生物质烘焙预处理对气流床气化的影响

为考查生物质在烘焙预处理过程中的能量产率和颗粒研磨变化规律及对气流床气化总体效率的影响情况,在一套小型烘焙试验台上,对4种不同种类的生物质进行烘焙试验,并对固体产物研磨后进行粒径分析.最后通过小型生物质气流床进行气化试验.结果表明:生物质的能量密度随着烘焙温度的提高而升高,其中,中温烘焙(～250℃)能获得较好的固体和能量产率,减少能量损失;烘焙温度是烘焙过程中最重要的影响因素;烘焙可减少生物质研磨时的电耗,使其易磨;气流床气化试验中,烘焙生物质能够改善煤气成分,提高气化的总体效率.总之,在生物质气流床气化过程中,烘焙预处理能为生物质的粒径减小和随后的大规模利用提供了-个良好的解决途径.     

生物质原料烘焙预处理研究

烘焙预处理是生物质气化或混合煤炭燃烧之前的预热处理过程。综述国外研究资料的基础上,建立了包括质量产率、能量产率、高热值、氧碳比、含水量、研磨能耗等6项参数在内的综合评价指标和标准,研究了草芦、秸秆、松木屑、锯末、柳树木屑等生物质原料的烘焙预处理方式。研究发现:松木屑、锯末、秸秆的理想烘焙条件为:烘焙时间0.5h,烘焙温度依次为250~275℃、250℃、230~250℃;柳树木屑的理想烘焙条件为:烘焙时间1h、烘焙温度230℃。草芦在各烘焙条件下均无法达到标准水平。     

锯末水热生物炭特征研究

以锯末(sawdust,SD)生物质为原料,采用水热炭化法在温度170、200、230℃,时间15、30 min下制备水热生物炭,分析水热生物炭的产率、能量产率、热值、元素组成、表面官能团、表观形貌、平衡含水率等变化等特征。工业分析、元素分析表明,温度是影响水热炭化的重要因素。锯末水热生物炭随温度的升高、时间的延长,C含量增大,O含量降低;生物炭产率、能量产率降低,热值增加。当温度为230℃,时间为30 min时,得到生物炭产率为68.78%,能量产率为78.27%,热值为21.57 MJ/kg。范式图、红外光谱分析显示,在低温短时炭化时,转化过程以脱水、脱羰基为主。扫描电镜显示水热炭化能破坏生物质微观结构,水热生物炭表面光滑,锯末在170、200℃炭化后有缝隙结构,230℃表面出现孔洞结构。平衡含水率结果表明,水热炭化能提高锯末生物炭的疏水性质,有利于生物炭燃料的保存利用。     

烘焙预处理对秸秆热解产物品质及能量分布的影响

以玉米秸秆为原料,研究烘焙温度(220、250和280℃)对秸秆热解产物产率、品质和能量分布的影响。结果表明:秸秆经220、250和280℃烘焙后,热解生物油水分相比原样分别降低11.4%、28.3%和41.8%;与此同时,生物油中酸类产物逐渐减少,酚类产物逐渐增多,生物油热值明显增大。烘焙对热解气中CH_4和H_2有一定促进作用,可燃气的热值逐渐增大。烘焙对生物质炭的化学组分无明显影响,但随着生物质炭产率的增大,其能量产率逐渐增大。烘焙脱氧预处理可改善生物油的品质、提高可燃气的热值、增大生物质炭的能量产率。     

烘焙预处理对杉木成型燃料理化性质及热解特性的影响

以杉木成型燃料为原料,研究在不同烘焙温度(200℃、230℃、260℃和290℃)对其烘焙产物及热解特性的影响.结果表明:随着烘焙温度的升高,杉木成型燃料的质量产率和能量产率逐渐降低,跌落强度和耐久性逐渐减小,一些含氧官能团的吸收峰逐渐变弱,氧元素含量大幅降低而高位热值逐渐升高,疏水性明显增强.热解实验结果显示,在26...     

