Liu Yiming, Wang Jingbo, Hoek Eric M V, Municchi Federico, Tilton Nils, Cath Tzahi Y, Turchi Craig S, Heeley Michael B, Jassby David
Department of Civil and Environmental Engineering, University of California Los Angeles, Los Angeles, California90095, United States.
California NanoSystems Institute, University of California Los Angeles, Los Angeles, California90095, United States.
Environ Sci Technol. 2023 Jan 10;57(1):643-654. doi: 10.1021/acs.est.2c07094. Epub 2022 Dec 29.
Surface-heated membrane distillation (MD) enhances the energy efficiency of desalination by mitigating temperature polarization (TP). However, systematic investigations of larger scale, multistage, surface-heated MD system with high water recovery and heat recycling are limited. Here, we explore the design and performance of a multistage surface-heated vacuum MD (SHVMD) with heat recovery through a comprehensive finite difference model. In this process, the latent heat of condensation is recovered through an internal heat exchanger (HX) using the retentate from one stage as the condensing fluid for the next stage and an external HX using the feed as the condensing fluid. Model results show that surface heating enhances the performance compared to conventional vacuum MD (VMD). Specifically, in a six-stage SHVMD process, 54.44% water recovery and a gained output ratio (GOR) of 3.28 are achieved with a surface heat density of 2000 W m, whereas a similar six-stage VMD process only reaches 18.19% water recovery and a GOR of 2.15. Mass and energy balances suggest that by mitigating TP, surface heating increases the latent heat trapped in vapor. The internal and external HXs capture and reuse the additional heat, which enhances the GOR values. We show for SHVMD that the hybrid internal/external heat recovery design can have GOR value 1.44 times higher than that of systems with only internal or external heat recovery. Furthermore, by only increasing six stages to eight stages, a GOR value as high as 4.35 is achieved. The results further show that surface heating can reduce the energy consumption of MD for brine concentration. The multistage SHVMD technology exhibits a promising potential for the management of brine from industrial plants.
表面加热膜蒸馏（MD）通过减轻温度极化（TP）提高了海水淡化的能源效率。然而，对于大规模、多级、具有高水回收率和热回收的表面加热MD系统的系统研究仍然有限。在此，我们通过一个综合有限差分模型探索了具有热回收功能的多级表面加热真空MD（SHVMD）的设计和性能。在此过程中，冷凝潜热通过内部热交换器（HX）回收，使用来自一级的截留液作为下一级的冷凝流体，并通过外部HX使用进料作为冷凝流体。模型结果表明，与传统真空MD（VMD）相比，表面加热提高了性能。具体而言，在六级SHVMD过程中，表面热密度为2000 W/m²时，水回收率达到54.44%，增益输出比（GOR）为3.28，而类似的六级VMD过程仅达到18.19%的水回收率和2.15的GOR。质量和能量平衡表明，通过减轻TP，表面加热增加了蒸汽中捕获的潜热。内部和外部HX捕获并再利用额外的热量，从而提高了GOR值。我们表明，对于SHVMD，混合内部/外部热回收设计的GOR值可比仅具有内部或外部热回收的系统高1.44倍。此外，仅将六级增加到八级，就可实现高达4.35的GOR值。结果进一步表明，表面加热可以降低MD用于盐水浓缩的能耗。多级SHVMD技术在处理工业工厂产生的盐水方面具有广阔的应用前景。
