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.     

生物质热解液化工艺及其影响因素

介绍了生物质的特点及生物质快速热解液化技术的一般工艺流程.综述了生物质热解过程中,反应温度、滞留时间、升温速率、反应压力、灰分、组成成分、分子结构、粒径和颗粒形状等条件对生物质热解及其产物组成和特性的影响,指出了生物质热解的技术关键.     

酸洗预处理对生物质热解焦物理化学特性的影响

选用松木、杨木、玉米秸秆和稻壳4种生物质为原料,采用3%（体积分数）乙酸溶液进行洗涤除灰后,进行快速热解实验,对比研究酸洗预处理对4种生物质热解焦物理化学特性的影响。结果表明：乙酸酸洗可有效去除松木、杨木、玉米秸秆和稻壳灰分中的大部分无机元素,从而促进热解过程中挥发分的释放、显著改善热解焦的表面化学特性。酸洗可促进热解焦孔隙结构的形成,提高比表面积和总孔容积,但会使平均孔径减小,这表明酸洗主要提高微孔率,对微孔的形成有较大的促进作用。同时,酸洗使得更多的含氧官能团保留在生物质热解焦表面,这种影响对玉米秸秆和稻壳尤为明显。气化焦油的吸附实验结果表明酸洗后热解焦的吸附能力有所增加。     

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。     

木质素与高密度聚乙烯共热解特性研究

生物质与塑料共热解是一种非常有效的生物质利用方法之一,但由于生物质结构的复杂性,共热解过程的机理尚不明晰。木质素是生物质的主要组分之一,本文通过热重-质谱联用仪和裂解器-气相色谱质谱仪研究其与高密度聚乙烯共热解过程,获取共热解特性及热解产物分布特性,以揭示共热解过程机制。结果显示,木质素与高密度聚乙烯共热解过程存在协同效应,使得热解失重速率加快,热解固体残渣含量减少。共热解过程有利于CH₄、H₂O、CO和C₂H₄的生成,抑制CO₂的生成。同时,酚类、醇类和糖类等含氧化合物产量减少,烷烃和烯烃类化合物产量增加。结果表明,共热解过程会发生氢转移现象,氢与木质素衍生热解产物结合发生反应,从而抑制含氧化合物的生成,促进烷烃类和烯烃类化合物生成。     

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.     

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．     

生物质焦及其特性

生物质焦是生物质热解的固体产物.文章综述了生物质焦的产生机理,热解反应条件及生物质的种类、颗粒大小、灰分含量、无机物含量等原料特性对生物质焦产量的影响规律,介绍了生物质焦的物理吸附特性,燃烧、气化的化学特性以及生物质焦的应用,其目的是为今后生物质焦的研究提供参考依据.     

生物质中K+、Ca2+对热解的影响及机理研究

为了研究K 、Ca2 对纤维素生物质热解的影响,利用热重—傅立叶红外(TG—FTITR)研究了通过室温水洗涤6、0℃热水洗涤以及0.5%硝酸洗涤方法等预处理玉米秸秆后的热解逸出特性。3种预处理方法的分析表明,不同的预处理方法对玉米秸秆结构及化学组成没有影响;酸洗好于水洗,能完全脱除K ,脱Ca2 为78%,水洗只能脱除K ;Ca2 、K 的脱除程度越深,焦残余量越少。预处理物料和原料的热解实验表明,K 、Ca2 在热解中起着明显的催化作用,促使玉米秸秆转化形成更多的羰基化合物、CO2和H2O。无K 、Ca2 等离子时,热解明显向形成含C-O-C基团等单键化合物转化,并促使液体产率增多;CO与CH4逸出几乎不受K 、Ca2 的影响。最后,从金属离子与生物质结合形式,解释了金属离子影响纤维素生物质热解的机理。     

纤维素类生物质热解影响因素分析

阐述了生物质的特点及其热解的定义和热解机理,生物质通过热解技术可获得木炭、生物油和可燃气,均具有较高发热量,其能量密度比原有机物大5倍-10倍。在生物质热解过程中,反应温度、升温速率、物料特性（种类、分子结构、粒径和颗粒形状等）、滞留时间、反应压力等条件对其气体产物分布的组成和特性具有重要的影响,指出了生物质热解的技术关键。     

