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

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

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

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

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

Gas Extraction Well and Header

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)

Gas Wellhead

LFG Wells and Collection Piping

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

LFG Treatment/Blower/Flare Station                                                                                                                           

LFG Flare

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)

Equilateral Triangular Distribution Radius of influence: 30 ft

Performance of LFG Extraction Wells Gas Pressure Well Radius of flow in well ft influence Medium Location scfm in of H2O ft 30 -7.5 40(4”/8”)* 200 Refuse Winnebago, WI 36 -6.5 45(6”/36”) 150 Refuse Kitchener, Ontario 41 -7.0 27(12”/24”) 100 Sand Kitchener, Ontario 45 - 27(12”/24”) 200 Refuse Winnebago, WI 235 -39 -(6”/-) 500 Refuse Seattle, WA 240 -40 40(6”/-) - Refuse Seattle, WA 320 -14 110(-/-) 500 Refuse Palos Verdes, CA * Well pipe diameter/borehole diameter

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

Landfill Gas Collection System Construction

Landfill Gas Extraction Well Landfill Gas Extraction Well Drilling

Horizontal Piping System

Horizontal Piping System

Horizontal Gas Extraction Trench

Biological Odor Control System

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

Examples Ex. 1 Estimate condensate water quantities. Pv = 490 kg/m2 = 0.048 atm; T = 273 + 32 = 305 K R = 0.082 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) = 0.0646 atm; Pv at 40°F (4.44°C) = 0.0082 atm

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

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

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 = 2116.8 lb/ft2 = 33.9 ft of H2O Q1 = 200 ft3/min; T1 = 460 + 60 =520°R P2 = 2116.8 lb/ft2-[(10 in/12 in/ft)×61.6 lb/ft3] = 2065.5 lb/ft2 T2 = 460 + 127.5 = 587.5°R Q2 = 231.6 ft3/min v = 231.6 ft3/min  0.545 ft2 = 425.0 ft/min = 7.0833 ft/sec

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 × 16 + 0.5 CO2 × 44 = 30.0 Rlandfill gas = 1543 ft·lb/lb·mol·°R 30 lb/lb·mol LFG = 51.43 ft·lb/lb-LFG·°R Specific 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 Reynolds number

Moody Diagram e/D = 0.00005/(10/12) = 0.00006 f = 0.02

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

Solution - continued Section Total friction loss Minor head loss Total head loss E-D 0.072a 0.1 0.172 D-C 0.267 0.1 0.367 C-B 0.570 0.1 0.670 B-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 18.320 a 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 valves

Headloss Factors for Various Fittings Equivalent pipe length Fitting Kf expressed in pipe diameters Elbow 45° 0.5 10 60° 0.6 14 90° 0.9 20 Tee 2.0 45 Branch into pipe 30° angle 0.2 10 45° angle 0.3 18 Sudden enlargement 1.0 20 Fitting losses, Hf Hf = Kf · hi

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

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

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

Blower/Flare Station