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Heat Exchanger Relief Valve


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#1 farid.k

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Posted 25 January 2015 - 08:47 PM

Hye guys

 

Looking for opinion regarding the relief gas at the heat exchanger.

 

There is a relief valve to protect the heat exchanger and the governing case is thermal expansion (as mention in the P&ID). Currently the heat exchanger size need to be increased since the service flowrate has been increased. The cold side (shell side) flow rate need to be increased and also the hot side. My question, do we need to re-study the governing case of the relief valve? I think it should be the same (thermal expansion case) since we just increase the size of the heat exchanger. The system remain same. Or is it possible to change from thermal expansion to fire case or something?



#2 fallah

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Posted 26 January 2015 - 02:21 AM

farid.k,

 

Lack of adequate info (all credible scenarios, specifying high pressure side,...) and the sketch of the system...

 

Anyway, considering the relief load due to thermal expansion is so low (normally a TSV of 3/4" * 1" is adequate), if the governing case would be thermal expansion appears it would be the only credible scenario. Then, if so exchanger size increment wouldn't affect the governing case and also the relevant relief load, but it should be evaluated carefully after provision of mentioned required information...



#3 Ajay S. Satpute

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Posted 26 January 2015 - 07:41 AM

Farid,

 

You might wish to use below link to calculate the relief load before and after heat exchanger upgrade. If the calculated relief load is less than existing TSV datasheet reported value, then no TSV resizing shall be needed.

http://www.cheresour...ise-calculator/

 

Regards.

 

Ajay S. Satpute



#4 farid.k

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Posted 26 January 2015 - 08:05 PM

farid.k,

 

Lack of adequate info (all credible scenarios, specifying high pressure side,...) and the sketch of the system...

 

Anyway, considering the relief load due to thermal expansion is so low (normally a TSV of 3/4" * 1" is adequate), if the governing case would be thermal expansion appears it would be the only credible scenario. Then, if so exchanger size increment wouldn't affect the governing case and also the relevant relief load, but it should be evaluated carefully after provision of mentioned required information...

Dear fallah,

The governing case stated in the P&ID is thermal expansion. Current PSV size is 25x25. No pressure relief device study has been done for other credible scenario. High pressure is at shell side (cold) which is operate at 8-8.5 barg. Low pressure side at tube side (hot) which is operate about 5-5.5 barg. Design pressure at shell and tube is same 14.8 barg.

 

Currently, we plan to increase size for the HE. I just afraid that by increase the HE, the current governing case change from thermal to others

 

Refer attachment for the simple sketch.

Attached Files



#5 farid.k

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Posted 26 January 2015 - 08:21 PM

Farid,

 

You might wish to use below link to calculate the relief load before and after heat exchanger upgrade. If the calculated relief load is less than existing TSV datasheet reported value, then no TSV resizing shall be needed.

http://www.cheresour...ise-calculator/

 

Regards.

 

Ajay S. Satpute

thanks ajay,

 

very impressive spreadsheet.

but i can't see and access the bottom part of the spreadsheet. and i think it should be applicable to thermal expansion at pipe only. for my case, the relief valve is at heat exchanger.



#6 Ajay S. Satpute

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Posted 26 January 2015 - 10:46 PM

Farid,

 

Try increasing your screen resolution (PFA).

 

Also please go through section 4.4.12.3 (Special Cases) of API 521, sixth edition, Jan. 2014. A part of this section is given below;

"

Two general applications for which thermal-relieving devices larger than a DN 20 × DN 25 (NPS 3/4 × NPS 1) valve can be required are long pipelines of large diameter in uninsulated, aboveground installations and large vessels or exchangers operating liquid-full. Long pipelines can be blocked in at or below ambient temperature; the effect of solar radiation raises the temperature at a calculable rate. If the total heat transfer rate and thermal expansion coefficient for the fluid are known, a required relieving rate can be calculated.

 

φ is the total heat transfer rate, expressed in watts;
NOTE For heat exchangers, this can be taken as the maximum exchanger duty during operation.

"

 

Regards.

 

Ajay S. Satpute

Attached Files



#7 colt16

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Posted 26 January 2015 - 11:59 PM

You definitely need to check the size of the relief valve because most likely you have increased the duty of the heat exchanger. 

 

as for whether fire case is relevant, check also the wetted surface area. there might be a possibility due to larger HX. 



#8 farid.k

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Posted 27 January 2015 - 01:21 AM

You definitely need to check the size of the relief valve because most likely you have increased the duty of the heat exchanger. 

 

as for whether fire case is relevant, check also the wetted surface area. there might be a possibility due to larger HX. 

dear tanykiat,

 

yes, the duty is increased, the flowrate for the cold site also increased. for me it still the same. if flowrate for the cold side remain same, and the duty increased, yes, make sense to re-check. are you agree with me?

