Jae K. (Jim) Park

Dept. of Civil and Environmental Engineering

University of Wisconsin-Madison

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Landfill Gas Collection and Recovery

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

http://www.ucsusa.org/clean_energy/renewable_energy/page.cfm?pageID=119 2

LGF

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

Header system

Gas pumphouseFlare system

Recovery plant(end user)

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Landfill

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 cover4

Types of Landfill Gas Recovery SystemVertical Piping

Horizontal Piping

Biodegradability Landfill methods Depth

Vertical Slow Cell > 45 ftHorizontal Readily Layer > 100 ft

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Landfill

Gas header piping

Gas pump house

Gas flare

Gas recovery plant

Gas pump house

Gas flare

Gas recovery plant

Gas header piping

Landfill

Gas Extraction Well and Header

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Gas Extraction Well Construction

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Bentonite seal

3 ft well casing

Non-calcareous gravel pack Continuous flight

auger (Φ up to 12 ft, depth 130 ft)

Gas Wellhead

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LFG Wells and Collection Piping

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Landfill Gas System

                                                                                                                          

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Landfill

Active gas collection

Processing plant

Landfill gas processing and treatment

Flare

Landfill gas transport and end users

Utility company to produce electricity

Boiler room

Building boiler to produce heat

LFG Treatment/Blower/Flare Station

                                                                                                                          

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LFG Flare

12

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Vertical Piping System

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Impermeable landfill cover (not present in older landfills)

Perforated pipeClay packing

Gravel packed gas wellsCompacted MSW

Impermeable landfill liner(not present in older landfills)

Compacted landfill or cell unit

Gas collection header

Blower

Gas cleanup equipment and generator sets

Electricity to power grid or other usage

Transformer substation

Equilateral Triangular Distribution

15Radius of influence: 30 ft

Performance of LFG Extraction Wells

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* Well pipe diameter/borehole diameter

Gas Pressure Well Radius offlow in well ft influence Medium Locationscfm in of H2O ft

30 -7.5 40(4”/8”)* 200 Refuse Winnebago, WI36 -6.5 45(6”/36”) 150 Refuse Kitchener, Ontario41 -7.0 27(12”/24”) 100 Sand Kitchener, Ontario45 - 27(12”/24”) 200 Refuse Winnebago, WI

235 -39 -(6”/-) 500 Refuse Seattle, WA240 -40 40(6”/-) - Refuse Seattle, WA320 -14 110(-/-) 500 Refuse Palos Verdes, CA

Possible Landfill Gas Collection System Layout

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Gas collection header

Landfill contours Condensate

Landfill gas blower/ flare/recovery system

Landfill Gas Collection System Construction

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Landfill Gas Extraction Well

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Landfill Gas Extraction Well Drilling

Horizontal Piping System

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Horizontal Piping System

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Horizontal Gas Extraction Trench

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Biological Odor Control System

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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

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ExamplesEx. 1 Estimate condensate water quantities.

Pv = 490 kg/m2 = 0.048 atm; T = 273 + 32 = 305 KR = 0.082 Latm/molK

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) = 0.0646 atm; Pv at 40°F (4.44°C) = 0.0082 atm

RT

MWP

V

m ;RT

MW

mnRTVP V

V

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LFG O/mH kg 0.035

L/10mK 305Katm/molL 0.082

gkg/10g/mol 18atm 0.048

RT

MWP

V

m

32

33

3V

Example 3

Determine the head loss in the landfill gas recovery system and required blower capacity

6 in

, 1

200

ft

6 in

, 1

000

ft

6 in

, 1

100

ft

6 in

, 1

250

ft

Horizontal gasrecovery wells

10 in

Gas collection header Gas cleanupequipment and

energy conversionfacilities

A

BCDE 2100 ft

300 ft

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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): 0.00005 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

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Solution1. 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-inch header

from Point E to D.

P1 = 1 atm = 14.7 lb/in2 = 2116.8 lb/ft2 = 33.9 ft of H2OQ1 = 200 ft3/min; T1 = 460 + 60 =520°RP2 = 2116.8 lb/ft2-[(10 in/12 in/ft)×61.6 lb/ft3] = 2065.5 lb/ft2

T2 = 460 + 127.5 (130 – 5/2) = 587.5°RQ2 = 231.6 ft3/min (computed)v = 231.6 ft3/min 0.545 ft2 = 425.0 ft/min = 7.08 ft/sec

2121 T

PQ

T

PQ

T

PV

T

PV

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𝜋  𝑑2

4=𝜋  ( 10

12 )2

4

Specific weight

Solution - continued

b. Determine the value of f in the Darcy-Weisbach eq. using the Moody diagram. Calculate molecular mass and gas constant.lb/lb·mole of LFG = 0.5 CH4 × 16 + 0.5 CO2 × 44 = 30.0Rlandfill gas (Universal gas law constant) = 1543 ft·lb/lb·mol·°R

30 lb/lb·mol LFG = 51.43 ft·lb/lb-LFG·°RSpecific weight of LFG, gas

µgas = 0.0137 (0.0125~0.015) × µwater at 68°F

µwater at 68°F = 1.009 centipoise = 2.11 × 10-5 lb·sec/ft2

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gas lb/ft 0.068R]127.5)[(460

RLFG-lb

lbft 51.43lb/ft 5.2065

RT

P

O

O

Reynolds number5

510432.0

102.11 0.013732.17

068.008.7)12/10(vv

gas

gas

gas

gasR g

ddN

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Moody Diagram

e/D = 0.00005/(10/12) = 0.00006 f = 0.0230

Solution - continued

c. Head loss per 100 ft of 10 in pipe

d. Velocity head, hi

2. Set up a computation table

O Hin 01.0s/min) (60

in/ft 12

lb/ft 61.60

LFG/ft-lb 0.068

ft/s 17.322

ft/min) (425

2 223

3

2

22

w

gasi g

vh

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 10 300 425 127.5 0.010 0.020 0.024D-C 10 300 850 125.0 0.041 0.018 0.089C-B 10 300 1275 122.5 0.093 0.017 0.190B-A 10 2100 1700 106.3 0.164 0.016 0.315

ft O/100Hin 0.024 OHin 0.01in/ft in/12 10

ft 10002.0 22

iL hd

Lfh

31=122.5-(122.5-90)/2

Solution - continued

Section Total friction loss Minor head loss Total head lossE-D 0.072a 0.1 0.172D-C 0.267 0.1 0.367C-B 0.570 0.1 0.670B-A 6.615 0.5 7.115

Pipe loss in inches of H2O 8.320 Vacuum at Point E in inches of H2O 10.000

Total 18.320a 0.024 in × 300 ft/100 ft = 0.072 in

Vacuum blower: 893 ft3/min at 18.32 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 valves32

Headloss Factors for Various Fittings

Equivalent pipe lengthFitting Kf expressed in pipe diameters

Elbow45° 0.5 1060° 0.6 1490° 0.9 20

Tee 2.0 45Branch into pipe

30° angle 0.2 1045° angle 0.3 18

Sudden enlargement 1.0 20

Fitting losses, Hf

Hf = Kf · hi

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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

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LFG Utilization

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050

100150200250300350400

365

13

124

Source: 2006 Update of U.S. landfill gas-to-energy projects

Electric generation

Pipeline quality

Medium BTU

CO2 Removal Technologies

Physical removal – CO2 removed by dissolved in water or KOH

Chemical removal by bonding [Ca(OH)2] 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

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Blower/Flare Station

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