NGL Fractionation Train 1
NGL Fractionation Train
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2007 AspenTech - All rights reserved.
EA1031.06.09
04_NGLFractionationTrain.doc
NGL Fractionation Train 3
I
Workshop
Recovery of natural-gas liquids (NGL) from natural gas is quite common in natural
gas processing. Recovery is usually done to:
Produce transportable gas (free from heavier hydrocarbons which may
condense in the pipeline)
Meet a sales gas specification
Maximize liquid recovery (when liquid products are more valuable than
gas)
Aspen HYSYS can model a wide range of different column configurations. In this
simulation, an NGL Plant will be constructed, consisting of three columns:
De-Methanizer (operated and modeled as a Reboiled Absorber column)
De-Ethanizer (Distillation column)
De-Propanizer (Distillation column)
Learning Objectives
After you have completed this section, you will be able to:
Add columns using the Input Experts
Add extra specifications to columns
Prerequisites
Before beginning this module you need to complete modules 1,2, and 3.
3
~
Process Overview
\F:7d1L i I ......
DC1 Ovhd
-+----
::s-
Ex Duty
-+-
P-100
Product Pressure
DC1 Re~b
-
Q .....-+---
DC2Feed ...
DC1
DC1 Btm
~
...
..'
P100
P-100-HP
DC2 Dist
----...-
Pro duct P ressu re
~: ~Cond
DC2 Reb Q ."::::=:': 1;: "DC3 Q
Feed1 Feed2 I L.-..J I I ~... : }:::: ...
DC2 8tm . DC3 Feed ":':'" DC3 Dist
Temperature 95.00 C Temperature 85.00 C
DC2 VLV100
...
Pressure 2275 kPa Pressure 2290 kPa
Molar FlolAl 1620 kgmole/h tt..1olar FlolAl 215.0 kgmole/h
Mole Frac Nitrogen 0.0025 Mole Frac Nitrogen 0.0057 DC3 Reb Q
Mole Frac CO2 0.0048
I .....
' --' =--t--+-
Mole Frac CO2 0.0029 DC3 Btm
DC3
Mole Frac Methane 0.7041 Mole Frac Methane 0.7227
Mole Frac Ethane 0.1921 Mole Frac Ethane 0.1176
Mole Frac Propane 0.0706 Mole Frac Propane 0.0750
Mole Frac i-Butane 0.0112 Mole Frac i-Butane 0.0204
Mole Frac n-Butane 0.0085 Mole Frac n-Butane 0.0197
Mole Frac i-Pentane 0.0036 Mole Frac i-Pentane 0.0147
Mole Frac n-Pentane 0.0020 Mole Frac n-Pentane 0.0102
Mole Frac n-Hexane 0.0003 Mole Frac n-Hexane 0.0037
Mole Frac n-Heptane 0.0002 Mole Frac n-Heptane 0.0047
Mole Frac n-Octane 0.0001 Mole Frac nOctane 0.0027
NGL Fractionation Train 5
Column Overviews
DC1: De-Methanizer
Figure 1
Dc1
Ovhd
Feed1
Feed2 Main TS
I'~urnber of Stages 10
Top Stage Pressure 2275 kPa
Ex Duty Bottom Stage Pressure 2310 kPa
Main T8
BOllup
Reboller
To
Reboiler DC1
Btrn
DC2: De-Ethanizer
Figure 2
To
Condenser DC2 Cand
:~ "",..--. ...L-_ _. . Q
Reflux Condenser DC2
Dlst
Main TS
Number of stages 14
DC2 Feed
Top Stage Pressure 2760 kPa
Bottom Stage Pressure 2795 kPa
Main TS
BOllup
To
Rebailer DC2
Btm
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6 NGL Fractionation Train
DC3: De-Propanizer
Figure 3
To
Condenser
~310nd
: 8 l I 4 - - - - -........ ---------'----+
Reflux Condenser DC3
Dist
Main TS
Nun1ber of Stages 24
DC3 Feed Top Stage Pressure 1620 kPa
Bottom Stage Pressure 1655 kPa
Main T8
Boilup
Reboiler
To L .......
Reboiler DC3
Btm
6
NGL Fractionation Train 7
Building the Simulation
Defining the Simulation Basis
1. Start a new case.
2. Select the Peng-Robinson EOS.
3. Add the following components:
Nitrogen Propane n-Pentane
CO 2 i-Butane n-Hexane
Methane n-Butane n-Heptane
Ethane i-Pentane n-Octane
4. Enter the Simulation Environment.
Adding the Feed Streams
1. Add a Material Stream with the following data:
In this cell... Enter...
