两种玉米秸秆热解过程动力学模型的比较

介绍了生物质热解的简单一级动力学模型和分布活化能模型,并利用这两种模型分别对玉米秸秆在15、25、30K/min升温速率下的热重分析数据进行了研究。利用简单一级动力学模型计算的活化能数值在7～54kJ/mol之间,指前因子在2.8×10~4～3.3×10~4min~(-1)之间;利用分布式活化能模型计算的活化能数值在65～80kJ/mol之间,指前因子在1.9×10~5～3.0×10~5min~(-1)之间。同时,分析了产生上述差异的原因,并通过研究分布活化能模型的计算结果得出分布活化能模型更能反映生物质热解动力学过程的结论。     

煤与杜氏盐藻共热解过程分析及动力学研究

在氮气气氛中,利用热重分析对煤与杜氏盐藻及其混合物的热解特性进行了研究,考察了煤与杜氏盐藻不同掺混比例对热解过程的影响,并研究了共热解动力学.结果表明,煤与杜氏盐藻共热解特性并不是两者单独热解特性的简单叠加,在200～500℃范围内两者之间存在明显的协同效应,其相对值高达28％.煤和杜氏盐藻单独热解均可分3个阶段,由于固定碳和灰分含量高,煤在相同热解阶段的失重率较杜氏盐藻低.动力学分析结果表明,以峰值温度为分界点,采用2个连续一级反应模型与实验数据拟合效果良好,计算得到共热解过程中的活化能和指前因子分别为16.06～28.20 kJ/mol和0.42～16.82 min-1;活化能与指前因子的对数之间具有良好线性关系.     

木质材料热解动力学及典型气体产物分析

采用热重分析法在不同升温速度(10～90K/min)和不同粒径(40～60目,100目)对两种家具加工剩余物(椴木和松木)进行热解实验研究,并通过质谱仪在线检测热解产生的部分气体产物.实验结果表明:木质材料的热解过程分为失水干燥、缓慢热解、快速热解及炭化4个阶段.进行热解动力学分析,得到相关的表观活化能及指前因子.快速热解阶段可由1.5级反应过程描述,根据1.5级反应由Coats-Redfern法计算椴木和松木的平均活化能E分别为77.3kJ/mol和67.8kJ/mol.利用质谱仪在线监测了CH4、H2O、CO2、H2等气体产物,其质谱曲线与对应的热重曲线相符合,也验证了各反应阶段的假设.     

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．     

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/塑料共热解热重分析及动力学研究

考察了生物质、塑料(高密度聚乙烯、低密度聚乙烯和聚丙烯)及其混合物的热重行为。结果表明,生物质的分解温度比塑料低,3种塑料HDPE、LDPE、PP有相似的热解失重行为,是由于分子结构的相拟性。生物质的失重率低是由于灰分和固定炭含量高。生物质和塑料存在重叠的热解温区,有利于塑料向生物质供氢。生物质/塑料共热解时在高温区存在明显的协同效应。动力学分析表明,采用1或3个连续一级反应模型可很好地拟合实验数据,活化能和指前因子分别为107～217 kJ/mol和2.99×10~8～7.51×10~(34),取决于材料本身的特性。     

生物质燃烧的气体产物及动力学分析

采用热重分析法对3种生物质样品进行燃烧特性试验,并利用质谱仪在线监测了燃烧排放的部分气体成分.对生物质样品进行燃烧反应动力学分析,得到相关的表观活化能及指前因子.研究结果表明:燃烧过程可以分为3个温度阶段:①吸附水的析出及铵盐的热分解(室温～150℃);②半纤维素、纤维素及部分木质素的热解(150～350℃);③木质素的热解及焦炭的燃烧(350～600℃).利用质谱仪在线监测了CH4,NH3,H2O,CO2,NOx等气体产物,其质谱曲线与对应的热重曲线相符合,也验证了各反应阶段的假设.     

生物质闪速热解挥发特性的研究

以等离子体为热源，利用层流炉热解试验台对稻壳等生物质进行了闪速热解挥发试验，得到了不同加热温度和挥发时间下的热解挥发百分比数据；根据试验数据，计算出了Arrhenius一级反应动力学模型的表观频率因子和表观活化能参数的值。研究发现，在闪速加热条件下，同一种生物质的热解动力学参数不随工况发生变化；不同生物质的表观频率因子和表观活化能的值不同；试验数据与模型具有很好的吻合性，该模型可以作为生物质闪速热解的计算模型之一。     

植物化工醇废液热解动力学研究

为了研究植物化工醇废液的热解反应机理,将废液置于氮气气氛下进行加热反应。利用热重分析仪考察了不同升温速率对废液热解反应影响,得到了TG/DTG曲线。实验结果表明废液热解反应有五个波动峰,以及蒸发、热解和无机盐反应三个过程,利用Coats-Redfern法计算了动力学参数,热解过程活化能和频率因子均最小,无机盐反应过程最大,活化能大小与升温速率和反应阶段有关。改变升温速率并不会明显改变热解反应特性,热解过程主要是挥发分析出,失重比和失重速率均最大。     

分布活化能模型在污泥热解特性研究中的应用

研究和推导了城市污泥热解的活化能分布模型(DAEM)．采用直接搜索法对模型进行求解,确定其热解动力学参数,并用实验数据对DAEM模型的可靠性进行验证．结果表明,DAEM模型能较好地描述污泥的热解过程,可靠性好．此外,还分析了积分上限对DAEM模型求解精度的影响以及指前因子K0、平均活化能E0和活化能分布的标准偏差δE对热解过程的影响．     

