Blade system for a scraped surface heat exchanger

Abstract: A blade system for a scraped surface heat exchanger comprises a number of blade rows which each consists of a number of successively arranged blade scrapers (1) mounted in cut-outs (15) in the surface of a rotor (4) which is mounted in a heating/refrigerating chamber (20) in the heat exchanger and wherein the individual blade, at the edge closest to the inner wall (21) of the chamber (20) is provided with a knife edge (2) and at the edge facing the rotor (4) with a basis (3), said blades (1) being provided with flaps (8), which are bent in the direction towards the rotational axis of the rotor (4), elements (9) on the rotor (4) to form abutment for the flaps (8) and engagement members (10) for receiving the basis (3) of the blades so as to permit removal of the blades from the heat exchanger without simultaneously dismounting the rotor (4).

Description: The invention relates to a blade system for a scraped surface heat exchanger of the type described in the introductory part of claim 1. Scraped surface heat exchangers are particularly suitable for use in the foodstuff industry where they are used for refrigerating or heating fatty products, bakery products and dairy products, such as margarine emulsion and ice cream. Such heat exchanger comprises a cylindrical treatment chamber, a rotor arranged in said chamber and a number of blade rows comprising a number of successively arranged blade scrapers mounted on the rotor so as to make the blades scrape the inner surface of the chamber during operation. A refrigerant or a heating medium, e.g. ammonia, freon, glycol, hot water or steam is circulated on the outside of the treatment chamber and provides heat exchange by a conventional heat exchange process. The treated product is introduced under pressure at the one end of the heat exchanger and leaves the heat exchanger at its opposite end. The scraping of the product off the inner surface of the chamber during its passage through the heat exchanger thereby provides a considerably improved heat transmission. In known apparatuses the blade scrapers are designed with apertures and/or slits and are secured to the rotor by use of pins or screws or combinations thereof. The use of this securing method makes it necessary to remove the rotor from the treatment chamber during control or replacement of the blades. This is a time consuming operation and in view of the fact that the manufacturing process must be discontinued in the production line where the heat exchanger is arranged, the control and replacement of the blades are also associated with a considerable financial loss. Furthermore such screws or pins with corresponding apertures or slits in the blades create dead spots wherein minor amounts of treated product and dirt may accumulate with an ensuing risk of bacteria growth. GB published patent application No. 2,232,469 discloses such scraped surface heat exchanger wherein the blades are mounted on the rotor by use of hinge means. A similar heat exchanger is known from EP publication No. 400 700. In both cases it is necessary to remove the rotor from the treatment chamber to check or replace the scraper blades. US patent No. 3,385,354 describes, e.g. in fig. 4, a scraped surface heat exchanger wherein the scraper blades are arranged in a V-shaped cut-out and wherein pins arranged on the rotor pass through apertures or recesses in the blades. Thus, in case of this known heat exchanger, it is also impossible to replace or check the blades without initially removing the rotor from the treatment chamber. It is the object of the present invention to provide a blade system for a scraped surface heat exchager which blade system is so designed as to permit dismounting of the blades without removal of the rotor from the treatment chamber and simultaneously ensuring that the blades are secured in a correct position during rotation of the rotor and also during rotation in directions towards the usual operation direction. This object is obtained with a blade system which is characterized by the features disclosed in the characterizing part of claim 1. Thereby the blade system permits dismounting of the individual blade by use of a tool which may be introduced into the treatment chamber where it catches or engages with the individual blade for drawing out the latter, the blade and its securing flap being constructed integrally. Hereby control and optionally replacement may be carried out substantially faster than usual and the manufacturing losses are substantially reduced. By constructing the engagement member for the blade integrally with the rotor the formation of dead spots is avoided in connection with screw apertures in the rotor body and thus an improved standard of hygiene is obtained during operation of the heat exchanger. By imparting a substantially waved appearance to the edge which forms the basis of the blade, i.e. a design without sharp corners, the hygiene standard is further