a simple and energy efficient approach to cleaning biogas
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A Simple and Energy Efficient Approachto Cleaning Biogas
Sid Arora, P.E., MMSDLindsey Busch, P.E., Carollo EngineersRudy Kilian, P.E., Carollo EngineersSean Snyder, Unison Solutions
CSWEA WI Section Operations Seminar: ResourceRecoveryOctober 31, 2017
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Outline
• Background• MMSD Pilot• Summary and Next Steps
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Outline
• Background• MMSD Pilot• Summary and Next Steps
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Biogas projects provide multiple benefits
• Generate renewable fuel with a low carboncontent
• Reduce reliance on fossil fuel- Reduce greenhouse gas (GHG) emissions- Reduce local air pollutant emissions
• Reduce the use of synthetic fertilizers- Generate a soil amendment- Offset fossil fuel use and reduce GHGs emissions from
fertilizer manufacturing
• Help achieve Federal and state goals
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Implementation of beneficial gas usemust analyze:
Cost Revenue
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Implementation of beneficial gas usemust analyze:
Cost Revenue
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Many states have climate change relatedgoals that incentivize bioenergy projects
20 States and D.C.have GHG emissionsreduction targets andassociated goals
https://www.c2es.org/us-states-regions/policy-maps
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More states have renewable andalternative energy standards
https://www.c2es.org/us-states-regions/policy-maps/renewable-energy-standards
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And even more states have goals thatincentivize biofuel production
http://www.c2es.org/us-states-regions
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Incentives for production/use of biogas areincreasing…
Renewable EnergyCredits
Renewable Fuel Standard
Low Carbon FuelStandard
Alternative & RenewableFuel & VehicleTechnology
OnsiteEnergy
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Cost Revenue
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Beneficial biogas use offsets fuel costs
VALUE
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$0
$5
$10
$15
$20
$25
$30
NaturalGas
Electricity Methanol Gasoline Diesel
Cos
t p
er M
MB
TUThe value of biogas depends on what fuelit is offsetting
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Cost Revenue
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Biogas conditioning is an importantcomponent for beneficial use
Parameter Typical RangeMethane, % by volume 50 – 65CO2, % by volume 35 – 50H2S, ppmv 100 – 10,000Siloxanes, ppbv 500 – 5,000
H2S and siloxanes damagemechanical equipmentCO2 reduces energy value andincreases compression cost
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The level of biogas treatment depends onthe type of beneficial use
1
10
100
1000
10000
Boiler Engine Fuel Cell CNG Fleet
H2S, ppmv
Siloxanes, ppbv
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Commercial biogas treatment can beachieved through different processes• H2S removal
- Iron salt addition- Adsorption systems- Caustic scrubbers
• Siloxane removal- Chillers- GAC systems
• CO2 removal- Pressure swing adsorption
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New Unison biogas scrubber addressesindustry challenges• Removes H2S• Removes CO2
• Reduces siloxanes• Chemical-free
treatment fordigester gas
• No moving parts• Only uses water
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Outline
• Background• MMSD Pilot• Summary and Next Steps
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300 MGD FullTreatment Capacity
90 MGD Annual Average
Liquid TreatmentProcesses
-Preliminary/Primary/Secondary/Disinfection-Chemical P removal
Solids Handling &Disposal
-Interplant pumping ofsolids-GBTs and Plate andFrame-Digesters Methane 1.3MMCF
NACWA Platinum Award 20
South Shore Water Reclamation Facility
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Anaerobic Digesters15 MG
98oF
Anaerobic Digesters15 MG
98oF
Feed Sludge-Primary Sludge-Airport Deicing Fluid-High Strength Waste-TWAS
Gas StorageSpheres
0.42 MMCF @ 50psi
Digested SludgeSent to Jones Islandfor Milorganite Production
Gas Compressors
Flares CAT Engine Generators- 0.9 MW each
White Superior Engine Generator- 1.5 MW
Dig
este
r Gas
Digester Gas/Natural Gas
Heat Recovery System
Boilers
Plant Electric Load 4.5 MW
Building Heat
South Shore Digester Gas Productionand Utilization
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South Shore Digester Gas Quality andQuantityMMSD Plant Data(1)
Information Item Unit Average Maximum NotesQuantity of digester gasavailable to be treated Scf/Day 1,320,000 2,120,000Gas Quality: Methane % 59 63
Low Heat ValueBtu-
LHV/scf 530 565 Carbon Dioxide % 33.2 38 Hydrogen Sulfide
(ppm) ppmv 21.7 34.9Iron added toprimary influent
Total SiloxanesmgSi/Nm3
CH4 22.16 320Concentration Si inmethane fraction
Total Siloxanes mgSi/Nm3 13.28 202Concentration indigester gas
Notes:(1)Based on 2014-2016 data.
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The technology itself is simple
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Pilot Unit Setup
• Located in digester gallery of South Shore WRF
RawBiogas
“Outlet” GasSample
TreatedBiogas
Waterback tohead ofplant
PlantEffluentWater
“Inlet” GasSample
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Venturi and Gas Contactor/MoistureSeparator
• Plant Effluent WaterUsed
• Inlet water Pressure30 psig
• Discharge waterpressure= 4 psig
• Water Inlet Flow =12 gpm
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Inlet Outlet Reading Hand Held Device
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Digester Gas Sampling
• Raw gas samples (INLET) and
• Treated gas samples (OUTLET)
• Grab samples collected in pressurizedCanisters analyzed for- Methane- CO2
- H2S
• 30 min samples collected withSorbent tubes and analyzed for- Siloxane
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H2S Removal Rate During the Pilot
• Average InletH2S= 90 ppm
• Average OutletH2S =0.14 PPM
• % H2S Removalrate was 99.8 %
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Siloxane Removal Rate During the Pilot
• Average InletSiloxane= 3,244µg/m3 as Si
• Average OutletSiloxane = 1143µg/m3 as Si
• % SiloxaneRemoval rate 65%
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CO2 Removal Rate During the Pilot
• Average InletCO2= 32%
• Average OutletCO2 = 6%
• % CO2 Removalrate 80%
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Methane Surge During the Pilot
• Average Inlet CH4= 63%
• Average OutletCH4 = 81%
• % Methane Surge29%
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Pilot Unit Results
Parameter Average InletConcentration
Average OutletConcentration
AveragePercentChange
H2S (ppmV) 90 0.14 99.8% ± 0.3%
Siloxanes (ppmV asSi)
2.9 0.92 65% ± 13.6%
Methane (%) 63 81 29% ± 16%
Carbon Dioxide (%) 32 6.3 80.3% ± 14%
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Challenges during the Pilot
• Too good to be true
• Plant Water Pressure and Flow impacts thetreatment
• Gas pressure Fluctuation causes additional timein sampling
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Preliminary Full Scale Estimate
• Pilot to be installed in the low pressure side• Recommended gas pressure <12 in H20• For 1.3 MMCF gas production we need ~12 MGD
plant water without recirculation (for MMSD)• If we add water recirculation loop the anticipated
water consumption can go down to < ~6 MGD• In general 7 to 10 gpm per 1 scfm depending on
available water pressure (without recirculation)
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Outline
• Background• MMSD Pilot• Summary and Next Steps
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Summary and Next Steps…
• Full scale pilot to be installed soon in Southern California
• Additional small scale “proof of concept” pilots aroundupper Midwest
• Refine water recycle loop which will reduce the inlet waterrequirement to the system
• Further improve methane quality in the product gasstream
• Collect additional data on various siloxane sources tobetter determine which species are efficiently removedusing this process