Note: Descriptions are shown in the official language in which they were submitted.
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Method and device for controlling foaming in a degassing
device for liquids and heat-exchanger system for such a
device
Technical Field
The invention relates to a method and to an apparatus for
controlling the foam formation in a degassing apparatus for
liquids, and to a register system for an apparatus of this
type. The liquids to be degassed (called liquids for short in
the following text) are preferably liquid foodstuffs such as
milk, semi-skimmed milk or fruit juices.
Prior Art
In the case of the liquids under scrutiny, admixed gases, in
particular admixed air with its proportion of atmospheric
oxygen, are harmful in many ways. For this reason, degassing
apparatuses are arranged in process plants which treat and
process the abovementioned gas-charged liquid foodstuffs. Said
process plants can be, for example, pasteurizing plants, UHT
plants or evaporators.
In the following text, two issues will be presented briefly
which explain in greater detail the necessity of degassing
milk, in particular, with regard to said process plants.
1. It is
well known that the charging capacity, for example,
of the milk with air or atmospheric oxygen is also dependent,
inter alia, on its fat content, skimmed milk or standardized
milk with a fat content between 1.5 and 3.5% being used, for
example, in UHT plants, in which the milk is heat-treated in
order to prolong its shelf life. It has proven advantageous
for the service life of the UHT plants with indirect heating
if the air content lies below 8 mg of air/dm3 (8 ppm) of milk.
Above a limit value in this regard, there is the increased
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risk of scorching, in particular in the heat exchangers of the
heater zone and of the heat holder, as a result of which the
service life of said heat exchangers is shortened
significantly.
2. In heat exchangers of dairy technology process plants,
independently of the configuration as plate heat exchangers
or tube heat exchangers, the raw milk or thermophilic
microorganisms or bacteria which come from its fractions
(skimmed milk, cream), have not been subjected to high
temperature heating and therefore have not been inactivated,
or the metabolic products of said bacteria can be deposited
and can form what is known as a biofilm. Said biofilm is
primarily produced in a heat exchanger, in which the milk is
treated thermally in the temperature range of approximately
from 50 C to 70 C. Although pathogenic bacteria can no longer
grow at temperatures above 50 C, other germs can, namely the
abovementioned thermophilic microorganisms or bacteria (for
short: thermophilic germs). Thermophilic germs utilize a
temperature range of approximately from 40 C to 80 C, the
temperature range for the optimum growth of the thermophilic
germs lying in the range of approximately from 63 C to 68 C.
In addition to said optimum temperature, there have to be
sufficient nutrients and oxygen for the growth. Since the
abovementioned biofilm significantly shortens the service life
of the suitable heat exchangers, it is a case of preventing
or at least inhibiting the growth of the thermophilic germs.
This is accomplished primarily by the fact that the content
of the air or the atmospheric oxygen is reduced, preferably
in degassing apparatuses at issue here. Here, the liquid to
be degassed is treated in a temperature range of from 40 C to
80 C, preferably between 50 C and 70 C.
In the two abovementioned applications, degassing apparatuses
are used to reduce the air content, in particular. A degassing
apparatus in this regard is known from EP 1 866 046 81. Herein,
the semi-skimmed milk to be degassed is fed centrally from
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below to a degassing container, and is introduced via an
outwardly dropping distributor screen in the form of a liquid
film above a free surface of the milk supply which is situated
in the degassing container. The liquid film is configured on
a surface of the distributor screen and enters into the free
surface at a greater or smaller radial spacing from the shell
surface of the degassing container. Here, the distributor
screen can be configured so as to be very flat and therefore
so as to drop only slightly in the axial direction. Embodiments
are also known, however, in which the distributor screen is
configured as a cone or in a conical manner, the apex angle
of which can be reduced as far as 45 degrees. If the flatly
dropping or the tapered or conical distributor screen ends at
a relatively great spacing from the shell surface of the
degassing container, the free surface which is as a rule level-
controlled or a free level of the liquid supply in the
degassing container is configured in the region of said
spacing. Here, as is the case as a rule, the outer edge of the
distributor screen can dip into the free surface or else can
end above the free surface at a small spacing. The discharge
of the degassed milk takes place via the lowermost, central
region of the degassing container.
As a rule, the degassing in the known degassing apparatuses
is accelerated by virtue of the fact that the liquid is
subjected to a vacuum which is generated by way of a vacuum
source, for example a liquid ring pump, which is connected to
the head space of the degassing container.
During the degassing in the known degassing apparatuses, the
output liquid film which is configured on the surface of the
distributor screen and, if significantly present, the free
surface of the liquid supply in each case generate foam which
grows on the surface of the liquid film and on the free surface
of the liquid supply in the direction of a head space of the
degassing container. Here, the foam formation can be so
intensive, and this is the case, for example, during the
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degassing of skimmed milk, that the entire head space of the
degassing container is filled with foam and, as a result, the
foam brings the degassing operation to a standstill or at
least impedes it considerably, with the result that the
process management is made much more difficult overall. If the
foam passes here into a possibly present vacuum source, the
degassing process has to be stopped anyway.
It is known to combat foam in a chemical, mechanical and
thermal way. Combating by way of the addition of chemical
media is disqualified as a rule in the case of liquid foodstuff
products, in order to avoid contamination. In the case of high
foam formation rates, mechanical foam breakers deliver
unsatisfactory results on account of excessively low
performance and a relatively great and partially also
complicated construction effort which has to be made with
regard to the production and/or the adaptation to a very wide
variety of application requirements.
The breaking of undesired foam bubbles proceeds from the
finding that the foam bubble collapses when its volume is no
longer stable. The volume of a foam bubble is defined by the
equilibrium between firstly the pressure of the trapped gas
and secondly the sum of two pressures, namely the pressure,
at which the treatment process of the liquid takes place, and
the pressure which is produced by way of the surface tension
of the foam bubble.
It therefore has to be the aim of foam breaking in a thermal
way, namely either by way of heating or by way of cooling, to
significantly disrupt the abovementioned equilibrium state.
