WO2020200403A1

WO2020200403A1 - A process of producing a heat storage material and a heat storage material

Info

Publication number: WO2020200403A1
Application number: PCT/EP2019/058050
Authority: WO
Inventors: Erkki LAITI; Fabrice Papa
Original assignee: Ahlstrom-Munksjö Oyj
Priority date: 2019-03-29
Filing date: 2019-03-29
Publication date: 2020-10-08

Abstract

The present invention relates to a process of producing a heat storage material and a heat storage material. More specifically the present invention relates to a process of producing a heat storage material web (26) formed of a reactive sub-stance and a fiber matrix. The present invention relates also to a heat storage material web (26) formed of a reactive substance and a fiber matrix to be used as a heat storage material in a chemical heat pump.

Description

A process of producing a heat storage material and a heat storage material

Technical field

[001] The present invention relates to a process of producing a heat storage material and a heat storage material. The present invention relates to a heat stor age material web to be used in a heat storage system. More specifically the pre sent invention relates to a process of producing a heat storage material web formed of a reactive substance and a fibrous suspension.

Background art

[002] The principle of the operation of the chemical heat pump is well-known, see for example U.S. patents 5,440,889, 5,056,591 , 4,993,239, 4,754,805 and the published International patent application WO 94/21973. In a chemical heat pump such a reactive substance, is used that performs the very process of the heat pump when interacting with a volatile medium which usually is a dipolar liquid, in most cases water.

[003] Such chemical heat pumps use chemical energy storage solutions that are typically based on the reaction between the reactive substance, usually a salt, and the volatile medium, usually water. In order to obtain high heat storage capacity, a high quantity of reactive substance per volume of the reactor is re quired. Good access of the volatile medium to the reactive substance as well as good heat conduction property to extract heat out of the reactor are required for a good performance for the chemical heat pump.

[004] In general, reactive substances, , used in chemical heat storage applica tions are powdered, typically ionic, inorganic or organic solids. These solids may have either high or low solubility in water. The powdered solids may also be func tionalized or surface treated to improve or modify their properties, as taught in WO-A1 -2016/166364, the full contents of which is incorporated as a reference herein. [005] GB-A-2010468 discusses a heat storage element, which may be heated by solar radiation. The heat storage element comprises a body of fibrous carrier material impregnated with a first substance, which, when heated, produces a gaseous medium and leaves a second substance, or with the second substance, said body being readily permeable to the corresponding medium in the gaseous phase. Heat so stored is recovered by allowing said medium to recombine with said second substance to reconstitute said first substance, with the evolution of heat. In the preferred embodiment, the first substance is a salt hydrate, such as a hydrate of calcium chloride, and said medium is water vapor. The fibrous carrier material may be in the form of sheets of paper or cardboard stacked in spaced relationship to allow heated air to be passed therethrough for charging the heat storage elements, by removal of moisture, or to allow moist air to be passed therethrough, to supply moisture to the salt hydrate, with the evolution of heat, to recover the heat stored. According to this document, the first substance is intro- duced to the carrier material after the manufacture of the carrier material. In other words, this document describes a process of adding soluble salts to the carrier material. The only two options disclosed to add soluble salts to the carrier mate rial are making a very concentrated solution (liquid) and let it impregnate the po rous carrier material, whereafter the salt is precipitated by drying, or, alternatively, as some salt hydrates have relatively low melting temperature, make a liquid melt of the pure salt hydrate and impregnate with such.

[006] However, the process discussed in this document is limited to the use of either soluble or meltable reactive substances, which greatly limits the number of applicable chemicals.

[007] Coating processes used typically in paper industry apply suspended min erals such as calcium carbonates and clays onto paper surface. The obvious similarity to the powdered solids used as the reactive substances in chemical heat storages, suggests that paper coating technologies could be used for ap plying suspended reactive substances onto a carrier web in order to create reel based material containing the reactive substance of the heat storage material.

[008] However, paper coating processes have several important disadvantages regarding applicability for creating reel based chemical heat storage material. [009] An important requirement or prerequisite of the heat storage is to use a high quantity of reactive substance per reactor volume. If realized by means of a coated carrier web it would be difficult to obtain high coating to carrier web ratio: current paper coating applicators are limited to about 15 g/m² coat weights per application unit. As an example, obtaining a web at coating to carrier web ratios above 7 could theoretically be achieved by coating 420 g/m² reactive substance on a 60 g/m² carrier web. Even without considering any binder content in such coating formulation it is clear that using existing paper coaters to obtain such coat weights would require of the order of 30 separate coating (and drying) steps, which means, in practice, that the process is not industrially viable.

[0010] A second important limitation relating to the use of the paper coating pro cess in the production of a chemical heat storage material concerns the density of the coating layer. The mineral pigment coating layers realized by traditional paper coating methods are very dense and contain little porosity. Thereby thick layers of coating become rigid and fragile which limit the ability to wind the web to a reel. Further, related to the high density of the coating layer, a third disad vantage of the coating process is the limited, in fact poor, accessibility of water, or, more generally, volatile medium, to the reactive substance.

[0011] As discussed already above the heat storage capacity of a chemical heat pump should be high to make the chemical heat pumps attractive on the market. To make the heat storage capacity high and, thereby, the heat storage commer cially interesting, the energy density of the heat storage should be high as well. Therefore, a problem or challenge in the production of sheet-like heat storage material is that as high amount of reactive substance, i.e. a solid substance that undergoes considerable exothermic or endothermic reactions in a heat storage system, as possible should be provided in or on a fibrous web to ensure desired high energy density. On the one hand, it would appear to be obvious to provide the reactive substance on the fibrous web by means of coating, as is well known in various mineral pigment paper coating applications. On the other hand, an- other prior art method proposes immersion of the web for impregnating the reac tive substance. Both prior art methods require that a significant amount of water has to be removed from the web by ordinary drying means. Such water removal means a high number of drying cycles that makes the production of the reactive substance-containing web expensive in view of both the time needed and the machinery required therefor. Furthermore coating a web to have a high amount of reactive substance on the web results in the web having a thick, dense and brittle coating on the top surface thereof that efficiently prevents the product from being reeled. Additionally, due to the dense coating the accessibility of water va- por to the reactive substance particles inside the coating is poor. A third prior art method is coating with a saturated salt solution of a soluble salt. It does not imply enormous amounts of water, but it is not applicable with low solubility salts.

[0012] For high productivity manufacturing of reel based material for chemical heat storage by conventional paper coating technology, thus, lacks industrial vi- ability and the resulting product has several disadvantages.

[0013] Wet laid methods (foam laid and water laid) such as used in paper and nonwoven industry for creation of high grammage webs, to the contrary, provide such a process suitable for manufacturing of reel based material for chemical heat storage that the reactive substance and the rest of the components of the heat storage material web form a cohesive structure, enable production with good production line runnability and are capable of being reeled.

