How do nitrogen oxides in flue gas come into being? What are the reasons for the production of nitrogen oxides?

Release time:

2022-08-09

Nitrogen oxides mainly come from natural and human industrial production activities. Natural sources mainly come from ammonia oxidation, biomass combustion, soil emissions, lightning formation and stratospheric entry in the biosphere. However, anthropogenic sources mainly come from NOx emissions from fuel combustion, industrial production, transportation and other processes. NOx in China mainly comes from the power industry, motor vehicle exhaust and non-metallic mineral products industry. The total emissions of these three regions account for 83% of the total NOx emissions.

Nitrogen oxide refers to compounds composed of only nitrogen and oxygen, including a variety of compounds, such as nitrous oxide (N2O), nitric oxide (no), nitrogen dioxide (NO2), nitrogen trioxide (N2O3), nitrogen tetroxide (N2O4) and nitrogen pentoxide (N2O5). Except for nitrous oxide and nitrogen dioxide, other nitrogen oxides are unstable and turn into nitrogen dioxide and nitric oxide when exposed to light, humidity or heat, and nitric oxide turns into nitrogen dioxide. Nitrogen oxides have different degrees of toxicity.

In flue gas denitration, NOx comes from the sintering flue gas in the flue at the head of the sintering machine. The reason for the generation of NOx in the sintering flue gas is that nitrogen or combustible nitrogen compounds in the air react with oxygen in the sintering environment. Among them, NOx includes fuel type NOx, thermal type NOx and fast type NOx.

The production of nitrogen oxides in gas-fired boilers is the combustion of boilers. There are five main ways to produce NOx: thermal NOx, fast NOx, fuel NOx, N2O intermediate NOx and NNH NOx. However, the fuel composition of natural gas boilers (CH4 ≥ 98%) is relatively single, and the NOx generated by them is mainly thermal NOx and fast NOx. The excess air coefficient a is greater than 1, which is conducive to reducing NOx emissions.

Motor vehicle exhaust is the exhaust gas produced by motor vehicles during operation, including carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons (HC) and solid suspended particles (PM), which is one of the main culprits of air pollution.

What are the reasons for the production of nitrogen oxides?

The production of nitrogen oxides in the incineration process is that the nitrogen oxides produced in the combustion process of coal are mainly nitric oxide and nitrogen dioxide, and their generation and emission are closely related to the combustion mode, especially the firing temperature and excess air coefficient. There are three ways of NOx generation: fuel type, thermal type and rapidity. Among them, the amount of rapid generation is very small and can be ignored.

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