HEAT EXCHANGER

Abstract: A heat exchanger (1), which is particularly intended for use in the exchange of heat between materials that are to be employed in a process for biogas production, and materials that have been employed in such a process, has two helical passages (2, 3) formed by two plate strips (4, 5), which are welded to a core (6) and a cylindrical casing (7), and which both have approximately the same angle of pitch theta . In order to avoid deposition and clogging, good flow conditions must be ensured. To obtain this, the inlet pipe stubs (8) and the outlet pipe stubs (9) of the heat exchanger are connected with the helical passages (2, 3) substantially without change of the cross-sectional area through the pipe stubs (8, 9) and the helical passages (2, 3).

Description: HEAT EXCHANGER . The invention relates to a heat exchanger' with two helical passages formed by two helical surfaces arranged between a core and a cylindrical casing, and both having substantially the same angle of pitch . The heat exchanger is especially intended for use in the exchan¬ ge of heat, preferably in counter flow, between flowable media, particularly between media that are employed as materials in a process for biogas production, and media that have been employed in such a process. However, the heat exchanger according to the invention is not limited to the above mentioned use, but can be used in other fields . A heat exchanger of the above mentioned type is known from the German patent specification No. 178,080. This describes a heat exchanger which is intended for use in the exchange of heat, either in concurrent flow or counter flow, between liquid or gaseous media, and which comprises a double helix . This helix is formed by helical surfaces, which divide the interior of the heat exchanger into two helical passages, which either have equal size or different sizes . In the German patent specification No. 178,080 no directions are given for the connection of the inlets and outlets to the helical passages of the heat exchanger. In the case of media having a relatively high viscosity pro¬ blems can arise from clogging in the areas of the inlet and the outlet, and it is therefore important to construct the inlets and outlets in such a manner as to ensure good flow conditions through the heat ex¬ changer. In the case of flowable media having an ϊnhomogenous composition , such as is often the case with materials intended for biogas production , it is particularly important to ensure good flow conditions in order to avoid depositions that may result in clogging or reduced flow through the heat exchanger. In either case, the efficien¬ cy will be reduced and it will be necessary to stop the operation of the heat exchanger in order to clean this by flushing the helical passages. It is the object of the present invention to provide a heat exchanger, in which good flow conditions are obtained at the connect¬ ion of the inlets and outlets with the heat exchanger itself, thereby to avoid clogging or at least to obtain a substantial reduction of clog¬ ging and deposition . With this object in view, the features characteristic of the invention are that the inlet and the outlet of the heat exchanger, which are connected to the helical passages, are constructed substan¬ tially without change of the cross-sectional area through the inlet/out- let and the helical passages, that the inlet and the outlet, which preferably consist of pipe stubs of suitable shape, are each directed tangentially relatively to the core and are disposed in a plane which together with a plane perpendicular to the longitudinal axis of the helical passages forms an angle, which substantially corresponds to the angle of pitch of the helical surfaces, that the pipe stubs are connected with the cylindrical wall of the casing, and that at the ends of each stub a guide plate is provided between two adjacent helical surfaces, said guide plate extending tangentially from the core towards the cylindrical wall of the casing. Thereby it becomes possible to obtain very advantageous flow conditions, because the flowing media are not subjected to sud¬ den changes of direction in connection with their passing into and out of the heat exchanger, and because certainty is obtained that no cavities will be formed upstream of the inlet pipe stub or downstream of the outlet pipe stub . Such cavities could give rise to a variation of the cross section and should therefore be avoided . According to a further feature of the present invention , the pipe stubs are connected directly with the mouth of the helical passa¬ ges so that it becomes unnecessary to provide guide plates or the like means . Though the pipe stubs are connected directly with the mouth , care should be taken that the inlet and the outlet are so directed as above mentioned in order to ensure the optimum flow conditions. I n order to be able to connect the heat