磁化水对细颗粒水汽凝结长大的影响

Effects of magnetized water on vapor condensation and growth of fine particles

为促进燃煤电厂烟气中细颗粒物水汽凝结长大,提高其脱除效率,提出了采用磁化水强化低过饱和度下颗粒长大效果的方法。以润湿性差的炭质颗粒为研究对象,测量了水磁化前后的表面张力变化以及对炭质颗粒接触角的影响;将热水与冷气溶胶接触形成过饱和环境,利用生长管实验研究了磁化水和普通水条件下炭质颗粒的水汽相变长大特性;基于经典异质核化理论,计算了磁化水对炭质颗粒长大所需的临界饱和度和过渡阶段长大速率的影响。实验结果表明:在800 mT磁场强度下,经过30 min循环磁化,水的表面张力降低了4.5 mN/m,与炭质颗粒的接触角降低了3°,炭质颗粒的润湿性得到改善;与普通水相比,磁化水条件下炭质颗粒几何平均粒径从原始的1.42μm长大到3μm以上,长大效果更佳,并且在较低过饱和水平下促进效果更明显。理论计算结果表明,在磁化水作用下,相同粒径的炭质颗粒异质凝结长大所需的临界饱和度明显下降,更有利于促进粒径较小的颗粒发生异质凝结;磁化水有助于提高低过饱和度下炭质颗粒过渡阶段的长大速率,磁化水条件下炭质颗粒过渡阶段的长大速率总是大于普通水;当生长管中过饱和水平较低时,相比于普通水,磁化水可明显提高过渡阶段炭质颗粒的长大速率,并且大颗粒凝结长大效果更好。磁化水耦合水汽相变技术将有助于促进炭质颗粒水汽凝结长大,间接提高烟气除尘效率。

In order to promote the vapor condensation and growth of fine particles in the flue gas of coal-fired power plants and improve removal efficiency,a method to enhance the effect of particle growth under low super-saturation with magnetized water was proposed.The surface tension of water before and after being magnetized and its influence on the contact angle of carbonaceous particles with a poor wettability were measured.The supersaturated environment was formed by contact between hot water and cool air sol.The growth characteristic of carbonaceous particles was investigated in growth tube under magnetized water and tap water.Based on the classical heterogeneous nucleation theory,the effects of magnetized water on the critical saturation and growth rate of carbonaceous particles in the transition stage were calculated.The experimental results indicated that the surface tension of water decreased by 4.5 mN/m after 30 min of cyclic magnetization at 800 mT and the contact angle with carbonaceous particles decreased by 3°,which implied the wettability of carbonaceous particles was improved.Compared with tap water,the geometric mean particle size of carbonaceous particles increased from 1.42μm to more than 3μm,with better growth effect,and the promotion effect was more obvious at a lower supersaturation level.The theoretical calculation results showed that when water was magnetized,the critical saturation for the heterogeneous condensation of carbonaceous particles with the same size decreases significantly,which is more conducive to promoting the heterogeneous condensation of particles with smaller size.Magnetized water can help to improve the growth rate of carbonaceous particles in the transition stage under low supersaturation.The growth rate of carbonaceous particles in the transition stage under magnetized water is always higher than that of tap water.When at a lower supersaturation level,the growth rate of carbonaceous particles in the transition stage was improved obviously by magnetized water,and the growth effect of large particles is better.Magnetized water coupled vapor phase transition technology will be beneficial to the condensation of carbonaceous fine particles and the improvement of dusting efficiency of flue gas indirectly.