Farid,

 

Try increasing your screen resolution (PFA).

 

Also please go through section 4.4.12.3 (Special Cases) of API 521, sixth edition, Jan. 2014. A part of this section is given below;

"

Two general applications for which thermal-relieving devices larger than a DN 20 × DN 25 (NPS 3/4 × NPS 1) valve can be required are long pipelines of large diameter in uninsulated, aboveground installations and large vessels or exchangers operating liquid-full. Long pipelines can be blocked in at or below ambient temperature; the effect of solar radiation raises the temperature at a calculable rate. If the total heat transfer rate and thermal expansion coefficient for the fluid are known, a required relieving rate can be calculated.

 

φ is the total heat transfer rate, expressed in watts;
NOTE For heat exchangers, this can be taken as the maximum exchanger duty during operation.

"

 

Regards.

 

Ajay S. Satpute

Ajay,

Thanks for the recommendations. Really appreciate it. I will check for that accordingly.

I tried but so upset. It didn’t work. Be default, the setting is at maximum.


Edited by farid.k, 27 January 2015 - 01:24 AM.


#9 fallah

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Posted 27 January 2015 - 06:18 AM

farid.k,

 

The governing scenario of a PSV isn't usually specified in relevant PID and specified in the PSV data sheet. Anyway, as I mentioned appears the only credible case for such PSV is thermal expansion. The fact from API 521 well mentioned by Ajay, is applicable for large heat exchangers; then if you is going to increase the size of the exchanger significantly you might recheck the adequacy of the PSV for new conditions using the method in mentioned API statement...


Edited by fallah, 27 January 2015 - 06:28 AM.


#10 farid.k

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Posted 28 January 2015 - 08:54 PM

Farid,

 

Try increasing your screen resolution (PFA).

 

Also please go through section 4.4.12.3 (Special Cases) of API 521, sixth edition, Jan. 2014. A part of this section is given below;

"

Two general applications for which thermal-relieving devices larger than a DN 20 × DN 25 (NPS 3/4 × NPS 1) valve can be required are long pipelines of large diameter in uninsulated, aboveground installations and large vessels or exchangers operating liquid-full. Long pipelines can be blocked in at or below ambient temperature; the effect of solar radiation raises the temperature at a calculable rate. If the total heat transfer rate and thermal expansion coefficient for the fluid are known, a required relieving rate can be calculated.

 

φ is the total heat transfer rate, expressed in watts;
NOTE For heat exchangers, this can be taken as the maximum exchanger duty during operation.

"

 

Regards.

 

Ajay S. Satpute

Dear ajay,

I don’t have API 521 6th edition. Is it valid for me to use previous version? I have 5th version 2007.

By referring to that version, clause 5.14.3 Special cases (page 32), I use equation 1.

  • For cubic expansion coefficient, I used the lightest one 0.00162 1/oC (worst case)
  • Relative density for my case is about 0.6
  • Specific heat capacity 2.78 kJ/kg-C. Converting to unit J/kg·K will be 10.1 J/kg·K
  • Total heat exchanged (watt), I have an issue for this value. Based on HE thermal study from local consultant, the value is quite small (320 watts). But when it comes to outside consultant, the value significantly change (390208 watt) and I don’t know which one is valid.

By calculating based on both condition,

 

Q (by using heat exchanged 320 watt) = 0.31 m3/h (184.6 kg/h). For this flow rate, existing relief valve is adequate.

 

Q (by using heat exchanged 390208 watt) = 375. 1744 m3/h (225104.7 kg/h). For this flow rate, existing relief valve is not adequate. By quick sizing using stated relieving rate, relief valve M size is needed and inlet outlet should be 4” x 6”. For me, this valve is too big for a heat exchanger.



#11 Ajay S. Satpute

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Posted 28 January 2015 - 10:51 PM

Farid,

 

Can you send the snapshot of both the calculations done (If you are using my TRV spreadsheet)?

 

Sp. heat capacity 2.78 kJ/kg.oC = 2780 J/kg.K. Please check if error in your calculations is due to wrong conversion of cp unit.

 

Regards.

 

Ajay S. Satpute



#12 farid.k

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Posted 29 January 2015 - 12:01 AM

Farid,

 

Can you send the snapshot of both the calculations done (If you are using my TRV spreadsheet)?

 

Sp. heat capacity 2.78 kJ/kg.oC = 2780 J/kg.K. Please check if error in your calculations is due to wrong conversion of cp unit.

 

Regards.

 

Ajay S. Satpute

Thanks ajay for being such a very helpful guy. And I am sorry for my stupid wrong conversion calculation. Kindly check the excel file for the calculation.

I did calculate using your spreadsheet, but too many parameter and the flowrate is mention negative. Kindly check.



