Condenser Condensate Drain Lines

November, 2018

Greetings!  Our topic for this month is condensate drain lines and how to properly pipe them so that they do not cause performance problems. As ejector motive steam and process vapors condense in a system’s condensers that liquid needs to be drained. This is typically achieved with condensate lines that drain liquid from elevation to a condensate vessel at grade level. The condenser elevation is determined by the condenser operating pressure and the pressure in the condensate vessel. It’s recommended that full vacuum is used for the condenser operating pressure as a measure of safety, given potential changes in the cooling water conditions and loading. A basic formula for condenser height is shown below alongside a few examples. Condenser Height Equation 144 in 2 /ft 2 [(Condensate Vessel Pressure (psia) - Condenser Pressure (psia)) / Condensate Density (lb/ft 3 )]

Example 1: Water Condensate Condenser Pressure = 0 psia Condensate Vessel = 14.7 psia Condensed Liquid = Water at Density of 62.4 lb/ft 3 Condenser Height = 144 in 2 /ft 2 ((14.7 psia - 0 psia)/62.4 lb/ft 3 ) = 34 ft                                               In this example the condenser has to be installed at an elevation at least 34 feet above the condensate vessel to ensure condensate does not flood up into the condenser.

Example 2: Water and Oil Condensate Condenser Pressure = 0 psia Condensate Vessel= 14.7 psia Condensed Liquid = Water/Oil Mixture at Density of 52 lb/ft 3 Condenser Height = 144 in 2 /ft 2 ((14.7 psia - 0 psia)/ 52 lb/ft 3 ) = 41 ft In this example the condenser has to be installed at an elevation at least 41 feet above the condensate vessel to ensure condensate does not flood up into the condenser. If the condensate is a mixture of water and condensed oil or some other material, then that impacts the density of the condensate and the minimum elevation requirement.

Example 3: Positive Pressure Condensate Vessel Condenser Pressure = 0 psia Condensate Vessel= 19.7 psia Condensed Liquid = Water/Oil Mixture at Density of 52 lb/ft 3 Condenser Height = 144 in 2 /ft 2 ((19.7 psia - 0 psia)/ 52 lb/ft 3 ) = 55 ft In this example the condenser has to be installed at an elevation at least 55 feet above the condensate vessel to ensure condensate does not flood up into the condenser. The higher pressure in the condensate vessel results in a higher differential pressure impacting the elevation that is required.

Each condenser should have its own condensate line, with each piped from the condenser to the condensate vessel. Condensers often operate at different pressures and if their drain lines are tied together it provides a path from the higher pressure condenser to the lower pressure condensers. This will cause the process flow to recycle back through the drain lines. The drain lines should be piped in the most direct manner between the condensers and the condensate vessel. Piping should continually pitch downward at an angle of 45 degrees minimum while avoiding horizontal runs. Care should be taken to avoid 90 degree elbows whenever possible. If horizontal runs are unavoidable, the horizontal pipe should be at least 2 pipe diameters larger and sloped. These piping recommendations help avoid vapor lock issues and plugging due to debris or process material buildup, all of which can prevent a condenser from draining correctly.

The size of the condensate vessel should be large enough to retain sufficient liquid for startup. The typical condensate vessel size is 1.5 times the tailpipe volume or greater. Additional volume will be needed if the condensate vessel is also being used for water / oil separation. The vessel’s size is important because at startup condensate will be drawn up into the condensate piping, lowering the liquid level. The tail pipe should also be submerged 12” or more to ensure there is a seal and at least 12” above the bottom of the condensate vessel to avoid blockages and plugging.  It’s also important to remember that the condensate lines are under vacuum down to the water level in the condensate vessel. The piping should be welded for this application if possible to reduce the possibility of air in-leakage. The internal surfaces will continually contact the condensate and should be made of a material that minimizes corrosion and subsequent air leaks. The size of the condensate lines should not be reduced down to a diameter less than the condensate connection on the condenser.

Graham's YouTube Channel More content is available at Graham's YouTube Channel. If you are interested please don't hesitate to click on the YouTube link and subscribe.

Graham Gulf Coast Office P.O. Box 3940 Covington, LA 70434 Eric Johnson 585-815-9432 Alicia Johnson 585-815-9463

WEBSITE

REQUEST A QUOTE

EMAIL US

VACADEMICS CLASS

SURVEY / INSPECTION

SITE TRAINING