Calculation of multistage countercurrent separation processes—II multicomponent multistage separation by relaxation procedure

The relaxation method used for solution of problems arising in design of multicomponent separation processes is discussed and new modifications are proposed. The use of certain techniques for convergence acceleration is studied. The number of iterations is then substantially reduced and effectiveness of relaxation method is thus highly improved.This method is useful also for columns with multiple feeds, intercoolers etc., however, nonideal mixture can be conveniently handled. A modification of the relaxation procedure resulting in a pentadiagonal matrix is presented.     

Simulation of stage separation columns based on the block short-cut approach

A generalization of the short-cut approach for the modelling and design of stage separation columns has been developed. The block short-cut method can be used for complex columns and non-standard problem specifications. The column is partitioned into several separation sections (blocks), each modelled by a universal short-cut model. The overall simulation model is solved by the global Newton-Raphson method. Very low memory and CPU time requirements enable the block short-cut approach to be utilized for fast simulation and control of columns in industrial practice.     

Gas separation by permeation Part I. Calculation methods and parametric analysis

Calculation methods for single- and multi-stage permeation of a multi-component mixture are presented. The use of the local permeate concentration in the formulation results in a relatively simple form of solution for the binary system in the cross-flow pattern. A parametric analysis of the permeation cascade is given. For a given permeability of the more permeable component, there exists a membrane selectivity which gives rise to a minimum membrane area requirement in the cascade. It is shown that the compression power requirement is dependent only on the operating pressure ratios, irrespective of actual pressure levels in each stage. A study on the effect of interstage mixing loss shows that the ideal cascade (with no interstage mixing loss) is not necessarily always the thermodynamically most efficient one; some non-ideal cascades may have higher efficiencies due to more effective permeation steps. Examples given relate to He/CH₄ and O₂/N₂ separations.     

Calculation of countercurrent separation processes—III. Computation of two interlinked columns.

The relaxation procedure is used for solution of two interlinked distillation columns. Both approaches-sequential iterative method and the block relaxation technique are compared. A new algorithm making use of simultaneous solution of all equations is proposed.     

Intensified process for aromatics separation powered by Kaibel and dividing-wall columns

Process intensification in distillation led to major developments, such as reactive distillation, heat-integrated distillation, cyclic distillation, as well as Kaibel and dividing-wall column. Still, the separation of aromatics at industrial scale is carried out typically in a series of conventional distillation columns, with severe penalties on the associated plant footprint, investment and operating costs. To solve this problem, this study investigates novel separation alternatives powered by dividing-wall column (DWC) and Kaibel distillation column. The new sequences using process intensification are able to separate five products (lights, benzene, toluene, xylene and heavies) at high purity levels, in only two distillation columns.AspenTech Aspen Plus^® was used as a computer aided process engineering tool to perform the rigorous simulation and optimization of the new separation alternatives, applied to a simplified industrial case study. In order to allow a fair comparison, all design alternatives were optimized using the sequential quadratic programming (SQP) method.Notably, the novel design with two consecutive DWC units reduces the energy demand by 14%, while the alternative combining a conventional stripper with a Kaibel column leads to over 17% energy savings as compared to the conventional direct distillation sequence. Moreover, the new separation schemes require less equipment and a reduced plant footprint.     

The generalised equation of separation in thermal diffusion columns by linear approximation

A generalised equation of separation applicable to the whole range of concentration in flat-plate thermal diffusion columns has been derived. The improvement in theoretical analysis was obtained by replacing the product form of the concentration dependence with a linear approximation instead of a constant.     

Calculation of reactive extraction in countercurrent columns

The kinetics of extraction processes with chemical reaction was studied experimentally on the system copper/Acorga PT 5050 and quantified according to meaningful kinetic models. These were coupled with other models describing the behaviour of dispersions in columns in order to permit a computer aided simultation of reactive extraction. Thus, a better prediction of column performance is achieved.     

空分填料塔设计中的流体力学特性

空分精馏主要在-200℃左右的深冷条件下进行,填料塔内流体力学特性参数难以由试验直接获取,如何将常压常温状态(简称常态)下空气-水物系的流体力学测试结果转换适用于空分设计变得尤为关键。通过Bain-Hougen公式及SRP(Ⅱ)模型结合Sp iegel持液量计算推导出泛点及压降关联式以预测填料的流体力学特性。对空分中常用的750Y型金属孔板波纹填料进行常态下流体力学特性测试,结果表明:采用的方法可用于填料流体力学特性的预测。对空分状态下的泛点与压降结果预测表明,空分设计中采用常态下的流体力学数据进行设计偏于保守。     

Long-term prediction of nonlinear hydrodynamics in bubble columns by using artificial neural networks

An artificial neural network (ANN) model was proposed for the long-term prediction of nonlinear dynamics underlying holdup fluctuations in bubble columns with three different diameters of 200, 400 and 800 mm. Local holdup fluctuations were measured with an optical probe in the bubble columns. The superficial gas velocity was varied in the range of 33–90 mm/s. The time intervals between successive bubbles were extracted from the time series of holdup fluctuations to represent hydrodynamic behaviors in the system and used as training and validation data sets. The effect of data preprocessing as well as the numbers of nodes in input and hidden layers on the ANN training behavior was systematically investigated. The prediction capability of the ANN was evaluated in terms of time-averaged characteristics, power spectra and Lyapunov exponents. It was observed that: the ANN model, which was trained with experimental time series and gas velocity, can be used for the long-term prediction of dynamic characteristics in bubble columns by using random data as the initial input. The results indicate that the trained ANN models have the potential of modeling nonlinear hydrodynamic behaviors in bubble columns.     

