AU2017280491B2

AU2017280491B2 - Method for operating a tube bundle heat exchanger for heating a temperature-sensitive concentrate of a food product under high pressure, and tube bundle heat exchanger for carrying out the method

Info

Publication number: AU2017280491B2
Application number: AU2017280491A
Authority: AU
Inventors: Hubert Assing; Ludger LÜTKE SUNDERHAUS; Ulrich ROLLE; Uwe Schwenzow; Ludger Tacke; Dietrich Zimmermann
Original assignee: GEA TDS GmbH
Current assignee: GEA TDS GmbH
Priority date: 2016-06-23
Filing date: 2017-06-16
Publication date: 2020-10-29
Anticipated expiration: 2037-06-16
Also published as: NZ750017A; ZA201900437B; WO2017220194A4; DE102016007637B4; DE102016007637A1; EP3475642B1; AU2017280491A1; EP3475642A1; DK3475642T3; CL2018003709A1; WO2017220194A1; JP2019529849A; JP6806803B2; PL3475642T3

Abstract

The invention relates to a method for operating a tube bundle heat exchanger (100) for heating a temperature-sensitive concentrate (P) of a food product under high pressure, having the preamble features of claim 1. The aim of the invention is to overcome the disadvantages of the prior art and provide a method of the generic type and a tube bundle heat exchanger for carrying out the method which reduce the tendency of the concentrate to denaturate at a high pressure level, the tendency of the viscosity of the concentrate to increase or the tendency of the concentrate to gelate, and the tendency of same to accumulate and which ensure an end product that is sterile, i.e. microbiologically clean. This is achieved by a method in that • the tube bundle heat exchanger (100) flow paths supplied with the concentrate (P) are designed such that a pressure (p) of maximally 350 bar can be applied to the concentrate (P), and • an increased concentrate (P) flow speed (v) maximally equaling 3m/s is provided in the inner tubes (300) and/or in the annular gap-shaped outlet-side channel (600b) in order to generate a defined flow mechanical shear stress of the concentrate (P).

Description

TECHNICAL FIELD The invention relates to a method for operating a tube bundle heat exchanger for heating a temperature-sensitive concentrate of a food product under high pressure according to the preamble of claim 1, as well as a tube bundle heat exchanger for performing the method according to the preamble of claim 5. The invention moreover relates to a method for controlling the operation of a tube bundle heat exchanger of the aforementioned type. "Temperature-sensitive concentrates" should in particular be understood to be such substrates that possess a high protein and dry material content and little water, that are easily denatured, that experience an increase in viscosity upon being heated, or respectively are subject to gelatinization, and do this while being processed under aseptic conditions into a germ-free end product.

PRIOR ART It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country. Indirect product heating such as in UHT systems (UHT: ultrahigh temperature) through an exchange of heat at a wall can be accomplished using so-called plate heat exchanger systems or, as in the invention described below, also using so-called tube bundle heat exchangers in which the thermal energy is transferred through the tube walls of a group of inner tubes. The food product to be treated flows within the inner tubes, whereas a heat transfer medium, hereinafter termed heating medium within the context of the invention, generally water or steam, flows within the annular gap of a jacket tube that surrounds the parallel-connected inner tubes. Such a tube bundle heat exchanger is known from DE 94 03 913 U1. DE 10 2005 059 463 Al also discloses such a tube bundle heat exchanger for a low pressure level and furthermore discloses how a number of tube bundles in this heat exchanger can be arranged in parallel and series-connected for the passage of liquid by means of connecting elbows or connecting fittings. Such an arrangement is shown in Fig. 1 of this document (prior art).

Particularly temperature-sensitive products such as concentrates, in particular with a high dry material content, require precise and quick adaptation of the product temperature to the required temperature conditions. This yields the requirement that all portions of a product to be subjected to a heat treatment of the kind under discussion simultaneously pass through the required same progression of temperature level over the same amount of time. Expressed otherwise, this means that all portions are subjected to the same thermal and fluid mechanical conditions for the same dwell time.

DE 103 11 529 B3 addresses the problem of branching the flow at the inlet region of the tube support plates of a tube bundle heat exchanger (such as DE 94 03 913 U1) as preferably used in UHT systems. The suggested expedient measures for the object presented therein exclusively relate to the branching of a product to inner tubes of the tube bundle heat exchanger that receive a number of portions of this product, wherein inter alia a displacement body is provided that is arranged so as to be axially symmetrical and concentric with the tube support plate. This prior art relates exclusively to a device for influencing the inflow region of a tube support plate of a tube bundle heat exchanger under discussion. The inner tubes are arranged distributed over the entire circular surface of the tube support plate with the exception of a narrowly delimited central region, and to more than one divided circle. Under these conditions, flow paths of different length to the inlet of the inner tubes, or from the outlet therefrom, exist both at the inlet region as well as at the outlet region of the respective tube support plate, and accordingly at the branching and the merging of the flow. For this reason alone, different dwell times arise for the portions of the product flowing through the respective inner tubes.

