Plantwide I/O approach streamlines plant start-up

Jan. 25, 2021
Sour gas plant shaves three months from schedule despite onrush of late design changes

Companies have long complained about automation budget over-runs and schedule delays, often due to late changes in project design. Traditional, hard-wired input/output (I/O) systems were a primary culprit because hardware procurement and software development necessarily proceeded sequentially. Design changes requiring more or a different mix of I/O resulted in expensive and time-consuming re-engineering that affected both budgets and schedules. These impacts, of course, got progressively worse as the project neared completion.

But gas processor SemCAMS Midstream (now part of Energy Transfer Canada) bucked that trend, beginning production at its greenfield Wapiti sour gas processing plant in northern Alberta in late January 2019—under budget and three months ahead of original schedule— despite late changes and additions to project scope.

How, you might ask? Project principals credit in part the plant’s pioneering use of ABB Select I/O, the Ethernet-based single-channel I/O system for the ABB Ability System 800xA control system. Importantly, Select I/O relies on industry-standard Profinet as the backbone of its plantwide I/O network. Use of this standard protocol dramatically streamlined the integration of even third-party I/O on skids that came late to the party. Indeed, changes during the engineering process had increased the I/O count from 1,200 to 2,400 as more gas streams and equipment were added.

The Wapiti plant also marked a successful effort by system integrator Blackrock Automation, which has earned a reputation for tackling tough automation assignments with skill and precision. The fact that project startup came when temperatures were dropping to -42 °C was another of the challenges for the project team to overcome.

Eliminating dependencies

ABB’s Select I/O was designed to eliminate the traditional, controller-centric methodology that made late changes so difficult to accommodate. Called xStream Engineering (now part of the ABB Adaptive Execution methodology), the approach provides multiple workstreams and late binding principles to promote engineering efficiency. At Wapiti, this enabled remote I/O cabinets to be installed and wired in the field while the Blackrock team configured the system at their Calgary office. Decoupling project tasks reduced the impact of late changes, and activities such as functional wiring and loop checks could be done much earlier.

“We designed, built and installed 27 identical remote I/O cabinets each with 96 I/O per cabinet,” says Galen Wilton, senior programmer at Blackrock Automation. "As a result, we were able to field-test all the cabinets in just two or three hours. Select I/O also saved a lot on cable by allowing us to use more flexible switching devices between panels and reassign them as needed. That meant most changes were no longer about asking for money, but were about new ways to save money."

Each of the Class 1, Div. 2 remote cabinets was assigned a device address on the Profinet network as it was added, enabling last-minute changes throughout the process. The project also featured motor-control-center (MCC) communications with more than 40 Multilin relays and 76 variable frequency drives over Profinet.

“Select I/O is perfect for remote I/O applications as it moves the I/O from the motor control center and electrical rooms into the field,” explains Brad MacDonald, product marketing manager for ABB. “Extra I/O can simply be ordered and installed as needed since field wiring doesn’t have to be brought back to the central control room. This eliminates marshaling, junction boxes, cabling and cable tray, ultimately reducing project costs by 30-40%.”

The control and network architecture at Wapiti includes two virtual servers, two servers working as historians, four operator stations, three engineering stations, PLC interfaces and two AC 800M controllers connected to the remote I/O cabinets. In addition, there were two local S800 I/O cabinets connected via Profibus for remote MCCs.

Redundancy requirements

“In addition to the virtual servers hosting redundant server functions, the system also included software-based controllers, which meant we could set up, simulate and test the entire project at our office in Calgary and even use them for training,” says Wilton.

Plant availability, and hence redundancy, was a top priority for control and communications. The plant processes about 200 million cubic feet of sour gas every day, so it’s critical that plant personnel are able to keep tabs on the process at all times to assure that hydrogen sulfide, propane, butane and other impurities are being properly removed from the final product.

For maximum uptime and visibility, the System 800xA’s redundant controllers were connected to the Select I/O cabinets and drives via Profinet utilizing a fault tolerant, redundant, fiber-optic ring of stars architecture. Profinet network designs are relatively straightforward, since standard, off-the-shelf Ethernet switches can be used. An optimized ISO model enables Profinet to connect with more than 1,000 remote I/O drops for communication over one network, along with millisecond performance and seamless failover on both ring and redundant architectures.

Operational transparency

Having various field equipment connected via Profinet—all tied back to one common platform—provides for effective facility-wide monitoring and maintenance on an ongoing basis.

“The diagnostic capabilities of Profinet make it a very good tool for information and analysis,” adds Rob Remeika, lead automation manager and safety system expert at Blackrock. “You can get more information faster, and you can plug in anywhere.”

Wilton says operators at the plant also like Profinet’s trending and alarming system. “It is quite simple and yet effective. We hardly had to do any training. They were able to run tasks and reorder them while the software was using the analysis tool, which enabled instant changes with quick results.”

About the author: Keith Larson
About the Author

Keith Larson | Group Publisher

Keith Larson is group publisher responsible for Endeavor Business Media's Industrial Processing group, including Automation World, Chemical Processing, Control, Control Design, Food Processing, Pharma Manufacturing, Plastics Machinery & Manufacturing, Processing and The Journal.

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