FIBONACCI SEARCH FOR OPTIMAL FEED LOCATION

Abstract

A Fibonacci search technique is used in conjunction with a rigorous mullicomponenl distillaiion computer module to find the optimal feed location within a section of a distillation column. The function lo be minimized can be one of the following:

?key component ratio difference

?reflux ratio or reboiler ratio

?condenser duty or reboiler duty

This technique has been used successfully in the relocation of feed stages of many existing distillation columns and thus saved energy consumption. We shall describe this technique with a sample problem.     

DIRECT COMPUTATIONS TO DESCRIBE BATCH DISTILLATION WITH RECTIFICATION

An analog of the Rayleigh Equation has been applied for many years to describe batch distillation with rectification for binary mixtures. A solution is obtained by iterative graphical computations followed by numerical integration. When the batch distillation algorithm is stated in terms of distillate composition a computational non-iterative soluton may be obtained. For a binary separation this expression may be solved on a programmable calculator and the integral may be obtained in segments to describe the progress of the operation expressed in terms of the quantity remaining in the still-pot. This variable is not a linear function of time since even at constant reboiler duty the boil-up rate varies as the still-pot composition changes. If the time rate of the operation is to be determined, this effect must be considered. Procedures have been developed to describe the time-responses of the plate compositions and temperatures, the boil-up rate as well as the conventional variable, the volume remaining in the still-pot

Application of this procedure is illuatrated by evaluating operating strategies for batch distillation. A capacity factor is based on the time required to make a complete separation so that both the distillate product and the heel meet specific composition and disposition of a slop cut (if any) is accounted for. The reboiler is specified to operate at capacity but it is recognized that the boil-up rate will then drop off as the still-pot material becomes heavier and warmer. The distillate composition profiles and the boil up profiles are used to designate changes in objectives during the over-all runs.

Batch processing. The chemical processing industry has been using batch operations increasingly during recent years and these procedures have been drawing increasing attention in chemical engineering publications. Batch distillation is often selected as a significant purification in these processes and has likewise enjoyed a resurgence in investigations and reported advances and results.

Major companies have reported a broad use of batch processing. Chowdhury (1988) has reported that DuPont and Rohm and Haas operate numerous processing lines for hundreds of product variations. Professor G.V. Reklaitis of Purdue has developed a simulation program for designing, scheme selection, and scheduling batch processes and has founded a company, Batch Processing Technologies, Inc. to distribute results from his program.

Batch processing units are most often used in one of two ways. A sequence of equipment may be required to manufacture several different products. This method is often encountered when the products are based on various formulations and rely primarily on mixing and purification to meet customer requirements. Batch processing may also be specified when a particular product is produced from different raw materials and through various processing routes. In either case the same equipment is used repeatedly to perform similar but different operations and is scheduled to operate almost continuously by rapid turnarounds between functions to minimize downtime.     

2,3-丁二醇分离纯化中反应精馏的实验和模拟

对反应萃取-水解精馏法分离发酵液中2,3-丁二醇工艺中的水解精馏进行了实验和模拟研究。实验验证了4,5-二甲基-2-丙基-1,3-二氧戊环(DPD)水解精馏得到2,3-丁二醇的可行性。采用Aspen Plus建立反应精馏模型,以UNIFAC为热力学方程,RadFrac为反应精馏模块,对常压下DPD的水解精馏进行模拟,模拟结果与实验结果吻合较好。以2,3-丁二醇的收率为主要优化目标,考察最佳塔板数、进料位置、进料比、回流比和塔顶馏出比。模拟结果表明,在最佳操作条件下,塔釜2,3-丁二醇的收率为0.981,摩尔分率为0.150。     

内部热耦合精馏塔的操作性能与模拟

对同轴式内部热耦合精馏塔的操作性能和节能效果进行了研究,考察了全回流操作条件下,压缩比对回流量、冷凝器负荷和再沸器负荷的影响。结果表明,随着压缩比的增大,回流量、冷凝器负荷和再沸器负荷均降低。通过实验数据计算得到了该塔的理论板数和两塔间的传热量,精馏段为9块理论板,提馏段为4块理论板,当压缩比为2.2:1时,两塔间传热量为9.98kW。连续操作条件下,对内部热耦合精馏塔的节能效果进行了分析,通过与常规精馏塔的比较,内部热耦合精馏塔可节约52.3%的冷量,输入的再沸器和压缩机总负荷可节约20.34%。另外,基于实验数据,对该内部热耦合精馏塔进行了动态模拟,经连续操作下的实验验证,该内部热耦合精馏塔可在2h后达到稳定操作。     

