(179f) Flooded Condensers Controls: Principles and Troubleshooting

Flooded condenser control is most popular with total condensers generating a liquid product only. The principles of flooded condenser control methods had been described in the literature several times over the last 60 years, yet some of these methods, like the hot vapor bypass and the flooded drum methods, continue to be among the most troublesome distillation controls in chemical plants and refineries. Most of the reported problems could have been avoided with a better understanding of the principles and learning from past experiences. This paper provides a detailed description of the principles and applies them to address many of the most common traps that had caused problems in the application of these methods.

With flooded condenser controls, some of the condenser surface is flooded with liquid at all times. The flow of condensate from the condenser is directly or indirectly manipulated to vary the flooded area. Little heat transfer takes place in the flooded regions, as heat is transferred by sensible heat exchange only. To raise column pressure, the flow of condensate from the condenser is lessened. This increases the flooded area in the condenser and lowers the surface area exposed for vapor condensation. This in turn reduces condensation rate, thereby raising pressure.

This paper discusses the hydraulics of flooded condensers, and presents the key equations. It emphasizes the interaction between the hydraulics and the vapor pressure behavior of the reflux drum liquid.  Lack of understanding of the role of vapor pressure in these methods has bred many of the operating problems with flooded condenser methods. Our paper then discusses experiences with the main operating issues: poor vapor and/or liquid line hook-up, poor decanting of water, presence of non-condensables, insufficient subcooling, the impact of heat loss in uninsulated reflux drums, and considerations unique to specific common variations of the flooded condenser method.