Numerical Simulation Of MILD Combustion Of Coal-water Slurry Under Low Preheating Conditions

With the continuous development of industry,the energy crisis and environment problems become more and more serious.It's urgent to find out clean energy and combustion technologies,which can achieve high energy efficiency and low pollutant emission.Our national energy resources determines that coal is the basic energy status and will be the major source of energy for a long time.Coal-water slurry technology has been proved to be an effective way for the clean and efficient utilization of coal.Compared with heavy oil,raw coal and other fuels,coal-water slurry has good economic,energy-efficient and environment-friendly characteristics,which release low NO_x emission and can be easily transported.MILD?Moderate&Intensive Low Oxygen Dilution?combustion is a new combustion technology,which has characteristic of low pollutant emission,high energy efficiency,uniform temparature,low noise emission and so on.Integrating the MILD combustion and coal-water slurry technology can solve several problems in the combustion of coal-water slurry and expand the application of MILD combustion,which has a good prospect of industrial application.Based on the IRFR?International Flame Research Foundation?furnace,firstly we studied the difference of combustion characteristics and pollutant emission between conventional swirl combustion and MILD combustion with different concentrations of coal-water slurry by numerical simulation method.Secondly,the influence of diffusion on the MILD combustion of coal-water slurry under low preheating conditions was studied.Specifically,injection parameters,such as the primary air velocity,the separation distance and the injection angle between the primary and secondary air were examined.At last,the effect of CO₂ and H₂O on the MILD-Oxy combustion and pressurized MILD-Oxy combustion of coal-water slurry were studied under low preheating conditions.The results show that,under low preheating conditions,compared with the conventional swirl combustion,MILD combustion of coal-water slurry has stronger flue gas circulating flow,more uniform temperature distribution and lower NO_x emission.Under non-premixed combustion,the fuel nozzle arrangement can affect the mixing between the fuel and the oxidant,the internal flow field and combustion intensity,thereby affecting the furnace temperature distribution,burn-off time of the coke,pollutant formation and so on.Compared with the MILD-air combustion,the MILD-Oxy combustion has lower temperature and burn-off time of the coke,which shows a greater potential on NO_x reduction.CO₂ is more beneficial to reach MILD combustion and reduce NO_x emission as compared to H₂O,while H₂O can expand the high temparature region and improve the ignition of the coke.Moreover,elevating the furnace pressure can increase furnace temperature,accelerate devolatilization,strengthen gas diffusion,enhance combustion intensity,promote gasification reaction and reduce coke ignition time,which is beneficial to NO_x emission reduction.