Summary

[0014] An object of the present invention is to solve, at least partially, the draw- backs of the prior art recited here-above by providing a novel process of produc ing a heat storage material.

[0015] Another object of the present invention is to simplify the production of the heat storage material needed in chemical heat pumps or energy storage sys tems.

[0016] A yet another object of the present invention is to provide such a process of producing the heat storage material that makes the production simpler, raises the production rate and lowers the costs of production.

[0017] A still another object of the present invention is to offer a heat storage material with easy convertibility, i.e. a material to which it is easy to join heat conductive layers, or a material which is easy to cut to correct shapes when as sembling the heat pump reactor. [0018] A further object of the present invention is to offer such a heat storage material that has high performance in the end use due to excellent accessibility of water vapour to the reactive substance.

[0019] A still further object of the present invention is to offer a heat storage ma- terial the porosity-density ratio of which is easily optimized by means of a calen der.

[0020] A yet further object of the present invention is to provide such a novel process of producing the heat storage material that makes it possible to formulate the furnish to enhance thermal conductivity of the heat storage material.

[0021 ] A still one more object of the present invention is to be able to use existing production equipment without a need to start designing and constructing, for in stance, new coating processes and equipment.

Disclosure of the Invention

[0022] At least one object of the present invention may be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the present invention.

[0023] According to an embodiment of the present invention, relates to a pro cess of producing a heat storage material by means of a fiber web machine, the process comprising the steps of:

a) preparing at least one fibrous suspension of at least one fibrous component and a suspending medium,

b) bringing a reactive substance in contact with the at least one fi brous suspension,

c) introducing the reactive substance and the at least one fibrous sus pension on a forming wire or between forming wires of the fiber web machine, and

d) removing liquid through the wire(s) and allowing a heat storage material web to be formed.

[0024] In step a) the amount of the at least one fibrous component may be comprised between 5 and 50% of the bone dry weight of the heat storage mate rial. [0025] In step b), the amount of the reactive substance may be comprised between 50 and 95% of the bone cry weight of the heat storage material.

[0026] According to a particular embodiment, in step a) a first and a second fibrous suspension of at least one fibrous component and a suspending medium may be prepared, the first and the second fibrous suspensions being either sim ilar or different.

[0027] According to an alternative, prior to step b), the reactive substance may be mixed with a suspending medium.

[0028] According to a first particular embodiment, a headbox having two sep- arate chambers may be used, the chambers being delimited by means of an in termediate wall to a first chamber and a second chamber such that, prior to step b), the fibrous suspension may be brought to the first chamber and the reactive substance to the second chamber.

[0029] According to a second particular embodiment, a headbox having three chambers may be used, the chambers comprising two outer chambers and an inner chamber, said inner chamber being disposed between the outer chambers, and the chambers being delimited by means of intermediate walls, and, before step b), bringing the at least one fibrous suspension to one outer chamber and the reactive substance to the inner chamber and the other outer chamber.

[0030] According to a third particular embodiment, a headbox having three separate chambers may be used, said separate chambers comprising two outer chambers and an inner chamber, said inner chamber being disposed between the outer chambers, and the separate chambers being delimited by means of intermediate walls, and by in step b), the fibrous suspension is brought to the outer chambers and the reactive substance to the inner chamber.

[0031] According to an alternative, in step c),

• at least a first headbox and a second headbox arranged at a dis tance from one another may be used,

• a fibrous layer may be formed by using the first headbox, and a reactive substance-containing layer may be formed on the fibrous layer by using the second headbox. [0032] A two layer heat storage material web having a fibrous layer and a reactive substance-containing layer thereon may be formed on the forming wire or between forming wires in step c).

[0033] As an alternative, a three layer heat storage material web (26) having outer fibrous layers and an inner reactive substance-containing layer may be formed on the forming wire or between forming wires in step c).

[0034] According to a particular embodiment, at least one heat tolerant com ponent may be added to the suspending medium.

[0035] According to this particular embodiment, the heat tolerant component may comprise at least one of aramid fibers, ceramic fibers (such as glass, glass microfiber), silica -or alumina.

[0036] The at least one fibrous component added in step a) may be a heat tolerant component.

[0037] According to an alternative, in step a), at least one organic fibrous component may be added to the at least one fibrous suspension.

[0038] According to this alternative, the organic fibrous component added in step a) to the at least one fibrous suspension may be chosen from at least one of cellulose pulp, highly refined cellulose, m i crof i bri Mated cellulose (MFC), nano cellulose (NFC) and short cut synthetic cellulose, such as lyocell and viscose.

[0039] Steps a) and b) may be performed simultaneously.

[0040] Steps b) and c) may be performed simultaneously.

[0041] Steps b), c) and d) may be performed simultaneously.

[0042] According to a particular embodiment, after step a), the at least one fibrous suspension may be binged to a headbox of the fiber web machine, and in step b) the reactive substance may be added to the at least one fibrous sus pension.

[0043] According to a specific alternative, in step c), the reactive substance may be added inside the headbox or on or between the wire/s of the fiber web machine.

[0044] A heat conductive medium may be provided to or on the heat storage material web. [0045] The heat conductive medium may be provided on the heat storage material web by applying, by means of a coating or printing device, a layer of the heat conductive medium on the heat storage material web.

[0046] As an alternative, the heat conductive medium may be provided on the heat storage material web by means of laminating a web-like support con taining the heat conductive medium on the heat storage material web.

[0047] According to another alternative, the heat conductive medium may be provided on the heat storage material web by means of applying a layer of the heat conductive medium on the heat storage material web by using a web-like heat conductive medium-coated transfer support.

[0048] According to an embodiment, the suspending medium may be re moved from the heat storage material web to be formed by means of foil tables or suction boxes, and suction means.

[0049] The heat storage material web may be wet-pressed after step c).

[0050] The reactive substance added in step b) may be in particle or powder form.

[0051] According to an alternative, the heat storage material web may be dried and calendered after step c) or after wet-pressing.

[0052] According to this alternative, the heat storage material web may be cut into sheets after calendering.

[0053] According to this alternative, the heat storage material web may be reeled after calendering.

[0054] The reactive substance brought into contact with the suspension in step c) may be selected from at least one of the following compounds:

· chlorides, chlorates, perchlorates, bromides, iodides, carbonates and ni trates of lithium, magnesium, calcium, strontium, barium, cobalt, nickel, iron, zinc, manganese, potassium, and aluminum;

• sulphides and hydroxides of calcium, lithium, sodium, and potassium, in cluding both anhydrous and hydrated forms;

• calcium oxides; • anhydrates and hydrates of ammonium zinc or aluminium sulfates or am- moniates; and

• compounds forming a redox system.

