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CHP & Anaerobic Digester Gas Applications

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CHP and Digester Gas Applications

Animal Waste / Manure Management

Food Processing

Waste Water Treatment

Many of the following slides came from:R.T. Burns, PhD, PE

Agriculture & Bio-systems Engineering Dep’tIowa State University

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Anaerobic Digesters

Natural Biological (bacterial) Process That Converts Organic Carbon From Large Molecules to Simple Molecules

When Properly Applied, Digester Technology Can Effectively Assist in:

• Sustainable• Economical• Environmentally Balanced• & Neighbor Friendly Agricultural Practices

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Anaerobic Digestion Process Overview

H2SManure

Carbon Dioxide (CO2)

Treated Effluent

pathogensmacronutrients

unstable organics

EnergyMethane (CH4)

pathogen freenutrient rich

stable (low odor)

Anaerobic Digester

Biological Process

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The anaerobic digestion process is sensitive to changes in:

Temperature

Alkalinity

Waste Strength (loading rate)

Flow (hydraulic retention time)

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Collection

Application / Application / UtilizationUtilization

Digester

Storage

Animal Waste Management System

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Many Types of Anaerobic Digesters

LoadingSchedule

FlowPattern

MicrobialGrowth

ClassificationMethods

TemperatureRegime

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Anaerobic Digester ConfigurationsAnaerobic Digester Configurations

• Covered lagoons (ambient and heated)

• Complete mix digesters (CSTR)

• Plug flow digesters

• Anaerobic sequencing batch reactors (ASBR)

• Fixed film digesters (anaerobic filters)

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Energy Recovery – Biogas(60% to 65% Methane)

Flare It

Use It for Heating – Displace Natural Gas / Propane

Use It for CHP– Displace Purchased Electricity– Displace Natural Gas / Propane

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Anaerobic Digester / CHP System

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Electric & Thermal Coincidence

Steady Use of Recovered Thermal Energy– Heat the Digester– Heat the Livestock Operation– Heat Potable Water

Steady Use for the Electricity– Displace Electricity Utilized on the Farm– Possibly Sell Excess Electricity to Utility

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CHP TechnologiesPrime Movers:– Reciprocating Engines– Micro-turbines

Gas Clean up possible

Gas Compression (micro-turbines)

Generator / Heat Recovery

Grid Interconnect Hardware

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Advantages & DisadvantagesCHP and Anaerobic Digesters

Advantages• Odor & Insect Mitigation

• Nutrient Management

• Pathogen Reduction

• Energy Savings

• Heating Fuel Savings

• Reduced Electric Bills

• Qualified for Net Metering

• Potential Farm Bill Funding

Disadvantages• Adding Complexity to

Farming

• Commitment to Digester System Management (labor & maintenance)

• Capital Costs

• Electric Utility Interconnect can be Tedious

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Iowa Net Metering RuleBiomass, MSW, PV, Wind, Hydro

System Size: 500kW

Total System Capacity: No Limit

Credited at Retail Rate

Industrial Owned Utilities Mandated

All Other Utilities Voluntary

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Expanded Applications

Adding Food Processing Waste to a Manure System Can Increase Biogas Production with Higher Methane Content

Community Digesters Provide Economic Development

Tipping Fees Normal for Handling Food Wastes

Bedding Material / Compost (potential revenues)

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Potential U.S. MarketAnaerobic Digester Gas

Over 3 GW of Potential Capacity

– 7,000 Dairy Farms

– 11,000 Hog Farms

– 6,800 WWTPs

Source: Resource Dynamics Corp. “Opportunity Fuels for CHP” www.rdcnet.com

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From Biogas to Btu

1000 Finish, or 5000 Sow Farrow to Wean– Both types of farms produce around 45,000 cubic

feet of biogas per day– With a Methane content of between 55% and

80%– Farm produces between 25 and 36 MMBtu per

day or between 9,000 and 13,000 MMBtu per year

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From Btu to kWAssume a Heat Rate of 14,000 Btu/kWh (24% efficient prime mover) such as a microturbine or recip. engine

25 MMBtu/day to 36 MMBtu/day can fuel prime movers of between 74 and 107 kW installed capacity

A 74 to 107 kW generator produces:– between 1,700 and 2,500 kWh per day– between 53,000 and 77,000 kWh per month– Between 650,000 and 940,000 kWh per year

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Electricity Savings

Annual Electricity Savings at Various Rates

$30,000$45,000$60,000$75,000$90,000

0.04 0.05 0.06 0.07 0.08 0.09 0.1

Electricity Rate ($/kWh)

Ann

ual

Sav

ings

74 kW Generator 107 kW Generator

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Heat Recovery

$24,500

$17,000

Savings from Heat Recovery

@ $5/MMBtu

Gas Cost per Year

4,900 MMBtu

3,400 MMBtu

Required Fuel Equivalent (at 80% Boiler Efficiency) per Year

$23,7002,700 MMBtu74 kW

3,900 MMBtu

Approximate Heat Recovery per Year

$34,300107 kW

Savings from Heat Recovery

@ $7/MMBtu

Gas Cost per Year

Installed Capacity

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Total Savings Potential

Approximate Savings AssumingLow Case: 5 cent/kWh avoided electricity charges and $5/MMBtu natural gas pricesHigh Case:9 cents/kWh avoided electricity charges and $7/MMBtu natural gas prices

71,400

49,400

Low Savings Case

$/Year

82,00074 kW

118,700

High Savings Case

$/Year

107 kW

Installed Capacity

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Installed Cost - Rules of Thumb

Reciprocating Engines <500kWRecoverable Useful Heat: 4,000 to 5,000 Btu/h per kW

O&M Costs: $0.012 to $0.015 per kWh

Installed Costs: $1,400 to $1,800 per kW (with heat recovery)

Micro-turbines 30 to 400 kWRecoverable Useful Heat: 6,000 – 7,000 Btu/h per kW O&M Cost (per kWh) $0.01 to $0.015

Installed Cost: $1,000 to $2,000(with heat recovery)

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System Paybacks –On Incremental CHP Facility Only

$12,000

$8,500

Yearly O&M Cost

107 kW

74 kW

Capacity

2.7

(6.6)

2.9

(8.7)

Low Savings Case

Years

1.6

(5.2)

$120,000

1.5

(4.0)

High Savings Case

Years

$160,000

Installed Cost

( ) includes cost of digester system at $300k

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Summary CHP / Digester Applications

Appropriate when digester being installed for odor mitigation or other reasons

Good match for thermal energy (digester)

Significant market (manure, food processing, waste water treatment, community digesters)

Farm Bill and Net Metering add incentives

Reasonable paybacks

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