Patti Craddock, PE Presents:
Fats, Oils, and Grease: Nuisance to Opportunity for Sioux Falls CSWEA 88th Annual Meeting, Oakbrook Terrace, Illinois May 20, 2015
Presentation Outline • Fats, Oils, and Grease (FOG) – nuisance to opportunity concept for Sioux Falls • Sioux Falls WRF business case evaluation and improvements plan
Fats, Oil, and Grease (FOG): Nuisance • Nuisance – Collection System – Treatment Facility
• Stop it at the Source Campaigns – Public outreach – Ordinances
FOG Program Outreach Education
Fats, Oil, and Grease (FOG): Opportunity • Yellow grease – Used cooking oil – Already a market
• Brown grease – Grease – down the drain (interceptors) – Evolving market – Energy rich waste stream
Grease as Energy Source at WWTFs • FOG is highly volatile – high energy/unit volume • Benefit – energy recovery – Anaerobic digestion – Incineration (thermal oxidation)
• Example: anaerobic digestion – Direct feed to digesters – co-digestion – VS Content: FOG-95%, Municipal-70-85% – VS Destruction: FOG-90%, Municipal-66%
Co-Digestion Drivers for Sioux Falls Aging Assets/Underutilized Assets CO2 Wastewater Sludge
CH4
CH4
CO2 Stripping CNG
CNG Vehicle Fuel Heat
CO2
• Digester heating • Energy recovery • Use at WWTP • Use on Base
Engine Liquid Wastes
Electricity
Sludge Liquor
Feed Stocks
• Return to WWTP • Liquid Fertilizer
Anaerobic Digester At WWTP Residuals
Solids Solid Wastes
• Soil Amendment • Further Energy Extraction
Co-Digestion Drivers Improved Collection System Operations CO2
Wastewater Sludge
CH4
CH4
CO2 Stripping CNG
CNG Vehicle Fuel Heat
CO2
• Digester heating • Energy recovery • Use at WWTP • Use on Base
Engine Liquid Wastes FOG
Electricity
Sludge Liquor
Feed Stocks
• Return to WWTP • Liquid Fertilizer
Anaerobic Digester At WWTP Residuals
Solids Solid Wastes
• Soil Amendment • Further Energy Extraction
Co-Digestion Drivers Power Savings Wastewater Sludge
CH4
CH4
CO2 CO2 Stripping CNG
CNG Vehicle Fuel Heat
CO2
• Digester heating • Energy recovery • Use at WWTP • Use on Base
Engine Liquid Wastes
Electricity
Sludge Liquor
Feed Stocks
• Return to WWTP • Liquid Fertilizer
Anaerobic Digester At WWTP Residuals
Solids Solid Wastes
• Soil Amendment • Further Energy Extraction
Co-Digestion Drivers Renewable Fuel Wastewater Sludge
CH4
CH4
CO2 CO2 Stripping CNG
CNG Vehicle Fuel Heat
CO2
• Digester heating • Energy recovery • Use at WWTP • Use on Base
Engine Liquid Wastes
Electricity
Sludge Liquor
Feed Stocks
• Return to WWTP • Liquid Fertilizer
Anaerobic Digester At WWTP Residuals
Solids Solid Wastes
• Soil Amendment • Further Energy Extraction
Co-Digestion Drivers Community Green Goals CO2
Wastewater Sludge
CH4
CO2 Stripping CNG
• Landfill Diversion CNG Vehicle Fuel • Less TruckHeat Traffic• Digester heating
CH4
CO2
• Energy recovery
• Smaller Carbon Footprint
• Use at WWTP • Use on Base
Engine Liquid Wastes
Electricity
Sludge Liquor
Feed Stocks
• Return to WWTP • Liquid Fertilizer
Anaerobic Digester At WWTP Residuals
Solids Solid Wastes
• Soil Amendment • Further Energy Extraction
Co-Digestion Drivers Reduced Residual Biosolids CO2
Wastewater Sludge
CH4
CH4
CO2 Stripping CNG
CNG Vehicle Fuel Heat
CO2
• Digester heating • Energy recovery • Use at WWTP • Use on Base
Engine Liquid Wastes
Electricity
Sludge Liquor
Feed Stocks
• Return to WWTP • Liquid Fertilizer
Anaerobic Digester At WWTP Residuals
Solids Solid Wastes
• Soil Amendment • Further Energy Extraction
Utility Drivers to Capture Grease and Co-Digest • Aging assets (with capacity) • Energy efficiency and sustainability practices – Additional energy for onsite and other energy use – Reduce aeration system costs for FOG entering collection system or with hauled waste – Part of utility/community sustainability metrics
