Live from WBF 2008- Batch Operations in a Continuous World

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

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