Grantee Research Project Results
Final Report: Sorbent Traps for Continuous Measurement of Metal HAP Emissions
EPA Contract Number: 68HERC22C0011Title: Sorbent Traps for Continuous Measurement of Metal HAP Emissions
Investigators: Cross, Jonathan
Small Business: Ohio Lumex Company, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: December 1, 2021 through May 31, 2022
Project Amount: $99,950
RFA: Small Business Innovation Research (SBIR) Phase I (2022) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air
Description:
During this Phase I SBIR research project, Ohio Lumex developed and evaluated three sorbent trap materials for continuous emissions monitoring of metal hazardous air pollutant (HAP) emissions. Metal HAP emissions from stationary sources are currently determined using emissions factors derived from intermittent stack testing measurements, input feed stream data, and plant operating parameters. Emissions factors may have significant uncertainty, particularly for sources where feed stream metal content is highly variable. Continuous measurements are needed to provide superior accuracy, but current technology is limited and cost prohibitive.
Metal HAP sorbent traps are designed to meet that need with repetitive in-stack sampling and periodic analysis of time-integrated samples collected over a period of several days. This approach is analogous to EPA Performance Specification 12B (PS 12B) for mercury measurement.
The sorbent trap method developed during this research project is applicable to several industries. It has been designed with particular focus on continuous sampling for hazardous waste combustors, metal smelting operations, iron and steel production, secondary smelting facilities, and coal -fired power plants. However, if the method sensitivity is improved and the sorbent background is reduced, metal HAP sorbent traps could also be used for short-term (1-4 hours) sampling in lieu of EPA Method 29.
Continuous measurement of metal HAP emissions will improve EPA's air emissions inventory and allow point sources to better understand their emissions. Sources that utilize control technologies to remove metals from the gas stream can use this information to optimize controls. For short-term testing, this method will benefit stack testers, who almost universally agree Method 29 is cumbersome, expensive, and hazardous.
The metals analyzed during this Phase I research project are Sb, As, Ba, Be, Cd, Cr, Co, Cu, Pb, Mn, Ni, Se, Ag, Tl, Zn, and Hg. However, Ba, Ag, Tl, and Zn are considered "noncritical metals" as their measurement is not required for any of the targeted applications.
Several sorbent materials were developed and tested during this Phase I research project. Background concentrations were measured on all materials, and those that had acceptable background concentrations were subjected to additional testing, including: a direct matrix spike recovery test and a simulated stack gas spike recovery test. Pass/fail criteria were established for these tests based on PS 12B spike recovery criteria.
Summary/Accomplishments (Outputs/Outcomes):
Measurement of Background Metals
All sorbent material samples, inert plug separators, and synthesis reagents were analyzed for background metals. Analytical methods used during this research include EPA Methods 6010 (ICP-OES), 6020 (ICP-MS), and 7470 (CVAAS). In some cases, multiple iterations of tests were performed on successive batches of material as treatment and synthesis processes improved over the course of research. Background concentrations were compared to acceptable limits for each metal. These limits were defined as 20% of the estimated capture with 2500L of sampled gas where the concentration of metals in the gas was equal to the Mercury and Air Toxics Standard (MATS) limits. 2500L is a typical sample volume for stationary sources that sample PS 12B sorbent traps using proportional flow sampling, and although there are several assumptions incorporated into the limits, these assumptions provide a reasonable benchmark against which the tested materials could be compared.
Two of the sorbent materials synthesized and/or treated during this Phase I research project contained background metals at concentrations below the acceptable limits, for all metals. A third sorbent material contained cadmium and arsenic above the acceptable limits, but this material can be purified further. All three materials are considered viable candidates for further research. All materials were subjected to the remaining tests during Phase I and will be evaluated further during Phase II. Each material provides unique advantages, and having multiple options provides a greater chance of success during Phase II testing.
Direct Matrix Spike Recovery
Three spike levels were selected, and three samples of each sorbent material were spiked at each level with aliquots of aqueous standards - resulting in nine spiked samples for each material. Additionally, blank sorbent material from each sorbent batch was analyzed for background metal content.
Direct matrix spike recovery was generally acceptable (85-115% recovery) for all three materials, although there were outliers. These outliers were primarily due to a small number of contamination events, as it is quite easy to inadvertently contaminate samples or batch blanks with common metals found in a laboratory environment. Silver also proved difficult to recover above 85%, and this was likely due to precipitation of silver chloride. Measurement of silver is not considered critical for the success of this method and will likely be removed from the range of metals analyzed during future tests.
Simulated Stack Gas Matrix Spike Recovery Test
Each sorbent material was used to create 3-section sorbent traps, with the third section of each trap spiked with all target metals. Each sorbent material was used to create six sorbent traps, with three traps spiked at a high mass loading, and three traps spiked at a low mass loading. These sorbent traps were then inserted into a simulated stack gas test environment at Ohio Lumex. The simulated stack gas mixture was sampled through each group of six sorbent traps continuously for seven days, resulting in a total of approximately 5000L of sample gas.
Spike recoveries were generally within the target range of 75-125%, with a small number of outliers. Again, these outliers were primarily the result of intermittent contamination events. A few low recoveries occurred with one of the sorbent materials, which may be indicative of poor retention for those metals. Further investigation will indicate whether those low recoveries were the result of actual sample loss or an artifact in sample preparation and analysis.
At the time of writing, analysis of the samples for the simulated stack gas matrix spike recovery test has only been completed for two materials. One material performed exceptionally well, while the second will need modification to the synthesis procedure to alter its physical properties and enhance retention.
Conclusions:
Ohio Lumex has developed and tested three sorbent materials for use in a metal HAP sorbent trap. All sorbent materials had acceptable background concentrations for compliance testing and gaseous fuel quality measurements, with the exception of cadmium and arsenic in the third sorbent material.
Aside from laboratory errors, the occasional failure due to intermittent contamination, and recovery of silver, direct spike recovery was acceptable (85-115%) for all tested sorbent materials. Most simulated stack gas spike recoveries were acceptable (75-125%) with the exception of occasional contamination events that affected low-level spike recoveries. The handling procedures for material during production, spiking, assembly, sample digestion, and analysis will need to be reviewed and improved to ensure measurements are consistently accurate.
The data acquired during Phase I indicates the tested sorbent materials are promising candidates for use in a metal HAPs sorbent trap.
The sorbent trap developed during this research project was designed to be applicable to two separate target markets. These markets are:
- Primary Market - Metal HAP Emissions: hazardous waste combustors, incinerators, secondary smelting plants, iron and steel mills, foundries, metal scrap recycling, and coal-fired utilities.
- Secondary Market - Gaseous Fuel Quality Analysis: Landfill and wastewater treatment biogas, renewable natural gas.
Commercialization efforts will begin for the secondary market during Phase II after the product is further along in development. Commercialization efforts for the primary market will likely begin towards the end of Phase II after an EPA Method 301 comparison study with Method 29 has been completed.
SBIR Phase II:
Sorbent Traps for Continuous Measurement of Metal HAP Emissions - Phase IIThe 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.