Generalized Least Energy of Separation for Desalination and Other Chemical Separation Processes
Generalized Least Energy of Separation for Desalination and Other Chemical Separation Processes
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DOI：
10.3390/e15062046
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发表时间：
2013-06-01
期刊：
影响因子：
2.7
通讯作者：
Lienhard, John H.
中科院分区：
文献类型：
--
作者：
Mistry, Karan H.;Lienhard, John H.
全球对淡水的需求不断增长，推动了各种海水淡化技术的开发和实施，这些技术由热能、功和化学能的不同组合驱动。本文开发了一个一致的基础上比较这些技术的能源消耗使用第二定律效率。化学分离过程的第二定律效率是根据有用的有效能输出来定义的，有效能输出是从给定组成的进料流中提取一单位产品所需的最小分离功。对于脱盐过程，这是从给定盐度的进料生产1千克产品水的最小分离功。虽然之前已经提出了功和热输入方面的定义，但这项工作概括了第二定律效率，以允许在包括燃料在内的能量输入组合下运行的系统。广义方程，然后通过考虑工作输入，在各种温度下的热输入，和各种化学燃料输入的参数研究进行评估。此外，由于大多数现代化的大型海水淡化厂在热电联产方案中运行，因此证明了一种基于一次能源输入正确评估海水淡化厂第二定律效率的方法。它表明，从严格的能量的角度来看，并根据目前可用的技术，热电联产使用电力反渗透系统是积极的上级的热系统，如多效蒸馏和多级闪蒸，尽管非常低的品位的热量输入通常应用在这些系统。
Increasing global demand for fresh water is driving the development and implementation of a wide variety of seawater desalination technologies driven by different combinations of heat, work, and chemical energy. This paper develops a consistent basis for comparing the energy consumption of such technologies using Second Law efficiency. The Second Law efficiency for a chemical separation process is defined in terms of the useful exergy output, which is the minimum least work of separation required to extract a unit of product from a feed stream of a given composition. For a desalination process, this is the minimum least work of separation for producing one kilogram of product water from feed of a given salinity. While definitions in terms of work and heat input have been proposed before, this work generalizes the Second Law efficiency to allow for systems that operate on a combination of energy inputs, including fuel. The generalized equation is then evaluated through a parametric study considering work input, heat inputs at various temperatures, and various chemical fuel inputs. Further, since most modern, large-scale desalination plants operate in cogeneration schemes, a methodology for correctly evaluating Second Law efficiency for the desalination plant based on primary energy inputs is demonstrated. It is shown that, from a strictly energetic point of view and based on currently available technology, cogeneration using electricity to power a reverse osmosis system is energetically superior to thermal systems such as multiple effect distillation and multistage flash distillation, despite the very low grade heat input normally applied in those systems.