In these days of Ethernet, wireless and smarty-pants interfaces, one may suddenly stop and ask, "Whatever happened to all those fieldbuses?" Well, just like any hardworking technology, the major fieldbus communication protocols and their low-power networks of twisted-pair wiring are hiding in plain site, laboring mightily and without fanfare in process applications worldwide. Besides collecting and delivering more sophisticated data than their predecessors, fieldbuses and their own Ethernet and wireless versions continue to replace increasing amounts of hard wiring and gain ground on the huge, point-to-point installed base they've been combating since their earliest days.
For instance, the San Jacinto Tizate geothermal power project is located near Léon, Nicaragua, about 90 kilometers northwest of Managua. The site consists of almost 10,000 acres or just over 40 square kilometers in the Nicaraguan Depression along the 70-kilometer Cordillera de Maribios chain of active volcanoes, and it has an estimated total capacity of 277 megawatts. The San Jacinto project was built in two phases and started up two 36-megawatt power plants in January and December 2012. This generating capacity is needed because Nicaragua has the greatest dependence on oil, lowest per-capita access to electricity and highest energy costs in Central America. But, like any geothermal or other alternative energy project, bringing the plants to commercial operation meant overcoming some unusual problems.
The project was originally awarded to Ram Power Corp. in Reno, Nev., and its design engineering firm, Power Engineers Inc. in Hailey, Idaho. Following updated site surveys and technical evaluations, Ram Power and Power Engineers decided to build the two-phase project using single-flash, condensing turbine development, which is designed to be the most efficient and cost-effective method for extracting geothermal energy. After building production wells and supporting steam-field installations, single-flash technology injects high-pressure, high-temperature, two-phase geothermal brine, which flashes into a low-pressure separator. The resulting steam is sent to a Fuji turbine to generate power, and remaining fluid is injected back into the well's geothermal reservoir where it's reheated.
Simplicity and Savings
However, with the long distances between the San Jacinto project's remote steam-field wells and its central control buildings, Ram Power and Power Engineers decided on and designed a decentralized control system to run the plants and opted for a traditional DCS and controllers in a central control room. These controls would communicate via Modbus TCP/IP and fiber-optic Ethernet cabling to FG-110 FF gateway switches from Softing at each of the individual wells. The gateway switches host the wells' remote field devices and their local Foundation fieldbus (FF) segments, and support data exchange between the field devices and the plants' overall control systems. Given the distances between the wells and the plants, these fieldbus-based networks and their control in the field (CiF) functions also save huge amounts of cabling, time and cost compared to old-fashioned hardwiring.
In addition, the FG-110 FFs gateways can each connect up to four FF H1 segments to run as many as 64 field devices, and the gateway and its linking device use Windows-based FF tools to configure individual field devices and define necessary software function block linking and scheduling. Next, the FF configuration, FF Link Active Scheduler (LAS) and FF Time Master cooperate to define and execute CiF.
Finally, San Jacinto also deploys redundant pressure process values to gain more benefits from the gateways' CiF features. Their input selector (IS) function block ensures redundancy, and resulting data is sent to the PID function block to calculate new inputs.
"After researching available options, Ram Power settled on the FG-110 FF gateways, and Power configured and installed them," says Tom McAuliffe, control system engineer at Power Engineers. "There are four FG-110 FF gateways installed in the San Jacinto geothermal well field, and they've been working reliably for the last year. Power also made several recommendations to Softing about how the gateways could be enhanced, and these modifications were incorporated in the next firmware version."
Back in the conventional energy realm, Foundation fieldbus has been installed and is being implemented in some of the largest process control projects in history, including Shell's Pearl GTL facility in Qatar and Reliance Industries' Jamnagar Refinery in Gujarat, India. This huge crude oil refinery already has more than 30,000 FF devices and recently reported an agreement to double its size, according to Larry O'Brien, global marketing manager for the Fieldbus Foundation. While most new process control projects are being built in developing regions like Asia, O'Brien adds that FF is also expanding in many migration and renovation projects in established areas such as North America and Europe, including BP's Whiting refinery in Indiana and Motiva's facility in Port Arthur, Texas.
