Landfill GasQuality and Quantity

Significance of Landfill GasPotential energy recovery of methaneMethane is a potent greenhouse gasExplosive danger Health hazards associated with trace gasesOdor nuisance

Legislative IssuesPublic Utility Regulatory Policy Act (PURPA-1978) governs the sale of electric power generated by LFG-to-energy plants (and other renewable energy sources)Federal tax credits and state regulations which provide financial assistance and incentives to recover and reuse LFGPURPA only calls for renewable energy if it is cost competitive with conventional polluting resources. Many of the benefits of renewables are not included in the price, such as clean air

RCRA Subtitle DRCRA, Subtitle D and Chapter 17-701, FAC, with respect to LFG monitoring, control, and recovery for reuseConcentration of methane cannot exceed 25% of the lower explosive limit in on-site structures

NSPS and Emission GuidelinesPromulgated under the Clean Air ActNew and existing landfillsCapacities equal to or greater than 2.75 million tonsRegulates methane, carbon dioxide and NMOCsRequireWell designed/operated collection systemControl device capable of reducing NMOCs by 98%

NESHAP RulesNational Emission Standards for Hazardous Air Pollutants: Municipal Solid Waste LandfillsAdditional requirements for landfills constructed since Nov. 2000Additional controls for HAPs identified in the CAA

AP-42 Emission Factors (EF)An EF is related to the quantity of pollutants emitted from a unit sourceImportant for developing control strategies, applicability of permitting programs, evaluating effects of sources and mitigationWhen site specific data are not available, EFs are used to estimate area-wide emissionsFor a specific facilityRelative to ambient air quality

EFs for LFGEFs provided for controlled and non-controlled and secondary emissions from landfillsEFs developed for NOx, CO, PM, SO2 NMOCs HAPs, others (HCl, H2S, CH4)

Methanogenesis ReactionsCH3COO- + H2O ---> CH4 + HCO3- acetate + water ---> methane + bicarbonate

4H2 + CO2 ---> CH4 + 2H2O hydrogen + carbon ---> methane + water dioxide

Favorable Conditions for MethanogenesisSufficient moisture contentSufficient nutrientsAbsence of oxygen and toxicsRelatively neutral pH, 6.7 - 7.2Alkalinity greater than 2000 mg/l as calcium carbonateVolatile Acids less than 3000 mg/L as Acetic AcidInternal temperature between 86o F and 131oF

Properties of MethaneMolecular Formula:CH4Heating value:2350 Jg-1Solubility in water:17 mg/LRatio of O2:CH4 req. for combustion:2

Gas Composition - Major GasesMethane (45 - 60 % by volume)Carbon Dioxide (40 - 60 % by volume)Nitrogen (2 - 5 % by volume)Oxygen (0.1 - 1.0 % by volume)Ammonia (0.1 - 1.0 % by volume)Hydrogen (0 - 0.2% by volume)

Gas Composition - Trace Gases (less than 0.6 % by volume)Odor causing compoundsAromatic hydrocarbonsChlorinated solventsAliphatic hydrocarbonsAlcoholsPolyaromatic hydrocarbons

Estimating Gas QuantitiesGas YieldDuration of Gas ProductionShape of Batch Production CurveLag Time Estimate

Gas Yields3 - 90 L/kg dry

Stoichiometric Estimate of Gas Potential

Problems with Stoichiometric EstimatesSome fractions are not biodegradable (lignin, plastics)Moisture limitationsToxinsSome fractions are not accessible (plastic bags)

Biochemical Methane Potential

Duration of Gas ProductionWaste composition (degradability)Moisture conditionsFor first order kinetic models, controlled by first order reaction rate constant (k)

Estimates of Gas Production RatesRapid degradation conditions: 3 to 7 years (4 to 10 L/kg/yr)Moderate degradation conditions: 10 to 20 years (1.5 t 3 L/kg/yr)Slow degradation conditions: 20 to 40 years (0.7 to 1.5 L/kg/yr)

New Source Performance StandardsApplies to MSW landfills onlyLandfill maximum design capacity > 100,000 metric tonsNMOC emission rate > 150 metric tons/yr

NSPS 3 tier CalculationTier 1 - use default values and determine whether NMOC > 150 tons/yr, if yes ---> Tier 2Tier 2 - Determine NMOC conc., redetermine whether NMOC > 150 tons/yr, if yes ---> Tier 3Tier 3 - Determine LFG generation rate, using site specific data, determine whether NMOC > 150 tons/yr, if yes, install controls

Landfill Gas Emission ModelsPalos Verdes Kinetic ModelSheldon Arleta Kinetic ModelScholl Canyon ModelLandfill Odor Characterization ModelMethane Generation Model (EMCON)LFGGEN (UCF)LANDGEM (EPA)

EPAs Landfill Gas Emissions Model

Susan ThorneloeUS EPAOffice of Research & DevelopmentResearch Triangle Park, NC 27711919/541-2709 PH919/541-7885 FAXThorneloe.Susan@epa..gov

Purpose of Model and SoftwareTo provide easy approach to estimating landfill gas emissions (e.g., carbon dioxide, methane, VOC, hazardous air pollutants) using type of data available at municipal solid waste landfillsDefaults are provided unless site-specific data are availableEmissions are projected over time using first-order decomposition equation

