温度和相对湿度对褐煤干燥动力学特性的影响

为确定褐煤干燥最佳工艺参数,在恒温恒湿热风干燥实验台上进行了温度为50～90℃,相对湿度为10％～30％条件下的褐煤颗粒热风干燥实验.将实验数据与9种经验、半经验模型进行拟合,利用相关系数、方差、均方根误差3种统计学参数对不同模型进行评价.结果表明:Page模型相比其他模型更适合用于描述干燥过程中褐煤颗粒水分随时间的变...     

褐煤等温干燥过程及动力学研究

为研究褐煤干燥过程,利用煤质水分分析仪和微分热重分析方法,对不同粒级的褐煤在不同干燥温度下进行等温干燥试验,得到了样品含水率与干燥时间、干燥速率与含水率的关系曲线。通过粒级分布系数对褐煤进行含水率折算,并用不同干燥模型对试验数据进行拟合,得到了在介质温度140℃下3个干燥阶段的干燥方程及干燥动力学参数。结果表明,引入粒级分布系数得到的干燥速率特征常数k值,与不同粒级的干燥速率特征常数k的均值相近。根据褐煤的干燥速率和水分的存在形式,将褐煤干燥过程分为3个干燥阶段,分析得出干燥方程模型分别用线性干燥模型、Wang经验模型、Page模型较为合理。根据Arrhenius经验公式建立了ln k与1/T的关系,得到褐煤干燥的界面蒸发活化能Ea=17.088 k J/mol,指前因子A=12.47 min~(-1)。     

Drying behavior of lignite under microwave heating

Because of lignite’s high moisture content, it must be dried before most applications. Microwave radiation may be suitable for efficient drying because of its special heating properties. This study investigated the drying behavior of lignite samples from eastern Inner Mongolia by microwave thermogravimetric analysis. Three stages of microwave drying were observed: preheating, fast weight loss, and falling rate drying periods. Samples’ surface temperatures increased dramatically during preheating, dropped slightly in the second period, and rose again in the final period. The measured surface temperature was <95°C during microwave heating. The overall moisture content decreased more rapidly under higher microwave power. Fine lignite particles (diameter <0.2?mm) and lump samples (particle size 10?mm) dried better than granular lignite (particle size 1–2?mm). The samples also underwent slight natural drying (1–2% point reduction in moisture content) after microwave treatment. The critical moisture content of lignite (11–15% under experimental conditions) was redefined. Energy consumption was analyzed to evaluate the feasibility of the proposed drying process.     

Microwave drying performance of lignite with the assistance of biomass-derived char

Microwave lignite drying with assistance of biomass-derived char was addressed and effect of bio-char on drying rate and energy consumption was investigated in this work. Effective diffusion coefficient and activation energy for the drying process were also analyzed. The results indicated the drying process was largely dependent on the variation of sample temperature. Bio-char originated from pine wood was most favorable for lignite drying, considering its better promoting effect and advanced security. There existed an optimal bio-char addition ratio for drying process at different power. The corresponding optimal ratio was 10% at 231?W and 15% at 385?W, at which the biggest drying rate and the least energy consumption were reached. It was compared lignite drying initiated at 385?W was better for energy conservation. Effective diffusivity was improved and activation energy was simultaneously reduced, with the addition of bio-char. The minimum activation energy was 15.54?W?·?g^?1, which was gained at bio-char addition ratio of 10%. The results revealed the effect of bio-char on depressing activation energy could rival that of metal-based additives. The drying process with assistance of microwave and bio-char could present technical and economical benefits on lignite upgrading.     

褐煤干燥特性的实验研究

为获得褐煤颗粒干燥器设计的基础数据,对宁夏褐煤进行了工业分析、热重分析,得到了褐煤水分、挥发分的质量分数,确定了宁夏褐煤干燥的温度范围.褐煤的热重分析表明:褐煤干燥温度应不高于250℃.在热重分析确定的温度范围内,采用薄层干燥方式进行了褐煤颗粒的等温干燥实验,获得了褐煤颗粒干燥速率随水分的变化关系,颗粒的干燥主要处于降...     

Combined conventional thermal and microwave drying process for typical Chinese lignite

A combined conventional and microwave drying process for Ximeng lignite was investigated in this paper. Samples were firstly dehydrated by hot air to achieve a conversion moisture content, and then were managed to final moisture content by microwave drying. Results showed that the drying rate was significantly improved in the decreasing rate period by microwave drying, approximately 3–5 times faster than that of conventional drying. Finally, the orthogonal test was used to clarify the effects of each factor on the energy consumption, and the magnitude ranking order was conversion moisture content?>?microwave power?>?hot air temperature.     

