Air-Cooled heat exchangers design considerations lessons learned

Asked by antonjoh 5 years, 7 months ago | 1 Answers


1 Answer

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ChemKB 5 years, 7 months ago

Design dry-bulb temperature:

  • The typically selected temperature => 2.5 percent of the warmest consecutive 4 months.
  • add 1 to 3°C (2 to 6°F) to the tabulated value.

Air recirculation:

  • Considering prevailing winds
  • Considering locations and elevations of buildings, equipment, fired heaters, etc.,
  • Use same bank type, i.e., all forced-draft or all induced-draft.
  • Place banks far enough apart to minimize air recirculation.

Winter time operations:

  • Provision weather conditions such as heavy rain, strong winds, freezing of moisture upon the fins, etc.

Noise:

  • Noise level at the plant site is affected by the exchanger position
  • Consider reflective surfaces near the fan, the hardness of these surfaces, and noise from adjacent equipment.

Ground area and space requirements:

  • Air-cooled units can be installed above other equipment such as pipe racks, shell-and-tube exchangers, etc.
  • Some operators avoid such installations because of safety requirements.

Safety:

  • Leaks in air-cooled units are directly to the atmosphere and can cause fire hazards or toxic-fume hazards.
  • However, the large air flow through an air-cooled exchanger greatly reduces any concentration of toxic fluids.

Atmospheric corrosion:

  • Locate away from corrosive vapors and fumes from vent stacks.

Air-side fouling:

  • Air-side fouling is generally negligible if kept away from corrosive sources.

Process-side cleaning:

  • Tube chemical or mechanical cleaning.

Process-side design pressure:

  • Keep high-pressure process fluid in the tubes

Bond resistance:

  • Bond resistance gets affected by vibration and thermal cycling.

Approach temperature:

  • The approach temperature, which is the difference between the process-fluid outlet temperature and the design dry-bulb air temperature.
  • For lower process-fluid outlet temperature, an air-humidification chamber can be provided to reduce the inlet air temperature toward the wet-bulb temperature.
  • Typically 5.6°C (10°F) approach is feasible.

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