The main classification and generation principle of NOx

Type thermal NOx

The generation of thermal NOx is mainly produced during combustion. Nitrogen in the combustion air is generated by oxidation under the high temperature flame. It is mainly generated in the region with a temperature higher than 1800K. Temperature, excess air coefficient and residence time in high temperature zone all affect the formation of thermal NOx. Temperature is the most important factor affecting the thermal type, and 1800K is the key temperature point for the generation of thermal NOx.

Excess air coefficient produces a double - sided effect on thermal NOx, and the actual combustion is more complex. When the excess air coefficient increases, the oxygen concentration increases, promoting the chemical reaction equilibrium movement, so that the production of NOx increases; At the same time, with the increase of excess air coefficient, the amount of gas generated also increases, reducing the combustion temperature, and thus reducing the formation rate. Therefore, the effect of excess air coefficient is more complex, which may be promoting or inhibiting, and should be analyzed according to the actual situation. Generally, the longer the reaction stays in the high temperature zone, the greater the production of NOx.

Type fast NOx

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 and decompose the CH under high temperature conditions. Free radicals react with N∶ N in the air to form HCN, NH, N. The above reaction products can react with O and OH atomic groups in the flame to form NO. Among them, HCN is the most important intermediate product for the rapid formation of NOx, which can rapidly generate NOx in the flame surface. The formation mechanism of rapid NOx is very complex and the intermediate reaction time is short.

Type fast NOx mainly is rapid response generated hydrocarbons in the fuel, the excess air coefficient, the pressure, combustion chamber of a stove or furnace zone N concentration are the main factors influencing the rapid type NOx formation, and temperature on its almost unaffected, at a certain temperature, with the excess air coefficient, NOx generation can appear larger decrease after the first peak.

Fuel type NOx

Fuel type NOx is formed by the nitrogen element contained in the fuel when the fuel is burned. Nitrogen containing organic compounds in fuel are decomposed by heat to form CN, HCN and NH. Such as intermediate products, further oxidation to NOX. The effect of temperature on the generation of fuel NOx is not obvious, mainly because the pyrolysis temperature of fuel containing nitrogen compounds is not high, about 600℃-800℃, fuel NOx can be generated.

Excess air coefficient has a great impact on the generation of fuel NOx, the conversion rate of nitrogen into NOx in the fuel increases with the increase of excess air coefficient; When the excess air coefficient a>1, the fuel NO production basically remains unchanged. When the excess air coefficient A <1, the conversion rate will drop quickly.