Next-generation fieldbus device couplers simplify chemical plant upgrade
Petrochemical plant adds new physical-layer technology to its long-running fieldbus networks.
Today's process industry operations require state-of-the-art automation technology in order to reduce raw material costs, increase yields, comply with regulatory standards, and maximize revenues. But plant managers must also ensure that control systems provide reliable operation and a low cost of ownership over the life of installed assets.
Although fieldbus-based control systems have been used in countless applications to optimize process operations, instrumentation, and control, engineers need effective solutions protecting the fieldbus physical layer from short circuits, improper termination, interference and other potential problems.
Industrial facilities can avoid many fieldbus installation issues from the beginning simply by utilizing the latest generation of device coupler technology. Current technology offerings simplify fieldbus system design and expansion, minimize capital equipment costs, and significantly reduce the time required to install and troubleshoot devices in the field.
Ashland Inc. is a global leader in providing specialty chemical solutions to customers in a wide range of consumer and industrial markets. The company includes four commercial units-Ashland Specialty Ingredients, Ashland Water Technologies, Ashland Performance Materials, and Ashland Consumer Markets-serving customers in more than 100 countries.
In August 2011, Ashland purchased International Specialty Products Inc. (ISP), which had acquired BP's world-class 1,4-butanediol (BDO) production operation in Lima, Ohio, six years earlier. The plant has an annual capacity of 65,000 metric tons of BDO, an intermediate ingredient in common industrial and commercial products. BDO is further processed to make items such as engineering plastics, polyurethane systems (e.g., golf balls, skateboard wheels, car bumpers) and carrier solvents in printing inks and cleaning agents.
The Lima plant's integrated butane-to-butanediol production process combines catalytic oxidation of butane in air with fixed-bed fatty acid hydrogenation technology. The facility processes butane and air to maleic acid in a fluidized bed reactor, and maleic acid to BDO in a high-pressure, H2-rich, fixed-bed hydrogenation reactor. It also utilizes an off-gas boiler for steam and environmental compliance (Figure 1).
Reasons for using fieldbus networking
When deciding to build the Lima BDO production operation, plant managers sought to achieve high reliability without the complexity and redundancy of a traditional process control system. John Rezabek, process control specialist for Ashland at the site, said, "In designing the BDO plant, we wanted to avoid older analog communications. Why would we build a new plant and shackle ourselves to 1980s technology?"
Rather than employ conventional automation technology, the Lima plant called on Emerson Process Management to supply a DeltaV DCS using the Foundation fieldbus protocol. This all-digital, two-way communications system interconnects interoperable field equipment from different suppliers-such as sensors, actuators, and controllers-on a single network. The fieldbus system infrastructure is designed to reduce the amount and complexity of wiring throughout a plant (Figure 2).
Foundation fieldbus also transmits multiple variables, enabling a reduction in process variability as well as device identification information. The technology allows collection and transmission of robust instrument diagnostics, thus reducing unnecessary shutdowns and improving safety and regulatory compliance.
As part of the fieldbus-based automation architecture at the Lima facility, PID control algorithms are located in a majority of the digital valve controllers. In addition, all dual-element transmitters are equipped with on-board signal-select blocks. A total of 80 fieldbus H1 (31.25 kbit/s) segments connect approximately 600 fieldbus instruments and valves, handling 150 control loops.
The facility's original 400 discrete I/O devices (mostly on-off valves) were wired directly to process controllers, which have since been supplemented with dozens of fieldbus-capable on-off valves. The system also includes approximately 400 emergency shutdown I/O and 200 RTD (resistance temperature detectors) sensors and motor statuses integrated through Modbus multiplexors.
With this configuration, the entire fieldbus architecture (with the exception of emergency shutdown functions) is covered by a single operating system.
According to Rezabek, one of the major advantages of Foundation technology at the Lima BDO plant is its ability to lower capital costs and operating expenses through reduced wiring and the extraordinary confidence and accuracy provided by an all-digital protocol. Speedy, robust, and deterministic process control proved to be a significant benefit as well.