Fire at oil seperation device

[miyo]

Our 50 hp screw air compressor was burned. the fire started inside the oil-air seperation device.
Originaly the seperator was made of 3 cloth cylinders, but recently it was replaced by 1 big "filter" - cylinderical screen inside a metal screen casing.
the question is - was it wise to use a metal screen, could it possibly create a spark that initiated the fire?
Are there other effects that could start the fire?

 

[chief]

Hot compressed air and oil makes a diesel engine effect ie combustion. Check out your oil cooler, maybe not effective for some reason

Offshore Engineering&Design

 

[MortenA]

Interesting about the diesel engine - but the pressure ratio in a diesel cylinder that ignites is 14:1-25:1 and i dount this can be generated in a screw compressor?

Best regards

Morten

 

[TPL]

Build up of static?

 

[zdas04]

It almost has to be static, probably in conjunction with an improperly grounded vessel. If there isn't an easy path to ground, then static can build up high enough to jump a gap to ground, if that gap is in the air section a fire is possible.

You can get 20:1 compression ratios in a flooded screw, but it happens over the length of the screw and the oil flood is a much better heat transfer medium than air--20 compression ratios would (depending on the oil flow rate) raise the gas temperature 50-60F, not nearly high enough to give you autoignition.

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[crjones]

All elements in the air/oil separator need to be grounded and the element needs to be grounded to the sump. Most manufacturers put a staple in the gasket to accomplish the grounding to the pressure vessel. Basically if you look at a cut away of a separator it looks like the combustion chamber of a jet engine. As a separator gets dirty, it 0.1-0.3 micron filtration, the velocities increase. The dirt gets heated and acts like an ignition source. The result is a football shaped pattern of burn on the inside of the element.

 

[gerhardl]

Interesting.

Static is of course be the most probable ignition source.

From basic the 'other two' factors is oxygen (air) and the correct mixture/temperature of 'something ignitable', in this case probably a mixture of oil/gas.

The second question then is if geometry, volume available, mixture, temperature or other differences created by rebuilding the filter could be considered as contributing to ignition.

Electrical faults could contribute to ignition and also static from plastics as well as metal.