CO2 gasification of wood charcoals derived from vacuum and atmospheric pyrolysis

The gasification of biomass derived char obtained via vacuum and atmospheric pyrolysis of Populus tremuloides has been studied in the ranges of 725–960°C and 0.1 to 6 MPa. CO₂ was used as the oxidizing gas. The results show that char reactivity is influenced by the preheating rates and that pressure effects are significant between 850°C and 950°C. A correlation based on the expression: df/dt = k₀{exp(-E/RT)}(1 - f)^af^βP^yCO₂ was used to fit the experimental data. In general, vacuum pyrolysis derived char showed a higher reactivity than atmospheric pyrolysis chars. An explanation based on a higher oxygen content of the vacuum pyrolysis char is suggested.     

Fast pyrolysis of wood: direct measurement and study of ablation rate

Quantitative measurements of the apparent rate of reaction of wood rods undergoing fast pyrolysis by contact with a hot spinning steel disc are reported. The variations in the apparent volatilization rate and in the thickness of the reacting layer were studied as a function of disc velocity, rod diameter, contact pressure and disc temperature. The results show that the rate of reaction is mainly limited by heat transfer outside and inside the wood (ablation conditions). The external heat transfer coefficient, studied as a function of contact pressure, is much more important than the heat transfer coefficient calculated on the basis of simple radiation transfer. The conclusion is that fast pyrolysis of wood in the ablation regime can be observed if two necessary conditions are fulfilled : high available heat flux and efficient removal of the primary products of the reaction.     

木材热解过程的热化学平衡分析

基于Gibbs自由能最小化法,利用HSC Chemistry软件对木材热解过程进行了热化学平衡计算。讨论了温度对热化学平衡产物组成和比例的影响,并把热解过程划分为4个阶段。首次根据自发反应的判据即反应的Gibbs自由能变与温度关系讨论了产物相互之间反应,由此确定热解各个阶段可能发生的反应。最后总结了文献中实验研究温度对木材热解产物影响情况,并与计算结果比较,结果表明,所预测的不同温度下木材热解产物分布特性与前人的实验结果相似。     

Characterization and catalytic gasification of the aqueous by-product from vacuum pyrolysis of biomass

Spruce wood residues were treated in a vacuum pyrolysis Process Development Unit with a throughput capacity of 28 kg/h. Two aqueous phase condensate samples with COD concentration varying between 190 and 255 g/L were produced and sequentially extracted with dichloromethane and ethylacetate solvents. The soluble organic matter was composed of acidic, phenolic, alcoholic and ketonic compounds. The insoluble fraction was sequentially distilled at 100 and 110°C under atmospheric pressure. Mainly water was recovered in the first distillate, while the second distillate contained 30.4% formic and acetic acids, 69.4% water and 0.2% residual organic compounds. The distillation residue was rich in oxygen and was essentially insoluble in any organic solvent. The two aqueous phase pyroligneous samples were treated in Bat-telle's Thermochemical Environmental Energy System (TEESr?), a registered service mark of Onsite*Ofsite, Inc. of Duarte, California, U.S.A. The results of the tests showed that similar results were obtained with either feedstock. In batch tests a COD reduction of 99% was achieved. The product gas composition was typically about 49% methane, 5% hydrogen, 1 % ethane and 45% carbon dioxide. Tests in a continuous stirred-tank reactor produced reproducible data which can be used for process scale-up. Catalyst lifetime was identified as needing further improvement. The preliminary results demonstrated the technical feasibility of the catalytic gasification process as a useful step in the recovery of energy from the secondary condensate stream and the cleanup of the by-product water from vacuum pyrolysis of wood.     

Flaming pyrolysis model of the fixed bed cross draft long-stick wood gasifier

The future industrial development of biomass energy depends on the application of renewable energy technology in an efficient manner. Of all the competing technologies under biomass, gasifiers are considered to be one of most viable applications. The use of biomass fuel, especially biomass wastes, for distributed power production can be economically viable in many parts of the world through gasification of biomass. Since biomass, is a clean and renewable fuel, gasification gives the opportunity to convert biomass into clean fuel gas or synthesis gas for industrial uses. The preparation of feedstock for a gasifier requires time, energy and labour and this has been a setback for gasifier technology development. The present work is focused on gasification of long-stick wood as a feed material for gasifiers. This application makes reduction not only in the cost but also on the power consumption of feed material preparation. A 50 m³/h capacity gasifier was fabricated in the cross draft mode. The cross draft mode makes it possible to produce low tar content in producer gas. This cross draft mode operates with 180 W of blower supply for air to produce 10 kW of thermal output. The initial bed heights of the long-stick wood and charcoal are 58 cm and 48 cm respectively. Results were obtained for various flow conditions with air flow rates ranging from 20 to 30 m³/h. For modelling, the flaming pyrolysis time for long-stick wood in the gasifier is calculated to be 1.6 min. The length of the flaming pyrolysis zone and char gasification zone is found to be 34 cm and 30 cm respectively. The rate of feed was between 9 and 10 kg/h. Continuous operation for 5 h was used for three runs to study the performance. In this study we measured the temperature and pressure in the different zones as a function of airflow. We measured the gas flow and efficiency of the gasifier in order to determine its commercial potential for process and power industries.     

