Oily exhaust air ducts – dangerous fuses

Ventilation ducts in production plants become a ticking time bomb

In metal cutting, temperatures of up to 1,000 degrees and above arise on the tool cutting edges. As a result, the cooling lubricant evaporates and releases oil mist, vapors and gases. These emissions must be extracted, otherwise the production hall and equipment will become oiled and the employees will breathe in the dangerous aerosols, gases and vapors.

gases and vapors during metal cutting

In larger companies in the metal industry, the machine tools are often connected to a ventilation system with a central oil mist separator. This sometimes means very long air ducts between the production system and the oil mist separator.

long air ducts between the production system and the oil mist separator
long air ducts between the production system and the oil mist separator

Due to the temperature drop in the collecting duct, the extracted aerosols can condense and build up a layer of fat in the duct. The larger particles in particular often fail to reach the far-away oil mist separator.

Very long air duct paths for aerosols
Very long air duct paths for aerosols

They put a static load on the air duct and – worse – they create a dangerous fire load. When using pure grinding and cutting oil as the cooling lubricant, the fire risk is particularly critical, because an oily air duct acts like a fuse in the event of a grease fire. Fresh fats and oils ignite only in temperature ranges of around 300 Gad C; in the case of resinous deposits, this ignition temperature can also be reduced considerably.

Oily and flammable deposits in an exhaust air duct
Oily and flammable deposits in an exhaust air duct

Such deposits and oil & grease residues in the exhaust air duct also impair the safe functioning of fire dampers, increase maintenance costs immensely and reduce the efficiency of heat recovery systems. These problems can only be solved with a pre-separator directly at the capturing of each production process. The compact separators are equipped with a mechanical X-Cyclone separator, which centrifugally ejects the aerosols and cleans itself by the drainage of the separated liquid.

Pre-separation of the exhaust air duct using a separation box
Pre-separation of the exhaust air duct using a separation box

The pre-separation keeps the exhaust air duct and the central separator largely free of oil and grease. Without pre-separation, up to 1000(!) Liters of condensate can accumulate in long collecting air duct channels. If maintenance is neglected, there is a risk that the oily exhaust air duct will sag or collapse due to the weight gain. A problem that is rarely discussed, but which occurs again and again, especially in old workshops, is leaky air ducts and condensate dripping from the ceiling.

Even with water-soluble cooling lubricants with 95% water and 5% emulsion additive, undesirable grease deposits occur because the water evaporates over time and leaves a flammable oil film. The ceiling turns black, the floor slippery and the windows go blind. All of this can be prevented with the pre-separation.

Pre-separation using a separation head with X-CYCLONE separator
Pre-separation using a separation head with X-CYCLONE separator

Such a pre-separation on every machine only makes sense if the separators are also flame-proof. This property is proven by a corresponding test mark. The test mark guarantees that in the event of a cutting oil fire or a deflagration, the fire does not penetrate the air duct. Simple baffle plates or mesh filters do not meet this requirement.

Examination of a separator for flame penetration

For critical applications, such as when using low-viscosity cutting oil as a cooling lubricant, Reven offers a multi-stage duct separator. It is equipped with pull-out elements: an agglomerator enriches the microfine aerosols into larger droplets, a downstream X-cyclone separator removes all of the aerosolate.

Duct separator at the end of an exhaust duct for oil mist separation
Duct separator at the end of an exhaust duct for oil mist separation

The duct separators from Reven are made of stainless steel and are available as standard for air volumes up to 1,000 (588cfm) to 80,000m³/h (47,000cfm).

Duct separator in the outside area at the end of an exhaust air duct for oil mist separation
Duct separator in the outside area at the end of an exhaust air duct for oil mist separation
Duct separator in the outside area at the end of an exhaust duct for oil mist separation integrated in the HVAC system
Duct separator in the outside area at the end of an exhaust duct for oil mist separation integrated in the HVAC system