CA3031357A1

CA3031357A1 - Method and installation for the treatment of heat-sensitive liquid food products, and centrifugal pump for an installation of said type

Info

Publication number: CA3031357A1
Application number: CA3031357A
Authority: CA
Inventors: Hubert Assing; Helmut Buss; Uwe Schwenzow; Roland Stange; Ludger Tacke; Dietrich Zimmermann
Original assignee: GEA TDS GmbH
Current assignee: GEA TDS GmbH
Priority date: 2016-06-03
Filing date: 2017-07-10
Publication date: 2018-01-18
Anticipated expiration: 2037-07-10
Also published as: KR102319037B1; AU2017295268A1; AU2017295268B2; KR20190029667A; AU2021204487A1; AU2024219538A1; BR112019000380B1; CA3031357C; BR112019000380A2

Abstract

A method for treatment of heat-sensitive liquid food products is provided. The method comprises: after the direct heating, the liquid food product is subjected to a first cooling at least on the vessel floor of the infuser vessel up to an outlet opening located there, a second cooling in a tubular section connecting directly to the outlet opening; and a third cooling in a housing cover of a pump housing of the centrifugal pump. The liquid food product serves for at least one planned flushing operation of the pump housing and of the impeller via a rear impeller gap provided between a housing rear wall of the centrifugal pump and the impeller, and via a front impeller gap provided between the housing cover and the impeller. The volume flows of the planned flushing operations are up to several times greater than the inevitable equalization flows within the pump housing.

Description

METHOD AND INSTALLATION FOR THE TREATMENT OF HEAT-SENSITIVE LIQUID FOOD PRODUCTS, AND CENTRIFUGAL PUMP FOR AN
INSTALLATION OF SAID TYPE
TECHNICAL FIELD
The invention relates to a method and installation for the treatment of heat-sensitive liquid baby food concentrates, nutritive beverages or milk used to make cheese, in which steam directly heats the liquid food product for the formation of a sterile state in an infuser vessel, in which water in an amount corresponding with that of the previously supplied steam is removed from the liquid food product by decompression to a lower pressure, and in which the liquid food product is subjected to a conveyance between the heating and the decompression by means of a first conveying apparatus designed as a centrifugal pump.
Furthermore, the invention relates to a centrifugal pump for such an installation and an impeller for such a centrifugal pump.
Heat-sensitive, liquid food products of the aforementioned type contain a relative high amount of protein, a lot of dry matter and little water; and they can have a low, medium or high viscosity. The term "heat sensitivity" should be understood below in that these food products, preferably at temperatures above 100 C, tend to burn, i.e. form deposits on the walls of the infuser vessel and the centrifugal pump conveying it under these conditions.
This deposit formation is also called product contamination. Product contamination reduces the service life or respectively the operating time of the infuser vessel and in particular the centrifugal pump between two cleaning cycles.
STATE OF THE ART
Particularly critical areas of the installation for carrying out the method are the bottom area of the infuser vessel, which tapers downwards into an outlet opening, and a conveying apparatus, which is arranged in a connection line between the outlet opening of the infuser vessel and a vacuum chamber serving to decompress the heated, liquid food product. The conveying apparatus can be a displacement pump, for example a geared pump, or also a centrifugal pump. The conveying apparatus is arranged at a distance from the infuser vessel or directly at its outlet opening. An accumulation of heated, liquid food product in the bottom area of the infuser vessel and in the connected connection line up to the conveying apparatus leads to an undesired and undefined dwell time. A sump of heated, liquid food product must be avoided in particular in the infuser vessel. There has thus been no lack of suggestions for remedying this deficiency.
It is known in the case of heating installations with an infuser vessel to perform the discharge of the directly heated liquid food product out of the infuser vessel with a rotating displacement pump, for example a geared pump, wherein its housing has a cooling and the housing connects directly to the outlet opening of the infuser vessel (EP 0 784 706 B1). A
geared pump has a design-inherent self-cleaning capability because the gear wheels cog together closely and rub along the associated housing walls and thus prevent a continuously increasing deposit formation (product contamination).
WO 2011/101077 Al, which utilizes the priority of DE 10 2010 008 448 Al, discloses a UHT installation for treating heat-sensitive liquid food products, in which among other things a first conveying device is arranged downstream of an infuser vessel in a connection line to a vacuum chamber, which is designed as a displacement pump.
In its bottom area, a bottom part tapering to an outlet opening, the infuser vessel has a cooling of this bottom part. The displacement pump can thereby be arranged at an unquantified distance to the outlet opening from the infuser vessel or, in an edge case, this outlet opening flows directly into the displacement pump. In the case of the displacement pump, a rotating version is preferably used, which can be designed for example, as mentioned above, as a geared pump or also as a vane pump, a mixed-flow pump, impeller pump or rotary-piston pump. Oscillating displacement pumps can also generally be used if the volume flow fluctuations caused by the oscillating operation are compensated for by suitable means or are irrelevant in the treatment process.
In WO 2016/012026 Al, the installation known from EP 0 794 706 B1 is modified for the heat treatment of heat-sensitive liquid food to the effect that, with an otherwise unchanged configuration of the individual aggregates of the installation, the cooling shell surrounding the floor of the infuser vessel, which serves to cool the floor, now extends down the pump and, according to an advantageous embodiment, into the pump housing. The pump is a displacement pump, preferably a geared pump or a piston pump. However, a centrifugal

2 pump is also claimed without specifying exactly how this centrifugal pump is structurally designed. It can thus be assumed that a conventional and hydraulically optimized centrifugal pump known in its general structure to a person skilled in the art is provided here.
WO 2010/086082 Al, which utilizes the priority of DE 10 2009 006 248 Al, describes an infusion system for a liquid food product to be heated, in which an infusion chamber has a lower bottom part with a cooling. The infusion chamber continues in an outlet pipe connecting to an outlet opening in the lower bottom part and also having a cooling. It remains open whether the outlet pipe flows directly or indirectly into a conveying apparatus designed in any way via a connection line.
A centrifugal pump for unproblematic liquid food products, such as water, is sufficiently known in its general structure. It is configured and designed such that it has the highest possible hydraulic efficiency, i.e. that it achieves the largest possible product of volume flow and delivery height with a certain operating power. An impeller with blades is arranged on a shaft in a pump housing generally consisting of at least two housing parts.
Within the pump housing, a distributor in the form for example of a spiral housing or a bladeless annular space connects to the outside of an impeller outlet cross-section surrounding it in an annular manner. On the intake-side housing part, a housing cover, an outlet is located coaxially to the impeller axis, generally designed as a so-called intake connector, and running tangentially on the circumferential side, an inlet, which is generally designed as a so-called pressure connector. With the housing part, the housing rear wall, facing away from the intake side, the impeller pressure rear side forms a so-called rear wheel side space, which generally has a low axial extension in terms of a good hydraulic efficiency of the centrifugal pump. This axial or gap-wide extension is measured .. just closely enough that the mechanical functionality of the centrifugal pump is guaranteed in the case of acceptable production tolerances. In the same manner, an impeller front side, and here this is the front, face-side free blade edges in the case of a so-called open impeller, is adjusted with the narrowest possible gap to the progression of the housing cover. In order to reduce an axial force resulting from the pressure forces acting on the impeller on both sides, several pressure compensation bore holes with relatively small diameters are generally arranged in the hub area of the impeller and distributed over its circumference on the rear side of the impeller.

