高入口浓度下PV型旋风分离器的分离效率计算

基于Muschelknautz 分离模型,以PV型旋风分离器为对象,针对高入口浓度的分离效率的计算,将旋风分离器分离空间的气固分离过程划分为2个区域,提出了串级分离模型。当入口浓度大于临界入口浓度时,旋风分离器内有器壁附近的颗粒支配区和中心区域的气体支配区。颗粒支配区内颗粒速度大于气体速度,颗粒夹带气体沿器壁螺旋下行进入灰斗被全部捕集,形成了颗粒的一级分离;气体支配区内气体速度大于颗粒速度,气体携带颗粒做旋转运动进行离心分离过程,形成了颗粒的二级分离。旋风分离器总的气固分离过程是一级分离和二级分离的叠加。通过高入口浓度的实验对串级分离模型进行了验证,基于串级分离模型给出的PV型旋风分离器的分离效率与实测值较吻合。研究表明旋风分离器临界入口浓度对总效率的计算影响较大。串级分离计算模型包含了结构参数和气、固相物性等参数,具有很好的通用性,可以满足PV型旋风分离器的工程计算和设计要求。     

Effect of Agglomerate Pore Structure on Efficiency of Solid-Liquid Separation by an Agglomeration Technique: Use of a Model System

Abstract

Solid-liquid separation is often difficult to achieve when the solids are finely divided. When the liquid involved is a hydrocarbon, the economics of any process involving such a separation will often depend on the ease and efficiency of liquid recovery. A process is described in which an enhanced solid-liquid separation is achieved by means of a size enlargement technique requiring agitation with a second immiscible liquid, which preferentially wets the solid surface. Potential applications for such a process include removal of ash particles in coal liquifaction and separation of solids from solvent extracted oil-sands. In this work a model system has been used in an attempt to better understand the process mechanics and the factors which affect the efficiency of liquid separation.     

Study of a novel uniflow cyclone design

A 5 cm diameter scale-down model of a new uniflow cyclone for the ultra-rapid fluidized (URF) reactor with a gas residence time under 20 milliseconds has been tested at high solids loading (5/1 wt. solids/wt. gas) under cold modeling conditions. The body length, gas exit diameter and amount of gas withdrawn with the existing solids (gas underflow) were varied to obtain high separation efficiency (over 99.9%). Silica sand of 55 and 105 micrometer Sauter mean diameter was used. Grade efficiency curves were determined for several specific configurations to get a deeper understanding of the mechanisms influencing the separation.     

A kinematic model of continuous separation and classification of polydisperse suspensions

Kinematic models for polydisperse suspensions are based on specifying the solid–fluid relative velocity for each solids species as a function of the local solids concentrations. One such model, the Masliyah–Lockett–Bassoon (MLB) model, is employed herein to simulate continuous separation and classification of polydisperse suspensions. To this end, the clarifier-thickener (CT) setup for the continuous separation of suspensions is extended to a generalized clarifier-thickener (GCT). Discharge streams (or products) are described by new singular sink terms. Combining the GCT setup with the MLB model yields a system of nonlinear conservation laws with a discontinuous flux and a new non-conservative transport term describing the sinks. A numerical algorithm for the solution of this equation is presented along with numerical examples. The model describes the GCT unit with all critical design parameters, and predicts the composition of the overflow, underflow and discharge streams and the spatio-temporal evolution of the solids species concentrations inside the unit.     

Design and Computational Fluid Dynamics Analysis of a Three-Phase Decanter Centrifuge for Oil-Water-Solid Separation

The separation of oil, water, and sand has always been a significant problem in the treatment of oily sludge in oil field and petroleum refinery. The flow field and separation performance in a new three-phase decanter centrifuge with vertical boards and annular liquid separation plate for oil-water-solids separation were investigated, using the computational fluid dynamics (CFD) software Fluent with Euler-Euler three-phase flow model, which provides a basis for the improvement and optimization of the centrifuge. After calculation, the velocity and pressure field were analyzed. The increase of solids content of the feed affected the separation efficiency regularly, and high or low treatment capacity also had a certain impact on the separation efficiency.     

