WO1998054530A1

WO1998054530A1 - Scraping heat exchanger

Info

Publication number: WO1998054530A1
Application number: PCT/NL1998/000299
Authority: WO
Inventors: Paulus Alfonsus Maria Keijser
Original assignee: Terlet N.V.
Priority date: 1997-05-29
Filing date: 1998-05-26
Publication date: 1998-12-03
Also published as: AU7790498A; NL1008309C2

Abstract

Scraping heat exchanger comprising a housing which is formed by a product-treatment cylinder (1), the walls of which can be cooled or heated and in which there is positioned a rotary shaft (18) provided with a drive (19), carriers (33) with scrapers (35) being attached to the rotary shaft (18), which carriers are able to interact with the internal surface of the product cylinder, and means being provided for feeding and discharging a heating or cooling medium to and from the outer surface of the product cylinder (1), and the product cylinder, which has a smooth inner wall, containing, at one of its ends, a product feed and, at its other end, a product discharge. The product cylinder (1) is formed by a seamless extruded pipe and the rotary shaft (18) is guided outwards to the external drive (19) only at one end of the product cylinder (1).

Description

Scraping heat exchanger

The invention relates to a scraping heat exchanger compri- sing a housing which is formed by a product-treatment cylinder, the wall of which can be cooled or heated and in which there is positioned a central rotary shaft provided with a drive, carriers with scrapers being attached to the rotary shaft, which carriers are able to interact with the internal surface of the product cylinder, and means being provided for feeding and discharging a heating or cooling medium to and from the outer surface of the product cylinder, and the product cylinder, which has a smooth inner wall, containing, preferably at one of its ends, a product feed and, preferably at its other end, a product discharge.

A heat exchanger of this kind is known from EP 0,271,459. Although this known device enables reasonable results to be achieved, investigations and experience have shown that there is room for improvement to the heat exchanger of this type. The outer surface of the product cylinder of the heat exchanger in accordance with EP-0,271,459 is formed entirely by successive grooves. Although these grooves have a positive effect on the heat transfer, they make production of the product cylinder considerably more expensive and more complicated. Furthermore, the product cylinder described in EP-0,271,459 consequently has a very irregular wall thickness, namely a wall thickness which differs considerably at the locations of the "peaks" and the "troughs" of the grooves. Partly as a result of the corresponding irregular strength of the cylinder wall, an irregular wall thickness of this nature will lead to undesirable stress concentrations, which may also entail unroundness of the inner surface of the product cylinder and consequently the action of the scraper members along the inner wall of the product cylinder can be adversely affected. Furthermore, the process which takes place in the product cylinder is more difficult to control as a result of the irregular, and in some cases relatively great, wall thickness. Another drawback of known heat exchangers of this type (cf . also NL 7809531) is that the starting point for producing the product cylinder is a flat stainless steel sheet, which is formed into a cylindrical pipe by rolling, after which the seam then has to be welded together. Since the inner surfa- ce of the pipe produced in this way has to be particularly smooth, owing to the high demands placed on the products to be treated, the weld seam then has to be smoothed away very carefully. It is also difficult to make the pipe produced by rolling entirely cylindrical.

The object of the invention is to provide an improved heat exchanger of the type mentioned in the preamble which eliminates the abovementioned drawbacks. The heat exchanger according to the invention is firstly characterized in that the product cylinder is formed by a seamless extruded pipe. A particularly simple and favourable embodiment of a heat exchanger with a product cylinder which is substantially formed preferably from metal, such as stainless steel, is characterized according to the invention in that the inner and outer surfaces of the product cylinder are formed by two concentric cylindrical surfaces, and in that the wall thickness of the product cylinder is constant over virtually its entire length and is for example 1 mm to 8 mm, but is preferably 3.0 mm to 7.0 mm. In this case, according to the invention the rotary shaft is guided outwards to the external drive only at one end of the product cylinder.

Advantageously, the product cylinder according to the invention is formed from austenitic or duplex stainless steel. According to the invention, the inner surface of the product cylinder may optionally be coated with a covering layer of polytetrafluoroethylene . This allows an even smoother surface and improved processing of the product to be treated to be obtained for specific applications, while cleaning the product cylinder is also easier.

