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Efficient Single-Stage Compressors for Fine Bubble Diffused Aeration Retrofit: A Detailed Look

This seminar discusses the installation of single-stage compressors for fine bubble diffused aeration at the Albany County Sewer District. It covers the technology, operating data, cost analysis, and more details of this retrofit project. The presentation outlines design assumptions, benefits, and cost-saving features, providing valuable insights from engineers and operators involved in the project.

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Efficient Single-Stage Compressors for Fine Bubble Diffused Aeration Retrofit: A Detailed Look

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  1. Single Stage Compressors As Part of a Fine Bubble Diffused Aeration Retrofit at the Albany County Sewer District A Look Back Nine Years Daniel W. Clayton RMWEA Operators Seminar 10/29/04

  2. Authors and Affiliations • Daniel W. Clayton, P.E. Principal Engineer, Brown and Caldwell(formerly of Malcolm Pirnie, Inc.) • Richard J. Lyons Superintendent of Operations, Albany County Sewer District (ACSD) • Peter Kyriacopoulos – Atlas Copco Comptec (ACC)

  3. Contact Information • Daniel W. Clayton, P.E. Principal Engineer, Brown and Caldwell1697 Cole Blvd., Suite 200, Golden CO 80401 – Phone: 303-239-5400 • Richard J. Lyons Superintendent of Operations, Albany County Sewer District (ACSD) PO Box 4187 Albany, NY 12204 - Phone: (518) 447-1619 • Peter Kyriacopoulos – District Sales Manager Atlas Copco Comptec (ACC) 20 School Rd. Voorheesville, NY 12186-9698 - Phone:(518) 765-3344 • Glenn Shultz (Alternate Contact)– Product Manager Atlas Copco Comptec (ACC) 20 School Rd. Voorheesville, NY 12186-9698 - Phone: (518) 765-5816

  4. Introduction/Outline – 1 • Background/project motivation • Design Assumptions • Single-stage compressor technology • Operating Data • Operating Cost

  5. Introduction/Outline – 2 • Payback • Operator’s comments • Engineer’s perspective • Comments/questions

  6. Background/Project Motivation • ACSD – two activated sludge plants • Treat primarily for BOD & TSS w/ seasonal nitrification

  7. Process Schematic – North and South Reprinted from: ACSD 2003 Annual Report

  8. North Plant Performance - 2003 Reprinted from: ACSD 2003 Annual Report

  9. South Plant Performance – 2003 Reprinted from: ACSD 2003 Annual Report

  10. Mechanical Aeration Systems • Three tanks in service • Single and dual-speed aerators

  11. Why Replace the Surface Aerators? • 20+ years old • Repair frequency increasing • NMPC contractor study showing projected savings (7/92) • NMPC grant eligible

  12. Planning: Design Assumptions – 1 • Little growth in treatment requirements • BOD and nitrification • Capacity available in remaining mechanical basins • Additional air capacity at North Plant desirable • Blower efficiency – 70%

  13. Planning: Design Assumptions – 2 Source: MPI Design Memorandum

  14. Planning – Cost Considerations • Capital • Equipment • Support Facilities • O&M • Single stage electrical cost savings significant (vs. multi-stage) • Other costs not given large consideration

  15. Single Stage Features – 1 • Energy efficiency at design point • Energy efficiency at turn-down (IGV; 9% better than throttling valve) • Overall ≥ 70% efficiency projected

  16. Single Stage Features – 2 • Wide range of flow/custom tuning • PLC – available for control use • Meet demanding industry standards (e.g. API)

  17. Single Stage Design Considerations • For wide variations in air requirements • For higher pressure situations (24 ft. WC – 10+psig) • Bigger units (2 S/S vs. 3 M/S) • Noise • Cooling

  18. Design: Major Elements – Each Plant • Three tanks with ceramic disk diffusers • One single-stage compressor on, one standby

  19. Design: Major Elements – Each Plant • Individual, 3-stage filters with 0.3 µm filtration • Mass flow control • Thermal-convective flow signal loop • Operator-entered set point • Blower PLC compares and adjusts • Auto start of standby compressor

  20. Design: Major Elements – Each Plant • Manual control • Operator-entered IGV setting • Blower PLC maintains setting • Blower protection – automatic • No D.O. control (monitor)

  21. Design: Cost Saving Features – 1 Blower Building • Pre–engineered metal building • Manual gantry; not bridge crane • Loading dock; not drive in