Heating of the foam bubbles brings about an increase and
cooling leads to a decrease of the respective internal
pressure of the foam bubbles. In this regard, document DE 21
63 666 Al discloses it being expedient to disrupt the
equilibrium state between the surface tension and the internal
pressure of all or part of the foam bubbles to be broken by
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way of a change in the internal pressure of the foam bubbles.
It is proposed in this regard to increase the internal pressure
by way of heating of all or part of the foam bubbles, to be
precise, for example, by way of heating of the foam bubbles
in an electric way by way of the installation of an
electrically conducting resistance wire in the foam zone.
A further proposal provides heating the foam bubbles by way
of hot heating gases being blown into the foam zone. In the
case of the first proposal, the operational reliability and
the temperature control are problematic and, in the case of
the second proposal, there is no longer the necessary product
and quality assurance on account of possible contaminations.
Another proposal which complies with the sanitary and hygienic
requirements which apply to the liquid foodstuff products to
be treated within the context of the invention, at least in
the case of a suitable configuration of its solvents, provides
that the foam bubbles are heated by way of a heat exchanger
which is loaded with warmer gaseous or liquid media and is
attached in the foam zone.
The disclosure of document DE 37 27 132 Al falls short of the
last-mentioned proposal, since it is proposed herein, in the
case of a method for destabilizing and breaking foams, to
greatly reduce the mechanical strength of the foam in a manner
known per se by way of the introduction of thermal energy, but
the introduction in this regard within the context of the
problem addressed here consists in a problematic feed of steam
or heated gas. Moreover, the problematic feed of said
materials is combined with means for mechanical foam breaking
or with means for ultrasound generation which require an
additional structural and costly effort.
DE 43 04 808 Al describes a method and an apparatus for filling
milk into containers. Bottles are used as containers, the
object being achieved of eliminating the foam which is
produced during the filling of milk into the containers even
during the filling process and at the same time of ensuring a
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precise filling quantity in the container. Said object is
achieved, inter alia, by the bottle being overfilled with milk
in the vacuum region and the excess milk then being extracted,
with all the foam which has formed, by way of vacuum as far
as the predefined filling level and being collected in a
separate container. From said prior art, an appropriate person
skilled in the art gathers the indications that it is not
possible or is at least problematic to break the foam (in
particular, milk foam) by way of heating by devices which
protrude into the foam. Instead, it is proposed to extract the
foam which has formed by suction and to collect it in a
separate container.
DE 1 017 140 Al discloses an apparatus for foam breaking in
liquid evaporators, in which the evaporation of the liquid
also takes place, in particular, under vacuum. Here, the
vacuum serves to lower the evaporation temperature and not,
for instance, to extract the foam. In order to stiffen the
vacuum-tight evaporator shell, it is known to provide a
reinforcing ring. The subject matter of the application
utilizes the known finding that foam bubbles collapse on
cooled walls, and solves the objective problem of configuring
the steam separator shell with an easy-to-clean reinforcement
and at the same time of utilizing said reinforcement for foam
breaking. The solution of said problem consists in providing
a welded ring, for instance, in the center of the stepped
evaporator shell, which welded ring serves to reinforce the
shell and to channel a coolant. From said prior art, an
appropriate person skilled in the art gathers the indication
that it is known to disrupt the equilibrium of the foam bubbles
by way of cooling and, as a result, to bring about breaking
of the foam and, furthermore, to step the diameter of the
container shell from the outside to the inside in the region
of the foam formation, the stepped portion being formed by way
of a pipe ring. Here, the cooling zone which is formed by way
of the pipe ring acts only tangentially from the outside on
the foam which grows over the entire evaporator cross section.
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DE 10 2004 062 804 B3 describes an apparatus for controlling
the temperature of objects and/or media. Said temperature
control (heating or cooling) takes place by way of at least
one so-called thermal element block. Said thermal element
block is a flat structure which consists of a plurality of
Peltier elements which are connected in an alternating manner
in series electrically and in parallel thermally, and are
covered toward the outside by way of an electrically
insulating and thermally conducting layer. Here, the medium
to be heated or to be cooled is received in at least one
funnel-shaped depression which has an inflow opening at its
lowest point and a circumferential outflow channel at the
upper edge, which outflow channel is loaded via an overflow
edge. The depression is flowed through by the medium from the
inflow opening toward the outflow channel. The outflow channel
is enclosed on the outside by a seal, via which the interior
space of the depression is closed in a sealed manner with the
thermal element block. A direct heat exchange (heating or
cooling) takes place between the medium which flows through
the depression and the flat thermal element block which acts,
as it were, as a cover of the depression. Said prior art does
not disclose an application which indicates breaking of foam
which is formed from a liquid, or render an application in
this regard obvious. Furthermore, the flat thermal element
block which heats or cools the respective medium can neither
be flowed around on the outside nor flowed through on the
inside.
It is an object of the present invention to specify a method
and an apparatus for controlling the foam formation in a
degassing apparatus for liquids, which method and apparatus
effectively control and limit the foam formation and, in the
process, prevent the growth of the foam beyond a tolerable
extent with ensuring of the sanitary and hygienic requirements
of the process control in the field of the treatment and
processing of liquid foodstuffs.
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Summary of the Invention
Said object is achieved by way of a method having the features
of independent claim 1. Advantageous refinements of the method
are the subject matter of the subclaims. A degassing apparatus
for liquids having an apparatus for controlling the foam
formation in the degassing apparatus, suitable for carrying
out the method according to the invention, is the subject
matter of independent claim 9. Advantageous refinements of the
apparatus are the subject matter of the associated subclaims.
A register system for the apparatus for controlling the foam
formation in the degassing apparatus is the subject matter of
claim 14. Advantageous refinements of the register system are
claimed in the associated subclaims.
The method according to the invention is carried out by way
of a degassing apparatus for liquids, which degassing
apparatus is fed the liquid, in which degassing apparatus the
liquid is treated for the purpose of gas separation and/or
dwells for a mean dwell time, and from which degassing
apparatus the liquid is discharged as a degassed liquid below
a free surface which is formed by the liquid in the degassing
apparatus. The liquid is configured as a liquid film above the
free surface and on a surface of a distributor screen, and
enters from there into the free surface. The liquid film is
preferably of screen-shaped configuration.
