17 replies to this topic

[CHEMSTRONG]

Dear Sir,

 

I have an urgent query regarding ASPEN PLUS now.

 

I have mixer with two inlet streams and one mixer outlet stream .

Stream no 1 is Hydrocarbon  Gas Mixture with know composition, P, and Flow 

Stream No 2 is Water with all known parameters

Stream no1 and stream no 2 are mixed together using mixer block in ASPEN PLUS and resultant stream no 3 is there

 

I know Stream no 3 Temp, pressure , Stream no2 is water, I know stream no 2 flow, T, P, Composition etc

For Stream no 1, I know Flow, Composition and P, but not Temperature.

 

How to get stream no1 temp using Design spec in ASPEN PLUS

 

I want to use Design spec to do this now.

 

If not Design spec, any other alternative method to do this ?

 

Regards,

CHEMSTRONG 

 

 

 

[latexman]

Can you attach the Aspen Plus file?  What version?

[CHEMSTRONG]

Dear Sir,

 

It is Version V11 only. I will share screenshot of flowsheet here for better understanding , can we do it using Design Spec? In ASPEN PLUS?

 

Regards,

CHEMSTRONG 

[CHEMSTRONG]

Dear Sir,

 

I will not able to share ASPEN PLUS file here as there is some error coming now.

But Please understand that I want to calculate inlet temp of stream no1 and i know all other streams parameters here. like T, P, Flow and Please advice me on this now.
 

[latexman]

No problem.  I suspect Aspen extension files cannot be uploaded.  Besides, I only have V10, so I could not open the file anyway.

 

I do not know Design Spec, sorry.

 

Can you reverse the problem and use FSplit?  I'm not an expert A+ user, but I'm no novice either.  On the surface, FSplit looks promising to me

[CHEMSTRONG]

Dear Sir,

 

Please advice if we can use any other method here. IT is very important for me right now.

 

Regards,

CHEMSTRONG 

[CHEMSTRONG]

I want to know about T1 Tempo of Stream no 1 when i know T2 temp and T3 Temp, T2 is Water and T3 is mixer outlet and T1 and T2 mix together , only unknown is T1 whihc is inlet stream temp.  IS there any method by which we can calculate back temp of T1 whihc is inlet stream now

[latexman]

I understand you need to "back calculate" temperature of stream 1.  That's why I suggested FSplit, which is the reverse of Mixer.  FSplit allows to split at the component level.  So, 100% of the water goes to stream 2 and everything else goes to stream 1, which should be the hydrocarbon gas mixture.  A+ will calculate temperature of stream 1 since it is an output from FSplit.

 

I know no other way, but maybe some other folks will help you.

[CHEMSTRONG]

Actually Sir, I want to calculate Inlet Stream Temp T1 when i know all other Parameters of other streams like T,P, Flow and Composition . Water 

[CHEMSTRONG]

How to use Fsplit here? As Fsplit is for Splitting the flow right ?

I tried with Fsplit but i have used two inlet streama and two outlets strea,ms but how to evaluate inlet temp using this blcok ?

[CHEMSTRONG]

Dear Sir(Latexman),

 

Can you please guide me in Fsplit use and configuration for solving this issue now? It is little bit urgent for me now

 

Regards,

CHEMSTRONG 

[CHEMSTRONG]

What is inlet of FSplit , outlet is stream no1 , strweam no 2 is water right and 

[latexman]

Inlet is your stream 3.  Only 1 stream.  You said stream 3 is fully specified.

 

Outlets are your streams 1 and 2.

[CHEMSTRONG]

Dear Sir,

 

Stream no 3 is fully specified and it outlet of mixer and stream no 2 is pure water with fully specified conditions and now, stream no 1 is also inlet to mixer along with stream no 2 , stream no 1 flow, P, comp are known but Temp is unknown and needs to be calculated .  

[latexman]

I understand the problem scope, but I cannot simplify my advice on FSplit any further.

 

It is just a simple heat and material balance.

[Pilesar]

latexman's explanation is good. AspenPlus is a calculation tool and the flowsheet does not have to look the same as a real-life PFD. You would input stream 3 to an FSplit unit and fully define output stream 2. Stream 1 would be whatever was left and you would find your answer about the temperature required.

 

If you want a Design Spec to solve the problem, below is an example input.

 

DESIGN-SPEC DS-1 

    DEFINE MIXTEMP STREAM-VAR STREAM=STRM3 SUBSTREAM=MIXED  &

        VARIABLE=TEMP UOM="F" 

    SPEC "MIXTEMP" TO "120" 

    TOL-SPEC ".1" 

    VARY STREAM-VAR STREAM=STRM1 SUBSTREAM=MIXED VARIABLE=TEMP  &

        UOM="F" 

    LIMITS "100" "200" 

[CHEMSTRONG]

Dear Sir,

 

Thanks.

 

With Design Spec, will it give exact answer even when process conditions are at its extremes?

[Pilesar]

The Design Spec unit works very similarly to the Goal Seek feature in Excel and applies mathematical algorithm to find a solution to the formulated problem. Design Spec looks for a solution within the Limits set by the user so make the Limits broad enough to include a feasible solution but narrow enough so that Design Spec does not get lost among the infinite numbers possible. Internally, Design Spec guesses a solution, evaluates the result and determines where it thinks a better guess would be. Then it makes a new guess and evaluates the result again. The process of guessing, evaluating, and changing the guess continues until the solution reached is close enough as defined by the tolerance (Tol-Spec) supplied by the user. In the example I provided, the solution attempt would stop when the last solution reached was within 0.1 F of the target. An answer found at the very limit boundary should be suspect and the limits adjusted until a solution is found within the constraints. 

Edited by Pilesar, 03 April 2022 - 06:47 AM.