Assessment strategies of different molten salts for heat transfer in tri-generation systems

Abstract

Tri-Generation Systems (TGS) are designed for combined cooling, heating, and power production within a single process. In this paper, the integration of Concentrated Solar Power (CSP) together with TGS is studied. The tri-generation setup consists of a CSP facility that is integrated onto a desalination plant, producing three different levels of steam (very high pressure, low pressure and very low pressure), in addition to power and freshwater, simultaneously. Due to the complexity of the process, it was found imperative to investigate different factors that would improve the overall performance of the system, and ultimately decrease associated costs and thermal losses. Moreover, the use of molten salts offers many advantages, compared to more conventional fluid options, such as mineral and synthetic oils. Hence, a Mixed Integer Nonlinear Program (MINLP) that allows the selection of optimal heat transfer media, in TGS, has been formulated, and the performance of three different molten salts (solar salt, Hitec, and Hitec XL) has been analysed. The operating temperature of molten salts was found to have a significant effect on the steam quality generated in TGS-CSP systems. Moreover, solar salt resulted in the lowest energy production cost (at 28 cents/kWh) amongst all options. On the other hand, Hitec and Hitec XL were found to yield higher energy costs, estimated at 45 and 47 cents/kWh, respectively.