煤气化过程中碱金属的迁徙规律及可控转化原位反应机理研究

Coal gasification is a key technology for the high efficiency and clean use of coal resources. Alkali metals in coal have catalytic effect on coal gasification, however, most of alkali metals could be volatilized below 1000℃, which can easily cause agglomeration during fluidized bed gasification. Additives can change the migration of alkali metals and inhibit agglomeration, but the reaction mechnism still needs to be studied. The migration of alkali metals and the controllable transformaton have become the research focuses at home and abroad. This project is based on tube furnace and fluidized bed experiment platform, selected nano-Al2O3 and nano-SiO2 as model compounds of additives, proposed three levels of real coal samples, pretreatment coal and nano-composite particles of coal and additives to explore the migration of alkali metals and in-situ reaction properties of controllable transformation, and employed thermodynamic equilibrium calculation software of FactSage to analyze. This project can achieve the purpose of clarifying the migration mechanism of alkali metals during coal gasification, revealing the in-situ reaction mechanism between additives and alkali metals, and realizing the prediction of alkali migration and controllable transformation. The above research has important scientific significance and practical value about solving the agglomeration problems caused by alkali metals during fluidized bed coal gasifiction and achieving the clean use of coal resources.

煤气化技术是煤炭资源高效清洁利用的关键技术，煤中的碱金属对气化过程具有催化作用，然而大部分碱金属在1000℃以下会挥发出来，在流化床气化中极易导致系统产生粘结问题。添加剂可以改变碱金属的迁徙行为、抑制粘结作用，但其中的反应机理需要深入研究。煤气化过程中碱金属的迁徙规律及可控转化已成为国内外研究的热点。本项目基于管式炉和流化床实验平台，选取纳米Al2O3和纳米SiO2作为添加剂的模型化合物，提出从真实煤样、预处理煤样和煤-添加剂纳米复合颗粒三个层面，探索煤气化中碱金属的迁徙规律及可控转化原位反应特性，并采用FactSage热力学计算软件进行理论分析。通过本项目研究，阐明煤气化中碱金属迁徙的共性规律，揭示添加剂与碱金属间的原位反应机理，实现对碱金属迁徙规律及可控转化反应的预测。上述研究对于优化解决流化床煤气化中碱金属引发的粘结问题、实现煤炭资源的洁净利用具有重要的研究意义和实际应用价值。

针对高钠煤气化过程中碱金属引发的粘结问题，本项目通过实验研究和理论分析，探索煤气化过程中碱金属的迁徙规律及可控转化反应特性。揭示了高碱煤中碱金属的赋存形态、含量及分布特征研究，发现575℃低温灰化是一种简单、快捷、较准确获得准东煤中钠元素含量的前处理方法，而逐级萃取法可较准确的获得煤中钠的含量，准东煤中钠主要以水溶性钠形式存在。阐明了高碱煤热解、气化和燃烧过程中碱金属的迁徙规律，发现气化温度、煤种及煤灰分中的碱金属均影响气化反应活性，准东煤中含钠组分与硅酸盐等反应生成低温共熔体是导致粘结的主要原因。揭示了流化床高钠煤气化碱金属的迁移规律、阐明防结渣机理，得出煤灰组分特性、试验操作条件、反应器结构及床料类型等因素均能影响高碱煤流化床气化的安全稳定运行，高熔点含钠化合物的生成是抑制准东煤气化过程结渣的必要条件。揭示了添加剂对碱金属迁移及粘结特性的影响规律，发现添加Al2O3促进了钠的析出，使得气化残留物中的钠含量较低。建立了碱金属迁徙、可控转化的热力学研究方法和预测机制，并通过配煤方式使煤灰组分向高温区移动，实现了高碱煤在循环流化床工业气化炉上的稳定运行。