太阳能膜蒸馏淡化水系统运行优化

该文旨在优化太阳能膜蒸馏淡化水系统运行过程。采用试验手段确定了该系统的最佳运行工况,测试了最佳工况下该系统的运行效果,说明了系统运行过程的电力平衡情况。测试结果表明:呼和浩特地区该系统光热部分最佳循环流量为150 L/h;光伏光热系统以连续跟踪方式运行;热工质加热过程控制方法为,当辐照度低于500 W/m~2时仅开启光伏发电系统加热热工质,当辐照度介于500~700 W/m~2时采用光伏光热互补方式加热热工质,当辐照度大于700 W/m~2时仅开启光热系统加热热工质;该系统于最佳工况运行时平均膜通量为14.92 kg/(m~2·h),且系统可维持电力平衡;该系统于优化工况下运行时7组膜组件串联即可满足1个4口之家的饮水需求。系统于优化工况下运行,单位产水量所需的膜面积为0.067 m~2。该研究可为膜蒸馏淡化水系统应用研究提供一定参考。

Running optimization of solar membrane desalination system

In this paper, a test device of solar membrane desalination system through distillation is designed in order to optimize the running process of solar membrane desalination system through distillation. The device uses photovoltaic-thermal system instead of conventional power to drive the power load during the running process of the system. The best operation condition is determined by means of test. The running performance of the system is tested in Hohhot, Inner Mongolia Autonomous Region, under the optimized circulation flow circumstance; the optimal heat flow rate is determined, the running effect of membrane desalination system in the best condition is tested, and the power balance of the system during the operation is illustrated. During the test outside, the average daily temperature is 21.78℃, the average wind speed is 2.94 m/s, and the main wind direction is northwest. The results show that there is a best endothermic circulation flow rate, which makes the total heat absorption decrease if it is too small or too large. The best circulation flow rate of solar thermal and photovoltaic system is 150 L/h. Corresponding temperature of the heat water increases by 2.5℃, which is the maximum value under all the circulation flow rates. The amount of heat absorbed by the heat exchanger in the unit time is the largest; the solar thermal and photovoltaic system should adopt the continuous track to run. After the incident angle of the sun's rays is greater than 20°, the heating rate of solar collector sharply declines and the temperature rise values at measuring points are close to 0℃. In the heating process, there are 3 kinds of control methods. When the irradiance is less than 500 W/m2, only the photovoltaic system is opened to heat the working medium; when the irradiance is 500-700 W/m2, the thermal and photovoltaic complementary mode is used to heat the working medium; when the irradiance is greater than 700 W/m2, the thermal system opens to heat the working medium. With the good thermal insulating performance of hot water tank, system runs efficiently. The average flux is 14.92 kg/(m2·h) after optimization. The single membrane area is 0.01 m2. The average human intake of water is 2.5 kg/d, and 10.44 kg water can be produced by 0.14 m2 hydrophobic membrane which runs for 5 h in the optimized conditions. Seven groups of membrane modules in series can meet the drinking water needs of a family of four. The power consumption of electric heating is much larger than the total power consumption of 3 pumps. The power consumption during the whole test is 2.61 kW·h. The DC (direct current) meter shows that the average electrical energy generation by photovoltaic system is 2.4 (kW·h)/d. The membrane desalination system runs 5 h/d, which meets the demand of the photovoltaic system. The balance of electric power is maintained in the process of system operation. At last, this research can determine the minimum membrane area that per unit water production requires, get the maximum water production with the minimum initial investment, and promote the practical application of the membrane desalination system. The results provide a reference for the application of membrane distillation for desalination.