MEASURED GAS VELOCITY AND MOISTURE CONTENT DISTRIBUTION IN A CONVECTIVE VACUUM KILN

Transferring the necessary heat of evaporation to the stack is the bottleneck in convective vacuum drying of wood. Higher gas velocities are applied to compensate for the lower gas density and to obtain similar heat and mass transfer characteristics as under normal pressure. Like in conventional kiln drying the region with the most unfavorable drying conditions determines drying time and product quality. To use the full potential of the meanwhile established superheated steam vacuum drying technology, it is therefore necessary to work on an improved uniformity of process conditions in the kiln.

To evaluate the fluid dynamics and its influence on the final moisture content, experimenls in a laboratory convective vacuum kiln were carried out. For different total pressures the profiles of dynamic pressure in the stack entry section were measured in a dry atmosphere. At normal pressure the profiles were determined between the board layers throughout the whole stack. For the same slack configuration vacuum drying tests were used to assess the impact of the velocity distribution in the slack on the final moisture content distribution-Regions of low gas velocities coincided well with regions of high final moisture content.     

THE CONVECTIVE VELOCITY OF HEAVY PARTICLES IN TURBULENT AIR FLOWS

This paper examines the influence of the “crossing trajectories” effect on the convective velocity for heavy particles suspended in a turbulent air flow. The fluid energy spectrum “experienced” by a falling particle is deduced from experimental data and is used to evaluate the turbulent component of the convective velocity. The results indicate a significant increase in the rms value of the turbulent component due to the “crossing trajectories” effect.     

窑炉用风量的合理匹配

预分解窑系统窑炉用风量的合理匹配对于稳定系统的热工制度,提高熟料的产量、质量都至关重要,但不同的窑炉结构及不同的操作条件,窑炉对煤粉的环境也不尽相同,燃烧所需要的气体量也不同,根据预分解窑系统煤粉燃烧的的特点,结合国内几家预分解窑的实际生产情况,探讨了窑炉在正常运行条件下用风量,即一、二、三次风的风量大小,并根据某厂家在生产过程中为强化炉内煤娄的燃烧,而对三次风风门开度进行了再次调整后的现场检测结果,讨论了窑炉用风量的合理匹配问题及其对系统正常运转的重要性,指出生产中一定注意风的分配、窑炉用煤量的比例,并兼顾整个系统风、煤、料的匹配关系。     

简析脱硫石膏含水高的成因

介绍烟气脱硫装置的基本情况,分析认为石膏脱水系统存在的主要问题是石膏含水量过高、脱水困难。针对存在问题提出了一些有效的解决方法,确保烟气脱硫装置的安全、稳定运行。     

浅谈料垛码法对倒焰式燃气窑内气流分布及温度均匀性的影响

通过料垛码法形成的气流通道大小对倒焰式燃气窑内气流分布以及温度均匀性的影响进行了分析,认为在一定的条件下,通道大小与气体流动速度和流量成正比,根据这一结论,可对倒焰燃气窑内料垛码法起到一定的指导作用。     

VELOCITY AND CONCENTRATION DISTRIBUTION IN A STEFAN DIFFUSION TUBE

Numerical solutions for the diffusion- and gravity-driven flow in a cylindrical Stefan tube were obtained from the coupled diffusion and Navier-Stokes equations for Peclet numbers, N_Pe = 0.3, 1 and 5. Distributions of binary component concentrations and velocities were calculated. The mass average velocity is parabolic in nature, except at high N_Pe . The solvent is not stagnant but recirculates, even in the absence of gravity. Radial concentration gradients develop which act convectively destabilizing. Consequences for the deduction of diffusion coefficients from Stefan tube experiments are discussed.     

