U.S. patent application number 15/777080 was filed with the patent office on 2018-12-27 for energy storage/withdrawal system for a facility.
The applicant listed for this patent is INSTITUT NATIONAL DES SCIENCES APPLIQUEES DE TOULOUSE, UNIVERSITE TOULOUSE III - Paul Sabatier. Invention is credited to Martin CYR, Stephane GINESTET, Khadim NDIAYE.
Application Number | 20180372421 15/777080 |
Document ID | / |
Family ID | 55542801 |
Filed Date | 2018-12-27 |
United States Patent
Application |
20180372421 |
Kind Code |
A1 |
CYR; Martin ; et
al. |
December 27, 2018 |
ENERGY STORAGE/WITHDRAWAL SYSTEM FOR A FACILITY
Abstract
The invention relates to a system (100) for storing/withdrawing
thermal energy. The main characteristic of a system according to
the invention is that it comprises: a monolithic cementitious
material (1) comprising a mass fraction of ettringite of greater
than 20%, said material being surrounded by a thermal insulation
material (12) and a water insulation material (11), a source (2) of
a heat transfer fluid, a device (3) for wetting said fluid in order
to carry out a withdrawal phase of the system (100), a device (4)
for heating said fluid in order to carry out a storage phase of
said system (100), an outlet (6) of the heat transfer fluid from
said material (1).
Inventors: |
CYR; Martin; (EAUNES,
FR) ; GINESTET; Stephane; (RAMONVILLE SAINT AGNE,
FR) ; NDIAYE; Khadim; (TOULOUSE, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INSTITUT NATIONAL DES SCIENCES APPLIQUEES DE TOULOUSE
UNIVERSITE TOULOUSE III - Paul Sabatier |
TOULOUSE
Toulouse |
|
FR
FR |
|
|
Family ID: |
55542801 |
Appl. No.: |
15/777080 |
Filed: |
November 22, 2016 |
PCT Filed: |
November 22, 2016 |
PCT NO: |
PCT/FR2016/053050 |
371 Date: |
May 17, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28D 20/003 20130101;
Y02E 60/14 20130101; F28D 2020/0086 20130101; F28D 2020/0078
20130101; F28D 20/0056 20130101 |
International
Class: |
F28D 20/00 20060101
F28D020/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2015 |
FR |
1561339 |
Claims
1. System for storing/withdrawing thermal energy, comprising a
monolithic cementitious material comprising a mass fraction of
ettringite of greater than 20%, said material being surrounded by a
thermal insulation material and a water insulation material, a
source of a heat transfer fluid, a device for wetting said fluid in
order to carry out a withdrawal phase of the system, a device for
heating said fluid in order to carry out a storage phase of said
system, an outlet of the heat transfer fluid from said material,
wherein said system comprises at least one heat transfer fluid
circulation circuit that passes through the heating device and
through the wetting device, said circuit being supplied by the
source of said fluid and leading to the cementitious material.
2. System according to claim 1, wherein the heat transfer fluid is
formed by an inert gas.
3. System according to claim 1, wherein the source of the heat
transfer fluid is placed upstream of the wetting device, which is
itself placed upstream of the heating device, and in that said
heating device is placed upstream of the cementitious material.
4. System according to claim 1, wherein the wetting device and the
heating device each operate to order, and can be activated
independently of one another depending on the use of said system,
either in storage phase, or in withdrawal phase.
5. System according to claim 1, wherein the mass fraction of
ettringite in the cementitious material is between 20% and 90%.
6. System according to claim 1, wherein the cementitious material
has a porosity of between 10% and 90%.
7. System according to claim 1, wherein the cementitious material
(1) has a permeability of between 10.sup.-17 m.sup.2 and 10.sup.-11
m.sup.2.
8. System according to claim 1, wherein the cementitious material
(1) has a compressive mechanical strength of between 0.1 MPa and 70
MPa.
9. System according to claim 1, wherein the water insulation
material is formed by an impermeable wall intended to prevent water
vapour from coming into contact with the cementitious material.
10. System according to claim 1, wherein the thermal insulation
material is formed by at least one material to be chosen from glass
wool and polystyrene and in that said at least one impermeable
material is placed around the water insulation material.
11. System according to claim 1, wherein the wetting device
comprises at least one humidifier suitable for charging said fluid
with water.
