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In 2007, Albright & Wilson (via Fidera) awarded Dickinson Autocon Systems a project to replace their existing obsolete Yokogawa µXL and Siemens PCS 3 systems with a single new Siemens PCS 7 system, incorporating many of the features available in a modern control system to increase productivity.
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The continuous process control involved a wide range of functions such as: air handling units with regenerating beds, a sulphur burner with a burner management system, converter beds, a reactor, and numerous mixers and blending vessels as well as services to support the site.
Whilst the front end of the process is continuous, recognition was also given to the fact that process outputs are prepared, blended and stored in batches. This need was addressed by the use of discrete sequences with batching functionality based upon the ISA 88 standard. These “phases” are initiated by the operators in response to work orders requiring batches of particular products.
Much of the existing control system wiring was preserved by incorporating the PCS 3 I/O racks into the replacement system and the introduction of marshalling terminals into the Yokogawa cabinets with connectors allowing the re-routing of existing control wiring allowing the old system to be easily reinstated should a problem during commissioning occur.
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Considerable effort was made to retrieve all tuning parameters from the existing systems and correlate them to equivalent parameters for use in the new system.
Using a single, unified system allowed a reduced cost of ownership owing to: less unique spares having to be held and a greater overall degree of knowledge held by those responsible for maintaining the system. Furthermore, the use of a single controller in order to control and monitor.
Sequences can be viewed graphically, allowing operators and engineers to evaluate the current step.
High availability of the system was ensured by the use of redundant Operator Stations each with their own connection to the controller.
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