Study of crosslinking of unsaturated polyester resins by relaxation methods

Radiation and thermal curing of unsaturated polyester resins with styrene were investigated by combining differential thermal analysis with electric and mechanical relaxation techniques. A microprocessor controlled combined relaxation equipment of special construction was used. By radiation initiated curing the reaction was interrupted at different stages and the products were analyzed. Relaxation and simultaneous differential thermal measurements were also made during the course of gamma radiation and peroxide initiated thermal curing. By this way the shift of the characteristic transitions of the resin as a function of conversion could be studied. Also the change of the phase-structure of the resin caused by the reaction was monitored. By deconvolution of the dielectric spectrum band the physical structure was found to become heterogeneous by crosslinking. Besides the shift of the transition temperatures the oscillator strength of the dielectric transition was found to decrease with conversion. Electrical polarization and depolarization studies were also performed. A special intermittent load thermomechanical technique was used for separating elastic from viscous response of the sample subjected to external mechanical force. The transitions exhibited by the thermomechanical curves were found to shift to higher temperatures by crosslinking and the compliance plateaus decreased.     

生物油萃取分离技术的研究进展

综述了国内外采用萃取技术分离生物油的研究进展,包括水萃取、有机溶剂萃取、络合萃取、超临界萃取、柱层析萃取等,总结了这些萃取方法的优点和缺点。指出可通过对生物质热解过程本身进行改进,如对原料进行预处理、引入催化剂进行催化热解、对热解蒸汽进行分级冷凝等,以获得富含目的产物组成的生物油,为萃取分离提供便利。最后,建议尝试一些新的萃取分离方法,如微波萃取和超声波萃取等,考察对生物油萃取分离的有效性。     

Calculation of the dimensions of columns with upward flows

Systems approach is used to derive a differential equation for the quasi-equilibrium of a power material in a liquid upward flow. A particular solution to the differential equation is given for the case of washing the tungsten metal powder produced from a molten soluble salt of potassium carbonate.     

规整填料精馏塔的设计计算

通过大量的文献调研，比较了规整填料精馏塔和板式塔的优缺点，对规整填料精馏塔内压降、传质及液泛时压降的计算公式进行了比较，总结出设计计算规整填料精馏塔的步骤与方法，为规整填料精馏塔的应用提供了基础。     

内部热耦合空分塔的节能优化分析

内部热耦合精馏是迄今为止所提出的节能效果最好,而唯一没有商业化的节能技术。将内部热耦合技术用于空分塔,可以带来良好的节能效果。根据低温空气分离过程以及三组分精馏的特点,提出了一种新的内部热耦合空分精馏塔优化模型。在优化模型基础上,对热耦合塔进行了深入的节能优化与分析,并且与常规空分仿真结果进行了比较分析,压缩机能耗下降20.75%,产值增加17.46%,单位产值能耗下降32.53%。内部热耦合空分塔的提取率以及能耗均优于常规热耦合空分塔,节能效果显著。     

Creep-based characterization of nonlinear relaxation behavior of plastics

It is a matter of fact that creep experiments can be conducted more easily and accurately than stress relaxation experiments, since it is easier to maintain a stress constant (for instance by a “dead weight”) than a strain constant. Nevertheless, in practice, structural parts made of plastics (which are nonlinear viscoelastic materials) are very often loaded under stress-relaxation conditions. The present paper presents an approach to predict the behavior of a nonlinear viscoelastic material under stress-relaxation-type loading, based on data obtained from creep-type experiments. The nonlinear creep compliance is described mathematically by an exponential series with a limited number of terms and a single nonlinearity function depicting the transient behavior. The nonlinear behavior of the material under constant strain (i.e., stress relaxation) is then obtained by dividing the considered time range into very short time intervals in which constant stresses are acting, while the different values of the applied stresses are chosen in a manner that guarantees the same stain at the end of each interval. In this way, one performs a numerical nonlinear superposition of the effects of the loadings in the various intervals, leading to the desired results under stress relaxation. A comparison of theoretical results with experiments conducted on some thermoplastic materials shows good agreement.     

Calculation of the drop size in pulsed sieve-plate extraction columns

A new method for the calculation of drop sizes in pulsed sieve-plate extraction columns is reported. Under certain assumptions for the motion of the drops in the vicinity of the plates, it is possible to develop an equation that is confirmed by measurements in a much greater range, especially of the pulsation intensity, than other equations being known up to now. Additionally, a dependence of the drop diameter on the hole diameter at constant fractional free area results from that new equation, which has been proven so far only experimentally. Finally, with the developed equation under consideration of the time-dependent variations of the effective forces it is possible to make qualitative predictions on the type of the drop size distribution to be expected.