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 PJ Total NZ Energy Use = 490 PJ Energy Overview, Ministry of Economic Development, 2002.

NZ Industrial Energy Use % 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

Example 1 – Industrial Spray Dryer 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

Capacity & Pulse Magnitude Negative pressure peak, Cp Maximum capacity, 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 Data from Luukonen et al, 2007

Rotor Power & Rotor Speed Data from Luukonen et al, 2007

Canfor-Northwood SW Kraft Trial 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 ??