HYGROSCOPIC COMPOSITE MATERIAL

Abstract

A composite material, notably for seasonal storage of energy in a domestic heating system, comprises grains having at least one of the following pairings of hygroscopic salt arranged within a porous material (table) with the hygroscopic metal concentration in the central zone of the grain being at least 0.7 times that in the peripheral zone.

Claims

1. A composite material comprising grains, the grains comprising at least one of the following pairings of a hygroscopic salt arranged within a porous material and having the following water adsorption and/or amount of hygroscopic salt: TABLE-US-00004 water adsorption amount of hygroscopic salt pairing of porous measured between of the composite material material and 80 C. and 30 C. in the grains with respect to hygroscopic salt at 12.5 mbar the total weight of the grains activated carbon and at least 0.19 g/g at least 29% wt strontium bromide activated carbon and at least 0.28 g/g at least 32% wt calcium chloride silicagel and at least 0.35 g/g at least 38% wt calcium chloride silicagel and at least 0.18 g/g at least 47% wt strontium bromide silicagel and at least 0.25 g/g at least 31% wt magnesium chloride wherein the grains have a peripheral zone and a central zone, the peripheral zone of a grain being a portion of the grain extending from a periphery of the grain towards the centre of the grain for a distance of about 1/10.sup.th of the diameter of the grain, and the central zone of a grain being a portion of the grain extending from the centre of the grain for a distance of about 1/10.sup.th of the diameter of the grain towards the periphery of the grain; wherein the peripheral zone has a peripheral zone hygroscopic metal concentration HMCp expressed as the mass percentage of metal(s) of the hygroscopic salt(s) at the peripheral zone HMp divided by the mass percentage of i) the carbon of the activated carbon or ii) the silicon of the silica gel at the peripheral zone HPp (i.e. HMCp=HMp/HPp) wherein the central zone has a central zone hygroscopic metal concentration HMCc expressed as the mass percentage of metal(s) of the hygroscopic salt(s) at the central zone HMc divided by the mass percentage of i) the carbon of the activated carbon or ii) the silicon of the silica gel at the central zone HPc (i.e. HMCc=HMc/HPc) and wherein the central zone hygroscopic metal concentration is greater than or equal to 0.7 times the peripheral zone hygroscopic metal concentration (HMCc0.7 HMCp).

2. A composite material in accordance with claim 1, wherein the water adsorption of the composite material measured between 80 C. and 30 C. at 20 mbar is: at least 0.19 g/g for the pairing activated carbon and strontium bromide at least 0.44 g/g for the pairing activated carbon and calcium chloride at least 0.25 g/g for the pairing silicagel and strontium bromide at least 0.60 g/g for the pairing silicagel and calcium chloride at least 0.35 g/g for the pairing silicagel and magnesium chloride

3. A composite material in accordance with claim 1, wherein the central zone hygroscopic metal concentration is greater than or equal to 0.8 times the peripheral zone hygroscopic metal concentration (HMCc0.8 HMCp).

4. A composite material in accordance with claim 1, wherein the amount of hygroscopic salt of the composite material in the grain with respect to the total weight of the grain is determined by X-ray fluorescence.

5. A composite material in accordance with claim 1, wherein the amount of hygroscopic salt of the composite material in the grains with respect to the total pore volume of the porous material in the grains is no more than 90%.

6. A composite material, notably in accordance with claim 1, comprising a pairing of a porous material and a hygroscopic salt arranged within the porous material, selected from the pairings of: activated carbon and strontium bromide activated carbon and calcium chloride silicagel and calcium chloride silicagel and strontium bromide silicagel and magnesium chloride wherein the difference in water adsorption of the composite material measured between 80 C. and 30 C. at 12.5 mbar or at 20 mbar between 5 successive cycles, preferably between 15 successive cycles, is less than 10%, preferably less than 5%.

7. A method of manufacturing a composite material comprising a pairing of a porous material and a hygroscopic salt arranged within the porous material, notably in accordance with any preceding claim, comprising: Impregnating a porous material with a solution of a hygroscopic salt to form a composite material; Subsequently drying the composite material in order to remove water; Subsequently re-impregnating the composite material with a solution of a hygroscopic salt to form a composite material;

8. A method in accordance with claim 7, comprising at least three impregnations each separated by a drying of the composite material.

