烘焙棉秆的成型特性影响研究及工艺优化北大核心CSCD

文章以棉花秸秆为研究对象,对其进行烘焙预处理以提升燃烧特性与热值并降低粉碎能耗。采用单因素实验研究了成型压力、成型温度和原料含水率对烘焙棉秆成型燃料的松弛密度、吸湿性和抗压强度3个特性评价指标的影响。基于单因素实验开展了正交实验,探讨三者间的相互作用并对热压成型过程进行工艺优化。结果表明:烘焙预处理提高了棉秆的燃烧稳定性及粉碎效率,烘焙棉秆的粉碎能耗与棉秆原样相比降低了66.6%;在烘焙棉秆的热压成型过程中,成型燃料的特性评价指标在合适的压力范围内(3~23 kN)均随着成型压力的增大逐渐提升;而随着成型温度和原料含水率的增加,特性评价指标均呈现先上升后下降的趋势,并分别在成型温度为115℃和含水率为9%时出现拐点。根据正交实验得出烘焙棉秆热压成型的最佳工艺条件:压力为18 kN,温度为100℃,含水率为9%,此时制得的成型燃料的松弛密度、抗压强度和吸湿性分别达到1.220kg/m3,8.17 MPa和8.45%,完全符合我国生物质颗粒燃料的行业标准。     

柠条热压成型工艺参数研究及燃料物性分析

针对柠条压块燃料成型过程工艺参数的选择和原材料前处理条件的确定,研究压力、温度、含水率和颗粒度对燃料密度及耐久性的影响,进行单因素和多因素试验并对各变量进行方差及回归分析。结果表明:较小颗粒度、低含水率、高温(以此顺序)是增大柠条块状燃料密度和耐久性的重要因素,压力为边际影响因素。柠条原料含水率应在5%~13%之间,为实现节能和低成本,成型温度和压力分别控制在80~150℃、60~120 MPa之间,压块燃料加工的最优参数组合为颗粒度小于0.63 mm,含水率8%、温度130℃、压力120 MPa。     

工业油料饼粕与黧蒴栲木屑协同成型实验研究

考察成型过程因素对黧蒴栲和工业油料饼粕协同成型行为的影响。结果表明,饼粕及其堆肥化产物的加入有利于提升颗粒强度。随着温度的升高及含水率、饼粕、饼粕堆肥化产物含量的增加,混合颗粒挤压能耗持续降低。推动能耗分别随温度的升高而增大、随含水率的增大先增大后减小、饼粕和饼粕堆肥化产物含量的增大先减小后增大。Meyer强度随温度的升高而增强,随饼粕和饼粕堆肥化产物含量的增加先增强后减弱,在含水率10%(质量分数)时强度最大。     

基于马氏距离法的谷秆固体燃料成型工艺参数优化

采用响应面法对影响谷子秸秆固体燃料物理特性的工艺参数(温度、压力和含水率)进行研究,并应用马氏距离法得到3响应优化结果。试验结果表明:谷秆燃料密度与压力成正比,与含水率成反比,随温度升高呈先增后减的趋势。耐久性和抗跌碎性均随压力、含水率的增大和温度的升高而先增后减。当压力在85~110 MPa,温度在80~110℃,含水率在8.5%~11.0%可加工得到优质谷秆固体燃料。最佳成型工艺参数为温度97℃、压力107 MPa和含水率10.7%,在此条件下密度、耐久性和抗跌碎性分别达到1.18 g/cm~3、99.75%和99.77%。     

向日葵秸秆固体燃料成型参数多响应优化设计

采用三因素三水平响应面试验设计研究含水率、温度、压力对向日葵秸秆成型燃料物理特性(密度、耐久性、抗跌碎性)的影响规律,并应用马氏距离法对工艺参数进行三响应优化设计。结果表明:向日葵秸秆固体燃料密度与含水率成反比,与压力成正比,随温度升高呈先增后缓趋势。耐久性和抗跌碎性均随含水率升高而降低,随温度、压力的升高而升高。当含水率在5%～8%,温度在110～140℃,压力在100～120 MPa时可成型优质向日葵秸秆燃料。三响应优化参数组合为:含水率5.8%,温度128.8℃,压力114.0 MPa,此条件下燃料密度、耐久性、抗跌碎性分别达1.03 g/cm~3、98.75%、99.76%,此结果可为向日葵秸秆固体燃料的工业化制备提供理论参考。     

