Authors: Tom Dunder, Ph.D. | July 18, 2016

From electricity generation to manufacturing to oil refining and beyond, air emissions compliance testing is performed at a wide variety of facilities to confirm that plants are operating within permitted emissions limits. Failing a compliance test has significant adverse consequences, including public notices of violations, potential fines and other penalties, increased scrutiny by regulating authorities, limits on production rate, and negative impact on the company’s reputation.

Engineering performance emission testing can do more for your business than just meet legal requirements and mitigate these risks. By working with an experienced testing consultant, you can leverage your results to optimize plant performance, provide a better understanding of the impact of various plant operating parameters on emissions, and reduce material costs.

Three tests in particular can have significant economic benefits across industries.

Dry sorbent injection and activated carbon injection systems involve injecting a chemical into the gas stream of a combustion source to control emissions of pollutants like NOx, SO2, HCl, and mercury. These pollution control systems have been installed at many coal-fired utilities and boilers because they require much lower capital costs and a smaller equipment footprint than alternate technologies, like scrubbers.

Sorbent injection systems use calcium-based (limestone, hydrated lime) or sodium-based (sodium bicarbonate, Trona) sorbents for control of SO2, SO3, and HCl, and powdered activated carbon (PAC) for removal of mercury. Sorbents react with the pollutant and are subsequently removed from the gas stream in the particulate control device (baghouse or electrostatic precipitator).

Selecting the sorbent is a complicated economic and operational calculation, because sorbents vary in cost, effectiveness, ease of handling, deleterious side effects, and disposal costs. Importantly, elevated carbon concentrations in cement can negatively affect concrete performance. Accordingly, facilities that use ACI want to minimize activated carbon use to both reduce mercury control costs and preserve the market value of their fly ash. At these injection rates, annual sorbent costs can exceed millions of dollars so there is a strong motivation to optimize sorbent injection to achieve compliance with emissions limits without over-injection.

Ammonia injection is similar to DSI, except the target pollutant is NOx and the reaction is between two gases rather than a particle and a gas. NOx removal can be performed in presence of a catalyst (SCR, selective catalytic reduction) or by simply spraying the ammonia (or urea) solution into the ductwork (SNCR, non-catalytic reduction) to convert NOx to nitrogen. Unreacted ammonia that exits the stack is referred to as “ammonia slip”, which in some cases is limited by regulation to a few ppm. However, even when ammonia emissions are not regulated, over-injecting the chemical incurs additional cost. Annual reagent costs can exceed $4,000,000 per year for a 500 MW coal-fired power plant achieving 90% NOx reduction.

What to look for in a testing partner

Engineering performance tests determine emissions, verify pollution control device performance, and study how changing plant operating parameters impacts emissions. The use of specialized equipment, including mobile testing labs is critical to obtain same day measurement of emissions as well as onsite analysis for immediate diagnostic use. Engineering performance tests require close collaboration and interaction between the plant engineers and the test team to collect and interpret the emissions data. Beyond the examples of sorbent and ammonia optimization, engineering performance tests are conducted at a wide variety of industries, to evaluate control equipment settings and to examine pollution impacts from production changes.

TRC has conducted numerous DSI optimization studies, in which on-site emissions measurements are used to determine pollutant removal efficiency as a function of sorbent, injection location, injection rate, and particle size. This type of study allows the plant and sorbent vendor to vary conditions, determining the optimal injection rate for each material. This is critical data for facilities to make economic decisions that will affect the plants for years to come.

For more information on how to implement performance engineering emissions testing programs at your facility, and the benefits you can achieve, please contact us.

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Tom Dunder

Tom Dunder is Technical Director in the Air Management Services Division at TRC Companies in Raleigh, North Carolina where he performs and manages air pollutant testing programs. He has degrees in Chemistry from Columbia (A.B.), Rutgers (M.S.) and the University of North Carolina (Ph.D.). Tom has 29 years of experience in gaseous pollutant emissions measurements at a wide variety of industries (refineries, chemical plants, power plants, paper mills, etc.) with recent work in biomass/biogas processes and emerging pollutants like PFAS. Contact Tom at tdunder@trcsolutions.com.