3种农林生物质的热解及动力学研究

以桉树叶、甘蔗叶和桑树杆3种农林生物质为原料,利用热重分析仪进行热分析研究。通过对TG和DTA曲线的对比,探讨了生物质的热解过程;采用Coats-Redfern积分法进行动力学分析,确定了反应级数,得到了3种原料在不同温度下的活化能。结果表明:生物质的热解可分为干燥、预热、热分解氧化和碳化还原4个阶段,其中在300～400℃时热解反应最为剧烈;利用n=2,3级动力学模型,均能较好地表述生物质热解过程;3种生物质低温段的热解活化能要高于高温段的活化能,就整个热解过程看,E甘蔗叶E桑树杆E桉树叶。     

秸秆类生物质热解特性及其动力学研究

该文对秸秆类生物质的热解行为进行了热重分析（TG）和差分热重分析（DTG）研究。加热速率分别为10K／min、20K／min和30K/min，加热终温为1173K；采用高纯氮气做保护气；样品粒径为250μm－1000μm。通过对TG、DTG曲线的分析，深入研究了加热速度、温度、加热时间等对热解过程的影响，建立了北方典型的秸秆类生物质的反应动力学方程，得出了该类物质热解反应动力学参数、表观活化能和频率因子，并提出了相应的热解机理。     

生物质加压热重分析研究

对两种生物质木屑和松针进行了不同压力和升温速率下的热重分析试验,通过生物质热重失重率（TG）和失重速率（DTG）曲线,获得了相关热解特性参数,提出了生物质的挥发分综合释放特性指数D．并通过热分析数学方法求取了生物质热解动力学参数．试验结果表明,氮气气氛中,木屑与松针常压和增压下主要热解阶段可认为两段一级反应;热解压力的提高,将延迟生物质挥发分初析温度和DTG峰值温度,降低最大析出率和DTG峰值,生物质的挥发分综合释放特性指数D也减小,增加了生物质挥发分的析出难度,并改变了热解反应活化能和频率因子．同一压力下,提高热解升温速率,生物质综合特性指数D将增加．     

北方地区典型生物质的热重分析及动力学研究

采用热重分析法对北方地区4种典型生物质玉米秆、棉花杆、杨树枝和苹果树枝做了热解与动力学特性的研究,实验采用了3种升温速率:20℃/min、40,℃/min和60,℃/min,加热终止温度900,℃.研究发现,生物质热解大致可以分为4个阶段,即失水阶段、过渡阶段、快速热解阶段、炭化阶段;玉米杆热解DTG曲线存在肩状峰现象;升温速率增加,生物质热解4个阶段的起始温度以及终止温度向高温侧移动,相对应的峰值温度升高,主要热解反应阶段温度区间变宽.建立了一级反应动力学模型,结果发现,随着升温速率的增加,生物质的活化能降低.     

废弃柞木段热解特性及其反应动力学研究

以废弃柞木段为研究对象,进行了不同升温速率(5,15,25℃/min)下的热解失重实验以及TG和DTG曲线分析,采用分布活化能模型(DAEM)和一级反应模型研究其反应动力学特性。结果表明,脱水干燥的废弃柞木段热解过程主要分为过渡、挥发分析出和碳化3个阶段,随着升温速率的提高,DTG曲线有向高温侧移动的趋势,不同升温速率下的最大热解速率所对应的温度在360~380℃;采用DAEM得到的主热解阶段活化能为210~260 k J/mol,一级反应模型得到的主热解阶段活化能约为62 k J/mol,两种模型都能够较好地描述废弃柞木段主热解阶段,而DAEM模型更为全面。     

草类生物质热解特性及动力学的对比研究

我国长江中下游地区有大面积分布的芒属、芦苇、狼尾草,研究很少,应用少.为草类生物质能的开发与利用提供又一途径.对芒属、芦苇、狼尾草进行常压热重分析,同时与常见的稻草相比较,通过生物质热解失重率(TG)和失重速率(DTG)曲线,获得相关热解特性参数,采用生物质挥发分综合释放指数(D),并通过热分析数学方法求取生物质热解动力学参数.试验结果表明:草类生物质热解过程可以分为4个阶段,在563 K附近存在一个肩峰,失重都集中在460 K～673 K.挥发分综合释放指数则芒属>稻草>狼尾草>芦苇,活化能则芒属>稻草>狼尾草>芦苇,固体剩余物则芒属>狼尾草>稻草>芦苇,所以总体上看芒属的热解稳定性相对较差,芦苇的热解稳定性较好,同时采用二级反应动力学模型由Coats-Redfern法求的相应得活化能和频率因子.也为今后更好、更合理高效的利用这些草类提供实验数.     