3 In the case of heat-sensitive liquid food products of the initially named type, it is paramount that there is the least possible tendency towards deposits on the walls of the centrifugal pump during their conveyance through a centrifugal pump. For example, in the case of the direct heating of very heat-sensitive liquid food products in an infuser vessel and subsequent discharge of the heated liquid food product out of the infuser vessel by means of a downstream centrifugal pump of the conventional construction, i.e.
a hydraulically optimized construction, it has been shown that this centrifugal pump became clogged and shut down due to product contamination in a very short period of time, which hereby involved seconds up to a few minutes. Particularly critical areas are the intake area of the impeller, because undissolved gases and in particular uncondensed steam can strengthen the product contamination, and the narrow, gap-wide rear wheel side space.
For the concrete design of a centrifugal pump in an installation for treating heat-sensitive liquid food products, in which the latter undergo direct heating by means of culinary steam, up until now, no satisfactory solution in terms of a sufficiently long service life of the centrifugal pump is known.
The object of the present invention is to create a method of the generic type, an installation for carrying out said method as well as a centrifugal pump for said installation and an impeller for said centrifugal pump, which reduce the tendency for production contamination in the infuser vessel and from there into the centrifugal pump during the treatment of heat-sensitive liquid food products of the initially named typeõ
wherein in particular the centrifugal pump has a considerably lengthened service life in relation to a hydraulically optimized centrifugal pump according to the prior art. A further object consists in modifying a preferably commercially available centrifugal pump such that it inhibits growth of product contamination in its critical areas and the desired service life extension is thereby achieved.
SUMMARY OF THE INVENTION
This object is solved by a method with the characteristics of the claim 1.
Advantageous designs of the method according to the invention are the subject matter of the associated dependent claims. An installation for carrying out the method is the subject matter of the subordinate claim 10. Advantageous embodiments of the installation according to the

4 invention are described in the associated dependent claims. A centrifugal pump for an installation according to claim 10 is the subject matter of claim 17.
Advantageous embodiments of the centrifugal pump according to the invention are the subject matter of the associated dependent claims. An impeller for a centrifugal pump of the claimed type is the subject matter of claim 38.
The invention emanates procedurally from a method for the treatment of heat-sensitive liquid food products, such as milk protein concentrates, baby food, liquid baby food concentrates, nutritive beverages or milk used to make cheese, in which steam directly heats the liquid food product for the formation of a sterile state in an infuser vessel, in which water in an amount corresponding with that of the previously supplied steam is removed from the liquid food product by decompression to a lower pressure, in which the liquid food product is subjected to a conveyance between the heating and the decompression by means of a first conveying apparatus designed as a centrifugal pump.
The object underlying the invention is solved if in the case of the method of the generic type the following treatment steps (a) to (d) after provided after the direct heating:
the liquid food product (a) is subjected to a generally known first cooling at least on the vessel floor of the infuser vessel up to an outlet opening located there;
(b) is subjected to a second cooling in a tubular section connecting directly to the outlet opening, which is formed either by an outlet pipe leading out of the infuser vessel or by an intake connector of the centrifugal pump;
(c) is subjected to a third cooling in a housing cover of a pump housing of the centrifugal pump, which connects directly to the outlet pipe or the intake connector;
(d) serves, with a part of its volume flow conveyed in an impeller of the centrifugal pump, which volume flow is configured to be open toward the housing cover of the centrifugal pump, for at least one planned flushing operation of the pump housing and of the impeller via a rear impeller gap, which is provided between a housing rear wall of the centrifugal pump and the impeller, and via a front impeller gap, which is provided between the housing cover and the impeller, wherein the volume

5 flows of the planned flushing operations are up to several times greater than the inevitable equalization flows within the pump housing, which result from a hydraulically optimized design of the centrifugal pump with an in each case minimal rear and front impeller gap, which ensure the mechanical functionality of the centrifugal pump.
Step (d) concerns a substantially inventive solution concept. The steps (a) to (c) ensure that a further inventive fundamental concept, namely the gapless cooling of the heated liquid food product accumulated in the floor area of the infuser vessel and conveyed up to the pressure connector of the centrifugal pump, is given a concrete solution.
In order to intensify the cooling, one design of the method provides that the liquid food product is subjected to a fourth cooling in the housing rear wall of the pump housing.
According to an advantageous design of the method, a first and a second flushing operation of the pump housing and of the impeller are generated respectively by recirculation via the impeller, driven respectively by pressure differences in the pump housing. The first flushing operation thereby takes place via the rear impeller gap between the impeller and the housing rear wall, wherein the first flushing operation engages in the flow through the impeller. The second flushing operation takes place via the front impeller gap between the housing cover and the impeller, wherein the second flushing operation also engages in the flow through the impeller. Furthermore, a third flushing operation takes place by equalizations flows between a respective pressure side and intake side of a blade of the open impeller and via the front impeller gap, wherein the measures generating the second flushing operation inevitably result in the third flushing operation.
The gapless cooling of the heated liquid food product is achieved as provided by a related first suggestion if the coolings are each operated separately from each other.
A second suggestion, which reduces the related technical cooling effort, provides with respect to the cooling that at least two coolings are connected in series. In both cases, the coolings are operated in the counterflow to the heated liquid food product for the optimization of the cold transfer performance, as provided by a third suggestion.
An installation according to the invention for carrying out the method according to the invention has the combination of the following, partially known characteristics:

6 = an infuser vessel, in which steam directly heats the liquid food product for the formation of a sterile state;
= a vacuum chamber in fluid-accessible connection with the infuser vessel via a connection line, in which water in an amount corresponding with that of the previously supplied steam is removed from the heated liquid food product by decompression to a lower pressure;
= a first conveying apparatus arranged in the connection line and designed as a centrifugal pump for conveying the heated liquid food product from the infuser vessel to the vacuum chamber;
= an outlet opening arranged in a vessel floor of the infuser vessel for the removal of the heated liquid food product;
= a tubular section connecting to the outlet opening for the transfer of the heated liquid food product, which is formed either by an outlet pipe leading out of the infuser vessel or by an intake connector of the centrifugal pump;
= a vessel-floor-side cooling medium space for the cooling of the heated liquid food product loading the vessel floor;
= an outlet-pipe-side cooling medium space or an intake-connector-side cooling medium space for the cooling of the heated liquid food product flowing through the tubular section;
= a pump housing of the centrifugal pump, which is formed at least by a housing cover and a housing rear wall and has a housing-cover-side cooling medium space for the cooling of the conveyed heated liquid food product;
= the centrifugal pump, which has an impeller open toward the housing cover and which is designed such that, with a part of the volume flow of the heated liquid food product conveyed in the impeller, at least one planned flushing operation of the pump housing and of the impeller takes place via a rear impeller gap, which is provided between the housing rear wall and the impeller, and via a front impeller gap, which is provided between the housing cover and the impeller, and wherein the volume flows of the planned flushing operations are up to several times greater than the inevitable equalization flows within the pump housing, which result from a hydraulically optimized design of the centrifugal pump with an in each case

