2 replies to this topic

[MCorray1]

Hi there, 

 

I am currently trying to design a packed stripping column for an MEA-CO2 system. I have found the height of packing required, but I was wondering if there was a way to estimate the height of the column itself, which would include allowances for column internals, safety related ,margins, etc. 

 

I have found a correlation for tower height which was used in the design of an SO2 scrubbing column, but I wasn't sure if I could use this for my CO2 stripper? 

Any help is appreciated, thanks. 

[Art Montemayor]

MCorray:

 

I have designed, built, installed, and operated several CO₂ - MEA systems - specifically the CO₂ stripper in question.  I have amassed a lot of engineering field data, experience, and data on the subject.  I am willing to discuss this subject if you are interested in reading my comments and advice.  Are you interested?

 

Don't waste your time trying to relate the SO₂ information with CO₂.  The only relationship between both is their Chemical formula.

Await your reply.  Be specific in directing your questions, queries, and basic data.  My advice is only as good as the quality of the queries.

[Pilesar]

After you have determined the bed height, you will need to determine how much residence time is wanted for the liquid in the sump. The liquid should settle a bit before feeding the pump to allow vapor bubbles to separate. This should be at least one minute for most columns. Since your system is a foaming service, five minutes of residence time does not seem unreasonable. So let's allow one minute between the column low level and the low-low level (LLL.) Let's give five minutes residence time between HLL and LLL. The LLL is measured at the height of the level nozzle on the side of the column near the bottom tangent. So adding these up, we estimate one foot to the bottom level tap, then add the five minutes of liquid residence time above that point to find the liquid height at HLL. (The liquid flow rate multiplied by the residence time will give the volume of liquid in the sump. If you know the column diameter, you can then calculate the height of the liquid in the sump.) Assuming a thermosiphon reboiler, you will want the reboiler return to be at least one-half a column diameter higher than the HLL. Then add another 1.5 column diameters in height above the reboiler return and underneath the bottom support tray to allow space for the vapor-liquid separation. So a 15 foot to 20 foot high sump area is not unexpected. At the top of the column above the bed, you will need space for a liquid distributor and room for vapor-liquid disengagement. So add an additional 6 feet or so between the top of the bed and the column top tangent line. Add an extra foot or two if have a demister in the column. Be generous with your column height estimates during the early stages of the project. It is usually not much money to have an extra few feet in height but can be troublesome to add missing height in later. Extra height can be useful when you discover changes needed during detail design. After determining tangent to tangent height, you will want to add a vessel skirt. A higher vessel elevation simplifies bottom piping, reboiler placement, and pump selection. Just state your criteria for skirt height -- it may be 10 foot, 20 foot, 30 foot, or some other height. None of these numbers and guides I gave for finding column height are unbreakable rules. Column designers often do it their own way and let someone else correct it later.