Flue gas from boiler systems in power plants forms a significant portion of the emissions from a fossil-fueled power plant.
The composition of the flue gas varies, but forms one notable pollutant: NOx, which encompasses nitric oxide and nitrogen dioxide. NOx forms whenever combustion occurs when nitrogen is present, and can enter the atmosphere via flue gas to create smog, acid rain, and tropospheric ozone.
For this reason, NOx emissions are controlled by regulations by which power plants must abide. The issue of lowering NOx emissions is handled primarily by a process called flue gas recirculation.
Finding the right flue gas recirculation systems for a power plant is essential in order to lower pollutants and be in accordance with any and all regulations.
About Flue Gas Recirculation Systems
The goal of flue gas recirculation systems is to gradually reduce the amount of NOx emissions.
Flue gas from the stack is sent back into the combustion chamber through the burner, which helps to cool down the flame peak temperature and slow down reactions in the combustion chamber. The degree of reduction varies and depends on a variety of factors, such as boiler type, burner type, air temperature, etc.
How does recirculation lower NOx content? The process decreases the average oxygen content of the air in the chamber, which slows the rate at which nitrogen bonds with oxygen to form the NOx.
There are two different methods by which this is accomplished:
- Air vitiation: This process uses an air blower to suck flue gas out of the stack and blend the gases with fresh air from the outside before they are sent back into the burner. This can be adapted with few, if any, modifications.
- Manifold/bustle ring: This process uses a blower to pull flue gas from the stack and push the gas through a manifold or bustle ring into the flame. Typically, a modified burner is required.
Advantages of FGR Systems
One main advantage of an FGR system is the cost. These systems are relatively inexpensive to install, even for a retrofit.
Plus, they can easily be retrofitted onto existing systems to take advantage of current infrastructure with a minimum of disruption to the overall process.
Keep in mind that certain processes cannot use FGR. The system works by reducing flame temperature and the percentage of oxygen in the combustion chamber. Flue gases can’t be too hot or too high in oxygen content; otherwise, they aren’t suitable for an FGR system. The gas has to be relatively cool and relatively low in oxygen content in order for it to work.
FGR systems have to be intricately engineered and designed, because they can directly impact the proficiency and efficiency of a boiler system. For example, you may experience loss of burner capacity, or burner instability, that have to be addressed when designing the system.
With that being said, flue gas recirculation systems are one promising way to lower NOx emissions for a facility and one of the more prevalent methods in place today in the industry.
ProcessBarron supplies the majority of components needed for a FGR system, including ductwork, manifolds, supports, access, seal boxes, control dampers, and expansion joints. Our specialists are skilled at designing and installing these systems, especially in a complex environment marked by pre-existing infrastructure. Request aquote on flue gas recirculation systems by contacting our professionals.