Double tube safety heat exchanger – steam generator

[KevinNZ]

Does anyone have experience using double tube safety heat exchanger for a steam generator?

We have 'dirty' steam to feed a shell and tube boiler and make clean steam. The double tubes will be used provide a low pressure barrier fluid space between the two steam streams.

 

[SnTMan]

KevinNZ, I have designed double tube / double tubesheet units but for a diffrent service, single-phase fluid.

I see no problem with boiling / condensing service, but will say the Part UHX calculations are really fun (not).

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[EdStainless]

I have seen them in food service. You need high flow velocities in the intermediate fluid in order to keep heat transfer at a reasonable level.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[chicopee]

SnTMan, I would like to see a cross sectional sketch-- any suggestion as to whereabout?

 

[GenB]

The most common staam to steam is that of the double Tube-Sheet to avoid cross cosscontamination if either expanded side of the tubes leak. The double wall use the same principle. The draw back is that the heat exchange suffers considerably but is not that impossible to build. Gen.Blr

 

[SnTMan]

chicopee, do not have a sketch at hand, but a description....

Fixed tubesheet, TEMA NEN. Double tubes, double tubesheets. Disremember the fluids, but I believe tubeside was cooling water, both sides single phase liquids. 304 tubes & tubesheets, balance carbon steel as I recall. Space between tubes / tubesheets filled with glycol and was static, i.e., no flow. As I understood, the purpose was to prevent mixing of the process fluids in the event of a tube leak, either wall or tubesheet joint. The shellside was kinda like having one NEN inside another.

I don't do thermal design, only mechanical, so can't tell you much about that side of things. In general followed Part UHX where it applied and TEMA RCB 7.15 (Double Tubesheets) where it didn't.

Might have a sketch at home, I'll try to remember to look later.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[KevinNZ]

Chicopee

some pictures here

http://fluiddynamics.com.au/fail-safe-heat-exchangers/

 

[SnTMan]

Chicopee, a so-called "poop sheet". Tubes not shown.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[john ambrose]

Difficulties for large capacity steam generator
Higher probability of tube failure. Late detection of water leakage makes large
propagation of tube failure

Difficulties on production
Solutions
Modular type SG
Monolithic SG with higher reliable tubes

Solutions
Modular type SG
Monolithic SG with higher reliable tubes