超细飞灰对烟气酸露点与酸凝结的影响研究

Research on effect of ultrafine ash particles on acid dew point and acid condensation for coal-fired boilers

准确预测燃煤锅炉尾部烟气的酸露点和酸凝结对深度降低排烟温度、保障尾部换热设备的安全高效运行十分重要。尾部烟气中存在的飞灰颗粒对酸露点和酸凝结液滴的发生有很大影响,不可忽略。考虑烟气中超细飞灰颗粒对酸露点和酸凝结的影响,提出了飞灰粒径对考虑局部凝结质量传输效果的酸露点和酸凝结迭代计算方法,实现了酸露点和壁面温度下酸凝结的准确预测。当飞灰粒径低于中肯半径(rash<r0)时,飞灰粒径对凝结率有显著影响;随着飞灰粒径的降低,硫酸蒸气、水蒸气以及酸液凝结率明显增加,尤其是硫酸蒸气凝结率;飞灰粒径越小,凝结越易发生。然而,过冷度超过30℃时,烟气中超细飞灰颗粒对低温壁面酸凝结的影响可以忽略不计。烟气携带而不被低温壁面捕获的凝结酸液量较少,烟气中超细飞灰颗粒对烟气酸蒸气的降低作用可以忽略不计。理论计算方法为分析现场酸-灰作用积灰层提供理论依据,对于优化燃煤锅炉尾部烟道的安全高效运行有重大指导意义。

Accurate prediction of acid dew point(ADP)and acid condensation is the key to deeply reduce the flue gas temperature and to ensure the safe and efficient operation of the heat exchange equipment in coal-fired power plants.The ash particles in the flue gas have great influence on the occurrence of ADP and acid condensation droplets.The iterative calculation method of ADP and acid condensation considering the effect of fly ash particle radius on local condensation mass transfer were proposed for the first time in this paper.When the fine ash particles radiuses are smaller than the critical radius(rash<r0),with the reduction of fine ash particle radius,the condensation rate around fine ash particles,especially acid condensation rate,is markedly increased at ADP.And the acid condensation is easier to occur with the smaller ash particle radius.However,when the supercooling degree exceeds 30℃,the effect of ultrafine ash particles on the acid condensation of heating surface can be ignored.The amount of acid solution condensed around fine fly ash particles,which can not be caught on the heating surface,is small,and the reduction effect of the fly ash particles on the acid vapor of flue gas can be negligible.The theoretical calculation method in this paper provides a theoretical basis for the analysis of acid-ash fouling layer on the field experiments,and useful guiding significance for the safe and efficient operation of the heat exchange equipment in the coal-fired boiler.