4 replies to this topic

[titim]

hi everyone, i would to simulate the entire CDU in one file (the real equipemnet in the real sizing) but i get some difficulties to do it, For exemple, if I have to simulate the preheat train with the preflash columnd the atmpheric column, which one i must start with ( i have all data to buid the simulation)

 Sould i start with the CDU column and go back to the preheat train or what?

some suggestions please

best regards.

[Bobby Strain]

It's usually best to start at the beginning. And I always use a simple heater and cooler for a heat exchanger. You will need lots of recycle convergence controls, so pick the right streams to tear. You can learn a lot by starting with pencil and paper to map your equipment. It seems that this approach takes a long time, but for the inexperienced, this approach will get you to a solution sooner. Unless, of course, one of your colleagues has a simulation close to what you need. You won't develop good skills with this method, but it will probably produce results sooner. So, whatever you choose you should have an outcome objective, including time required.

 

Good Luck!

Bobby

[Saml]

Never simulated a CDU, but ran many simulations of other processes.  My recommendation would be similar to Bobby's

- Start simple: i.e. use simple heater instead of two streams exchangers to begin and specify the columns in a way it is sure to give you a result (any result), like bottom rate and reboiler duty

- If you have recicle streams, tighten your flash convergence spec to max and pay attention to traces cuttoff. Accumulation of errors is usually a cause of non convergence.

- Then start to modify/add one thing a time. In many situations, you will find that changing one little thing causes the problem to never converge. Perhaps you added efficiencies to trays, or modified an spec, or added a recycle stream. If you modify more than one thing, you will never know what went wrong and will start touching many things like convergence algorithms, number of iterations, etc, etc... until your are lost.

- Always save a converged solution along the way, so you have a point to backtrack to.

[titim]

Hi, thank you alot for your very helpful and valuable advices.

 

 

[mhamdi khaled]

Titim,

 

firstly, you have to replace the preheat train with a simple heater because you don't have products ( naphtha, kerosene, ...) and after runing the simulation of the column return to the preheat train and you can put exchangers.

 

good luck.