improved. Thus, the construction of blade and rotor so as to comprise elements which inhibit the radial and tangential movements of the blades relative to the rotor only requires seal able securing of each blade row at their ends. At the one end it may be in the form of a fixed abutment and at the end intended for removal of the blade, it may be a dismountable securing means mounted in connection with e.g. a rotor gudgeon. Further advantageous embodiments of the invention will appear from the subclaims. A particular embodiment of the invention will now be explained with reference to the non-limiting drawings, wherein: Figure 1 is a sectional view as seen in the longitudinal direction of a scraped surface heat exchanger mounted with a blade system according to the invention, Figure 2 is a cross sectional view through the scraped surface heat exchanger shown in Figure 1, Figures 3a and 3b are sideviews of the blade rows in their mounted and dismounted states, respectively, Figure 4 is a more detailed partially sectional view of a blade row and rotor according to the line A-A in fig. 3, Figure 5 is an axial sectional view illustrating a securing means for a blade row at the rotor bearing. Figure 1 shows a scraped surface heat exchanger comprising a static portion wherein an internal heat transmission pipe 21 delimits a treatment chamber 20. In a chamber 27 between the internal heat transmission pipe 21 and an external pipe 22 a heating medium/refrigerant is circulated which provides heat exchange by a usual heat exchange process. At its one end the treatment chamber 20 is provided with a supply opening 23 and at its opposite end with a discharge opening 24 through which a treated material may pass. In the chamber 20 a rotor 4 is mounted and on the rotor 4 a number of blade rows 1 are secured at bevels 26 (Fig. 2) on the outside of the rotor 4. The rotor 4 is provided with a shaft 25 which extends through the one end wall of the chamber for communication with a driving means, such as a not shown electromotor, and with an axially mounted pin 28 embedded in the opposite end wall of the chamber 20. Figure 2 is a sectional view through a scraped surface heat exchanger wherein two blade rows of the blade system according to the preferred embodiment are mounted. Figure 3a is a sideview of the blade system comprising a number of blade scrapers 1 mounted on the rotor 4, and Figure 3b shows the dismounted blade system. Figure 4 is a more detailed sectional sideview of a blade. At the edge which is closest to the inner surface of the heat transmission pipe 21, the individual blade is provided with a knife edge 2 and at the edge facing the rotor 4, with a basis 3. Herein between the individual blades may be provided with at least one recess 16 wherein a portion of the blade material extends in the form of a flap 8 which is bent in the direction towards the rotational axis of the rotor 4 (fig. 4). At the bevels 26 the rotor 4 is provided with protruding pins 9, on which the flaps 8 may abut. Moreover, the rotor is constructed with engagement members 10 for receiving the blade basis 3. During usual operation the rotor rotates in the direction indicated by the arrow, cf. Fig. 2, in such a manner that the engagement members 10 alone ensure that the blades are secured in a correct scraping position. In connection with e.g. cleaning, the rotor 4 may optionally be caused to rotate in the opposite direction and the flaps 8 will then abut on the adjacent sides of the pins 9 and ensure that the blades 1 are secured relative to the rotor 4. Thus, irrespective of the rotational direction of the rotor 4 radial and tangential securing of the blades relative to the rotor 4 is ensured. At their one end the blade rows are secured in an axial direction by use of a securing means 17,18, cf. Fig. 5. The securing means 17,18 may for example be mounted in connection with the rotor pin 28. The securing means 17,18 may be dismounted by use of a handle 14 and after removal of the end wall of the chamber 20, the blades 1 may be removed when the securing means has been dismounted. The securing means comprises arms 18 for securing the individual blade row which arms 18 are secured to a sleeve 19 which is displaceable on the rotor pin 28 and mounted in a bearing 29. For the sake of hygiene the basis 3 of the individual blade is of a substantially wave-shaped construction, cf. Figs. 3a and 3b, with wave crests 11, which in the mounted state abuts on the rotor 4, and wave troughs 12 which extend substantially parallel to the knife edge 2. In each blade row several blades 1 are successively arranged and where the individual blades abut on each other they are provided with U-shaped or arched recesses 13 to minimise the extent of dead spots and at the same time to facilitate cleaning of the apparatus. The engagement members 10 are so positioned (fig. 3a) that they abut on the blade basis 3 between wave crests 11. Thereby the formation of dead spots between the engagement members 10 and