杨木屑热解过程及动力学研究

运用热重分析法研究了氮气下杨木屑的热解过程.在不同的升温速度(5、15、30℃/min)下,对热解TG、DTG、DSC曲线分析,得出杨木屑热解分干燥、预热解、热解和煅烧4个阶段,并且热解随着升温速度的提高出现了热滞后现象.最后通过比较1、1.5、2、3级反应动力学模型,确定1级反应为杨木屑热解的动力学模型,并求出了热解反应的活化能和频率因子.     

生物质废弃物热解特性的热重分析研究

采用热重分析方法,以氮气为载气,在室温和973K之间,以三种升温速率(10,20,30K/min)对三种生物质废弃物试样(稻秆、稻壳和白松木屑)进行热解实验。确定了起始分解温度D。采用了生物质整体热解分区、生物质化学组分热解分区、活化热解与消极热解分区等三种热解分区方法进行分析。由于三种试样化学成分的差别导致热解特性的差异。得到了三种试样热解动力学参数。     

核桃壳热解特性及几种动力学模型结果比较

利用热重分析在不同升温速率和氮气气氛下对核桃壳的热失重行为进行研究.根据热重实验数据,采用4种热分析动力学方法(Coats-Redfern法、Doyle法、Ozawa法和DAEM模型),计算核桃壳热解反应活化能E、反应级数n及频率因子A,并进行比较.结果表明:采用不同的动力学分析处理方法,得出的热解动力学参数不同.利用Coats-Redfem法,核桃壳在热解主要阶段(失重10％ ～95％)可由一段一级反应过程描述,升温速率20K/min时活化能为55.37k J/mol.Doyle法和DAEM模型得到的结果较为接近,Ozawa法求得的活化能值最高.核桃壳热解包含分子键能断裂的一系列复杂、连续反应过程,并获得核桃壳的热解反应活化能随失重率的变化曲线.     

生物质热解的TGA-FTIR分析

基于TGA-FTIR联用技术,在线分析研究稻壳、稻秆及麦秆3种典型生物质在不同升温速率下的热解特性.分析生物质种类及升温速率对生物质的热解动力学参数及热解产物的影响.研究表明:由于生物质组成不同,其热失重特性也不同,生物质热解反应的活化能较低,为40～60 kJ·mol-1;红外分析表明试验用生物质热解过程中产物的析出规律相似,热解初始阶段先析出游离水,随后发生解聚和脱水反应,生成各种烃类、醇类、醛类和酸类等物质.随后,这些大分子物质又二次降解为一氧化碳为主的气体产物.     

下降管式生物质热解液化装置的计算分析

综合考虑了下降管式生物质热解液化装置中的流动、传热和热解反应，在假设简化的基础上对在该装置中的热解过程进行了计算，计算结果和实验结果基本一致。计算表明：在合理操作条件范围内，载体初始温度、粒径、流量对热解结果的影响显著；采用粒径为2．5mm载体时，载体初始温度为773K左右，载体和生物质质量比为20左右时液体产物得率最高。这些结果为该类设备的设计和操作参数的确定提供了参考。     

Numerical simulation on biomass-pyrolysis and thermal cracking of condensable volatile component

We studied the physical and chemical properties of the condensable volatiles of biomass pyrolysis products. We redefine the liquid product and divide the condensable volatiles into two categories, biomass oil and tar, the latter of which comes from the secondary pyrolysis or cracking reaction of the former. We further establish a kinetic model of biomass pyrolysis and secondary cracking. The chemical reaction kinetics equation and heat transfer equation are coupled to simulate the biomass pyrolysis process. For biomass solid particles, the model not only considers the initial reaction of biomass and secondary cleavage reaction of condensable gas, but also introduces a reaction mode in which biomass oil is converted into tar. When the pyrolysis temperature is below 500 °C, the pyrolysis products are essentially biomass oil. However, when the pyrolysis temperature exceeds 500 °C, the biomass oil gradually converts into tar. The model also considers characteristics of the reaction medium (porosity, intrinsic permeability, thermal conductivity) and the unsteady gas phase process based on Darcy's law of velocity and pressure, heat convection, diffusion, and radiation transfer. We analyze the relationships among the internal temperature of the particles, particle size and position, mass fraction of the reactants and products, the gas mixture, the production share of tar and biomass oil, and the relationship between gas pressure and time. The results show that the effects of the secondary cracking reaction and internal convective flow in the biomass pyrolysis process are coupled because the flow field in the porous medium determines the volatile residence time and thus species that affect the secondary cracking reaction. The rate of volatile formation in the initial and secondary cracking reactions affects the pressure gradient and gas diffusion. Additionally, the endothermic effect influences the temperature field of the pyrolysis reaction but has no apparent effect on small particles whose chemical reaction is the control mechanism. For large particles, heat transfer inside the particles is the diffusion control mechanism and the chemical reaction on the particle surface is the speed control mechanism. Two peaks are observed in the pyrolysis gas mass proportion curve, which result from the consumption of biomass oil and tar as they flow toward hot surfaces. The first peak is the decomposition of biomass oil into non-condensable volatile matter and tar, and the second peak is the further cracking of tar into gas and coke at high temperature.     

