Converting Digester Gas to Steam and Electricity at the Blue Plains AWTF Michael B Shafer, PE

1. Converting Digester Gas to Steam and Electricity at the Blue Plains AWTFMichael B Shafer, PE • Black & Veatch Presented at the NC AWWA/WEA Annual Conference 2013

2. DC Water Anticipates the following benefits: Reduces hauling of biosolids by 50% Produces a Class A beneficial byproduct for use as a soil amendment Reduces annual O&M cost by $20M/year Cogen plant generates 15 MW of power ~ 30% of daily power demand for Blue Plains AWTP Reduces DC Water’s Green House Gas (GHG) emissions by 41% Provides DC one of the greenest projects on the East Coast

3. DC Water and Sewer Authority • Wastewater service to over 2 million people in DC, MD, VA • Blue Plains AWTP –largest advanced WWTP in the world • 370 mgd average annual flow • 1,076 mgd wet weather • Largest power user in Washington, DC

4. Existing Biosolids Disposal 1200 wet tons per day lime stabilized biosolids Agriculture – 39 counties in MD and VA Silviculture – 40,000 acres permitted in 8 Virginia counties Poplar plantation on a gravel mine Reclamation projects – three sites to date

5. Aerial of Blue Plains Site I-295 N BIOSOLIDS PROJECT SITE

6. 3D Rendering of Biosolids Site COMBINED HEAT AND POWER N I-295

7. Program Elements Combined Heat and Power Emissions Gravity Thickeners Biogas Treatment and CHP Electricity Final Dewatering Steam Biogas R Mesophilic Anaerobic Digestion Class A Loadout Screening & Pre- Dewatering Thermal Hydrolysis Final Dewatering Main Process Train Dissolved Air Flotation Thickeners Recycle Processing R Lime R R Dewatering Mix Store & Loadout Class B R R = Return to plant

8. Major Biosolids Management Program Components: • COMBINED HEAT AND POWER • Turbine Building • Gas Conditioning Bld. • Gas Blower Bld. • Siloxane Flare • FINAL DEWATERING FACILITY • Expansion of Existing Solids Processing Bld. MAIN PROCESS TRAIN • Solids Screening Building • PreDewatering Building • Thermal Hydrolysis Process • Digesters (4) • Digester Building • Enclosed Flares

9. Biosolids Aerial Rendering Blower Building Combined Heat and Power Facilities Gas Conditioning Building Turbine Building

10. Project Rendering

11. Design-Build-Operate Pepco Energy Services (PES) – Prime DBO Contractor • Ulliman Schutte Construction • Black & Veatch PES has 15 year operations contract • Extensive operations experience with combustion turbines DC Water reduces financial risks • Volatile energy markets Schedule Benefits • Early release of foundation design • Early procurement

12. Process Overview Electricity Exhaust Combustion Turbines Duct Burner Heat Recovery Steam Generator Heat Heat Steam High Pressure Digester Gas Medium Pressure Digester Gas Water

13. Combustion Turbines • Three Solar Mercury 50 • Each unit rated at 5 MW at 13.8 kV • Self-contained enclosure Exhaust Air Intake Recuperator Generator Turbine

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15. Heat Recovery Steam Generators (HRSG) Stack • Convert heat and water to steam • Deliver 47,500 pph of steam to Cambi Steam Drum Turbine Exhaust Duct Duct Burner Section

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17. Combustion Turbines and HRSG HRSG Duct Burner Steam Dump Condenser Combustion Turbine Deaerator

18. Supplemental Steam Facilities • Auxiliary Boiler (backup supply) • Water Treatment (RO and softener treatment) • Deaerator • Steam Dump Condenser

19. Water and steam flow diagram Makeup Water Deaerator Feed WaterPumps Water Water Turbine Exhaust Digester Gas Natural/ Digester Gas CondensatePumps Auxiliary Boiler HRSG (TYP of 3) Steam Steam Excess Steam DumpCondenser Process Steam To Cambi

20. Turbine Building Floor Plan Water Treatment Combustion Turbine HRSG Deaerator Steam Dump Condenser Instrument Air System Auxiliary Boiler

21. Turbine Building Lower Level Restrooms Mech Room Combustion Turbine Control Room Remote I/O 480 V Electrical 13.8 kV Switchgear Auxiliary Boiler

22. GAS Flow Diagram Flare Wet Scrubber Digester Gas Blowers Moisture Removal Siloxane Removal Static Mixer Natural Gas Condensate Particulates Blowers Compressors MPDG to HRSG Duct Burner and Auxiliary Boiler HPDG to Combustion Turbines

23. Gas Facilities Chiller Wet Scrubber Chilled Water HEX (2) Siloxane Polishers Blowers Cooling Water HEX (2) Gas Reheat HEX (2) Siloxane Removal Compressors Siloxane Flare Regen Skid

24. WET scrubber • Impingement tray scrubber • Remove particulates and foam • Uses plant effluent spray

25. Gas blowers • Boost pressure (12 psi) for conditioning process • Multi-stage centrifugal blowers • Modulated to maintain upstream pressure in digesters

26. Moisture Removal • Dry gas required for downstream siloxane removal • Digester gas is saturated at ~ 100°F • Series of heat exchangers to reduce gas to 40°F • Plant effluent and chilled water used to cool gas

27. Blower Building Layout Wet Scrubber Chiller Gas Reheat HEX (2) Chilled Water HEX (2) Blowers Cooling Water HEX (2)

28. Siloxane Removal • Siloxanes limit the useful life of the recuperator • Primary removal system uses a regenerative adsorptive desiccant media • Secondary system uses carbon polishers

29. Siloxane Regeneration & Flare • Hot air used drive off VOCs from media • Flare is used to incinerate off-gas

30. Gas Compressors • Send high pressure digester gas (200 psi) to combustion turbines • Rotary screw compressors • Modulated to maintain pressure for the combustion turbines

31. Gas Conditioning Building Compressors Regen Skid Siloxane Removal Siloxane Polishers

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