Use of Ports and Streams II – Using Streams to Connect Units

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In this section the flash created in the third example for functions is used twice to assemble a flowsheet that is connected via ports and streams.

Workflow

Notation of flowsheet

First, we need to define the notation of the flowsheet, which will be used for our ports and streams. Use the following base names and indices:

Base names

$F$ , stream in kmol/h
$z_i$ , mole fraction in mol/mol

Indices

$i$ , component index 1..NI
$c$ , component index 1…NC (this should not be required, but there seems to be a bug at the moment)

The resulting notation has ID 182828.

Interface for ports and streams

Go to the Interface tab and take the following steps:

Load the notation created above
Click on “+ Field Name” and add the variable $S$ , name it “Stream” with Dim Scalar and activate In/Out
Click on “+Field Name” and add the variable $z_i$ , name it “Composition” with Dim Vector and activate In/Out
Save the interface

The interface is available with ID 182823.

Connectors for inlet and outlet port

Go to the Connector tab and proceed as follows:

Load the notation from the example “Use of Functions III – Parameter Lists and Indices” as Sub Notation
Load the flowsheet notation created above as Super Notation
Add the variables $F$ and $z_c$ as variables in the Sub Notation
Add the variables $S$ and $z_i$ as variables in the Super Notation
Match $F$ and $S$ , then match $z_c$ and $z_i$
Save the connector for the inlet port
Repeat these steps with the variables $L$ and $x_c$ (Sub Notation) and $S$ and $z_i$ (Super Notation)
Save this connector for the outlet port

Both connectors are available with IDs 182824 and 182825.

Equation system and ports

Go to the Equation System tab and take the steps explained below:

Load the equation system from the example “Use of Functions III – Parameter Lists and Indices”
Add a reasonable description
Go to the Flowsheeting tab and then to the External Ports tab
Click on “+ Port”, add the Name “Inlet”, select the interface and connector for the inlet created above
Click on “Check Port Configuration” and then on “Confirm”
Click on “+ Port” again, change Direction to “out”, add the Name “Outlet”, select the same interface and then the created outlet connector
Click on “Check Port Configuration” and then on “Confirm”
Save the equation system; recommendation: save it with “unit” in the filename as you have just created a unit with an inlet and an outlet port
Go to the Flowsheeting tab and click on “Print Unit(s)”. You can now see the unit you created with an inlet and an outlet port

The equation system of the unit is available with ID 182826.

Flowsheet

Click on “New” in the Equation system tab and do as follows:

Load the flowsheet notation
Add a reasonable description
Add the flash unit you just saved twice
Go to the Flowsheeting tab and then to the Internal Streams
Click on “+ Stream” and load the interface from above
Click on “Port 1”, which will open a popup window. Select the equation system with Id “0” and select the output port at the bottom of the window; confirm
Click on “Port “, which will again open a popup window. Select the equation system with Id “1” and select the inlet port at the bottom of the window; confirm
Click on “Check Stream Connection” and then on “Confirm”
Save the equation system; recommendation: save it with “flowsheet” in the filename
Go to the tab Visualization and click on “Print Unit(s)”. You can now see the connections between your two flash units

The equation system is available with ID 182827.

Evaluation / Simulation

Next, we can move to the “Simulation” section and load the flowsheet we just created. Then, take the following steps:

Add a description for your simulation
In the tab on the Generic System and load your flowsheet
In the Indexing tab, enter 2 as Max Value for all appearing indices and then click on “Confirm Index Data”
Go to the Specifications tab and assign the following variables as design values:
- $S$ from the namespace >Inlet e0p1
- $P$ in the namespaces e0e0 and e0e1
- $T$ in the namespaces e0e0 and e0e1
- $z_{i=1}$ in the namespace >Inlet e0p1
- $z_{i=2}$ in the namespace >Inlet e0p1
Assign the remaining variables as iteration values (except of course for the calculated values, i.e., the vapor pressures)

Initialization and results

To initialize and specify the model, take the following steps:

Initialize this example with the design values and initial guesses given in Table 1
Save the variable specification
Enter the parameter values given in Table 1 for both namespaces
Save the parameter specification
Save the simulation
Go to the Evaluation tab and generate the code for your preferred environment / software package
Simulate the flash

This simulation is available with ID 182828 with variable specification 182829 and parameter specification 182831. The solution for all iteration variables is also given in Table 1.

Name	Description	Value / Initial guess	Solutions
$S$	Feed mole flow in kmol/h in namespace e0p1	1.0
$P$	Pressure in Pa in namespace e0e0	101325
$P$	Pressure in Pa in namespace e0e1	80000
$T$	Temperature in K in namespaces e0e0 and e0e1	354.6
$z_{i=1}$	Feed mole fraction of component 1 in mol/mol in namespace e0p1	0.5
$z_{i=2}$	Feed mole fraction of component 2 in mol/mol in namespace e0p1	0.5
$A_{c=1}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	82.718
$B_{c=1}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	-6904.5
$C_{c=1}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	-8.8622
$D_{c=1}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	7.4664E-6
$E_{c=1}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	2.0
$A_{c=2}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	73.649
$B_{c=2}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	-7258.2
$C_{c=2}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	-7.3037
$D_{c=2}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	4.1653E-6
$E_{c=2}$	Parameter in DIPPR equation in namespaces e0e0 and e0e1	2.0
$P_{c=1}^{LV}$	Calculated vapor pressure of component 1 in Pa in namespaces e0e0 and e0e1		190176.44
$P_{c=1}^{LV}$	Calculated vapor pressure of component 2 in Pa in namespaces e0e0 and e0e1		50216.55
$S$	Liquid mole flow in kmol/h in namespaces s0 and e0p2	0.5	0.579 / 0.278
$V$	Vapor mole flow in kmol/h in namespaces e0e0 and e0e1	0.5	0.421 / 0.300
$z_{i=1}$	Liquid mole fraction of component 1 in mol/mol in namespaces e0s0 and e0p2	0.5	0.365 / 0.213
$z_{i=2}$	Liquid mole fraction of component 2 in mol/mol in namespaces e0s0 and e0p2	0.5	0.635 / 0.787
$y_{c=1}$	Vapor mole fraction of component 1 in mol/mol in namespaces e0s0 and e0e1	0.5	0.685 / 0.506
$y_{c=2}$	Vapor mole fraction of component 2 in mol/mol in namespaces e0s0 and e0e1	0.5	0.315 / 0.494

Table 1: Overview of parameter values, initial guesses, and the solution.