【作者】 周国莉；

【导师】 武建军；

【作者基本信息】 中国矿业大学 ， 化学工艺， 2014， 博士

【摘要】 我国拥有丰富的褐煤资源，但因其含水量高、热值低、易风化和自燃等特性，使得褐煤利用效率低，经济性差，并且脱水后褐煤易复吸自燃，造成资源浪费和环境污染。因此，研究褐煤高效、安全的脱水技术以及抑制脱水褐煤复吸技术势在必行。本文分析了褐煤基本特性，并表征了脱水褐煤的官能团和孔结构；采用不同能量形式对胜利褐煤进行脱水实验研究，揭示了不同能量形式含氧官能团和孔结构的变化规律；分析了不同能量形式褐煤脱水动力学；探讨了褐煤低温传热传质过程中颗粒内部水分随时间和位移的变化；并获得不同能量形式作用褐煤的复吸热力学和动力学特性；完成了低温热烟气快速干燥褐煤的实验装置的设计。褐煤基本特性分析包括含氧官能团、孔结构和矿物质赋存形态的分析。结果表明，褐煤全水分28.11%，低位发热量为12.68MJ/kg。FTIR和XPS结果表明褐煤中含有大量亲水基团，如羟基、羧基、羰基和醚氧基。BET结果表明，不同粒度褐煤的吸脱附曲线都属于Ⅱ类，并且出现滞洄环，说明褐煤的孔隙结构比较发达。由kelvin方程计算褐煤孔隙中产生毛细凝聚的最大孔半径为0.43nm。粒度<1mm的褐煤吸脱附曲线上有拐点，说明在较小的孔隙中存在着一端封闭的不透气性孔，即第Ⅱ类孔；而>1mm的没有拐点，是因为褐煤中存在两端都开放的孔型，也可能存在Ⅱ类孔。随着粒度的增大，褐煤的比表面积和孔容降低，而孔径集中分布在10-50nm之间。通过不同能量形式（热能和微波能）和能量强度（时间）对褐煤脱水特性的实验研究，获得褐煤脱水曲线和脱水褐煤含氧官能团和孔结构随能量形式和强度的变化规律。随着能量强度的增加和褐煤粒度的减小，其干燥速率增加。但真空干燥速率大于热风干燥速率。随着微波能量强度的增加，脱水速率增加。以温度为尺度，对于热强度作用褐煤的脱水过程，可分为两个阶段，120℃之前脱除褐煤中的自由水和部分孔隙水，120℃之后脱除少量的孔隙水和部分分子水；并且120℃之后将水分脱除到8%以下需25-30min。热强度和微波能量作用褐煤后，其表面部分含氧官能团-OH、-C=O和-COOH脱落。温度对官能团脱除较时间因素影响大。微波干燥褐煤的N2吸脱附曲线属于第Ⅲ类吸附等温线，而热风干燥与真空干燥褐煤的N2吸脱附曲线属于第Ⅱ类。随着温度的增加，真空与热风干燥褐煤的孔容和比表面积都减小，平均孔径增大；微波作用褐煤的比表面积和孔容随着时间的增加而减小。三种能量形式作用褐煤的孔结构分形维数都在2.35-2.5之间。不同能量形式作用褐煤脱水的过程动力学研究，结果表明，真空和热风干燥褐煤的动力学过程符合Logarithmic模型；微波干燥褐煤符合Two Term模型，R2均大于0.97。不同温度下，真空干燥褐煤(0.5-1mm)的有效水分扩散系数分布在4.906×10-12-1.727×10-11m2/s之间，水分扩散活化能为18.00kJ/mol。热风干燥褐煤（0.5-1mm）的有效扩散系数分布在4.84×10-10-7.09×10-9m2/s之间,水分扩散活化能为25.24kJ/mol；微波干燥褐煤的有效扩散系数随着粒度的增加而增大。褐煤脱水动力学的不同主要是由脱水机理不同引起。热风干燥过程中的水分传递的推动力主要是湿度梯度和温度梯度。而真空干燥过程中水分传递的推动力主要是由湿度梯度、温度梯度和压力梯度共同作用的形成。真空干燥褐煤和热风干燥褐煤过程中传热传质方向相反。而微波干燥褐煤过程中形成的温度梯度和湿度梯度方向一致，更有利于颗粒内部水蒸气的扩散。褐煤脱水过程中水分迁移与颗粒内部干湿界面的移动有关，受干湿界面产生的压强梯度、温度梯度和湿度梯度控制。颗粒内部的毛细管水分的迁移主要与褐煤中的孔结构有关，颗粒孔隙内的毛细管势为2.68kJ/kg。脱水过程中，褐煤颗粒内部由于产生湿应力和热应力而发生收缩现象，产生干燥应力。褐煤的干燥应力主要受颗粒表面的湿度梯度控制。将水势理论应用于褐煤脱水的过程，得到褐煤颗粒内部水分差分模型及相关系数K，随着温度的升高，K值增大。对不同能量形式作用的褐煤的水分复吸实验的研究结果表明，在相对湿度相同时，微波作用褐煤的水分复吸量最少。ZKHM的等温吸附Ⅱ类等温曲线，ZKHM和RFHM的吸附曲线上，在相对压力较低时都具有明显的滞洄环。三种脱水煤样的吸附势随着吸附空间的增加而降低。吸附势相同时，WBHM表面吸附同体积水蒸气，所需要的压力最大。水分在WBHM表面的等量吸附热最大，FRHM的等量吸附热最低，主要与褐煤表面的活性位点和表面含氧官能团有关。三种脱水褐煤的等量吸附热随着水蒸气吸附量的增加都呈下降趋势。水蒸气在三种脱水褐煤表面的吸附过程中，有效扩散系数大小关系是：WBHM>REHM>ZKHM。设计了褐煤低温热烟气干燥系统，计算了不同温度下热烟气的焓值和出口烟气的含水量为3.47%。当干燥装置进口烟气的含氧量为6%时，干燥装置的漏风系数为0.15。根据热量衡算，干燥装置消耗的总热量为212.95kJ/h，干燥装置中消耗的烟气总量为2473kg/h。更多还原

