U.S. patent application number 15/575660 was filed with the patent office on 2018-04-26 for container for storing a liquid, and use thereof.
The applicant listed for this patent is BASF SE. Invention is credited to Katharina FEDERSEL, Michael LADENBERGER, Stephan MAURER, Jurgen WORTMANN.
Application Number | 20180112929 15/575660 |
Document ID | / |
Family ID | 53268660 |
Filed Date | 2018-04-26 |
United States Patent
Application |
20180112929 |
Kind Code |
A1 |
WORTMANN; Jurgen ; et
al. |
April 26, 2018 |
CONTAINER FOR STORING A LIQUID, AND USE THEREOF
Abstract
The invention relates to a container for storing a liquid, which
tends to decompose into gaseous decomposition components in the
case of the conditions prevailing in the container (1) and in the
case of which a chemical reaction equilibrium results between
gaseous decomposition components and liquid, wherein a floating
roof (29) is accommodated in the container (1) and the floating
roof (29) comprises floats (33), using which the floating roof (29)
floats on the liquid, and wherein the floating roof (29) is guided
using a sliding seal (45) in the container (1). The invention
furthermore relates to a device for storing heat, comprising a
first container (57) for storing a colder liquid and a second
container (59) for storing a hotter liquid and a use of the
container and the device for storing heat.
Inventors: |
WORTMANN; Jurgen;
(Limburgerhof, DE) ; LADENBERGER; Michael;
(Annweiler Am Trifels, DE) ; FEDERSEL; Katharina;
(Eppelheim, DE) ; MAURER; Stephan; (Neustadt,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen |
|
DE |
|
|
Family ID: |
53268660 |
Appl. No.: |
15/575660 |
Filed: |
May 19, 2016 |
PCT Filed: |
May 19, 2016 |
PCT NO: |
PCT/EP2016/061262 |
371 Date: |
November 20, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 10/46 20130101;
F03G 6/067 20130101; F24S 60/30 20180501; F24S 80/20 20180501; F28D
20/0034 20130101; Y02B 10/20 20130101; F28D 2020/0069 20130101;
Y02E 10/40 20130101; Y02E 60/14 20130101; F28D 2020/0095 20130101;
F28D 2020/0047 20130101 |
International
Class: |
F28D 20/00 20060101
F28D020/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 21, 2015 |
EP |
15168599.7 |
Claims
1-13. (canceled)
14. A container for storing a liquid, which tends to decompose into
gaseous decomposition components in the case of the conditions
prevailing in the container (1) and in the case of which a chemical
reaction in equilibrium results between gaseous decomposition
components and liquid, wherein a floating roof (29) is accommodated
in the container (1), wherein the floating roof (29) comprises
floats (33), using which the floating roof (29) floats on the
liquid, and wherein the floating roof (29) is guided using a
sliding seal (45) in the container (1), characterized in that the
sliding seal (45) is thermally insulated from the liquid stored in
the container (1).
15. The container of claim 14, wherein the floating roof (29) is
constructed from at least two segments (61), wherein the segments
(61) are connected to one another in a movable manner.
16. The container of claim 14, wherein the floating roof (29) has
at least one chamber, which contains thermally insulating
material.
17. The container of claim 14, wherein feedthroughs (35, 37) are
formed in the floating roof (29).
18. The container of claim 17, wherein the feedthroughs (35, 37)
are sealed using a movable sealing plate (39).
19. The container of claim 14, wherein the sliding seal (45) has
protective units (53) against liquid creeping upward.
20. The container of claim 14, wherein the floating roof (29) is
guided on at least one guide in the container.
21. The container of claim 14, wherein the floating roof (29) has
units to compensate for thermal expansion.
22. The container of claim 14, wherein the liquid is a molten
salt.
23. The container of claim 22, wherein the molten salt is a mixture
of nitrite and nitrate salts.
24. A device for storing heat, comprising a first container (57)
for storing a colder liquid and a second container (59) for storing
a hotter liquid, wherein the containers (57, 59) are connected to
one another, so that the colder liquid flows out of the first
container (57), after absorbing heat, into the second container
(59) and flows out of the second container (59), after emitting
heat, into the first container (57), wherein at least the second
container (59) is a container according to claim 14.
25. The device of claim 24, wherein a gas compartment (41) is
formed in the first container (57) and in the second container (59)
above the floating roof (39), and the gas compartments (41) of the
first (57) and the second (59) container are connected to one
another via a connecting line (67).
26. A solar-thermal power plant comprising the container of claim
14.
