Advanced Monitoring of Fouling in Gasoline Fractionators

The gasoline fractionators in the two sister ethylene units at an ethylene producer's facility historically ran from turnaround to turnaround without issue. However, after the units’ feed slate shifted towards appreciably more gas, fouling in the towers became more problematic.

This paper will briefly review the general mechanisms of fouling in the gasoline fractionators, with a particular focus on the impact of moving from a primarily liquid to a primarily gas feed slate. The process treatment program will then be described, with a primary focus on the monitoring strategy.

The gasoline fractionator is a rather complex system with many correlated process variables. As a result, it is generally difficult to discern an increase in the fouling rate with conventional monitoring techniques until it becomes truly problematic and potentially irreversible. The use of sophisticated multivariable regression modeling and a modified statistical process control strategy allows us to monitor the performance of the tower and clearly distinguish between common cause variation (variation attributable to normal changes in the various operating parameters) and special cause variation (variation due to a statistically significant, unexpected event such as fouling). As a result, we can immediately respond to subtle changes in the fouling rate.