/Nm3(@7.67%O2)in the outlet of 30 MW furnace.With the help of CFD simulation,the original swirl burner was optimized where the structure of primary air,inner secondary air,outer secondary air,and the position of pulverized coal concentrator and flame-stable bluff body in the burner exit were involved.CFD results showed the combustion-stable tooth can decrease the expansion angle and increase NO_x emission slightly;the rich coal particle holding the inner position is more good for NO_x emission and burn-off rate as the opposite structure caused very high NO_x concentration;the swirl number of inner secondary air is somewhat complex,its impact to the recirculation flow and ignition is not in one-way;the whole swirl number has a positive effect to the expansion angle and negative to the ignition distance.The optimized swirl burner was verified by cool model experiments,and wasinstalled in the 600 MW power plant,where the NOX emission was reduced to453.2mg/Nm3(2.9%O2)at 100% boiler load.