Dakota Gasification Company – June 7, 2013
The Great Plains Synfuels Plant is buzzing around the clock with more than 1,000 contractors on site diligently working with Dakota Gasification Company employees to complete the list of thousands of work order tasks needing to be completed during the black plant maintenance outage.
One of the major jobs being completed during the black plant outage is the changeout of the economizer on A-Riley boiler. It is being replaced after nearly 30 years of service. Inspection data determined the U-bends on the tubes of the economizer had started to reach retirement wall thickness. The skin/shell of the economizer was removed June 2 in preparation for replacement of the entire vessel.
Boiler feed water is preheated in the economizer by cross exchange with the hot flue gases leaving the boiler. From the economizer, the feed water enters the main steam drum to be routed to the steam generation tubes, resulting in steam which is then used in the gasification process and throughout the plant.
Madison Industrial Services Team Ltd. is on site to complete the economizer work. Pre-turnaround work on the economizer began with insulation and protective tin removal prior to the shutdown of A-Riley on May 28. A-Riley boiler is scheduled down through June 23 for the economizer change out as well as three-year recertification work.
Also, construction on the clean cooling water system project at the synfuels plant is nearly complete with the testing and tie-in portion of the project in progress.
The $77-million project will segregate the dirty water from the main plant heat exchangers. A dedicated closed-loop clean water system will remove heat from the process units. Fourteen plate and frame heat exchangers, including ancillary equipment, will be used to transfer heat from the new clean water system to the existing dirty water. The addition of the system will represent a significant maintenance cost savings for equipment associated with the plant cooling system.
Testing was completed May 24 on the clean water side of the project, according to Keith Harildstad, project manager. The testing consisted of filling the water tank with clean water, operating the four pumps and operating the 14 heater exchangers in a closed loop. Harildstad said each exchanger has 1,000 plates and it is critical to run the clean water through the system to verify it is sound.
This test proved that the tank, pump and heat exchangers function without tying into the existing system. The testing provides an opportunity to mitigate risk when coming online with an unproven system after the tie-ins are complete.
“The test met all the acceptance criteria,” Harildstad said. “A victory for sure!”
A few punch list items remain, like touching up paint, but the project construction is now considered complete. Post-test items include draining the tank and preparing the system for the remaining tie-ins. These tie-ins include four large 60-inch diameter cooling water pipelines and an additional 80-plus smaller tie-ins scattered throughout the Synfuels Plant.
The tie-ins will be completed over a 10-day period during the black plant maintenance outage currently under way. Beginning June 7, the existing cooling water system are being drained and prepared for the tie-ins to take place.
“The existing 60-inch in diameter supply and return water headers will be cut apart,” Harildstad said. “Next the new tie-ins will be installed on the existing pipe headers. They will be fitted, welded, blasted, coated and cured during the 10-day stretch.”
Once the tie-ins are complete, the system will be returned to operations and brought back into service.
Westcon is on site and will be conducting the tie-in work. State Electrical remains on the project as well completing heat tracing and providing start-up support. At the peak of the completion of the project, about 50 contractors will be onsite working on the tie-ins. The new clean cooling water system should be fully functional June 17.