烟秆和木屑生物质颗粒燃料成型工艺参数优化

文章以烟秆和木屑为研究对象,首先研究了当生物质成型颗粒的成型特性最佳时,烟秆和木屑的混合比,并在此基础上进行了单因素试验和多因素正交试验,得到了关于生物质成型颗粒径向抗压力和密度的回归方程。研究结果表明:当烟秆含量为50%时,生物质成型颗粒的成型特性最佳;成型温度、原料含水率和成型压力对生物质成型颗粒密度和径向抗压力影响的大小顺序均为成型压力﹥成型温度﹥原料含水率;当成型压力为6.5 kN,成型温度为101℃,原料含水率为13.5%时,生物质成型颗粒的径向抗压力取得最大值1.73 kN,颗粒密度取得最大值1 334.56 kg/m~3。     

成型参数对桉树加工剩余物成型颗粒品质影响的实验研究

以桉树加工剩余物为研究对象,在龙门液压机YM-10T上进行原料压缩成型实验,在INSTRON5564型万能材料试验机上进行颗粒径向压缩实验,分析成型参数对颗粒品质(颗粒松弛密度、抗变形性和抗渗水性)的影响。考虑实际生产过程相关设备能耗、产量及运行状况,针对桉树加工剩余物原料,粒径范围1~2 mm、成型压力5~6 kN、原料水分10%~15%、成型温度90~120℃、保压时间6~9 s适合于颗粒燃料的生产。     

桉木屑与玉米秸秆混配成型的最佳参数

为解决桉木屑成型困难、能耗高、燃料强度低等问题,采用其与玉米秸秆混配成型的技术手段,设计五因素的响应面中心组合实验方法,在WD-100KE型电子压力机上进行单颗粒压缩实验,研究玉米秸秆配比(0~40%)、水分(4%~20%)、温度(40~160℃)、压力(4000~8000 N)、粒径(1.00~5.00 mm)对比能耗、松弛密度、Meyer强度的影响。选定比能耗为二因素交互关系模型(2FI)、松弛密度和Meyer强度为二次优化模型(quadratic),得到响应面方程,对优化的成型参数验证实验表明,实验值与预测值误差在10%内,可为实际生产提供理论依据。     

高热值垃圾制备RDF成型特性及可行性

为高效能源化处理城市废物,文章提出了城市生活垃圾分质收集、分别处理、以废治废的新理念,即将高热值垃圾与其它废物联合制取RDF(垃圾衍生燃料)为工业应用提供能源;研究不同水分含量、不同塑料含量及不同附加物(生物质)对RDF成型特性的影响,对RDF制取过程进行部分能耗分析。结果表明:随着塑料含量增加RDF颗粒热值明显增大,但颗粒变得松散易破碎,堆积密度和颗粒长度降低,塑料含量小于50%为宜;随着含水率的增加热值有下降趋势,但利于颗粒压缩成型,堆积密度和颗粒长度降低,含水率控制在10%¹4%时,颗粒成型效果较好;锯末作为辅料制备的RDF成型效果比秸秆好。     

秸秆颗粒冷态压缩成型过程的比能耗回归分析

对5种秸秆颗粒冷态压缩成型过程进行开式试验研究,将其压缩成型过程分为松散、过渡、压紧和推移4个阶段,回归了不同阶段的压力方程,采用Matlab软件计算出整个压缩成型过程中的比能耗值。以小麦秸秆为例,采用二次回归通用旋转组合设计,建立了压缩速度、物料含水率2个因素与比能耗的数学模型,结果表明,压缩速度的影响比含水率大,且二者均为负效应。     

Ultrasonic vibration-assisted pelleting for cellulosic biofuel manufacturing: Investigation on power consumption

Cellulosic ethanol produced from cellulosic biomass is an alternative to petroleum-based transportation fuels. Raw cellulosic biomass has low density, causing high costs in their storage, transportation, and handling. Ultrasonic vibration-assisted (UV-A) pelleting can increase the density of cellulosic biomass. Effects of UV-A pelleting variables on pellet quality (density, durability, stability, and strength) and sugar yield have been reported. However, power consumption in UV-A pelleting has not been fully investigated. This paper presents an experimental investigation on power consumption in UV-A pelleting of wheat straw. Effects of input variables (biomass moisture content, biomass particle size, pelleting pressure, and ultrasonic power) on power consumption are investigated. Results show that power consumption in UV-A pelleting increases as moisture content and particle size decrease, and as pelleting pressure and ultrasonic power increase.     

