Analysis on the Causes of Fouling in Air Preheater under Sludge Co-Burning Conditions and Research on the Methods of Descaling
Urban wastewater sludge is mixed with coal as a low calorific value fuel and enters the boiler for combustion.Mixing sludge and coal in a certain proportion will not affect the combustion of the boil-er.The blending of sludge with coal changes the moisture,ash and even sulfur content of the fuel,and the composition of the flue gas after combustion also changes accordingly,increasing the risk of fouling and clogging in the air preheater.A study was carried out on the fouling phenomenon of an air preheat-er of a power station boiler in Shanghai when burning about 8％sludge.Through the analysis of the scale samples,it was found that the scaled scale samples contained ammonium bisulfate(NH4HSO4).Ammonium bisulfate was highly viscous and absorbed fly ash to form relatively hard scale.The forma-tion and precipitation of ammonium bisulfate is related to the ratio of sulfur trioxide(SO3)concentration to ammonia(NH3)concentration in the flue gas,water content and temperature field.The temperature field provided by the air preheater just meets the formation and precipitation of ammonium bisulfate.Based on the scale formation mechanism,the method of scale inhibition and scale removal was stud-ied,and it was confirmed that adding calcium alkali to neutralize the sulfur trioxide in the flue gas can reduce the production of ammonium hydrogen sulfate and effectively slow down the production of scale.Increase the temperature and add calcium base.Ammonium bisulfate in the scale will react with calcium base to produce calcium sulfate(CaSO4),gaseous ammonia and carbon dioxide(CO2).The analysis of the viscous substance ammonium bisulfate reduces the adhesion of scale,and the gaseous products after the reaction can also play a role in loosening the scale,thus achieving the effect of re-moving scale.
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