[0055] According to a particular embodiment, the first and the second sus- pensions may be produced simultaneously.

[0056] A heat conductive medium may be applied to the at least one fibrous suspension in step a) to provide the heat storage material web with the heat con ductive medium.

[0057] A chemical binder may be added in step a) to the at least one fibrous suspension.

[0058] A chemical binder may be applied on the heat storage material web between the steps of forming of the web and drying of the web.

[0059] According to a particular embodiment, the suspending medium may be a foam or a liquid.

[0060] The fibrous suspensions used for producing the fibrous layers may be either similar or different.

[0061] According to an alternative, the suspending medium with which the reactive substance is mixed may be the same suspending medium by means of which the at least one fibrous component forms a fibrous suspension.

[0062] The present invention further relates to a heat storage material for use in an energy storage system comprising a web formed of:

• a reactive substance for an amount comprising between 50 and 95 wt% of the bone dry weight of the heat storage material web, and

• a fibrous component for an amount comprising between 5 and 50 wt% of the bone dry weight of the heat storage material web.

[0063] According to a particular embodiment, the heat storage material web may further comprise a heat tolerant component for an amount comprised be tween 0,1 wt% and 20 wt%.

[0064] According to this particular embodiment, the heat tolerant component may comprise at least one of inorganic fibers, ceramic fibers, aramid fibers, car bon fibers [0065] The heat storage material web may comprise at least one of cellulose pulp, highly refined cellulose, microfibrillated cellulose (MFC), nanocellulose (NFC), synthetic pulp, binder and short cut synthetic cellulose, such as lyocell and viscose for an amount comprised between 0 and 50 wt%.

[0066] As an alternative or in addition, the heat storage material web may comprise a reactive substance-containing layer provided on top of a fibrous layer.

[0067] The heat storage material web may comprise a central reactive sub- stance-containing layer and two fibrous layers on both sides of the reactive sub- stance-containing layer.

[0068] According to a particular embodiment, the heat storage material web may be provided with a heat conductive medium.

[0069] The exemplary embodiments of the invention presented in this patent ap plication are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as charac teristic of the invention are set forth in particular in the appended claims.

Brief Description of Drawings

[0070] In the following, the present invention will be described with reference to the accompanying embodiments that are described as an illustrative and not a limitative way, and schematic drawings, in which

Figure 1 illustrates schematically the production of a heat storage material web formed of a reactive substance and a fibrous suspension in accordance with a first particular embodiment of the present invention,

Figure 2 illustrates schematically the formation of a three layer heat storage ma terial web formed of a reactive substance and a fibrous suspension in accordance with a second particular embodiment of the present invention,

Figure 2a illustrates schematically the headbox of Figure 2 from above, Figures 3a and 3b illustrate schematically two further alternatives for a headbox for use in the process of the present invention,

Figure 4 illustrates schematically a third particular embodiment of the present invention, a first way of introducing heat conductive medium on the heat storage material web formed in accordance with, for instance, the first or second particu lar embodiments of the present invention,

Figure 5 illustrates schematically a fourth particular embodiment of the present invention, a second way of introducing heat conductive medium on the heat stor age material web formed in accordance with, for instance, the first and second particular embodiments of the present invention, and

Figure 6 illustrates schematically a fifth particular embodiment of the present in vention, a third way of introducing heat conductive medium on the heat storage material web formed in accordance with, for instance, the first and second par ticular embodiments of the present invention.

[0071 ] On these figures, the same elements have the same numeral references.

[0072] Furthermore, the embodiments described here-after are only exemplary ones, some specific technical features of several different embodiments can be combined to offer additional embodiments.

Detailed Description of Drawings

[0073] In the present specification, the terms“reactive substance” have to be interpreted as a substance capable of reacting with a volatile medium (usually water) to generate a heat transfer reaction.

[0074] In the following, heat is stored during an endothermic reaction step (i.e. charging) and release during an exothermic one.

[0075] The present invention proposes the heat storage material web to be formed of a reactive substance and a fibrous suspension such that it is not cre ated by coating or immersion of the base web, but forming directly a fibrous web with a very high reactive substance content. In specialty papers and nonwoven industry there are some existing wet laid lines (including both foam-laying and water-laying ones) capable of forming and dewatering very high basis weight webs as to enable providing webs with high grammage or areal weight, as the liquid, or foam, removal capacity of the forming sections of wet laid lines is supe rior to that of drying sections of wet laid lines.

[0076] In principle, there are two types of headboxes that may be taken in use in the production of the heat storage material web of the present invention. In the first headbox type the water or foam removal may be started already at the head- box by using such a headbox that has no bottom but the furnish delivered to the headbox is laid on a wire or felt. Now that the wire or felt is provided with wa ter/foam removal or dewatering means on the side opposite to the introduced furnish the water or foam removal may be started at the headbox. In the second headbox type the furnish is discharged from a slice lip of the headbox on a wire provided with water/foam removal means on the side opposite to the introduced furnish. The water/foam removal means comprise one or more foil tables or suc tion boxes, sometimes suction rolls, all of which are normally connected to suc- tion means, i.e. vacuum pumps or barometric legs for improving the water/foam removal capacity of the forming section. Naturally the above discussed forming section may be formed of two wires or felts between which the furnish is intro duced. In such a case also the water/foam removal means are provided on both the top and the bottom sides of the wires or felts. The web-forming section may be a Fourdrinier having at least one water/foam removal means below the wire or felt, a twin wire former, a Rotoformer or inclined wire HydroFormer, just to name a few options without any intention to limit the invention to the use of the listed alternatives. By using above described forming sections, in the specialty papers and nonwoven industry, web grammages over 1000 g/m² are feasible. Thereby a web containing the required amount of reactive substance bound in lower amount of fibrous component/s may be produced with such equipment.

[0077] Thus, the present invention proposes the use of a web-like heat storage material structure where high amount of reactive powdered substance is already in the production stage of the web bound to a smaller amount of fibrous compo- nent/s. Existing wet laid processes (water-laid or foam-laid), as described above, designed for higher grammages or area weights, such as used in paper and nonwoven industries, may be used for manufacturing such a heat storage mate rial web. [0078] The wet laid processes provide a solution to the problems related to the traditional coating process. Many existing operating wet laid lines are designed to produce high grammage webs. For instance webs above 1000 g/m² and be yond are not extraordinary in the specialty papers and nonwovens business. Ac- cordingly such machines are equipped to form and dry high heavy weight webs in one single step. With a specifically designed fiber mixture large quantities of reactive substance may be retained evenly distributed in the web structure. The web remains porous and thereby allows for the volatile medium (typically water vapor) relatively open access to the reactive substance. Due to its structure the web remains flexible and reelable even at high grammages.

