The Use of Computational Fluid Dynamics (CFD) in Achieving Energy

Reductions in New Zealand’s Industrial Energy Consumption

Energy Research Group

Department of Engineering

University of Waikato

Martin Atkins

Presentation Overview

• Industrial Energy Usage in NZ

• What is CFD?

• How can CFD Save Energy?

• Industrial Air Heater Example

• Pulp Screening Example

• Obstacles to Uptake

NZ Energy Usage by Sector

0

50

100

150

200

250

Transport Industrial Argricultural Commercial Residential

PJ

Total NZ Energy Use = 490 PJ

Energy Overview, Ministry of Economic Development, 2002.

NZ Industrial Energy Use

0

5

10

15

20

25

30

35

40

45

50

Basic metals Pulp & Paper Woodprocessing

Dairy Meat Other

%

Energy Overview, Ministry of Economic Development, 2002.

What is CFD?

• Computational Fluid Dynamics involves;– Numerical simulation of complex

• Fluid flow• Heat transfer• Mass transfer• Chemical reactions/processes

The Basic CFD Process

Define & Simplify Problem

Create Geometry & Mesh

Define Boundary Conditions & Model Parameters

Solving

Post Processing

Verification &Validation

Experimental & Plant Data

How can CFD help reduce energy use?

• Increase Process Insight & Understanding– Fundamental understanding is vital for optimisation– Move away from a black box approach

• Optimise Process Settings– Can see effects of changes without altering the

process

• Evaluate Possible Alterations• Extend Experimental Work

– Can gain data that is difficult to measure experimentally

Cyclones

200 °C

PRODUCT

DRYER

Milk Concentratefrom

Homogenizers

Concentrate

Example 1 – Industrial Spray Dryer

Air Heater

Industrial Air Heater

Industrial Air Heater

Centrifugal Supply Fan

•Sizing ≈ 5kW to 300kW

Air Inlet

• May have pre-filter

•Air flow rates between ≈ 5 T/hr and 350 T/hr depending on unit size

Diffuser

•Used to slow & spread high velocity air from the fan

Heat Exchanger

•Typically between 300 kW and 25MW in rating, thermal energy is transferred through three main mediums

•Condensing steam

•Heated oil

•Flue gas heating - Direct Gas Fired

Hot air leaves to drier

Flow Contraction

2D – Diffuser Flow Regimes

Flow Distribution Problems

• Flow distribution problems– High fan power required– Low heat exchanger efficiency– Potential increase in maintenance costs

Improved Flow Distribution

• Potential savings;– Fan power– Increased thermal efficiency of the heat exchanger– Tube maintenance

Benefits – Specific Energy Reduction

• Reduction in condensate temperature– Increased efficiency of the steam use

• Increased production ~ 3 – 4 %– Reduced specific energy

• Reduced possible tube failure

Example 2 – Pulp Pressure Screen

• Used to screen pulp• Complex flow fields due to screen rotor

Rotor Pressure Pulse

• Pressure pulse • Forward & reverse flow occurs through the screen during

each pressure pulse

0 .00 0 .01 0 .02 0 .03 0 .04

Tim e, s

-200

-150

-100

-50

0

50

100

P, kP

a

A

B

Capacity & Pulse Magnitude

6

7

8

9

10

11

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

Negative pressure peak, Cp

Ma

xim

um

ca

pa

cit

y, t

/d

Data from Luukonen et al, 2007

Optimise Rotor Element

Low Energy Rotor

Capacity & Power Consumption

Increasing tip speed– Increases pressure pulse magnitude – Increases capacity– Increases power

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60

Power (HP)

Ma

xim

um

Ca

pa

cit

y (

t/d

)

Pump Maxmum

Conventional foil rotor

EP - Foil rotor

GHC - Solid core rotor

Data from Luukonen et al, 2007

Rotor Power & Rotor Speed

3 2pt

PC const

V D

0

10

20

30

40

50

60

70

15 17 19 21 23 25 27 29 31 33

Tip Speed (m/s)

Po

wer

(kW

)

M200 GHC

M400 GlHC

M800 GHC

Data from Luukonen et al, 2007

Canfor-Northwood SW Kraft Trial

0

20

40

60

80

100

120

140

18 20 22 24 26 28 30

Tip Speed (m/s)

Po

we

r (k

W)

GHC

Conventional

52% Energy Savings

Data from Luukonen et al, 2007

Obstacles to Uptake in NZ

• Cost $$$– Single Commercial license US$20K+ per year– Computational Costs

• Relatively low R&D spend• Lack of expertise• Lack of understanding of potential benefits• Turn around time• Unsure of CFD capabilities & applications

Important Considerations

• What are you trying to achieve?• Model Verification & Validation

– Verification - Is the model correctly implemented? Independent? – Validation - Is it realistic? Real world?

Conclusions

• CFD can be a powerful engineering tool for use in energy reduction

• Can increase understanding of the process and important variables

• Validation & Verification is important for good results

Acknowledgements

• Waikato Energy Research Group– Prof. Peter Kamp– Dr Michael Walmsley– Jonas Hoffmann - Vocke

• University of Waikato

QUESTIONS ??