Experimental and numerical analysis of oil shale drying in fluidized bed

The main objective of this work was to experimentally and numerically investigate the Liu Shu River oil shale drying by the means of flue gas in a fluidized bed dryer. Several experiments were performed under different temperatures conditions. The moisture content of oil shale was measured during the experiments. The two-stage drying model was incorporated in computational fluid dynamics (CFD) package FLUENT via user-defined functions (UDF) and utilized for simulation of heat and mass transfer of oil shale drying in the fluidized bed dryer. The simulation results for solid moisture content agreed well with experimental data. The effects of the temperature and velocity of flue gas, initial bed height, and the particle size on the drying characteristics were predicted and analyzed. It is shown that the gas temperature and velocity are the important parameters in the whole drying process. The particle size has more obvious influence in the falling drying period than the constant drying period. The temperatures of gas and solid phases were monitored. It is shown that the so-called “near gas distributor zone” is the most effective heat transfer zone, which agrees well with the calculated value. The system quickly reached thermal equilibrium, characterizing a nearly isothermal bed. The developed model provides a very good demonstration to describe the oil shale drying in the fluidized bed dryer, and may provide important information for design, optimization of operation conditions.     

A comprehensive review on modeling of pneumatic and flash drying

Pneumatic conveying drying (PCD) is a widely used process in the industries and is a combination of heat and mass transfer and pneumatic handling technology. Drying processes consume large amounts of energy and, therefore, reduction in operating cost will be extremely beneficial for the industry. Many studies have been conducted to model and optimize the pneumatic drying. This review article focuses on the different strategies used in the literature to model pneumatic drying processes. An analysis is provided for the different mathematical modeling and its components such as balance and complementary equations and modeling assumptions. Two-fluid theory, Eulerian granular, and the discrete element method are reviewed as well as gas–solid flow modeling methods. In addition, the numerical methods and the main studied parameters in the field of pneumatic drying are investigated. To this end, heat and mass transfer coefficients, gas and dispersed phase properties are reviewed.     

Three-dimensional modelling of pneumatic drying process

Steady-state three-dimensional calculations of heat and mass transfer in vertical pneumatic dryer were performed. The theoretical model of the drying process is based on two-phase Eulerian-Lagrangian approach for gas-particles flow and incorporates advanced drying kinetics for wet particles. The model was utilized for simulation of the drying process of wet PVC and silica particles in a large-scale vertical pneumatic dryer. The influence of wall thermal boundary conditions was investigated by assuming either known value of the wall temperature or adiabatic flow in the dryer. Analyzing the predicted particle drying kinetics, an uneven product quality was predicted due to non-uniform drying conditions in the central and peripheral zones of the pneumatic dryer. Moreover, for the case of non-insulated chamber walls such quality unevenness was estimated to be substantially greater than for the case with thermally insulated drying chamber. The examination of the predicted temperature profiles within the silica and PVC wet particles showed that the latter is subjected to higher temperature gradients potentially resulting in the greater rate of thermally-degraded final product.     

柳树河油页岩微波干燥特性及干燥模型

干燥预处理对油页岩的利用具有重要的意义,微波干燥是一种快速、高效和节能的干燥方式。在家用微波炉改造基础上搭建了微波干燥实验台,研究了不同微波功率对柳树河油页岩微波干燥特性的影响。并采用单项扩散模型等13个薄膜干燥模型等对微波干燥分别进行动力学分析,结果表明：微波干燥所需的时间远小于传统干燥所需的时间;微波干燥速率要远大于传统干燥干燥速率;油页岩微波干燥过程适用于双项扩散的半经验模型,油页岩微波干燥机理为湿分（液体或蒸气）双项扩散控制过程;300、400和550 W三个功率干燥时能耗相差不大。为了以较少的能耗达到相同的干燥效果,对于柳树河油页岩,以功率550 W干燥为佳。     

