4 replies to this topic

[invssse]

Dear Members,
 
I got a question at relief analysis for a Check Valve Failure Scenario.
 
Please see the sketch attached. The basic information is as follows.
 
* A liquid pump is used to send the product from a Surge Drum through a series Heat Exchangers and Furnace to A high pressure Vapor-Liquid operating Reactor. Two Check Valves are installed at the Pump Exit line.
 
* The Scenario is Check Valve Failure when high pressure vapor from reactor flow reversely through the heat exchangers, Furnace as well as Check Valves. The Vapor in the Reactor is about 400 DegC.

* The Rate Estimation of Reverse Flow is done.

The Question is,
* As the relieving flow goes through the HXs and Furnace in a REVERSE direction, how to estimate the duties in these heat exchangers and further to estimate the temperature of relieving flow?

Thank you in advance.

Invssse

Attached Files

•  Example_CheckValve Failure.jpg   20.3KB   2 downloads

[fallah]

Invssse,

 

Appears the process fluid goes through the tube side of the HXs; then if the flow rate of the fluid in the shell side is being unchanged, you have to evaluate the new duty of HXs as well as temperature of the outlet gas by a thermal study using the reverse flow rate and conditions of hot gas...

[invssse]

Hi Fallah

 

Thanks for the reply.

 

But the problem is that it is difficult to determine the U*A of HXs since at early design phase detailed config. of these HXs are still unknown.

 

The simplest way to do this would be to assume U*A of these HXs keep the same as the normal forward flow. but this is unlikely to be a reasonable assumption. 

 

Do you have further comments on this? thanks.

 

Regards,

Invssse

[fallah]

 

 

But the problem is that it is difficult to determine the U*A of HXs since at early design phase detailed config. of these HXs are still unknown.

 

The simplest way to do this would be to assume U*A of these HXs keep the same as the normal forward flow. but this is unlikely to be a reasonable assumption. 

 

Do you have further comments on this? thanks.

 

 

Invssse,

 

You are completely right and U*A of HXs in reverse flow can't be the same as the normal forward flow; but I think although using U*A of forward flow with liquid in tube side can't be reasonable it would be conservative comparing to the reverse flow with gas in tube side, then appears using U*A of forward flow just will result in a little bit over estimation in relieving temperature calculation...
 

[shan]

Just use 400 DegC because the possible reverse flow under the condition the pump is off and heat exchangers are all off too.  If you consider the pump is off but the heat exchangers are not off, you may use higher temperature of 400 DegC and the possible temperature (1000 DegC+?)from the fired heater.