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Reasonable selection considerations for low nitrogen burners
- Categories:Company News
- Author:Shenzhen Zhongli Weiye Electromechanical Equipment Co., Ltd.
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- Time of issue:2019-12-26 09:47
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Reasonable selection considerations for low nitrogen burners
Information
Low-NOx burners and low-NOx burners refer to burners with low NOx emissions during the fuel combustion process. The use of low-NOx burners can reduce the NOx emissions during the combustion process.
The nitrogen oxides produced in the combustion process are mainly NO and NO2, which are generally referred to as nitrogen oxides NOx. A large number of experimental results show that the nitrogen oxides emitted by the combustion device are mainly NO, accounting for about 95% on average, while NO2 only accounts for about 5%.
Generally, NO generated by fuel combustion mainly comes from two aspects: one is the oxidation of nitrogen in the air used for combustion (combustion air); the other is the thermal decomposition and reoxidation of nitrogen compounds contained in the fuel during the combustion process. In most combustion devices, the former is the main source of NO, which we refer to as "thermal reaction NO", the latter as "fuel NO", and there is also "prompt NO".
The NO formed during combustion can react with intermediates containing nitrogen atoms to reduce NO to NO2. In fact, in addition to these reactions, NO can also form NO2 with various nitrogen-containing compounds. When the reaction reaches chemical equilibrium in the actual combustion device, the ratio of [NO2]/[NO] is very small, that is, the conversion of NO to NO2 is very small and can be ignored.
Combustion technology to reduce NOx
NOx is produced by combustion, and the combustion method and combustion conditions have a great influence on the formation of NOx. Therefore, NOx can be reduced by improving combustion technology. The main ways are as follows:
Select fuels with lower N content, including fuel denitrification and conversion to low-nitrogen fuels;
Reduce the excess air coefficient and organize excessively rich combustion to reduce the oxygen concentration around the fuel;
In the case of low excess air, the temperature peak is reduced to reduce "thermal reaction NO";
At lower oxygen concentrations, increase the residence time of combustibles in the flame front and in the reaction zone.
The specific methods usually used to reduce the formation and emission of NOx are: staged combustion, afterburning method, low oxygen combustion, concentration deviation combustion and flue gas recirculation.
Brief Introduction of Commonly Used Low NOx Burners
The burner is an important equipment of the industrial furnace. It ensures the stable combustion of the fuel and the complete combustion of the fuel. Therefore, to suppress the generation of NOx, the burner must be started. According to the combustion technology to reduce NOx, low NOx burners are roughly divided into the following categories:
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 equivalence ratio, the generation of NOx can be reduced.
2. Self-recirculating burner
One is to use the pressure head of the combustion air to suck back part of the combustion flue gas, enter the burner, and mix and burn with the air. Due to flue gas recirculation, the heat capacity of the combustion flue gas is large, the combustion temperature is reduced, and the NOx is reduced.
Another self-recirculating burner is to recirculate part of the flue gas directly in the burner and add it to the combustion process. This kind of burner has the dual effects of suppressing nitrogen oxides and saving energy.
3. Concentration burner
The principle is to make part of the fuel burn too rich and the other part burn too lean, but the overall air volume remains unchanged. Since both parts are burned off-stoichiometric, the NOx is very low. This type of combustion is also known as off-stoichiometric or non-stoichiometric combustion.
4. Split flame burner
The principle is to divide a flame into several small flames. Due to the large heat dissipation area of the small flames and the lower flame temperature, the "thermal reaction NO" decreases. In addition, the small flame shortens the residence time of oxygen, nitrogen and other gases in the flame, and has obvious inhibitory effects on "thermal reaction NO" and "fuel NO".
5. Hybrid booster burner
The residence time of the flue gas in the high temperature area is one of the main factors affecting the amount of NOx generation. Improving the mixing of combustion and air can reduce the thickness of the flame surface. Under the condition of constant combustion load, the flue gas is at high temperature on the flame surface. The residence time in the zone is shortened, thereby reducing the amount of NOx generated. Mixing-promoting burners are designed according to this principle.
6. Low NOx pre-chamber burner
The pre-combustion chamber is a high-efficiency, low-NOx 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 the primary air are rapidly mixed. A fuel-rich mixture is formed in the primary combustion zone in the pre-combustor. Due to lack of oxygen, only part of the fuel is burned, and the fuel precipitates volatiles in the primary flame zone with lean oxygen and lower flame temperature, thus reducing the generation of NOx.
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