【作者】 高宁博；

【导师】 李爱民；

【作者基本信息】 大连理工大学 ， 热能工程， 2009， 博士

【摘要】 生物质气化制氢技术是一项富有前景的制氢技术,目前还处于探索阶段。虽然很多学者对生物质制氢技术进行了较为深入的研究,但由于气化手段的差异,以及气化因素的影响所取得的效果也各不相同。这些研究大多集中于用低温气化介质进行气化,气化产气中H₂含量较低,气体中焦油含量较高。针对这个问题,开展了生物质高温水蒸气气化多孔陶瓷气化重整制氢的研究。本文首先进行了高温蒸气发生器的研制并进行了高温过热蒸气和高温空气的制备实验,对高温蒸气发生器进行了热效分析;对高温蒸气发生器的运行过程进行了数值模拟。在非等温与等温加热条件下研究了大物料量物料的气化动力学特性。研究了序批式与连续式进料模式下的生物质高温气化、多孔陶瓷重整制氢实验研究,最后建立了生物质高温热解气化耦合模型,对气化过程进行了数值模拟。主要研究内容如下:（1）介绍了自制蓄热式高温带压蒸气发生器的工作原理及运行过程,对炉体结构进行了设计计算,设计并计算了保温层的厚度,根据运行特性,相应地提出了运行控制方案和参数检测方式。在对高温过热蒸气发生器进行调试运行以后,开展了高温水蒸气、高温空气制备的热态实验研究。开展了不同换向周期的高温水蒸气、高温空气制备实验,考察了不同换向周期以及一个换向周期内的高温介质的温度变化情况,并对不同状况下的尾气余热排放进行了探讨。研究了不同工况条件下的温度效率和热回收效率情况。以水蒸气为介质时60s的换向周期条件下热回收效率最大,而以空气为介质时30s为最佳换向周期。对系统热平衡及热效率进行了计算,通过对系统输入能量和系统输出能量的分析,计算了系统热效率,系统热效率可达73.56%,热收入与热支出误差为5.03%,测定结果正确。（2）通过数值模拟的方法研究了高温过热蒸气发生器的运行特性,考察了燃烧半周期和水蒸气余热半周期的炉体换热情况。对数值模型的有效性进行了验证,通过开展数值实验主要研究了不同换向周期,燃气进口速度,空气过量系数以及不同介质（水蒸气、空气）的换热特性。数值实验结果表明:换向周期越长,尾气带走的热量也就越多。换向周期过小,过大都不是最佳的选择。根据计算,60s的换向周期为最佳时间;燃气进口速度越大,释放出的热量就越多,但进口速度过大将导致燃烧不充分,不利于发生器效率的提高;当量比为1.5时,在陶瓷体的0.2-0.35m这一部分,陶瓷体温度处于较高水平,其后温度较低。在蓄热室中心线上的温度分布上,以空气为介质的温度分布低于以水蒸气为介质的温度分布,水蒸气和空气的预热曲线受二者物理性质影响较大。（3）通过热重差热分析仪在氮气和空气气氛条件下,考察了不同工况条件（升温速率、粒径大小、载气流速等）的生物质微量物料热解和燃烧特性;在自行设计的大物料热重分析装置上,开展了热解、燃烧和水蒸气气化的热重实验和大物料量物料水蒸气气化的等温热重实验,根据这些实验获得的TG和DTG曲线的变化趋势,分析微量物料与大物料量物料两种不同模式的热失重行为,并在此基础上建立了生物质表观动力学模型,进行了生物质热解、燃烧以及气化的动力学参数求解。对相同工况条件下的微量物料与大物料量物料的热失重过程进行了比较分析。实验结果表明:大物料量热重过程和微量物料热失重过程的动力学参数差异明显。（4）在自行设计的固定床气化炉实验台上开展了序批式进料模式的生物质高温气化实验研究,重点考察了反应温度、水蒸气流率以及物料粒径等不同工况条件对生物质气化产气特性的影响,实验结果表明不同温度条件下,每kg生物质的氢产率从800℃的21.91g H₂增加到950℃的71.63g H₂。不同水蒸气流率下CO平均浓度随着蒸气流率的增加略有增大,气体平均热值在11.87-12.04kJ/m³范围变化,水蒸气流率为20.2g/min时的氢气产率最大。随着生物质给料粒径的减小,气体产率和气化效率均减小。（5）研究了连续进料模式下的生物质高温水蒸气、高温空气气化重整实验,以多孔陶瓷为重整介质,分别研究了气化温度、水蒸气与物料之比（S/B）、当量率（ER）、重整室温度以及有无多孔陶瓷重整对气化产气的影响,研究了多孔陶瓷重整的焦油去除特性。实验结果表明,高温反应条件有利于气化反应的进行及H₂的生成。以水蒸气与氧气联合气化中,最优当量率为0.05。随着S/B的增大,H₂浓度表现出增大的趋势,2.05是比较理想的S/B值。在重整温度为800℃时H₂浓度最高。多孔陶瓷重整对焦油具有明显的去除作用,焦油的TOC的转化率为29.93-50.31%。以空气为气化剂时,随着反应温度的增加,气化产气中CO浓度增大并占有较大比例,而产氢率及气体LHV随温度的增大而增大;随着ER值的增大,CO浓度逐渐减小,而CO₂浓度则逐渐增大,气体热值显著降低。6)生物质气化过程中,将热解区和还原区联合起来模拟气化过程。而以前的数值模拟大多为独立考察这两个过程,并进行数值模拟。本模型在时间和空间上整体模拟了气化过程的温度场和气化产气浓度场分布。主要考察了两种不同加热条件下的产气浓度,一是热解区升温条件为25K/min,另一种是热解区温度恒定为1400K。在两种加热模式中,还原区温度场和气体浓度场存在明显差异。更多还原

【Abstract】 Biomass gasification process is one of promising ways of producing hydrogen-rich gas, and it is still in the primary exploring stage.Although many researchers had performed experimental study in hydrogen production by biomass gasification and the reforming of product gas and tars,these gasification studies were conducted on low temperature gasification agents,low concentration of H₂ and high content of tars in producing gas.Thus,a new treatment process which integrated the high temperature steam generation and biomass gasification process was presented for hydrogen-rich production.In this paper,a high temperature steam generator was invented for high temperature steam and air production,and the thermal efficiency of high temperature steam generator was analyzed.Numerical simulation on the process of high temperature steam generator was carried out.The kinetic characteristics of isothermal and non-isothermal thermo-gravimetric analysis were studied on different