Simultaneous optimization of size and short-term operation for an RO plant

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.

► Optimized RO plant size and operation simultaneously with total annualized cost model
► Highly fluctuating electricity prices result in high TAC savings.
► Oversizing and long shut-off duration produce high TAC savings.
► Reducing operation costs can be more beneficial than reducing capital costs.
► TAC savings are also possible for day-by-day operation over a year with oversizing.