What is X-ID®?

 

• X-ID is an internally enhanced tube.
• Tube augmentation (passive or active) techniques are used to increase the heat transfer rate.
• The augmentation in an X-ID tube is achieved by helical ribs on the inside of the tube.
• Ribs modify the behavior of the fluid flow leading to heat transfer augmentation.

 

Why do we need tube-side enhancement?

 

• Four resistances to heat transfer.

From the flue gas in the tubes to the tube wall	91 %
Through the thickness of the tube wall	0.75 %
Fouling	6.25 %
From the tube wall to the water on the shell-side	2 %

• Overall heat transfer controlled by the tube side.
• Increasing the tube-side heat transfer significantly increases the overall heat transfer.

 

 

How does the X-ID tube work?

 

• In flow over a plate or in a pipe, the fluid boundary layer builds up with distance and provides increased resistance to heat transfer.


 

Developed View – Helical Ribs

 

• Rib height, pitch, profile, spacing, helix angle are all design parameters.

 

Increased steam space in X-ID boilers

 

	4-pass bare tube	2 pass X-ID
Tube count	232 x 2.5” o.d.	224 x 2.0” o.d.
Heating surface	2558	2126
Heating surface / BHP	5.12	4.25
Steam volume (ft3)	95.36	155.6
Boiler efficiency	82.4	81.2
Boiler pressure drop	6.0	2.5

 

X-ID Tubes in Firetube Boilers

Advantages of X-ID tubes

 

• Inside heat transfer rate 85% greater than bare tube.
• Increased boiler efficiency.
• Number of tubes in boiler can be reduced.
• X-ID boiler requires less space (smaller design size).
• Cost savings on larger boilers up to 20%.