)5 WO 2011/085784 A2 proposes a solution to the aforementioned problem of differing dwell times from the branching and merging of the flow by arranging all inner tubes of the tube bundle as a circular ring on a single circle and in an outer channel of the tube bundle heat exchanger designed as an annular gap, wherein the inner tubes with a parallel flow extend in the longitudinal direction of the outer channel and are each supported at the end in a tube support plate. This arrangement of the inner tubes is combined with an axially symmetrical displacement body fixedly arrange concentrically on the tube support plate at both the inlet and outlet for the product. The respective displacement body extends centrally through an exchanger flange associated with the tube support plate, wherein the exchanger flange has a connection opening on its side facing away from the associated tube support plate. At least subsequent to the outer channel, the end-side regions of the known tube bundle heat exchanger are designed mirrored with an identical shape and dimensions, wherein this symmetry also expressly includes the two displacement bodies and the two annular channels.

This yields nearly congruent flow paths for all portions of the product branching and merging between the product inlet and outlet in the inner tubes, and basically uniform thermal transition conditions at all relevant regions of the tube bundle heat exchanger. However, "congruent flow paths" does not also mean that the flow sections of the individual portions are constructed with an unchanging flow speed without acceleration, or respectively delay.

With regard to the formation of deposits on the tube support plates, it was revealed during actual operation that the above-described symmetrical flow geometry produces deposits that restrict the service life at the outlet-side, flow-discharging tube support plate but not at the inlet-side, i.e., flow-receiving, tube support plate when viscous dairy products such as concentrates are heated.

In this context, to avoid deposits at the outlet-side, flow-discharging tube support plate, DE 10 2013 010 460 Al proposes that the annular, outlet-side channel has a channel passage cross-section, at least consistently in its region between a greatest outer diameter of the outlet-side displacement body and the connection opening, that corresponds to an overall passage cross-section of all inner tubes with a parallel flow. Such a tube bundle heat exchanger has proven to be suitable for heating processes of the kind under discussion at the normal, relatively low pressure level.

Powdered food products, in particular milk products such as easily-soluble foods for small children, are produced in many cases by vaporization or spray drying in a so called drying tower. There, a concentrate previously concentrated to a specific amount of dry substance in an evaporator, or respectively a condenser, and then heated in a heater to a specific temperature, is atomized in a hot air stream, for example through nozzles, in particular single substance nozzles. The concentrate leaving the heater is fed to these so-called pressure atomizer nozzles by means of a high-pressure piston pump, a so-called nozzle pump, at a pressure that can extend up to a maximum of 350 bar.

The statics of the dryer towers are generally insufficient to bear the heavy high pressure piston pump for it to be installed directly adjacent to the pressure atomizer nozzles, which would be desirable for technical and procedural reasons. A high pressure piston pump arranged adjacent to the pressure atomizer nozzles would operate at ambient temperatures of 75 to 800 C in this region, the so-called hot chamber in the headspace of the dryer tower, and would require aseptic operation. Additional thermal neutralization of microorganisms above and beyond this would be impossible.

For the aforementioned reasons, the high-pressure piston pump has been arranged to date in the bottom region of the dryer tower. A significant difference in height between the high-pressure piston pump and the pressure atomizer nozzles is bridged by a riser which also functions as intended or necessarily as a thermal maintenance line.

To ensure the longest possible and hygienically safe storage of the powdered food product, the end product must exhibit effective solubility and be as sterile as possible. The required sterility results from killing microorganisms to the greatest extent possible in the concentrate leaving the heater by conveying the concentrate at a suitable temperature and dwell time, and by including in the equation the riser to the pressure atomizer nozzles functioning as a thermal maintenance line. A maximum temperature of 77 0 C is required to produce a so-called "low heat powder", approximately 850 C is required to produce so-called "high heat powder", and up to 1250 C is required to produce "ultra high heat powder".

The necessary average dwell time of the concentrate in the riser after prior high pressure treatment together with a hot temperature undesirably influences the solubility of the end product. Furthermore, being kept hot for a long time in the riser can lead to an uncontrolled denaturing of the concentrate. Accordingly, the average dwell time of the concentrate is about 42 seconds, for example, when it is conveyed in a 30 m riser with a diameter of DN50 and a volumetric flow of 5,000 L/h. This generally also means that the quality of the end product is reduced. Such a denaturation can for example influence the powder quality of baby food so that there is no guarantee of it being completely soluble, which causes unacceptable lumps in the prepared baby foods. In addition, the long dwell time at high temperatures causes chemical reactions in the concentrate and the formation of deposits, so-called product fouling, on the walls of the riser and the pressure atomizer nozzles which undesirably extends the production time of a scheduled batch concentrate.

For example, the temperature of milk concentrates in the riser and hence up to the pressure atomizer nozzles may not exceed 65 to 68C to prevent crystallization processes in the lactose. Consequently, the long riser limits the permissible temperature at that location.