9. A method in accordance with claim 7, wherein the pairing of the hygroscopic salt and the porous material is selected from the pairings: activated carbon and strontium bromide activated carbon and calcium chloride silicagel and calcium chloride silicagel and strontium bromide silicagel and magnesium chloride.

10. A method in accordance with claim 7, wherein the method does not comprise washing the composite material between impregnations.

11. A method in accordance with claim 7, wherein the amount of hygroscopic salt of the composite material in the grains with respect to the total weight of the composite material in the grains is at least 25% wt, preferably at least 35% wt.

12. A method of storage and recuperation of thermal energy comprising: a) at least partially dehydrating a hydrated form of i) a composite material in accordance with claim 1, or ii) a composite material manufactured by a method in accordance with claim 1, by subjecting the composite material to a temperature in the range 30 C. to 150 C. for a period of at least 30 minutes; b) Subsequently storing the at least partially dehydrated composite material for a period of at least 4 hours; c) Subsequently exposing the at least partially dehydrated composite material to water to at least partially re-hydrate the composite material whilst removing heat from the composite material at a temperature in the range 20 C. to 80 C.

13. A method in accordance with claim 12, wherein: a) at least partially dehydrating the composite material comprises subjecting the composite material to a temperature in the range 70 C. to 100 C. for a period of least 30 minutes; and b) at least partially hydrating the composite material comprises removing heat at a temperature in the range 30 C. to 80 C.

14. A domestic heating system comprising: a) a composite material in accordance with claim 1, or ii) a composite material manufactured by a method in accordance with claim 1; b) a system for at least partially dehydrating the composite material by subjecting the composite material to a temperature in the range 30 C. to 150 C. for a period of at least 30 minutes; c) a system for storing the at least partially dehydrated composite material for a period of at least 4 hours; d) a system for exposing the at least partially dehydrated composite material to water to at least partially re-hydrate the composite material whilst removing heat from the composite material at a temperature in the range 20 C. to 80 C.

15. A heating system in accordance with claim 14, in which the heating system is adapted to store at least 2000 kWh of energy for a duration of at least 3360 hours (about 140 weeks).

Description

[0033] Non limiting examples are described below with reference to:

[0034] FIG. 1: a graph of water adsorption and desorption over successive cycles; and

[0035] FIG. 2: a cross-section through a grain of composite material.

EXAMPLES 1-5

[0036] The composite materials of Table 1 were made by: [0037] Dehydrating the porous material in an oven at 200 C. for 4 h until the mass of the porous material was constant; [0038] Impregnating, with agitation, the dehydrated porous material during 30-60 minutes with a volume of an aqueous solution of the hygroscopic salt equal to the pore volume; [0039] Dehydrating the composite material in an oven for 60 minutes at 200 C. (except for example 5 which was dehydrated at 110 C.); [0040] Repeating the impregnation/drying cycle as indicated in Table 1

TABLE-US-00002 TABLE 1 Final amount of hygroscopic salt of the composite Water Water material in adsorption adsorption Concentration the grains measured measured of hygroscopic with respect between between salt in solution Number of to the total 80 C. and 80 C. and for the impregnation weight of the 30 C. at 30 C. at Example Pairing impregnation steps grains 12.5 mbar 20 mbar 1 activated 40% 2 29.50% 0.200 0.200 carbon/ SrBr2 2 activated 20% 3 32.47% 0.292 0.450 carbon/ CaCl2 3 silicagel/ 20% 4 42.92% 0.387 0.640 CaCl2 4 silicagel/ 40% 2 47.68% 0.218 0.285 SrBr2 5 silicagel/ 20% 2 36.00% 0.284 0.390 MgCl2

[0041] The activated carbon SRD 10034 (AC) used has a specific surface of 1250 m.sup.2/g and a pore volume of 0.42 cm.sup.3/g. The silicagel SG 100 (SG) used has a specific surface of 360 m.sup.2/g and a porous volume of 0.8 cm.sup.3/g. Another type of silicagel may be used such as the silicagel SG 62 (SG) which has a specific surface of 320 m.sup.2/g and a porous volume of 1.15 cm.sup.3/g.

Reproducibility Test

[0042] The composite material of Example 4 was tested during 5 successive adsorption/desorption cycles between 30 and 80 C. at 12.5 mbar. The results shown in FIG. 1 were measured by a thermogravimeter TG-DSC 111 and show: [0043] a difference in water adsorption of the composite material between the first and last of 5 successive cycles of less than 5%. [0044] a difference between water adsorption and subsequent water desorption in each cycle of less than 5%.

