Last month, the EPA finalized mercury and air toxic standards for coal- and oil-fired electric utility steam-generating units (EGUs) larger than 25 MW (see IBO 12/31/11). The so-called Utility MACT (maximum achievable control technology) establishes emissions standards for air pollutants, including mercury, arsenic, chromium, nickel and acid gases. One type of instrument for which demand is expected to rise dramatically due to the regulation is particulate matter (PM) continuous emissions monitoring systems (CEMS). PM measurements are used as a surrogate for the emissions of arsenic, chromium, nickel and other non-mercury metallic hazardous air pollutants (HAP). Although PM CEMS are already installed at some US power plants, the regulation opens up a sizable market for the product.

According to EPA estimates, there are 1,400 EGUs at 600 power plants that will be affected by the Utility MACT. Depending on the type of EGU, filterable PM emission limits under the Utility MACT range from 2.0E-2 lb/MWh (pounds pollutant per megawatt-hour electric output) to 9.0E-2 lb/MWh. Companies have three years to comply with the rules and can request an addition year to install controls.

PM CEMS are one choice for meeting the non-mercury metallic HAP requirements. Power plants can also choose to measure the emission of non-mercury toxic metals through manual stack testing on a quarterly basis or to directly measure each non-mercury metallic metal HAP. Chuck Dene, senior project manager for Environmental Controls Research at the Electric Power Research Institute (EPRI), a nonprofit provider of R&D for the electricity industry, told IBO that compliance using either of these options is unlikely.

PM CEMS employ one of five main technologies: light scattering, beta-ray attenuation, probe electrification, optical scintillation and light extinction (opacity monitors). The most common technologies used in newly installed PM CEMS are light scattering and beta-ray attenuation due to their higher sensitivity and ability to work on wet stacks (furnace flues whose emissions are cleaned with wet scrubbers).

One of the biggest changes in light-scattering PM CEMS technology in recent years, according to Mr. Dene, has been the introduction of forward light-scattering systems. “The reason for that shift was due to some research in the past that has shown that the forward-scattered light instruments are less sensitive to changes in the particle-size distribution in the stack and less affected by changes in the color of the ash or other optical properties,” he said. “So what you are seeing now is that most of the new light-scattering devices that are hitting the market are forward-scattering devices.”

Mr. Dene also noted advancements in beta-ray attenuation devices, which are known as beta gauges. Beta gauges operate by collecting and comparing batch beta counts on filter media. “In a wet stack, you have some particles that in any optical system would be measured as particulate, and it gives you a false high reading. So you need to get rid of the droplets, and that’s really the advancements that have been made by beta gauges: how to better do that and stay reliable,” he explained.

SICK MAIHAK US offers light-scattering PM CEMS in in-situ configurations for dry stacks and extractive configurations for wet stacks. Among SICK’s PM CEMS products is the FWE200 scattered probe, a close-coupled extractive forward-scattering CEMS that can be mounted on the wet stack. Asked about the advantages of light-scattering techniques, Dan Kietzer, Business Development manager for SICK’s Process Automation Division, told IBO: “Light scattering as a technology for measuring tends to be, obviously, much more sensitive to changes in dust, so it’s much faster responding to process changes. Typically, it tends to be very low maintenance as opposed to something like a beta attenuation–type device and also much more cost effective than something like beta ray attenuation.” According to Mr. Kietzer, the price of a forward-scattering SICK PM CEMS for a gas stack is about $20,000. The price for a wet stack system is about $80,000–$90,000.

Also differentiating SICK’s PM CEMS is the company’s experience with the technology and the system’s maintenance requirements, according to Mr. Kietzer. ”The versions of our light scattering we sell now are third-generation light-scattering devices, so we’ve learned a lot of lessons: learned things that work well; things that don’t work well,” he explained. “What really sets us apart mostly from other scattered light, and even some other technologies, is our maintenance intervals . . . . All of our products on the dust side come with maintenance intervals greater than three months.”

SICK offers back-scattering and forward-scattering PM CEMS. For compliance with the Utility MACT, a forward-scattering system is required. “For anything that requires compliance-level measurement for PS-11 [the EPA’s performance standard 11], then we would almost exclusively sell forward-scattering devices because forward scatter is much more sensitive to small levels of dust and also much less sensitive to particle-size differential and things like that.”

