Page 118 - Compression Machinery for Oil and Gas

Centrifugal Compressors Chapter 3 105

Solid-particle erosion is managed by ensuring cleanliness during commission-
ing and operation. Liquid droplet erosion is managed by several techniques.
Liquids should be removed at a properly sized knockout drum prior to entering
the compressor. Compressor operation must keep the inlet condition above the
dew point. Wash systems must be operated and maintained such that the com-
pressor is not over loaded with liquids.
Fouling describes a buildup of solids on aerodynamic surfaces and other
locations. Deposit buildup is often in the form of salts (chlorides), polymers,
or particulates. Of these foulants, salts are perhaps the most common and dif-
ficult to deal with in the refinery whereas polymers are most common in the
chemical industry. The causes of fouling are not always known (Fig. 3.70).
Foulant buildup causes a number of potential problems. Aerodynamic path-
ways can become congested adversely affecting the compressor performance.
Clearances can decrease altering the thrust balance on the compressor. Laby-
rinth seal cavities can get plugged, increasing leakage. The rotor can become
imbalanced if the foulant is unevenly distributed or if a piece of foulant breaks
off. Further, barrel compressors can be difficult to open and clean. Numerous
problems may also be experienced outside of the compressor. Foulant can build
up at flowmeters and other instrument locations causing erroneous readings.
Check valves can collect fouling deposits and leak. Antisurge valves and lines
can be a concern. Heat exchangers are a location that is particularly prone to
fouling.

FIG. 3.70 Fouled compressor rotor due to salt buildup. (Photo courtesy of Elliot Group.)