27. A solar-thermal power plant comprising the device of claim 25.
Description
[0001] The invention is directed to a container for storing a
liquid, which tends to decompose into gaseous decomposition
components in the case of the conditions prevailing in the
container, and in the case of which a chemical reaction equilibrium
results between gaseous decomposition components and liquid. The
invention furthermore relates to a device for storing heat, in
which such a container is used, and a use of the container or the
device for storing heat.
[0002] Liquids which tend to decompose into gaseous decomposition
components are, for example, molten salts, which are used as a heat
carrier medium and heat storage medium. Molten salts are used in
particular where classic heat carrier media and heat storage media
can no longer be reasonably used as a result of the required high
temperatures. An important field of use of molten salts as a heat
carrier medium are solar power plants, in which the heat carrier
medium is heated in receivers by solar radiation and temporarily
stored in a hot store. Water is vaporized and superheated using the
hot heat carrier medium and a generator is driven to generate power
using the superheated steam.
[0003] In particular in the case of molten salts, which are used in
solar power plants, for example, parabolic trough solar power
plants, Fresnel solar power plants or tower solar power plants, and
which are based on nitrates or nitrites of the alkali metals or
alkaline earth metals, wherein a mixture of nitrates and nitrites
is frequently used, the risk exists that the salt will decompose to
form gases as a result of the high temperatures. Thus, for example,
nitrate salts of alkali metals and alkaline earth metals form the
respective corresponding alkali metal oxides or alkaline earth
metal oxides, respectively, at high temperatures while
simultaneously forming nitrogen monoxide and nitrogen dioxide,
summarized hereafter under the term nitrogen oxides. The nitrogen
oxides physically dissolve in the molten salt and can back-react
with dissolved alkali metal oxides or alkaline earth metal oxides
in the meaning of a chemical reaction equilibrium. The nitrogen
oxides can also pass into the gas state in particular in the event
of sinking pressure or increasing concentration, however, and are
then no longer available for a back reaction. In this way, a
harmful accumulation of alkali metal oxides or alkaline earth metal
oxides can occur in the molten salt.
[0004] Since the decomposition of the nitrate salts is an
equilibrium reaction, the nitrogen oxides dissolved in the molten
salt also inhibit the further decomposition of the nitrate salt.
This safeguard becomes less effective due to outgassing of the
nitrogen oxides and the reduction linked thereto of the
concentration of nitrogen oxides in the molten salt, and the salts
in the molten salt can decompose further.
[0005] The formation of the oxides due to the decomposition of the
nitrate salts is disadvantageous. On the one hand, the
decomposition reaction results, in the case of melts having a high
nitrate content, in sinking of the nitrate concentration and thus a
rise of the melting point. On the other hand, the corrosivity of
the melt increases in relation to the metallic materials which are
typically used, in particular steel. Furthermore, solids can form
in the molten salt because the solubility limit of the alkali metal
and alkaline earth metal concentration is exceeded, and these salts
can result in abrasion on the surfaces of the facility parts
through which flow occurs and therefore also in damage to the
facility parts. In addition to the abrasion by entrained solid
particles, it is also possible that solids will precipitate from
the molten salt and result in deposits and baked-on material on the
facility parts. This can furthermore result in the blocking of
pipelines or heat exchangers.
[0006] It is presently typical, for example, to regenerate the
molten salt as described in WO-A 2014/114508, to lengthen the
service life of molten salts containing nitrates.
[0007] Alternatively, the possibility also exists of covering the
molten salt with a gas phase, the content of nitrogen oxides of
which is sufficiently high that a sufficiently high concentration
of dissolved nitrogen oxide is obtained in the molten salt, and the
decomposition of the nitrate salts can thus be inhibited. In
particular in the case of use in large containers, which are used,
for example, as heat stores in a solar power plant, however, this
has the disadvantage that the heat stores are subjected to cyclic
heating and cooling as a result of the cyclic operation, which
result in substantial pressure and volume changes in the gas
compartment in particular. Because of the large volume changes, it
is difficult to transfer out a sufficiently large quantity of
nitrogen oxides and provide them again for regeneration.
On-location production would therefore be necessary for providing a
sufficiently large quantity of nitrogen oxides.
[0008] Keeping the gas compartment in a state which manages without
relevant emission of gases to the environment by way of consistent
sealing in a gas pendulum system together with the use of gas
pressure stores or gas volume stores is known. In this way, it is
not necessary to supply large quantities of nitrogen oxides or
starting products for the production of nitrogen oxides. However,
it is disadvantageous that an additional large investment
expenditure and maintenance expenditure are linked to the required
use of the gas pressure stores or gas volume stores. The container
is terminated on top toward the environment using the floating roof
in the case of the known floating roof tanks.
