EP3475642B1 - 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 - Google Patents

Description

TECHNICAL AREA

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 and a tube bundle heat exchanger for carrying out the method according to the preamble of claim 5. The invention further relates to a method for control the operation of a tube bundle heat exchanger of the type in question. Temperature-sensitive concentrates are to be understood in particular to mean those substrates which have a high content of proteins and drying agents and little water, which easily denature, which undergo an increase in viscosity during heating or one Gelation subject and are processed under aseptic conditions to a sterile end product.

STATE OF THE ART

Indirect product heating, for example in UHT systems (UHT: ultra-high temperature), by heat exchange on a wall can be carried out with so-called plate heat exchanger systems or, as in the invention described below, with so-called tube bundle heat exchangers which the heat energy is transmitted through the tube walls of a group of inner tubes. The food product to be treated flows in the inner tubes, while a heat transfer medium, hereinafter referred to as heating medium in the context of the invention, usually water or steam, flows through the annular gap space of a jacket tube, which surrounds the parallel connected inner tubes. A related tube bundle heat exchanger is from the DE 94 03 913 U1 known. The DE 10 2005 059 463 A1 also discloses such a tube bundle heat exchanger for a low pressure level and also shows how a number of tube bundles can be arranged in parallel in this heat exchanger and connected in series through the fluid by means of a connecting bend or connecting fittings. An arrangement in this regard shows Figure 1 this document (state of the art).

Particularly temperature-sensitive products, such as concentrates, especially those with a high dry matter content, require the product to be precisely and quickly adjusted to the required temperature conditions. This results in the requirement that all partial quantities of a product to be subjected to the heat treatment of the type in question pass through the required same temperature-level curve at the same time and over the same period of time. In other words, this means that all subsets are subject to the same thermal and fluid-mechanical conditions with the same dwell time.

The branching problem of the flow in the inlet area of the tube support plates of a tube bundle heat exchanger (e.g. DE 94 03 913 U1 ), as he prefers to use in UHT systems, is dedicated to DE 103 11 529 B3 , The targeted measures proposed under the task specified there relate exclusively to the branching of a product onto the inner tubes of the tube bundle heat exchanger which hold a number of partial quantities of this product, wherein, among other things, a displacement body is provided which is arranged axially symmetrically and concentrically with the tube carrier plate. This prior art thus relates exclusively to a device for influencing the flow area of a tube support plate of a tube bundle heat exchanger in question. The inner tubes are arranged over the entire circular area of the tube support plate, with the exception of a narrowly limited central area, and are generally distributed over more than one partial circle. Under these conditions, flow paths of different lengths for entering and exiting the inner pipes exist both in the entry and in the exit area of the respective tube support plate, that is to say when branching and combining the flow. This alone results in different dwell times for the partial quantities of the product flowing through the respective inner tubes.

The WO 2011/085784 A2 proposes to solve the above-described problem of different dwell times in the branching and the unification of the flow, to arrange all the inner tubes of the tube bundle in a circular shape, on a single circle and in an outer channel of the tube bundle heat exchanger designed as an annular space, the inner tubes flowing in parallel in the longitudinal direction of the outer channel and support each end in a tube support plate. This arrangement of the inner tubes is combined with an axially symmetrical displacer which is fixedly arranged concentrically on the tube support plate at the inlet and at the outlet of the product. The respective displacer body extends centrally through an exchanger flange assigned to the tube support plate, the exchanger flange having a connection opening on its side facing away from the associated tube support plate. The end regions of the known tube bundle heat exchanger are, at least in each case adjacent to the outer channel, of mirror-image design and of identical dimensions, this symmetry expressly also encompassing the two displacement bodies and the two annular channels.

This results in almost congruent flow paths and largely uniform heat transfer conditions in all relevant areas of the tube bundle heat exchanger for all parts of the product that branch and unite between product entry and exit into the inner tubes. However, congruent flow paths do not mean that the flow patterns of the individual subsets are designed with an unchanged flow speed that avoids acceleration or deceleration.

With regard to the formation of deposits on the tube support plates, it has been shown in practical operation that when viscous dairy products, for example concentrates, are heated, the symmetrical flow geometry shown above on the inlet-side, ie on the flowed tube support plate, does not lead to any deposits which impair the service life. but probably on the outlet-side, the outflowed tube support plate.

In order to avoid deposits on the outlet-side, the outflowed tube support plate beats the DE 10 2013 010 460 A1 in this context, the annular space-shaped outlet-side channel has a channel passage cross-section at least everywhere in its area between a largest outer diameter of the outlet-side displacer body and the connection opening, which corresponds to a total passage cross-section of all inner tubes with parallel flow. Such a tube bundle heat exchanger has proven suitable for heating processes of the type in question at the usual, relatively low pressure level.

The production of powdered food products, in particular milk products, such as, for example, easily soluble foods for small children, is carried out in many cases by atomizing or spray drying in a so-called drying tower. There, a concentrate which has previously been concentrated to a certain dry substance content in an evaporator or an evaporator and then warmed to a defined temperature in a heater is atomized into a hot air stream, for example via nozzles, in particular single-substance nozzles. The concentrate emerging from the heater is fed to these so-called pressure atomizing nozzles by means of a high-pressure piston pump, a so-called nozzle pump, with a pressure which can reach up to a maximum of 350 bar.

