The Minimum Separation Work for Desalination Processes
Abstract A general relation is obtained for the minimum work input requirement for desalination processes using the second-law of thermodynamics. The relation developed can be used to determine the minimum work input for any salinity of the incoming water, and the recovery ratio. It is also shown that there is a lower and an upper limit for the minimum work, corresponding to recovery ratios of 0% and 100%, respectively. The minimum work input per unit mass of fresh water produced is determined for various salinities of incoming water, and the salinities of fresh water produced, and the results are tabulated and plotted. It is shown that the minimum work is a strong function of salinity, and increases with salinity and the recovery ratio. It is also shown that the minimum work input requirement remains fairly constant for recovery ratios of up to about 80%; the minimum work increases drastically at high recovery ratios; and an optimum value of recovery ratio exists to minimize the power consumption of actual desalination plants. But the value of this optimum recovery ratio decreases with increasing salinity of the incoming saline water. The results presented in this paper can be used as a basis to evaluate the performance of actual desalination plants.