Von Rittinger theory adapted to wood chip and pellet milling,in a laboratory scale hammermill

The study draws upon the milling theories developed for the ore processing industry (Von Rittinger, Kick and Bond theories) in order to define a method for characterising wood chip and pellet energy consumption during milling.Energy consumption during wood milling depends on three main factors: the material moisture content, the particle size difference between the feed and the milled product, and the material itself. The latter may be characterised by a single parameter based on an adaptation of Von Rittinger's constant.A relation characterising wood pellet energy consumption as a function of the particle size distribution of the pellet ingredients and the milled pellets is proposed. This is characteristic of each type of pellet for each moisture content value considered.     

Ultrasonic vibration-assisted pelleting of cellulosic biomass for ethanol manufacturing: An investigation on pelleting temperature

Ethanol made from cellulosic biomass is an alternative to petroleum-based liquid transportation fuels. However, large-scale manufacturing of cellulosic ethanol is hindered by the low density of cellulosic biomass. Experiments have shown that ultrasonic vibration-assisted (UV-A) pelleting could compress low-density raw biomass into high-density pellets, and pelleting temperature increased during pelleting process. However, pelleting temperature was not fully investigated. This paper reports an investigation on pelleting temperature in UV-A pelleting of wheat straw. The precision of temperature measurement was first evaluated. Relationships between pelleting temperature and pelleting time were then investigated. Also, the pattern of pelleting temperature distribution was evaluated by ranking the pelleting temperatures at six different locations in a pellet. Finally, effects of three input variables (ultrasonic power, pelleting pressure, and pellet weight) on pelleting temperature were discussed. Results reported in this paper are the foundation of a follow-up paper reporting relationship between pelleting temperature and pellet quality (density, durability, and sugar yield).     

Experimental trials to make wheat straw pellets with wood residue and binders

Crude glycerol, bentonite, lignosulfonate, and softwood residue (wood residue) were investigated in this study as binders for biomass fuel pellets for thermochemical conversion to enhance pellet quality for transportation and storage. The mass fraction of water of the wheat straw and the wood residue used for pelleting were 0.0676 and 0.0949, respectively. Wheat straw with crude glycerol, bentonite, lignosulfonate, wood residue, and pretreated wood residue with crude glycerol were compressed in a single pelleting unit at a temperature of 95 °C. The specific energy consumption, density, dimensional stability, tensile strength, calorific value, ash content, and chemical composition of the pellets made were determined. Results showed that the specific energy consumption for wheat straw pelletization significantly decreased with the addition of lignosulfonate, bentonite, wood residue, and pretreated wood residue with crude glycerol. With the addition of binders chosen in this study, the tensile strength of wheat straw pellets was improved with values ranging from 1.13 to 1.63 MPa. There was a significant increase in the higher heating value (17.98 MJ kg⁻¹ to 18.77 MJ kg⁻¹) when crude glycerol, wood residue, and pretreated wood residue were used as binders. The addition of both pretreated and non-pretreated wood residue significantly decreased the ash content of wheat straw pellets.     

Thermodynamic methodology to support the selection of feedstocks for decentralised downdraft gasification power plants

Thermodynamic criteria as a feedstock selection tool for decentralised downdraft gasifiers coupled to spark-ignition engines are presented in this work. The methodology consists of an energy and exergy analysis of gasification process. The analysis is carried out by computational modelling of the gasification process as a function of biomass type (ultimate analysis, moisture content and heating value) and fuel/air ratio. Considering a system operating with different wood species, analysed parameters are gas heating value, energy and exergy efficiencies and engine fuel quality (EFQ). With a fixed fuel/air ratio (2.6) and moisture content (20%wt), it is highlighted that as the carbon-oxygen molar ratio of wood decreases from 2.0 to 1.78 as model input, reaction temperature increases by 9%, energy and exergy efficiencies diminish by 1.8% and 4.2%, respectively, while EFQ increases by 3.2%. Therefore, for decentralised power plants, biomass should be selected to produce higher EFQ.     

