30 replies to this topic

[imtinan mohsin]

dear members.
I want to design a vaporizer to cool sea water with liquid nitrogen.
can any body help me in finding the literature.
imtinan

[Art Montemayor]

imtinan:

I think there is going to be some confusion when comparing what your post title states and what you are writing within your post. There is a great deal of difference in the scope of work between a vaporizer and a cooler.

Which is it that your scope wants to do: cool or vaporize?

[imtinan mohsin]

dear art,
I will clarify you my problem:
we have multistage compressors.
sea water is being used as cooling medium in intercoolers and aftercoolers.

Also we have excess liquid nitrogen available.
we are considering the option to use this liquid nitrogen to cool the sea water and then recycle it to the intercoolers.

heat load= 40 million Btu/hr
liquid nitrogen available = 24000 lb/hr
temperature = -284.4 oF
pressure = 74 psig

kindly help me.
imtinan

[Andrei]

My calculations using Hysys are showing that your nitrogen is vapour at the the specified contitions.
I don't know how you gonna prevent seawater freezing at those conditions, probably you will have to circulate a huge amount of it. But maybe somebodyelse has more experience with it.

[Art Montemayor]

Andrei:

Thanks for keeping watch on the details. imtinan is furnishing erroneous basic data.

imtinan:

I have to repeat what I asked before: What is your scope of work? Do you want to primarily vaporize the LIN? (at this point the question is baseless) Or do you want to cool the seawater?

As the REAL basic data becomes obvious, the facts start to reveal themselves. If you really have a cold gas, the heat transfer is going to be very expensive besides troublesome. If you don't have a steady supply of the vapor nitrogen flowrate, then your seawater temperatures will vary. This is all assuming you can justify pumping in enough seawater flow rate in order to prevent any freeze-ups. This type of operation is very risky and hardly ever practical.

You must furnish complete, accurate, and detailed basic data as well as a Scope of Work in order to have a reasonable and practical answer to your query.

[imtinan mohsin]

dear Art,
thanks for reply.
I will try to clarify your points:

1- Scope of work: our main aim is to cool the sea water. This sea water is being used as cooling medium in the intercoolers of air compressors.
2- We have excess liquid nitrogen is available. We are finding the ways to use it.
The flow rate of sea water available is 62000 lb/hr @ 110 oF and to cool it to 41 oF.

I hope that i have clarified your points.
waiting for your response.
imtinan mohsin

[Qalander (Chem)]

Dear Imtinan mohsin Hello,

You seem to miss/exclude some data, somehow this may not serve to help you.
A better approach might be a rough sketch with appropriately ear marked point process conditions of what you

1) Have?
2) Envisage?

Moreover your case if true, somehow may be tackelled to have Liquid Nitrogen evaporated on shell side with running sea water on tube side of Kettle type S&T Heat exchanger (Expanded Shell with (a)Liquid level Control and (b)pressure and c)possibley temperature controls in-place) .
To curb possibilities of freezing of tube side fluid you will require thoroughly designed high flow rates and probably units in parallel.

This is all hypothetical ,unless proper Details are forwarded by you to the forum learned professionals to help you indeed!
Best regards
Qalander

[djack77494]

I'm sorry, imtinan, but you seem to be getting some significant facts wrong. It seems as if the principle objective is to provide adequate cooling of the air stream being compressed. The very concept of essentially "throwing away" valuable cryogenic energy (liquid nitrogen) to cool 110 ^oF seawater to cool warm air sounds very wrong. It was very expensive to bring the nitrogen's temperature down low enough to liquify it.

Now you want to throw that energy away? Also, you state the seawater temperature is 110 ^oF. I don't believe it. There are few places in the world where the daytime temperatures routinely reach 110 ^oF in summer. Seawater temperatures should be much lower. Please prepare better and re-post when you have all the facts.

[Andrei]

djack,

I've seen this kind of seawater temperatures, and even higher in some areas around the Persian Gulf. That is because the wide spread practice there to use seawater as cooling medium, once-through. There are areas around industrial cities where the actual seawater temperatures are very high because everybody dumps hot water used for cooling. I personally faced this kind of challenge in a few projects in the area.
I totally subscribe to idea that using liquid Nitrogen to cool water is a total waste of energy.
One idea for Imtinan: there are people that built seawater intake lines a few hundred meters off-shore, where the temperature is lower.

