9 replies to this topic

[shakila21]

Hi everybody

  I need to design internal coils for an ammonia storage tank with the capacity of 50 m^3. In side this tank liquid Ammonia should be kept at the temperature of 22 C.

I was wondering if anyone help me out to find the number and spesification of the coils. In fact I do not know how to start and what to do.

 

thanks

[Art Montemayor]

 

Shakila:

 

You haven’t told us the scope of work of your assignment, so I can’t comment on why you would cool an ammonia storage tank by installing a cooling coil.  A practical engineer would not cool an ammonia storage tank that way at all.

 

The engineer would look for the practical, simplest, and safest, and most direct way to do it and that way would entail using the natural, inherent properties of the fluid (ammonia) to the utmost advantage.  The place to start is in the Mollier Diagram or thermodynamic properties table for ammonia.  Here, you will find that the critical properties of ammonia (132.3 ^oC & 113.3 bara) allow you to have a saturated equilibrium existing between liquid and vapor ammonia at ambient temperatures.  Therefore, what is conventionally done is to install a single-stage, small compressor to compress excess ammonia vapors and pass them on to a water-cooled or air-cooled aftercooler where the compressed ammonia vapor is condensed to the saturated liquid state.  This saturated liquid is subsequently allowed to flow back to the storage tank where the original vapors originated.  This method can be automated to stop and start very easily as the pressure in the storage tank increases, indicating the build-up of excess vapor.

 

No internal coil using an external refrigerant and subject to corrosion and contamination of the stored ammonia is used.

 

[shakila21]

Dear Art Montemayor,

Thank you very much for your quick and perfect reply.

I am working(as a beginner) in a company in the field of pharma equipment. This is a project to design and build a storage tank for liquid Ammonia in order to use in pharma industry. As I saw the thermodynamic properties of Ammonia here  http://thermofluids....atAmmonia.html, Ammonia in our design pressure( 1 bar) is vapor and as you said definitly it needs compressor to keep it liquid.

again I appreciate your kind reply.

 

shakila

[gegio1960]

shakila,

it's not very clear what you're asking for....

Anyway, (pure) ammonia storage (for large quantities) is usually at atmospheric pressure; the equilibrium temperature is -33°C.

You'll have a little part of NH3 evaporating: the quantity is depending on external temperature, Of course the tank shall be well insulated!

These vapors are recovered, compressed, condensed and returned to the tank thru a refrigeration package.

The alternative is a pressurized storage, that could be more adequate to the volume you're mentioning (50 m3).

The storage pressure should be high enough to avoid vaporization at the max external temperature, the so called black body temperature.

The case you're mentioning is something in the between but not well assessed and, according to Art, not used in the normal practice.

Regards

[shakila21]

Dear gegio1960,

  Thanks a lot for your kind reply.

I have read the data sheet again. The storage ammonia is not pure but it is ammonia water.

The desired ammonia is ammonia water(20%) with the density of 125 G/L at the design pressure 1 atm(almost 1bar). we need to keep the mentioned ammonia water in a storage tank with the capacity of 50m^3 at the temperature of around 18-22C.

As I asked it they need just a storage tank(without compressor or the other device). Now I don know if there is any possibility to use a jacket of coil on this vessel in order to avoid ammonia water from vaporizing.

I would be grateful if you give me a tip to design this storage tank.

thanks

shakila

[jrtailor09]

Dear Shakila,

 

Please find attached calculation for the steam coil sizing considering the pure ammonia.

 

I request you to follow similiar process for your calculation. Please change fluid steam to chilled water or brine whatever you are useing.

 

I hope you will find it useful.

 

Regards,

Jatin Tailor

 

 

Attached Files

•  Steam coil For amonia.pdf   75.35KB   76 downloads

[latexman]

Shakila,

 

Before designing, one must know exactly which raw material is involved.  As a beginner, be patient until you research and know the raw material.  Aqueous ammonia and andydrous ammonia are easily confused because they share the same chemical, NH3.  They share some similarities, but they are also very different.  In fact, since you confused some of those who posted above, their advice is suspect!  I should know, I've been involved with aqueous and anhydrous ammonia for many years.  IMO, the optimum solution to your design with aqueous ammonia 20 wt. % at 20 C will not involve a compressor to compress vapors so they can be condensed.  You might use a compressor to offload tank trucks though.

 

It will be your job from this point on to use the correct and thorough terminology to prevent this confusion from spreading!

 

An excellent resource for you to know is http://www.rmtech.net/  Notice as you drill down into that website there is information from a couple suppliers on storage and handling of aqueous ammonia that can help you.  There is other information on the internet on aqueous ammonia besides this.  Remember, Google is your friend.

Edited by latexman, 07 April 2013 - 08:27 AM.

[Art Montemayor]

Latex, thank you for bringing this topic back down to earth.  I hope Shakila takes your valued recommendations to heart and follows through.

 

This is just another continuing example of very bad communication skills on the part of Chemical Engineering students who don't understand the importance accurate and specific communications play in industry and why it is vitally important that they place high priority on practicing that skill.

[shakila21]

Dear Jatin Tailor

 Thank you very much for your kind reply and sorry for delay to answer you.

I will study your file and try to use it in the related projects.

Thanks a lot to spend time to attach this file for me.

 

 

 

Dear Latexman

   Thanks a lot for your kind reply and I really appreciate your tip. actually I was searching in google about pure ammonia... after I read the Art Motemayor answer, I told my colleague about compressor and other details which Art Motemayor recommended. Then he gave me the data sheet so I realized the raw material is not pure ammonia but ammonia water 20%. it was not my fault.I had just been told to search about ammonia storage tank and using internal coil...anyway thanks again for your great advise and also for introducing the mentioned source.

 

 

Dear Art Motemayor

  again I appreciate your answer. according to what you said in the first answer and comparing the price of the contract we realized that something is going wrong and there should be a mistake... so we ended in finding the mistake in the type of material which is going to be used in this Tank...all in all now we are going to use a jacket for this storage tank...

 

 

I wanna thank every body to help me in this topic. as I told I am a beginner. my field of study is M.Sc in Mechanical engineering and I have no job experience in industrial field. I am glad to find this useful site and I hope one day I could be a good designer as all of you.

I am really grateful of all of you for spending time to answer my question. and sorry if my English is not good enough to say what I exactly mean.

 

 

kind regards

shakila

[Art Montemayor]

Shakila:

 

As Latexman has so ably explained, it is vitally important to establish detailed and accurate basic data very early on any project.  This avoids wasted time, bad reputations, and more importantly hazardous and dangerous accidents.

 

We, as professionals, have all learned this one way or another:  the unfortunate amongst us has learned it through their own mistakes; the more fortunate ones have learned this same lesson through the mistakes of others.  But the important thing is: we all have learned.