褐煤低温干燥特性的实验研究

中国褐煤储量丰富,但较高水分极大地限制了其开采和利用,对其进行脱水提质是解决褐煤高效利用的关键。通过热重分析仪（TGA）对HL和YN的不同粒径褐煤,分别在50,80和110℃等温干燥2h。结果表明：在每个干燥温度下煤样都能达到恒重,随着温度的升高煤样总失重增加,说明煤中水分与煤表面之间具有不同的结合强度;随着水分的降低,水分蒸发所需能量增加,煤水之间的相互作用加强,其中包括氢键和微孔对水的束缚力。粒径0．250～0．150mm、水分26．61％的HL褐煤在50c（二干燥后,水分降至6．96％,此时水分以分子层水的形式存在;干燥温度升至110℃时,煤中水分并未明显降低,说明煤中官能团与水分子间形成的氢键对水分有强烈的吸附作用。HL褐煤50℃干燥后,0．150～0．074mm和0．074～0．038mm煤样残留水分分别为6．52％和3．93％,均低于0．250～0．150mm煤样的6．96％,说明0．250～0．150mm煤样中不能脱除的残留水是孔隙水,被禁锢在狭小空间内。     

维多利亚褐煤干燥气化技术进展

为实现褐煤清洁高效利用,在分析维多利亚褐煤煤质特性的基础上,综述了国外先进的褐煤干燥及气化技术。褐煤干燥工艺主要有蒸发干燥和非蒸发脱水2种,重点分析了磨煤机干燥工艺、褐煤浆生产高致密褐煤球干燥工艺、回转蒸汽管干燥工艺和机械热挤压脱水工艺的工艺流程和应用现状,其中磨煤机干燥工艺和回转蒸汽管干燥工艺技术比较成熟,工业应用较多。论述了维多利亚褐煤气化工艺中的褐煤集成干燥气化工艺和增压流化床气化工艺,提出若将褐煤集成干燥气化工艺中的空气气化改为富氧或纯氧气化,并通入一定比例水蒸气,该工艺有望应用于中国煤化工领域,生产化工合成原料气,为中国褐煤高效洁净利用提供途径。     

微波热解煤的实验研究

采用微波加热的方式对褐煤进行了热解实验研究,研究结果表明,用微波进行煤的热解,温度可以达到800℃,是一种热解煤的有效方法,其热解速度快,微波热解产生的炉气,其有效成分浓度高,热解后的最终固体产物与兰炭的成分相近。     

褐煤干燥提质和无粘结剂成型技术的研究现状及进展

论述了褐煤中水分的存在形式,即褐煤中的水分主要由外在水分、内在水分和结晶水组成,其中外在水分较易脱除。介绍了国内外褐煤干燥提质技术、针对高水分褐煤干燥研发的新技术及与褐煤干燥相关的其他提质技术的研究进展,其中,新研发的褐煤干燥技术中,过热蒸汽流化床褐煤干燥技术(WTA)具有效率高、能耗低、安全等特点,在单位能耗方面具有明显优势。通过对褐煤无粘结剂型煤的成型工艺及型煤耐水性能的试验研究,说明褐煤无粘结剂成型技术制备的型煤样品质量良好,吸收水分的速率大大降低,热解与燃烧活性也有所下降。最后分析了褐煤无粘结剂成型机理,即主要有沥青假说、腐植酸假说、毛细孔假说、胶体假说和分子粘合假说5种。     

新型滚筒式褐煤干燥系统的应用

高水分褐煤无论作为燃料还是其它工业利用都很困难,利用新型滚筒式干燥系统干燥褐煤,为后续的加工利用提供了方便。     

典型褐煤干燥技术比较

分析了国内外典型褐煤干燥技术的原理、关键参数、技术特点等,并从技术适应性、工艺条件、干燥效果、环境影响等方面进行综合评价比较。结果表明:美国K-Fuel工艺要求入炉粒度较其它技术大,适应性稍差;褐煤提质后均可作为锅炉燃料。干燥温度越高,褐煤干燥效果越好。德国泽玛克管式干燥成型技术、美国K-Fuel工艺为带压干燥,其他工艺为常压工艺。5种工艺可降低水分7.0%～25.0%,增加热值3.24～5.94kJ/g;澳大利亚BCB工艺、神华HPU-06工艺、德国泽玛克管式干燥成型技术产品为型煤,规格可调;其他工艺产品粒度变小。神州干燥-干选联合工艺回吸可能性大、自燃特性改善不明显,其余工艺深度脱水后可防止自燃,不易回吸。5种工艺污染物排放均较为简单,对环境影响较小。     

褐煤干燥技术发展及应用现状

论述了国内外褐煤干燥提质技术的发展现状。针对传统热力干燥在褐煤电厂应用中存在的高能耗、高投资和低安全性等问题,开展了褐煤过热蒸汽干燥机理的试验研究和中试试验。结果表明：过热蒸汽的干燥效果优于常规热空气;中试试验系统能稳定、连续地对褐煤进行干燥,且干燥产品符合褐煤干燥实际工业应用的要求。最后提出了过热蒸汽预干燥低质煤提质洁净煤技术（SCU技术）,对其在节能、安全等方面的技术先进性作了具体的对比分析,结果表明：SCU技术节能节水、安全性高,符合中国可持续发展战略和节能减排的要求。     

