WEB TOOLS FOR CHEMICAL ENGINEERING EDUCATION

COUPLING FUNDAMENTALS WITH PROCESS DESIGN

The Distillation Case Study

M. G. Rasteiro, A. Ferreira and J. Granjo

Department of Chemical Engineering, University of Coimbra, Rua Sílvio Lima, Coimbra, Portugal

Keywords: On-line Tools, Simulators, Virtual Laboratories, Chemical Engineering, Distillation.

Abstract: In this paper the “Unit Operations and Separation Processes” area of a virtual platform called

LABVIRTUAL (http://labvirtual.eq.uc.pt) is presented. The objective is to support the study of students

engaged in a Chemical Engineering degree, especially in Portuguese-speaking countries. It is argued that

these web tools support the autonomous study of the students, contributing to develop their critical and

creative thinking, and enabling more practical approaches to the different chemical processes. Moreover, it

is shown how coupling, in the same platform, sections directed to basic concepts/mechanisms, with sections

directed to process design, contributes to knowledge integration and to a better understanding of the design

methodologies for each process.

1 INTRODUCTION

In recent years, there have been many changes in

teaching methodologies, namely in Engineering

Education. Throughout Europe, the Bologna process

required deep transformations in higher education

curricula and courses organization. One of the

consequences of the Bologna process is the

reduction of lecturing hours to allow more time for

the students to develop important skills such as: self

learning, critical thinking, teamwork and knowledge

integration between the different subjects.

Furthermore, in parallel to the scientific and

theoretical background, engineering students need to

develop a more practical training. These fast

changes and the rise of new technologies at the

world scale have been inducing changes in teaching

methodologies, having in mind the need to avoid

dependent learners in the classroom (Bell and Fogler

1998, Shacham et al. 2009 and Hasna 2010).

Additionally, it is also important to take advantage

of the new skills, namely competences on

informatics, the students possess nowadays. To

achieve these objectives a demand for web and

computational tools to support learning and teaching

activities in Engineering education is increasing.

Some authors (Bell and Fogler 1998, Henry

2005, Streicher et al. 2005, Felder 2006, Edgar 2006,

Henry et al. 2008, Shacham et al. 2009 and Garcia-

Herreros and Gomez 2010) support that these tools

contribute to engaging students and to the

development of active learning attitudes. Web tools

can facilitate the development of additional teaching

strategies for simulation, demonstration,

experimentation, operation, etc. Therefore, using

different and complementary resources, the

dynamics in the classes can increase (Bell and

Fogler 1998, Felder 2006, Shacham et al. 2009 and

Hasna 2010). The Chemical Engineering

Departments of both the Universities of Coimbra

and Porto have developed a virtual platform called

LABVIRTUAL (http://labvirtual.eq.uc.pt, Rasteiro

et al. 2009), with a wide scope, directed to the

teaching of Chemical Processes, aiming at

complementing and supporting the student’s study

and help in developing his autonomy. The

integration of the different Chemical Engineering

subjects was the main goal. LABVIRTUAL brings

together contents (multimedia libraries), simulators,

virtual experiments and remotely controlled

experiments, as well as links to other sources,

aiming at getting the student acquainted with the

subject under study.

The Chemical Processes area comprises four

sections: Unit Operations and Separations, Chemical

Reaction, Process Systems Engineering (PSE), and

Biological Processes. These sections present funda-

235

G. Rasteiro M., Ferreira A. and Granjo J..

WEB TOOLS FOR CHEMICAL ENGINEERING EDUCATION COUPLING FUNDAMENTALS WITH PROCESS DESIGN - The Distillation Case Study.

DOI: 10.5220/0003937102350240

In Proceedings of the 4th International Conference on Computer Supported Education (CSEDU-2012), pages 235-240

ISBN: 978-989-8565-06-8

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

mental concepts and applications aimed at leading

the students to understand, for instance, how

different operating conditions result in different

process designs, or which alternatives are available

for a certain process. Whenever possible, process

integration is also addressed. Moreover, each section

includes case studies illustrating some of the features

of the applications developed. These tools can be

used in a wide range of disciplines in a Chemical

Engineering degree curriculum, and be accessed

either in classroom or at home.

This article focuses in more detail on the features

of the Unit Operations and Separation Processes area

of LABVIRTUAL. A special attention will be given

to the tools developed to study the Distillation

process, including the simulation and web

methodologies adopted. Moreover, we will stress

how fundamental insight of the underlying

mechanisms is addressed in this platform, and

integrated later to a better understanding of the

design methodologies of each chemical process.

