# SIMULATION OF PROCESS PLANTS

## AIMS AND CONTENT

AIMS AND LEARNING OUTCOMES

At the end of the module, the student will have acquired knowledge and understanding about the 'Chemical engineering computing'. In particular, the student will know, at a basic level, how to simulate Chemical Engineering equipment and systems, following the following steps:

1) evaluate the most suitable type of model for the study of a specific chemical engineering problem, also considering the software tools available: 0-D, 1-D, 2-D, 3-D models, stady-state and transient;

2) model development: choice of the equations;

3) model development: choice of the numerical method;

4) check of the results obtained.

The Case Studies are solved by working in groups in the INFAL1 computer lab. Thus, students will enforce transversal skills such as communication skills and ability to work in teams.

Teaching methods

The module is divided into theoretical lessons (25 hours) and laboratory lessons in the computer lab (35 hours).

During the lessons in the computer lab, wide space is devoted to the resolution of the 'Case Studies' at the computer. The 'Case Studies' in the computer lab, are carried out in groups and allow to improve transversal skills such as communication skills and ability to work in a team. The 'Case Studies' form the basis for preparation for the final practical test.

SYLLABUS/CONTENT

The module includes a series of theoretical lessons concerning the various types of models that can be formulated for the Chemical Engineering equipment and systems. In particular, the following topics are dealt with:

- overview of the various types of models that can be formulated for the Chemical Engineering equipment and systems. Concentrated parameters and distributed parameters models;
- equations typically used: algebraic and / or differential. DAE (mixed systems of algebraic and ordinary differential equations) and PDAE (mixed systems of algebraic and partial differential equations);
- a summary of the numerical methods available to solve the equations;
- overview of the software available to solve the typical chemical engineering problems.

In the central part of the module, the attention is focused on the simulation of process plants. Theoretical aspects and mathematical approaches are analyzed. Particular attention is paid to plants with recycle streams and to the related numerical calculation methods:

- simultaneous method: analytical solution of the equations;
- sequential-modular method. Convergence problems;
- sequential-modular method modified according to Wegstein.

The theoretical concepts are translated into practice through a series of examples ('Case Studies') having as their object some typical problems of Chemical Engineering. Each 'Case Study' is articulated in a brief theoretical reference, aimed at the choice of the equations suitable to describe the chemical-physical phenomenon, followed by some lessons in which the equations are solved numerically at the computer. The calculation program is developed in the INFAL1 computer lab under the guidance of the teacher who, working personally on the computer (thanks to the connected projector), explains the techniques to be adopted, and then invites the students to reproduce and complete. In this phase, the students work in groups, using the PCs available in the INFAL1 classroom. The teacher coordinates and supervises the work, and offers practical support. In some cases, the calculation program is developed in C language. In other cases, the equations are solved numerically by one of the following softwares: Excel, Matlab, COMSOL, UniSim. All the softwares are installed on PCs available to students at the INFAL1 computer lab. In many 'case studies', the same problem is solved through two or more different softwares, in order to appreciate the differences. For each 'Case Studies', the final step of the work is a critical discussion of the results obtained.

Here is a detailed list of the 'Case Studies' (texts and solutions are available in aul@ web).

Case Study 1: Calculation of the specific volume of a non-ideal gas using the Redlich-Kwong (RK) state equation. From a mathematical point of view, the problem leads back to the root-finding methods. The problem is solved using MS Excel, Matlab, UniSim and by developing a code in C programming language.

Case Study 2: Distillation: calculation of the isothermal flash of an ideal multicomponent mixture using the Rachford-Rice equation (RR). From a mathematical point of view, the problem leads back to the root-finding methods. The problem is solved using MS Excel, Matlab, UniSim and by developing a calculation code in C programming language.

Case Study 3: Simulation of an ammonia production plant. Development of macroscopic mass balances for each unit operations of the plant. Simplified calculation using Excel. Detailed calculation (mass and energy macroscopic balance) based on a sequential-modular approach (Wegstein method) using UniSim.

Case Study 4: Simulation of a plant for the production of propylene glycol, consisting of a CSTR chemical reactor coupled with a plate distillation column. Resolution through UniSim. Analysis of temperature profiles and composition in the distillation column.

