Tutorial on Aspen Hysys Dynamics - Separator level controller

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Tutorial Aspen HYSYS v8.8- Dynamic mode
Dynamic separator
Author: Hamed Hoorijani

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: Hamed Hoorijani
Tutorial 1. A feed stream consisting of i-Butane (0.04), n-Butane (0.2), i-Pentane
(0.1), n-Pentane (0.3), n-Hexane (0.25), n-Heptane (0.04), n-Octane (0.03), and n-
Nonane (0.04) (mole fractions) goes to an adiabatic separator at 2300kPa (ΔP=0),
180°C and 1200 kgmolehr. Control the liquid level of this vessel in dynamic mode.
The pressure drop of all valves remains 20kPa.

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Solution.
The solution is presented stepwise to help understand each the step more easily.
1. Start Aspen HYSYS and open a new case.
2. In the Components tab, add the given components.

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3. In the Fluid Package, choose the Peng-Robinson package for the chosen
components. (In this specific tutorial since there is no high pressure equipment
and all the components are hydrocarbons, we can choose Peng-Robinson
package even though some materials have polar characteristics)
4. In the simulation section, define the Feed of the separator by putting a material
stream on the workspace and defining its temperature and properties.
Caution: Just make sure you have OK for this part.

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5. After that before setting the separator a valve is required to control the
pressure and the vapor fraction of the feed of the separator. (set the pressure
drop of the valve in the DesignParameters section as 20 kPa)

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6. After that put the separator at the way of the process stream. Define the
overhead product with “Vap” and the bottome product as “Liq”.
7. Put a control valve at the way each product stream of the separator to control
the pressure and as before the vapor fraction of the stream. (set the pressure
drop of each valve as before 20 kPa in the DesignParameters section of each
valve )
8. To use PID controller we must have the volume of the separator and valve
sizes that the software could do the calculation in the dynamic mode.
To do so Aspen HYSYS offers a quick valve sizing and quick sizing of the
separator which for this tutorial we use, but for industrial use you should
consider using the specs and standards such as API 520.
9. To size each valve using the correlations implemented in Aspen HYSYS, use
the “Size Valve” option in the Rating section of each valve. Do these for all
the three valves.

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10. For sizing the separator Aspen HYSYS offers a quick way to size the
equipment. You can use this option to have a quick sizing for the separator.
Use the “Quick Size” in the RatingSizing section of the separator’s settings.
Sizing method
1
2
3
Quick size
Geometry

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11.After that put a PID controller from the object pallet on the workspace or the
PFD.
12.In the PID define the liquid percent level of the V-100 (the separator) as the
Process Variable Source. In other word this parameter is your measuring
variable in the process. For Output Target Object choose “Object: VLV-102
(the bottom product valve), Variable: Actuator Desired Position”. This
parameter will be the controlled variable by the controller in the process.
Measured variable Output (Controlled variable)
Set
point

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13. In the ParametersConfiguration tab of the controller you can define the
controller’s specification such as Gain (Kc), Integral time constant (τi) and so
on. You can define minimum and maximum of the PV to have the scale of
changes and set your desired set point at the SP. You can also choose the type
of action and mode for which the controller acts in the process.
Action: Reverse Direct.
Mode: Auto Man Indicator.
Set the below settings for the LIC-100 controller.
Action Direct
Mode Auto
Kc 20
Ti 40
Pv Minimum 0%
PV Maximum 100%
SP 50%
Controller Specification Gain
Integral time constant
Derivative time constant
1
2

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14. Find the “Dynamics Assistant” button on the DynamicsDynamic Simulation
Tab and press it to assess the model for further dynamic simulation.
Press it the Dynamics Assistant and in the table shown you can see the
required changes for further dynamic simulation. Press the Make Changes
button to do the necessary changes in the model.
1
2
3
Required changes for switching t dynamic mode
00

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15. After that return to the PID controller and change the mode to Man and set
the OP (operating variable) to 0%.
16. Open the “Stripchart” tab of the controller and in the Variable Set choose the
“SP, PV, OP Only” option and press the Create Stripchart button. In the shown
tab you can see and select which Object you like to see in your chart and if
don’t like deactivate it in your display. Press display button to see the changes
of the chosen variables in the controller.

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17.To switch to dynamic mode of the HYSYS you should press the integrator in
the path of “DynamicsRunIntegrator” and set the start time, time step and
end time of the simulation for dynamic simulation of the model.

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18. Back on the Display of the Strip Chart you can see a constant and uniform
line for the chosen parameters. This is due to the static behavior and values in
the system. In order to see a change in the system and observe the
performance of the controller, you should change the set point of the controller
and see the changes in the variables as the controller attempts to maintain the
process at the specific set point for the measuring variable.
Back on the controller parametersconfiguration, set the mode to Auto for
which the controller could decide and control the process and set the set point
at 50%. Now you must see the changes in the variables of the Stripchart as
they attempt to reach steady state value of 50% for the set point.

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: Hamed Hoorijani

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Tutorial on Aspen Hysys Dynamics - Separator level controller