LFG Generation & Collection

7/28/2019 LFG Generation & Collection

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LFG Generation & Collection During

Enhanced Biostabilization of MSW

Mike Michels, P.E. Vice President

877-294-9070

November 2006


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Outline of Presentation

Background

LFG Modeling LFG Collection


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Background

LFG Modeling LFG Collection


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Ways to Enhance Biostabilization

In-Situ Anaerobic

Aerobic

Hybrid

Leachate Recirculation IsIncluded With All In-Situ

Methods

Prior to Disposal Composting

Recycling

This Presentation Focuses on Anaerobic Biostabilization


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Key Factors Impacting LFG

Generation

Waste Organic Content

Waste Moisture Content

Waste Temperature Waste Partial Size


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Detailed Factors Impacting LFG

Generation

Organic Content

Paper, Cardboard,

sludge, etc.. are the

largest organic load in

most MSW Landfills

Recycling Impact

Moisture Content Achieving Waste Field

Capacity is Important to

Maximize Biostabilization

Liquid Distribution is

Challenging Short

Circuiting Occurs

Leachate Recirculation,

Alone, May Not be Enough


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How Much Liquid Is Needed To

Reach Field Capacity (FC) Definition of FC

FC is the quantity of waterthat can be held against thepull of gravity

Typical MSW FC = 40 to

50% Moisture Content

Moisture Content of MSW AsReceived = 20 to 25%

Moisture Content =Ww/Ws*100%

FC Example

If FC = 40% & as receivedMC = 25%, then 15% liquid

must be added to reach FC.

If the LF accepts 700 tpd ofMSW then 22,500 gallons

per day must be added to

reach FC.

Rule of Thumb

To Reach Field Capacity add

25 to 55 gallons per ton of

MSW


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Impact of Adding Liquids To

MSW Landfills

Pros

Moves NutrientsThroughout the Waste to

Promote Better Waste

Decomposition Increase Waste Density

= More Airspace

Reduces Initial Leachate

Treatment Costs

More LFG Generation

for Energy Recovery

Cons

Can Flood the LFGCollectors

Can Seep Out The Cover

Waste Settlement CausesLFG Collectors To Sag

& Get Blocked

More LFG Can Mean

More Odors

More LFG = Larger

Collection System

Can Create StabilityIssues


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LFG Generation and Collection During



Background

LFG ModelingDownload The EPA Model At:

http://www.epa.gov/ttn/atw/landfill/landflpg.html

LFG Collection


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LFG Modeling With EPAsLANDGEM Model

k = Methane Generation Decay Rate (1/year) Depends Primarily on Moisture Content of the

MSW

Lo = Methane Generation Potential (m3/Mg)

Depends Primarily on Organic Content of theMSW


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Varying k Results In Higher Peak ProductionBut Same Area Under The Curve

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40 45 50

MethaneGeneration(MMc

f/yr)

Lo = 100

k = .20

k =.05

k = .04

k = .02

150,000 tons per year of MSW for 10 years


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Varying Lo Results In Higher PeakProduction & More Area Under The Curve

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40 45 50

MethaneGene

ration(MMcf/yr)

k = .04

Lo =250Lo =170

Lo = 100

Lo =85

150,000 tons per year of MSW for 10 years


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LFG Modeling Assumptions Moderately Dry

k=0.04 200,000 TPY of MSW

26 years of filling

5.2 million tons ofMSW in place at closure

Waste Density = 1500

lbs / cy

Biostabilized

k=0.08 200,000 TPY of MSW

30 years of filling

6.0 million tons ofMSW in place at

closure (at $30/ton =

$24 million morerevenue)

Waste Density = 1730

lbs /cyLo = 100 m3/Mg Used For Both Scenarios


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LFG Modeling ResultsLFG Generation Estimate with EPA LANDGEM Model

0

500

1,000

1,500

2,000

2,500

2005

2010

2015

2020

2025

2030

2035

2040

2045

2050

2055

2060

2065

2070

2075

2080

Year

LFG

at50%M

ethan

eConcentration(scfm)

Mod Dry

Bio


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WDNR NR 514.07 (9)(c) Definition

of Stable as it Relates to LFG1. A monthly average total methane plus carbon dioxide gas production

rate less than or equal to 5% of the maximum monthly average total

gas production rate observed during the life of the facility, or less

than 7.5 cubic feet of total gas per year for each cubic yard of waste

in the facility.

MD example occurs 70 years after waste receipts stop

Bio example occurs 38 years after waste receipts stop

2. A steady downward trend in the rate of total methane plus carbon

dioxide gas production. MD example occurs 2 years after waste receipts stop



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WDNR NR 514.07 (9)(c) Definition

of Stable as it Relates to LFG3. Production of total methane plus carbon dioxide gas cumulatively

representing 75% or greater of the projected total gas production of

the landfilled waste.



