SAJJAD KHUDHUR ABBASCeo , Founder & Head of SHacademyChemical Engineering , Al-Muthanna University, IraqOil & Gas Safety and Health Professional – OSHACADEMYTrainer of Trainers (TOT) - Canadian Center of Human Development

Episode 52 : Flow sheeting Case Study

A Standard Test Problem for Flowsheeting

The Cavett Problem

* A typical flowsheeting problem from the petroleum industry

* The flowsheet consists of mixers and TP-flash units

* The mixture consists of ethane, propane, 1- butane, n-butane, i-pentane, n-pentane

* The problem is interesting because tear-stream convergence is not easy and process is very

sensitive to changes to the condition of operation

Cavett Problem : Process Flowsheet

Cavett Problem : Problem Definition

T=311.12, P=13.609

T=322.22, P=10.207

T=307.78, P=5.444

T=302.78, P=2.722

ethane propane 1-butane n-butane i-pentane n-pentane

Solution Statistics: Solve mass balance & then energy balance - mass balance converged in 3 iterations. Note that there were 2 tear-streams

Solution Statistics: Solve mass balance & then energy balance - energy balance converged in 1 iteration. Note that there were 2 tear-streams

Steady State Simulation Results: Stream Summary

Tutorial Outline

The objective of the tutorial is not an attempt to make the participant an expert in process simulation or in the software used in the tutorial. The

objective is to illustrate and highlight what is available currently and how they can be used to solve practical problems. Currently, large collections of computational tools (commercial or academic) are available and ready to be used. Many practical problems can be solved more efficiently through their use. The lecture and the tutorial are aimed at providing participants with sufficient background information so that when they come across process

simulation problem that may require the use of a process simulator, they will be able to start without too much extra training.

* Introduction to the software: ICAS - Integrated Computer Aided System* Problem Description: Mass balance, mass & energy balance, use of the

integrated system concept (flowsheet analysis, properties prediction, separation technique identification, …)

ICAS: TOOLS (Use only the underlined features)

* Integrated Option/Stand-alone tools

Integrated Option

Modeling, simulation, toolbox (properties utilities, synthesis, modeling, solvent design,

data/parameter estimation)

Stand-alone

ProPred, ProCamd, ModGen/MoT, CAPSS, Data

Use of ICASGetting Started (when the PC is ready for use)

1. Double click on the ICAS icon2. Click once on the ICAS icon

on the ICAS starting screenICAS Starting Screen

ICAS starting screen shows various tools that can be selected to solve any problem. The ICAS

icon takes the user to the ICAS main screen from which problems can be solved in an

integrated manner. In this workshop we will work from ICAS main screen only (see also

On-line Help).

Problem Description

We take the case of the reactioni-C4 + MeOH = MTBE ; 1-C4 is inert

One stream containing i-C4 & 1-C4 and another stream containing methanol,

enters the reactor. There is 50% conversion of methanol. The effluent from

the reactor is separated in a split fractionator. MeOH and MTBE all go down while the two butenes go up. The butene-stream is purged 20% and the

remaining is recycled back to the mixer Perform steady state mass balance only (as

the first step) - please follow the

Problem Solution Steps

Problem Definition in ICAS (use of thermo-utilities)1.Enter the ICAS main screen2. Draw a stream or flowsheet

3.Select the compounds in the mixture (if compounds are not available in the database, use

ProPred to estimate properties)4. Define the stream (stream specification page)

5. Select calculation options6. Select thermo-model options

7. Start the computations

Draw the flowsheet by using the drawing tools

Drawing tools

Explanation of the tool-bar icons (see also on-line help)

SynthesisStart simulation

Select compounds

Choice of balance equations and flowsheet decomposition

Simulation task definition and selection

The next step is to specify the compounds. Click on the ICON on the tool-bar for adding compounds.You will enter the databank of your choice. Click on the compound to see their pure component

properties. Click on PROPRED for their prediction (if necessary).

On return to the ICAS main screen, double click on the input stream. The mixture specification screen appears. Give T, P & x. Click on the first ICON on the left

Before the calculations can be started, thermo-models must be selected. A selection is shown on the screen below. Click OK to return.

From ICAS main screen, click on the reactions icon to select a predefined reaction. Note that a stoichiometric model is being selectd.

Details of the model can be viewed by clicking on the lower tool-bar reaction icon

Double click on tank (CSTR) to enter the reactor module. Click on the reactions ICON to specify the conversion. Note that from the ICAS main screen, the MTBE reaction must be chosen first

Reaction ICON on ICAS main screen

Reaction ICON on the tank module

Double click on one of the streams going out of the splitter to define the split factors. Set these variables as known. Also, check the “split factor” box

Repeat the same procedure for the divider by double clicking on the purge stream

Click on the icon for flowsheet decomposition and the recycle loop will be shown within the red boundary together with the dotted line for the tear stream (stream 3)

Click here for flowsheet decomposition

Click here for choosing the balance option (mass balance only -in this example)

After flowsheet decomposition, the simulation task needs to be defined and then from the predefined tasks, one or more is selected (as shown in the figure)

Simulation task selection

Define simulation task Choose default options

Final step is to choose the method of solution and then to start the simulation, click on the run icon (as indicated on the figure)

Choose the default options

Click here to run thesimulation problem

We can continue to proceed forward with generating different alternatives, performing steady state simulation and then analyzing the results to check if our design objectives

have been satisfied.

If solvents are needed, the tool CAMD can be used to find a solvent. If a new compound is

to be introduced, ProPred can be used to predict the properties of this compound.

Finally, if a new model is needed, MoDef can be used to generate a new model.

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