What are the possible reasons for flooding ? &and Action to be taken while flooding in Distillation Tower.

Flooding in tray tower of distillation column can occur or observed in either of the following ways.

1. Jet Flooding:-

• In distillation operation froth of liquid-vapour mixture forms on each tray from which nearly clear vapour is seperated and rises upward to meet the liquid on the next above tray. When froth of liquid-vapour mixture touches the next above tray it is called jet flooding.

2. Downcomer Flooding:-

• In distillation column, liquid flows in downward direction by gravitational force but it flows against the pressure.
• When liquid flows from one tray to next below tray, it flows from lower pressure to higher pressure. Hence, to compensate that, it elevates certain level inside the downcomer.
• When the liquid level in downcomer on any tray rises above the weir, it is called downcomer flooding.

In simple language when the liquid hold up on the tray increase to certain or beyond the limit is called flooding.

Reason of Flooding:-

In distillation column vapour goes up and liquid comes down but if any one flow disturb by any reason other flow disturbed by sure.

1. If perforation of the tray choked by scaling or any reason then liquid flowrate coming down from the tray decrease and so liquid hold up increase and it cause flooding in distillation column.
2. If vaporization rate of reboiler is high then liquid partical carryover by the vapour from below tray to above tray if it is continue then liquid holdup on the above tray increase and it cause flooding.

How can you identify flooding by observing operating parameters:-

1. Pressure difference (Pressure drop) of distillation column( top and bottom) increase.
2. Bottom pressure of distillation column increase because of liquid hold up on the tray vapor required more force to go up and so bottom pressure of distillation column increase.
3. If bottom pressure increase then bottom temperature also increase.

Action to be taken while flooding:-

1. Reduce re-boiler duty on temporary basis so liquid hold up comes down and then again do it normal.
2. Reduce feed to the distillation column because column already flooded with the liquid.
3. If it is continue for long time it means perforation of tray choked so operate column on minimum capacity for better purity.