Landfill Gas Collection and Recovery

Jae K. (Jim) ParkDept. of Civil and Environmental EngineeringUniversity of Wisconsin-Madison1Landfill Gas Collection and RecoveryLandfill Gas Collection and RecoveryLandfill 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 resourcePublic 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 specificQuantity and quality of gas recoverable, availability of a market for the recovered gas, and unit price obtainable for the energy productMin. waste quantity of 0.5 to 1 mil. ton and a min. depth of 15 m.Extensive recycling of biodegradable componentshttp://www.ucsusa.org/clean_energy/renewable_energy/page.cfm?pageID=119 2LGFComponents of Gas Recovery SystemOne or more wells placed within the refuseA header system to connect the wells to the gas pumphouse system creating the suctionA flare system providing the opportunity to combust the landfill gas in the event that the gas is not neededAn end user of the gas Header systemGas pumphouseFlare systemRecovery plant(end user)3LandfillGas Extraction WellsVertical piping system: installed following the refuse placementHorizontal piping system: installed as the refuse is placedDesign considerationsSpacing: zone of influence - apparent zone of vacuum influence around a wellLocation: site topography, age of refuse, and system expansion over timeDepth: refuse depth, leachate mound, and cell constructionFactors affecting performance of gas extraction systemDaily coverElevated or perched liquidsShallow depth Sludge or liquid depth Permeability of final cover4Types of Landfill Gas Recovery SystemVertical PipingHorizontal PipingBiodegradabilityLandfill methodsDepthVerticalSlowCell> 45 ftHorizontalReadilyLayer> 100 ft5

LandfillGas header piping

Gas pump house

Gas flare

Gas recovery plant

Gas pump house

Gas flare

Gas recovery plantGas header pipingLandfill

Gas Extraction Well and Header6Gas Extraction Well Construction7

Bentonite seal3 ft well casingNon-calcareous gravel pack

Continuous flight auger ( up to 12 ft, depth 130 ft)Gas Wellhead8

LFG Wells and Collection Piping

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Landfill Gas System10LandfillActive gas collectionProcessing plantLandfill gas processing and treatmentFlareLandfill gas transport and end usersUtility company to produce electricityBoiler roomBuilding boiler to produce heat

LFG Treatment/Blower/Flare Station

11LFG Flare

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13Vertical Piping System 14

Impermeable landfill cover (not present in older landfills)Perforated pipeClay packingGravel packed gas wellsCompacted MSWImpermeable landfill liner(not present in older landfills)Compacted landfill or cell unitGas collection headerBlowerGas cleanup equipment and generator setsElectricity to power grid or other usageTransformer substationEquilateral Triangular Distribution15

Radius of influence: 30 ftPerformance of LFG Extraction Wells16* Well pipe diameter/borehole diameterGasPressureWellRadius offlowin wellftinfluenceMediumLocationscfmin of H2Oft30-7.540(4/8)* 200RefuseWinnebago, WI36-6.545(6/36)150RefuseKitchener, Ontario41-7.027(12/24)100SandKitchener, Ontario45-27(12/24)200RefuseWinnebago, WI235-39-(6/-)500RefuseSeattle, WA240-4040(6/-)-RefuseSeattle, WA320-14110(-/-)500RefusePalos Verdes, CAPossible Landfill Gas Collection System Layout17

Gas collection headerLandfill contoursCondensateLandfill gas blower/ flare/recovery systemLandfill Gas Collection System Construction18

Landfill Gas Extraction Well19

Landfill Gas Extraction Well DrillingHorizontal Piping System20

Horizontal Piping System21

Horizontal Gas Extraction Trench22

Biological Odor Control System

23Potential Problems in GRSPipe failure due to differential settlingCondensate 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 tanksUnbalanced extraction: spatial variabilitySubstantial water in gas extraction wellsAir intrusion Breaks in collection linesPrecautionary measures to minimize problemsUse 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 mud24ExamplesEx. 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 100F and then cools to 40F in the piping.Pv at 100F (37.74C) = 0.0646 atm; Pv at 40F (4.44C) = 0.0082 atm

