Diffuser Technology Evaluation Case Study Andrea White, PE Coenraad - - PowerPoint PPT Presentation

January 31, 2018

Andrea White, PE Coenraad Pretorius, PE

Diffuser Technology Evaluation Case Study

Aeration System Components

www.xylemwatersolutions.com www.fluidcomponents.com www.dezurik.com www.apg-neuros.com http://www.procoproducts.com www.hach.com www.energy.siemens.com

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Existing Aeration System and Design Upgrades

• All aeration equipment 20+ years old and nearing end of useful life
• Membrane tube diffusers (4,032 split between 6 basins and 12 grids)
• Single-stage centrifugal blowers (4 @ 400 HP, each)

Unreliable, no discharge flow control, 3 in poor condition

• Technology evaluation conducted including life cycle cost analysis

High speed turbo blowers Ammonia based DO control with option for DO control only Fine bubble membrane diffusers

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Process Flow Diagram

Aer1 Aer2a Aer2b

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Diffuser Upgrade Alternatives

Alt 1: Replace tube diffusers in-kind (‘Do Nothing’) Alt 2: Replace tube diffusers with higher SOTE tubes Alt 3: Replace tube diffusers with disc diffusers Alt 4: Replace tube diffuser with panel diffusers

Installed Capital Cost (2017$/MGD)

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$121K $133K $183K $254K $0K $50K $100K $150K $200K $250K $300K Replace Tubes In- Kind Replace Tubes with Higher SOTE Tubes Replace Tubes with Discs Replace Tubes with Panels

Annual O&M Cost (2017$/MGD)

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$0K $20K $40K $60K $80K $100K $120K Replace Tubes In-Kind Replace Tubes with Higher SOTE Tubes Replace Tubes with Discs Replace Tubes with Panels Power Cost Maintenance Cost Replacement Cost

Power Cost Assumptions:

• $0.125/kWh
• Clean diffusers
• Constant Annual Avg Flow
• DO setpoint = 2 mg/L

$90K $117K $65K $86K

Daily Power Draw (kWh/MG)

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832 783 654 613 100 200 300 400 500 600 700 800 900 Replace Tubes In-Kind Replace Tubes with Higher SOTE Tubes Replace Tubes with Discs Replace Tubes with Panels

30-Year Life Cycle Cost (2017$/MGD)

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$1.6M $1.7M $1.4M $1.5M $1.3M $1.4M $1.5M $1.6M $1.7M $1.8M Replace Tubes In- Kind Replace Tubes with Higher SOTE Tubes Replace Tubes with Discs Replace Tubes with Panels

Benefit Over ‘Do Nothing’ (2017$)

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• $0.8M

$1.1M $0.9M

• $1.2M
• $0.8M
• $0.4M

$0.0M $0.4M $0.8M $1.2M $1.6M Replace Tubes In- Kind Replace Tubes with Higher SOTE Tubes Replace Tubes with Discs Replace Tubes with Panels

Payback Period

Alternative Payback Period (Years) Replace Tubes with Discs 23 Replace Tubes with Panels 26

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• Payback period greater than typical useful life of aeration system
• Replace tubes in-kind has lowest installed capital cost
• Decision -> replace tubes in-kind

Alternative Installed Capital Cost Replace Tubes In-Kind $917,000 Replace Tubes with Higher SOTE Tubes $1,004,000 Replace Tubes with Discs $1,385,000 Replace Tubes with Panels $1,920,000

Standard Oxygen Transfer Efficiency

Xylem.com

Driving Force

Oxygen transfer theory

• Basis for aeration system design
• Transfer of oxygen from gas phase to liquid phase
• Rate of transfer is proportional to driving force

OTR = KLa x (Cs – C) Where: OTR = O2 transfer rate, mg/L per time KLa = overall mass transfer coefficient,1/time Cs = saturation concentration of O2 in solution, mg/L C = concentration of O2 in solution, mg/L Bulk Liquid O2 Air Bubble Driving Force, mg/L

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WWD Webinar - Aeration System Design Basics

Blower Power Consumption and DO

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500 1,000 1,500 2,000 2,500 3,000 1 2 3 4 5 6 Blower Power Consumption, hp Dissolved Oxygen Concentration, mg/L

Fouling Factor, F

Accounts for loss in OTE

• ver time due to fouling

Realistic range? Effect blower operation & power demand?

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Rosso et al, 2013

Blower Power and Fouling Factor

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500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

Blower Power Consumption, hp Diffuser Fouling Factor, F

Diffuser Head Loss, Ψ

Accounts for increased diffuser head loss over time Realistic range? Effect blower operation & power demand?

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Rosso et al, 2013

Blower Power Consumption and Headloss

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200 400 600 800 1,000 1,200 1.00 1.50 2.00 2.50 3.00 3.50

Blower Power Consumption, hp Diffuser Headloss Factor, Ψ