Summary of Mercury Data from Long-Term Injection Test No 1

Figure 6-14 shows the SCEM total mercury concentrations measured at the ESP inlet, ESP outlet, and FGD outlet over the course of the first 2-week continuous injection test. Figures 6-15 through 6-17 show hourly averages of the total and elemental mercury concentrations measured at each of the three locations.

As noted in the discussion of the parametric test results, there was a negative bias in the measurement of total vapor-phase mercury upstream of the scrubber. This bias was caused by the presence of bromine in the flue gas. The bias was not confirmed until after the test program was completed and coal and ash mercury concentrations were available for data analysis. This bias is explored further at the end of this report, when the coal and ash mercury results are presented. For the long-term tests, the total vapor-phase mercury concentrations are presented in Figures 6-14, 6-15, and 6-16, with the caveat that the values are likely biased low at the scrubber inlet.

This bias does not exist at the scrubber outlet because the scrubber removes the flue gas bromine; therefore, the total mercury concentrations at the scrubber outlet should be reliable. Because the scrubber inlet elemental mercury concentrations matched well with the scrubber outlet total mercury concentrations, it is believed that the scrubber inlet elemental mercury concentrations were not subject to the measurement bias.

Figure 6-14. Hourly averaged total mercury concentration from SCEM data collected during CaBr injection at approximately 55 ppm Br equivalent in the dry coal, first 2-week long-term

Figure 6-15. ESP inlet total and elemental mercury concentrations measured during CaBr2

injection at approximately 55 ppm Br equivalent in the dry coal, first 2-week long-term test at MoSES.

Figure 6-16. ESP outlet total and elemental mercury concentrations measured during CaBr2

injection at approximately 55 ppm Br equivalent in the dry coal, first 2-week long-term test at MoSES.

Figure 6-17. FGD outlet total and elemental mercury concentrations measured during CaBr2

injection at approximately 55 ppm Br equivalent in the dry coal, first 2-week long-term test at MoSES.

In the long-term data analysis, test average coal mercury values were used in place of the scrubber inlet total vapor-phase mercury concentrations measured by the SCEMs. The average coal mercury concentration for each entire test period was compared to the average SCEM data for the entire test period. Calculations were not made for individual days because of the difficulty in obtaining single coal samples that were representative of the flue gas mercury concentration. The coal mercury data were coupled with the inlet elemental mercury data to determine average mercury oxidation during the long-term injection test periods. Using this methodology, the vapor-phase mercury at the scrubber inlet was on average 67% oxidized at an injection rate of 55 ppm Br in the coal.

The weight fraction of Texas lignite coal fired by Unit 3 varied over the course of the first long-term test, ranging from 47% to 69%. Figure 6-18 plots the percent oxidation of mercury at the ESP outlet and the percent removal of vapor-phase mercury across the FGD versus the weight fraction of Texas lignite fired. For the range of coal blends tested, there is no clear relationship between mercury oxidation/removal and the fraction of Texas lignite in the coal blend.

The average coal mercury data were coupled with the average scrubber outlet mercury concentration to quantify the overall mercury removal obtained during the long-term injection test period. Using this methodology, the vapor-phase mercury removal for the system was

Figure 6-18. Effect of coal blend on oxidation and removal of flue gas mercury during long-term test No. 1.

Prior to the start of the injection test, the scrubber inlet elemental mercury concentration and the scrubber outlet total mercury concentration ranged from 10 to 20 µg/dNm3 (3% O2).

During the first day of the injection test, the ESP inlet and ESP outlet elemental mercury concentrations decreased significantly, and the scrubber outlet mercury concentration decreased to 3–7 µg/Nm3. On the following 6 days, the scrubber outlet mercury concentration steadily increased to approximately 12 µg/Nm3; however, the ESP inlet concentration also increased during this time period. On November 11, 2005, the scrubber C module (which is the module on which SCEM measurements were being made) was taken out of service for 2 days. The scrubber C module was placed back in service on November 13. During the first 2 days back in service, the scrubber outlet mercury concentration steadily increased from 5 to 12 µg/Nm3. For the remainder of the test period (November 15 to 18), the scrubber outlet mercury concentrations remained in this range.

