U.S. patent application number 13/118573 was filed with the patent office on 2011-12-01 for heat conveyance and storage system.
Invention is credited to Shmuel Erez, Ben Shelef.
Application Number | 20110290445 13/118573 |
Document ID | / |
Family ID | 45021107 |
Filed Date | 2011-12-01 |
United States Patent
Application |
20110290445 |
Kind Code |
A1 |
Shelef; Ben ; et
al. |
December 1, 2011 |
Heat Conveyance and Storage System
Abstract
A heat conveyance system particularly suitable for solar
applications is described, based on the mechanical conveyance of
heat-storage solid bodies containing a bulk that is capable of
undergoing phase change. The invention covers the conveyance system
itself, and means of inserting and extracting heat into and out of
it.
Inventors: |
Shelef; Ben; (Mountain View,
CA) ; Erez; Shmuel; (San Jose, CA) |
Family ID: |
45021107 |
Appl. No.: |
13/118573 |
Filed: |
May 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61349859 |
May 30, 2010 |
|
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|
61351941 |
Jun 7, 2010 |
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Current U.S.
Class: |
165/6 |
Current CPC
Class: |
F28D 20/026 20130101;
Y02E 70/30 20130101; F24S 60/10 20180501; Y02E 10/40 20130101; Y02E
60/14 20130101 |
Class at
Publication: |
165/6 |
International
Class: |
F28D 19/04 20060101
F28D019/04 |
Claims
1. A heat conveyance system having a hot end at a hot temperature
and a cold end at a cold temperature comprising multiple heat
storage bodies and a conveyance means to move them between said hot
end and cold end.
2. The system of claim 1, where said heat storage bodies comprise
an inner bulk that changes phase between the cold and the hot
temperatures, and an external shell that remains solid at the hot
temperature.
3. The system of claim 1, where said conveyance means comprises an
enclosed conduit that fits around said bodies.
4. The system of claim 3, where said bodies are further configured
to roll inside said conduit.
5. The system of claim 3, where said conduit further comprises a
locomotion system.
6. The system of claim 2, where said phase transition occurs
between 500 C and 1500 C.
7. The system of claim 2, where said inner bulk is made out of an
ionic salt containing the chemical element Na.
8. The system of claim 2, where said inner bulk is made out of an
ionic salt containing the chemical element K.
9. The system of claim 2, where said inner bulk is made out of an
ionic salt containing the chemical element Li.
10. The system of claim 2, where said inner bulk is made out of a
material belong to the group consisting of NaCl, KCl, LiCl, NaF,
KF, LiF, NaBr, KBr, LiBr, NaI, KI, LiF, Ionic Salt, Aluminum,
Copper, Bronze, Steel, Lead, Zinc, Tin, Nickel, Chromium, Bismuth,
Cadmium, Metal alloy, Calcium Nitrate, Potassium Nitrate, Tempering
salt.
11. The system of claim 2, where said outer shell is made out of
material belonging to the group consisting of SiC, Carbides,
Alumina, Quartz, Beryllia, Ceramics, Steel, Tungsten, Cobalt,
Metallic alloy.
12. The system of claim 1, where said heat storage bodies consist
of an inner bulk that is solid at the cold temperature and liquid
at the hot temperature and an external shell that remains solid at
the hot temperature.
13. The system of claim 1, where said heat storage bodies consist
of an inner bulk that is solid at the cold temperature and gaseous
at the hot temperature and an external shell that remains solid at
the hot temperature.
14. The system of claim 1, where said heat storage bodies consist
of an inner bulk that is liquid at the cold temperature and gaseous
at the hot temperature and an external shell that remains solid at
the hot temperature.
15. The system of claim 1, additionally containing an absorbing
layer capable of converting sunlight into heat.
16. The system of claim 15, where said absorbing layer contains
graphite.