流化床氛围下多孔物料干燥传热传质的数值模拟

用有限差分法数值求解一个热、质传递耦合模型,理论研究多孔物料流化床干燥过程。方程离散采用全隐格式的控制容积方法,三对角矩阵法（TDMA）用来求解线性方程组。选用球形的苹果丁作为多孔物料。在典型操作条件下,通过分析温度、饱和度和压力的分布侧形,讨论了物料内部的热、质传递机理。在对比条件下,考察了气体入口温度、气速和床面积因子对干燥过程的影响。结果表明：干燥过程受气、固相间的耦合传热传质的影响十分明显,干燥时间随气体入口温度和气速的提高而减少;随床面积因子的增大而增加。     

Heat transfer in layered media with application to oil shale materials

The problem of heat conduction in layered materials has been investigated. Equations for heat conduction developed earlier by Murakami et al. have been used to perform numerical studies for oil shale materials. The resulting solutions are compared to the solutions of the heat equation with effective thermal properties. The comparison yields limits on the validity of using effective medium values of thermal properties for time-dependent problems. The anisotropic nature of heat conduction in layered materials is also studied.     

气流干燥含湿氧化铝颗粒传热传质数值模拟

基于二相流理论,提出了一个描述含湿氧化铝颗粒气流干燥过程的一维数学模型。模型考虑了干燥管内气固二相间的传热传质和动量传递、含水质量分数和气固二相温度的变化。根据B ird所提出的努赛尔数经验公式,利用标准四阶龙格-库塔法对由非线性常微分方程组成的气流干燥耦合模型进行计算,得到了含湿氧化铝颗粒在不同气流干燥条件的干燥曲线。整个干燥过程中数值计算结果与试验实测数据吻合得很好,可以用来预测含湿氧化铝颗粒的干燥含水质量分数。     

Conjugate heat and mass transfer model for predicting thin-layer drying uniformity in a compact,crossflow dehydrator

Abstract

A conjugate heat and mass transfer model was implemented into a commercial CFD code to analyze the convective drying of corn. The Navier–Stokes equations for drying air flow were coupled to diffusion equations for heat and moisture transport in a corn kernel during drying. Model formulation and implementation in the commercial software is discussed. Validation simulations were conducted to compare numerical results to experimental, thin-layer drying data. The model was then used to analyze drying performance for a compact, crossflow dehydrator. At low inlet air temperatures, the drying rate in the compact dehydrator matched the thin-layer drying rate. At higher temperatures, heat losses through the external walls resulted in temperature and moisture variations across the dehydrator.     

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。     

CFD modeling of a pilot-scale countercurrent spray drying tower for the manufacture of detergent powder

A steady-state, three-dimensional, multiphase computational fluid dynamics (CFD) modeling of a pilot-plant countercurrent spray drying tower is carried out to study the drying behavior of detergent slurry droplets. The software package ANSYS Fluent is employed to solve the heat, mass, and momentum transfer between the hot gas and the polydispersed droplets/particles using the Eulerian–Lagrangian approach. The continuous-phase turbulence is modeled using the differential Reynolds stress model. The drying kinetics is modeled using a single-droplet drying model, which is incorporated into the CFD code using user-defined functions (UDFs). Heat loss from the insulated tower wall to the surrounding is modeled by considering thermal resistances due to deposits on the inside surface, wall, insulation, and outside convective film. For the particle–wall interaction, the restitution coefficient is specified as a constant value as well as a function of particle moisture content. It is found that the variation in the value of restitution coefficient with moisture causes significant changes in the velocity, temperature, and moisture profiles of the gas as well as the particles. Overall, a reasonably good agreement is obtained between the measured and predicted powder temperature, moisture content, and gas temperature at the bottom and top outlets of the tower; considering the complexity of the spray drying process, simplifying assumptions made in both the CFD and droplet drying models and the errors associated with the measurements.     