The static of the dryer towers is usually not sufficient to support the heavy high-pressure piston pump and to install it in the immediate vicinity of the pressure atomizer nozzles, which would be desirable for technological and procedural reasons. A high-pressure piston pump located in the vicinity of the pressure atomizer nozzles would work in this area, the so-called hot space in the head space of the drying tower, at ambient temperatures which are between 75 and 80 ° C. and would require aseptic operation. A further thermal inactivation of microorganisms would also not be possible.

For the reasons mentioned above, the high-pressure piston pump has hitherto been arranged in the lower region of the drying tower. A significant difference in height between the high-pressure piston pump and the pressure atomizer nozzles is bridged via a riser, which, according to plan or inevitably, also functions as a hot holding section.

In order to ensure that the powdered food product is stored for as long and as hygienically as possible, the end product must have good solubility and be as germ-free as possible. The necessary sterility results from the killing of microorganisms as far as possible for the concentrate escaping from the heater if this is carried out with a suitable temperature and holding time profile and if the riser to the pressure atomizer nozzles, which acts as a heat retention section, is taken into consideration. For the production of so-called "low heat powder" a temperature of maximum 77 ° C, of so-called "high heat powder" of approx. 85 ° C and of so-called "ultra high heat powder" of up to 125 ° C is required.

The inevitable mean residence time of the concentrate in the riser after high pressure treatment in connection with a hot temperature has an undesirable effect on the solubility of the end product. In addition, the long heat retention in the riser can lead to an uncontrolled denaturation of the concentrate. For example, the average residence time of the concentrate is 42 seconds when it is conveyed in a 30 m long riser pipe with a diameter of DN50 with a volume flow of 5,000 liters / h. This usually means a reduction in the quality of the end product. Denaturation in this regard can, for example, influence the powder quality of baby food in such a way that its complete solubility is no longer ensured and an unacceptable lump formation occurs in the prepared baby food. In addition, the long dwell time at high temperatures leads to chemical reactions in the concentrate and formation of deposits, so-called product fouling, on the walls of the riser and in the pressure atomizer nozzles, which undesirably increases the production time for a batch of concentrate.

For example, in the case of milk concentrates to avoid crystallization processes in lactose, the temperature in the riser and thus up to the pressure atomizer nozzles must not be higher than 65 to 68 ° C. The long riser therefore limits the permissible temperature there.

The necessary sterility up to the entry into the pressure atomizer nozzles can also be endangered by the high pressure piston pump, since this cannot pump the concentrate under aseptic conditions with reasonable technical effort. Aseptic production conditions, on the other hand, require considerable technical effort, which in practice is usually not or cannot be operated. Germs from the ambient air can be introduced into the concentrate via the pistons of the high-pressure piston pump, so that reinfection can take place there. The pulverulent end product can then have germs and the germination will increase over time under the influence of the residual moisture notoriously remaining in the end product.

According to the prior art, aseptic conveyance of the liquid starting product emerging from the heater is only possible in the downstream high-pressure piston pump with increased technical outlay.

• die Steigleitung wirkt wie eine technologisch an sich unerwünschte Verweilzeitstrecke und ein Heißhalter;
• die Verweilzeit verringert zwangsläufig die Eintrittstemperatur in die Druckzerstäuber-Düsen;
• durch die Verweilzeit ergibt sich ein unerwünschter Viskositätsanstieg (Geliereffekt);
• der Zustand des temperatursensiblen Konzentrats ist vor den Druckzerstäuber-Düsen nicht klar definiert, weil die Verweilzeit in der Steigleitung nicht klar definiert werden kann;
• durch die Verweilzeit in Verbindung mit der Heißhaltung kann es zur Denaturierung des Konzentrats kommen, die mit verstärkten Konzentratablagerungen einhergeht;
• es ergibt sich eine geringere Standzeit der Anlage, die dadurch öfter zu reinigen ist;
• die Hochdruck-Kolbenpumpe müsste steril arbeiten, d.h. das Konzentrat muss durch die Pumpe aseptisch behandelt werden, was mit hohen Kosten verbunden ist;
• Hochdruck-Kolbenpumpen, die nicht aseptisch arbeiten, können zu einem stark verkeimten Endprodukt führen;
• durch die relativ niedrige Temperatur vor den Druckzerstäuber-Düsen ergibt sich eine reduzierte Mengenleistung des Trocknerturms.

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

• the riser acts like a technologically undesirable dwell time and a hot holder;
• the dwell time inevitably lowers the inlet temperature into the pressure atomizing nozzles;
• the dwell time results in an undesirable increase in viscosity (gelling effect);
• the state of the temperature-sensitive concentrate is not clearly defined in front of the pressure atomizer nozzles because the residence time in the riser cannot be clearly defined;
• the dwell time in connection with keeping hot can lead to denaturation of the concentrate, which is accompanied by increased concentrate deposits;
• there is a shorter service life of the system, which means that it must be cleaned more often;
• the high-pressure piston pump would have to work sterile, ie the concentrate must be treated aseptically by the pump, which is associated with high costs;
• High pressure piston pumps that do not work aseptically can lead to a highly contaminated end product;
• The relatively low temperature upstream of the pressure atomizer nozzles results in a reduced output of the dryer tower.

