More than 95% of NOx in the combustion flue gas is NO and hardly soluble in water. The wet flue gas denitrification technology is a dissolution medium other than water, such as acid, especially nitric acid to absorb NO, or oxidize NO to water Or alkali N2O5 and NO2, then adsorption or absorption.

1) Oxidation

The oxidation method uses strong oxidants, such as ozone, hydrogen peroxide, and oxychloride, to oxidize NO in the flue gas to N2O5 and NO2 that are easily soluble in water or alkali, and achieve removal in subsequent wet desulfurization. Currently widely studied liquid oxidants are HNO3, KMnO4, NaClO2, NaClO, H2O2, KBrO3, K2CrO7, Na2CrO4, (NH4)2CrO7, and the like. Oxidation catalysts include V2O5 (in acidic solution), activated carbon, molecular sieves, and the like.

Ozone is the most widely used method. O2O5 generated by ozone oxidation is easily soluble in water to form HNO3, and reacts with alkalis to generate NaNO3, Mg(NO3)2 and other inorganic substances during the process of flue gas desulfurization. salt.

Oxidation and denitrification have some disadvantages. For example, the acidic waste liquid produced during the absorption process is difficult to handle and requires high equipment requirements.

2) Complex absorption method

NOx in the flue gas is mainly in the form of NO, while NO is basically insoluble in water and cannot enter the liquid medium. For this reason, the principle of wet complexation absorption method is to use some metal chelates such as Fe(E)·EDTA, Fe(NTA), Fe(II)-EDTA, Fe(II)-EDTA-Na2SO3 and FeSO4 etc. Dissolved NOx, especially NO, rapidly react to form a complex, and the complex heats to release NO, thereby enriching NO for recovery or further reduction or oxidation treatment. The complex absorption method has a high NOx removal rate. However, the recycling of chelates is difficult. In the reaction, chelates are lost, the absorbing liquid is easily deactivated, the regeneration is difficult, the utilization is low, the treatment of the waste liquid is complicated, and the operating cost is high.

3) Acid absorption method

The acid absorption denitrification is the absorption of NOx in flue gas with acid substances such as nitric acid, because the solubility of NOx in acid is much higher than the solubility in water. NOx can be sufficiently absorbed by concentrated sulfuric acid. Utilizing this property, NO and NO2 can be absorbed into concentrated sulfuric acid to produce nitrous sulfuric acid (NOHSO4) and recovered. The denitrification efficiency of the acid absorption method is affected by factors such as absorption temperature and pressure, and there are technical problems such as high energy consumption, large requirement for the circulation amount of the acid in the absorption process, and the like.

4) Alkali absorption method

Alkali absorption denitrification is the use of some alkaline solution as absorbent, such as NaOH, KOH and NH3 · H2O solution. Alkaline absorption denitration process is relatively simple, while denitrification products (nitrites, nitrates, etc.) can be recovered, but there are also disadvantages such as low denitration efficiency and limitation of NOx concentration in flue gas.