HEAT EXCHANGER WITH EXTERNALLY ENAMELLED BAYONET-TUBES

Abstract: A heat exchanger with a tube bundle constituted by externally enamelled bayonet-tubes (1) which are individually fixed to the tube plate (4) using a special system of sealing by pressing against a frusto-conical seat (13), and which comprises a single PTFE gasket (10) for the entire tube bundle.

Description: This invention relates to a new type of heat exchanger constituted by externally enamelled bayonet-tubes. More particularly, the invention relates to a type of heat exchanger in which the enamelled tubes are fixed individually to the tube plate by a new method which offers particular advantage in terms of seal effectiveness, efficiency and life of the equipment. Heat exchangers with an enamelled tube bundle are known, but these have several drawbacks, because of which they have found little application up to the present time. In particular, problems exist in fixing the tubes to the tube plate. This is because currently available enamelled heat exchangers are constructed with a tube plate which is enamelled or coated with attack-resistant materials such as PTFE, and to which the various bayonet-tubes are fixed using a sealing system which is of poor reliability. Fixed tube-bundle heat exchangers have also been constructed by welding the individual tubes to the metal plate and then enamelling both the tubes and the plate. For this type of heat exchanger, the enamelling is extremely difficult and is often defective, so that the equipment is subject to corrosion during its use with corrosive process liquids. In addition, both with the removable tube construction and, more particularly, with the welded tube construction, the pitch which has to be used between the various tubes in order to obtain a simple and reliable apparatus is so large as to make the exchanger poorly efficient and particularly costly. These drawbacks are obviated by the heat exchanger according to the present invention, which ensures a seal of high reliability, prevents the possibility of defects or cracks in the enamelling, and enables a reduced pitch to be used between the tubes to thus attain high heat transfer surfaces per unit of volume. In addition, as the tubes of the heat exchanger according to the invention are fixed individually, they can be rapidly replaced in the case of breakage. The heat exchanger with externally enamelled bayonet-tubes according to the present invention is characterised in that said tubes comprise, in proximity to the head, a suitably frusto-conically machined portion arranged to fit in a sealed manner into a corresponding seat provided in the inner tube plate, the seal being provided by a PTFE gasket kept elastic by a cup spring. These and further characteristics and advantages of the heat exchanger with enamelled bayonet-tubes according to the present invention will be more apparent from the detailed description given hereinafter with reference to the figures, which show a preferred embodiment of the invention and are given by way of non-limiting example. Figure 1 is a vertical section through a part of the heat exchanger, and Figure 2 is a cross-section corresponding to the section A-A of Figure 1. Referring to the reference letters and numerals shown in the figures, the heat exchanger is constituted by a series of enamelled tubes 1 which comprise a frusto-conical portion 1a in proximity to the head. At their upper end, the enamelled tubes 1 comprise a thread 14 for screwing the ring nut 8. Inside the enamelled tubes 1 and coaxial therewith there are located tubes 2, which are either welded to or expanded into the outer tube plate 3. The inner tube plate 4 comprises the seats 13 for the enamelled tubes, they being of frusto-conical termination but with a lesser taper than that of the frusto-conical portion 1a of the enamelled tubes 1. These seats internally house the steel cup springs 9, having a taper equal to that of the frusto-conical portion 1a of the tube and greater than that of the seat 13. The result is that the cup springs rest on their inner side completely against the frusto-conical portion 1a of the enamelled tube by way of the PTFE gasket 10, whereas on their outer side they rest only against the greater-diameter zone of the frusto-conical seat of the tube plate. On tightening the ring nut 8, the tube becomes fixed to the tube plate 4 to form a high-efficiency seal with a pressure on the gasket 10 which varies from the major base to the minor base of the cone frustum. The pressure on the gasket is maintained with time, and is ensured even if temperature changes occur, by virtue of the cup spring 9 which having a free end provides the necessary elasticity to the entire system. A single PTFE gasket 10 is provided to accomodate all the tubes, being cup-shaped in each position corresponding with a tube, and besides forming a seal element it covers the entire surface of the inner tube plate 4, so making its enalling superfluous. The ring nut 8 and thread 14 are protected from contact with the cooling or heating fluid by means of the backing plate 5, which seals against the upper end of the enamelled tube 1 by means of an O-ring 7. The backing plate 5 comprises channels 11 through which any leakages of cooling or heating fluid or of process fluid are conveyed to the outside through the outlet 12. A detector can be installed at the leakage outlet to sound an alarm in order to enable the plant to be shut down. Thus if the O-ring 7 or gasket 10 does not provide a perfect seal, the leakages are conveyed through the channel 11 to the outlet 12. The cooling or heating fluid is fed to the tube bundle through an inlet pipe (not shown) fitted to the head, enters the tubes 1, flows along their whole length through the interspace between said tubes 1 and the inner tubes 2, then rises again along the tubes 2 to leave them at the outer tube plate 3. The cooling or heating fluid can also circulate in the opposite direction. From the aforegoing description and the illustrated figures it is apparent that the heat exchanger according to the invention attains the proposed objects, and in particular enables effective seals to be obtained between the tubes, which are of reduced pitch.

Claims: 1. A heat exchanger with externally enamelled bayonet-tubes, characterised in that said tubes comprise, in proximity to the head, a frusto-conically machined portion arranged to fit in a sealed manner into a corresponding frusto-conical seat provided in the inner tube plate, the seal being provided by a PTFE gasket kept elastic by a cup spring. 2. A heat exchanger as claimed in claim 1, characterised in that said frusto-conical seat provided in the inner tube plate is of lesser taper than said frusto-conically machined portion of the tubes. 3. A heat exchanger as claimed in claim 1, characterised in that a single said PTFE gasket is provided for all the tubes, and is of cup shape in each position corresponding with a tube. 4. A heat exchanger as claimed in one or more of the preceding claims, characterised in that said PTFE gasket covers the entire inner surface of the inner tube plate, thus making its enamelling superfluous. 5. A heat exchanger as claimed in claim 1, characterised in that said cup spring, of steel construction, keeps the PTFE gasket constantly pressed against the frusto-conical abutment of the tube. 6. A heat exchanger as claimed in claim 1, characterised in that channels provided in a backing plate convey any leakages of cooling or heating fluid or of process fluid to the outside. 7. A heat exchanger as claimed in claims 1 to 6, as heretofore described and illustrated, and for the specified objects.

Inventors: ARTUSI, GIANNI
Applicants: TYCON SPA
Application year: 1986
Main classification: F28D7
IPC codes: F28F19, F28F9, F28D7