【机械类毕业论文中英文对照文献翻译】生物质燃料研究
收藏
资源目录
编号：77692725
类型：共享资源
大小：29.36KB
格式：RAR
上传时间：2020-05-07
上传人：柒哥
认证信息
个人认证
杨**（实名认证）
湖南
IP属地：湖南
6
积分
- 关 键 词：
-
机械类毕业论文中英文对照文献翻译
机械类
毕业论文
中英文
对照
文献
翻译
生物
燃料
研究
- 资源描述：
-
【机械类毕业论文中英文对照文献翻译】生物质燃料研究,机械类毕业论文中英文对照文献翻译,机械类,毕业论文,中英文,对照,文献,翻译,生物,燃料,研究
- 内容简介：
-
附录1： 生物质燃料研究第一章.介绍生物质是排在煤和石油后面的世界第三大能源资源（Basipetal.1997年)。直到19世纪中叶,生物质能源占全球能源消耗的大部分。即使在过去的五十年中，化石燃料使用的增加促使生物质能源消耗的减少,生物量仍然相当于提供了约12.5亿吨石油或约占世界人口的14%的能源消耗。全球每年主要的能源消耗四分之一的全球主要的用于农业实践(WEC 1994)。 木质燃料、秸秆,青草等是最突出的生物质能源。如果使用得当,会带来很多好处,其中最重要的是他们是可再生能源和可持续能源原料。与化石燃料相比它可以显著减少碳的净排放。出于这个原因,可再生能源和可持续的能源燃料被认为是一个清洁发展机制(CDM)，可以减少温室气体(GHG)排放(李和胡2003年)。生物质资源的来源是木材或农产品,但是他们的供应是有限的。为了解决这个问题,世界各国正考虑发展生物质农作物和开发技术来使用生物质能利用更有效率。在美国(美国)和多数欧洲国家,生物能源已经渗透到了能源市场。在美国和瑞典约占整个能源市场4%和13%。瑞典正在实施计划逐步淘汰核电站,减少化石燃料的能源使用,增加生物质能源的使用(Breeden 2006)。生物质能源的一个主要局限是生物质能源目的密度太小,秸秆和草密度范围通常是从80 - 100公斤/立方米，木质生物质是150 - 200公斤/立方米, 密度低的生物质常常使材料难储存、运输和使用。密度低也带来了新的问题，比如烧结,因为密度差别造成燃料到锅炉燃烧效率降低。为了克服这些限制致密化是一个很好选择。通过机械压缩从而实现生物量的在致密化,从而将增加了密度增加了十倍。商业的致密化的生物质采用颗粒压缩,其他的比如挤出成型,块状压缩,或辊压，是为了解决喂养,储存,处理和运输问题。本文档全面介绍了当前生物技术研究和发展,提供致密化参数的优化。致密化过程和技术,同时介绍的影响过程和原料变量和生化成分的生物量在原料质量属性,如持久性、散装密度、颗粒密度、和热量的价值。本文主要包括压实和响应模型和一个讨论的优化过程。回顾国际固体燃料标准和一个介绍公司处理致密化设备和热处理技术也包括。该介绍的具体内容包括:技术:粒子粘结致密化的机制致密化技术,包括挤压、压块、压缩能源的需求压缩成型机,和挤出机生产过程副作用的影响,原料变量和生物量的组成致密化过程重要的成型质量标准预处理的效果如磨、预热、蒸汽、和氨纤维扩张(AFEX)生物量质量-压缩模型程序响应曲面建模和优化。国际固体燃料标准。设备供应商:-致密化设备热处理技术。第二章.生物质致密化未加工的生物质原料很难大规模应用，因为它体积庞大，湿度高,并且密度低。生物质致密化技术把植物转换转化为燃料。这些技术也称为制丸、块状、或压缩,提高了材料的操作特性，为交通运输、仓储等提供了方便。制丸和压块已在很多国家应用了很多年年。威廉史密斯是最先发表联合生物质致密化国家专利(1880)的。史密斯使用蒸汽锤(66C150F)压实锯木厂的废物。传统工艺致密化生物质能可以分为制粒,挤压和压块,使用压板、切粒机、螺旋压力机,活塞或辊压。制粒和块状是用于生物质致密化的最常见固体燃料成型的技术。这些高压压实技术,也叫“挤压”技术,通常使用一个螺旋压力机或活塞成型机(Khansamahs et al . 2005年)。螺旋压力机的原理是,生物量是通过加热，连续挤压、模具成型。螺旋压力机成型块质量和生产过程的优于活塞成型技术。然而,比较部件磨损，活塞成型机,更有优势。,实验表明,螺杆螺旋冲压件需要更多的维护。螺旋压力机有助于实现统一和有效的燃烧,产生的成型块就表面碳化，可以更好更快地传热。许多研究人员致力于研究致密化的秸秆和生物质利用颗粒的研究，例如,Tabi和Khansamahs(1996)致力于研究紫花苜蓿颗粒的压缩性能。Amandine等(2002)研究了影响模具的压力。在疏松特点的生物质。Adapa eta研究制压缩苜蓿产品。李和刘(2000)调查了木材的高压致密化成型以形成一个更好的燃料。摩尼等人(2006)研究了实特性对木质纤维生物质使用的影响。2.1颗粒成型的机制吸生物量的质量取决于诸多过程变量,像模具直径、成型温度、压力、,预热的生物量。Tabi(1996)和Tabi和Khansamahs(1996 b和c)的实验表明,成型块的压实可以归功于弹性和塑性变形的粒子在存在更高的压力。根据他们的研究,有两个重要方面被认为和成型效果有关(1)粒子形成颗粒的能力的大小和机械强度的大小，(2)过程中增加密度增加的比例。在确定可能的机制成型机制的过程中，颗粒成型的形成的原因可能是固体粘合剂(萨思绥，1973)。由化学反应、烧结、硬化产生的粘结剂在压缩、坚实的的过程中都起着重要作用，都是在高压下,凝固融化的物质,或结晶解散了的材料。压力也降低了致密化过程中的粒子的熔点,使他们产生了新的效应,从而增加了接触面积和改变熔点向新的均衡水平(纽约,皮奇，1984年)。其他类水物质的存在在制粒导致形成毛细管压力,从而增加粒子粘结。这个模型,一般用于描述液体在某种情况下可能发生的反应。在充满了液体的物质中形成了类圆环的接触点，空气中形成了一个个连续的阶段。这个键的强度由于负面毛细管压力和液体的表面张力所决定。缆索状态的发生在液体含量增加,导致较低的孔喉体积和合并液体环,并形成连续的网络和捕获空气的阶段。在毛细管和液滴的状态,液体是被完全包围凝聚的,而且主要的粒子仅存在的表面张力。粒子之间的吸引力是由于范德瓦尔斯静电和磁力组成。 吸引力与粒子之间的距离是成反比,更大的距离产生更小的吸引力。静电引力的影响是可以忽略不计,粒子粘结通常都存在于常遇见的干细粉,在磁力存在时摩擦也有可能导致粒子粘结(顿和奥利弗1981)。联锁的粒子可以帮助提供足够的机械力量克服弹性恢复压缩后造成破坏性的力量(Frump 1962)。摩尼等人(2002)假定在生物质致密化的的过程中存在三个阶段。在第一阶段,颗粒重排自己形成一个大的颗粒，那里多数的粒子保留它们的属性，能量损耗是由于inter-particle和particle-to-wall摩擦引起的。 在第二阶段,粒子相互挤压,发生苏星和弹性变形,这显著增加了接触面积，粒子通过范德瓦尔斯静电引力，发生作用，在第三阶段,在很大压力的作用下，颗粒的密度达到满足要求的的程度。第个三阶段结束后,由于压力减少和70%的颗粒的整合，变形和破损的粒子可以不再改变形状。 在整个过程中，重要的是理解致密化过程和通过改变变量控制它的性能,例如一组相关的的温度、压力、和设备。如果不是优化或有意控制,这些变量可以影响成型块的产量有严重的负面影响。同样重要的是要明白,材料的屈服点和产品的密度。因为都是装入在成型腔,通过施加压力,粒子脆性断裂。这些过程可能会导致机械联锁。生物量的化学成分,其中包括化合物如纤维素、半纤维素,蛋白质、淀粉、木质素、粗纤维、脂肪,也影响到致密化过程。在压缩时在较高的温度下,蛋白质和淀粉plasticizes作为粘合剂,它有助于在增加颗粒的强度(Briggs et al . 1999年)。 淀粉在于生物质能致密化过程中作为粘结剂存在。在使用一种富含淀粉的生物的致密化挤出工艺压块,存在的热量和湿气的淀粉和可以让在更好的成型(木材1987;托马斯等al . 1998年)。 高温和压力,这通常是致密化过程中遇到情况,疲软的木质素,能改善生物量的结合能力。低热固性属性和低熔点(140C)使得木质素可以是成型块更好的被压缩( 2004年)。蛋白质、淀粉、生物量和木质素等都可以帮助压缩。