operation conditions.The type of sequence batch and continuous batch biomass high temperature gasification were researched on fixed-bed gasifier combined with a porous ceramic reformer.Finally,a pyrolysis and reduction zone models was established to simulate the global process of biomass gasification.The following works are carried out main experimental results and conclusions are as follows in this dissertation:（1） This paper introduced the operational principle of the high temperature pressured steam generator.The stove structure and insulating layer were designed and computed.Based on the features and control requirements,the running and controlling programme was proposed.The hot experiments of high temperature steam and air were performed after finishing the installation of high temperature steam generator.And then,the variety of temperature for high temperature agents and exhaust gas in different switching periods and one switching period were studied.The efficiency of temperature and heat recycle was also investigated.It was found that the steam efficiency of heat recycle reach maximum value in 60s switching period,however,that of air in the optimum value is 30s.The heat balance and efficiency of system were calculated through the analysis of generator energy input and output.It is concluded that the efficiency of whole system obtained 73.56%and the error of heat balance is 5.03%. （2） The heat exchange of half cycle of combustion and steam preheating were investigated with numerical simulation method.The validity of model was verified through compared the values of experiment and calculation.Several operation parameters such as switching period,fuel inlet velocity,equivalent ratio and preheat agents were studied with numerical simulation.The results show that more heat was carried away by exhaust gas with longer switching period.It is not the optimum option to choose too long and too short switching period for high temperature steam generation,and 60s is the fine value by calculation for system.The release heat increases with the increasing fuel inlet velocity,and it is unfavorable for too fast inlet velocity due to incomplete combustion.The porous ceramic is in high temperature state in the first part 0.2-0.35m as equivalent ratio is 1.5.For the centre line of regenerative chamber,the temperature distribution of air preheating was below steam one,the curves of preheating temperature was affected greatly by their physical properties.（3） Thermogravimetry of biomass pyrolysis,gasification and combustion were investigated in thermo-balance and a small batch laboratory-scale externally heated fixed-bed. Different operation conditions（heating rate,particle sizes and flow rates of carrier gas） were investigated.The kinetic characteristics of isothermal thermo-gravimetric analysis were studied on different operation conditions.Comparison the two different modes of weight loss from TG and DTG,it was found that the behavior of thermogravimetric process of small and large amount samples are different obviously.