An expedient embodiment of the heat exchanger is characterized according to the invention in that an outer cylinder is arranged around the product cylinder, the annular space between the product cylinder and the outer cylinder being connected to a feed and a discharge for the heating or cooling medium, and in that the cylinders are provided with a removable cover at the end which is remote from the external drive. In order to improve the heat transfer, according to the invention a helical guide member, which extends over the length of the cylinders, for the heating or cooling medium is arranged in the annular space between the product cylinder and outer cylinder.

A simple embodiment of the scraping heat exchanger is characterized according to the invention in that the rotary shaft is provided with a number of transverse arms which are placed at an angular interval of, for example, 90°, a rod extending parallel to the rotary shaft being removably attached to the outer ends of each transverse arm and a number of scraper members being removably attached to each of the rods which form a type of cage. In this case, the heat exchanger according to the invention is advantageously characterized in that the removable rods are each fixedly connected, preferably by means of a weld joint, to a bracket, which in the region of the cover of the product cylinder is removably attached to the rotary shaft and locked by means of a spring clip or key ring. The brackets form a handle for easy fitting and removal of the rods with scrapers and guarantee correct positioning of the scrapers and axial retention of the rods with the scrapers attached thereto. No tools are required for fitting and removal.

A more flexible attachment, with less risk of accumulation of product remainders, is obtained if the heat exchanger according to the invention is characterized in that the scraper members, preferably with a flat surface part, are attached to the cylindrical cage rods in such a manner that the contact between the scrapers and the cage rods is substantially formed by linear contact. An improved design is also obtained if the heat exchanger according to the invention is characterized in that the product cylinder and the outer cylinder are provided at each end with a flange, and in that the two cylinders are each welded, preferably by means of a butt weld, to annular rims which project out of the flange surface. This counteracts the initiation of cracks and results in a more favourable stress concentrati- on, so that the mechanical strength is increased. This design is also beneficial for reasons of corrosion.

A particularly simple embodiment of the heat exchanger according to the invention is characterized in that the rotary shaft is supported at the one end situated on the side of the external drive. In this case, according to the invention limiting means, such as for example three pins, which are positioned at a mutual angular interval of 120° around the end of the shaft and are preferably coated with polytetrafluoroethylene, may be arranged at the other free end of the rotary shaft .

A stable design of the heat exchanger according to the invention is characterized in that a first support disc is arranged against the support flange at the one end of the rotary shaft provided with a bearing, which support disc is provided, at the location where the rotary shaft passes through it, with a seal, and in that a second support disc, which is parallel to the first support disc, is arranged at a certain distance from and rigidly connected to the said first support disc, in such a manner that an accessible space is formed between the two plane-parallel support discs. In this case, according to the invention the bearing housing for the rotary shaft is attached to the second support disc, preferably on the outside thereof. According to the invention, the bearing housing is connected to a transmission which is coupled to the drive motor for the rotary shaft. According to the invention, the two plane- parallel support discs may be held at a distance of, for example, 200-300 mm by means of a number of support columns arranged between the said discs .

A particularly favourable embodiment of the heat exchanger according to the invention is characterized in that means for collecting and/or warning of leaking liquid, such as a collar which is arranged around the rotary shaft and has a sloping surface which runs downwards towards the outside, are arranged around the shaft in the space between the two plane-parallel support discs.

According to the invention, the product cylinder has an internal diameter of from 180 to 320 mm. The scraping heat exchanger according to the invention is particularly effi- cient and simple and is suitable for heating and/or cooling (very) viscous products.

The invention will be explained in more detail with reference to the diagrammatic drawing, in which:

Fig. 1 shows the assembly of a vertical scraping heat exchanger . Fig. 2 shows the rotary shaft with the cage bars and the positioning of the scrapers. Fig. 3 shows the attachment of the product cylinder and the outer cylinder to the top flange.

The vertical scraping heat exchanger shown in Fig. 1 contains a product -treatment cylinder 1, which is formed by a seamless extruded pipe made of stainless steel. An outer cylinder 2 is arranged around the product cylinder 1, which has an internal diameter of, for example, 205 mm and a wall thickness of 6 mm.

