combined heat and power systems using biogas in wastewater
TRANSCRIPT
Combined Heat and Power Systems Using Biogas in Wastewater Treatment Plants
North Dakota Water and Pollution Control Conference
Grand International Inn Minot, ND
October 16, 2012
Tracy Ekola, Principal | Regional Practice Center Leader
John Fisher, Principal | Senior Design Leader
Did You Know? US EPA Reports • CHP systems are engine-generators that use biogas as fuel to
produce electricity or as boiler fuel to produce heat. • There are over 75,000 wastewater treatment plants (industrial
and municipal) in the US.
• Most of these treatment plants use aerobic digestion and about 5,000 currently contain anaerobic digesters.
• Energy costs can account for 30 percent of the total operation and maintenance (O&M) costs of WWTPs (Carns 2005).
• WWTPs account for approximately 3 percent of the electric load in the United States.
US EPA - Combined Heat and Power (CHP) Partnership Report
As of June 2011, CHP systems using biogas were in place at 104 WWTPs, representing 190 megawatts (MW) of capacity. CHP systems are technically feasible at 1,351 additional sites Nationwide, WWTFs have the potential to provide more than 400 MW in generating capacity and 38,000 million Btu per day of thermal energy. 3 million metric tons of carbon dioxide emissions could be prevented annually, which is the equivalent of emissions from 596,000 vehicles.
WWTPs Use Electricity! Process Energy Breakdown
4
Building Systems 2%
Prelim/Primary Treatment 7%
Biological System 37%
Secondary/RAS Pumps 9%
Sludge Thickening/Dewatering 12%
Digestion 14%
Sludge Drying 11%
Plant Water & Disinfection 8%
How Do Treatment Plants Work?
Solids Can Be Digested 2 Ways Aerobic Digestion Aerobic organisms need oxygen and mixing Typically used in plants with small population (less than
15,000) and low industrial load
Anaerobic Digestion Anaerobic organisms function without oxygen Typically used in plants with large populations and high
industrial load
Anaerobic digestion offer many potential benefits. Less solid waste is left over – 1 lb solids in, ½ lb solids out Biogas (methane) is produced and reused
Biogas 101
Biogas is a by-product of the anaerobic decomposition of organic solid waste
300 scfm of biogas = ~ 800 kW electricity
Biogas–~ 65% methane (CH4)–~ 35% carbon dioxide (CO2)
By using the energy from biogas, a WWTP can save $1,000’s of dollars per year in heating costs and reduce greenhouse gas emissions.
A Look Inside an Anaerobic Digester
A large covered tank which is mixed and heated
Operates biologicially without air
Biogas accumulates at the top of the digester
Sludge volume is reduce by ½ within 15 days
Biosolids become beneficial and are applied to farmland
One WWTP that Uses Bio Gas to Heat Sludge and Plant Buildings
Austin, MN 2 separate WWTPs with combined flow of 4.5 mgd City population 23,000 Hormel Foods waste load has population equivalent to
115,000 BioGas produced is estimated at 250,000 scfm per day and
is burned through large boilers Remaining biosolids are stored then land applied in
Spring and Fall
Austin Municipal WWTP
Trickling Filter
Clarification
Excess BioGas is Flared – Normally in Summer
Austin Industrial WWTP
Industrial WWTP - Anaerobic Digesters
Industrial Plant – Boiler / Heat Exchangers
2 WWTPs That Use BioGas to Generate Electricity and Heat Ames, IA Population 56,700 Generating electricity and thermal energy for 22
years 20% electrical savings annually
Owatonna, MN Population 25,600 and has some large industries Generating electricity and thermal energy for 25 years Also recovering heat from wastewater effluent Biogas provide 30% electrical savings annually =
$200,000
Ames, Iowa
Trickling Filters
Anaerobic Digester Cover
BioGas Powered Engine Generator
Thermal Heat Piping
Thermal Heating System
Sludge is Land Applied
Owatonna, MN
Activated Sludge Process
Anaerobic Digester Complex