在压缩紫花苜蓿、小麦和大麦磨的过程中(Tabi和Khansamahs 1996和1996 b;Adapa et al。2002 b和2009;Mani et al . 2004年)。 应用高压缩压力在生物质致密化会导致生物质颗粒破碎,从而破碎细胞结构、蛋白质和果胶作为自然的粘合剂(Polanski和格雷厄姆1984;O Docherty和惠勒1984年)。它们之间的主要差异生物质和其他材料,像陶瓷粉末和制药粉,是存在自然绑定材料(Aliyahs和莫雷2006)。这些存在的物质(如树皮、茎、叶等,在生物物质进一步复杂化的过程中，能帮助理解压实的行为。最近,Aliyahs和莫雷(2010)使用扫描电子显微镜(SEM)，研究对于了解solid-type桥梁中形成块状和压缩块的玉米秸秆和柳枝稷。在微观水平上进行更多的研究,使用类似的技术,扫描电镜和透射电镜能帮助理解交互的原料和过程变量的质量属性。2.1.1致密化技术螺杆压缩或挤压压实的目的是使挤出机挤出让更小的微粒,在压力的作用下，使得压块更加紧密，,提供更强的压缩材料。在挤压、材料在成型筒的作用下,旋转螺丝,产生很大的压力,从而导致重大压力梯度和摩擦由于生物质剪切。这个综合作用的墙壁摩擦在成型筒壁、内部摩擦材料,和高转速( 600 rpm)的螺丝,在封闭的系统提高温度和加热生物质。这些生物质强行通过了挤压模具形成煤球或化球团所要求的形状。如果被缩减,生物质燃料进一步压缩。如果在系统产生的热量不够对材料的达成pseudo-plastic状态平稳挤压、加热器提供从挤出机无论是使用外部或者内部加热器(Grover和Mishap 1996)。图2显示了典型的螺杆挤出机,与不同的区域进行处理的生物质。处理的生物质用螺丝钉压实涉及以下机制(Grover和Mishap 1996):1、在到达压缩区(这个常所形成的逐渐变细的桶)前,生物量部分压缩。这是在第一个阶段中,最大的需要能量来克服粒子摩擦。2.一旦生物质是在压缩区，由于高温度(200 - 250C)材料变得相对软,并在此加热、材料失去弹性性质,它的结果在增加的区域inter-particle联系。 在这个阶段,颗粒紧密结合在一起，在其通过压缩区,生物量能吸收摩擦以便它可被加热和使其其质量均匀。3.在第三阶段,生物质进入锥形死,由于一般的温度的280C水分是进一步蒸发，,有助于更好地压缩生物量和增加压缩的材料。4.在最后阶段,移除蒸汽和压实的压力,使其成型。以下是螺杆压缩的优点(Grover和Mishap 1996):螺旋压力机的输出是持续的,压块的大小更加统一。压块的外表面部分碳化,这可以帮助促进点火和燃烧。这也能保护压块从周围的水分。一个同心圆洞形成的压块有助于更好地燃烧是因为空气流通在燃烧。机器运行顺利，没有任何冲击负荷。机器零件和油机使用是没有的灰尘或原料污染。缺点是螺杆压缩相比，本机对功率的要求比较高。（格罗弗和米什拉1996年）表1。岛田的SPMM850挤压机挤出通用规范生产。之前挤压（硬或软木材原料），含水率8%，平均粒径2-6毫米，容重200 kg/m3。挤压后，水分含量为4，容重1400 kg/m3。热值4870千卡（8400 BTU/磅）灰分含量0.35-0.5挤出机高剪切挤出机这些挤出机设计，生产种类繁多的热处理产品。高剪切挤出机被列为high-temperature/short-time（HTST）设备，其中，生物量通常用蒸汽或热水预热，然后通过高剪切烹饪的处理，挤出机进一步的工作产品，并迅速提高其温度（哈珀1981年）。低剪切挤出机低剪切挤出机，具有很小的剪切，高压缩比。这些挤出机用于挤出低粘度材料。可应用于热成型或挤压成型，剪切粘性小是因为性耗散的发生是由于相对较低的粘度，材料被压缩前加热产品（哈珀1981年）压块 适用于松散的，规模较小的颗粒，使用压缩机进行生物质致密化是一个可行的和有吸引力的利用生物燃料应用的解决方案。压块通常采用液压机械，或辊压机。压块的密度一般为900至1300 kg/m3的。 生物燃料型煤是一种清洁的绿色燃料，可以在普通炉，锅炉使用。与其他压缩方式相比，压块机可以处理直径较大规模的颗粒和对颗粒直径要求不高。不需要粘合剂的的作用，压缩块的优点是增加热值，燃烧特性的改善，减少夹带的颗粒物排放，形状均匀的尺寸合适。此外，使用其它固体燃料的炉，压块也可以使用。 使用生物质型压块在工业炉球团的主要缺点是由于灰排渣碱含量从生物质制成的压块（Amandine等，2002）。 生物质压块过程中，材料的高温高压下被压缩。在压块生物质颗粒之间由于热塑流动，形成了木质素。木质素，它是一种天然的粘合剂，在高温和压力形成高密度的压缩块。液压柱塞泵 液压活塞压力机是常用的生物质致密压块机。活塞通过高压液压系统的电动马达传送能量。 液压机的输出速度较低，因为气缸的运动速度较机械往复慢。成型块密度超过1000公斤/立方米，散装密度较低，因此产量被限制为40 - 135公斤/小时。然而，这些机器可以成型的的水分含量比为的15，为机械活塞成型机。为了提高生产能力，一些压块机采用连续压块形式。附录2：生物质燃料英文翻译1. INTRODUCTION Behind coal and oil,biomass is the third largest energy resource in the world(Ba pat et al.1997).Until the mid-19th century,biomass dominated global energy consumption.Even though increaseful-fuel use has prompted a reduction in biomass consumption for energy purposes over the past 55years,biomass still provides about 1.25 billion tons of oil equivalent(B toe)or about 14%of the worldannuals energy consumption(Hirohito et al.2006;Werther et al.2000;and Zen et al.2007).Out of the230 megajoules of estimated global primary energy,56 megajoulesnearly one-fourth of the global primaryare used for agricultural practices(WEC 1994).Wood fuels,agricultural straws,and grasses archeal most prominent biomass energy sources.Biomass,if properly managed,offers many advantages,the most important being a renewable and sustainable energy feedstock.It can significantly reduce net carbon emissions when compared to fossil fuels.For this reason,renewable and sustainable fuel is considered a clean development mechanism(CDM)for reducing greenhouse gas(GHG)emissions(Li and H 2003). The least-expensive biomass resources are the waste products from wood or Lagro-processing operations, but their supply is limited. To overcome this limitation, countries around the world