Studies On Ignition Characteristics Of Two Parallel Bias Pulverized Coal Jets And Application

The Horizontal Bias Combustion?HBC?technology has been widely used in the tangentially fired utility boilers by the large scale boiler works of Harbin,Shanghai,Dongfang and Wuhan.In this technology,the fuel-rich and fuel-lean streams are respectively burned in the reducing atmosphere and oxidizing atmosphere,and most current study concentrated on the ignition characteristics of single atmosphere and single Primary Air?PC?/Pulverized Coal?PC?stream,which can't illuminate the ignition process of bias combustion accurately.Now days,the primary zones of tangentially fired utility boilers with air-staging combustion technology are in a reducing atmosphere,therefore the bias PC combustion simulator which can simulate ignition and combustion process of one bias PC straight jet burner in actual tangentially fired boilers was set up in this paper,and the ignition characteristics,formation characteristics of Particle Matter?PM?in a reducing atmosphere were studied,which are not only advance the existing PC combustion theory,but also enable the rational development of HBC techniques and industrial application.The Thermal Gravimetric Analysis?TGA?of combustion test of Australia bituminous coal,Indonesia sub-bituminous and their 1:1 blended coal were carried out,and the parameters of ignition temperature and ignition stability index of experimental coal were acquired.The numerical simulation on parallel bias PC jets ignition was conducted to optimize the design of the simulator.The 250-k W bias combustion simulator?BCS?with six jets coaxial intersection and ignition was set up.The standoff distance and combustion reaction intensity magnitude of volatile and char were analyzed quantitatively by the method of flame spectrum respectively,combined with analysis of combustion temperature distribution trend in the ignition zone,to get the ignition characteristics of parallel bias PC jets,such as ignition mode and flame stability.The gas analyzer and Electrical Low-Pressure Impactor?ELPI?were applied at the outlet of primary zone and back-end flue gas duct respectively,and the effects of combustion conditions and fuel properties on the formation characteristics of PM and NO_x under reducing atmosphere were studied.The key design parameters of HBC burner were acquired basing on the principle of shorter standoff distance,higher peaks of subsequent combustion temperature and visible-light intensity,stronger flame stability,higher PC burnout rate and less NO_x formation under homogeneous–heterogeneous combined ignition mode.The experimental results of the PA properties effect on ignition characteristics of parallel bias PC jets indicate that the radiation heat transfer from the hot environment had more effect on the ignition than the convection heat transfer from high-temperature flue gas in the initial stage,while the convection heat transfer from high-temperature flue gas played a greater role in the subsequent combustion of the char.While PAV was no less than 16m/s,the ignition of PC fuel-rich jet was better that of the fuel-lean jet,and the continuous flame region of parallel bias PC jets leant more obviously in the direction of the fuel-rich jet.While the PAV was16m/s,the standoff distance was shortest,the peaks of subsequent combustion temperature and visible-light intensity were highest,the flame was strongest,the burnout rate was highest and the NO_x formation was least.For bituminous,at PAVs of 13 and 16 m/s,there was homogeneous–heterogeneous combined ignition mode.For sub-bituminous,at PAV of 16 m/s,there was homogeneous–heterogeneous combined ignition mode.For blended coal,at PAVs of 14,16 and 22 m/s,there was homogeneous–heterogeneous combined ignition mode.With increasing of Primary Air Temperature?PAT?,the standoff distance gradually decreased,the peaks of subsequent combustion temperature and visible-light intensity gradually increased,the flame stability gradually increased and the NO_x formation became less.At PATs of 85°C and 100°C,there was homogeneous–heterogeneous combined ignition mode;there was homogeneous ignition mode at PAT of 70°C.Based on the research results in this paper,the recommended PAV of HBC burner was 16²0m/s.The experimental results of the effects of Pulverized Coal Concentration?PCC?on ignition characteristics of parallel bias PC jets indicate that with the increasing of initial PCC and Concentration Ratio?CR?within the range of experiment,the standoff distance gradually decreased,the peaks of subsequent combustion temperature and visible-light intensity gradually increased,the flame stability gradually increased,the burnout rate gradually increased and the NO_x formation decreased.For bituminous,as initial PCC increased from of 0.28 to 0.47kg/kg,there was homogeneous–heterogeneous combined ignition mode.For sub-bituminous,at initial PCCs of 0.33 and 0.41kg/kg,there was homogeneous–heterogeneous combined ignition mode;there was homogeneous ignition mode at PCC of0.53kg/kg.While CR was no less than 3,there was homogeneous–heterogeneous combined ignition mode.Based on the research results in this paper,the recommended CR of HBC burner within the range of experiment was 4⁵.The experimental results of fuel properties effect on ignition characteristics of parallel bias PC jets indicate that with the decreasing of Raw Coal Equivalent Moisture?RCEM?and Pulverized Coal Fineness?PCF?within the range of experiment,the standoff distance gradually decreased,the peaks of subsequent combustion temperature and visible-light intensity gradually increased,the flame stability gradually increased,the burnout rate gradually increased and the NO_x formation decreased.The RCEM had negative effects on the ignition in the early stage but had positive effects on the subsequent combustion.At PCFs R₇₅of 12%and 16%of bituminous,there was homogeneous–heterogeneous combined ignition mode;there was homogeneous ignition mode at PCF R₇₅of 26%.When the RCEM of PA/PC jets reached to respective moisture content of each raw coal,as the sequence from bituminous,blended coal to sub-bituminous,the standoff distance gradually increased,the peaks of subsequent combustion temperature and visible-light intensity gradually decreased,the flame stability gradually decreased,the burnout rate gradually decreased and the NO_x formation increased.Bituminous was homogeneous ignition mode,sub-bituminous and blended coal was homogeneous–heterogeneous combined ignition mode.The ignition characteristics of blended coal tended to sub-bituminous,and the burnout characteristics of blended coal tended to bituminous.There are six elevations of PC burners in the#4 boiler of one power plant from South Korea.The PC burner of HBC was designed based on the research results of this paper,which was installed on the elevation E of boiler#4.Under same conditions,the NO_x emission concentration at inlet of boiler SCR was reduced to236 mg/Nm³ from 265mg/Nm³,the NO_x emission per generation power reduced 11%and the ammonium spraying amount reduced 42 kg/h.The experimental results of formation characteristics of PM under bias PC jets combustion process in a reducing atmosphere indicate that particle size distributions of PM₁₀from bias PC combustion in a reducing atmosphere differed from those in the tail flue gas of a PC boiler,which exist only one peak at most.The least PM_0.38and PM_0.38–₁₀were produced for sub-bituminous at initial PCC of 0.41kg/kg.With increasing of CR,the ignition characteristics of blended coal gradually became better,the reducing atmosphere of PC fuel-rich jet gradually strengthened,and the formation of PM_0.38and PM_0.38–₁₀0 gradually decreased.The most amounts of PM_0.38and PM_0.38–₁₀were produced at PAV of 16m/s which provided the best ignition characteristics.For different coal type,the least PM_0.38-10.38-10 was produced for sub-bituminous;least PM_0.38.38 was produced for blended coal.As PCF and RCEM increased,the formation of PM_0.38.38 and PM_0.38-10.38-10 decreased.