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A Model for Purging a 15,000 ton LAR TPC tank

Explore the purging process of a 15,000-ton tank, analyzing air purging goals, calculations, and examples. Safety measures and strategies for efficient purging are discussed.

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A Model for Purging a 15,000 ton LAR TPC tank

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  1. A Model for Purging a 15,000 ton LAR TPC tank Richard Schmitt Fermi National Accelerator Lab March 13, 2006

  2. Topics • Large flat bottom tanks • Purging goal • Calculation results • Examples • Plans Purging a 15,000 ton tank

  3. Flat Bottom Tank • Commonly used for largest LNG (liquefied natural gas) storage • Well known technology • Excellent safety record • Reasonable cost • Can not withstand vacuum Purging a 15,000 ton tank

  4. Purging a 15,000 ton tank

  5. 50 m diameter Purging a 15,000 ton tank

  6. Air Purging Goals • Purge to less than 10 ppm O2 • Liquid Argon arrives with 1 ppm oxygen and is purified • Warm gas contain 0.1% of the contamination that must be removed • Purge in a reasonable length of time Purging a 15,000 ton tank

  7. Analysis & Calculations • ANSYS-CFX, finite volume analysis • Hand calculations • Fick’s law • Boundary layer • Perfect mixing Purging a 15,000 ton tank

  8. Uniform Inlet, Single Outlet • Tank Diameter 24.5 m • Tank Height 24.5 m • Total flow 8.5 m3/minute • Tank volume change every 22 hours • Isothermal at 20C Purging a 15,000 ton tank

  9. One volume change Purging a 15,000 ton tank

  10. Concentration after nine volume changes • Center of tank is in upper left Purging a 15,000 ton tank

  11. Single Outlet Conclusions • Residual air is left in the outer, upper part of the tank • Average oxygen concentration is 300 ppm • A single outlet is inadequate Purging a 15,000 ton tank

  12. Local inlet model • Inlet spacing 2.1 m • 100 inlets • Model height 2.4 m Purging a 15,000 ton tank

  13. Distribution plot • One ppm reached in 30 hours at 2.4 m elevation • Some mixing occurs Purging a 15,000 ton tank

  14. Red 3200 to 3600 ppm oxygen Orange 2800 to 3200 ppm oxygen Purging a 15,000 ton tank

  15. Hand Calculations • As a rough check of ANSYS analysis • Diffusion calculations per Fick’s Law • Boundary layer diffusion • Perfect mixing Purging a 15,000 ton tank

  16. Purging Examples • LNG tank purging • SELEX Ring Imaging Cherenkov • Small test tank Purging a 15,000 ton tank

  17. LNG tank purging • One inlet/one outlet • Purged with nitrogen at room temperature • Typically achieve 1% oxygen in one day, one volume change • This rough number compares well with the single outlet model • Initially outlet is all air • later oxygen concentration drops rapidly Purging a 15,000 ton tank

  18. SELEX RICH • Purged with Neon • 44 m3 volume, horizontal cylinder • Purge headers along the top and bottom • Purge rate 0.5 m3/minute • Outlet reached 2 ppm oxygen in 7 hours Purging a 15,000 ton tank

  19. Small tank • Vertical, cylindrical tank • 1.5m diameter, 4.5m3 volume • Mean velocity 1.2m/hour • Dispersed inlet, single outlet Purging a 15,000 ton tank

  20. Small tank model early results 0.3 hours One hour Purging a 15,000 ton tank

  21. one volume change Purging a 15,000 ton tank

  22. Purging a 15,000 ton tank

  23. Small Tank - outlet Ten volume changes Supply argon contains 8.5 ppm oxygen Purging a 15,000 ton tank

  24. Planning • Analyze more details with ANSYS • Importance of other contaminants, nitrogen, water, carbon dioxide • Test 10 m diameter water tank with distribution and venting pipe system • Palladium catalyst vs. venting cost comparison Purging a 15,000 ton tank

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