Note: Descriptions are shown in the official language in which they were submitted.
CA 03031357 2019-01-21
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
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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
794 706 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
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CA 03031357 2019-01-21
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 haying 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.
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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 waits 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
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
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Date Recue/Date Received 2021-07-07
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) are 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
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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:
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= 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
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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.
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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
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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.
CA 03031357 2019-01-21
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
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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 are
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
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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.
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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 Di is
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CA 03031357 2019-01-21
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 505 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 505 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 P5 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.
CA 03031357 2019-01-21
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
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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 sl, 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 s21 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
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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
sl, 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 sl 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
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CA 03031357 2019-01-21
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
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CA 03031357 2019-01-21
a 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
10
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
CA 03031357 2019-01-21
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 s1*. 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.
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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
= Treated food product
Water
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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
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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
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s2 Front impeller gap
s2'' Minimal front impeller gap
Direction of rotation