7 minimal rear and front impeller gap, which ensure the mechanical functionality of the centrifugal pump.
The latter characteristic complex represents, in addition to the characteristics for the cooling, an important aspect of the installation according to the invention.
In order to intensify the cooling, a further embodiment provides that the pump housing has a housing-rear-wall-side cooling medium space.
In order to realize a first flushing operation, it is suggested that it takes place via the rear impeller gap between the impeller and the housing rear wall en route via at least one flushing bore hole arranged in the impeller rear side. With respect to a second flushing operation, a further suggestion provides that it takes place via the front impeller gap between the housing cover and the impeller. Furthermore, a third flushing operation takes place by equalization flows between a respective pressure and intake side of a blade of the open impeller and via the front impeller gap, wherein the measures generating the second flushing operation inevitably result in the third flushing operation.
The gapless cooling of the heated liquid food product is achieved as provided by a related first suggestion if the vessel-floor-side cooling medium space, the outlet-pipe-side or the intake-connector-side cooling medium space, the housing-cover-side cooling medium space and the housing-rear-wall-side are supplied with cooling medium separately from each other. A second suggestion, which reduces the technical cooling effort, provides with respect to the cooling that at least two cooling medium spaces are connected with each other in series.
A centrifugal pump according to the invention, which is suitable for an installation for the treatment of heat-sensitive liquid food products, emanates from a generally known centrifugal pump with an inlet, an outlet, a pump housing, which is formed by at least one housing cover and one housing rear wall, a pump chamber designed in the pump housing and being in fluid-accessible connection with the inlet and the outlet, and an impeller with blades rotatably accommodated in the pump chamber. A blade channel, which is designed open toward the housing cover and closed by an impeller rear side toward the housing rear wall, is respectively designed between two neighboring blades. A rear impeller gap is provided between the housing rear wall and the impeller and a front impeller gap is provided between the housing cover and the impeller.

The inventive fundamental idea is that the impeller itself and its adjacent critical areas up to the immediate pump-housing-side boundary of the impeller front side and the impeller rear side are flushed with the liquid food product to be conveyed and product contamination is thus inhibited there, wherein a further inventive fundamental idea consists in that at least pump-housing-side boundaries in the area of the housing cover are simultaneously cooled in the course of the flushing operation according to the invention.
The liquid food product thus serves with a part of its volume flow conveyed in the impeller planned flushing operations of the pump housing and the impeller itself. The volume flows of the planned flushing operations are thereby up to several times greater than the inevitable equalization flows in the pump housing, which result from a technically notorious hydraulically optimized design of the centrifugal pump. This design area is not to be understood by a person skilled in the art as an area specification that is open on the top, but is rather designed in the specific application such that a required service life of the centrifugal pump is achieved while ensuring the required throughput rate of the installation and thus the centrifugal pump under economical criteria. The ratio of the planned volume flows, resulting from the measures according to the invention, to the volume flows of the inevitable equalization flows, as a consequence of the technically notorious hydraulically optimized design, lies between 1.5 and 10, preferably between 2 and 5, in the case of the specific realization and depending on the application. By cooling, the tendency for the liquid food product to burn onto the walls of the centrifugal pump is reduced. This occurs under a planned abandonment of an optimal hydraulic efficiency. In the centrifugal pump according to the invention, a volume flow is conveyed in the impeller, which is increased by the sum of all quasi recirculating flush volume flows with respect to the volume flow suctioned via the intake connector. The flush volume flows convey volumes out of the core of the blade channels to the cooled walls of the housing and from there back into the impeller, wherein the cooling contact allows unprecipitated steam to precipitate and the tendency for product contamination is thus reduced.
The correlations shown above demonstrate that a centrifugal pump flushed with the liquid food product conveyed by it according to the invention has an impeller, the hydraulic conveying capacity of which, with respect to the impeller, must be greater than the hydraulic conveying capacity of the centrifugal pump actually arising at the pressure connector in the end result. If, in order to realize a flushed centrifugal pump of the discussed type, a hydraulically optimized centrifugal pump is selected, then its nominal conveying capacity must be selected accordingly higher by the aforementioned conveying capacity difference. In the case of the same nominal conveying capacity, an outer impeller diameter of the flushed centrifugal pump will thus need to be greater than one for a hydraulically optimized centrifugal pump.
The specific solution for converting the aforementioned inventive fundamental idea consists in that the rear and/or the front impeller gap, which must inevitably exist respectively between the impeller and the pump housing, is/are increased up to several times with respect to such a minimal front and rear impeller gap, which ensures the mechanical functionality of the centrifugal pump, by reducing the width of the impeller in the area of the front and the rear impeller gap. By enlarging this impeller gap, the generation of the desired and necessary flushing flows is first enabled. The respective width of the front and rear impeller gap can be calculated depending on the specific properties of the liquid food product.
In order to intensify the cooling, a further embodiment provides that the housing rear wall also be provided with a cooling medium space through which a cooling medium can flow.
A gapless cooling of the pump housing is ensured if, as is also suggested, in addition to the housing-cover-side cooling medium space and the housing-rear-wall-side cooling medium space, the inlet of the centrifugal pump is designed in the form of an intake connector protruding on the housing cover, which is provided with an intake-connector-side cooling medium space. Such a design is not mandatory in terms of the centrifugal pump according to the invention. Like a centrifugal pump in which the formation of an intake connector is foregone, the centrifugal pump is suitable for a direct connection between the intake connector of the centrifugal pump and an infuser vessel provided in its bottom part with a cooling medium space, wherein this cooling medium space extends down to an outlet opening leading out of the bottom part, which then represents the final end of the infuser vessel. The intake connector can then fulfill in this arrangement the function of a tubular section, which connects to the final outlet opening of the infuser vessel. An arrangement with the centrifugal pump according to the invention is also possible, in which the outlet opening as the final end of the infuser vessel is arranged directly on the housing cover of the centrifugal pump, wherein the formation of an intake connector is foregone there.

