Measures for reducing nitrogen oxides by low-nitrogen gas boiler
The nitrogen content in natural gas is relatively low, so fuel NOx is not the main control type.
The thermal type NOx refers to the oxidation of N2 in combustion air to NOx at high temperature. The generation mechanism of thermal NOx is generally adopted by the czechis Vicky mechanism: when the temperature is below 1500 C, the generation of thermal NOx is few, and the reaction speed will increase by 6~7 times when the temperature rises at 100 degrees C when the temperature is higher than 1500. In the actual combustion process, the temperature distribution in the combustion chamber is not uniform. If there is a local high temperature area, more NOx will be generated in these areas. It may play a key role in the generation of NOx in the whole combustion chamber.
The fast NOx will generate NOx rapidly in the reaction zone when the hydrocarbon fuel is burning and rich in fuel. In the actual combustion process, various factors are changed individually, and many parameters are in constant change. Even the simplest combustion of gas fuels will also undergo a mixture of fuel and air, burning smoke, until finally out of the hearth. The temperature of the furnace, the mixing degree of fuel and air, the retention time of the flue gas in the furnace and so on, all the parameters which have great influence on the NOx emission are in constant change.
When the mixture of fuel and air enters the furnace, the temperature of the mixture increases rapidly due to the convection and radiation heating of the surrounding high temperature flue gas. When the ignition temperature is reached, the fuel starts to burn, and the temperature rises sharply to the adiabatic temperature level. At the same time, because of the convection and radiation heat transfer between the flue gas and the surrounding medium, the temperature gradually decreases, until the temperature of the surrounding medium is the same, that is, the cooling edge of the flue gas flow through the whole furnace. It can be seen that the flame temperature distribution in the furnace is actually uneven. Usually, the temperature at a certain distance from the outlet of the burner is the highest, and the temperature at the front and rear is low, that is, there is a local high temperature zone. Because the temperature in the area is much higher than that in the furnace, it has a great effect on the amount of NOx production: the higher the temperature, the more NOx generation is. Therefore, in order to restrain the formation of NOx in the furnace, in addition to reducing the average temperature in the furnace, the temperature distribution in the furnace must be evenly distributed to avoid the local high temperature.