Numerical investigation of turbulent non-premixed combustion of a wood pyrolysis gas

A fully compressible database of turbulent non-premixed flames of a wood pyrolysis gas is developed by means of direct numerical simulation (DNS). A reduced kinetic mechanism is used to model the combustion of a pyrolysis gas-air mixture. The instantaneous flame surface density evolution equation based on the concept of a displacement speed is examined. The normal component of the displacement speed is nearly constant with respect to curvature, while the curvature-related component tries to restore the flame front to a planar shape. The strain-rate term is mainly a source as the flame is mostly extended. The normal displacement is responsible for both positive and negative contributions to the flame area. The displacement/curvature term is primarily a sink, since it is dominated by its curvature component. Effects of strain and curvature are analyzed by considering their correlations with reaction rates. Reaction rates are enhanced with increased positive strain rates owing to an increase in the flame surface area and to a decrease in curvature. The analyzed results aid in the development of turbulent combustion models. Finally, a new model for a mean variance of the scalar dissipation rate, based on a scale similarity approach, is proposed and examined. A comparison with DNS results shows that the proposed model provides a significant improvement over existing models. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 15–34, May–June, 2007.     

木质素类生物质催化热解制备精细化学品研究进展

能源和环境是当今世界的两大挑战,将生物质转化为燃料和化学品是应对该挑战的低碳方案。其中,催化热解木质素获得燃料和化学品是低碳方案的重要部分。本文以能源和环境问题为出发点,阐述了木质素催化热解制备燃料和化学品的可行性和必要性,并对催化裂解行为、催化裂解过程和催化产物等方面的国内外研究现状进行了系统介绍。文章首先对木质素的结构和转化过程进行了概述;然后从催化热解行为、催化热解产物以及催化剂的研究现状等方面进行了系统阐述,并对现有的催化木质素热解过程的机理研究进行了讨论。通过对木质素催化热解制备燃料和化学品的发展前景、技术瓶颈以及逻辑方面进行评估表明,木质素转化为燃料和化学品过程中提高产品的产率和能量效率是今后的总体目标,而原料供给和生产、催化剂开发、产品分离纯化、反应机理和动力学以及计算模拟等方面将是深入研究木质素高效利用的重要研究内容。     

Development of polyimide membranes for the separation of water vapor from organic compounds

Attempts were made to develop solvent‐resistant polyimide capillary membranes with integrally skinned asymmetric structure to be used for the treatment of wood dryer emissions or vacuum pyrolysis aqueous effluents. Model mixtures of 1‐propanol (1‐PrOH)/H₂O and acetic acid (AA)/ H₂O, with concentrations of 10–90 wt % of organic components, were used as vaporous feeds. Solvent‐resistant membranes with good mechanical and excellent vapor separation properties were prepared from polyimides based on PMDA and BPDA by the dry/wet phase‐inversion technique. Molecular structure largely influences membrane properties. For the asymmetric polyimide membranes studied, a tendency similar to that of homogeneous dense membrane was found. Membranes prepared from polyimides with diamine and dianhydride moieties, both containing rigid backbone and aromatic rings, displayed higher permeability and selectivity. Test conditions exhibited influences on membrane separation performance. Membranes prepared from copolyimide BPDA–50DDS/50ODA and PMDA–50DDS/50ODA exhibited the best mechanical and chemical properties as well as water vapor separation properties, which are considered to be of practical usefulness for applications of these membranes in the removal of water from water/organic mixtures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 139–152, 2002     