The necessary sterility up to the inlet of the pressure atomizer nozzles can also be threatened by the high-pressure piston pump since it cannot convey the concentrate under aseptic conditions with a reasonable technical outlay. Aseptic conveying conditions require a significant technical outlay, however, which in practice generally is not or cannot be realized. Germs from the surrounding air can enter the concentrate through the pistons of the high-pressure piston pump so that reinfection can occur at that location. The powdered end product can therefore be contaminated, and the contamination increases over time under the effect of the residual moisture normally remaining in the end product.

In the state-of-the-art, aseptic conveyance of the liquid initial product leaving the heater to the downstream high-pressure piston pump is only feasible with greater technical outlay.

The known spray drying systems with low pressure heating, a subsequent pressure increase in the foot region of the dryer tower to a maximum of 350 bar, and conveyance of the concentrate in a riser up to the pressure atomizer nozzles, have the following disadvantages:

• the riser functions like a dwell time section - technologically undesirable per se - and a thermal maintenance unit;

• the dwell time necessarily reduces the inlet temperature into the pressure atomizer nozzles;

• the dwell time yields an undesirable rise in viscosity (gelation effect);

• the state of the temperature-sensitive concentrate before the pressure atomization nozzles is not clearly defined because the dwell time in the riser cannot be clearly defined;

• due to the dwell time together with the thermal maintenance, the concentrate may experience denaturing which is associated with increased concentrate deposits;

o • there is a reduction of the service life of the system which therefore must be cleaned more frequently;

• the high-pressure piston pump must operate in a sterile manner, i.e., the concentrate must be handled in an aseptic manner by the pump which is associated with high costs;

• high-pressure piston pumps that do not function in an aseptic manner can produce a highly contaminated end product;

• the output of the drying tower is reduced by the relatively low temperature before the pressure atomizing nozzles.

To achieve the necessary sterility of the liquid concentrate exiting the high-pressure piston pump under high pressure, it has already been proposed that this concentrate appropriately undergo high pressure heating along the path to the pressure atomizer nozzles. This high-pressure heating could occur directly before the pressure atomizing nozzles which could allow the temperature in the riser to be reduced to a noncritical level. This arrangement would also still permit the operation of a high-pressure piston pump with non-aseptic delivery at the foot of the drying tower.

In this context, it has also already been proposed that high-pressure heating occur in a sufficiently pressure-resistant monotube which is supplied with steam or a heated gas for heating from the outside (US 3,072,486 A). This proposal is however not expedient since even injection of heat over the outside and over the entire length of the monotube, and hence an even dwell time for all the particles of the concentrate flowing through the monotube, are not ensured.

A heat exchanger that satisfies the requirements of sufficiently even heat injection and an approximately consistent dwell time for all concentrate particles at a low level of pressure would in principle be a so-called tube bundle heat exchanger of the aforementioned type (DE 10 2013 010 460 Al), which in principle could replace the aforementioned monotube.

In the interim, a manifold, or respectively a connection fitting for product pressures up to 350 bar, has become available for connecting the tube bundle in a relevant tube bundle heat exchanger (DE 10 2014 012 279 Al; DE 10 2005 059 463 Al), wherein the known embodiments of tube bundle heat exchangers are unsuitable in principle for this high pressure level.

However, the processing problem remains unsolved of subjecting a concentrate, such as for atomized drying, to a treatment directly before the pressure atomization nozzles that reduces the tendency of the concentrate to denature, the concentrate viscosity to rise, or respectively the concentrate to become gelatinous and form deposits, and ensures a sterile, i.e., microbiologically acceptable end product.

The present invention may therefore overcome the disadvantages of the prior art and may provide a method of the generic type as well as a tube bundle heat exchanger for performing the method that, at a high level of pressure, reduce the tendency of the concentrate to denature, the tendency of the concentrate viscosity to rise, or respectively the tendency of the concentrate to become gelatinous and form deposits, and ensure a sterile, i.e., microbiologically acceptable end product.

SUMMARY OF THE INVENTION

The present invention is based on a tube bundle heat exchanger, the basic design of which is described in DE 10 2013 010 460 Al. It has at least one tube bundle that consists of a number of parallel-connected inner tubes through which concentrate flows on the inside. The inner tubes are annular, arranged on a single circle, and are in each case braced at the end in a first and second tube support plate, and they extend in the longitudinal direction of an outside channel formed as an annular gap through which a heating medium flows. The inner tubes may be arranged in the outer edge region of the respective tube support plate.

The inner tubes possess a common inlet designed in the form of a first connection opening that is in a first exchanger flange connected to the first tube support plate and is arranged centrally relative to an axial axis of symmetry of the tube bundle, and the inner tubes possess a common outlet that is designed in the form of a second connection opening that is in a second exchanger flange connected to the second tube support plate and is also arranged centrally at that location. Furthermore, at least at the outlet side, the inner tubes fluidically terminate in a circumferential annular gap that is formed in the second tube support plate, and/or the second exchanger flange. The circumferential annular gap is connected across an annular outlet-side channel to the second connection opening, and the annular outlet-side channel is bordered radially to the outside by the second exchanger flange, and radially to the inside by a displacement body that is arranged in an axially symmetrical manner on the second tube support plate. The annular outlet-side channel has a specific extension length, and a specific length-dependent progression of its channel passage cross-sections. The inlet-side of the inner tubes in conjunction with their surroundings can be designed as disclosed in DE 10 2013 010 460 Al. However, this is not essential in conjunction with the present invention.

