Experimental Research On Waste Heat Recovery And Purification System Of Direct Expansion Heat Pump

The energy system of modern society is developing in the direction of cleanliness and efficiency,China actively optimizes the energy supply structure and promotes the improvement of energy quality.The proportion of natural gas in the country's total energy consumption has continued to increase,and has risen to 7.8%in 2018.The flue gas temperature of conventional gas boilers is high,and the flue gas contains a large amount of latent heat of condensation that needs to be recovered;and Beijing has implemented a 30 mg/Nm³ gas boiler exhaust smoke nitrogen oxide concentration emission limit to limit the environmental pollution caused by smoke exhaust.In order to comprehensively deal with the problems of latent heat of condensation in flue gas and nitrogen reduction of flue gas,this article combines combustion air humidification technology and direct expansion compression heat pump technology,and proposes a direct expansion heat pump type flue gas waste heat recovery and purification system.Recycling system composition.In the humidification system,the humidified water is used as the medium to transfer the high-temperature sensible heat of the flue gas to the combustion air.The driving force is the temperature difference between the heat exchange materials.The high temperature heat in the flue gas can ensure the effect of preheating and humidifying the combustion air,thereby improving the nitrogen reduction effect of the boiler exhaust.In the waste heat recovery system,driven by a heat pump,the latent heat of medium and low temperature flue gas is transferred to the return water of the heat network to achieve low temperature emission of flue gas.In order to analyze the effect of the increased water vapor of combustion air humidification on combustion air and flue gas composition,this paper first uses the EES software to analyze the amount of combustion air required and the amount of flue gas produced per unit gas combustion,and the moisture content of each combustion air The effect of conversion of flue gas nitrogen oxides concentration is discussed.Then,the 58kW gas boiler is used as the flue gas source to conduct an experimental study on the direct expansion heat pump type flue gas waste heat recovery and purification system.According to the characteristics of the system structure,the experiment was conducted from three aspects:the humidification effect of the humidification system composed of the finned tube high-temperature heat exchange section and the combustion air humidification tower and its effect on the nitrogen reduction of the boiler;Effect;the spray system formed by the spray water loop has an influence on the recovery of waste heat and the performance of the heat pump.The main parameters that can be controlled are boiler load,humidification water flow,waste heat recovery water flow,waste heat recovery water temperature and spray water flow.The results show that the experimental system has good nitrogen reduction and waste heat recovery effects.The nitrogen oxide concentration is reduced by up to 54.38%,and the exhaust temperature can be reduced to 24.46?.The NO_X content of boiler exhaust gas decreases with the increase of the moisture content of the combustion air,and the moisture content of the combustion air increases with the increase of the boiler load and the increase of the liquid-gas ratio.When the boiler load rate is 90%and the liquid-to-gas ratio is 25.16,the maximum moisture content of the combustion air is 59.54 g/kg_dry.At this time,the NO_X content of the boiler exhaust gas is 47.61 mg/m³,far lower than the concentration of 104.35mg/m³ without humidification.The amount of waste heat recovery increases with the increase of the flow rate of waste heat recovery water and the decrease of water temperature.At 40?water temperature and 1853 L/h flow rate,the amount of waste heat recovery is 5.390 kW;with the increase of the boiler load and the decrease of the humidified water liquid ratio,the90%load When the liquid-gas ratio is 3.39,the amount of waste heat recovered is 5.448 kW.The heat pump power consumption decreases as the boiler load decreases,waste heat recovery water temperature decreases,and water flow increases.At 90%load,40?water temperature,and 1853 L/h flow rate,the heat pump COP is up to 3.1.The effect of the sprinkling water system on the recovery of waste heat is enhanced,and the heat gain from waste heat can be increased by 0.25 kW⁰.46 kW.The shortest investment payback period for the system is 3.0 years.Due to the introduction of additional power consumption in the heat pump,improper operating strategies have caused an increase in operating costs.