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Genzyme Corp. recently installed a multiple-fieldbus control system platform at its pharmaceutical manufacturing facility in Allston, Mass. This plant produces enzyme-replacement therapies for rare lysosomal storage disorders (LSDs), which are classified as orphan diseases. The Allston site was built approximately 12 years ago with a conventional distributed control system (DCS) that’s used for manufacturing two enzyme replacement therapies. These drugs include Cerezyme for Gaucher’s disease and Fabryzyme for Fabry’s disease.
The new multi-bus control system is exclusively for manufacturing Myozyme, which is a drug therapy for Pompe’s disease. We renovated an existing manufacturing suite to facilitate the new process equipment and multi-bus control system.
Process areas included in the multi-bus control system include mammalian cell culture, purification, clean-in-place (CIP) and steam-in-place (SIP). Bus technology has been deployed on skid equipment, which includes bioreactor skids, chromatography skids, ultra-filtration skids, and CIP skids. Also, bus technology has been deployed on stick-built fixed vessels, associated piping, and transfer panels. Fieldbus protocols included in the facility are Foundation fieldbus, Profibus-DP, AS-interface (AS-i), and DeviceNet.
This was our first introduction to bus technology at Genzyme, and our subsequent selection of fieldbus technologies was based on the process equipment needs in a cell culture and protein purification manufacturing environment. We use fielbuses in process areas, which are electrically-rated as general purpose and Class 1, Division 2. We’ll highlight issues associated with using bus technology in each of these areas. We’ll also talk about fieldbus implications for facility constructability, software design, commissioning, metrology and calibration, validation, and maintenance.
Which Fieldbus Where?
During the preliminary design phase for building the new Myozyme manufacturing suite, we asked our design team, which included Genzyme personnel, a systems integrator, and our construction/engineering firm, to evaluate fieldbus as a viable technology. We felt fieldbuses might offer our project value that we couldn’t get from a conventionally instrumented system. We knew our process space was limited, and that we’d need to minimize the space that controller cabinets would consume to maximize space for process equipment. We also looked at fieldbuses as a way to reduce controller cabinet size, cable count, and conduit sizes and quantity. This all seemed quite appealing initially, and now I’d say bus technology did achieve our space-saving goal. Other attributes of fieldbuses, such as their capability to help with predictive maintenance, weren’t as tangible at the outset, but could be explored and exploited after startup and commissioning. The main task at the outset was to have all this equipment fit in the space available, and fieldbus technology was a means to this end.
We selected DeltaV from Emerson Process Management as the host controller, primarily for its batch capabilities. DeltaV is fieldbus-ready for the following fieldbuses: Foundation fieldbus, Profibus-DP, AS-i, and DeviceNet. The project’s total I/O count was approximately 4,000 points.
Our collective assessment revealed that fieldbus instrumentation availability was adequate when our project began in early 2003. Pressure, temperature, flow, pH, conductivity, level, and modulating control valve applications were well-represented fieldbus options. However, there were some instruments, which measure dissolved oxygen (in-situ measurement for bioreactors), vessel weight (strain gauge type), and UV analyzers (for liquid chromatography), that weren’t available in fieldbus versions. This obstacle could be overcome with 4-20 mA current-to-fieldbus converters. Also, mass flow controllers, which are used extensively with bioreactor equipment, weren’t found to be Foundation fieldbus ready, but were available with a Profibus-DP interface. Since it appeared that two fieldbuses would be required to address the traditional analog-type signaling, we selected Foundation fieldbus and Profibus-DP.
Open/close valves and discrete input devices deployed in a general-purpose, electrical environment were easily addressed with the simple AS-i bit-bus. There were many opportunities for actuating rising-stem or quarter-turn valves, which are used primarily for sanitary diaphragm valves and quarter-turn ball valves. Also, AS-i was used for discrete input devices, such as valve limit switches and proximity switches found on process transfer panels. Though simple in its implementation, we recognized early that AS-i would require a close eye to make sure we didn’t exceed its segment-length criteria. Typically, this is 100 meters, and then it’s time to add a repeater and power supply, and then extend another 100 meters. This could be repeated one more time for a total of 300 meters per segment. We didn’t recognize the length limit as a non-starter because most of the valves are clustered in close proximity to one another, especially on skid equipment, and so we embraced this bus for most of the discrete I/O requirements.
However, AS-i bus isn’t suitable for use in electrically classified process spaces due its high power requirements. Open/close valving and discrete input devices in electrically classified environments were addressed with intrinsically-safe remote I/O using Profibus-DP.
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