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Example 3Determine the head loss in the landfill gas recovery system and required blower capacity6 in , 1200 ft6 in , 1000 ft6 in , 1100 ft6 in , 1250 ftHorizontal gasrecovery wells10 in Gas collection headerGas cleanupequipment andenergy conversionfacilitiesABCDE2100 ft300 ft26Assumptions/ConditionsDiameter 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 ftAllowance for minor loss in header between extraction wells (EWs): 0.1 in. H2OAllowance for minor loss in header between last extraction well and blower: 0.5 in. H2OEst. gas flow per horizontal gas EW: 200 ft3/min (60F, 1 atm)Gas composition by vol.: 50% CH4 and 50% CO2Temp. of landfill gas at the wellhead: 130FTemp. loss in manifold section between extraction wells: 5FTemp. of landfill gas at the blower station: 90FLandfill gas saturated in water at the wellheadVacuum to be maintained at the wellhead of the farthermost horizontal gas extraction well (Point E): 10 in. H2OVacuum at blower: to be determined, in H2O

27Solution1.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 =520RP2 = 2116.8 lb/ft2-[(10 in/12 in/ft)61.6 lb/ft3] = 2065.5 lb/ft2T2 = 460 + 127.5 (130 5/2) = 587.5RQ2 = 231.6 ft3/min (computed)v = 231.6 ft3/min 0.545 ft2 = 425.0 ft/min = 7.08 ft/sec

28Specific weightSolution - continuedb.Determine the value of f in the Darcy-Weisbach eq. using the Moody diagram. Calculate molecular mass and gas constant.lb/lbmole of LFG = 0.5 CH4 16 + 0.5 CO2 44 = 30.0Rlandfill gas (Universal gas law constant) = 1543 ftlb/lbmolR 30 lb/lbmol LFG = 51.43 ftlb/lb-LFGRSpecific weight of LFG, gas

gas = 0.0137 (0.0125~0.015) water at 68Fwater at 68F = 1.009 centipoise = 2.11 10-5 lbsec/ft2

Reynolds number

29Moody Diagram

e/D= 0.00005/(10/12) = 0.00006 f = 0.0230Solution - continuedc. Head loss per 100 ft of 10 in pipe

d. Velocity head, hi

2. Set up a computation table

PipePipeGas vel.Ave. gashihLSectiondia., inlength, ftft/mintemp., Fin H2Ofin/100 ftE-D10300425127.50.0100.0200.024D-C10300850125.00.0410.0180.089C-B103001275122.50.0930.0170.190B-A1021001700106.30.1640.0160.315

31=122.5-(122.5-90)/2Solution - continuedSectionTotal friction lossMinor head lossTotal head lossE-D0.072a0.10.172D-C0.2670.10.367C-B0.5700.10.670B-A6.6150.57.115 Pipe loss in inches of H2O8.320 Vacuum at Point E in inches of H2O10.000Total18.320a 0.024 in 300 ft/100 ft = 0.072 inVacuum blower: 893 ft3/min at 18.32 in H2O vacuumTypical vacuum level at the blower inlet for landfill gas recovery system: 18~60 in H2OAdd the head loss through discharge facilities including meters, silencers, and check valves32Headloss Factors for Various FittingsEquivalent pipe lengthFittingKfexpressed in pipe diametersElbow450.51060 0.61490 0.920Tee2.045Branch into pipe30 angle0.21045 angle0.318Sudden enlargement1.020

Fitting losses, Hf Hf = Kf hi

33Options for LFG UtilizationIncineration: combustion of LFG as extractedLow Btu gas: removal of only free moisture; ~450 Btu/ft3; steam power plants; generating stations - limitedMedium 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 recoveryChemical products: conversion of LFG into chemical fractions such as methanol34LFG Utilization35Source: 2006 Update of U.S. landfill gas-to-energy projectsElectric generationPipeline qualityMedium BTUCO2 Removal TechnologiesPhysical removal CO2 removed by dissolved in water or KOHChemical removal by bonding [Ca(OH)2]Adsorption of a thin layer of molecules to activated carbonMembrane removal (CO2 faster than CH4)Other UsageManufacture of urea [CO(NH2)2]PharmaceuticalsDyesPigments36Blower/Flare Station37