【作者】 赵辉；

【导师】 周劲松； 方梦祥； 岑可法；

【作者基本信息】 浙江大学 ， 工程热物理， 2007， 博士

【摘要】 生物质能的开发和利用可缓解当今常规能源短缺和环境污染所带来的压力，如何能有效地使生物质转化成高品位的液体燃料成为目前研究的焦点。本文基于国内外在生物质间接液化制取液体燃料领域已经开展的研究工作，对生物质定向气化大规模制取合成气技术路线进行了理论探讨，并对生物质气流床气化进行了深入的试验研究和动力学分析。本文首先介绍了研究背景。在着重对比分析几种主要的生物质液化技术基础之上，得出了生物质间接液化在制取液体燃料过程中的优势。生物质间接液化的关键在于合成气的制取，于是从生物质气化工艺出发，结合煤基合成气气化技术，总结出生物质气流床气化在大规模制取合成气过程中具有广阔的发展前景。然后，对生物质气流床气化制取合成气的研究进行了综述，并得出生物质气流床气化的技术难点主要是：灰的特性、颗粒研磨、原料给料和系统高效加压。为了系统地开展相关领域的试验及理论研究，根据气流床气化原理，自行设计与搭建了一套小型生物质高温气流床气化试验台，对其进行了介绍。为了研究生物质在气流床气化过程中的气化特性及残炭特性，利用小型气化系统对木屑进行了气化试验，主要考查了反应温度和氧气／生物质比对煤气组分、碳转化率、气化产物分布以及残炭特性的影响。结果表明，生物质气流床气化具有合成气含量高，碳转化率高，煤气产率高，CH₄和焦油含量少的优点。为了正确地解释上述试验数据，综合分析了气流床气化炉内的流动和加热特性，从基本的微分方程入手，用数值方法对生物质单颗粒在气流床内的气化过程进行数值模拟。结果显示，该数值计算能够较好地模拟生物质单颗粒在气流床气化过程中的加热过程、停留过程和质量变化过程，并能与试验结果较好吻合。针对碱金属及其相关无机元素在生物质气流床气化中的挥发问题，进行了木屑在不同反应温度下和不同氧／生物质配比下的气化试验，对其残炭进行了收集，并通过ICP及EDX-SEM仪器对残炭灰成分和残炭形态进行分析，得出了无机元素在生物质气流床气化过程中析出挥发规律。然后，采用三种不同的助熔剂，分别以不同的比例添加到稻壳和水曲柳两种生物质中，再吹入到气流床中进行气化，来考查助熔剂在生物质气流床气化过程中对生物质碱金属及其相关元素的固留影响，最后选出了合适的助熔剂及添加比例。为了考查气化参数对生物质气流床气化过程的影响，利用小型生物质气流床气化系统对生物质的热解及气化特性进行了试验研究。研究了反应温度、氧气／生物质比率（O／B）、水蒸汽／生物质比率（S／B）以及停留时间对不同生物质气流床气化合成气组分的影响。研究表明，反应温度是影响生物质热解和气化最重要因素；生物质在常压气流床气化生成合成气最佳O／B范围为0.2～0.3（1300℃）；高温气化时合成气中CH₄含量很低：停留时间为1.6s时其气化反应基本完毕；加大水蒸气含量可增加H₂／CO比率，但水蒸汽的过多引入会影响煤气产率。为了给生物质气流床气化反应过程和最终状态进行系统详尽地描述，为此，综合考虑平衡模型和动力学模型的优点，结合生物质半焦与水蒸汽及CO₂气化反应动力学的试验数据，建立了一个全面描述生物质气流床气化过程的动力学模型。并从系统反应进程和最终煤气组分两方面与生物质小型气流床气化试验进行对比验证，确认了该动力学模型的可靠性。表明所建模型可以用于预测气化参数对生物质气流床气化的影响特性。为了考查烘焙预处理对生物质固体产率、能量产率、颗粒研磨及在气流床气化过程中总体效率的影响，本文在一套小型烘焙试验台上，对四种不同种类的生物质进行烘焙试验，并对研磨过的固体产物进行粒径分析，最后在小型生物质气流床上进行了气化试验。结果表明，生物质的能量密度随着烘焙温度的提高而升高，其中，中温烘焙（～250℃）能获得较好的固体和能量产率，减少能量损失；烘焙温度是烘焙过程中最重要的影响因素：烘焙能够减少生物质研磨的耗电量，同时能够破坏生物质内部的纤维结构，变得易磨；气流床气化过程中，烘焙生物质能够改善煤气成分，提高气化的总体效率。因此，在生物质气流床气化过程中，烘焙预处理能为生物质的粒径减小和随后的粉体气力输送提供了一个良好的解决途径。更多还原