[0009] For liquids which have a high vapour pressure, for example,
in petrochemistry, using floating roof tanks in which a roof floats
in a movable manner on the liquid in the container is known. The
roof can be sealed by membranes or friction systems. Such floating
roof tanks are known, for example, from U.S. Pat. No. 2,536,019 or
U.S. Pat. No. 4,371,090. Furthermore, JP-A 56484887 describes a
floating roof which is used in a hot water tank. However, none of
the tanks described here is used under the conditions prevailing in
a solar power plant, in particular at the prevailing temperatures
of the heat carrier medium in a solar power plant.
[0010] The object of the present invention was to provide a
container for storing a liquid, in particular a heat carrier medium
in a solar power plant, which tends toward decomposition into
gaseous decomposition components in the case of the conditions
prevailing in the container and in the case of which an equilibrium
results between gaseous decomposition components and liquid, which
does not have the disadvantages known from the prior art.
[0011] The object is achieved by a container for storing a liquid,
which tends toward decomposition into gaseous decomposition
components in the case of the conditions prevailing in the
container and in the case of which a chemical reaction equilibrium
results between gaseous decomposition components and liquid,
wherein a floating roof is accommodated in the container and the
floating roof comprises floats, using which the floating roof
floats on the liquid, and wherein the floating roof is guided using
a sliding seal in the container.
[0012] In contrast to the known systems, in which the gas which
results due to the decomposition of the liquid is stored in a
central gas store, the size of the gas store can be greatly reduced
or a gas store can even be dispensed with by way of the floating
roof. The gas collects in a gas compartment underneath the floating
roof and exit of the gas into the environment or into a gas phase
in the container above the floating roof is prevented. In this way,
damage to the liquid, in particular a molten salt containing
nitrates, can be prevented or at least greatly slowed.
[0013] A further advantage results in the case of use in a
two-store system, in which hotter liquid is stored in a first
container and colder liquid is stored in a second container,
wherein the first and the second container are connected to one
another, so that liquid can be removed from the first container,
cooled, and introduced into the second container or alternatively
liquid can be taken from the second container, heated, and
introduced into the first container. Thus, for example, in a solar
power plant, the liquid from the second container is heated by
incident solar radiation either in a solar field of a parabolic
trough or Fresnel solar power plant or in a central receiver of a
tower power plant and introduced into the first container. The
liquid from the first container is used to vaporize and superheat
water, wherein heat is emitted. The liquid thus cooled is then
introduced into the second container. Since the liquid level in the
first container and in the second container cyclically changes due
to the operation, the gas volume above the liquid in the container
also changes. Typically, the gas is transferred in each case from
the container into which the liquid is introduced via a gas
pendulum system into the container from which the liquid is
removed. A molten salt is suitable in particular as a liquid which
is used in a solar power plant as a heat carrier medium. Typical
salts, which are used in the form of their melts, are nitrates or
nitrites of the alkali metals and the alkaline earth metals and
also arbitrary mixtures thereof. A mixture made of potassium
nitrate and potassium nitrate is particularly preferred in this
case.
[0014] However, the hotter liquid and the colder liquid have large
temperature differences in a solar power plant. This has the result
that the gas in the first container having the liquid having higher
temperature has a very much greater specific volume at equal
pressure than the gas in the second container having the colder
liquid. To prevent the pressure from rising in the first container
as a result of the greater specific volume of the gas, it is
necessary to remove gas from the system or temporarily store it in
a gas store during filling of the first container and emptying of
the second container.
[0015] If the container according to the invention having floating
roof is used in such a system as the first container for the
storage of the hot liquid, the floating roof is preferably embodied
so that the floating roof has at least one chamber, which contains
thermally insulating material. Thermal insulation of the liquid in
relation to the gas compartment formed above the floating roof is
thus achieved. The insulation of the floating roof is preferably
designed in this case so that the gas in the gas compartment of the
first container has the same temperature as the gas in the second
container. In this way, pressure variations of the gas can be
equalized as a result of the same specific volume at equal
temperature and equal pressure. It is therefore no longer necessary
to additionally provide a gas store, in which the gas can be
temporarily stored.
[0016] In such a system having two containers, it is also possible
to provide a floating roof in the second container having the
colder liquid. The floating roof has the task here in particular,
however, of preventing foreign materials, for example, carbon
dioxide, water or aerosol particles, in particular chlorinated
aerosol particles, from being able to reach the liquid from the gas
phase.
