1. Landfill Gas Collection and Recovery
Jae K. (Jim) Park
Dept. of Civil and Environmental Engineering
University of Wisconsin-Madison

2. Landfill Gas Collection and Recovery
Landfill gas (LFG): a saturated gas consisting of CH4 and CO2 with other trace contaminants
Recovery of LFG: to prevent migration onto adjacent properties and to use it as an energy resource
Public Utility Regulatory Policies Act of 1978 (PURPA)
Utilities are mandated by PURPA to purchase all co-generated electricity and pay the fair market value for that electricity based on cost avoided by the utilities.
PURPA made it possible for private individuals and firms to require utilities to accept generated electrical power at an economically acceptable price.
LFG recovery: site specific
Quantity and quality of gas recoverable, availability of a market for the recovered gas, and unit price obtainable for the energy product
Min. waste quantity of 0.5 to 1 mil. ton and a min. depth of 15 m.
Extensive recycling of biodegradable components
LGF

3. Components of Gas Recovery System
One or more wells placed within the refuse
A header system to connect the wells to the gas pumphouse system creating the suction
A flare system providing the opportunity to combust the landfill gas in the event that the gas is not needed
An end user of the gas
Flare system
Gas pumphouse
Recovery plant
(end user)
Landfill
Header system

4. Gas Extraction Wells
Vertical piping system: installed following the refuse placement
Horizontal piping system: installed as the refuse is placed
Design considerations
Spacing: zone of influence - apparent zone of vacuum influence around a well
Location: site topography, age of refuse, and system expansion over time
Depth: refuse depth, leachate mound, and cell construction
Factors affecting performance of gas extraction system
Daily cover
Elevated or perched liquids
Shallow depth
 Sludge or liquid depth
 Permeability of final cover

5. Types of Landfill Gas Recovery System
Vertical Piping
Gas header piping
Gas pump house
Gas flare
Gas recovery plant
Landfill
Biodegradability Landfill methods Depth
Vertical Slow Cell > 45 ft
Horizontal Readily Layer > 100 ft
Horizontal Piping
Gas header piping
Landfill
Gas pump house
Gas flare
Gas recovery plant

6. Gas Extraction Well and Header

7. Gas Extraction Well Construction
Bentonite seal
3 ft well casing
Non-calcareous gravel pack
Continuous flight auger (Φ up to 12 ft, depth 130 ft)

8. Gas Wellhead

9. LFG Wells and Collection Piping

10. Landfill Gas System Landfill gas processing and treatment Flare
                                                                                                                          
Flare
Active gas collection
Processing plant
Landfill
Landfill gas transport and end users
Boiler room
Utility company to produce electricity
Building boiler to produce heat

11. LFG Treatment/Blower/Flare Station
                                                                                                                          

12. LFG Flare

14. Vertical Piping System
Compacted landfill or cell unit
Impermeable landfill cover (not present in older landfills)
Gas collection header
Blower
Electricity to power grid or other usage
Perforated pipe
Clay packing
Gas cleanup equipment and generator sets
Gravel packed gas wells
Transformer substation
Compacted MSW
Impermeable landfill liner
(not present in older landfills)

15. Equilateral Triangular Distribution
Radius of influence: 30 ft

16. Performance of LFG Extraction Wells
Gas Pressure Well Radius of
flow in well ft influence Medium Location
scfm in of H2O ft
(4”/8”)* 200 Refuse Winnebago, WI
(6”/36”) 150 Refuse Kitchener, Ontario
(12”/24”) 100 Sand Kitchener, Ontario
(12”/24”) 200 Refuse Winnebago, WI
(6”/-) 500 Refuse Seattle, WA
(6”/-) - Refuse Seattle, WA
(-/-) 500 Refuse Palos Verdes, CA
* Well pipe diameter/borehole diameter

17. Possible Landfill Gas Collection System Layout
Gas collection header
Landfill contours
Condensate
Landfill gas blower/ flare/recovery system

18. Landfill Gas Collection System Construction

19. Landfill Gas Extraction Well
Landfill Gas Extraction Well Drilling

20. Horizontal Piping System

21. Horizontal Piping System

22. Horizontal Gas Extraction Trench

23. Biological Odor Control System

24. Potential Problems in GRS
Pipe failure due to differential settling
Condensate blockage in header pipes: min. 3% slope, condensate trap installed at the low spots in the line, condensate returned to the landfill or to holding tanks
Unbalanced extraction: spatial variability
Substantial water in gas extraction wells
Air intrusion
Breaks in collection lines
Precautionary measures to minimize problems
Use steep pipe grades (2% or better)
Use many condensate traps (e.g., 1 per 300 m)
Adjust screening openings in the collection system to filter out particulates and mud

