1 reply to this topic

[irshadaliii]

dear all
as i am working in sulphur recovery unit in refinary,here, we have four unit first is amine regeneration unit, second is sour water stripper unit, third is tail gas treating unit and fourth is sulphur recovery unit.
my question is that, why we use reflux drum in case of amine regenerator (there is no chimney tray in this column, only simple trays are there),but in sour water stripper we do not use reflux drum (in sour water stripper column there is chimney tray at which suction of reflux pump is taken), we use only pump around system, reflux is directly taken by the pump from chimney tray and goes to fin fan cooler and then to the column.

second question is why we do not using chimney tray in amine regenerator column.

capacity of amine regeneration unit is 470 meter cube per hour.
and capacity of sour water stripping unit is 125 meter cube per hour.

[Art Montemayor]

Irshadaliii:

In my opinion, this is a very good and insightful question. I raised this same identical query in 1962, as a young engineer running acid gas units using MEA as the amine solution. My question had to do with what was the usefulness and reason for having a “reflux stream” in an acid gas stripper when the return of the reflux did absolutely nothing to improve the purity of the overhead acid gas. I did not get a response from anyone, but I went ahead and changed the process. I stopped sending the overhead condensate collected after the acid gas cooler-condenser back to the stripper and pumped it to the top of the amine absorber where I used it to scrub and recover MEA carryover from the exiting gases there. I reduced my amine consumption that way and realized a handsome return in reduced operating costs.

Later in my career, I had the opportunity to challenge some engineering company process design engineers and I finally got one to admit that I was right: reflux was not really “reflux”, but rather the condensate was used as a means to scrub the overhead acid gas exiting the stripper. However, this returned reflux was adding more reboiler load to the regeneration of MEA so I continued with my design of not returning any condensate to the top of the stripper unless I was forced to do so by anyone who could prove to me that it improved or allowed the operation to work. My modification worked – and it worked for many years without any process problems and a net operating cost reduction, so I never had any reason not to use the modification. I do not recommend the use of a “refluxed” condensate in acid gas strippers. I see no purpose or logic in using it that way.

I have used amine strippers that only incorporated flat plates without any attempt to used downcomers or any other internals – and they worked. I did design calculations and found that approximately 1-1/2 theoretical plates are required in an MEA stripper and that is the reason why you can get away with that type of simple trays in an MEA stripper. I have also used bubble caps, tunnel caps, and packed beds. These types of strippers showed no marked improvement from the simple plate in an MEA stripper.

You do not tell us who designed and fabricated your amine units and you furnish no P&ID or a schematic drawing of how your stripper and reboiler are configured and fabricated. I don’t know how your chimney tray is installed nor how it works, so I can’t give any comment on it.

You should furnish us with specific, detailed information, drawings, and data if you expect specific responses from our Forum. For example, you state:

“capacity of amine regeneration unit is 470 meter cube per hour.
and capacity of sour water stripping unit is 125 meter cube per hour.”

But we don’t know WHAT capacity you are referring to – the amine flow rate?, the acid gas flow rate?, the sour water flow rate? Draw a schematic sketch and indicate the flow rates where they apply and fully identify them as to pressure, temperature, and composition. If you give us a gas flow rate in m3/hr, we need to know AT WHAT CONDITIONS. Compressible gases must be identified as to temperature and pressure when you describe them in volumetric terms. That’s why it’s easier to describe gas flow in mass flow rate – kg/hr.

I hope these comments address your query and concerns.