ergent help required: concentrated nitric acid plant (aspen)

[arad]

my project is simulating a distillation column of nitric acid in present of sulfuric acid. i used aspen plus but have some problems and the answers seem wrong.
1-for physical properties method, i used electnrtl. but i doubted it's right or wrong.
2-this system (nitric acid-water) has a azeotrope but in existence of sulfuric acid it's vanished. i don't know how to draw a XY curve for nitric acid with different concentration of sulfuric acid. (sulfuric acid effect on xy nitric acid curve).
3-when i run my simulation it sometimes converges but sometime not without changing any parameters. does anybody know why this happens? and is it something commonplace?

[sniperel]

The column exist or you have to design a new one?

If your column exist in reality, then you should take plant data from the existing column and talk to the plant operators, they will give you important informations. If you build one new, try to search data from an existing one, you will see then if the data from your simulator is matching the real life data.

Good luck!

[superandy]

Dear friend ARAD,

first of all you must be more specific about your problem.

For strong mineral acid Electr-NRTL property method is the good choice.

I guess you have to concetrate a diluite HNO3 solution (about 60% w/w/) to 99%, using H2SO4 (96 - 98% w/w).

Are you using live steam injection (superheated steam at 300°C) at the bottom of your column? Or reboiler plus steam injection?

Normally for each kg of diluite nitric acid solution you must use 4 - 5 kg of concentrated sulfuric acid at the top of your column, operating near atmosferic pressure.

Let me know.

If you have your Aspen Plus file send me it, in order I can review your assumptions.

Regards
Superandy

[arad]

hi dear superandy
thank you for ur post and ur help
i'm using a open steam column, the diluite nitric acid is about 97% with 50% tray efficiencies.
some times without any change it reports an error (mass balance is't converge), i think i should increase iteration number (default iteration number is 25) but i dont know how.
would you mind sending me ur Email adress to send u my file?

[arad]

hi sniperel
thanks for ur help
yes the column is exist and i have it's information but the column in to old and it's efficiencies is low.
first i want to simulate the column then optimize it for better performance.