Alstom’s Limestone Chemical Looping Gasification Process for High Hydrogen Syngas Generation
Alstom Power Inc., a wholly owned subsidiary of the General Electric Company (GE), is developing Limestone-based Chemical Looping (LCL™) Processes, utilizing limestone derived calcium sulfate as an oxygen carrier to transport oxygen from air to the fuel. The LCL™ process is a breakthrough technology with the potential to capture CO 2 and SO 2 from new and existing coal-fired power plants at reduced costs while maintaining high plant power generation efficiency. Chemical looping is a next generation advancement to oxy-combustion which would not require the significant investment in a cryogenic distillation type oxygen production plant. Instead of the energy-consuming oxygen plant, chemical looping uses a benign material to directly remove oxygen from the air and bring that oxygen into contact with the fuel. This "game changing" technology is the lowest cost-of-electricity technical approach that GE Power has identified to date for coal power with carbon capture. The technology has significantly lower capital costs compared to a conventional steam power plant with first generation carbon capture technologies. This new power plant concept is based on a hybrid combustion-gasification process utilizing high temperature chemical and thermal looping technology. In the air reactor, a solid oxygen carrier picks up oxygen from air through an oxidation reaction and leaves nitrogen behind. The hot oxygen-carrying solid carrier is then transported to a fuel reactor, where it releases oxygen. The released oxygen then converts the coal in the fuel reactor into combustion gases. The solid carrier is recycled back to the air reactor for regeneration completing the “chemical loop.” The regeneration step produces heat from which steam is produced for power generation while the process results in a concentrated carbon dioxide stream in which the carbon is captured for use or sequestration (CCUS). Limestone as a precursor for the oxygen carrier is abundant, benign, low cost, and is used in CFB and PC boilers for sulfur control. Challenges associated with this carrier include a complex reaction mechanism with possible side reactions leading to the release of SO 2 . The development of the Limestone Chemical Looping Gasification (LCL-G™) technology was co-funded by the Department of Energy under the DOE/NETL Cooperative Agreement No. DE- FE0023497, in parallel with the collaborative combustion (LCL-C™) program. In this report, the LCL-G™ experimental testing from the electrically-heated, once-through, 100 kW Pilot-Scale Test Facility (PSTF) is analysed and reviewed. The PSTF Oxidizer is a 50-foot tall, 100-mm diameter transport reactor, while the PSTF Reducer reactor is based upon a bubbling-bed design. The experimental data from four (4) test campaigns (denoted “Weeks”) are reviewed and discussed. The LCL-G™ (DE-FE0023497) project objectives for gasification are >90% carbon gasified in the Reducer and a H 2 :CO molar generation ratio of 2:1. These project performance metrics were not met by a single coal test, but they were individually approached in two separate tests.