No. 20 Boiler upgrades
Engineer-of-record for upgrades of wood fired boiler to increase maximum steam production.
The Client’s No. 20 Boiler needed upgrades and replacement of an existing dust collector (multicone), replacement of an existing induced draft (ID) fan and replacement of their ID and forced draft (FD) fan steam turbine drives with medium voltage speed electric drives.
Replacement of the multicone, ID fan and the fan drive conversions needed to be accomplished on an annual shutdown scheduled for only twelve days.
How We Did It
Detailed engineering was required for the new unit substation, electrical room, equipment foundations/piling, duct work, ash handling system, and system controls. Multiple packages were prepared and released in a fast track mode to support an aggressive project schedule and meet the mill’s annual shutdown dates. Harris Group developed and maintained the engineering and overall project schedule throughout the project.
Harris Group worked closely with mill engineering, operations and maintenance to prepare equipment specifications and facilitate ordering of long lead equipment.
Harris Group’s Structural engineering team developed innovative design concepts to minimize the shutdown duration by utilizing pre-fabricated motor pedestal for the ID Fan motor in lieu of traditional reinforced concrete foundation. Extensive field engineering and verification resulted in clearly defined scope for demolition and relocation project elements resulting in minimal change orders during project construction. Harris Group’s electrical engineering team successfully implemented the first medium voltage variable speed drive installation at this site. Harris Group provided functional descriptions and PLC programming for the new medium voltage electric fan drives, multiclone, and ash handling system.
The electrical room was constructed, and new electrical equipment installed and energized prior to the boiler shutdown. The remainder of the construction was successfully completed during a twelve-day boiler shutdown. The new equipment and systems were successfully started up and system performance targets were met or exceeded.
New equipment and systems were successfully started up and system performance targets were met or exceeded.
The existing ID fan had become a high maintenance item due to the relatively high temperature and wear experienced in the boiler flue gas stream.
A new slower speed fan was specified with wear liners to provide maximum life for the fan in this service. The new slower speed fan resulted in a significantly larger fan which required significant modifications to existing building structures and augmentation of the fan foundation including new piling.
The existing multiclone was inadequate to meet new environmental emission limits at the desired peak steaming rate on wood. The replacement multiclone was significantly heavier than the existing unit creating significant structural support challenges for the design team.
A new unit substation and electrical room were needed to support the conversion of the fan steam drives to medium voltage electric drives. The drive for the ID fan is 3500 HP and the drive for the FD fan is 700 HP. The new electrical room needed to be designed to contain the drives and medium voltage switchgear to serve the new fan motors as well as additional future loads.
Replacement of the multiclone, ID fan and the fan drive conversions needed to be accomplished on an annual shutdown scheduled for twelve days.
