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ALDEN
30 Shrewsbury Street
Holden, MA 01520-1843 USA

phone: +1 508-829-6000
fax: +1 508-829-5939
e-mail: info@aldenlab.com

Selective Catalytic Reduction (SCR) Systems

	Physical Flow Model

	Selective Catalytic Reduction System



	Operators of fossil fuel boilers are being required to reduce NOx emissions. Many are turning to SCRs in which a reagent, typically ammonia, is mixed with the flue gas and then passed through a NOx reducing catalyst. Optimal system performance is achieved when uniform distributions of flue gas, reactant, and gas temperature are presented to the catalyst. High liquidated damages for failure to meet performance guarantees are an impetus for suppliers of SCR systems to evaluate these critical flow parameters through physical or computational flow modeling prior to installation and operation at the candidate site.

Researchers at Alden have been modeling selective catalytic reduction (SCR) systems both physically and computationally for over a decade. Our ability to define and improve on the fluid flow phenomena, species/thermal mixing and particulate transport dynamics within SCR models leads to practical recommendations for optimal SCR performance.

Using physical and/or computational flow modeling techniques, Alden can determine the uniformity of the fluid and thermal distributions. To ensure that the SCR systems will perform up to the stated levels of NOx reduction with minimal reactant "slip," our models are used to develop the flow controls and mixing devices to achieve the targeted levels of uniformity.

SCRs operate in a hot gas environment (T ≈ 700º F) and are typically situated upstream of air preheaters and flyash collection equipment. Particulate modeling is employed to develop modifications that enhance ash collection in the economizer outlet and SCR inlet duct hoppers in order to prevent large particle ash (LPA) from reaching the SCR module and plugging the catalyst passages.

Alden's Gas Flow Engineering Group maintains a facility for determining the true aerodynamic characteristics of LPA. This information is critical for the accurate flow modeling of LPA/SCR interactions.