13 replies to this topic

[farid.k]

Dear friends,

 

I just come across an existing design (existing steam piping) that supplied to existing heat exchanger. Steam piping is supplied to tube side of HE.

 

The question is: the existing facility will be demolished. Steam piping will be increased in size (form 2” to 4”). The HE also will be change to a new one (bigger one) in order to increase the capacity.

Shall I re-evaluate back the existing vacuum breaker that attached to the existing steam piping? I plan to re-use back the existing vacuum breaker. I never come across sizing for the vacuum breaker at pipe. This should be to protect the shell side of new HE I guess. Anyone can share opinion?

i think this vacuum breaker is to protect during the change of temperature from high temperature to ambient especially during turn around.

[curious_cat]

If steam is supplied to the tube side of the HEX why is there a need to "protect the shell side of new HE " from a vacuum & how will a breaker attached to the steam piping accomplish this?

[fallah]

Farid.k,

 

Would you please upload a simplified sketch of the HX system?

 

The VB might be put there to protect the shell in the case of tube rupture, as it might not allowed to put the VB on the shell (pressure vessel); please clarify...

[farid.k]

If steam is supplied to the tube side of the HEX why is there a need to "protect the shell side of new HE " from a vacuum & how will a breaker attached to the steam piping accomplish this?

sorry, to protect tube site

[farid.k]

Farid.k,

 

Would you please upload a simplified sketch of the HX system?

 

The VB might be put there to protect the shell in the case of tube rupture, as it might not allowed to put the VB on the shell (pressure vessel); please clarify...

refer attachment for the sketch. i just put the tube site piping, new HEX and vacuum breaker. hope the sketch can give clear picture of the location of the arrangement

Attached Files

•  Capture.PNG   42.66KB   4 downloads

[fallah]

farid.k,

 

Please specify the note 5 and also design pressures (and vacuum) of tube side/shell side...

[farid.k]

Nothing at note 5. It just specify vacuum breaker.. Shell side design pressure is 14barg and vacuum. For tube side is 14 barg only. Because of not having vacuum for tube side I pre assumed that existing vacuum breaker to protect the tube side. Just that, if we increase the steam flow, increase the heat exchanger size, does we need to check the vacuum breaker?

[fallah]

farid.k,

 

As I well investigated on your system, found that the VB on the tube side not only protect the tube side against full/partial vacuum but also allows the condensate return line being well drained in the case of steam supply interruption. Then, because VB nothing to do in normal operation, appears it doesn't need to be checked if the steam flow rate would be increased...

[farid.k]

farid.k,

As I well investigated on your system, found that the VB on the tube side not only protect the tube side against full/partial vacuum but also allows the condensate return line being well drained in the case of steam supply interruption. Then, because VB nothing to do in normal operation, appears it doesn't need to be checked if the steam flow rate would be increased...

Yes. I trust that nothing to do during normal operation. Is it common to other typical system that has steam that goes to HEX? How they specify the vacuum breaker? What if I don't put it? Do I need to specify design pressure for tube side 14 barg and full vacuum?

[fallah]

 

Yes. I trust that nothing to do during normal operation. Is it common to other typical system that has steam that goes to HEX?

 

It's not common; mostly applied to the elevated HX heated with steam or cooled by, say, sea water where return line goes downward...

 

How they specify the vacuum breaker?

 

Based on emptying rate of condensate at the moment of steam supply interruption...

 

What if I don't put it?

 

Vacuum in tube side and condensate couldn't be drained...

 

Do I need to specify design pressure for tube side 14 barg and full vacuum?

 

Yes...

 

 

[curious_cat]

Regarding protecting the tube side against a vacuum:

 

Are there typical tube dimensions that wouldn't be able to withstand a full vacuum? Or is the worry about the heads / bonnets collapsing under the vacuum?

[farid.k]

Yes. I trust that nothing to do during normal operation. Is it common to other typical system that has steam that goes to HEX?

It's not common; mostly applied to the elevated HX heated with steam or cooled by, say, sea water where return line goes downward...

How they specify the vacuum breaker?

Based on emptying rate of condensate at the moment of steam supply interruption...

What if I don't put it?

Vacuum in tube side and condensate couldn't be drained...

Do I need to specify design pressure for tube side 14 barg and full vacuum?

Yes...

Thanks so much for the response.
1 more thing is, at outlet of tube side which is condensate outlet, there is a steam trap before it goes to condensate collecting header. New steam flowrate is 540 kg/h and all expected to be converted to condensate (based on thermal sizing of HEX). I think I need to re-size the existing steam trap isn't? Because I trust that for existing HEX, the steam flowrate is much2 smaller than proposed new steam flowrate. Thus the existing condensate load would be small. I afraid that existing steam trap can't cater the new condensate load.
However it is very hard to check because normally plant don't have the steam trap datasheet that specify the design condensate load. What say you?

[fallah]

farid.k,

 

Because the steam trap type/data sheet isn't specified/available, i think so and you need to size and specify the supply/return lines of steam/condensate and all facilities along them such as steam trap based on new steam flow rate...

[chemsac2]

Farid K.,

Just out of curiosity, what is process outlet temperature for your system.

Vacuum is typically formed in steam exchangers when exchanger has flow control valve on steam cascaded to process temperature, operating under turndown, has high overdesign on area, has process outlet temperature is below 100 deg C etc.

Vacuum breaker might be to break that vacuum and enble transfer of condensate from the system.

Does your system have any of these characteristics?

If yes, I would be glad to know how vacuum breakers function in plant. In my present design, I am deliberating on ways to avoid or design for vacuum in exchangers. My concern with vacuum breakers is that air introduced in exchanger may lead to blanketing of tubes by inerts and reduction in heat transfer coefficient.

Any other inputs from experts would be great to have.

Regards,

Sachin

Edited by chemsac2, 19 April 2015 - 10:00 PM.