Computer Simulation of the Performance of a Downer‐Regenerator CFB for the Partial Oxidation of n‐Butane to Maleic Anhydride

A reactor model for a downer‐regenerator circulating fluidized‐bed (CFB) during the partial oxidation of n‐butane to maleic anhydride is presented. Upflow reactors (risers) suffer from severe solids back mixing and gas‐solids‐separation, in comparison down flow reactors exhibit a more uniform gas‐solids flow and reduced backmixing, resulting in narrower residence time distributions. Due to the sensitivity of the VPO catalyst to over‐reduction, downer reactors present an interesting alternative to riser reactors. The reactor models for the downer and the regenerator fluidized‐bed are coupled with reduction and oxidation kinetics for the catalyst, respectively. The influence of the solids residence time distributions for the combined system of both reactors on the oxidation state of the catalyst is explored by a novel newly developed oxygen loading distribution. Simulation results suggest the limited solids‐flux in downers restrict the maximum butane concentrations, while the scale‐up is predicted to be uncritical.     

Key operations in the wet-rendering of peanut for the isolation of protein,oil and starch

Separation of oil and suspended solids from peanut slurry are two important interdependent operations in wet rendering of peanuts. A 3-way centrifuge cannot be used efficiently for the separation of the different phases due to the large volume of fibrous suspended solids in peanut slurry. Removal of suspended solids from the slurry by filtration is too slow and incomplete, as the fine particles tend to block the screen. The alternative method of centrifugal sedimentation of the suspended solids causes emulsification of the oil and results in the inefficient separation of the oil. It is shown in the paper that efficiency of the separation of oil and carbohydrate fraction from peanut by wet rendering method depends on careful conditioning of the seed.     

Performance of a large-cone-angle hydrocyclone—II: Separation properties

The separation properties of large-cone-angle hydrocyclones of two different sizes have been determined at different cyclone configurations and input variables. Experiments have been carried out with a mixture of sand and a low fraction of magnetite of almost equal free-fall velocities. Also residence time distributions of magnetite have been determined.Analysis of the experimental results shows that for each volume flow of solids through the cyclone there will be a specific apex opening at which a maximum separation efficiency is reached. If a high separation efficiency is wanted at a high throughput of solids and a low energy consumption, the cyclone should operate with a high vortex finder bottom clearance.     

Effect of the Solid Loading on a PFBC Cyclone with Pneumatic Extraction of Solids

This paper presents the effects of solid loading on the performance of a cyclone with pneumatic extraction of solids. The cyclone is a non‐conventional design, especially used for hot‐gas cleaning applications such as pressurized fluidized bed combustors (PFBC). A scaled‐down cold‐flow model was employed for the research. Experiments were conducted at 9–14 m/s inlet gas velocities, inlet solid loadings ranging from 30 to 230 g/kg gas, and bottom gas extraction percentages from 0.3 to 1.5%. Experimental results of pressure drop resistance coefficients and collection efficiency were compared with literature predictions. At PFBC operating conditions, cyclone geometry and solid concentration are the main parameters influencing cyclone pressure drop and collection efficiency. The vortex penetration in dipleg causes lower pressure drop values and higher collection efficiencies than predicted. These parameters can be suitably predicted for PFBC cyclones by introducing a modified penetration length in Muschelknautz's model [1]. For the present cyclone design, a new correlation of pressure drop, including the influence of solid loading, is proposed. A new method for detecting cyclone fouling, not previously addressed, is also presented, based on the evolution of the pressure drop resistance coefficient. An enhanced separation efficiency has been found, related to collection efficiency, which is especially important for particle sizes below 10 μm revealing agglomeration effects.     

