CBE_317_Linking Aspen Plus with Aspen Shell_Rev2

							Preliminary Design – Aspen Plus and Aspen Shell & Tube Exchanger


Key Messages:
    Integration of Aspen Shell & Tube Exchanger with Aspen Plus supports an efficient conceptual
    design process:

       Part of conceptual design – Natural Gas Liquids process

       Aspen Plus process model

       Use Aspen Shell & Tube Exchanger within the simulator

       Powerful design optimization

       Prepare model to explore changes in process conditions

File: Linking Aspen Plus with Shell Tube.bkp


Problem overview:
The case file contains a simulation of a natural gas process that features a number of unit operations
including a shell & tube exchanger. The process engineer first creates a conceptual design case using the
Heatx shortcut method. The shortcut method provides for a heat and material balance including the
shell & tube heat exchanger but no reliable modeling of the exchanger performance. The 2nd run
changes the Heatx block from the shortcut method to use of Aspen Shell & Tube to optimize the sizing
of a heat exchanger using the full rigor of AspenTech’s research-based exchanger modeling technology.
We will explore how to further optimize the design. We will see how to prepare a simulation model
which can be used to evaluate the overall effect of changes in process conditions with a rigorous
representation of our newly-designed heat exchanger.




Aspen Plus and Aspen Shell & Tube Exchanger                                                        Page 1
Preliminary Design – Aspen Plus and Aspen Shell & Tube Exchanger

Initial Case
Open the Aspen Plus file: Linking Aspen Plus with Shell Tube.bkp

The initial case represents the heat exchanger in Aspen Plus using the Heatx block “Shortcut” model.




We will change the specification of the Heatx block to use the Aspen Shell & Tube Exchanger program.
We will use this to produce an optimized design of heat exchanger. The results will be generated by the
rigorous Aspen Shell & Tube program calculate actual geometry, film coefficients, pressure drops, with
reports available to identify potential operating problems for real item of heat transfer equipment.


Produce an Optimized Design
In the Setup of the Heatex block called SHELLTUB change the calculation radio button from the Shortcut
method to Shell&Tube. Set the location of the Hot fluid to Shell.




Aspen Plus and Aspen Shell & Tube Exchanger                                                      Page 2
Preliminary Design – Aspen Plus and Aspen Shell & Tube Exchanger




In EDR Options the name of the Aspen EDR file to be created: NGL-CHECK.EDR,




Aspen Plus and Aspen Shell & Tube Exchanger                                   Page 3
Preliminary Design – Aspen Plus and Aspen Shell & Tube Exchanger


Under EDR Options | Analysis Parameters set the basic process specifications such as fouling factors
and allowable pressure drops as shown.




Re-run the simulation case now and have Aspen Shell &Tube Exchanger optimize the sizing of a real heat
exchanger.

After the run has complete the user can open the Aspen Shell & Tube Exchanger user interface inside of
the Aspen Plus environment in order to view the Shell & Tube detailed results. Go to SHELLTUB | EDR

Aspen Plus and Aspen Shell & Tube Exchanger                                                     Page 4
Preliminary Design – Aspen Plus and Aspen Shell & Tube Exchanger
Browser from the navigator. We will first look at the optimization path to see if we can interact with the
program to improve the initial design selected by the program.




We can now look at the Resistance Diagram in the results to see which of the 5 resistances is requiring
the largest percent of the area. If we can make a change to reduce the resistance then we should be
able to reduce the cost of an alternative exchanger.




Approximately 50% of the area is required to satisfy the resistance due to the film coefficient on the
tube side. We will make a change to reduce this resistance that should reduce the required surface area
of the heat exchanger along with the cost of the exchanger.




Aspen Plus and Aspen Shell & Tube Exchanger                                                        Page 5
Preliminary Design – Aspen Plus and Aspen Shell & Tube Exchanger

Re-optimize the Design
We will try a smaller tube outside diameter (o.d.) to increase the velocity and thus the film coefficient
on the tube side.




 Using the Run Enable box we can make the change and re-run the program to produce an alternative
design without leaving the Aspen Plus environment. First check the “Run Enable” box as shown then
select Run from the drop-down list. This allows us to run Aspen Shell & Tube Exchanger without
perturbing the simulation.




If we again look at the Optimization Path we can see that the smaller tube size has resulted in a smaller
and lower cost exchanger.




Aspen Plus and Aspen Shell & Tube Exchanger                                                         Page 6
Preliminary Design – Aspen Plus and Aspen Shell & Tube Exchanger




This is an acceptable preliminary design.

You might want to look at the Setting Plan and the Tube Layout to get an impression of the physical
arrangement of your exchanger.


Switch to Simulation
We now want to transfer the geometry that is the output of our design optimization to the specified
geometry of the exchanger in order to simulate the performance of this exchanger subject to different
process conditions.

We still have the Run Enable box checked. Select Update from the drop down to automate the transfer
of the geometry into the rating section of the input.




We can now simulate the operation of this real heat exchanger in the specified process.


Aspen Plus and Aspen Shell & Tube Exchanger                                                     Page 7
Preliminary Design – Aspen Plus and Aspen Shell & Tube Exchanger
Go to the Heatex block: SHELLTUB | Setup and change the Type from Design to Simulation and then re-
run Aspen Plus.




We may now make changes to process conditions such as stream flowrates or compositions and
simulate how this exchanger would perform. We can see how it’s heat transfer and pressure drop
performance might influence the process as a whole.




Aspen Plus and Aspen Shell & Tube Exchanger                                                  Page 8