Maximum economic design life for desalination plant: The role of auxiliary equipment materials selection and specification in plant reliability

Abstract

The role of material selection in optimising plant costs has been already subject of several studies [1–3]. These studies focused on the main plant items such as tube bundle, vessels, vessel linings, tubeplates etc. as they are the major components to the plant costs and therefore represent the main source of expenditure in term of economic optimisation of the plant life. Similarly for SWRO plants at least 40% of the plant costs are concentrated in the membranes and in the supporting racks and auxiliary connections. However despite the fact that these cost aspects are of major importance to evaluate the plant life and the economic aspects related to material design, the operational reliability of the desalination plants depends largely on the dynamic components of the plants. Pumps, screens ejectors and piping are subject to a more intense maintenance routine and spare parts replacement and are usually less robust than the static components of the evaporator vessels. Whereas the design and procurement of these items of equipment accounts for a limited part of the desalination plant budget the operation reliability and hence availability is very dependent on these components. In some respects this is taken into account in the design of the plant by adopting redundancy policy of ( n + 1) components, where n is the number of the components in service. The analysis proposed in the paper indicates that these aspects are mainly related to the plant auxiliary equipment where the dynamic component is higher. By a proper material selection and design of these components, the plant reliability and operation can be enhanced and the purchase of strategic spare parts could be optimised. This paper follows in principle the study presented in the previous EuroMed conference held in Jerba “Forty years design life — the next target: material selection and operating conditions in thermal desalination plant” but aims at analysing in more depth desalination plant reliability and maintenance aspects.