Distillation Column Steam Sparger

[HuaCl]

Hi,

Because this is my first time sizing a steam sparger, I would like to get some outside inputs to see if I'm going about it correctly.

I am designing a steam sparger to be used in a distillation column operating at 17psia (bottom). The steam sparger will be 8" in diameter with 20 holes (10 on each side). Steam enters the column at 45 psia, 9539 lb/hr. My main difficulty have been sizing the holes. To do this, I used Bernoulli's equation for compressible fluid (P1 = 45psia, P2 = 17 psia + liquid head pressure, Cp/Cv = 1.244). My resulting diameter for each hole is 1.27". Does the hole diameter sound reasonable for the desired pressure drop?

Thank you.

 

[25362]

For choked steam flow I suggest reading thread124-139392.
If my memory doesn't fail me the Cp/Cv value seems low. Is your sparging submerged in liquid ?

 

[katmar]

Bernoulli is the wrong way to do this. It is giving you far too much area for the flow you want (unless you have an enormous submergence). If you want to stick with 20 holes you need a diameter of about 0.6".

I would go for a larger number of smaller holes. With 1.27" (or even 0.6") holes you will get a lot of vibration from cavitation, especially at startup. It would be better to use 0.25" or less, but of course the drilling can become a problem with so many holes.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[MJCronin]

Hau,

In what country will this sparger be installed ?

These people have a sparger design guideline:

http://www.mottcorp.com/resource/pdf/sparger_guide.pdf

-MJC

 

[katmar]

On re-reading my earlier post I see that it comes across rather negative - telling you how not to do it rather than giving a positive guideline on how to do it. What I intended, but did not say, is that the thread referenced by 25362 is the way to go. Especially look at the advice from Milton Beychok in that thread and have a look at his web site. If anyone can tell you how to do it, it is Milton.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[sshep]

A while back I needed a sparger for a steam stripping application. In my case I chose to get the advantages of injecting steam directly into the water level at the bottom-not sure if this is your case. I got some good suggestions from this post:

thread124-144594

The result was that we bought a set (4) of these

http://www.komax.com/det-shscepter.html

which worked fine. From a cost standpoint there would have been essentually no savings in building a custom sparger.

best wishes,
sshep

 

[HuaCl]

I want to first thank everyone for your inputs. 25362, the link you provided was very useful. I went back and recalculated the sparger holes and I came up with 0.59" diameter hole. This value agrees with katmar assessment. Katmar, I actually found your first message informative rather then negative. If 0.25” or 0.125” holes were used, the number of holes required will be 100 or 450 respectively. This seems like a lot. Is it common to have that many holes (or more) on a sparger? Also, a “U” bolt will be used in the backend to hold the sparger in place and reduce the amount of vibration. Because I lack the experience, I’m not sure if this will be sufficient to correct for the vibration problem if 0.6” hole was used. I’m glad I posted my question, I found all of your inputs and links informative and very helpful. Thank you again.

In regards to 25362 question, the sparger will be submerged in water. I’m currently not sure how much water will be above the sparger but I was guessing about 1 foot.

In regards to MJCronin question, the sparger will be place in a distillation column in Thailand.

 

[katmar]

The vibration that I spoke of can affect the entire column, and not just the sparger. It can sound like you have a captive locomotive trying to escape from inside the column!

If you do not have experience with this type of sparger I believe it would be better to go with one of the proprietary types as recommended by sshep. I think Spirax, and probably Armstrong, make them as well. I agree with sshep that any additional cost for the proprietary units is insignificant when looking at the cost of the column as a whole.

I have installed spargers with many more than 100 holes. If you can get them punched or laser cut it is easier and faster than drilling.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Mech85]

Hi HuaCl,

Obtain a copy of "Design of Gas Distributors" by W.J. Litz, Tennessee Eastman Co. in the November 13, 1972 edition of Chemical Engineering magazine.

It describes several factors such as how to obtain adequate distribution and avoid sparge plugging in straight-pipe, ring and plate gas distributors/spargers for process vessels.

 

[TBP]

Spirax Sarco used to publish a series of booklets, one of which was specifically on direct steam injection. My recollection is that they said a larger number of smaller holes is better than fewer larger ones, minimum distances from the sides.bottom of the tank to avoid excessive noise & vibration, etc.

 

[Milutin]

Hi all,

According to Mr Henry Z. Kister book Distillation Operation, it is not recommended introducing gas streams in column liquid level, but if it is necessary sparger must be used. Only reason for do this, as I see, is lack of space in column bottom.

I have experience on crude unit, stripping steam for main column and all strippers are introduced by sparger into liquid level. No problems with strippers but for main column (stripping of long residue) we have foam formation due effects of submerged stripping steam. Because of that level control was very difficult, it is possible to control level up to 40%, if level indication go up it was possible to flood all column by residue. Finally we revamped that and put steam sparger in gas phase.

Regards,

Milutin

 

[sshep]

Milutins story reminds me to point out that its a good point bring up that your level instruments should be located on a bridle which will also act as a stilling well. Injecting into the water is nice because it significantly reduces problems with contamination in the bottom sump below the steam injection point.

With respect to sparging steam into a mixure, this is for heat input and it is not as important to have the same dispersion as for mass transfer with a gas. The important considerations are hammers (esp start-up), noise, vibrations, etc. I think 45psig steam is more pressure than neccessary, and can only cause problems- better to let the steam down through a valve and reduce the noise at the sparger if you are determined to build one.

best wishes,
sshep