[Qalander (Chem)]

Dear Imtinan,

Andrei's Last suggestion seems fairly adequate/possibly feasible with slight depth consideration to ensure avoidance of near surface hotter conditions; those might be prevalent.

Regards
Qalander

[imtinan mohsin]

dear members,
thanks for reply.
But the sea water is coming from the intercoolers of the air compressors.
The sea water will be warm (@110 oF).

We have no other option but to cool the sea water with liquid nitrogen.
please help.
imtinan

[Art Montemayor]

imtinan:

It is NOT TRUE that you "have no other option but to cool the sea water with liquid nitrogen". Besides being insufficient and erroneous, your basic data has been changing as you have been answering questions on this thread. Please read the attached Workbook carefully and note the simple and straight-forward solution presented at the end in flow sketches I have made.

It is increasingly difficult - if not impossible - to help someone who won't answer direct questions or supply needed and essential information when requested. This has been the case in this thread. You only answer in the manner that you want to answer - not in the way you have been asked to answer. You also fail to address the very important error (or miscue?) at the very beginning regarding the state of the nitrogen. We still have to assume that in spite of what you say, the cold nitrogen is in the gaseous state, not in the liquid state. You simply do not address this question and, therefore, leave the basic heat transfer up in the air: is it a vaporizer or is it a cooler? It all depends on whether the inlet nitrogen is a liquid or a gas. This is a very critical and important point and must be thoroughly cleared up before proceeding any further. The folks at Eng-Tips are just as confused about what you propose (or don't propose) as we are. This clearly should prove to you that you are failing to communicate with clarity and true, accurate basic data.

You have made erroneous and flawed claims that you cannot use a low-temperature heat transfer fluid instead of seawater. This is a very impractical claim that is not explained or described. What you are proposing makes no practical sense. What you state (the need for an additional heat exchanger) is simply not true in the case of using a low temperature heat medium. Simply look at my sketches to see the point I make.

If you continue to insist upon using valuable cryogenic nitrogen (as a liquid or a vapor) as a cooling fluid, then the obvious, lowest cost, and most practical way to do this is to follow the flow diagram that I have done for you. I am not showing the critical cold nitrogen instrumentation that is required to ensure that the cooling medium is kept at a constant temperature. That is another subject that can be dealt with in another thread. The important thing NOW is to nail all the basic data down together with the Scope of Work. Without this information being totally revealed and communicated, we are all wasting our valuable time.

I hope what I have generated and recommend helps you out.
 Compressor_Cooling_Fluid.zip   160.44KB   637 downloads

[imtinan mohsin]

dear Art,
Thanks for reply.

I understand that i am presenting data in some erraneous way.

here i will again try to clarify you.
1- The nitrogen will be in liquid phase with the saturation pressure for -284.8 oF.
2- (option -I) We will be using inline heat exchanger before compressor intercoolers and after cooling the sea water will be wasted away.
3-The sea water is coming from treament plant.

I hope it will calrify you.
imtinan

[Mehrdad]

Dera imtinan

please give your e-mail address for a completely theoretical proposal.

mehrdad

[Art Montemayor]

imtinan:

You have changed the Scope of Work; this doesn't mean you "clarified" it. That's OK, as long as you supply clear and accurate basic data and scope of work.

As my comments show in the attached Rev1 workbook, your information continues to lack details and information.

I have revised the workbook to show what I believe you mean to describe. Please read my comments and review my sketch in detail. Correct or add anything you find that you don't agree with or want to change.

You will note that I still recommend a surge, baffled tank to add capacitance to the proposed system. This I consider vital if you are to avoid any freeze-ups. I also recommend the use of an agitator in the surge tank in order to maximize the heat transfer by increasing the convection currents and the film heat transfer coefficient.

I hope this helps.

[Art Montemayor]

mehrdad:

There is nothing wrong with trying to help some members out by communicating directly with them and offering information that you don't want to share with others. However, when this is done through the use of the Forum, you are negating the efforts made by the other members contributing to the same thread.

