典型多元硫酸盐/氯化盐蒸气下熔融细颗粒的壁面粘附/反弹模型研究

The condensation of sulfate/chloride vapors and sebsequent thermophoresis deposition on wall are commonly happened during thermo-chemical convernsion of high potassium biomass, high sodium lignite, Zhundong coal and municipal solid wastes. The condensation behavior of salt vapors within boundary layer is parallelly involved in many sub-processes, which including gas-to-solid conversion, direct difusion condensation, heterogeneous condensation and chemical reaction. This program intends to investigate the deposition mechanism of fine particle under the typical and mixed multivariate salt vapors. Meanwhile, a sticking/rebound model of molten fine particle is developed based on the stickness of various eutectic compound, particle kinetic energy, propeties of impacting surface and condensed form of salt vapors. First, the database is established on the stickness and melting fraction of typical binary or ternary sulfate/chloride which are function of temperature and molar ratio of each component. The condensation behavior of mixed salt vapors and its effect on the sticking propensity of molten Si-Al rich fine particle are experimentally investigated. On a basis of experimental results, then the calculation model considering both the gas-to-solid conversion and direct diffusion condensation of salt vapors is developed. The key parameter is obtained for the sticking model in which particle reference viscosity is associated with particle kinetic energy and impacting angle. These models mentioned above are considered in CFD simulation calculation to identify the dynamic formation and development mechanism for initial condensation and deposition layer.

高钾生物质、高钠褐煤、准东煤和城市固体废弃物热化学转化中换热面普遍存在硫酸盐/氯化盐蒸气的冷凝效应和细颗粒热泳沉积行为。边界层内盐蒸气的冷凝涉及气固转变(成核、聚集与表面生长)、直接扩散冷凝、异相冷凝以及化学反应等过程。本项目结合实验与模拟计算，旨在探究典型多元混盐蒸气下熔融细颗粒的壁面沉积机制，并发展基于多种共晶化合物粘性、颗粒动能、壁面属性和盐蒸气冷凝相分布的细颗粒粘附/反弹模型。首先，构建典型二元/三元硫酸盐/氯化盐混合物粘度与熔融分数随温度与组分变化的数据库；实验研究混盐蒸气的壁面冷凝行为和冷凝效应对熔融富硅铝细颗粒粘附行为的影响。基于实验结果，然后建立考虑盐蒸气气固转变和直接扩散冷凝行为的计算冷凝模型，获取颗粒参考粘度同颗粒动能与撞击角相关联粘附判定模型的关键参数，耦合CFD模拟计算，揭示初始冷凝与沉积层的动态形成与发展机制。

在双碳背景下燃煤机组掺烧高碱生物质或固废燃料时虽可以实现一定比例的碳减排，但同时也面临受热面严重结焦风险。本项目首先根据生物质灰的失重特性与吸放热曲线、灰熔融特征温度，以失重曲线中灰样不损失质量与DSC曲线中吸热量大幅增加的温度为初始点，构建了生物质灰熔融分数的计算方法，分析了硅铝颗粒对生物质灰熔融分数的影响行为，获得了生物质灰颗粒的熔融分数随温度的变化特性和外来矿物相对熔融分数的影响。研究了含Zn/Pb气态盐组分作用下受冷壁面盐组分的冷凝沉积行为与富硅铝颗粒的粘附行为，揭示了含Zn/Pb气态盐组分对灰颗粒粘附与金属腐蚀行为的作用机制。然后，实验研究了高碱金属燃料燃烧中不同烟气温度下壁面的颗粒沉积特性，通过分析灰熔融特性变化规律与矿物相演变行为，提出了弱化盐蒸气冷凝沉积与颗粒熔融粘附的结焦缓解方法。建立了考虑Na/S/Cl等组分释放、气相组分相互反应、钠盐组分冷凝和盐冷凝耦合灰颗粒粘附行为等多个子过程的颗粒粘附模型，获得了燃用高碱金属燃料炉内盐蒸气组分分布特性与沉积行为。项目研究成果将能为更好地利用低碳高碱燃料且同时减缓壁面结焦倾向能够提供可行的解决方案。