In its general operating principle, the method according to
the invention treats a foam which is generated on the surface
of the liquid and out of the latter, and which, starting from
said surface, grows over it into the free space. Said surface
can be a free surface of the liquid supply in the degassing
container, a level of said liquid supply, which level is as a
rule height-controlled, and/or the surface of a liquid film
which is configured on the surface of the possibly present
distributor screen. The surface in question of the liquid film
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is that surface which faces away from that surface of the
distributor screen which forms the liquid film.
In the case of the degassing apparatus, from which the present
invention proceeds, the foam is released in each case above
and from the free surface and/or above the liquid film and
from the liquid film, and in both cases grows into a free
space above the liquid which generates the foam, in particular
into a head space of the degassing container. Here, the foam
is at the temperature of the liquid, possibly at a slightly
lower temperature. In the following text, the terms "grow" and
"growth direction" are intended to be understood as the
movement direction of the foam which takes place, it also
being possible for said movement direction to run in a manner
which differs from the direction of gravity.
In all the above-described cases, therefore, said growth of
the foam is a dynamic process of foam propagation. The
inventive basic concept starts at the boundary surface of the
foam propagation. Beginning at a first heating spacing from
the free surface which releases the foam and beginning at a
second heating spacing from the liquid film which releases the
foam, the respective foam which grows at the liquid
temperature first of all experiences heating from the liquid
temperature to a heating temperature in a register system
which consists of a heating register and a cooling register.
Said heating spacing has to first of all be crossed by the
associated growing foam, before the heating starts. The
respective heating spacing can be predetermined fixedly in a
manner which is dependent on the liquid, or else can be capable
of being set in the degassing container. Here, the region, in
which the heating takes place, is limited and predefined as
measured in the growth direction. The foam bubbles will
necessarily expand as a result of the local heating, primarily
limited in said region, as a result of the thermodynamic laws,
the above-discussed equilibrium state is disrupted, and the
foam bubbles become unstable. The boundary surface of the foam
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propagation will spread out in a manner which is forced by way
of the heating.
Subsequently, beginning at a first cooling spacing from the
first heating spacing and beginning at a second cooling
spacing from the second heating spacing, the respective
further-growing heated foam experiences cooling to a cooling
temperature which can undershoot the liquid temperature. The
first and the second cooling spacing can also be related to
the respective associated foam-generating surface, the first
cooling spacing then being greater than the first heating
spacing, and the second cooling spacing then being greater
than the second heating spacing. Here, the region, in which
the cooling takes place, is likewise limited and predefined
as measured in the growth direction. As a result of the sudden
cooling of the liquid lamellae which enclose the foam bubbles,
the equilibrium state of the foam bubbles is once again
disrupted, to be precise in an opposite manner to the heating.
The foam bubbles become more unstable and burst as a result
of the changing viscosity of the liquid lamellae, as a result
of which the foam in said region collapses and is reduced to
an associated liquid volume which flows away in the direction
of gravity. In this way, the foam propagation, as viewed in
the growth direction, is ended at the end of the cooling or
cooling zone or at a tolerable spacing from said end.
The means for carrying out the heat exchange for heating and
cooling the foam, namely the register system which consists
of a heating register and a cooling register, are configured
in a manner which is permeable to flow in a growth direction
of the foam.
The heating temperature and/or the cooling temperature are/is
set in a manner which is dependent on the properties of the
liquid and/or the physical boundary conditions. The properties
of the liquid are understood to mean the volumetric flow, the
viscosity, the pressure, the temperature and/or the
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composition of the liquid in the region of the feed into the
degassing apparatus. The properties of the degassed liquid are
understood to mean the oxygen concentration in the region of
the discharge from the degassing apparatus, and the physical
boundary conditions are understood to mean the pressure and/or
the result of the foam breaking in the degassing apparatus.
The result of the foam breaking is shown in the fact whether
foam is still present above the cooling of the foam and
possibly grows further. A signal which is generated from said
foam can then be used to set the heating temperature and/or
cooling temperature.
The heating spacings and cooling spacings (in each case viewed
separately) are not necessarily different. Within the context
of method simplification and optimization, they are
advantageously designed to be identical to one another (in
each case viewed separately).
The method according to the invention is fundamentally applied
in such a way that the foam regions which are temperature-
controlled differently, owing to their heating and their
cooling, either engage into one another or overlap to a limited
extent or are side by side, without engaging into one another
or overlapping in this regard. It has proven advantageous, as
one proposal provides, if an extent region of the heating and
heated foam and an extent region of the cooling and cooled
foam are directly side by side, as viewed in an associated
growth direction of the foam, without overlapping mutually
completely or at least partially. In this refinement of the
method, the foam can first of all be heated and expanded in
an unimpeded manner over its entire generation front, from
which it grows, in order then subsequently to experience
unimpeded cooling and breaking under the same geometrical
conditions.
The hygienic and sanitary requirements which are to be made
of the treatment and processing of liquid foodstuffs are
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complied with sufficiently within the context of the method
according to the invention by virtue of the fact that the
heating and the cooling of the foam take place by way of an
indirect heat exchange, for example on walls of heat
exchangers which are as far as possible permeable for foam in
the growth direction of said foam. A heating medium,
preferably hot water, and a coolant, preferably cold water,
are provided as heat exchange medium for the indirect heat
exchange. Hot steam or hot gas can also be used, however. The
heating medium preferably has a heating medium temperature of
up to 90 C in a manner which is expedient and dependent on the
liquid temperature of the liquid. The coolant preferably has
a coolant temperature of as low as from 12 to 14 C for milk
and as low as 6 C for fruit juices in a manner which is
expedient and likewise dependent on the respective liquid
temperature, as a result of which cooling of the foam can also
be realized to a temperature level below the liquid
temperature.