Case Study 5: Simulation of an ideal isothermal steady-state tubular reactor. Development of the model and in particular of the mass balance equation (microscopic balance). From a mathematical point of view, the problem needs to the solution of an ordinary differential equation (ODE). The problem is solved using MS Excel, Matlab, Comsol, and by developing a calculation code in C programming language.

Case Study 6: Short notes about the simulation of a non-ideal tubular reactor, with laminar flow field and axial dispersion. Development of the model and in particular of the mass and energy local balance equations. From a mathematical point of view, the problem leads back to the resolution of a PDAE system (mixed system of non-linear NLAE algebraic equations and partial differential equations PDEs). The problem is solved using Comsol.

RECOMMENDED READING/BIBLIOGRAPHY

All the slides projected during the lessons and all the teaching material concerning the 'Case Studies' (including texts and solutions) are available in aul@web.

The books listed below are suggested as supporting texts:

- B.A. Finlayson, Introduction to Chemical Engineering Computing, John Wiley and Sons, Inc., Ney Jersey, USA (2006).
- R. Sinnott & G. Towler, Chemical Engineering Design, Fifth edition, Elsevier Science (2009).
- H.S. Fogler, Elements of Chemical Reaction Engineering, Fourth Edition, Pearson Education, NJ, USA (2006).

## TEACHERS AND EXAM BOARD

**Ricevimento:** Please contact via e-mail:
paola.costamagna@unige.it

Exam Board

PAOLA COSTAMAGNA (President)

PATRIZIA PEREGO (President)

VALERIA TACCHINO

CATERINA SANNA

ALESSANDRO ALBERTO CASAZZA

## LESSONS

Teaching methods

The module is divided into theoretical lessons (25 hours) and laboratory lessons in the computer lab (35 hours).

During the lessons in the computer lab, wide space is devoted to the resolution of the 'Case Studies' at the computer. The 'Case Studies' in the computer lab, are carried out in groups and allow to improve transversal skills such as communication skills and ability to work in a team. The 'Case Studies' form the basis for preparation for the final practical test.

LESSONS START

Lessons start on March 2nd, 2020.

## EXAMS

Exam description

This teaching module includes a final test divided into two parts (the same day):

- Practical test in the INFAL1 computer room (in the morning, starting at 9:30, duration about 3 hours);
- Oral test (in the afternoon).

At the end of the practical test, the teacher will indicate the place and time (for each student) of the afternoon oral test. The oral test consists of a discussion of the practical test, with possible questions concerning the theoretical part of the module.

Additional information:

- an example of practical test is available in aul@web (with solution);
- the practical test takes place at the computer. Only the computers available in INFAL1 can be used. It is allowed to bring a USB stick containing the codes developed during the module (Case Studies), and any other material (texts, notes, programs, etc.) considered useful by the student. During the test, it is allowed to access personal texts and notes (in paper format). However, during the test it is not allowed to use personal laptops, cell phones or smart phones. Furthermore, it is not allowed to access the Internet during the test;
- the dates of the final test are available on-line;
- the INFAL1 computer classroom is widely available for practicing. The day before the final test, the INFAL1 classroom is reserved for the students of the 'Chemical Engineering Computing' module for practicing.

Assessment methods

The final test consists of a practical test followed by an oral discussion. The practical test aims at checking that the student has learnt the basics of chemical engineering computing. To this end, the teacher proposes a problem to be solved by using the computer, using two different methodologies (one simplified and the other one more detailed, outlined in the text of the problem) that require the use of two different software.

The problem proposed in the practical test must be solved by applying the methodology followed in the 'Case Studies':

- evaluate the most suitable model for solving the problem (0-D, 1-D, 2-D, 3-D);
- write the equations;
- solve the equations using the computer;
- check the results obtained.

In the oral part, the codes prepared during the practical test by each student will be discussed individually. The teacher will evaluate the level reached by the student in terms of knowledge and ability to use the various softwares. The evaluation of the computer codes will take into account the following aspects (listed in decreasing order of importance):

- a functioning code that produces meaningful results (minimum requirement for passing the test);
- style and readability of the code;
- calculation efficiency of the code.