The feature with respect to the arrangement of a number of inner tubes with a parallel flow is to be understood as an arrangement that, independent of the number of inner tubes, such as 4 through 19 or more in number, does not fill an entire circular cross section of the tube support plate. Instead, all the inner tubes are arranged on said single circle that leaves an inner region free, and not just a limited center, from inner tubes. This arrangement makes it possible for the inner channel formed by the annular inner tubes arranged on a single circle to be designable in the form of the circumferential annular gap after the inner tubes, viewed in the direction of flow.

The basic concept of the invention is to first increase the pressure of the concentrate up to a maximum pressure of 350 bar as is necessary for a treatment of the concentrate following heating. At this high level of pressure, the concentrate is then heated. This heating is combined with a specific fluid mechanical shearing stress which occurs while heating, and/or may occur directly after heating. The specific fluid mechanical shearing stress which is sufficient without moving elements and/or supplied outside energy occurs in the respective inner tube with its specific passage cross-section and its specific flow-experiencing length, and at an elevated flow speed, and/or may be in an annular outlet-side channel adjoining the inner tubes. The channel has a specific extension length and a specific length-dependent progression of its channel passage cross-sections, and a flow flows through at the elevated flow speed. In this regard, it is proposed that the elevated flow speed be up to 3 m/s at most.

In some forms:

• the concentrate-side flow paths of the tube bundle heat exchanger are designed so that the concentrate can be subjected to a pressure up to a maximum of 350 bar, • a specific fluid mechanical shearing stress is generated on the concentrate that on the one hand tends to reduce and on the other hand standardizes the rise in viscosity, termed the gelling effect, in the concentrate, • when heating the concentrate in the inner tubes to generate the specific fluid mechanical shear stress, an elevated flow speed of the concentrate is provided in the inner tubes, and/or

• to generate specific fluid mechanical shearing stress on the concentrate, an elevated flow speed of the concentrate is provided in the annular outlet-side channeland • the elevated flow speed is max. 3 m/s .

To achieve a uniform dwell time for all parts of the heat-treated concentrate, it is advantageous, as provided by another proposal, when the elevated flow speed is constant over the entire extension length of the annular outlet-side channel.

The disadvantageous maintenance of heat between the increase in pressure to the high-pressure level following low-pressure heating, and further treatment of the concentrate following the increase in pressure that had to be tolerated in the prior art is more or less eliminated with the high pressure heating according to the invention, and the heating can be defined, or respectively the heat treatment can be configured to be reproducible, directly before this further treatment such as pressure atomization. The heat treatment can be specifically adjusted depending on and adapted to the concentrate, desired thermal loads, mass flow and contents. Furthermore, controlled denaturing of the concentrate with regard to the desired end product is feasible by adjusting the temperature and dwell time for high-pressure heating. An effective microbiological improvement in the end product, or a specific swelling of the protein or starch, for example, is thereby achieved.

The increased viscosity of the concentrate, the so-called gelling effect that arises from crystallization processes and/or product-specific properties, is less than is case with known methods due to the reduced temperature up to high-pressure heating, and the reduced dwell time at a high temperature during high-temperature heating. On the one hand, this gelling effect is somewhat reduced by the specific shearing stress and, on the other hand, the gelling effect is standardized which decreases the tendency of deposits to form in the processing system for further handling the concentrate. This reduces the cleaning and setup times.

Since the increased flow speed in comparison to a relevant process design practiced to date only occurs at a high-pressure level, the associated additional pressure drops in the respective high-pressure heating process do not play a significant role. The elevated flow speed improves thermal transfer to the concentrate which yields additional advantages: • thermal transfer with less heat exchanger surface is possible; • a protein concentrate at a high concentration is possible; • greater volumetric flow and hence greater throughput are possible; • due to the improved thermal transfer, the concentrate can be heated to a higher temperature which, for example in pressure atomization, enables greater drying performance; • the concentrate is specifically denatured as desired according to plan.

The invention furthermore proposes a tube bundle heat exchanger for performing the method which has inter alia at least one tube bundle in a manner known per se which consists of a number of inner tubes through which concentrate flows in parallel, and which are annular, arranged on a single circle, and are braced at the end in a first and second tube support plate. At least at the outlet side, the liquid-conveying inner tubes terminate in a circumferential annular gap that is formed in the second tube support plate, and/or the second exchanger flange.

The means for applying specific fluid mechanical shearing stress on the concentrate consists of an annular outlet-side channel which is connected to convey liquid on the one hand to the outlet of the circumferential annular gap which is formed in the second tube support plate, and/or in the second exchanger flange, and is connected to convey liquid on the other hand to the second connection opening. The annular outlet-side channel is bordered radially to the outside by the second exchanger flange, and radially to the inside by a displacement body that is arranged in an axially symmetrical manner on the second tube support plate. In the most general instance, the annular outlet-side channel has a specific extension length and a specific progression of its channel passage cross-sections that depends on the extension length.

