When implementing chemical process control systems, the control engineer must thoroughly understand the flow of materials through the process equipment. Flow is not always apparent as chemical species change through reaction operations. These changes can create different behaviors through various separation operations in the process sequence.

Several methods aid control system developers in representing the flow paths in process applications. The methods vary in complexity and cost. Some involve use of multiple packages to accomplish key functions of graphical representation and material balance calculation.

Ae-S 2001 by Applied e-Simulators (West Richland, Wa.) is one software package that allows users to create process flow diagrams (PFDs) and calculate material balances. This package also is low cost compared to full process simulation packages.

Within this package the user can create a PFD and an associated material balance in the following three steps:

• Draw the PFD using the 'point-and-click' icon library. These include both process units and interconnections within the 'Problem,' as the package defines the application.
• Enter unit parameters into the function-specific input dialogs provided for each process unit.
• Instruct the package to calculate the material balance by selecting the 'Calculate' icon.

The material balance that is created can be easily viewed on screen or printed for reference during control system design efforts.

Complex systems can be depicted and documented easily using a small set of functions.

On-line help includes a good library of example problems and a fairly detailed, context-sensitive help file. All required documentation is provided within the help file, which eliminates need for a separate reference book.

When creating a PFD, the software automatically tracks each graphical element (process unit and 'piping') by assigning a unique ID tag to the element as placed. ID tags are sequential unless one or more are deleted. In this case, ID values are lost and not reused. The user also has the capability of editing the system ID values to give meaningful names for the specific application.

During PFD creation, users can use the software's scroll controls to provide a large work field. Additionally, size of the process operation box (large or small) can be selected. Once placed, default box elements can be changed to column or vessel symbols.

After all process functions are placed, they must be connected. Care must be taken to ensure the interconnecting lines, which can vary in weight and position, are drawn to make contact with each element as intended. Contact of the line elements to operation boxes is how the package links data for the material balance.

When opening 'Existing Problems' it is important to note that the program allows opening of multiple 'problem' files that are overlaid on each other in the display. It is important to select 'Create new Problem' between each opening to prevent program failures. Users need to be aware that clicking on the 'New Problem' icon calls up a screen without saving what has been done since the last save command. This provides for an 'undo' function but it can also cause the loss of work.

The material balance function is automatically linked from the PFD and then uses function-specific tables for data entry. Data entry into these forms is simple but care must be taken to use consistent measurement units. While any system is accepted (volume, mass, etc.), all flows must be in 'mass' to support the calculations associated in the reaction tables if a reaction block is involved.

This review is based upon Ae-S 2001 operating under Microsoft Windows 98. The package operates under any Microsoft Windows 95 or higher operating system.

For more information on Ae-S 2001, go online at www.controleng.com/free info .