exchanger with outer equipment, such as pumps, storage tanks or fermentation tanks, by means of conventionally produced cylindrical pipes, it will be advantageous to construct the pipe stubs in such a manner that they change gradually from an approximately polygonal cross section at the connection with the heat exchanger to a circular cross section at their connection with supply and discharge tubes for the heat exchanger. In cases where the need of heat exchange is such that a heat exchanger according to the invention would have an inconveniently great length, it is possible to connect a heat exchanger in series with one or more similar heat exchangers in side by side arrangement. In this manner it becomes possible, within a relatively small construction length , to obtain long lengths of flow without substantial losses as a consequence of changes of direction of the flow of material through the heat exchangers . If advantageous from the point of view of construction , one may use an arbitrary combination of the described methods of connect¬ ing the pipe stubs with the heat exchanger. E . g . the supply to and discharge from a heat exchanger consisting of a plurality of units can be provided by means of pipe stubs connected directly with the mouths of the helical passages, while the mutual connection of the units is provided by means of pipe stubs connected with the cylindri¬ cal walls of the individual casings . The invention will now be described in further detail with reference to the drawing , in which Fig . 1 is a diagrammatic view of one end of an embodi¬ ment of the heat exchanger according to the in¬ vention, where an inlet and an outlet are passed through a cylindrical wall of a casing of the heat exchanger, Fig . 2 an end view of the heat exchanger of Fig . 1 , and Fig . 3 a diagrammatic part section through one end of the heat exchanger of Figs . 1 and 2 along the line I l l - I l l of Fig . 2. Referring more particularly to Fig . 3 of the drawing , an embodiment of the heat exchanger according to the invention is illustra¬ ted , only one end being shown for the sake of clarity, the other end being constructed in the same manner. This heat exchanger 1 has two helical passages 2, 3 formed by two helical surfaces 4, 5, which are provided in the form of two plate strips, which are helically coiled and are welded along their inner edges to a core in the form of a tube 6, while their outer edges are welded to the cylindrical wall 10 of the casing 7. The two plate strips 4, 5 have the same angle of pitch Θ and are arranged substantially midway between one another so that the helical passages have approximately equal cross-sectional areas . The cylindrical wall 10 may either consist of a cylindrical tube or may be provided in the form of coiled plate strips, which are welded to the outer edges of the plate strips 4, 5 so as to close the spaces between the plate strips 4,5 and thereby to provide the helical passages 2,3. The plate strips 4,5 may alternatively be arranged at a displacement relative to one another so that the helical passages 2, 3 will have different cross-sectional areas. In the embodiment illustrated, an inlet 8 and an outlet 9 are welded to the cylindrical wall 10 of the casing 7 in such a manner that there will be no sudden changes of direction, cavities or substan¬ tial changes of the cross-sectional area. To get access to the helical passages 2, 3, a window is provided in the wall 10 for each of the pipe stubs 8,9. These windows will now be described with reference to the inlet pipe stub 8 shown in the drawing. The window, which extends across an angle of approxi¬ mately 90°, Is delimited at a first side by a first generatrix 12 of the cylindrical wall 10. The first generatrix 12 is located at the line of Intersection between a tangential plane to the cylindrical wall and the wall 10 Itself. The window has a width corresponding to the distance between two adjacent plate strips 4,5 and is thus delimited in the longitudinal direction of the heat exchanger by two edges 13, 14 located at the welding line between the plate strips and the wall . The last side of the window is delimited by a second generatrix 15 of the cylindrical wall 10. The second generatrix 15 is located at the point - of intersection between the wall 10 and a plane, which is parallel to the beforementioned tangential plane, and which is a tangential plane to the tube 6. The pipe stubs 8,9 are arranged in such a manner that a front wall 16, as viewed from the end (see Fig . 2) , is directed tan¬ gentially relatively to the wall 10 of the casing 7 and is welded to this wall along the first generatrix 12. A rear wall 17, which is parallel to the front wall 16, and which Is located in a plane that is tangential relatively to the outer surface of the tube 6, is welded to the wall 10 along the second generatrix 15. The pipe stubs 8,9 have two side walls 18, 19, which connect the front wall and the rear wall and are welded to the wall 10 along the edges 13 and 14. The pipe stubs 8,9 are arranged in a plane, which together with a plane perpen¬ dicular to the longitudinal axis of the helical passages forms an angle Θ (see Fig . 