低密度循环流化床反应器床层截面平均颗粒速度的变化规律

本文在高8m,内径186mm 的循环流化床中采用 FCC 颗粒,利用 TSI 光纤激光多普勒测速仪测定了局部颗粒速度的径向分布,并获得了床层截面平均颗粒速度。实验结果表明:截面平均颗粒速度随操作气速的增大而增大,随固体循环速率的增大而略有减小。由实验数据回归得到了计算本实验条件下低密度速度的经验关联式。论文还从基本流体力学理论出发,在考虑颗粒加速运动的条件下,建立了一维气、固两相流模型,可以用于预测床层截面平均颗粒速度和空隙率的变化规律,模型计算结果和实验数据吻合较好。     

CIRCULATION OF GAS AND LIQUID PHASES IN EXTERNAL-LOOP AIRLIFT REACTORS

The effects of the horizontal connection length (0.3 ≤ L_c ≤ 0.6 mrpar;, the cross-sectional area ratio of downcomer-lo-riser (0.28≤A_d/A_r≤0.53rpar;, and the superficial gas velocity on the circulation gas flow rate were studied. The circulation liquid velocity, the downcomer gas holdup, and the bubble size in the downcomer were also investigated. In order to measure the circulation gas flow rate, a gas-liquid separator was installed at the bottom connection between riser and downcomer. Both of the circulation gas flow rale and the circulation liquid velocity strongly depended on the superficial gas velocity as well as the cross-sectional area ratio of downcomer-to-riser and the horizontal connection length. An useful correlation for the circulation gas flow rate was obtained in terms of the superficial gas velocity, the cross-sectional area ratio of downcomer-to-riser and the horizontal connection length.     

采用气体膜分离技术降低高温陶瓷窑炉内NOx的研究

本文根据陶瓷窑炉的特定燃烧环境，分析了NOx的生成以及对环境的危害，探讨了采用新兴的气体分离技术—膜分离法降低高温陶瓷窑炉助燃空气中的N2，从而达到减少NOx的目的。     

隧道窑主要热工测定参数的校核

本文对隧道窑热工测定后数据校核的重要性进行了论述,其目的是为了精确计算热平衡。本文介绍了燃料量,排出烟气量,抽热风量、气幕风量、漏风量等主要热工测定参数的校核方法,并附有实例。     

空间晶体生长流体效应的实验研究和理论分析

在空间晶体生长实时观察装置上,利用溶液中形成的铌酸钾微晶作示踪粒子,首次在空间高温氧化物熔液内,实时观察和记录了空间表面和力对流效应。利用测量的结果计算了熔体内空间表面张力对流的速度场,并与地面表面张力对流的速度场进行了对比,理论计算与实验结果基本吻合。探讨了空间均匀分布铌酸钾微晶的形成机理。结果表明：表面张务对流在空间晶体生长过程中起主要作用,是形成均匀分布胞状晶体的主要机理。     

CFD simulation of corn drying in a natural convection solar dryer

A computational fluid dynamics model was developed to simulate the corn drying process in a solar cabinet dryer. Incident solar radiation was modeled using a dual-band spectrum to simulate the absorption of shortwave radiation by corn and account for the greenhouse effect caused by glazing materials. The performance of the dryer was simulated at fair and overcast weather conditions. The model allowed visualization of temperature, humidity, and air velocity profiles in the dryer. The model was validated with experimental results, which showed an overprediction of temperature (8.5%) and humidity (21.4%). The experimental humidity profile suggests that there was stagnation in the airflow of the dryer, which was accurately predicted by the model. The model was used to simulate the dryer’s performance under overcast conditions, and the predicted moisture removal was 32% less than the simulated fair-weather case.     

外循环型鼓泡式反应器气含率及循环液速率

对直径２８０ｍｍ、扩大直径５００ｍｍ、外循环管直径６５ｍｍ、总高２９００ｍｍ的外循环型鼓泡式反应器，在气体空塔线速Ｕｇ为０．０４－０．５５ｍ／ｓ时，用静压差法和脉冲示踪法测定了不同部位的气含率Ｅｇ，Ｅｐｇ和循环液速率ｕ１，并获得了它们的关联式：对反应段，Ｅｇ＝０．４５５６Ｕ＾０．３１９８ｇ〔Ｕｇ／（Ｕｇ＋Ｕ１）〕＾０．７３９６；对反应器扩大段，Ｅｕｇ＝０．９３８９Ｕ＾０．４４３１ｕｇ；对循环管，Ｅ     

