SUPERCRITICAL WATER PARTIAL OXIDATION PHASE I - PILOT-SCALE TESTING/FEASIBILTY SUDIES FINAL REPORT [electronic resource].
- Washington, D.C. : United States. Dept. of Energy. Office of Energy Efficiency and Renewable Energy, 2005.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
- Additional Creators:
- General Atomic Company
United States. Department of Energy. Office of Energy Efficiency and Renewable Energy
United States. Department of Energy. Office of Scientific and Technical Information
- General Atomics (GA) is developing Supercritical Water Partial Oxidation (SWPO) as a means of producing hydrogen from low-grade biomass and other waste feeds. The Phase I Pilot-scale Testing/Feasibility Studies have been successfully completed and the results of that effort are described in this report. The key potential advantage of the SWPO process is the use of partial oxidation in-situ to rapidly heat the gasification medium, resulting in less char formation and improved hydrogen yield. Another major advantage is that the high-pressure, high-density aqueous environment is ideal for reacting and gasifying organics of all types. The high water content of the medium encourages formation of hydrogen and hydrogen-rich products and is especially compatible with high water content feeds such as biomass materials. The high water content of the medium is also effective for gasification of hydrogen-poor materials such as coal. A versatile pilot plant for exploring gasification in supercritical water has been established at GA's facilities in San Diego. The Phase I testing of the SWPO process with wood and ethanol mixtures demonstrated gasification efficiencies of about 90%, comparable to those found in prior laboratory-scale SCW gasification work carried out at the University of Hawaii at Manoa (UHM), as well as other biomass gasification experience with conventional gasifiers. As in the prior work at UHM, a significant amount of the hydrogen found in the gas phase products is derived from the water/steam matrix. The studies at UHM utilized an indirectly heated gasifier with an activated carbon catalyst. In contrast, the GA studies utilized a directly heated gasifier without catalyst, plus a surrogate waste fuel. Attainment of comparable gasification efficiencies without catalysis is an important advancement for the GA process, and opens the way for efficient hydrogen production from low-value, dirty feed materials. The Phase I results indicate that a practical means to overcome limitations on biomass slurry feed concentration and preheat temperature is to coprocess an auxiliary high heating value material. SWPO coprocessing of two high-water content wastes, partially dewatered sewage sludge and trap grease, yields a scenario for the production of hydrogen at highly competitive prices. It is estimated that there are hundreds if not thousands of potential sites for this technology across the US and worldwide. The economics for plants processing 40 tpd sewage sludge solids augmented with grease trap waste are favorable over a significant range of cost parameters such as sludge disposal credit and capital financing. Hydrogen production costs for SWPO plants of this size are projected to be about $3/GJ or less. Economics may be further improved by future developments such as pumping of higher solids content sludges and improved gasifier nozzle designs to reduce char and improve hydrogen yields. The easiest market entry for SWPO is expected to be direct sales to municipal wastewater treatment plants for use with sewage sludge in conjunction with trap grease, as both of these wastes are ubiquitous and have reasonably well-defined negative value (i.e., the process can take credit for reduction of well-defined disposal costs for these streams). Additionally, waste grease is frequently recovered at municipal wastewater treatment plants where it is already contaminated with sewage. SWPO should also be favorable to other market applications in which low or negative value, high water content biomass is available in conjunction with a low or negative value fuel material. For biomass slurries primary candidates are sewage sludge, manure sludge, and shredded and/or composted organic municipal solid waste (MSW) slurries. For the high heating value stream primary candidates are trap grease, waste plastic or rubber slurries, and coal or coke slurries. Phase II of the SWPO program will be focused on verifying process improvements identified during ...
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