the blade, where bacteria growth may occur, is avoided. During operation of the surface scraped heat exchanger a foodstuff is introduced under pressure into the heat exchanger through the opening 23. During its passage through the chamber 20 the viscosity of the foodstuff changes due to changes in temperature and therefore, portions of the treated material will stick to the wall. This results in deterioriated heat transmission. When the rotor 4 with the blades 1 rotates in the direction indicated by the arrow as shown in Fig. 2, the blades 1 will scrape the food substance which sticks to the inside of the refrigerating/heating pipe thereby enhancing efficient heat transmission so as to allow refrigeration/heating of the foodstuff to be effected in a continuous heat exchange process. Following treatment the foodstuff leaves the heat exchanger through the opening 24 (Fig. 1). If the blades are to be checked or replaced due to e.g. wear, the dismounting is effected by removal of the securing means 17,18 whereupon a catching tool is caused to engage with a recess 16 in a blade and in the axial direction it draws it out of the rotor without removing the rotor as such from the apparatus. The mounting of the blades is effected by pushing them into position in the rotor (4) still without dismounting the latter. During cleaning the rotor may, as mentioned above, optionally be caused to rotate in the opposite direction. The blade basis 3 is thereby lifted off the bottom of the cut-out 15 of the engagement member 10 until the flap 8 abuts on the pin 9 and the cleaning is thus facilitated. Detergents are then conveniently introduced and removed through the openings 23,24 as are also used for the passage of the treated material through the heat exchanger. The present invention makes it possible to clean a heat exchanger efficiently in about 15 minutes whereas it has required as much as two hours in case of blades mounted by use of known securing means.

Claims: A blade system for a scraped surface heat exchanger said system comprising rotor (4) mounted in a treatment chamber (20) and a number of blade rows comprising a number of successively arranged blade scrapers (1) mounted on the rotor, and wherein each blade has a knife edge (2) at the longitudinal edge which is closest to the inner wall of the chamber (20), and which at the longitudinal edge facing the rotor (4) forms a basis (3), and wherein the rotor (4) is provided with means forming abutment for the blade, characterized in that in the region between the knife edge (2) and the basis (3) the individual blade (1) is designed with at least one flap (8) which is bent in a direction towards the rotational axis of the rotor (4), and that the rotor (4) is provided with protruding pin elements (9) which form abutment for the blade flaps (8) so that the blades (1) may be removed from the heat exchanger without initially dismounting the rotor (4). A blade system according to claim 1, characterized in that at its basis (3) the individual blade (1) is substatially wave-shaped forming wave crests and (11) and wave troughs (12). A blade system according to claims 1 or 2, characterized in that the means which form abutment for the blade comprise spaced-apart engagement members (10), wherein the mutual spacing of the engagement members (10) and the wave crests (11) is such that the engagement members (10) abut on the blade basis (3) between the two wave crests (11). A blade system according to claim 3, characterized in that the engagement members (10) form outwardly protruding elevations on the rotor (4) and is constructed with a substantially U-shaped cut-out (15). A blade system according to claim 1, characterized in that the blade flaps (8) are constituted of portions of the blade material in a recess (16) of the central portion of the individual blade (1), said flaps (8) extending into the recesses and being bent so as to form an angle with the remaining portion of the blade plane. A blade system according to claim 2, characterized in that the edge of the blade opposite the knife edge (2) is constructed with said wave crests (11) and said wave troughs (12) which run parallel with the knife edge (2). A blade system according to claims 1 through 6, characterized in that the individual blade (1) has a substantially U-shaped or arched recess (13) at its end. A blade system according to one or more of the preceding claims, characterized in that the blades (1) are secured in the longitudinal direction of the blade rotor by use of a securing means (17,18). A blade system according to claim 8, characterized in that the securing means (17,18) is mounted on a sleeve (19) around a rotor pin (28) and so designed that it may be removed without dismounting of the blade rotor thereby allowing the blades to be mounted and dismounted from the blade rotor.

Inventors: ZEUTHEN KLAS, ZEUTHEN, KLAS
Applicants: GERSTENBERG & AGGER AS, GERSTENBERG & AGGER A/S
Application year: 1993
Main classification: F28G3
IPC codes: F28F19