Mr. Kietzer expects a big change in the market as a result of the Utility MACT, as well as the Portland Cement MACT, which is a MACT rule for cement kiln emission. In 2010, the EPA amended this MACT, adding emission limits for mercury, THC (a surrogate for PCB) and PM (a surrogate for nonvolatile metal HAP). “Starting in about 2005, we saw a lot of consent decrees where individual facilities or plants got a consent decree from their local EPA board because of some violations or things like that to install PM CEMs. For us, the market really started in 2005 or so,” he explained. “Since then, I think we’ve installed 130 to 150. So, now, we’re talking about market sizes that are going to increase tenfold over the next three or four years in both cement (about 150 units) and the power sector (about 1,400 units).”

Installation of PM CEMS to comply with the Portland Cement MACT, which requires compliance by fall 2013, has been slow due in part to the economy, according to Mr. Kietzer. “I’m sure we’ll see this pick up as 2012 rolls into quarter two and quarter three, because the last thing I think they’ll want to do is wait till the last minute. But I think they’ll try to wait as long as they can.” He expects the power industry to be more proactive. “If the power industry has to comply by January 2015, which is the date as it is today, then I would expect at the end of 2013 we would start to see a large ratcheting up. But I wouldn’t expect them to wait as long in the power market just because of the size of the market.” According to him, about 80% of the stacks covered under the Portland Cement MACT are dry stacks. For the Utility MACT, the ratio of dry to wet stacks is about 50/50 but may change depending on legislation.

Another firm that offers forward light-scattering PM CEMS is Apex Instruments. Apex Instruments is the exclusive US distributor for PCME, a UK-based provider of particulate-monitoring emission systems. Apex Instruments recently announced an agreement with Rev1 Power Services’ Air Quality Services division to provide a turnkey solution for monitoring and controlling stack pollution for the Utility MACT.

Describing how PCME’s PM CEMS forward light-scattering technology differs from competitors’ technology, Chris Green, director of Business Development and Outside Sales, told IBO, “One of the most significant design features in our forward-scatter device is that we don’t have any moving parts at all in the measurement volume. This gives our device a huge reliability advantage.” Apex offers PCME’s Wet Stack 181 PM CEMS, in which the withdrawn flue gas and water make contact with the wall of a vaporizing chamber to increase thermal conductivity. “Additionally, we transmit the light back to the controller via a quartz rod, [which is] more robust: it does not age [or] deteriorate as with fiber optic cable.” He also described how the instrument’s performance can be monitored. “We are able to ‘challenge’ the instrument’s performance whilst installed—continually checking the instrument’s accuracy in measuring scattered light and diagnosing any contamination at the earliest opportunity.”

Asked about the new regulation, Mr. Green told IBO, “EPA’s new rule will see demand for ‘reliable measurement’ increase.” According to him, reliability has been a focus of technology development. “Measurement technology for PM CEMS has developed significantly as improved manufacturing techniques have evolved, and microprocessor data handling has been implemented alongside.” In addition to R&D, he also cites partnerships between a manufacturer and local market representative as important to product development, noting that Apex Instruments and PCME jointly developed the Wet Stack 181.

Despite the advances in PM CEMS technology, calibration remains costly and time consuming. “All of these techniques can give you sensitivity in the range of the MACT rule, so it’s not a question of can they measure that low. They can. The question is how do you show that in a calibration,” said Mr. Dene. PM CEMS are calibrated by “de-tuning” a stack to create a calibration curve to correlate the device in accordance with PS-11. According to Mr. Dene, creating a calibration curve for a dry stack is relatively easy but not for a wet stack. Generally, such calibration curves consist of two points representing the normal operating point and zero emissions. “And the way the regulations are written, if at any time the output of your PM monitor exceeds 1.25 of your highest calibration point, you have to repeat the test. So that’s a pretty expensive proposition to go out and redo a PS-11 test.” The EPRI has been conducting tests to develop alternative calibration approaches without de-tuning control equipment. Approaches under development include quantitative aerosol generators and reinjection techniques.

As for the PM CEMS outlook, Mr. Dene expects other beta gauge firms to enter the US market. MSI/Mechanical Systems and Altech Environment, an Environnement SA firm, currently offer such systems. Thermo Fisher Scientific is expected later this year to introduce a hybrid device that combines real-time elastic light-scattering and semi-continuous Tapered Elemental Oscillating Microbalance (TEOM). TEOM allows for the direct measurement of PM.