12. Process for storing/withdrawing thermal energy using a
storage/withdrawal system in accordance with claim 1, wherein, in
the heat storage phase, it comprises the following steps: a step of
heating the heat transfer fluid by means of the heating device in
order to obtain a hot gas, the temperature of which is above
30.degree. C., a step of directly passing said hot gas through the
cementitious material comprising ettringite, giving rise to an
endothermic dehydration of said material and constituting a heat
storage phase.
13. Process according to claim 12, wherein the heat storage phase
extends over a period of several days, said period being dictated
by the amount of cementitious material and the flow rate of fluid
used in said process.
14. Process according to claim 12, wherein, in the heat withdrawal
phase, it comprises the following steps: a step of wetting the heat
transfer fluid by means of the wetting device in order to obtain a
wetted gas, a step of directly passing said wetted gas through the
cementitious material comprising ettringite and which adsorbs water
vapour then is hydrated, a step of exothermic reaction which
generates heat transported by the heat transfer fluid, converting
the initially cold and wet gas into a hot and dry gas.
15. Process according to claim 12, wherein said process comprises a
step of removing the carbon dioxide in the heat transfer fluid
before it passes through the cementitious material comprising
ettringite in order to prevent a carbonation reaction of said
material.
16. Material comprising ettringite for creating a system in
accordance with claim 1.
17. Material according to claim 16, wherein said material comprises
an ettringitic binder, the porosity and the permeability of which
are increased by chemical foaming and/or by mechanical foaming.
Description
[0001] The invention relates to an energy storage/withdrawal system
for a facility.
[0002] The global overconsumption of energy has significant
consequences at the environmental and socio-economic level. The
gradual depletion of nonrenewable energies and the hike in energy
prices have led to the emergence of directives that aim to increase
the energy efficiency by 20% from now until 2020 in the European
Union. The building sector is the most energy-consuming sector,
ahead of industry and transport, the major part of this energy
being consumed in calorific form in order to maintain a certain
thermal comfort.
[0003] In Europe, the building sector is the highest consumer of
primary energy, representing 40% of the total energy consumed, and
is responsible for 36% of the CO.sub.2 emissions, more than half of
this energy being consumed in the form of heat. This sector
therefore has the highest energy-saving potential.
[0004] The use of solar energy is essential nowadays to improve the
energy performance of buildings and to limit their impact on the
environment. However, one major drawback of solar energy is its
intermittence. Specifically, in summer the solar energy exceeds the
energy requirements, unlike in winter where there is a shortage of
thermal energy. Seasonal thermal energy storage can prevent this
phase difference and increase the use of solar energy in the
building sector. Materials with a high heat capacity (sensible heat
storage) and phase-change materials (latent storage) are widely
used in the building sector for short-term solar energy
storage.
[0005] Patent application WO2009144233 describes a system for
storing sensible heat in a monolithic concrete block. One drawback
of this system is that it has a low storage density. Furthermore,
this system requires permanent heating and perfect insulation to
prevent the heat losses that get bigger with the duration of heat
storage, these two actions constituting significant
constraints.
[0006] Therefore, the drawbacks linked to the systems for storing
sensible heat are a low storage density at low temperature, heat
loss during this storage, the bulkiness thereof and a limited
storage time.
[0007] Storage systems that involve phase change materials (latent
heat storage), even though they have an energy storage density
greater than that of the storage systems involving materials with a
high heat capacity (sensible heat storage), also have, for some of
them, a certain number of drawbacks: [0008] a low phase-change
enthalpy, [0009] an inflammability, [0010] a fast phase change,
[0011] a limited storage time, [0012] a volume instability
[0013] Another solution consists in using sorption heat storage
systems. Sorption storage materials are highly porous materials,
often in the form of minuscule porous beads (powder bed). Heating
the adsorbent material leads to an endothermic desorption (rupture
of the bonds between the solid and the gaseous molecules). This is
the charging phase. The desorption enthalpy stored in the material
is returned during the adsorption (exothermic reaction) of the
desorbed molecules. This is the discharging phase. Depending on the
material used, these storage process may be due to a physical
and/or chemical adsorption. These storage systems have the drawback
of possessing a low storage density and a short withdrawal
time.
