3 replies to this topic

[tomr91]

I was given a static simulation of an atmospheric distillation column in Petrosim that converges for a specific crude oil composition. The outbound streams' flow rates are configured using specifications. When changing to a different crude oil composition, the model stops converge. How do I find the necessary adjustment to the specifications to make the model converge again?

[breizh]

Hi,

I don't see other solution than trials and errors tests.

You should start to perform a sensitivity analysis of the model you have on hands to see how variation of composition is affecting the convergence.

It's a matter of time !

Good luck

Breizh 

[Pilesar]

The product streams of the column should be specified according to their composition, not according to their flow rates. Typically, you spec the product temperatures at the 5% point. It is essential to characterize the feed properly. There must be enough pseudo components to allow separation between side products. Think of each section of the column between products as its own distillation which requires separation between light and heavy components. If there are not enough distributed components in that section, then the model will not converge. Crude columns require some training and will be difficult for you if you know nothing about how the models work. Blind trial and error will be extremely frustrating for you.

[PingPong]

I was given a static simulation of an atmospheric distillation column in Petrosim that converges for a specific crude oil composition. The outbound streams' flow rates are configured using specifications. When changing to a different crude oil composition, the model stops converge. How do I find the necessary adjustment to the specifications to make the model converge again?

 

Try following procedure:

(1) Make a TBP graph of the "old" crude. Plotting the "old" product quantities will give you the TBP cutpoints of these products.

 

(2) Then make a TBP graph of the "new" crude and, using the TBP cutpoints from step (1) above, determine the "new" product quantities.

 

(3) When you have a converged solution based on those new product quantities you should verify whether the product properties (such as flash point, 5% ASTM, 95% ASTM, specific gravity, viscosity, cetane index, et cetera) meet the specifications. If not then make small changes to the specified product quantities to adjust the product properties towards the specifications.