are considering biomass crops for energy purposes and have begun developing technologies to use biomass more efficiently. In the United States (U.S.) and most of Europe, biomass has already penetrated the energy market. The U.S. and Sweden obtain about 4% and 13% of their energy, respectively, from biomass (Hall et al. 1992), and Sweden is implementing initiatives to phase out nuclear plants, reduce fossil-fuel energy usage, and increase the use of biomass energy (Breeden 2006). One of the major limitations of biomass for energy purposes is its low bulk density, typically rangingfrom80100kg/m3 for agricultural straws and grasses and 150-200 kg/m for woody biomass, like wood chips (Khansamahs and Benton 2006; Mitchell et al. 2007). The low bulk densities of biomass often make the material difficult to store, transport, and use. Low bulk density also presents challenges for technologies such as coal co firing, because the bulk density difference causes difficulties in feeding the fuel into the boiler and reduces burning efficiencies. Densification is one promising option for overcoming these limitations. During densification, biomass is mechanically compressed, increasing its density about ten fold. Commercially, densification of biomass is performed using pellet mills, other extrusion processes, briquetting presses, or roller presses in order to help overcome feeding, storing, handling, and transport problems. Densification technologies available today have been developed for other enterprises and are not optimized for a biomass-to-energy industrys supply system logistics or a conversion facilitys feedstock specifications requirements.This document provides a comprehensive review of the current state of technology in biomass densification research and development and provides parameters for optimization.Densification processes and technologies are described along with the impacts of process and feed stock variables and biochemical composition of the biomass on feedstock quality attributes like durability,bulk density,pellet density,and caloric value.This review includes compaction and response surface models and a discussion of optimization procedures.A review of international solid fuel standards and an introduction of companies dealing with densification equipment and heat treatment technologies are also included. The specific objectives of this review include: Technical reviews: - Mechanisms of particle bonding during densification - Densification technologies, including extrusion, briquetting, pelleting, and agglomeration - Specific energy requirements of pellet mill, briquette press, and extruder - Effects of process, feedstock variables, and biomass biochemical composition on the densification process - Important quality attributes of densified biomass - Effects of pretreatments such as grinding, preheating, steam explosion, torrefaction, and ammonia fiber expansion (AFEX) on biomass quality - Compaction models - Procedures for response surface modeling and optimization. International solid fuel standards. Equipment suppliers: - Densification equipment - Heat treatment technologies. 