高温干燥对褐煤孔隙结构及水分复吸的影响

利用卧式固定床实验炉制得不同温度下干燥处理的煤样,采用低温氮吸附法测试煤样的比表面积、孔体积和孔径分布等孔隙特征参数,使用复吸实验装置测定不同干燥程度褐煤煤样的平衡含水量,探索了高温干燥处理后褐煤孔隙结构的演变与其复吸特性之间的关联规律。结果表明：褐煤原煤及不同干燥温度(600~800℃)下半焦的等温吸附曲线均属于第Ⅱ类吸附等温线,褐煤原煤、600℃和700℃干燥半焦的吸附回线均属于L1型,800℃干燥半焦的吸附回线有从L1型转变为L2型的趋势;随着干燥温度的增加,干燥半焦的比表面积先增大后减小,介孔峰值的孔径微分同样先增大后减小,而大孔孔径微分基本保持不变;分形维数D₁和D₂呈相反的变化趋势,且D₂>D₁;不同干燥程度半焦的复吸曲线变化趋势相同,且平衡含水量随着干燥温度的升高而减小;半焦复吸特性与孔隙结构有关,平衡含水率与其孔容积之间呈较好的线性关系。     

褐煤煤粉干燥立管提质干燥的流动特性研究

通过实验研究褐煤煤粉在提质干燥过程受哪些因素的影响,利用FLUENT6.3.26对实验得到的数据进行温度、速度和压力场的数值模拟(气固两相流).对实验得到的数据和FLU-ENT6.3.26的数值模拟情况进行分析可知,褐煤煤粉在低气固比(体积比)进行提质干燥时,褐煤煤粉微粒的湿度有很大变化,提质干燥效果理想;在褐煤煤粉提质干燥过程中提高入口烟气温度,煤粉的干燥效果有很大提高;褐煤煤粉在提质干燥过程中烟气速度对褐煤粉颗粒湿度的影响很小.     

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。     

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.     

干燥对褐煤爆炸危险性的实验研究

为探究干燥前后褐煤的爆炸危险性,基于粉尘爆炸机理,通过粒度分析和爆炸性测定实验,分析了干燥前后褐煤粒径分布变化、扬尘特性及爆炸危险性变化.结果表明,干燥褐煤大粒径颗粒频数减小,小粒径颗粒频数增加,粒径变小,扬尘量增加;干燥褐煤最小点燃能量、粉尘云/层最低着火温度较干燥前褐煤都有所降低.干燥褐煤较原煤更易扬尘达到爆炸极限浓度,且更易发生着火燃烧爆炸,干燥褐煤爆炸敏感性和危险性都增加.     

干燥后褐煤的物理结构变化

从微观角度研究了褐煤在不同干燥温度时物理结构的变化.发现褐煤的孔结构尺寸在干燥过程中发生了显著变化,随着干燥温度的升高,褐煤的比表面积逐渐升高,孔隙率和孔容增大,而孔径减小.比表面积和塌陷程度都随着干燥温度的升高而呈现明显增加的趋势,但在干燥温度为210℃表现出下降趋势.干燥温度的升高导致大孔和中孔的明显转化和坍塌,而...     

低温干燥对褐煤含氧基团及其吸水性能的影响

采用红外光谱法确定褐煤中含氧官能团的种类,利用化学法分析干燥前后褐煤表面含氧官能团的变化,吸水性能用最高内在水分来表征,研究低温干燥过程中温度、干燥程度和干燥气氛对褐煤含氧基团及其吸水性能的影响.结果表明,褐煤中羧基和酚羟基含量较高;惰性气氛低温干燥时,酚羟基含量基本不变,羧基发生少量分解;空气下干燥时,羧基含量先减小,之后在氧化作用下,羧基和酚羟基含量同时增大.随着干燥程度的加深,煤样最高内在水分先减小后增大.     

单颗粒褐煤高温烟气干燥过程研究

以褐煤颗粒中水分蒸发界面为基础,将褐煤颗粒分为干区和湿区,干区考虑传热传质,湿区只考虑传热,并采用有限体积法,建立了一维球坐标系下单颗粒褐煤干燥脱水过程模型.利用Crank-Nicolson六点差分格式对其离散,模拟得到不同工况(初始烟温、停留时间和颗粒粒径等)下的单颗粒褐煤含湿量及其内部温度分布的动态变化.实验结果与模型模拟结果对比表明二者吻合度较好,所建干燥模型可以较好地反映褐煤干燥的实际过程.研究发现,初始烟温越高、停留时间越长以及颗粒粒径越小,干燥效果越好.当粒径为20mm的褐煤颗粒在初始温度为873K的热气流下停留131s时,其含水量即可从25.3%降到12%以下,此时颗粒表面的温度为537K,略高于挥发分初析温度(520K),此工况可以作为褐煤实际干燥过程中的最佳工况参照.     