基于Aspen Plus抚顺式油页岩干馏工艺数值模拟

在Aspen Plus平台上建立了抚顺式油页岩干馏工艺模型,利用Aspen Plus的灵敏分析模块研究了抚顺炉气化段温度对产气组分的影响、空气/水蒸汽质量流率比值对产气组分和产气热值的影响,以及干馏段温度对收油率的影响,模拟结果与实际数据吻合良好。结果表明,抚顺炉气化段温度在650～750℃反应最为剧烈,生成的气体量收益最好。随着空气/水蒸汽质量流率比的逐渐增加,CH4和CO2量逐渐减少,CO、H2和N2量逐渐增加,热值也随之降低。干馏段温度在550℃时,收油率达到6.85%,可作为干馏炉热解段的最佳运行温度。     

表观气速对密相气力输送流型影响的模拟研究

针对目前密相气力输送数值模拟关于流型演变方面所存在的问题,提出了一种基于颗粒所在局部空间的固相浓度及颗粒群运动特征来描述颗粒间相互作用的数学模型。该模型能够对气力输送,甚至是颗粒发生大量堆积情况下的密相输送进行数值模拟,使得长期以来缺乏有效模型对密相输送流型进行数值模拟研究的问题得到一定解决。利用该模型,对水平管中煤粉高压密相气力输送的颗粒流动过程进行了数值模拟,获得了输送过程中管道内所发生的气固两相之间的分离、沉积现象,展现了沙丘流及栓塞流等流型的演变特征,模拟结果与实验观察到的现象吻合较好,从而进一步验证了新数学模型的有效性。此外,通过对不同表观气速下固相流态分布的定量分析,揭示了输送流型变化的一些内在规律。     

油页岩过热蒸汽的干燥动力学

以油页岩颗粒作为干燥物料,以过热蒸汽和热空气分别作为干燥介质,进行了油页岩干燥实验的研究。当颗粒粒径减小时,油页岩干燥速率越大;过热蒸汽和热空气温度增大时,干燥速率也越大。对比相同条件下过热蒸汽和热空气干燥油页岩的平均干燥速率,发现当干燥介质温度超过逆转点温度时,过热蒸汽条件下的平均干燥速率大于热空气下的数值。实验得出粒径分别为9,7,5 mm的油页岩颗粒逆转点温度值分别是154,179,177℃;逆转点温度值是个变量,随颗粒粒径大小变化而变化。颗粒粒径越大时逆转点温度值越小,粒径较小时逆转点变化不大。采用薄层干燥模型对油页岩的干燥数据进行动力学模拟,可得修正Page模型(Ⅱ)干基水分比w模拟值与实验值的最大绝对偏差是12%,综合比较发现修正Page模型(Ⅱ)能较好地描述油页岩在过热蒸汽条件下的干燥过程。     

中国油页岩开发利用现状及发展前景

简单介绍了油页岩的用途及中国油页岩开发利用的历史,总结了油页岩的干馏工艺技术和开发利用现状,展望了油页岩的发展前景。     

A rationally based model applicable for heat pump tumble dryer

The present study proposes a rationally based heat pump clothes dryer model which is capable of handling transient behaviors of both air-side and refrigerant side. The model can take into account the geometrical variation of the heat exchangers. Yet the proposed model is free from extra constraints that were normally imposed by previous studies. The simulation shows that there exist three stages in a typical drying process, including a preheat stage, followed by a constant evaporation stage, and finally a falling drying rate period. The calculation indicates that the variation of the clothes temperature and the system suction/discharge pressure show an appreciable rise in the first stage, remain nearly unchanged at the second stage, and increase again at the final stage of drying process. Also, the corresponding maximum specific moisture extraction rate (SMER) peaks at the end of the second stage while the corresponding coefficient of performance (COP) drops continuously. The simulation also indicates that increasing the air volumetric flowrate yields a lower discharge/suction pressure, a higher COP value, and a shorter drying time. The results also suggested that a good strategy to maximize COP is initiated by a low volumetric rate during the preheat stage, increasing it during the second stage and lowering it to an intermediate flowrate at the end of the drying period. Increasing heat exchanger size, either by increasing heat exchanger width or the number of tube row, results in a lower suction/discharge pressure and a shorter drying time. Although both approaches adopt larger surface area to promote overall performance, it is found that increasing the width of heat exchanger yields more effective results.     

