Novel Design And Performance Research Of Mechanical Vapor Recompression For Low Temperature Drying

Drying is a traditional high-energy processes. Currently, the mainstream hot air drying andvacuum drying in the market exist the problem of thermal inefficiencies. Especially for heat-sensitivematerials,overheating the material will lead to generate pyrolysis and combustion phenomena. Withthe increasingly significant issue of the world energy crisis, the design and development of newlow-power and low-temperature drying system is imminent.In this paper, mechanical vapor recompression (MVR) technology will be used to design two setsof low-temperature drying systems, and conducting process simulation by Aspen Plus. The resultsshow that the MVR low-temperature drying system optimized by pinch technology energyconsumption is19.57kW, only7.7%of the conventional temperature drying system.In the mean while,the MVR low temperature drying system with air circulation energy consumption is minimum whichis18.55kW,7.3%of the conventional temperature drying system.But the complexity of the latter ismore than the former.Through analyzing the two sets of low temperature dying systems thermal economics, the authorfind both of them reach to the minimum total cost,when the the minimum temperature difference isbetween15K and20K,which should be the optimal design rang and provides experience for the futuredesign of low-temperature drying system. In addition, for the MVR low temperature drying systemwith air circulation, when the air flow is1300kg/h, the total energy consumption of the system reachesto minimum. Since then the the energy consumption increases. At the same time, with the fan pressureratio increases, the total energy consumption of the system decreases at first and then graduallyincreasing. So fan pressure ratio exists a value, which total energy consumption is minimal.Calculation result show that when fan pressure ratio near2.0, the system total energy consumption isminimal.Further, through comparing the two design solutions, the result show that with the increase of theevaporation temperature, the total energy consumption of both systems are increased, too. The MVRlow-temperature drying system total energy consumption is always greater than the MVR lowtemperature drying system with air circulation.When the compressor pressure ratio is2.6,the MVRlow-temperature drying system total energy consumption is minimal.While the MVR low temperaturedrying system with air circulation compressor ratio is2.0. The author also analyze the lower cost andenergy consumption ratio under the different temperature difference.The result is when the minimum temperature difference is less than20K, the MVR low temperature drying system with air circulationenergy efficiency is higher than the MVR low-temperature drying systems.Setting up the exergy model of each main component, and analyzing the systems exergy loss tofind the main damage parts of the systems, then research the affect of the different evaporationtemperature and minimum temperature difference for these systems. The analysis results show that theexergy loss of heater dryer and compressor are largest, MVR low temperature drying systemaccounted for the total exergy loss94.6%and74.8%since the MVR low temperature drying systemwith air circulation.With the increase of evaporation temperature, the system exergy efficiency islower;MVR low-temperature drying systems and the MVR low temperature drying system with aircirculation exergy efficiency also increase with the minimum temperature difference decreasing.When the minimum temperature difference is15K, both of systems are almost equal efficiency andthen exergy efficiency of the MVR low temperature drying system with air circulation is lower thanMVR system exergy efficiency, the gap is increased.Finally, the thesis introduces the principle of the entransy and simplifies the optimized principles.Establishing entransy dissipation model of system based on the principle. The result shows that thedryer dominates the system entransy dissipation.Reducing the minimum temperature difference orincreasing the moisture content of the final product can reduce system entransy dissipation.