Experimental study on the solid velocity in horizontal dilute phase pneumatic conveying of fine powders

The calculation reliability of pressure drop and gas-solid drag force in horizontal dilute phase pneumatic conveying strongly depends on the accuracy of gas-solid velocity correlation. However, there are limited studies on the solid velocity in horizontal dilute phase pneumatic conveying and it is important to further validate suitability of existing correlation of gas-solid velocity, especially for fine particles (such as pulverized coal). Consequently, in this paper, a negative pressure pneumatic conveying test rig is set up and two kinds of powders with different sizes are adopted. Optical fiber probe (OFP) was used to measure the volumetric solid concentration and particle velocity. The volumetric solid concentration was also calculated by using the measured particle velocity. The results show that the solid concentrations obtained by the two methods have good agreement, and discrepancy is within ± 20%. It was found the particle velocities are different in the upper and lower part of the cross-section in the horizontal pipe. However, the difference is generally no more than 2 m/s. The velocity difference will decrease with the increasing gas velocity, and increases with the solid mass flow rate. In the experimental condition of 0.06 mm < d_s < 0.35 mm, 1400 kg/m³ < ρ_s < 2600 kg/m³, the implicit correlation based on Yang's Unified Theory gives the best prediction of particle velocity among existing studies but still with noticeable discrepancy with the comparison of the present experimental data. By modifying the solid friction factor, an improved correlation of the particle velocity was obtained, which agrees better with the experimental data given in the present and literature studies.     

An effective voidage model for sedimentation of bidisperse solid suspension

An effective voidage model of a liquid-fluidized bed that takes into account particle–particle interaction has been used to predict the slip and interface velocities of sedimenting zones for bidisperse solid–liquid systems. The model visualizes that a ‘test particle’ in the bed is surrounded by particles of ‘average size’ but enjoys an effective voidage different from the average voidage. The model was successfully used before to interpret and predict phase inversion as well as mixing and segregation in a liquid-fluidized bed. A little modification of the original model was done to make it suitable for interpreting batch sedimentation data. The model does not necessarily need the experimental values of the relevant parameters. Predictions of the model over a range of particle sizes and liquid properties are more accurate than those of the previous models.     

水相悬浮法CPVC生产新工艺

介绍了水相悬浮法CPVC生产新工艺:分段控制温度(45~55℃,65~75℃,80~85℃),分次加入复合引发剂,并用有机碱稀溶液进行稳定化处理,可以得到氯含量高、氯化均匀、热稳定性良好、色泽理想的CPVC。     

Dynamic and steady-state sedimentation of polydisperse suspension and prediction of outlets particle-size distribution

The Kynch theorem was extended to non-linear system of conservation laws of polydisperse suspensions of spherical particles. The simulation predicts overflow of light particles and heavy particles at steady state and dynamic mode of batch and continuous sedimentation. The model eliminated the need for imposed non-theoretical parameters or functions to predict hindered settling and effluent concentrations. Particle-size distribution is also predicted at the effluent and the underflow. We examined several cases and predicted dynamic behaviour of rarefaction waves and overloaded continuous settler. A new concept of dynamic flux curves is also used and introduced.     

A new method for the reconstruction of the particle radius distribution function from the sedimentation curve

A new method for the reconstruction of the particle radius distribution function from the sedimentation curve is proposed. This method permits us to obtain a continuous smooth distribution function. Two approaches are compared. The first approach is based on the calculation of the second derivative from the sedimentation curve. The second one is based on the solution of the original integral equation which describes a sedimentation process. Both of these approaches can be reduced to the problem of the solution of the Fredholm integral equation of the first kind. From the theory of integral equations, it is known that this problem is ill-posed. The usual methods lead to unstable solutions and we are forced to use special regularizing algorithms. In this paper, the Tikhonov regularization method is used to stabilize the solution of the integral equation. It is shown that the accuracy of both methods is higher than the accuracy of the graphical method, but the approach based on the solution of the original integral equation gives a more stable solution than that based on the derivative. The accuracy of the new method permits us to reconstruct the fine structure of the particle radius distribution function. Such an analysis cannot be carried out with the rough bar diagram obtained from the graphical method. The new method is absolutely indispensable in technology for controlling the degree of powder fineness.     

