How Low NOx Burners Work

How Low NOx Burners Work

The primary goal of a low NOx burner is to reduce the formation of nitrogen oxides (NOx) during combustion. NOx is a significant air pollutant, harmful to both the environment and human health. Low NOx burners reduce NOx production through several technical approaches, which include the following:

1. Staged Combustion

Principle: Staged combustion involves dividing the fuel combustion process into multiple stages to control combustion temperature and oxygen concentration, thereby reducing NOx formation.

Operation:

• Primary Combustion: In the first stage, the fuel-to-air ratio is set to have insufficient excess air (i.e., less air), resulting in a lower combustion temperature, which reduces thermal NOx formation.

• Secondary Combustion: In the later stages or secondary phase, additional air is introduced into the burner to ensure complete combustion of the remaining fuel while maintaining low temperatures, further reducing NOx production.

2. Air Staging

Principle: Introducing air in stages creates a more even oxygen concentration during combustion, avoiding the formation of high-temperature zones, and thus reducing NOx formation.

Operation:

• Instead of introducing all the air at once, air is introduced in stages at different locations within the burner. This helps control the combustion temperature and prevents high temperatures that could lead to increased NOx production.

3. Flue Gas Recirculation (FGR)

Principle: Recirculating a portion of the combustion flue gas (which primarily contains no oxygen) back into the burner, mixing it with fresh air before entering the combustion zone. The nitrogen and carbon dioxide in the flue gas do not participate in combustion, helping to dilute the combustion temperature and reduce NOx formation.

Operation:

• A portion of the flue gas is routed back into the burner through ducts. This recirculated flue gas effectively lowers the combustion zone temperature, thus inhibiting NOx formation.

4. Fuel Staging

Principle: Dividing the fuel into different portions and burning them in different zones or at different times within the burner to lower local combustion temperatures, thereby reducing NOx formation.

Operation:

• The burner is designed with multiple combustion chambers, and fuel is added gradually in these chambers. This allows control over the temperature and oxygen levels at each stage of combustion, achieving NOx reduction.

5. Low NOx Burner Structural Design

Principle: Optimizing the burner’s structural design to minimize the formation of high-temperature flame cores and to optimize the mixing of air and fuel, ensuring more uniform combustion at lower temperatures, thus reducing NOx formation.

Operation:

• Low NOx burners often use unique nozzle designs and combustion chamber shapes. By precisely controlling the way air and fuel mix, they avoid the creation of high-temperature zones, thereby effectively lowering NOx production.

6. Catalytic Reduction Technologies (such as Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR))

Principle: Although not strictly part of the burner itself, these technologies are often used in conjunction with low NOx burners to further reduce NOx emissions.

Operation:

• A reducing agent (such as ammonia or urea) is added to the post-combustion flue gas, where, under the influence of a catalyst, NOx is reduced to harmless nitrogen and water.

Summary

Low NOx burners effectively reduce NOx formation by lowering combustion temperatures, optimizing fuel and air mixing, and introducing recirculated gases. These technologies can be used individually or in combination to meet stricter emission standards and comply with environmental regulations.