Real Time Detection of Gaseous Metal Contaminants in Coal Flue and Fuel Gas
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The Integrated Gasification Combined Cycle (IGCC) is a promising technology for the future use of coal to provide energy. During this process, many of the trace elements present in coal are volatilized, and remain in the gas phase through the gas turbine, only to be released in the flue gas. Trace metals are of particular environmental concern, and thermodynamic studies have indicated that Hg (as elemental Hg), Se (as hydrogen selenide, H2Se) and As (as arsine, AsH3), as well as P (as phosphine, PH3) will be present as gaseous metal species. While mercury has long been of environmental concern, there is increasing evidence that the other trace metals will have a significant environmental impact if coal continues to be a primary source of energy as expected. It will become valuable to develop a method for real-time detection of the gaseous trace metals to determine the actual concentration in the flue gas, and the effectiveness of sorbents for the removal of the trace metals. A commercial gas chromatography/ion trap mass spectrometry system has been used to detect AsH3, H2Se, PH3 and elemental Hg. Detection limits in He carrier gas range from 0.1 ppmv for PH3 and AsH3 and 0.5 ppmv for H2Se were observed. Elemental Hg was observable, down to a 0.5 ppmv level, although repeatability was decreased due to the need for manual injections using a gas tight syringe. AsH3, PH3 and H2Se were simultaneously detectable in the same He carrier gas stream at similar detection limits. The trace elements were detectable in a simulated fuel gas containing CO, CO2, H2 and N2. In all situations, a linear response to concentration was demonstrated, with no decrease in signal over time.