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A Cavity Ring-Down Spectroscopy Mercury Continuous Emission Monitor Progress Report

Description: Accurate reporting of mercury concentration requires a detailed model that includes experimental parameters that vary, such as: pressure, temperature, concentration, absorption cross-section, and isotopic structure etc. During this quarter a theoretical model has been developed to model the 253.7 nm mercury transition. In addition, while testing the interferent species SO{sub 2}, SRD was able to determine the absorption cross-section experimentally and add this to the theoretical model. Assuming that the baseline losses are due to the mirror reflectivity and SO{sub 2}, SRD can now determine the concentrations of both mercury and SO{sub 2} from the data taken. For the CRD instrument to perform as a continuous emission monitor it will be required to monitor mercury concentrations over extended periods of time. The stability of monitoring mercury concentrations over time with the CRD apparatus was tested during the past quarter. During a test which monitored the mercury concentration every 2 seconds it was found that the standard deviation, of a signal from about 1.25 ppb Hg, was only 30 ppt. SRD continued interferent gas testing during this past quarter. This included creating a simulated flue gas composed of the gases tested individually by SRD. The detection limits for mercury, although dependent on the concentration of SO{sub 2} in the simulated gas matrix, remained well below the ppb range. It was determined that for the gases tested the only measurable changes in the baseline level occurred for SO{sub 2} and mercury. Speciation studies continued with mercury chloride (HgCl{sub 2}). This included checking for spectral speciation with both Hg and HgCl{sub 2} present in the CRD cavity. There was no observable spectral shift. Also a pyrolysis oven was incorporated into the gas delivery system both for tests with HgCl{sub 2} as well as atomization of the entire gas stream. The pyrolysis tests conducted …
Date: April 1, 2003
Creator: Carter, Christopher C.

A Cavity Ring-Down Spectroscopy Mercury Continuous Emission Monitor Progress Report

Description: Previous work on the detection of mercury using the cavity ring-down (CRD) technique has concentrated on the detection and characterization of the desired mercury transition. Interferent species present in flue gas emissions have been tested as well as a simulated flue gas stream. Additionally, work has been done on different mercury species such as the elemental and oxidized forms. The next phase of the effort deals with the actual sampling system. This sampling system will be responsible for acquiring a sample stream from the flue gas stack, taking it to the CRD cavity where it will be analyzed and returning the gas stream to the stack. In the process of transporting the sample gas stream every effort must be taken to minimize any losses of mercury to the walls of the sampling system as well as maintaining the mercury in its specific state (i.e. elemental, oxidized, or other mercury compounds). SRD first evaluated a number of commercially available sampling systems. These systems ranged from a complete sampling system to a number of individual components for specific tasks. SRD engineers used some commercially available components and designed a sampling system suited to the needs of the CRD instrument. This included components such as a pyrolysis oven to convert all forms of mercury to elemental mercury, a calibration air source to ensure mirror alignment and quality of the mirror surfaces, and a pumping system to maintain the CRD cavity pressure from atmospheric pressure (760 torr) down to about 50 torr. SRD also began evaluating methods for the CRD instrument to automatically find the center of a mercury transition. This procedure is necessary as the instrument must periodically measure the baseline losses of the cavity off of the mercury resonance and then return to the center of the transition to accurately measure the …
Date: June 30, 2003
Creator: Carter, Christopher C.
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