Admissibility and calculation of Interim Relief granted to the State ...
Calculation of Relief Load on Column
6
aniljani aniljani Junior Member Members 19 posts Posted 19 November 2009 - 03:22 AM Dear All, I have a splitter operating at top pr 1.05 Kg/cm2g, bottom 1.55 Kg/cm2g... Relieving pr of Ovhd PSV is 6.38 Kg/cm2g, My Reboiler heating medium is HP steam at 251 deg C. Normal btm op. temp is 234 deg C. But at relieving pres. (6.38 + 0.5 (col delta P))the bottom temp raises to 297 degC (is more 251 degC (where reboiler pinch at 251 Degc)). How to calculate Vapour rate from Reboiler where my feed to the column continues and my reboiler heating continues and btm, overhead and reflux pumps trips condition? Plz help.... Back to top #2 fallah
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Calculation of Relief Load on Column
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aniljani
aniljani
Junior Member
Members
19 posts
Posted 19 November 2009 - 03:22 AM
Dear All,
I have a splitter operating at top pr 1.05 Kg/cm2g, bottom 1.55 Kg/cm2g... Relieving pr of Ovhd PSV is 6.38 Kg/cm2g,
My Reboiler heating medium is HP steam at 251 deg C. Normal btm op. temp is 234 deg C. But at relieving pres. (6.38 + 0.5 (col delta P))the bottom temp raises to 297 degC (is more 251 degC (where reboiler pinch at 251 Degc)).
How to calculate Vapour rate from Reboiler where my feed to the column continues and my reboiler heating continues and btm, overhead and reflux pumps trips condition? Plz help....
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#2 fallah
fallah
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Posted 19 November 2009 - 05:59 AM
'aniljani', on 19 Nov 2009 - 01:32 AM, said:
How to calculate Vapour rate from Reboiler where my feed to the column continues and my reboiler heating continues and btm, overhead and reflux pumps trips condition? Plz help....
All above pumps trip simultaneously?Do you mean the scenario is plant power failure?
Edited by fallah, 19 November 2009 - 06:17 AM.
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#3 CMA010
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Posted 19 November 2009 - 12:00 PM
'aniljani', on 19 Nov 2009 - 01:32 AM, said:
Dear All,
I have a splitter operating at top pr 1.05 Kg/cm2g, bottom 1.55 Kg/cm2g... Relieving pr of Ovhd PSV is 6.38 Kg/cm2g,
My Reboiler heating medium is HP steam at 251 deg C. Normal btm op. temp is 234 deg C. But at relieving pres. (6.38 + 0.5 (col delta P))the bottom temp raises to 297 degC (is more 251 degC (where reboiler pinch at 251 Degc)).
How to calculate Vapour rate from Reboiler where my feed to the column continues and my reboiler heating continues and btm, overhead and reflux pumps trips condition? Plz help....
How would you have vapour generation in your reboiler when the temperature on the hot side (MP steam) is 251 °C and the temperature on the cold side (column bottoms) is 297 °C at relief conditions? The 297 °C would never be reached, the heat input would stop when the temperature in the bottom of the column reaches 251 °C. What kind of configuration do you have, once through or circulating?
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#4 S.AHMAD
S.AHMAD
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Posted 11 December 2009 - 03:49 AM
'aniljani', on 19 Nov 2009 - 01:32 AM, said:
Dear All,
I have a splitter operating at top pr 1.05 Kg/cm2g, bottom 1.55 Kg/cm2g... Relieving pr of Ovhd PSV is 6.38 Kg/cm2g,
My Reboiler heating medium is HP steam at 251 deg C. Normal btm op. temp is 234 deg C. But at relieving pres. (6.38 + 0.5 (col delta P))the bottom temp raises to 297 degC (is more 251 degC (where reboiler pinch at 251 Degc)).
How to calculate Vapour rate from Reboiler where my feed to the column continues and my reboiler heating continues and btm, overhead and reflux pumps trips condition? Plz help....
Dear friend
Under this situation there is no heat transfer at the reboiler.
If the feed continues, bur bottom pump stop you should worry more about liquid overfill. So, if this is a credible scenario, then you should size the PSV for liquid overfill and/or install ESV at the feed line to stop flow that prevent liquid overfill.
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#5 NATU
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Posted 27 December 2009 - 08:39 AM
Dear friend,
I agreed with S. Ahemed. Have you checked bubble point of feed stream at relief pressure? In your case there might be possibility that the bubble point of feed stream at relief pressure is greater than that of reboiler hot side HP steam temperature. If it is less you can do one thing whatever the reboiler vapor you will get at relief pressure mix that with feed stream (feed at relief pressure and normal operting temperature) that will be the relieving rate.
Calculation of reboiler vapor rate: You can easily calculate it by using Hysis
Calculate the pinch out duty of the reboiler based on the 'clean UA'(conservatively) of Reboiler and the normal HP steam flowrate at normal operating conditions. Fed the reboiler cold side inlet stream with normal flowrate (at relief pressure and bubble point temperature) and hot side HP steam at normal operating condition to the reboiler. Apply "UA" Of the reboiler. you will get the pinch out duty of the reboiler. Fed reboiler outlet stream to the flash drum. Overhead vapor from the flash drum will be the reboiler vapor rate at relief.
Kind Regards,Natu