木醋液制备及形成机理研究进展

生物质能具有来源广泛、绿色无污染、可再生和低廉易得等优点,开发高附加值产品对生物质资源多元化利用和解决能源危机具有重要的战略意义。木醋液是生物质热解制炭工艺中的高价值酸性副产物,已被广泛应用于农业、林业、畜牧业、工业和医药业等多个领域,均显现出正面的促进作用。本文综述了木醋液制备工艺、理化性质、分离方法及形成机理的研究进展,从生物质组分（半纤维素、纤维素和木质素）热解的角度阐述了木醋液中主要有机化合物的形成机理。木醋液颜色呈浅黄色或红褐色,密度为1.00~1.13g/cm³,pH为2.27~3.32,有机酸含量为2.07%~13.82%,热解温度170~350°C下制得的木醋液的物理及化学性质满足日本农用木醋液标准。文章指出木醋液富含酸类、酚类、酮类、呋喃类、醛类、醇类、酯类和醚类有机物,酸类化合物（主要是乙酸）和酚类化合物（主要是愈创木酚）使木醋液具备优良的抗微生物活性和抗氧化活性,并且酚类化合物使其具有烟熏气味的独特性质。联合不同单一分离法精制木醋液的效果最佳,可适用于不同领域的多种用途。在生物质热解过程中,游离水、吸附水和结合水随着温度升高依次析出,半纤维素、纤维素和木质素再分解成挥发性有机物质与水,共同冷凝后形成木醋液。但是,传统热解工艺制备得到木醋液的产率低及温度对成分含量的影响显著是限制木醋液发展的主要瓶颈。水热法是一种新兴的木醋液制备技术,其产率高,焦油成分少,包含的有机化合物种类更多。此外,从生物油中直接萃取也可快速制备含有相同有机组分的木醋液。因此,本文提出未来研究应着重于开发和研究高效且便捷的木醋液制备技术、分离技术及其机理,同时结合先进的催化技术与膜分离技术,以便利于制备高品质木醋液和直接地应用于不同领域,早日实现木醋液的规模化应用。     

Antioxidant properties of compounds isolated from wood vinegar by activity-guided and pH-gradient extraction

The chemical profile of wood vinegar (WV) was studied by gas chromatography-mass spectrometry (GC/MS), and 48 organic compounds were identified, including phenols which accounted for 2.0%. Antioxidant compounds were isolated from WV by an activity-guided isolation method for further investigation. The dichloromethane extract from WV exhibited the highest total phenolic content and demonstrated more potent antioxidant activity than the other extracts. Then, the phenols were enriched by pH gradient extraction method from the dichloromethane extract. Seven phenols were isolated from the WV using a sequence of column chromatographic purification steps over silica gel and C18 column, followed by semi-preparative HPLC and their structures were identified by ¹H NMR and ¹³C NMR spectra. All the compounds showed potent antioxidant activities in the 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline- 6-sulphonic acid (ABTS), and ferric-reducing antioxidant power (FRAP) assays. This study demonstrates that phenols isolated from WV have the potential to be used as antioxidant agents.     

Heterogeneous and homogeneous reactions of pyrolysis vapors from pine wood

To maximize oil yields in the fast pyrolysis of biomass it is generally accepted that vapors need to be rapidly quenched. The influence of the heterogeneous and homogeneous vapor‐phase reactions on yields and oil composition were studied using a fluidized‐bed reactor. Even high concentrations of mineral low char (till 55 vol %) appeared not to be catalytically active. However, the presence of minerals, either in biomass or added, does influence the yields, especially by the occurrence of vapor‐phase charring/polymerization reactions. Contradictory, in the absence of minerals, homogeneous vapor‐phase cracking reactions were dominant over polymerization/charring reactions (400–550°C, 1–15 s). With increasing vapor residence time, the oil yield reached an asymptotic value, which decreased with temperature. At a vapor temperature of 400°C no decrease in oil yield was observed, but dedicated analysis showed that homogeneous vapor to vapor reactions had occurred. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Recycling polymeric wastes by means of pyrolysis

Different polymeric wastes, which include materials from the automobile industry, such as tyres, automobile shredder residues (ASR) and sheet moulding compound (SMC), and materials from municipal solid wastes (MSW), such as cardboard, tetrabrik and plastics (LDPE, PP, PS, PET and PVC), pure and mixed, have been pyrolysed in a 3.5 dm³ autoclave at 500 °C for 30 min in a nitrogen atmosphere. The amount and characteristics of the solid, liquids and gases obtained are presented. The suitability of the different materials for the pyrolysis recycling process is discussed. It is concluded that pyrolysis is a very promising technique for recycling tyres, SMC, one type of ASR (heavy ASR), and LDPE, PP and PS, either pure or mixed; with all of them valuable solid, liquid and gaseous products are obtained in pyrolysis. On the contrary, light ASR, tetrabrik and cardboard do not yield valuable products in the pyrolysis process and therefore their recycling by pyrolysis is not of interest, except as a way of volume reduction. PET and PVC turned out to be troublesome in the pyrolysis experiments; for a proper study of their recycling by pyrolysis other operating conditions and installations are required. © 2002 Society of Chemical Industry     

