| Strengthening low-temperature waste heat recovery is of great significance for further improving the economics and improving energy efficiency of cogeneration units.This article starts the research on the energy-saving transformation of a 330MW cogeneration unit,this paper proposes to use absorption heat pump technology to recover the low-temperature waste of recycling water and flue gas after wet FGD.Option 1 uses an absorption heat pump to directly recover the low-temperature waste heat of the circulating water;Option 2 uses a flue gas heat pump quality improvement and utilization system which is coupled with a flue gas deep waste heat recovery device and an absorption heat pump unit.The technical route is:energy exchange occurs between refrigerant water and flue gas in the fluoroplastic heat exchanger,the refrigerant water in the heat exchange tube absorbs the heat of the flue gas,then enters the heat pump as the low-temperature heat source of the heat pump,and the heat network backwater is heated by the heat pump driven by the high-temperature heat source.By analyzing the low-temperature waste heat resources and heating status of a cogeneration unit during the heating season,36℃/30℃ is used as the design parameter of the low-temperature heat source of the heat pump unit.Then compare the calculation results of the mathematical model of the absorption heat pump unit built with Excel with the simulation results of the absorption heat pump model built by Ebsilon software,and results show that the relative error of the two calculation methods is within the allowable range of industrial design.Under the design conditions,the COP value of this absorption heat pump unit is 1.73,which can recover 17.40MW of low-temperature waste heat of circulating water.After the 55℃heating network circulating waterwas to heated to 75℃ by absorption heat pump,it continues to be heated by high temperature and high pressure steam to 130v to supply heat users.In this paper,a simple energy conservation model for the desulfurization tower is constructed,and the flue gas at the outlet of the wet FGD tower is calculated to be 1585.11t/h,the moisture content is 0.083kg/kg dry flue gas,and the temperature is 50.25℃ at the rated coal burning capacity of the boiler.Observing the conservation of energy and the conservation of mass,a set of flue gas-water fluorine plastic heat exchanger coupled with the absorption heat pump is designed.The heat transfer coefficient of this heat exchanger is 120.93W/(m2.K),which decreases the temperature of the flue gas to 46.40℃.The heat exchanger can recover 17.40MW waste of low-temperature flue gas,of which 15.44MW is latent heat,accounting for 88.74%of all waste heat.At the same time,the moisture in the flue gas can be recovered at 23.34t/h then returned to the desulfurization tower.In addition,when the water vapor in the wet flue gas is condensed,it can carry part of the dust,thereby playing a role of deep purifying the flue gas.Using Ebsilon software to build three models of unit steam extraction heating scheme(as the benchmark scheme),circulating water waste heat heat pump quality improvement and utilization system scheme(Option 1)and wet desulfurization flue gas waste heat heat pump quality improvement utilization system scheme(Option 2).The thermal economic indicators of three different models of heating schemes when the power generation rate is 295MW and the heating load is 157.21MW are compared.Option 1 and Option 2 can decrease the standard coal power generation by 3.40kg/kW.h,and reduce the amount of standard coal for heating by 2.12 kg/GJ,reduce coal consumption by 6340t in the heating season,and increase fuel utilization factor by 1.50%,and recover low-temperature waste heat of the power plant by 17.40MW.It can save 6340t of standard coal,and reduce the emissions of S02,C02,NOX and soot by 104.13t,153.38kt,98.90t and 60.86t respectively.Option 2 can also recover 23.34t/h of water in the whole heating season.This paper estimates the system investment and benefits of Option1 and Option 2.Based on the theory of time value,dynamic evaluation methods are used to calculate the dynamic investment payback period,annual cost value,and NPV value of Option 1 and Option 2.It is concluded that the dynamic investment recovery period of Option 2 is slightly longer than that of Option 1,but the former has the functions of recovering waste heat,moisture,and purifying flue gas deeply,so the overall benefit of Option 2 is better.In the case of higher emission requirements,priority is given to the Option 2 heating system. |
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