1. Background of low nitrogen combustion

China's "Thirteenth Five-Year Plan for Energy Development", the proportion of non-fossil energy consumption will be increased to more than 15%, and the proportion of natural gas consumption will strive to reach 10%. As a clean energy, natural gas combustion products hardly contain sulfur dioxide and dust particles. The pollutant emissions are nitrogen oxides - NOx. In addition to harming human health, NOx is also the main driver of acid rain, photochemical smog and ozone destruction, and an important culprit in the production of atmospheric ultra-fine particulate matter PM2.5.

Smog is mainly composed of sulfur dioxide, nitrogen oxides and inhalable particulate matter . Combined with fog, they can instantly turn skies overcast and gray, clouding the atmosphere, blurring vision and causing visibility deterioration. With the development of industry and the ardent desire of the people to improve their living standards, stricter requirements have been put forward for ultra-low emission of nitrogen oxides.

2. The basic principle of nitrogen oxides production

The nitrogen oxides produced during the combustion of fossil fuels are mainly fuel-type, rapid-type and thermal-type.

1) Thermal NOx
is produced by the oxidation of N2 in the air with O2 at high temperature. The higher the reaction temperature, the faster the formation of NOx. The influencing factors are flame temperature, oxygen concentration, burning time, turbulence and so on.

2) Fast type NOx

Nitrogen oxides are produced by the thermal decomposition of hydrocarbons in the high temperature region during the combustion process, and the reaction time is very short.

3) Fuel type NOx

The fuel generally contains a small amount of nitrogen-containing compounds, which are easily decomposed and oxidized to NOx during the combustion process.

3. Introduction of low nitrogen combustion technology

Low nitrogen combustion technology mainly inhibits the formation of various nitrogen oxides. Burner low nitrogen technology methods include: staged combustion technology, rich-lean combustion technology, premixed combustion technology, low excess air combustion technology, FGR technology and SCR technology. Through the selection and combination of low-nitrogen technologies, ultra-low emissions of nitrogen oxides NOx <30mg can be effectively achieved.

4. Relevant specifications and standards for low-nitrogen combustion

1. The European Union stipulates the emission of nitrogen oxides from industrial production in 2010/75/EC "European Industrial Emissions and Pollution Prevention and Control Integration Directive" issued by the European Parliament and the Council of the European Union; "Combustion devices fueled by natural gas ( excluding gas turbines and internal combustion engines) the NOx limit is 100mg/m3.”

2. The most stringent nitrogen oxide emission standards in California, the United States, in the Nox emission concentration limits of gas-fired boilers in the Southern California Air Quality Management District:

a) 1.5——6MW gas equipment application, Nox<18mg/m3;

b) Gas equipment application of ≥6MW, Nox<10mg/m3;

3. In 2015, the Beijing air pollutant emission standard officially kicked off the prelude to China's low nitrogen emissions. So far, Shandong, Hebei, Shanghai, Hangzhou, Xi'an, Urumqi, Tianjin, Zhengzhou, Taiyuan and other provinces and cities have issued Low nitrogen emission standard; in the industrial field, Henan Province has launched the "Implementation Plan for Ultra-Low Emission Transformation of the Iron and Steel Industry" in the cement and iron and steel industries in Henan Province, and similar requirements for nitrogen oxide emission NOx <50mg.

4. In GB/T 36699-2018, it can be seen that it is clearly stated that all kinds of industrial kilns, industrial heating furnaces and burners for other purposes shall be implemented with reference to this standard. Many automobile production and exhaust gas environmental protection enterprises in Beijing and Shandong have required lower nitrogen oxide emissions for drying heating furnaces and RTO incinerators.

5. Application of low nitrogen combustion technology

Low-nitrogen technology mainly includes low-nitrogen combustion technology and exhaust gas treatment technology. Low-nitrogen combustion technology is more widely used due to its high maturity, simple system, and low investment and operating costs. Daiding Industrial Co., Ltd. has low nitrogen emission application experience in various industrial fields such as environmental protection treatment, automotive field, coating drying, food drying, textile, steel, cement and so on.