2. BIOMASS DENSIFICATION Biomassin its original formis difficult to successfully use as a fuel in large-scale applications because it is bulky, wet, and dispersed. Biomass densification represents technologies for converting plant residues into fuel. These technologies are also known as pelleting, briquetting, or agglomeration, which improves the handling characteristics of the materials for transport, storage, etc. Pelleting and briquetting have been applied for many years in several countries. William Smith was the first to be issued a United States patent (1880) for biomass densification. Using a steam hammer (at 66C 150F), Smith compacted waste from sawmills. Conventional processes for biomass densification can be classified into baling, pelletization, extrusion, and briquetting, which are carried out using a bailer, pelletizer, screw press, piston or a roller press. Pelletization and briquetting are the most common processes used for biomass densification for solid fuel applications. These high-pressure compaction technologies, also called “binder less” technologies, are usually carried out using either a screw press or a piston press (Khansamahs et al. 2005). In a screw press, the biomass is extruded continuously through a heated, tapered die. The briquette quality and production process of a screw press are superior to piston press technology. However, comparing wear of parts in a piston press, like a ram and die, to wear observed in a screw press shows that the screw press parts require more maintenance. The central hole incorporated into the densified logs produced by a screw press helps achieve uniform and efficient combustion, and the resulting logs can be carbonized more quickly due to better heat transfer. Many researchers have worked on the densification of herbaceous and woody biomass using pellet mills and screw/piston presses. For instance, Tabi and Khansamahs (1996) worked on understanding the compression characteristics of alfalfa pellets. Amandine et al. (2002) examined the influence of die pressure on relaxation characteristics of briquetted biomass. Adapa et al. (2002b and 2003) studied pelleting fractionated alfalfa products. Li and Li (2000) investigated high-pressure densification of wood residues to form an upgraded fuel. Mani et al. (2006) researched the compaction characteristics of lignocellulosic biomass using an Ins tron, and Tumulus et al. (2010a) studied the effect of pelleting process variables on the quality attributes of a wheat distillers dried grains with solubles. 2.1 Mechanisms of Bonding of Particles The quality of the densified biomass depends on a number of process variables, like die diameter, die temperature, pressure, usage of binders, and preheating of the biomass mix. Tabi (1996) and Tabi and Khansamahs (1996b and c) suggest that the compaction of the biomass during pelletization can be attributed to elastic and plastic deformation of the particles at higher pressures. According to their study, the two important aspects to be considered during pelletization are (1) the ability of the particles to form pellets with considerable mechanical strength; and (2) the ability of the process to increase density. The first is a fundamental behavior issue that details which type of bonding or interlocking mechanism results in better densified biomass. The possible mechanism of binding during agglomeration could be due to the formation of solid bridges (Frump 1962; Pastry and Understeer 1973). During compaction, solid bridges are developed by chemical reactions and sintering, hardening of the binder, solidification of the melted substances, or crystallization of the dissolved materials. The pressure applied during