[0017] The penetration of gaseous contaminants from the gas phase
above the floating roof into the liquid or of decomposition gases
formed from the liquid into the gas phase above the floating roof
is prevented by the use of the gas-tight sliding seal. In
particular if the container is used as a heat store in a solar
power plant, seals made of organic materials, in particular made of
polymers such as polytetrafluoroethylene, cannot be used due to the
high temperatures of the liquid accommodated in the container,
specifically the molten salt used as the heat carrier medium. One
possibility is to provide membrane seals which are manufactured
from stainless steel. In this case, the membrane seals have at
least one membrane, which presses in a springy manner against the
inner wall of the container. In the case of large containers, as
are used as heat stores in solar power plants, it is also possible
to embody the membrane seal without contact to the inner wall of
the container. In this case, complete sealing is not achieved, but
the emission of nitrogen oxides from the molten salt, which
contains nitrate salts, used as the heat carrier is sufficiently
reduced in this way so that a sufficiently long service life of the
molten salt is achieved. However, a sliding seal having membranes
which press in a flexible manner against the wall of the container
to obtain a gas-tight seal is preferred.
[0018] To obtain complete sealing against exiting or entering
gases, it is furthermore advantageous if the sliding seal is
thermally insulated against the liquid stored in the container. In
this case, the sliding seal may be arranged in a region of the
container having lower temperature, so that more
temperature-sensitive materials can also be used as the seal
material. A further advantage of the thermal insulation and the
arrangement in a region having lower temperature is that the
sliding seal is subjected to less corrosion, since the corrosivity
increases with rising temperature in particular in the case of
molten salts. Since the sliding seal is to prevent the exit of
gases from the liquid or the entry of contaminants into the liquid,
contact of the sliding seal with the liquid is also not
required.
[0019] Further improved sealing can be achieved in that sealing
chambers are arranged below the sliding seal on the floating roof.
The sealing chambers can comprise multiple membranes, as can the
sliding seal also, for example, these membranes pressing against
the inner wall of the container, wherein there is a sufficiently
large interval in each case between the individual membranes so
that the membranes do not touch even during movement of the
floating roof.
[0020] The thermal insulation of the sliding seal can be
implemented, for example, in that insulation is applied around the
circumference of the floating roof between the liquid and the
sliding seal. Such insulation can be implemented, for example, by
multiple parallel ring-shaped ribs along the circumference of the
floating roof. Gas cushions which have an insulating effect form
between the ring-shaped ribs. Alternatively, it is also possible to
introduce an insulating material, for example, inorganic fibres
having a high proportion of Al.sub.2O.sub.3, i.e., having a
proportion of Al.sub.2O.sub.3 of at least 80%, between the ribs. If
the insulation is embodied by multiple parallel ring-shaped ribs
along the circumference of the floating roof and a gas cushion
between the ribs, the insulation can simultaneously also assume the
function of the sealing chambers. If an insulating material is
used, it is particularly preferably provided with a steel jacket
because of the corrosivity of the molten salt.
[0021] To prevent the sliding seal and possibly the membranes of
the seal chambers or the ribs of the insulation from exerting an
excessively large force on the container wall when the floating
roof is moved, it is preferable if the floating roof is constructed
from at least two segments, wherein the segments are movably
connected to one another. The force action on the inner wall of the
container can result, for example, in that the walls do not extend
ideally with continuous constant spacing, but rather deviate from
the ideal profile due to manufacturing tolerances. By way of the
movable segments, the floating roof can be moved up or down inside
the container in the event of rising or falling liquid level,
respectively, without tilting or jamming.
[0022] To enable interference-free movement of the floating roof
and to hold the floating roof at its position inside the container,
it is preferable if the floating roof is guided on at least one
guide in the container. The guide can be formed, for example, in
the form of a rail on the container inner wall and a groove, which
runs on the rail, on the floating roof. Alternatively, it is also
possible, for example, to provide guide rods in the container
interior and to form openings in the floating roof, through which
the guide rods are guided.
[0023] In one embodiment of the invention, feedthroughs are formed
in the floating roof. Installations can be guided through the
feedthroughs through the floating roof into the liquid. Thus, for
example, a submersible pump can be provided, using which the liquid
can be pumped out of the container. The pump shaft for operating
the submersible pump, which is typically guided in a pump shaft
guide, and a flow pipe for removing the liquid can be guided in an
envelope pipe in this case, for example, wherein the envelope pipe
is guided through the feedthrough in the floating roof. The
envelope pipe is particularly advantageous if the pump shaft, the
pump shaft guide, and the flow pipe are embodied as segmented, as
is typical in particular in the case of long submersible pumps.
