褐煤密相输运床气化过程流动反应特性及放大规律

Dense transport-bed gasifier is a novel gasification technology that is suitable for lignite. The flow behavior of the gas and solid phases inside the gasifier with single particle class have been investigated systematically in the past twenty years. However, some key scientific problems, such as the flow/mixing behavior, the reaction coupling mechanism and the scale-up rule, needs to be further explored in the gasifier with multi-particle classes. This program aims at investigating these key scientific item by using theory analysis, experiment investigation and CFD method. The flow and mixing behavior are first explored in a dense transport bed at the operating conditions of high flux and high density. Then, the pyrolysis and the gasification process of lignite(char) as well as their coupling mechanism are experimentally investigated. Further, the dimensionless scale-up number and the scale-up rule are established, and validated by the laboratory experiment and the pilot scale test. The scale-up of dense transport-bed gasifier is subsequently obtained. The implementation of this program could reveal the flow/mixing behavior in the complex multi-phase flow system, push our understanding on the gasification mechanism of lignite(char) and obtained the scale-up principle of the dense transport-bed gasifier. These results provide necessary design information and theoretical foundation for the development and the scale-up of the novel transport-bed coal gasification process.

密相输运床是适合褐煤的气化型式，且在单组分颗粒体系气固流动特性方面己取得较大进展，但气化炉内多组分颗粒的流动混合特性、反应耦合特性和放大规律等关键科学问题有待进一步深入研究。本项目针对"褐煤密相输运床气化"这种新型物质转化过程，采用理论分析、实验研究和数值模拟相结合的方法，从多相流角度认识高通量、高密度循环流化床内多组分颗粒体系的流动和混合特性；从气化反应角度探索褐煤、褐煤焦等的热化学转化特性和热解/气化耦合规律；进而建立无因次放大参数和放大准则，并结合小试和中试实验研究结果，确定褐煤密相输运床气化过程的放大规律。通过本项目的研究，不仅可以掌握复杂多相流动体系的流动与混合特性，提升目前对褐煤热解/气化化学机理和反应耦合规律的认识水平，而且能够揭示多相传递反应耦合体系的放大规律，从而为新型输运床褐煤气化技术的开发提供基础数据和理论支撑。

本项目针对密相输运床褐煤气化过程，从多相流角度研究了高通量高密度循环流化床多组分颗粒体系的流动和混合特性；从气化反应角度探索了流化床内褐煤气化规律；进而建立了密相输运床褐煤气化数学模型；以确定褐煤密相输运床气化过程的放大规律。(1) 密相输运床内B类颗粒固含率沿轴向呈上稀下浓分布；增加循环量或减小表观气速，轴向固含率增加但分布更不均匀。双组分颗粒体系在流化床底部进料段和顶部出口段表现出分离特性，而在中间充分发展阶段表现为混合；增大颗粒循环量或减小表观气速有利于颗粒混合。团聚物颗粒浓度与局部颗粒浓度关系密切，循环量增加或表观气速降低均使得团聚物颗粒浓度增加。(2) 褐煤流化床气化实验研究表明，床层温度、给水流量和煤粒径对褐煤气化有着重要影响。酸洗脱出矿物质后，煤的热解速率更快更彻底。与原煤气化相比，酸洗褐煤气化的碳转化率略有升高，而气化产率和效率略有降低，合成气中各成分浓度降低。褐煤气化反应活化能为104.75~131.36 kJ/mol，修正体积模型优于均匀反应模型及缩核反应模型。(3) 密相输运床褐煤气化的数值模拟研究表明，气固两相速度均随气化炉高度的增加而增加，但在进煤口附近有所波动。固相含量沿气化炉高度先逐步减小，在返料口附近出现局部极大值，10 m高度后固相浓度基本不变。合成气各重要组分在进煤口附近大量生成，之后沿气化炉高度方向逐步增加。所建立的数学模型能较好地预测不同尺度气化炉内流动特性、关键组分的轴向分布以及气化炉出口的产品分布。通过本项目的研究，掌握了复杂多相流动体系的流动与混合特性，深化了对褐煤气化化学机理和反应耦合规律的认识水平，揭示了多相传递反应耦合体系的放大规律，为密相输运床褐煤气化技术的开发提供了基础数据和理论支撑。