【Abstract】 The exploitation and utilization of biomass energy is an effective method for relieving the pressures of conventional energy resources shortage and serious environment pollution. How to effectively convert low quality biomass to higher quality liquid fuel has attracted more and more attention of the whole world. On the basis of the investigation of biomass indirect liquefaction to synthesize liquid fuel, technology options available on large scale to produce syngas from biomass by directional gasification have being discussed extensively, and a systematic research on both experimental and kinetic was performed on the biomass entrained flow gasification.The research background was introduced at the beginning of this paper. Based on the comparison among the several major biomass liquefaction technologies, the advantages of the biomass indirect liquefaction to synthesize liquid fuel were obtained. The key of biomass indirect liquefaction is the production of syn-gas. So focusing on the process of the biomass gasification combined with coal-based gasification technology, it summarizes that biomass entrained flow gasification for synthesizing the syn-gas on large scale is heading for a great future. Then an extensive review was made on the development of the technologies of biomass entrained flow gasification. From the analysis, it is shown that ash behavior, particle milling, feedstock feeding and system pressuring have been said to be the major hurdle if biomass is converted in a entrained flow gasifier. For developing a systematic experimental research on biomass entrained flow gasification, a lab-scale entrained flow reactor was designed and put up on the basic principle of the entrained flow gasification. Furthermore, the component and performance of the gasification system were introduced.In order to investigate the characteristics of biomass gasification in an entrained flow reactor, a lab-scale biomass entrained flow gasification system was characterized and was used to test sawdust gasification including gas composition, carbon conversion, products distribution and solid residue behavior with different reaction temperatures and oxygen/biomass ratio. The results reveal that syn-gas content increases and CH₄ content decreases with increasing reaction temperature; tar content can be considered very low; the carbon conversion rate and gas yield rate increase to a maximum value at high reaction temperature. In addition, a finite difference model was employed to simulate the fluidynamics, the energy balance and the mass transfer during the partial oxidation of biomass particles. The application of this model allows the residence time, the thermal history and the mass conversion of the particle inside the reactor to be estimated. The experimental and model results are in agreement.Considering the critical role of inorganic elements in biomass utilization, experiments of the sawdust gasification were done for studying emission behavior of inorganic elements with different reaction temperatures. The contents of different residues captured by cyclone and filter were measured. The composition and morphology of the residue ash were analyzed using ICP and EDX-SEM. The major emission mechanisms of inorganic elements at different temperatures were obtained.This work is very helpful to understand the inorganic elements transformation during biomass entrained flow gasification or combustion, as well as to find the solution of alkali problems.In order to investigate the influence of gasifying parameters in an entrained flow gasification, the effects of reaction temperature, oxygen/biomass （O/B） ratio, steam/biomass （S/B） ratio and residence time on gasification performance including gas composition, carbon conversion, H₂/CO ratio and CO/CO₂ ratio were tested in a lab-scale biomass entrained flow gasification system with rice husk, manchurian pine, korean pine and camphorwood as feed-stocks respectively. The results reveal that the reaction temperature is the most important effect in biomass entrained flow gasification. The optimum O/B ratio is in the range 0.2～0.3 at the gasification condition of 1300℃and atmospheric pressure, there is little CH₄ in the syngas at high reaction temperature and syngas composition becomes uniform while residence time exceed 1.6s. The H₂/CO ratio can increase with steam injected, and exceed 1 when S/B is more than 0.8. The steam injection affects the gasification efficiency but has little impact on the carbon conversion.A kinetic biomass gasification model combining chemical equilibrium was developed to evaluate and optimize gasifying parameters in entrained flow bed gasification. Model calculating results are in good agreement with the measurement data from previous gasification tests in entrained flow reactor. Model simulations of biomass gasification processes in entrained flow reactor were found to be reasonable. It implies the established model may be used to predict the effects of operation parameters on biomass entrained flow gasification.In order to research the torrefaction influence for biomass solid yield, energy yield, size reduction and overall efficiency during the gasification process, torrefaction experiments were carried out in a lab-scale reactor using four biomass feed-stocks. This paper also studied the size reduction and gasification characteristics of torrefied biomass experimentally. The results reveal that torrefaction can be applied with high biomass to solid energy yield with increasing the temperature and reaction time. The torrefaction temperature is more influential than the reaction time on the characteristics of torrefaction. Torrefaction can lead to a great decrease in power consumption since the destruction of fibrous structure and lead to a very substantial improvement of the grindability behavior. Torrefaction also can increase the overall efficiency of the gasification system. It therefore provides a solution to the problems concerned with entrained flow gasification related to size reduction of biomass and the subsequent pneumatic transport of the powder.更多还原