The Clean Air Act by the EPA (last amended in 1990) created National Ambient Air Quality Standards (NAAQS) to address six principal “criteria” pollutants that they considered harmful for public health and the environment. State and local agencies use the information created by the EPA in developing emission reduction strategies, plans and programs to assure they meet NAAQS. Current criteria pollutants include: nitrogen compounds (NOx), Sulfur compounds (SOx) Carbon Monoxide (CO), Particulate Matter (PM), ozone (03) and lead.
With industrial boilers, nitrogen oxides (NOx) are one of the most regulated pollutants. NOx leads to the production of ozone in the upper atmosphere and is a leading contributor to the recognizable ‘brown haze’ seen in some larger cities. NOx is formed naturally during the combustion process and NOx levels are also influenced by the content of fuel-bound NOx. Prompt NOx emissions are also created, but are relatively small. Thermal NOx is the major source of NOx from gas and oil fired boilers and is affected by flame temperature. Fuel NOx is more applicable to oil fired boilers and can be reduced by switching to natural gas.
Several control techniques exist to control NOx emissions: (1) combustion controls and (2) post- combustion control methods. Combustion control methods include low excess air firing, flue gas recirculation, water/steam injection, and burner modifications. Post-combustion control methods include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). Each method results in a different degree of NOx control and each can affect the turndown, efficiency, and performance of the boiler.
Overall, emissions levels are a critical consideration when selecting a boiler. Understanding your federal and state requirements is essential and will help ensure you make the correct decision when it comes to maintaining and improving your boiler’s performance and efficiency.
Over the last twenty years Nationwide Boiler has been an industry leader in supplying low and ultra low NOx boilers. Nationwide Boiler’s exclusive CataStak™ SCR System was developed over ten years ago to easily help industry achieve over 95% NOx reduction while meeting and exceeding a 5 ppm NOx limit (mainly on natural gas firing installations). With over 100 successful installations, Nationwide Boiler’s CataStak™ SCR System has yet to fail a third-party source test. Contact Nationwide Boiler today to discuss NOx control technology options that are best suited for your needs.