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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
7
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:
8
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
9
Combined Heat and Power Facilities
Turbine Building
Gas Conditioning Building
Blower Building
PROJECT RENDERING
10
• 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
12
• 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
2013-10-28 (2)
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
18
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
19
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
21
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
22
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
24
• Boost pressure (12 psi) for conditioning process
• Multi-stage centrifugal blowers
• Modulated to maintain upstream pressure in digesters
GAS BLOWERS
25
• 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
26
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
30
GAS CONDITIONING BUILDING
Regen Skid
Siloxane Removal
Compressors
Siloxane Polishers
2013-10-28 (3)