2 replies to this topic

[FFTF21]

I am required to design a reflux drum that separates vapour and liquid from a stream coming from a partial condenser. The feed to the condenser is 6004 kmol/hr. The flow rate of vapour leaving the drum is 24.82 Kmol/hr. The flow rate of the liquid product leaving the drum is 300 Kmol/hr and the flow rate going back to the column as reflux is 5679Kmol/hr. The streams consists mostly of water and ammonia.
My question is should i use a vertical or horizontal reflux drum, and why wolud you choose a horizontal or vertical?
Thank You

[Art Montemayor]

FFTF:

The main factors that determine what type of reflux drum (horizontal or vertical) you need is the degree of good vapor-liquid separation and the amount of liquid flow rate going through the drum.

In a partial condenser application you will remember that you want to take credit for a separation stage at the condenser – i.e., put the condensed liquid in equilibrium with the exiting vapor. This is an important process design feature of using a partial condenser and you don’t want to jeopardize it. Therefore, you want to maximize intimate liquid-vapor contact and separation. A horizontal vessel, by nature (inherently), has the physical features that you are looking for:

• The surface area available for liquid-vapor disengagement is much larger than that of a comparable vertical vessel;
• The amount of vapor space available in the horizontal vessel is usually much larger;
• The liquid level travels much slower in a horizontal vessel than in a vertical vessel and is, therefore, much easier to control in a fixed, pre-determined position.

For this application, I would favor a horizontal drum. You have furnished mol flow rates, so that I can’t evaluate the ratio of vapor volume to liquid volume. I suspect the ratio of V/L in the drum is rather small. You should evaluate the amount of liquid you will be managing in a vessel described in volumetric terms, not molecular. At this stage of the design you are now in the real-life and mechanical sector and not in the conceptual design arena. Therefore, you have to leave your simulator and mol balance behind and concentrate on the actual hardware you have to design and select for the application. As in the case of your reflux pump, to do that you have to describe your conditions in mass and volumetric flow rates.

FFTF:

The main factors that determine what type of reflux drum (horizontal or vertical) you need is the degree of good vapor-liquid separation and the amount of liquid flow rate going through the drum.

Art,

I am a little bit confused here, it's clear that the main factor to determine what type of reflux drum depends on degree of separation of liquid and vapor phase, so in the case where the drop size in vapor phase is not important (this process provides the intermediate products to another process and the product has enough time to cool down along the piping system) the selection of reflux drum could be vertical drum because vertical type requires less space, is it right? please advise

Thanks

anhzai2000