17. A system for extracting heat from multiple hot bodies into a
fluid, said system having a cold end at a cold temperature and a
hot end at a hot temperature, said bodies having an inner volume
that freezes as they move from said hot end to said cold end,
consisting of a conveyance means for moving said bodies from the
hot end to the cold end, a conduit enclosing said conveyance means,
a cold fluid port at the cold end of said conduit, a hot fluid port
at the hot end of said conduit, and a means for flowing said fluid
from the cold fluid port to the hot fluid port.
18. The system of claim 17, where said conduit is pressurized and
further contains two sealing means at the hot end and cold end
allowing said bodies to enter and exit the conduit while preventing
free flow of the fluid across the sealing means.
19. The system of claim 17, where said fluid belongs to the group
consisting of water, steam, air, gas, Helium, Hydrogen.
20. A system for extracting heat from multiple hot bodies into a
working fluid, said system having a cold end at a cold temperature
and a hot end at a hot temperature, said bodies having an inner
volume that freezes as they move from said hot end to said cold
end, consisting of a conveyance means for moving said bodies from
the hot end to the cold end, a volume enclosing said conveyance
means and filled with a heat transfer liquid, a conduit for working
fluid that passes through said volume and having a cold fluid port
at the cold end of said conduit, a hot fluid port at the hot end of
said conduit, and a means for flowing said fluid from the cold
fluid port to the hot fluid port such that heat is transferred from
the bodies to the heat transfer liquid and from the heat transfer
liquid to the working fluid.
21. The system of claim 20, where said working fluid belongs to the
group consisting of water, steam, air, gas, Helium, Hydrogen.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
patent applications 61/349,859 filed on May 30, 2010, and
61/351,941 filed on Jun. 7, 2010, the entirety of which is
incorporated herein by reference.
FIELD
[0002] The present application is of the field of thermal power
transfer and storage systems.
BACKGROUND
[0003] Transferring heat from a heat producer to a heat consumer
(e.g. heater and boiler, respectively) is a common task in many
industrial applications, especially in the field of solar thermal
power generation. For example, in solar power generation (e.g.
heliostat fields or dish receivers) heat collection is optimal
typically at scales smaller than the optimal scale of the turbines
it drives. There is also the need to store heat for use when the
sun is not shining--either night use or during times of cloud
coverage. Heat conveyance is also required in other energy fields,
such as metal production, cement production, and nuclear power
plants.
[0004] Heat conveyance and storage is typically done using a
variety of thermal transfer fluids, including steam, oil, and
molten nitrate salts.
[0005] Turbines become more efficient at higher working
temperatures. Steam turbines with steel blades typically work at
560-580 C, using superheated steam (this is the creep limit for
steel). Ceramic bladed gas turbines can work at much higher
temperatures and achieve higher efficiencies. When only low
temperature heat is available, less efficient condensing steam
turbines are used.
[0006] Every heat conveyance system has a hot end (where it
consumes the heat) and a cold end (where it relinquishes it). Since
heat exchangers require a temperature difference to operate, and
become large and expensive when the temperature difference is
small, the heat conveyance system has to have its cold end
significantly hotter than the steam it is generating, and its hot
end colder than the heat generation temperature. Every additional
medium transfer that requires additional heat exchanger (e.g.
steam-to-salt) adds to these temperature differences, and thus
increases cost and reduces the efficiency of the turbine.
[0007] The most common method of heat conveyance in solar fields
today is by piping oil in tubes, which has a temperature limit
lower than 400 C. A substitute for oil is molten salt (commonly a
mixture of Sodium nitrate and Potassium nitrate) which melts at 220
C and allows for working temperatures of up to about 500 C. More
advanced fluoride-based heat conveyance fluids promise higher
working temperatures. When pumping molten salt through pipes, care
must be taken that the temperature never drops below the melting
temperature of the salt, or it will freeze in the pipes, and the
system is not able to take advantage of the latent heat of the
phase change.
