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。     

锯末制备生物质成型燃料的试验研究

分别采用冷压成型和炭化成型工艺以锯末制备生物质成型燃料。冷压成型工艺主要考察原料水分、成型压力对燃料的成型性能影响。试验结果表明:原料水分为12%~16%,成型压力为60 MPa的条件下能够制得成型性能较好的生物质成型燃料,其密度与抗跌强度分别能够达到0.94 g/cm3和99%;炭化成型工艺主要考察混合料水分、无烟煤配比、J型粘结剂添加量、成型压力对燃料的成型性能影响。试验结果表明:无烟煤配比为50%、混合料水分为30%、J型粘结剂添加量为8%、成型压力为45 MPa的条件下能够制得成型性能较好的优质生物质成型燃料,其密度与抗跌强度分别为0.93 g/cm3和99.3%。     

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。     

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。     

成型生物质流化床气化及结渣影响因素研究

为提高生物质气化产物的品质,采用成型桉树皮和成型玉米秸秆2种典型农林废弃物,并选取稻壳和木屑作为对比,在中试规模的流化床实验台上进行气化实验,得到成型桉树皮、成型玉米秸秆、稻壳和木屑的最佳空气当量系数,分析了成型生物质在气化中出现结渣现象的原因。结果表明：在实验条件下,成型桉树皮、稻壳和木屑的最佳空气当量系数为0.20,其燃气热值分别为5.5 MJ/m³、5.5 MJ/m³、6 MJ/m³,气化效率分别为60%、45%、52%;成型玉米秸秆由于其高灰分、低热值,所需空气量更大,最佳空气当量系数为0.24,燃气热值为4 MJ/m³,气化效率为35%;气化温度提高可促进不同生物质的气化反应,碱金属、碱土金属含量较多的成型生物质在气化过程中更易结渣。     

棉秆炭与生物质焦油混合成型及燃烧特性研究

为研究棉秆炭与生物质焦油混合成型及燃烧特性,以成型压力、成型温度和焦油添加量为试验因素,采用正交试验方法,开展成型条件对抗压强度、跌落强度、松弛密度及吸潮率影响规律的试验研究,并采用差热热重同步分析仪,分析棉秆炭、焦油混合试样燃烧特性。试验结果表明：最优成型工艺参数为成型压力8 kN、成型温度20 ℃、焦油添加量6%。棉秆炭与焦油混合试样的综合燃烧特性指数（28.86~24.21）×10^-8 K^-3·min^-2随焦油添加量（0%~6%）的增加而逐渐减小,说明在棉秆炭中加入适量焦油制备成型炭可获得良好的成型及燃烧性能。     

复合粘结剂对生物质成型颗粒密度与能耗的影响

以棉秆、麦秆和油菜秆为原料,通过向其中加入不同的复合粘结剂于台式模压单元上进行成型实验来考察生物质成型颗粒的特性。结果发现,对于棉秆和麦秆而言,加入粘结剂后的成型颗粒比未添加粘结剂的成型颗粒的松弛密度大幅提高,并且能耗减少20%以上。综合考虑成型颗粒品质、能耗以及经济成本等因素,棉秆和麦秆成型颗粒的最优复合粘结剂(羧甲基纤维素、Al₂O₃、Fe₂O₃和黏土)的质量比分别为4∶4∶5∶7和3∶5∶6∶6,而油菜秆由于自身特性,需进一步探讨其最佳成型方式。通过红外光谱和金相显微镜图像分析,粘结剂中的羧甲基纤维素与成型颗粒中微小粒子相互交联形成"桥键"加强原料粒子间的粘结力,但由于油菜秆中提取物含量较高,导致原料粒子表面形成的角质层阻碍粘结剂与原料粒子之间的相互作用。     

生物质三组分对成型颗粒物理性能的影响

为探究生物质三组分(纤维素、半纤维素和木质素)对成型颗粒物理性能的影响,以棉秆、木屑以及生物质三组分为研究对象,单独或按一定掺混比例混合后制备成型颗粒,使用电子万能材料试验机分析了成型颗粒的表观密度和抗压强度,利用X射线光电子能谱仪分析了生物质成型前后分子结构的变化。结果表明：纤维素直接影响成型颗粒的抗压强度,半纤维素和木质素主要作为黏结剂,协同纤维素间接提高成型颗粒的抗压强度。向棉秆中加入纤维素或半纤维素后,其混合成型颗粒中的C—OH官能团均明显提高,且产生了新的C=C官能团,有利于形成分子间作用力和提高分子结构的稳定性,增强成型颗粒的物理性能。     

