CORROSION AND FLOW RESISTANCE OF METAL FILTER ELEMENTS USED IN THE CLEANUP OF SYNGAS FROM THE TRANSPORT GASIFIER AT THE POWER SYSTEMS DEVELOPMENT FACILITY

At the Power Systems Development Facility (PSDF), a variety of filter elements and failsafes are being tested for the cleanup of coal-generated syngas from the Kellogg Brown and Root (KBR) Transport Gasifier. Through 2007, the maximum accumulated syngas exposure for each element type was: 9,959 hours for iron aluminide sintered metal powder elements; 8,249 hours for HR-160 sintered metal fiber failsafes; 3,007 hours for HR-160 sintered metal fiber elements; 2,281 hours for Fecralloy sintered metal fiber media in coupon form; and 481 hours for Fecralloy sintered metal fiber elements. Thus far, no evidence of corrosion or plugging has been found in the HR-160 failsafes or elements. However, a progressive corrosion and increase in pressure drop has been noted in the iron aluminide elements. The corrosion was first detected as reddish-brown spots of iron oxide after about 2,000 to 3,000 hours of syngas exposure. As the corrosion progressed, the spots of iron oxide merged to form a continuous scale after about 5,000 to 5,500 hours of exposure. With additional exposure, a black scale containing iron sulfide also appeared, and localized areas of sulfidation and plugging were noted in element cross sections. These effects have not resulted in any significant reduction in tensile strength, but a gradual increase in the clean element pressure drop has been noted. Flow test results suggest that there is an interaction between the corroded filter surface and the dustcake that effectively increases the residual cake flow resistance and baseline pressure drop. INTRODUCTION In Integrated Gasification Combined Cycle (IGCC) plants, gasification ash must be removed from the syngas to protect the gas turbine from the effects of solids erosion and deposition. Since 1999, the Power Systems Development Facility (PSDF) has been demonstrating efficient removal of gasification ash from syngas using a Siemens-Westinghouse candle filter [1], [2], [3], [4]. Extensive testing with ceramic, sintered metal powder, and sintered metal fiber elements has shown that the mass concentration of gasification ash can be reduced from 10,000-30,000 ppmw at the filter inlet to less than 0.1 ppmw at the filter outlet [4]. Experience at the PSDF has shown that ceramic filter elements are prone to crack and fail during thermal excursions associated with coal feeder trips and other system upsets. To avoid these failures, recent testing at the PSDF has focused on the metal filter elements, primarily iron aluminide (Fe3Al) sintered metal powder, HR-160 sintered metal fiber, and Fecralloy sintered metal fiber. Through 2007, the maximum accumulated syngas exposure for each media type was: 9,959 hours for Fe3Al sintered metal powder elements; 3,007 hours for HR-160 sintered metal fiber elements; 8,249 hours for HR-160 failsafes; 2,281 hours for Fecralloy media in coupon form; and 481 hours for Fecralloy elements. Filter element testing at the PSDF has been conducted during gasification runs with Powder River Basin (PRB) subbituminous coal, several types of North Dakota lignite, Hiawatha bituminous coal, Illinois-basin bituminous coal, and Alabama bituminous coals. After each test run, selected filter elements have been removed for detailed inspection under the optical microscope, flow testing to check for any change in pressure drop characteristics, and bubble testing to identify any media or