Controlling boiler combustion conditions is also a method to reduce the emission of dust nitrogen oxides and sulfur dioxide. When the air enters the furnace, reducing the oxygen content of excess air will increase the oxygen concentration in the restricted zone to a certain extent. Thus, the oxidation reaction of oxygen and sulfur, oxygen and nitrogen is reduced, so as to reduce the generation rate of sulfur dioxide and nitrides. However, if oxygen content is over controlled, carbon monoxide will increase, which will affect boiler combustion and boiler efficiency. The lower the oxygen content, the less sulfur dioxide and nitrogen oxide emissions; Bed temperature is also a major factor affecting SO2 and NOx emissions. The operating conditions of each boiler are different. According to the practice summary of the six \n\e boilers we operate, the oxygen content is controlled to 3-4%, the bed temperature is scientific between 850 and 950, the emission of dust, nitrogen oxide and sulfur dioxide is relatively low, and does not affect the boiler efficiency (generally, the bed temperature is kept at about 950). Generally speaking, under the condition of stable boiler load, controlling boiler working conditions is helpful for desulfurization and denitration control. If the boiler load is unstable and the emission of nitrogen compounds and sulfur dioxide is excessive, it is faster to use the method of direct ammonia injection.
The large change of NOx at the denitration inlet is closely related to the change of coal quality, oxygen content, primary air volume and secondary air volume control during combustion adjustment. The denitration platform is set at the inlet of the cyclone separator, and the distance from the inlet to the outlet of the denitration reaction zone is very short. If the nitrogen oxide at the inlet rises rapidly, we should input slowly when we inject ammonia. Because the reaction between ammonia and nitrogen oxide has a certain time lag, the reaction will not be complete, and the nitrogen oxide at the outlet will decline rapidly after the corresponding rise. If we input too much, ammonia without complete reaction will escape. The danger of ammonia escape is great. The ammonia injection on the denitration platform is increased. The excess ammonia will react with sulfur trioxide in the flue gas to generate ammonia bisulfate. When the temperature in the flue gas is low, the ammonium bisulfate will form a liquid. After reacting with the surface substances of fly ash, it will change the surface shape of particles, and eventually form sticky corrosive substances, which will adhere to the air preheater and the cloth bag, resulting in the blockage of the air preheater and the paste belt of the cloth bag, And increase the power consumption of induced draft fan. Sometimes, the frequency modulation opening of the induced draft fan will gradually increase during our operation, so we should try to avoid ammonia escape during our operation, and try to avoid large increase during ammonia injection, which should be carefully adjusted.
Denitration is the selective reaction with nitrogen oxides using reduction method (ammonia) to generate harmless nitrogen and water. So as to achieve the purpose of removing nitrogen oxides. How do nitrogen oxides form? It is a mixed gas formed after the chemical reaction between nitrogen and oxygen in the flue gas. It is mainly nitric oxide and nitrogen dioxide, which are relatively stable. There are also nitrogen trioxide, nitrogen tetroxide and nitrogen pentoxide. These mixtures are collectively referred to as nitrogen oxides, that is, nitrous smoke. The formation of sulfur dioxide is the chemical reaction between sulfur and oxygen in the flue gas, which produces sulfur dioxide. The oxidation of sulfur and nitrogen will compete with each other, so the emission of sulfur dioxide in the boiler will increase, and the emission of nitrogen oxides will decrease accordingly.