Optimization of three power and desalination plants and exergy-based economic and CO2 emission cost allocation and comparison

Abstract

In this work, a multi-effect distillation with thermal vapor compression desalination unit is proposed to satisfy the freshwater demand of Sao Mateus, Espirito Santo, Brazil. The desalination unit is driven by saturated vapor produced by boiler or heat recovery steam generator. The goal and main contribution of this work are, respectively, to compare and evaluate the most feasible configuration among a steam power cycle, gas turbine and combined cycle power plant. To accomplish this objective, the first and second laws of thermodynamics are used, and economic analyses are carried out for each option. In consequence, an optimization using a genetic algorithm shows the optimal results. The usage of an exergy-based approach for cost allocation assists in the best judgment. For instance, the combined cycle power plant driving a desalination unit presents the highest net power generation of 51.7 MW and a total cost rate of 24,811 US$ h−1, which means a Leveled Cost of Energy of around 0.132 US$ kWh−1. In addition, it has the lowest exergetic and monetary costs of net power (2.316 kJ kJ−1 and 0.132 US$ kWh−1) and freshwater (17.9 kJ kJ−1 and 2.684 US$ kWh−1). However, it also has the highest environmental cost for net power (22.451 kgCO2 kWh−1) and the second highest one for freshwater (196.120 × 10−3 kgCO2 m−3).