| Closed-circuit circulation drying is a drying operation with drying medium circularly moisture absorption and dehumidifying in the system.With the advantages of solvent recovery,safety,environmental friendly,and high product quality,but relatively high energy consumption.A heat pump is a method which absorbing heat from low temperature heat source and emitting heat under high temperature.Application heat pump method to the closed-circuit circulation drying can not only recovering heat of the hot and humid gas before dehumidification,but also saving the cooling and dehumidifying cooling capacity,resulting in significant energy savings.In this paper,heat pump method with two condensers was applied to secondary drying process of closed circuit circulation.In the process,wet material was dried in the first dryer to remove water,then further dried in the second dryer to obtain the final product.While the wet-hot exhaust gas of the first dryer was first treated by dust removal and pre-cooling,then dehumidified by the low-temperature heat pump working fluid in the evaporator;after the dehumidification,the gas was heated by the high-temperature heat pump working fluid in the second condenser and then used in the second dryer as carrier gas;the exhaust gas of the second dryer should go through a dust remover then be pressurized,then heated by the high-temperature heat pump working fluid in the first condenser to obtain hot carrier gas for the first dryer.The gas was circulated in the system.The process owns one more condenser than a traditional heat pump drying system,which can adjust the inlet gas temperature of the first and second dryers.In the process,Regenerators are used to further reduce the energy consumption of the heat exchange between wet-hot gas and dehumidified gas.In this research,R134 a was selected as the heat pump working fluid.The effects of evaporation temperature,condensation temperature,and superheat degree of superheat on the COP of the heat pump performance parameters were simulated and analyzed.The results showed that the evaporation temperature increased from 0°C to 20°C.The COP increased from 2.68 to 4.81;when the condensation temperature was increased from 50°C to 70°C,the COP decreased from 3.9 to 2.56;the degree of superheat is lower than undercool the degree of COP.The effects of different auxiliary heat sinks,regenerators,cycle ratios,and number of condensers and drying stages on the dehumidification energy ratio(SMER)were simulated and analyzed.The results show that the combined heat sink of the auxiliary cooler and the regenerator has a higher SMER;the regenerator recovers energy.With the increase,COP increased from 3.66 to 4.21,SMER increased from 2.89kg/(kW·h)to 3.66kg/(kW·h);as the cycle ratio increased,SMER showed a trend of increasing first and then decreasing.A maximum of 3.4kg/(kW·h)occurs at 1.0.Increasing the number of condensers and drying stages can increase SMER.Based on the simulation analysis,under the conditions of an evaporation temperature of 5°C,a condensation temperature of 55°C,and a superheat degree of overcool of 5°C each,heat balance of material in the double-condenser heat pump closed-circuit circulation secondary drying system was calculated.Major equipment calculation and auxiliary equipment selection have been achieved.The construction drawings of major equipment were drawn using CAD and SolidWorks software.PLC control system was designed.A double condenser heat pump closed-circuit circulation secondary drying experimental platform for drying the first and second stage fluidized beds with two vertical inert supports was customized and built.The experiment was carried out under spraying water into the bed of two vertical inert fluidized beds condition.The device was commissioned and tested.The results show that: SMER is between 1.1kg/(kW·h)~1.5kg/(kW·h).The effects of evaporation temperature,circulation ratio,and the flow rate of the two condensers on COP and SMER were studied experimentally.The results showed that when the evaporation temperature increased from 13.8°C to 29.4°C,the COP increased from 1.67 to 1.86,and the SMER increased from 1.48kg/(kW·h)to 1.65kg/(kW·h);large,SMER first rises and then falls,there is a maximum 1.86kg/(kW·h)at 1.0;when the dryer 1,dryer 2 are in the dry constant speed phase,deceleration phase,increase the condenser 1 The flow rate of the working fluid can increase SMER.Reheater before and after evaporator can increase SMER.The efficiency of the entire heat pump drying device is about 20%-40%.The experimental value is smaller than the theoretical value,but the two trends are the same. |
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