Nox Control Method
Other Techniques for Removal of Nox
1. Staged Combustion
In this NOx reducing method, only a portion of the fuel is burned in the main chamber. All of the fuel is eventually burned, producing the same amount of energy, but this method greatly reduces the temperature in the main chamber. As temperatures decreased, the amount of thermal NOx is reduced.
2. Catalytic Converters
These devices are utilized to lower the toxicity of the emissions of many combustion processes such as stationary engines, boilers, heaters and internal combustion engines. Catalytic converters break down nitrogen oxides into separate nitrogen and oxygen particles. Some catalytic converters are also used to reduce the high CO levels produced when reducing NOx, as low CO levels are important to ensuring complete combustion.
3. Flue Gas Recirculation (FGR)
Flue Gas Recirculation, FGR, is a method of NOx reduction that lowers the temperature of the flame, and therefore reduces thermal NOx. A portion of the exhaust gas is re-circulated into the combustion process, cooling the area. This process may be either external or induced, depending on the method used to move the exhaust gas. Flue Gas Recirculation may also minimize CO levels while reducing NOx levels.
4. Reducing O2 level
By reducing the amount of O2 that is available to react with the nitrogen, NOx is reduced. This is achieved through the use of oxygen trim controls. To minimize the O2 levels, a combustion analyzer is used to adjust the fuel and air mixture. This method can reduce the level of NOx produced by up to 10%, but it may increase the emissions of Carbon Monoxide (CO) very significantly. This method is widely used in many processes such as in rich burn engines.
5. Low NOx Burners
By changing the shape and formation of the flame by using plates to control airflow, a more elongated flame is created in the burner. The temperature is decreased due to the extended flame and surface area, and the lower temperature reduces the amount of thermal NOx. CO levels may be elevated when using low NOx burners. It is important to monitor CO and True NOx levels to better control Low NOx burners.
6. Low Nitrogen Fuel Oil
The use of low nitrogen oils, which can contain up to 15-20 times less fuel bound nitrogen than standard No. 2 oil, can greatly reduce NOx emissions as fuel bound nitrogen can contribute anywhere between 20-50% of total NOx levels.
7. Water/Steam Injection
Water or steam injection reduces the amount of NOx produced by lowering the temperature of the flame during combustion. The lower temperature allows for the decrease of thermal NOx.This method can result in an increase of 3-10% boiler efficiency losses and excess amounts of condensation may form.Some advanced designs of steam injection technology do not have significant impact on boiler efficiency.