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

生物质是中国的一大能源，但能量比含量低，导致其储存和运输投入较大。为了避免这一问题，近年来，造粒生物质得到了大量的利用。造粒可以以更高的效率处理致密的无尘产品。由于造粒技术的快速发展，目前的生物质利用模式有可能被生物质颗粒所取代。化学环流气化(CLG)是一种独特的气化方案，它与传统的气化工艺直接相关，但又有显著的不同。CLG工艺不需要传统的空分制氧，可以在最小的能量损失下，利用氧气载体强化生物质气化和焦油重整制合成气。我们的多学科团队由中国和德国在化学循环和颗粒技术领域的领先研究小组发起，共同回答流态化、单颗粒技术、化学反应科学和反应器/过程建模等关键的、相互关联的科学问题，从微尺度到反应器和工艺尺度，涉及生物质颗粒CLG技术。提出的基础性研究主要集中在四个方面。流态化行为(1)：沸腾床内气泡和生物质颗粒的动力学。单粒生物质颗粒(2)：生物质颗粒在脱挥过程中机械强度的发展、单粒颗粒内部的热传导以及颗粒与床料之间的热传递。此外，还将研究单个球团在脱挥过程中的结构变化。在BPM模型的基础上，建立了单颗粒生物质气化模型。化学反应(3)：生物质颗粒的气化动力学和氧气载体上的焦油重整。工艺优化(4)：采用MP-PIC方法，建立CLG工艺的三维欧拉-拉格朗日数值模型。将关联床层的流体动力学、颗粒流态化、单颗粒微尺度模型、气化和焦油重整动力学耦合在一起，模拟整个CLG过程。这项工作将在互联的沸腾床气固两相流动特性和CLG反应器的放大方面进行。拟议研究获得的基本发现将大大加快高效生物质气化CLG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.