生物质半焦CO2气化反应动力学研究

采用热天平研究生物质半焦CO2气化反应动力学特性。考察半焦粒径、热解制焦温度以及热解制焦气氛对气化反应碳转化率的影响。采用随机孔模型、未反应芯缩核模型和混合模型对生物质半焦气化反应速率随碳转化率变化的趋势进行拟合,并求出半焦气化的动力学参数,结果表明随机孔模型的拟合效果最好。     

Kinetic modeling and optimization of parameters for biomass pyrolysis: A comparison of different lignocellulosic biomass

A primitive element for the development of sustainable pyrolysis processes is the study of thermal degradation kinetics of lignocellulosic waste materials for optimal energy conversion. The study presented here was conducted to predict and compare the optimal kinetic parameters for pyrolysis of various lignocellulosic biomass such as wood sawdust, bagasse, rice husk, etc., under both isothermal and non-isothermal conditions. The pyrolysis was simulated over the temperature range of 500–2400 K for isothermal process and for heating rate range of 25–165 K/s under non-isothermal conditions to assess the maximum pyrolysis rate of virgin biomass in both cases. Results revealed that by increasing the temperature, the pyrolysis rate was enhanced. However, after a certain higher temperature, the pyrolysis rate was diminished which could be due to the destruction of the active sites of char. Conversely, a decrease in the optimum pyrolysis rate was noted with increasing reaction order of the virgin biomass. Although each lignocellulosic material attained its maximum pyrolysis rate at the optimum conditions of 1071 K and 31 K/s for isothermal and non-isothermal conditions, respectively, but under these conditions, only wood sawdust exhibited complete thermal utilization and achieved final concentrations of 0.000154 and 0.001238 under non-isothermal and isothermal conditions, respectively.     

Co-pyrolysis of textile dyeing sludge and four typical lignocellulosic biomasses: Thermal conversion characteristics,synergetic effects and reaction kinetics

In this work, the thermal conversion characteristics, interactive effects and reaction kinetics during co-pyrolysis of textile dyeing sludge (TDS) and four typical lignocellulosic biomasses (peanut vine – PV, wheat straw – WS, cotton stalks – CS and sawdust – SD) were comparatively investigated based on thermogravimetric analysis. The results indicated that the more contents of cellulose and hemicelluloses in the raw materials, the larger pyrolysis characteristic index D was. Meanwhile, the type of biomass played an important role on the interactive effect during co-pyrolysis process, which could be inhibitive and accelerative. Moreover, CS pyrolysis with the simulation ash showed that the metallic oxide in TDS ash would react with the residue carbon to increase the mass loss at the final stage. According to kinetic analysis result, the reaction mechanism of TDS, biomasses and their blends can be well predicted by the reaction order model and the diffusion models, i.e. 0, 3rd and 1-D model. The kinetic analysis also suggests TDS co-pyrolysis with biomass could reduce the theoretical activation energy for thermochemical conversion. About 50% CS content was turned out to be the optimal additive for the co-pyrolysis.     