[0014] Another solution consists in using chemical heat storage
systems involving the thermal energy derived from a chemical
reaction in the storage material. In the charging phase, the
material is heated, for example with solar energy, to the chemical
decomposition thereof into two stable separate elements. The
thermal energy stored, corresponding to the decomposition enthalpy,
is returned during an exothermic chemical reaction of the two
stable elements. Despite their high heat storage density, the main
drawbacks of most of the chemical storage materials are the
following: [0015] a high storage temperature, [0016] the
irreversibility of the reaction, [0017] a certain complexity of the
storage process, [0018] a significant toxicity, [0019] a high
cost.
[0020] Another solution consists in storing heat using ettringite,
which is a mineral composed of calcium sulfate, calcium aluminate
and water. This material has both the behaviour of the sorption
storage materials (short-term performance) and that of the chemical
reaction storage materials (long-term performance). Indeed,
ettringite has the advantage of having a high thermochemical
storage density at low temperature (below 70.degree. C.) owing to
the physicochemical process implemented. Heat is stored therein by
endothermic heating (desorption+dehydration) of the material, which
is dehydrated then becomes metaettringite. The heat can then be
withdrawn by exothermic adsorption (adsorption+hydration). The use
of this cementitious material as thermochemical storage material in
the building sector is limited by durability, carbonation and
reversibility problems.
[0021] An energy storage/withdrawal system according to the
invention overcomes all the drawbacks found in the prior art.
[0022] In order to facilitate the understanding of the description,
an energy storage phase comprises an active phase of charging said
energy into the material and a passive phase of conserving said
energy in said material. During this passive phase, the
storage/withdrawal system is not the site of any thermochemical
reaction and the heat transfer fluid does not circulate in said
system.
[0023] One subject of the invention is a system for
storing/withdrawing thermal energy.
[0024] The main characteristic of an energy storage/withdrawal
system according to the invention is that it comprises: [0025] a
monolithic cementitious material comprising a mass fraction of
ettringite of greater than 20%, said material being surrounded by a
thermal insulation material and a water insulation material, [0026]
a source of a heat transfer fluid, [0027] a device for wetting said
fluid in order to carry out an energy withdrawal phase, [0028] a
device for heating said fluid in order to carry out an energy
storage phase, [0029] an outlet of the heat transfer fluid from
said material.
[0030] Such a system can be used, either to store heat, or to
return this heat once it has been stored. Thus, in the heat storage
phase, the heating device is activated to heat the heat transfer
fluid in order to obtain a hot (temperature above 30.degree. C.)
and dry gas. This hot gas then passes through the monolithic
cementitious material comprising ettringite, which is gradually
dehydrated, giving rise to the heat storage phase. For this
configuration, the hot gas interacts directly with the cementitious
material by being diffused homogeneously through the whole of its
volume. This narrow interaction is made possible owing to the good
porosity of the cementitious material comprising ettringite.
Indeed, owing to this marked porosity, it is not necessary to use a
device for distributing hot gas within the cementitious material
comprising ettringite, such as for example a network of pipes for
circulating hot gas. During this heat charging phase, the wetting
device is not needed, and the heat stored by the cementitious
material is not returned while said material is not in contact with
water, in liquid or vapour form. In the heat discharging phase, the
wetting device is needed in order to charge the heat transfer fluid
with water vapour. The resulting wetted gas passes through the
cementitious material which adsorbs the water vapour, then is
hydrated, generating an exothermic reaction, which then produces
heat. For this configuration, the wetted gas interacts directly
with the cementitious material by being diffused homogeneously
through the whole of its volume. This narrow interaction is made
possible owing to the good porosity of the cementitious material
comprising ettringite. Indeed, owing to this marked porosity, it is
not necessary to use a device for distributing hot gas within the
cementitious material comprising ettringite, such as for example a
network of pipes for circulating hot gas. During this heat
restoring phase, the initial cold and wetted gas is converted into
hot and dry gas at the outlet of the cementitious material. The
passage of a gas through the material is made possible owing to the
high porosity of the cementitious material comprising ettringite.
