How do you squeeze an entire liquefied natural gas (LNG) plant onto an ocean-going vessel? Before Petronas and Emerson Automation Solutions collaborated to commission the PFLNG Satu, no one knew. It had never been done before.
Now we know that digital technology—along with appropriate project execution methodologies—can make it happen with certainty.
Petroliam Nasional Berhad (Petronas) is a $46 billion Malaysian oil and gas company founded in 1974. It constructed its 2.5-sq-km LNG plant in Korea. “That’s a very big area,” said Petronas FLNG instrument manager Harun Ab Rashid, who co-presented the story at the 2017 Emerson Global Users Exchange in Minneapolis. “The ship is 365 meters in length, about the size of four American football fields. The plant will have a 20-year life of producing 1.2 million tonnes of LNG per annum.”
Aboard the PFLNG Satu, gas is extracted from the wellhead through the turret and then processed onboard. The gas is liquefied at -160 °C, shrinking the volume by 600 times, because it needs to be transported on LNG carriers. The LNG is then stored in 177,000 cubic-meter membrane-type cargo tanks until it is offloaded.
“This had never been done before,” explained Rashid. “It was the world’s first. We had many challenges, and we didn’t have any records. We had to develop a lot of new things.”
Some of the challenges included the remote location, 180 km offshore, with limited staff onboard, as well as thousands of fire-and-gas (F&G) detectors, instruments and valves to manage and operate safely and reliably.
New digital capabilities were needed to tackle tough challenges. “We needed to infuse digital technology to execute the project with confidence, and we needed to infuse digital practices in plant operations to run and maintain with confidence,” said Rashid.
Analog yields to digital
It was through the use of mostly digital signals that Petronas was able to minimize the footprint enough to fit on the vessel, while enhancing the maintenance-and-reliability capabilities of the equipment.
“We wanted to use digital signals from the sensors to the actuators,” explained Jonas Berge, Emerson senior director of applied technology, who co-presented. “We used digital transmitters, digital controllers and digital valves, and there were digital I/O signals between them. In addition, we also had some analog 4-20 mA devices with some digital capability.”
Redundant DeltaV H1 cards with built-in power supplies were used, so no additional power supplies were needed, reducing the system footprint and the weight. “There’s no marshalling cabinet because there are no power conditioners,” explained Berge. “The fieldbus cable lands directly on the H1 card. It simplifies the design and the commissioning.”
The project was designed based on device count, not I/O signal count or signal type, so the exact signal count didn’t really matter. “It doesn’t matter if a device has one signal or three signals or eight signals,” Berge said. “They didn’t have to wait until late in the project to count I/O. They just counted the number of devices. There’s also no I/O card selection because there’s only one type of card. All of the signals are grouped together, so there’s one tag for the whole device. You don’t have tags for each signal. It makes configuration a lot simpler.”
“The ship is only so long,” explained Berge, “so we put a maximum number of devices in each segment and made a worst-case design. We can put up to 12 or 16 devices on each segment.” Most segments were loaded with only eight devices, however, to allow additional instrumentation to be added in the future.
Virtual remote seals, instead of traditional remote seals with capillaries, were used. “It makes installation simpler and reduces measurement errors,” explained Berge. “Seventy-three multi-point temperature transmitters, instead of 584 single-point transmitters, were used, mostly for the cargo tanks. They reduced the number of transmitter devices and the wiring needed.”
For valve positioners, the feedback happens over the same two wires. “There’s no additional wiring or proximity switches or limit switches,” said Berge. “It’s all provided in real time over the fieldbus. It reduces system I/O count, and you get the flexibility to turn on the valve-position feedback.”
Commissioning also was simplified. The devices are automatically detected and identified when they’re connected, so configuration is automatically downloaded.
“Several of the team members weren’t familiar with digital technologies at the start,” noted Berge. “As the project progressed, the personnel got to learn the benefits of digital technology.”
Digital diagnostic capabilities also benefited the maintenance team. “We have very limited space onboard the ship,” explained Rashid. “The system I/O is installed indoors in the equipment room, so we don’t have to go out into inclement weather. There are no I/O cards out on the deck.”
The system includes intelligent device management (IDM) software, and the fieldbus devices are in the database by default. “Not all 4-20 mA/HART devices are in the database yet, but their incorporation is almost completed,” explained Rashid. “Advantages include reduced maintenance costs and easy configuration and calibration. We also incorporated smart-meter verification on the Coriolis flowmeters to tell if meters are drifting or not.”
Future process equipment diagnostics include monitoring pumps and other equipment health, adding instruments for equipment condition and performance monitoring and adding sensors for energy management.
Several changes were made after the factory acceptance test, but the flexibility of the architecture made these easy to handle. “Commissioning was smooth, thanks to the device diagnostics,” said Berge.
“So far, we’ve had two instances of saves” due to the availability of device diagnostics, said Rashid. “The result was we avoided downtime.”
Many lessons were learned along the way, including the need to educate contractors on the use of HART communicators and the importance of entering any 4-20 mA/HART devices into the IDM database from the beginning. But the end result is floating in open waters and documented.
“We managed to fit an entire LNG plant onboard a ship for the first time ever,” Berge reminded. “By using digital practices in project execution and plant operation and by infusing more digital technology into the automation, we achieved smooth project execution and plant operation.”
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