硫酸废液机械蒸汽再压缩减压膜蒸馏特性分析

为了高效回收处理工农业生产过程中产生的硫酸废液，该研究提出了一种机械蒸汽再压缩减压膜蒸馏系统。首先，基于质量和能量守恒定律建立数学模型，并设计搭建了系统试验装置，初步以自来水为测试对象开展了可行性验证试验；然后以硫酸溶液为研究对象，借助Matlab软件进行迭代求解计算，模拟分析操作参数对系统热力特性的影响规律。试验结果表明系统膜通量和电导率分别为1.6 kg/(m2•h)和48 μS/cm，单位加热能耗Shec和系统性能系数Cop分别为71.88 kWh/t和8.88，比常规蒸汽加热的减压膜蒸馏系统节能74.7%。模拟结果表明，进料浓度增加，压缩机功耗增加，但性能系数Cop减小；进料温度、进料流速以及渗透侧压力增加，压缩机功耗减小，Cop增加。因此，该系统具有良好的节能性、经济性和环境效益，应用前景广阔。

Characteristics analysis of the combined system for the mechanical vapor recompression and vacuum membrane distillation of sulfuric acid wastes

In order to efficiently recover and treat sulfuric acid waste produced in the industrial and agricultural production and utilization process, a combined system of mechanical vapor recompression (MVR) and vacuum membrane distillation (VMD) was proposed and designed in this paper. A compressor was employed to compress the secondary vapor evaporated from the sulfuric acid solution in the VMD module. Then, the compressed vapor with a higher pressure and temperature was used to heat the feed solution in the heat exchanger, which not only recovered the latent heat of internal secondary vapor but also saved the external heat source and cooling water. The proposed system could complete the entire evaporation process by itself, and realize the efficient recovery and utilization of sulfuric acid waste through the complement advantages of VMD and MVR. Firstly, mathematical models were established in the light of the mass and energy conservation principles, the system experimental setup was constructed and then the experiments were carried out to verify the accuracy and reliability of the established mathematical models as well as the feasibility of MVR coupled with VMD. Then, the calculation program of thermodynamic performance was then developed and solved by the iteration with the aid of the Matlab software. The effects of operating parameters including feed concentration, feed temperature, feed velocity and permeate side pressure on thermodynamic characteristics were investigated. The following conclusions could be obtained: A series of experiments were carried out with the tap water as feed, under the conditions of feed temperature, feed velocity, permeate side pressure and heat transfer temperature difference of heat exchanger were 358.15 K, 2.8 m/s, 54.0 kPa and 2 K, membrane flux and condensate water conductivity were tested to be 1.6 kg/(m2•h) and 48 μS/cm, and specific heating energy consumption (Shec) and performance coefficient (Cop) were found to be 71.88 kWh/t and 8.88. The simulated results indicated that when the heat transfer temperature difference of the heat exchanger was constant, increasing the feed concentration increased the saturation temperature difference between inlet solution and outlet vapor of the VMD module (ΔTVMD) and saturation temperature difference between inlet vapor and outlet vapor of the compressor (ΔTcom), which led to the increase of the compression ratio and power consumption of the compressor while the decrease of the Cop; increasing the feed temperature, feed velocity and permeate side pressure would decrease the values of ΔTVMD and ΔTcom, resulting in the decrease of the compression ratio and power consumption of the compressor while the increase of the Cop. Compared with single-effect evaporation, double-effect evaporation, three-effect evaporation and MVR systems, the separation efficiency of VMD, Heat pump-VMD and MVR-VMD systems was up to 99.9%, with obvious advantages in separation performance. However, compared with VMD and Heat pump-VMD systems, the current MVR-VMD system was more efficient and energy-saving. Obviously, considering the characteristics of separation and energy saving, the MVR-VMD system has greater advantages and broad prospects for development and application.