Furthermore, the invention proposes that the heating and/or
the cooling of the foam takes/takes place by way of a direct
heat exchange on the basis of the Peltier effect. In this
case, in the case of a suitable configuration of the Peltier
elements, the heating register and cooling register can be of
very easy-to-clean configuration with regard to CIP cleaning.
It has proven particularly expedient if a cooling capacity in
the region of the cooling of the foam is designed to be greater
than a heating capacity in the region of the heating of the
foam. Beyond the dimensional relationship between a necessary
heating area and cooling area, as a result of the geometric
design conditions, the relationship between the heating
capacity and the cooling capacity can be changed via the
effective driving temperature difference in the respective
heat exchangers of the heating zone and cooling zone. Here,
the heating medium temperature and coolant temperature are
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available as influencing variables which can be changed within
limits.
As a further proposal provides, the heating temperature and/or
the cooling temperature are/is set by means of a setting
function which is generated and stored before or during the
start up of the degassing apparatus. Firstly the optimum
condition relationships between the properties of the liquid
to be degassed and the degassed liquid and/or the physical
boundary conditions and secondly the heating temperature and
the cooling temperature are stored in said setting function,
with the result that a fully automated method for controlling
the foam formation in the degassing apparatus for liquids can
be carried out.
The degassing apparatus for liquids having an apparatus for
controlling the foam formation in the degassing apparatus,
suitable for carrying out the method according to the
invention, consists in a manner known per se of a degassing
container which has an inlet for the liquid and has an outlet
for a degassed liquid, which outlet opens out of the degassing
container in the lowermost, central region. In the degassing
container, the liquid configures a free surface, the level of
which is preferably controlled by a level control device. A
distributor screen is arranged above the free surface, which
distributor screen is preferably of screen-shaped
configuration and on the surface of which distributor screen
the liquid is configured as a liquid film. A feed pipe is
provided which is connected on one side on the end side to the
inlet and on the other side on the end side to a
circumferential annular gap which opens out at the upper end
of the distributor screen. The liquid for the liquid film is
output via the circumferential annular gap.
According to the invention, the apparatus for controlling the
foam formation in the degassing apparatus is distinguished by
the fact that a register system which consists of a heating
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register and a cooling register is provided, which register
system encloses, by way of the heating register, the free
surface and that surface of the distributor screen which forms
the liquid film, in a manner which is annular in the region
of the foam formation and which is spaced apart at a first
heating spacing from the free surface and at a second heating
spacing from that surface of the distributor screen which
forms the liquid film. The cooling register is arranged
offset, as viewed in a respective growth direction of the
foam, with respect to the heating register by a first cooling
spacing in the region of the free surface and by a second
cooling spacing in the region of the distributor screen.
The heating register and the cooling register for the indirect
heat exchange are to be understood to mean in each case a heat
exchanger which has a multiplicity of hollow structures which
are delimited in each case by planar or curved walls. The
hollow structures are flowed through on the inner side by the
heat exchange medium, the heating medium or coolant. The
hollow structures in combination with one another are
permeable to flow on the outer side in the growth direction
of the foam. The planar walls form chambers which can be flowed
through and can have different geometries, such as
rectangular, square or triangular geometries. The curved walls
delimit, for example, oval, elliptical or circular throughflow
cross sections. The hollow structures are flowed through on
the inner side by a heat exchange medium, a heating medium in
the heating register and a coolant in the cooling register.
In accordance with one proposal, the heating register and/or
the cooling register for the direct heat exchange are/is
configured in each case as a Peltier element.
The register system is assigned a control device which changes
a heating capacity of the heating register and/or a cooling
capacity of the cooling register in a manner which is dependent
on the properties of the liquid and/or the physical boundary
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conditions. The control device is connected to a measuring
device which determines at least one of the properties of the
liquid and the degassed liquid and/or the physical boundary
conditions. With regard to the physical boundary conditions,
the measuring device can be set up in such a way that it is a
measuring device for the detection of foam (for example, a
foam sensor), said foam growing above the cooling register and
generating a foam signal there, which foam signal is
transmitted to the control device.
It has proven advantageous and particularly expedient if the
control of the foam formation in the degassing apparatus is
oriented directly toward the result of the degassing
operation. To this end, one refinement provides that the
measuring device is a measuring device for oxygen, which
measuring device determines an oxygen concentration of the
degassed liquid in or at the outlet or in a pipeline which
opens out of the outlet, and transmits it to the control
device.
The degassing operation is intensified if a vacuum source in
the form of a liquid ring pump or in the form of a single
stage or multiple stage ejector is connected to a head space
of the degassing container.
Furthermore, for the indirect heat exchange using in each case
one heat exchange medium, the invention proposes embodiments
of the register system for the apparatus for controlling the
foam formation in the degassing apparatus for liquids, the
register system consisting of a heating register and a cooling
register, and the degassing apparatus, suitable for carrying
out the method according to the invention, having been
described in the above text.
A uniform treatment and breaking of the foam and a simplified
structural embodiment are achieved if the heating register and
cooling register in each case enclose the distributor screen
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in an axially symmetrical manner and if, moreover, both the
first and the second heating spacing among themselves and the
first and the second cooling spacing among themselves are in
each case identical to one another.
It has proven particularly expedient with regard to effective
foam breaking if an overall cooling area of the cooling
register is designed to be greater than an overall heating
area of the heating register. The entire cooling area and the
entire heating area are to be understood in each case to mean
the sum of all heat exchanger areas of the cooling register
and the heating register which act on the foam in a heating
or cooling manner.
One embodiment which is structurally simple and ensures the
hygienic and sanitary requirements during the treatment and
processing of liquid foodstuff products is provided in
accordance with one proposal if the heating register consists
of first pipes, and the cooling register consists of second
pipes. Here, the first pipes and the second pipes, in each
case among themselves, are arranged in a row next to one
another and spaced apart from one another. In relation to the
respective foam-generating surface in the degassing container,
the first pipes are positioned at the first heating spacing
from the free surface and at the second heating spacing from
that surface of the distributor screen which forms the liquid
film. The cooling register which is likewise realized with
pipes in this way is arranged offset with respect to the
heating register, as viewed in the respective growth direction
of the foam, to be precise by virtue of the fact that the
second pipes are positioned at the first cooling spacing,
starting from the first heating spacing, and at the second
cooling spacing, starting from the second heating spacing.
