ACOUSTO-ULTRASOUND NONDESTRUCTIVE CHARACTERIZATION OF RIGID CERAMIC HOT GAS FILTERS

摘要

In commercial advanced coal-fired power generation utility stations, one technology under development to clean up hot gases before their use as fuel for gas turbines is the use of rigid ceramic hot gas candle filters. These porous filters are typically 1.5 m long and 60 mm in diameter and are made of various ceramic materials, including clay-bonded SiC. The high costs of downtime in a large utility demands that nondestructive characterization (NDC) methods be available so that at shutdowns, decisions can be made about which filters are still useable and which need to be replaced, and if possible, estimates can be made about remaining lifetimes. Recently, an NDC technology referred to as acousto-ultrasonics (AU) has been developed and applied to rigid ceramic filters. 150 kHz transducers (both fixed and in a wheel system for high-speed throughput) were used to study filter elements from a wide variety of exposure conditions. Lamb waves generated by the AU method were studied, and from the detected Lamb wave signal a stress-wave factor (SWF) was obtained. The SWF data were then correlated to measured strength values of the filters. Strength was measured by several methods, including internal hydrostatic burst pressure, 4-point bend, C-ring compression, and O-ring compression. The filters examined by the AU method included exposures in various coal pilot plant facilities, as well as in laboratory tests where they were exposed at 900℃ in air and in air with water vapor. The AU data correlated very well with the strength data regardless of the method used for determining the retained strength of the filters. The AU method, SWF-strength correlation obtained, and other details will be discussed.