生物质混合物与褐煤共热解特性的试验研究

选取秸秆、稻壳、玉米芯、木屑、沙柳枝和叶、旱柳枝和叶、紫花苜蓿、芦苇、碱草等13种农业和林业废弃物、草木类等生物质，按相同比例混合为生物质混合物，采用热重分析仪分析研究该生物质混合物与某典型褐煤在不同混合比例下的共热解特性，计算了生物质挥发分析出终止温度并合理定义了褐煤挥发分析出温度。热解试验表明：不同比例的生物质混合物与褐煤在共热解过程中，热解产物的产率基本等于单独热解生物质和褐煤的产率加权平均值；生物质混合物的比例在20％～400％时，褐煤挥发分析出温度低于褐煤单独热解时挥发分析出温度，生物质中的高碱金属和CaO含量及H／C比较大等因素的存在具有一定的促进作用；生物质混合物的比例在50％以上时，由于生物质密度较小且易软化，阻碍煤挥发分的选出和扩散，使褐煤挥发分析出温度显著高于褐煤单独热解时挥发分初始析出温度，生物质对褐煤热解有抑制作用。     

温度对玉米秆烘焙及热解的影响

为了研究生物质烘焙后冷却速度对其表面形貌及后续热解产生的影响,以不同温度（200、230、260、290 ℃）对玉米秆进行烘焙,并用快速冷却（TF）与缓慢冷却（TS）两种方式进行降温处理。采用扫描电镜（SEM）观察烘焙前后样品的表面形貌发现,TS样品表面相比同一烘焙温度下TF样品及原样表面更加疏松;将烘焙前后样品放入热重分析仪中进行热解实验得出,随着烘焙温度的升高,样品的最大失重速率总体呈下降趋势;同一烘焙温度下,TS样品与TF样品的最大失重速率相差不大,290 ℃烘焙温度下TS样品的最大失重速率最慢,为2.94%/℃;在200、230、290 ℃烘焙温度下TS样品的热解活化能均小于TF样品,260 ℃时则相反,且其TS样品的活化能最高,达到100.43 kJ/mol。     

生物质制备燃料炭实验研究

利用管式固定床炭化装置对棉秆、木屑和竹屑进行炭化实验,利用工业分析仪、快速量热仪和热重分析仪对炭化实验制得的生物质炭进行分析,用木炭和烧烤炭质量指标评价生物质炭质量,用着火温度、燃尽温度和综合燃烧特性指数S评价生物质炭燃烧特性。结果表明:随着炭化温度的升高,生物质炭产率和干基挥发分产率减小、干基固定碳产率增大,相应的变化速率减小;着火温度和燃尽温度随着炭化温度的升高而升高,S值减小;相比木屑炭和竹屑炭,棉秆炭的燃烧特性最好。对比生物质炭与木炭和烧烤炭的燃烧特性和炭质量发现,木屑和竹屑可用于生产木炭替代品,棉秆可用于制作烧烤炭,500℃为棉秆制备烧烤炭的最佳炭化温度。     

烘焙对玉米秸秆碱金属释放动力学的影响

为研究烘焙对玉米秸秆碱金属释放动力学的影响,利用多点LIBS测量烘焙玉米秸秆燃烧过程中碱金属释放,并进行碱金属释放动力学模拟。结果表明,低温烘焙玉米秸秆燃烧时,在挥发分阶段释放至气相中的钾浓度高,在焦燃烧阶段钾释放浓度较低;高温烘焙玉米秸秆燃烧时,在挥发分阶段释放的钾浓度低,在焦燃烧阶段释放的钾浓度高。在挥发分阶段,碱金属释放动力学的活化能随烘焙温度升高,先升高后下降;在焦燃烧阶段,活化能随烘焙温度升高整体降低。     