"Process companies know their modernizations will have to serve for 20 to 30 years into the future, so why would they want to reuse 50-year-old, point-to-point networking that these plants had when they were first built?" says O'Brien "That's why they're going with Foundation fieldbus, HART and WirelessHART, and it's the reason why fieldbus technologies collectively continue to grow by double-digit percentages each year."
Safety and Flexibility
Besides simplifying process networks, fieldbuses can also free many applications from traditional hardware constraints. But after this freedom arrives, many users gain previously unexpected benefits, such as more easily enabled safety functions or valves that are simpler to monitor and control.
For example, Precision Drilling Corp. in Calgary, Alberta, is one of North America's largest providers of drilling equipment and services. Precision's Darcy Falardeau reports that fieldbuses such as Profinet are making its drilling rigs and other on-site equipment smarter, which makes the overall drilling process safer and more efficient.
"Our customers can benefit from real-time information from their drilling equipment, and that's what our new centrifuge control system and its Profinet network provide," says Falardeau, who is operations vice president of Precision's Completion & Production Services division. "Engineers and operators can now monitor, in real time via Profinet, centrifuge performance and other key information from various other support equipment, such as our horizontal tanks for mud storage. This integration has the ability to reduce downtime and improve worker safety, which are key industry priorities in today's performance-driven marketplace. And when potential problems occur, we can troubleshoot them remotely, which means reduced travel out to the field. The end result is a more productive and safe operation."
The new centrifuge control and communication system was first used in conjunction with one of Precision's Tier-1 Super Single drilling rigs, which are most often used to drill for oil and natural gas in shale deposits. The centrifuge, which is typically required on wells over 1,500 meters deep, cleans and screens out formation cuttings from drilling mud during drilling. The mud also acts as lubrication during drilling operations, so having a way to continually monitor centrifuge performance is crucial. This system also includes a soft PLC plus HMI residing on one industrial PC from Phoenix Contact. The soft PLC controls the distributed I/O and the drives for the motors that power the centrifuge, and then Profinet connects everything.
Similarly, fruit syrup maker Teisseire recently gained better performance and flexibility with fieldbuses when it upgraded its main production plant in Crolles, France, following its recent acquisition by Britvic. The revamp consisted of adding new process components from Bürkert Fluid Control Systems on its main production line, which produces 300,000 to 550,000 liters of fruit syrups per day (Figure 2). Stéphane Gonin, Teisseire's on-site automation and electrical maintenance manager, explains that the production line's former valve controls were about 15 years old and included a variety of manual and automatic valve heads that didn't interact well or perform efficiently. Also, the existing air supply produced oil mist, which prevented upgrading to more hygienic valves and controls.
Consequently, during the plant's annual three-week shutdown, Gonin and her team implemented Bürkert 8681 control heads, which altered how Teisseire's process valves are controlled and actuated. In essence, the Bürkert 8681s are optimized for decentralized automation of hygienic process valves, and they're mounted right onto the valves. This eliminates the valves' former, long, direct-air connections to their control cabinets, and instead turns them into intelligent devices on a fieldbus. This decentralized automation also means the new control heads take over all pneumatic actuation, feedback and diagnostic functions—up to and including fieldbus communications. The team also installed new compressed air systems and an electricity supply with DC circuits.
"Control heads on valves such as the 8681 allow pneumatic control of the valves, but also provide manual activation, electrical feedback, visual status indicators, fieldbus communication and position sensing," explains Gonin.
Just as Ethernet and wireless have extended the reach of fieldbuses, cooperative efforts and new technologies are emerging to help implementations.
"Fieldbuses are alive and well and working behind the scenes," says Carl Henning, deputy director of PI North America, the trade organization that administers Profibus and Profinet in North America. "It's important to remember that Profibus still outsells Ethernet-based Profinet because a lot of people are still waking up to fieldbuses for the first time."
To aid these fieldbus users, PCN Technology Inc. reports its software algorithms and hardware modules can support fieldbuses and save users from having to throw away older networks by allowing them to be accessed via the Internet protocol (IP). "Our devices scan the existing network's physical layer infrastructure and find the most appropriate channels for participants are on the fieldbus," says Daniel Drolet, PCN's executive vice president. "This means low- and high-bandwidth devices can still run on the same copper, but our firmware and algorithms organize them, eliminate anomalies and allow them to run more efficiently."