2 replies to this topic

[sunrisetofu]

Hello,

 

I'm an intern working in the oil and gas industry. I would like to build a model of the LPG recovery portion of our gas plant in unisim.

 

The LPG portion of our plant has 4 distillation towers, for recovering methane, ethane propane and butane. I've built the skeleton in unisim but I'm having trouble converging the columns.

 

Gas coming into the LPG recovery section is cooled via turbo expander to around -100 C. Any cooled liquid portion is seperated and pumped to the top of the fist column, the De-Meth column.  

 

The de-meth column is a packed bed with 4 sections, with a side reboiler that collects liquid from the bottom of the 2nd section from the top (warms the liquid from -43 to -11 C) , and an once-through kettle type reboiler that draws all the liquid from the column bottom chimney tray at -2 C and heat it up to 9 C, both the vapor and liquid portion are returned to the bottom of of the tower (below the -2 C chimney tray). Vapor leaving the top of the column goes into a accumulator vessel without any condensing, and is pumped to sales.

 

Do you guys have any idea as to the best approach to modelling such a column? Should I break this up into 4 distillation columns or combine it into one? what column specs should I set this at? Or would it be best if I somehow simplified it?

 

I'm still learning the ins and outs of modeling with unisim so i'll apologize now for any any stupid questions/mistakes  

 

Thanks!

 

 

 

[Bobby Strain]

It is 4 columns. If you have trouble converging a solution on the demethanizer, try changing the specification variables and/or values.
When it converges, then you can select the specifications you wish. This is one of the simplest exercises you will encounter. So work hard at it and don't be too timid to experiment.

 

Bobby

[Erwin APRIANDI]

Hi sunrisetofu,

 

As Bobby said, and also as you have said "our plant has 4 distillation towers" means you have to modelled 4 different column with different spec on the column variable.

Try to use the actual value from the operating record to be used for spec value in order to converged each column.

Further more try to use the same value for the column data (datasheet) as the actual data for the UNISIM or HYSYS input of the column.

 

UNISIM or HYSYS has also gives a sample file for Distilation Column in the sample case so you can start to learn from there on how to do it.