[0079] At this stage it should be noted that the wet laid process may be provided with a simultaneous multilayer forming, too. An improved retention for the reac tive substance may be achieved either by covering the layer containing the reac tive substance from one side thereof with a relatively thin fibrous surface layer or by enveloping the layer containing the reactive substance between thin fibrous surface layers.

[0080] The foam laid lines have certain unique advantages for manufacturing chemical heat storage material. The foam laid lines may operate, if needed, with higher headbox solid consistencies than conventional water-laid lines. The foam laid lines give better formation. They make it possible to disperse furnish compo nents with different densities. Their use ensures more open structure for the heat storage material end product enabling better access for the water vapor to the reactive substance particles. Furthermore, excellent homogeneity may be ob tained for furnishes containing cellulosic polymer fibers, inorganic fibers, mineral powders and even metallic fibers. The foam laid process generates higher po rosity and superior evenness and formation as compared to the water laid line. Due to better formation potential the foam forming process provides more effi ciently thin fibrous surface layer/s for a multilayer product than the water forming, see for instance Doctoral thesis of Karita Kinnunen-Raudaskoski:“Foam as a carrier phase - a multipurpose technology for industrial applications”, 2017.

[0081] With the foam laid process the dissolution of materials of high solubility may be significantly limited: Foam, by nature, contains less water and the use of foam ensures a very efficient way to disperse solid powders in short time. A pro cess may be designed where the solid powders are introduced to a foam flow going directly to the headbox or the solids are introduced directly to the headbox, see for instance US-B1-6,238,518 and US-B2-7, 416,636 filed by the Applicant. In such a case the drying of the powder takes place within seconds after having been introduced to the process whereby virtually no dissolution may occur.

[0082] The production of a heat storage material of the present invention may be performed by using a wet-laid process, i.e. either so called water-laid process or so called foam-laid process. In a water-laid process the components of the web as well as liquid, usually water, suspending the components are introduced into a headbox as a furnish. According to this particular embodiment, the fibrous com- ponents of the furnish are mixed upstream of the headbox and the reactive sub stance is, for instance, added to the headbox feed pump to be mixed evenly with the fibrous components and liquid. The reactive substance may also be mixed in the furnish by means of a specific mixer in a line between the headbox feed pump and the headbox. Further, the reactive substance may also be introduced directly to the headbox where it, for the first time, gets into contact with the fibrous sus pension just upstream of its introduction onto the wire or between wires. Natu rally, if the reactive substance is a weakly dissolving one or treated by, for in stance, coating with such a coating that prevents the dissolution of the substance the reactive substance may be mixed with the fibrous suspension in a mixing chest upstream of the headbox feed pump. From the headbox a dilute suspen sion or furnish is bled on the wet-forming section, discussed in more detail al ready above as well as in connection with Figure 2, of the fiber web machine, where most of the liquid from the suspension is removed through the wire or the wires by means of water removal or dewatering means, i.e. one or more suction boxes or the like. The water removal means include suction means like for in stance a vacuum pump or a barometric leg. Next the thus formed heat storage material web may, in particular but not necessarily, proceed supported by the wire to a wet-press where most of the remaining liquid is removed from the web. After the (optional) wet-pressing the heat storage material web advances to a drying unit where remaining water is removed by evaporation. The heat storage material web may be dried to desired final humidity. Typically the final humidity content of the web is 0.5 - 8%. However, if conversion steps following the drying so require the drying may be carried out to lesser extent on condition that the cohesion of the web allows. The heat storage material web is, then, taken out of the support of the wire and transferred to a calender, which compacts the web to a desired thickness and porosity. Finally the heat storage material web formed of the reactive substance and at least one fibrous component is rolled to a reel for delivery to a next process phase.

[0083] However, due to advantages of the foam-laid process the particular em bodiment of the present invention is a schematic presentation of the foam laid process shown in Figure 1. It should also be understood that the same schematic presentation is valid also for the water-laid process with the difference that in water-laid process the furnish components are dispersed in liquid, usually water, while in the foam-laid process the furnish components are dispersed in foam.

[0084] Figure 1 illustrates the production of a heat storage material web 26 formed of a reactive substance and at least one fibrous component in accordance with a first particular embodiment of the present invention. The production of the heat storage material web 26 takes place by means of a fiber web machine 10 applying a foam-laid process. The components of the heat storage material web 26 as well as the suspending medium, in this case foam, are introduced into a headbox 12 as a furnish. According to this first particular embodiment, a foaming chemical, i.e. a surfactant is introduced to the dispersing liquid to generate foam into which the furnish components, including one or more fibrous components, are mixed upstream of the headbox 12 to form a fibrous suspension. The reactive substance may be, depending on its solubility, for instance, mixed to the fibrous suspension upstream of the headbox 12, or it may as well be added to the head- box 12 separate from the fibrous suspension as shown by line 14 in Figure 1. Normally the reactive substance is mixed with a suspending medium, in this case foam, just upstream of their introduction into the headbox 12. The foam may also contain other web forming components than the reactive substance, like for in stance organic or inorganic fibrous components or various binders as it is dis closed in more detail here-after, just to name a few alternatives without any in tention of limiting the scope of the invention to the listed options. When added to the headbox 12 the reactive substance may be introduced as an even layer to the full width of the headbox 12. When the layer is introduced at the center, in vertical direction, of the headbox 12 or its slice opening 16 such a three layer product is formed that has layers containing more fibers on both sides of the reactive substance-containing layer. The reactive substance may also be intro duced near the top wall of the headbox 12 whereby a kind of a two layer product is formed. Naturally, the reactive substance may be added also such that it is spread all over the foam in the headbox 12 or its slice opening 16, i.e. it may be fed from several introduction nozzles or openings positioned at different heights in the headbox 12 or its slice opening 16, whereby such a heat storage material web is formed that has relatively even reactive substance concentration all over the cross-section thereof. At or from the headbox 12 the fibrous suspension as well as the reactive substance are bled on the wire 18 of the wet-forming section 20, discussed in more detail already above, of the fiber web machine 10, where most of the foam (i.e. the liquid thereof) from the furnish is removed through the wire by means of one or more dewatering or liquid removal means 22 including a suction means 24, i.e. a vacuum pump or a barometric leg. As discussed al ready earlier there may be foam removal or dewatering means on one or both sides of the heat storage material web 26 to be formed. In a latter case the fibrous suspension and the reactive substance are introduced between the wires of the fiber web machine 10.

