Views: 1779 Author: Site Editor Publish Time: 2022-09-03 Origin: Site
① Thermal type
Thermal NOx is mainly generated during combustion. Nitrogen in combustion supporting air is oxidized under high-temperature flame. It is mainly generated in the area with temperature higher than 1800K. Temperature, excess air coefficient and residence time in high-temperature zone will all affect the generation of thermal NOx. Among them, temperature is the most important influencing factor of thermal type, and 1800K is the key temperature point of NOx generation of thermal type.
The excess air coefficient has a double-sided effect on thermal NOx, and the actual combustion situation is more complex. When the excess air coefficient increases, the oxygen concentration increases, which promotes the shift of the chemical reaction equilibrium and increases the amount of NOx generated; At the same time, as the excess air coefficient increases, the amount of flue gas generated also increases, which reduces the combustion temperature and thus reduces the generation rate. Therefore, the influence of excess air coefficient is more complex, which may be promoting or inhibiting, and it should be analyzed according to the actual situation. In general, the longer the reaction stays in the high-temperature zone, the greater the amount of NOx generated.
② Rapid NOx generation mechanism
The nitrogen element in the rapidly generated NOx also comes from the air during combustion. The rapid generation is mainly due to the fact that hydrocarbons can decompose a large number of CH, CH ∶ and C ∶ groups during combustion, which can destroy the molecular bonds of nitrogen. Under high temperature conditions, the decomposed ch; Free radicals react with n ∶ in the air to generate HCN, NH, n. The above reaction products can react with O and oh atom groups in the flame to generate No. among them, HCN is the most important intermediate product of rapid NOx generation, which can rapidly generate NOx in the flame surface. The formation mechanism of fast NOx is very complex and the intermediate reaction time is short.
The rapid NOx is mainly generated by the rapid reaction of hydrocarbons in the fuel. Among them, the excess air coefficient, furnace pressure and N concentration in the combustion zone are the main factors affecting the rapid NOx generation, while the temperature has almost no effect on it. When the temperature is constant, with the increase of the excess air coefficient, the NOx generation will first increase and then decrease, and there will be a peak.
③ Fuel NOx
The fuel type NOx is formed by the nitrogen element contained in the fuel during the combustion of the fuel. The nitrogen-containing organic compounds in the fuel generate CN, HCN and NH through thermal cracking; And other intermediate products are further oxidized to generate NOx. The influence of temperature on the generation of fuel type NOx is not obvious, mainly because the temperature required for the pyrolysis of fuel nitrogen-containing compounds is not high. When it is about 600 ℃ - 800 ℃, fuel type NOx can be generated.
The excess air coefficient has a great influence on the generation of fuel type NOx, and the conversion rate of nitrogen into NOx in the fuel increases with the increase of the excess air coefficient; When the excess air coefficient a > 1, the fuel NO production remains basically unchanged; When the excess air coefficient a < 1, the conversion rate will decrease rapidly.
The above is the answer of Jiangsu Sifang boiler to this question. If you have any doubts about other boiler related problems, please consult the online customer service of Jiangsu Sifang boiler or call 0516-85871846 or 0516-85532705. The professional technicians of Jiangsu Sifang boiler will answer your questions in time.