1 ) , which is identical to the angle of pitch θ of the plate strips 4,5 (see Fig . 3) . The pipe stubs 8,9 are gradually changed to a circular shape (not shown) from the approximately polygonal shape at the connection with the wall 10, whereby It becomes possible to connect the heat exchanger with other equipment by means of conven¬ tionally produced cylindrical pipes (not shown) . For illustration, the pipe stubs 8,9 are shown with an exaggerated length and can be shorter than shown . In this embodiment, two guide plates 20, 21 are connected by welding between two adjacent plate strips 4, 5, and these guide plates are directed tangentially relatively to the tube 6. The guide plate 20 is moreover welded to a first generatrix 22 of the tube 6 and the above mentioned second generatrix 15 of the cylindrical wall 10. The heat exchanger constructed as above described will have very advantageous flow conditions, and it is particularly suitable for use in the exchange of heat between materials employed in a pro¬ cess for biogas production, and materials that have been used in such a process . I n such an inhomogenous mass there will be a minimum of precipitation and deposition owing to good flow conditions, and conse¬ quently it will rarely be necessary to clean the heat exchanger by flushing . Should it still become necessary to clean the heat exchanger, this can easily be done by flushing, because the cleaning medium can be passed in and out through the pipe stubs 8 and 9 and produce a sweeping of all interior surfaces . Thus, it is not necessary to provide special conaecting stubs for flushing or to construct the heat exchanger with removable end covers in order to obtain flushing of all interior surfaces . I n the drawing , the flows of the media are indicated by ar- rows as being in counter flow, but the heat exchanger may just as well be used for heat exchange in concurrent flow. Though only one specific embodiment has been described , the heat exchanger according to the invention can also be constructed in other ways. E . g . the pipe stubs can be welded directly to the mouth of the helical passages as long as the orientation of the pipe stubs in space, as above described, is observed . Moreover, it is pos¬ sible to produce the connections between the individual parts of the heat exchanger otherwise than by welding, e.g . by means of an adhesive.

Claims: P a t e n t C l a i m s. 1. A heat exchanger (1) with a double helical passage (2,3) formed by two helical surfaces (4,5) arranged between a core (6) and a cylindrical casing (7), and both having substantially the same angle of pitch (β), c h a r a c t e r i z e d in that the Inlet (8) and the outlet (9) of the heat exchanger, which are connected to the helical passages (2,3), are constructed substantially without change of the cross-sectional area through the inlet/outlet (8,9) and the helical passages (2,3), that the inlet (8) and the outlet (9), which preferably consist of pipe stubs of suitable shape, are each directed tangentially relatively to the cylindrical wall (10) and to the core (6) and are disposed in a plane which together with a plane perpendicular to the longitudinal axis of the helical passages forms an angle (θ), which substantially corresponds to the angle of pitch of the helical surfaces (4,5), that the pipe stubs are connected with the cylindrical wall (10) of the casing, and that at the ends of each stub a guide plate (20,21) is provided between two adjacent helical surfaces, said guide plate extending tangentially from the core towards the cylindrical wall of the casing. 2. A heat exchanger according to claim ^ c h a r a c t e ¬ r i z e d in that the pipe stubs are directly connected with the mouth of a helical passage. 3. A heat exchanger according to either of the beforegoing claims, c h a r a c t e r i z e d in that the cross-sectional areas of the two helical passages (2,3) are substantially equal. 4. A heat exchanger according to any of the beforegoing claims, c h a r a c t e r iz e d in that the pipe stubs are gradually changed from a substantially polygonal cross section at their connect¬ ion with the heat exchanger to a substantially circular cross section at their connection with supply and discharge pipes for the heat ex¬ changer. 5. A heat exchanger according to any of the beforegoing claims, c h a r a c t e r i z e d In that it is connected in series with one or more similar heat exchangers in side by side arrangement.

Inventors: THAGAARD NIELS, THAGAARD, NIELS
Applicants: BIGADAN A S HOEJBOGAORD BIOGAS, BIGADAN A/S, HOEJBOGAORD BIOGASTEKNOLOGI
Application year: 1986
Main classification: F28D7
IPC codes: F28D7