（4） The type of sequence batch biomass high steam temperature gasification was studied on fixed-bed gasifier combined with a porous ceramic reformer.Reaction temperature,steam flow rate and particle sizes as different effect factors were studied on producer gas composition.The experimental results show that H₂ production increases from 21.91g/kg biomass to 71.63g/kg biomass as reaction temperature increases from 800 to 950℃.With increase of steam flow rate,the concentration of carbon monoxide increase slightly and low heating value（LHV） changed between 11.87 and 12.04kJ/m³,H₂ production reach maximum value as steam flow rate is 20.2g/min.With particle sizes of biomass decreased,producer gas production declined（5） Hydrogen-rich gas produced from biomass employed an updraft gasifier with a continuous biomass feeder were studied in this paper.A porous ceramic reformer was combined with the gasifier for producer gas reforming.The effects of gasifier temperature, equivalence ratio（ER）,steam to biomass ratio（S/B）,reforming temperature and the effect of porous ceramic reforming on the gas characteristic parameters（composition,density,yield, low heating value,and residence time,etc.） were investigated.The results show that a higher temperature favors the hydrogen production.With the increasing gasifier temperature varying from 800℃to 950℃,the hydrogen yield increased from 74.84 to 135.4g H₂/kg biomass, irrespectively.The low heating values vary first increased and then decreased with the increased ER from 0 to 0.3.A steam/biomass ratio of 2.05 was found as the optimum in the all steam gasification runs.H₂ production reaches maximum at the reforming temperature is 800^C.The effect of porous ceramic reforming showed the water soluble tar produced in the porous ceramic reforming,the conversion ratio of total organic carbon（TOC） contents show is between 29.93%and 50.31%,and the hydrogen concentration obviously higher than that of without porous ceramic reforming.With reaction temperature increases,CO concentration accounts for a large proportion in producer gas as air is agents,H₂ production and LHV increases with temperature rises.However,CO concentration decreases and CO₂ increase with ER increase,as a result,LHV of producer gas declines.（6） The behavior of a globe fixed bed biomass gasification reactor was simulated with a self-programming software.Pyrolysis zone and reduction zone models are combined to simulate the global process of biomass gasification.The volatile and gases broken up from pyrolysis zone were assumed to crack into an equivalent amount of CO,CH₄ and H₂O.It is considered that the volatile and gas leave pyrolysis zone instantaneously and then entering reduction zone as initial gas concentrations.The numerical method applied is Runge-Kutta forth order for the solution of pyrolysis zone model and finite difference for the reduction zone model to solve numerically the coupled ordinary differential equations.Simulations are carried out for the varying pyrolysis temperature with heating rate of 25K/min and constant temperature 1400K as the initial reduction zone temperature at the same time.The simulation results for temperature and concentration of gaseous species are in good agreement with published experimental data.更多还原