烘焙对生物质热化学转化特性影响的研究进展

生物质是可再生能源的重要组成部分,储量巨大,但其含水量高、能量密度和热值低等缺点致使其研磨难度大、存储运输不便,难以资源化利用。本文对烘焙预处理技术的过程及特点、能耗分析和较为理想的烘焙标准进行了简述;并重点阐述了烘焙对生物质燃烧、热解和气化特性影响的研究进展。经烘焙处理后的生物质在炉膛内可快速、稳定燃烧,炉内温度迅速升高,产生的烟气量减少;热解产生的生物质焦油中水和乙酸含量明显减少,苯酚含量增加,热值总体升高;气化合成气品质明显提升,能量密度增大,总气化效率显著提高。此外,对烘焙预处理技术在城市固体废弃物处理的应用进行了简要的概述,并对其在生物质和城市固体废弃物研究方向上进行了展望。     

麦秆酶解残渣热解特性及动力学分析

对比分析了麦秆及其酶解残渣的基础物化特性,利用热重−红外联用技术研究了酶解残渣的热解反应过程及其主要气体产物的析出特性,并用混合反应模型计算了酶解残渣热解过程的表观动力学参数。结果表明,麦秆酶解残渣是一种富含木质素的高灰分、低热值的生物质原料,与麦秆原料相比,其热解过程相对平缓,主要失重温度区间为200℃ ~ 800℃,最大失重峰为350℃,与木质素的热解特性相近;提高升温速率可以使酶解残渣热解反应剩余产物质量明显减少,最大失重速率提高;热解主要气体产物中CH4析出的温度区间为400℃ ~ 700℃,CO和CO2在380℃、450℃和650℃都存在析出峰。动力学分析结果表明,酶解残渣热解过程在低温区（200℃ ~ 350℃）和高温区（350℃ ~ 800℃）分别遵循一级和二级反应动力学规律。     

中国南方典型农业生物质结渣特性实验研究

实验研究了广东省典型农业生物质稻杆、甘蔗渣/叶的燃烧结渣特性。采用GB/T212-2001和ASTM E1755标准进行灰化实验,采用角锥法和一步法检测生物质的熔融特性。实验结果证实ASTM的低温灰化标准更适合稻杆类高无机盐含量的生物质原料。稻杆中碱金属氧化物含量达20%以上,是导致灰渣粘结和熔融的主要因素。由于角锥法灰熔点检测法提前将部分碱金属和Cl元素转化和析出,导致检测结果远高于实际燃烧的熔融温度;相比而言,一步法更具有直观性和指导作用。通过一步法实验获得稻杆临界结渣温度为700℃ ~ 750℃,甘蔗渣为850℃ ~ 900℃,甘蔗叶为900℃ ~ 950℃。CaO和Al₂O₃添加剂对于生物质燃烧过程具有一定的抗结渣功能,CaO通过与SiO₂ (s) 反应生成高熔点的固态Ca₃Si₂O₇ (s) 和MgOCa₃O₃Si₂O₄ (s),因此能消耗物料周围的SiO₂ (s),抑制低温共融;Al₂O₃则通过生成高熔点温度的固态KAlSiO₄和固态KAlSi₂O₆,减少低温共熔现象的发生。     

An evaluation on improvement of pulverized biomass property for solid fuel through torrefaction

The improvement on physical and chemical properties of pulverized biomass from torrefaction is investigated to evaluate the potential of biomass as solid fuel used in boilers and blast furnaces. Three biomasses of bamboo, banyan and willow are considered. The results indicate that when the torrefaction temperature is relatively low such as 230 and 260 °C, the weight loss of biomass depends significantly on the temperature, as a result of consumptions of hemicellulose and cellulose. However, once the torrefaction temperature is as high as 290 °C, the weight losses of various biomass materials tend to become uniform. The decreased O/C ratio in biomass from torrefaction can be explained by intensified lignin content in that the O/C ratio in lignin is low compared to that in hemicellulose and cellulose. Furthermore, the enriched element C in torrefied biomass results in an increase in the calorific value of the torrefied materials. However, the enlarged higher heating value (HHV) of biomass from torrefaction cannot keep up with the weight loss; this leads to the decrease in total energy of biomass as the torrefaction temperature rises. The conducted correlation in predicting the HHV of raw biomass can also be utilized for torrefied biomass. The raw pulverized biomasses are characterized by agglomeration in the regime of smaller particle size. Once the biomasses undergo torrefaction, the dispersion of powder is improved, thereby facilitating the injection of biomass powder. This enhances the applications of pulverized biomass in boilers and blast furnaces.     

