EVALUATION OF INNOVATIVE FOSSIL CYCLES INCORPORATING CO 2 REMOVAL 2000 Gasification Technologies Conference

Over the past decade, a growing concern has developed about the potential impacts of carbon dioxide (CO2) emissions on the future global environment. Much of this concern has focused on the coal-fired power plants that now produce 56 percent of U.S. electricity. The main reason for the continued use of coal as the major power plant fuel in the U.S. is its significantly lower cost compared to other fossil fuels. There are several choices of power plant fuels available today including coal, oil, and natural gas. Since deregulation of the electric utility industry was initiated several years ago, the use of natural gas by electricity generating companies has steadily grown. Coal use is projected to continue to rise slowly in the U.S. as the total amount of electricity that is generated increases. As a result, the coal-fired option for new electricity generating plants remains important to utility generating companies that have been historically dependent on coal for the bulk of their power generation. However, there have been recent indications that permissible levels of CO2 emissions may be curbed in the future. A natural gas-based power plant will produce less CO2 per kW of power output compared to a coal-based plant with the same net plant power output. This is due to two fundamental factors: (1) natural gas has a lower carbon-to-hydrogen ratio compared to that of coal for the same level of thermal input, and, (2) natural gas-based systems have higher powergenerating efficiencies compared to coal-based systems utilizing the same, or similar, power generation equipment. In conventional gas and coal-fired units, CO2 can be removed from the exhaust gas following heat recovery in an absorber/stripper system. As such, the partial pressure of CO2 is usually low due to the near ambient pressure of the stack gas as well as the dilution effect of substantial amounts of N2 contained in the flue gas. Low CO2 partial pressure yields large and costly removal equipment. However, advanced coal-based technologies, such as gasification -because they produce concentrated streams of CO2 at high pressure -offer convenient opportunities that may be exploited for low-cost CO2 removal. In an oxygen-blown integrated gasification combined cycle power plant, CO2 may be removed from the synthesis gas prior to combustion power generation. The high pressure of the synthesis gas stream, as well as the absence of diluent N2, yields high CO2 partial pressures. This, in turn, results in a relatively cheaper separation due to increased driving force. Innovative coal gasification-based systems may therefore be the most cost-effective coal-based power plants if CO2 removal is required. The objective of the work presented in this paper is to evaluate preliminary designs of several advanced coal-fired power plants to determine whether they have the potential to be competitive, in the period after year 2010, with conventional natural gasand coal-fired power plants. Future conventional natural gas-fired power plants are assumed to be H class combined cycles. Conventional coal-fired plants are assumed to be pulverized coal (PC) supercritical steam power plants. Each power plant concept evaluated was configured both with and without a CO2 removal system. For the advanced coal-fired power plant designs that meet competitive cost targets, DOE will define the R&D effort required to develop and demonstrate the technology to be a commercially attractive alternative.