HEAT STORAGE TANK OPTIMISED USING CALCIUM CARBONATE PARTICLES

Abstract

Provided is a heat storage tank including at least one chemically inert solid heat storage material containing at least calcium carbonate particles, in which the calcium carbonate particles have a size distribution with a diameter d50 of from 0.5 mm to 200 mm.

Claims

1. A heat storage tank comprising at least one chemically inert solid heat storage material containing at least calcium carbonate particles, wherein the calcium carbonate particles have a size distribution with a diameter d.sub.50 of from 0.5 mm to 200 mm.

2. The heat storage tank as claimed in claim 1, not containing any glass particles.

3. The heat storage tank as claimed in claim 1, further comprising at least one heat-transfer fluid (6).

4. The heat storage tank as claimed in claim 4, wherein the heat-transfer fluid is liquid at ambient temperature.

5. The heat storage tank as claimed in claim 3, wherein the heat-transfer fluid is chosen from molten salts and oils.

6. The heat storage tank as claimed in claim 5, wherein the molten salts are chosen from nitrate salts, carbonate salts or a mixture thereof.

7. The heat storage tank as claimed in claim 5, wherein the oil is chosen from synthetic oils, mineral oils, vegetable oils and mixtures thereof.

8. The heat storage tank as claimed in claim 5, wherein the oil comprises at least one aromatic ring.

9. The heat storage tank as claimed in claim 5, wherein the oil comprises at least two rings separated by at least one carbon bond, at least one of said at least two rings being an aromatic ring.

10. The heat storage tank as claimed in claim 5, wherein the oil is chosen from the group consisting of: a mixture of diphenyl ether and biphenyl, a mixture of dibenzyltoluene isomers, sold notably under the trade name Jarytherm® DBT, an oil corresponding to a mixture of terphenyls, sold notably under the trade name Therminol® 66, and an oil comprising 1,2,3,4-tetrahydronaphthalene, sold notably under the trade name Dowtherm RP®.

11. The heat storage tank as claimed in claim 5, wherein the oil does not comprise any terphenyl.

12. The heat storage tank as claimed in claim 3, wherein the heat-transfer fluid and the chemically inert solid heat storage material including at least calcium carbonate particles are in direct contact.

13. The heat storage tank as claimed in claim 1, wherein it includes a vessel filled with a heat-transfer fluid and a chemically inert solid heat storage material including at least calcium carbonate particles, a first longitudinal end, located at its upper part, and a second longitudinal end located at its lower part; the heat-transfer fluid being capable of circulating between the first longitudinal end and the second longitudinal end.

14. The heat storage tank as claimed in claim 13, in which the first longitudinal end is equipped with means for collecting and feeding the heat-transfer fluid at a first temperature ranging from 110° C. to 650° C. and the second longitudinal end is equipped with means for collecting and feeding the heat-transfer fluid at a second temperature ranging from 100° C. to 640° C.; the first temperature being higher than the second temperature.

15. A facility for recovering free heat of industrial origin, comprising a heat storage tank as claimed in claim 1.

16. A solar power plant including at least one heat storage tank as claimed in claim 1.

17. The use of at least one chemically inert solid heat storage material including at least calcium carbonate particles for limiting the rate of degradation of a heat-transfer fluid that is capable of circulating in a heat storage tank as defined in claim 1.

18. A method of circulating a heat transfer fluid, comprising circulating a heat transfer fluid in the heat storage tank as defined in claim 1.

Description

[0143] Other features and advantages of the invention will emerge on detailed examination of an embodiment taken as a nonlimiting example of a heat storage tank according to the invention and illustrated by the appended drawings, in which:

[0144] FIG. 1 is a view in longitudinal cross-section of a heat storage tank according to the invention including a vessel filled with a heat-transfer fluid and a solid heat storage material,

[0145] FIG. 2 schematically shows the heat storage tank according to the invention during a charging phase,

[0146] FIG. 3 schematically illustrates the heat storage tank according to the invention during a discharging phase (destocking step).

[0147] FIG. 1 represents a heat storage tank 1 according to the invention made in accordance with one embodiment.

[0148] The tank 1 includes a vessel 2 having a parallelepipedal shape with a vertically oriented longitudinal axis A-A. As a variant, the vessel 2 may have an oblong shape, in particular a cylindrical shape, having a vertically oriented longitudinal axis A-A.

[0149] Also as a variant, the vessel 2 corresponds to a ferrule having two domed ends.

[0150] In accordance with FIG. 1, the vessel 2 is preferably thermally insulated with an envelope 3 made using an insulating material.

[0151] Preferably, the envelope 3 is in contact with the vessel 2 so as to cover both the sidewalls and the upper and lower parts of the vessel 2. The envelope 3 notably has the same shape as the vessel 2.

[0152] The vessel 2 has a first upper longitudinal end 2a equipped with an orifice 4 acting as inlet or outlet for a fluid as a function of the charging and discharging phases of the system, and a second lower longitudinal end 2b equipped with an orifice 5 acting as an inlet or outlet for a fluid as a function of the charging and discharging phases of the system.

[0153] The orifices 4 and 5 thus function to feed and/or collect the heat-transfer fluid that is liable to fill the vessel 2. The orifices 4 and 5 may be equipped with fluid feed and collection means.

[0154] The insulating envelope 3 is also open at the orifices 4 and 5.

[0155] The vessel 2 is filled with a heat-transfer liquid 6, preferably a synthetic oil as defined above, and a chemically inert solid heat storage material 7, consisting solely of calcium carbonate particles. The calcium carbonate particles 7 rest on a support 7a which serves to retain them while at the same time allowing the passage of the heat-transfer liquid 6 throughout the vessel 2.