  22. North BB Exterior 1

  23. North BB Exterior 2

  24. North BB Interior 1

  25. North BB Interior 2

  26. Design: Cost Saving Features – 2 • Aeration Basins • Painted steel air piping • Manual air balancing to basins • Single set of DO monitoring • No gas cleaning features (bid option)

  27. North BB Exterior 3

  28. Modus Operandi – North Plant • Process demand driven • Automatic mode (mass flow) • Periodic operator adjustments • Target DO 0.5 to 2.0 mg/L

  29. Performance Comparison – North Plant • Flow and BOD loading changes • HP and unit power changes • ML Temperature – up • FESS – up

  30. Fine Bubble to Mechanical Aeration Comparison – North Plant

  31. Fine Bubble Aeration System 1994/96 to 2003 Comparison –North Plant

  32. Unit Power Consumption – North Plant

  33. Fine Bubble Aeration System Design Predictions to 1994/96 Comparison – North Plant • Data availability constrained assumptions

  34. Cost Analysis: Capital Expense • Total capital cost: ~$2.7M (incl. Eng.) • NMPC grant: ~$0.9M (incl. Eng.) • ACSD Net cost: ~$1.8M (for 2 plants)

  35. Cost Analysis:– O&M North Plant • Power costs (1.36%/yr) • Labor (4.26%/yr) and material increases • DWP up – more power • Maintenance costs

  36. Average Cost kWH North Plant1996 – 2003

  37. Cost Analysis: Est. Maintenance Cost – 1 • Compressors • Oil and filter changes • Every 2 years of operation; test oil annually • Using ACC Roto-H oil ($1,000/yr for all 4 units) • “Schedule C” Maintenance – @ 30,000 hrs ($5,000 /ea.)

  38. Cost Analysis: Est. Maintenance Cost– 2 • Inlet air filters (say $1,000/unit-yr) • Roll filter changes too frequent • Roll filters replaced with disposable sheets • Diffusers – gas cleaning • North Plant – cleaned 1x/year ($9,000) • South Plant – not cleaned

  39. Payback Analysis: Overall Project - Electrical Costs (9 years) • Estimated based upon power cost • Present value to before project (i=8%) • Compare to $1.8M

  40. Payback Analysis: – Single vs. Multi-stage Power – North Plant (20 yrs.)

  41. Payback Analysis: – Single vs. Multi-stage • Capital Cost Assumptions • Blowers and installation – factored • Assume others equal • Cost of money (i=8%) • O&M Cost • Power cost inflation (1.36%) • Labor and material inflation (3%) • S/S maintenance/filter changes ($2500/yr) • M/S maintenance/filter changes ($1500/yr)

  42. Payback Analysis: – Single vs. Multi-stage – 400+HP (2 units)

  43. Operator Comments – 1 • Operation – pleased with equipment performance • One of the best features – automatic compensation for air temperature

  44. Operator Comments – 2 • ACC single stage compressors: • Operator friendly • Minimal maintenance • Schedule “C" maintenance (4 compressors): • Machines are still like new, bearings, guide vane, gears, etc. • Quality of inlet air cited.

  45. Operator Comments – 3 • Power meters – a big help in trending operator costs • D.O. control: • 24/7 staffing • NYSERDA study –D.O. control conversion payback long (that clinches it !!! )

  46. Operator Comments – 4 • Why project turned out so well: • ACSD Staff input • Sufficient # of trains converted • Time spent on loadings to get design parameters, etc.

  47. Engineer’s Perspectives – 1 • General • Get involved • Provide best data (diurnal, seasonal, daily, etc.) • Turn-down often issue • Look at non-electrical O&M costs, too (carefully) • Match technology and operational philosophy/experience

  48. Engineer’s Perspectives – 2 • Single-stage blowers • For wide variations in air requirements • For higher pressure situations • Bigger units (2 S/S vs. 3 M/S) • New approaches (match with multi-stage) • Control features

  49. Engineer’s Perspectives – 3 • Maintain System Efficiency • Baseline/Monitor performance (auto.) • Perform regular maintenance (e.g. gas clean diffusers) • Automate operation (e.g. filter blinding; lag start) • Grid DO control? • Time of day/demand management

  50. Wrap-up • Review Key Points • Get involved • Provide best data • Perform meaningful comparisons • Automation/instrumentation • Electrical billing, future and incentives • Questions/Comments

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