1 reply to this topic

[jprocess]

Dear All,
As you know process simulators' solver can be categurised in 2 forms :sequential modular like ProII and Aspen+ in default mode and equation-oriented like hysys and Aspen+ in EO mode.
In sequential mode the solver solves material and energy balance equations module by module and in forward direction.So,in cases that exist recycle stream loop the user or software should select a tear stream and puts the recycle block there that is basically a mathematic algorithm like direct substitution,wegstein,newton and etc.
But in EO mode the solver solves all the equations simultanously for all blocks that user include them in pfd.So I think that there is not any necessity to use recycle block for example in hysys .I tried hysys cases files like Gas Sweetening process and deleted recycle block and solved it again and it converged very good .
I should be grateful if you would send me your valuable comments about it.

[abhi_agrawa]

Hi!
Really speaking, if you are using the EO approach, you would not need the recycle block in HYSYS. However, be cautious, While EO gives you an exact solution, it may take a lot of memory as it has to solve several equations. Also you require an initial guess to start solving in the EO mode. You may not see these problems when you are using HYSYS as it solves on the fly. However, when you use ASPEN in EO mode for solving, you need to have an initial estimate for the problem. SM on the other hand, does not require initial estimate (howver, a good initial estimate will increase the chances of convergence) and is also less computationally intensive than EO. However, when you use SM, convergence is not guarenteed.

-abhishek

Dear All,
As you know process simulators' solver can be categurised in 2 forms :sequential modular like ProII and Aspen+ in default mode and equation-oriented like hysys and Aspen+ in EO mode.
In sequential mode the solver solves material and energy balance equations module by module and in forward direction.So,in cases that exist recycle stream loop the user or software should select a tear stream and puts the recycle block there that is basically a mathematic algorithm like direct substitution,wegstein,newton and etc.
But in EO mode the solver solves all the equations simultanously for all blocks that user include them in pfd.So I think that there is not any necessity to use recycle block for example in hysys .I tried hysys cases files like Gas Sweetening process and deleted recycle block and solved it again and it converged very good .
I should be grateful if you would send me your valuable comments about it.