【Abstract】 In this paper, the characteristics of lignite were analyzed and the functional groupand pore structure of dewatering lignite were measured. Dewatering experiments forShengli lignite was carried by different methods. It revealed that contain of oxygenfunctional group and pore structure were changed. Lignite dehydration kinetics wasanalyzed. The heat and mass transfer processes were discussed.It’s obtained that thecharacteristics of thermodynamics and kinetics for lignite dried by different methodsand also the experimental apparatus of lignite dried by hot flue gas at low temperaturewas designed.The oxygen-containing functional group, pore structure and mineral occurrenceform of lignite were analyzed. It turned out that total water content and lower heatingvalue of lignite respectively were28.11%and12.68MJ/kg. FTIR and XPS resultsshowed that it contained a large number of hydrophilic group in lignite, such ashydroxyl, carboxyl, carbonyl and ether oxygen radicals. BET results indicated that theabsorption and desorption curves of lignite with different granularity were typeⅡ andit displayed an increase in hysteresis, particularly at high relative pressures. Thebiggest pore radius of capillary condensation was0.43nm by equation Kelvin. Andthere were differences between the adsorption and desorption curves <1mmand>1mm, because the pore shapes were different. The specific surface area and porevolume of lignite decreased with the increasing of granularity. Pore diameters weredistributed between10to50nm.Dewatering properties of lignite dried by different form of energy andenergy intensity were studied in Chapter3.The results showed that drying curvesdisplayed acceleration and slacken stages. When the energy intensity decreased andthe granularity of lignite reduced, the drying rate increased.But the drying rate oflignite dried at vacuum condtions was greater than the lignite dried by hot air. Withthe increase of the intensity of microwave energy, drying rate of ligniteincreased.Thermal drying lignite strength, microwave drying can reach higher dryingrate in a relatively short time. After drying by heat intensity and microwave energy,the oxygen containing functional groups of lignite surface fell off, such as-OH, C=O and-COOH. The influence of temperature on functional groups removal wasgreater than the time. The absorption and desorption curves of lignite dried bymicrowave were type Ⅲ,where as the absorption and desorption curves of lignitedried by hot air and vacuum were typeⅡ.The pore volume and specific surface area of lignite dried by vacuum and hot air decreased, but the average pore size increased.The pore volume and specific surface area of lignite dried by microwave decreasedwith the time increased. The fractal dimensions of pore structure were2.35-2.5.Dehydration dynamics of lignite dried by different methods were studied inChapter4.The results showed that Logarithmic model were fit for describing thedehydration dynamics of lignite dried by vacuum and hot air. Two Term model wassuited to the dehydration dynamics of lignite dried by microwave. And the correlationcoefficients were more than0.97.The effective moisture diffusion coefficient oflignite dried by vacuum and hot air(0.5-1mm) respectively were4.906×10-12-1.727×10-11m2/s-1and4.84×10-10-7.09×10-9m2/s-1. The moisturediffusion activation energy of lignite dried by vacuum and hot air(0.5-1mm)respectively were18.00kJ/mol and25.24kJ/mol.The effective moisture diffusioncoefficient of lignite dried by microwave increased with the increase of lignitegranularity.The effective moisture diffusion coefficients of lignite dried by differentmethods were mainly influenced by the pore structure. The differences fordehydration kinetics of dried lignite were mainly controlled dehydrationmechanism.The results showed that the driving force of water transfer in lignite driedby hot air were moisture gradient and temperature gradient. The results showed thatthe driving force of water transfer in lignite dried by vacuum were moisture gradient,temperature gradient and pressure gradient. The direction for heat and mass transfer inthe lignite dried by vacuum and hot air were opposite. While the direction for heat andmass transfer in the lignite dried by microwave were the same.Moisture migration for drying lignite was related to the dry wet interface in theparticles. Moisture migration in the capillary of particles was related to the shape ofpore. The capillary potential in the pore was2.68kJ/kg.The contractions in the lignitedue to wet stress and thermal stress during the process of lignite dehydration. Dryingstress was mainly controlled by the moisture gradient on the surface of the particles.The water potential theory was applied to the process of lignite dewatering. Particlesinternal Moisture difference model was obtained. The water content distribution atdifferent time and location were obtained.Moisture re-absorption experiment of lignite dried by different methods werecarried out in the Chapter6.The results showed that the lignite dried by microwavere-absorbed least water.The absorption and desorption curves of lignite dried byvacuum were type Ⅱ.And it displayed hysteresis at low relative pressure.The adsorption potential of dried lignite declined with the increasing of adsorption space.The heat of adsorption on WBHM was most, while FRHM was least. It was mainlyrelated to active sites and oxygen-containing functional group on the surface oflignite.The heat of adsorption of the lignite dried by different methods decreased withthe increasing of the water vapor adsorption amount.The water vapor effectivediffusion coefficient was WBHM>REHM>ZKHMThe drying system of lignite dried by hot flue gas at low temperature wasdesigned.The enthalpies of hot flue gas at different temperatures were calculated. Thewater content of exports of flue gas was3.47%.when the oxygen content of importflue gas was6%, the air leakage coefficient of the drying device was0.15. Accordingto heat balance, the total consumption quantity of heat of drying device was212.95kJ/h, and the consumption amount of the flue gas was2473kg/h.更多还原