From last few days i am getting a request to post stress analysis methodology for vertical reboiler connected piping system. So accordingly this topic is taken up. The article being a bit lengthy it is published in three parts.
Vertical Reboilers plays a significant role in Process industry. Reboilers are a type of Heat exchangers which are used for heating the bottom fluid of industrial Distillation columns. Normally heat from steam (or any other high temperature fluid) is utilized to boil the liquid from the bottom of a Distillation column . Normally this heating effect generates vapor which are then returned back to the Column at a higher elevation to drive the distillation separation. The piping arrangement between column and reboiler for this action is normally very stiff and require careful Analysis to keep the column and Reboiler nozzle loadings within acceptable limit. The following article will provide the Stress analysis methodology of a vertical Reboiler connected piping system using software tool Caesar II , developed by Coade Inc.
Applicable codes and standards:
-ASME B 31.3-Process Piping,
-ASME Section VIII-Pressure Vessel design (Normally column and reboilers are manufactured based on this codes),
-WRC 107 and WRC 297- Sometimes it is required to qualify the Nozzle loads by using WRC modules if actual nozzle loads exceed the vendor allowable received.
Inputs required for analysis:
Before you start modeling of reboiler and column in Caesar II please be ready with at least the following documents:
1. Column general arrangement drawing
2. Reboiler general arrangement drawing
3. Process P&ID and Line list (Also known as line Designation Table or LDT) for the connected piping
4. Piping Material Specification or PMS
5. Equipment Nozzle allowable loads
6. Piping Isometrics , if any
7. Column and Reboiler allowable nozzle Loads (Should be taken from Equipment Vendor in case no standard Project specific load is not available)
Temperature Application Criteria during modeling in Caesar:
In absence of project specific guidelines, the Operating/ Design temperature of Column shall be considered same as the average of operating / design temperature of the column outlet piping attached on each draw-off nozzle
For Reboiler use the following information in absence of project specific guidelines:
• Tube side Inlet Temperature = bottom (outlet) Piping temperature of tower.
• Temperature of the tube = average temperature between tube inlet and outlet piping.
• Tube side outlet temperature = temperature of the tower inlet piping.
• If the temperature of Column inlet piping (channel outlet) is not known, consider the reboiler tube outlet temperature as mentioned in vendor drawing or confirm from process engineer.
• Shell side temperature = average of the Shell inlet (Normally Steam) and outlet piping (Normally Condensate).