4 replies to this topic

[Steve Hall]

Client provided the attached "Heat Curve". It's for a slurry where propionaldehyde is being boiled off. The tank contains 50,000 lb of the slurry. Client wants to me to verify that the boil-off is completed within 11 hours. I can calculate the rate of heat transfer into the tank, but I do not understand why this tabular data provides me the information I need to know how fast propionaldehyde is boiled off. There's no composition data. I've asked Client repeatedly but all he will say is that the heat curve provides all of the information I need. Am I missing something? The latent heat values are particularly confusing - what do they mean?

 

Attached Files

•  Heat Curve.pdf   62.81KB   44 downloads

[Bobby Strain]

Steve,

   This is not quite a heat curve. It appears to be a series of flash calculations at various temperatures of whatever the starting material is. But it is most likely that the real operation is a batch operation where the vapor is continuously removed. So it then is a simple calculation, step-wise, to find the total heat from start to finish. The data is not quite accurate to represent the operation, but should be close enough. The client's process engineer doesn't quite understand how to simulate the batch operation which would give a Q-Temp curve. So, give them an Oklahoma guarantee.

 

Good luck,

Bobby

Edited by Bobby Strain, 08 July 2016 - 08:47 PM.

[DB Shah]

Dear Steve,

As Bobby suggested this will require step wise batch calculation. In your file steam jacket requirement is indicated, I understand that this is a steam jacketed vessel.

 

If it is steam jacketed tank, you may calculate as follow-

 

Break the calculation in 11 intervals of 1 hr each.

Ud =Assume Ud 

Area =With the vessel dimension, find out heat transfer available considering the liquid level  as height.

LMTD =For first step, use 260°F & 269.1°F for LMTD calculation.

 

Calculated Q from above

 

Mass evaporated =  Q/latent heat for first step ie 11.4 BTU/lb

 

IMPORTANT for next step is to reduce your liquid level in vessel as per the mass evaporated in the first step.

This will reduce Area for heat transfer.

Repeat step with next temperature set and next latent heat.

Continue till 11th hour.

 

Vary Ud to get all mass evaporated.

If the Ud for which the mass evaporates fully is reasonable, your calculation is OK, else heat transfer area is limiting.

 

This was done for one my vessel (1 M3 volume)and is working as desired. My Ud was @ 500 kcal/hr-m2-C. 

 

Attached Files

•  limpet coil.xlsx   30.08KB   37 downloads

[breizh]

Hi Steve ,

 

These resources may help you : http://www.chemicalp...tillation-time/

 

http://www.cheric.or....php?cmpid=1233

 

Breizh

Edited by breizh, 09 July 2016 - 09:18 AM.

[Steve Hall]

Thank you Breizh, DB, and Bobby. You gave me the information I needed to tackle the problem with confidence even though my source data lacked some expected details.