Design and Control of Extraction Distillation for Dehydration of Tetrahydrofuran

Design and control of an extractive distillation system for tetrahydrofuran (THF) dehydration with ethylene glycol as entrainer is investigated. The main module is a two‐column system containing an extractive distillation column, whose top stream is the desired product THF, and an entrainer recovery column. Economic analysis with total annual cost as the objective function is developed. Two kinds of control strategies are explored for THF dehydration. The responses reveal that the control structure with fixed reflux ratio cannot maintain the bottom liquid level of the entrainer recovery column, while the control scheme with fixed reboiler heat duty/feed flow ratio exhibits good control performance in spite of large deviations in feed flow rate and feed composition.     

DYNAMIC SIMULATION OF A DISTILLATION COLUMN SEPARATING A MULTICOMPONENT MIXTURE

In this work, a dynamic model was developed to simulate the transient behaviour of a pilot scale, continuous, siagewise, 15 plate distillation column separating a mixture of ethanol, iso-propanol and isobutanol. The accuracy of the predictions was assessed by transient response data collected during experiments under step changes in reflux ratio, feed flow rate and feed composition.

Results demonstrated the feasibility of simulating multicomponent distillation under unsteady state conditions with fairly good success. Further improvements were suggested for a better accuracy     

METHODOLOGY FOR SENSITIVITY ASSESSMENT OF PETROLEUM FRACTIONATORS TO FEED COMPOSITION VARIATIONS

The environmental constraints coming into place on aromatics in petroleum products makes it necessary to develop an analytical technique that explicitly accounts for their effect. Furthermore, the multicomponent nature of petroleum fractions makes it difficult to analyze feed composition sensitivities without a large number of tests. This paper presents a convenient way to analyze the sensitivity or, as sometimes called, the switchabilily of petroleum fractionators. The technique depends on “lumping” all the paraffinics, naphthenic and aromatic components into three “pseudo components”: P, N and A.

Although this approach may appear simplistic, it is based on rigorous physical data. It, therefore, has a clear advantage over the traditional characterization methods. In addition, the method is inherently linked to the conventional TBP-Analysis of the ASTM type.

The utility of this technique is presented with an application to the sensitivity and switchability of a refinery stabilizer. Assuming fixed recovery of C₄ and C₅ in the bottom and overhead products, the various effects of feed variations on reflux, reboiler and condenser duties, and distillate product are demonstrated. Further, the effect on column temperature and composition profile is also analyzed.     

反应精馏隔壁塔生产乙酸正丁酯的优化与控制

对反应精馏隔壁塔生产乙酸正丁酯过程进行了模拟、优化与控制的系统研究。利用Aspen Plus软件模拟乙酸甲酯与正丁醇的酯交换反应过程,以年总费用（TAC）为目标函数进行过程优化,通过稳态敏感性分析及相对增益矩阵（RGA）判据得到不同的操纵变量与控制变量匹配关系,以此为基础,在Aspen Dynamics平台建立了若干控制结构并进行分析对比。结果表明,利用两股反应物呈比例进料可较为有效地抵抗进料扰动,最后提出的无再沸器热负荷与混合物进料量比值（Q_r/F）控制的改进控制结构CS3,在降低反应精馏隔壁塔控制过程超调量方面有较大的优越性。     

Fracture Toughness of Adhesive Joints

To define the influence of the processing variables on the resistance of epoxy joints to brittle crack extension during short loading times, the fracture toughness, g_ic, of the joints was measured as a function of the following variables:

1. Hardener type (TEPA vs. HHPA)

2. Ratio of hardener to resin content

3. Post-cure temperature

and 4. Joint geometry (thickness and width)

It was found that the toughness of the TEPA hardened system varied by a factor of four-to-one as the ratio of hardener to resin content and post-cure temperature varied within what might be considered reasonable limits for manufacturing. The toughness of the HHPA hardened system varied only over the middle half of this same range.

