开式吸收式热泵型真空干燥系统建模及性能分析

针对传统谷物干燥能耗高,粉尘、废热污染严重,干燥品质较差的问题,提出了一种连续型谷物真空干燥系统,该系统采用开式吸收式热泵回收利用谷物在干燥过程中产生的水蒸气及其汽化潜热,兼具低温真空干燥与热泵节能的双重优势。以连续型真空干燥滚筒实验为依据,设计了基于开式吸收式热泵的连续型真空干燥系统;建立了该系统的物质、能量守恒数学模型;并依托Aspen Plus软件对整个系统流程进行建模,分析了干燥压力、溶液热交换器效率、加热温度和稀溶液浓度对系统性能系数(coefficient of performance,COP)及干燥能耗的影响。结果表明:设计工况下系统COP为1.728 5,干燥能耗为3 346.92 kJ/(kg·H_2O),降低当前传统谷物干燥机能耗的37%;该系统在理论上具有可行性且节能效果显著。提高溶液热交换器效率、降低加热温度以及降低稀溶液浓度均能提高系统COP,降低干燥能耗。

Modeling and Performance Analysis of Vacuum Drying System Based on Open Absorption Heat Pump

In order to solve the problems of high drying energy consumption, serious waste heat pollution and poor drying quality caused by traditional grain drying, a continuous grain vacuum drying system was proposed. An open absorption heat pump was used in the system to recycle the water vapor and its latent heat of vaporization generated during the grain drying, so this system has the dual advantages of low temperature vacuum drying and energy saving of the heat pump. Based on the experiments of continuous vacuum drying drum, a continuous vacuum drying system based on open absorption heat pump was designed. The mathematical model of matter and energy conservation of the system was established. The whole system process was modeled by Aspen Plus software, and the effects of drying pressure, solution heat exchanger efficiency, heating temperature and dilute solution concentration on the coefficient of performance(COP) and drying energy consumption were analyzed. The results show that under the design condition, the COP is 1.7285, and the drying energy consumption is 3 346.92 kJ/(kg·H20), which reduced 37% of the current energy consumption of the traditional grain dryer. Improving the efficiency of the solution heat exchanger, reducing the heating temperature and reducing the concentration of dilute solution can improve the COP and reduce the drying energy consumption.