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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).

7 sl gravitox icheme mar09

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