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A large number of resources are dedicated to seawater desalination and will only grow as worldwide water scarcity increases. Seawater desalination methods, in particular thermal desalination methods, are highly energy intensive and are associated with CO2-emitting electricity production. The purpose of this article is to investigate the integration of thermal desalination methods with carbon capture and sequestration (CCS) electricity production in order to implement emissions-free thermal desalination facilities. Specifically, the advanced zero emissions plant (AZEP) oxy-combustion concept is utilized for integration in this study. The performance of several bottoming cycle integrations coupled to multi-effect distillation (MED) with and without thermal vapor compression (TVC) is estimated in order to evaluate the thermodynamic and economic feasibility of such power and water emissions-free plants. It is found that AZEP plants could utilize industry-standard dual-purpose technology and produce water near typical power-to-water ratios as compared to dual-purpose plants without CCS.

The single day operation and size of a seawater reverse osmosis (RO) plant subject to a half-hourly varying electricity price is optimized. The study herein is an extension of Ghobeity and Mitsos, 2010 Desalination. Their model is modified to have a variable plant size controlled by the number of modules. The operating and capital costs are calculated as a function of size and operation. The objective of the optimization is to minimize the total annualized cost of the plant. The number of modules and the half-hourly varying operating frequency constitute the decision variables. The operation and size are optimized for four different electricity price functions: constant, moderately fluctuating, highly fluctuating, and actual electricity prices from a given day in Spain. The results show that variable operation and oversizing can produce savings of up to 7% for a highly fluctuating electricity price. The plant has a higher operating frequency when electricity is cheap and shuts off during periods of high electricity price when oversized. The size and day-by-day operation are also optimized for one year subject to Spain's electricity price. Little savings via oversizing are obtainable for the day-by-day optimization due to low fluctuations in the electricity price during the year.

The operation of seawater reverse osmosis (SWRO) plants is systematically optimized with the objective to reduce the electricity charges, which constitute the largest portion of the operation costs. Variable operating conditions and a time-of-use electricity tariff rate schedule are considered. A well-established model is extended to model a reverse osmosis (RO) system equipped with highly efficient pressure exchangers (PXs) and variable frequency drives (VFDs). All major performance factors are considered, including membrane's permeability, concentration polarization, temperature effects, membrane fouling, and efficiency dependency of the VFD on the loading conditions. The proposed formulation minimizes the electricity cost per day, given a desired daily production rate. The problem is formulated as a mixed-integer nonlinear program (MINLP), allowing for periods without operation. The time domain (24 h) is discretized into 0.5 h increments, and a pseudo steady-state assumption is used. The optimal operation plan resulting in maximum electricity cost-savings is established with standard global optimization tools. The results show significant electricity and production cost-saving potentials. More savings in electricity can be achieved by oversizing the plant, thus allowing shutting-off at periods of high electricity cost. The cost-saving potentials are particularly promising in electricity markets in which the electricity rate schedule is widely distributed.