Studying the reduction of water use in integrated solar combined-cycle plants

Abstract

With vast amounts of water consumed for electricity generation and water scarcity predicted to rise in the near future, the necessity to evaluate water consumption in power plants arises. Cooling systems are the main source of water consumption in thermoelectric power plants, since water is a cooling fluid with relatively low cost and high efficiency. This study evaluates the performance of two types of power plants: a natural gas combined-cycle and an integrated solar combined-cycle. Special focus is made on the cooling system used in the plants and its characteristics, such as water consumption, related costs, and fuel requirements. Wet, dry, and hybrid cooling systems are studied for each of the power plants. While water is used as the cooling fluid to condense the steam in wet cooling, dry cooling uses air circulated by a fan. Hybrid cooling presents an alternative that combines both methods. We find that hybrid cooling has the highest investment costs as it bears the sum of the costs of both wet and dry cooling systems. However, this system produces considerable fuel savings when compared to dry cooling, and a 50% reduction in water consumption when compared to wet cooling. As expected, the wet cooling system has the highest exergetic efficiency, of 1 and 5 percentage points above that of dry cooling in the conventional combined-cycle and integrated solar combined-cycle, respectively, thus representing the lowest investment cost and highest water consumption among the three alternatives. Hybrid and dry cooling systems may be considered viable alternatives under increasing water costs, requiring better enforcement of the measures for sustainable water consumption in the energy sector.