Grantee Research Project Results

Final Report: Sample Conditioning System for Real-Time Mercury Analysis

EPA Contract Number: 68D00228
Title: Sample Conditioning System for Real-Time Mercury Analysis
Investigators: Sjostrom, Sharon M.
Small Business: Apogee Scientific Inc.
EPA Contact:
Phase: I
Project Period: September 1, 2000 through March 1, 2001
Project Amount: $69,935
RFA: Small Business Innovation Research (SBIR) - Phase I (2000) RFA Text |  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 (EPA) has submitted a Mercury Study Report to Congress that states that 52 of the 158 tons of anthropogenic Hg emissions in the United States is from coal-fired utility boilers. On December 14^th 2000, EPA announced that it would regulate mercury emissions from coal-fired boilers under Title III of the Clean Air Act Amendments of 1990. EPA plans to issue final regulations by December 15^th 2004 and is expected to require compliance by December 2007. Although a few mercury analyzers show promise for measuring elemental mercury, a reliable sampling system that will allow these analyzers to measure total and speciated mercury 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 mercury (Hg), elemental mercury (Hg⁰), and oxidized mercury (Hg²⁺) 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 is currently being considered, and when implemented will likely cost billions of dollars each year. Most of the Hg control strategies being proposed for coal-fired utility boiler flue gas include some type of sorbent injection. 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 would also provide options for advanced process control feed-back as well as for monitoring the performance of the control system, thus minimizing sorbent usage and 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 program specifically targeted the design of a 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:

1. Mercury 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).
   
2. Mercury in flue gas is present as both elemental and oxidized mercury. It is important to be able to distinguish between these two forms, but not important to distinguished between the different forms of oxidized mercury.
   
3. Currently available analyzers such as CVAAS and CVAFS are sufficiently sensitive, fast, and reliable for this application. However, these analyzers can only measure elemental mercury directly 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.
   
4. Elemental mercury can be transported through sample tubing if appropriate precautions are taken. Oxidized forms of mercury are very difficult to transport through sample tubing.
   
5. It is important to test a flue gas sampling system on actual flue gas.
   
6. Any system to be used for field monitoring must be reliable, easy to operate, and require minimal routine maintenance.

Apogee conducted this program to define a new state-of-the-art mercury measurement by developing a novel SCS for the continuous real-time monitoring of mercury in flue gas from coal-fired utility boilers. The system is a dual-pass design, where total vapor-phase mercury passes through one line and the elemental fraction through the second line. Particulate matter is removed from a common sampling probe and the flow is split to the two lines. All components in the two lines are identical except that oxidized mercury is removed from the sample gas stream upstream of other components in the second line. In both lines, the gas stream then passes through a reduction catalyst to convert mercury to the elemental form. The gas is then conditioned to remove possible interfering gases and to stabilize the elemental mercury prior to transport to an analyzer for measurement. In the new system, sample conditioning takes place at the stack and only elemental mercury is being conveyed from the stack to the analyzer. Thus, problems related to reactivity and surface losses are minimized.

The research carried out during this Phase I program included the design and fabrication of the SCS, performance testing in the laboratory with simulated flue gas representing a wide range of coal types, and performance testing at a field site burning Powder River Basin coal.

The overall technical objective was to demonstrate a sampling system that allows commercially available on-line mercury analyzers (e.g. CVAAS and CVAFS) to measure total mercury and to differentiate between elemental and speciated mercury without interference from typical gas constituents. The contents of this report will show that this objective was successfully completed.

Summary/Accomplishments (Outputs/Outcomes):

Following testing of the individual components, the system was assembled in the lab for parametric testing. The specific tests were designed to evaluate the effectiveness of the system over a variety of test conditions. The SCS was evaluated in 5 different test series representing various flue gas compositions. The flue gas compositions tested are shown in Table ES-1.

Table ES-1. Sampling Conditioning System Assembly: Laboratory Test Matrix

Gas	Series I	Series II	Series III	Series IV	Series V
O2	4%	4%	4%	4%	4%
CO2	8.8%	8%	8%	7.5%	7.5%
H2O	10%	10%	10%	10%	10%
N2	balance	balance	balance	balance	balance
SO2	0	200 ppm	0 ppm	1500 ppm	1500 ppm
SO3	0	0	0	0	10 ppm
NO	0	0	200 ppm	600 ppm	600 ppm
NO2	0, 50 ppm	0, 50 ppm	0, 50 ppm	0, 50 ppm	50 ppm
HCl	0, 100 ppm	0, 100 ppm	0, 100 ppm	0, 100 ppm	100 ppm
Cl2	0, 2 ppm	0, 2 ppm	0, 2 ppm	0, 2 ppm	0 ppm
Hg0	0, 1 ppb	0, 1 ppb	0, 1 ppb	0, 1 ppb	0, 1 ppb
HgCl2	0, 1 ppb	0, 1 ppb	0, 1 ppb	0, 1 ppb	0, 1 ppb

