I have a debutanizer column with feed consist of C1 hydrocarbon up to
180degC FBP Heavy Naphtha cut. The column is meant to split light hydrocarbon which ends up at the top and naphtha (light and heavy naphtha) down at the bottom. Light hydrocarbon at the top is basically C1 up to LPG components. LPG is drawn as reflux drum distillate while C1 and C2 is released as offgas from the reflux drum.The column overhead cooling is provided by 2 fin fan cooler and a water cooled trim cooler before condensed vapor enters into the reflux drum. Some of the liquid from the reflux drum is routed back to the column top tray as reflux beside being drawn as the distillate.
Control of the top LPG quality is by way of controlling tray 11 temperature.
Theoretically when reflux temperature is low, the tray 11 temperature would drop. However, an instance happened when a sharp drop in fin fan and the water cooled exchanger outlet temperature raised the tray 11 temperature drastically. At the same time, the reflux drum level also drops.
Can someone explain how this could happened?