微波热气耦合作用对提质褐煤的物化结构及水分复吸的影响及机理

The high water content of lignite and high water re-adsorption capacity of upgraded lignite are major issues on its commercial utilization. The couple upgrading method of microwave and hot gas has high drying efficiency, and also gets the dramatic collapse of the pore structure by microwave and the effective removal of the oxygen containing functional groups by hot gas. The physical-chemical properties of upgraded lignite can be controlled effectively by the couple upgrading method, thereby the water re-adsorption capacity of upgraded brown coal can be restrained. In this project, the upgraded lignite with different water contents are obtained by microwave, hot gas and the couple upgrading method respectively. The chemical-physical property changes of upgraded lignite will be compared. The coupling effect on the chemical-physical property changes of upgraded lignite will be revealed. The water re-adsorption behaviors of upgraded lignite will be compared. The physical-chemical properties of upgraded lignite and their water re-adsorption capacity will be correlated. The mechanism of pore structure changes by microwave and oxygen functional groups changes by hot gas on water re-adsorption characteristics of upgraded lignite will be illustrated. The pore structure of upgraded lignite and porous model materials and their water re-adsorption capacity will be correlated. The mechanism of pore structures on water re-adsorption capacity of upgraded lignite will be elucidated. The changes of surface chemical functional groups of upgraded lignite during the D2O re-adsorption process will be studied. The oxygen containing functional groups of upgraded lignite and its water re-adsorption capacity will be correlated. The mechanism of oxygen functional groups on water re-adsorption capacity of upgraded lignite will be clarified. The outcome of this project will provide the fundamental support to effective restrain water re-adsorption capacity of upgraded lignite.

褐煤的高含水量和提质后易复吸水的特点限制了其大规模利用。微波热气耦合提质方式干燥效率高，且兼具微波对孔隙结构显著破坏及热气可高效脱除表面含氧官能团的优势，可对提质褐煤物化结构高效定向调控，进而有效抑制提质褐煤水分复吸。本项目通过微波、热气及微波热气耦合提质方式下不同干燥程度提质褐煤物化结构对比，揭示微波热气耦合作用对提质褐煤物化结构影响规律。通过三种提质方式下提质褐煤水分复吸特性的对比，及提质褐煤的物化结构与其水分复吸特性的关联，阐明微波强化后孔隙结构的改变、及热气强化后含氧官能团的变化对提质褐煤水分复吸特性的影响机制；通过提质褐煤及多孔模型物的孔隙结构及其水分复吸特性的关联，阐明孔隙结构对水分复吸影响的本质；通过提质褐煤复吸D2O过程中表面化学结构变化，结合提质褐煤含氧官能团与其水分复吸特性的关联，揭示含氧官能团对水分复吸影响机理。本项目的研究结果将为抑制提质褐煤水分复吸提供科学依据。

褐煤的高含水量和提质后易复吸水的特点限制了其大规模应用。针对褐煤因高水分含量限制其利用的“瓶颈”问题，本研究利用微波热气耦合提质方式，可实现褐煤的高效提质，同时实现褐煤物化结构高效定向调控，进而有效抑制提质褐煤水分复吸。.项目选取了一种云南及一种内蒙褐煤为研究对象。首先通过褐煤的低温冻结特性将褐煤中的水分划分为自由水分、可冻结束缚水分及不可冻结水分；基于褐煤的高温脱水失重及复吸水分等特征，将褐煤中的水分划分为自由水分、毛细水分及分子水分；这两种划分方式具有一定的对应性。通过对比两种褐煤的固定床热气干燥特性及微波热气耦合干燥特性，得出相对于固定床热气干燥，微波热气耦合通过对可冻结束缚水分的快速脱除，显著提高褐煤的干燥效率。.对于提质后褐煤的物化结构研究发现，微波场中，褐煤的孔隙结构发生不可逆的坍塌，提质褐煤的大孔体积显著减小的同时微孔体积增加，导致微波热气耦合干燥后样品的比表面积增加；提质后褐煤的化学结构主要受到干燥气氛及耦合干燥温度的影响，在所选定的微波干燥温度160 oC条件下，微波热气耦合干燥对提质褐煤的含氧官能团的分解表现的脱除优势不是十分显著。通过对提质后褐煤的高相对湿度下及低相对湿度下的复吸水特性研究发现，微波热气干燥后煤样的复吸水量在相对度为96%条件下明显降低，不同气氛下，CO2干燥后煤样的复吸水分比Ar气氛下略微减少。相对于热气不同温度，不同功率对干燥褐煤的复吸水影响更显著。得出CO2气氛下，热气温度140 oC，微波功率500W左右时，可实现对褐煤的高效干燥同时，干燥后提质褐煤的复吸水性可明显被抑制。.此外研究还利用碳纳米管为模型物得出含氧官能团和5-10nm孔是控制水分复吸的关键。利用D2O代替普通H2O与提质后褐煤相互作用，揭示了复吸的水分在温度高达330 oC仍稳定存在，证明了复吸的水分参与了褐煤中氢键的重排过程。