For both systems, toughness increased with joint thickness over the range of 2 to 50 mils.     

INVESTIGATIONS INTO PUMPING CHARACTERISTICS OF AXIAL FLOW IMPELLERS IN AN INTERNAL LOOP REACTOR FOR ANIMAL CELL CULTURE

This investigation was intended to aid in the selection of impeller design and operating conditions, which would exhibit minimum turbulence in an internal loop reactor for axial flow velocities up to 18 cm/s.

For this purpose we measured power consumption, liquid flow velocity and mixing time with two marine propellers (pitch ratio tan alpha =1 and 0.57, respectively) and with flat-blade fan-type impellers (blade angles 10 to 90°).

The present results showed that at flow velocities between 7 and 14 cm/s a reduction in the pitch ratio (tan alpha) of the marine propeller from 1 to 0.57 increased the mechanical flow efficiency.

In addition, the fan-type impeller with a blade angle of 20° displayed flow characteristics comparable to the marine propellers; therefore, owing to its simple design, the fan-type impeller offers a practical substitute for the marine propellers.

In cell culture, draft-tubes used in impeller-driven reactors (internal loop reactors) offer two important features:

1. They simplify the design and scale-up process over that of open-blade impellers (flow patterns are more uniform);

2. They provide a mechanical support for bubblte-free membrane oxygenators;

Furthermore, on the assumption that loop reactors display lower bulk turbulence than open blade impellers for similar power consumption, this investigation was intended to aid in the selection of impeller design and operating conditions which would exhibit maximum pumping efficiency (with minimum mixing).

For this purpose, using a pH tracer method, we determined mechanical flow efficiency and dimensionless mixing time, which served as parameters for pumping efficiency to establish the following specific design characteristics:

1. Bulk mixing decreases relative to bulk flow with increasing bulk flow (mixing therefore conforms to the flow-in-pipe model) for two marine propellers (pitch tan alpha = 1 and 0.57) and for fan-type impellers (variable pitch) up to a blade angle of 30°;

2. Liquid velocity increases directly proportional to impeller speed up to 17 cm/s for (above) propellers, as well as fan-type impellers with blade angles of less than 30°;

3. The mechanical efficiency of axial flow (liquid velocity/power input) increases by decreasing the impeller pitch of marine impellers from tan alpha = 1 to tan alpha = 0.57, in the range of 7-14 cm/s;

4. A fan-type impeller (variable pitch) with a pitch angle of 20° displayed flow velocity and mechanical efficiency values, which lay between those of the (above) two marine propellers.

Fan-type impellers are considerably simpler in construction and are simpler to modify than marine propellers; for this reason this impeller type serves as a useful investigational tool. In addition we have found that at an impeller of 20° this type of impeller may be used to substitute marine propellers with a pitch ratio between 1 and 0.57.

We also suggest that square pitch marine propellers are not the most suitable for reactors in which mechanical efficiency of axial flow is critical, such as those for “shear sensitive” animal and plant cells.     

萃取精馏分离苯/环己烷共沸体系的控制策略

将常规萃取精馏、差压热耦合萃取精馏以及隔壁塔萃取精馏技术应用于以糠醛为萃取剂的苯和环己烷共沸物分离过程。在稳态模型的基础上,利用Aspen Dynamics软件进行控制研究,对三工艺流程提出了若干控制策略。结果表明,对于常规萃取精馏过程,再沸器热负荷与进料量比值控制结构在降低控制过程超调量方面表现出明显优势;对于差压热耦合萃取精馏过程,带有压力-补偿控温策略的方案控制效果更佳;而对于隔壁塔,则选择了无隔板下方气液分离比控制的结构来作为较优的控制策略。     