Name Feed1
Temperature
Pressure 2275 kPa (330 psia)
Flowrate 1620 kgmole/h (3575 Ibmole/hr)
Nitrogen 0.0025
CO 2 0.0048
Methane 0.7041
Ethane 0.1921
Propane 0.0706 \
i-Butane 0.0112
n-Butane 0.0085
i-Pentane 0.0036
n-Pentane 0.0020
n-Hexane 0.0003
n-Heptane 0.0002
n-Octane 0.0001
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8 NGL Fractionation Train
2. Add a Material Stream with the following data:
In this cell... Enter...
Name Feed2
Temperature
Pressure 2290 kPa (332 psia)
Flowrate 215 kgmole/h (475 Ibmole/hr)
Nitrogen 0.0057
CO2 0.0029
Methane 0.7227
Ethane 0.1176
Propane 0.0750
i-Butane 0.0204
n-Butane 0.0197
i-Pentane 0.0147
n-Pentane 0.0102
n-Hexane 0.0037
n-Heptane 0.0047
n-Octane 0.0027
8
NGL Fractionation Train 9
Adding the Unit Operations
De-Methanizer
The De-Methanizer is modeled as a reboiled absorber operation, with two feed
streams and an energy stream feed which represents a side heater on the column.
1. Add an Energy streanl with the following values:
In this cell... Enter...
Name Ex Duty
Energy Flow 2.1 e+006 kJ/h (2.0e+06Btu/hr)
Note:
In Aspen HYSYS, there are two types
of streams you can create:
Blue arrow - Material Stream
Red Arrow - Energy Stream
Reboiled Absorber
Column icon
2.
3.
Double-click the Reboiled Absorber icon on the Object Palette. The first Input
Expert view displays.
Complete the view as shown in the following figure:
Monitor
The Input Experts provide
Spees
the new user with step by
Spees Summary
step instruction for defining
a column. Subeoohng
Notes
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10 NGL Fractionation Train
4. Click the Next button to proceed to the next page.
5. Supply the following information to the Pressure Estimates page. If you are
using field units, the values will be 330 psia and 335 psia for the Top Stage
Pressure and Reboiler Pressure, respectively.
iI
~ Figure 5
:.
'0: :
The Next button is only
available when all of the
necessary information has
been supplied.
6. Click Next to proceed to the next page.
7. Enter the temperature estimates shown in the following figure. In field units, the
top stage temperature estimate will be -125F, and the reboiler temperature
estimate will be 80F.
Figure 6
Temperature estimates are
not required for the column
to solve, but they will aid in
convergence.
\
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NGL Fractionation Train 11
8. Click Next to continue.
9. For this case, no information is supplied for the Boil-up Ratio on the last page
of the Input Expert, so click Done.
II
'~
'f
.... "..
The basic Reboiled
Absorber has a single
Degree of Freedom (DOF)
I 10. When you click the Done button, Aspen HYSYS will open the Column
It property view. Select the Monitor page on the Design tab.
t
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12 NGL Fractionation Train
Before you converge the column, make sure that the specifications are as shown in
the preceding figure. You will have to enter the value for the Ovhd Prod Rate
specification. The specified value is 1338 kgmole/h (2950 lbmole/hr).
11. Click Run to run the column.
What is the mole fraction ofMethane in DCI Ovhd? _
Although the colunm is converged, it is not always practical to have flow rate
specifications. These specifications can result in columns which cannot be converged
or that produce product streams with undesirable properties if the colunm feed
conditions change.
An alternative approach is to specify either component fractions or component
recoveries for the column product streams.
1. Go to the Specs page on the Design tab of the Column property view.
Monitor
Specs
Specs Sl.lmmary
Subcoohng
Notes
2. Click the Add button in the Column Specifications group to create a new
specification.
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NGL Fractionation Train 13
....
"
3. Select Column Component Fraction from the list that displays.
... .
,
t
t
t
t
-
~
~
-~
~
~
,
4. Click the Add Spec(s) button.
5. Complete the spec as shown in the following figure.
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14 NGL Fractionation Train
6. When you have finished, close the view.
The Monitor page of the Column property view shows 0 Degrees of Freedom,
even though you have just added another specification. This is because the
specification was added as an estimate, not as an active specification.
7. Go to the Monitor page. Deactivate the Ovhd Prod Rate as an active
specification and activate the Comp Fraction specification (C 1 in Overhead)
that you created.
Q)
~
What is the flowrate ofthe overheadproduct, DCI OVhd? _ _t_~.=.....-:............::~ _
~
After the column has converged, you can view the results on the Performance tab.
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NGL Fractionation Train 15
Adding a Pump
Pump icon
The pump is used to move the De-Methanizer bottom product to the De-Ethanizer.
