1 a look back nine years rmwea operators seminar 10/29/04 single stage compressors as part of a fine...

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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

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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

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Introduction/Outline – 2

Payback Operator’s comments Engineer’s perspective Comments/questions

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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%

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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

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Single Stage Features – 1

Energy efficiency at design point Energy efficiency at turn-down

(IGV; 9% better than throttling valve) Overall ≥ 70% efficiency projected

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Single Stage Features – 2

Wide range of flow/custom tuning PLC – available for control use Meet demanding industry standards

(e.g. API)

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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

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Design: Major Elements – Each Plant

Manual control Operator-entered IGV setting Blower PLC maintains setting

Blower protection – automatic No D.O. control (monitor)

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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

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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)

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Cost Analysis:– O&M North Plant

Power costs (1.36%/yr) Labor (4.26%/yr) and material increases DWP up – more power Maintenance costs

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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.)

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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

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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

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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)

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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

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Operator Comments – 1

Operation – pleased with equipment performance

One of the best features – automatic compensation for air temperature

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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.

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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 !!! )

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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.

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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

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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

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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

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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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