基于薄层干燥模型的褐煤干燥动力学研究

在不同颗粒直径和不同的干燥介质温度下,对褐煤进行干燥动力学实验研究。得到了褐煤的干燥曲线和干燥速率曲线,采用薄层干燥模型对实验数据进行模拟,得到了褐煤的干燥方程和干燥速率方程。提出了褐煤干燥速率常数的经验公式k=A exp[（-E_v（1+C_dlnd））/（RT）],其中指前因子A=5.819min^-1,界面蒸发活化能E_v=21347.5KJ/mol,经验常数C_d=0.0409m^-1,干燥时间指数n=1.516。     

基于量纲分析方法的苜蓿干燥特性参数确定

应用量纲分析方法,建立了苜蓿的干燥温度、样品质量、茎秆长度、介质流速和初始含水率与其干燥常数k的经验公式,并得到了温度特性系数n与干燥温度的函数关系,提出了改进苜蓿薄层干燥方程,为分析干燥条件对苜蓿干燥速度的影响提供了理论依据。     

碱式氯化镁纳米棒干燥动力学方程及参数的确定

在不同床层厚度和不同干燥介质温度下，对碱式氯化镁纳米棒进行干燥动力学实验，得到其干燥曲线和干燥速率曲线。采用薄层干燥模型对所得干燥动力学实验数据进行数学处理，得到碱式氯化镁纳米棒的干燥方程为MR=exp[-（kτ）^n]，干燥速率方程为-dMR／dτ=knMR（-lnMR）^（n-1）/n，干燥速率常数k=Aexp[-Ev（1＋CLL）／RT]，干燥时间指数n=1．821，界面蒸发活化能Ev=11．228kJ／mol，指前因子A=4．237min^-1，经验常数CL=55．556m^-1。     

基于薄层干燥模型的碱式碳酸镁纳米花干燥动力学研究

在不同干燥介质温度和不同物料床层厚度下,对碱式碳酸镁纳米花进行干燥动力学实验,得到其干燥曲线和干燥速率曲线。采用薄层干燥模型对所得干燥动力学实验数据进行数学处理,得到碱式碳酸镁纳米花的干燥方程为M_R=exp[-(kt)~n],干燥速率方程为-(dM_R)/(dt)=knM_R(-lnM_R)~((n-1)/n),干燥速率常数k=A exp[(-E_v(1+C_LL))/(RT)],干燥时间指数n=1.738,界面蒸发活化能E_v=16.521kJ/mol,指前因子A=7.214min~(-1),经验常数C_L=29.900 m~(-1)。     

单颗粒褐煤高温烟气干燥过程实验研究

针对10mm~25mm粒径的大唐五间房褐煤,通过单颗粒高温烟气干燥实验,得到了600℃~900℃烟气温度下的干燥特性曲线,研究了干燥介质温度和粒径对褐煤高温脱水效果的影响,发现干燥过程主要处于降速干燥阶段;高温条件下,温度对干燥速率的影响并不显著;针对褐煤水分在干燥过程中的迁移特点以及大唐五间房褐煤的孔隙特征,基于努森扩散定律,建立了水分蒸发为蒸汽再扩散出煤粒的缩核干燥动力学模型;得到了不同温度下的有效水分扩散系数,并利用Arrhenius公式求出了10mm~25mm粒径下的干燥活化能.     

印尼高水分褐煤干燥特性研究

以印尼高水分褐煤为试验对象,采用蒸汽管回转干燥技术对其进行静态、动态干燥试验研究。褐煤干燥速率特性试验表明,褐煤粒径和质量基本相同时,干燥蒸汽温度越高,水分蒸发速率越快,褐煤干燥速率越大;褐煤质量相同时,褐煤粒径越小,干燥时间越短,干燥速率越大;褐煤粒径相同时,褐煤质量越小,干燥时间越短,干燥速率越大;褐煤干燥速率曲线常在煤中水分低于空干基水分前出现拐点,即进入干燥降速阶段。通过对褐煤干燥前后的粒径分布、热稳定性分析可知,褐煤干燥过程伴随着细颗粒煤粉的产生,褐煤干燥后细颗粒煤粉增加了14.87%;褐煤干燥前后TS6分别为10.3%和19.2%,均属于低热稳定性煤,且干燥后褐煤的热稳定性好于干燥前;干燥后褐煤的反应开始温度RI和燃尽指数Cb分别降低了7℃和0.1112,相差较小,均极易着火和燃尽。     

碱式碳酸镁纳米花的热分析干燥动力学研究

以六水氯化镁和尿素为原料,采用均匀沉淀法制备出碱式碳酸镁纳米花。在不同干燥介质温度和不同物料床层厚度下,得到碱式碳酸镁纳米花的干燥曲线和干燥速率曲线。采用热分析动力学技术对干燥动力学实验数据进行处理后,得到碱式碳酸镁纳米花的干燥微分机理函数为f(1-MR)=6MR2/3(1-MR1/3)1/2,干燥积分机理函数为g(1-MR)=(1-MR1/3)1/2,干燥方程为MR=〔1-(kt)2〕3,干燥速率方程为-dMR/dt=6k2tMR2/3,干燥速率常数为k=Aexp〔-Ev(1+CLL)RT〕;指前因子A=4.0725min-1,界面蒸发活化能Ev=16.9334kJ/mol,经验常数CL=30.3135m-1。     