干燥褐煤的自燃与爆炸特性试验研究

为抑制褐煤堆放时发生自燃与煤粉爆炸,利用自燃装置试验台和煤粉爆炸试验台,对褐煤及其干燥到不同水分的干燥煤进行试验研究,分析其自燃特性和爆炸特性。结果表明,对于自燃特性而言,褐煤水分减少10%,耗氧速度增加约0.17%/min,粒径减小一个等级,耗氧速度增加约0.11%/min;对于爆炸特性而言,褐煤水分减少5%,平均煤粉爆炸下限质量浓度约降低0.015 kg/m~3,温度每升高10℃,平均煤粉爆炸下限质量浓度降低约0.03 kg/m~3;总体而言,随着干燥程度的加深,褐煤自燃、爆炸特性均增强,危险性增加。     

褐煤热水干燥改质后的性能研究

褐煤在我国煤炭能源中占有很大比重,因其含水量高、灰分大、容易风化、发热量低的缺点使褐煤的利用率较低。为了提高褐煤的利用率,采用高压釜热水干燥工艺对褐煤进行改质,并将改质的褐煤成型,研究其改质成型后的特性。实验结果表明：经热水干燥后褐煤中的水分、灰分、挥发分的含量有所降低,但固定碳和发热量有所提高;煤样粒度、干燥温度、成型压力对褐煤抗压强度的影响较为显著;热水干燥后褐煤的成型性明显增强,使煤球的抗压强度接近褐煤有粘结剂冷压成型煤球的强度,并且成本低于有粘结剂成型煤球的强度。     

DRYING OF PARTICULATE SOLIDS: DETERMINATION OF THE CHARACTERISTIC CURVE OF BROWN COAL.

Variation on the rate of drying of brown coal powder as a function of environmental and intrinsic properties has been studied in a gravimetric laboratory-scale drier.

Raw data have been treated to correlate the constant rate of drying and the equilibrium moisture content as a function of flow rate and temperature of the gas phase, particle size and surface additives. The characteristic drying curve occurs when the reduced rate of drying is plotted as a function of a dimensionless moisture potetial.     

Experimental study on microwave drying of Chinese and Indonesian low-rank coals

Drying characteristics of low rank coals in a local microwave oven operating at 2.45 GHz were investigated. Effects of coal particle size, microwave power level, and coal sample size on drying characteristics were studied. Weight losses and temperature history of the samples were measured during drying. Drying rates were then obtained vs. drying time and moisture content. It was found that drying rate was increased with increasing coal particle size showing different trends from conventional drying methods reported in the literature. It was also observed that drying rate increased with increasing power output of the microwave oven or with decreasing coal sample weight. Effects of coal ash content and coal type were also investigated by comparing Chinese and Indonesian low rank coals. Ash content seems to be the governing factor in determining the drying characteristics for coal samples with small particle sizes. Drying mechanism of coals under microwave drying conditions was also discussed.     

补气料仓中宽筛分粒煤的下料特性

在自行设计的有机玻璃补气料仓系统上对宽筛分粒煤下料特性进行了实验研究,结果表明,料仓出口直径、粒煤粒径和外水分对宽筛分粒煤在补气料仓中的下料特性有显著影响.宽筛分粒煤的下料流率随料仓出口直径的增大而增加,但增加量随着补气量的增加而减小.增加宽筛分粒煤的平均粒径使料仓出口有效尺寸减小,导致物料下料流率减小.增加宽筛分粒煤...     

DRYING OF PARTICULATE SOLIDS: DETERMINATION OF THE CHARACTERISTIC CURVE OF BROWN COAL.

ABSTRACT

Variation on the rate of drying of brown coal powder as a function of environmental and intrinsic properties has been studied in a gravimetric laboratory-scale drier.

Raw data have been treated to correlate the constant rate of drying and the equilibrium moisture content as a function of flow rate and temperature of the gas phase, particle size and surface additives. The characteristic drying curve occurs when the reduced rate of drying is plotted as a function of a dimensionless moisture potetial.     

褐煤干燥特性及产品特性研究

通过对内蒙古锡林浩特褐煤的热重分析可知,褐煤干燥过程约30 min,干馏过程约1.5 h。对不同粒径褐煤进行了干燥特性研究,说明+100,100～50,-50 mm原煤完全干燥分别需要4.0,1.0,0.5 h,粒径越小,煤样失重率越大,干燥速度越大,达到相同干燥效果所需的干燥时间也越短。最后分析了干燥温度对产品特性的影响,同时测试了干燥、干馏提质产品的自燃特性和复吸水特性,结果表明:与原煤相比,150,200℃产品挥发分分别提高了33.72%和31.13%,更易发生自燃,而550℃干馏过程中挥发分降低了30.89%,热稳定性大幅增加;150,200,550℃产品吸氧量分别提高了0.43,0.65,0.72 cm3/g;干燥产品燃点要低于原煤,而干馏产品燃点则高于原煤;干馏煤因改变了孔隙结构,最高内在水分降低,即复吸水的能力降低。因此,干燥提质产品与褐煤性质基本一致,而干馏提质产品性能则获得较大改善。     

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)。     

Efficient <Emphasis Type="Italic">in situ</Emphasis> drying of low rank coal in a pressurized down-flow flash dryer

Flash drying of low rank coal with synthesis gas was addressed by using a pressurized down-flow dryer. The proposed method is a potential approach to secure gaseous water that is required in coal processing by utilizing moisture in the low rank coal. The drying process was promoted by increasing the initial temperature of the synthesis gas as a drying medium and decreasing the particle size of the coal. The moisture removal rate of the coal using synthesis gas at 9 bars and 500 °C reached up to 97% within ten seconds. Although it is a higher temperature than that of fixed bed or moving bed dryer, outlet moisture laden synthesis gas had the low level of tar enough to be a feedstock of downstream catalytic process due to the short residence time in the dryer. The chemical composition changes of the coal during the drying resulted in reducing oxygen content to the atomic ratio of oxygen to carbon as 0.1 and enhancing its calorific value. Disappearance of hydroxyl functional group from the surface and physical reduction of the surface area of the coal decreased the moisture re-adsorption capacity, which could prevent the spontaneous combustion of the low rank coal.     

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.