[0085] Next the thus, in the forming section of the fiber web machine 10, formed heat storage material web 26 proceeds supported by the wire 18, particularly, but not necessarily, to a wet-press 28 where most of the remaining foam (or rather liquid) is removed from the heat storage material web 26. In other words, de pending on the final porosity target and the drying arrangement of the production line one may choose to use or not to use the wet-press 28. After the optional wet pressing the heat storage material web 26 advances to a drying unit 30 where remaining water is removed by evaporation. The heat storage material web 26 may be dried to a desired final humidity. Typically the final humidity content of the web is comprised between 0.5 and 8%. However, if conversion steps follow ing the drying so require the drying may be carried out to lesser extent on condi tion that the cohesion of the web allows. The heat storage material web 26 is, then, taken out of the support of the wire 18 and transferred to a calender 32, which compacts the heat storage material web 26 to a desired thickness and porosity. Finally the heat storage material web 26 formed of the reactive sub stance and at least one fibrous component is rolled to a reel 34 for delivery to a next process phase. It should be noted, however, that the heat storage material web 26 may be rolled to a reel 34 without calendering and the web compaction may be realized as a separate off-line step by calendering the heat storage ma terial web 26 or pressing sheeted material. The web compaction may also be included in the next process phase.

[0086] In addition to what is explained above and shown in Figure 1 the heat storage material web 26 may be provided with a chemical binder before drying of the heat storage material web 26. The chemical binder may be applied by spraying or curtain applicator, just to name two options without any intention of limiting the invention to the listed alternatives, on the heat storage material web 26. Particularly, but not necessarily the chemical binder application unit is pro vided with a suction box, or another liquid removal means, on the opposite side of the heat storage material web 26 such that excess moisture may be removed from the heat storage material web 26 before drying.

[0087] The foam-laying process described above has a number of advantages, of which some may have already been discussed above. Firstly, the formation of the heat storage material web 26 formed of a reactive substance and a fibrous suspension is better than when using liquid-laid process. The retention of reac tive substance is better, as the speed the foam is removed through the wire is smaller than when removing water, whereby smaller forces withdrawing the re- active substance particles from the fiber network are subjected to the reactive substance particles. The entire short circulation of the fiber web machine 10 is subjected to lower chemical stress as less reactive substance is dissolved in the circulation.

[0088] It is possible to further increase or adjust the reactive substance to fiber ratio depending on the performance criteria of the final heat storage battery or application. With a multi-layer forming option one or more thin protective surface fiber layer/s may be added on one or both sides of the reactive substance-con taining layer in order to improve the retention of the reactive substance. Figures 2 and 2a illustrates schematically, as a second specific embodiment of the pre- sent invention, the manufacture, or rather the formation, of a three layer product. Figure 2a is a horizontal cross section of the headbox 42 between the intermedi ate walls 50 and 52 and seen from above. The forming section of the fiber web machine 10 has two opposite loops of forming wires 38’ and 38”, respectively, equipped with a dewatering equipment 40’ and 40” arranged inside each forming wire loop. A headbox 42 comprises three chambers 44, 46 and 48, i.e. two outer chambers 44 and 48 and an inner chamber 46, the inner chamber 46 being dis posed between the outer chambers 44 and 48. The chambers 44, 46 and 48 are separated by means of intermediate walls 50 and 52 from one another. The in- termediate walls 50 and 52 extend in width direction from one side wall 54 of the headbox 42 to the opposite side wall 56 thereof (see Figure 2a). In the direction of the flow shown by arrows within the headbox 42 the intermediate walls 50 and 52 may be arranged to terminate within the headbox 42 or they may extend, as shown in Figure 2, between the forming wires 38’ and 38”, i.e. up to the area of the dewatering means 40’ and 40”. By adjusting the length the intermediate walls 50, 52 extend from the end wall 58 of the headbox 42 towards the forming section the mixing of the fibrous surface layers to the center layer may be controlled. The longer the intermediate walls 50, 52 extend the more independently the different layers are formed, and vice versa. The center or inner chamber 46 of the headbox 42 is used for introducing the reactive substance into contact with the fibrous suspensions introduced into the outer chambers 44, 48 and to form the center layer at the forming section of the fiber web machine. The outermost chambers 44 and 48 introduce the fibrous suspensions for forming the outer or fibrous sur face layers. The fibrous surface layers may be similar whereby the fibrous sus- pension they are made of may be prepared by common equipment. Naturally, it is possible to make different suspensions for the fibrous surface layers, too, whereby separate equipment for preparing the fibrous suspensions is needed. The center layer needs equipment of its own as the active substance is not in cluded in the fibrous surface layers, and may require specific handling, for in- stance reduced contact time with the suspending medium.

[0089] It should also be understood that there is a possibility of producing a three-layer heat storage material even if the available headbox has a construc tion designed for more than three layers, i.e. the headbox containing more than three chambers. In such a case an option is to use at least the outermost cham- bers for providing the heat storage material web with fibrous surface layers and the inner chambers (one or more) for providing the heat storage material web 26 with the reactive substance. Another option, if there are five or more chambers in the headbox, could be to provide the heat storage material web 26 with outer fibrous surface layers, and one or more additional fibrous layers between two layers formed of the reactive substance.

[0090] Also, if so desired it is possible to use a headbox with only two chambers, i.e. a bottom chamber used for preparing a fibrous bottom layer from a fibrous suspension and a top chamber used for laying the suspension containing the reactive substance onto the fibrous suspension. The headbox used for laying the above mentioned two layers may be, for instance, like one shown in Figure 2 with, however, such a modification that the upper chamber, the fibrous suspen sion inlet therein and the upper intermediate wall 50 are removed.

[0091 ] A two-layer product may also be manufactured by a headbox having more than two chambers. In such a case at least one chamber, for example the bottom one, may be used for producing the fibrous surface layer and the other chambers may be used for producing the reactive substance containing layer.

[0092] In accordance with a variation of the embodiment of Figure 2 the headbox 42, which is shown in horizontal direction in Figure 2, may be arranged in vertical direction, whereby the feed of the layer forming materials take place from above. In such a case the reactive substance may be brought to the headbox 42 by gravity, i.e. without a need to bring such into contact with the suspending medium until when introduced between the outer layers.

[0093] In accordance with yet another variation of the present invention a two layer product may be manufactured as follows and as shown in Figure 3a. First, a bottom layer is formed by means of a first headbox 42’ feeding a suspension suitable for a bottom layer onto a forming wire 38. Second, after the bottom layer is formed to a desired extent the reactive substance is laid, for instance by means of scattering or by means of a second headbox 42” arranged at a distance from the first one, on the bottom layer, whereafter the two layers may be taken, op tionally, to a wet-press, drying and calendering. Naturally, it would also be possi ble to divide the first 42’ or the second 42” headbox by means of an intermediate wall into at least two chambers, as taught in Figure 2, whereby a third layer could be produced.

