5 replies to this topic

[chem_buddy]

Hi All

 

I know that normally TSV size of 3/4" X 1" is sufficient in most of the thermal relief cases for liquid expansion.

 

However I would like to know how to calculate relieving temperature for Thermal expansion case when exchanger cold side blocked in.

 

Normally I have seen that Cold side fluid (normally CW) outlet temperature is considered as relief temperature. 

Is it ok to consider cold side outlet temp. as relief temp.

 

I think cubical expansion of coefficient should also be calculated on relief temp which can affect the relief load though TSV size will be same 3/4" X 1".

 

Your suggestions / opinion on this matter would be highly appreciated.

Edited by chem_buddy, 19 September 2014 - 02:57 AM.

[lokeshmiddha]

Max. Relief Temperature in case of thermal expansion is the maximum temperature it can attain when blocked in. for example when exchanger cold side (cooling water) blocked in, in that case relief temperature will be hot side inlet fluid temperature.

 

You can calculate relief load and TSV size at different relief temperature and check which is governing.

 

Please note that at Max. relief temperature and relief pressure if cold side fluid is vaporizing then PSV should be sized to handle that vapor generation.

[fallah]

Hi,

 

To estimate the relieving temperature in thermal expansion case you can use the equation (3) of API 521 for blocked-in liquid in a pipe and for a tube side exchanger it should be modeled as a pipe to be able to use such equation...

 

Anyway, even though it might be conservative, the temperature of hot side inlet temperature can be considered as relieving temperature for the case you described...

Edited by fallah, 19 September 2014 - 04:53 AM.

[Somnath Abhale]

Hi,

 

I agree with Fallah and lokeshmiddha.

 

if the cold side fluid bubble point temperature at relief pressure is greater than the hot side operating temperature, consider hot side inlet temperature as relieving temperature.

 

and if the cold side fluid bubble point temperature at relief pressure is less than the hot side operating temperature, consider the bubble point temperature of cold side fluid as relieving temperature. Note that for this case, relief device will be sized for cold side vaporization (i.e. for vapor service).

 

Also want to add one thing, a minimal orifice size relief device (i.e. ¾" x 1") will not be always sufficient for this case.

Edited by Somnath Abhale, 19 September 2014 - 06:43 AM.

[chem_buddy]

Thank you all for replying to this query. Just wanted to ask one more thing related with cubical expansion coefficient.

 

Suppose if the cold fluid is Cooling water, then cubical expansion coefficient shall be calculated on relieving temperature or it can be taken as 0.0001 (1/degF) @ 60 Deg F as given in API.  

 

According to my understanding, it should be taken at relieving temperature. However presently I am reviewing some calculation where it is taken as 0.0001 as per API irrespective of relieve temperature. Is it OK to consider value @ 60 Deg F.

 

I am asking this question because if I take expansion coefficient at relieving temperature then area will be higher than orifice letter D area in one the TSV I am checking now.

 

Please provide your valuable inputs on this matter.

 

Thanks 

Edited by chem_buddy, 03 October 2014 - 02:54 AM.

[Somnath Abhale]

Hi,

Consideration of API method is generally for petroleum and high dense fluid where density does not changes significantly with change in temperature. Still it can be used for cooling water but it Is not that much accurate.

 

Perry's handbook method (i.e. temperature bracketing method) is also available for the calculations of cubical expansion. Use of this method gives conservative and appropriate result as compare to API method    Try this method and consider hot side normal operating temperature as relieving temperature.

 

Also check for the pinch duty calculations for exchanger at relief condition during relief load calculations.

 

Regards,

Somnath

Edited by Somnath Abhale, 05 October 2014 - 02:21 AM.