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Computational Analysis of Water Atomization in Spray Desuperheaters of

Steam Boilers

A Thesis by Paul Bovat

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• Background• Objectives• Main Equations• Model• Main Results• Conclusions• Recommendations

Outline

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Background• What is a desuperheater?• What are the components?• Common problem with desuperheaters• How is the problem corrected?

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Objectives

• Determine pressure drop across spray nozzles– Compare to industry standard

• Determine final steam temperature• Determine droplet life• Determine full droplet evaporation location

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Equations• Turbulent dissipation and kinetic energy equations

• Energy equation

• Equation for mass diffusion in turbulent flows

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• Particle inertia Equation (Lagrangian reference frame)

• Spherical drag law coefficients

• Equations for heat and mass exchange

• Film Formation thickness equation

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• Atomizer spray half-angle

• Secondary Break-up– Webber #

• Droplet evaporation

• Droplet lifetime

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Model

• ANSYS Fluent CFD– Realizable k-ε turbulent model– Energy equation– Species model– Discrete Phase Model• Pressure Swirl Atomizer

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Model

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Results• Pressure loss across then nozzle– 17% higher results between the empirical and

computational results

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Results

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Results

• Desuperheater spray system– Inlet temp of desuperheater 650 deg F– Outlet temp of desuperheater 645.5 deg F– 4.5 deg F reduction in temperature– Total evaporation is ≈1.48ft

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Results

13.5

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Results

2.01.81.61.41.21.00.80.60.40.20.0E+00

1.0E-06

2.0E-06

3.0E-06

4.0E-06

5.0E-06

6.0E-06

7.0E-06

8.0E-06

9.0E-06

1.0E-05

Injection - 1Injection - 2Injection - 3Injection - 4Injection - 5Injection - 6Injection - 7Injection - 8Injection - 9Injection - 10Injection - 11Injection - 12Injection - 13Injection - 14Injection - 15Injection - 16Injection - 17Injection - 18Injection - 19Injection - 20

Distance (ft)

Diameter

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Conclusion

• Pressure drop across nozzle– Limitations of elements– Second Order Up-Wind

• Desuperheater temperature– Temperature not regulated enough– Evaporated time is as designed

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Recommendations

• Re-run pressure drop analysis with more elements

• Lower spray water temperature• Increase spray half angle