Investigating pellet charring and temperature in ultrasonic vibration-assisted pelleting of wheat straw for cellulosic biofuel manufacturing

Biofuels are only alternative solution for liquid transportation fuels among different kinds of renewable energy. To avoid the competition with the food, cellulosic biomass has been proposed as feedstock for manufacturing of cellulosic biofuels. Costs associated with collection, transportation, and storage of cellulosic biomass account for more than 80% cost of the feedstock. By processing cellulosic biomass into high density pellets, handling efficiency of cellulosic feedstocks can be improved, leading to costs reduction in transportation and storage. Ultrasonic vibration-assisted (UV-A) pelleting is a recently developed pelleting method, which can not only produce higher density but also break the lignin shell, to some extent, to increase cellulose accessibility and then increase sugar and biofuel yield. The reported investigations on UV-A pelleting provided little information about the relationship between charring and pelleting temperature under different input variables of pelleting. In this paper, effects of different input variables of pelleting on both charring ratio and pelleting temperature were studied. This paper, for the first time, reported the relationship between charring ratio and pelleting temperature. The obtained results will be helpful in understanding the mechanism of UV-A pelleting and providing guide to control pellet charring for a higher biofuel yield.     

Energy and exergy analysis of biomass gasification at different temperatures

Biomass is usually gasified above the optimal temperature at the carbon-boundary point, due to the use of different types of gasifiers, gasifying media, clinkering/slagging of bed material, tar cracking, etc. This paper is focused on air gasification of biomass with different moisture at different gasification temperatures. A chemical equilibrium model is developed and analyses are carried out at pressures of 1 and 10 bar with the typical biomass feed represented by CH_1.4O_0.59N_0.0017. At the temperature range 900–1373 K, the increase of moisture in biomass leads to the decrease of efficiencies for the examined processes. The moisture content of biomass may be designated as “optimal” only if the gasification temperature is equal to the carbon-boundary temperature for biomass with that specific moisture content. Compared with the efficiencies based on chemical energy and exergy, biomass feedstock drying with the product gas sensible heat is less beneficial for the efficiency based on total exergy. The gasification process at a given gasification temperature can be improved by the use of dry biomass and by the carbon-boundary temperature approaching the required temperature with the change of gasification pressure or with the addition of heat in the process.     

Simulation of temperature and moisture changes during storage of woody biomass owing to weather variability

The objective of this study is to describe moisture content and temperature profile in the woody biomass pile by a two dimensional mathematical model. Woody biomass in the form of wood chips and bundles was stored for a period of one year. Heat and moisture transfer model for drying processes was solved by finite element method using MATLAB programming. The simulation was performed using the recorded climate conditions during the experiment and constant drying air conditions. The temperature change inside the bundles shows the same trend and effect with ambient air temperature, however, in case of wood chips shows lesser effect at various ambient air temperature. Uniformly declined moisture content was observed inside the covered wood chips pile during the storage period. The proposed two dimensional model is in close agreement with experimental data to describe the moisture and temperature profile of the pile wood chips and bundles. However, as the wood chips pile height increases more than 3 m temperature development inside the pile could be rapid and the effect of chemical reaction in the wood chips pile has to be included for better accuracy of prediction.     

Influence of process parameters and biomass characteristics on the durability of pellets from the pruning residues of Olea europaea L.

The present work aims to investigate the influence of the main process parameters (pressure and temperature) and biomass characteristics (moisture content and particle size) on some mechanical properties (density and durability) of olive tree pruning residues pellets. By means of a lab scale pellet press, able to control process parameters, the biomass, ground with three different hammer mill screen sizes (1, 2 and 4 mm) and conditioned at different moisture contents (5, 10, 15 and 20% w.b.), was pelletized at various process temperatures (60, 90, 120 and 150 °C) and pressures (71, 106, 141 and 176 MPa). Compressed sample dimensions and mass were measured in order to calculate pellet density, while compressive strength tests were carried out to estimate the durability of the final biofuel. The relationships between the factor settings and the responses (density, compression strength and modulus of elasticity) were examined by univariate and multivariate statistical analysis.Temperature resulted the most important variable influencing pellet mechanical properties, followed by the initial moisture content and the particle size of the raw material. In particular, high process temperature, low moisture contents and reduced particle sizes allowed obtaining good quality pellets. The effect of compression force resulted scarcely relevant.