The seawater greenhouse in the United Arab Emirates: Thermal modelling and evaluation of design options

The Seawater Greenhouse combines a solar desalination system with an environment for cultivating crops in which transpiration is minimised. Results from the prototype greenhouse in the United Arab Emirates (UAE) are used to calibrate a computational fluid dynamic (CFD) model. With the UAE design taken as a baseline, the model is used to evaluate three proposed options for improving performance. These differ with respect to how the plants are shaded and how air flows through the greenhouse. In the baseline design, a semi-opaque plastic sheet is used to provide shade. The first option uses a similar sheet; however the air flows in a C-shaped path, travelling in opposite directions above and below the sheet. The second option uses a perforated sheet through which air is drawn. In the third option, an array of plastic pipes carrying seawater provides shade. The warmed seawater from the pipes is fed into the back evaporator to boost fresh water production. We present results for freshwater production, evapotranspiration and temperatures inside the greenhouse, covering a range of ventilation airflows. The first option gives only marginal improvements in freshwater production and cooling. In contrast, the second option significantly increases water production. Air temperature in the greenhouse increases, whereas the mean radiant temperature decreases. The third option gives the greatest increase in water production in addition to slightly lower air temperature in the greenhouse and significantly lower mean radiant temperature. Evapotranspiration varied little over all the cases studied. The reasons for these findings and their implications for the design of the system are discussed.     

聚丙烯平板微孔膜膜蒸馏海水淡化研究

采用热致相分离法制备了聚丙烯平板微孔膜,并对自制平板膜组件的膜蒸馏海水淡化性能进行了研究。探讨了膜制备条件及海水流量、温度、膜后真空度等真空膜蒸馏过程操作条件对聚丙烯平板膜组件海水淡化性能的影响,自制组件连续运行的小试结果表明:当真空侧压力为3kPa,进料温度为323.15K,流量为50L/h时,天津市渤海湾海水膜蒸馏过程的平均水通量达10.56kg/m·2h,产品水的脱盐率均在99.8%以上。     

露点蒸发淡化技术

露点蒸发淡化技术是一种新的苦咸水和海水淡化方法。本文从常规增湿一去湿淡化过程出发，在比较的基础上详细地描述了露点蒸发淡化过程的原理。分别介绍了露点蒸发淡化的水平级连装置和竖直连续接触装置。对过程的经济分析表明，露点蒸发淡化工艺在使用低位热能时具有明显的优势。本文总结了露点蒸发淡化工艺的技术特点，并指出了其研究重点和应用前景。     

Hydrophobic mullite ceramic hollow fibre membrane (Hy-MHFM) for seawater desalination via direct contact membrane distillation (DCMD)

A low-cost hydrophobic mullite hollow fibre membrane (Hy-MHFM) fabricated via phase inversion/sintering technique followed by fluoroalkyl silane (FAS) grafting is presented in this study. The prepared CHFMs were characterized before and after the grafting step using different characterization techniques. The pore size of the CHFM surface was also determined using ImageJ software. The desalination performance of the grafted membrane was evaluated in direct contact membrane distillation (DCMD) using synthetic seawater of varying salt concentrations for 2 h at various feedwater temperatures. The outcome of the evaluations showed declines in the permeate flux of the membrane at increasing feed concentration, as well as increased flux with increased feed temperature. The long-term stability of the membrane was achieved at time 20 h, feed temperature 60 °C, and permeate temperature 10 °C, the membrane achieved a salt rejection performance of about 99.99 % and a water flux value of 22.51 kg/ m² h.     

Binary metal oxides incorporated polyethersulfone ultrafiltration mixed matrix membranes for the pretreatment of seawater desalination

In this study, an attempt was made to pretreat seawater using polyethersulfone (PES) mixed matrix membranes (MMMs) incorporated with titania-based binary metal oxides. Two different titania-based binary metal oxides were prepared, namely titania-zirconia (TiZr) and titania-zinc oxide (TiZn). The influence of hydrophilic and negatively charged sulfonated poly(ether ether ketone) (SPEEK) polymer as additive of PES MMMs was also studied. Morphological and elemental analysis revealed that both ZrO₂ and ZnO were well dispersed in the as-prepared binary metal oxide TiZr and TiZn, respectively._. Thermogravimetry analysis indicated the good compatibility of TiZr and TiZn with the SPEEK/PES polymer. The binary metal oxide incorporated SPEEK/PES MMMs exhibited improved hydrophilic properties with a low water contact angle of 57° ± (0.6). SPEEK/PES MMMs incorporated with 0.5 wt% TiZr exhibited the highest permeability of 3.11 × 10⁻⁷ ± (0.2) m/s·kPa. Seawater pretreatment performance of membranes evaluated using natural organic matters containing high salinity feed water. TiZr and TiZn incorporated SPEEK/PES MMMs exhibited 95% rejection for humic acid. SPEEK/PES MMMs loaded with 0.5 wt% TiZr also showed the highest water flux and 87% water recovery within 90 min of seawater filtration. Both PES/SPEEK/TiZr and PES/SPEEK/TiZn MMMs exhibited superior antibacterial activity.     

可旋转的太阳能集热—减压膜蒸馏式脱盐研究

设计构建了1套新型可旋转的太阳能集热—减压膜蒸馏脱盐系统装置,以太阳能集热提供热源,以3.5%的氯化钠溶液模拟海水进行脱盐实验。研究了不同进料液温度、冷侧真空度、进料液流量对膜组件性能的影响,以及1个工作日内膜通量、淡水电导率和截留率的影响变化。结果表明:当系统运行稳定时,膜组件入口进料液温度、冷侧真空度和进料液流量是影响系统性能的主要因素,且在1个工作日内系统所产淡水的电导率可达到10μS/cm以下,截留率可达到99.9%以上。     

HAl77-2铜合金管在低温多效海水淡化装置中的耐蚀性

采用实验室模拟研究的方法,通过腐蚀电化学测试和腐蚀形貌观察,借助表面物相结构和元素成分分析,比较了3种海水淡化所用的HAl77-2铜合金热交换管的耐蚀性以及平均晶粒度,分析了它们在海水介质中的腐蚀失效机制。结果表明:HAl77-2铜合金管的电化学阻抗均随浸泡时间的延长而逐渐增大,在达到极大值后,又会出现在极大值附近波动的现象;相比较而言,1号管样的耐蚀性最好、晶粒度最小,而3号管样的耐蚀性最差、晶粒度最大。     

发展海水淡化产业为沿海经济区提供补充水源

对国内外水资源短缺情况及海水淡化技术的发展与应用进行了简述，论述了发展海水淡化产业，为我国沿海经济区提供补充水源的重要性和紧迫性，认为这是确保用水安全和经济持续增长所必需的重要措施．指出，发展海水淡化产业应不受本地区是否存在缺水问题的限制；技术出口、设备出口将会取得很高的经济效益．同时还对海水淡化工业与其它工业的关系做了探讨。     

二级反渗透技术制备高纯水工艺研究

分析了二级反渗透系统制备高纯水工艺中二级系统进水pH值、CO2含量及膜类型的配置对脱盐率的影响,总结了进水电导率与脱盐率的关系.试验研究表明:以引黄入津的水为特定原水,二级系统进水pH值对脱盐率影响较大,pH值在7.5左右时脱盐率最高,淡水电导率可达到0.15μS/cm(6.7MΩ·cm);由于进水CO2含量较低,脱盐率几乎不受其影响;表面带负电荷ESPA4型膜的脱盐率高于带正电荷的LFC2型膜.