Heat Recovery Thermal Calculation On Reconstructed Terminal Heating Surface Of District Heating Boiler

As is known to all,coal,as one type of fossil fuel is non-renewable.Because of the reserve characteristics of China's natural resources,coal is the most consumable primary energy,it is one of the most important issue to reduce coal consumption at this stage.Therefore,it is one effective solution to reduce coal consumption without impacting the heating effect by further improving the efficiency of district heating industrial boiler.There is a lot of flue gas with high temperature to be formed in the boiler during the combustion process.The working fluid will be heated in the heat exchanger inside the boiler.Then the temperature of the flue gas will go down but be still high relatively.It will be apparent to reduce the energy efficiency if the flue gas is discharged directly.Therefore,generally the tail heating exchanger will be considered to take full advantage of such part of energy.The tail heating exchanger,such like the economizer and air pre-heater will be installed in the boiler to reduce the exhaust gas temperature and improve the boiler efficiency.And the configuration of the tail heating exchanger has a great influence on its efficiency.Such study is based on the boiler with type no.of QXL90-1.6/150/90-A?of the boiler renovation project from one heating company in Shenyang,China.The boiler grate and furnace in the foresaid boiler had been renovated to improve the boiler efficiency.The thermal calculation of the tail heating exchanger of the boiler has been done and further the new configuration scheme has been released and applied on such renovated boiler.The outlet temperature and pressure of the flue gas in the tail part of the boiler under six different boiler operation conditions has been measured after the renovation.And further the revised thermal calculation of the tail heating exchanger of the boiler has been done based on the measured data.Then the factors on heat transfer amount and the inlet & outlet temperature are obtained by comparing the data from the revised thermal calculation with the data from the theoretical calculation under same boiler operation condition.After calculation and studying,it turns out that cross flow heat transfer is superior than lengthways flow heat transfer.It will fulfill the requirement of exhaust gas temperature and improve the capacity of heat transfer and the economical efficiency under the same boiler structure by replacing two units of air pre-heater with economizer.The biggest change of heat transfer happens on tube tank No.1 of the tail part of the boiler and the second biggest change of heat transfer happens on the ceiling tube tank when boiler load is changed.The actual volume of flue gas changes all the time because of the pressure difference between the inlet and the outlet and the flue gas regulating valve opening.The temperature of the inlet & outlet of air pre-heater and economizer will change caused by the change of the fuel gas distribution ratio.It is found out that it is complicated and time-wasting to look up numerous tables again and again during the iteration process of the thermal calculation.It will reduce the value error and increase the accuracy of the calculation by replacing the interpolation calculation and reduplicative table look-up with multiple fitting for the enthalpy of the fuel gas and the physical property of the working fluid.It is not flexible that the structure of the heating exchanger should be considered again when the form of the boiler is changed.The thermal calculation will be adjusted based on the simulation analysis conclusions,which is really helpful to reduce the deviation between the thermal calculation value and actual measured value of the boiler furnace and improve the practical applicability of the calculating value.