[0008] As the working temperature increases, however, fluid
handling (pumping, valving, sealing) becomes progressively more
difficult. Additionally, with all molten fluid systems, the risk of
fluid freeze-out in case of a malfunction and drop in temperature
is an ever-present problem.
[0009] When superheated steam is used as the working fluid, there
is no freeze-out problem, but the combination of high temperature
and high pressure also makes the pumping and sealing difficult and
expensive. Additionally, the heat capacity of steam is low relative
to the salts.
[0010] With a fluid phase-change system, the system cannot take
advantage of the solid-liquid phase transition, since the solid
medium cannot flow. Instead (as in the case of steam) the system
takes advantage of the liquid-gas phase change, which typically
carries less latent heat.
SUMMARY
[0011] The following summary of the invention is included in order
to provide a basic understanding of some aspects and features of
the invention. This summary is not an extensive overview of the
invention and as such it is not intended to particularly identify
key or critical elements of the invention or to delineate the scope
of the invention. Its sole purpose is to present some concepts of
the invention in a simplified form as a prelude to the more
detailed description that is presented below.
[0012] The invention described herein is a heat conveyance and
storage system based on discrete spherical pods filled with a
phase-change medium, each capable of transitioning between the
solid and liquid phases, and thus storing large amounts of latent
heat, but being transported as individual solid objects.
[0013] In various embodiments of this invention, the pods are
placed inside tubular conduits. Once inside the conduits, the pods
act as their own heat exchangers into fluids (gas or liquid) that
flows in the conduit, since they present a large surface area and
induce turbulent flow in flowing medium. The tube itself only has
to sustain the temperature of the flowing medium, not of the molten
salt.
[0014] In various embodiments of this invention, The pods are
transported either by rolling them on rails inside the tubular
conduits, or by moving entire sections of tubular conduits with
pods in them. The system allows transfer of heat at high
temperatures (exceeding 1000 C in some configurations) and over
large distances, and so works well, for example, for collecting
heat from solar dishes and into a central steam generator.
[0015] In various embodiments of this invention, Each pod is
comprised of an inner heat-storing medium which undergoes a
solid-to-liquid phase change somewhat below the temperature at the
hot end of the system, and an outer structural shell which is
capable of containing the heat storage medium and supporting the
rolling of the pod at the high operating temperature. By wholly
encapsulating the phase-change medium by a solid shell, the
heat-storage medium is equally transportable in both its liquid and
solid states, and so the system is able to take advantage of latent
heat storage from the solid-liquid phase transition. Additionally,
the hot fluid is not at risk of being contaminated by exposure to a
long conduit system.
[0016] In addition to describing the pods and conduits, this
application also describes a steam or gas heat-exchangers for
turbines and Stirling engines that operate with the pods.
DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings, which are incorporated in and
constitute a part of this specification, exemplify the embodiments
of the present invention and, together with the description, serve
to explain and illustrate principles of the invention. The drawings
are intended to illustrate major features of the exemplary
embodiments in a diagrammatic manner. The drawings are not intended
to depict every feature of actual embodiments nor relative
dimensions of the depicted elements, and are not drawn to
scale.
[0018] FIG. 1: Power transfer pod according to an embodiment of the
invention
[0019] FIG. 2: Transfer conduit according to an embodiment of the
invention
[0020] FIG. 3: Heat Exchanger according to an embodiment of the
invention
[0021] FIG. 4: Conduit with stationary pods according to an
embodiment of the invention
[0022] FIG. 5: Liquid-based heat exchanger according to an
embodiment of the invention
[0023] FIG. 6: None-spherical pods according to an embodiment of
the invention
DETAILED DESCRIPTION OF THE INVENTION
[0024] The invention described herein is heat conveyance and
storage system based on the enclosure of a liquid-solid
phase-change medium inside a solid heat-resistance shell, and
handling the conveying the entire structure, labeled a "pod", so
that the phase change medium never comes in contact with anything
but the shell. In this manner, the conveyance of the heat is
decoupled from the heat-storing medium.