It is important to ensure that carbon dioxide does not come into
contact with the monolithic cementitious material, at the risk of
resulting in a carbonation of the material, and therefore an
irreversible degradation and then a drop in efficiency of the
storage/withdrawal system. In order to prevent such prejudicial
contact, the heat transfer fluid may be formed by an inert gas such
as for example nitrogen. On the other hand, if the chosen heat
transfer gas was caused to transport carbon dioxide, it is then
necessary to make provision to trap these carbon dioxide particles
upstream of the cementitious material, for example by means of a
selective membrane. Provision may be made for a system according to
the invention to simultaneously carry out a heat storage and
withdrawal phase, in particular by creating two heat transfer fluid
circulation circuits in parallel. Preferentially, an energy
storage/withdrawal system according to the invention comprises at
least one heat transfer fluid circulation circuit that passes
through the heating device and through the wetting device, said
circuit being supplied by a source of said fluid and leading to the
cementitious material. It is assumed that the storage phase
comprises an active phase of charging heat into the cementitious
material and a passive phase of conserving this heat in said
cementitious material, the heating device being activated only
during this charging phase. The water insulation material
constitutes a barrier intended to prevent water vapour from coming
into contact with the cementitious material.
[0031] Advantageously, the heat transfer fluid is formed by an
inert gas. Preferentially, this inert gas is nitrogen. Such a fluid
makes it possible to avoid polluting the cementitious material with
carbon dioxide.
[0032] Preferentially, the source of the heat transfer fluid is
placed upstream of the wetting device, which is itself placed
upstream of the heating device, said heating device being placed
upstream of the cementitious material. This is one embodiment
suitable for a system according to the invention.
[0033] Preferentially, the wetting device and the heating device
each operate to order, and can be activated independently of one
another depending on the use of said system, either in storage
phase, or in withdrawal phase. The various constituent elements of
a storage/withdrawal system according to the invention are
necessary for these energy storage/withdrawal functions, but are
not necessarily intended to operate simultaneously.
[0034] Advantageously, the mass fraction of ettringite in the
cementitious material is between 20% and 90%. The ettringite must
be present in massive amounts in the monolithic cementitious
material in order to carry out, under optimized conditions, the
heat storage and withdrawal phases.
[0035] Advantageously, the cementitious material has a porosity of
between 10% and 90%.
[0036] Preferentially, the material has a permeability of between
10.sup.-17 m.sup.2 and 10.sup.-11 m.sup.2.
[0037] Advantageously, the cementitious material has a mechanical
strength of between 0.1 MPa and 70 MPa.
[0038] Preferentially, the water insulation material is formed by
an impermeable wall intended to prevent water vapour from coming
into contact with the cementitious material. This wall may for
example be formed by PVC. This is a nonlimiting example of a water
insulation material that has a good water insulation while
remaining lightweight.
[0039] Advantageously, the thermal insulation material is formed by
at least one material to be chosen from glass wool and polystyrene,
said at least one material being placed around the water insulation
material.
[0040] Advantageously, the wetting device comprises at least one
humidifier suitable for charging said fluid with water. This
humidifier may for example be formed by a bubbler.
[0041] Another subject of the invention is a process for
storing/withdrawing thermal energy using a storage/withdrawal
system in accordance with the invention.
[0042] The main characteristic of a process according to the
invention is that, in the heat storage phase, it comprises the
following steps: [0043] a step of heating the heat transfer fluid
in order to obtain a hot gas, the temperature of which is above
30.degree. C., [0044] a step of directly passing said hot gas
through the cementitious material comprising ettringite, giving
rise to an endothermic dehydration and constituting a heat storage
phase.
[0045] Passing the hot gas into the cementitious material makes it
possible to bring said material to a temperature between 30.degree.
C. and 100.degree. C. It is assumed that the cementitious material
comprising ettringite is at atmospheric pressure. The decomposition
temperature of ettringite increases greatly with the water vapour
pressure. For example, if the material was subjected to a water
vapour pressure of 8000 Pa, the storage temperature of said
material could reach 80.degree. C., without decomposing the
ettringite. The heat storage phase mentioned during the step of
passing the gas through the cementitious material, corresponds to
the phase of charging heat into the cementitious material. The term
"directly" means that the hot gas passes through the cementitious
material comprising ettringite without the aid of any specific
transportation device, such as for example pipes that would be
placed around and/or within said material. The gases pass through
the entire volume of the cementitious material, owing to its good
porosity.
[0046] Advantageously, the heat storage phase extends over a period
of several days, said period being dictated by the amount of
cementitious material used in a system according to the invention.
More specifically it is the period of the phase of charging heat
into the material.
