Study On Mixed Combustion Characteristics Of Coal-bed Methane & Pulverized Coal In A 600MW Boiler

Coal-bed methane is a harmful gas produced in mining process,in which the main combustible gas is methane.Coal-bed methane resources are abounded in China,and the recoverable resource is the third in the world.However,the methane concentration is too low in the most of mine.It is difficult to use by conventional technologies,and the methane is discharged into air directly after diluted.The greenhouse effect of methane is twenty-three times of CO2,therefore,the diluted coal-bed methane discharged into air will lead to energy waste and environmental damage.Based on the above analysis,this thesis aims to achieve the double benefits of energy conservation and environmental protection by using coal bed methane as auxiliary fuel in current thermal power generation technologies.The author takes a 600 MW pulverized coal boiler as the research object.Based on the practicability analysis of the coal-bed methane as primary air or secondary air admixed in the boiler,the effect of combustion characteristics is studied by numerical simulation.The research results provide the support for the technical transformation of the boiler.As this technical transformation of sending coal-bed methane into boiler has not been applied in practical,the practicability should be analyzed at first.Based on the study of the geographical location,safety,economic and environmental,62955.6 tons(standard coal)are saved every year and the emission of greenhouse gas is been reduced if both the primary air and secondary air are replaced by Ventilation Air Methane(VAM),which means that the boiler blended with VAM has great potential in energy conservation.Based on the single burner,the effect of the way sending the ventilation into burner is studied.The results show that compared with the original condition,the temperature in furnace decreases by 66 K when both the primary air and secondary air are replaced by VAM,and the scope is the most obvious.The area of carbon monoxide in the center of furnace increases,which is helpful to reduce NOx formation.The combustion characteristics in furnace under different conditions has been analyzed for the research object when both the primary air and secondary air replaced by VAM.The influence of VAM concentration,the OFA volume and the boiler load on combustion and NOx emission is studied.The results show that the average temperature of the horizontal section in C-D burner decreases by 22 K when VAM concentration increases from 0 to 1.5%.Meanwhile NOx concentration in furnace outlet decreases from 540.57mg/Nm~3 to 519.24mg/Nm~3,and the scope is obvious comparatively.The retention time of pulverized coal in furnace has been reduced by 0.43 s,which means the combustion efficiencydecreases.When the methane concentration in VAM is 1%,the temperature in main burner region decreases,and the temperature at OFA region increase.NOx concentration in furnace outlet decreases by 17.82% at most.However,the efficiency of carbon conversion reduces from 96.95% to 96.07%,which means the increase of the heat loss from solid incomplete combustion.When the boiler loads decrease from 600 MW to 300 MW,the temperature in furnace decreases,and NOx concentration in furnace outlet decreases from 503.86mg/Nm~3 to392.84mg/Nm~3.The retention time of pulverized coal in furnace increases from8.03 s to 17.00 s,so the combustion efficiency of pulverized coal increases.