The double tube sheet heat exchanger and the single tube sheet heat exchanger are compared from the aspects of structure, application and manufacturing. Compared with the single tube plate heat exchanger, the leakage probability between the tube side shell side of the double tube plate heat exchanger is much lower; the stress condition is better. From the structural point of view, the double tube sheet heat exchanger adopts a fixed tube sheet structure, and the tube bundle cannot be drawn out for cleaning. The actual use shows that the double tube sheet heat exchanger manufactured by the mechanical expansion method can meet the requirements of use.
Comparison of the structure of double tube sheet and single tube sheet heat exchanger
The double tube plate heat exchanger adopts a fixed tube plate structure, and the tube bundle cannot be drawn out for cleaning. The single tube plate heat exchanger can adopt various structural types, and the tube bundle can be drawn out for cleaning. For double-tube plate heat exchangers with large temperature difference, corrugated expansion joints can be added to the simplified version; in addition to single-plate plate heat exchangers, in addition to the corrugated expansion joints to the simplified version, floating heads or U-tube types are often used to compensate .
For the double tube sheet heat exchanger, there are two kinds of design concepts: one is that the double tube sheet heat exchanger is used to absolutely prevent the mixing of medium between the shell and tube side, and it is designed to be installed on the cavity between the inner and outer tube sheets The draining and pouring valve is used for daily observation and discharge when the inner tube sheet leaks, so that the medium on the shell side is effectively isolated by the inner and outer two-layer tube sheet. This is the main purpose of adopting the double tube sheet structure type.
Another is that the double tube sheet heat exchanger can be used in the occasion of a large pressure difference between the shell and tube side. It is designed to add a medium to the cavity between the inner and outer tube plates to reduce the pressure between the shell and tube side. difference. This is the same as the general single-tube plate heat exchanger, and it cannot be absolutely guaranteed that there will be no leakage at the nozzle of the outer tube plate.
Comparison of the use of double-tube plate and single-tube plate changer
Single tube plate heat exchangers are the most common. In addition to the frequent leakage of gasket bolt flange joint seals during use, there will also be nozzle leaks on the tube plate, and welding cracks. Most of the nozzle leaks on the tube sheet of the single tube sheet heat exchanger occur at the welding receiving arc. The gas was not put cleanly when receiving the arc, and there were blisters.
The double tube sheet heat exchanger has inner and outer double tube sheets. If the inner tube sheet orifice leaks, there is protection from the outer tube sheet.
Welding cracks of single-tube plate heat exchangers often occur at the junction of the simplified small flange of the heat exchanger and the simplified end of the cone. The main reason for the problems here is that one is the stress at the junction of the small end of the large flange cone and the simplified Chinese; the other is that the geometric size and shape are abrupt, and it is easy to bury defects.
Comparison of manufacturing
Generally, there are four types of connection between the heat exchange tube and the tube sheet, namely strength welding (common argon arc welding), strength expansion, strength welding + paste expansion, strength expansion + sealing welding, the difference is mainly reflected in whether the tube hole is Grooves and welding grooves and pipe extension lengths. Expansion joints can be divided into non-uniform expansion joints (mechanical ball expansion joints), uniform expansion joints (hydraulic expansion joints, fluid bag expansion joints, rubber expansion joints, explosion expansion joints, etc.).
The design of the double-tube plate heat exchanger requires strength welding + strength expansion, and the hydraulic expansion method is recommended. The general design requirements of single-tube plate heat exchangers are to use strength welding + paste expansion, mechanical expansion or manual expansion.
At present, most domestic manufacturers do not have hydraulic tube expansion equipment, even if there are, due to the high cost of hydraulic expansion head purchase and large losses (an average of more than 100 nozzles, you need to change a hydraulic expansion head). The hydraulic expansion head is used once and cannot be repaired.
Therefore, the hydraulic expansion method is rarely used to manufacture heat exchangers. These three double-tube plate heat exchangers are manufactured by the mechanical expansion method. After field installation, the pressure test and more than one year of use show that the double-tube plate heat exchangers can be manufactured by the mechanical expansion method.
As a more reliable heat exchanger structure than a single-tube plate heat exchanger, the double-tube plate heat exchanger can be better promoted and applied; but there is a primary premise that the quality of the double-tube plate heat exchanger is better, especially the heat exchange tube It is better to ensure that the wall of the heat exchange tube does not break during use.
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