生物质成型燃料的热重分析及动力学研究

对三种生物质成型燃料在不同气氛下和不同升温速率下进行热重实验,研究反应条件对生物质成型燃料失重特性的影响规律,并对其空气气氛下的动力学特性进行了分析。研究结果表明,生物质在空气气氛下的挥发分析出速率比N₂气氛下高,随着温度升高,N2气氛下主要是纤维素、半纤维素以及木质素的分解,而空气气氛下还伴随有其分解产物的燃烧。生物质中挥发分含量较高时,反应活性也比较高。实验温度由室温升至800℃时,在升温速率为10℃/min ~ 25℃/min范围内,随着升温速率的升高,松木热重曲线先向低温区移动再向温度较高的一侧移动,最大失重速率对应的温度也表现出相同规律,当升温速率为20℃/min时最大失重速率对应的温度最低,升温速率为25℃/min时失重峰值最大。动力学特性分析表明,采用2组分动力学模型可以较好地表征生物质在空气中的失重特性,计算结果与实验结果吻合度较高。     

基于化工流程模拟平台的生物质移动床热解多联产系统模拟研究

在Aspen Plus平台上构建生物质移动床热解多联产系统模型,通过对秸秆热解过程的模拟,研究了生物炭、生物油和生物燃气三态热解产物特性,以及热解温度对系统燃料投入、水耗和电耗的影响。结果表明,随热解温度升高,生物炭热值逐渐增大。生物油和生物燃气的产率分别在450℃和650℃附近达到最大值。当热解温度为450℃时,生物油重质组分主要由糖衍生类和脂肪酸类物质构成,而轻质组分主要包括醛类、醇类和水;当热解温度为650℃时,生物燃气则主要由CO₂和CO构成。生产过程中,系统的燃料消耗和电耗均随着热解温度的升高而增大,冷却水消耗量则经历先减少后增加的过程,并在450℃附近达到最小值。     

Torrefaction of pine in a bench-scale screw conveyor reactor

Numerous works are reported in the literature regarding the torrefaction of biomass in batch processes. However, in industrial applications, continuous reactors and processes may by more interesting as this allows for the integration of continuous mass and heat flows. To shed light on the operation of continuous torrefaction processes, this work presents the findings of continuous, bench-scale (2.5 kg h⁻¹) torrefaction experiments using pine wood particles as a feed material in a screw conveyor reactor. The shifts in product mass yields were in line with theoretical expectations for changes in reactor temperature and reactor residence times whereas the degree of filling within the screw reactor and the flow of the nitrogen purge gas were found to be negligible. The process allowed for the measurement of the particle surface temperatures throughout the length of the reactor and significant temperature differences where measured between the wall of the reactor and the reactor screw. The proximate composition and the higher heating value of the torrefied biomass were found to be correlated to the ratio of the mass of dry biomass feed to the mass of the torrefied biomass produced. Important observations regarding the operability of such a process, also relevant to larger-scale processes, include the need to prevent the occurrence of torrefaction vapour condensation (which leaves the torrefaction reactor in the form of a saturated vapour) in the presence of fine, solid particles as this leads to rapid particle agglomeration and process blockage.     