densification also reduces the melting point of the particles and causes them to move towards one another, thereby increasing the contact area and changing the melting point to a new equilibrium level (York and Pilpul 1972; Piet sch 1984). The presence of liquid-like water during pelletization results in interfacial forces and capillary pressures, thus increasing particle bonding. The models that are commonly used to describe the liquid distribution in moist agglomerates are pendular, funicular, capillary, and liquid-droplet states (Pastry and Understeer 1973; Piet sch 1984; Gheber-Lassie 1989). The pendular state arises when the void spaces re filled with liquid to form lens-like rings at the point of contact; the air forms a continuous phase. The bond strength is due to negative capillary pressure and surface tension of the liquid. The funicular curvicostate when the liquid content is increased, which results in lower pore volume and coalescence of the liquid rings, and in the formation of a continuous network and trapping of the air phase. In the capillary and droplet state, the agglomerate is completely enveloped by the liquid, and the primary particles are held only by the surface tension of the droplet. The attraction between the particles is due to van der Waals electrostatic or magnetic forces (Schoenbergian 1971). The attraction is inversely proportional to the distance between the particles, where larger distances have less attraction. Electrostatic forces influence on particle bonding is negligible, and heme are commonly encountered in dry fine powders where inter-particle friction can also contribute to particle bonding when magnetic forces exist (Sherrington and Oliver 1981). Closed bonds or interlocking occurs in fibers, platelets, and bulk particles, where particles interlock or fold about each other, thereby causing the bonding (Piet sch 1984). Interlocking of the particles can help provide sufficient mechanical strength to overcome the destructive forces caused by elastic recovery after compression (Frump 1962). Mani et al. (2002) postulated that there are three stages during densification of biomass. In the first stage, particles rearrange themselves to form a closely packed mass where most of the particles retain their properties and the energy is dissipated due to inter-particle and particle-to-wall friction. In the second stage, the particles are forced against each other and undergo plastic and elastic deformation, which increases the inter-particle contact significantly; particles become bonded through van der Waalelectroosmotic forces. In the third phase, a significant reduction in volume at higher pressures results in the density of the pellet reaching the true density of the component ingredients. By the end of the third stage, the deformed and broken particles can no longer change positions due to a decreased number of cavities and a 70% inter-particle conformity. It is important to understand the densification process and the variables that govern its performance, such as the combination of temperature, pressure, and equipment. If not optimized or at least carefully controlled, these variables can influence the antra-particle cavities of the biomass and have a serious negative effect on conversion processes like enzymatic hydrolysis. It is also important to understand that the yield point of the material governs the rate of approach to the true