[0156] The support 7a may be made as a single piece or may be formed from several pieces to facilitate its mounting in the vessel 2.

[0157] In FIG. 1, the calcium carbonate particles 7 have an identical diameter. However, according to another preferential embodiment, the carbonate particles 7 have different sizes.

[0158] The heat-transfer liquid 6 occupies, along the longitudinal axis A-A, the upper part of the vessel 2 at a first temperature (known as the HT temperature), the lower part of the tank at a second temperature (known as the CT temperature), the median part of the vessel 2 corresponding to an intermediate region known as the thermocline, intercalated between the upper part and the lower part. The first temperature (HT) is higher than the second temperature (CT).

[0159] The heat-transfer liquid 6 thus includes a hot zone 6C (at a temperature HT) located in the upper part of the vessel 2, a cold zone 6F (at a temperature CT) located in the lower part of the vessel 2 and an intermediate zone 6T intercalated between the hot zone 6C and the cold zone 6F, known as the thermocline and constituting a heat gradient.

[0160] In other words, the heat-transfer liquid 6 is thermally stratified in the vessel 2, these strata forming layers having different temperatures which are superposed on each other, from the coldest zone to the hottest zone along the longitudinal axis A-A.

[0161] The temperature HT may range from 110° C. to 650° C. and the temperature CT may range from 100° C. to 640° C.

[0162] The temperature in the intermediate zone 6T is below the temperature HT of the hot zone 6C and above the temperature CT of the cold zone 6F.

[0163] Preferably, the heat-transfer fluid 6 is an oil, in particular a synthetic oil, corresponding to a mixture of dibenzyltoluene isomers, notably the product sold under the trade name Jarytherm® DBT.

[0164] FIG. 1 represents the storage phase, i.e. the step during which the heat-transfer liquid 6 is stored in the tank 1 and the thermocline is in equilibrium at the center of the tank 1.

[0165] As indicated above, FIG. 2 describes schematically the storage tank according to the invention, notably illustrating the direction of circulation of the heat-transfer liquid 6 in the vessel 2 during the charging phase.

[0166] During this charging phase, the hot heat-transfer liquid 6, coming from a solar power collection system (not shown in FIG. 2), is introduced into the upper part 2a by means of the orifice 4 and flows downward (along the longitudinal axis A-A) through the calcium carbonate particles 7, inducing a downward shift of the thermocline 6T. During its circulation through the calcium carbonate particles 7, the heat-transfer liquid 6 is cooled to reach the temperature CT and is evacuated through the orifice 5 of the lower part 2b of the tank 1 to the solar power collection system.

[0167] FIG. 2 shows, by means of arrows, the direction of circulation of the heat-transfer liquid 6 through the tank 1, i.e. from the top downward along the longitudinal axis A-A. The intermediate zone 6T moves axially downward during the charging phase.

[0168] As indicated above, FIG. 3 illustrates schematically the storage tank according to the invention, notably illustrating the direction of circulation of the heat-transfer liquid 6 in the vessel 2 during the discharging (or destocking) phase.

[0169] During this discharging phase, the cold heat-transfer liquid 6, coming from a thermodynamic conversion system (not shown in FIG. 3), is introduced through the orifice 5 of the lower part 2b of the vessel 2 and flows upward (along the longitudinal axis A-A) through the calcium carbonate particles 7, inducing an upward shift of the thermocline 6T. During its circulation through the calcium carbonate particles 7, the heat-transfer liquid 6 is heated to reach the temperature HT and is evacuated through the orifice 4 of the upper part 2a of the tank 1 to the thermodynamic conversion system, namely the turbine.

[0170] FIG. 3 shows, by means of arrows, the direction of circulation of the heat-transfer liquid through the tank 1, i.e. from the bottom upward along the longitudinal axis A-A. The intermediate zone 6T moves axially upward during the discharging phase.

[0171] FIGS. 1 to 3 thus describe an embodiment of a one-tank heat storage system which may contain a heat-transfer fluid and containing at least one solid heat storage material comprising at least calcium carbonate particles.

[0172] As a variant, the tank 2 may be divided into several compartments superposed along the longitudinal axis A-A, each compartment including the calcium carbonate particles 7 arranged in the form of a bed, covered with the heat-transfer liquid 6 which is capable of circulating through all of the compartments.

[0173] Again as a variant, the calcium carbonate particles 7 may be in the form of spheres or flakes and/or may have totally free forms.

[0174] The example that follows relates to tests of thermal stability of the heat-transfer fluid as a function of the nature of the solid storage material employed.

Example of Thermal Stability

[0175] In this example, the thermal stability of a synthetic oil sold under the trade name Jarytherm® DBT by the company Arkema was studied, in a heat storage tank, alone or in the presence of various types of chemically inert solid heat storage materials at a temperature of 340° C. for a time of 500 hours or 2000 hours.

[0176] The amount of undegraded synthetic oil was measured at the end of the study period.

[0177] The results are collated in the following table:

TABLE-US-00001 Content of Operating conditions DBT in the oil Fresh oil 98 Oil alone/500 hours at 340° C. 92 Oil + calcium carbonate particles/ 90.6 500 hours at 340° C. Oil + rock/500 hours at 340° C. 83.4 Oil + sand/500 hours at 340° C. 81.2 Oil alone/2000 hours at 340° C. 80.8 Oil + calcium carbonate particles/ 79.7 2000 hours at 340° C.

[0178] The results show that the content of DBT in the oil is significantly higher with calcium carbonate particles relative to that measured in the presence of rocks or sand after a time of 500 hours at a temperature of 340° C.