(676c) Optimal Synthesis of a Pulverized Coal Power Plant with Carbon Capture

Coal constitutes an important source of fuel for the production of power in the United States. For instance, in January 2009, pulverized coal (PC) power plants alone contributed to over 45 percent of the Nation's total electric power production [1]. However, PC power plants also contribute to increased emissions of greenhouse gases principally carbon-dioxide (CO2). Recently, various carbon capture strategies have been under active investigation so as to make these plants compete with the more environmental friendly renewable energy sources. One such technology that has received considerable success is the capture of CO2 by an amine-based solvent extraction process. However, an aqueous absorption/stripping technology when used in a PC power plant can reduce the net power output of the plant by as much as 20?40%. The energy penalty comes from heating up the solvent in the regenerator, balancing the enthalpy of reaction, and water stripping. This energy penalty poses considerable limitations on commercial viability of the solvent extraction process and, as a result, various energy-saving modifications have been proposed in the literature ranging from the use of hybrid solvents to novel stripper configurations. In this paper, we show that the energy penalty can be further reduced by heat integration of various PC plant components with the carbon capture system.

In addition to the release of greenhouse gases to the environment, PC plants also consume a large amount of freshwater. It is estimated that subcritical and supercritical PC plants have water losses of 714 gal/MWh and 639 gal/MWh, respectively [2]. Water loss is based on an overall balance of the plant source and exit streams. This includes coal moisture, air humidity, process makeup, cooling tower makeup (equivalent to evaporation plus blowdown), process losses (including losses through reactions, solids entrainment, and process makeup/blowdown) and flue gas losses. The primary source of water used in PC power plants is the closed-loop steam-based (Rankine) power cycles. These plants need to condense large quantities of low-pressure steam back to water so that it can be reused to produce high pressure steam. However, this requires the removal of large quantities of heat from the low pressure steam in the condensation process. This is usually done by transferring the heat to cooling water, which in turn transfers this heat to the environment by evaporation to the atmosphere. Also, the inclusion of a carbon capture process can increase the raw water usage by as much as 95 percent [3]. In this work, we use heat exchanger network synthesis followed by an optimization approach to process synthesis for developing strategies for reducing water use in a supercritical PC power plant with a carbon capture and compression system. Uncertainties associated with dry bulb temperature, relative humidity, and demand will also be considered in this analysis.

References:

1) Energy Information Administration- Official Energy Statistics from the US Government, http://www.eia.doe.gov/cneaf/electricity/epm/epm_sum.html - Last Accessed: April 2009

2) DOE/NETL, Power Plant Water Usage and Loss Study, May 2007, http://www.netl.doe.gov/technologies/coalpower/gasification/pubs/pdf/Wa…

3) DOE/NETL, Cost and Performance Baseline for Fossil Energy Plants, (2007). DOE/NETL-2007/1281, http://www.netl.doe.gov/energy-analyses/pubs/Bituminous%20Baseline_Fina…