[studentinuni]

Hi everyone,

I'm stuck with this question I came across in a past paper. (I'm studying chemical engineering in Strathclyde Uni - 2nd year)

The question is as follows:

Gaseous Ammonia and 22mol% aqueous nitric acid are fed to a reactor in stoichiometric proportions where they react completely to form aqueous ammonium nitrate:

NH₃ + HNO₃ > NH₄NO₃

The ammonium nitrate solution passes to an evaporator where water is removed. The solution leaving the evaporator is saturated at 70*C and passes to a cooler/crystalliser which produces anhydrous NH₄NO₃ crystals. Mother liquor at 20*C is recycled to the evaporator. The wet crystals, containing 10mol% mother liquor pass finally to a dryer.

For a Production rate of 1250kmols/day of Ammonium nitrate, find the mother liquor recycle rate.

Data:

Solubility of NH₄NO₃ in water (mol %)                     Temperature (*C)
30.2                                                                      20
52.9                                                                      70


Diagram of Process is attached.

I have tried various methods but i cant seem to get past the dryer stage (working backwords). I'm absolutely stumped and dont know what to do. Any hints or procedure to how to solve this problem will be greatly appreciated. Please help me out.

[studentinuni]

Can anyone help me please ? I have exam tomorrow and something of this sort is going to come up, so i want to learn how to do this problem.

Thanks.

[sudanese engineer]

dear
         i stuck in such like your problem
 pleas contact me
sudanese student

[eugenedakin]

Hello studentinuni,

Could you please provide the mathematics that you calculated? This way I can help you with the logic behind your calculations. This method of explanation usually helps you the best when preparing for exams.

I am looking forward to discussing this more.

Thank you,

Eugene

[studentinuni]

Hey,

I'm right now in London, it will be atleast a week before I can reply until i get back to glasgow. Ill upload all the working I done.

Thanks,

studentinuni

[eugenedakin]

Thanks studentinuni,

I am looking forward to it.

Enjoy your time in London!

Eugene

[skyish]

hi did anyone solve this question then? i met this problem

[Lukec]

Hint... once you solve how much solution you have to feed the crystalizer the problem is almost solved. You must know that 10% of the mother liquor (121,324kmol) leaves with the crystals and these 10% must be deductet from the recycling mother liqour. I got 2396,266kmol of recyle.

[Lukec]

F - Feed ; Xf = 0.529
L - mother liqour ; Xl = 0.302
W - dry crystals
P - product
R- Recyle

P=1250kmol/day
1) P= W + (W*0.1)*0.302
2) F = L + W
2) F*Xf = L*Xl + W
3) R = L - (P-W)/0.302

This is how i solved it.

please correct me if I'm wrong. Thanks