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Seoul National University

Chemical Process and Product Design (3/20)

Example Ethylene Glycol Plant

Ethylene glycol has many industrial uses: a feed stock for polyester resins,

a hydrate inhibitor in natural gas pipelines, an all-weather antifreeze and

coolant, or an industrial solvent. Ethylene oxide and water are fed to a

reactor to produce ethylene glycol. The product stream is fed to adistillation column where the excess water and ethylene oxide are stripped

off the top and the ethylene glycol is the bottom product.

Seoul National University

Chemical Process and Product Design (4/20)

Defining the Simulation Basis

Fluid Package : NRTL Activity Model.

Components : Ethylene Oxide (C2H4O), Water (H2O)

and Ethylene Glycol (C2H6O2).

On the Binary Coeffs tab,

Select UNIFAC VLE as the Coeff. Estimation method to estimate the missing

binary coefficients and press Unknowns Only.

On the Rxns tab,

Add the following reaction (Kinetic) to the Fluid Package :

C2H4O + H2O C2H6O2

Basis and

Parameters pages,

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Seoul National University

Chemical Process and Product Design (5/20)

Defining the Simulation BasisNo reverse reaction is defined in this example.

Return to the Simulation Basis Manager by closing the Kinetic Reaction window.

Return to the Rxns tab of the Fluid Package. Press the Add Set button to add the

Global Rxn Set to the Current Reaction Sets group. Close the Fluid Packageview.

Press the Enter Simulation Environment button.

Seoul National University

Chemical Process and Product Design (6/20)

Adding the Feed Stream

(Mole Fraction)

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Chemical Process and Product Design (7/20)

Adding the CSTR Reactor

On the Reactions tab, select the Global Rxn Set and Rxn-1 as the Reaction.

Specify the temperature of stream Rx Liquid to be 65C (150F).

From the Reaction results, what is the % Conversion of Ethylene Oxide?

_______99.70

Seoul National University

Chemical Process and Product Design (8/20)

Ethylene Glycol Tower - Overview

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Chemical Process and Product Design (9/20)

Adding the Ethylene Glycol Tower

?

No. of Trays

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Chemical Process and Product Design (10/20)

Adding the Ethylene Glycol TowerPress the Run Button

In stead of Specifying the Distillate Rate, Specify the reboiler Temperature

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Chemical Process and Product Design (11/20)

Adding the Ethylene Glycol Tower

In stead of Specifying the Distillate Rate,

Specify the reboiler temperature !!

Seoul National University

Chemical Process and Product Design (12/20)

Adding the Ethylene Glycol Tower

On the Performance tab, analyze the column result !

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Chemical Process and Product Design (13/20)

Installing the Recycle

The stream Distillate contains mostly unreacted water. This water can be recycle

d to the reactor in order to reduce the feed water requirements

Seoul National University

Chemical Process and Product Design (14/20)

Installing the Recycle

A Recycle operation is a mathematical unit operation and is installed as

any other. It has an inlet (calculated) stream and an outlet (assumed)

stream. The operation is called/calculated whenever changes to the

inlet stream fall outside of the converged tolerance.

HYSYS uses the conditions of the assumed stream (outlet)

and solves the flowsheet up to the calculated stream (inlet).

HYSYS then compares the values of the calculated stream to

those in the assumed stream.

Based on the difference between the values, HYSYS modifies

the values in the calculated stream and passes the modified

values to the assumed stream.

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Seoul National University

Chemical Process and Product Design (15/20)

Installing the Recycle

Attach the Stream

Delete the specified molar flow rate of the Water Feed stream. This value will

be back-calculated from the outlet of the mixer. Specify the molar flow of the mixer outlet stream, Water to Reactor, as 150

kgmole/h (330 lbmole/hr). Once the flow rate in this stream is set, HYSYS will

automatically calculate the flowrate of the Water Feed stream.

Seoul National University

Chemical Process and Product Design (16/20)

Installing the Recycle

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Seoul National University

Chemical Process and Product Design (17/20)

Recycles

What is a Recycle operation?

mathematical / logical unit operation

When to use a Recycle operation?

Required when downstream material stream(s) mix with

upstream material stream(s) and when there is mass I/O acrossthe flowsheet

R

Assumed Calculated

Seoul National University

Chemical Process and Product Design (18/20)

Adding Recycle Operations (1)

Procedure 1

1. Solve flowsheet without recycled stream

2. Add Recycle, and only attach the calculated stream(calculated = estimated)

3. Connect assumed stream to flowsheet

12

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Chemical Process and Product Design (19/20)

Adding Recycle Operations (2)

Procedure 2

1. Guess (estimate) assumed stream

2. Solve flowsheet up to calculated stream

3. Add and connect recycle operation

2

1

Chemical Process and Product Design

To minimize the number of tear locations, add recycles

Downstream of gathering points (mixer)

Upstream of distribution points (column, tee, separator)

To minimize the number of recycle variables (T, P, etc.) Choose a tear location that maximizes number of fixed variables

Add recycle operations at separator inlets

Compressor after cooler outlets

Choose a stable tear location

To minimize effect of fluctuations

Tear Locations