#13 farid.k

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Posted 29 January 2015 - 12:02 AM

Farid,

 

Can you send the snapshot of both the calculations done (If you are using my TRV spreadsheet)?

 

Sp. heat capacity 2.78 kJ/kg.oC = 2780 J/kg.K. Please check if error in your calculations is due to wrong conversion of cp unit.

 

Regards.

 

Ajay S. Satpute

Thanks ajay for being such a very helpful guy. And I am sorry for my stupid wrong conversion calculation. Kindly check the excel file for the calculation.

I did calculate using your spreadsheet, but too many parameter and the flowrate is mention negative. Kindly check.

Attached Files



#14 breizh

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Posted 29 January 2015 - 12:32 AM

farid

 

Kj/Kg.F=Kj/Kg.C

 

 

Breizh



#15 Ajay S. Satpute

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Posted 29 January 2015 - 01:49 AM

Farid,

 

1. P1 is 14.8 barg and P_ref is 0 barg. G1 at P1 is 0.6, so when you decrease pressure from 14.8 barg to 0 barg (both at T1), G2 shall be less than G1. But you have mentioned G2 as 0.68. 

 

2. Similarly, if you heat the liquid, from 25 oC to 160 oC, the final sp. gr. (G3) shall be less than G1. But you have mentioned, G3 as 0.65.

 

3. I have assumed G2 = 0.55 and G3 = 0.54 and calculated again. PFA case 1 result.

 

4. As you have assumed alphaV = 0.00162 1/oC, then you could have entered "Yes" for "Is the value of "alphaV" available for the given liquid" question in "Userform1". Then you could see the result as per case 2. Here I have assumed G2 as 0.55.

 

5. Metal wall thk mentioned is 12.7 inch. Should it be 12.7 mm?

 

6. Is P1 (initial gage pressure of system) equal to 14.8 barg, which is equal to pipe/equipment design pressure?

 

Breizh: I think there is a typo in your post. Did you mean kJ/kg.K, instead of kJ/kg.F?

 

 

 

Regards.

 

Ajay S. Satpute

Attached Files



#16 farid.k

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Posted 29 January 2015 - 01:53 AM

Farid,

 

1. P1 is 14.8 barg and P_ref is 0 barg. G1 at P1 is 0.6, so when you decrease pressure from 14.8 barg to 0 barg (both at T1), G2 shall be less than G1. But you have mentioned G2 as 0.68. 

 

2. Similarly, if you heat the liquid, from 25 oC to 160 oC, the final sp. gr. (G3) shall be less than G1. But you have mentioned, G3 as 0.65.

 

3. I have assumed G2 = 0.55 and G3 = 0.54 and calculated again. PFA case 1 result.

 

4. As you have assumed alphaV = 0.00162 1/oC, then you could have entered "Yes" for "Is the value of "alphaV" available for the given liquid" question in "Userform1". Then you could see the result as per case 2. Here I have assumed G2 as 0.55.

 

5. Metal wall thk mentioned is 12.7 inch. Should it be 12.7 mm?

 

6. Is P1 (initial gage pressure of system) equal to 14.8 barg, which is equal to pipe/equipment design pressure?

 

Breizh: I think there is a typo in your post. Did you mean kJ/kg.K, instead of kJ/kg.F?

 

 

 

Regards.

 

Ajay S. Satpute

dear ajay,

 

can you kindly please re-send the zip file? i can't open it



#17 breizh

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Posted 29 January 2015 - 02:06 AM

Ajay ,

Of Course .......K

 

Breizh



#18 Ajay S. Satpute

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Posted 29 January 2015 - 02:08 AM

Try this.

Attached Files



#19 farid.k

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Posted 29 January 2015 - 02:24 AM

Try this.

thanks ajay!

i will go each parameter in detail and get back to you.



#20 farid.k

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Posted 01 February 2015 - 03:56 AM

Team,

 

Inlet of the heat exchanger (HE) is 100% liquid.

Outlet of HE is 70% vapor, and 30% liquid.

Thus I expecting that, during PSV pop-up, the fluid will be 2 phase.

 

Question: is it applicable to use equation as stated in the API 521 to estimate the thermal expansion relieving rate? I think it is only applicable for liquid. what say you?

 


Edited by farid.k, 01 February 2015 - 09:23 AM.


#21 Ajay S. Satpute

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Posted 02 February 2015 - 01:00 AM

Farid,

 

Please refer to below link;

http://www.chemwork....l_expansion.pdf

 

 

 

Regards.

 

Ajay S. Satpute



#22 farid.k

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Posted 02 February 2015 - 04:21 AM

Farid,

 

Please refer to below link;

http://www.chemwork....l_expansion.pdf

 

 

 

Regards.

 

Ajay S. Satpute

thanks ajay for the sharing






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