Energy Efficient MBR Design: Rabigh Refinery, Saudi Arabia · MBR Aeration Power Consumption •...

Energy Efficient MBR Design:Rabigh Refinery, Saudi ArabiaEnergy Efficient MBR Design:

Rabigh Refinery, Saudi Arabia

Water Arabia

Wednesday, February 2, 2011

Dr. Dirk HeroldKoch Membrane Systems

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Power Consumption MBRPower Consumption MBR

• Aeration

• RAS Pumping

• Air Scour

• Permeate

• Other

• Lighting

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Relevant Aspects for MBR Energy ConsumptionRelevant Aspects for MBR Energy Consumption

• Matching membrane area with design flowsReduce peak flowsAdequate flux rate to reduce membrane areaMBR membrane train layout

• Efficient return activated sludge (RAS) pumping designPump feed versus gravity feedVariable speed control

• Minimize air scour requirementsModule designMBR membrane train layout

• Maximize aeration tank alpha valueMixed liquor suspended solids (MLSS) selected based on

loading/process

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MBR Aeration Power ConsumptionMBR Aeration Power Consumption

• Aeration power consumption elevated in MBR due to depressed alpha value associated with increased MLSS concentration of MBR process.

• α-factor indirectly proportional to power required to supply air for adequate oxygen transfer.

• α-factor: ratio of oxygen mass transfer coefficient (Kla) in wastewater to the same coefficient in clean water.

MLSS

Alpha (α)

Power

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Offgas Alpha Testing Fine Bubble Diffusers

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000MLSS (mg/l)

Alph

a

Site #1Site #2 Site #3Site #4German Research - (Gunder)German Research - (Krampe & Krauth)

Alpha as a Function of MLSSAlpha as a Function of MLSS

German Research – (Cornel & Wagner)

Design range

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Relevant Aspects for MBR Energy ConsumptionRelevant Aspects for MBR Energy Consumption

• Matching membrane area with design flowsReduce peak flowsAdequate flux rate to reduce membrane areaMBR membrane train layout

• Efficient return activated sludge (RAS) pumping designPump feed versus gravity feedVariable speed control

• Minimize air scour requirementsModule designMBR membrane train layout

• Maximize aeration tank alpha valueMixed liquor suspended solids (MLSS) selected based on

loading/process

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MBR RAS Pumping PowerMBR RAS Pumping Power

• RAS pumping in MBR typically 4x influent flow rate.

• MBR RAS important to balance MLSS between membrane tank and bioreactor.

3 mm PT

DN N

1Q 1Q

5Q

4Q

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MBR RAS Gradient MBR RAS Gradient

MLSSm = MLSSb * (R+1)/R

MLSSm : MLSS membrane

MLSSb : MLSS bioreactor

R : Recirculation factor

Selection of bioreactor MLSS impacts:

1.Alpha value2.Recycle rate

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Pumped Feed and Gravity ReturnPumped Feed and Gravity Return• Better control over MLSS distribution • Pumping additional Q compared to gravity feed but usually at lower pumping head

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Relevant Aspects for MBR Energy ConsumptionRelevant Aspects for MBR Energy Consumption

• Matching membrane area with design flowsReduce peak flowsAdequate flux rate to reduce membrane areaMBR membrane train layout

• Efficient return activated sludge (RAS) pumping designPump feed versus gravity feedVariable speed control

• Minimize air scour requirementsModule designMBR membrane train layout

• Maximize aeration tank alpha valueMixed liquor suspended solids (MLSS) selected based on

loading/process

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Influencing Factors on Permeate FluxesInfluencing Factors on Permeate Fluxes

Membrane Module

permeateflux

membranematerial

membranefouling

biologydesign

moduledesign

module operation

membraneage

moduleclogging

membranecleaning

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Optimizing Membrane AreaOptimizing Membrane Area

AVERAGE Q

PEAK Q

20%80%

Buffer peak flows

Multiple train design

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Optimizing Membrane EnergyOptimizing Membrane Energy

• How do we fine tune membrane operation to conserve energy?