Neue Wege bei der flotativen Aufbereitung und Abwasserreinigung in der chemischen Industrie

New approaches in flotational processing and waste water treatment in the chemical industry . Flotation has not yet become universally accepted in the chemical industry as a separation technique for the solids/liquid system. This article attempts to discover the reason why. It also presents possibilities enhancing the attractiveness of the flotation technique for recovery of materials and waste water purification in the chemical industry. A brief indication of the phenomena exploited by the flotation technique is followed by a discussion of chemical engineering aspects of this technique in ore and coal flotation and in mechanical waste water purification. A flotation cell without stirrer is presented, as has been designed specifically for the chemical industry. In conclusion, some flotation tasks performed with a laboratory version of this type of cell are presented and discussed. They show that the flotation technique can be a favourable alternative to classical separation techniques in many solids/liquid and liquid/liquid separation tasks, and should therefore be considered in future for appropriate separation problems (particle size ca. 100 μm, solids content ≤ 20 g/l).     

矿物在气固流化床中的分选研究

通过对气固流化床的基本特性的研究分析,指出了气固流化床具有良好的分选性能,并研究了矿粒在流化床中的分选机理。试验结果表明：气固流化床可以有效地分选矿物,开辟了一条亲的矿物干法分选途径。     

High solids concentration agitation for minerals process intensification

By using mixing intensification involving high solids concentration as a means to achieve process intensification for the mineral process industry is discussed here. Improving agitator energy efficiency is essential for operating at high solids concentrations. It is shown that improved agitator energy efficiency can be achieved by removing baffles and using higher power number impellers at high solids loadings. Power consumption (50–80%) reductions were demonstrated in the experiments. It is also suggested that slurry stratification in tanks can be used to boost either solids residence time or slurry mass flow. Basic equations related to solids residence time and solids throughput are presented for guidance toward minerals process intensification. An example on doubling throughput via intensification is presented. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

MATHEMATICAL MODELING OF FLUIDIZED BED HEAT REGENERATORS

Based on the two-phase theory of fluidization, a fairly rigorous model is developed to describe the dynamic behavior of fluidized-bed heat regenerators. This model takes into account the major hydrodynamic aspects of bubbling fluid beds. Based on the assumption that the gas leaves the bed in thermal equilibrium with the solids, a rather simplified model is presented. Exact analytical solutions are obtained for both models. The predictions of the more rigorous model are found to be in good agreement with many experimental observations. On the other hand, the simplified model gives satisfactory results only when the value of the parameter m₁is relatively large. Using the rigorous model, it has been shown that the bed thermal efficiency can be improved by reducing the time of operation, increasing the mass of solids or decreasing the bed aspect ratio. Also it has been found that when the gas flow-rate is increased, the amount of heat transferred to the solids displays a non-monotonic behavior and passes through a maximum.     

Filtration of Colloidal Suspensions – MRI Investigation and Numerical Simulation

The principle mechanisms of solid‐liquid separation processes are sedimentation and filtration, both including the formation and compression of a liquid‐saturated bulk. The compressive properties of the bulk determine the operating parameters of solid‐liquid separation devices and the achievable separation results. Information about the solids volume fraction of the bulk is essential for a better understanding of the physical mechanisms and precise modeling. A numerical model for the calculation of the local solids volume fraction during formation and compression of filter cakes and sediments was developed. The calculated results are compared with experimental NMR data.     

The influence of design and operating variables on energy consumption and separation efficiency of a hydrocyclonic concentrator

The problem of physical separation of solids from liquids in very dilute concentrations by hydrocyclone concentration is considered in two parts. First, the effect of feed concentration, volume split, feed flowrate, cone angle, inlet diameter and vortex finder length on separation efficiency and energy loss are investigated. The relationship between the separation efficiency; and the energy loss is also studied. Secondly, the effect of three different designs of body shape on the separation efficiency and energy loss is investigated. In this study statistical concepts are used extensively in the design of experiments and the analysis of experimental results.     

