New Boiler Technology Helps Facilities Meet Ultra-Low NOx Regulations

November 11, 2012

In 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.  

Computational fluid 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.

When 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). 

When 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. 

To 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.

To 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%.

Adding 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.

Certain 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.

Download: Ultra-Low NOx Regulations with New Boiler Technology