Design and thermo-economic evaluation of an integrated concentrated solar power – Desalination tri-generation system

Abstract

In this work, a concentrated solar power (CSP) tri-generation system that is capable of the simultaneous production of steam, power and freshwater is introduced. The abundantly available direct normal irradiance can potentially allow concentrated solar power systems to become major energy contributors in the desalination market. Since CSPs can generate both thermal and electrical energy, they have been found to be excellent candidates for sustainable operation of large scale desalination systems, in the long term. This paper presents a mathematical model in the form of a Mixed-Integer Nonlinear program (MINLP), which involves a tri-generation system for combined steam and power production, primarily using solar energy to operate steam turbines. Moreover, the option of freshwater production using various desalination technology choices, such as reverse osmosis (RO) and multi-stage flashing (MSF), is also accounted for within the model. Hence, the proposed model offers a very convenient and eco-friendly tri-generation route for steam, power and water production. The proposed systematic method was tested using different feedwater salinities, as well as using different product water flowrates, and electricity prices. According to the results obtained, the water production cost (WPC) associated with a water salinity of 25 g/L resulted in a value of 1.83 USD/m3, which is significantly lower than the WPCs obtained at 35 g/L (2.09 USD/m3) and 45 g/L (2.24 USD/m3). Moreover, a large scale tri-generation system with an overall production capacity of 100,000 m3/d of freshwater resulted in a 60% reduction of the attained WPC value, when compared against a small scale system with a production capacity of 10,000 m3/d of freshwater. The option of exporting electrical energy to the grid using the proposed tri-generation system was also investigated, and a sensitivity analysis was conducted by varying the price of electrical energy. The attained breakeven energy prices were 0.74, 0.79 and 0.82 cent/kWh at 25, 35 and 45 g/L of feedwater salinity, respectively.