Research And Application Of Ammonia Removal Technology In Fly Ash

In order to meet ultra-low emission requirements,coal-fired power plants have almost installed flue gas denitrification devices based on selective catalytic reduction technology（SCR）.The NH₄HSO₄ generated during flue gas denitration will not only cause air preheater blockage and corrosion,but also be adsorbed by fly ash caused the ammonia content increase of fly ash.A series of problems have appeared in practical application of ammonia-containing fly ash,which greatly affects the resource utilization of fly ash,so it is necessary to find a cost-effective method for removing ammonia from fly ash..In the thermogravimetric analysis,it is found that NH₄HSO₄ can be quickly decomposed at 296.8°C and above,and the decomposition behavior tends to be completed in one step.When NH₄HSO₄ is mixed into fly ash,its thermal weight loss characteristics change,the initial temperature of rapid weight loss decreases and stepwise weight loss occurs.This is the result of the combined effect of the main components of fly ash such as Si O₂,Al₂O₃,Fe₂O₃,and Ca O.Heating ammonia-containing fly ash at different temperatures found that the temperature of 210°C and below have little effect on the removal of ammonia in fly ash.To reduce the ammonia content of fly ash from 500ppm to below 100ppm,heating at 260°C for 30 minutes and 310°C for 20 minutes is required;while at 360°C,the ammonia removal rate is very fast,and only heating for 5 minutes can remove alkaline ash more than 90% ammonia.Heating at the same temperature,the removal rate of ammonia in alkaline ash is significantly higher than that of acid ash.Different amounts of alkali and water were added to the ammonia-containing fly ash at room temperature with an ammonia content of 500 ppm and stirred.It is studied that for alkaline ash,only 2%H₂O（mass percentage,the same below）is added and stirred for 10minutes to remove 58.1%ammonia in the ash.Add 1%Ca（OH）₂,2%H₂O to acid and alkaline ash,and stir it with a stirring rod at 300r/min for 5 minutes to remove about 95%of the ammonia in the ash.Compared with Ca O,adding Ca（OH）₂ allows ammonia in fly ash to be removed more quickly.The test device for ammonia removal device in fly ash based on the alkali addition method has good ammonia removal effect.The device puts a set ratio of fly ash and alkali into the stirring mixer through feeders,and adds water through the water injection port on the stirring mixer.The ash,alkali,and water are fully mixed in it,and the ammonia in the ash starts to be released.Then the fly ash enters the hollow blade dryer,where the fly ash is repeatedly stirred,compressed,and relaxed.During the heating and stirring process,the ash is dried and the residual ammonia is further removed.The ammonia content can be reduced by about 90%after fly ash with an average ammonia content of nearly 300ppm is treated by the device.The finished ash is dry and the ammonia content is small,which has high resource utilization value and low cost.Therefore,it is an economical and efficient method for ammonia removal from fly ash.