[0094] If a three layer product is desired, yet another headbox 42”’ may be ar ranged, as is shown in Figure 3b, at a distance from the position where the reac tive substance is laid on the bottom layer from the second headbox 42”, and a top layer is laid on the layer containing the reactive substance. Thereafter the three layers may be taken, optionally, to a wet-press 28, drying 30 and calender ing 32 (shown on figure 1 ).

[0095] According to a further embodiment not represented here, and if the num- ber of headboxes exceed two, or three, depending on what kind of product it is to be produced, two consecutive headboxes may be used to feed the same ma terial, most probably reactive substance onto the web such that a desired product configuration is reached. In other words, the multi-ply forming known before from board machines may be applied in the production of heat storage material webs.

[0096] We have also identified possible means to further increase or decrease the porosity of the formed heat storage material web 26 formed of a reactive substance and a fibrous suspension to optimize the design. For increased poros ity, should that be needed, for providing additional voids, larger bubble size foam may be used or such low density organic furnish components may be added that will easily burn away upon heat treatment.

[0097] The above discussed direct forming of a heat storage material web 26 formed of a reactive substance and at least one fibrous component overcomes a number of problems related to drying, as the liquid removal capacity of the form ing section of a fiber web machine 10 is superior to that of a drying section thereof. The direct forming of a heat storage material web 26 formed of a reactive substance and at least one fibrous component has several other benefits, too. The forming of the heat storage material web 26 formed of a reactive substance and at least one fibrous component takes place in accordance with the present invention in a single production step compared to coating/immersing where the web produced in one step needed to be, thereafter, subjected to a high number of repeated sequences of coating/immersing and drying steps for high enough loading on the web or required the use of soluble or meltable salts. In accordance with the present invention the complete energy storage material, i.e. the heat storage material web 26 formed of a reactive substance and at least one fibrous component, may thus be manufactured in a single step. This is not a necessity. However, with a heat storage material web 26 formed of a reactive substance and at least one fibrous component an adequate reactive substance layer poros ity, a required property of the reactive substance layer to enable accessibility to water vapour, may be easily provided by choosing a proper combination of fi brous component(s), liquid/foam forming process, wet-press, drying and calen dering. Frequently energy storage applications work in high temperatures and the reactive substance-conductivity layers are pre-treated by a pyrolysis step be- fore use. This heat treatment may be used to induce additional voids (porosity) to the web structure by choosing suitable organic fibers or fillers in the fibrous suspension. Also, calendering may conveniently be used in optimizing the den sity - porosity ratio of the heat storage material web 26 formed of a reactive sub stance and the fibrous suspension.

[0098] Performed tests have shown that the fibrous suspension used for sus pending the reactive substance within the heat storage material web 26 needs at least one, more particularly but not necessarily, several components to provide the heat storage material web 26 with required porosity, cohesion, integrity and processability as for example described here-after. A good starting point for the fibrous suspension is that at least one fibrous component is needed to ensure that the heat storage material web has sufficient cohesion and physical stress tolerance while it is produced. According to another frequent requirement, many thermochemical heat storage systems with high reaction enthalpy and energetic density operate at temperatures over 300°C. For instance, chemical energy stor- age based on the reaction Ca(OH)2 + AHr = CaO + FhO (in which AHr corre sponds to the reaction enthalpy of the reaction considered) charging temperature is in the range of 500°C and operating temperature can be as high as 400°C. Other heat storage systems based on carbonate systems or ammonium system may involve charging temperatures over 900°C. Accordingly, a frequent require- ment for a heat storage material containing chemical systems operating at high temperatures must have sufficient cohesion and physical stress tolerance to re main intact when operating continuously in high temperatures. The heat toler ance requirement may be fulfilled by providing the fibrous suspension with a heat tolerant component, which may comprise inorganic fibers like microfiber glass or glass strands or other ceramic fibers, such as alumina or silica, as well as metal fibers. In addition also ceramic binders also ceramic binders such as those pro duced and sold by Aremco Products, Inc., aramid and carbon fibers may be used. [0099] Other high thermostable fibers may be used such as for example fibers based on polyetheretherketones (PEEK), polyethersulfones (PES), polyeth- erimides (PEI), polyamideimide (PAI), polyparaphenylene (PPP). Such fibers could be used for lower-temperature heat storage systems than those disclosed just before, for example a thermochemical reaction can be implemented or other kinds of reactions can be envisioned to enable the charging or the release of the heat into the heat storage system. Performed tests have shown that the amount of heat tolerant component/s is from about 3 to about 20 wt-% of the bone dry weight of the end product, i.e. the heat storage material web.

[00100] To further improve the porosity, cohesion, integrity and processa bility of the end product one or more types of organic fibers may be added to the fibrous suspension. Therefore, the furnish may contain 0 to 10 wt-% cellulose pulp to give the web integrity, for the same purpose also 0 to 10 wt-% short cut synthetic cellulose fibers, such as lyocell and viscose, as such or in fibrillated form may be used, 0 to 10 wt-% nano fibrillated cellulose (NFC), micro fibrillated cellulose (MFC), very highly refined cellulose pulp, synthetic pulp or binder, such as latex binder by beater addition, may be used for binding reactive substance, i.e. for reactive substance retention and improved strength. It should be noted that all percentage values for the weight refer to the bone dry weight of the end product or, for a multilayer structure, to the bone dry weight of the reactive sub stance containing layer. The use of NFC as binder is not absolutely necessary; it may be replaced, in case binder is needed with very highly refined cellulose, which is also an efficient filler binder. All above components of the heat storage material web formed of a reactive substance and a fibrous suspension, except for the reactive substance and the mentioned inorganic furnish components, are of organic material, i.e. combustible, whereby, by combusting the heat storage material, voids are created and the porosity of the heat storage material is in creased considerably. A chemical binder may not only be added to the fibrous suspension or to the suspending medium carrying the reactive substance but it may be applied on the heat storage material web 26 between formation of the web and drying of the web. Such a binder may be chosen from polymeric binders, high temperature binders, ceramic binders and their suitable mixtures.

[00101] The present invention outlines and demonstrates ways to formu late furnish for a high solid reactive substance containing webs. [00102] In addition to the fibrous suspension the furnish of which the end product, i.e. heat storage material web 26, is made, also comprises the reactive substance, which is a solid pulverous or particulate material and has a content of 50 to 95 wt-%, particularly 60 to 95 wt-%, more particularly 70 to 95 wt% of the bone dry weight of the final heat storage material web 26 or, for a multi-layer structure, that of the reactive substance containing layer. To optimize the reactive substance content and convertibility of the heat storage material web 26 while still maintaining a good runnability of the wet laid line upon production, a 70 to 85 wt-% reactive substance content in the final product may be considered as a typical practical target. However, depending on the strength requirements of the final product, lower or higher reactive substance portions may be considered.