This prevents liquid from the container from being able to
penetrate into the pump shaft and damage it in the region of the
connecting points of the individual segments, for example. If the
pump shaft guide and flow pipe are not segmented, the envelope pipe
can also be emitted. In this case, pump shaft guide and flow pipe
are each guided through separate feedthroughs in the floating
roof.
[0024] Furthermore, a dip tube, through which the liquid is
introduced into the container by a bottom-up filling, can also be
guided as an installation through a feedthrough in the floating
roof. To damp oscillations during the introduction of liquids, it
is possible to fix the dip tube on the container floor. For this
purpose, for example, the dip tube can be inserted into a liquid
distributor and clamped therein.
[0025] A further possibility for damping oscillations is to provide
a baffle plate below the mouth of the dip tube in the container.
During the introduction of liquid, it firstly flows against the
baffle plate and is deflected in this case. Influence can be taken
on the flow within the liquid by suitable geometry of the baffle
plate. The baffle plate can be provided with openings or can be
formed as conical, for example.
[0026] To prevent gas from being able to flow out of the gas
compartment above the liquid into the gas compartment above the
floating roof or contaminants or gases from being able to reach the
liquid from the gas compartment above the floating roof at the
feedthroughs in the floating roof, the feedthroughs are preferably
sealed using a suitable seal. For this purpose, it is possible, for
example, to seal the feedthroughs using a movable sealing plate. It
is ensured by the movable sealing plate that the sealing plates do
not exert excessively large forces on the installations when the
floating roof rises or falls. For this purpose, the movable sealing
plates are designed so that they can move horizontally on the
floating roof. At the same time, the sealing plates must be
fastened on the floating roof so that they can move with it during
the rising and falling of the floating roof and do not remain
hanging at one position. The sealing plates preferably lie loosely
on a level surface on the upper side of the floating roof and are
guided by the installations. Therefore, small manufacturing and
mounting deviations of the installations from the ideal
perpendicular profile can be compensated for. Alternatively, it is
also possible to implement the sealing of the feedthroughs using
elastic sliding seals.
[0027] In particular if the liquid in the container is a molten
salt, which tends to creep, it is advantageous if the sliding seal
has protective units against liquid which creeps upward. This
prevents the sliding seal from coming into contact with the liquid
and being damaged by the liquid, for example, by corrosion. A drip
edge can be formed on the floating roof as a protective unit
against liquid creeping upward, for example. In addition, a minimum
spacing between surface of the liquid and sliding seal is to be
maintained. The minimum spacing is preferably at least 50 cm in
this case.
[0028] During usage of the container as a heat store in a solar
power plant, high temperature differences can occur between the
lower side of the floating roof and the upper side of the floating
roof. These result due to the high temperature of the liquid,
generally of 450 to 550.degree. C., and the colder gas in the gas
compartment above the floating roof. This is the case in particular
if the floating roof is embodied as thermally insulating. To
compensate for the differing thermal expansion occurring as a
result of the temperature differences and the stresses linked
thereto, the floating roof preferably has units to compensate for
thermal expansions. Since the temperature differences remain
substantially constant in normal operation, for example,
compensation sections and/or a suitable pre-tension can be provided
as units to compensate for thermal expansions.
[0029] In order that the floating roof floats on the liquid, it is
equipped with floats. In order that the floating roof is not
immersed in the liquid, even over a long operating time, it is
necessary for the floats to maintain their volume and not be
compacted. This could occur, for example, due to high pressure or
pressure variations. For a pressure-resistant embodiment, for
example, it is possible to fill the floats with an insulation
material having low density and high pressure resistance. Suitable
insulation materials of this type are, for example, ceramics having
gas inclusions, for example, ceramic foams.
[0030] The container is particularly preferably used in a solar
power plant as a heat store. However, usage is also conceivable in
any other arbitrary device in which a liquid is used which tends
under storage conditions to decompose while forming gaseous
decomposition products, wherein the liquid and the gaseous
decomposition products are in chemical reaction equilibrium.
[0031] A device for storing heat comprises a first container for
storing a colder liquid and a second container for storing a hotter
liquid, wherein the containers are connected to one another so that
the colder liquid flows out of the first container, after absorbing
heat, into the second container and flows out of the second
container, after emitting heat, into the first container, wherein
at least the second container is a container as described
above.