In all designs, namely in the case of a centrifugal pump according to the invention with or without an intake connector in combination with an infuser vessel, in which the outlet opening or a tubular section connecting to it represents the final end, an accumulation of heated liquid food product in the bottom part of the infuser vessel and in the connecting .. areas if applicable up to the inlet into the centrifugal pump is undesired since such an accumulation leads to an undesired and undefined dwell time, which should be prevented.
In a connection with an infuser vessel, the centrifugal pump according to the invention has the object of immediately and completely discharging from it heated, liquid food product accumulated in the infuser vessel, without thereby becoming clogged even in the case of intermittent formation.
In order to intensify the flushing operation, it is further suggested that each blade channel between two neighboring blades of the impeller is in fluid-accessible connection in the area of its restricting impeller rear side with the rear impeller gap via at least one flushing bore hole penetrating the impeller rear side. The radial depth of engagement of the associated flushing flow can hereby be determined. In the most general case, the flushing bore hole involves passage openings of any type; i.e. an easy-to-produce circularity is not mandatory.
A preferred design provides that the front impeller gap on an outer impeller diameter of the impeller is subjected to a maximal enlargement and that this enlargement continuously decreases down to the minimal front impeller gap up to the area of the inlet into the blade channels. It is suggested in this regard that a reduction in the width of the impeller on the outer impeller diameter is 40 to 55%, preferably 50 to 55% of the width of a hydraulically optimized impeller. In the area of the front impeller gap, a second flushing flow forms, which extends from the area of the outlet of the centrifugal pump into the area of the inlet of the impeller. Through the enlargement of the front impeller gap, the circulation of the free leading edge of the blade of the open impeller present there even in the case of a narrow impeller gap, driven by the pressure difference between the pressure and intake side of the blade, is considerably strengthened, whereby a third flushing flow is generated according to plan.
With respect to the dimensioning of the rear impeller gap, it has been determined to be conducive if the access to the minimal rear, radially oriented impeller gap, which starts from the outer impeller diameter of the impeller and extends up to a hub of the impeller, is extended by up to 5 mm by reducing the outer impeller diameter. Moreover, an advantageous enlargement of the rear impeller gap according to the invention consists in that the impeller rear side in the area between the flushing bore hole and the hub of the impeller is subjected to an annular-surface-shaped cutout, the axial depth of which is up to 2 mm, preferably 0.5 to 1 mm.
The positioning, formed design and dimensioning of the flushing bore hole arc characteristics with which the associated flushing flow is determined with respect to its radial depth of engagement, its molding and quantitative intensity. In the case of the arrangement of a single flushing bore hole in each blade channel, it is advantageous from a flow and production point of view if all of these flushing bore holes are arranged on a single hole circle with corresponding spacing.
With respect to the positioning of the flushing bore hole within the blade channel, it has been determined to be advantageous if the geometric location for the respective penetration point of the flushing bore hole with the impeller rear side, which also determines a hole circle diameter, is determined as follows:
= approximately through the center of the blade channel, with respect to the separation distance of the blades at the penetration point and = approximately through the center of a maximal flow filament length of the blade channel between its inlet and outlet.
The flushing bore hole is either designed circularly with a bore hole diameter or it has a shape deviating from the circular shape with a hydraulic diameter relevant for this shape.
The hydraulic diameter is dimensioned as is generally known as a quotient of fourfold the passage cross-section of the flushing bore hole and the circumference of the flushing bore hole. It has been determined to be conducive if the bore hole diameter or the hydraulic diameter is 30 to 50% and in this area preferably 40 to 50% of the separation distance of the blades at the penetration point.
According to a further design, the invention also provides more than one flushing bore hole in each blade channel, wherein each of the several flushing bore holes of a blade channel is arranged on an associated hole circle and the hole circles are radially spaced with respect to each other. It is thereby conducive if the passage cross-sections of the flushing bore holes on the different hole circles become smaller with a decreasing hole circle diameter because the impulsive pressure difference at the flushing bore hole with a decreasing radial separation difference of the flushing bore hole from the rotational axis of the centrifugal pump becomes greater.
In order to ensure a cooling that satisfies the specific properties of the heated liquid food product, the invention provides the following circuits of the cooling medium space.
According to a first suggestion in this regard, the if applicable present intake-connector-side cooling medium space, the housing-cover-side cooling medium space and the housing-rear-wall-side cooling medium space are supplied with cooling medium separately from each other. A second suggestion provides a design variant, in which at least two of the aforementioned cooling medium spaces are connected with each other in series. It is provided according to a third suggestion that the intake-connector-side cooling medium space is an integral section of the housing-cover-side cooling medium space.
In order to create the prerequisites for the flushing operation of the rear and/or the front impeller gap, the invention provides, starting from a hydraulically optimized centrifugal pump, preferably a commercially available centrifugal pump, that the rear and the front impeller gap are enlarged. This is realized = either by bilateral turning of the impeller = or by a spacer element acting axially in the direction of a pump shaft, which is arranged between the housing cover and the housing rear wall, wherein the impeller is not offset with respect to the housing rear wall or is correspondingly axially offset for or with the pump shaft in the pump chamber.
The selection of the hydraulically optimized centrifugal pump for this purpose is made with respect to the aforementioned difference of the nominal conveying capacity between the flushed and hydraulically optimized centrifugal pump.
The invention also comprises an impeller for a centrifugal pump, wherein the impeller is accommodated in a rotatable manner in the pump chamber of the centrifugal pump and the centrifugal pump is designed as explained above.

BRIEF DESCRIPTION OF THE DRAWINGS
A more detailed representation of the invention results from the following description and the attached figures of the drawing as well as from the claims. While the invention is realized in the various designs of a method of the generic type, the various embodiments of an installation for carrying out the method and the various embodiments of a centrifugal pump for such an installation, a preferred exemplary embodiment of a centrifugal pump according to the invention, which accommodates an impeller according to the invention in its pump housing and which is in fluid-accessible connection with an outlet opening of an infuser vessel is described below based on the drawing. In the figures Figure 1 shows in a schematic representation an installation for the treatment of heat-sensitive liquid food products according to the prior art;
Figure 2 shows in a schematic representation an infuser vessel for the direct heating of a liquid food product in a direct connection with a rotating displacement pump, wherein the arrangement is known from the prior art;
Figure 3 shows a view of the centrifugal pump in the perpendicular direction both on its rotational axis as well as on the longitudinal axis of its pressure connector, wherein the rotational axis is oriented in the direction of gravitation force and the centrifugal pump is arranged directly on an outlet opening of an infuser vessel;
Figure 4 shows a front view of the impeller of the centrifugal pump according to Figure 3 with the approximate indication of a first and a third flushing flow Si, S3 and Figure 5 shows in the lateral view a meridian section through the impeller according to Figure 4 according to a cutting line labeled with A-A with the approximate indication of the first and a second flushing flow Si, S2.
An installation 1000 according to Figure 1 (for example WO 2011/101077 Al) known from the prior art contains an infuser vessel 50, which has, as a known infuser vessel of the first type 50* (for example WO 2010/086082 Al) in its head space, a product inlet 60, via which a liquid food product P, which should be heat-treated, is supplied centrally and in an annular manner to this infuser vessel of the first type 50*. A first steam D1 is supplied radially outside to the supplied liquid food product P for the direct heating via an outer steam inlet 62, and a second steam D2 is supplied radially from inside via an inner steam inlet 64. The infuser vessel of the first type 50' is subjected to supply of cooling medium via an infuser-side cooling medium inlet 66 to a vessel-floor-side cooling medium space 50.4 for the cooling K of a floor of the infusion chamber of the first type 50*. The discharge of the cooling medium takes place via an infuser-side cooling medium outlet 68.
An outlet opening of the infuser vessel of the first type 50* is connected with a first conveying apparatus 54 via an outlet pipe 52, which is surrounded by an outlet-pipe-side cooling medium space 52.1, said first conveying apparatus 54 being designed as a displacement pump, preferably as a rotating one, and is arranged in a connection line 70 leading from the first conveying apparatus 54 to an inlet of a vacuum chamber 56. The first conveying apparatus 54 conveys the heated liquid food product P from the infuser vessel of the first type 50* to the vacuum chamber 56. The vacuum chamber 56 is designed to remove any amount of water W as so-called vapor steam from the heated liquid food product P cooling due to the pressure reduction, which is supplied to the infuser vessel of the first type 50* in the form of steam D, in the present case consisting of the first steam D1 and the second steam D2, and to divert it via a vapor outlet 72 preferably arranged in the upper area. A liquid food product P* treated in this manner exits the vacuum chamber 56 via a discharge line 74 preferably arranged in the bottom area on a tapering floor en route via a second conveying apparatus 58, which is preferably designed as a centrifugal pump.
Figure 2 shows an infuser vessel 50, which, as a known infuser vessel of the second type 500, is connected directly with a rotating displacement pump 540 at an outlet opening, which discharges the heated liquid food product P downwards (WO 2016/012026 Al).
The liquid food product P is supplied centrally to the head area of the infuser vessel of the second type 540 via the product inlet 60 and the first steam D1 is introduced in a manner surrounding the central product stream via the outer steam inlet 62 radially from outside.
A bottom part of the infuser vessel of the second type 500 is provided with a cooling K, which extends down to the rotating displacement pump 540 and into the pump housing.
The supply of the cooling medium takes place at the rotating displacement pump 540 via a pump-side cooling medium inlet 67, its discharge via the infuser-side cooling medium outlet 68.