褐煤高温烟气干燥过程中挥发分析出实验研究

对伊敏褐煤和大唐五间房褐煤在高温烟气环境下的干燥过程进行了实验研究.实验中对大粒径煤颗粒采用固定床干燥法,对小粒径煤粉则采用下降管顺流干燥法.根据实验获得的煤颗粒和干燥介质温度曲线研究了初始烟气温度、粒径和初始含水率对褐煤中水分和挥发分析出的影响,结果表明,褐煤高温烟气干燥过程主要分为预热阶段和降速干燥阶段,褐煤在下降管中的干燥过程主要处于预热干燥阶段;在800℃的烟气初温下,增大粒径,提高初始含水率,可以避免挥发分析出;两煤种在下降管干燥过程中均比较稳定,且伊敏褐煤相比五间房褐煤吸收和脱除水分更为容易,但也更易受热分解.研究表明,下降管高温烟气干燥技术适用于伊敏和大唐五间房褐煤这两种煤种的干燥过程.     

碱式氯化镁纳米棒的干燥动力学方程

以六水氯化镁和轻质氧化镁为原料,采用液相法制备出碱式氯化镁纳米棒。在不同干燥介质温度和不同物料层厚度下,对碱式氯化镁纳米棒进行干燥动力学实验,得到其干燥曲线和干燥速率曲线。利用Origin软件对实验数据进行拟合,得到碱式氯化镁纳米棒的干燥方程为MR=exp[-(kt)n],干燥速率常数k=Aexp(-ERT)=Aexp[-EV(1+CLL)RT],n=1.808,A=6.3min-1,CL=37.4m-1,EV=14.1kJ/mol;以分段函数形式表示的干燥方程分别为:MR=exp[-(kt)n1](升速干燥阶段),n1=1.361;MR=a-mkt(恒速干燥阶段),a=1.074,m=0.633;MR=exp[-(kt)n2](降速干燥阶段),n2=2.109。     

石灰石立式磨磨矿动力学试验研究

基于半工业立式磨磨矿系统对石灰石原料开展磨矿试验，采用磨矿动力学原理，通过磨矿试验数据分析求解磨矿参数k和n值，并建立立式磨的磨矿动力学方程以及探究立式磨磨矿特性，优化石灰石粒级级配。结果表明：立式磨具有鲜明的磨矿特征，且采用传统的幂函数形式建立的磨矿动力学方程精度较高，可以很好地预测粒度分布和揭示粒级演化规律。在探讨不同磨矿条件（喂料量、压力和含水率）对不同粒级石灰石磨矿速率的影响时，发现石灰石磨矿速率较大的粒级区间为-1.25+0.63，在此粒级区间内更有利于进行磨矿作业。增大液压缸压力，有利于提高磨矿速率；含水率越大，团聚现象越严重，磨矿速率越小。优化磨矿条件，有利于提高立式磨磨矿速率。     

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.     

甘露醇喷雾干燥过程中液滴粒度分布变化的群体粒数衡算模拟和实验研究

利用群体粒数衡算（population balance，PB）计算机模拟和实验研究了甘露醇水溶液的喷雾干燥过程中液滴的粒度分布的变化规律。液滴干燥过程中的颗粒粒度的萎缩速率，在群体粒数衡算模型中描述为液滴的逆（或负）生长项，通过单个液滴反应动力学方法（reaction engineering approach，REA）获得。基于单个液滴干燥的反应工程方法模型REA和群体粒数衡算模型PB集成建立了PBREA模型。PBREA 模型的求解是通过高分辨率数值方法。本文模拟研究了不同工况下，不同粒径液滴的干燥时间、液滴平均含湿量以及液滴粒度分布随时间的变化。结果显示，液滴粒径越大，干燥时间越长，模型预测的颗粒平均粒径为实验值的1.0~1.5倍，粒度分布跨度是实验值的0.61~0.89倍。模拟误差主要来源于液滴及颗粒粒径分布统计精度、单个静止液滴与群体运动液滴干燥的差异、热导率及扩散系数是经验值3个方面。在使用Buchi 290 小型喷雾干燥仪进行的实验中，使用了图像采集和分析方法得到了液滴及颗粒的数密度分布，并和模拟结果做了对比。结果表明该模型可以有效地预测喷雾干燥过程中干燥颗粒的平均粒度及分布跨度。     

