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

 Landfill gas (LFG): a saturated gas consisting of CH 4 and CO 2 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 2 LGF

 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 pumphouse Flare system Recovery plant (end user) 3 Landfill

 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 4

Vertical Piping Horizontal Piping BiodegradabilityLandfill methodsDepth VerticalSlowCell> 45 ft HorizontalReadilyLayer> 100 ft 5 Landfill Gas header piping Gas pump house Gas flare Gas recovery plant Gas pump house Gas flare Gas recovery plant Gas header piping Landfill

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

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10 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

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14 Impermeable landfill cover (not present in older landfills) Perforated pipe Clay packing Gravel packed gas wells Compacted 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

15 Radius of influence: 30 ft

16 * Well pipe diameter/borehole diameter GasPressureWellRadius of flowin wellftinfluenceMediumLocation scfmin of H 2 Oft (4”/8”) * 200RefuseWinnebago, WI (6”/36”)150RefuseKitchener, Ontario (12”/24”)100SandKitchener, Ontario 45-27(12”/24”)200RefuseWinnebago, WI (6”/-)500RefuseSeattle, WA (6”/-)-RefuseSeattle, WA (-/-)500RefusePalos Verdes, CA

17 Gas collection header Landfill contours Condensate Landfill gas blower/ flare/recovery system

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19 Landfill Gas Extraction Well Drilling

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 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 24

Ex. 1 Estimate condensate water quantities. P v = 490 kg/m 2 = 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. P v at 100°F (37.74°C) = atm; P v at 40°F (4.44°C) = atm 25

Determine the head loss in the landfill gas recovery system and required blower capacity 6 in , 1200 ft6 in , 1000 ft6 in , 1100 ft6 in , 1250 ft Horizontal gas recovery wells 10 in  Gas collection headerGas cleanup equipment and energy conversion facilities A BCDE 2100 ft 300 ft 26

 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. H 2 O  Allowance for minor loss in header between last extraction well and blower: 0.5 in. H 2 O  Est. gas flow per horizontal gas EW: 200 ft 3 /min (60°F, 1 atm)  Gas composition by vol.: 50% CH 4 and 50% CO 2  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. H 2 O  Vacuum at blower: to be determined, in H 2 O 27

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-inch header from Point E to D. P 1 = 1 atm = 14.7 lb/in 2 = lb/ft 2 = 33.9 ft of H 2 O Q 1 = 200 ft 3 /min; T 1 = =520°R P 2 = lb/ft 2 -[(10 in/12 in/ft)×61.6 lb/ft 3 ] = lb/ft lb/ft lb/ft 3 T 2 = (130 – 5/2) = 587.5°R Q 2 = ft 3 /min (computed) v = ft 3 /min  ft 2 = ft/min = 7.08 ft/sec 28 Specific weight

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 CH 4 × CO 2 × 44 = 30.0 R landfill gas (Universal gas law constant) = 1543 ft·lb/lb·mol·°R  30 lb/lb·mol LFG = ft·lb/lb-LFG·°R Specific weight of LFG,  gas µ gas = (0.0125~0.015) × µ water at 68°F µ water at 68°F = centipoise = 2.11 × lb·sec/ft 2 Reynolds number 29

e/D= /(10/12) = f =

c. Head loss per 100 ft of 10 in pipe d. Velocity head, h i 2. Set up a computation table PipePipeGas vel.Ave. gash i h L Sectiondia., inlength, ftft/mintemp., °Fin H 2 Ofin/100 ft E-D D-C C-B B-A =122.5-( )/2

SectionTotal friction lossMinor head lossTotal head loss E-D0.072 a D-C C-B B-A Pipe loss in inches of H 2 O8.320 Vacuum at Point E in inches of H 2 O Total a in × 300 ft/100 ft = in Vacuum blower: 893 ft 3 /min at in H 2 O vacuum Typical vacuum level at the blower inlet for landfill gas recovery system: 18~60 in H 2 O Add the head loss through discharge facilities including meters, silencers, and check valves 32

Equivalent pipe length FittingK f expressed in pipe diameters Elbow 45° ° ° Tee2.045 Branch into pipe 30° angle ° angle0.318 Sudden enlargement1.020 Fitting losses, H f H f = K f · h i 33

 Incineration: combustion of LFG as extracted  Low Btu gas: removal of only free moisture; ~450 Btu/ft 3 ; 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 CO 2 (~1000 Btu/ft 3 )  High Btu gas/CO 2 recovery: removal of all moisture, trace gases, and CO 2 recovery  Chemical products: conversion of LFG into chemical fractions such as methanol 34

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

 Physical removal – CO 2 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 (CO 2 faster than CH 4 ) Other Usage  Manufacture of urea [CO(NH 2 ) 2 ]  Pharmaceuticals  Dyes  Pigments 36

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