Principle Of Low NOx Burner (The Latest One)
Principle Of Low NOx Burner (The Latest One)
Low NOx burner and low NOx burner refer to the burner with low NOx emission during fuel combustion. The use of low NOx burners can reduce NOx emissions during combustion.
The nitrogen oxides produced during combustion are mainly NO and NO2 usually called NOx. A large number of experimental results show that the NOx emission of combustion devices is dominated by NO, accounting for 95% on average, while NO2 only accounts for 5%.
The NO produced by general fuel combustion mainly comes from two aspects: one is the oxidation of nitrogen in combustion air (combustion support air); The second is the thermal decomposition and re-oxidation of nitrogen compounds in the combustion process. In most combustion devices, the former is the main source of NO, which we call “thermal reaction NO”, and the latter is called “fuel NO” and “instant NO”.
The NO formed during combustion can react with the intermediate 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 proportion of [NO2]/[NO] is very small, that is, the conversion of NO to NO2 is very small and can be ignored.
NOx reduction combustion technology
NOx is generated through combustion, and combustion methods and conditions have a great impact on the generation of NOx. Therefore, NOx can be reduced by improving combustion technology. The main methods are as follows:
Select fuels with low nitrogen content, including fuel denitrification and conversion to low nitrogen fuels;
Reduce the excess coefficient of air and the oxygen concentration around the fuel;
In the case of less excess air, reduce the peak temperature and “thermal reaction NO”;
At low oxygen concentrations, the duration of the fuel in the flame front peak and reaction zone increases.
The specific methods commonly used to reduce NOx formation and emission are staged combustion, burning, low oxygen combustion, shadow bias combustion and flue gas recirculation.
General Application of Low NOx Burner
A burner is an important equipment of in an industrial furnace, which ensures stable ignition and complete combustion of fuel and other processes. Therefore, the inhibition of NOx generation must start from the burner. According to NOx reduction combustion technology, low NOx burners can be roughly divided into the following categories:
1. Stage burner
The burner of this stage is designed according to the fractional combustion principle so that the fuel and air are partially mixed for combustion. As the combustion deviates from the theoretical equivalence ratio, NOx can be reduced.
2. Self-circulating burner
One is to use the combustion air pressure head to suck part of the smoke back into the burner and mix it with air for combustion. Due to flue gas recirculation, the combustion flue gas has a large heat capacity, large combustion temperature, and reduced NOx.
Another kind of self-circulation burner directly recycled part of the flue gas into the burner and adds it to the combustion process. The burner has dual functions of restraining nitrogen oxides and saving energy.
3. Sunshade burner
The principle is to make some fuels burn too strongly and some fuels burn too lightly, but the total amount of air above them remains unchanged. Since both parts burn with a skewed adsorption ratio, NOx is very low. This combustion is also called deflective combustion or noninert combustion.
4. Split flame burner
The principle is to divide the flame into several small flames. Due to the large heat dissipation area of a small flame and low flame temperature, the “thermal reaction NO” is reduced. In addition, the small flame reduces the residence time of oxygen, nitrogen, and other gases in the flame, and has an obvious inhibition effect on “thermal reaction NO” and “fuel NO”.
5. Mixed supercharging burner
The residence time of flue gas in the high-temperature zone is one of the main factors affecting the generation of NOx. Improving the mixing of combustion and air can make the thickness of the flame surface thinner. Under the same combustion load, the residence time of flue gas on the flame surface, i.e. in the high-temperature zone, is shortened, thus reducing the generation of NOx. The mixed supercharging burner is designed according to this principle.
6. Low NOx precombustion chamber burner
The development of precombustion chamber developed in China in the past 10 years is an efficient and low NOx combustion technology. Generally speaking, it is a kind of air or secondary air and fuel injection system of the precombustion chamber. It mixes fuel and air to form a mixture of fuel in the precombustion chamber in the combustion area. Due to the lack of oxygen, it is only a part of fuel combustion. The fuel has areas where flame volatilization precipitates under the conditions of oxygen deficiency and low flame temperature, thus reducing the formation of NOx.