[0032] Such a device for storing heat is particularly
advantageously used in solar-thermal power plants, solar power
plants in short, for example, parabolic trough, Fresnel or tower
power plants.
[0033] In a particularly preferred invention, a gas compartment is
formed in each case in the first container and in the second
container above the floating roof and the gas compartments of the
first and the second container are connected to one another via a
connecting line. The gas can flow in each case from the container
which is filled into the container which is emptied through the
connecting line. A pressure equalization is implemented in the
respective containers in this way without additional gas
supply.
[0034] Exemplary embodiments of the invention are illustrated in
the figures and will be explained in greater detail in the
following description.
[0035] In the figures:
[0036] FIG. 1 shows a container having a floating roof according to
the invention,
[0037] FIG. 2 shows a detail of the floating roof,
[0038] FIG. 3 shows a schematic illustration of a solar-thermal
power plant in which a container having floating roof is used.
[0039] FIG. 1 shows a container having floating roof designed
according to the invention.
[0040] A container 1, as is used, for example, in a solar-thermal
power plant as a store for hot heat carrier medium, in particular a
molten salt, comprises a container floor 3, a container wall 5, and
a ceiling 7.
[0041] Liquid can be introduced into the container via a dip tube
9. Due to the supply of the liquid through the dip tube 9, an
unacceptably large amount of turbulence can be prevented from
occurring in the liquid during the introduction of the liquid into
the container 1. A further reduction of turbulence during the
decanting of the liquid into the container 1 can be achieved in
that a baffle plate 11 is positioned below the dip tube 9. The
liquid flowing in through the dip tube 9 flows onto the baffle
plate 11, and is thus deflected and distributed, so that in
accordance with the design of the baffle plate 11 or the angle at
which the baffle plate 11 is arranged below the dip tube 9,
targeted flow widening can be set. A further advantage of the
baffle plate 11 is that the inflowing liquid does not strike the
container bottom 3 directly and entrain and swirl up solids
possibly accumulated there in this way, so that they are
distributed in the liquid. The container is designed in the
embodiment shown here in this case so that there is always enough
liquid in the container 1 that the dip tube 9 is still immersed in
the liquid when the container 1 is emptied.
[0042] The removal of the liquid is performed, for example, via a
submersible pump 13. The submersible pump 13 is also submersed in
the liquid in this case. Liquid can be removed from the container
via the submersible pump 13 until the intake connecting piece 15 of
the submersible pump 13 is no longer submersed in the liquid. The
minimal fill level of the liquid in the container 1 thus results
due to the location of the intake connecting piece.
[0043] The liquid sucked in by the submersible pump 13 flows out of
the container 1 through a flow pipe 17. The drive of the
submersible pump 13 is performed using a pump shaft 19, which is
guided through the cover 7 of the container 1. For protection
against entering liquid, the pump shaft 19 is guided in a pipe 21.
Since in particular in the case of long submersible pumps, i.e., in
the case of great height of the container 1 and correspondingly
long flow pipe 17 and pump shaft 19, the flow pipe 17 and the pump
shaft 19 are segmented, flow pipe 17 and pump shaft 19 are
preferably guided in an envelope pipe 21. The envelope pipe 21
prevents uncontrolled gas exchange between the lower side and the
upper side of the floating roof. It is preferable for the envelope
pipe to be sealed against the gas phase above the floating roof,
while it is open at the lower end. This prevents gas loaded with a
high concentration of nitrogen oxides from penetrating into the gas
compartment above the floating roof. The envelope pipe preferably
has a sufficiently large diameter that the dip tube can be pulled
through the envelope pipe, for example, for maintenance
purposes.
[0044] In the embodiment shown here, a distributor 25 is located
below the submersible pump 13. It can be embodied in the form of a
perforated floor, for example. The distributor is located in this
case at the position of the lowest liquid level in the container 1.
The distributor 25 is used to dampen turbulence which can arise due
to the inflow of the liquid, so that the liquid remains calm above
the distributor 25 and no waves arise on the surface, due to which
the floating roof 29 can begin to move. If, as shown here, a
distributor 25 is provided, the possibility exists of, for example,
guiding the dip tube 9 through a feedthrough 27 in the distributor
25 and fixing it on the distributor 25. In addition, the envelope
pipe 21 of the submersible pump 13 can also be fixed on the
distributor 25. The fixing of dip tube 9 and submersible pump 13
prevents them from beginning to oscillate and thus being able to
cause damage to installations or to the container 1.
