Use a compressed air heater to protect your equipment

Posted by Cas at 6:04 AM on Sep 6, 2013

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When we talk about air compressors and compressed air, we always talk about cooling. Compression of air generates a lot of heat. Therefore a compressor needs to be cooled. The produced compressed air is always hot.

TN20469_CLEARPOINT_Heizer

So, why do we need a compressed air heater?

This has everything to do with preventing condensation of water vapor to prevent sensitive equipment.

Let me first explain you something about compressed air, relative humidity and dewpoint.

Relative humidity and (pressure) dewpoint.

The air that leaves your compressor is typically:

  • About 30 degrees Celsius
  • Saturated with water (100 relative humidity)

This is if you have an aftercooler.

100% relative humidity means that if the temperature drops, more water drops (condensate) will form.

But I have an air dryer!

That’s great and it helps a lot! Compressed air dryers remove a lot of water vapor from the air.

The most common type of compressed air dryer dries the air to a pressure dewpoint of 4 °C.

This means, that as long as the temperature stays above 4 °C, there will not be any condensate formed. This is suitable for most applications. Only if you have compressed air piping running outside of the building in the winter, you might get some problems with water condensate.

Expansion of compressed air

But, we use the compressed air for some purpose. It drives a pneumatic actuator, actuates valves or does other work. In all compressed air uses, the compressed air is expanded back to ambient pressure.

When air expands (goes from high pressure to low pressure), it cools down. Remember that air heats up when it compressed? The opposite is true when it expands.

When a lot of air is expanded at one certain part in your equipment, that part will get cold. It can even get freezing cold!

Valve icing

Pneumatic control valves that are continuously switching (read: using compressed air) can get very cold because of the expansion of compressed air.

Valve icing can be a big problem in industrial applications, the valve can get stuck in open or closed position when condensate water freezes up inside the valve. Since we have a dewpoint of 4 °C with a typical refrigerated compressed air dryer, condensate will form when the air cools down below that temperature.

Small valves and openings can completely freeze shut when enough ice deposits on the inside.

Lowering the dewpoint

We could of course use a desiccant compressed air dryer, that can dry the air to a dewpoint as low as -50 °C, but those dryers are expensive!

Also, while there won’t be any condensate formed inside the valve or part, it still get’s very cold. This could be a problem with precision devices.

Compressed air heaters

An good solution is to use a compressed air heater to pre-heat the compressed air just before it is used (expanded). Since we start the expansion with hot air, the end temperature will be well above freezing point.

A compressed air heater consists of a heating coil inside a housing. Sometimes it is combined with a compressed air filter as an all-in-one solution.

The desired temperature can usually be set. Sometimes it is a fixed value.

Buying a compressed air heater

Make sure that you buy a compressed air heater of enough power. Also make sure that it can reach the temperature that you need.

The power that you need (in kW) depends on the air flow (volume) of compressed air to heat up.

For applications above 7 bar, make sure that the heater is rated for your pressure, as some heaters only go up to 7 or 8 bar max.

Here are some places I found online where you can buy a compressed air heater:

Beko

Beko is famous for it’s compressed air treatment products. And of course, they also sell compressed air heaters! Temperature adjustable from +30°C to +60°C

Sinus Jevi

For large industrial compressed air systems, Sinus Jevi has a big explosion-proof compressed air heater.

Airlines UK

Airlines in the UK has a compressed air heater that can heat up your compressor to anywhere between 20 and 120 °C.

Walker Filtration

Walker Filtration has a compressed air heater/filter combination unit. It can heat up the air up to 120°C (248°F).