摘要
生物质能源是一种可再生能源,对生物质能的开发和利用能够缓解能源短缺的压力、减少环境污染、改善未来的能源结构。利用生物质热解转化技术,将生物质转化成高品位的液体燃料是生物质能开发利用的重要方式。本文基于国内外生物质热解液化制取生物油领域已经开展的研究工作,对生物质悬浮流化床技术进行了理论探讨,并对生物质在悬浮流化床内的运动规律、热解规律和悬浮流化床的设计理论进行了理论分析和模拟仿真。
本文首先提出了课题的研究背景,对生物质的种类和生物质能转化利用技术进行了阐述,对国内外生物质流化床热解液化制取生物油技术的研究进行了综述分析,全面掌握了该领域的研究方向和研究热点,确定了论文的研究内容和研究目标。
分析了生物质原料的颗粒特性和化学特性,建立了生物质流化冷态实验装置,对玉米芯和稻壳进行了单独流化实验,对玉米芯和稻壳与石英砂进行了混合流化实验。生物质单独流化实验表明,生物质是可以实现流态化的;生物质原料颗粒较小,流化特性没有显著区别;流化风速变化时,每一个测压点的压降变化不大,没有一定的规律性。生物质混合流化实验表明,生物质质量分率较小时,质量分率不同,流化状态和压差变化没有明显的差别,混合流化临界流化速度较小。
通过高速摄像法得到床内颗粒瞬时流动形态的图像,对图像分析得到颗粒的速度变化图。对图像的分析表明,生物质与石英砂床内混合较好,没有明显的分层现象,对于轴向混合,石英砂在床下部积聚浓度较大。床内颗粒运动速度变化剧烈,速度分布不均匀。由于生物质流化运动复杂,实验重复性差,难以测得准确的实验参数值。
由于生物质流态化运动的复杂性,通过有限的实验难以全面理解床内气固两相流动的规律,为此,建立了气固流动的基本微分方程,应用Fluent软件,采用欧拉双流体计算模型对床内气固两相运动进行模拟仿真,得到随时间变化沿床高方向固体体积分数分布云图、固体速度分布云图。模拟仿真结果表明,床内出现稠密相和气泡相两种不同的结构,固相颗粒在床层内循环运动,气泡生成、破裂周期性变化,有利于生物质的混合和分离。通过模拟仿真,较为准确地描述床内气固两相流体的运动特性,提高了对生物质流化特性的认识。
根据Waterloo大学的热解机理模型,建立了生物质热解动力学方程式,对方程式进行了求解,得到生物质质量及热解产物质量随热解温度变化的曲线。对曲线的分析表明,温度是影响生物质热解的重要参数,炭产量随温度的增加而增加,并逐渐趋向于一固定值;生物油的产量随温度的升高而增加,在800～900K时,生物油的产量达到最大值。方程求解得到的热解曲线与前人研究结果基本一致,说明建立的方程是可信的,可以利用该方程式预测热解参数温度对生物质热解产物的影响。生物质热解传热复杂,通过对热解过程的分析,建立了颗粒传热的方程式。
根据悬浮流化生物质热解设计理论和实验结果,设计了一套新型生物质悬浮流化热解反应系统。该系统燃烧生物质气化燃气为反应器供热,热解后的不可冷凝气体经过预热作为流化气体进入反应器。利用生物质燃气燃烧提供热源,可以减少其它能源的使用,就地取能,就地生产,最大限度地将地产生物质原料转化为可利用的清洁能源,降低生物质热解制油的成本。设计了生物质燃气气体燃烧器,并对反应器的能量平衡进行了计算。
论文最后对全文进行了总结。
Biomass energy is a kind of renewable energy.It is important to exploit and utilize biomass energy.Energy shortage can be relieved,fossil fuels utilization can be reduced and energy construction can be modified in the future.It is an important method of biomass energy development and research to transform biomass to high quality liquid fuels through fast pyrolysis of biomass technology.This paper based on research achievement of the biomass of the civil and foreign country about making bio-oil from fast pyrolysis of biomass.The theory is developed on the biomass suspension fluidized bed.The theory analysis and simulation can be executed.The theory involved the law of motion,the law of pyrolysis and design theory about biomass suspension fluidized bed.
In the first place,the research background of science project is putted forward.The biomass species and biomass energy transformation and utilization technology are expounded. The domestic literature review and foreign literature review are analyzed on the making bio-oil technology form biomass fluidized pyrolysis.The research direction and research hot spot are grasped roundly in this domain.
The granule and chemistry characteristic of biomass raw material are analyzed.The biomass cooling fluidization test-bed is established.Corn cob and rice hull fluidization experiments are executed separately,then,the mixture fluidization experiments are executed. Biomass fluidization experiment indicated that pure biomass fluidization is well achieved.The granule of biomass raw material is small and fluidized characteristic.The variety of pressure of every test point is not distinct.The variety pressure has not definite regularity.The mixed biomass fluidization experiment indicated that the biomass quality ratio is different and fluidization and pressure variety have not prominent difference.The mixed biomass critical velocity is small.
The instantaneous flow of images of granule in bed has been received by the method of high-speed camera.The granule speed chart have been received by analysis of the particles image.Image analysis shows that the biomass and quartz sand mixed well in the bed and no obvious phenomenon of layered.The quartz sand at lower part of the bed accumulates a larger concentration for the axial mixing.Particles in the bed have a violent change in velocity and have a uneven distribution in velocity.As the biomass flow of movement complexity,poor reproducibility experiments,it is difficult accurately measured experimental values.
As a result of the complexity of the fluidized movement of biomass,it is difficult to comprehensive understand the flow discipline of gas-solid phase through a limit test in the bed. So,the basic differential coefficient equations of gas-solid phase have been established.The movement simulation of gas-solid phase has been carried using Euler two-fluid model calculation of Fluent software.The solid speed distribution of cloud chart and solid volume fraction distribution of cloud chart have been received along the direction of the bed as the time change.The results show that two different structures of the bubble phase and dense phase can be seen inside the bed.Solid-phase particles in the bed have the circle of movement.The formation and the breakdown of the bubble have a cyclical change.These behaviors are in favor of mixture and separation of biomass.Through the simulation,the gas-solid characteristics of the movement in the bed have more accurate description and more knowledge of biomass fluidization characteristics.
According to the Waterloo university pyrolysis mechanism model,the pyrolysis kinetics equation of biomass has been established.The biomass quality along with the pyrolysis temperature change curve has been received through solving equation.The curve analysis shows that the temperature is an important parameter influencing biomass pyrolysis.The production of Char increases with temperature,and gradually moving to a fixed value.The bio-oil production with the temperature increases and in the 800-900K,bio-oil production to reach the maximum.The pyrolysis curve by solving equation with the previous results are basically the same.It is illustrated that the establishment of the equation is credible.The formula can predict the impact of the temperature with biomass pyrolysis product.The heat transfer of biomass pyrolysis is complex,through the pyrolysis process analysis,the heat transfer equation of biomass have been established.
According to the preceding design theory and testing results,the heat input of reactor are discussed,the new set of suspension biomass pyrolysis for bio-oil is developed.The method of the heat input use burning fuel gas by biomass gasification.Non condensation gas producted by pyrolysising biomass entered reactor by conducted fluidized gas.The heat of burning biomass fuel gas can reduce the use of other energy sources.Be able to take energy and produce on the spot.To maximize the conversion of local raw materials to produce material for the use of clean energy and reduce bio-oil costs by biomass pyrolysis.The heat input gas burner by burning fuel gas is designed,and energy balance of the reactor were calculated.
In the end,the full-text of the final paper is summarized.
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