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。     

热解条件对生物质焦气化活性的影响及等温气化动力学参数求解方法

生物质气化是生物质利用研究的一个重点。生物质气化包含生物质的热解和热解所得焦炭的气化两个过程。不同的热解条件将得到具有不同气化活性的生物质焦炭,不同热解条件制取的焦炭的动力学参数也不相同。本文主要概述了热解条件对生物质焦气化活性的影响。同时基于阿伦尼乌斯公式介绍了生物质焦等温气化动力学参数的两种获取方法,非等转化率法是通过选择动力学模型中的结构因子f(x) 来获取动力学参数,而等转化率法是通过避开选择动力学模型中的结构因子f(x) 来获取动力学参数。基于简单碰撞理论提出了获取等温气化动力学参数的新方法,对阿伦尼乌斯公式中的指数项、指前因子A提出了明确的物理意义。基于简单碰撞理论的等温求解气化动力学参数方法类似于基于阿伦尼乌斯公式的等温求解气化动力学参数方法。     

Effect of pore structure on CO2 gasification reactivity of biomass chars under high-temperature pyrolysis

The CO₂ gasification reactivity of pine sawdust chars (PS char) obtained from the different high-temperature pyrolysis is studied based on non-isothermal thermogravimetric method. Results show that the order of gasification reactivity is PS char-1073 > PS char-1273 > PS char-1473. Under the effect of high-temperature pyrolysis, the surface structure of biomass char is gradually destroyed and the pore structure parameters of specific surface area, total pore volume and average pore diameter increase. By means of the N₂ adsorption-desorption isotherms, it is seen that biomass char has more micro- and mesoporous at higher pyrolysis temperature. Besides, the PS char-1073 mostly has rich closed cylinder pores and parallel plate pores, and the PS char-1273 and PS char-1473 have plentiful open cylinder pores and parallel plate pores. An increase of pyrolysis temperature contributes to the development of porosity and improves diffusion path, which promotes the gasification reactivity. But, its effect on the decline of active site hinders the gasification reactivity. What's more, the kinetic model of distributed activation energy model (DAEM) is applied to calculate activation energy and pre-exponential factor with the integral and differential methods. The calculation results of integral method is more accurate and precise because the differential method is more sensitive than integral method for experimental noise. There is a compensation effect in the CO₂ gasification process.     

Hydrogen production by supercritical water gasification of biomass: Explore the way to maximum hydrogen yield and high carbon gasification efficiency

Supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. In this paper, orthogonal experimental design method, which can minimize the number of experiments compared with the full factorial experiments, was used to optimize the operation parameters of SCWG with a tubular reactor system. Using this method, the influences of the main parameters including pressure, temperature, residence time and solution concentration on biomass gasification were also investigated. Simultaneously, in order to further improve the gasification efficiency of biomass, acid hydrolysis pretreatment of feedstock, oxidizers addition and increasing reaction temperature were employed. Results from the experiments show that in the range of experimental parameters, the order of the effects of the factors on H₂ yield of corn cob gasification in SCW is temperature > pressure > feedstock concentration > residence time. Temperature and pressure have a significant and complicated effect on biomass gasification. Hydrogen yield increases by the acid hydrolysis pretreatment of feedstock, and oxidizer addition reduces the hydrogen yield but it promotes the increase in carbon gasification efficiency. Biomass feedstock with high concentration was gasified successfully at high reaction temperature.     

浑源煤焦CO_2气化反应的影响因素及动力学特性分析

研究了热解温度、热解时间以及气化温度对浑源煤焦CO2气化反应的影响,并获得了气化反应的动力学模型.结果表明：浑源煤焦的气化活性随热解温度的提高而降低;每个热解温度都对应着一个最佳热解时间,且存在最佳热解时间随温度升高而缩短的趋势;提高气化温度能够显著提高煤焦的气化反应性能,气化温度对气化反应的影响大于热解温度的影响;低温度煤焦的气化活性随气化温度的提高而增加更为剧烈;900℃及以上的高温使活性点数增加,从而使煤焦间的活性差距分布均匀;浑源煤焦的气化反应适宜用体积模型来描述,所求取的动力学参数之间存在补偿效应,其等动力学温度约为1 199.6℃.     

