Use of S88 Techniques in Semi-Continuous Applications
Dr. Wayne Gaafar, Honeywell Process Solutions
Batch Operations in a Continuous World
Continuous Operations do not (like to) admit to having batch processes
But they do…
Water Treatment
Polymer Reactors
De-Cokers
Pressure Swing Adsorption
Guard Reactors
Etc..
Anatomy of a Semi-Continous Process
Process Traits
Continuous process stream inputs and outputs
Multiple (nearly) identical units
Each unit has similar formulation
One or more units is processing (on-line) all the time
Off line units are either being prepared to go or ready to go on-line
History of Semi-Continuous Solutions
Totally Manual
Operator and clipboard
Prone to large process variances and errors
Continuous Logic Applications
Use of function blocks (OR, NAND, AND, OUT, etc)
Limited functionality (very difficult to do large sequences and interrupts)
Extremely complex
Prone to disuse (lack of understanding) and operator errors.
PLC Ladder Logic can be difficult to program and maintain.
Structured Text Solutions
FORTRAN, C, CL, VisualBasic, etc
Complete functionality
Not interrupt driven
Requires CS skills for handling off normal solutions
Code can get very complex
One person becomes the owner
Reduces Variability
Enhancements are difficult
S88 Methodology is designed for batch, interrupt driven, and structured.
Here's a semi-continuous example:
Process Treatment: Removal of Impurity
Three Units (columns)
One inlet process stream
One outlet process stream
Purge inlet/outlet stream
Simple On/Off Valves to control
One level indicator per column
Using S88:
Start at top of Methodology
Decide where Cell and process boundaries are located
Next Decide on the Unit boundaries
And then the phases
Equipment and Control Phases can be examined next.
Check the “off-normal” conditions.
Conclusions:
Continuous processing plants have batch application needs
Processes are typically semi-continuous
Solutions have ranged from totally manual to structured text programming solutions
S88 methodology offers a well thought out methodology to solving these problems
An example of a three column semi-continuous process was used to show S88 methodology.
S88 type solutions can be easier to develop and maintain