A study on torrefaction of various biomass materials and its impact on lignocellulosic structure simulated by a thermogravimetry

Torrefaction processes of four kinds of biomass materials, including bamboo, willow, coconut shell and wood (Ficus benjamina L.), were investigated using the thermogravimetric analysis (TGA). Particular emphasis is placed on the impact of torrefaction on hemicellulose, cellulose and lignin contained in the biomass. Two different torrefaction processes, consisting of a light torrefaction process at 240 °C and a severe torrefaction process at 275 °C, were considered. From the torrefaction processes, the biomass could be divided into two groups; one was the relatively active biomass such as bamboo and willow, and the other was the relatively inactive biomass composed of coconut shell and wood. When the light torrefaction was performed, the results indicated that the hemicellulose contained in the biomass was destroyed in a significant way, whereas cellulose and lignin were affected only slightly. Once the severe torrefaction was carried out, it further had a noticeable effect on cellulose, especially in the bamboo and willow. The light torrefaction and severe torrefaction were followed by a chemically frozen zone, regardless of what the biomass was. From the viewpoint of torrefaction application, the investigated biomass torrefied in less than 1 h with light torrefaction is an appropriate operation for producing fuels with higher energy density.     

Effects of torrefaction on the physiochemical properties of oil palm empty fruit bunches,mesocarp fiber and kernel shell

In this work, the effects of torrefaction on the physiochemical properties of empty fruit bunches (EFB), palm mesocarp fiber (PMF) and palm kernel shell (PKS) are investigated. The change of properties of these biomass residues such as CHNS mass fraction, gross calorific value (GCV), mass and energy yields and surface structure when subjected to torrefaction process are studied. In this work, these materials with particle size in the range of 355–500 μm are torrefied under light torrefaction conditions (200, 220 and 240 °C) and severe torrefaction conditions (260, 280 and 300 °C). TGA is used to monitor the mass loss during torrefaction while tube furnace is used to produce significant amount of products for chemical analyses. In general, the study reveals torrefaction process of palm oil biomass can be divided into two main stages through the observation on the mass loss distribution. The first stage is the dehydration process at the temperature below than 105 °C where the mass loss is in the range of 3–5%. In the second stage, the decomposition reaction takes place at temperature of 200–300 °C. Furthermore, the study reveals that carbon mass fraction and gross calorific value (GCV) increase with the increase of torrefaction temperature but the O/C ratio, hydrogen and oxygen mass fractions decrease for all biomass. Among the biomass, torrefied PKS has the highest carbon mass fraction of 55.6% when torrefied at 300 °C while PMF has the highest GCV of 23.73 MJ kg⁻¹ when torrefied at the same temperature. Both EFB and PMF produce lower mass fraction than PKS when subjected to same torrefaction temperature. In terms of energy yield, PKS produces 86–92% yield when torrefied at light to severe torrefaction conditions, until 280 °C. However, both EFB and PMF only produce 70–78% yield at light torrefaction conditions, until 240 °C. Overall, the mass loss of 45–55% of these biomasses is observed when subjected to torrefaction process. Moreover, SEM images reveal that torrefaction has more severe impact on surface structure of EFB and PMF than that of PKS especially under severe torrefaction conditions. The study concludes that the torrefaction process of these biomass has to be optimized based on the type of the biomass in order to offset the mass loss of these materials through the process and increase the energy value of the solid product.     

太阳能驱动的有机朗肯-喷气增焓（带二次吸气的增效）蒸汽压缩制冷系统性能分析

为有效利用太阳能,以有机朗肯−喷气增焓（带二次吸气的增效）蒸汽压缩式制冷系统为研究对象,建立了系统的热力学模型,分别选取R236fa、R245fa、RC318和R141b作为系统工质,研究了发生温度、凝结温度、冷凝温度、蒸发温度、膨胀机等熵膨胀效率及压缩机等熵压缩效率对系统性能的影响,并以系统性能最佳为目标对工质进行了优选。计算结果表明：对整个系统而言,R141b是最合适的工质,凝结温度和冷凝温度对系统性能有重要影响。以R141b为例,当发生温度在85℃、凝结温度为40℃、冷凝温度为40℃、蒸发温度为 −15℃时,系统COP_s达到0.2528,采用喷气增焓技术对于环境温度很低、太阳能资源丰富的北方地区具有很大的优势。