Multi-scale analysis and optimization of chemical looping gasification of biomass

生物质在中国是一种重要的能源资源，但其能量比含量低，导致其储存和运输投资高。为了避免这一问题，近年来生物质颗粒化得到了广泛的应用。造粒允许以更高的效率处理压实，无尘产品。随着制粒技术的快速发展，生物质颗粒有可能取代现有的生物质利用模式。化学循环气化（CLG）是一种独特的气化方案，与传统的气化工艺直接相关，但又有显著不同。在CLG工艺中不需要传统的空气分离制氧，它可以通过使用氧气载体以最小的能量损失增强生物质气化和焦油转化为合成气。由中国和德国在化学环和颗粒技术领域的领先研究小组发起，我们的多学科团队汇集在一起，回答在流化，单颗粒技术，化学反应科学和反应器/过程建模方面的关键，相互关联的科学问题，从微观层面到反应器和过程规模，涵盖生物质颗粒的CLG技术。本文提出的基础研究主要集中在四个方面。流态化行为(1)：流化床中气泡和生物质颗粒的动力学。单球团(2)：生物质球团在脱挥发过程中机械强度的发展，单球团内部的热传导以及球团与床料之间的传热。此外，还将研究单球团在脱挥发过程中的结构修饰。单一生物质颗粒气化模型将基于BPM （bond Particle model）模型开发。化学反应(3)：生物质颗粒的气化动力学和焦油在氧载体上的重整。工艺优化(4)：采用MP-PIC （Multiphase Particle in Cell）方法，建立CLG工艺的三维欧拉-拉格朗日数值模型。将互联流化床流体动力学、球团流化动力学、单颗粒微观模型、气化动力学和焦油重整动力学耦合在一起，模拟整个CLG过程。本文将对互连流化床中的气固流体特性和CLG反应器的放大进行研究。从拟议的研究中获得的基本发现将大大加速CLG用于高效生物质气化的开发和部署。

Biomass is a great energy resource in China, but characterized by a low energy specific content, resulting in a high investment on its storage and transport. In order to avoid this problem the pelletized biomass is intensively used in recent years. Pelletizing allow to treat compacted, dustless products with higher efficiency. The present biomass utilization model is potentially to be substituted by using biomass pellets due to the fast development of the pelletizing technology. Chemical Looping Gasification (CLG) represents a unique gasification scheme that is directly related yet notably different from conventional gasification processes. The conventional oxygen production by air separation is not needed in CLG process, which allows enhanced biomass gasification and tar reforming to syngas by using oxygen carrier with minimal energy penalty. Initiated by the leading Chinese/Germany research groups in the areas of chemical looping and particle technology, our multidisciplinary team brings together to answer critical, interrelated scientific questions in fluidization, single particle technology, chemical reaction science and reactor/process modeling, spanning from micro-scale level to reactor and process scales on the CLG technology of biomass pellets. The proposed fundamental research focuses on four aspects. Fluidization behavior (1): dynamics of bubbles and biomass pellets in the fluidized bed. Single pellet (2): the development of mechanical strength of biomass pellet during devolatilization, heat conduction inside single pellet and heat transfer between pellets and bed materials. Moreover structural modification of single pellet during devolatilization will be investigated. The single biomass pellet gasification model will be developed based on BPM (Bonded Particle Model) model. Chemical reactions (3): gasification kinetics of biomass pellets and tar reforming over oxygen carriers. Process optimization (4): with the MP-PIC (Multiphase Particle in Cell) methodology, three-dimensional Euler-Lagrangian numerical model will be developed for CLG process. The fluid dynamics of interconnected fluidized beds, pellets fluidization, single particle micro scale model, gasification and tar reforming kinetics will be coupled together to simulate the whole CLG process. It will be done with regard to the gas-solid fluid characteristics in interconnected fluidized beds and scale-up of the CLG reactors. Fundamental findings obtained from the proposed research will significantly accelerate the development and deployment of CLG for efficient biomass gasification.