Coal Adaptability Analysis In A 240t/h Tangentially Pulverized Coal-fired Boiler

The research on wide coal type adaptability for the operation of existing boilers is a key technical problem that urgently needs to be solved in recent years.For a 240 t/h tangentially fired cogeneration boiler,which is designed for anthracite,the combustion of the inferior bituminous coal is expanded by modifying the existing burner without changing the main structure of the boiler.As the range of fuel application is broadened,it is necessary to conduct a comprehensive analysis and evaluation of the operational impacts of the boiler's milling system,furnace combustion,heat transfer,flue gas side heat exchange,fly ash,desulfurization and denitrification.By analyzing the operational status of the current pulverized coal burners,it is proposed to replace the existing concentrating and separating burners with a blunt body burner.Without changing the size of the burner nozzle,the primary air nozzles can be replaced within a certain length,to accommodate the burning of low calorie bituminous coal.In this paper,the combustion characteristics of five bituminous coals are analyzed experimentally,including proximate analysis,ultimate analysis calorific value analysis,ash melting point test and ash composition analysis.The purpose of the comparison with those of the original design coal is to discuss the changes of primary air temperature,wind speed,smoke volume and fly ash amount from anthracite to bituminous coals,and thus proposing the adjustment strategy of the operating parameters of the milling system.On this basis,the reasonable distribution of the exhaust air,combustion air and SOFA is analyzed to maintain the proper temperature of the furnace exit flue gas.On the basis of the analysis of coal quality characteristics and the corresponding adjustment of the operating parameters,FLUENT 16.0 software was used to simulate the combustion process of different coals in the furnace.The temperature field,velocity field,wall heat flux density,component concentration distribution and the furnace outlet parameters were obtained,to explore the response of the coal type change in the furnace process and analyze the adaptability of the boiler burning bituminous coal.The results show that after the conversion of anthracite to bituminous coal,the tangential combustion of the furnace is in good condition,and the average heat flux density of the overall wall of the furnace is basically consistent with the designed coal type.Due to the delay of ignition,the center position of the combustion flame is slightly elevated under the condition of bituminous coal,and the temperature level of the burner area is about 100°C lower than that of the designed coal type.The increase of the amount of low-calorie bituminous coal approximately offsets the difference in heat release and transfer in the furnace.The simulation results show that the temperature level of the middle and upper zone of the furnace is basically the same as the design coal type working condition,and the furnace outlet flue gas temperature is similar to the designed coal type.When the bituminous coal is burned,the CO concentration in the center of the furnace increases obviously.The concentration of O₂ in the furnace wall and the burner jet area is higher,maintaining a relatively high oxygen concentration environment,which is beneficial to prevent water wall from slagging and high temperature corrosion.At the same time,taking into account the increase in fuel amount,the amount of fly ash is increased?about 10%at full load?,while the total flue gas volume in bituminous coal conditions is slightly reduced.The simulation results show that the flue gas velocity at the boiler exit is slightly reduced,and the smoke density does not change significantly,meaning the increased amount of fly ash does not have a serious impact on boiler operation.The paper achieves a combustion control of the existing boiler with a small transformation.It provides a basis for the use of wide range of coal types,and also provides an effective method for the modification and operation optimization of similar systems.