Removal of intractable fine solids from bitumen solutions obtained by solvent extraction of oil sands

During solvent extraction of bitumen from oil sands, the bitumen solutions produced are usually contaminated with fine solids. The water-wettable fines may be eliminated by utilizing simple solids agglomeration techniques during extraction. Intractable oil-wetted solids can also be removed by chemical treatment to improve settling rates, allowing separation without the need for centrifugation. Some data from small-scale batch and continuous experiments are presented to illustrate the techniques employed.     

Rate‐based‐Modellierung von CO2‐Absorptionskolonnen mit Anstaupackungen

The efficiency of columns for fluid separation can be increased by the application of sandwich packings. During the operation, different load‐dependent regimes with peculiar separation performance arise. In order to account for the effects of the individual flow regimes in a single model, both separation performance measurements and tomographic imaging are applied. A rate‐based model is presented, which takes the heterogeneous regimes in sandwich packings into account by means of appropriate correlations. The model is tested with experimental data for CO₂ absorption.     

Online measurement and control of solids moisture in fluidised bed dryers

Currently, two main methods are used to take online measurement of the solids moisture in fluidised bed dryers, namely microwave resonance and near infrared spectroscopy. In this paper, a new online approach to solids moisture measurement of batch fluidised bed dryers by electrical capacitance tomography (ECT) is presented for the first time. Based on online measurement of solids moisture, it is possible to implement feedback control and process optimisation of batch fluidised bed drying processes, aiming to increase the operation efficiency and to improve product quality. A twin-plane ECT sensor with eight electrodes in each plane is mounted in the bottom of a glass fluidisation chamber. From the adjacent electrode pairs, the water content of the solids is estimated based on the correlation between the moisture content and the permittivity value. To reduce measurement error, the effect of temperature on moisture measurement is compensated. The fluidisation velocity is estimated by a semi-empirical function based on the measured water content. The acquired information is sent to a controller to adjust the air flow rate of the fluidised bed dryer. To validate the moisture measurement by ECT, a mathematical model has been developed, based on the measured temperature and relative humidity of the outlet air. The Landweber iteration method is applied to reconstruct images. The averaged solids concentration along the radial direction at different fluidisation conditions is given and compared with results by the linear back-projection (LBP) method. Results from batch drying processes with online measurement and feedback control are given and compared with no feedback control. To compare the operation efficiency, the thermal efficiency is considered and the results show the possibility of online control and optimisation of the fluidised bed drying processes, based on online measurement of solids moisture by ECT. Some challenges and future work are discussed.     

催化裂化沉降器旋流快分系统内两种旋流头的性能对比

通过冷态对比实验,研究了旋流快分系统（VQS）内两种新型旋流头的分离性能,结果表明B型旋流头采用大弧切向出口后,对含尘气流具有加速旋转的作用,可使颗粒喷出后获得更高的切向速度,从而提高系统的分离效率。采用Fluent软件对VQS内气固两相流进行了数值模拟,重点考察了A、B型旋流头的流场分布和分离特性。模拟结果表明：含尘气流由B型旋流头喷出后,切向速度较大,离心力较强,增加了颗粒在稳定分离区内分离的概率;同时,含尘气流喷出后气量大部分集中在封闭罩内壁附近下行流动,下行轴向速度较大,有利于颗粒下行分离。此外,相比于A型旋流头,B型旋流头的分离优势在于可大大提高对中粗颗粒的捕集能力。因此工业应用中推荐采用B型旋流头,以更好地满足工业生产的需求。     

Extended cyclone theory for gas flows with high solids concentrations

Large recirculation cyclones with high concentrations of particulate solids have gained considerable importance in the field of circulating fluidized bed technology. To calculate a combustion process, the influence of the cyclone on the circulating quantity of solids and their grain size distribution must be known. Measurements in a 105-MW-plant in 1989 showed that the existing cyclone theory was not sufficient for this purpose. In a laboratory cyclone (900 mm in diameter), the separation and classification of solids in a gas flow was investigated. The cyclone was fed from a fluidized bed and operated with cold air and quartz of various grain size distributions. Based on this experimental device and the theory of momentum transfer between solids and gas flow, a new, more accurate method of calculating the separation efficiency was developed.