[0047] Preferentially, a storage/withdrawal process according to
the invention comprises, in the heat withdrawal phase, the
following steps: [0048] a step of wetting the heat transfer fluid
by means of the wetting device in order to obtain a wetted gas,
[0049] a step of directly passing said wetted gas through the
cementitious material comprising ettringite and which adsorbs water
vapour then is hydrated, [0050] a step of exothermic reaction which
generates heat transported by the heat transfer fluid, converting
the initially cold and wet gas into a hot and dry gas.
[0051] It is the restoring of this dry and hot gas that constitutes
the production of heat.
[0052] Preferentially, a storage/withdrawal process according to
the invention comprises a step of removing the carbon dioxide in
the heat transfer fluid before it passes through the cementitious
material comprising ettringite in order to prevent a carbonation
reaction of said material. Indeed, if the heat transfer fluid is
not an inert gas, it may be capable of transporting CO.sub.2. In
order to prevent a carbonation of the cementitious material
comprising ettringite, which would be greatly detrimental to the
efficiency of a system according to the invention, it is necessary
to trap the CO.sub.2 before it comes into contact with said
cementitious material. A membrane may thus advantageously be used
to stop the CO.sub.2 molecules upstream of this cementitious
material. The term "directly" means that the wetted gas passes
through the cementitious material comprising ettringite without the
aid of any specific transportation device, such as for example
pipes that would be placed around and/or within said material. The
gases pass through the entire volume of the cementitious material,
owing to its good porosity.
[0053] Another subject of the invention is a cementitious material
comprising ettringite for creating a storage/withdrawal system
according to the invention.
[0054] Advantageously, a cementitious material according to the
invention comprises an ettringitic binder, the porosity and the
permeability of which are increased by chemical foaming and/or by
mechanical foaming. Chemical foaming consists of additions of
aluminium powder or of other foaming agents, and mechanical foaming
consists of additions of surfactant and of a mechanical mixing. A
high permeability combined with a high porosity of the ettringitic
material favours the accessibility of the water vapour to the
ettringitic crystals, and therefore the effectiveness of the
process for storing heat in the material.
[0055] An energy storage/withdrawal system according to the
invention has the following advantages: [0056] A storage density
considerably greater than that of the existing low-temperature
storage/withdrawal systems. The ettringitic material has the
advantage of combining both energy storage by physisorption and
storage by chemisorption. This gives it a high storage density
relative to the low-temperature sensible, latent, physical sorption
or chemical sorption heat storage material. [0057] The use of
ettringite does not require thermal insulation during the
intermediate storage phase. In a storage/withdrawal process
according to the invention, there is an active heat charging phase,
a heat conservation phase and a heat withdrawal phase, said active
phase and said conservation phase constituting the heat storage
phase. The conservation phase may generally last for a long time,
around several months for a seasonal storage. With ettringite, the
heat stored by chemical reaction is conserved while the material is
insulated from water in liquid or vapour form. [0058] Such a system
is both suitable for the short term and the long term. The lack of
need for thermal insulation makes it efficient for long-term
storage phases unlike the existing storage/withdrawal systems.
[0059] Such a system enables good control of the heat storage
phase. The heat charging phase (desorption and dehydration) may be
carried out in several steps staggered over time, making the
storage/withdrawal system suitable for the seasons where the
sunshine is fleeting. Several days are needed to obtain a complete
dehydration of the material depending on the size of the material
used, and therefore to completely charge said material with heat.
This dehydration may be carried out intermittently, the sunshine
may for example partially dehydrate the material on the first day,
and may complete the dehydration over the following days with a
possibility of discharging heat if need be. [0060] Such a system
enables a good control of the heat withdrawal phase. As during the
heat charging phase, the heat stored may be returned in several
steps, by controlling the amount of gas adsorbed. [0061] The
ettringite has a low storage temperature, of the order of
60.degree. C. This temperature may easily be achieved by means of a
conventional solar collector. [0062] The ettringitic material is a
monolithic material, which is perfectly suitable for use in a
facility in the form of walls and/or bricks and/or partitions,
unlike a powder bed. The cementitious material may either be
self-supporting or be used as a load-bearing structure within an
edifice consisting of several materials. Indeed, its compressive
mechanical strength is between 0.1 MPa and 70 MPa. [0063] It may
lead to long heat withdrawal phases. Indeed, the physicochemical
combination of the storage process gives the material a long
discharging phase. During the initial heat-discharging phase it is
the physical adsorption (exothermic reaction) which leads to the
increase in the temperature over several hours, then the
temperature is maintained or even increased by the exothermic
hydration, of which the kinetics are slow and may last several
days.
