Objectives 2A:

This study evaluates a Crude preheat exchanger service heat transfer performance with the following tube material and coatings and estimates the energy savings and CO2 Emissions Reduction:

  • Carbon Steel
  • Stainless Steel
  • Carbon Steel Tube ID Coated
  • Stainless Steel Tube ID Coated

Assumptions

  • Service – Desalted Crude vs Heavy Vacuum Gas Oil (HVGO)
  • Tube ID Coating Thickness – 25 Microns (0.001 inch)
  • Coating Thermal Conductivity – 0.722 Btu/hr-ft-F
  • Fuel Value -$3.50 per MBtu/hr
    [Note fuel prices in Asia can be 3X compared to US]
  • Furnace Efficiency = 0.9
  • Network Factor = 0.75
    [Part of the Duty Gain in the Exchanger Diminishes Heat Transfer on other Exchangers in the Preheat Train due to changes in temperature differentials]
  • CO2 Reduction based on EPA Conversion Equations
  • Heat Transfer Calculation performed with HTRI XIST
  • Assumed Fouling Factor shown in the Comparison Tables below
  • Coated bundles are cleaned at 2 year frequency
  • Non coated bundles are cleaned yearly
  • Assumed Inlet Operating
    • Crude Inlet Temp – 370 F
    • Crude Rate – 650 klb/hr
    • HVGO Inlet Temp – 505 F
    • HVGO Rate – 675 klb/hr
  • 7 Days Oil Out to Oil In for Exchanger Cleaning
  • Maintenance Cost for Cleaning – $40k
  • Margin Cost Per Day During Cleaning – Approx $15k per day
image 34

Heat Exchanger Geometry

  • TEMA – AES
  • Shell Id = 50”
  • 1054 Tubes
  • 1” Tube OD
  • 083” tube wall thickness
  • 4 Tube Passes
  • 20 ft length
  • 11 Baffle Cross Passes, Single Vert Seg , 20.9% Cut
image 33

Results

Comparison Tables

image 32
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Economic & CO2 Reduction Benefit

Coated Carbon Steel (cleaned 2yr interval) Versus Carbon Steel (cleaned yearly)

  • Annualized Duty Reduction = 0.6 MBtu/hr
  • Energy benefit = $28k over 2 years
  • Margin + Maintenance benefit from increasing cleaning interval = $105k+$40k=$145k
  • CO2 Equivalent Benefit = 423 Tons over 2 years
  • Overall Benefit = $28k + $145 k = $173k

Coated Stainless Steel Versus Stainless Steel

  • Annualized Duty Reduction = -0.9 MBtu/hr
  • Energy benefit = -$46.8k over 2 years
  • Margin + Maintenance benefit from increasing cleaning interval = $96.8k+$40k=$136.7k
  • CO2 Equivalent Increase Emissions = 708 Tons over 2 years
  • Overall Benefit = -$46.8k + $136.7k = $89.9k