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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