用于分离三氯氢硅合成过程中主副产品的隔壁塔模拟

以三氯氢硅合成过程中得到的主副产品混合物二氯二氢硅-三氯氢硅-四氯化硅为分离物系,提出采用隔壁塔代替常规精馏序列分离的新工艺.利用Aspen Plus软件对隔壁塔进行模拟,考察回流比、隔板位置、进料位置、侧线采出位置、液相分配比以及气相分配比对塔顶、侧线以及塔釜产品摩尔分数的影响,得到隔壁塔的最佳工艺参数,并通过模拟比较隔壁塔与常规精馏序列分离此混合物的能耗情况.模拟结果表明:当回流比为6、隔板位置为主塔的第8块板和第24块板、进料位置为预分馏塔的第10块板、侧线采出位置为主塔的第15块板、液相分配比为0.21、气相分配比为0.5时,隔壁塔的分离效果最佳,主产品三氯氢硅的摩尔分数为99.999%;相比于常规精馏序列,隔壁塔再沸器节能29.09%以上,冷凝器节能29.48%以上.     

响应面法优化一水硫酸氢钠流化催化精馏生产乙酸乙酯工艺条件

以新型的一水硫酸氢钠为催化剂,采用粉末状催化剂混合乙酸一起进料的加入方式,即流化催化精馏工艺,并利用响应面法优化乙酸乙酯催化精馏过程条件.首先,通过单因素灵敏度分析法对乙酸进料量、酸醇进料摩尔比、回流比、催化剂用量、釜底加热功率5个因素进行实验考察,确定了乙酸进料量、酸醇摩尔进料比、回流比3个关键因素的优化值及取值范围.根据单因素实验结果与精馏塔设备要求,塔釜加热功率和催化剂用量分别设定为68 W和2.0%(质量分数)乙酸,采用中心组合设计原则对乙酸进料量、酸醇进料摩尔比和回流比3个关键因素进行实验设计.以乙醇转化率为响应值,基于响应实验结果,利用响应面法对实验结果进行了方程回归,得到3个关键因素与响应值的二次关联模型.通过方差分析和平行实验,证明该模型准确可用.优化后的乙酸乙酯流态化催化精馏工艺条件为乙酸进料量3.2 mol·h^-1,酸醇进料摩尔比为3.1,回流比为3.3,在此优化条件下进行实验,乙醇转化率为88.67%,比基于单因素灵敏度分析法得到的优化工艺条件下乙醇转化率高1.0%.     

Welding Mechanisms of Plastics: A Review

Strength of welded joints is a function of technological parameters of the production process. The type of function is dependent on the welding mechanism. Different mechanisms were found under various welding conditions. The processes included in the plastic welding mechanism are divided into two groups:

1) Processes which realize the joining of the parts.

2) Processes which create conditions for the first group to proceed. The first series of processes includes:

a) diffusion of macroradicals, molecular segments or molecules of the polymer which can be either in a solid, melted or dissolved state.

b) convective mass transfer.

c) recombination of macroradicals across the contact surface.

d) physical (surface) interaction.

e) any combination of processes described above.

The second group contains:

a) formation of the real contact surface.

b) formation of the macroradicals.

c) destruction and removal of inert layers which prevent real contact of active material.

Each process and the conditions of its proceeding are discussed individually.     

On the multiple solutions of the reactive distillation column for production of fuel ethers

A systematic study of the operating conditions and parameter sensibility of multiple steady states in a reactive distillation column for production of fuel ethers is presented. The multiplicity analysis is performed using bifurcation diagrams for several scenarios using the process simulator Aspen One Aspen Plus. Our results indicate that the main variables that affect both the presence and behavior of multiple solutions in the reactive distillation column are the reflux ratio, the reboiler duty and the thermal condition in the feed stream. In particular, we have determined that the vapor–liquid stream in the feed has a major influence on the occurrence of this phenomenon and this parameter especially establishes the type of multiplicity that can occur in the reactive distillation column for production of fuel ethers.     

Application of Macromonomers for Pressure Sensitive Adhesives I. Adhesive and Surface Properties

Adhesive and surface-chemical properties of poly(styrene macromer-butyl acrylate) copolymers, poly (styrene-butyl acrylate macromer) copolymers and poly (styrene-butyl acrylate) random copolymers were investigated. The results were as follows:

(1) The adhesive properties of the copolymers which were prepared by the macromer-technique were different from the random copolymers.

