Download - 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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LFG Generation & Collection During
Enhanced Biostabilization of MSW
Outline of Presentation
Background
LFG Modeling LFG Collection
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LFG Generation & Collection During
Enhanced Biostabilization of MSW
Outline of Presentation
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
Enhanced Biostabilization of MSW
Outline of Presentation
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
Bio 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.
MD example occurs 23 years after waste receipts stop
Bio example occurs 5 years after waste receipts stop
4. Reduction of the time necessary to reach landfill organic stability to40 years or less after site closing.
MD example occurs 70 years after waste receipts stop
(does not does achieve stability fast enough)
Bio example occurs 38 years after waste receipts stop
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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
Enhanced Biostabilization of MSW
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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