Leading the students to establish this connection is

most important for the effective understanding of the

different chemical processes, and has been

accomplished with success in this platform.

2 WEB METHODOLOGIES

The Web infrastructure of the Virtual Laboratories

of Chemical Processes is based on standard open-

source software. This approach allows similar

functionalities to existing commercial software, with

good flexibility for the specific needs of the portal.

A Virtual Server is used that can integrate contents

from various sources and present these contents in a

consistent way to the user. Most of the materials

available are stored in a Content Management

System (CMS), for flexibility and to simplify the

inclusion of new material. Joomla! was used for this

task. Predefined presentation templates simplify the

addition of new contents and the management of

several kinds of information.

The integration of simulators and data

acquisition systems with the Web portal is a critical

point. The simulations are entirely run on the server

and the user just needs a regular browser to access

and interact with the platform. Since, as referred, the

CMS used allows the construction of customized

templates for the presentation of information, the

integration with the simulators is made by

developing forms to visualize and manage real-time

data, and for the insertion of input parameters used

by the simulators to run calculations and for

presentation of the results to the users. This layer

validates the user input and executes a system call to

autonomous simulation codes. As a result of a

successful simulation, graphical and numerical

results can be returned, to be displayed on the web

page. The communication between the

computational applications and the web platform

itself is done through a simulation gateway using a

CGI (Common Gateway Interface) protocol.

3 DESIGN OF DISTILLATION

PROCESSES

Distillation is one of the most used separation

processes in the manufacturing of chemical

products, generally speaking. Thus, this subject must

always be present in any Chemical Engineering

curriculum. The underlying principle of a separation

by distillation is the difference in volatility of the

different components in the feed mixture. Therefore,

a good understanding of vapour/liquid equilibrium is

essential to understand the design of distillation

equipment. In the Chemical Engineering curricula

this subject is usually taught in a course of Chemical

Thermodynamics.

In the platform LABVIRTUAL we have

integrated fundamental subjects with the design of

process equipment. This is the case in the section of

“Unit Operations and Separation Processes”, where

we start with the area of basic principles (Heat and

Mass Transfer and Chemical Thermodynamics) in

parallel with the area of Unit Operations design.

Figure 1 describes this arrangement.

Figure 1: Scheme of the Unit Operations and Separation

Processes area (from Granjo et al. 2009).

3.1 Basic Principles – Vapour/Liquid

Equilibrium

The “Chemical Thermodynamics” area addresses, in

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236

general, the subject of the equilibrium of phases. In

the case of vapour/liquid equilibrium (VLE) it is

split in two parts: pure substances and mixtures. In

the VLE Fundamentals of pure substances’ section,

the significance of temperature and pressure

diagrams, the concepts of vaporization, vapour

pressure, substance’s fugacity and critical properties

are explained. Regarding the VLE of mixtures the

binary composition diagrams (Txy) and (Pxy) are

studied and common VLE problems are addressed:

bubble point pressure and temperature, BUBLP and

BUBLT; dew point pressure and temperature,

DEWP and DEWT, and isothermal flash.

Regarding VLE of mixtures, particularly important

for the design of distillation processes, homogeneous

and heterogeneous methods can be used. The VLE

simulator carries out calculations of BUBLP,

BUBLT, DEWP, DEWT and isothermal flash for

mixtures, from a database with 25 substances. The

following important thermodynamic model options

are included for the heterogeneous methods: the

ideal liquid and the perfect gas behaviour; the

UNIFAC method to model liquid non-ideality and

perfect gas; UNIFAC and the virial equation of state

to predict liquid and vapour non-idealities.

These simulators are directly connected to case

studies, to help the users to approach the simulator

in the correct way and to enhance their learning

experience. The main purpose is to allow discussing

the need of using methods of non ideal behaviour of

both liquid and vapour phases, which is mainly

determined by the type of mixture and the operating

pressure and temperature. For some of these case

studies the results obtained are compared to those in

the literature, as shown in Figure 2.

Figure 2: Txy diagram for a binary mixture (benzene/

toluene) produced with the VLE simulator - comparison

with experimental data (legends in Portuguese).