The arrangement position of a centrifugal pump 54 according to the invention shown in Figure 3, in which the rotational axis of a pump shaft 96 is oriented in the direction of the gravitational force, is suitable for connecting this centrifugal pump 54 with an inlet 76 designed as an intake connector directly to an outlet opening 50.3 in a vessel floor 50.2 of an infuser vessel 50, which can be designed as an infuser vessel of the first or second type 50*, 500 and subsequently stands for these designs. The infuser vessel 50 transitions into a preferably cylindrical vessel casing 50.1 above the preferably downwards tapering vessel floor 50.2. The vessel floor 50.2 and a partial section of the vessel casing 50.1 connecting to it are provided with a vessel-side cooling medium space 50.4, which has a first cooling medium inlet 78 for supplying and a first cooling medium outlet 80 for discharging a cooling medium for the cooling of the vessel floor K1.
The centrifugal pump 54 is suitable in a special manner for conveying heat-sensitive liquid food products P, such as milk protein concentrates, baby food, liquid baby food concentrates, nutritive beverages or milk used to make cheese, which enter the connection line 70 leading to the vacuum chamber 56 via the inlet 76 and exit from an outlet 94 designed as a pressure connector. The centrifugal pump 54 also has in the generally known manner a pump housing 12, which is formed by at least one housing cover 8 and a housing rear wall 10. A pump chamber 98 in fluid-accessible connection with the inlet 76 and the outlet 94, which accommodates an impeller 100 (for this, see Figures 4 and 5) in a rotating manner, is designed in the pump housing 12. A tubular section 52, 76 connects to the outlet opening 50.3, which can be formed either by the outlet pipe 52 leading out of the infuser vessel 50 or by an intake connector 76 of the centrifugal pump 54. If the tubular section 52, 76 is designed as an outlet pipe 52, then it can be surrounded by the outlet-pipe-side cooling medium space 52.1; if it is designed as an intake connector 76, then it can be surrounded by an intake-connector-side cooling medium space 76.1. In both cases, cooling medium for the cooling of the outlet pipe or the intake connector K2 is supplied to the cooling medium space 52.1, 76.1 via a second cooling medium inlet 82 and is discharged via a second cooling medium outlet 84.
The housing cover 8 is provided with a housing-cover-side cooling medium space

