Chemical Process Engineering and Troubleshooting

Typically, refineries don’t calculate it themselves but get the companies selling them the packing to guarantee performance. Prior to that, they or the company contracted to do their construction, would come up with an estimate. There is no simple “grand unifying theory” for HETP. For the design of packed distillation columns it is simpler to treat the separation as a staged process. Use the concept of the height of an equivalent equilibrium stage or HETP (Height Equivalent to theoretical plate) to convert the number of ideal stages required to a height of packing. HETP is the height of packing that will give the same separation as an equilibrium stage. Eckert (1975) has shown that in distillation the HETP for a given type and size of packing is essentially constant , and independent of the system physical properties ; providing good liquid distribution is maintained and the pressure drop is at least above 17 mm water per meter of packing height. Follo

Flooding occurs if vaporization rate of reboiler is higher, then liquid partially carryover by the vapors from below tray to above tray, if it is continue then liquid hold up on the above tray increases and causes flooding Naturally we don’t want to over pressure the tower and open the safety valve, Same way if tower pressure goes too low then we could not condense the reflux, then the liquid level in reflux drum would fall and the reflux pump would lose suction. Now Take 1. Raising the tower pressure Higher pressure reduce volumatric flow of vapor, (As the Pressure is inversely proportional to Volume), So increasing the tower pressure does not Causes Flooding but its a one of the option to reduce the effect of Flooding . Now the question is why we are increases the Tower Pressure? so the answer is to permit higher reflux rates. 2. Decreasing the tower pressure Generally Distillation columns are operated at low pressure, Because as the tower pressure will decrease

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