New Boiler Technology Helps Facilities Meet Ultra-Low NOx Regulations
recent years, government authorities have enacted legislation to reduce
emissions, particularly NOx and CO. Innovations in packaged boiler and burner
technology continue to focus on meeting increasingly strict emissions
regulations while boosting efficiency.
dynamics (CFD) and mathematical modeling are at the forefront of these
endeavors. Using these tools, along with years of proven operational field
data, engineers strive to optimize boiler designs to achieve the proper balance
of heat transfer and gas-side pressure drop to maximize efficiency, reduce
power consumption, and lower emissions. The end result is a fully integrated, state-of-the-art
steam generating solution capable of meeting today’s most stringent regulations.
For example, Dole Packaged
Foods, LLC, Atwater, Calif., operates a 700,000-square-foot fruit processing
facility in California’s San Joaquin Valley Air Pollution Control District,
which has enacted some of the most stringent emissions regulations in the
country. Today, the district requires less than 5 ppm NOx emissions for new
boilers with an input of 20 MMBTU/hr or greater.
Dole was in the market for a new firetube boiler, their management team chose to
purchase a Cleaver-Brooks 700 HP CBEX Elite with fully condensing economizer. According
to Dole’s Director of Atwater Operations David Shankel, the CBEX was selected
due to its controls technology and low NOx capability without selective
catalytic reduction (SCR).
Dole commissioned the new boiler in early 2012, the facility began monitoring
NOx and CO levels. Over the summer, during the facility’s peak operating
season, the first CBEX source test was conducted. The test revealed an average
NOx level of 3.7 ppm and CO of 1.4 ppm, corrected to 3% O2. The CBEX
Elite is the first boiler in the industry to achieve these ultra-low emissions
levels without SCR.
Other steam users, like the City of
Medicine Hat Power Plant in Alberta, Canada, are planning ahead for future, stricter
emissions regulations. Recently, the plant was in the market for a superheated industrial
watertube boiler designed to meet Alberta’s future emissions requirements. The
boiler also had to be maintained in a hot-standby mode, so in the event of an
unexpected turbine trip, the auxiliary boiler could be brought online in less
than five minutes. The City of Medicine Hat team selected a custom Cleaver-Brooks’
Nebraska boiler to address the plant’s needs.
be compliant with Alberta’s future 15 ppm NOx limit, engineers developed an
optimum configuration, taking into consideration both current and future
operating scenarios. Among other features, an innovative tube finning strategy was
utilized that lowered boiler gas-side pressure drop to accommodate future
higher flue gas recirculation (FGR) rates.
achieve hot standby, Cleaver-Brooks engineers incorporated their proprietary Natcom
burner, which includes a unique “Center Core” gas injector that typically is used
to improve flame stability. For this application, it was modified to allow
operation at 15:1 turndown to keep the boiler ready for emergency ramp-up while
maintaining compliance with their air permit’s NOx emissions. Natcom industrial
burners, available new or as a retrofit, can reduce NOx emissions of a boiler
system to <7 ppm.
In addition to new products, boiler
companies help their customers achieve and maintain low NOx levels on existing installations
with a wide array of solutions, such as FGR, SCR, and controls.
FGR works by metering a percentage
of the flue gas into the combustion air supply, increasing or decreasing the
percentage of FGR based on the amount of reduction in NOx required.
Appropriate for large utility and
industrial boilers, SCR is a post-combustion, NOx-control
technology using a catalyst to facilitate a chemical reaction between NOx and
ammonia, producing only nitrogen and water. SCR is one of the most
efficient ways of reducing NOx in a flue gas system, with reductions up to 95%.
an advanced control system is another option available to manage NOx emissions.
One of the factors influencing NOx formation in a boiler is the excess air level.
Limiting the amount of excess air entering a flame can be accomplished through
the use of oxygen trim controls.
NOx reduction techniques can weaken boiler performance, while others can
improve performance. Aspects of the boiler performance that could be affected
include: turndown, capacity, efficiency, excess air, and CO emissions. Failure
to take into account all of the boiler operating parameters can lead to
increased operating and maintenance costs, loss of efficiency, elevated CO
levels, and shortening of the boiler's life.
Cleaver-Brooks works with customers to tailor solutions that
help them decrease emissions levels without sacrificing efficiency. For
more information, visit www.cleaverbrooks.com.
Jason Jacobi is Sales Manager for the Engineered
Boiler Systems division of Cleaver-Brooks. Cleaver-Brooks is the
only manufacturer in the world that offers a completely integrated boiler,
burner, and heat recovery system.
Featured in November 2012 issue of Today’s Boiler.
Ultra-Low NOx Regulations with New Boiler Technology