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Nh3 Vapor Formation While Filling Liquid Ammonia In Tank.

ammonia

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#1 Prashkrans

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Posted 01 June 2016 - 04:39 AM

Liquid ammonia is fed to a storage tank at the rate of 100833kg/hr at -33 deg C at 0.02 kg/cm2 G pressure.

How much is the vapor formed in kg/hour?

Specs for strorage tank.

 

Volume = 17145 m3

Storage Temp. = -33 deg C

Storage press. = 0.02 kg/cm2

No heat ingress.

All the feed is getting stored

a.Tank is closed

b. Vapours are taken out.

 

 



#2 Art Montemayor

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Posted 01 June 2016 - 08:47 AM

Prashkrans:

 

In accordance with our general Student Forum policy, I am not going to do your homework problem, but I will help you find and work out your own problem:

  • You know the feed of liquid ammonia going in: 100,833 kg/hr of Liquid ammonia;
  • You know the conditions of the feed: -33 deg C at 0.02 kg/cm2 G pressure;
  • You also know the conditions of the storage product: -33 deg C at 0.02 kg/cm2 G pressure;
  • You know that: there is No heat ingress;
  • You also know - from the conditions of the feed and the tank contents - that there is no expansion taking place.

One of the cardinal rules in all chemical engineering is: "when in doubt, immediately do a heat and mass balance".

 

If you do the heat and mass balance, you will quickly realize what the correct answer is.



#3 Prashkrans

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Posted 01 June 2016 - 11:25 PM

Thank you Art for your feed.

I had already tried the mass balance and enthalpy balance. I got my answer of vapour formation rate to be around 23 kg/h. But the answer given is different. That is why I wanted to know the correct answer as I think my method is correct or if any different method.

 

Thanks



#4 Art Montemayor

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Posted 02 June 2016 - 06:36 AM

If you already tried to work the problem, know the right answer and didn't get it, why haven't you submitted your calculations so our members can check them and help you by telling you where you did the wrong steps?

 

Do not be shy, embarrassed, or reluctant to submit your work for review and checking.  If you succeed in becoming an engineer you are going to have to do that all your working life - whether you like it or not.  How do you expect your peers to believe your results if you are not willing to submit them for review and checking?



#5 Pilesar

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Posted 02 June 2016 - 01:19 PM

I would approach this as a volume balance since the pressure is constant. Because the liquid feed and the storage tank are the same conditions, I would assume the ammonia is at the bubble point. Determine the volume rate of the feed. The same volume rate of ammonia vapor must be displaced. Calculate the mass rate of the ammonia displaced for the answer. (I do not particularly like the way the question is worded. No vapor is 'formed' from the liquid if there is no heat transfer and no pressure or temperature change. My approach is based on what I perceive to be the intent of the question.)



#6 Prashkrans

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Posted 03 June 2016 - 01:01 AM

I am sorry for posting the question incorrectly. Here is the correct question. 

Liquid ammonia is fed to a storage tank at the rate of 100833kg/hr at -33 deg C at 3.5 kg/cm2 G pressure.

How much is the vapor formed in kg/hour?

Specs for strorage tank.

 

Volume = 17145 m3

Storage Temp. = -33 deg C

Storage press. = 0.02 kg/cm2 forl liquid but can assume loss of 15mbar for vapour formation.

No heat ingress.

All the feed is getting stored

a.Tank is closed

b. Vapours are taken out.

 

 

I tried to solve it the following way.

Hl1=Hl2+Hv2.........................................(1)

hl1 = 50.55 kJ/kg at p = 3.5 kg/cm2 G

hl2 = 50.22 kJ/kg at p = 0.02 kg/cm2 G

hv2 = 1429.92 kJ/kg at p = (0.02-0.15mbar) kg/cm2 G

Assuming vapour formation rate to be x and solving equation (1), I get my answer of vapor formation rate to be 24.12 kg/hr.

 

Please let me know whether I am correct or not.

 

Thanks 


Edited by Prashkrans, 03 June 2016 - 02:14 AM.


#7 breizh

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Posted 03 June 2016 - 02:55 AM

Hi ,

To support your work you can use this calculator .

http://www.questcons...properties.html

 

Hope this helps

Breizh


Edited by breizh, 03 June 2016 - 07:06 AM.


#8 S.AHMAD

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Posted 03 June 2016 - 12:05 PM

Hi,

The information given is not detailed enough:

1. Is the tank pressure at 0.02 kg/cm2g is controlled by pressure control valve to flare or BOG compressor.

2. the pressure is the initial pressure of the tank? & the final pressure 3.5 kg/cm2g? & the tank initially full of ammonia vapor?

The above options give different answer.

 

Hope it helps

 

S ahmad


Edited by S.AHMAD, 03 June 2016 - 12:14 PM.


#9 Pilesar

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Posted 03 June 2016 - 12:07 PM

Prashkrans,

Your method deals with vaporization due to pressure drop as if the storage tank were not essential to the problem. I did not check your numbers, but you do not deal with the displaced vapor due to the incoming volume of liquid. Perhaps the professor expects you to include both contributors to the vapor vent rate.






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