Plasma ignition technology has good flexibility in load variation,short ignition/start-up time,low emission,and high economic efficiency.It is widely used in the deep peak shaving transformation of coal-fired power units and is one of the main measures to achieve low load stable combustion in power plant boilers.In recent years,the promotion of medium speed coal mills in high moisture lignite units has provided convenient conditions for the application of high moisture lignite plasma oil-free ignition technology.However,traditional plasma ignition technology is mostly suitable for coal of high-quality such as bituminous coal.There are problems with insufficient ignition energy,the need for oil gun to assist ignition,and poor fuel economy when burning high moisture and low calorific value lignite.A bias con-centration slit type multi-stage cylinder structure plasma ignition burner for pulverized coal was developed.Tests under different operat-ing conditions using plasma oil-free ignition were conducted on a 660 MW lignite unit with a total moisture content of 35％-40％of the raw coal.The effects of coal quality and unit operating parameters on the oil-free ignition characteristics of high moisture lignite were ana-lyzed.An improvement plan for the plasma burner was proposed based on the test results.A numerical simulation was conducted on the high moisture lignite plasma burner under the benchmark operating conditions.The effectiveness of the burner modification was compared and discussed.The ignition test results show that the new plasma ignition system can ignite high moisture lignite with a heat generation of 10 900-13 400 kJ/kg and achieve oil-free start-up of the unit.The burner has a small adaptability range to coal quality.Excessive igni-tion energy,small gap between the central and the secondary cylinder of the burner,and poor cooling effect is prone to overheating of the secondary cylinder,causing coke formation and burning damage.Putting the plasma generator into operation has little effect on NOx emis-sion when the units are under steady operation.The numerical simulation results show that the burner used in the ignition test burns prema-turely due to the excessive concentration of plasma heat absorbed by the coal powder in the first stage combustion tube,resulting in over-heating of wall of the combustion tube and coke formation on the inner wall.The central flame temperature inside the first and second stage combustion tubes of the burner significantly decreases after being improved.The flame temperature at the end of the third stage com-bustion tube tend to be consistent.The highest wall temperature of the burner is 376℃,which is about 74℃ lower than that before im-provement.The improvement plan reduces the erosion of concentrated pulverized coal on the end face of the inlet of the first stage combus-tion cylinder.The amount of coal in the first stage combustion cylinder is increased and the ignition process is optimized.In short,the de-velopment and optimization of new plasma burners can achieve stable and efficient ignition of high moisture lignite units with a wide range of coal quality.It can provide technical support for the construction of the first high moisture lignite oil-free power plant in China.
high moisture ligniteburnerplasmanumerical simulationoil-free ignition
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