8.1, which preferably completely surrounds the housing cover 8 or partially borders it for example in the form of cooling pockets. Cooling medium for the cooling of the housing cover K3 is supplied to the housing-cover-side cooling medium space 8.1 via a third cooling medium inlet 86 and is discharged via a third cooling medium outlet 88. The housing rear wall 10 can be provided with a housing-rear-wall-side cooling medium space 10.1, which borders the housing rear wall 10 preferably completely or partially, for example in the form of cooling pockets. Cooling medium for the cooling of the housing rear wall K4 is supplied to the housing-rear-wall-side cooling medium space 10.1 via a fourth cooling medium inlet 90 and is discharged via a fourth cooling medium outlet 92.
Finally, Figure 3 shows, indicated approximately and schematically, a first flushing flow Si, a second flushing flow S2 and a third flushing flow S3 according to the invention, which are explained in greater detail in the Figures 4 and 5.
.. The Figures 4 and 5 show the impeller 100 open toward the housing cover 8 and closed by an impeller rear side 4 toward the housing rear wall 10 with blades 2 bent backwards in one plane and with respect to a rotational direction n (see Figure 4), which are respectively preferably located perpendicularly on the impeller rear side 4, wherein a blade channel 2.1 is formed respectively between two neighboring blades 2. The backwards-bent blading is not a mandatory characteristic of the impeller 100 for the centrifugal pump 54 according to the invention. A forwards-bent or a purely radially oriented blading in a planar or even spatial bend can be executed without restriction in terms of the realization of a flushed centrifugal pump 54 according to the invention. A rear side RS of the impeller 100 mainly formed by the impeller rear side 4 is distanced from the housing rear wall 10 by a rear impeller gap sl (Figure 5). A front side VS of the impeller 100 mainly formed by the leading edges of the blades 2 is also distanced from the housing cover 8 by a front impeller gap s2.
The rear and/or the front impeller gap s1, s2 is/are enlarged up to several times (by a factor of 1.5 to 10, preferably 2 to 5) with respect to this type of minimal rear and front impeller gap s1*, s2 which ensures the mechanical functionality of the centrifugal pump 54, by reducing the width of the impeller 100 in the area of the front and rear impeller gap s1, s2.
A preferred embodiment provides that the front impeller gap s2 is subject to a maximal enlargement on an outer impeller diameter DL of the impeller 100, which decreases continuously down to the minimal front impeller gap s2* up to into the area of the inlet into the blade channel 2.1. This type of reduction of the width of the impeller 100 on the outer impeller diameter DL is preferably 40 to 55%, here preferably 50 to 55%, of the width of a hydraulically optimized impeller.
A further preferred embodiment provides that the access to the minimal rear, radially oriented impeller gap sl*, which starts from the outer impeller diameter DL of the impeller 100, and extends up to a hub of the impeller 100, is expanded by reducing the outer impeller diameter DL by up to 5 mm, whereby the impeller 100 retreats back a bit radially outside with respect to the pump housing 12. An enlargement of the rear impeller gap sl consists according to the invention and preferably in that the impeller rear side 4 is subjected to an annular-surface-shaped cutout 2.3 in the area between the flushing bore hole 6 and the hub of the impeller 100 (see Figure 5), the axial depth of which is up to 2 mm, preferably 0.5 to 1 mm. A dimensioning of the front and/or of the rear impeller gap s1, s2 in the manner described above depends on the specific properties of the heated liquid food product P and is preferably determined in field tests.
Each blade channel 2.1 between two neighboring blades 2 of the impeller 100 is in fluid-accessible connection with the rear impeller gap s1 in the area of its adjacent impeller rear side 4 via at least one flushing bore hole 6 penetrating the impeller rear side 4 (Figure 5).
According to a preferred embodiment, all of these flushing bore holes 6 are arranged on a single hole circle 2.2 with a hole circle diameter d in the case of a single flushing bore hole 6 in each blade channel 2.1. The geometric location for the respective penetration point of the flushing bore hole 6 with the impeller rear side 4, which also determines the hole circle diameter d, is thereby approximately determined by the center of the blade channel 2.1, with respect to the separation distance of the blades 2 at the penetration point, and approximately by the center of a maximal flow filament length of the blade channel 2.1 between its inlet and outlet.
The flushing bore hole 6 is designed either preferably circularly with a bore hole diameter Db or it has alternatively a shape deviating from the circular form with a hydraulic diameter Dh relevant for this shape (Figure 4). It is thereby preferably suggested that the bore hole diameter Db or the hydraulic diameter Dh is 30 to 50% and in this area preferably 40 to 50% of the separation distance from the blades 2 at the penetration point.
The invention further provides that more than one flushing bore hole 6 is provided in each blade channel 2.1, that each of the several flushing bore holes 6 of a blade channel 2.1 is arranged on an associated hole circle 2.2 and that the hole circles 2.2 are spaced radially from each other. The flushing bore holes 6 on different hole circles 2.2 can be designed with the same diameters Db or respectively hydraulic diameters Dh or with different diameters Db or respectively hydraulic diameters Dh from hole circle to hole circle. Due to the pressure difference decreasing from inside to outside in the radial direction between the rear wheel side space and the blade channel 2.1, an advantageous embodiment provides that the passage cross-sections of the flushing bore holes 6 on the different hole circles 2.2 become smaller with a decreasing hole circle diameter d. The bore hole diameters Db or the hydraulic diameters Dh of the flushing bore holes 6 thus tend to be smaller the closer they get to the hub area of the impeller 100 if a certain flushing volume flow needs to be achieved.
At least the housing cover 8 with the housing-cover-side cooling medium space 8.1 that a cooling medium can flow through is provided. If necessary, the housing rear wall 10 can be cooled via a housing-rear-wall-side cooling medium space 10.1. According to an .. advantageous embodiment, in addition to the housing-cover-side cooling medium space 8.1 and the housing-rear-wall-side cooling medium space 10.1, the inlet 76, if designed as an intake connector, is provided with the intake-connector-side cooling medium space 76.1. It is suggested that the intake-connector-side cooling medium space 76.1, the housing-cover-side cooling medium space 8.1 and the housing-rear-wall-side cooling medium space 10.1 are supplied with cooling medium separately from each other.
Another embodiment provides that at least two cooling medium spaces 76.1, 8.1, 10.1 are connected with each other in series. According to a further suggestion, the intake-connector-side cooling medium space 76.1 is an integral section of the housing-cover-side cooling medium space 8.1.
.. The following measures, with which a centrifugal pump according to the prior art is to be modified according to the invention, ensure in combination with each other or respectively also alone the flushing operation of the impeller 100 according to the invention:
= Enlargement of the rear impeller gap sl and/or the front impeller gap s2 (see Figure 5) either o by bilateral turning of the impeller 100 o or by a spacer element acting axially in the direction of the pump shaft 96, which is arranged between the housing cover 8 and the housing rear wall 10, wherein the impeller 100 is not offset with respect to the housing rear wall or is correspondingly axially offset with the pump shaft 96 in the pump chamber 98.
= Arrangement of the aforementioned flushing bore holes 6 in the manner described above.
The Figures 4 and 5 illustrate the effects of the aforementioned measures according to the invention. By the widening of the rear impeller gap s1 or respectively by the expanded access to it, the associated rear wheel side space is supplied in a more or less unrestricted manner with the prevailing static pressure on the outlet side of the impeller 2, which there has the outer impeller diameter DL, over its entire radial extension area. A
lower static pressure than in the rear wheel side space is present at the respective flushing bore hole 6 in the blade channel 2.1. The first flushing flow Si directed radially from inside to outside, as shown in Figure 5 and in Figure 4, in the latter only as an example on a blade channel 2.1, thereby results in the blade channel 2.1 due to the causal flow-through of the flushing bore hole 6 from the rear wheel side space into the blade channel 2.1. Since the heated liquid food product P located in the rear wheel side space can be cooled at the housing rear wall 10, because the cooling of the housing rear wall K4 is provided there if applicable, liquid food product P permanently cooled by the first flushing flow Si now makes its way preferably into the core area of the flow in the blade channel 2.1.
By the described widening of the front impeller gap s2, the third flushing flow S3 can form, as is shown in Figure 4 in the left upper quadrant of the impeller 100, seen via the respective front-side, free leading edge of the blade 2 and over its radial extension area.
The driving forces for this third flushing flow S3 result from the pressure difference at each blade 2, which is given by the static pressure on the blade top side, a pressure side DS, and by the static pressure on the blade bottom side, an intake side SS.
The third flushing flow S3 ensures an additional movement with respect to the housing cover 8 and predominantly in the circumferential direction to it and thus a forced cooling of the liquid food product P, because the cooling of the housing cover K3 is installed in this housing cover 8 (see Figure 5). The third flushing flow S3 also effectuates here an exchange of the liquid food product into and out of the core area of the flow in the associated blade channel 2.1. Through the widened front impeller gap s2, the radially oriented second flushing flow S2 can form due to the difference between the static pressure at the outlet of the impeller 100 and the static pressure in the intake-side inlet of the impeller 100 (see Figure 5), which superimposes the third flushing flow S2. This second flushing flow S2 also ensures here an exchange of the liquid food product P into and out of the core area of the flow in the associated blade channel 2.1.
Exemplary Embodiment of a Centrifugal Pump 54 According to the Invention:
The centrifugal pump 54 is driven by a drive motor with a nominal capacity of 15 kW at a nominal speed n = 2900 1/min. The outer impeller diameter DL is reduced from an original 205 mm to 195 mm. The impeller width on the outer impeller diameter DL is reduced from an original 19 mm to 9 mm, wherein the reduction declines continuously until the area of the inlet into the blade channel 2.1 down to the minimal front impeller gap s2*. The rear impeller gap sl is enlarged by 0.7 mm in the area of the annular-surface-shaped cutout 2.3 with respect to the minimal rear impeller gap sl*. Each flushing bore hole 6 in the associated blade channel 2.1 of the total of six blade channels 2.1 is designed circularly and has a bore hole diameter Db = 10 mm.
The measures described above according to the invention can also be applied analogously to a closed impeller, wherein a third flushing flow S3 is then inevitably impossible via the front-side leading edge of the respective blade 2 in the aforementioned manner. As a replacement for these flushing paths, a cover plate of the impeller 100 would then be provided with further flushing bore holes, which connect the respectively associated blade channel with a front wheel side space, formed between the cover plate and the housing cover 8. A flushing flow adequate for the first flushing flow Si described above would then arise.

REFERENCE LIST OF THE USED ABBREVIATIONS
Figures 1 and 2 (Prior Art) 1000 Installation 50 Infuser vessels, general 50* Infuser vessel of the first type 500 Infuser vessel of the second type 50.4 Vessel-floor-side cooling medium space 52 Outlet pipe 52.1 Outlet-pipe-side cooling medium space 54 First conveying apparatus 540 Rotating displacement pump 56 Vacuum chamber 58 Second conveying apparatus 60 Product inlet 62 Outer steam inlet 64 Inner steam inlet 66 Infuser-side cooling medium inlet 67 Pump-side cooling medium inlet 68 Infuser-side cooling medium outlet 70 Connection line 72 Vapor outlet 74 Discharge line (for treated food product) = Steam D1 First steam D2 Second steam = Cooling = Liquid food product P* Treated food product Water Figure 3 50 Infuser vessel 50* Infuser vessel of the first type 500 Infuser vessel of the second type 50.1 Vessel casing 50.2 Vessel floor 50.3 Outlet opening 50.4 Vessel-floor-side cooling medium space 8 Housing cover 8.1 Housing-cover-side cooling medium space 10 Housing rear wall 10.1 Housing-rear-wall-side cooling medium space 12 Pump housing 54 Centrifugal pump 76 Inlet (intake connector) 76.1 Intake-connector-side cooling medium space 78 First cooling medium inlet 80 First cooling medium outlet 82 Second cooling medium inlet 84 Second cooling medium outlet 86 Third cooling medium inlet 88 Third cooling medium outlet 90 Fourth cooling medium inlet 92 Fourth cooling medium outlet 94 Outlet (pressure connector) 96 Pump shaft 98 Pump chamber 100 Impeller K1 Cooling of the vessel floor K2 Cooling of the outlet pipe or the intake connector K3 Cooling of the housing cover K4 Cooling of the housing rear wall Si First flushing operation S2 Second flushing operation S3 Third flushing operation Figures 4 and 5 2 Blade 2.1 Blade channel 2.2 Hole circle 2.3 Annular-surface-shaped cutout 4 Impeller rear side 6 Flushing bore hole DL Outer impeller diameter Db Bore hole diameter Dh Hydraulic diameter DS Pressure side (blade) RS Rear side (impeller) SS Intake side (blade) VS Front side (impeller) Hole circle diameter s1 Rear impeller gap sl* Minimal rear impeller gap s2 Front impeller gap s25 Minimal front impeller gap Direction of rotation