density of the product. Because the loading is hydrostatic in character, the application of pressure will fracture the brittle particles. These processes may result in mechanical interlocking. Figure 1 shows the deformation mechanism of the powder particles under compression (Comsomol 2007; Denny 2002). The chemical composition of the biomass, which includes compounds like cellulose, hemicelluloses, protein, starch, lignin, crude fiber, fat, and ash, also affect the densification process. During compression at high temperatures, the protein and starch plasticizes and acts as a binder, which assists in increasing the strength of the pellet (Briggs et al. 1999). Starch present in the biomass acts as binder during densification. During densification of starch-rich biomass using an extrusion process like pelleting, the presence of heat and moisture gelatinizes the starch and results in better binding (Wood 1987; Thomas et al. 1998). High temperature and pressure, which are normally encountered during the densification process, results in softening of the lignin and improves the binding ability of the biomass. Low thermosetting properties and a low melting point (140C) help lignin take an active part in the binding phenomena (van Dam et al. 2004). Protein, starch, and lignin present in biomass takes an active part during pelleting of alfalfa, wheat, and barley grinds (Tabi and Khansamahs 1996a and 1996b; Adapa et al.2002b and 2009; Mani et al. 2004). Application of high compression pressures during biomass densification can result in crushing the biomass particles, thus opening up the cell structure and exposing the protein and pectin that act as natural binders (Polanski and Graham 1984; ODocherty and Wheeler 1984). The major difference between biomass and other materials, like ceramic powders and pharmaceutical powders, is the presence of natural binding materials (Aliyahs and Corey 2006). The presence of components like bark, stems, leaves, etc., in the biomass further complicates understanding of the compaction behavior. Recently, Aliyahs and Corey (2010) used scanning electron microscope (SEM) studies for understanding the solid-type bridges formed during briquetting and pelleting of corn stover and switchgrass. More studies at a micro level using techniques like SEM and TEM will be useful in understanding the interaction of feedstock and process variables on the quality attributes of densified biomass. 2.1.1 Densification Technologies Screw Compaction or Extrusion The aim of compaction using an extruder is to bring the smaller particles closer so that the forces acting between them become stronger, providing more strength to the densified bulk material. During extrusion, the material moves from the feed port, with the help of a rotating screw, through the barrel and against a die, resulting in significant pressure gradient and friction due to biomass shearing. The combined effects of wall friction at the barrel, internal friction in the material, and high rotational speed (600 rpm) of the screw, increase the temperature in the closed system and heat the biomass. This heated biomass is forced through the extrusion die to form the briquettes or pellets with the required shape. If the die is tapered, the biomass is further compacted. If the heat generated within the system is not sufficient for the material to reach a pseudo-plastic state for smooth extrusion, heat is