The NOx in the burner flue gas mainly comes from the nitrogen in the fuel, and in general the higher the nitrogen content of the fuel, the higher the NOx emissions. There are also many factors that affect the amount of NOx in boiler flue gas, including the fuel type, operating conditions, and boiler load.
(1) Fuel characteristics influence
The ratio of various elements in the volatile components of coal affects the NOx generation during combustion, and the larger the oxygen/nitrogen (O/N) ratio in coal, the higher the NOx emissions; even under the same O/N ratio conditions, the conversion rate is also related to the excess air coefficient, and a large excess air coefficient results in a high conversion rate, which increases NOx emissions. In addition, the sulfur/nitrogen (S/N) ratio in coal also affects the emission levels of SO2 and NOx. S and N will compete with each other when they oxidize, therefore, as SO2 emissions rise in flue gas, NOx emissions will decrease accordingly.
(2) Excess air coefficient influence
When the air is not graded into the furnace, reducing the excess air coefficient will, to a certain extent, play a role in limiting the oxygen concentration in the reaction zone, and thus has a significant control effect on the generation of NOx, using this method can reduce the generation of NOx by 15%-20%, but the CO increases and the combustion efficiency decreases. When the air is graded into, it can effectively reduce NOx emissions, and as the primary air volume decreases and the secondary air volume increases, the rate of N being oxidized decreases, and the NOx emissions also decrease accordingly.
(3)Effect of combustion temperature
The effect of combustion temperature on NOx emissions has achieved consensus, that is, as the combustion temperature increases, NOx emissions rise.
(4) Influence of load rate
Usually, when the load rate is increased and the coal feed is increased, the smoke temperature in the combustion chamber and at the tail heat surface increases, and the NOx generated increases.
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