Number of trains in operationFlux

TRAINS

1 4

2 3

FLUX

offopt

max

Max Day

Avg Day

QMin Flow

Max Day

Avg Day

No. of Trains

N trains

Min Flow N-X

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Flux & Membrane Train OperationFlux & Membrane Train Operation

0

50

80 96Bioreactor Level [%]

MS1

Foff

Fopt

Flow[m³/h]

MS 5

Fmax

88 92

MS 3 MS 2L H 1 H 2100

Tank Level

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MBR Train DesignMBR Train Design

• Multiple train design allowsEnergy friendlyRedundancyCyclical air supplyStand-by of membranes under low flow conditions

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Relevant Aspects for MBR Energy ConsumptionRelevant Aspects for MBR Energy Consumption

• Matching membrane area with design flowsReduce peak flowsAdequate flux rate to reduce membrane areaMBR membrane train layout

• Efficient return activated sludge (RAS) pumping designPump feed versus gravity feedVariable speed control

• Minimize air scour requirementsModule designMBR membrane train layout

• Maximize aeration tank alpha valueMixed liquor suspended solids (MLSS) selected based on

loading/process

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Membrane Air ScouringMembrane Air Scouring

• Major power consumer with regard to membrane operation

• Critical to membrane operation/permeability

• Efficient design allows intermittent air supply and variable air delivery rate without compromising membrane permeability

• Air scour systems vary with manufacturers

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How to Optimize the Membrane Aeration?How to Optimize the Membrane Aeration?

• Membrane module design• Plant design

Design aspects:Design aspects:

Both aspects have to be optimized

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PURON® Air Scour ConceptPURON® Air Scour Concept

Membrane Bundle

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Specific Instantaneous Air FlowSpecific Instantaneous Air Flow

2004 2008

Spe

cific

Inst

anta

neou

s Ai

r Flo

w[N

m3 /

hm2 ]

0.70.8

0.53

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General Operation ModesMembrane Module AerationGeneral Operation ModesMembrane Module Aeration

2 Trains: 50 % Aeration3 Trains: 33 % Aeration4 Trains: 25 % Aeration

at average flow treatment

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4 Train SystemAlternating Membrane Aeration4 Train SystemAlternating Membrane Aeration

• At average hydraulic capacity, only 1 blower is operated

• Air is switched alternating between the four filtration lines

• Only at peak hydraulic capacity, 2 blowers are operated parallel

• Air is switched alternating between 2 x 2 filtration lines

• Air supply is realized depending on hydraulic capacity

Membranes1

Membranes2

Membranes3

Membranes4

Duty

Assist

Standby

25 % Aeration management during average flow conditions for a 4 train membrane filtration systems

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Advantages of Intermittent Air Scour Advantages of Intermittent Air Scour

Specific aeration rate 0.53 Nm³/m²h

Specific aeration rate (@ 50 % aeration) 0.27 Nm³/m²h

Specific aeration rate (@ 25 % aeration) 0.14 Nm³/m²h

Aeration pressure for operation 300 mbar

Overall energy consumption 0.15 – 0.09 kWh/m³

Highly energy efficientIntermittent aeration management

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Example Project (4 trains): Total Energy Consumption of Membrane Filtration Example Project (4 trains): Total Energy Consumption of Membrane Filtration

• Sludge circulation => 0,025 kWh/m³

Energy consumed by:Energy consumed by:

Total Membrane filtration:≤ 0,20 kWh/m³ treated effluent

• Membrane aeration => 0,128 kWh/m³

• Permeate & Backwash pumps => 0,046 kWh/m³

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Rabigh Design BasisRabigh Design Basis

MBR plant realized by:Parkson ME in cooperation with Al-Busaili

MBR plant realized by:Parkson ME in cooperation with Al-Busaili

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Rabigh LayoutRabigh Layout

Pre-treatment

Equalization

Denitrification

Nitrification

Membrane tanks

Design MLSS Nitrification: 8.5 g/L

Multiple train layout

Equalization (~ 7 h buffer

capacity)Energy efficiency

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Rabigh LayoutRabigh Layout

Start of commissioning: December 2010

Adaptation of biologyIncrease of influent flows

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SummarySummary

• Minimize membrane area to optimize power consumption• Effective management of solids• Flexible membrane operation• Effective air scour device• Multiple trains allow intermittent air scour• Bioreactor operation

© 2010, Koch Membrane Systems, Inc. All rights reserved.

Questions & CommentsQuestions & Comments

Thank youfor your attention!