Transversely with respect to the respective growth direction,
the first and second pipes are likewise arranged offset with
respect to one another, to be precise in a simple way such
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that second pipes are positioned in and distributed to the
respective gaps between the first pipes.
In order to prevent the cooling register which is realized by
way of pipes not engaging into the heating register or
overlapping with the latter entirely or in part regions, it
is proposed that the first and the second cooling spacing are
in each case consistently greater than a greatest first
diameter of the first pipes at the associated cooling spacing.
There is a simplification of the respective construction if
the first pipes and the second pipes in each case have
identical diameters among themselves, and the desired
relationship between the cooling area and the heating area can
be designed more easily and more flexibly under the above
diameter conditions if the first pipe has a greater diameter
than the second pipe.
It is proposed, furthermore, to configure the first pipes
and/or the second pipes in each case as a monopipe. As a result
of said embodiment, problems in terms of the flow are avoided
during the distribution of the heating medium and the coolant.
Furthermore, it is proposed for the first pipe and the second
pipe, in each case configured as a monopipe, to be in each
case of spiral configuration in a region which is assigned to
the free surface, and to be in each case of helically wound
configuration in a region which is assigned to that surface
of the distributor screen which forms the liquid film.
Furthermore, this embodiment provides the possibility to
arrange the monopipes which are wound in this way, in relation
to the growth direction of the foam and transversely with
respect thereto, very simply in such a way that, as viewed in
the growth direction, they are firstly in each case permeable
to flow and secondly realize the required series connection
of the heating register and the cooling register. This is
expediently achieved by virtue of the fact that the monopipes
of the cooling zone are firstly arranged in the growth
direction axially offset with respect to the monopipes of the
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heating zone, and secondly are positioned in the radial
direction over the respective gaps between the monopipes of
the heating zone. One advantageous embodiment in this regard
provides that in each case two second pipes are positioned in
a symmetrical and uniformly distributed manner over the
respective gap between two adjacent first pipes.
With regard to a simple and easily variable adjustment and
fastening of the register system in any desired configuration
or in the configuration with first and second pipes, two
solutions are proposed. The two solutions both propose that
the heating register and cooling register are supported on the
degassing container via a plurality of carriers which are
arranged in a uniformly distributed manner over the
circumference of the degassing container and extend in a star-
shaped manner toward the center of the degassing container.
The first solution is distinguished by the fact that the course
of each carrier in relation to the heating register results
from a lower contour of the heating register, against which
lower contour each carrier bears tightly from below. In the
case of the second solution, the course of each carrier in
relation to the heating register results from the positioning
of the first pipe, against which each carrier bears tightly
tangentially from below. In the case of the two solutions,
four carriers are preferably provided.
In the case of the refinement of the register system with
first and second pipes, the positioning and fastening of the
pipes which are required according to the invention both in
the growth direction of the foam and also transversely with
respect thereto are achieved in a very simple way by virtue
of the fact that an imaginary contact line is utilized as
reference line for positioning and fastening, which imaginary
contact line results from the contact points between the first
pipes and the carrier which bears in each case tangentially
against them. Securing means for the first and the second
pipes are provided on the carrier in the course of the contact
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line, which securing means are connected fixedly to the
carrier. The securing means are preferably of plate-shaped
configuration and are oriented upright firstly in the
direction of a longitudinal axis of the degassing container
and secondly in the direction of the contact line, as a result
of which the growth of the foam is impeded as little as
possible. Here, two adjacent securing means in each case fix
a first pipe and .at least one second pipe non-displaceably in
the direction of the contact line.
Brief Description of the Drawings
A more detailed summary of the invention results from the
following description and the appended figures of the drawing,
and from the claims. Whereas the invention is realized in a
very wide variety of embodiments, the drawing describes one
preferred exemplary embodiment of a degassing apparatus for
liquids, configured with a lower, lateral inlet and combined
with an apparatus according to the invention for controlling
the foam formation in the degassing apparatus, suitable for
carrying out the method according to the invention. Moreover,
one preferred exemplary embodiment of a register system which
consists of a heating register and a cooling register is shown
for the apparatus according to the invention, and will be
described in the following text with respect to the
construction and function. In the drawing:
figure 1 shows a degassing apparatus of a second type
in accordance with the prior art, configured
with a lower, central inlet, from which the
present invention proceeds apart from a
modification of the positioning of the inlet,
shown in figure 2,
figure 2 shows a perspective and
transparent
illustration of one preferred embodiment of a
degassing apparatus of a first type, configured
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with a lower, lateral inlet, from which the
present invention proceeds, together with the
apparatus according to the invention, and a
register system, consisting of a heating
register and a cooling register,
figure 3 shows a perspective illustration of the
degassing apparatus in accordance with figure
2, the apparatus according to the invention
being exposed by way of the omission of a shell
and an upper floor of the degassing container,
and a diagrammatic illustration of a control
device with associated means for loading a
heating register and a cooling register with a
heating medium and a coolant,
figure 4 shows the front view of the degassing apparatus
in accordance with figures 2 and 3 in a viewing
direction which is labeled by "Z" in figure 3,
figure 5 shows the plan view of the degassing apparatus
in accordance with figures 2 to 4,
figure 6 shows a meridian section of the degassing
apparatus in accordance with figures 2 to 5 in
accordance with a sectional course which is
labeled by A-A in figure 5,
figure 7 shows an enlarged illustration of a first
detail (labeled by "B" in figure 6) in the
region of the apparatus according to the
invention,
figure 8 shows a once again enlarged illustration of a
second detail (labeled by "C" in figure 7) from
the first detail in accordance with figure 7,
and
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figure 9 shows a front view and a plan view of a securing
means (shown in figures 7 and 8) for pipes of
the heating register and cooling register
according to the invention in an enlarged
illustration.
