Study On Operation Characteristic Of Self-driving Wet-hot Flue Gas Total Heat Recovery System

Absorption heat exchange technology is a widely used energy-saving technology at home and abroad.The technology uses lithium bromide absorption heat pump unit to recycle the flue gas generated during combustion,which can greatly improve the thermal efficiency and fuel utilization rate of the boiler.However,at present,common absorption heat exchanger units need to be driven by external heat source,which to some extent increases the construction and operation cost of the system,and thus has an impact on the overall energy saving effect of the system.In order to solve the above problems,a new type of boiler flue gas waste heat recovery system without external heat source is proposed.The system is driven by the waste heat of the high-temperature section of flue gas,thus completing the deep recovery of its own waste heat.According to the characteristic of gas that " the process of condensation heat transfer is carried out in stages",the flue gas heat exchanger is designed as a threestage structure,and then the overall structure of the system is determined.After determining the calculation method of flue gas composition and thermal parameters,the mathematical models of lithium bromide absorption heat pump unit and flue gas heat exchanger were established respectively.The degree of freedom of the whole system’s mathematical model is analyzed,and the number of known parameters for solving the thermal state of the system is determined.Based on the thermodynamic model of the self-driving wet heat flue gas full heat recovery system,the solution model for the maximum heat recovery capacity of the system is constructed by using the concept of terminal temperature difference.The indicators to characterize the applicability of the system are put forward from the technical and economic perspectives respectively.The influence trends of flue gas and secondary water inlet parameters on the minimum outlet temperature of flue gas,heat recovery rate of flue gas,energy-saving enlargement factor,static investment recovery period and net income balance period of waste heat recovery of the system are studied.The maximum heat recovery rate of the system can reach 11.6%,and the minimum in the balance period of net income of waste heat recovery is 5.2 years.The thermodynamic characteristics of the condensation heat transfer process are studied when the flue gas’ s temperature and humidity change greatly.A new calculation principle of the flue gas’ s condensation heat transfer process is proposed.On this basis,the calculation model is solved by using the "two-stage iteration" algorithm.A practical example is introduced to compare and analyze the difference between the calculation results obtained by using the calculation principle and the dry-bulb humidity efficiency method.The dates show that the disparity of heat transfer between the two methods is 22.5%.The piecewise algorithm presented in this paper has high reliability and is more suitable for the calculation of heat and mass transfer process of flue gas with large temperature drop and large dehumidification capacity.The operation simulation model of the self-driving wet-hot flue gas total heat recovery system is constructed and is solved by iteration algorithm.The operating characteristics of self-driving system under different working conditions are studied,and the changing trends of flue gas outlet temperature,secondary water outlet temperature and total heat transfer of flue gas are analyzed when the inlet temperature,flow rate of flue gas and the inlet temperature and flow rate of secondary water change.The debugging and data acquisition of a mine air supply preheating project in Jixi City using the self-driving system are completed,and the economic analysis of the system is carried out by using the measured data.The results show that the flue gas flow rate and the inlet temperature have great influence on the total heat transfer of the system.The heat transfer increases by 37.6% when the flow rate increases by 50%.The research results of this paper can provide theoretical guidance for the design,calculation and operation debugging of the self-driving wet-hot flue gas total heat recovery system.