In order to achieve the necessary sterility of the liquid concentrate emerging from the high-pressure piston pump under high pressure, it has already been proposed to provide suitable high-pressure heating of this concentrate on the way to the pressure atomizer nozzles. This high-pressure heating could take place immediately upstream of the pressure atomizer nozzles, as a result of which the temperature in the riser pipe could be reduced to an uncritical level. This arrangement would continue to allow the operation of a non-aseptic high pressure piston pump at the foot of the dryer tower.

In this context, it has also already been proposed to carry out the high-pressure heating in a sufficiently pressure-resistant monotube which is heated with steam or a heated gas from the outside ( US 3,072,486 A ). However, this proposal is not expedient, since no uniform heat input over the outside and over the entire length of the monotube and thus no equal dwell time for all particles of the concentrate flowing in the monotube is ensured.

A heat exchanger that would meet the requirements for a sufficiently uniform heat input and for a residence time that was approximately the same for all particles of the concentrate, but at a low pressure level, would be fundamental a so-called tube bundle heat exchanger of the type described above ( DE 10 2013 010 460 A1 ; DE 10 2005 059 463 A1 ), which could in principle take the place of the aforementioned monotube.

In the meantime, a bend or a connection fitting for product pressures up to 350 bar is available for connecting the tube bundle in a tube bundle heat exchanger in this regard ( DE 10 2014 012 279 A1 ), whereby the known embodiments of the tube bundle heat exchanger are generally not suitable for this high pressure level.

The procedural problem, however, is also not solved, which consists in subjecting a concentrate, for example for atomizing drying, immediately before the pressure atomizer nozzles to a treatment by means of which the tendency to denaturate the concentrate, to increase the viscosity in the concentrate or to gel the Concentrate and deposits of the same reduced and a germ-free, ie microbiologically perfect end product is ensured.

The object of the present invention is therefore to overcome the disadvantages of the prior art and to provide a method of the generic type and a tube-bundle heat exchanger for carrying out the method which, at a high pressure level, have a tendency to denaturate the concentrate and to increase the viscosity in the concentrate or to reduce the gelation of the concentrate and its deposits and a germ-free, ie Ensure the microbiologically perfect end product.

SUMMARY OF THE INVENTION

This object is achieved by a method with the features of independent claim 1. An advantageous embodiment of the method is the subject of the subclaim. A tube bundle heat exchanger for performing the method is specified with the features of claim 5. Advantageous embodiments of the tube bundle heat exchanger according to the invention are the subject of the associated subclaims. A method of controlling the Operation of a tube bundle heat exchanger according to claim 1 or 2 is the subject of claim 3.

The present invention is based on a tube bundle heat exchanger, as it is in its basic structure in the DE 10 2013 010 460 A1 is described. This has at least one tube bundle, which consists of a number of inner tubes connected in parallel and inside each of which the concentrate flows. The inner tubes are circular, arranged on a single circle, they are supported at the ends in a first and a second tube support plate and they extend in the longitudinal direction of an outer channel designed as an annular space through which a heating medium flows. The inner tubes are preferably arranged in the outer edge region of the respective tube support plate.

The inner tubes have a common inlet, which is formed in a first exchanger flange connected to the first tube carrier plate in the form of a first connection opening arranged centrally there with respect to an axial axis of symmetry of the tube bundle, and they have a common outlet, which is in one with the second Tube carrier plate connected second exchanger flange is formed in the form of a second connection opening also arranged centrally there. Furthermore, the inner tubes end in a fluid-permeable manner at least on the outlet side in a circumferential annular space which is formed in the second tube carrier plate and / or the second exchanger flange. The circumferential annulus is fluidly connected to the second connection opening via an annulus-shaped outlet-side channel, and the annulus-shaped outlet-side channel is delimited radially on the outside by the second exchanger flange and radially on the inside by an axially symmetrically arranged displacer body. The annulus-shaped outlet-side channel has a defined extension length and a defined length-dependent course of its channel passage cross sections. The entry side of the inner tubes in connection with their surroundings can, as in the DE 10 2013 010 460 A1 shown, designed. However, this is not mandatory in connection with the present invention.

The feature with regard to the arrangement of a number of inner tubes with parallel flow is to be understood as an arrangement which, regardless of the number of inner tubes, for example 4 to 19 or more in number, does not occupy an entire circular cross section of the tube carrier plate. Rather, all inner tubes are arranged on said single circle, which leaves an inner area, not just a limited center, unoccupied by inner tubes. This arrangement makes it possible for the inner channel, formed by the inner tubes arranged in the form of a ring and arranged on a single circle, in the flow direction, to be designed in the form of the circumferential annular space following the inner tubes.

