Impact of climate change on fossil fuel power-plant efficiency and water use

Abstract

Thermoelectric plants consume large amounts of water for electricity generation, mainly for cooling purposes. The performance and cooling capacity of power plants is thus strongly dependent on rising ambient temperatures. This study investigates the effect of rising ambient temperatures on power-plant performance and water use. A natural gas combined-cycle and a coal power plant, using both recirculating and once-through cooling systems, have been analyzed under increasing cooling water temperature and increasing ambient air temperature. Higher ambient temperatures lead to higher pressure at the steam turbine outlet, decreasing power-plant performance. The efficiency of the power plants is found to be more sensitive to ambient temperature variations when a recirculating cooling system is used, as opposed to once-through cooling. For example, a 10 °C temperature increase leads to an efficiency decrease in coal plants of 0.5–0.7 percentage points, when they are equipped with recirculating systems, versus a 0.3–0.4 percentage-point decrease, when they are equipped with once-through systems. The cooling-water mass flow is also found to be more sensitive to temperature increases in plants with recirculating cooling than in plants with once-through cooling. When comparing coal to natural gas plants, it is seen that the cooling water quantity of coal-fired plants is more sensitive to temperature changes. On the other hand, the efficiency of natural gas plants is more sensitive to temperature changes overall. This is related to higher losses in gas turbine systems caused by increased ambient temperatures and to the fact that the gas turbine system delivers approximately two-thirds of the total power output in the natural gas plants.