Testing results indicate that the SCS was effective at conditioning a mercury-laden gas sample for total mercury measurement in a commercially available, real-time mercury analyzer. For the five gas mixes evaluated in the laboratory, there was a 98% correlation between measurements made with a CVAAS using either the SCS or an impinger-based method. A comparison of results from these methods for all test series is presented in Figure ES-1. In addition, 92% of the vapor-phase mercury reported as elemental mercury by the impinger method was reported as elemental mercury by the SCS method. These results are presented in Figure ES-2. No flue gas species that interfered with mercury measurement were observed downstream of the SCS. Further testing is required to improve the effectiveness of the speciation technique, to package the system for prolonged field use, to conduct extensive verification tests in the laboratory, and to conduct longer-term field performance evaluation.

Conclusions:

Several questions were posed in the Phase I proposal and answered during this program to determine the feasibility of this approach for a sampling system. Answers to several key questions as determined throughout this program are provided here.

• Will a reduction catalyst effectively reduce Hg₂+ to Hg₀?
  
  • Phase I results demonstrate that the reduction catalyst effectively reduces Hg₂+ to Hg₀ in a wide range of typical flue gas mixes.
    
• Is the effectiveness of the reduction catalyst affected by variations in typical flue gas constituents?
  • Laboratory tests were conducted in five different flue gas mixes and the correlation between total mercury measured with wet impingers and with the sample conditioning system was 98%. This indicates that the catalyst effectively reduced Hg₂+ to Hg₀. The gas mixes included 4% O₂, 10% H₂O, 8% CO₂, 0 to 2 ppm Cl₂, 0 to 1500 ppm SO₂, 0 to 600 ppm NO, 0 to 50 ppm NO₂, and 0 to 100 ppm HCl.
• Will the high surface area HgCl₂ removal module eliminate most of the HgCl₂ from the gas stream without converting Hg₀ to Hg₂₊, regardless of typical flue gas constituent concentrations?
  
  • The HgCl₂ removal module, or Nautilus Reactor, removed 100% of the HgCl₂ during component screening tests and an average of 92% during system testing. Minor improvements to the Nautilus design should improve the effectiveness. No conversion of elemental mercury to oxidized mercury was measured. The Nautilus is also an effective HCl trap. Laboratory measurements indicated 99.8% of the incoming HCl was removed in the Nautilus.
    
• Does any flue gas species remaining in the sample stream downstream of the catalyst and HCl trap interfere with mercury measurement for common on-line Hg analyzers such as Zeeman-modulated CVAAS or gold amalgamation CVAAS or CVAFS analyzers?
  
  • The sample conditioning system effectively removed common interfering species including a significant fraction of the SO₂ and NO and virtually all of the HCl, H₂O and NO₂. Although not measured, most of the SO₃ and HF should have been removed by the system.

This Phase I report represents a successful completion of the objectives defined in the Phase I proposal including a demonstration of the prototype sample conditioning system in the laboratory and in the field. The Phase I efforts also provided concise answers to technical questions posed in the proposal.

Figure ES-1. Comparison of total vapor mercury measured using the impinger method and SCS method for five simulated flue gas mixes.

Figure ES-2. Oxidized mercury from the HgCl2 permeation source as measured using the impinger method and the SCS for Series II-V Tests.

Supplemental Keywords:

Mercury, mercury measurement, speciated mercury, mercury analysis, emissions monitor, sample conditioning system., RFA, Scientific Discipline, Toxics, Air, Waste, Ecosystem Protection/Environmental Exposure & Risk, air toxics, HAPS, Chemistry, Monitoring/Modeling, Environmental Monitoring, tropospheric ozone, 33/50, Engineering, Chemistry, & Physics, Environmental Engineering, Incineration/Combustion, monitoring, combustion byproducts, continuous measurement, mercury, real time, emission control technologies, coal fired utility boiler , stratospheric ozone, combustion-related pollutants, real time mercury analysis, analyzer, elemental mercury, air pollution, combustor/incinerator emissions, mercury monitoring, mercury & mercury compounds, Mercury Compounds, continuous emissions monitoring, atmospheric monitoring

SBIR Phase II:

Sample Conditioning System for Real-Time Mercury Analysis  | 2000 Progress Report  | Final Report