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

January 31, 2018 Diffuser Technology Evaluation Case Study Andrea White, PE Coenraad Pretorius, PE

Aeration System Components http://www.procoproducts.com www.energy.siemens.com www.xylemwatersolutions.com www.apg-neuros.com www.dezurik.com www.fluidcomponents.com www.hach.com WWD Webinar - Aeration System Design Basics

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 3

Process Flow Diagram Aer1 Aer2a Aer2b 4

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 5

Installed Capital Cost (2017$/MGD) $300K $254K $250K $183K $200K $133K $150K $121K $100K $50K $0K Replace Tubes In- Replace Tubes with Replace Tubes with Replace Tubes with Kind Higher SOTE Tubes Discs Panels 6

Power Cost Assumptions: Annual O&M Cost (2017$/MGD) • $0.125/kWh • Clean diffusers • Constant Annual Avg Flow $117K • DO setpoint = 2 mg/L $120K $90K $86K $100K $65K $80K $60K $40K $20K $0K Replace Tubes Replace Tubes Replace Tubes Replace Tubes In-Kind with Higher with Discs with Panels SOTE Tubes Power Cost Maintenance Cost Replacement Cost 7

Daily Power Draw (kWh/MG) 900 832 783 800 654 700 613 600 500 400 300 200 100 0 Replace Tubes In-Kind Replace Tubes with Replace Tubes with Replace Tubes with Higher SOTE Tubes Discs Panels 8

30-Year Life Cycle Cost (2017$/MGD) $1.8M $1.7M $1.7M $1.6M $1.6M $1.5M $1.5M $1.4M $1.4M $1.3M Replace Tubes In- Replace Tubes with Replace Tubes with Replace Tubes with Kind Higher SOTE Tubes Discs Panels 9

Benefit Over ‘Do Nothing’ (2017$) $1.6M $1.1M $1.2M $0.9M $0.8M $0.4M $0.0M -$0.4M -$0.8M -$0.8M -$1.2M Replace Tubes In- Replace Tubes with Replace Tubes with Replace Tubes with Kind Higher SOTE Tubes Discs Panels 10

Payback Period Payback Period Installed Capital Alternative Alternative (Years) Cost Replace Tubes with Discs 23 Replace Tubes In-Kind $917,000 Replace Tubes with Panels 26 Replace Tubes with Higher $1,004,000 SOTE Tubes Replace Tubes with Discs $1,385,000 Replace Tubes with Panels $1,920,000 • Payback period greater than typical useful life of aeration system • Replace tubes in-kind has lowest installed capital cost • Decision -> replace tubes in-kind 11

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 = K L a x (C s – C) Driving Bulk 4 3 Force, mg/L Liquid 2 1 Where: O 2 Air OTR = O 2 transfer rate, mg/L per time Bubble K L a = overall mass transfer coefficient,1/time Cs = saturation concentration of O 2 in solution, mg/L C = concentration of O 2 in solution, mg/L WWD Webinar - Aeration System Design Basics

Blower Power Consumption and DO 3,000 Blower Power Consumption, hp 2,500 2,000 1,500 1,000 500 0 0 1 2 3 4 5 6 Dissolved Oxygen Concentration, mg/L 14

Fouling Factor, F Rosso et al, 2013 � Accounts for loss in OTE over time due to fouling � Realistic range? � Effect blower operation & power demand? 15

Blower Power and Fouling Factor 4,000 3,500 3,000 Blower Power Consumption, hp 2,500 2,000 1,500 1,000 500 0 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 Diffuser Fouling Factor, F 16

Diffuser Head Loss, Ψ Rosso et al, 2013 � Accounts for increased diffuser head loss over time � Realistic range? � Effect blower operation & power demand? 17

Blower Power Consumption and Headloss 1,200 1,000 Blower Power Consumption, hp 800 600 400 200 0 1.00 1.50 2.00 2.50 3.00 3.50 Diffuser Headloss Factor, Ψ 18