[0025] Each pod is thus comprised of an inner heat-storing medium
which undergoes a solid-to-liquid phase change between the
temperatures of the cold and the hot ends of the conveyance system,
and an outer structural shell which is capable of containing the
heat storage medium and supporting it structurally at the high
operating temperature.
[0026] By wholly encapsulating the phase-change medium by a solid
shell, the heat-storage medium is equally transportable in both its
liquid and solid states, and so the system is able to take
advantage of latent heat storage from the solid-liquid phase
transition. Additionally, the hot fluid is not at risk of being
contaminated by exposure to a long conduit system.
[0027] The conveyance system, meanwhile, has only to handle solid
objects and can do so by contacting them only along small areas,
thus being able to keep the contact points cold, and minimizing
heat loss. The conveyance system is not required to seal, valve, or
pump hot liquid. This allows the system to transport heat at very
high temperatures.
[0028] In one embodiment described here, the phase change medium is
simple ionic salts such as NaCl (sea salt) which are formed by one
element from the first column of the period table (Alkali metals
such as Na, K, Li) and one element from the second-to-last column
(Halogens such as F, Cl, Br, I). The melting temperature of these
materials is in the 700-800 C range, the latent heat is high, and
they are generally abundant, inexpensive, and non-toxic. In other
embodiments, the heat-transfer medium can be a metal such as
Copper, with a melting point of 1000 C.
[0029] In an embodiment of this invention, the outer shell is made
out of SiC (Silicon Carbide), which has good thermal conductivity
and can operate at temperatures in excess of 1500 C. Other
materials can be used for the shell including other carbides,
ceramics such as Alumina, or high temperature metals ranging from
Steel to Tungsten. The outer surface of the shell is optionally
pitted, to improve heat transfer to and from it.
[0030] In an embodiment of this invention, to improve thermal
conductivity of the heat storage medium, especially when it is in
solid form, a heat conductive structure is embedded inside of it.
This structure is made out of copper, or other high-temperature
conductive materials.
[0031] In an embodiment of this invention, if necessary, a thin
inert isolation layer is added around the heat-storage bulk to
prevent any chemical interaction between it and any residual
components of the shell. Such a layer can be made from a material
such as Quartz.
[0032] In an embodiment of this invention, the pod is heated
directly by radiation, and so an absorbent layer is added around
the structural shell, made from a material such as graphite, and a
thin transparent protection layer placed around it.
[0033] FIG. 1 shows the structure of the pod in cross section. The
inner heat storage bulk [10] is enclosed within the outer shell
[11], and a conductivity aid [13] is embedded in the heat storage
bulk. A void [12] is left in the solid heat-storage bulk to
accommodate thermal expansion and phase-change expansion. The inert
isolation layer is shown as [16].
[0034] In solar applications, if the shell material is reflective
(e.g. Alumina) it is coated with a thin absorption layer [14] made
out of graphite, and finally a thin and transparent outer
roll-bearing layer [15] is added, made out of Alumina, Quartz, or
from high purity SiC. If the shell material is absorbent enough
(e.g. black SiC) then no such layer is necessary.
[0035] FIG. 2 shows a cross section of an embodiment of the
invention comprising a transfer conduit for spherical pods that
allows the pods [25] to roll inside of it. The tubular conduit [20]
provides isolation from the environment and is purged with Nitrogen
to suppress oxidation at high temperatures. Reduced pressure can
also be employed to reduce heat transfer to the walls of the
conduit, but it is more cost effective to insulate the conduit
using an external layer [21]. The conduit has two creases in it
[22] with Alumina or Carbide lining to resist the temperature of
the pod. The creases are supported by external rails [23] which
also serve as heat sinks to prevent the conduit wall from reaching
high temperatures at the point of contact. A gap [24] at the bottom
of the conduit prevents any particulate contamination from
hindering the rolling motion of the pods. Motion of the pods [25]
in the conduit is induced either by gravity, or by pneumatic
pressure.