Claims

1. A method for the treatment of heat-sensitive liquid food products (P), in which steam (D) directly heats the liquid food product (P) for the formation of a sterile state in an infuser vessel (50; 50*, 500), in which water (W) in an amount corresponding with that of the previously supplied steam (D) is removed from the liquid food product (P) by decompression to a lower pressure, in which the liquid food product (P) is subjected to a conveyance between the heating and the decompression by means of a first conveying apparatus (54) designed as a centrifugal pump and in which the following treatment steps (a) to (e) are provided after the direct heating:
the liquid food product (P) (a) is subjected to a first cooling (K1) at least on the vessel floor (50.2) of the infuser vessel (50; 50*, 500) up to an outlet opening (50.3) located there;
(b) is subjected to a second cooling (K2) in a tubular section (52, 76) connecting directly to the outlet opening (50.3), which is formed either by an outlet pipe (52) leading out of the infuser vessel (50; 50*; 500) or by an intake connector (76) of the centrifugal pump (54);
(c) is subjected to a third cooling (K3) in a housing cover (8) of a pump housing (12) of the centrifugal pump (54), which connects directly to the outlet pipe (52) or the intake connector (76);
(d) serves, with a part of its volume flow conveyed in an impeller (100) of the centrifugal pump (54), which volume flow is configured to be open toward the housing cover (8) of the centrifugal pump (54), for at least one planned flushing operation of the pump housing (12) and of the impeller (100) via a rear impeller gap (s1), which is provided between a housing rear wall (10) of the centrifugal pump (54) and the impeller (100), and via a front impeller gap (s2), which is provided between the housing cover (8) and the impeller (100), wherein the volume flows of the planned flushing operations are up to several times greater than the inevitable equalization flows within the pump housing (12), which result from a hydraulically optimized design of the centrifugal pump (54) with an in each case minimal rear and front impeller gap (s1*, s2*), which ensure the mechanical functionality of the centrifugal pump (54).

2. The method according to claim 1, characterized in that the liquid food product (P) is subjected to a fourth cooling (K4) in the housing rear wall (10) of the pump housing (12).

3. The method according to claim 1 or 2, characterized in that a first and a second flushing operation (S1, S2) are generated respectively by recirculation via the impeller (100), driven respectively by pressure differences in the pump housing (12).

4. The method according to claim 3, characterized in that the first flushing operation (S1) takes place via the rear impeller gap (s1) between the impeller (100) and the housing rear wall (10), wherein the first flushing operation (S1) engages in the flow through the impeller (100).

5. The method according to claim 3 or 4, characterized in that the second flushing operation (S2) takes place via the front impeller gap (s2) between the housing cover (8) and the impeller (100), wherein the second flushing operation (S2) engages in the flow through the impeller (100).

6. The method according to one of the previous claims, characterized in that a third flushing operation (S3) takes place by equalization flows between a respective pressure and suction side of a blade (2) of the open impeller (100) and via the front impeller gap (s2).

7. The method according to one of the claims 2 to 6, characterized in that the coolings (K1, K2, K3, K4) are each operated separately from each other.

8. The method according to one of the claims 2 to 6, characterized in that at least two coolings (K1, K2, K3, K4) are connected in series.

9. The method according to one of the claims 2 to 8, characterized in that the coolings (K1, K2, K3, K4) are operated in the counterflow to the heated liquid food product (P).

10. An installation (1000) for the treatment of heat-sensitive liquid food products (P), .cndot. with an infuser vessel (50; 50*, 500), in which steam (D) directly heats the liquid food product (P) for the formation of a sterile state, .cndot. with a vacuum chamber (56) in fluid-accessible connection with the infuser vessel (50; 50*, 500) via a connection line (70), in which water (W) in an amount corresponding with that of the previously supplied steam (D) is removed from the liquid food product (P) by decompression to a lower pressure, .cndot. with a first conveying apparatus (54) arranged in the connection line (70) and designed as a centrifugal pump for conveying the heated liquid food product (P) from the infuser vessel (50; 50*, 500) to the vacuum chamber (56), .cndot. with an outlet opening (50.3) arranged in a vessel floor (50.2) of the infuser vessel (50; 50*, 500) for removal of the heated liquid food product (P), .cndot. with a tubular section (52, 76) connecting to the outlet opening (50.3) for the transfer of the heated liquid food product (P), which is formed either by an outlet pipe (52) leading out of the infuser vessel (50; 50*, 500) or by an intake connector (76) of the centrifugal pump (54), .cndot. with a vessel-floor-side cooling medium space (50.4) for the cooling of the heated liquid food product (P) loading the vessel floor (50.2), .cndot. with an outlet-pipe-side cooling medium space (52.1) or an intake-connector-side cooling medium space (76.1) for the cooling of the heated liquid food product (P) flowing through the tubular section (52, 76), .cndot. with a pump housing (12) of the centrifugal pump (54), which is formed at least by a housing cover (8) and a housing rear wall (10) and has a housing-cover-side cooling medium space (8.1) for the cooling of the conveyed heated liquid food product (P), and .cndot. with the centrifugal pump (54), which has an impeller (100) open toward the housing cover (8) and which is designed such that, with a part of the volume flow conveyed in the impeller (100) of the heated liquid food product (P), at least one planned flushing operation of the pump housing (12) and of the impeller (100) takes place via a rear impeller gap (s1), which is provided between the housing rear wall (10) and the impeller (100), and via a front impeller gap (s2), which is provided between the housing cover (8) and the impeller (100), and wherein the volume flows of the planned flushing operations are up to several times greater than the inevitable equalization flows within the pump housing (12), which result from a hydraulically optimized design of the centrifugal pump (54) with an in each case minimal rear and front impeller gap (s1*, s2*), which ensure the mechanical functionality of the centrifugal pump (54).

11. The installation according to claim 10, characterized in that the pump housing (12) has a housing-rear-wall-side cooling medium space (10.1).

12. The installation according to claim 10 or 11, characterized in that a first flushing operation (S1) takes place via the rear impeller gap (s1) between the impeller (100) and the housing rear wall (10) en route via at least one flushing bore hole (6) arranged in the impeller rear side (4).

13. The installation according to one of the claims 10 to 12, characterized in that a second flushing operation (S2) takes place via the front impeller gap (s2) between the housing cover (8) and the impeller (100).

14. The installation according to one of the claims 10 to 13, characterized in that a third flushing operation (S3) takes place by equalization flows between a respective pressure and intake side of a blade (2) of the open impeller (100) and via the front impeller gap (s2).

15. The installation according to one of the claims 11 to 14, characterized in that the vessel-floor-side cooling medium space (50.4), the outlet-pipe-side or the intake-connector-side cooling medium space (52.1, 76.1), the housing-cover-side cooling medium space (8.1) and the housing-rear-wall-side cooling medium space (10.1) are supplied with cooling medium separately from each other.