All of the flow paths of the tube bundle heat exchanger impinged upon by the concentrate are designed in terms of strength to withstand an inner pressure up to a maximum of 350 bar. According to the invention, the first connection opening transitions smoothly, i.e., flush and without a change in cross-section, into an inner passage of a connecting elbow or connecting fitting that is upstream from the first connection opening viewed in the direction of flow. The second connection opening transitions smoothly, i.e., flush and without a change in cross-section, into an inner passage of a connecting elbow or connecting fitting that is downstream from the second connection opening viewed in the direction of flow.

To establish favorable conditions of strength for the high inner pressure at the critical connecting site between the respective exchanger flange and the associated connecting elbow/fitting, the respective connecting elbow/fitting extends somewhat into the associated exchanger flange by at least the wall thickness of the connecting elbow/fitting at this location, i.e., by an engagement depth. The connecting elbow, or respectively connecting fitting is welded on the outside to the associated exchanger flange with a high-pressure resistant, multilayer orbital first weld seam, may be a so called fillet weld, and on the inside with an orbital, second weld seam, may be a so called V-weld. Furthermore to ensure a high pressure-resistant design, the end of each inner tube is welded at the outlet side in the associated tube support plate circumferentially to said plate with a third weld seam, may be a fillet weld or corner weld.

To achieve a uniform dwell time for all parts of the heat-treated concentrate, it is advantageous and suggested that the channel passage cross-sections of the annular outlet-side channel are constant over the entire extension length. This desirable equal treatment is further promoted in that the elevated flow speed is highly uniform throughout the entire tube bundle heat exchanger up to the end of the specific shearing stress on the concentrate, wherein an additional embodiment in this regard provides that the channel passage cross-section of the annular, outlet-side channel corresponds to the overall passage cross-section of all inner tubes with a parallel flow.

The method according to the invention and tube bundle heat exchanger for performing said method can be advantageously controlled depending on the concentrate. In this regard, the invention proposes a method for controlling the operation of a tube bundle heat exchanger, wherein the heating control parameters and the specific fluid mechanical shearing stress are determined by the properties of the concentrate to be heated and the physical conditions. The properties of the concentrate to be heated are understood as being its volumetric flow, viscosity, pressure, temperature and concentration of dry material, and the physical conditions are understood as being the pressure and temperature at the site at which the concentrate is handled following the specific fluid mechanical shearing stress. The control parameters with reference to the concentrate are the pressure, the outlet-side heating temperature, the elevated flow speed and intensity of the specific fluid mechanical shearing stress generated by a specific design of the annular outlet-side channel.

The control parameters are set by means of a calibration function set or saved before or while starting up the tube bundle heat exchanger. The calibration function is obtained in that: • control parameters of the relevant type are obtained while starting and stopping the tube bundle heat exchanger with a discrete concentrate (recipe) until obtaining a satisfactory product quality • said control parameters are recorded and saved in a control in the form of the "calibration function" (control parameter = function of concentrate or recipe).

In a later treatment of the same concentrate (recipe), these empirical values can be accessed in the form of this calibration function, and the required control parameters can be correspondingly adjusted.

The method according to the invention and the method for controlling the operation of a tube bundle heat exchanger can be advantageously applied to atomized drying of concentrates in drying systems with a drying tower, wherein the concentrate, after being heated and after the specific fluid mechanical shearing stress, is then immediately, i.e., directly transferred to where it is atomized under pressure. The transfer time for direct transference is determined by a corresponding effective distance in terms of flow between the means for applying the specific fluid mechanical shearing stress and the pressure atomization site. Directly in this context means ideally that the outlet of the means for producing the definitive fluid mechanical shearing stress terminates directly, i.e., without inserting a length of pipeline, in the pressure atomizer nozzle(s), or leads to them.

BRIEF DESCRIPTION OF THE DRAWINGS A detailed representation of the invention is given in the following description and the accompanying figures of the drawing and from the claims. Whereas the invention is realized in designs of an independent method and in a wide range of embodiments of a tube bundle heat exchanger for performing the method, the drawing depicts a tube bundle heat exchanger with a familiar basic design, with reference to which a preferred design of the method according to the invention will be described below. In the figures:

Fig. 1 shows a meridian section of an embodiment of a preferably used tube bundle heat exchanger corresponding to a section designated as A-A in Fig. 2, wherein the representation is restricted to its inlet and outlet-side region; Fig. 2 shows a side view of the tube bundle heat exchanger according to Fig. 1 corresponding to a perspective toward the outlet side; Fig. 3 shows a meridian section of just the outlet-side region of the tube bundle heat exchanger according to Fig. 1, and Fig. 4 shows a meridian section of the outlet-side region of the tube bundle heat exchanger enlarged in comparison with Fig. 3.

