	Conference Papers
	Commercialization of a Continuous Emissions Monitor for Mercury in Flue Gas P. C. Efthimion & A. Morozov
	The 1990 Clean Air Act Amendments and other legislation have raised the concerns over low trace concentrations of metals, especially mercury, in flue gas from electrical generation plants, municipal waste incinerators, and heavy industry. Monitoring will be used to determine the extent of the environmental impact and offers the possibility of empirically minimizing it. Mercury Continuous Emission Monitor During the past three years a continuous emissions monitor has been developed by EEI for the measurement of total mercury in flue gas. The development was supported by EPA SBIR grants. The instrument is based upon plasma emission spectroscopy. EEI developed a unique high-pressure plasma source that is highly efficient in exciting trace metals in gas streams, such as mercury (Fig. 1). The operation of the plasma source gives EEI’s mercury monitor its extraordinary characteristics.
	Figure 1: High-pressure plasma source for mercury monitoring.
	The instrument has a minimum sensitivity of 0.1 mg/m3 with a signal-to-noise of 3. The instrument can provide measurements on a continuous basis every 7 minutes. A faster time response can be provided if necessary. The instrument pulls a gas sample of flue gas through heated sample lines. There is no processing of the flue gas before the instrument can make measurements. Furthermore, there is no known interference. Last year field measurements were completed at a 300 MW wet-bottom boiler burning eastern bituminous low-sulfur coal. A probe was placed in the duct at the output of the precipitator. At this location a particle filter was not employed. The instrument was mounted adjacent to the duct to keep the heated sample line as short as possible. The instrument schematic is shown in Fig. 2. The gas flow into the plasma source is controlled with a standard pump. Flue gas from the power plant is sampled for 5 minutes and is passed over a mercury absorbent. Typical mercury levels were on the order 1 mg/m3. After collection of flue gas, a carrier gas is flowed over the absorbent while it is heated to desorb the mercury. The mercury latent carrier gas enters the plasma source where it emits light. UV measurements are made at the 253 nm mercury line with a low resolution spectrometer with a CCD camera. Field tests with this instrument configuration were made over a one-month period of time. After setting the sample line temperature to that of the stack, the mercury concentrations were reproducible and in the range of 0.6 - 1.4 mg/m3. Previous measurements of the mercury concentration at this facility using wet chemistry techniques were near 1.5 mg/m3. The mercury levels were calibrated with a NIST standard mercury source whose concentration was verified by independent laboratory analysis. The field measurements were more than a factor of 10 above the instrument’s minimum detection level. During the field tests tuning the instrument’s spectrometer enabled the detection of Arsenic and Selenium in the flue gas.
	Figure 2: Schematic of instrument during initial field testing.
	To verify that the measurements by the mercury monitor during the field tests were only due to mercury, a high sensitivity UV CCD camera was mounted on the spectrometer. Measurements with this configuration were made in the field and in the laboratory. Figure 3 shows the measured spectra near the 253 nm mercury line from the two locations. The spectra are nearly identical and clearly show a large mercury line at the appropriate wavelength, verifying the laboratory and field measurements.
	Figure 3: Hg spectra from Hg collected from laboratory source and utility plant.
	The successful measurement of mercury in the field with our instrumentation technology permitted the commercialization of the instrument. EEI anticipates completing commercialization of a fully integrated instrument with self-calibration capability during the last quarter of year 2000. Only the automation of the instrument needs to be completed. Mercury Sorbent Tests Recently, the EEI instrumentation was used to evaluate zeolyte mercury sorbents at a coal fired utility plant. The ambient mercury levels were low (1.2 mg/m3 ) at the plant and the flue gas was spiked with mercury (5 - 8 mg/m3) for the sorbent tests. The EEI instrumentation verified these mercury levels and they were later confirmed with wet chemistry. Low influx of sorbent only reduced the mercury levels to 1.67 – 3.34 mg/m3. However, with higher influx of sorbent the mercury levels were reduced to 0.3 – 0.43 mg/m3.