The Commercial Boiler: Burners That Optimize Efficiency and Minimize Emissions

The burner in your commercial boiler is crucial to the unit’s performance and efficiency. As demand has increased for higher efficiency levels and lower amounts of emissions, new technology has emerged to help balance the performance trade-off between these two important factors. Two of the most recent and most effective trends in commercial boiler burners are flue-gas recirculation (FGR) and metal-fiber technology. These two forms of burner technology help ensure that commercial boiler burners do not lose efficiency in the quest for lower emissions or vice-versa.

Flue-Gas Recirculation

Flue-gas recirculation burners reduce nitrogen oxide emissions while allowing the boiler to keep working at high efficiency. FGR processes take a portion of the exhaust gases (also known as flue gases) and recirculates it into the burner’s combustion area. This process lowers the temperature of the burner flame and reduces the amount of nitrogen oxide formed by the combustion process. During the recirculation process, the exhaust gas is metered and mixed with air from combustion. This mixture produces air that is at a higher temperature than regular ambient air. The air mixture serves to cool the combustion flame without putting it out. The lower flame temperature reduces the amount of nitrogen oxide produced while still letting the system operate effectively. Some factors to keep in mind when using FGR technology include:

• Boiler efficiency may decrease slightly when using FGR burners. Typical levels of efficiency reduction range from 0.25 percent to 1 percent.
• FGR processes may influence the fan size required for effective air circulation. Depending on the amount of mass flow and air temperature, the fan may need to be smaller or larger than the one currently installed in the unit.
• Horsepower requirements can also be affected by the use of FGR technology.
• FGR burners require more maintenance and attention to manage condensation in the gas recirculation lines. System components, particularly the blower impeller and the burner head, can be damaged if accumulated condensation leaks into the burner.
• When burner flame temperatures are reduced, there can be noticeable negative effects in boiler operation. The boiler may rumble and produce unexpected noises. The lower-temperature flame could also produce more soot and the dangerous exhaust gas, carbon monoxide. For this reason, qualified professional technicians should be responsible for installing an FGR system.

Metal-Fiber Technology

Metal-fiber technology is another recent technological advancement from the last decade that helps manage and reduce emissions from commercial boiler burners. Surface-stabilized metal-fiber combustion often can be found in larger industrial-sized burners. In this process, fuel and air are pre-mixed before combustion. The flame is stabilized using a metal-fiber material that contains the flame on its surface. The flame is stretched, which produces more consistent flame temperatures and eliminates higher-temperature zones within the flame. This flame stabilization reduces the formation of nitrogen oxide by significant levels, often dropping nitrogen oxide levels to the single digits without the need for additional flue-gas recirculation. Some factors to remember about metal-fiber burner technology include:

• Higher levels of excess air are generally required when using metal-fiber burners. Excess air levels are usually required at 50 to 60 percent to reach single-digit nitrogen oxide emissions.
• Metal-fiber burners may still require flue-gas recirculation to achieve the best level of emission control and efficiency.

Additional Efficiency Features for Commercial Boilers

System components and features are available that will increase commercial boiler efficiency even further. They include:

• High-efficiency control systems that maintain a consistent burner-firing rate and allow the burner to modulate from low to high.
• Efficiency advances that allow burners to operate at as little as 10 percent of capacity before cycling, which reduces energy usage.
• Excess air reductions that improve efficiency by limiting the amount of excess air not used during the combustion process.

Our goal is to help educate our customers about Plumbing, HVACR, Fire Protection and Alarm Systems in Mechanical, Commercial and Residential settings. For more information about commercial boiler burners and the new technologies that are making them more efficient and less polluting, or to view projects we’ve worked on, visit our website!