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Monday, April 4, 2011

Remove Condensate with Minimal Air Loss

Removing condensate is important for maintaining the appropriate air quality level required by end uses. However, significant compressed air (and energy) losses can occur if condensate removal is done improperly.
Excess compressed air loss during condensate removal can occur due to several factors. Following shows several condensate removal methods and the characteristics of each method.

Manual operation:
  • Operators manually open valves to discharge condensate.
  • Depends on people opening valves at the appropriate time for the necessary amount of time.
  • Often leads to excess loss because air escapes when the valves are left open to drain the condensate.
Level-operated mechanical float traps:
  • Use a float connected by linkage to a drain valve that opens when an upper setting is reached and closes when the drain is emptied.
  • Require considerable maintenance.
  • Are prone to blockage from sediment in condensate.
  • Are prone to getting stuck in open position (leak excess air) and in the closed position (does not allow condensate to be drained).
  • Inverted bucket traps may require less maintenance, but will waste air if the condensate rate is inadequate to maintain the liquid level in the trap.
  • Most suited for a fully-attended powerhouse operation with scheduled maintenance.
Solenoid-operated drain valves:
  • Have timing devices that can be set to open for specified amounts of time at pre-set adjustable intervals.
  • The period during which the valve is open may not be long enough for adequate drainage of accumulated condensate.
  • The valve will operate even if little or no condensate is present, resulting in air loss.
  • Require strainers to reduce contaminants, which can block the inlet and discharge ports of these devices.
Zero-loss traps:
  • Have a float or level sensor that operates an electric solenoid or ball valve to maintain the condensate level in the reservoir below the high level point, or a float activates a pneumatic signal to an air cylinder to open a ball valve through a linkage to expel the condensate in the reservoir to the low level point.
  • Wastes no air.
  • Considered very reliable.
  • Reservoir needs to be drained often to prevent the accumulation of contaminants.
Other Points to Consider

Drain the condensate often and in smaller quantities rather than less frequently and in larger quantities. Consider oversized condensate treatment equipment to handle unexpected lubricant loading and to reduce maintenance. All drain traps should be inspected periodically, with parts repaired or replaced as required. If replacement is the decision, consider using zero loss drain traps.

Source: http://www1.eere.energy.gov/industry/bestpractices/pdfs/compressed_air13.pdf

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