[0045] According to the invention, a floating roof 29 is
accommodated in the container 1. The floating roof 29 floats in
this case on the surface 31 of the liquid in the container. For
this purpose, floats 33 are formed on the floating roof 29, which
float on the liquid and support the floating roof 29. In the
embodiment shown here, the entire floating roof 29 is not in
contact with the surface 31 of the liquid, but rather only the
floats 33. However, it is alternatively also possible to form the
entire floating roof 29 in the form of floats, so that the entire
floating roof 29 floats on the surface 31 of the liquid. In
particular in the case of use as a hot tank of a solar-thermal
power plant, it is preferable if the floating roof is embodied as
thermally insulating. For this purpose it is possible, for example,
to design the floating roof 29 as a hollow body and to fill it with
an insulation material. Alternatively, the possibility also exists
of manufacturing the floating roof 29 entirely from the insulation'
material. In particular steel-plate-clad ceramics having gas
inclusion, for example, foamed ceramic or foamed glass, which are
temperature-stable and pressure-stable and enable very thin
cladding plates to be used, are suitable as insulation materials.
Alternatively, it is also possible, for example, to use typical
inorganic fibre mats for thermal insulation, but then occurring
external pressures must be absorbed by an envelope which is
embodied as sufficiently stable.
[0046] Feedthroughs for installations are formed in the floating
roof in the embodiment shown here. The dip tube 9 is guided through
a first feedthrough 35 and the submersible pump 13 is guided
through a second feedthrough 37. In this case, the second
feedthrough 37 is made sufficiently large that the pump head of the
submersible pump 13 can be inserted through the feedthrough into
the container.
[0047] In order that no gas can escape from the liquid through the
floating roof 29, the feedthroughs 35, 37 are preferably provided
with a movable sealing plate 39. The movable sealing plate 39 is
designed in this case so that it can both rise and fall vertically
with the floating roof 29 and a horizontal movement is additionally
possible, to prevent excessively large force action on the
installations, by which damage can be induced, in the event of
pipes of the installations which do not extend completely
vertically, for example, dip tube 9 and envelope pipe 23.
[0048] To prevent tilting of the floating roof 29 when the floating
roof 29 rises and falls, a guide 40 is preferably provided, along
which the floating roof 29 is guided. For example, a guide rod can
be attached on the container wall 5 as the guide 40 and the
floating roof 29 encloses the guide rod so that the floating roof
29 is moved along the guide rod. Alternatively, it is also possible
to provide guide rods in the container interior, which are guided
through corresponding feedthroughs in the floating roof 29. In
addition, the installations, for example, the dip tube 9 or the
envelope pipe 23 of the submersible pump 13, can also be used as
the guide.
[0049] A gas compartment 41 is above the floating roof 29, between
floating roof 29 and cover 7 of the container. To prevent the gas
in the gas compartment from being compressed when the floating roof
29 rises, a gas outlet 43 is provided in the cover.
[0050] If the container 1 is part of a two-tank system, for
example, as is used in solar-thermal power plants, in which the
colder liquid is stored in a first container and the warmer liquid
is stored in a second container, so that in each case one container
is emptied and the other is filled accordingly, it is preferable if
the containers are connected to one another via the gas outlet 43
in the cover, so that in each case the gas can flow out of the
container which is emptied into the container which is filled. In
the case of thermal insulation of the floating roof 29, it is
possible in this case that the gas phases in the first container
and in the second container have essentially equal temperature and
therefore, at equal pressure, also equal specific volume.
[0051] FIG. 2 shows a detail of the floating roof 29.
[0052] The floating roof 29 is guided using a sliding seal 45 on
the container wall. The compartment below the floating roof 29 is
sealed off in relation to the gas compartment 41 using the sliding
seal 45, so that no decomposition gas arising from the liquid can
escape into the gas compartment 41. Furthermore, this also prevents
gaseous and liquid contaminants in particular from being able to
reach the liquid from the gas compartment 41.
[0053] To improve the leak-tightness, it is advantageous if a
sealing lip 47 is additionally located above the sliding seal. The
sealing lip 47 is guided in this case along the container wall 5
and has an additional sealing action.
[0054] Below the sliding seal 45, ribs 49 are formed on the floats
33. The ribs 49 are spaced apart from one another, so that a gas
compartment 51 is formed in each case between the ribs 49. The ribs
49 can be used as an additional seal. Furthermore, in particular
the gas compartment 51 acts as additional insulation, so that the
temperature in the region of the sliding seal 45 is lower than
directly above the liquid. In this way, the sliding seal 45 is
protected from excessively high temperatures and possible damage as
a result of the high temperatures. In particular, it is also
possible in this way to use sealing materials which would be
damaged at the high temperatures of the liquid.