DETAILED DESCRIPTION In the following detailed description, reference is made to accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure. A tube bundle heat exchanger 100, of which a tube bundle 100.1 is shown, has congruent flow paths between an inlet E through which all the concentrate P passes, and an outlet A (see Fig. 1) for all portions of the concentrate P branching and merging between the latter. This is objectively achieved in that all inner tubes 300 of the tube bundle 100.1, consisting of a group of parallel-connected inner tubes 300 through which concentrate P flows on the inside, are annular, arranged on a single circle K (Fig. 3) and are arranged in an outer channel 200* configured as an annular gap, and extend in its longitudinal direction and are braced at the end in a first and second tube support plate 700, 800. The inner tubes 300 are arranged in the largest possible circumferential region of the tube support plate 700, 800, preferably over the circumference of the circle K. A number N (Fig. 4) of the inner tubes 300 that extend axially parallel to an outer jacket 200.1 of the outer channel 200* and extend through the latter and jointly form an inner channel 300*, is guided at the end through the first tube support plate 700 and the second tube support plate 800 (both of which are also termed a tube mirror plate), and are welded there, in a manner resistant to high pressure, on their respective tube outer diameter and their respective end face by means of a third weld seam S3.

The inner tubes 300 (Fig. 1) possess, on the one hand, the common inlet E designed in the form of a first connection opening 500a that is in a first exchanger flange 500 connected to the first tube support plate 700 and is arranged centrally relative to an axial axis of symmetry "a" of the tube bundle 100.1 and on the other hand, the inner tubes 300 possess the common outlet A that is designed in the form of a second connection opening 600a that is in a second exchanger flange 600 connected to the second tube support plate 800 and is arranged centrally at that location.

The first tube support plate 700 is screwed high-pressure-resistant to the associated first exchanger flange 500, and the second tube support plate 800 is screwed high pressure-resistant to the associated second exchanger flange 600. For this purpose, depending on the respective flange diameters, a plurality of screwed connections (Fig. 2, 3) is provided that preferably consist of threaded bolts 1100 anchored in the tube support plates 700, 800 together with nuts 1200 and washers 1300. In the exemplary embodiment, 8 such screw connections 1100, 1200, 1300 are provided. The first exchanger flange 500 is sealed by a flange seal 900 against the first tube support plate 700. The same holds true for the second exchanger flange 600 and the second tube support plate 800.

In the embodiment shown in Fig. 1, the end-side regions of the tube bundle 100.1 of the tube bundle heat exchanger 100 - with the exception of an inlet-side and the outlet-side displacement body 11, 12 and its direct surroundings in the region of the exchanger flange 500, 600 following the outer channel 200*- are preferably designed mirrored with an identical shape and dimensions. Because the present invention relates to the downstream side of the tube bundle 100.1, the following description can primarily be restricted to the outlet-side end region (Fig. 4), and the corresponding reference numbers of the other end region are merely listed. The design of the inlet side region can accordingly be deduced from the design of the outlet-side region.

On its side facing away from the associated tube support plate 800, 700, the exchanger flange 600, 500 has a connection opening 600a, 500a which possesses a nominal diameter DN and hence corresponds to a nominal passage cross-section Ao of the connecting elbow/fitting 1000 (Ao = DN 2 rr/4) connected at that location. The connection opening 600a, 500a passes without a transition into an inner passage of the connecting elbow/connecting fitting 1000 which is downstream from the second connection opening 600a, or respectively upstream from the first connection opening 500a viewed in the direction of flow. The respective connecting elbow/connecting fitting 1000 engages somewhat in the associated exchanger flange 600, 500 at engagement depth t to ensure the required high pressure resistance, and is welded to the outside of the exchanger flange 600, 500 with a high-pressure-resistant, multilayer first weld seam S1, preferably a fillet weld, and to the inside with a second weld seam S2, preferably a V-weld. At the outlet side in the associated tube support plate 800, 700, the end of each inner tube 300 is circumferentially welded to said tube support plate with the third weld seam S3, preferably a corner weld.

Generally, the tube bundle heat exchanger 100 is composed of more than one tube bundle 100.1. In its middle part, the tube bundle 100.1 consists of the outer jacket 200.1 bordering the outer channel 200* with the first tube support plate 700 arranged on the right side with reference to the depicted position, and the second tube support plate 800 arranged on the left in the same manner. In the region of the left-side end of the outer jacket 200.1, a first coupling 400a is provided thereupon, and in the region of the right-side end of the outer jacket 200.1, a second coupling 400b is provided thereupon to be supplied with a heating medium M. The outer channel 200* for the heating medium M is bordered on the inside by an inner jacket 200.2.

At least at the outlet side, the liquid-conveying inner tubes 300 terminate in a circumferential annular gap R (Fig. 4) viewed in the direction of flow that is formed in the second tube support plate 800, and/or the second exchanger flange 600. The circumferential annular gap R is fluidically connected across an annular outlet-side channel 600b to the second connection opening 600a. The annular outlet-side channel 600b is bordered radially to the outside by the second exchanger flange 600, and radially to the inside by an outlet-side displacement body 12 that is arranged in an axially symmetrical manner on the second tube support plate 800. The annular outlet side channel 600b has a specific extension length, and a specific length-dependent progression of its channel passage cross-sections As.