Install a pump and enter the following information:
In this cell... Enter...
P-100
. . . .: . , ::"r--~~ Dc~
Inlet DC1 8tm
DC1 '. Feed
Btm .
~----_ .. _._---
Outlet DC2 Feed
P-100-HP
Energy P-100-HP
P-100
Product Pressure I 2790 kPa
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16 NGL Fractionation Train
De-Ethanizer
The De-Ethanizer column is modeled as a distillation column, with 16 stages, 14
trays in the column, plus the reboiler and condenser. It operates at a pressure of2760
kPa (400 psia). The objective of this column is to produce a bottom product that has
a ratio of ethane to propane of 0.01.
1. Double-click the Distillation Column button on the Object Palette and enter the
following information.
Distillation Column icon
Name DC2
No. of Stages 14
Inlet Stream/Stage DC2 Feed/6
Condenser Type Partial
Overhead Vapour Product DC20vhd
Overhead Liquid Product DC2 Dist
Bottoms Liquid Outlet DC2 Btm
Reboiler Duty Energy Stream DC2 Reb Q
Condenser Duty Energy Stream DC2 Cond Q
Condenser 2725 kPa (395 psia)
Condenser Delta P 35 kPa (5 psi)
Reboiler 2792 kPa (405 psia)
Condenser -4C (25F)
111::_JlII'1111<"I~IJ~""lt~11Iil'iIJilllll:i.illilI1I1tllt'lilllllllli11IJlltJ!111
Overhead Vapour Rate 320 kgmole/h (700 Ibmole/hr)
Distillate Rate o kgmole/h
Reflux Ratio 2.5 (Molar)
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NGL Fractionation Train 17
2. Click the Run button to run the column.
What is the flowrate 0/Ethane and Propane in DCl Btms?
Cz'--- , C3:.-..-_---"- , Ratio 0/C-/C3:.-..- _
3. On the Specs page, click Add to create a new specification.
4. Select Column Component Ratio as the Column Specification Type and
provide the following information:
In this cell... Enter...
Name C2/C3
Stage Reboiler
Flow Basis Mole Fraction
Phase Liquid
Spec Value 0.01
Numerator Ethane
Denominator Propane
5. On the Monitor tab, deactivate the Ovhd Yap Rate specification and activate
the C2/C3 specification that you created.
What is the flowrate 0/DCl Ovhd? _
Adding a Valve
V alve icon
A valve is required to reduce the pressure of the stream DC2 Dtm before it enters the
final column, the De-Propanizer.
Add a Valve operation and provide the following information:
In this cell... Enter...
............~.-- __ ..~
.:; ~ ~.
DC2 DC3 Feed
VLV-100
Btm Inlet DC2 Btm
r------------------------VLV~-1-00------------------------1
Outlet DC3 Feed
I Product Pressure i 169~
'----~-~---
DC3 Feed Pressure 1690 kPa (245 psia)
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18 NGL Fractionation Train
De-Propanizer
The De-Propanizer column is represented by a distillation column consisting of 25
stages, 24 trays in the column, plus the reboiler. (Note that a total condenser does not
count as a stage.) It operate$ at 1620 kPa (235 psia). This colunm has two process
objectives:
Distillation Column icon To produce an overhead product that contains no more than 1.50 mole
percent of i-Butane and n-Butane combined
To keep the concentration of propane in the bottonl product less than 2.0
mole percent.
1. Add a distillation column and provide the following information:
Name DC3
No. of Stages 24
Inlet Streams/Stage DC3 Feed/11
Condenser Type Total
Ovhd Liquid Outlet DC3 Dist
Bottom Liquid Outlet DC3 Btm
Reboiler Duty Energy Stream DC3 Reb Q
Condenser Duty Energy Stream DC3 Cond Q
Condenser 1585 kPa (230 psia)
Condenser Delta P 35 kPa (5 psi)
Reboiler 1655 kPa (240 psia)
Condenser 38C (100F)
Liquid Rate 110 kgmole/h (240 Ibmole/hr)
Reflux Ratio 1.0 Molar
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NGL Fractionation Train 19
2. Run the column.
What is the molejraction ojPropane in the overhead and bottoms products?
_ _ _ _ and _
3. Create two new Component Fraction specifications for the column.
In this cell... Enter...
Name iC4 and nC4
Stage Condenser
Flow Basis Mole Fraction
Phase Liquid
Spec Value 0.015
Components i-C4 and n-C4
Name C3
Stage Reboiler
Flow Basis Mole Fraction
Phase Liquid
Spec Value 0.02
Component C3
4. Deactivate the Distillate Rate and Reflux Ratio specifications.
5. Activate the new specifications that you created.
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