EPA LandGEMLandGEM is available (http://www.epa.gov/ttn/catc/). Windows 95-based softwareRead.me fileUsers ManualQuestions/comments on software - instructions in read.me file on where to send

Equation and InputsFirst Order Decomposition Rate Equation -Design Capacity of LandfillAmount of Refuse in place in landfill or the annual refuse acceptance rate for the landfillMethane generation rate (k)Potential methane generation capacity (Lo)Concentration of total nonmethane organic compounds (NMOC) and speciated NMOC found in landfill gasYears the landfill has been in operationWhether the landfill has been used for disposal of hazardous waste

EPA Emission Rate Model Where:QT = total gas emission rate from a landfill, mass/timek = landfill gas emission constant, time-1Lo= methane generation potential, volume/mass of wastetI= age of the ith section of waste, timeMI= mass of wet waste, placed at time in= total time periods of waste placement

EPA Emission Rate Model - ContdCAA Default Values:k = 0.05 yr-1Lo=170 m3/Mg

AP 42 Default Values:k = 0.0 yr-1Lo=140 m3/Mg

Gas Enhancement TechniquesMoisture Content Shredding Leachate Recycle Inoculum AdditionBuffer Nutrient AdditionTemperature

Field Measurements - Gas CompositionSurface SweepPassive samplingVent sampling

Field Measurements - Emission RatesArea of InfluenceFlux Chamber/TubeGas meter

Estimating Landfill Gas Production Rates - Gas GenerationMinimum:Tons in place x 0.25= ft3/dAverage: Tons in place x 0.5 = ft3/dMaximum: Tons in place x 1.0 = ft3/d

Tons in place = Average Depth X Acres x 1000(Assumes 1200 lb/yd3)

Estimating Landfill Gas Production Rates - CollectionNo Cap:Minimum: LFG x 0.25 Average: LFG x 0.50 Maximum: LFG x 0.75Cap:LFG x (0.8 - 0.9)

Economic IssuesGas quantity/qualitySite age and projected gas production lifeAvailability of an end user for LFG or energy

Economic Issues ContdEconomics of utilizationadministrative costs/project developmentcapital costsoperating and maintenance costsroyalty payments to landfill owner ...federal tax credits (Section 29 of Internal Revenue Code)revenue from energy sales

Beneficial Reuse ApplicationsFlaresBoilersMicroturbinesVehicular FuelSynthetic FuelsElectric Power GenerationPipeline Quality Natural Gas

Gas CleanupParticulate removalCondensate removalTrace compound removalUpgrading to natural gas quality

Gas Cleanup

Gas Cleanup

Electric Power GenerationAdvantages:

Large market of stable, continuous demandEasy access to wide energy distribution networkLow pollutant emissionsPractical for a large range of landfill sizesWide variety of viable technologies

Electric Power GenerationDisadvantages:

Air pollution emissions may restrict LFG utilizationRelatively high capital, operating and maintenance costs

Generator

Power Generation - MicroturbinesAdvantagesLow gas flowLower temperatureLower emissions of pollutantsFlexibleDisadvantagesLow flow rangeNew technology

Microturbines

Medium BTU Use -Boilers, Dryers, Space Heating

Disadvantages:Requires stable, continuous, end user demandMay be uneconomical to pipe LFG long distances (typically > 2 miles)

Medium BTU Use -Boilers, Dryers, Space HeatingAdvantages:

Low capital, O & M costsLow system equipment and design requirementsHigher LFG extraction rates possibleLower NOx emissions than conventional fuels

Landfill Gas-Fed Boiler

Pipeline Quality Natural GasAdvantages

Large market of stable, continuous, long-term demandEasy access to wide energy distribution networkLow pollutant emissionsBy-product CO2 has market value

Disadvantages:Strict limits on oxygen and nitrogen restrict LFG extractionHigh parasitic energy requirementsHigh capital and operating costsUneconomical for smaller landfillsLow current and forecast energy prices hinder feasibilityPipeline Quality Natural Gas

Pipeline

Vehicular FuelAdvantages:Potential large market of stable, continuous, long-term demandLow pollutant emissionsSimplified modular processing system designLow area requirementsby-product CO2 has market value

Vehicular FuelDisadvantages:Strict limits on oxygen and nitrogen restrict LFG extractionHigh parasitic energy requirementsHigh capital and operating costsMajor engine modifications requiredLimited distribution networkUneconomical for small landfills

Vehicular Fuel

Synthetic Fuels and ChemicalsAdvantages:

Large and varied markets for fuels and chemicalsLow pollutant emissions in processingSimplified modular processing system designBy-product CO2 has market value

Synthetic Fuels and ChemicalsDisadvantages:

Strict limits on oxygen and nitrogen restrict LFG extractionHigh parasitic energy requirementsHigh capital and operating costsUneconomical for smaller landfills

Steps for Gas Collection System DesignCalculate annual gas production (peak)LandGEM (use realistic k, Lo values, for example k = 0.1 yr-1 for 20 yrs)Pick type of system (passive, active, vertical, horizontal, combination)Layout wells 30-40 scfm/well100-300 ft spacing

Steps for Gas Collection System Design - Contd

Size blowers (calculate pressure drop)Calculate condensatePrepare gas monitoring planNSPS calculations using default values

With fossil fuel cost so low, PURPA not effective