Detailed Description
The invention proceeds from a degassing apparatus 10 for
liquids P in accordance with the prior art, to be precise
either in an embodiment of a second type, called a degassing
apparatus 10.2 in the following text, as shown in figure 1 for
the description of the general construction of the degassing
apparatus in question, or in an embodiment of a first type,
called a degassing apparatus 10.1 in the following text, as
disclosed in figures 2 to 6 in conjunction with an apparatus
according to the invention, the essential part of which
consists of a register system 20. The degassing apparatus 10,
10.2 consists of a degassing container 2 in the form of a
substantially cylindrical container shell 2c with a lower
floor 2b and an upper floor 2a. The lower floor 2b has a
central outlet stub 2d with an outlet A for a degassed liquid
P', the outlet stub 2d being penetrated concentrically by a
feed pipe 4 which engages from below into the degassing
container 2 with an inlet E for the liquid P. A distributor
screen 3 is connected fixedly to the feed pipe 4 at the upper
end of said feed pipe 4 which is guided into the degassing
container 2, in such a way that the feed pipe 4 opens out
centrally in the distributor screen 3 on the inner side via
an outlet opening 4a which is preferably sufficiently rounded
with respect to the distributor screen 3. The feed pipe 4
establishes a connection to a circumferential annular gap 6
which is formed between the upper end of the distributor screen
3 and a baffle plate 5 which is arranged concentrically with
respect to and spaced apart above said distributor screen 3.
Here, the baffle plate 5 reaches over the upper end of the
distributor screen 3 to a certain extent, and is guided axially
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and fastened on its side which faces the upper floor 2a, and
can be adjusted within limits in terms of its spacing from the
upper end of the distributor screen 3. The liquid P which is
fed in via the inlet E leaves the feed pipe 4 via the outlet
opening 4a, is deflected there by the baffle plate 5, and is
applied to the distributor screen 3 in a star-shaped manner
via the circumferential annular gap 6 and, as viewed radially,
from the inside to the outside, and is configured as a liquid
film F on the surface of said distributor screen 3. Admixed
gases can be separated easily from the surface (facing away
from the distributor screen 3) of the liquid film F which runs
down over the distributor screen 3, as a consequence of the
buoyancy. A free surface N or a level N of the liquid P', P
which has already been degassed to a very great extent or is
still to be degassed and forms a liquid supply in the degassing
container 2 is set by way of a level control device (not
shown). The liquid film F which has been partially degassed
or degassed to a very great extent enters at the lower end of
the distributor screen 3 into the free surface N. The liquid
fractions which are layered via the distributor screen 3 in
the form of the liquid film F onto the free surface N and
enter into the latter dwell in the degassing container 2 for
a mean dwell time and can degas further there with the aid of
the gas bubble buoyancy over the free surface N.
The distributor screen 3 and the first baffle plate 5 which
corresponds with it are expediently of circular and in each
case screen-shaped configuration, that is to say so as to fall
radially to the outside. In one preferred embodiment, the
distributor screen 3 (as shown) has a tapered or conical
configuration, it being possible for the angle at the cone tip
to be reduced to approximately from 80 to 90 . As a rule, the
lower end of the distributor screen 3 reaches as far as the
free surface N or dips slightly into the latter.
If foam S is formed during the degassing of the liquid P, said
foam S is generated in part from the liquid supply below the
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free level N and in part from the liquid film F. Said foam S
is released in each case above and out of the free surface N
and/or above the liquid film F and out of the liquid film F,
and grows in the direction of an interior space which is formed
by the container shell 2c and in the direction of a head space
which is formed by the upper floor 2a. A respective growth
direction of the foam is denoted by r(S).
Just like the lower and central arrangement of the inlet E,
the further components which are shown in figure 1 and are not
denoted, such as a head hole, various connectors and stubs as
well as level indicator windows, are not of significance for
the invention in question here.
The invention is configured specifically in the degassing
apparatus 10.1 for liquids P, an embodiment of the second type
(figures 2 to 6). It differs substantially only by way of the
location of the arrangement of the inlet E of the degassing
apparatus 10.2, the embodiment of the second type. The inlet
pipe 4 is introduced from the side into the lower floor 2b,
and the outlet stub 2d with its outlet A therefore remains
free and undiminished. Said difference is insignificant for
the present invention. In the transparent illustration of
figure 2 and in figures 3 to 8, in contrast to the degassing
apparatus 10.2, a register system 20 according to the
invention can be seen, consisting of a heating register 20.1
and a cooling register 20.2, which register system 20 will be
described in more detail in the following text.
The register system 20 in a generalized embodiment which is
not shown in detail encloses the free surface N and that
surface of the distributor screen 3 which forms the liquid
film in the region of the foam formation in an annular manner
by way of its heating register 20.1, and is spaced apart here
from the free surface N at a first heating spacing hl and from
that surface of the distributor screen 3 which forms the liquid
film at a second heating spacing h2 (figures 7, 8 and 6). The
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heating register 20.1 is designed for the indirect and the
direct heat exchange with a heating capacity HL, and the
cooling register 20.2 is designed in the corresponding method
of operation with a cooling capacity KL.
Within the context of the indirect heat exchange, the heating
register 20.1 is flowed through by a heating medium WH which
is at a heating medium temperature TH, and the cooling register
20.2 is flowed through by a coolant WK which is at a coolant
temperature TK (figures 3 and 5). As viewed in the respective
growth direction of the foam r(S), the cooling register 20.2
is arranged offset with respect to the heating register 20.1
by a first cooling spacing kl in the region of the free surface
N and by a second cooling spacing k2 in the region of the
distributor screen 3 (figures 7, 8 and 6). The heating and
cooling register 20 preferably in each case enclose the
distributor screen 3 in an axially symmetrical manner. The
first and the second heating spacing hl, h2 and/or the first
and the second cooling spacing kl, k2 are in each case
preferably of identical configuration among themselves. An
overall cooling area OK of the cooling register 20.2 is
preferably designed to be greater than an overall heating area
OH of the heating register 20.1.
