Fouling and Foaming in a Caustic Tower

The Caustic Tower in an ethylene plant is subject to fouling and foaming. Both can cause significant operational issues for the operator. Fouling is caused primarily by the base catalyzed condensation of acetaldehyde with itself. Foaming can be a result of fouling.

Across the industry, there appears to be an increase in caustic tower operational issues as plants crack lighter and shale ethane is brought into the plant. An increase in differential pressure (“delta P” or DP) across the caustic tower is one of the key performance indicators of fouling and foaming, and it can sometimes be difficult to determine which processing issue is occurring. Generally, a continuous dP increase is attributed to fouling, while a dumping and loading effect to the dP is attributed to foaming. The caveat to this is the stable foam that builds and stays. High salts, including rust, can help stabilize foam as well as high temperatures and throughput.

The paper will focus on fouling and foaming mechanisms in a caustic tower, changes in the industry, how to monitor a caustic tower and troubleshoot problems. As part of the troubleshooting discussion, a recent foaming event at a gulf coast ethylene producer will be discussed, including the steps taken to identify foaming vs fouling and ultimately how the foaming was controlled operationally instead of chemically at this plant.