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Selecting the Best Dewatering Technology for a Challenging Ash Slurry

Selecting the Best Dewatering Technology for a Challenging Ash Slurry. Presented by: Elijah Williams, PE, City of Greensboro Christopher Crotwell , PE, HDR. NC AWWA-WEA Annual Conference 2013. AGENDA. 1. 2. 3. 4. 5. Background. Available Technologies. Testing. Selected Equipment.

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Selecting the Best Dewatering Technology for a Challenging Ash Slurry

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  1. Selecting the Best Dewatering Technology for a Challenging Ash Slurry Presented by: Elijah Williams, PE, City of Greensboro Christopher Crotwell, PE, HDR NC AWWA-WEA Annual Conference 2013

  2. AGENDA 1 2 3 4 5 Background Available Technologies Testing Selected Equipment Summary and Conclusions

  3. Background 1

  4. TZ Osborne WRF BACKGROUND Rated for 40 mgd In service since 1983 Major Processes: Preliminary Treatment Primary Treatment Secondary Treatment Biosolids Treatment Incinerator Ash Clarifier Courtesy: Bing.com

  5. TZ Osborne WRF BACKGROUND Major Processes (continued): • Biosolids Treatment • Thickening • Storage • Dewatering • Incineration • Disposal Incineration: • (2) incinerators • (3) centrifuges for dewatering of thickened sludge before entering incinerator • Ash slurry is formed from quenching process • Thickener/clarifier for ash slurry • Effluent to head of plant • Ash slurry feeds (1) belt filter press

  6. TZ Osborne WRF BACKGROUND Existing Belt Filter Presses • Concerns: • High maintenance • Low cake percent solids after switch in type of incinerator sand • Nearing end of useful life • Low capture rate • City developed dewatering screw to pilot • Operated for short period but would clog and not allow water to drain back down the spiral conveyor

  7. Schematic of Ash Slurry Dewatering Process Existing Ash Dewatering Schematic Clarifier/ Thickener Cake Primary Sludge Cake WAS Belt Conveyor Water Cake Fluidized Bed Incinerator Drain to head of WWTP Scrubber Cake BFP (Klampress Circa 1980’s) To Landfill Centrifuge

  8. Ash Slurry Characteristics

  9. Ash Slurry Sieve Analysis

  10. Available Technologies 2

  11. Potential Dewatering Technologies • Centrifuge • Belt Filter Press • Filter Press (Plate and Frame) • Rotary Fan Press • Rotary Screw Press • Dewatering Bin • Vacuum Filters • Dewatering Screw

  12. Belt Filter Press • Andritz • Phoenix BDP

  13. Recessed Chamber Filter Press (Plate and Frame Type) Andritz MW Watermark

  14. Rotary Fan Press Fournier

  15. Rotary Fan Press

  16. Rotary Fan Press Screen (pressure side) Screen (drain side)

  17. Screw Press FKC

  18. Screw Press

  19. Comparison of Technologies

  20. Testing 3

  21. Sample Testing Results

  22. Pilot Testing • Selected Rotary Fan Press and Screw Press for pilot testing • Rotary Fan Press (Fournier) in March 4 – 8, 2013 • Screw Press (FKC) onsite twice, February 7-8, 2013 and March 11, 2013 Pilot Location

  23. Screw Press Pilot • Results: • 50% solids, • 86% capture, • 6.48 lb/dry ton poly (Greensboro’s polymer)

  24. Rotary Fan Press Pilot • Results: • 47% solids, • 86% capture, • 3 lb/dry ton poly (Greensboro’s polymer)

  25. Economics

  26. Selected Equipment 4

  27. Selected Equipment • Built in redundancy • Small footprint • Smaller overall weight • Quick results during piloting • Worked well with Greensboro’s polymer • Ability to expand in the future • Selected the Fournier Rotary Fan Press based on:

  28. Conclusions and Summary 5

  29. Summary and Conclusions Ash slurry is uncharacteristic of other municipal sludges (fine particles) Sample testing not representative, pilot testing is preferred Project is currently in the Bid Phase Rotary fan press is best for this unique ash slurry and situation Suggest investigating both the rotary fan press and screw press for future projects Rotary Fan press can have advantages based on location and application including: • Small footprint • In place redundancy • Closed system

  30. Acknowledgements • City of Greensboro • Lori Cooper • Don Howard • Mike Buck • HDR • Will Shull • Mary Knosby

  31. Questions? Elijah Williams, PE Elijah.Williams@greensboro-nc.gov Christopher Crotwell, PE Christopher.Crotwell@hdrinc.com THANKS!

  32. Mass Balance

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