油棕废弃物及生物质三组分的热解动力学研究

主要利用热重分析仪(TG)对油棕废弃物和生物质的三组分(半纤维素,纤维素和木质素)的热解特性进行了系统研究,对比分析了热解特性,计算了其热解动力学参数,并研究了升温速率对生物质热解特性的影响。研究发现半纤维素和纤维素易于热降解而木质素难于热解;油棕废弃物的热解可以化分为:干燥、半纤维素热解、纤维素热解和木质素热解4个阶段;生物质的热解反应主要是一级反应,油棕废弃物的活化能很低,约为60kJ/kg;升温速率对生物质影响很大,随升温速率加快,生物质热解温度升高,热解速率降低。     

Kinetics,thermodynamics and synergistic effects analyses of petroleum coke and biomass wastes during H2O co-gasification

In this study, the H₂O co-gasification of petroleum coke (PC) with low (sulfur and V₂O₅ contents) and different five kinds of biomass wastes were conducted using a thermogravimetric analyzer (TGA). The biomass used were the agricultural wastes (rice husk (RH), rice stalk (RS), and cotton straw (CS)) and by-product wastes (sawdust (SD) and sugar cane bagasse (SCB)). Their reactivities, kinetics and thermodynamics parameters were investigated and compared in detail as well as a synergistic effect during co-gasification of the blends. The kinetics and thermodynamics parameters were estimated by using the homogeneous model (HM) or the first-order chemical reaction (O1) and shrinking core models (SCM) or Phase boundary controlled reactions (R2 and R3). It was found that the biomass wastes was significantly improved the blends gasification reactivity. The obvious significant synergistic effect was observed in the char gasification stage of the blends compared with the pyrolysis stage. Compared to other models the phase boundary controlled reaction (R2) was found to be the best model to predict the experimental data of the co-gasification process. For both reaction stages of single fuels, SD showed the lowest values of activation energy and thermodynamics parameters. The blends of PC: SD and PC: CS provided the lowest activation energy and thermodynamics parameters for the pyrolysis stage and the char gasification stage, respectively. The co-gasification of PC and biomass wastes are a promising technique for the efficient utilization of PC and biomass wastes.     

生物质玉米芯热解动力学实验研究

以玉米芯为对象,利用热重-质谱联用技术,以高纯氩气为载气对其进行了详细的热重分析研究。通过对10℃/min和30℃/min升温速率及其不同温度下的失重曲线分析,发现玉米芯的主要失重温度区间为200~400℃,峰值温度为328~345℃。随着升温速率的提高,玉米芯热解的初始温度升高,热解向高温侧移动。同时通过质谱分析获得了温度和升温速率对热解气化产物的影响规律。在此基础上建立了热解动力学模型,并根据实验数据对模型进行了求解,结果表明玉米芯热解在低温段属一级反应而在高温段属三级反应。     

沥滤对玉米残余物结构和反应性能影响

为研究沥滤预处理对玉米残余物(玉米秸秆和玉米芯)结构、反应性能和动力学的影响,通过热重分析仪考察了生物质的反应特性,包括热解反应和气化反应,并对生物质的理化结构进行分析,包括晶格度、主要官能团和碳晶结构.结果表明,在N 2和CO 2气氛中,生物质热解反应特性类似,主要由其组成和反应温度决定.沥滤可除去生物质中的部分无机...     

Catalytic copyrolysis of metal impregnated biomass and plastic with Ni-based HZSM-5 catalyst: Synergistic effects,kinetics and product distribution

The present work aims to investigate the thermal behavior, kinetics, thermodynamics, and product distribution during copyrolysis of transition metal salt (Ni, Co, Zn, Cu, and Fe)-added biomass and model compounds with low density polyethylene(LDPE) over a Ni-based HZSM-5 catalyst by TGA and fixed bed reactor. The interactions and reaction mechanisms during copyrolysis were evaluated. The influence of Ni-impregnated biomass (C-M) and Ni-modified HZSM-5 (Ni/HZ) on the formation of pyrolysis bio-oil from biomass and model compounds and its subsequent effect on catalytic pyrolysis vapor upgrading was discussed. The results indicated that the presence of transition metal decreased the thermal degradation temperature and thermodynamics parameters; maximum decomposition rate, and reaction complexity. Ni/HZ catalyst could further decrease the activation energy, accelerate the reaction rate and change reaction process, and the modified samples/LDPE under copyrolysis with HZSM-5 catalyst presented a more significant effect than Ni/HZ catalyst. Subsequently, the Ea of pine, cellulose and lignin changed from 24.11, 18.29, and 28.68 kJ/mol (CP@Ni/HZ) to 56.04, 69.84, and 16.21 kJ/mol (CP-Ni@HZSM-5), respectively. In addition, Ni could inhibit the depolymerization of cellulose and promoted the formation of char, coke, and lignin derived phenolics. And Ni-impregnated biomass reduced the formation of desired aromatic hydrocarbons, but result in increasing of the char and non-condensable gases. But Ni/HZ catalysts promote the conversion of biomass to target products.