Nitrogen oxide is a common pollutant in the atmosphere, usually referred to as nitric oxide and nitrogen dioxide. Nitrogen oxides (NOx) as air pollutants usually refer to no and NO2, which are discharged by natural and human activities, as follows:
NOx emitted from nature: mainly from the decomposition of soil and marine organic matter, which belongs to the natural nitrogen cycle process, and the natural release of nitric oxide to the atmosphere accounts for about 90% of the total.
NOx emitted by human activities: most of the combustion processes from fossil fuels, such as those of automobiles, aircraft, internal combustion engines and industrial boilers; It also comes from the production and use of nitric acid, such as nitrogen fertilizer plant, organic intermediate plant, nonferrous and ferrous metal smelter, etc., accounting for about 10% of the total.
The harm of nitrogen oxide to the environment
NOx has a great impact on the environment. It is not only one of the main substances forming acid rain, but also an important substance to form photochemical smoke in the atmosphere and an important factor (a bit terrible) for O3 consumption.
Under the high temperature combustion conditions, NOx mainly exists in the form of no, and no accounts for about 95% of the original NOx emission. However, no is easily reacted with oxygen in the air to generate NO2. Therefore, NOx in the atmosphere is generally in the form of NO2.
No and NO2 in air are balanced by photochemical reaction and transformation. When the temperature is large or there is cloud, NO2 further interacts with water molecules to form the second important acid component in acid rain, nitric acid (HNO3).
When there is catalyst, the conversion of NO2 to nitric acid is accelerated if the appropriate meteorological conditions are added. Especially when NO2 and SO2 exist at the same time, they can catalyze each other and form nitric acid faster.
The effect of nitrogen oxide on human body
Nitrogen oxide is a stimulant gas, and the toxicity of nitrogen dioxide is 4-5 times of nitric oxide, which can cause discomfort after being inhaled by human body.
Because nitrogen dioxide is difficult to dissolve in water, it has little stimulation effect on eyes and upper respiratory tract, but it is easy to invade bronchioles and alveoli in the deep part of the respiratory tract, destroy collagen fibers of alveoli and develop emphysema like symptoms.
Nitric oxide enters the blood and combines with hemoglobin to produce high-iron hemoglobin, which reduces the oxygen carrying capacity of hemoglobin, and makes the tissue hypoxia. The effect of low concentration of nitrogen oxide can lead to emphysema like symptoms, and the ability of respiratory tract anti infection is decreased, and the syndrome of neurasthenia is accompanied.
Control method of nitrogen oxide
There are two types of control for NOx at present:
One is source control and low NOx combustion technology, which is characterized by various technical means to control the generation reaction of NOx in the combustion process.
The other is tail control, namely, flue gas denitrification, which reduces the NOx generated by denitration device to N2, thus reducing the emission.
The treatment methods of nitrogen oxides can be divided into three types: catalytic reduction, absorption and adsorption.
The main principle of catalytic reduction is to put NOx in the exhaust gas under the condition of high temperature and catalyst. The reduction to pollution-free N2 requires catalyst due to the high reaction temperature, and the equipment investment is large and the operating cost is large.
Adsorption method mainly uses absorption materials and adsorbents to absorb NOx waste gas. Because of the small adsorption capacity, this method is only applicable to NOx. The waste gas treatment with low concentration and small gas volume.
Absorption method: water or acid, alkali, salt water solution to absorb nitrogen and oxygen compounds in the waste gas, so that the waste gas can be purified. The method has a low cost of equipment investment and low operating cost.
Post time: May-06-2021