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1
A Look Back Nine Years
RMWEA Operators Seminar10/29/04
Single Stage Compressors As Part of a Fine Bubble Diffused Aeration Retrofit
at the
Albany County Sewer District
Daniel W. Clayton
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)
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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 4187Albany, NY 12204 - Phone: (518) 447-1619
Peter Kyriacopoulos –District Sales ManagerAtlas Copco Comptec (ACC)20 School Rd.Voorheesville, NY 12186-9698 - Phone:(518) 765-3344
Glenn Shultz (Alternate Contact)–Product ManagerAtlas Copco Comptec (ACC)20 School Rd.Voorheesville, NY 12186-9698 - Phone: (518) 765-5816
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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
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Process Schematic – North and South
Reprinted from: ACSD 2003 Annual Report
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North Plant Performance - 2003
TABLE 1PROCESS PERFORMANCE DATA - 2003
NORTH PLANT
Parameter Influent (mg/L)
Effluent (mg/L)
Discharge Permit Limit (mg/L)
Efficiency %
Tons Removed Per Day
Tons Discharged
Per Day
BOD 125 3.1 25.0 97.5 12.56 0.32
S.S. 212 8.4 30.0 96.0 20.97 0.87
NH3 9.3 5.3 43.0 0.41 0.55
TKN 20.6 7.9 15.2* 61.7 1.31 0.81Average Flow – 24.7 MGD *Seasonal June 1 to October 31
Reprinted from: ACSD 2003 Annual Report
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South Plant Performance – 2003
TABLE 1APROCESS PERFORMANCE DATA - 2003
SOUTH PLANT
Parameter Influent (mgLl)
Effluent (mg/L)
Discharge Permit Limit (mg/L)
Efficiency%
Tons Removed Per Day
Tons Discharged
Per Day
BOD 69 3.0 25.0 95.7 7.35 0.33
S.S. 108 8.6 30.0 92.0 11.07 0.96
NH3 7.3 1.3 82.2 0.67 0.14
TKN 15.3 2.5 15.4* 83.7 1.43 0.28Average Flow – 26.7 MGD * Seasonal June 1 to October 31
Reprinted from: ACSD 2003 Annual Report
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Mechanical Aeration Systems
Three tanks in service Single and dual-speed aerators
PLANT
No. OF TANKS IN SERVICE
TANK L x W (ft)
No. of Aerators
Average running HP
North 3 of 6 260 x 65 12 577
South 3 of 4 195 x 69 9 500
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Why Replace the Surface Aerators?
20+ years old Repair frequency increasing NMPC contractor study showing
projected savings (7/92) NMPC grant eligible
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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 – 2Average Daily Conditions
Plant
BOD5(1)
Removed (lb/d)
NH3(2)
Removed (lb/d)
Total(3) AOR (lb/d)
Air Requirements (scfm)
Process(4)
C = 2 mg/lProcess(5)
C = 1 mg/l Mixing(6)
North 12,950 1,640 21,720 7,670 6,780 6,500
South 7,950 1,150 13,990 4,950 4,370 4,850
Max. Month Conditions
Plant
BOD5(1)
Removed (lb/d)
NH3(2)
Removed (lb/d)
Total(3) AOR (lb/d)
Air Requirements (scfm)
Process(4)
C = 2 mg/lProcess(5)
C = 1 mg/l Mixing(6)
North 14,400 1,960 24,800 8,760 7,740 6,500
South 12,600 1,520 20,800 7,350 6,500 4,850
Source: MPI Design Memorandum
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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
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Design: Major Elements – Each Plant
Three tanks with ceramic disk diffusers One single-stage compressor on, one
standby
PLANT No. OF
TANKS IN SERVICE
NO. OF DIFFUSERS
PEAK AIR FLOW (per
diffuser)
North 3 of 6 7,0008,760(1.3)
South 3 of 4 6,0007,350(1.2)
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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
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North BB Exterior 1
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North BB Exterior 2
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North BB Interior 1
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North BB Interior 2
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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)
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North BB Exterior 3
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Modus Operandi – North Plant
Process demand driven Automatic mode (mass flow) Periodic operator adjustments Target DO 0.5 to 2.0 mg/L
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Performance Comparison – North Plant
Flow and BOD loading changes HP and unit power changes ML Temperature – up FESS – up
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Fine Bubble to Mechanical Aeration Comparison – North Plant
AERATIONSYSTEM
AVE.FLOW(mgd)
SECOND.BOD
TREATED(lb/day)
MLTEMP.