电涡流制动器在卧螺离心机差转速定值控制中的应用

介绍了电涡流制动器的结构和特性,以及由电涡流制动器、数字转速表、ＰＩＤ调节器和程控稳压稳流电源构成的卧螺离心机差转速定值控制装置。     

悬浮法聚氯乙烯质量指标控制方法总结

详细分析了悬浮法聚氯乙烯产品质量指标的影响因素,提出了在生产实践中的具体控制方法．保证了质量达标。     

A new method to evaluate horizontal solid dispersion in a bubbling fluidized bed

A new method to evaluate horizontal dispersion of solids in bubbling fluidized beds is proposed: a carbon-loaded bed material prepared using the capacitance effect (volatile matter captured by porous particles) is used as a tracer. The tracer particles are identical to the remainder of the bed material, except for carbon-loading of a few weight percent. The extent of solid dispersion is evaluated by measuring the horizontal concentration profile of CO, which is formed by the reaction of carbon in the tracers with CO₂ in the fluidizing gas. Transient change in the horizontal CO concentration profile is measured in the freeboard and the experimental results are compared with the theoretically calculated results of one-dimensional diffusion of solids. Thereby, the horizontal dispersion coefficient is determined. The experimental results agree with results obtained from the literature.     

稀悬浮液回收净化流程与磁选机选择探讨

分析了重介质选煤厂设计中采用的磁选—浓缩—磁选、磁选—磁选及一段磁选三种不同稀悬浮液回收流程的优缺点;提出在选择磁选机时,要考虑矿浆通过量、最大入料粒度及入料的矿浆浓度等三个主要因素。     

Real-time analysis of the growth of granular media by an ultrasonic method: Application to the sedimentation of glass balls in water

In this work, we propose a real-time analysis of the growth of a granular material by a high frequency ultrasonic method (around 5 MHz) based on normal incidence reflectometry. This method is non-destructive. It can be applied to the general case of cloudy solutions in optically opaque sedimentation cells. Results were obtained on glass balls used as a model granular material. Glass balls were sedimenting in water. Measurement of the deposit thickness (varying from several dozen of micrometers to several millimeters) leads to morphological and dynamic properties such as the volume solid fraction and the deposit growing rate. The strong influence of the particle size distribution (median diameter, broadness of the size distribution) on the dynamic properties of the particle packing was determined quantitatively. Our results are in good agreement with the classical model of sedimentation for an isolated sphere (Stokes law).     

提高悬浮法PVC产品白度的技术研究

研究了各种影响悬浮法PVC树脂白度指标的因素,并有针对性地提出了提高树脂产品白度的各种措施和对策。     

Experimental test of a model for laminar slurry flow with sedimentation

The ability of a flow-sedimentation model to simulate the flow of a slowly-settling suspension being transported in the laminar regime through a pipeline with a constant overall pressure drop imposed on it was assessed using experimental scaled-down pipeline data. Comparison of predicted volumetric flow rate versus time profiles to those observed suggested that the blockage process took place in two steps. Initially, a sediment grew on the lower pipe wall and the flow gradually lessened, as was modelled. As the flow slowed down, ultimately a plug, which enclosed the full cross-section of the pipe, formed and lead to the rapid blockage of the pipe. It was envisioned that the granular properties of the concentrated suspension became dominant during the final blockage process. A deposit velocity criterion was also developed from the flow-sedimentation model and was used to generate a deposit velocity versus pipe diameter plot. Results from the plot indicate that the laminar pipeline flow of a slowly-settling suspension is possible in small diameter pipes.     

