the use of computational fluid dynamics (cfd) in achieving energy reductions in new zealand’s...
TRANSCRIPT
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 ??