4 replies to this topic

[Gian]

Hi! We were tasked to design a kettle reboiler using HTRI. I already entered the necessary values for a BKU reboiler. However, even if I already adjusted multiple times to correct the warning message, there were 2 runtime messages that continuously popped out.

 

Errors:

1. The bundle entrance and exit vibration analysis is not available for TEMA K shells. The entrance and exit areas cannot be accurately define with information available in the program, and the nozzle flow rates often do not accurately represent the flow across the bundle due to fluid circulation.

 

2. For the ketteles (TEMA K or C shells), Xist assumes that the vapor in the two-phase fee bypasses the bundle, flowing directly to the outlet nozzle. If this assumption is incorrect for your case, the shellside heat transfer coefficient calculated will be conservative and the internal recirculation rate will be incorrect.

 

What does these errors mean? And how can I resolve these?

[Pilesar]

Are you sure these are errors and not warnings given to you for information? If they are warnings, understand their meaning and move on.

[srfish]

What did you mean by "two-phase fee" ?

 

There is nothing you can change on your input to prevent these messages from being printed. They are information about the software Xist.

[Padmakar Katre]

Hi! We were tasked to design a kettle reboiler using HTRI. I already entered the necessary values for a BKU reboiler. However, even if I already adjusted multiple times to correct the warning message, there were 2 runtime messages that continuously popped out.

 

Errors:

1. The bundle entrance and exit vibration analysis is not available for TEMA K shells. The entrance and exit areas cannot be accurately define with information available in the program, and the nozzle flow rates often do not accurately represent the flow across the bundle due to fluid circulation.

 

2. For the ketteles (TEMA K or C shells), Xist assumes that the vapor in the two-phase fee bypasses the bundle, flowing directly to the outlet nozzle. If this assumption is incorrect for your case, the shellside heat transfer coefficient calculated will be conservative and the internal recirculation rate will be incorrect.

 

What does these errors mean? And how can I resolve these?

 

These are not errors but informative messages, the 1st one tells that vibrational analysis is not carried out for kettles due to the fact that there is unidirectional flow i.e. bottom to top and hence no tubes will get excited which happens where there is change in flow directions like in case of other shell types in which segmental baffles are employed. Kettle uses support baffles so all tubes are well supported at all baffle locations.

 

The second warning might have come if the inlet stream is not pure liquid but has some vapor in it. In actual if the inlet stream to kettle is two-phase, best practice is to put it with 45 deg angle and just above the bundle to avoid turbulence that might be there if it enters in liquid pool. In addition provide a deflector plate which would knock-down the liquid from two-phase for heat transfer and vapor will simply bypass the bundle. So change the inlet nozzle position, which is critical.
 

[srilakshmisathyanarayana]

Hi ,

 

We have to design a kettle type (TEMA-BKU) reboiler using HTRI. Though we checked all the process inputs we end up in getting the following message:

 

The calculated internal kettle circulation rate is same as the feed rate. Please check the reboiler geometry, Process conditions, and physical properties. If no problems are found with the input data, rerun the case as a TEMA X shell to check the performance. It appears that the kettle is operating as a cross flow exchanger and not a kettle reboiler.

 

How can we resolve the above ?