[0045] This indicates suitability for domestic or other heating systems, for example non domestic heating systems.

Determination of the Hygroscopic Metal Concentration at the Peripheral and Central Zones

[0046] The impregnation of a grain of the composite material of Example 3 (silica gel with calcium chloride) was analysed using a scanning electron microscope and is shown in FIG. 2.

[0047] Grains of the composite material were imprisoned in an inert resin or matrix. This was polished to provide a cross section through grains that could be analysed using an electron microscope. Chemical analysis was obtained using an EDX analyser provided with the scanning electron microscope.

[0048] During sample preparation and analysis it was ensured: [0049] that the planarity of the surface was sufficient to provide a quantitative chemical analysis; [0050] that the preparation technique did not bring any element that would interfere with chemical analyses (i.e. in the case of EDX, peaks should not overlap). For example, a conductive carbon layer should not be deposited before imaging if the composite contains activated carbon; [0051] that the composite material was not contaminated by any other mean, for example, the polishing media; [0052] that none of the elements to be measure was removed by the preparation technique (i.e., C or Si, O and Sr, Br or Ca, Cl or Mg, Cl).

[0053] Once the sample was imaged, it was verified that no crust of salt was present on the outer areas of the cross section. Such a crust would imply an interface between an imperfectly impregnated core and an outer area. A check using EDX can be done in case of doubt. On FIG. 2, no such phenomenon can be observed.

[0054] An analysis zone was defined across the width of a grain as an inscribed rectangle with at least three corners in contact with the grain periphery. The length of the analysis zone should be at least 1/10 of the diameter of the grain and the ratio length/width should be equal to 10. Preferably, the analysis zone passes through the centre of the grain. The analysis zone was then divided into ten identical juxtaposed squares numbered sequentially from 1 to 10, as shown in FIG. 2.

[0055] Square 1 (at the periphery of the grain) defines the peripheral zone and square 5 towards the centre of the grain defines the central zone at which the concentrations were determined. Table 2 gives the elements analysed (any other element was excluded from the analysis) and the condition used to verify a good quality of impregnation:

TABLE-US-00003 TABLE 2 Elements Pairing analyses Impregnation is of good quality if: activated carbon and strontium bromide C, Sr, Br [00001]${\left(\frac{\left[\mathrm{Sr}\right]}{\left[C\right]}\right)}_{5}0.7.Math.{\left(\frac{\left[\mathrm{Sr}\right]}{\left[C\right]}\right)}_1$ activated carbon and calcium chloride C, Ca, Cl [00002]${\left(\frac{\left[\mathrm{Ca}\right]}{\left[C\right]}\right)}_{5}0.7.Math.{\left(\frac{\left[\mathrm{Ca}\right]}{\left[C\right]}\right)}_1$ silicagel and calcium chloride Si, O, Ca, Cl [00003]${\left(\frac{\left[\mathrm{Ca}\right]}{\left[\mathrm{Si}\right]}\right)}_{5}0.7.Math.{\left(\frac{\left[\mathrm{Ca}\right]}{\left[\mathrm{Si}\right]}\right)}_1$ silicagel and strontium bromide Si, O, Sr, Br [00004]${\left(\frac{\left[\mathrm{Sr}\right]}{\left[\mathrm{Si}\right]}\right)}_{5}0.7.Math.{\left(\frac{\left[\mathrm{Sr}\right]}{\left[\mathrm{Si}\right]}\right)}_1$ Silicagel and magnesium chloride Si, O, Mg, Cl [00005]${\left(\frac{\left[\mathrm{Mg}\right]}{\left[\mathrm{Si}\right]}\right)}_{5}0.7.Math.{\left(\frac{\left[\mathrm{Mg}\right]}{\left[\mathrm{Si}\right]}\right)}_1$

[0056] In Table 2, [x] denotes the mass percentage of element x and the indices 1 and 5 denote measurements performed on squares 1 and 5 respectively.

[0057] The mass percentages of Ca, Cl, Si and O were measured. On square 1, [Ca]/[Si]=0.3255 and on square 5, [Ca]/[Si]=0.6307.

[0058] Preferably, the measurement is repeated on a plurality of grains and the average is taken.

[0059] Thus, in this example the central zone hygroscopic metal concentration was 1.94 times the times the peripheral zone hygroscopic metal concentration (HMCc=1.94 HMCp); this satisfies the condition HMCc0.7 HMCp.