Modeling Power Generation Water Usage

Climate change can have a large effect on thermoelectric power generation. Typical thermoelectric power plants rely on water to cool steam in the condenser in order to produce electricity. Increasing global temperatures can increase average water temperatures as well as decrease the amount of water available for cooling due to evaporation. It is important to know how these parameters can affect power generation and efficiency of power systems, especially when assessing the water needs of a plant for a desired power output and whether a site can fulfill those needs. This paper explains the development of a model that shows how power and efficiency are affected due to changing water temperature and water availability for plants operating on a Rankine cycle. Both a general model of the simple Rankine cycle as well as modifications for regeneration and feedwater heating are presented. Power plants are analyzed for two different types of cooling systems: once-through cooling and closed circuit cooling with a cooling tower. Generally, rising temperatures in cooling water have been found to lower power generation and efficiency. Here, we present a method for quantifying power output and efficiency reductions due to changes in cooling water flow rates or water temperatures. Using specified plant parameters, such as boiler temperature and pressure, power and efficiency are modeled over a 5°C temperature range of inlet cooling water. It was found that over this temperature range, power decrease ranged from 2–3.5% for once through cooling systems, depending on the power system, and 0.7% for plants with closed circuit cooling. This shows that once-through systems are more vulnerable to changing temperatures than cooling tower systems. The model is also applied to Carbon Plant, a coal fired power plant in Utah that withdraws water from the Price River, to show how power and efficiency change as the temperature of the water changes using USGS data obtained for the Price River. The model can be applied to other thermoelectric power stations, whether actual or proposed, to investigate the effects of water conditions on projected power output and plant efficiency.