Low-nitrogen burner refers to a burner that emits low NOx during fuel combustion. Conventional natural gas boiler burners usually emit NOx around 120~150mg/m³. The usual NOx emissions of low-nitrogen burners are around 30~80mg/m³. NOx emissions below 30mg/m³ are usually called ultra-low nitrogen burners. At present, low-nitrogen burners can be roughly divided into the following categories according to their principles:
1) Stage burner
The stage burner designed according to the principle of staged combustion makes the fuel and air mixed and combusted in stages. Since the combustion deviates from the theoretical equivalent ratio, the production of nitrogen can be reduced.
2) Self-recirculating burner
One is to use the pressure head of the combustion-supporting air to suck back part of the combustion flue gas, enter the burner, and mix and burn with the air. Due to the recirculation of the flue gas, the heat capacity of the combustion flue gas is large, the combustion temperature is reduced, and the NOx is reduced.
3) Another type of self-recirculating burner is to recirculate part of the flue gas directly in the burner and join the combustion process. This kind of burner has the dual effects of suppressing nitrogen oxides and energy saving.
The principle is to make a part of the fuel burned richly, and another part of the fuel burned too lightly, but the overall air volume remains the same. Since both parts are combusted at a deviating stoichiometric ratio, the NOx is very low. This type of combustion is also called deviated combustion or non-stoichiometric combustion.
4) Split flame type burner
The principle is to divide a flame into several small flames. Due to the large heat dissipation area of the small flames, the flame temperature is lower, which reduces the "thermal reaction NO". In addition, the small flame shortens the residence time of oxygen, nitrogen and other gases in the flame, and has a significant inhibitory effect on "thermal reaction NO" and "fuel NO".
5) Mixing promotion burner
The residence time of the flue gas in the high temperature zone is one of the main factors that affect the amount of NOx generated. Improve the mixing of combustion and air, which can reduce the thickness of the flame surface. Under the condition of the combustion load unchanged, the flue gas is at a high temperature on the flame surface. The staying time in the zone is shortened, thus reducing the amount of NOx generated. The mixing-promoting burner is designed according to this principle.
6) Low nitrogen pre-combustion chamber burner
The pre-combustion chamber is a high-efficiency, low-nitrogen staged combustion technology developed and researched in my country in the past 10 years. The pre-combustion chamber is generally composed of primary air (or secondary air) and a fuel injection system. The fuel and primary air are rapidly mixed. A fuel-rich mixture is formed in the primary combustion zone of the pre-combustion chamber. Due to the lack of oxygen, only part of the fuel is burned. The fuel releases volatiles in the primary flame zone where the oxygen is lean and the flame temperature is lower, thus reducing the generation of NOx.