[0064] Given below is a detailed description of a preferred
embodiment of an energy storage/withdrawal system according to the
invention and of the associated storage/withdrawal process, by
referring to the following figures:
[0065] FIG. 1 is a general schematic view of a storage/withdrawal
system according to the invention,
[0066] FIG. 2 is a schematic view of the part of the system from
FIG. 1 required for the heat storage phase,
[0067] FIG. 3 is a schematic view of the part of the system from
FIG. 1 required for the heat withdrawal phase,
[0068] FIG. 4 is a schematic view of a thermochemical reactor of a
storage/withdrawal system according to the invention,
[0069] FIG. 5 is a diagram illustrating an example of the variation
of the temperature in a cementitious material of a
storage/withdrawal system according to the invention, during a heat
withdrawal phase,
[0070] FIG. 6 is a diagram illustrating an example of the variation
of the temperature in a cementitious material of a
storage/withdrawal system according to the invention, during two
heat withdrawal cycles.
[0071] In order to facilitate the reading of the detailed
description, a "storage/withdrawal system" will be denoted under
the simple designation "system". Similarly, a "storage/withdrawal
process" will be denoted under the simple designation
"process".
[0072] A cementitious material 1 of a system according to the
invention is intended to form the constituent material of the walls
and/or various partitions of an industrial facility or of a
domestic dwelling. In order to describe the operating principle of
such a system and the various steps of the associated process, the
detailed description will focus on a system comprising a
thermochemical reactor, the structure and the physicochemical
properties of which are representative of those of the walls or
partitions that would be formed by this cementitious material.
[0073] By referring to FIG. 1, a system 100 according to the
invention comprises a circuit 8 for circulation of a heat transfer
fluid, comprising a source 2 of said fluid, a wetting device 3, a
heating device 4, the thermochemical reactor 5 comprising the
cementitious material 1, and an outlet 6 of this heat transfer
fluid. In the example considered, the source 2 of heat transfer
fluid is a nitrogen cylinder. The wetting device 3 comprises at
least one bubbler 7 suitable for charging the nitrogen with water,
it being possible for said water to be present in the form of a
liquid or vapour. The circuit 8 has at least one flowmeter 9 that
makes it possible to measure the nitrogen flow rate and therefore
to control it. The heating device 4 comprises at least one solar
collector or another source of preferentially renewable energy able
to recover heat over a temperature range between 30.degree. C. and
100.degree. C. The heating device 4 and the wetting device 3 may be
activated independently of one another and may therefore operate
alternately. The circuit 8 passes firstly through the wetting
device 3, then through the heating device before passing through
the thermochemical reactor 5, the fluid resulting from the passage
through said reactor 5 then being discharged to the atmosphere in
order to heat a room or a premises.
[0074] By referring to FIG. 4, the thermochemical reactor 5
comprises a shell 10 consisting of a cylindrical wall enclosing a
monolithic cementitious material 1 comprising a large mass fraction
of ettringite, of between 20% and 90%. This material 1 constitutes
a cylindrical block having the following characteristics: [0075] a
high porosity of between 10% and 90%, [0076] a permeability of
between 10.sup.-17 m.sup.2 and 10.sup.-11 m.sup.2, [0077] a
mechanical strength of between 0.1 MPa and 70 MPa.
[0078] The shell 10 is split into an inner shell 11 formed by a
layer of PVC (polyvinyl chloride) that comes into contact with the
outer lateral surface of the cementitious block 1 and an outer
shell 12 formed by a layer of glass wool surrounding the PVC layer
11 and being in contact therewith. The PVC layer 11 acts as a water
insulation material and the glass wool layer 12 acts as a thermal
insulation material. This thermochemical reactor 5 has an inlet 13
for nitrogen originating from the heating device 4 or from the
wetting device 3, and a nitrogen outlet 14 after this nitrogen has
passed through the monolithic cementitious block 1. Thermal
sensors, such as for example thermocouples, and water sensors may
be inserted into the cementitious block 1 in order to enable the
control of the temperature of said block 1 and of the water vapour
pressure in the reactor 5, over time.
