Continuous Emission Monitor for Toxic Metals in the Off-Gases of Thermal Treatment Facilities
Self-calibration procedures for continuous monitoring of toxic metals in the off-gases of thermal treatment facilities using laser-induced breakdown spectroscopy (LIBS) were tested. The tests were performed using a heated aerosol/gas flow system that generated simulated off-gas conditions with calibrated amounts of metal in an optical cell. Calibration curves of LIBS signal for metal concentration in the cell were obtained for various gas and optical conditions. Gas conditions that were varied include water in either vapor and condensed aerosol droplet form, the presence of easily ionizable elements (i. e., potassium), speciation of the metal analyte, and the gas temperature. In addition, laser pulse energy, focal length, and detector alignment were independently varied. Two different sets of calibration curves were obtained, one set with Mn(II) and N(II) emission obtained simultaneously and a second set with Cd(I) and Cd(II) emission obtained simultaneously with N(I) emission obtained in a sequential manner. For both sets of data, calibration curves were obtained using 1) single line intensities, 2) the ratio of metal single line intensity to nitrogen single line intensity, and 3) the ratio of total metal emission to total nitrogen emission obtained using the temperature and electron density. Results show that correction using the ratio of metal single line intensity to nitrogen single line intensity does help in maintaining a constant slope of calibration curves for various conditions. However, the total emission self-calibration procedure shows better performance in most cases.
- Research Organization:
- Federal Energy Technology Center, Morgantown, WV, and Pittsburgh, PA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC21-96MC32194
- OSTI ID:
- 1970
- Report Number(s):
- DE-AC21-94MC32194-99; ON: DE00001970
- Country of Publication:
- United States
- Language:
- English
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