4. Reduction of the time necessary to reach landfill organic stability to40 years or less after site closing.


(does not does achieve stability fast enough)



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Challenges with LFG Modeling

Older Waste Inflow Rates Often Unknown.

Relating MSW Composition to Lo isDifficult (BMP testing).

Relating In Place Moisture to k isDifficult.

For example: what moisture content must beachieved to reach a k = 0.08?


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Overcome Modeling Challenges ByCalibrating k Calibrate k by Using Historical LFG Flows

Model the waste with an active LFG system inplace

Adjust for LFG collection efficiency, considering

SEM data

Wellfield tuning data

Perimeter migration probe data

Based on the Calibrated k, Predict the

Future


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Relationship of kto Rainfall

SWANA (2004)


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LFG Generation and Collection During


Outline of Presentation Background

LFG Modeling

LFG Collection


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Key LFG Collection Issues During

Organic Stabilization

Collecting What You Generate Can BeDifficult

Especially in active or wet waste areas

Plan For Leachate Well spacing

Seeps

Dual LFG/leachate extraction

Oversize the Blowers, Flares, Headers, etc


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Devices to Collect LFG Vertical Wells

Rule of Thumb - 1 well per acre

Closer along perimeter

Closer if cover is not installed

Minimum 40 feet deep

Horizontal Collectors Max. 600 feet long (no vacuum after 600)

Cant turn them on till at least 20 feet of trash is over them

Combine leachate injection and LFG extraction

Leachate Cleanouts Critical for early LFG collection

Remember to manage the condensate


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Well Spacing

Many Methods Employed Throughout

Industry Regulatory Spacing

Empirical From Pump Testing

Fluid Flow - Darcy

Rule of Thumb (1 well per acre, dry or 1.5 wellsper acre, wet)

All Methods Are Only Estimates


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Empirical Well Spacing(The Math) Concept: ROI can only expand until air

breakthrough occurs.

Considers cap, refuse moisture, & well design.

ROI = Fs*(Sp+(Ms*Cd)) ROI = Radius of Influence (feet)

Fs = Refuse Permeability Factor (ie: 3.5 wet to 6.5dry)

Sp = Solid Pipe Length at Top of Well (feet) Cd = Landfill Cover Depth (feet)

Ms = Cover Permeability Factor


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Well Spacing - ROI Example

12" Intermediate Cover

50.00

100.00

150.00

200.00

15 20 25 30

Length of Solid Casing on LFG Well (feet)

R

adius

ofInfluence

(feet)

Very Wet Waste Wet Waste Moist Waste Dry Waste


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Typical Horizontal LFG Collector

Layout


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LFG Header Issues Slope of Header Pipes

Greater Than 3% Within WasteLimits

Steeper Slopes if Biostabilization isPlanned

Loops and Redundancies

Absolutely Needed, But Design Header Size Without Them

To Be Conservative


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Leachate In LFG Headers Reduces

The Area Available for LFG Flow

20 GPM Leachate Flow in SDR 17 HDPE LFG

Header

0

10

20

30

40

4 6 810

Nominal Header Diameter (inches)

%A

reaofHeader

Taken

Upby

Leachate

2% Slope 4% Slope 6% Slope 10% Slope


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LFG Blower Issues Fan Vs Blower

Fans Typically have a Max 40WC vacuum

Blower Typically > 50 WC

Vacuum

Blowers Dont Like Water (KOP

Mandatory)

Consider Redundancy to

Address SSM Plan


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LFG Header Sizing Several Methodologies

KYGAS Computer Program That Considers Looped

Headers

Low Pressure Mueller

Check Gas Velocity Max 40 to 42 ft/sec (concurrent)

Max 20 to 22 ft/sec (countercurrent)


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Condensate Management

Condensate is Formed as Warm, Wet Gas

Cools During the Extraction Process

How Much Condensate? 3000 scfm of Saturated LFG at 110 Degrees F

Will Create 1800 GPD of Condensate as it

Cools to 50 Degrees F


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Condensate Management Structures

Dripleg

Gravity Drain Barometric U-Trap

Collection Sumps/Tanks

Pneumatic vs. Elec Pumps Design to Remove Pump

While Still Extracting LFG

Drain Field (not recommended inBiostabilization LFs)


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Control Devices for LFG Flares

Utility Enclosed

Others Engines

Turbines

Leachate Evaporators

Consider

Turndown


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More LFG Collection Tips

LFG Follows the Path of Least Resistance Make Sure That Path Is Into Your CollectionSystem

Seal the Granular Blanket at the Top of Berm

Air Regulations Are Complex Read Your Air Permit Carefully & Read It Again

Dont Forget to Modify Your Air Permit for IncreasedLFG Flow Due to Biostabilization


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