碱金属富集型燃料焦炭燃烧与多模态PM生成特性及其耦合机理

High alkali metals in Zhundong coal and biomass result in unique char combustion characteristics and PM formation and also cause complex interaction between combustion and PM formation. However, current researches are mainly focused on either separated char combustion or PM formation, and the complex interaction mechanism on char combustion and multi-modal PM formation are still unclear. Therefore, we aim to reveal the unique char combustion characteristics and PM formation mechanisms of the alkali-enriched fuels by experiments and intrinsic kinetics modeling, meanwhile, the complex interaction between char combustion and PM formation are also elucidated. On basis of the experiments conducted in drop tube furnace, stationary bed, and the laser diagnostic and optical test facility in Sandia national laboratories, the reaction rate coefficients of gasification by H2O and CO2 relative to that of oxidation and the kinetic parameters of the detailed alkali kinetic mechanisms containing the effects of ash compositions on alkali typed PM formation are obtained, and both the char combustion characteristics and the formation and accumulation characteristics of the multi-modal PM (alkali and non-alkali typed ultrafine PM, fragmentation typed fine PM, and residual ash typed coarse PM ) will be revealed. Based on cellular automata theory, Monte Carlo method, and the preliminary self-developed char burning and ultrafine PM formation kinetics model, a sophisticated intrinsic kinetics model on char combustion and multi-modal PM formation will be developed by coupling with the detailed alkali kinetic mechanisms that has considered the effect of ash compositions and the fragmentation model containing both random pore model and mass transfer kinetic model of cracking. Taking fully into account the experiment results and modeling prediction, the new developed and sophisticated model will be used to predict and elucidate the uniqueness and complex coupling interaction mechanism of multi-modal PM formation and char combustion of alkali-enriched fuels. All those provide theoretical guidelines for combustion optimization, and PM predication, prevention, and control.

准东煤与生物质内高的碱金属导致焦炭燃烧与PM生成的独特性，而当前研究分别聚焦于单一燃烧或PM生成，交互作用研究甚微，且焦炭燃烧与多模态PM生成机理不甚清晰。故本项目拟通过实验与动力学模拟揭示碱金属富集型燃料焦炭燃烧与多模态PM生成特性及机理，阐明其交互机制。借助沉降炉、固定床与激光-光学实验台，获取气化相对氧化反应速率常数和灰组分-碱金属动力学反应机理，揭示焦炭燃烧、碱金属型和非碱金属型超细模态、破碎型细模态和残灰型粗模态PM生成及富集特性；借助元胞自动机理论、蒙特卡罗方法、基于申请人初步发展的焦炭本征动力学燃烧模型与超细PM生成动力学模型，耦合灰组分-碱金属动力学反应机理、随机孔模型与质量传递动力学破碎理论，发展焦炭颗粒本征动力学燃烧-多模态PM生成耦合模型。模型预测与实验结合，预测并阐明碱金属富集型燃料独特的焦炭燃烧与多模态PM生成特性及耦合机制，为燃烧优化与PM预测防治等提供理论支撑。

本项目针对煤焦颗粒燃烧多模态PM生成，通过制取合成煤焦及煤制煤焦，实验及动力学模拟相结合，详细研究了多变燃烧条件下煤焦颗粒燃烧特性与多模态PM生成特性，为燃烧优化与PM预测防治等提供理论支撑。主要结果如下：.1）煤焦燃烧碳转化率是氧化促进效应、H2O/CO2气化反应促进效应、H2O/CO2气化吸热抑制效应与H2O/CO2热抑制效应相互作用结果。H2O/CO2热抑制效应随H2O/CO2浓度增加先升高后降低，随O2浓度和停留时间增加持续降低。H2O热效应对超细颗粒物生成总体上呈现负效应。.2）煤焦燃烧过程中，矿物质内含物以灰气化挥发、灰膜与灰渗透三重形式相转化。灰气化挥发量随燃烧温度、O2浓度、煤焦颗粒初始粒径、灰含量、内含物浓度增加而升高。灰膜比例随温度和碳转化率增加而增加，随煤粉粒径增大而减小，灰膜形成比例F随碳转化率N呈幂增加F=aN23.66Y。.3）燃烧温度是矿物质蒸发与超细PM生成的决定因素；超细PM总量随H2O浓度呈现先减小后增大的趋势，5%H2O浓度时达到最低点；富氧燃烧降低超细PM生成。PM0.1主要成分都是Ca、Na、Si、K、Fe、Mg和Al；但富氧促进PM0.1中Na、Si、Fe和Al的富集。煤焦矿物质对气化和超细PM生成起主要作用的依次是碱土金属、碱金属、Si和Al。.4) 相比于高孔隙率煤焦，致密煤焦破碎细模态PM质量浓度较低，破碎程度轻，以矿物熔融聚并为主。动力控制区煤焦燃烧均匀破碎，飞灰粒径呈单峰分布；扩散控制区煤焦燃烧边界破碎，飞灰粒径呈双峰分布。高灰煤焦粗模态PM质量浓度高于低灰煤焦。.5）基于煤焦颗粒燃烧过程中灰气化挥发生成超细PM、灰膜与灰渗透通过煤焦颗粒逾渗破碎-灰分熔融聚并生成细模态与粗模态PM的机理耦合，发展了煤焦颗粒燃烧与多模态PM生成动力学模型，可实现煤焦物性、空气、富氧及烟气再循环等多变燃烧条件下多模态PM生成进行了精确预测与机理揭示。