Grantee Research Project Results
Final Report: Sample Conditioning System for Real-Time Mercury Analysis
EPA Contract Number: 68D01060Title: Sample Conditioning System for Real-Time Mercury Analysis
Investigators: McLaren, Scott
Small Business: Apogee Scientific Inc.
EPA Contact: Richards, April
Phase: II
Project Period: September 1, 2001 through September 1, 2003
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2001) Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)
Description:
Mercury (Hg) from combustion sources is recognized as a major concern to the Nation's air quality. The U.S. Environmental Protection Agency's (EPA) Mercury Study Report to Congress states that 52 of the 158 tons of anthropogenic Hg emissions in the United States are from coal-fired utility boilers.1 On December 14, 2000, EPA announced that it would regulate Hg emissions from coal-fired boilers under Title III of the Clean Air Act Amendments of 1990. On December 15, 2003, EPA proposed regulation to limit the emissions of Hg from utility boilers. The proposed regulation is phrased such that there exist two possible forms of control, which currently are undergoing public commentary. Under the regulations proposed by EPA there will be either a "Cap and Trade" or Maximum Achievable Control Technology standard approach. Regardless of which regulation option is enacted, monitoring of Hg emissions will become both necessary and required. Although a few Hg analyzers show promise for measuring elemental Hg, a reliable sampling system that will allow these analyzers to measure total and speciated Hg continuously and in real time in the flue gas of coal-fired utility boilers is needed.
Apogee Scientific, Inc. (Apogee), has investigated an innovative Sample Conditioning System (SCS) that, in conjunction with currently available analyzers (e.g., cold vapor atomic absorption spectrometers [CVAAS], cold vapor atomic fluorescence spectrometers [CVAAFS]), will enable real-time monitoring of total vapor Hg, elemental Hg, and oxidized vapor Hg in flue gas. Real-time continuous monitoring of Hg in flue gas is essential for several reasons. Control of Hg emissions from coal-fired utility boilers currently is being considered, and when implemented likely will cost billions of dollars each year. Prior to installing a control system, more accurate measurements of Hg emissions would allow EPA and the utility to make more informed decisions concerning their needs and control options. Real-time continuous monitoring of Hg also would provide options for advanced process control feedback as well as for monitoring the performance of the control system, thus lowering the cost of controls. Other applications of this technology include Hg emission monitoring from other sources, such as municipal waste incinerators, commercial/industrial boilers, medical waste incinerators, and crematories. This research project specifically targeted the further design and evaluation of Apogee's SCS that can be used for the continuous real-time monitoring of Hg in flue gas from coal-fired utility boilers. The essence of this program was based upon the following premises:
• Vapor-phase Hg concentration in flue gas needs to be monitored in real time (less than 5 minutes per measurement) and on a continuous basis (operation for at least 1 week without operator intervention).
• Vapor-phase Hg in flue gas is present as both elemental and oxidized Hg. It is most important to be able to measure the total (elemental + oxidized) Hg concentration. Distinguishing between the elemental and oxidized forms of Hg is important for designing control systems and other research activities.
• Currently available analyzers such as CVAAS and CVAFS are sufficiently sensitive, fast, and reliable for this application. However, these analyzers can only measure elemental Hg directly2 and suffer interference from commonly encountered flue gas constituents (e.g., fine particles, SO2, SO3, HCl, HF, H2O, NO, NO2) either in the sample conditioning process or in the actual measurement.
• Elemental Hg can be transported through sample tubing if appropriate precautions are taken. Oxidized forms of Hg are very difficult to transport through sample tubing.3
• It is important to test a flue gas sampling system on actual flue gas and various fuel sources.
• Any system to be used for field monitoring must be reliable, easy to operate, and require minimal routine maintenance.
The Phase II research project was conducted to further define and evaluate Apogee's new state-of-the-art Hg measurement SCS for the continuous real-time monitoring of Hg in flue gas from coal-fired utility boilers. The system is a dual-pass design, in which total vapor-phase Hg passes through one line and the elemental fraction through the second line. Particulate matter was removed from the flue gas using a QSISTM filter and the flow then was split into the two lines. All components in the two lines are identical, except that oxidized Hg is removed from the sample gas stream upstream of other components in the second line. In both lines, the gas stream was passed through a reduction catalyst to convert all vapor-phase Hg to elemental Hg. The gas then was conditioned to remove possible interfering gases and to stabilize the elemental Hg prior to transport to an analyzer for measurement. In this system, sample conditioning takes place at the extraction point and only elemental Hg is being transported from the extraction point to the analyzer. Thus, problems related to reactivity and surface losses are minimized.