短管中粉气两相流粉粒速度的实验研究

利用激光测速仪在自制的喷粉系统中对等直径短管内粉气两相流粉粒的出口速度进行了测定．应用实验技巧确定了管道内粉粒的加速，并且利用传感器测定了粉粒的质量流量．根据实验研究结果．对等直径管内粉气两相流的基本方程作了修正。     

AIR FLOW, TEMPERATURE AND HUMIDITY PATTERNS IN A CO-CURRENT SPRAY DRYER: MODELLING AND MEASUREMENTS

In a co-current pilot plant spray dryer measurements were done of the airflow pattern (no spray) and the temperature and humidity pattern (water spray). These patterns were simulated with a computational fluid dynamics package (FLOW3D)

The measured air velocities showed large fluctuations. The measured and predicted flow pattern showed good agreement qualitatively, but the measured profiles showed less variation than the predicted ones

The measured temperatures and humidities showed good agreement in large areas of the dryer, but the agreement in the zone near the central axis leaves room for improvement.     

气相色谱法分析合成塔进出口氨含量

介绍利用气相色谱法测定氨合成塔进出口氨含量的分析方法,通过实验说明该方法的准确性。     

AIR FLOW,TEMPERATURE AND HUMIDITY PATTERNS IN A CO-CURRENT SPRAY DRYER: MODELLING AND MEASUREMENTS

ABSTRACT

In a co-current pilot plant spray dryer measurements were done of the airflow pattern (no spray) and the temperature and humidity pattern (water spray). These patterns were simulated with a computational fluid dynamics package (FLOW3D)

The measured air velocities showed large fluctuations. The measured and predicted flow pattern showed good agreement qualitatively, but the measured profiles showed less variation than the predicted ones

The measured temperatures and humidities showed good agreement in large areas of the dryer, but the agreement in the zone near the central axis leaves room for improvement.     

HYDRODYNAMICS AND MASS TRANSFER IN A SPOUTED BED DRYER

ABSTRACT

The disposal of sludge generated by water treatment plants poses major financial and environmental problems. Drying of the sludge is an essential pan of any disposal process which may include incinerating, landfilling or upgrading. In the present study, experiments were carried out to investigate the drying of sludge in a spouted bed and to characterize the hydrodynamics and mass transfer mechanisms. The effect of bed moisture content on the minimum spouting velocity (U_ms) was examined for sludge granules. U_ms was found to increase with increasing the moisture content of the sludge particles. The gas phase mass transfer coefficient in the dryer was determined using porous calcined alumina particles and the results were compared with predictions by correlations available in the literature. The existing correlations gave poor predictions for the mass transfer coefficient. A new correlation for the mass transfer coefficient in a spouted bed dryer was developed based on the experimental results.     

气液逆流鼓泡塔中的气含率与液速分布和数值模拟

分别采用线－线电导探针和背靠背式皮托和测定了气液逆流鼓泡塔中局部气含率和液体轴向速度的径向和轴向分布,讨论了操作条件对气含率与液体轴向速度分布的影响,利用双流体模型对塔内两相湍流流动进行了数值模拟。     

矩形截面气升式环流反应器中非牛顿流体的气含率与传质系数的研究

研究了一种矩形截面气升式环流反应器,用幂律τ=η_ογ~n(n<1)来表示流体流变学特性的变化.在这类反应器中,假塑性非牛顿流体的气含率ε_g与传质系数K_La的变化规律可用半经验关联式表示ε_g=0.2535(η_ο5000~(n-1))~(-0.161)(1+A_d/A_r)~(-0.434)u_(gr)~(0.856-0.161n)K_La=0.0192(η_ο5000~(n-1))~(-0.902)(1+A_d/A_r)~(-1.228)u_(gr)~(1.955-0.902n)并讨论了该类反应器结构及运行状况,流体性质变化时,反应器传质动力学特性、流动特性和操作弹性变化的规律.