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A new approach to improving heater efficiency


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A new approach to improving heater efficiency

  1. 1. A new approach to improving heater efficiency <ul><ul><li>Ashutosh Garg, Furnace Improvements </li></ul></ul>
  2. 2. Typical Fired Heater Fluid------  Convection section  Radiant section
  3. 3. Conventional Approach to Efficiency Improvement Additional Heat Transfer Surface in Convection Section
  4. 4. Split flow Fired Heater
  5. 5. Typical Reformer Heater <ul><li>Process heated in radiant section </li></ul><ul><li>Parallel passes, high volume, low pressure drop </li></ul><ul><li>Convection-Waste Heat Recovery ( HC reboiler or steam generation service) </li></ul>
  6. 6. Split Flow Reformer Heater <ul><li>Process fluid split into two streams </li></ul><ul><li>Main flow is heated through radiant section </li></ul><ul><li>Split flow is heated in the convection section. </li></ul><ul><li>Fluid mixed together at the radiant outlet </li></ul>
  7. 7. Case Studies <ul><li>Citgo Corpus Christi No. 4 Platformer Heater </li></ul><ul><li>Valero Texas City No. 2 Platformer Heater and NHT heaters (Reboilers) </li></ul>
  8. 8. Citgo, Corpus Christi No. 4 Platformer Heater <ul><li>Objective: </li></ul><ul><li>Improve Efficiency </li></ul><ul><ul><li>Stack temperature was 1100 F </li></ul></ul><ul><li>No steam generation </li></ul><ul><li>No air preheater </li></ul>
  9. 9. Current Heater Operation Parameter Units Operating Value Total Heater Duty MMBtu/hr 158.10 Radiant Heat Duty MMBtu/hr 120.19 Convection Heat Duty MMBtu/hr 37.91 Firing Rate MMBtu/hr 229.20 Efficiency % 68.98
  10. 10. Flow Scheme - Before Revamp #4 Platformer Heater
  11. 11. Existing #4 Platformer Heater
  12. 12. Proposed Conventional Design High Pressure Drop
  13. 13. Conventional Design with Series Flow
  14. 14. Comparison of Pressure Drop at 22,000 BPD Pressure Drop, psi Original Design Series flow Design Cell 1 3.1 4.5 Cell 2 3.3 4.6 Cell 3 1.2 2.5 Cell 4 1.1 2.3 Total 8.7 13.9
  15. 15. Disadvantages <ul><li>Higher pressure drops </li></ul><ul><li>Large Size piping </li></ul><ul><li>Large Convection Sections </li></ul><ul><li>Higher costs </li></ul>
  16. 16. FIS Split Flow* Scheme * Split flow - US Patent
  17. 17. FIS Split flow * design - Proposed * Patented.
