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Water Injection In Liquid Ammonia Line

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#1 Guest_talha_*

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Posted 12 April 2009 - 06:27 AM

Hi friends
i need some help in one problem.
We are producing ammonia with following specifications
NH3 = 99.9 %wt
moisture = 0.1 %wt
I need to increase the moisture content to meet the following specification
NH3 = 99.5 %wt
moisture = 0.5 %wt
In order to increase the water content we have proposed to inject the demin water in the main liquid ammonia transfer line through dosing pump.
The temp of liquid ammonia is -33 deg C and 8 kg/cm2
demin water is 35 deg C and 8.5 kg/cm2
following are the concern with reference to above proposal
during injection of water in liquid ammonia line is there any chance of water freezing,
is this proposal is correct interm of safety wise,
any reference of using similiar kind of scheme at other site
addition of water will increase the temperature of ammonia due to sensible heat and heat of absorption
what will impact on refrigeration load?

thank you

#2 Guest_emathis_*

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Posted 26 May 2009 - 11:12 AM

I suggest you try using nominal 20% aqueous ammonia to adjust your product spec. If you check the freezing point I think you will find it will not freeze at your temperature. Since the major heat effect can be handled in the make-up tank, you will have minimal effect on you refrigeration system. The calculation/control is a little more complex, but that's why they pay you the big bucks.



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Posted 22 July 2009 - 10:06 PM

Dear friend

I agree with emathis. Using aqua ammonia is the right way. Commercially, aqua ammonia is produced by injecting ammonia into water but injecting water into ammonia is something I have never heard before. I am pretty sure the injection line will eventually get clogged with water ice since the temperature at the point of injection is very much lower that the freezing point of water. The freezing point of 20% aqua is about -35 oC at atmospheric pressure. At higher pressure, the freezing point is expected to be higher.

best regards



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Posted 22 July 2009 - 10:08 PM

Sorry. I meant to say that the freezing point is expected to be lower at a higher pressure...

#5 imran.idris


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Posted 22 April 2010 - 10:55 PM

Dear Talha, following are the answers to you queries
1) Yes there is a chance of freezing at the mixing point if you are using a mixing Tee, and it will only happen if demin water flow stops due to any reason.you can avoid icing by jacketing Demin water branch of the Tee with steam. Provide double block and bleed arrangement on demin line inlet to the Tee, with check valve installed in between. This scheme will not only prevent icing, in case it happens, steam jacketing will help in melting it.
2) If above measures are taken I assure u that u'll never face any safety hazard at all. use ss tubing / piping of smallest possible dia for demin service.
3)I am working on Ammonia Urea complex and we are also adding demin water to Ammonia to avoid stress corrosion cracking in our Ammonia storage vessel, but it is at a bit higher temperature of Ammonia (-15C).
4)Temperature of resulting Ammonia Water mixture will change from -33 C to -31.9 C even if demin water mixed at 100 C. So once again no significant impact on refrigeration load.
I hope this can help you in making a safe decision
Imran idris

Edited by imran.idris, 23 April 2010 - 02:02 AM.

#6 Francorius


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Posted 21 January 2011 - 09:45 AM

Can someone give me some information how the mechanics work by injecting H2O in liquid ammonia storage to prevent stress corrosion?
I dont have a clue whats the principle of preventing corrosion by injecting water.


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