A fixed tube sheet heat exchanger is the cheapest because of the ease of fabrication. This heat exchanger requires periodic cleaning, replacement of tubes etc. and inside of the tubes can be easily cleaned by mechanical means (by forcing wire brush or worm )and cleaning of the tubes from outside require removal of the tubes bundles from the heat exchanger, in addition to the above-cited difficulty many heat exchangers are provided with removable tubes bundles.
 |
Floating head type shell and tube heat exchanger |
So as to make removal of the tube bundles possible and to allow for considerable expansion of the tubes, a floating head exchanger is used. In this, exchanger tubes are fixed at both the ends of the floating and stationary tubes sheet. The stationary tubes sheet is clamped between shells.
The floating tubes sheet is clamped between the floating head and a clamp ring. The ring which is split in half to permit dismantling is placed at the back of the tube sheet shows the details of a split ring assembly. The floating tubes sheet is kept slightly smaller in diameter than the inside diameter of the shell so as to withdraw the entire tube bundle from channel end. The channel is provided with inlet and outlet connection for tubes side fluid. The shell is closed by shell cover or bonnet on a floating head side. Shell cover at the floating head end is larger than the other end so as to enable the tubes to be placed as near as possible to the edge of the fixed tube sheet. The tube sheet along with floating head is free to move and take the differential thermal expansion between the shell and the tubes bundle.
It is widely used in chemical industry and suitable for rigorous duties associated with high pressure and temperature and also with dirty fluids.
Types:
1. Internal floating head
a. With clamp ring
b. Without clamp ring
2. External floating head
Application:
1. Used as steam superheaters
2. Phase change units (Reboilers)
Advantages:
1. The tubes of the exchanger are removable for inspection and mechanical cleaning of the outside of the
tubes
2. It eliminates differential expansion problems