[0055] To furthermore prevent liquid creeping upward from the
container from coming into contact with the sliding seal 45, it is
advantageous to attach a drip edge 53 above the sliding seal 45.
Liquid creeping upward drips off on the drip edge 53 and falls back
downward into the liquid.
[0056] In contrast to the embodiment shown in FIG. 1 having
unfilled floats 33, the floats are filled with a thermally
insulating material 55 in the embodiment shown in FIG. 2. This
prevents the floats from acting as thermal bridges and dissipating
heat from the liquid to the gas compartment 41 above the floating
roof 29.
[0057] FIG. 3 shows a solar-thermal power plant in which at least
one container 1 having floating roof 29 is used.
[0058] In a solar-thermal power plant having a first container 57
for storing a colder liquid and a second container 59 for storing a
hotter liquid, at least the second container 59 is equipped with a
floating roof 29. In the embodiment shown here, the floating roof
29 is constructed from multiple segments 61, which are connected to
one another so they are movable. The segments 61 are each equipped
with floats in this case, so that each segment floats per se on the
surface of the liquid. The liquid which is stored in the first
container 57 and in the second container 59 is used as a heat
carrier medium and is typically a molten salt. Salts which are used
for the molten salt are in particular nitrates and nitrites of the
alkali metals and alkaline earth metals and also arbitrary mixtures
thereof. A typically used salt is a mixture of sodium nitrate and
sodium nitrite in the weight ratio of 60:40.
[0059] In operation of the solar-thermal power plant, at times
having incident solar radiation, the liquid is removed from the
first container 57 and conducted through a solar field 63. The
solar field 63 has receivers 65, in which the liquid is heated by
incident solar energy. The liquid thus heated is introduced into
the second container 59. In this case, the liquid volume decreases
in the first container 57, whereby the gas compartment enlarges. At
the same time, the liquid volume increases in the second container
59, so that the gas compartment 41 in the second container 59
shrinks. In this case, the gas from the gas compartment of the
second container 59 is introduced via a gas pendulum line 67 into
the first container 57. Excess gas, which can arise, for example,
due to outgassing of gases dissolved in the liquid, which can enter
the gas phase, for example, if the first container 57 is not
equipped with a floating roof, can be removed via a gas outlet
69.
[0060] To generate power, the hot liquid from the second container
59 is supplied to a first heat exchanger 71 of a steam cycle 73. In
the first heat exchanger 71, the water is vaporized and superheated
by a heat transfer from the hot liquid to the water cycle. The
superheated steam thus generated drives a steam turbine 75, which
in turn drives a generator 77 to generate power. The superheated
steam is relaxed in this case in the steam turbine 75.
[0061] The steam flowing out of the steam turbine 75 is condensed
in a second heat exchanger 79, wherein the heat from the water of
the steam cycle 73 is transferred to a cooling cycle 81. The cycle
81 is typically also operated using water, wherein the water of the
cooling cycle 81 is cooled down in a cooling tower 83.
[0062] After the condensation, the water of the steam cycle 73 is
compressed using a pump back to the pressure which is required to
drive the steam turbine 75, before the water again flows into the
first heat exchanger 71 for vaporization and super heating.
[0063] For example, parabolic troughs or Fresnel receivers can be
used as the receivers 65 in the solar field 63. Alternatively, it
is also possible to use a central receiver of a tower power plant
instead of the solar field 63, wherein the liquid is then heated in
the tower.
TABLE-US-00001 List of reference numerals 1 container 3 container
bottom 5 container wall 7 cover 9 dip tube 11 baffle plate 13
submersible pump 15 intake connecting piece 17 flow pipe 19 pump
shaft 21 pipe 23 envelope pipe 25 distributor 27 feedthrough 29
floating roof 31 surface of the liquid 33 float 35 first
feedthrough 37 second feedthrough 39 movable sealing plate 40 guide
41 gas compartment 43 gas outlet 45 sliding seal 47 sealing lip 49
rib 51 gas compartment 53 drip edge 55 thermally insulating
material 57 first container 59 second container 61 segment 63 solar
field 65 receiver 67 gas pendulum line 69 gas outlet 71 first heat
exchanger 73 steam cycle 75 steam turbine 77 generator 79 second
heat exchanger 81 cooling cycle 83 cooling tower
* * * * *