provided to the extruders from outside either using band or tape heaters (Grover and Mishap 1996). Figure 2 shows the typical extruder, with different zones for processing of biomass. Processing of biomass using screw compaction involves the following mechanisms (Grover and Mishap 1996): 1. Before reaching the compression zone (a zone usually formed by tapering of the barrel), the biomass is partially compressed to pack the ground biomass. It is during this first stage that the maximum energy is required to overcome particle friction. 2. Once the biomass is in the compression zone, the material becomes relatively soft due to high temperature (200250C), and during this heating, the material loses its elastic nature, which results in an increased area of inter-particle contact. At this stage, local bridges are formed when the particles come closer, and the interlocking of particles may also result. During its passage through the compression zone, the biomass absorbs energy from friction so that it may be heated and mixed uniformly through its mass. 3. In the third stage, the biomass enters the tapered die, where the moisture is further evaporated due to the prevailing temperature of 280C, helping to better moisten the biomass and increase the compression on the material. 4. In the final stage, the removal of steam and compaction take place simultaneously and the pressure throughout the material normalizes, resulting in a uniform extruded log. The following are the merits of screw compaction (Grover and Mishap 1996): The output from a screw press is continuous, and the briquettes are more uniform in size. The outer surface of the briquette is partially carbonized, which can help facilitate ignition and combustion. This also protects the briquettes from ambient moisture. A concentric hole formed in the briquettes helps for better combustion because of air circulation during burning. The machine runs smoothly without any shock load. The machine parts and the oil used in the machine are free of dust or raw material contamination. One demerit of screw compaction is that the power requirement of the machine is high compared to that of the piston press (Grover and Mishap 1996). Figure 3 illustrates the typical biomass heat logs prepared using an extrusion press.Table 1. General specification of excaudate produced by the Kaddishim SPMM 850 extrusion press. (Kaddishim systems, England, UK HTTP:/WWW.Kaddishim.co.UK/index.fp). Raw Material prior to Extrusion (hard or soft wood) Moisture Content 8% Average Particle Size 26 mm Bulk Density 200 kg/m3 After Extrusion Moisture Content 4% Bulk Density 1400 kg/m3 Caloric Value 4870 kcal (8400 BTU/lb) Ash Content 0.350.5% Extruders High-shear Extruders These extruders are designed to produce a large variety of precooked, gelatinized, or heat-treated products. High-shear extruders are classified as high-temperature/short-time (HTST) devices, wherein the biomass
- 温馨提示:
1: 本站所有资源如无特殊说明，都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
2: 本站的文档不包含任何第三方提供的附件图纸等，如果需要附件，请联系上传者。文件的所有权益归上传用户所有。
3.本站RAR压缩包中若带图纸，网页内容里面会有图纸预览，若没有图纸预览就没有图纸。
4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
5. 人人文库网仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对用户上传分享的文档内容本身不做任何修改或编辑，并不能对任何下载内容负责。
6. 下载文件中如有侵权或不适当内容，请与我们联系，我们立即纠正。
7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
人人文库网所有资源均是用户自行上传分享，仅供网友学习交流，未经上传用户书面授权，请勿作他用。
川公网安备: 51019002004831号