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From the perspective of the mechanism of NOx formation, the technologies for controlling NOx in oil/gas boilers also primarily focus on two aspects: reducing the combustion flame temperature and decreasing the oxygen content. Therefore, an important measure to suppress the formation of NOx is to start with the burner. So what is a low-nitrogen burner? What is its principle? Low-NOx burners refer to burners that produce low levels of NOx emissions during the fuel combustion process. The typical NOx emissions from conventional natural gas boiler burners are around 120–150 mg/m3. The typical NOx emissions from low-nitrogen burners are around 30–80 mg/m3. NOx emissions below 30 mg/m³ are generally referred to as ultra-low nitrogen emitters. Currently, low-NOx burners can be broadly classified into the following categories based on their principles: 1) Staged burners: These are burners designed based on the principle of staged combustion, allowing fuel and air to mix and burn in stages. Since the combustion occurs at a ratio deviating from the theoretical stoichiometric ratio, nitrogen formation can be reduced. 2) The self-recirculating burner is a type that uses the pressure of the combustion air to draw back some of the combustion flue gases into the burner, where they mix with the air and burn. Due to flue gas recirculation, the heat capacity of the combustion flue gas increases, the combustion temperature decreases, and NOx is reduced. Another type of self-recirculating burner involves directly recirculating a portion of the flue gas back into the burner to be included in the combustion process. This type of burner has the dual effects of suppressing nitrogen oxide formation and saving energy. 3) The principle of the rich-lean burner is to allow part of the fuel to burn in a rich condition while another part burns in a lean condition, with the total amount of air remaining unchanged. Since both portions burn at a deviation from the stoichiometric ratio, the NOx levels are very low; this type of combustion is also known as off-stoichiometric combustion or non-stoichiometric combustion. 4) The principle of the split-flame burner is to divide one flame into several smaller flames. Since these smaller flames have a larger heat dissipation area, their temperature is lower, which results in a reduction in \"thermally generated NO\". In addition, the small flame reduces the residence time of gases such as oxygen and nitrogen in the flame, thereby exerting a significant inhibitory effect on both “thermal NO” and “fuel NO”. 5) The residence time of flue gas in the high-temperature zone in mix-promoting burners is one of the main factors affecting NOx generation. Improving the mixing of fuel and air allows the flame front to become thinner; with the combustion load remaining unchanged, the residence time of the flue gas in the flame front, i.e., in the high-temperature zone, is reduced, thereby lowering NOx production. The mixed-promotion burner is designed based on this principle. 6) Low-NOx pre-combustion chamber burners: The pre-combustion chamber is a high-efficiency, low-NOx staged combustion technology developed and researched in China over the past decade. It generally consists of primary air (or secondary air) and a fuel injection system. Fuel and primary air mix rapidly, forming a fuel-rich mixture in the primary combustion zone within the pre-combustion chamber. Due to oxygen deficiency, only a portion of the fuel burns. Volatiles are released from the fuel in this oxygen-deficient primary flame zone where the flame temperature is relatively low; consequently, NOx formation is reduced. Any low-nitrogen combustion technology is essentially a technique for controlling the combustion process. Based on 20 years of experience with low-nitrogen burners in Europe and the United States, to achieve truly consistent and reliable low-nitrogen combustion in industrial boilers, it is not sufficient to simply replace or modify the burners; it is also necessary to upgrade the combustion control systems, such as by installing \"timely control\" combustion management devices.