CONVERTING DIGESTER GAS TO STEAM AND ELECTRICITY AT THE BLUE PLAINS AWTF

MICHAEL B SHAFER, PEBLACK & VEATCH

Nov

embe

r 12,

201

3

PRESENTED AT THE NC AWWA/WEA ANNUAL CONFERENCE 2013

• 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

DC WATER ANTICIPATES THE FOLLOWING BENEFITS:

2

• 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, DC3

DC WATER AND SEWER AUTHORITY

• 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

EXISTING BIOSOLIDS DISPOSAL

4

AERIAL OF BLUE PLAINS SITE

5

N

I-295

BIOSOLIDS PROJECT SITE

3D RENDERING OF BIOSOLIDS SITE

6I-295

N

COMBINED HEAT AND POWER

Main Process Train

Screening & Pre-Dewatering

FinalDewatering

RecycleProcessing

R

R R

GravityThickeners

R

R

Class ALoadout

Biogas Treatment and CHP

Lime

ThermalHydrolysis

SteamBiogas

Emissions

Store &Loadout

Class B

Dissolved Air Flotation Thickeners

MixDewatering

MesophilicAnaerobicDigestion

Electricity

PROGRAM ELEMENTS

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Combined Heat and Power

Final Dewatering

R = Return to plant

MAIN PROCESS TRAIN• Solids Screening

Building• PreDewatering Building• Thermal Hydrolysis

Process• Digesters (4)• Digester Building• Enclosed Flares

MAJOR BIOSOLIDS MANAGEMENT PROGRAM COMPONENTS:

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COMBINED HEAT AND POWER• Turbine Building• Gas Conditioning Bld.• Gas Blower Bld.• Siloxane Flare

FINAL DEWATERING FACILITY• Expansion of Existing Solids

Processing Bld.

BIOSOLIDS AERIAL RENDERING

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Combined Heat and Power Facilities

Turbine Building

Gas Conditioning Building

Blower Building

PROJECT RENDERING

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• 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

DESIGN-BUILD-OPERATE

3 October 2012

PROCESS OVERVIEW

CombustionTurbines

Heat Recovery Steam

Generator

Electricity

Duct BurnerHeat Steam

Heat

Medium Pressure Digester Gas

Exhaust

High Pressure Digester Gas

Water

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• Three Solar Mercury 50• Each unit rated at 5 MW at 13.8 kV• Self-contained enclosure

COMBUSTION TURBINES

Recuperator

TurbineGenerator

ExhaustAir Intake

2913-09-18 (4)

• Convert heat and water to steam• Deliver 47,500 pph of steam to Cambi

HEAT RECOVERY STEAM GENERATORS (HRSG)

Turbine Exhaust Duct

Duct Burner Section

Stack

Steam Drum

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COMBUSTION TURBINES AND HRSG

Steam Dump Condenser

HRSG

Duct Burner

Combustion Turbine

Deaerator

• Auxiliary Boiler (backup supply)

• Water Treatment (RO and softener treatment)

• Deaerator• Steam Dump Condenser

SUPPLEMENTAL STEAM FACILITIES

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WATER AND STEAM FLOW DIAGRAM

Deaerator

DumpCondenser

Feed WaterPumps

CondensatePumps

MakeupWater

ExcessSteam

Auxiliary Boiler

HRSG(TYP of 3)

Natural/Digester Gas

Steam

TurbineExhaust

Water Water

Process SteamTo Cambi

Digester Gas

Steam

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TURBINE BUILDING FLOOR PLAN

Steam Dump Condenser

HRSG

Auxiliary Boiler

Combustion Turbine

Deaerator

Water Treatment

Instrument Air System

TURBINE BUILDING LOWER LEVEL

Auxiliary Boiler

13.8 kV Switchgear

480 V Electrical

Control Room Remote

I/O

Mech RoomRestrooms

Combustion Turbine

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GAS FLOW DIAGRAM

BlowersSiloxane Removal

Blowers Compressors

Wet Scrubber

MoistureRemoval

Condensate

MPDG to HRSG Duct Burner and Auxiliary Boiler

HPDG to Combustion

Turbines

Natural Gas

Flare

Static Mixer

Digester Gas

Particulates

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GAS FACILITIES

Chiller Wet Scrubber

Blowers

Cooling Water HEX (2)

Chilled Water HEX (2)

Gas Reheat HEX (2)

Regen Skid

Siloxane Removal

Compressors

Siloxane Polishers

Siloxane Flare

• Impingement tray scrubber

• Remove particulates and foam

• Uses plant effluent spray

WET SCRUBBER

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• Boost pressure (12 psi) for conditioning process

• Multi-stage centrifugal blowers

• Modulated to maintain upstream pressure in digesters

GAS BLOWERS

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• 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

MOISTURE REMOVAL

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BLOWER BUILDING LAYOUT

Chiller

Wet Scrubber

Blowers

Cooling Water HEX (2)

Chilled Water HEX (2)

Gas Reheat HEX (2)

• Siloxanes limit the useful life of the recuperator

• Primary removal system uses a regenerative adsorptive desiccant media

• Secondary system uses carbon polishers

SILOXANE REMOVAL

28

• Hot air used drive off VOCs from media

• Flare is used to incinerate off-gas

SILOXANE REGENERATION & FLARE

29

• Send high pressure digester gas (200 psi) to combustion turbines

• Rotary screw compressors• Modulated to maintain pressure for the combustion

turbines

GAS COMPRESSORS

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GAS CONDITIONING BUILDING

Regen Skid

Siloxane Removal

Compressors

Siloxane Polishers

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