Boiler SCR Technology: A Pivotal Step Towards Environmental Sustainability
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Emission regulations for combustion systems have been in place for more than half a century and in the 1990’s, the Clean Air Act put a spotlight on emissions specifically from industrial boilers. Boiler owners were required to retrofit or replace equipment that did not meet the new limits set for emissions of nitrogen oxides (NOx), carbon monoxide (CO), particulate matter (PM), and sulfur dioxide (SO2). While low NOx burner technology was one option that addressed NOx reduction, these burners had limitations including the ability to handle load swings and maintain flame stability. With evolving requirements in areas such as California, burners alone were not able to reliably accomplish the single-digit emissions performance so alternative “back-end” solutions were explored.
Focusing on environmentally sustainable solutions is something that we are all very familiar with today and, while the focus has shifted to reducing our carbon footprint, NOx emission limits in some areas have reached an all-time low of 2½ ppmvd @ 3% O2. Although there are more reliable ultra-low NOx burner solutions available now, that was not the case back in the 90’s. The solution in the years that followed the Clean Air Act was, and still is, Selective Catalytic Reduction (SCR).
Nationwide Boiler developed the CataStak™ SCR to address stringent emissions regulations specifically for their fleet of package watertube rental boilers and eventually, they applied the technology to firetube boilers, gas turbines, and other fired equipment applications. The CataStak is a post-combustion, selective catalytic reduction system proven to achieve ultra-low, single-digit NOx performance. The CataStak provides both economical and practical benefits to users through improved operating efficiency and lower emissions, it provides a reasonable return on investment, and it often exceeds emission limits beyond what is required. With the ability to reduce NOx, CO, and VOC, the CataStak was a pivotal step towards sustainable steam solutions for the boiler industry.
Larry Day, Nationwide Boiler’s current President & CEO, drove the integration of such back-end solutions into the company’s fleet of rental boilers. The objective was clear: to develop an SCR system that would reliably meet and exceed current and future emission limits without compromising critical boiler functionalities. Known today as the CataStak, Nationwide Boiler started off as a user operating these SCR’s across their fleet of rental boilers. The CataStak was proven to offer dependable performance through experience, testing as low as 1 ppm NOx time and time again, before it was ever applied to permanent applications.
In one case study, the CataStak reduced NOx emissions to less than 1 ppm NOx and resulted in an Energy Efficiency Rebate of almost $300,000 for a prominent Food Processing facility in California. The end-user purchased a new Babcock and Wilcox 50,000 lb/hr, 275 psi boiler equipped with a standard 30 ppm low NOx burner, a CataStak SCR system, an EconoStak fuel economizer, and a condensing economizer. Once installed and commissioned, it was certified to operate at better than 95% fuel-to-steam efficiency with less than 1 ppm NOx emissions. Rather than what was available at the time - a more expensive and complex ultra-low NOx burner with an oversized FD fan - the CataStak proved to be the ideal solution for reducing NOx emissions economically, efficiently and with minimal operator intervention.
With more than 250 installations across the country, the CataStak was an early innovation and just one step towards a more sustainable future for steam production.