内蒙古某褐煤干燥特性的实验研究

利用热风干燥实验装置对内蒙古某褐煤进行不同温度、不同风速、不同粒度的干燥特性研究。结果表明：降低褐煤的粒度可有效缩短干燥时间;热风风速对褐煤的干燥速率影响很小,干燥适宜温度为150~165℃,在此温度区间内干燥时间较理想,进一步提高风温虽然有助于提高干燥效率,但有发生自燃的危险。     

A kinetic study of microwave and fluidized-bed drying of a Chinese lignite

The drying kinetics of Chinese lignite in nitrogen fluidized-bed, superheated steam fluidized-bed and microwave were investigated. The changes in the mass as a function of drying time were measured under various drying conditions. The variations of moisture ratio with time were used to test ten different thin-layer empirical drying models given in the literature. In studying the consistency of all the models, some statistical tests, such as χ², residual sum of squares (RSS) and F-value were also used as well as coefficient of determination R². In nitrogen fluidized-bed and superheated steam fluidized-bed, the Midilli–Kucuk model best described the lignite drying process. Drying data in microwave were best described by the Page model, indicative of a difference in kinetics between the two drying methods. This difference was attributed to different heat transfer mechanisms under conventional and microwave drying conditions. The effects of drying parameters in nitrogen fluidized-bed, superheated steam fluidized-bed and microwave drying on the constants and coefficients of the selected models were studied by multiple regression analysis. The apparent diffusion coefficient of moisture in samples was obtained from the kinetics data and the apparent activation energies under nitrogen fluidized-bed, superheated steam fluidized-bed and microwave drying were found to be rather similar.     

Experimental study and energy analysis on microwave-assisted lignite drying

For value-added utilization of high-humidity lignite, an investigation on its drying behavior was carried out, using a method of Microwave Thermogravimetric Analysis (MTGA). The characteristic of heat and mass transfer during drying process was studied. The effects of initial lignite mass on its drying process and energy consumption were also addressed. In addition, changes of lignite pore structure, sulfur content, and calorific value were tested after drying experiment. The results indicated that lignite microwave drying was divided into three stages: incubation stage, high-efficient dehydration stage, and deep dehydration stage. It was in agreement with the variation of temperature inside the sample. High-efficient dehydration stage and deep dehydration stage were separated at a critical moisture content. Microwave power and initial mass could be properly matched, which was effective to increase dehydration rate and decrease energy consumption. It was further noted that the best power for achieving the least energy consumption was in advance to that for achieving the greatest dehydration rate, especially for initial mass of 20?g and 25?g. The optimum power for initial mass of 20?g and 25?g was found to be 385?W and 539?W, respectively. Pore structure of dried lignite was basically deteriorated. Meanwhile, lignite microwave drying at 231?W for 6?min could lead to an increase of calorific value by 8.1% and a decrease of sulfur content by 68.6%.     

印尼褐煤干燥和水分再吸收特性的试验研究

利用热重分析仪(TGA)和等温吸湿实验装置对一种印尼褐煤干燥和水分再吸收过程进行了试验研究.结果表明干燥过程的平均表观活化能为25.77 kJ/mol,脱去吸附水的表观活化能为33.14 kJ/mol.吸湿等温线的形状为S型等温线,Chung Pfost数学模型更适合于拟合印尼褐煤的等温吸湿过程.     

干燥褐煤替代烟煤作为电厂燃料的可行性

介绍了SZ型振动混流低温干燥系统的技术特点、工作原理和设备构成情况,以600 MW机组电厂掺烧50%褐煤需要的干燥生产系统为例,分析了干燥提质工程投资、加工成本及经济效益,该技术的成功应用,拓展了褐煤使用空间。     

The effect of freezing on the hot air and microwave vacuum drying kinetics and texture of whole cranberries

Abstract

The aim of this study was to evaluate the effect of convective and cryogenic freezing, hot air convective drying (HACD) at 60, 70, 80, and 90?°C and microwave vacuum drying (MWVD) at 100, 150, 200, 300, 450, and 500?W on the drying kinetics and texture of whole cranberries. Effective moisture diffusivities and drying rates were higher, whereas drying times were shorter for the samples dried by MWVD compared with the samples processed by HACD. The drying kinetics of cranberries during MWVD was discussed based on the hypothesis postulating that changes in the drying rate of cranberries during MWVD can be explained by and correlated with changes in the pressure gradient on material surface. Cranberries processed by MWVD were characterized by significantly greater hardness, gumminess, and chewiness in comparison with HACD samples. MWVD was found to be an effective method for producing dried snacks characterized by hard and crispy texture and considerable resistance to stress associated with manufacturing, packaging, storage, and delivery. HACD produced brittle fruit that were difficult to store and transport and were not fully suitable for direct consumption. Convective freezing before MWVD improved the overall appearance of cranberries, whereas cryogenic freezing combined with high temperature HACD adversely influenced the drying rate and produced dried cranberries with suboptimal overall appearance.