Optimal design of cogeneration plants for seawater desalination

Multi-stage flash (MSF) and reverse osmosis (RO) are the most common techniques for seawater desalination. A significant difference between these methodologies consists of their different energy requirements, i.e., thermal energy for MSF and mechanical energy for RO plants. The presence of both desalination systems (MSF and RO) appears to be suitable for cogeneration plants. The reject heat from the power cycle can feed an MSF section, while some power feeds the RO section and the MSF auxiliary equipment; the rest is sold to the grid. A criterion for the optimal design of such tri-functional cogeneration plants is proposed, based on exergo-economics and on profit maximization. In particular, in this work the analytical model is presented by examining the required data, expressing the physical and cost balances and furnishing a comprehensive definition of the objective function. The proposed model is flexible and suitable for comparative applications in all Mediterranean countries.

where (36) An optimization methodology was presented for the design of tri-functional power–MSF–RO plants. The objective function is the maximum overall profitability of plant operation in order to consider all cases where the minimum water cost does not lead to maximum revenue. In the least rainy parts of the countries in the northern Mediterranean rim, profitability is the main obstacle.