  18. 18. Comparison (Cell 1) Parameters at 22,000 BPD Parameter Original Design Split flow Design Pressure Drop, psi 3.1 2.1 Firebox temperature, F 1,615 1,551 Radiant flux, Btu/hr ft2 19,823 15,047 Radiant tube metal temp, F 1,151 1,120 Firing rate, MMBtu/hr 116.35 82.65
  19. 19. #4 Platformer Heater Data Comparison Item Units Before Revamp After Revamp Capacity BPD 18,500 24,000 Heat Duty MM Btu/hr 158.0 194.5 Heat Release MM Btu/hr 234 225 Efficiency % 67.50 86.60 Stack Temp. °F 1,092 478 Fuel MSCFH 244 242.8 Fuel Savings $/annum 5.8 Million* *Based on $6.0 / MM Btu
  20. 20. #4 Platformer Heater Before and After Revamp
  21. 21. Case Study-2
  22. 22. Platformer Heaters - Existing <ul><li>Common Convection section with H-18/H-19 and H-23 </li></ul><ul><li>Process heating-all Radiant </li></ul><ul><li>Steam Generation in Convection </li></ul><ul><li>Common Stack </li></ul><ul><li>Natural Draft </li></ul>
  23. 23. Platformer Heaters (H-20/21/22) Parameter Units Original Design Total Heater Duty MMBtu/hr 155.98 Radiant Heat Duty MMBtu/hr 74.09 Convection Heat Duty MMBtu/hr 81.89 Radiant Fuel Efficiency % 54.2
  24. 24. Plan View of heater
  25. 25. Convection Section <ul><li>Steam Generator Bank </li></ul><ul><li>Steam Superheater Bank </li></ul><ul><li>BFW Preheater Bank </li></ul><ul><li>Steam Generation: 73,669 lbs/hr@464 psig </li></ul><ul><li>14 tubes per row </li></ul><ul><li>Eighteen rows </li></ul><ul><li>Two future rows </li></ul>
  26. 26. H-18- Hydrotreater Charge Heater <ul><li>Duty-11.97 MMBtu/hr </li></ul><ul><li>All Radiant </li></ul><ul><li>Single pass </li></ul><ul><li>5 burners </li></ul><ul><li>24 tubes </li></ul><ul><li>P9 metallurgy </li></ul><ul><li>8“ NPS tubes </li></ul><ul><li>16” spacing </li></ul><ul><li>Efficiency -55% </li></ul>
  27. 27. H-19 Hydrotreater Stripper Reboiler <ul><li>Duty-18.45 MMBtu/hr </li></ul><ul><li>All Radiant </li></ul><ul><li>Four passes </li></ul><ul><li>5 burners </li></ul><ul><li>56 tubes </li></ul><ul><li>CS </li></ul><ul><li>4” NPS tubes </li></ul><ul><li>8” spacing </li></ul><ul><li>Efficiency -54% </li></ul>
  28. 28. H-23 Depropanizer Reboiler <ul><li>Duty- 15.15 MMBtu/hr </li></ul><ul><li>All Radiant </li></ul><ul><li>Two pass </li></ul><ul><li>6 burners </li></ul><ul><li>52 tubes </li></ul><ul><li>CS </li></ul><ul><li>4” NPS tubes </li></ul><ul><li>8” spacing </li></ul><ul><li>Duty- 56% </li></ul>
  29. 29. Field Survey <ul><li>High draft in all the radiant cells </li></ul><ul><li>Burners flame spread out </li></ul><ul><li>Very high fuel gas pressures </li></ul><ul><li>Bowed tubes in H-21/H-22 </li></ul><ul><li>Stack dampers are fully open </li></ul><ul><li>High excess Oxygen in all the cells </li></ul><ul><li>Burner registers practically closed </li></ul>
  30. 30. Operating Data Simulation Results <ul><ul><li>Convection section was in bad state </li></ul></ul><ul><ul><li>Fins are burnt out / fouled </li></ul></ul><ul><ul><li>Steam superheater temperature is 40 F lower than design </li></ul></ul><ul><ul><li>Thermal Efficiency is 78-81% compared to 88% design. </li></ul></ul><ul><ul><li>Stack temperature is higher by almost 275 F. </li></ul></ul><ul><ul><li>Stack temperature ~ 675 F </li></ul></ul>
  31. 31. Conventional Scheme <ul><li>Waste heat recovery( with new convection section retubed in kind ) </li></ul><ul><li>It would not have solved any of the problems linked to over firing of the heaters </li></ul> Description Units Design Stack temperature °F 404 BFW flow rate Lb/hr 94,000 SSH flow rate Lb/hr 92,120 SSH temperature °F 623 Steam pressure psig 472
