A Correlation for the Impact of Extracting Steam From Power Plants for Carbon Capture Processes

A Correlation for the Impact of Extracting Steam from Power Plants for Carbon Capture Processes Adam H Berger and Abhoyjit S Bhown Electric Power Research Institute (EPRI), Palo Alto, CA AbstractPost combustion carbon dioxide capture and storage (CCS) from power plants is an energy intensive process often consuming one quarter to one third of the total power generated by the base power plant. This parasitic energy is comprised of two main terms: the auxiliary load , which accounts for pumping, compression, and other mechanical or electrical work; and the thermal load , which is typically steam extraction for process heating. It is important to understand how these two terms interact with the base power plant so that accurate parasitic energy can be calculated and CCS materials or processes can be developed and compared based on actual impact on the power output of power plants. While the impact of the auxiliary load on the power plant output is immediately apparent, the impact of the thermal load on the power plant is more difficult to quantify. The thermal load is used to provide heating energy to a CCS process in the form of steam extracted from the steam cycle of the power plant. The extracted steam is used to provide process heating such as in the reboiler of a solvent stripper or heating solid material in a temperature swing adsorption process. The electrical impact of extracting steam is defined as the power loss in the turbines from the decreased steam flow rates. This power loss is a function of the temperature and pressure of steam extraction as well as the quantity of steam extracted. The heating energy has components, the energy from de-superheating the steam extracted and energy from the heat of vaporization of steam condensing at the pressure of extraction. This condensation at the saturation temperature also determines the temperature at which process heating can be provided. In addition to the temperature and pressure of the steam extracted, the quantity of steam extracted is also important because the effect of steam extraction on low-pressure turbine operation and efficiency. In this work, we use state-of-the-art models of low pressure turbines in power plant steam cycles to quantify the effect of steam extraction on power plant operation. We further develop a correlation for the impact on a power plant of providing thermal energy at a specified quantity and temperature to a CCS process. This correlation can be used in any process or material development to more accurately compare the effect of different process configurations or material properties on the total energy impact of CCS and thus compare trade-offs between mechanical work and thermal load or between capital and operating expenses.