Phase II research included the further design and fabrication of the SCS, further performance testing in the laboratory, and performance evaluations at multiple field sites burning various coal types. The overall technical objective was to demonstrate a sampling system that allows commercially available online Hg analyzers (e.g., CVAAS and CVAFS) to measure total vapor Hg and to differentiate between elemental and speciated Hg without interference from typical flue gas constituents. These evaluations have been completed.
Summary/Accomplishments (Outputs/Outcomes):
Following the conclusion of the Phase I initial testing of the system both in laboratory and field settings, the Apogee SCS needed to be proven on actual flue gas for longer periods of time. Evaluations of the novel SCS were performed at different utilities burning various coal types. Testing included all aspects of the SCS, the total vapor mercury module (TVM), and the elemental mercury module (EM). The SCS performance was verified by either a series of Ontario Hydro measurements, concurrent measurements made with an accepted wet-chemical impinger system, or overboard calibration. The SCS was tested at four sites representing the three most common fuel types; North Dakota lignite, Eastern bituminous, and Powder River Basin (PRB) sub-bituminous coals.
The first test site was Great River Energy's Coal Creek Station (Site 1) in Underwood, ND, representing North Dakota lignite coal. SCS evaluations at Site 1 occurred during May 2002. The test location was downstream of the unit's cold-side electrostatic precipitator (ESP), but upstream of the wet scrubber. Testing at this site went according to the original plan, with Ontario Hydro measurements made to verify the performance of the SCS, and both the EM and TVM modules were subjected to the Draft PS-12 test program. The SCS performance was within the specifications laid out under EPA's Draft PS-12 for the majority of the test period at Site 1. However, the Ontario Hydro measurements made to verify the performance of the system were rendered suspect by mishandling and operator error at the analysis laboratory.
The second test site, representing Eastern bituminous fuel, was Public Service Gas and Electric's Hudson Station (Site 2), in Jersey City, NJ. The test location was downstream of the unit's cold-side ESP. Testing at this site began in late July 2002, and was completed in October 2003. Problems with the performance of the system were encountered almost immediately; the TVM module encountered Hg loss in the transport line after the reduction catalyst. This was remedied by either replacing the transport line or cleaning the line with distilled water; however, the tubing became fouled again in a short time. This particular problem was encountered on several trips to the site. It was decided that modifications to the system were required, and that further test efforts would focus on evaluating the TVM module alone, because the EM module had performed within expectations. Although several theories were formulated to explain the behavior observed in the TVM module, the solution prescribed by each was never effective. Upon further investigation, it was concluded that selenium present in the gas stream was being reduced in the TVM module to hydrogen selenide, which was responsible for the observed performance. This theory was tested in the laboratory, and the results concluded that hydrogen selenide reacted with and acted to scrub Hg from the gas stream. To resolve the selenium issue, an injection of ammonia gas at the exit point of the TVM module prevented the reoccurrence of the previously observed behavior. Laboratory testing of this solution indicated that it did allow the SCS to operate on gas streams containing selenium. After modifications to the SCS, the system was able to operate at Site 2 over an extended period without failure.
The third test site (Site 3) was a PRB coal-burning utility at which the TVM module was tested in conjunction with an EPRI test program running at the site. This opportunity allowed for the TVM module to be comparatively tested against an accepted wet chemical (impinger) system for long periods of time. Performance of the SCS was good, and it appeared that the SCS presented mercury measurements consistently within 10-20 percent of the accepted wet chemical system. This level of agreement is typical of two wet chemical systems operated side by side. In addition, during the test period the analyzer utilizing the wet chemical system experienced regular gold failures, while the analyzer equipped with the TVM module of the SCS did not.