[00103] The reactive substance may be selected from at least one of chlo rides, chlorates, perchlorates, bromides, iodides, carbonates and nitrates of lith ium, magnesium, calcium, strontium, barium, cobalt, nickel, iron, zinc, manga- nese, potassium, and aluminum as well as form sulphides and hydroxides of lith ium, sodium, calcium and potassium including both anhydrous and, where exist ing, hydrated forms of the above mentioned substances. Also, calcium oxide and anhydrates and hydrates of ammonium zinc or aluminum sulfates or ammoniates are conceivable as reactive substances. Example of substances include but are not limited to: CaO, CaCI₂, CaBr2, Ca , Ca(OH)2, LiCI, LiBr, Lil, MgCI₂, MgBr2, Mgl₂, Zn(NH₄)₂, Zn(S0₄)₂, ZnCI₂, ZnBr₂, Znl₂, KOH, NaOH, Ca(OH)₂, AICIs, AIBr₂, and AII3. According to another embodiment, the reactive substance may be a compound forming a redox system. According to a non-limiting example, this re active substance can be barium oxide, based on the reaction: 2 Ba0₂ + AHr = 2 BaO + 0₂. According to another non-limiting example, when the reactive sub stance is a compound forming a redox system, this reactive substance may be cobalt tetraoxide, based on the reaction: 2 C03C + AHr = 6 Co + 4 0₂. In both of these examples, AHr corresponds to the reaction enthalpy of the reaction con sidered. It should be understood that the above list is a mere collection of exem- plary substances that may be used as the reactive substance of the present in vention. Thereby the list is by no means limiting the scope of protection to the listed alternatives only. The reactive substance may also be treated to reduce its solubility or totally preventing such from being dissolved. As to the above list of substances, it has to be considered as containing examples of substances used generally in chemical heat storage systems. However, the process of the present invention is especially suited for the use of such substances the solubility of which is not excessive.

[00104] As the objective of the present invention is to add as much solid reactive substance as possible to the heat storage material web, the correct choice of other components for the rest of the furnish becomes a very important part of the web design. Regarding the fiber and additive choices to the fibrous suspension there is a number of options to choose from. However the following aspects must be taken into account.

[00105] Sufficient initial wet web cohesion is required in order to enable web forming: For the wet web cohesion such fibers that enable a high number of mechanical interlocking points may be used. Fine inorganic fibers such as micro glass fibers may be used as a part of the fibrous suspension to improve the initial web cohesion in webs having a very high reactive substance content.

[00106] Sufficient dry strength is required in order to enable handling and converting of the final product: Cellulosic pulp, synthetic cellulose (such as lyocell and/or viscose short cut fibers), synthetic polymer short cut or stable fibers, ther moplastic binder fibers, inorganic reinforcement fibers, i.e. ceramic fibers such as glass, alumina or silica fibers and glass microfibers, may be used. A part of these fibers may need an addition of chemical binders.

[00107] Retention of the reactive solid substance: Appropriate retention may be achieved satisfactorily by a suitable combination of high surface area providing fibers, such as nano-fibrillated cellulose (NFC), microfibrillated-cellu- lose (MFC), very highly refined pulp preparation, fibrillated synthetic cellulose (for instance fibrillated lyocell), polymeric binders, fine thermoplastic binder fibers, and retention improving chemicals that may be provided in the form of a poly meric or natural binder or a fixation agent (such as Polyethylene imine) as an example. Depending on the web design additional surface layers may be formed or co-formed to envelope the solid powder containing layer for improved reten- tion.

[00108] Integrity of the heat treated web: Certain chemical heat storage reactors require functioning in high temperatures. Therefore it may become nec- essary that the web maintains a certain level of integrity so that it tolerates phys ical stress after exposed to high temperatures. To achieve sufficient web integrity for high temperature applications a quantity of inorganic fibers or high tempera ture inorganic binders may be used as a part of the fibrous suspension.

[00109] Porosity: The web needs to remain relatively open as to enable good gas exchange in the final product. Larger fibers, either synthetic or natural may be used to provide higher porosity of the web. It should be noted that organic content in the web may contribute to voids creation and porosity after heat treat ment. In some cases this phenomenon may be used for the benefit of the design.

[00110] For industrial feasibility the web design should still be kept as sim ple as possible.

[0011 1] In the following there are two particular examples of a web con struction (500-700 g/m²) with have shown good performance in a chemical heat storage application.

Example 1

[00112] According to the particular example disclosed here-after, a num ber of single-layer heat storage material webs having a grammage of about 600 g/m² is produced by foam-laying, and calendered to reduce thickness by 20 to 50%. The tested compositions of the heat storage material webs 26 comprise 70 to 80 wt% solid reactive substance, for instance Ca(OH)2 solid powder, 5 to 10 wt% cellulose pulp, 5 to 10 wt% lyocell, 0 to 10 wt% microfiber glass, and 5 to 10 wt% nanofibrillated cellulose. The wt% used refers to the bone dry weight of the single layer heat storage material web, the single layer heat storage material representing 100 wt%.

[00113] According to other embodiments, the grammage of the layer of the heat storage material web can be changed. In order to modify the grammage of such layer, the manufacturing process may be adapted. For example, it is pos sible to have layers of heat storage material web having a grammage less or equal to 300 g/m². According to another example, the grammage of the layer of the heat storage material web may be equal or more than 800 g/m², and more particularly equal or more than 1000 g/m². Furthermore, the upper the grammage of the layer of the heat storage material web is, the easier the optimization of the relative quantity of used product is.

Example 2

[001 14] A three-layer web is produced by foam-laying and calendered to reduce thickness by 20 to 50%. The top and bottom layers are made of 100% NBSK (Nordic Bleached Softwood Kraft, Botnia Nordic Pine (AKI)) pulp and have a grammage or areal weight of 20 g/m². The middle or centre layer is basically the same as in one of the single layer webs of Example 1 , i.e. has a basis or areal weight of 600 g/m² and comprises 75 wt% solid reactive substance, Ca(OH)2 solid powder (Nordkalk SL90T), 7,5 wt% NBSK (Botnia Nordic Pine (AKI) ) pulp, 7,5 wt% lyocell Tencel, 10 mm/1 ,4 dtx), 5 wt% microfiber glass (Lauscha B26R), and 5 wt% microfibrillated cellulose (Borregaard, Exilva P). Ac cording to other embodiments, not further disclosed here, and in view of the de sired properties of the heat storage material web, the relative amount of the sev eral elements disclosed here-above may be adapted.

