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GRAVITOX a fundamentalapproach to aeration design
Dr. Son Le & Ian Carline
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The Carbon Crunch Technology Solutions for the Water Industry
Haweswater House, 4th March 2009
GRAVITOX a fundamental approach to aeration design
____________________________________________________________
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Dr. Son Le & Ian Carline
Asset Management & RegulationUNITED UTILITIES PLC, Warrington WA5 3LP
Email [email protected]; web http://enzymichydrolysis.com/
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GRAVITOX developmentOverview
1. Background2. Introduction to Aeration
. RAVIT X n
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4. Theoretical considerations5. Experimental programme
6. Summary
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UK Government target for CO2 emissions:20% below 1990 levels by 201060% reduction by 2050real ro ress b 2020 1.2MtC a
Background
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UU target for CO2 emissions:
37M to achieve 8% reduction 201250% reduction by 203560% reduction by 2050
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Framing the challenge
UU Group GHG emissions 1990 - 2050
400000
500000
600000
C O 2 e
4
0
100000
200000300000
1990 1994 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050Year
T o n n e s o f
Actual carbon emissions (1990-2005) and projections to 2020
Linear reduction of 60% from 1990 baseline
Impact of mitigation activities to 2020
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Delivering our carbon strategyto 2050
488,000 tCO 2eCHP and IPM = 38,000 tCO2e
Cost = 37m
Wind = 80,000 tCO2e
Cost = 80m
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What we are doing:
Reducing footprint of existing assets
Extending renewable energy
Embracing R&D and innovation 122,000 tCO 2e
Cost = ??
Low carbon technology= 80,000 tCO2e
170,000 tCO2e = TBD
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Energy Use Analysis
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Activated sludge aeration accounts for
55.6% of the energy used in sewage treatment
Source: Yorkshire Water
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The purpose of aeration is two-fold:
1) Supply oxygen to microorganisms
Introduction to Aeration
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2) Mixing to provide contact betweenmicroorganisms and nutrients
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orifice types
Coarse bubble aerators
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Maximumoxygentransfer
efficiency(OTE)0.75% perfoot of depth
Static tube
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FLEXIBLE MEMBRANE DIFFUSER
(DISC & TUBE)
Fine Bubble Aerators
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Typical Oxygen Transfer Rates (kgO2/kWh , EPA 1984)Diffuser Type Clean water Activated sludgeCoarse Bubble Diffusers 1.2 0.96
Oxygen Transfer EfficiencyCommon aeration systems
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Fine Bubble Diffusers 3.9 1.76Surface Mechanical Aerators 1.8 1.53Submerged Turbine Aerators 1.2 1.02
Jet Aerators 1.68 1.26
These values represent OTE of 8 to 15% only
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DEEPSHAFT Process
RAS
Typical energy efficiency5 - 8 kg O
2 /kWh
(42-67% OTE)
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Influent
ClarifierSAS
FE
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GRAVITOX Development
Deep-Shaft efficiency without the high capital
Simple Retrofit existing ASP assets
Problems
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Bubble generation Aerated sludge pumping Bubble behaviour / Flow Distribution
Performance data
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GRAVITOX (Gravity Oxygenator)
GRAVITOXConcept
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Theoretical considerations
Energy Demand Bubble Formation
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Hydrodynamics Oxygen transfer
Performance Prediction
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Energy considerationsbubblegeneration
MixingTotal power demand
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Bubble transport
Sludge transport
= + + + BG = Bubble Generation BT = Bubble Transport ST = Sludge Transport M = Mixing Power
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Bubble FormationFilm pressureLaplace-Young(surface tension )
Bubble Surface energy
10.00
100.00
1,000.00
/ m
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Work donein creating a bubble
(bubble surface energy )W = PV (Nm or J)
0.01
0.10
1.00
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
bubble dia (mm)
k J
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Bubble Transport
Depth
(1) Overcoming buoyancy
E = force acting on bubble x depth( Archimedes' principle, single bubble)
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m
work done dragging bubbles from top to bottomW = W1 + W2
(2) Isothermal Compression(bubble volume basis, = air density)
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Bubble HydrodynamicsAfter formation, a bubble rapidly accelerates to its terminal velocity
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Oxygen Transfer
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For a given depth, oxygen transfer only depends
on gas hold up ratio
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Performance PredictionGRAVITOX DEVELOPMENT Process ModelVersion 1.3a ( 4th February 2008)
Bioreactor Working volume, L 700,000Flow L/h 116,667 Flow Ml/d 2.80PE 10,036INFLUENT mg/L g/h EFFLUENT(settled sewage)BOD 215 25,083 BOD
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Design 600L Acrylic tank. U tube setup Aerator and Pump on sep shafts Air and Water Flow meters. Power meter
Experimental programmeBench Scale Research
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Operating ParametersMonitor: bubble generation, bubblesize and distribution.
Measure: Aerator & Pump efficiencyPressure (Head)Power consumptionContact time (Flow rate)
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Bench Scale ResearchBubble Generation
Marine Bubbler 50mm, 70mm and 110mm Good Flow low head coarse bubbles
(5mm)
Axial Flow Bubbler
Produced goodflow Okay head 2-3
meters
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quantity and size
Centrifugal bubbler
Produced goodbubble quantityand size.
CF+AF BubblerPlanned forwork withcompositebubblers.
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Construction of Prototype Test Plant Boreholes - Ground Source
Solutions. Refit old ASP plant -Newton
Industrial
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2 metres
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Metal casing required forfirst 30m to protect hole.
Metal U Tube atbottom
50mm internaldiameter
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What's Next ?
Prototype Test Plant delivery (end March 09).Baseline performance data (conventional ASP
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w , - mon s
GRAVITOX prototypes testing & optimisation
(6-9 months)
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GRAVITOX development
Part of UU strategy to deliver carbon savings to 2050 Tar et 75% ener reduction
SUMMARY
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(potential reduction 82,000tCO2 pa, 16% UU Group)
2007 Concept
2008 Prototype R&D 2009 Prototype testing & optimisation 2010 Demonstration & Roll out
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Thank youACKNOWLEDGEMENTSThe authors would like to thank United Utilities PLC for permission
to present this work. This paper represents the opinion theauthors and does not necessarily represent the view of their
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employers.The GRAVITOX development is supported by the Carbon Trust
(Project reference:076-068 Low carbon sewage treatment).
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