At their top and bottom ends, the product cylinder 1 and the outer cylinder 2 are each welded by a butt weld to annular rims 5, 6 and 7, 8 (cf . also Fig. 3) which project from the top flange 3 and the bottom flange 4. As a result, an enclosed annular space 9, which is provided with a feed 10 and a discharge 11 for a heating or cooling medium, is formed between product cylinder 1 and the outer cylinder 2.

A helically running strip 12, by means of which the heating or cooling medium is guided through the annular space 9, also in a helical manner, is situated in the annular space 9. A casing 13 comprising insulation material is arranged around the outer cylinder 2, which casing is delimited at the top and bottom by the flanges 3 and 4. A cover 14 is attached to the top flange 3. A discharge 15 for the product treated in the product cylinder 1 is arranged in the cover 14. The bottom flange 4 is attached to a first rigid support disc 16, which is provided with a feed 17 for the product to be treated.

The rotary shaft 18 is situated in the centre of the product cylinder 1, which shaft, at only one end, i.e. the bottom end, of the product cylinder 1, is guided outwards towards the external drive, which is designed as a compact unit 19 and is substantially formed by an electric motor 20, and a bearing housing 21 with a ball-bearing or roller bearing (not shown) for the rotary shaft 18 is attached to the second support disc 22. The two plane-parallel support discs 16 and 22 are held at a distance from one another and are connected rigidly together. The top support disc 22 is provided with a seal 23 at the location of the passage opening for the rotary shaft 18. The two plane-parallel support discs 16 and 22 together form a rigid and stable support for the heat exchanger. Three limbs 24, which are placed at a mutual angular interval of 120°, extend obliquely outwards and are provided at their bottom ends with adjustment members 25 which are supported on the industrial flooring 26, are attached to the bottom support disc 22.

A collar 28 is arranged in the externally accessible space between the support columns 27 and the two plane-parallel support discs 16 and 22, which collar is formed around the rotary shaft 18, is preferably made of plastic and can be used to warn of and discharge any liquid which leaks out of the space 29 for treating the product.

Means 31 for limiting any undesirable lateral movement of the free shaft end 30 are arranged in the region of the free end 30 of the rotary shaft 18. With the rotary shaft 18 in the central position in the product cylinder 1, a small free space is provided between the limiting means 31 and the rotary shaft 18.

At its top free end, the rotary shaft 18 is provided with four diametral transverse arms 32 which are placed at an angle of 90°. At their ends, the transverse arms 32 are provided with bores in which a rod 33 is removably attached to each end of the transverse arms 32. One end of a bracket 34 is welded fixedly to each of the four rods 33, which form a type of cage. The bracket 34 extends inwards towards the circumference of the rotary shaft 18 (cf. Fig. 2) and is secured in position.

This design allows each of the cage rods 33 to be fitted or removed in a simple manner and without an auxiliary tool after the cover 14 has been opened.

In the heat exchanger shown, six staggered scraper members 35 are removably fitted to each of the four cage rods 33

(cf . Fig. 2) . As indicated in Fig. 2, each of the cage rods 33 is provided with a relatively narrow flat edge 36.

Owing to the relatively narrow edge 36 on which the scra- pers are fitted, the contact between the scrapers 35 and the cage rods 33 is virtually linear.

The result is a flexible attachment of the scrapers, which promotes the efficient and supple action of the scrapers and makes them easier to clean.

According to the invention, the product cylinder 1 may be internally coated with a polytetrafluoroethylene coating.

Various modifications lie within the scope of the invention, and the invention is not limited to the embodiment shown. In particular, the heat exchanger according to the invention may also be disposed horizontally instead of vertically.

Claims

1. Scraping heat exchanger comprising a housing which is formed by a product-treatment cylinder, the walls of which can be cooled or heated and in which there is positioned a rotary shaft provided with the drive, carriers with a scraper member being attached to the rotary shaft, which carriers are able to interact with the internal surface of the product cylinder, and means being provided for feeding and discharging a heating or cooling medium to and from the outer surface of the product cylinder, and the product cylinder, which has a smooth inner wall, containing, preferably at one of its ends, a product feed and, preferably at its other end, a product discharge, characterized in that the product cylinder (1) is formed by a seamless extruded pipe.