(°C)FESS(mg/L)
kWH/lbBOD
TREATEDAVE.HP
COSTkWH
(CENTS) $/Day
Mechanical(Sep 93 – Aug 94) 20.1 12,700 15.4 4.2 0.83 577 7.732 800
Fine Bubble(Sep 94 – Mar 96) 19.3 12,300 17.4 5.9 0.51 347 7.451 463
Delta % –4.0 –3.1 13 40 –38 –40 –3.6 –42
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Fine Bubble Aeration System 1994/96 to 2003 Comparison –North Plant
AERATIONSYSTEM
AVE.FLOW(mgd)
SECOND.BOD
TREATED (lb/day)
MLTEMP.
(°C)FESS(mg/L)
kWH/lbBOD
TREATEDAVE.HP
COSTkWH
(CENTS) $/Day
Fine Bubble(Sep 94 – Mar 96) 19.3 12,300 17.4 5.9 0.51 347 7.451 463
Fine Bubble(2003) 24.7 11,500 16.7 8.3 0.58 366 8.654 566
Delta % 28 –6.5 –4.0 41 14 5.5 16 22
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ACSD - NORTH PLANTPOWER PER POUND OF BOD
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Mechanical(Sep93-Aug94)
1997 1999 2001 2003
YEAR
kWH
/# B
OD
kWH/ lb BOD – applied
kWH/ lb BOD – treated
Unit Power Consumption – North Plant
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Fine Bubble Aeration System Design Predictions to 1994/96 Comparison – North Plant
AERATIONSYSTEM
Ave. Air (scfm)
AVE.BHP
Max. Month Air
(scfm)Max. Month
BHP
Fine Bubble(Design) 7,700 289 8,800 330
Fine Bubble(Sep 94 – Mar 96) 10,500 347 13,400 415
Delta % 36 20 52 26
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 Plant 1996-2003
7.563 7.8107.333
6.480 6.821 6.810 7.084
8.645
0.000
1.000
2.000
3.000
4.000
5.000
6.000
7.000
8.000
9.000
10.000
Average Cost YearCents
1996 1997 1998 1999 2000 2001 2002 2003
Average Cost kWH North Plant1996 – 2003
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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
PLANT (conv. date) Gross Savings Present Value
North (8/94) $864,000 $601,000
South (9/94) $1,330,000 $919,000
Totals $2,190,00 $1,520,000
40
Payback Analysis: – Single vs. Multi-stage Power – North Plant (20 yrs.)
ParameterMechanical
MixersNorth Plant
Single Stage
Theoretical Multi-stage
(+12%)
Average HP 577 377 422
Average KW 430 282 315
Initial Unit cost ($/KWH; 1994) 0.076 0.076 0.076
Base value of power ($/yr) 287,000 188,000 210,000
Savings average annual ($) 111,000 85,700
Savings 20 present value ($) 1,030,000 800,000
Savings in Present Value ($) 230,000
Capital Cost ( Est. $) 1.2M 0.90M
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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 ($1500/yr)
42
Payback Analysis: – Single vs. Multi-stage – 400+HP (2 units)
ParameterScenario 1 Scenario 2 Scenario 3
Average HP 400 700 1,000
Average KW 298 522 746
Unit cost ($/KWH; 1994) 0.076 0.076 0.076
Base value of power ($/yr) 198,400 347,500 496,700
Inefficiency (%) 12 12 12
Initial value of power ($/yr) 222,200 389,200 556,300
Initial value of O&M ($/yr) 2,500 3,500 4,300
Initial value of Overhaul ($/yr) 10,000 14,000 17,300
12% Ineff. 20 present value ($) 2,530,000 4,310,000 6,160,000
Base 20 year Present Value ($) 2,220,000 3,870,000 5,520,000
Difference in Present Value ($) 310,000 440,000 640,000
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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