[0036] FIG. 3 shows the cross section of the steam heat exchanger
that uses rolling pods. A long conduit [30] holds the pods [31]
while steam [32] is counter-flowed [33] over them, so that the cold
steam meets the cold pods [34], and the hot steam meets the hot
pods [35]. Two load-locks [36][37] manage inserting and extracting
the pods from the conduit, which operates under high pressure. The
conduit is slanted so the pods move against the flow of the steam
by gravity. The conduit is constructed from a thin metallic wall,
fiber-reinforced along its circumference to resist the
pressure.
[0037] In other embodiments, the conduit itself is filled with
stationary pods that are not able to move inside of it, but the
conduit itself can be carried from the location of the heat
producer (such as the bottom of a central heliostat tower) to the
location of the heat consumer (such as the boiler that powered a
turbine). The purpose of the conduit in this case is simply to
contain the pods and allow fluid to flow across them. In these
embodiments, the pods are much smaller than the diameter of the
conduit.
[0038] FIG. 4 shows such an embodiment that uses stationary pods
[41], and a movable section of conduit [40]. Instead of load-locks
there are simple gate valves [42] that allow the conduit to be
coupled to either a heat producer or a heat consumer, and the
entire section of conduit containing the hot pods is moved on
wheels [43] from one to the other. Once connected, steam or another
transfer fluid is then flowed through the gate valves [42] and into
the conduit section to either heat the pods or be heated by them.
On the consumer side of the system, once the pods cool down to
below the phase-change temperature, the entire section of conduit
is taken back to the heat producer, and vice versa. Since the pods
do not move within the conduit they can be of any shape, such as
for example elongated tubes parallel the axis of the conduit.
[0039] FIG. 5 shows a different embodiment, the pods traverse a
trench filled with heat-transfer fluid [50] with a lower melting
temperature than the cold side of the steam generator (possibly a
Nitrate salt) so it remains liquid throughout the process. When the
pods exit [51] the trench (aided by a mechanical lift, not shown),
an air-blade cleans off the exceed fluid that might be present on
their outer surface. Steam pipes [52] are immersed in the same
trench, parallel and in proximity to the path of the pods, with
steam flowing in the opposite direction [53] to the thermal
gradient in the trench. In this embodiment, the pods do not have to
enter the high-pressure conduit, and so the need for load-locks is
eliminated and the steam system remains isolated from the pods. The
heat-transfer medium, being liquid, can transfer heat from the pods
faster than direct steam, and then distribute it efficiently to the
steam tubes which can be made small and numerous to increase the
heat transfer area. The steam tubes can also be made to coil around
the path of the pods to increase the dwell time of the steam.
[0040] Finally, since the pods can operate at very high
temperatures, the turbine can operate using a working gas other
than steam, such as ambient air or a gas such as Helium. In these
case, the steam generator will become a gas heater, and the turbine
will be a Brayton cycle gas turbine rather than a Rankine cycle
steam turbine.
[0041] It is also possible to store hot pods inside an insulated
holding chamber or conduit for later (overnight) use. The walls of
a holding chamber will rise in temperature close to the temperature
of the pods, and so are made out of a ceramic or other
high-temperature material.
[0042] In other embodiments, pods can be of shapes shown in FIG. 6,
including cylindrical, barrel shaped, or even non-round.
[0043] In these embodiments, the dimension of the pod is between
0.1 and 0.5 m. However, the system can be used at much different
scales, both smaller and larger.
[0044] Other embodiments of the system can be used with other power
sources such as nuclear reactors where the bulk of the pod can be
heated up by absorbing energetic particles, or using a heat
exchanger similar to the one used on the electricity-generation
side of the system.
* * * * *