The heating and cooling register 20 is assigned a control
device 13 which changes the heating capacity HL (in the present
exemplary embodiment, the volumetric flow of the heating
medium WO and/or the cooling capacity KL (in accordance with
the volumetric flow of the coolant WK) in a manner which is
dependent on the properties of the liquids P, P' and/or the
physical boundary conditions (figure 3). The control device
13 is connected to a measuring device 14, 14.1 which determines
at least one of the properties of the liquids P, P' and/or the
physical boundary conditions. Via a first valve 15 which is
connected by way of signaling components to the control device
13, the throughflow of the heating medium WH through the
heating register 20.1 is controlled, and the throughflow of
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the coolant WK through the cooling register 20.2 is controlled
via a second valve 16.
According to one advantageous and preferred embodiment, the
heating register 20.1 consists of first pipes 8, and the
cooling register 20.2 consists of second pipes 9 (figures 2
to 8). In each case among themselves, the first pipes 8 and
the second pipes 9 are arranged in rows next to one another
and spaced apart from one another (figures 6 to 8). The first
pipes 8 are positioned at the first heating spacing h1 from
the free surface N and at the second heating spacing h2 from
that surface of the distributor screen 3 which forms the liquid
film. The necessary offset of the first and the second pipes
with respect to one another and as viewed in the growth
direction r(S) of the foam S is ensured by virtue of the fact
that the second pipes 9 are positioned at the first cooling
spacing kl, starting from the first heating spacing hl, and
at the second cooling spacing k2, starting from the second
heating spacing h2. A complete coverage of the foam-generating
surfaces is ensured by virtue of the fact that second pipes 9
are arranged over and distributed to the respective gaps
between the first pipes 8.
If, as is preferably provided, the first and the second cooling
spacing kl, k2 are in each case consistently greater than a
greatest first diameter DE of the first pipes 8 at the
associated cooling spacing kl, k2, complete or at least
partial engagement into one another or overlapping in this
regard of the heating and cooling registers 20.1, 20.2 is
prevented.
The first pipes 8 and the second pipes 9 are preferably
configured with identical diameters in each case among
themselves, and the first pipe 8 preferably has a greater
diameter (the first diameter DH) here than the second pipe 9
with a second diameter DK.
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The construction of the register system 20 in the pipe
embodiment is simplified substantially if the first pipes 8
and/or the second pipes 9 are configured in each case as a
monopipe. Further simplification of the construction results
from the fact that the first pipe 8 and the second pipe 9, in
each case configured as a monopipe, are in each case of spiral
configuration in a region which is assigned to the free surface
N, and are in each case of helically wound configuration in a
region which is assigned to that surface of the distributor
screen 3 which forms the liquid film. A simple and gap-free
coverage of the foam-generating surfaces is preferably
achieved by virtue of the fact that in each case two second
pipes 9 are positioned in a symmetrical and uniformly
distributed manner over the respective gap between two
adjacent first pipes 8 (figures 8 and 9).
With regard to an appropriate and expedient design of the
register system 20 in the tubular embodiment and, here,
preferably in the respective embodiment as a monopipe heat
exchanger, in particular with regard to the ratio between the
heating area and the cooling area OH, OK, the specific
objective embodiment in this regard provides, for example, to
design the cooling area OK over the second pipe 9 in such a
way that it has the second diameter DK = 8 mm and an overall
length, a second length LK. In the context of the
abovementioned cooling area OK, the heating area OH is designed
over the first pipe 8 in such a way that it has the first
diameter DH = 10 mm and an overall length, a first length LH =
LK/2. With regard to the ratio required above between the
cooling capacity KL and the heating capacity HL, a ratio of
the cooling area OK and heating area OH of
OK/OH - dkLK/dFILH = 8 LK/10 LH = 8 LK/(10 LK/2) = 2 x 8/10 = 1.6
thus results in the exemplary embodiment, whereby the
condition that the cooling area OK is to be designed to be
greater than the heating area OH is sufficiently met.
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The register system 20 has a form, as can be seen from figures
2 to 7, in particular, and is owing to the course of the free
surface N and the course of the distributor screen 3. It is
essential in the case of the embodiment of the register system
20 that the foam formation in the growth direction of the foam
r(S) is not impeded or is impeded merely insignificantly by
the first and second pipes 8, 9. For this purpose, the first
and second pipes 8, 9 are firstly spaced apart from one another
sufficiently and are secondly, however, so numerous that a
universal and sufficient thermal treatment of the foam S is
ensured.
A heating temperature and/or a cooling temperature T1, T2 of
the foam S (figures 7 and 8) are/is set in a manner which is
dependent on the properties of the liquid P and the physical
boundary conditions via the control device 13 (figure 3) with
the aid of the heating medium WH at the heating medium
temperature TH and the coolant WK at the coolant temperature
TK, with the result that it is possible to control the foam
formation by way of this.
The foam S grows approximately at a liquid temperature T3 out
of the free surface N and/or out of the liquid film F and is
situated first of all in the region of the first and the second
heating spacing hi, h2 (figures 7, 8). A foam SH which is being
heated and is heated on the heating area OH (said heated foam
being at the heating temperature Tl) is situated in the region
of the first and the second cooling spacing kl, k2, and a
cooling and cooled foam SK (said cooled foam being at the
cooling temperature T2) which disintegrates during the cooling
to form liquid is situated in the region above the first and
the second cooling spacing kl, k2.
The register system 20 is preferably supported on the
degassing container 2 via a plurality of carriers 7 which are
preferably arranged in a uniformly distributed manner over the
circumference of the degassing container 2 and preferably
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extend in a star-shaped manner toward the center of the
degassing container 2 (figures 2 to 8). Four carriers 7 are
preferably provided (figure 3), it being possible for said
number to also vary by from one to two in both directions. In
a generalized embodiment (not shown) of the register system
20, the course of each carrier 7 in relation to the heating
register 20.1 preferably results from a lower contour of the
heating register 20.1, against which lower contour each
carrier 7 bears tightly from below.