If you do not wish to share your information or solution with the other contributing members, that is OK. You are free to communicate with the Origianl Poster (OP) directly and offer your services using the email feature in this website. But please do that outside the Forum because it causes confusion and questions as to what is being discussed and evaluated within the thread and being shared with others. Offering a solution to only one or only some selected thread participants in private takes away the basic principle of sharing engineering information freely to all who particpate and read our threads.

Thank you.

[imtinan mohsin]

my email address:

imtinan_mohsin@yahoo.com


imtinan mohsin

[Qalander (Chem)]

my email address:

imtinan_mohsin@yahoo.com


imtinan mohsin

Dear Imtinan/Other Colleagues;
May I suggest that this forum's PM (Personal Message) option is much better/safer for email sharing in general terms.
Best regards
Qalander

[Mehrdad]

Dear art

Thanks for your advice and i'm so sorry .
I did try to upload my proposal plan but i couldn't. maybe some problem is in my internet account or
Other net problems.but i will appreciate if imtinan upload it for all to professional forum.

Thank you

[Mehrdad]

imtinan

please find the attachment in your mailbox.
i will appreciate if you upload it for all.
it is a theoretical proposal only.

mehrdad

[Mehrdad]

Imtinan please view the attachment . i'd succeed to upload the excel file. mehrdad

Attached Files

•  N21.xls   22.5KB   465 downloads

[Andrei]

mehrdad,

I am sorry but my first reaction seeing what you are proposing was "OUCH!".
I wouldn't do that in any circumstances, most probably your "ice catcher" will have to "catch" pretty soon the whole tower.
Anybody doing this kind of thing should be congratulated for being a champion of the In-efficiency or wasting the resources just like that. I hope there is a regulatory body that will forbid implementation of any kind of this outfit.

Wow, the topic became really hot, as the icon in front of it shows.

Intinan, why don't want to recognize that this kind of water-nitrogen combination is not the best idea, and look for something else?
Let's assume that nitrogen cooling is your only option, assume, not more than that.
Putting together two fluids in contact when one of them is at below freezing temperature of the other will only result in, of course, freezing it, nothing else.
Depending on what kind of gas you have in the compressor, you didn't reveal it yet, you may consider having heat exchange between nitrogen and compressed gas, without water as an intermediary. But you have to look what kind of gas is there, temperatures, pressures, liquid drop, again freezing, in one word to redesign your compression.

[imtinan mohsin]

We are using air copmressors.
For their intercoolers, we are using sea water as cooling media.
We have to cool sea water before entering the intercoolers.
imtinan

[Mehrdad]

Andrei

with respect about your opinion.
according to the required outlet temperature 41^.F the rate of liqud nitrogen is adjustable for outlet temperature control and preventing of freezing..
the ICE CATCHER is a sieve for trapping the ice that immediately forms after contact liquid nitrogen with water then the pieces of ice moves on surface of water in flow direction and will melt after catched behind the sieve by water stream.
a controlling device for freezing and sight glasses can prevent the freezing of system.
this is not the exactly engineering optimized plan and maybe gives an idea to imtinan.
anyway i'm appreciated for your advice .

regards

mehrdad

[Qalander (Chem)]

Andrei

with respect about your opinion.
according to the required outlet temperature 41^.F the rate of liqud nitrogen is adjustable for outlet temperature control and preventing of freezing..
the ICE CATCHER is a sieve for trapping the ice that immediately forms after contact liquid nitrogen with water then the pieces of ice moves on surface of water in flow direction and will melt after catched behind the sieve by water stream.
a controlling device for freezing and sight glasses can prevent the freezing of system.
this is not the exactly engineering optimized plan and maybe gives an idea to imtinan.
anyway i'm appreciated for your advice .

regards

mehrdad

Dear mehrdad
I understand that your indicated contacting system coupled with appropriately designed & controlled/ throttled sparger Nitrogen injection system; should be workable.
However I am convinced that
direct trace amounts injection of live liquid nitrogen into air stream can also be thought about/discussed ; since the air Mol. Wt. must not get heavily disturbed (may seem novel idea; but worth trying).Some of the more learned/experienced colleagues may guide us indeed.
Regards
Qalander