An additional PRB utility (Site 4) was used to test the TVM module in conjunction with an existing Department of Energy/National Energy Technology Laboratory testing effort. The TVM module was tested downstream of the unit’s cold-side ESP. The TVM module tested at this location consisted of an optimized catalyst system, which had been redesigned since the previous testing at Site 3. The TVM module again was tested in comparison to an accepted wet chemical system. Testing continued for over 3 weeks. Performance of the SCS at Site 4 was very good, with little to no supervision or maintenance required for the duration of the test period. As at Site 3, the measurements from the SCS were consistently within 10-15 percent of those made by the accepted wet chemical system.
Although some difficulties were encountered during the Phase II testing of the Apogee SCS, overall the system performed well and demonstrated that it is a technology that is an improvement over existing methods at providing an Hg sample to existing mercury analyzers from a wide variety of actual flue gases.
Conclusions:
The primary focus of this Phase II research project was to conduct field testing on the SCS to demonstrate the feasibility of this technology. Progress made during this project is summarized below:
• The SCS is capable of conditioning gas streams for Hg measurements at a variety of utility locations encompassing a variety of fuel types. Successful testing and demonstration at four individual field locations, encompassing three major fuel types and a variety of control device configurations, indicates that the SCS is capable and effective at conditioning a variety of gas streams.
• The SCS can be used to monitor Hg in flue gas from multiple types of coal. The ultimate success of the Site 2 test program in adapting the SCS to a chemical interferent of a difficult nature proves the technology can be adapted to difficult chemistries while maintaining accuracy.
• The SCS is capable of long-term operation without supervision and frequent maintenance. The long-term testing at Site 4 demonstrates that the SCS can be operated for long periods of time, under typical environmental conditions, and without need of excessive maintenance or monitoring.
• Testing at the Site 1 indicated that the SCS was able meet the criteria specified in the Draft PS-12. However, due to problems with the Ontario Hydro measurements and a plant outage that occurred during the test period, the SCS did not meet the exact requirements for the entire test period.
This Phase II report represents a successful completion of the objectives defined in the Phase II Statement of Work, including demonstration of the SCS technology at various utility locations. The efforts under this Phase II research project have demonstrated the feasibility and effectiveness of the SCS technology.
References:
1. U.S. Environmental Protection Agency. Mercury study report to Congress. Volume I: executive summary, Office of Air Quality Planning and Standards and Office of Research and Development, EPA-452/R-97-003, December 1997.
2. Heidt M, Laudal D. Evaluation of continuous monitors for mercury measurements in pilot-scale tests. In: Proceedings of the Air and Waste Management Association's 91st Annual Meeting and Exhibition, San Diego, CA, June 14-18, 1998 (98-WP79A.04).
3. Roberts DL, Sjostrom S. Issues and progress in the quantitative, continuous monitoring of mercury. Presented at the EPRI-DOE-EPA Joint Workshop, Mercury Measurement and Speciation Methods for Stationary Sources, Research Triangle Park, NC, January 29-30, 1997.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
mercury, Hg, mercury measurement, total vapor mercury module, TVM, elemental mercury module, EM, elemental mercury, speciated mercury, mercury analysis, emissions monitor, sample conditioning system, SCS, combustion, coal-fired boiler, flue gas, Maximum Achievable Control Technology, cold vapor atomic absorption spectrometer, CVAAS, cold vapor atomic fluorescence spectrometer, CVAAFS, small business, SBIR., RFA, Scientific Discipline, Air, Toxics, Waste, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, air toxics, mercury transport, HAPS, Monitoring/Modeling, Environmental Monitoring, tropospheric ozone, Incineration/Combustion, Engineering, 33/50, Engineering, Chemistry, & Physics, Environmental Engineering, monitoring, particulates, stratospheric ozone, coal fired utility boiler , continuous measurement, mercury, real time, combustion sources, particulate mercury, flue gas monitor, continuous monitoring, flue gas, emissions, analyzer, continuous emissions monitoring, mercury & mercury compounds, Mercury Compounds, measurement, sample conditioning system (SCS), atmospheric monitoring, coal combustion, real time monitoring, measurement methods , combustion flue gases, flue gasesSBIR Phase I:
Sample Conditioning System for Real-Time Mercury Analysis | 2001 Progress Report | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.