Chemical Looping Combustion Reference Plant Design and Sensitivity Studies Using NETL's Oxygen Carrier

摘要

The U.S. Department of Energy (DOE) provides a worldwide leadership role in the development of advanced fossil fuel-based energy conversion technologies, with a focus on electric power generation with carbon capture and storage (CCS). As part of DOE's Office of Fossil Energy, the National Energy Technology Laboratory (NETL) implements research, development and demonstration (RD&D) programs that address the challenges of reducing greenhouse gas emissions. To meet this challenge, FE/NETL is interested in evaluating advanced power cycles that will maximize system efficiency and performance, while minimizing carbon dioxide (CO_2) emissions and the costs of CCS. An emerging coal-fired power plant technology, chemical looping combustion (CLC), is part of NETL's R&D portfolio due to its potential to significantly reduce the cost of producing power from coal while capturing CO_2. In CLC, oxygen carrier particles replace the oxygen source (air or produced high-purity oxygen) used in a conventional or oxycombustion coal plant. The reduced form of the carrier material extracts oxygen via reaction air - the oxidized carrier is then reduced in reaction with the fuel, producing a CO_2 and water-rich combustion effluent stream. As in oxycombustion-based systems, CO_2 separation in CLC is facile - condensation of the water from the combustion effluent results in a nearly-pure CO_2 stream. However, in an oxycombustion plant, high-purity oxygen is derived from air via a cryogenic air separation unit (ASU), which adds significant auxiliary load and capital cost. CO_2 separation in a conventional plant must be accomplished from CO_2 -dilute flue gas (12-15 vol% CO~2) via a post-combustion CO~2 capture technology (e.g., solvent, sorbent, membrane, etc.), with significant attendant auxiliary load and capital cost to the plant. CLC holds promise for efficient, low-cost power generation from coal, without the capital cost and efficiency penalty associated with the use of an ASU or dedicated CO_2 capture system. The objective of the presented study is to evaluate the performance and cost of a CLC system which utilizes a novel, NETL-developed Cu/Fe-based oxygen carrier material. This is a highly reactive, but expensive, material. Performance and cost sensitivity to key CLC parameters is assessed to determine if the increased reactivity can overcome its cost penalty relative to conventional Fe-based oxygen carriers. An atmospheric pressure, circulating fluidized bed CLC plant design incorporating a supercritical steam Rankine cycle and conventional CO_2 compression technology, studied previously by NETL, was chosen as the basis for this study. The analysis will be presented and results compared to the performance and cost of: (i) a conventional, state-of-the-art pulverized coal (PC) power plant using solvent-based CO_2 capture, and (ii) a circulating fluidized bed-based CLC power plant using an Fe-based oxygen carrier material. The significance of carrier properties and key operating parameters will be discussed in relation to predicted plant performance and/or cost.