1. Consider objectives Control migration of gas Control emission Control odors Maximize gas...
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Landfill Gas Collection System Design and Construction Jim Park 1
Transcript of 1. Consider objectives Control migration of gas Control emission Control odors Maximize gas...
Landfill Gas Collection System
Design and Construction
Jim Park
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Landfill Gas Collection System Design Steps (1)
Consider objectivesControl migration of gasControl emissionControl odorsMaximize gas collection fir energy
recoveryComply with regulations
Define limits of landfillHorizontal and vertical limits
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Landfill Gas Collection System Design Steps (2)
Gas extraction wells or trenchesWell diameter and spacingWell materials(HDPE/PVC) and depthNon-well (leachate collection risers and
trench systems) extraction points
Layout gas wellsShallow wells - small ROIDeep wells - large ROITypically 150’ ROI (per NR 500)Liquid levels in landfillAffected by landfill design,
permeability, waste type, and operating pressure/vacuum
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Landfill Gas Collection System Design Steps (3)
Locate gas header pipe Monitoring capability Liquid level accessibility Resistance to environmental effects Versatility after installation
Establish condensate management
Adjust gas wells, if needed
Prepare a well schedule (example) 0.5 to 1.5 cfm/slotted foot of pipe
Determine gas generation and flow
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Landfill Gas Collection System Design Steps (4)
Header and blower sizing calculationsCalculate by handSpreadsheetComputer model KY GAS (Hardy cross
method)
Condensate Headers need to be sloped so condensate
does not pool in them Need to size headers to carry condensate
along with LFGNeed to size the pipe Calculate by hand
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Landfill Gas Collection System Design Steps (5)
Condensate Management StructuresKnock-outsLift stationsBarometric drip legsTransfer stationsDrip legs - Potential for air intrusionPneumatic vs. ElectricConsequences of inadequate condensate
management Flooded headers Low vacuum at well heads Effectively reduces pipe diameter Increased operating cost
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Landfill Gas Collection System Design Steps (6)
Select blower/flare systemCalculate by handSpreadsheetComputer model KY GAS (Hardy cross
method)Enclosed vs. open (destruction efficiency,
cost, and simplicity of operation)Sizing – gas rate, operating temperature,
ignition source, etc. Capacity ranges (turndown capability)May be importance for some of the closed
sites with very little gas
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Condensate Knockout Pump
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Rules of Thumb for Header Design (1)
A velocity of 50 ft/sec is the maximum allowed during concurrent flow conditions
A velocity of 30 ft/sec is the maximum allowed during countercurrent flow conditions
A velocity of 30 ft/sec is the maximum allowed within condensate management structures
A pressure drop of 1 inch water column per 100 feet of header is the maximum allowed under any flow conditions
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Flow conditions within a header must not exceed either pressure loss nor velocity limitations
10 inches of vacuum required at furthest extraction well
10 to 20 inch loss of vacuum at blower flare station
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Rules of Thumb for Header Design (1)
Well Pipe Materials PVC Rigid Higher temperature Structurally functional when slotted Easy to extend Higher cost Variety of manufactured fittings
HDPE Los cost Very flexible Temperature effects
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Landfill Gas Movement Patterns
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Landfill Gas Movement Patterns
Looping systemBenefits vs. costDesigned to be
redundantAccepts
expansions Control valves at
strategic locations in header system
Isolation portions of the system for maintenance, etc.
TypesButterfly, gate or
other values
Landfill Gas Collection System
Design and Construction
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Typical Landfill Gas Well(Active System)
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Vertical Gas Well Construction (1)
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Vertical Gas Well Construction (2)
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Vertical Gas Well Construction (3)
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Vertical Gas Well Construction (4)
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Vertical Gas Well Construction (5)
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Vertical Gas Well Construction (6)
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At some landfills, gas collection wells are installed after the facility reaches grade. At others, the gas collection network is continuously built and expanded.
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Gas Collection Well
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LFG Collection Pipe Systems
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Header Pipe Trench
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Vertical Extraction Wells
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Landfill
Perimeter Vertical LFG
Collection WellPerimeter Vertical LFG
Collection Well31
Example of Radius of Influence Calculation
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Q
Extraction Well Grade
D-S
D
SH
Zone ofInfluence
LandfillBottom
IsobarsRI Rw
Horizontal Wells
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Shredded Tires for Drainage Media
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Horizontal Extraction Wells
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Gas Collection from Leachate Collection System
Leachate collection system retrofitted for gas collection 36
Change in Vacuum before and after Leachate Recirculation
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LFG Collection and Beneficial Use
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Typical LFG Production Curves for Bioreactor and Traditional Landfill
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Bioreactor
Traditional
Time, yrs
Meth
an
e P
rodu
ctio
nC
fm o
f LF
G
Landfill closure