The basic idea of the invention is to first increase the pressure of the concentrate to a maximum pressure of 350 bar, as is necessary for a treatment of the concentrate following heating. The concentrate is then heated at this high pressure level. This heating is combined with a defined fluidic shear stress, which is provided in the course of the heating and / or preferably immediately after the heating. The defined fluidic shear stress, which does not require any moving elements and / or the supply of external energy, takes place in the respective inner tube with its defined passage cross-section and its defined flow-through length and with an increased flow rate and / or preferably in an annular space-shaped outlet-side connecting to the inner tubes Channel. The latter has a defined extension length and a defined length-dependent course of its channel passage cross sections and is flowed through with the increased flow velocity. In this regard, it is proposed that the increased flow speed be up to a maximum of 3 m / s.

• dass die konzentratseitigen Strömungswege des Rohrbündel-Wärmeaustauschers derart ausgelegt sind, dass das Konzentrat mit einem Druck bis maximal 350 bar beaufschlagt ist,
• dass eine definierte strömungsmechanische Scherbeanspruchung des Konzentrats erzeugt wird, die den als Geliereffekt bezeichneten Viskositätsanstieg im Konzentrat einerseits tendenziell reduziert und andererseits standardisiert,
• dass bei der Erhitzung des Konzentrats in den Innenrohren zur Erzeugung der definierten strömungsmechanischen Scherbeanspruchung eine erhöhte Strömungsgeschwindigkeit des Konzentrats in den Innenrohren vorgesehen ist
• und/oder dass zur Erzeugung der definierten strömungsmechanischen Scherbeanspruchung eine erhöhte Strömungsgeschwindigkeit des Konzentrats im ringraumförmigen austrittsseitigen Kanal vorgesehen ist und
• dass die erhöhte Strömungsgeschwindigkeit bis maximal 3 m/s beträgt.

To solve the problem on which the present invention is based, it is specifically provided

• that the flow paths of the tube bundle heat exchanger on the concentrate side are designed in such a way that the concentrate is pressurized to a maximum of 350 bar,
• that a defined fluidic shear stress is generated on the concentrate, which on the one hand tends to reduce the viscosity increase in the concentrate referred to as the gelling effect and on the other hand standardizes it,
• that when the concentrate is heated in the inner tubes to generate the defined fluidic shear stress, an increased flow rate of the concentrate is provided in the inner tubes
• and / or that an increased flow velocity of the concentrate is provided in the annular space-shaped outlet-side channel in order to generate the defined fluid-mechanical shear stress and
• that the increased flow speed is up to a maximum of 3 m / s.

It is advantageous in terms of the same dwell time for all parts of the heat-treated concentrate, as another proposal provides, if the increased flow velocity is constant over the entire length of the outlet channel on the annular space.

With the high-pressure heating according to the invention, the disadvantageous keeping of pressure between the increase in pressure to the high-pressure level, which is followed by the low-pressure heating, and a further treatment of the concentrate following the increase in pressure, which has hitherto been accepted in the prior art, is virtually eliminated and succeeds immediately this further treatment, for example pressure atomization, to define the heating or to set up the heat treatment in a reproducible manner. Depending on and adapted to the concentrate, the desired heat loads, the mass flow and the ingredients can be defined. In addition, it is also possible to denature the concentrate in a controlled manner with a view to the desired end product by setting the temperature and residence time during high-pressure heating. In this way, for example, an effective microbiological improvement of the end product or a defined swelling of protein or starch is achieved.

Due to the lower temperature up to high-pressure heating and the shorter dwell time at high temperature in the course of high-pressure heating, the viscosity increase in the concentrate, the so-called gelling effect, due to crystallization processes and / or product-specific properties, is lower than in known processes. This gelling effect tends to be reduced on the one hand by the defined shear stress and on the other hand the gelling effect is standardized, which reduces the tendency to form deposits in the process plant for further treatment of the concentrate. This reduces cleaning and set-up times.

• es ist ein Wärmeaustausch mit geringerer Wärmeaustauscherfläche möglich;
• es ist ein Eiweißkonzentrat mit höherer Konzentration möglich;
• es sind ein höherer Volumenstrom und damit eine höhere Durchsatzleistung möglich;
• es sind, bedingt durch den besseren Wärmeübergang, eine höhere Erhitzung des Konzentrats und dadurch, beispielsweise bei der Druckzerstäubung, eine höhere Trocknungsleistung möglich;
• es erfolgt eine definierte, planmäßig gewünschte Denaturierung des Konzentrats.

Since the increase in flow velocity compared to a process design previously practiced in this regard only takes place at the high pressure level, the associated additional pressure losses do not play a significant role in the respective high pressure heating process. The increased flow rate results in better heat transfer on the concentrate side, which has the following additional advantages:

• heat exchange with a smaller heat exchange surface is possible;
• a protein concentrate with a higher concentration is possible;
• a higher volume flow and thus a higher throughput are possible;
• due to the better heat transfer, a higher heating of the concentrate and thereby, for example during pressure atomization, a higher drying capacity are possible;
• there is a defined, planned denaturation of the concentrate.

