水汽相变耦合撞击流作用下燃煤电站PM2.5长大脱除的研究

coal-fired power plant boiler has become one of the most important emission sources of fine particulate matter (PM2.5). It is difficult for any single conventional PM2.5 removal technology to meet the increasingly strict regulations on emission standards. Thus, it is a urgent to develop the coupling or synergistic technology based on two or more physical or chemical mechanisms for efficient removal of PM2.5. It is considered to be one of the most expected methods to promote the removal of PM2.5 by water vapor heterogeneous condensation coupling impinging streams. However, the physical or chemical growth and removal mechanisms of PM2.5 is not completely clear. The growth and removal of PM2.5 under the effect of heterogeneous condensation coupling impinging streams is a complex process, which involves the heat and mass transfer, multiphase flow with phase transformation, heterogeneous condensation growth, collision and coalescence and other physical phenomena. The preliminary research results of the project applicant show that, compared to under the effect of heterogeneous condensation, the removal efficiency of fine particles improved significantly under the effect of heterogeneous condensation coupling impinging streams, and the power consumption is not the main obstacle in the application of this technology. Therefore, the project aims to the formation mechanism of supersaturated water vapor and the heat and mass transfer law, growth mechanism and motion behavior of PM2.5 in impinging streams heterogeneous condensation chamber, the removal of PM2.5 under the effect of water vapor heterogeneous condensation coupling impinging streams. This provides theoretical basis for the efficient removal of PM2.5 and enrich the multiphase flow theory.

燃煤电站已成为细颗粒物(PM2.5)的重要污染源之一，在日益严格的PM2.5排放标准下，采用任何单一传统的控制技术均难以满足需求，因此发展不同控制方式的协同脱除技术日益迫切。水汽相变耦合撞击流是协同促进PM2.5脱除的重要方法之一。PM2.5在水汽相变耦合撞击流作用下的长大脱除是涉及热质交换、多相流并伴有相变、非均相凝结长大、碰撞聚并等多种物理现象的复杂过程，其热质传递规律及PM2.5长大机理尚不完全清晰。前期研究发现，与仅靠水汽相变作用相比，PM2.5在水汽相变耦合撞击流作用下的脱除效率明显增大，而且阻力适中；为此，本申请项目拟对强化PM2.5凝结长大的过饱和水汽的形成机制及热质传递规律、PM2.5在撞击流相变室中长大机理及其运动行为规律、PM2.5在水汽相变耦合撞击流作用下的脱除规律加以研究。通过本项目的研究可丰富和发展细颗粒物多相流理论，为实现PM2.5高效脱除提供重要基础。

PM2.5污染已成为突出的大气环境问题，发展高效脱除PM.5的新技术及相关装备日益迫切。水汽相变耦合撞击流是促进燃煤PM2.5长大与高效脱除的重要方法。针对燃煤湿法烟气脱硫（WFGD）净烟气处于饱和状态的特点，如何构建均匀过饱和水汽环境并强化PM2.5凝结长大和碰撞团聚长大，是迫切需要解决的关键科学问题。本项目为实现PM2.5的长大与高效脱除，研究了强化PM2.5凝结长大的过饱和水汽的形成机制及热质传递规律，理论研究了细颗粒在过饱和水汽环境中的异质核化和凝结长大特性，数值模拟了细颗粒或含尘液滴在撞击流中碰撞团聚长大及其运动行为规律，同时，试验研究了撞击流相变环境下PM2.5的长大与脱除性能。结果表明，只需向湿法脱硫净烟气中添加少量(如0.02kg/Nm3)水蒸汽即可形成过饱和水汽环境；撞击流相变室内过饱和水汽分布非常均匀，各处温差最大不超过0.2℃、过饱和度相差最大不超过0.003；撞击流极佳的混合性能，非常适合用于PM2.5的相变凝结长大；随着细颗粒物粒径增大，异质核化的成核速率增大，临界过饱和度减小；细颗粒在几毫秒至几十毫秒内即可完成长大为含尘液滴；在基于Fletcher理论数值预测异质核化特性时，有必要考虑颗粒表面吸附水分子的扩散凝结机制、线张力和粗糙度等影响因素；撞击流中细颗粒在撞击区域做往复运动和富集，细颗粒或含尘液滴在粘附作用下发生碰撞团聚长大；在蒸汽添加量为0.04 kg/Nm3时，倾斜撞击流相变室中细颗粒物的数量浓度脱除率可由普通立式、卧式相变室的33.1%、34.1%增至66.1%；水汽相变耦合撞击流作用可显著促进细颗粒物脱除。研究成果不仅可为控制湿法烟气脱硫净烟气中PM2.5排放问题提供重要参考，同时还丰富和发展了多相流理论。