生物油组分分离与化学品提取的研究进展

生物质在高温无氧条件下热解可以生成富含高附加值化学品和燃油成分的生物油。有效分离技术和高效提取手段的发展是生物油质量提升的关键。基于此,本文在介绍生物油性质与生物质快速热解工艺的同时,对目前国内外的生物油分离技术如蒸馏、液-液萃取、柱色谱、超临界萃取、膜分离等进行了较为详细的分析和评述。常规蒸馏和溶剂萃取等技术,工艺成熟、操作简单,但存在生物油的热敏性差、萃取剂回收难度大和污染严重等问题;分子蒸馏技术分离过程安全环保,但工艺复杂,设备成本高;超临界萃取和膜分离等技术安全环保,技术成熟,具有较大的潜力。文章还综述了目前生物油中具有高附加值的组分和单一化学品的分离提取研究进展,为生物油的有效分离和高效利用提供了理论参考,也为未来生物油分离技术的发展提供了研发方向。     

Microwave assisted barking of frozen wood

Thawing pulpwood with microwave energy could be an effective means to improve winter barking operations in Canadian interior mills. Complete bark thawing requires 140 MJ per tonne of wood for average 25 cm diameter logs at 90 mass % moisture, dry basis. However, complete thawing may not be necessary, as warming both spruce and aspen bark from ?20°C to ?5°C, decreases the bark/wood bond strength from 2.5–4.5 MPa to room temperature values of 0.5–1.5 MPa. This improves the economics of winter operation, but the expenditure for capital which has no year-round use is not easily justified. Also the design of safe large-scale microwave generators and applicators remains a technical challenge.     

A model for the pyrolysis of two Nordic structural timbers

Performance-based design of the timber structures' fire resistance is often based on the reduced cross section and thus relying on empirical and numerical assessment of the charring propagation. The current work aims to construct models for the pyrolysis of spruce and pinewoods to allow coupled simulations of the cross-section reduction and burning rate in fire models. Kinetic models are formulated based on thermogravimetric data and supported by the heats of pyrolysis and combustion measurements by differential scanning calorimetry and microscale combustion calorimetry, respectively. The results from these small-scale measurements are consistent with each other, and the heats of pyrolysis and combustion are determined for the wood primary components by fitting the simulations to the experimental results. Heat release models are constructed based on the small-scale tests, and cone calorimeter experiments are used for the estimation of the physical properties and for the heat release model validation.     

废旧电路板真空热解

采用热重分析仪和固定床热解反应器对废旧电路板进行了低真空条件下的热分解实验.研究了混合废旧电路板在真空下的降解特性、热解动力学以及热解条件对热解产品产率的影响,并讨论了真空和氮气条件下电路板热解的差异.实验结果表明真空降低了电路板热解的表观活化能,提高了热解产物的挥发性,减少了二次裂解反应,因而真空有利于提高液体产品的产率,降低气体和固体产品的产率.废旧电路板的真空热解液体产品主要由酚、烷基酚、双酚A、水以及各种溴酚构成,液体中总溴高达13.47％,其中一半左右以有机溴的形式存在,因此液体产品适合用于分离提取化工原料而不宜用于作燃料.     

Analysis and modelling of wood pyrolysis

In many industrial processes wood is treated as big fragments or pellets. In such conditions kinetics and yields are different with respect to the case of particles with few mg weight. However most of published kinetic models were based on experimental data obtained with very small samples. In this work pyrolysis of wood pellets was investigated by using a special experimental device which allowed to determine kinetics of total weight loss, gas and tar production. Two different heating rates, 0.05 and 1 K/s, were employed to determine kinetic parameters. Dynamic and isothermal pyrolysis tests were carried out on beech and pine wood previously dried in an oven. A simple but realistic kinetic scheme was proposed able to take into account the phenomena that happen in big wood particles. The numerical parameters were determined from the results of experimentation on beech wood. The proposed kinetic model takes into account the presence of two different stages during pyrolysis: a first one involving only unreacted wood and a second one where the products not yet escaped from the solid matrix react further. This kinetic model allowed to fit the experimental data quite well. The model was successfully validated with tests performed at an elevated heating rate (approximately 60–100 K/s) of the external surface of the pellets. In these conditions, the pellets showed a marked gradient of temperature inside, which was suitably considered.