中国油页岩干馏技术现状与发展趋势

中国油页岩资源丰富,换算成页岩油储量高达476亿吨.目前中国页岩油生产企业仍然采用以抚顺炉为主的干馏技术,该技术成熟稳定,但油收率不高.本文介绍了目前国内已投产运行和即将工业化的干馏技术以及曾经投入生产、后因多种原因停产的干馏技术.分析表明,我国油页岩产业正处于技术快速发展和产业成长阶段:为显著提高油收率,针对抚顺炉的改进技术已有一些进展,自主研发的成大气体热载体干馏工艺已经开始商业化运行,我国自主知识产权的固体热载体干馏技术出现.但依然存在诸多问题:国内干馏炉单炉处理量小、油收率偏低、半焦无法利用等问题亟需解决,国内固体热载体干馏自主技术依然处于试验阶段,引进国外先进的干馏技术尚没有实质性进展,国内页岩油回收技术亟待改进,油洗技术亟需完善和推广.     

Experimental study of paddy drying in a vortex chamber

The intensification of interfacial mass, heat, and momentum transfer makes vortex chambers potentially interesting for the efficient drying of paddy, allowing shorter drying times and/or more compact equipment. The presence of a shell introduces particular challenges. Intraparticle diffusion limitations are strong and may reduce the advantage from intensified interfacial mass and heat transfer and the efficiency of air usage. Furthermore, high shear and normal stresses in the fast rotating particle bed may cause damage to the paddy shell, posing problems for transport and storage. With these specific aspects in mind, the use of vortex chambers for paddy drying is experimentally evaluated.     

水平管加压密相煤粉气力输送数值模拟

针对加压密相气力输送,对现有的颗粒静摩擦力模型进行适当修正,并将其与颗粒动理学理论相结合,建立了可以描述加压密相气力输送的气固湍流流动状况的多相流模型。该模型充分考虑了颗粒间碰撞和摩擦力作用,以及气相和颗粒团湍流脉动之间的相互作用。采用该模型对水平管内加压密相气力输送进行了三维数值模拟研究,模拟得到了气相和固相的速度、浓度和湍流强度分布,以及压降梯度的变化规律,再现了颗粒沉积层的形成和运动的动态过程。并进行了加压密相煤粉气力输送试验研究,预测的压降梯度与试验测量结果相符合。     

木材纤维管道气流干燥系统的流体力学分析

在中密度纤雏板（MDF）纤维管道气流干燥系统分析中常用的管道断面各项物理参数相同和纤雏在管道断面上均匀分布等多项假设，具有可靠的理论依据。与其说是假设，不如说是忽略次要因素的一种近似，或一种简化。     

油页岩气体热载体干馏炉内干馏特性研究

文章利用自行设计搭建的处理量120 kg/d的瓦斯全循环气体热载体干馏炉,通过试验的方法,研究新型气体热载体干馏炉在干馏过程中的一些运行参数和产生的页岩油的一些特性,对现有干馏工艺的改进具有指导意义。试验通过改变油页岩颗粒的粒径,进而改变物料之间的空隙率、空隙结构和进气流量,来研究不同粒径的样品对干馏特性和干馏产物的影响。结果表明:油页岩颗粒的粒径不同,物料之间的空隙率和干馏炉的进气流量不同,导致炉内传热传质的不同,不同粒径的油页岩干馏油收率不同,粒径为20—25 mm的页岩油收率最高。由于气体热载体流量不同,干馏炉内传热传质情况和冷却器的工作负荷也不相同,因此不同粒径的页岩干馏之后,在4个收油点所收到的页岩油质量分数也不相同。