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By Gregory Hale
ExxonMobil was looking to expand their facility in Baytown, TX, by doing a heat recovery steam generator (HRSG) duct burner upgrade.

They were creating a greenfield unit next to an existing brownfield facility and they wanted to create more energy for the process so there were two lines of thought.

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“We could put in boilers or draw in steam from a neighboring facility,” said Shawn Koshy, instrumentation engineer at ExxonMobil in Baytown, TX, during his talk at the 2017 27th Annual Triconex User Group meeting in Lake Forest, CA, entitled, “SIS Upgrade Considerations for Brownfield Plants.” “That is what we did.” They decided to install 12 duct burners to the HRSGs.

Part of the process was to include 200 points of new I/O to the existing Triconex safety solution. They decided to partition the project additions as much as possible. In addition, logic additions were kept as separate as possible from existing logic, Koshy said. Also, the new Triconex V10.5 hardware ended up integrated into separate cabinet. They utilized terminal block knife switches to isolate at the new Triconex cabinet.

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Duct burners are added to HRSGs to increase the steam production with the heat from the gas turbine exhaust. A large duct burner can more than double the HRSG’s high-pressure unfired steam production. After a duct burner, the design exhaust gas temperature can be fired as high as 1,600°F–1,700°F (871°C–927°C) in a conventionally designed HRSG. Duct burner operation increases overall unit heat rate, but is a relatively inexpensive method of increasing unit capacity with current gas market prices.

When working on the project, the duct burner upgrade execution considerations included:
• Upgrades limited to outages prescribed by running plant
• Upgrades were performed across three outages with the final checkout timing limited to 5 days including: Loop checks, functional checks, and safety critical checks
• Online versus offline equipment checkout discussion
• Readiness checklists and multiple alignment meetings organized to ensure efficient coordination
• Resource planning was critical to ensure having an “A-team” at all times
• Pre loop checks were performed on field devices
• Custom checkout screens were developed for Tristation, which included planning of system checkout sequence

With upgrades limited to outages, the team really had to go above and beyond the usual planning approach to ensure they were able to step in and hit the ground running. So, they planned ahead for all functions and developed simulated programs for functional testing process, Koshy said.

“We planned the exact sequences for our loop checkout,” he said. “We were able to achieve check out in less than five days.”

Communication with Management
At one point, in an effort to streamline efforts, Koshy said management was thinking about testing online, but the engineering team came to the conclusion that would not be the safe call.

“There is a criticality to communicate to management to emphasize the right engineering call,” he said.

One of the smart moves they made when creating the project group was to have a cross functional team.

“It is not about the plant, it is about the people around the plant,” Koshy said. “We had a small tight group that could execute quickly. We had a leader that could act as a quarterback and act quickly.”

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