  32. 32. Split Flow Scheme <ul><li>H-20/H-21/H-22 </li></ul><ul><ul><li>Limit radiant heat flux to 15,000 Btu/hr ft2 </li></ul></ul><ul><ul><li>Shift the balance duty to convection section </li></ul></ul><ul><li>H-18/H-19/H-23 </li></ul><ul><ul><li>Limit heat flux to 8,000-9,000 Btu/hr ft2 </li></ul></ul><ul><ul><li>Limit the firing to design rate </li></ul></ul><ul><ul><li>Limit the volumetric heat release to 10000 Btu/ft3 </li></ul></ul><ul><ul><li>Shift the balance duty to convection section </li></ul></ul>
  33. 33. Valero Proposed Revamp – Split Flow Scheme
  34. 34. Split Flow for H-20/H-21 <ul><li>H-20- 3 Bare Rows </li></ul><ul><li>H-21- 2 Finned Rows </li></ul>
  35. 35. H-18/H-19/ H-23 Revamping Options <ul><li>H-18/H-19/H-23 Heaters </li></ul><ul><ul><li>All Radiant Heaters </li></ul></ul><ul><ul><li>Design Efficiency- Low -51-53% </li></ul></ul><ul><ul><li>Operating Efficiency- 42-52% </li></ul></ul><ul><ul><li>High Draft </li></ul></ul><ul><ul><li>Very tight design </li></ul></ul>
  36. 36. H-18/H-19/H-23 Revamping Options <ul><li>Do nothing </li></ul><ul><ul><li>High firing rates, firing limitation </li></ul></ul><ul><ul><li>Existing burners may not handle </li></ul></ul><ul><li>Add convection sections on each heater </li></ul><ul><ul><li>Good option </li></ul></ul><ul><ul><li>Expensive </li></ul></ul><ul><li>Add heat transfer surface in main convection </li></ul><ul><ul><li>Two rows </li></ul></ul><ul><ul><li>Economical </li></ul></ul>
  37. 37. Valero Proposed Revamp – Split Flow Scheme
  38. 38. H-18/H-19/H-23 Split Flow <ul><li>H-18- 8 tubes </li></ul><ul><li>H-19-12 tubes </li></ul><ul><li>H-23- 8 tubes </li></ul><ul><li>Total- 2 rows of tubes </li></ul>
  39. 39. Split flow Convection Section <ul><li>Heat Recovery Sequence </li></ul><ul><ul><li>H-20 </li></ul></ul><ul><ul><li>H-21 </li></ul></ul><ul><ul><li>H-18 / H-19 / H-23 </li></ul></ul><ul><ul><li>Steam Superheating </li></ul></ul><ul><ul><li>Steam Generation </li></ul></ul><ul><ul><li>BFW Preheating </li></ul></ul><ul><li>Total no. of rows – 20 </li></ul><ul><li>Convection section dimensions unchanged </li></ul>
  40. 40. Proposed Split Flow Revamp <ul><ul><li>Advantages </li></ul></ul><ul><ul><li>Lower Pressure drop in all heaters </li></ul></ul><ul><ul><li>Reduce Heat Flux – 15,000 Btu /hr ft2 </li></ul></ul><ul><ul><li>Lower Firing Rate – 203 MMBtu /hr </li></ul></ul><ul><ul><li>Lower Volumetric Heat Release </li></ul></ul><ul><ul><li>More efficient system - 88% </li></ul></ul><ul><ul><li>No civil works </li></ul></ul>
  41. 41. Split flow – Control Scheme <ul><li>Balancing of heat transfer and pressure drop by: </li></ul><ul><ul><li>Variable resistance (butterfly control valve) </li></ul></ul><ul><li>Split stream outlet temperature control by adjusting convection section flow </li></ul>
  42. 42. Advantages of FIS Split flow scheme <ul><li>Lower pressure drop (process) </li></ul><ul><li>Lower firing rate </li></ul><ul><li>Lower fire box temperatures </li></ul><ul><li>Lower radiant heat fluxes </li></ul><ul><li>Lower tube metal temperatures </li></ul><ul><li>Lesser turnaround time </li></ul><ul><li>Lower installation cost </li></ul>
  43. 43. Thank you very much <ul><li>Questions and comments are welcome </li></ul>