Short-term plan needed
The Beluga steam plant is needed until at least 2014, and possibly beyond, to meet regional load requirements. The HP deaerator system is critical to proper operation of the steam plant and to preventing pitting and related damage from affecting all carbon steel components--including piping, certain valves, and most of the HRSG boiler. Based on the apparent rate of degradation identified by late 2007, it was clear that the remaining HP deaerator vessel was degrading at a rate that precluded a high probability of long-term reliable operation.
As a result, corporate management decided in late 2007 to proceed with procurement and replacement of the existing HP deaerator and the previously abandoned LP deaerator to restore the plant to its original configuration. The project schedule for procurement, fabrication, and delivery of the new vessels was very aggressive. Fabrication shop backlog and delivery uncertainties added to the project’s challenges.
A purchase specification was prepared by Chugach with the joint support of Black & Veatch and Tetra Engineering. Then an order was placed by Chugach in early 2008 with Kansas City Deaerator for fabrication and delivery of the new vessels and storage tanks to the Port of Anchorage. Corporate purchasing and engineering worked closely with the supplier to ensure an on-schedule delivery.
Delivery scheduling is critical for the Beluga plant, as large component deliveries are possible only via barge due to the plant’s remote location. By land, the plant is accessible only by a local gravel road that has no access to the south central Alaska road system around Anchorage. The barge landing, rebuilt every spring to repair winter damage, can only be accessed during periodic high-high tides that provide sufficient draft for a barge to land.
The new vessels and tanks were delivered slightly ahead of schedule in late June (Figure 6). Removal of the old vessel and storage tank commenced in early July, as planned, using the plant’s crane and a specially constructed temporary steel structure (Figure 7). Installation is expected to be complete later in the summer. Hydrotesting, performance verification, and insulation work should be complete before cold weather arrives in October (Figure 8).
6. New tank upgrade. New deaerator vessels and storage tanks in the construction staging area, ready for installation. Courtesy: Kansas City Deaerator
7. Tanks for the lift. In July 2008 the HP deaerator storage tank was ready for installation. Courtesy: Chugach Electric Association Inc.
8. Tight squeeze. A temporary structure was erected for removal and installation of the replacement vessels. Courtesy: Chugach Electric Association Inc.
Future preventive measures
A comprehensive review of the plant water chemistry program and monitoring system capabilities and related operating procedures was conducted in late 2007 to address deficiencies and to implement operational improvements. Many recommendations were provided to align plant operations and instrumentation with industry practice, with emerging recommendations from the ASME committee with oversight on HRSG water chemistry guidelines, and with the recently issued (2006) ASME Consensus Operating Practices for Sampling & Monitoring of Feedwater/Boiler Water Chemistry for Modern Industrial Boilers (ISBN 0791802485).
Since then, plant management has obtained additional outside support for its water chemistry program and procured needed instrumentation. Corporate management has committed to a series of improvements and plant upgrades to water chemistry to reduce future risks of corrosion and degradation.
In addition, inspections of such elements as piping wall thickness (Figure 9) were recently performed to assess the extent of FAC damage on other components in the feedwater, condensate, and LP steam system--all of which connect to the deaerator system. Areas with significant wall thinning will be trended by future inspections, evaluated for fitness for service by the ASME FFS-1 procedure, or replaced, as necessary, to maintain a highly reliable steam plant.
9. Detailed examination. Inspection of the HP economizer inlet piping elbow found FAC damage. Courtesy: Chugach Electric Association Inc.
--Peter S. Jackson, PE (pjackson@tetra-eng.com) is director of field services for Tetra Engineering Group Inc. Trey Acteson (trey_acteson@chugachelectric.com) is the plant manager of the Beluga River Power Plant, Chugach Electric Association.
Email
Comments
Print
Reuse