16. The installation according to one of the claims 11 to 14, characterized in that at least two cooling medium spaces (50.4, 52.1, 76.1, 8.1, 10.1) are connected with each other in series.

17. A centrifugal pump (54) for conveying heat-sensitive liquid food products (P), with an inlet (76), an outlet (94), a pump housing (12), which is formed by at least one housing cover (8) and one housing rear wall (10) , a pump chamber (98) designed in the pump housing (12) and being in fluid-accessible connection with the inlet (76) and the outlet (94), an impeller (100) with blades (2) rotatably accommodated in the pump chamber (98), a blade channel (2.1) respectively designed between two neighboring blades (2), which is designed open toward the housing cover (8) and closed by an impeller rear side (4) toward the housing rear wall (10), a rear impeller gap (s1) provided between the housing rear wall (10) and the impeller (100) and a front impeller gap (s2) provided between the housing cover (8) and the impeller (100), characterized in that .cndot. the rear and/or the front impeller gap (s1, s2) is/are enlarged up to several times with respect to this type of minimal rear and front impeller gap (s1*, s2*), which ensures the mechanical functionality of the centrifugal pump (54), by reducing the width of the impeller (100) in the area of the front and rear impeller gap (s1, s2), and .cndot. at least the housing cover (8) is provided with a cooling medium space (8.1) through which a cooling medium can flow.

18. The centrifugal pump according to claim 17, characterized in that the housing rear wall (10) is provided with a cooling medium space (10.1) through which a cooling medium can flow.

19. The centrifugal pump according to claim 17 or 18, characterized in that in addition to the housing-cover-side cooling medium space (8.1) and the housing-rear-wall-side cooling medium space (10.1), the inlet (76) is designed in the form of an intake connector protruding on the housing cover (8), which is provided with an intake-connector-side cooling medium space (76.1).

20. The centrifugal pump according to one of the claims 17 to 19, characterized in that each blade channel (2.1) is in fluid-accessible connection with the rear impeller gap (s1) in the area of its adjacent impeller rear side (4) via at least one flushing bore hole (6) penetrating the impeller rear side (4).

21. The centrifugal pump according to one of the claims 17 to 20, characterized in that the front impeller gap (s2) on an outer impeller diameter (DL) of the impeller (100) is subjected to a maximal enlargement, which decreases continuously down to the minimal front impeller gap (s2*) into the area of the inlet into the blade channels (2.1).

22. The centrifugal pump according to claim 21, characterized in that a reduction in the width of the impeller (100) on the outer impeller diameter (DL) is 40 to 55% of the width of a hydraulically optimized impeller.

23. The centrifugal pump according to claim 22, characterized in that the reduction is 50 to 55% of the width of a hydraulically optimized impeller (100).

24. The centrifugal pump according to one of the claims 21 to 23, characterized in that .cndot. the access to the minimal rear, radially oriented impeller gap (s1*), which starts from the outer impeller diameter (DL) of the impeller (100) and extends up to a hub of the impeller (100), is extended by up to 5 mm by reducing the outer impeller diameter (DL), and .cndot. an enlargement of the rear impeller gap (s1) consists in that the impeller rear side (4) is subjected to an annular-surface-shaped cutout (2.3) in the area between the flushing bore hole (6) and the hub of the impeller (100), the axial depth of which is up to 2 mm.

25. The centrifugal pump according to claim 24, characterized in that the axial depth of the cutout (2.3) is 0.5 to 1 mm.

26. The centrifugal pump according to one of the claims 20 to 25, characterized in that in the case of a single flushing bore hole (6) in each blade channel (2.1), all of these flushing bore holes (6) are arranged on a single hole circle (2.2).

27. The centrifugal pump according to one of the claims 20 to 26, characterized in that the geometric location for the respective penetration point of the flushing bore hole (6) with the impeller rear side (4), which also determines a hole circle diameter (d), is determined:
.cndot. approximately through the center of the blade channel (2.1), with respect to the separation distance of the blades (2) at the penetration point, and .cndot. approximately through the center of a maximal flow filament length of the blade channel (2.1) between its inlet and outlet.

28. The centrifugal pump according to one of the claims 20 to 27, characterized in that the flushing bore hole (6) is designed circularly with a bore hole diameter (Db).

29. The centrifugal pump according to one of the claims 20 to 28, characterized in that the flushing bore hole (6) has a shape deviating from the circular shape with a hydraulic diameter (Dh) relevant for this shape.

30. The centrifugal pump according to claim 28 or 29, characterized in that the bore hole diameter (Db) or the hydraulic diameter (Dh) is 30% to 50% of the separation distance between the blades (2) at the penetration point.

31. The centrifugal pump according to claim 30, characterized in that the bore hole diameter (Db) or the hydraulic diameter (Dh) is 40 to 50% of the separation distance between the blades (2) at the penetration point.

32. The centrifugal pump according to one of the claims 20 to 31, characterized in that .cndot. more than one flushing bore hole (6) is provided in each blade channel (2.1), .cndot. each of the several flushing bore holes (6) of a blade channel (2.1) is arranged on an associated hole circle (2.2), and .cndot. the hole circles (2.2) are spaced radially from each other.

33. The centrifugal pump according to claim 32, characterized in that the passage cross-sections of the flushing bore holes (6) on the different hole circles (2.2) become smaller with a decreasing hole circle diameter (d).

34. The centrifugal pump according to one of the claims 19 to 33, characterized in that the intake-connector-side cooling medium space (76.1), the housing-cover-side cooling medium space (8.1) and the housing-rear-wall-side cooling medium space (10.1) are supplied with cooling medium separately from each other.

35. The centrifugal pump according to one of the claims 19 to 33, characterized in that at least two cooling medium spaces (76.1, 8.1, 10.1) are connected with each other in series.

36. The centrifugal pump according to one of the claims 19 to 35, characterized in that the intake-connector-side cooling medium space (76.1) is an integral section of the housing-cover-side cooling medium space (8.1).

37. The centrifugal pump according to one of the claims 17 to 36, characterized in that starting from a hydraulically optimized centrifugal pump, the rear and/or front impeller gap (s1, s2) is/are enlarged .cndot. either by bilateral turning of the impeller (100) .cndot. or by a spacer element acting axially in the direction of a pump shaft (96), which is arranged between the housing cover (8) and the housing rear wall (10), wherein the impeller (100) is not offset with respect to the housing rear wall (10) or is correspondingly axially offset for or with the pump shaft (96) in the pump chamber (98).

38. An impeller (100) for a centrifugal pump (54) with blades (2), which is rotatably accommodated in a pump chamber (98) of the centrifugal pump (54), and a blade channel (2.1) respectively designed between two neighboring blades (2), which is designed closed toward an impeller rear side (4) and open on the other side, characterized in that each blade channel (2.1) is provided with at least one flushing bore hole (6) penetrating the impeller rear side (4) in the area of its adjacent impeller rear side (4), on a front side (VS) of the impeller (100), a reduction of the width of the impeller (100) at an outer impeller diameter (DL) is 40 to 55% of the width of a hydraulically optimized impeller, wherein the reduction declines continuously until the area of the inlet into the blade channel (2.1) down to the associated width of the hydraulically optimized impeller, and the outer impeller diameter (DL) is reduced by up to 10 mm with respect to the outer impeller diameter of the hydraulically optimized impeller.