单颗粒褐煤高温烟气干燥过程数值模拟

褐煤干燥对于提高其品质具有重要意义。为了模拟高温烟气干燥这一高温差、变温差非稳态传热传质过程中褐煤内水分蒸发过程,采用有限体积法建立了一维球坐标系下蒸发界面向内迁移的单颗粒褐煤干燥数学模型,并利用该模型分析了初始烟气温度和颗粒粒径对单个褐煤颗粒干燥特性的影响。模型模拟结果与实验结果对比表明二者变化趋势一致,所建模型能较好地反映出高温烟气干燥过程中褐煤内水分蒸发过程。结果表明,初始烟气温度越高,颗粒粒径越小,蒸发界面向内迁移速度越快,水分脱除越快,干燥时间越短;蒸发界面平均迁移速度均与初始烟气温度和颗粒粒径呈线性关系;在初始烟气温度700℃下,较短的停留时间使得颗粒表面温度未达到挥发分析出温度,本研究中不同粒径褐煤颗粒在干燥过程中基本没有挥发分的析出。     

印尼褐煤在蒸汽管回转干燥机中干燥特性研究

针对印尼褐煤的物料特性,利用蒸汽管回转干燥机对其进行不同温度,不同粒度的干燥特性研究。试验结果表明,煤粉粒径为0～20 mm范围时干燥效果较好;工业干燥机的停留时间应在45 min左右;根据试验机传热系数放大后得到工业干燥机的传热系数为94W/(m2.K);干燥过程对煤具有一定的破碎作用,干燥尾气当中不含可燃物质,生产中控制氧含量即可满足安全生产的要求。     

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...     

不同干燥程度胜利褐煤燃烧与自燃特性

为了探究高水分褐煤干燥后的燃烧与自燃特性变化,采用一维火焰炉、煤粉着火炉以及自燃试验台对不同干燥程度的胜利褐煤进行了试验研究。试验结果表明,试验样品的着火温度随着干燥程度的增加而降低,随着风煤比的增加而增加,煤粉细度同样会对着火温度产生影响。在燃用干燥褐煤过程中宜采用较高一次风率以提高制粉系统的安全性。胜利褐煤及其干燥褐煤均属于极易燃尽煤种,燃尽率均在99.4%以上,水分的变化对燃尽率影响不大。建议胜利褐煤与20%水分干燥褐煤的运行氧含量控制在3.5%左右。随着干燥程度的加深和粒径的减小,褐煤越容易自燃。胜利褐煤干燥到20%以下可能有自燃的风险。     

Drying characteristics of particles using thermogravimetric analyzer

The drying characteristics (critical moisture content, equilibrium moisture content, constant drying rate and effective diffusivity) of various particles (gypsum, millet, polyvinyl chloride and silica gel) using a thermogravimetric analyzer were measured. The experiments were performed in the gas temperature range of 40 to 100 °C under isothermal conditions. The drying rate curve was mainly dependent on the moisture content, particle size, gas temperature and the internal structure of the solid particles. The equilibrium moisture content of solid particles decreased with increasing gas temperature, while the critical moisture content and the effective dispersion coefficient increased with increasing gas temperature. The effective diffusion coefficients of both PVC and gypsum particles were not able to be determined by Fick’s law since the experimental data were not well matched with the model predicted values, which consisted of the drying time in the falling-rate drying period.     

Effect of Drying Conditions on Moisture Re-Adsorption Performance of Dewatered Lignite

In order to improve the drying efficiency of lignite and restrain the moisture re-adsorption of dewatered coal, the drying characteristics of typical Chinese lignite, the re-adsorption performances of dewatered samples and the change in pore structure throughout the entire processes were investigated in this study. Lignite samples with four different particle size fractions were dried in a fixed-bed reactor in the temperature range 60–160°C. The re-adsorbing moisture behaviors of dewatered coal samples containing different water contents were investigated at temperatures of 20–40°C and humidities of 55–95%. The changes in the pore structure of raw coal and different dried samples were measured by mercury intrusion porosimetry (MIP) and the relations between their re-adsorption performance and change in pore structure were explored. The moisture removal yields of lignite increased with an increase in drying time and temperature and was close to 100% above 120°C and over 100% after holding 40 and 15 min at temperatures of 140 and 160°C due to the release of CO₂ from the decomposing carboxyl group in the coal matrix. The re-adsorbed moisture content in dewatered coal was influenced by drying temperature and coal particle size through varying pore structure. The temperature and relative humidity in the re-adsorbing process were the main factors that influenced the moisture re-adsorption capacity of dewatered lignite, in which the re-adsorbing temperature mainly operated by varying the bonding ability of water on the surface of dewatered coal, and the relative humidity was connected with the pore structure as well. The mesopore was the main factor that influenced the re-adsorption of dewatered coal and the re-adsorption of moisture in dewatered coal at 100°C was highest due to the narrow range of the pore radius and because the relative volume ratio of 5 to 50 nm mesopore (above 91%) was high. The water loss yield of lignite with smaller particle size was higher due to its larger pore volume and surface area, but its re-adsorption capacity was lower because of lower volume ratio of 5 to 50 nm mesopore volume in dewatered coal obtained from the smaller size lignite.