毛竹颗粒燃料成型工艺研究

以毛竹废弃物为原料,采用自制设备制备毛竹成型颗粒,分析了粉碎粒径、含水率、预热温度、成型压力对颗粒成型的影响,并以松弛密度、耐久度为指标,采用单因素及正交试验对毛竹成型颗粒制备工艺参数进行了优化。结果表明:当粒径小于0.38 mm,含水率为15%,预热温度为125℃,成型压力为20 MPa时,成型效果最好,此时成型颗粒的松弛密度为1.110 g/cm3,耐久性为0.955。该工艺的优化设计为毛竹废弃物制备成型颗粒工艺参数的选择提供了参考。     

桉树木屑热压成型特性研究

以桉树木屑为原料,在自制的成型模具上,利用万能力学试验机研究物料粒径、含水率、温度以及成型压强变化对物料密度和压缩功率的影响。试验结果表明:木屑在粒径较小时,颗粒间比表面积大,加强粘结剂和分子引力作用,成型效果较好;含水率增加会降低压缩功率,同时会导致成型质量降低,物料含水率为4%～12%时有较好的成型效果;提升物料温度在一定范围内可显著降低压缩功率,提高物料成型密度,温度也间接地改变物料含水率和粘结剂等因素来影响成型效果,在约100℃时成型效果最佳;增大压强有利于提高物料成型的质量,当压强达到100 MPa后,增加压强对成型起到的作用甚微,成型质量保持在相对稳定的水平。     

Biomass granular screw feeding: An experimental investigation

Successful feeding is critical to biomass utilization processes, but difficult due to the heterogeneity, physical properties and moisture content of the particles. The objectives of the present study were to find the mechanisms of blockage in screw feeding and to determine the effects of particle mean size (0.5-15 mm), size distribution, shape, moisture content (10-60%), density and compressibility on biomass particle feeding at room temperature. Wood pellets, sawdust, hog fuel and wood shavings were tested in a screw feeder/lock hopper system previously employed to feed sawdust into a pilot-scale circulating fluidized-bed gasifier. Experimental results showed that large particles, wide size distributions, large bulk densities and high moisture contents generally led to larger torque requirements for screw feeding. The “choke section” and seal plug play important roles in determining the torque requirements.     

Quality properties of pelletised sawdust,logging residues and bark

The dominant raw material for wood pellet production in Sweden is sawdust, planer shavings and dry chips. However, other types of biomass, such as bark and logging residues, are also interesting raw materials due to the large volumes available. These alternative raw materials differ from stemwood with regard to physical characteristics and chemical composition. In order to produce high-quality pellets of such materials, it is necessary to understand the role of these variations. Nine pellet assortments, made of fresh and stored sawdust, bark and logging residues (a mixture of Norway spruce and Scots pine) were tested for moisture content, heating value and contents of ash, sulphur, chlorine and Klason lignin. Dimensions, bulk density, density of individual pellets, durability and sintering risk were also determined. The heating value was highest in logging residue pellets. The ash content was highest in the bark and logging residue pellets, implying higher sintering risk compared with sawdust pellets. The results showed that bark pellets had the highest durability, whereas sawdust pellets had the lowest. Pellet density had no effect on durability, unlike lignin content which was positively correlated. It is concluded that bark and logging residues are suitable raw materials for pellets production, especially if the ash content is controlled.     

Optimisation of the manufacturing variables of sawdust pellets from the bark of Pinus caribaea Morelet: Particle size, moisture and pressure

Different variables affect the processes of compacting biomass, and these variables depend on the raw material, such as the type of wood or type of biomass being compacted, its moisture, size, as well as on other aspects relating to the manufacturing process, such as the pressure applied and the temperature reached during compaction.This work analyses the influence of the size of the sawdust particles from the bark of the species Pinus caribaea var. Morelet, which ranges from 0.63 to 2 mm; it had a moisture content in dry basis of 6; 9.5; 13 and 20%; and the force applied in the laboratory was 8000, 12,000, 16,000 and 20,000 N. These values are relatively high given that they do not take into account the heat caused by the matrixes chafing with the material to be compacted, as occurs in industrial processes.The different experimental treatments were processed and statistically analysed using SSPS version 12.0, and Statgraphics version 5.0. Once the data had been tested in the ANOVA and in various comparison tests, it was observed that the results did not show any significant differences between the pellets obtained with forces of 16,000 and 20,000 N, or between pellets obtained with 9.5 and 13% moisture, and that the pellets with higher qualities were obtained from particle sizes of between 1 and 2 mm.     