A possibility for this phenomenon could be a positive bias in the scrubber outlet extraction system, caused by the vaporization of mercury in the FGD slurry accidentally captured in the extraction loop. However, the scrubber outlet extraction loop was kept under constant supervision, cleaning, and maintenance during this test program. Typically, when the scrubber outlet mercury concentrations were biased high, the biased period lasted for a finite period of time on the order of a few to several hours. In this case, the elevated scrubber concentrations were maintained for several days, despite cleaning of the scrubber extraction loop.

Figure 6-19 compares the scrubber outlet total mercury concentration to the scrubber inlet (ESP outlet) elemental mercury concentration. In a situation with complete removal of oxidized mercury and no mercury reemissions across the scrubber, these two values should be equal. Figure 6-19 shows that the values are equivalent for the baseline period prior to the injection test and for the first half of the injection test (through November 14, 2005). After that period, the scrubber outlet total mercury concentration was, at times, more than double the scrubber inlet elemental mercury concentration.

Appendix K measurements were made at the stack during the first long-term injection test. The results are provided in Table 6–9. The stack flue gas is composed of approximately 60% gas that is treated by the FGD scrubber and 40% gas that bypasses the FGD scrubber. To compare the SCEM data to the Appendix K data, a composite stack SCEM concentration was calculated as follows:

Composite Stack SCEM Hg = 0.6 × Scrubber Outlet SCEM + 0.4 × ESP Outlet Hg SCEM

The composite stack concentration was alternatively calculated with the ESP inlet (rather than ESP outlet) mercury concentration from the SCEM. Figure 6–20 shows a comparison of both of these methodologies to the Appendix K data. All three data sets show the same trend in the concentration over the course of the test program. The composite concentration calculated from the ESP inlet data matches very well with the Appendix K data. All seven runs were within

Table 6-9. Appendix K Measurements at Unit 3 Stack During Long-Term Test No. 1 Condition Date Start Time End Time

Stack Flue Gas Hg Concentration (µg/dNm3 at 3% O2)* 55 ppm 11/08/05 09:45 13:45 9.6 55 ppm 11/08/05 09:45 13:45 9.5 55 ppm 11/09/05 13:06 17:06 14.5 55 ppm 11/09/05 13:06 17:06 12.6 55 ppm 11/11/05 10:35 14:35 21.2 55 ppm 11/11/05 10:35 14:35 18.9 55 ppm 11/14/05 13:50 17:50 15.4 55 ppm 11/14/05 13:50 17:50 14.8 55 ppm 11/16/05 08:07 12:07 14.4 55 ppm 11/16/05 08:07 12:07 13.6 55 ppm 11/16/05 12:41 16:41 15.5 55 ppm 11/16/05 12:41 16:41 13.9 55 ppm 11/17/05 11:35 15:35 10.0 55 ppm 11/17/05 11:35 15:35 9.0 55 ppm 11/18/05 08:28 12:28 13.8 55 ppm 11/18/05 08:28 12:28 14.6

* Oxygen concentrations were not originally reported with Appendix K measurements. Assumed 7% O2 concentration on the stack, based on a weighted average of O2 concentrations measured by EPRI SCEMs at the ESP outlet and FGD outlet.

±20% of each other, with five of the seven runs within ±7% of each other. When the ESP outlet SCEM data are used to calculate the composite stack concentration, the composite stack data are within –5% to –35% of the Appendix K data. The agreement between the Appendix K and SCEM data indicate that elevated mercury concentrations measured by the SCEM at the scrubber outlet may have been real and not the result of a sampling artifact.

Based on a preliminary evaluation of these data made immediately following the conclusion of the first 2-week injection test, the project team elected to conduct the second 2-week injection test at double the CaBr2 injection rate. The results for the second 2-week

injection test are presented in the next subsection.