[0079] All the measurement elements present in the system 100 make
it possible to acquire the operating parameters of said system 100,
which may then be recorded and processed by a computer 15.
[0080] A system according to the invention makes it possible to
become charged with heat, then to store this heat over an unlimited
given period of time, before restoring it to order, when the
heating requirements take effect.
[0081] A storage/withdrawal process using a system 100 according to
the invention comprises the following steps: [0082] A--In the
charging phase, illustrated in FIG. 2 (this phase may for example
take place in summer where the amount of sunshine is considerable)
[0083] A step of heating the heat transfer fluid 2 in order to
obtain a hot gas, the temperature of which is between 50.degree. C.
and 70.degree. C., and preferentially is equal to 60.degree. C.
This heating step is carried out by means of the heating device 4,
and in particular by means of the solar collector. [0084] A step of
passing said hot gas through the cementitious material 1 comprising
ettringite, giving rise to an endothermic dehydration and
constituting a heat storage phase. Indeed, the nitrogen is thus
heated between 30.degree. C. and 100.degree. C. before passing
through the cementitious block 1 housed in the thermochemical
reactor 5, the passage through said block 1 being facilitated by
the high porosity thereof. The nitrogen then heats the cementitious
block 1 of ettringite, which is dehydrated, simulating the heat
storage phase. The endothermic desorption of water over the
ettringite, which is a physicochemical reaction, makes it possible
to store heat. The thermal energy is thus stored and conserved in
the cementitious material 1, while said material 1 remains
insulated from water. For this charging phase, the device 3 for
wetting the nitrogen is not needed and is not therefore activated.
A complete charging phase lasts around several days depending on
the amount of cementitious material 1 used and on the fluid flow
rate. By way of example, on average 3 days are required for several
kilograms of material and a nitrogen flow rate of 2 l/min. The
chemical part of the heat charging process (endothermic
dehydration) is linked to the reversible conversion of ettringite
to metaettringite, by loss of 18 water molecules per ettringite
molecule:
[0084]
3CaO.Al.sub.2O.sub.3.3CaSO.sub.4.3H.sub.2O.fwdarw.3CaO.Al.sub.2O.-
sub.3.3CaSO.sub.4.12H.sub.2O+18H.sub.2O [0085] B-- In the
discharging phase, illustrated in FIG. 3 (this phase may for
example take place in winter where the heating requirements are
high) [0086] A step of wetting the heat transfer fluid 2 by means
of the wetting device 3 in order to obtain a wetted gas. This
wetting step is carried out by means of the wetting device 3, and
in particular, by means of bubblers. The gas resulting from the
wetting device 3 is thus charged with water vapour. The wetted gas
can pass through the monolithic cementitious material 1 comprising
ettringite since said material 1 is porous and permeable. [0087] A
step of passing said wetted gas through the cementitious material 1
comprising ettringite and which adsorbs water vapour then is
hydrated. The adsorption is a physical phenomenon and the hydration
is a chemical phenomenon. The chemical part of the heat restoring
process is linked to the rehydration of metaettringite to
ettringite by a gain of 18 water molecules per ettringite
molecule:
[0087] 3CaO.
Al.sub.2O.sub.3.3CaSO.sub.4.12H.sub.2O+18H.sub.2O.fwdarw.3CaO.
Al.sub.2O.sub.3.3CaSO.sub.4.30H.sub.2O [0088] A step of exothermic
reaction at the cementitious material, which generates heat
transported by the heat transfer fluid 2, transforming the
initially cold and wet gas into a hot and dry gas. During this heat
withdrawal phase, the heating device 4 is not needed and is not
therefore activated.
[0089] By referring to FIG. 5, the maximum temperature increase in
the cementitious material 1 may for example reach 16.degree. C.,
during a heat withdrawal phase. This temperature increase depends
on the amount of material, on the relative humidity and on the flow
rate of fluid used. Such a diagram shows that the heat withdrawal
phase may last up to 3 days, which remains a long period relative
to that of the systems using zeolite type materials, for which this
period does not exceed 24 h.
[0090] FIG. 6 illustrates the reversibility of the storage process
of a system according to the invention. The reversibility of the
heat storage process is linked to that of the chemical reaction for
dehydrating and rehydrating ettringite.
* * * * *