Educational Simulators for Industrial Process Control - Simulation and Modeling Methodologies, Technologies and Application - page 147

• Automatic valves. To study the importance of the control valves, the simulated

system allows selecting the inherent characteristics of the valves and characteriz-
ing its digital smart positioners.

• Heat exchangers. The module aims to study the beneficial effect of using feedfor-

ward compensators and cascade control in simple systems such as heat exchangers.

• Centrifugal compressors. This module shows a control structure that prevents

centrifugal compressors can enter in an unstable operation region:”anti-surge”
mechanism.

• Alternative compressors. The simulated process is composed by an alternative

compressor and a recycling system which aim is to compress all the gas that
reaches the system. To avoid problems in the working of the compressor, the suc-
tion pressure is controlled using this recycled gas flow and the compressor load.
Two control techniques can be compared: load steps or split-range control.

• Centrifugal pump. Minimum recycling control of centrifugal pump.

• ON-OFF level controller. The simulated system allows to study the well-known

on-off control and pays attention in the hysteresis effect of the dead band and the
logic of the controller.
When a module is selected, from one of the main menus, the corresponding dynamic
simulator and its graphical user interface (GUI) are started. Later, some details about
the simulation are given. Now, the GUI of each module will be the focus of attention.
Each GUI of the selected module corresponds to a P&ID [14], Piping and Instru-
mentation Diagram. These schematics have passive components that show informa-
tion as standing or running equipment indicators, trend and historical charts, other
types of charts (characteristic valve curves), value displays,... and active components
that allow acting over the system: starting or stopping pumps, valves or process units;
selecting automatic/manual/cascade mode in controllers; modifying the boundary
condition and the process and control parameters,...
By default the simulation runs in real time, but the user can change the simulation run
speed using a time scale factor that can be greater than 1 to accelerate it, if the PC allows
it, or lower than 1 to decelerate it (Fig. 2). In this kind of process simulators is unusual to
reduce the time scale factor because the system dynamic is slow or not so fast.

Fig. 2. Time factor

3 Example

In order to show how works the simulation tool, one of the simplest modules has been
selected (minimum recycling control of centrifugal pump). First, a physical system
description and the GUI will be outlined. Second, an experiment is run.