Assessment of the catalytic effect of various biomass ashes on CO2 gasification of tire char

The aim of this study was to determine the effect of various biomass ashes, comprising catalytically active components, on tire char reactivity during the CO₂ gasification process. Ashes from the combustion of corn cobs, beet pulp, sunflower husks and beech chips were selected for the research. Moreover, industrial fly ash from a coal-fired power plant was used as a reference. The tire char-ash blends with different ash contents (0–15 wt%) were gasified in the CO₂ atmosphere under non-isothermal conditions using dynTHERM Rubotherm thermobalance. Based on the n-order Coats and Redfern method, gasification reactivity indicators and kinetics parameters were calculated. The results showed that the addition of biomass ashes enhanced reactivity of tire char, and the magnitude of these changes depended on both the quantity and type of the additive. With the increase in the amount of added biomass ashes, the catalytic effect increased, and their efficiency can be ranked as follows: sunflower husk ash > corn cobs ash ≅ beet pulp ash > beech chips ash. In turn, reference fly ash from a power plant slightly affected the CO₂ gasification of tire char, regardless of its amount. Moreover, a statistically significant correlation between the reactivity indicator and the amount of K₂O, MgO and P₂O₅ in ashes analysed has been proved (reactivity indicator improved with an increase in these components amount). The performed analysis provides valuable information regarding the composition of catalysts characterised by high catalytic activity in the tire char gasification process.     

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.     

生物质膜法富氧气化制气技术试验研究

利用膜法富氧制气与生物质热解气化技术相结合,在半工业试验的基础上,通过改变固定床气化试验台中的氧浓度等关键反应因素,研究子玉米秸秆在常压固定床气化炉中的气化特性,并总结出燃气热值及燃气主要成分随氧气浓度变化的主要规律.试验研究表明,膜法富氧气化技术是可行的,对改善生物质燃气组分和热值具有较好作用,可用于工程实践.     

生物质半焦气化的反应动力学

利用热重分析仪研究了CO2气氛下的生物质半焦的反应性。研究发现，所研究的4种生物质半焦都表现出了相同的反应性趋势。其反应性随着转化率的增加而增加。这可能是由于生物质焦样中的碱金属含量，尤其是钾的含量较高的原因。对比生物质气化反应动力学参数研究表明，4种焦样的气化行为可以用收缩核模型来描述，并求出了4种生物质焦样的反应动力学参数。在不同的CO2分压下进行了花生壳焦样的反应性实验研究，发现焦样的反应性正比于反应气体浓度，求出了花生壳焦样的反应动力学方程式。     

Identifying the roles of MFe2O4 (M=Cu,Ba, Ni,and Co) in the chemical looping reforming of char,pyrolysis gas and tar resulting from biomass pyrolysis

Biomass chemical looping gasification (BCLG), which employs oxygen carriers (OCs) as the gasification agent, is drawing more attention for its low cost and environmental friendliness. However, the complex products of biomass pyrolysis and the reactions between OCs and the pyrolysis products constrain its development. In this study, MFe₂O₄ (M = Cu, Ba, Ni and Co) ferrites synthesized via the sol-gel method were investigated as OCs in BCLG for hydrogen-rich syngas production. The properties of the as-prepared and spent OCs were characterized by X-ray diffraction (XRD), H₂-temperature programmed reduction (TPR), scanning electron microscopy (SEM), and automatic surface area porosimetry (BET). The three-phase products (char, pyrolysis gas and toluene) derived from biomass pyrolysis were employed as the reactants to investigate the reactivity of the ferrites. Then, BCLG experiments using biomass were conducted on the four ferrites to further determine their performance. The characterization results suggested that the four ferrites are all attractive for the chemical looping process, exhibiting good oxygen transferability and wide distributions of metal cations because of their metal synergistic effects in the spine structure. Reactions with pyrolysis gas and biomass char indicated that BaFe₂O₄ has a higher reactivity via a solid-solid reaction but a lower reactivity with pyrolysis gas, which make it very favorable for the production of hydrogen-rich syngas. Furthermore, BaFe₂O₄ showed excellent performance for toluene catalytic cracking with small amounts of carbon deposition. The synergetic effects between Ba and Fe metals considerably enhanced selective oxidation to produce 26.72% more H₂ than CoFe₂O₄ and 13.79% more H₂ than NiFe₂O₄ and CuFe₂O₄ for biomass gasification. The hydrogen yield produced by BaFe₂O₄ with the assistance of steam for biomass gasification can reach 41.8 mol/kg of biomass.