The invention further proposes a tube-bundle heat exchanger for carrying out the method, which, in a manner known per se, has, inter alia, at least one tube bundle which consists of a number of inner tubes through which the concentrate flows in parallel, which are arranged in an annular manner and in a single circle Support each end in a first and a second tube support plate. The inner tubes end in a fluid-permeable manner at least on the outlet side in a circumferential annular space which is formed in the second tube carrier plate and / or the second exchanger flange.

The means for the defined fluidic shear stress of the concentrate consist of an annular channel on the outlet side, which is fluidly connected to the outlet of the circumferential annular space, which is formed in the second tube support plate and / or the second exchanger flange, and fluidly connected to the second connection opening. The annular space on the outlet-side channel is delimited radially on the outside by the second exchanger flange and radially on the inside by an displacer body arranged axially symmetrically on the second tube support plate. The annular space has in the most general case, the outlet-side channel has a defined extension length and a defined course of its channel passage cross sections which is dependent on the extension length.

All flow paths of the tube bundle heat exchanger acted upon by the concentrate are designed so that they can withstand an internal pressure of up to a maximum of 350 bar. According to the invention, the first connection opening is seamless, i.e. in alignment and without changing the cross-section, into an inner passage of a connecting bend or a connecting fitting which, viewed in the direction of flow, is arranged upstream of the first connection opening. The second connection opening is seamless, i.e. aligned and without changing the cross-section, into an inner passage of a connecting bend or a connecting fitting, which, viewed in the direction of flow, is arranged downstream of the second connection opening.

In order to create favorable strength requirements for the high internal pressure at the critical connection point between the respective exchanger flange and the associated connection bend / connection fitting, the respective connection bend / connection fitting reaches into the assigned exchanger flange to a certain extent by at least the wall thickness of the person Connection bend / connection fitting at this point, namely by a depth of penetration. The connecting bend or the connecting fitting is welded to the associated exchanger flange on the outside with a high-pressure-resistant, multi-layer, orbital first weld seam, preferably a so-called fillet weld, and on the inside with an orbital second weld seam, preferably a so-called V-seam. Furthermore, in order to ensure a high-pressure-resistant design, the end of each inner tube on the outlet side is welded all around to the associated tube carrier plate with a third weld seam, preferably a fillet or corner seam.

It is advantageous in the sense of the same dwell time for all parts of the heat-treated concentrate, as is also proposed that the channel passage cross sections of the annular-shaped outlet-side channel are constant over the entire length of the extension. This desirable equal treatment is further promoted by the fact that the increased flow velocity through the entire tube bundle heat exchanger is as uniform as possible up to the end of the defined shear stress of the concentrate, a further embodiment providing in this regard that the channel cross-section of the annular-shaped outlet-side channel corresponds to the total cross-section of all inner tubes with parallel flow.

The method according to the invention and the tube bundle heat exchanger for carrying it out can be controlled in an advantageous manner depending on the concentrate. To this end, the invention proposes a method for controlling the operation of a tube bundle heat exchanger, the control parameters for the heating and the defined fluidic shear stress being determined by the properties of the concentrate to be heated and the physical boundary conditions. The properties of the concentrate to be heated are understood to mean its volume flow, viscosity, pressure, temperature and dry substance concentration, and the physical boundary conditions are understood to mean pressure and temperature at the location of a treatment of the concentrate which follows the defined fluid mechanical shear stress. The control parameters, based in each case on the concentrate, are the pressure, an outlet-side heating temperature, the increased flow speed and an intensity of the defined fluidic shear stress, generated by a specific design of the annular-shaped outlet-side channel.

• beim An- und Einfahren des Rohrbündel-Wärmeaustauschers mit einem diskreten Konzentrat (Rezeptur) bis zur Gewinnung einer befriedigenden Produktqualität Steuerungsparameter der in Rede stehenden Art erhalten werden,
• die registriert und in einer Steuerung in Form der "Kalibrierfunktion" (Steuerungsparameter = Funktion von (Konzentrat bzw. Rezeptur)) abgespeichert werden.

The control parameters are set using a calibration function created or stored before or when the tube bundle heat exchanger is started up. The calibration function is obtained by

• control parameters of the type in question are obtained when starting up and running in the tube bundle heat exchanger with a discrete concentrate (recipe) until a satisfactory product quality is obtained,
• which are registered and stored in a control system in the form of the "calibration function" (control parameter = function of (concentrate or recipe)).

When the same concentrate (formulation) is subsequently treated, these empirical values can be accessed in the form of this calibration function and the necessary control parameters can be set accordingly.

The method according to the invention and the method for controlling the operation of a tube bundle heat exchanger can advantageously be applied to the atomizing drying of concentrates in drying plants with a drying tower, the concentrate then immediately after heating and the defined fluidic shear stress, i.e. is immediately transferred to a place where it is atomized. A transfer time for the direct transfer is determined by a corresponding fluidically effective distance between the means for carrying out the defined fluidic shear stress and the location of the pressure atomization. In this context, directly in the ideal case means that the exit of the means for carrying out the defined fluidic shear stress immediately, i.e. without the interposition of a pipeline section into which the atomizer nozzle (s) opens or is brought up to it.