Effect of process parameters and raw material characteristics on physical and mechanical properties of wood pellets made from sugar maple particles

The aim of the current study was to investigate the influence of process parameters and raw material characteristics on physical and mechanical properties of wood pellets made from particles of sugar maple trees of different vigor. Pellets were made in a single pelletizer while controlling temperature (75, 100 and 125 °C), moisture content (8.1, 11.2 and 17.2%), compression force (1500, 2000 and 2500 N) and particle size (<0.25, 0.25–0.5 and 0.5–1.0 mm). Particle size was the most important factor influencing friction in the die, followed by moisture content, compression force and temperature. Moisture content was the most important factor affecting pellet density, followed by temperature, compression force and raw material particle size. Temperature was the most important factor for pellet compression strength, followed by compression force, particle size and moisture content. Friction in the die decreased with increasing particle size and moisture content of the material and increased with increasing compression force. It decreased initially with increasing temperature from 75 °C to 100 °C, and then increased with temperature. Density and strength of pellets increased with temperature and compression force, decreased with increasing particle size, and decreased with increasing moisture content. Pelletizing should be performed at 100 °C to minimize friction and a moisture content of 11.2% to maximize density and compression strength of the pellets. Wood particles from sugar maple trees of low vigor were more suitable for making wood pellets in terms of friction in the pelletizer and compression strength than those from vigorous trees.     

微波热解生物质废弃物的研究

利用微波热裂解生物质废弃物,使其转化为可直接利用的能源,是一种非常重要的处理工艺。运用自行研发的单模谐振腔微波设备对生物质废弃物进行热解反应试验,考察了微波功率、反应时间、含水率和物料粒径对木屑热解的影响,得到较优的反应工艺条件:微波功率为2.0 kW,反应时间为8 min,含水量为20%,物料粒径为0.5~0.8 mm。分析研究了固、液、气3种热解产物:固体产物(炭)的性质得到了改善;生物油主要是芳香烃类化合物和呋喃类化合物的复杂混合物;热解气体产物主要为CO,CO2,甲烷等,热值相对较高。     

Energy efficient pilot-scale production of wood fuel pellets made from a raw material mix including sawdust and rapeseed cake

Presently, most fuel pellets are made from sawdust or shavings. In Sweden, these materials are used to the maximum extent. As the demand for pellets increases, the supply of sawdust will be insufficient and other raw materials or mixes of raw materials will be used. This work investigates sawdust mixed with rapeseed cake. The latter is a residual product from the production of chemically unmodified oil refined from cold-pressed rape oil. At the Department of Energy, Environmental and Building Technology at Karlstad University, Sweden, a complete pilot-scale pellet production unit is located. The pellets are produced and tested for mechanical durability, length, bulk density and moisture content according to the Swedish Standard for pellets. During production, the load current, the die pressure and the die temperature were measured along with other parameters. The main purpose was to examine how the mixture of rapeseed cake and pine sawdust affected the energy consumption of the pelletising machine and mechanical durability of mixed fuel pellets. The results show that the energy consumption decreased and the amount of fines increased with increasing rapeseed cake in the wood fuel pellets. These results indicate that we must compromise between a decrease in the use of energy and a decrease in durability.     

Industrial processes for biomass drying and their effects on the quality properties of wood pellets

This paper contributes to the discussion of how different kinds of industrial scale dryers for biomass influence the quality properties of wood pellets. It also discusses how the drying technique can affect the environment. The most common biomass drying processes in use, i.e., convection dryers are discussed. The discussion of drying techniques is based on advantages and disadvantages with a focus on the drying medium, temperature and residence time. The choice of drying technique is particularly important if the end-user’s choice of pellets is made due to the specific requirements for the heating system used. Some specific parameters were tested in order to investigate how the choice of drying technique affects the pellet quality. The parameters tested were moisture content and the emissions of volatile hydrocarbons. Pellets available on the market were chosen for the tests. The amount of volatile hydrocarbons left in sawdust after drying vary with drying technique, as emissions of terpenes are larger in dryers with long residence times. Low emissions of volatile hydrocarbons would improve the energy content of the sawdust, and by decreasing air pollution improve the work environment and the environment in the surroundings of the dryers.     

Effects of compressive force,particle size and moisture content on mechanical properties of biomass pellets from grasses

Mechanical properties of wheat straw, barley straw, corn stover and switchgrass were determined at different compressive forces, particle sizes and moisture contents. Ground biomass samples were compressed with five levels of compressive forces (1000, 2000, 3000, 4000 and 4400 N) and three levels of particle sizes (3.2, 1.6 and 0.8 mm) at two levels of moisture contents (12% and 15% (wet basis)) to establish compression and relaxation data. Compressed sample dimensions and mass were measured to calculate pellet density. Corn stover produced the highest pellet density at low pressure during compression. Compressive force, particle size and moisture content significantly affected the pellet density of barley straw, corn stover and switchgrass. However, different particle sizes of wheat straw did not produce any significant difference on pellet density. The relaxation data were analyzed to determine the asymptotic modulus of biomass pellets. Barley straw had the highest asymptotic modulus among all biomass indicating that pellets made from barley straw were more rigid than those of other pellets. Asymptotic modulus increased linearly with an increase in compressive pressure. A simple linear model was developed to relate asymptotic modulus and maximum compressive pressure.     

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.