• Reduce collection system maintenance and related costs
Sioux Falls FOG Receiving and Digester Complex Improvements • FOG Opportunity incorporated with aged infrastructure improvements • Study completed in 2013 with Sioux Falls, SEH and Kennedy/Jenks Consultants (KJ) team • Design/construction of phased improvements in progress
Digester Improvements Require Coordination for Success • Digester mixing • Digester covers
• Heat exchangers • Engine generators
• Gas conditioning • FOG receiving
Improvements Plan 5
2 6
3
4 Project 1 2 3 4 5 6 7 8
Capital Improvement Heat Exchangers Secondary Digester Cover Digester Gas Conditioning Digester Mixing & Cover #3 Digester Mixing & Cover #2 Digester Mixing & Cover #1 Feedstock Receiving and Processing Energy Recovery
7 Weigh Stationlocation to be determined
Heat Exchanger Replacement Tube-in-Shell – 1980s
Replaced with Spiral
Secondary Digester Cover Replacement • Floating cover-1980s replaced with fixed steel cover • Ability to convert to primary digester
Digester Mixing • Maximum active volume
• Maximum volatile solids destruction • Effective and energy efficient process control
• High reliability Effective mixing is critical with FOG - No grit build-up - No mat build-up
Digester Improvements - Mixing
Digester Gas Conditioning Required for Engine Performance • Quality Issues – Hydrogen sulfide > 2,000 mg/L – Siloxanes
• New Facilities – Biofilter to reduce hydrogen sulfide – Iron sponge for polishing hydrogen sulfide – Activated carbon for siloxane removal
FOG Receiving and Processing
Weigh Stationlocation to be determined
FOG Processing
Digester
Dosing Pumps
Recirculation Pump Grinder Mixing Pump
Mixing Nozzles
Fog Receiving Tank
Rock Trap
Business Case Evaluation Criteria Units Base Value Description Planning Period years 20 Discount Rate 4% FOG Capture Rate 75% Electricity Current Rate $/kWh $0.072 Escalation Rate per year 5% FOG Program Administration per year $100,000 Collection Sys Maint Deferred per year ($200,000) Tipping Fee $/gal $0.10 3% Tipping Fee Escalation Engines/MT Energy Recovery (Future-Engines and/or Microturbines (MT)) Electrical Efficiency 38%/31% Generation Uptime 90%/95% Cost to Operate $/kWhr $0.034/$0.023 OTHER: Labor, Maintenance, Solids Disposal, unit process power costs
Biogas Production and Energy Savings $800,000
400
$700,000
350
$600,000
300
$500,000
250
$400,000
200 Energy $-FOG
$300,000 $200,000
Energy $-Base Biogas-FOG
150 100
Biogas-Base $100,000
$-
50
0
Biogas Production, cfm
Annual Energy Produced, $
Capacity of Existing Primary Digesters (337 cfm)
FOG Co-Digestion Annual Costs and Benefits $1,000,000
$500,000 O&M-CHP/Dig
Annual Cost/Benefit, $
$-
Solids Handling O&M-FOG
$(500,000)
Power Demand Tipping Fees
$(1,000,000)
$(1,500,000)
$(2,000,000)
$(2,500,000)
Power Benefit
FOG Receiving Facility Payback Analysis 18 Cost
16
Revenue
Savings=$4.5M
14
2023 - 2027
Millions
12
10 8 Cumulative Cost
6
Breakeven = 7 years
4 2
Cumulative Revenue
0 2015
2017
2019
2021
2023
2025
2027
Sensitivity Analysis Savings Over 20 years, $ Millions
Sewer Tipping Fee FOG Capture Maintenance $8 $7
5
5
$6
7
$5
7
7
$4
$3 $2 $1 $0
9
9 11
12
Payback Period, years
Improvements Summary • Aging Assets – – – –
Heat exchangers Digester mixing Secondary digester cover Energy recovery (future)
• Process Performance/Optimization – – – –
Digester gas conditioning Primary digester covers Feedstock receiving and processing FOG ordinance & enforcement
Co-Digestion Maximizes Asset Value & Achieves Sustainability Goals • Digestion equipment - end of useful life • Digester & energy recovery systems have capacity • Annual benefits exceed costs • City initiatives for sustainability – Waste minimization – Water resources – Energy
Nuisance
Opportunity
Thank You!