BRIEF DESCRIPTION OF THE DRAWINGS

Figur 1

im Meridianschnitt eine Ausführungsform eines bevorzugt verwendeten Rohrbündel-Wärmeaustauschers entsprechend einem in Figur 2 mit A-A gekennzeichneten Schnittverlauf, wobei die Darstellung auf dessen eintritts- und austrittsseitigen Bereich beschränkt ist;

Figur 2

eine Seitenansicht des Rohrbündel-Wärmeaustauschers gemäß Figur 1 entsprechend einer auf die Austrittseite gerichteten Blickrichtung;

Figur 3

im Meridianschnitt allein den austrittseitigen Bereich des Rohrbündel-Wärmeaustauschers gemäß Figur 1 und

Figur 4

im Meridianschnitt den austrittseitigen Bereich des Rohrbündel-Wärmeaustauschers in einer gegenüber Figur 3 vergrößerten Darstellung.

A more detailed description of the invention results from the following description and the accompanying figures of the drawing and from the claims. While the invention is implemented in the form of an independent method and in the most varied of embodiments of a tube bundle heat exchanger for carrying out the method, the basic structure of a tube bundle heat exchanger known per se is shown in the drawing, based on the preferred embodiment of the method according to the invention is described. Show it

Figure 1

in meridian section an embodiment of a tube bundle heat exchanger preferably used corresponding to an in Figure 2 AA marked section, the illustration is restricted to the area on the entry and exit side;

Figure 2

a side view of the tube bundle heat exchanger according to Figure 1 according to a direction of view directed towards the exit side;

Figure 3

in the meridian section alone according to the outlet area of the tube bundle heat exchanger Figure 1 and

Figure 4

in the meridian section the outlet-side area of the tube bundle heat exchanger in one opposite Figure 3 enlarged view.

DETAILED DESCRIPTION

A tube bundle heat exchanger 100, of which a tube bundle 100.1 is shown, has between an inlet E penetrated by an entire concentrate P and an outlet A (see Figure 1 ) have congruent flow paths for all subsets of the concentrate P which branch and unite between the latter. This is achieved objectively in that, in the case of the tube bundle 100.1, which consists of a group of inner tubes 300 connected in parallel and flowed through by the concentrate P on the inside in each case, all the inner tubes 300 are annular, on a single circle K ( Figure 3 ) and are arranged in an outer channel 200 * designed as an annular space and extend in the longitudinal direction thereof and are supported at the ends in a first and a second tube support plate 700, 800. The inner tubes 300 are arranged in the largest possible circumferential area of the tube support plate 700, 800, preferably evenly distributed over the circumference of the circle K. A number N ( Figure 4 ) the inner tubes 300, which extend axially parallel to an outer jacket 200.1 of the outer channel 200 * through the latter, together forming an inner channel 300 *, are passed through the end of the first tube support plate 700 and the second tube support plate 800 (both also referred to as tube mirror plate) and there at their respective Pipe outer diameter and welded to its respective end face by means of a third weld S3 high pressure resistant.

The inner tubes 300 ( Figure 1 ) have on the one hand the common inlet E, which is formed in a first exchanger flange 500 connected to the first tube support plate 700 in the form of a first connection opening 500a arranged centrally there with respect to an axial axis of symmetry a of the tube bundle 100.1, and on the other hand the inner tubes 300 have the common outlet A, which is formed in a second exchanger flange 600 connected to the second tube support plate 800 in the form of a second connection opening 600a arranged centrally there.

The first tube support plate 700 is screwed to the assigned first exchanger flange 500 and the second tube support plate 800 is screwed to the assigned second exchanger flange 600 in a pressure-resistant manner. Depending on the respective flange dimensions, a number of screw connections ( Figures 2, 3 ) are provided, which preferably consist of screw bolts 1100 anchored in the tube support plates 700, 800 in connection 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 against the first tube support plate 700 by a flange seal 900. The same applies to the second exchanger flange 600 and the second tube support plate 800.

In the in Figure 1 The embodiment shown are the end regions of the tube bundle 100.1 of the tube bundle heat exchanger 100, with the exception of an inlet and outlet displacement body 11, 12 and its respective immediate vicinity in the region of the exchanger flange 500, 600, each following the outer channel 200 *, preferably mirror image of identical shape and dimensionally identical. Because the present invention relates to the downstream side of the tube bundle 100.1, the following description can primarily refer to the outlet-side end region ( Figure 4 ) limit and the corresponding reference numerals of the other end range are only given. The structure of the entry-side area is derived from the construction of the exit-side area.

The exchanger flange 600, 500 has on its side facing away from the associated tube support plate 800, 700 the connection opening 600a, 500a, which has a nominal diameter DN and thus corresponds to a nominal passage cross section A _{0 of} a connecting bend / connecting fitting 1000 connected there (A _o = DN ² π / 4). The connection opening 600a, 500a merges seamlessly into an inner passage of the connection bend / connection fitting 1000, which, viewed in the flow direction, is arranged downstream of the second connection opening 600a or upstream of the first connection opening 500a. The respective connection bend / connection fitting 1000 engages to a certain extent in the assigned exchanger flange 600, 500 to ensure the necessary high-pressure strength, and does so with an engagement depth t, and is on the outside with the exchanger flange 600, 500 with a high-pressure-resistant, multi-layered first weld S1, preferably a fillet weld, and welded on the inside with a second weld S2, preferably a V-seam. The end of each inner tube 300 is welded all around on the outlet side into the associated tube support plate 800, 700 with the third weld seam S3, preferably a corner seam.