(2) It was found that there were differences in the surface and molecular structure between the copotymers which were prepared by the macromer technique and the random copolymers. These differences were evident from the results of measurements of the surface free energy of the copolymers and of the interfacial tension of water/toluene in the presence of the copolymers.

(3) The reason why there were differences in the surface and molecular structure seemed to be that the copolymers which were prepared by the macromer technique had graft chains and a different inner-structure from the random copolymers. Therefore, it was suggested that the graft copolymers which were prepared by the macromer technique had a phase-separated structure.     

APPLICATION OF TURBULENCE FUNDAMENTALS TO REACTOR MODELLING AND SCALEUP

Applications of the fundamentals of turbulent mixing become clear once those fundamentals are understood. The first article in this series presented those fundamentals, in order to show how to apply turbulent mixing fundamentals modelling and scaleup, this article covers the following topics:

1. reaction types and their interaction with mixing;

2. closure of the Reynolds equations for mixing and reactions;

3. application to complex geometries;

4. random coalescence-dispersion modelling;

5. application to complex chemistry.

The most difficult problem in applying our knowledge of turbulence to mixer modelling and scaleup is the choice of model complexity. The levels of model complexity available and how to apply them to various problems are presented following the introduction.     

Argon production from air distillation: Use of a heat pump in a ternary distillation with a side rectifier

A ternary feed mixture ABC can be separated into individual components through the use of a main distillation column with a thermally linked side rectifier. To enhance such a separation, a heat pump can be implemented to transfer heat from the condenser at the top of the side rectifier to the reboiler at the bottom of the main column. In this paper, one such heat pump is described and applied to an air distillation system separating the ternary mixture containing nitrogen, oxygen and argon. The separation is performed by a conventional double column with a crude argon side column. When this system is operated at an elevated pressure to obtain higher product pressures, the separation of oxygen and argon becomes very difficult and leads to reduced argon recovery. The proposed heat pump enhances the separation by providing a supplementary crude argon condensing duty through the vaporization of a liquid oxygen stream from the bottom of the low pressure (LP) column. This scheme improves the liquid/vapour ratio (L/V) in the bottom section of the LP column and, more importantly, increases the vapour feed to the crude argon column. This increased feed rate leads to a substantial increase in argon recovery for the elevated pressure air distillation process.     

用新离子交换树脂催化剂优化连续催化精馏塔中乙基叔丁基醚的合成(英文)

Liquid phase synthesis of one of the important fuel oxygenate, ethyl tert-butyl ether （ETBE）, from etha-nol and tert-butyl alcohol （TBA） has been studied in catalytic distillation column （CDC） using ion exchange resin catalyst CT-145H. A packed CDC of 1.2 m height and 50 mm diameter with indigenously developed reactive sec-tion packing was used to generate experimental data. Effect of different key variables on product purity in distillate, was investigated to find the optimum operating conditions for ETBE synthesis. The optimum conditions for 0.2 kg·s-1 of ethanol feed were found：reboiler duty of 375 W, molar feed ratio of 1︰1.3 of reactants, and reflux ratio of 7. Concentration profiles for each component along each column section at optimum conditions were also drawn. Neither output nor input multiplicity was observed at experimental conditions.     

APPLICATION OF MULTIVARIABLE GENERALIZED PREDICTIVE CONTROL TO A PACKED DISTILLATION COLUMN

The present work deals with the application of Multivariate Generalized Predictive Control (MGPC) systems to a packed distillation column. The steady-state and dynamic behaviour of the system have been simulated using two film plug flow model. The model solutions have been obtained employing orthogonal collocation on finite element. The Jacobi polynomials within the finite element procedure was tested to determine the phase flow rates, the liquid and vapour composition profiles and the temperature profiles. All the theoretical results were compared with experimental data obtained from a pilot-plant packed distillation column distilling methanol-water mixture. Decoupling and MGPC control of overhead and/or bottom compositions were examined. Perturbation in feed composition and, reflux ratio and the reboiler heat duty were utilized as the disturbance and the manipulated variables respectively. Performance of these systems was tested by using an integral square of error (ISE and IAE) criterion.