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Suspects Causing Poor Dryer Performance in your Steam-Heated Process

Do you find yourself frequently frustrated because your steam-heated dryers are not performing properly? Do you find yourself constantly running through a list of suspects as to what is causing the dryer to act up? Is it the steam supply, the air vents, the internal syphon or scoop, the rotary joint, the steam trap, or the condensate return system?

Typically, you start with what you do know. If you’re lucky, your equipment has controls and visibility to easily see where the problem stems from. If you’re not, you might feel like you are trying to find your way in the dark. Questions you should ask include:

  • Has the temperature or flow rate of the product feed changed?
  • Is the equipment’s steam pressure holding steady?
  • Are the air and non-condensable gases being purged?
  • What is the pressure differential across the rotary joint?
  • What is the pressure differential across the steam trap?
  • What is going on back at the condensate recovery tank?

Answers to these questions will be your flashlight while finding your way in the dark. If you can’t answer these questions, it will be nearly impossible to find out what is affecting your dryer’s performance.

As you walk around to find answers to the questions, the following explanations may add light.

Air vent By not allowing the air and non-condensable gases to escape, the vessel will fill with both robbing the steam of its heat. It is the law of partial-pressures that states that a gas in a mixed gas will have properties based on its percentage of that mixed gas. For example, a 100 psia mixed gas of 90% steam and 10% air will be the same temperature as 90 psia 100% steam.

Steam header If your steam header was too pushed too hard until it snapped, it may be that it was sized too small to start with or maybe you just keep asking it to do more and it burns out. Either way, when you are at peak load the velocity is so great that the pressure drops due to line lose.

Extra-production flow and colder-than-normal Initial product are often the steam header’s partners in crime. They increase steam demand until the steam header can’t coupe anymore.

The syphon, scoop, screw or other method of lifting condensate from the shell to the center of the equipment can have a number of character flaws that could also make them guilty contributors to poor performance. Incorrect orientation, leaky seals, cracks, holes, plugging with debris or broken welds will diminish their effectiveness. Some rely on differential pressure between the inlet to the steam and condensate connections while almost all benefit from having some differential pressure. Knowing what it should be and monitoring it will typically prevent fault.

The rotary joint is a critical component of the steam-heated dryer and rarely ever the culprit of the issue. It is simply a device that lets you mount fixed pipe to rotating equipment. A failure will usually result in a visible steam leak.

Steam traps gets a lot of bad rap for poor performance, especially if it is an issue related to things not being hot enough. The conundrum here is that if the steam trap is physically sound, something else is causing the issue. Traps only work if the water gets to them and there is sufficient differential to pass the water through it. Again, start looking at your differential pressure across equipment to make sure there isn’t another suspect the issue.

Finally, condensate return piping and tanks. Often undersized, twisted, and having many rises and drops, these pipes are often the cause of bumps and noises in the night. Too much back pressure here and it is the end of heat transfer for you.

  • Written by:

    Erich Bernhardt

    Senior Applications Engineer, Kadant Johnson

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