As a rule, the tube bundle heat exchanger 100 is composed of more than one tube bundle 100.1. In its central part, the tube bundle 100.1 consists of the outer jacket 200.1 delimiting the outer channel 200 * with the first tube support plate 700 arranged on the right-hand side with respect to the illustration, and the second tube support plate 800 arranged in the same way on the left-hand side. In the area of the left-hand end of the outer jacket 200.1 on the latter a first connection piece 400a and in the area of the right-hand end of the outer casing 200.1 a second connection piece 400b is provided on the latter for the application of a heating medium M. The outer channel 200 * for the heating medium M is delimited from the inside by an inner jacket 200.2.

The inner tubes 300, viewed in the direction of flow, terminate in a circumferential annular space R (at least on the outlet side) Figure 4 ), which is formed in the second tube support plate 800 and / or the second exchanger flange 600. The circumferential annular space R is via an annular outlet side Channel 600b fluidly connected to the second connection opening 600a. The annulus-shaped outlet-side channel 600b is delimited radially on the outside by the second exchanger flange 600 and radially on the inside by the outlet-side displacement body 12 arranged axially symmetrically on the second tube support plate 800. The annulus-shaped outlet-side channel 600b has a defined extension length L and a defined length-dependent course of its channel passage cross sections A _S.

With a view to the distribution problem to be solved, it is also expedient for the inlet side of the tube bundle 100.1 of the tube bundle heat exchanger 100 ( Figure 1 ), adequate to the outlet side, in the form of an annular-shaped inlet-side channel 500b, which is delimited radially on the outside by the first exchanger flange 500 and radially on the inside by the inlet-side displacement body 11 arranged symmetrically on the first tube support plate 700. With regard to the defined fluidic shear stress, this is not aimed at on the inlet side; it is located in the inner tubes 300 and preferably in the annulus-shaped outlet-side channel 600b.

A medium increased flow velocity in the inner tube 300 and thus in the inner channel 200 * is marked with v ( Figures 1 . 4 ). The annulus-shaped outlet-side channel 600b has, at least everywhere in its area between a largest outer diameter of the outlet-side displacer 12 and the second connection opening 600a, the defined extension length L and, in the most general case, the defined length-dependent course of its channel passage cross sections A _S.

The annulus-shaped outlet-side channel 600b is preferably designed with a constant passage cross-section over the entire defined extension length L (A _S = const), the channel passage cross-section A _S in this area being a total passage cross-section NA _{i of} all inner tubes 300 through which the flow is parallel and of the number N, each having a single passage cross-section A _i own corresponds. The individual passage cross-section is measured with A _i = D _i ² π / 4, where D _i is the inner tube diameter of the inner tube 300.

As already described above in connection 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 under a high pressure p is distinguished in that, on the one hand, the concentrate P acts on it Flow paths of the tube bundle heat exchanger 100 are designed in such a way that the concentrate P can be pressurized with 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 in such a way that the increased flow velocity v of the concentrate P in the inner tubes 300 and / or in the annular-shaped outlet-side channel 600b is provided to generate a defined fluidic shear stress of the concentrate P. which is up to a maximum of 3 m / s ( Figure 4 ).

The tube-bundle heat exchanger 100, which is designed as a high-pressure heat exchanger, has on the output side means for defined fluid-mechanical shear stress on the concentrate P being conveyed, these means being effective without mechanical elements and / or supply of external energy purely in terms of fluid mechanics through defined passage cross-sections, defined lengths of the flow paths and defined increased flow velocities are. The means for the defined shear stress of the concentrate P preferably consist in the annular space-shaped outlet-side channel 600b, which on the one hand has the exit of the circumferential annular space R, which is formed in the second tube support plate 800 and / or the second exchanger flange 600, and on the other hand has the second connection opening 600a connected is. In the most general case, the annulus-shaped outlet-side channel 600b has the defined extension length L and the defined course of its channel passage cross sections A _S which is dependent on the extension length L.

It is advantageous in terms of the same dwell time for all parts of the heat-treated concentrate P, as is also proposed, that the channel passage cross sections A _S are constant over the entire extension length L. This desirable equal treatment is further promoted in that the increased flow velocity v through the entire tube bundle heat exchanger 100 or the respective tube bundle 100.1 is as uniform as possible until the end of the defined shear stress of the concentrate P, a further embodiment providing in this regard that the channel passage cross section A _{S of} the annular outlet-side channel 600b corresponds to the total passage cross section NA _{i of} all inner tubes 300 through which flow occurs in parallel.