With regard to distribution, it may also be useful to also adequately design the inlet side of the tube bundle 100.1 of the tube bundle heat exchanger 100 (Fig. 1) on the outlet side in the form of an annular, inlet-side channel 500b which is bordered radially to the outside by the first exchanger flange 500, and radially to the inside by the inlet- side displacement body 11 that is arranged in an axially symmetrical manner on the first tube support plate 700. With regard to the specific fluid mechanical shearing stress, said stress is not desired at the inlet side; it is localized within the inner tubes 300 and preferably in the annular outlet-side channel 600b.

An average elevated flow speed in the inner tube 300 and hence in the inner channel 200* is identified with v (Fig. 1, 4). The annular outlet-site channel 600b has the specific extension length L and, in the most general case, the specific length-dependent progression of its channel cross-sections As, at least consistently in its region between a greatest outer diameter of the outlet-side displacement body 12 and the second connection opening 600a.

Preferably, the annular outlet-side channel 600b is designed with a constant passage cross-section over the entire specific extension length L (As = const.), wherein the channel passage cross-section As in this region has an overall passage cross-section NA of all inner tubes 300, numbering N, with a parallel flow which corresponds to an individual passage cross-section Ai. The individual passage cross-section measures Ai = D 2 r/4, wherein Di is the tube inner diameter of the inner tube 300.

As already described above in association with the specific design of the tube bundle heat exchanger 100, the method according to the invention for operating a tube bundle heat exchanger 100 for heating a temperature-sensitive concentrate P at a high pressure p is characterized on the one hand in that the flow paths of the tube bundle heat exchanger 100 impinged upon by the concentrate P are designed so that the concentrate P can be subjected to the pressure p up to a maximum of 350 bar. On the other hand, the tube bundle heat exchanger 100 is operated at this pressure p and an outlet-side heating temperature T so that, in order to generate specific fluid mechanical shearing stress on the concentrate P, the elevated flow speed "v" of the concentrate P is provided within the inner tubes 300 and/or within the annular outlet-side channel 600b which is 3 m/s at most (Fig. 4).

At the outlet-side, the tube bundle heat exchanger 100 designed as a high-pressure heat exchanger has means for applying specific fluid mechanical shearing stress on the conveyed concentrate P, wherein these means act purely by fluid mechanics without moving elements and/or supplied outside energy through specific passage cross-sections, specific lengths of the flow paths, and specific elevated flow speeds. The means for applying specific shearing stress on the concentrate P preferably consists of an annular outlet-side channel 600b which is connected on the one hand to the outlet of the circumferential annular gap R which is formed in the second tube support plate 800, and/or in the second exchanger flange 600, and is connected on the other hand to the second connection opening 600a. In the most general instance, the annular outlet-side channel 600b has the specific extension length L and the specific progression of its channel passage cross-sections As that depends on the extension length L.

To achieve a uniform dwell time for all parts of the heat-treated concentrate P, it is advantageous and suggested that the channel passage cross-sections As are constant over the entire extension length L. This desirable equal treatment is further promoted in that the elevated flow speed "v" is highly uniform throughout the entire tube bundle heat exchanger 100, or respectively up to the respective tube bundle 100.1, up to the end of the specific shearing stress on the concentrate P, wherein an additional embodiment in this regard provides that the channel passage cross-section As of the annular outlet-side channel 600b corresponds to the overall passage cross-section NAi of all inner tubes 300 with a parallel flow. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

REFERENCE LIST OF THE ABBREVIATIONS 11 Inlet-side displacement body 12 Outlet-side displacement body

100 Tube bundle heat exchanger 100.1 Tube bundle

200* Outer channel 200.1 Outer jacket 200.2 Inner jacket

300* Innerchannel 300 Inner tube

400a First coupling 400b Second coupling

500 First exchanger flange 500a First connection opening 500b Annular inlet-side channel

600 Second exchanger flange 600a Second connection opening 600b Annular outlet-side channel

700 First tube support plate (tube mirror plate) 800 Second tube support plate (tube mirror plate) 900 Flange seal 1000 Connecting elbow/connecting fitting 1100 Threaded bolt 1200 Nut 1300 Washer

a Axial axis of symmetry p Pressure t Engagement depth v Elevated flow speed

A Outlet

Ai 2 r/4)) Single passage cross-section (of the inner tube) (Ai = Die NAi Overall passage cross-section (of all tubes with a parallel flow) As Channel passage cross-section Ao Nominal passage cross-section (of the connecting elbow; Ao= DN 2Tr/4)

Di Tube inner diameter (inner tube 300) DN Nominal diameter (of the connecting elbow (Ao= DN 2 /rr4))

E Inlet K Circle L Extension length M Heating medium N Number (of inner tubes 300) P Concentrate R Circumferential annular gap

