maintaining bar screen operations safely and efficiently · 2019. 5. 13. · 4/25/2019 1...
TRANSCRIPT
4/25/2019
1
Maintaining Bar Screen Operations Safely and Efficiently
Thomas Hahn, PE
Water and Sewer Authority of Cabarrus County
Agenda
• Background / Overview• RRRWWTP
• Main Pump Station Bar Screens
• Design Criteria
• Bar Screen Review and Selection
• Construction
• Operational Experience
• Acknowledgements
• Questions
4/25/2019
2
Background and OverviewRocky River Regional WWTP
• Concord, NC
• 26.5 MGD capacity
• Serves Cabarrus County and portions of Mecklenburg County
• Built in 1978
Background and OverviewMain Pump Station Bar Screens
• Main Pump Station accepts gravity flow from eastern portion of service area primarily
• Existing Bar Screens Original to Plant (1978)
• Four bar screens, four feet wide each
• Nearly 50 feet tall overall• Belt conveyor for screenings removal
Main Pump Station
4/25/2019
3
Background and OverviewScreening Issues
• Maintenance issues• Grit accumulation and shear pin failure
• Difficulty of access
• Reliability• Varying levels of reliability for each individual screen• December 2015 screen failure
Background and OverviewConfined Space Access Issues
Problem Area
4/25/2019
4
Background and OverviewConfined Space Access Issues
Problem Area
Technicians to RemoveGrit Accumulation
Background and OverviewConfined Space Access Issues
Problem Area
Confined Space Attendantand Tool Runner
4/25/2019
5
Background and OverviewConfined Space Access Issues
Problem Area
Confined Space Attendant
Tool Runner
Background and OverviewConfined Space Access Issues
• 6 people total required to remove grit accumulation
• Increasing frequency of grit accumulation
Problem Area
4/25/2019
6
Design Goals
• Improved Access
• Improved Reliability
• Decreased Maintenance Requirements
Problem Area
Design SolutionsImproved Access
• What if we could remove a “level” of confined space and improve access?
• Solution• Grading• Access Drive• Access Door
Problem Area
4/25/2019
7
Design SolutionsImproved Reliability and Decreased Maintenance Requirements
• What if we could reduce the number of times we need to access the bar screens?
• Solution• New Bar Screens• Channel Modifications
Design SolutionsDesign Constraints
• Pump Station Configuration
• Pump Station Depth
• Access Limitations
4/25/2019
8
Bar Screen Review and Selection
• Initial Review
• Site Visits• 8 installations• 5 manufacturers
• Screen Selection
Construction
• Removal of Existing Bar Screens
• Channel Modifications
• Installation of New Bar Screens
• Ventilation Upgrades
4/25/2019
9
ConstructionRemoval of Existing Bar Screens
• Construction / Operations Coordination
• 2 bar screens (of 4 total) required to be available
• Embedded portions of existing bar screens
ConstructionRemoval of Existing Bar Screens
4/25/2019
10
ConstructionChannel Modifications
• Concrete Fill• Pit in Channel Floor• Embed Areas from Existing Bar Screens
• Downstream Weir / Wall Modifications
ConstructionChannel Modifications
4/25/2019
11
ConstructionInstallation of New Bar Screens
ConstructionInstallation of New Bar Screens
4/25/2019
12
ConstructionVentilation Upgrades
• New Supply Fan
• Exhaust Fans
Operational Experience
• More reliable and flexible operations, including through slugs of grit
• Performance through Hurricane Florence
• Better access for inspection and maintenance
4/25/2019
13
Acknowledgements
• Design and Services During Construction – Black & Veatch
• Contractor – Dellinger, Inc.
• Bar Screen Manufacturer –Duperon
• WSACC
Questions?
Thomas Hahn
WSACC