REFERENCE SIGN LIST OF ABBREVIATIONS USED

11

inlet-side displacer

12

outlet-side displacement body

100

Shell and tube heat exchangers

100.1

tube bundle

200 *

outer channel

200.1

outer sheath

200.2

inner sheath

300 *

internal channel

300

inner tube

400a

first connection piece

400b

second connecting piece

500

first exchanger flange

500a

first connection opening

500b

Annular duct on the inlet side

600

second exchanger flange

600a

second connection opening

600b

Annular duct on the outlet side

700

first tube support plate (tube mirror plate)

800

second tube support plate (tube mirror plate)

900

flange

1000

Connection bend / connection fitting

1100

bolts

1200

mother

1300

washer

a

axial axis of symmetry

p

print

t

depth of engagement

v

increased flow velocity

A

exit

A _i

Single passage cross section (of the inner tube (A _i = D _i ² π / 4))

NA _i

Total cross section (of all inner tubes with parallel flow)

A _S

Channel flow cross-section

A _o

Nominal cross-section (of the connecting bend; A _o = DN ² π / 4)

D _i

Inner tube diameter (inner tube 300)

DN

Nominal diameter (of the connecting bend (A _o = DN ² π / 4))

e

entry

K

circle

L

length of extension

M

heating medium

N

Number (of inner tubes 300)

P

concentrate

R

circumferential annulus

S1

multilayered first weld

S2

second weld

S3

third weld

T

outlet-side heating temperature

Claims (7)

1. A method for operating a tube bundle heat exchanger for heating a temperature-sensitive concentrate (P) of a food product under high-pressure with the tube bundle heat exchanger (100) that has the following features:

   • at least one tube bundle (100.1) that consists of a number (N) of parallel-connected inner tubes (300) through which concentrate (P) flows on the inside,

   • the inner tubes (300) are annular, arranged on a single circle K, and are in each case braced at the end in a first and a second tube support plate (700, 800),

   • the inner tubes (300) extend in the longitudinal direction of an outside channel (200*) formed as an annular gap through which a heating medium (M) flows,

   • the inner tubes (300) possess a 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 there,

   • the inner tubes (300) possess a common outlet (A) 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 there,

   • at least at the outlet side, the inner tubes (300) fluidically terminate in a circumferential annular gap (R) 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 a 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 (L), and a specific length-dependent progression of its channel passage cross-sections (A_s),

   characterized 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 a pressure (p) up to a maximum of 350 bar,

   • a specific fluid mechanical shearing stress is generated on the concentrate (P) 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 (P),

   • when heating the concentrate (P) in the inner tubes (300) to generate the specific fluid mechanical shear stress, an elevated flow speed (v) of the concentrate (P) is provided in the inner tubes (300), and/or

   • to generate the specific fluid mechanical shearing stress, an elevated flow speed (v) of the concentrate (P) is provided in the annular outlet-side channel (600b), and

   • the elevated flow speed (v) is max. 3 m/s.
2. The method according to claim 1,
   characterized in that
   the elevated flow speed (v) is constant over the entire extension length (L) of the annular outlet-side channel (600b).
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 (P) to be heated and the physical conditions,

   • wherein the properties of the concentrate (P) 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 (P) is handled following the specific fluid mechanical shearing stress,

   • wherein the control parameters with reference to the concentrate (P) are the pressure (p), the outlet-side heating temperature (T), the elevated flow speed (v) 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 one of claims 1 to 3 in a system for atomized drying, wherein the concentrate (P), 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 (Δt) 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 (100.1) that consists of a number (N) of parallel-connected inner tubes (300) through which concentrate (P) flows on the inside,

   • the inner tubes (300) are annular, arranged on a single circle K, and are in each case braced at the end in a first and a second tube support plate (700, 800),

   • the inner tubes (300) extend in the longitudinal direction of an outside channel (200*) formed as an annular gap through which a heating medium (M) flows,

   • the inner tubes (300) possess a 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 there,

   • the inner tubes (300) possess a common outlet (A) 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 there,

   • at least at the outlet side, the inner tubes (300) fluidically terminate in a circumferential annular gap (R) 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 a 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 (L), and a specific length-dependent progression of its channel passage cross-sections (A_s),

   characterized in that

   • the first connection opening (500a) transitions smoothly into an inner passage of a connecting elbow or connecting fitting (1000) that is upstream from the first connection opening (500a) viewed in the direction of flow,

   • the second connection opening (600a) transitions smoothly into an inner passage of a connecting elbow or connecting fitting (1000) that is downstream from the second connection opening (600a) viewed in the direction of flow,

   • the respective connecting elbow/connecting fitting (1000) engages somewhat in the associated exchanger flange (500; 600), and is welded to the outside of the exchanger flange (500; 600) with a high-pressure-resistant, multilayer first weld seam (S1), and to the inside with a second weld seam (S2), and

   • at the outlet side in the associated tube support plate (700; 800), the end of each inner tube (300) is circumferentially in a welded high-pressure resistant manner to said tube support plate with a third weld seam (S3).
6. The tube bundle heat exchanger according to claim 5,
   characterized in that
   the channel passage cross-sections (As) of the annular outlet-side channel (600b) are constant over the entire extension length (L).
7. The tube bundle heat exchanger according to claim 6,
   characterized in that
   the channel passage cross-section (A_S) corresponds to the overall passage cross-section (NA_i) of all inner tubes (300) with a parallel flow.

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