S1 Multi-layer first weld seam S2 Second weld seam S3 Third weld seam

T Outlet-side heating temperature

Claims

Claims

A method for operating a tube bundle heat exchanger for heating a temperature sensitive concentrate of a food product under high-pressure with the tube bundle heat exchanger that has the following features: • at least one tube bundle that consists of a number of parallel-connected inner tubes through which concentrate flows on the inside, • the inner tubes are annular, arranged on a single circle, and are in each case braced at the end in a first and a second tube support plate, • the inner tubes extend in the longitudinal direction of an outside channel formed as an annular gap through which a heating medium flows, • the inner tubes possess a common inlet designed in the form of a first connection opening that is in a first exchanger flange connected to the first tube support plate and is arranged centrally there, • the inner tubes possess a common outlet designed in the form of a second connection opening that is in a second exchanger flange connected to the second tube support plate and is arranged centrally there, • at least at the outlet side, the inner tubes fluidically terminate in a circumferential annular gap that is formed in the second tube support plate, and/or the second exchanger flange, • the circumferential annular gap is fluidically connected across an annular outlet-side channel to the second connection opening ,

• the annular outlet-side channel is bordered radially to the outside by the second exchanger flange , and radially to the inside by a displacement body that is arranged in an axially symmetrical manner on the second tube support plate, • the annular outlet-side channel has a specific extension length, and a specific length-dependent progression of its channel passage cross sections ,

wherein • the flow paths of the tube bundle heat exchanger impinged upon by the concentrate are designed so that the concentrate can be subjected to a pressure up to a maximum of 350 bar, • a specific fluid mechanical shearing stress is generated on the concentrate that on the one hand tends to reduce and on the other hand standardizes the rise in viscosity, termed the gelling effect, in the concentrate, • when heating the concentrate in the inner tubes to generate the specific fluid mechanical shear stress, an elevated flow speed of the concentrate is provided in the inner tubes, and/or • to generate specific fluid mechanical shearing stress, an elevated flow speed of the concentrate is provided in the annular outlet-side channel, and • the elevated flow speed is max. 3 m/s.
2. The method according to claim 1, wherein the elevated flow speed is constant over the entire extension length of the annular outlet-side channel.
3. The method to control the operation of a tube bundle heat exchanger according to claim 1 or 2, wherein the heating control parameters and the specific fluid mechanical shearing stress are determined by the properties of the concentrate to be heated and the physical conditions, • wherein the properties of the concentrate to be heated are understood as being its volumetric flow, viscosity, pressure, temperature and concentration of dry material, and the physical conditions are understood as being the pressure and temperature at the site at which the concentrate is handled following the specific fluid mechanical shearing stress, • wherein the control parameters with reference to the concentrate are the pressure, the outlet-side heating temperature, the elevated flow speed and intensity of the fluid mechanical shearing stress, and • wherein the control parameters are set by means of a calibration function set or saved before or while starting up the tube bundle heat exchanger.
4. A use of the method according to any one of claims 1 to 3 in a system for atomized drying, wherein the concentrate, after being heated and after the specific fluid mechanical shearing stress, is then directly transferred to where it is atomized under pressure, wherein a transfer time for direct transference is determined by a corresponding effective distance in terms of flow between the means for applying the specific fluid mechanical shearing stress and the pressure atomization site.
5. The tube bundle heat exchanger for performing the method according to claim 1, • having at least one tube bundle that consists of a number of parallel connected inner tubes through which concentrate flows on the inside, • the inner tubes are annular, arranged on a single circle, and are in each case braced at the end in a first and a second tube support plate, • the inner tubes extend in the longitudinal direction of an outside channel formed as an annular gap through which a heating medium flows, • the inner tubes possess a common inlet designed in the form of a first connection opening that is in a first exchanger flange connected to the first tube support plate and is arranged centrally there, • the inner tubes possess a common outlet designed in the form of a second connection opening that is in a second exchanger flange connected to the second tube support plate and is arranged centrally there, • at least at the outlet side, the inner tubes fluidically terminate in a circumferential annular gap that is formed in the second tube support plate, and/or the second exchanger flange, • the circumferential annular gap is fluidically connected across an annular outlet-side channel to the second connection opening, • the annular outlet-side channel is bordered radially to the outside by the second exchanger flange, and radially to the inside by a displacement body that is arranged in an axially symmetrical manner on the second tube support plate, • the annular outlet-side channel has a specific extension length, and a specific length-dependent progression of its channel passage cross sections, wherein • the first connection opening transitions smoothly into an inner passage of a connecting elbow or connecting fitting that is upstream from the first connection opening viewed in the direction of flow, • the second connection opening transitions smoothly into an inner passage of a connecting elbow or connecting fitting that is downstream from the second connection opening viewed in the direction of flow, • the respective connecting elbow/connecting fitting engages somewhat in the associated exchanger flange, and is welded to the outside of the exchanger flange with a high-pressure-resistant, multilayer first weld seam, and to the inside with a second weld seam, and • at the outlet side in the associated tube support plate, the end of each inner tube is circumferentially welded to said tube support plate with a third weld seam and is high-pressure resistant.
6. The tube bundle heat exchanger according to claim 5, wherein the channel passage cross-sections of the annular outlet-side channel are constant over the entire extension length.
7. The tube bundle heat exchanger according to claim 6, wherein the channel passage cross-section corresponds to the overall passage cross section of all inner tubes with a parallel flow.