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

A Model for Purging a 15,000 ton LAR TPC tank. Richard Schmitt Fermi National Accelerator Lab March 13, 2006. Topics. Large flat bottom tanks Purging goal Calculation results Examples Plans. Flat Bottom Tank. Commonly used for largest LNG (liquefied natural gas) storage

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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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