2 Tutorial 2 - Modifying the

Control Scheme

To use this tutorial, you must have successfully completed tutorial

1 of this book.

In this tutorial, you will use Aspen Dynamics to:

Modify the control scheme associated with the column in the

MCHDYN simulation by adding a composition controller to

maintain the purity of the distillate stream (stream 3).

The controller will measure the MCH composition in the

distillate stream and manipulate the phenol solvent stream

(stream 2).

Modify the controller tuning parameters (gain and integral

time) for better control performance.

Allow about 25 minutes for this tutorial.

2-2  Tutorial 2 - Modifying the Control Scheme Getting Started Guide

About Aspen Dynamics Control

Features

In Aspen Dynamics you can easily:

Add, change and remove control elements

Select measured and manipulated variables from selection lists

Configure cascade control loops

Import control structures from other Aspen Dynamics

generated input files

When an Aspen Dynamics simulation is created, level, pressure

and temperature controllers are automatically included where

appropriate. For flow-driven dynamic simulations, these controllers

are configured as shown in this table:

For this type

of control

This type of controller

Is used

To directly

manipulate

Liquid level Proportional only Liquid flow rate

Pressure Proportional integral Vapor flow rate or duty, as

appropriate

Temperature Proportional integral Duty

Getting Started Guide Tutorial 2 - Modifying the Control Scheme  2-3

Starting Aspen Dynamics

To start Aspen Dynamics:

➤ Click your desktop Start button, then point to:

Programs | AspenTech | Aspen Engineering Suite | Aspen

Dynamics 11.1

When you first start Aspen Dynamics, you will see that there is no

simulation information and you start with a blank simulation. The

following diagram shows the three windows of Aspen Dynamics:

2-4  Tutorial 2 - Modifying the Control Scheme Getting Started Guide

The three windows of Aspen Dynamics are:

The Process Flowsheet window

The Simulation Messages window

The Simulation Explorer, which is split into two panes:

All Items pane, which contains the library or folder of

models

Contents pane, which contains all the individual objects of

the selected library or folder

The default pane orientation of the Simulation Explorer has the All

Items pane above the Contents pane. If your panes are currently

displayed side by side, it is recommended that you change back to

the default pane orientation to make it easier to follow the tutorial.

To do this:

1. Ensure the Simulation Explorer window is active by clicking

in it.

2. From the View menu, point to Pane Orientation, then click

Top to Bottom.

Tip You can rearrange, resize and reposition any of your

windows.

To open an existing simulation:

1. From the File menu, click Open.

2. In the Open dialog box that appears, locate the drive or folder

that contains the Mchdyn files that you exported from

tutorial 1.

3. In the Files of type list, ensure Aspen Dynamics Files (*.dynd,

*.dynf) is selected.

Opening an Existing

Simulation

Getting Started Guide Tutorial 2 - Modifying the Control Scheme  2-5

4. Select Mchdyn, then click Open to load the Mchdyn

simulation.

The file takes a few moments to open, then the flowsheet

appears.

Each automatically-generated controller has a Process variable,

Operator set point, and Controller output whose values are

calculated from the steady-state results of the Aspen Plus run. Each

controller also has its own tuning parameters such as gain, integral

time, derivative time, and so on. You can modify the values of

these control parameters as shown on page 2-14.

For this example, Aspen Dynamics creates these controllers by

default:

Reflux drum liquid level (LC1)

Top stage pressure (PC2)

Sump liquid level (LC3)

The pressure controller PC2 is defined as a Proportional Integral

(PI) action controller, with defaults for gain and integral time,

while the level controllers are proportional-only controllers with

default values for gain.