3.2 Distillation Simulator

The area “Models Used in the Simulation” describes

the general case of distillation of a mixture with any

number of components. The shortcut methods are

discussed with reference to the Fensk, Underwood,

Gilliland and Kirkbride equations (FUGK) (Seader

and Henley 2006). As far as the rigorous methods of

calculation are concerned, the Wang-Henke (WH)

method is covered (Wankat 2007 and Seader and

Henley 2006). Empirical correlations and heuristics

incorporated in the Distillation simulator to design

and dimension tray distillation columns are also

addressed (Wankat 2007).

The Distillation Simulator, which has been

developed in MATLAB, allows the design of a

distillation column with one feed stream; two liquid

products (residue and distillate) streams; saturated

reflux; total condenser; adiabatic stages and constant

pressure. There are no limitations to the feed thermal

state and the user can specify the temperature (T

) or

the feed thermal condition. The feed components

database is the same as for the VLE simulator. Also,

the thermodynamic models options are the same as

for the VLE simulator. To carry out the simulation

calculations two strategies are available.

Three mixtures are treated in the Case studies

section: i-butane/n-butane/pentane/hexane; benzene/

methyl-cyclohexane/toluene and ethanol/water. With

the first two examples it is pretended to show the

influence of some of the distillation operating

variables (e.g. reflux ratio, pressure) for a system

with a non-ideal behavior, in the first example, and

for a system close to an ideal behavior, in the second

example. In the case of the ethanol/water mixture it

is examined the impact on the distillation process of

a mixture which exhibits an azeotropic point.

The user can experience as well the influence of

several variables on the column dimensions and

features, for instance, how changes in the operating

pressure or on the feed conditions influence the

column design and energy balance. Moreover, the

user is also directed to evaluate which is the best

thermodynamic model to describe VLE for each set

of components, that is, for each feed.

3.2.1 Example of the Use of the Distillation

Simulator – Distillation of a Mixture of

Hydrocarbons

This example corresponds to one of the case studies

in the distillation section and illustrates the use of

the distillation simulator to design a continuous

fractionating distillation column to separate a

mixture of hydrocarbons (n-pentane – nC

, n-hexane

- nC

and n-octane - nC

). The main separation

aimed at is between nC

and nC

, nC

being

considered a contaminant. The feed stream has got,

WEBTOOLSFORCHEMICALENGINEERINGEDUCATIONCOUPLINGFUNDAMENTALSWITHPROCESS

DESIGN-TheDistillationCaseStudy

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Table 1: Summary of the design results for the distillation column to separate nC

, nC

and nC

D,LK

= 0.934; x

D,HK

=0.066;

B,LK

= 0.014; x

B,HK

=0.9;

LK recovery in distillate = 98%;

HK recovery in residue = 95 %

Residue molar flow rate (B) = 58 kmol·h

-1

Distillate molar flow rate (D) = 42 kmol·h

-1

Equilibrium stages, N = 22

Feed stage, N

= 10

Reflux ratio, R = 1.63

= 332 K; T

= 367 K.

Heat duty in condenser = -781 kW

Heat duty in reboiler = 810 kW

Column height = 21.4 m

Column diameter = 0.99 m

D,LK

, x

D,HK

are the mole fractions of light-key and heavy-key components in the distillate, respectively.

B,LK

, x

B,HK

are the mole fractions of light-key and heavy-key components in the residue, respectively.

, T

are the distillate and residue temperatures, respectively.

in mole percentages, 40, 55 and 5% of nC

, nC

and

respectively (nC

, is considered as the light key

(LK) while nC

is the heavy key (HK)). The column

operates at 2 bar. In the results presented here it is

assumed that the feed stream enters the distillation

column as a saturated liquid, and that both the liquid

and vapour phases are taken as non-ideal (UNIFAC

and virial equation being used, respectively, for the

liquid and gas phases, Poling et al. 2001). The

recovery targets have been established as 98% of the

LK in the distillate and 95% of the HK in the bottom

product. The operating reflux ratio (R) is assumed to

be 1.2 times the minimum reflux ration (R

min

Figure 3 presents an image of the input form for the

distillation simulator for this case study.

Figure 3: Input form to the distillation simulator: example

for the case study (in Portuguese).

Table 1 shows the solution of this design

problem, giving the specifications of the resulting

distillation column, which must have 22 theoretical

stages (including the reboiler) the feed stream being

introduced in the 10th stage from top. The recoveries

of both the LK and HK have met the specifications

required. The column is expected to have a total

height of around 21 m with a diameter around 1 m.

