Inside process: Industrial gas producer upgrades control
Airgas Madison plant runs sold out, so downtime is very costly. Upgrading its DCS helped maximize production and maintain operational data.
Merchant gas distributors cannot get enough of the products produced by the Airgas air separation plant near Madison, Wisc. Commissioned in 1994, the plant is owned and operated by Airgas Merchant Gases, LLC, and is constantly oversold. Sales of its liquid oxygen, nitrogen, and argon have helped Airgas, through its subsidiaries, become the nation’s largest distributor of industrial, medical, and specialty gases as well as welding supplies.
When the plant first opened, a Bailey INFI 90 distributed control system (DCS) with a LAN-90 Process Control View 4.3 console human machine interface (HMI) controlled all processes. In 2007, the Airgas team determined that the DCS performed satisfactorily; however, the HMI was well behind the technological curve when it came to memory, speed, and other important functions, including alarm management. The availability of spare parts for the HMI was also a concern.
“The old HMI system was handcuffing the plant,” said Airgas plant manger Bernard Malnarick. “Troubleshooting was a big problem, and data management was impossible because the HMI did not have enough memory.”
After conducting comprehensive market comparisons, the Airgas team—including Malnarick, director of operations Dan Wharmby, and Mulberry, AR, plant manger Jay Hollenstein—formed a migration strategy that would avoid downtime and maximize existing equipment investments.
The strategy would not only deliver the benefits of a current HMI platform, but also help the team meet capital expenditure goals by retaining the existing Bailey controller hardware as well as the validated applications configurations at the site. Airgas chose Siemens’ Simatic PCS 7/90 OS HMI as the heart of its Madison plant migration strategy because of the product’s automatic connectivity tools to Infi 90. Installed in June of 2008 by Siemens Solution Partner AMCS Corp, the new HMI allowed Airgas to continue to use its Bailey controllers without making modifications to the application software on the controllers, which eliminated the need for controller revalidation.
“AMCS had completed several other jobs for us successfully, but what really attracted me to them was their knowledge of our industry,” said Malnarick. “They knew how to integrate the HMI, and how we would use it to operate our facility and make our product.”
Airgas estimates it prevented at least one week of downtime by eliminating the need to replace the hardware and I/O. The PCS 7/90 OS cGMP design and readily available Siemens documentation further reduced the time needed for the transition. “We wanted to retain our investments in the existing controllers, and we did not want to have to change out everything,” said Wharmby, who leads production management at several Airgas plants in the region. He also oversees capital projects for process improvements at those plants, including the Madison facility. “At the same time we needed to perform the validation that would be required for new controller code. AMCS worked closely with us to make sure the PCS 7/90 OS met or exceeded our expectations for operational improvements and cGMP adherence for validation.”
Parallel operation avoids downtime
Work began on the migration soon after AMCS and the Siemens platform were selected for the upgrade. During the transition phase of the project, parallel operation of the existing and new systems facilitated system conversion, validation, and operator training.
“The parallel operation was accomplished by temporarily using one CIU for communication with the two PCS 7/90 OS servers, while the other CIU remained connected to the Bailey consoles,” said Wai Wong, vice president of engineering at AMCS. “Once the system verification was complete and operations were ready, the remaining Bailey consoles were disconnected. Then the remaining PCS 7 OS Server was connected, providing Airgas with full HMI redundancy.”
AMCS installed one of four workstations in the central control room with approximately 300 of the I/O points to provide a pilot to facilitate the phased strategy. One line migrated to PCS 7 OS, while the other lines remained connected to the Bailey INFI 90. Malnarick said the parallel operation “gave us time to get used to the system and train the operators.”
According to Malnarick, the operators had not worked previously on any HMI other than the Bailey INFI 90 system. As a result, they were apprehensive at first about the migration; however, it did not take long for them to embrace the new system. He credited the service provided by AMCS and the compatibility of the new system for the seamless transition and quick operator acceptance.
“From previous work with AMCS and Siemens, I knew what to expect,” Malnarick said. “When the operators got used to the new HMI they could not believe how they had lived without it. This easy transition was borne out of AMCS’s willingness to work with us to ensure that everything would run correctly when the system was fully operational.” As part of the transition, AMCS converted the basic MS DOS black outline screens to Windows using the Simatic PCS 7 90/OS software. Dedicated legacy keyboards and customer printers were replaced with conventional QWERTY keyboards and USB mouse hardware along with printers.
“At a basic level, AMCS took the screens, as old as they were, and integrated them in shape and outline into the new HMI,” said Malnarick. “Everything was there: the valves were even in the same positions as before. We only changed a couple things, like where the controllers were located. Before, the controllers were indicated by a single letter—A through D. Even the valves showed up as single letters. AMCS added a button during the integration and now the letters still come up, but so do the controller and valve names and tags. This further helped the operators with the transition.”
Better trending, maintenance
After the transition, the plant immediately began reaping the benefits of the up-to-date HMI. In the past, approximately 50% of the plant’s I/O was trended with the old system, and even that limited data was available for only eight hours before it was automatically deleted. Moreover, building new trends was an arduous task.
Today, all of the plant’s I/O and all information coming back into the HMI are trended and automatically saved for 30 days in the real-time historian. Furthermore, this data can be archived from the historian. It takes just seconds to pull up valve, controller, and other data on any one of the workstations in the control room. Additionally, Malnarick can now monitor and control the plant remotely and wirelessly via the Internet.
“The migration has helped our preventive maintenance immensely,” said Malnarick. “In the past we only had a four- to eight-hour window before the data would disappear. It was almost impossible to troubleshoot. Now we have an enormous amount of data to comb through, which helps maximize production and efficiency as well as electrical consumption trends. With this data, and a better way to manage our alarms, we can instantaneously identify and head off a potential problem. Once, we had a failure on a piece of equipment and the trending helped us to determine that it was not a process failure, but a mechanical failure. We were able to identify the source of the failure within minutes, which saved many operator hours and prevented downtime.”
Tom Mulqueen, Airgas vice president of operations, said that reliability is the name of the game at all Airgas plants. At the Madison plant, which is always oversold, downtime is particularly expensive. “Our plants should run 99% of the time,” he said. “If the Madison plant were to go down, we would have to buy product from our competitors. That takes away from the bottom line and slows down delivery to our customers. As a result, our expectations are very high. The PCS 7 90/OS has operated at 100% since it was commissioned and has met our expectations.”
The reliability and high performance of the upgrade to the PCS 7 90/OS HMI has also provided the Airgas plant in Madison with many options for future improvements. “Our next priority is to phase out the older controllers on an as-needed basis,” said Wharmby. “The new HMI system gives a wide range of options, including Siemens Simatic controllers, Profibus, and new I/O products. We can phase everything in without excessive downtime and without exceeding our capital expenditure goals.”
Malnarick adds, “With this system, we can improve our operational performance and schedule our future capital expenditures as schedules and resources permit. This improves our plant performance and management of our existing capital.”
Rich Chmielewski is chemical and biofuels marketing manager for Siemens Industry.
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