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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. Authors and Affiliations. Daniel W. Clayton, P.E.

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a look back nine years
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

authors and affiliations
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)
introduction outline 1
Introduction/Outline – 1
  • Background/project motivation
  • Design Assumptions
  • Single-stage compressor technology
  • Operating Data
  • Operating Cost
introduction outline 2
Introduction/Outline – 2
  • Payback
  • Operator’s comments
  • Engineer’s perspective
  • Comments/questions
background project motivation
Background/Project Motivation
  • ACSD – two activated sludge plants
  • Treat primarily for BOD w/ seasonal nitrification
process schematic north and south
Process Schematic – North and South

Reprinted from: ACSD 2003 Annual Report

north plant performance 2003
North Plant Performance - 2003

Reprinted from: ACSD 2003 Annual Report

south plant performance 2003
South Plant Performance – 2003

Reprinted from: ACSD 2003 Annual Report

mechanical aeration systems
Mechanical Aeration Systems
  • Three tanks in service
  • Single and dual-speed aerators
why replace the surface aerators
Why Replace the Surface Aerators?
  • 20+ years old
  • Repair frequency increasing
  • NMPC contractor study showing projected savings (7/92)
  • NMPC grant eligible
planning design assumptions 1
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%
planning design assumptions 2
Planning: Design Assumptions – 2

Source: MPI Design Memorandum

planning cost considerations
Planning – Cost Considerations
  • Capital
    • Equipment
    • Support Facilities
  • O&M
    • Single stage electrical cost savings significant (vs. multi-stage)
    • Other costs not given large consideration
single stage features 1
Single Stage Features – 1
  • Energy efficiency at design point
  • Energy efficiency at turn-down (IGV; 9% better than throttling valve)
  • Overall ≥ 70% efficiency projected
single stage features 2
Single Stage Features – 2
  • Wide range of flow/custom tuning
  • PLC – available for control use
  • Meet demanding industry standards (e.g. API)
single stage design considerations
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
design major elements each plant
Design: Major Elements – Each Plant
  • Three tanks with ceramic disk diffusers
  • One single-stage compressor on, one standby
design major elements each plant1
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
design major elements each plant2
Design: Major Elements – Each Plant
  • Manual control
    • Operator-entered IGV setting
    • Blower PLC maintains setting
  • Blower protection – automatic
design cost saving features 1
Design: Cost Saving Features – 1

Blower Building

  • Pre–engineered metal building
  • Manual gantry; not bridge crane
  • Loading dock; not drive in
design cost saving features 2
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
modus operandi north plant
Modus Operandi – North Plant
  • Process demand driven
  • Automatic mode (mass flow)
  • Periodic operator adjustments
  • Target DO 0.5 to 2.0 mg/L
performance comparison north plant
Performance Comparison – North Plant
  • Flow and BOD loading changes
  • HP and unit power changes
  • ML Temperature – up
  • FESS – up
fine bubble aeration system design predictions to 1994 96 comparison north plant
Fine Bubble Aeration System Design Predictions to 1994/96 Comparison – North Plant
  • Data availability constrained assumptions
cost analysis capital expense
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)
cost analysis o m north plant
Cost Analysis:– O&M North Plant
  • Power costs (1.36%/yr)
  • Labor (4.26%/yr) and material increases
  • DWP up – more power
  • Maintenance costs
cost analysis est maintenance cost 1
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.)
cost analysis est maintenance cost 2
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
payback analysis overall project electrical costs 9 years
Payback Analysis: Overall Project - Electrical Costs (9 years)
  • Estimated based upon power cost
  • Present value to before project (i=8%)
  • Compare to $1.8M
payback analysis single vs multi stage north plant
Payback Analysis: – Single vs. Multi-stage – North Plant
  • 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)
operator comments 1
Operator Comments – 1
  • Operation – satisfied with equipment performance
  • One of the best features – automatic compensation for air temperature
operator comments 2
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.
operator comments 3
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 !!! )
operator comments 4
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.
engineer s perspectives 1
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
engineer s perspectives 2
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
engineer s perspectives 3
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
wrap up
Wrap-up
  • Review Key Points
  • Questions/Comments
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