Figures 4 and 5 are examples of the output

graphs from the simulator, showing how the liquid

composition and temperature vary along the column.

The students are guided to criticize these results by

observing, for instance, that the composition profiles

vary smoothly along the column, the same

happening to the temperature profile, which is an

indication of a well designed column where the feed

stream is being admitted at its optimal location.

Moreover, they can also verify that the heaviest

component (nC

) almost disappears in the

rectification section (stages above the feed). At a

later stage the students can be guided to evaluate,

easily, the influence of changing certain operating

parameters, such as the reflux ratio, operating

pressure, feed temperature or the feed location, on

the column design. Another feature that can also be

tested by the students is the influence of the

thermodynamic model selected to describe the liquid

and gas phases on the output results (design of the

distillation column). They can choose between ideal

gas and liquid phases, ideal gas and non-ideal liquid

phase and non-ideal gas and liquid phases. In this

way they can perceive better that for some mixtures,

as is the case for the example presented, the

hypothesis of ideality does not affect the final

equipment design. For other mixtures, like for

instance azeotropic mixtures (see Granjo et al.

2009), or for very severe operating conditions,

ideality is a completely invalid hypothesis.

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238

Figure 4: Liquid composition (mole fraction – x) profile –

optimal feed location (10

stage).

Figure 5: Temperature (T, K) profile – optimal feed

location (10

stage).

Furthermore, the students can also compare the

validity of different models for the design of a

distillation column, going from approximate and

short-cut methods to rigorous design methodologies

(Wankat 2007 and Seader and Henley 2006). This

case study can be used in the classroom to illustrate

the influence of the aforementioned aspects on the

design of a distillation column, serving as the basis

for a discussion with the students. Additionally, the

students can later go to the laboratory and perform

lab trials which they will be asked to compare with

the simulated results.

We have been monitoring the use of the portal by

the students and collecting their opinions about the

tools available, asking them to fill out an anonymous

questionnaire in each course.

The questionnaire is very similar for the different

courses. Figure 6 (a) presents the questionnaire

which is being used in the course of “Separation

Processes” of the Chemical Engineering Masters

degree of the University of Coimbra. The questions

addressed different aspects of the learning

experience, students frequency and purpose of use,

which facilities they had used, as well as their

evaluation of the interface and of the structure of the

portal. The results of the students’ responses to the

questionnaire handled during the three last editions

(since 2008), corresponding to a total of 78

respondents, are given in Figure 6 (b).The students’

response was, as a whole, very positive: 82% had

used the platform in the Process Separations I

discipline and about 91% had also used it in other

subjects. Moreover, it was observed that the majority

of the students had used LABVIRTUAL as a

support to their study, with most of them using the

platform several times. Another good point was that

the vast majority of the students considered the Unit

Operations and Separation Processes area of the

platform as useful, very easy to use and very well

structured. Globally, LABVIRTUAL had a very

good rate among the students enquired.

4 END NOTES

Web tools are important complementary instruments

for the teaching and learning process. They can be

accessed with maximum flexibility, from any place

at any time, and contribute to the students autonomy.

In the case of the multi-functional web platform

presented here, there are advantages from the

combination, in a single platform, of several

features: co-existence of teaching tools for a broad

range of Chemical Processes, which motivates

knowledge integration; diversity of approaches for a

deeper insight of each chemical process, going from

multimedia libraries, supplying the theoretical

concepts, to simulators and case studies, used for the

design of the different processes and, finally, virtual

experiments. The student should be able to:

understand and relate basic concepts and principles

associated to each process; establish analogies

between different processes; understand, apply and

know the limitations of the modelling methodologies

commonly used to interpret and troubleshooting

industrial problems; have an idea of the impact of

operational parameters on the equipment design,

dimensioning and cost. This makes it easier to

introduce the students to more practical and realistic

approaches to Chemical Engineering problems.

The experience of using this multi-purpose

platform, during three school years, has been

evaluated very positively by the students.

WEBTOOLSFORCHEMICALENGINEERINGEDUCATIONCOUPLINGFUNDAMENTALSWITHPROCESS

DESIGN-TheDistillationCaseStudy

239

Figure 6: LABVIRTUAL assessment: a) enquiry; b) enquiry’s results (A- bad, D- very good).

ACKNOWLEDGEMENTS

The authors wish to acknowledge the receipt of

financial support from POSC, Portugal, contract

743/4.2/C/REG, which enabled the development of

the platform partially described here.

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