Defining the cost of water impact for thermoelectric power generation

Abstract

Thermal power plants use large amounts of water, mainly for cooling purposes. Over a long operational period, power-plant cooling can have a large impact on the water source: elevated temperatures of return flows alter the local physical and chemical properties of the water (i.e., quality impact), while water consumption reduces the available water reserves for future and down-stream uses (i.e., Quantity impact). The vulnerability of the energy sector to water availability is an important problem and measures to confront or mitigate this challenge have not yet been adopted. Here, a novel, straightforward methodology to calculate the cost of water impact caused by coal and natural-gas (combined-cycle) plants with once-through and wet-recirculating cooling systems is developed. The goal is to internalize systemic costs related to water use impacts and thereby incentivize more sustainable energy generation practices. The impact is calculated here as a theoretical feedback on the plant's operational costs, since altered water properties will eventually lead to malfunction or part-load operation. The main parameter affecting the cost of water impact is found to be the temperature rise of the cooling water in the condenser. In plants with once-through cooling systems, the quantity and quality impacts of water use are of a comparable magnitude. The cost of water impacts in facilities with wet-recirculating cooling systems, on the other hand, is determined only by their quantity impact on water resources. Overall, recirculating systems result in a significantly lower water cost when compared to once-through systems. Furthermore, an approximately three times higher cost of water impact is calculated for coal plants in comparison to natural gas plants, which clearly demonstrates the importance of operational efficiency on the water use of power plants.