水相悬浮法生产氯化聚氯乙烯树脂

介绍了氯化聚氯乙烯树脂的几种生产方法 ,着重研究了利用热引发水相悬浮法生产CPVC的生产工艺。试验结果表明 :反应时的温度、压力、引发剂添加量及后处理条件对PVC的氯化均有影响 ,因此氯化反应温度最好控制在 80～ 14 0℃ ,压力控制在 0 .1～ 0 .5MPa ,引发剂添加量在 0 .0 1%～ 0 .3%。     

疏松砂岩水平井临界生产压差预测模型的建立

油井的出砂已经成为困扰疏松砂岩油藏生产的一个严重的问题,科学有效地进行出砂预测对于指导油田高效开发具有重要的意义。本文分析了疏松砂岩油层出砂机理,在油层出砂机理的基础上,从井壁稳定性的力学机理出发,对水平井井壁三维应力进行了分析,利用Mohr-Coulomb破坏准则,建立了水平井出砂临界生产压差模型,并通过对某区块的8口井进行了计算,数据结果表明：此8口井的临界压差与实际生产状况基本相近,因此利用该模型计算临界生产压差,可以为油田生产提供指导依据。     

提高悬浮法PVC热稳定性的研究

介绍了悬浮法PVC热稳定性的分析方法,建议采用调整分散体系和引发体系的方法提高PVC的热稳定性。     

The use of dilute acetic acid for butyl acetate production in a reactive distillation: Simulation and control studies

The recovery of dilute acetic acid, which is widely found as a by-product in many chemical and petrochemical industries, becomes an important issue due to economic and environmental awareness. In general, separation of acetic acid in aqueous solution by conventional distillation columns is difficult, requiring a column with many stages and high energy consumption. As a result, the primary concern of the present study is the application of reactive distillation as a potential alternative method to recover dilute acetic acid. The direct use of dilute acetic acid as reactant for esterification with butanol to produce butyl acetate in the reactive distillation is investigated. Simulation studies are performed in order to investigate effect of the concentration of dilute acetic acid and key process parameters on the performance of the reactive distillation in terms of acetic acid conversion and butyl acetate production. In addition, three alternative control strategies are studied for the closed loop control of the reactive distillation. The control objective is to maintain the butyl acetate in a bottom product stream at the desired purity of 99.5 wt%.     

水相悬浮法氯化反式-1,4-聚异戊二烯的反应动力学

对现行工艺条件下水相悬浮法氯化反应,采用经验式y=10.391 lnx 21.602预测氯化反应程度,即根据氯化反应时间(x)计算氯质量分数(y),相关系数R2=0.985 4;利用方程式y=0.061 9e0.042 8X,用实际所测得的氯质量分数(X),计算出氯化反应相应的转化率(y),相关系数R2=0.997 2;水相悬浮法氯化工艺条件下的表观反应级数为:n=0.95;经过恒定反应时间,对不同反应温度对氯含量的影响进行考察,计算出氯化反应的表观活化能为13.36 kJ/mol.     

A CFD methodology for the design of sedimentation tanks in potable water treatment: Case study: The influence of a feed flow control baffle

Computational fluid dynamics simulations are employed to assess the effect of adding a vertical baffle at the feed section of a full-scale sedimentation tank for the improvement of solids settling in potable water treatment. A general CFD-based simulation strategy is developed based on the specific features and conditions met in practice for potable water treatment. The linearity of the particle conservation equations allows separate calculations for each particle size class – but performed for all classes of interest – leading to the uncoupling of the CFD problem from a particular inlet particle size distribution. The usually unknown and difficult to be measured particle density is found by matching the theoretical to the easily measured experimental total settling efficiency. The proposed strategy is computationally much more efficient than the corresponding strategies used for the simulation of wastewater treatment. This work compares simulations from a standard and a baffle-equipped tank. It is found that the baffle decreases the inlet recirculation zone and enhances the settling of solids by directing them towards the bottom of the tank with high velocities. It is noteworthy that even small differences in the particle velocity can cause large changes in the percent of settled particles; in this work, the overall solids removal efficiency increased when using the baffle from 90.4 to 98.6% leading to a reduction of the effluent solids concentration of approximately 85%.     

水相悬浮相转移法氯化石蜡-70生产工艺

在传统的水相法氯化石蜡-70生产工艺的基础上,开发出水相悬浮相转移法工艺。该工艺氯化反应温度低（≤120℃）,氯化周期短,在反应中完成二相（气、液）转化为三相（气、液、固）的水相悬浮相转移,形成粉末悬浮液,后期反应温度低于物料软化点。该工艺先进,生产安全。