In the above-described specific embodiment of the register
system 20 in the form of a monopipe at least for the heating
register 20.1, the course of each carrier 7 (as shown in
figures 2 to 8) in relation to the heating register 20.1
results from the positioning of the first pipes 8, against
which each carrier 7 bears tightly from below in a tangential
manner. The contact points between the first pipes 8 and the
respective carrier 7 which bears tangentially against them
result in an imaginary contact line PL on each carrier 7. In
the course of the contact line PL, securing means 12 for the
first and the second pipes 8, 9 are provided on the carrier
7, which securing means 12 are connected fixedly to the carrier
7. The securing means 12 are preferably of plate-shaped
configuration and are oriented upright firstly in the
direction of a longitudinal axis of the degassing container 2
and secondly in the direction of the contact line PL. Two
adjacent securing means 12 in each case fix a first pipe 8
non-displaceably in the direction of the contact line PL, and
each securing means 12 likewise fixes at least one second pipe
9 non-displaceably in the direction of the contact line PL.
In the embodiment which is shown by way of example, the
register system 20 consists of the first and the second pipe
8, 9 which are configured in each case as a monopipe and are
preferably spirally or helically wound. The first pipe lies
on the carriers 7 and is positionally fixed between two
securing means 12. It acts as a heating pipe and, as measured
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from the free surface N, is at the first heating spacing hl,
and is at the second heating spacing h2 from the distributor
screen 3 (figures 7, 8), which therefore defines the inlet of
the foam S into a warming or heating zone in the respective
growth direction of the foam r(S). In relation to the
intermediate spacing between two adjacent first pipes 8, two
immediately adjacent second pipes 9 are arranged in the region
above the first cooling spacing kl, as measured from the first
heating spacing hl, and in the region of the second cooling
spacing k2, as measured from the second heating spacing h2.
The second pipes 9 are supported in recesses of the securing
means 12 in such a way that there is the spacing both among
one another and in relation to the first pipes 8, also with a
view to ensuring the first and the second cooling spacing kl,
k2.
Merely the carriers 7 and the securing means 12 which are of
as narrow configuration as possible in terms of strength lie
in the growth direction of the foam r(S), without appreciably
treating said foam thermally. In relation to the growth
direction of the foam r(S), in a correspondingly projected
direction, they contribute rather to a mechanical impairment
of the foam S and therefore to the desired foam breaking.
It has proven advantageous if the heating and/or the cooling
temperature Ti, T2 of the foam S are/is set indirectly via the
heating medium temperature and the coolant temperature TH, TK
in a manner which is dependent on an oxygen concentration 0(02)
of the degassed liquid P', which oxygen concentration 0(02) is
measured in or at the outlet A or in a pipeline which opens
out of the outlet A. To this end, it is provided that the
measuring device 14 is a measuring device for oxygen 14.1
which determines the oxygen concentration c(02) and transmits
it to the control device 13 (figure 3). Furthermore, a
measuring device 14 can be arranged in the head space of the
degassing apparatus 10, 10.1, 10.2 above the cooling register
20.2, which measuring device 14 is a measuring device for the
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detection of foam (for example, a foam sensor), said foam
growing above the cooling register 20.2 and generating a foam
signal LS there, which foam signal LS is transmitted to the
control device 13 (figure 3).
Tests with the degassing apparatus 10, 10.1, 10.2 according
to the invention have shown that the oxygen concentration in
skimmed milk or semi-skimmed milk of c(02) = 9 ppm can be
reduced to 0.9 ppm. The effective control of the foam formation
which leads as a result to breaking of the foam S which is
formed and grows ensures that the degassing apparatus 10,
10.1, 10.2 operates over the entire operating time under
optimum degassing conditions, which is ultimately reflected
in the above-specified measuring result.
Moreover, the method according to the invention and the
apparatus for carrying it out show a further positive result.
This consists in that the highly effective foam breaking at
the location of the foam generation leads to a recovery of
pure liquid. The aromas which are contained in the foam S and
are possibly highly volatile and therefore readily leave the
head space of the degassing container 2 under the forcing
action of a possibly present vacuum source remain in the
recovered liquid and are returned on a short path via the free
surface N into the liquid supply and via the surface of the
liquid film F into the latter.
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List of Designations of the Abbreviations which are Used
Figure 1 (Prior Art)
10 Degassing apparatus (general)
10.1 Degassing apparatus of a first type (with a lower,
lateral inlet)
10.2 Degassing apparatus of a second type (with a lower,
central inlet)
2 Degassing container
2a Upper floor
2b Lower floor
2c Container shell
2d Outlet stub
3 Distributor screen
4 Feed pipe
4a Outlet opening
5 Baffle plate
6 Circumferential annular gap
A Outlet
E Inlet
F Liquid film
N Free surface (free level)
P Liquid to be degassed (liquid food product)
P' Degassed liquid
S Foam
/(S) Growth direction of the foam
Figures 2 to 9
7 Carrier
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8 First pipe (heating pipe)
9 Second pipe (cooling pipe)
12 Securing means
13 Control device
14 Measuring device
14.1 Measuring device for oxygen
First valve
10 16 Second valve
Register system
20.1 Heating register
20.2 Cooling register
DH First diameter (first pipe; heating pipe)
DK Second diameter (second pipe; cooling pipe)
HL Heating capacity
KL Cooling capacity
LH First length (first pipe; heating pipe)
LK Second length (second pipe; cooling pipe)
LS Foam signal
OH Heating area (first pipe; heating pipe)
OK Cooling area (second pipe; cooling pipe)
PL Contact line
SH Heating and heated foam
SK Cooling and cooled foam
Ti Heating temperature (of the foam S)
T2 Cooling temperature (of the foam S)
T3 Liquid temperature (of the liquid P, P')
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TH Heating medium temperature
TK Coolant temperature
WH Heating medium
WK Coolant
c(02) Oxygen concentration
hl First heating spacing (first pipe; heating pipe)
h2 Second spacing (first pipe; heating pipe)
kl First cooling spacing (second pipe; cooling pipe)
k2 Second cooling spacing (second pipe; cooling pipe)
33