2. Heat exchanger according to Claim 1, with a product cylinder which is substantially formed preferably from metal, such as stainless steel, characterized in that the inner and outer surfaces of the product cylinder (1) are formed by two concentric cylindrical surfaces, and in that the wall thickness of the product cylinder is constant over virtually its entire length and is preferably 1 mm to 8 mm.

3. Heat exchanger according to Claim 2, characterized in that the constant wall thickness of the product cylinder

(1) is 3.0 mm to 7.0 mm.

4. Heat exchanger according to Claim 2, characterized in that the rotary shaft (18) is guided outwards to the exter- nal drive (19) only at one end of the product cylinder (1) .

5. Heat exchanger according to Claim 1, characterized in that the rotary shaft (18) is supported only at the one end situated on the side of the external drive (19) .

Heat exchanger according to Claim 5, characterized in that the bearing housing (21) is combined with a transmission which is coupled to the drive motor (20) for the rotary shaft (18) .

7. Heat exchanger according to Claim 3, characterized in that an outer cylinder (2) is arranged around the product cylinder (1) , the annular space (29) between the product cylinder and the outer cylinder being connected to a feed (10) and a discharge (11) for the heating or cooling medi- um, and in that the cylinders are provided with a removable cover (14) at the end which is remote from the external drive (19) .

8. Heat exchanger according to Claim 7, characterized in that the product cylinder (1) and the outer cylinder (2) are provided at each end with a flange (3, 4), and in that the two cylinders are each welded, preferably by means of a butt weld, to annular rims (5, 6, 7, 8) which project out of the flange surface.

9. Heat exchanger according to Claim 1, characterized in that the product cylinder (1) has an internal diameter of from 180 to 320 mm.

10. Heat exchanger according to Claim 1, characterized in that the inner surface of the product cylinder (1) is coated with a covering layer based on wear-resistant polytetrafluoroethylene .

11. Heat exchanger according to Claim 7, characterized in that a helical guide member (12) , which extends over the length of the cylinders, for the heating or cooling medium is arranged in the annular treatment space (29) between the product cylinder (1) and the outer cylinder (2) .

12. Heat exchanger according to one or more of the preceding claims, characterized in that the rotary shaft (18) is provided with a number of transverse arms (32) which are placed at an angular interval of, for example, 90┬░, a rod (33) extending parallel to the rotary shaft being removably attached to the outer ends of each transverse arm and a number of scraper members (35) being removably attached to each of the rods which form a type of cage.

13. Heat exchanger according to Claim 5, characterized in that limiting means (31) , such as three pins which are positioned at a mutual angular interval of 120┬░ around the end of the shaft and are preferably coated with polytetraf- luoroethylene, are arranged at the other free end (30) of the rotary shaft (18) .

14. Heat exchanger according to Claim 12, characterized in that the rods (33) are each fixedly connected, for example by means of a weld joint, to an associated bracket (34) , which is removably attached, in the region of the cover (14) of the product cylinder (1) , for example by means of a spring clip or key ring, to the rotary shaft (18) .

15. Heat exchanger according to one or more of the preceding claims, characterized in that a first support disc (16) is arranged against the support flange (4) at one end of the rotary shaft (18) provided with a bearing, which support disc is provided, at the location where the rotary shaft passes through it, with a seal (23), and in that a second support disc (22), which is parallel to the first support disc, is arranged at a distance from and rigidly connected to the said first support disc (16) , in such a manner that an accessible space is formed between the two plane-parallel support discs (16, 22).

16. Heat exchanger according to Claim 15, characterized in that the bearing housing (21) for the rotary shaft (18) is attached to the second support disc (22), preferably on the outside thereof.

17. Heat exchanger according to Claim 15, characterized in that means for collecting leaking liquid, such as a collar (28) which is arranged around the rotary shaft and has a sloping surface which runs radially downwards towards the outside, are arranged in the space between the two plane-parallel support discs (16, 22) around the rotary shaft (18) .

18. Heat exchanger according to Claim 12, characterized in that the scraper members (35) , preferably with a flat surface part, are attached to the substantially cylindrical cage rods (33) in such a manner that the contact between the scrapers and the cage rods is substantially formed by linear contact.

19. Vertical heat exchanger according to Claim 15, cha- racterized in that three limbs (24) , which are placed at an angular interval of 120┬░ and extend obliquely outwards, are attached to the second, bottom support disc (22) .