The formation mechanism of NOx nitrogen oxides
For natural gas boilers, the production of Nox mainly comes from the thermodynamic Nox produced by nitrogen in the air and excessive oxygen. The production of thermodynamic Nox has an exponential relationship with the combustion temperature, which usually starts when the combustion temperature is higher than 1000 degrees Celsius, and the generation speed of Nox above 1400 degrees will increase sharply. The figure below reflects the relationship between NOx emission and temperature of coal-fired boilers, in which the temperature relationship of thermal NOx is also suitable for natural gas boiler burners.
The relationship between NOx emission and temperature of coal-fired boilers is based on the growth mechanism of NOx mentioned above. The technology of controlling NOx of low-nitrogen burners also focuses on two directions:
1. Reduce the flame temperature;
2. Reduce oxygen content.
Types of low-nitrogen and ultra-low nitrogen burners
Conventional gas boiler burners typically emit about 120 to 150 milligrams of NOx. Low nitrogen burners are usually defined as NOx burners that discharge between 30 and 80 mg. NOx emissions below 30 mg are commonly known as ultra-low nitrogen burners.
The high NOx emission of traditional burners is mainly caused by the following reasons:
1. In order to ensure sufficient combustion, large excess air is used.
2. The combustion temperature is usually around 1800 degrees.
Low nitrogen burners low nitrogen burners are usually based on the following technologies
1. Electronic proportional regulation and oxygen content control technology; To precisely control the oxygen content;
2.FGR flue gas recirculation technology to reduce flame temperature and oxygen content;
3. Fully premixed surface combustion technology to reduce flame temperature and achieve full combustion;
In the above technology, it is usually necessary to configure the low nitrogen burner. Based on the above technology, the market for low-nitrogen burners is mainly divided into the following types:
The advantages and disadvantages of each low nitrogen burner are introduced
1. FGR low nitrogen burner
FGR low nitrogen burners can usually control NOx to 65 mg in full fire range with a limit of about 40 mg. Further reduction of NOx emissions may lead to combustion instability or sacrifice of adjustable ratio and other disadvantages.
2. Ultra-low nitrogen combustion burner is burned on the surface
Surface combustion ultra-low nitrogen burners can usually control NOx within 30 mg of full fire range. Its main drawback is the need to filter the air, increased maintenance work; At the same time, the oxygen content is around 7%, which reduces the partial combustion efficiency.
3. Surface combustion +FGR ultra-low nitrogen burner
The surface combustion +FGR ultra-low nitrogen burner combines the advantages of NOx control of surface combustion with the advantages of reducing oxygen content of FGR. It can control the level of NOx to 20 mg in the whole fire range and the content of oxygen within 3% to maximize the combustion efficiency. Its main shortcoming is the increase of equipment cost.
For more information on low nitrogen burners, please consult Beijing chuangwei electromechanical equipment co., LTD.