Lignocellulosic biomass pyrolysis mechanism: A state-of-the-art review

The past decades have seen increasing interest in developing pyrolysis pathways to produce biofuels and bio-based chemicals from lignocellulosic biomass. Pyrolysis is a key stage in other thermochemical conversion processes, such as combustion and gasification. Understanding the reaction mechanisms of biomass pyrolysis will facilitate the process optimization and reactor design of commercial-scale biorefineries. However, the multiscale complexity of the biomass structures and reactions involved in pyrolysis make it challenging to elucidate the mechanism. This article provides a broad review of the state-of-art biomass pyrolysis research. Considering the complexity of the biomass structure, the pyrolysis characteristics of its three major individual components (cellulose, hemicellulose and lignin) are discussed in detail. Recently developed experimental technologies, such as Py-GC–MS/FID, TG-MS/TG-FTIR, in situ spectroscopy, 2D-PCIS, isotopic labeling method, in situ EPR and PIMS have been employed for biomass pyrolysis research, including online monitoring of the evolution of key intermediate products and the qualitative and quantitative measurement of the pyrolysis products. Based on experimental results, many macroscopic kinetic modeling methods with comprehensive mechanism schemes, such as the distributed activation energy model (DAEM), isoconversional method, detailed lumped kinetic model, kinetic Monte Carlo model, have been developed to simulate the mass loss behavior during biomass pyrolysis and to predict the resulting product distribution. Combined with molecular simulations of the elemental reaction routes, an in-depth understanding of the biomass pyrolysis mechanism may be obtained. Aiming to further improve the quality of pyrolysis products, the effects of various catalytic methods and feedstock pretreatment technologies on the pyrolysis behavior are also reviewed. At last, a brief conclusion for the challenge and perspectives of biomass pyrolysis is provided.     

常压及加压条件下生物质热解特性的热重研究

在常压热重分析仪和自行研制的加压热重分析仪上进行了生物质热解特性的系统研究 ,得到了升温速率、压力等因素对生物质热解过程的影响规律。对不同试验条件下的反应动力学参数进行了求解和比较 ,并作了机理分析。试验表明 :与常压热解相比 ,在加压条件下 ,生物质的反应速率有明显提高 ;随着升温速率的增加 ,热解反应趋于更加激烈。上述研究结果为生物质的合理利用提供了一定的理论基础。     

Pyrolysis rates of biomass materials

A method is proposed by which pyrolysis rates of biomass materials can be predicted from the species compositions in terms of the basic constituents (cellulose, hemicellulose and lignin) and their individual kinetic parameters. The activation energies, frequency factors and reaction orders for cellulose, hemicellulose and lignin have been determined in a conventional manner. The measured rates of pyrolysis of different biomass species (hazelnut, wood, olive husk and rice husk) compare well with literature data.     

农林生物质废弃物的热重实验研究

利用TGA对甘蔗渣、花生壳、谷壳、松木屑等4种农林废弃物进行热重实验研究,并建立了生物质热解反应的表观动力学模型.实验研究发现:甘蔗渣的DTG曲线不同于其他3种生物质的DTG曲线,它呈现出两个明显的双峰形状.对于甘蔗渣,由于其DTG曲线的双失重峰,其动力学模型在低温段的反应级数为2.5,高温段则为1.5;其他3种生物质的热解动力学模型的反应级数为2.5.     

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...     

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。     

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.     

Kinetic and experimental characterizations of biomass pyrolysis in granulated blast furnace slag

With the objective of abating the energy crisis and greenhouse gas emissions, biomass pyrolysis to recover waste heat from granulated blast furnace (BF) slag was investigated via thermogravimetric and continuous fixed-bed experiments. The results showed that the mass conversion of biomass pyrolysis increased with the increasing heating rate. At the same time, a higher gas yield and lower heating value (LHV) and concentrations of H₂ and CO were obtained with the increasing temperature. Granulated BF slag can promote the pyrolysis and reforming of biomass tar, increasing the gas yield and LHV and H₂ concentration. Thus, granulated BF slag not only provided heat for the pyrolysis reaction but also promoted the pyrolysis and reforming of biomass tar, which might block and corrode pipes in practical production. The shrinking core model (R2) selected using a two-step calculation method interpreted the biomass pyrolysis in granulated BF slag. The reaction activation energy ranged from 60.743 kJ/mol to 65.963 kJ/mol as the heating rate decreased from 40 K/min to 10 K/min.     

Co-pyrolysis and co-gasification of biomass and polyethylene: Thermal behaviors,volatile products and characteristics of their residues

Co-pyrolysis and co-gasification of biomass and plastics could be a promising method to alleviate environmental pollution and provide renewable energy. In this paper, co-pyrolysis and co-gasification of eucalyptus wood (EW) or rice straw (RS) with polyethylene (PE) were investigated by a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer (TG-FTIR) and a scanning electron microscope coupled with energy-dispersive spectroscopy (SEM/EDS). Results showed that the pyrolysis behaviors were characterized by two stages. The first stage was the decomposition of EW and RS, and the second stage primarily consisted of the degradation of PE. The gasification exhibited a third stage for the reaction of products with CO₂. A synergistic effect was presented in the pyrolysis and gasification of biomass with PE, and it could have a positive effect on the decomposition of biomass. Compared to individual pyrolysis and gasification, co-pyrolysis and co-gasification generated no new substances, but the yield of some products was changed in these processes. In co-pyrolysis, the decomposition of biomass was promoted. In co-gasification, the production of CH₄, CO and oxygenated compounds was inhibited, while the reaction to generate H₂O was promoted. Gasification and the addition of PE both increased the carbon content and reduced the oxygen content of volatile products. Additionally, more metal elements could be deposited in residues when PE was added.