25. Examples
Ex. 1 Estimate condensate water quantities. Pv = 490 kg/m2 = atm; T = = 305 K R = Latm/molK Ex. 2 Estimate the quantity of condensate arising from gas pumping. The gas leaving the landfill is at 100°F and then cools to 40°F in the piping. Pv at 100°F (37.74°C) = atm; Pv at 40°F (4.44°C) = atm

26. Example 3 A
300 ft
10 in 
2100 ft E D C B
Gas collection header
Gas cleanup
equipment and
energy conversion
facilities
6 in , 1200 ft
6 in , 1000 ft
6 in , 1100 ft
6 in , 1250 ft
Horizontal gas
recovery wells
Determine the head loss in the landfill gas recovery system and required blower capacity

27. Assumptions/Conditions
Diameter of header used to collect gas from the horizontal landfill gas recovery wells: assumed to be 10 in
Absolute roughness for the PVC pipe (e): ft
Allowance for minor loss in header between extraction wells (EWs): 0.1 in H2O
Allowance for minor loss in header between last extraction well and blower: 0.5 in H2O
Est. gas flow per horizontal gas EW: 200 ft3/min (60°F, 1 atm)
Gas composition by vol.: 50% CH4 and 50% CO2
Temp. of landfill gas at the wellhead: 130°F
Temp. loss in manifold section between extraction wells: 5°F
Temp. of landfill gas at the blower station: 90°F
Landfill gas saturated in water at the wellhead
Vacuum to be maintained at the wellhead of the farthermost horizontal gas extraction well (Point E): 10 in H2O
Vacuum at blower: to be determined, in H2O

28. Solution
1. Determine the head loss used to collect gas from the individual horizontal gas extraction wells starting at Point E. a. Determine the velocity of flow of LFG in the 10 in header from Point E to D. P1 = 1 atm = 14.7 lb/in2 = lb/ft2 = 33.9 ft of H2O Q1 = 200 ft3/min; T1 = =520°R P2 = lb/ft2-[(10 in/12 in/ft)×61.6 lb/ft3] = lb/ft2 T2 = = 587.5°R Q2 = ft3/min v = ft3/min  ft2 = ft/min = ft/sec

29. Solution - continued
b. Determine the value of f in the Darcy-Weisbach eq. using the Moody diagram. Calculate M.W. and gas constant. lb/lb·mole of LFG = 0.5 CH4 × CO2 × 44 = 30.0 Rlandfill gas = 1543 ft·lb/lb·mol·°R 30 lb/lb·mol LFG = ft·lb/lb-LFG·°R Specific weight of LFG, gas µgas = (0.0125~0.015) × µwater at 68°F µwater at 68°F = centipoise = 2.11 × 10-5 lb·sec/ft2
Reynolds number

30. Moody Diagram
e/D = /(10/12) = f = 0.02

31. Solution - continued
c. Velocity head, hi d. Head loss per 100 ft of 10 in pipe 2. Set up a computation table
Pipe Pipe Gas vel. Ave. gas hi hL
Section dia., in length, ft ft/min temp., °F in H2O f in/100 ft
E-D
D-C
C-B
B-A

32. Solution - continued
Section Total friction loss Minor head loss Total head loss
E-D 0.072a
D-C
C-B
B-A
Pipe loss in inches of H2O
Vacuum at Point E in inches of H2O
Total
a in × 300 ft/100 ft = in
Vacuum blower: 893 ft3/min at in H2O vacuum
Typical vacuum level at the blower inlet for landfill gas recovery system: 18~60 in H2O
Add the head loss through discharge facilities including meters, silencers, and check valves

33. Headloss Factors for Various Fittings
Equivalent pipe length Fitting Kf expressed in pipe diameters Elbow 45° ° ° Tee Branch into pipe 30° angle ° angle Sudden enlargement Fitting losses, Hf Hf = Kf · hi

34. Options for LFG Utilization
Incineration: combustion of LFG as extracted
Low Btu gas: removal of only free moisture; ~450 Btu/ft3; steam power plants; generating stations - limited
Medium Btu gas: compression and removal of moisture and heavy-end hydrocarbons; compression, refrigeration, and chemical processes; reciprocating engines and gas turbines - widely used (23~28% efficiency); steam turbines and combined cycle - for large-scale landfills (35~40% efficiency)
High Btu gas: removal of all moisture, trace gases, and CO2 (~1000 Btu/ft3)
High Btu gas/CO2 recovery: removal of all moisture, trace gases, and CO2 recovery
Chemical products: conversion of LFG into chemical fractions such as methanol

35. LFG Utilization Electric generation Pipeline quality Medium BTU
Source: 2006 Update of U.S. landfill gas-to-energy projects

36. CO2 Removal Technologies
Physical removal – CO2 removed by dissolved in water or KOH
Chemical removal by bonding
Adsorption of a thin layer of molecules to activated carbon
Membrane removal (CO2 faster than CH4)
Other Usage
Manufacture of urea [CO(NH2)2]
Pharmaceuticals
Dyes
Pigments

37. Blower/Flare Station