Component-based, dynamic simulation of a novel once through multistage flash (MSF-OT) solar thermal desalination plant

Abstract

The present study further investigates a novel concentrating solar thermal desalination process using a dual tank system, which addresses one of the biggest challenges in wider adoption of solar applications: 24-h dispatching of solar energy. Direct use of solar energy only during daily sun hours might be acceptable on a small scale, but not economically viable on a larger scale. In this study, a complete once through multi-stage flash (MSF-OT) desalination plant powered by solar thermal energy was modeled using the TRNSYS modeling environment. The model results are in good agreement with previous general studies, but the novelty here is development and use of a component-based, dynamic simulation model of the entire desalination plant, which more accurately represents real situations, and allows parametric analyses of important design variables such as the number of stages, top brine temperature, operating pressures, and solar concentrator area. Key indicators were used to evaluate this novel concept, which included the performance ratio, PR (the ratio of the total energy required to evaporate the brine to the total solar energy gained), the recovery ratio, RR (the relative amount of distillate extracted from the feed water), the specific mass feed water flow, SMF (the ratio of the feed water mass to the mass of the produced distillate water), as well as a detailed economic analysis. System improvements relative to previous studies included use of series/parallel configuration of the solar concentrator array and improved thermodynamic modeling of vacuum pressures in flashing tanks. Results of this study showed that the size of the solar concentrator array can be reduced by 54 % relative to previous studies. The average daily values of the performance ratio (PR). the recovery ratio (RR), and the specific mass feed water flow (SMF) were approximately15.2, 13.8 %, and 7.25. Finally, based on a detailed economic analysis, it was found that the water price could be reduced by nearly 15 % to $2.33/m3.