The price of compressor fouling

Steve Ingistov is Principal Engineer BP/WCC at Los Angeles refinery. He says:

The topic which Klaus Brun and Rainer Kurtz addressed under the “Myth Busters”, Turbomachinery International,

March/April 2011 Edition, is of great interest not only to designers of axial compressor but also to the end Users.

From the end-user perspective the fouling of axial compressor is a continuous problem especially in typical industrial areas such as petrochemical and oil refining.

In these areas there is typical presence of sub-micron particles in the ambient air which are difficult to arrest even by the most efficient intake air filters.

The most damaging in fouling of axial compressor blading are sub-micron particles. These particles will not cause any erosive damage to compressor blades, however having virtually no mass they cannot be centrifuged when deposited on the surface of the blade aerofoil. Despite their negligent mass the sub-micron particles adhere firmly to the blade surface especially if it is rough and pitted and if it is moist, in the region of first, several stages of compression.

The moisture can be natural that is in the ambient air when the relative humidity is high, say over 80%, or it can be artificial and caused cooling the intake air using an evaporative cooler or a fogging system. 

In addition to the moisture in the air there is always some amount of lubricating oil in the air. The source of the fine oil mist is compressor bearing No 1.

The fine oil mist generated in bearing No 1 is then ingested into the compressor suction, where it combines with water moisture and further encourages the sub-micron particles to stick to the blade surfaces.

In the past during the on-line cycle of compressor blade cleaning, clean condensate was mixed with the cleaning chemical, detergent which efficiently removed the oily and dirty deposits from the compressor blades.

With time environmental laws have changed and nowadays only so-called bio-degradable on-line cleaners are allowed. Unfortunately bio-degradable cleaners are not as effective as original detergents in removing the oily deposits from the surface of the blades.

In combating the ingress of oil mist, specially designed non-metallic brush seals successfully reduce (up to 80%) the lubricating oil leak from bearing No 1 into the compressor suction.

Finally despite all the precautions and latest technologies the end-user may be in a situation where the only solution is to remove the compressor rotor from its housing and manually clean the blades.