2 replies to this topic

[smk18]

I am simulating a vacuum column in a refinery facility (a rating problem) in SimSci pro/II software. The column features are listed below.

• The column doesn't have a conventional overhead condenser+reflux system, (though a vacuum system is present that pulls the non-condensables and creates the vacuum).
• There are three product streams. Two of them are fed back into the column as both cold reflux (pump-arounds) and internal reflux (hot reflux) while one of them is fed to a side striipper (hence a vapour return) and also partly fed back as an internal reflux
• Stripping steam is provided so there's no reboiler in the column.
• The column has 5 sections of packings followed by the flash zone and a tray section for stripping.
• The data for packings and pressure profile are available.
• The assay data (TBP vs liquid vol%) for each of the product streams and the feed stream is available

When I tried to simulate this column, the error encountered is that "primary section refers to a non-existent stream"? What is the meaning of this error?

[smk18]

Hi all,

 

I also encounter one more error while using both Inside Out/Sure algorithm for distillation column. UNIT 31, 'T1' - WATER SUPERSATURATION DETECTED on 7 trays. Column solution is likely to be erroneous. Rerun using the SURE column with the FREEWATER (DECANT) option enabled." Even on re-running with SURE algorithm, the same error appears. How to mitigate this?

[PingPong]

Without a flow scheme that also indicates flowrates, (estimated) temperatures and pressures nobody understands what this system looks like and what the problem might be. Maybe you try to do something that is simply not possible.

 

Most likely you made input error(s), so check your input again and again until you find some. Let a coworker check it too.

 

Specify a liquid water outlet near the top of the column to get rid of any condensed water during the convergence process.

 

Specify estimated temperatures for each stage. They don't need to be accurate as long as they are high enough to avoid the supersaturation error.

Specify also flowrate estimates using your best thumb.

 

Maybe you specified way too much stripping steam. Reduce it until it runs without errors. Then update estimates and increase stripping steam a little. And again. And again, until you reach the right stripping steam quantity.