Anaerobic Digester – Biogas Cover
BioGas Piping
BioGas Powered Engine Generator
Controls
Hot Water Recirculation System
Digester Sludge Heat Exchanger
Effluent Heat Recovery System
Non-Municipal Anaerobic Digestion
Anaerobic digestion is gaining poplularity One of the oldest processes used for solids stabilization at wastewater treatment plants
Increased use due to driving factors - Energy costs as well as decreasing loading limits
Many variations developed over the last several decades as a result of anaerobic digestion being more closely evaluated by industry and agriculture
Food processors (dairy, vegetable, brewing, meat packers) Ag/manure digesters Co-digestion
Motivations For Agriculture:(as size increases so does problem/opportunity)
1) Public pressure for reduced odor 2) Increased environmental scrutiny –
greenhouse gas emissions/nutrient issues 3) Energy generation 4) Digested solids used for bedding
For Industry: 1) Cost avoidance – WW charges, electricity charges,
natural gas usage, waste disposal 2) Interest in renewable energy or corporate
sustainability
For Co-digestion: Energy Generation
Feasibility Factors
Feedstock Characteristics, strength and availability
Technical Feasibility – inhibitory/toxic components, C:N ratio
Regulatory Issues
Site Constraints
Economics – Payback period
Funding Assistance
Motivation
Anaerobic Digestion Differences Municipal • Uniform waste composition • CSTR
Non-Municipal • Variable waste composition • Many types & configurations
CHP Technology is at Work Everywhere
Number of Installed Ag Systems
Some Energy Stories Found on the Web McDonalds successfully transformed waste into
electricity earlier this year at several United Kingdom restaurants
Chrysler is converting used paint solids from two St. Louis assembly plants into electricity.
Heinz is working on a program to transform used potato peels into energy.
Kraft - Two cheese plants in New York will turn used whey into energy in a move that will supplant a third of the facilities' natural gas purchases. The company also will avoid the expense of hauling the waste away.
SEH AD Case Studies
• Village of Turtle Lake, WI
• Southern MN Community
• Northeastern MN Community
• Potato Industry, MN
• Dairy, WI
AD Project Success Factors By-product disposal/reuse
options available
Strong motivating factor
Ownership model/Cohesive team
High current operational costs (WW treatment, energy, propane)
Pima County Arizona Wastewater Treatment Plant – CHP
Seven Waukesha engine/generator packages
Produces 243 cfm biogas @ 60% methane
Provides 35 percent of energy needs
Thermal energy: Digester heat, HVAC, domestic hot water
Electricity generation = 5 cents/KWh (includes maintenance) rebuild 28-year-old engines, each with 40,000 hours of operation
San Francisco, CA East Bay Municipal Utility District
• Nine Communities send 75 mgd of sewage to the WWTP.
• Located in the San Francisco Bay area - cogenerating electricity and thermal energy anaerobic digester gas (biogas)
• Generates enough energy for approximately 125 % of its energy needs resulting in cost savings estimated $1.7 million annually
Metropolitan Council Environmental Services
Maintains approximately 600 miles of sewers that collect flow from 105 communities.
Treats an average of 250 million gallons of wastewater daily at 7 regional treatment plants.
Energy use is a major expense -- approximately $15 million per year.
MCES 2015 Energy Goal is to reduce purchased of energy by 25%
Europe’s Vision is for WWTPs to Become Energy Neutral
• Why? – Gasoline costs over $8.00 per gallon – Power costs are $0.26 per kwh – Government initiatives and funding incentives in place to
reduce carbon footprint – Beneficial reuse is part of social framework – Photos of a BioGas Refueling Station in Germany
Questions?
Combined Heat Projects in Wastewater Plants Have Worked Very Well in the Past and Will
Become Even Better in the Future!