[001 15] Earlier, it was proposed that both the reactive substance as the heat storage and the heat conductive medium could be coated on a fibrous web. However, as it has been discussed in detail above the coating of reactive sub stance is not possible due to the fact that the high amount of reactive substance needed for giving sufficient heat storage capacity would require such a high amount of liquid that could not be removed from the fibrous web by ordinary dry ing means. Also, due to the high share of the coating in relation to the fibrous suspension results in that the coating is thick, dense and brittle, which means many undesired features as discussed already earlier in this description.

[001 16] However, a layer of heat conductive medium for improving the heat conductibility of the heat storage material web may be provided on the heat storage material web formed of a reactive substance and a fibrous suspension of the present invention. Thus, online coating of the heat conductive medium would be possible on top of the heat storage material web formed of a reactive substance and a fibrous suspension, see Figure 4. Depending on the complexity of the process, the coating of heat conductive medium could also be realized by means of the offline coating or even by laminating a coated web-like support to the heat storage material web formed of a reactive substance and a fiber matrix, see Figure 5. The proposed invention opens also an interesting opportunity to produce the layer of heat conductive medium on the heat storage material web of the present invention even without the paper containing the heat conductive medium. For this solution the layer of heat conductive medium is transferred from a web-like transfer support onto the surface of the heat storage material web and the transfer support carrying the heat conductive medium is stripped off in the process, see Figure 6. The processes described in Figure 5 and Figure 6 enable optimized consolidation (calendering) of the heat conductive layer separately from the reactive substance containing heat storage material web. Naturally, all the various options discussed in Figures 4 - 6 for providing the heat storage ma terial web 26 with a heat conductive medium may be performed off-line, i.e. such that the heat storage material web 26 is rolled and taken to another location for providing the web with the heat conductive medium.

[00117] Figure 4 depicts schematically the production of a heat storage material web 26 formed of a reactive substance and a fiber matrix in accordance with a third particular embodiment of the present invention. Here the production process of the heat storage material web 26 formed of a reactive substance and a fiber matrix is basically the same as shown on Figure 1. The only exception in the third embodiment and in the following two embodiments is that the heat stor age material web formed of a reactive substance and a fiber matrix is not rolled for taking in roll-form to a further process stage, but the introduction of heat con ductive medium into contact with the heat storage material web 26 formed of a reactive substance and a fiber matrix takes place before rolling. In accordance with Figure 4 heat conductive medium is coated by means of a coating or printing device 60 as a dispersion on the heat storage material web 26 formed of a reac tive substance and a fibrous suspension whereafter the heat conductive medium- wetted heat storage material web formed of a reactive substance and a fibrous suspension is dried by means of a drying device 62. The heat conductive me- dium-coated heat storage material web 26 formed of a reactive substance and a fibrous suspension may be calendered after drying with another pair of calender rolls or both the coating (done with the coating or printing device 60) with the heat conductive medium and drying of the heat conductive medium (performed with the drying device 62) may be performed prior to the single calender 32. [00118] Figure 5 depicts schematically the production of a heat storage material web 26 formed of a reactive substance and a fiber matrix in accordance with a fourth particular embodiment of the present invention. Here the production process of the heat storage material web 26 formed of a reactive substance and a fiber matrix is basically the same as shown on Figure 1. The only exception in the fourth embodiment is that the heat storage material web 26 formed of a re active substance and a fibrous suspension is not rolled for taking in roll-form to a further process stage, but the introduction of heat conductive medium into con tact with the heat storage material web formed of a reactive substance and a fibrous suspension takes place before the rolling. In accordance with Figure 5, a web-like heat conductive medium support 64 is unrolled from a roll 66, is then introduced on the heat storage material web 26 formed of a reactive substance and a fibrous suspension and is laminated thereon by means of another pair of calender rolls 68. However, it should also be understood that the web-like heat conductive medium support 64 may be introduced on the web 26 prior to the first pair of calender rolls 32, too. In this embodiment the web-like conductive medium support 64 comprises textile, nonwoven and paper materials.

[00119] Figure 6 depicts schematically the production of a heat storage material web 26 formed of a reactive substance and a fiber matrix in accordance with a fifth particular embodiment of the present invention. Here the production process of the heat storage material web 26 formed of a reactive substance and a fiber matrix is basically the same as shown on Figure 1. The only exception in the fifth embodiment is that the heat storage material web 26 formed of a reactive substance and a fibrous suspension is not rolled for taking in roll-form to a further process stage, but the introduction of heat conductive medium into contact with the heat storage material web 26 formed of a reactive substance and a fibrous suspension takes place before rolling. In accordance with Figure 6 a web-like heat conductive medium-coated transfer support 70 is unrolled from a first roll 72, the heat conductive medium-coated web-like transfer support 70 is intro- duced on the heat storage material web 26 formed of a reactive substance and a fibrous suspension, the heat conductive medium layer from the web-like heat conductive medium-coated transfer support 70 is attached thereon by means of a pair of rolls 74 and the web-like heat conductive medium-coated transfer sup port 70 is again rolled on a second roll 76 for recycling. In this embodiment the web-like heat conductive medium-coated transfer support 70 comprises textile, nonwoven and paper materials.

[00120] With regard to the above three embodiments it would be worth while using a two layer heat storage material web as the web on which the heat conductive medium is provided. In such a case the heat conductive medium is brought as close to the heat storage material as possible. However, also a single layer and three layer heat storage materials have advantages of their own.

[00121] In accordance with a sixth particular embodiment of the present invention the heat conductive medium may also be introduced to the furnish in order to help to extract heat out of the heat storage material, either in the mix chest where the fiber matrix is mixed with the suspending medium, i.e. foam or water, or in the headbox together with the reactive substance or separate there from. In other words, the heat conductive medium may appear in any layer of the heat storage material web.

[00122] The heat conducting medium discussed above may comprise one or more of the following compound: graphite, graphene, graphene oxide and metal powders or fibers such as steel, copper, aluminum, just to name a few alternatives without any intention to limit the invention to the listed alternatives.

[00123] It may also be worthwhile mentioning the use of films, foils mem- branes or scrims laminated, in place of the fibrous top layer, on the heat storage material web. Laminating a thin aluminium (or copper) metal foil onto the web may also be an alternative to be used in place of or in addition to a fibrous layer. Also vapour deposition coatings may be used for metallizing the web if such is desired.

[00124] With regard to the foam discussed earlier in the description there are three optional ways of producing the foam. The first method is to produce the foam in a foam pulper where appropriate foaming chemical is mixed with suitable liquid, most often water, under high shear mixing. As the foam is produced rela tively far away from the position it is used, the foam needs to be stable and, accordingly, a high amount of foaming chemical is needed. The second method is to produce the foam in-line, i.e. as close to its use as possible. In case of the present invention the foam may be produced in the headbox or just upstream thereof. In this method a foaming chemical and an efficient mixer is still needed, but as the foam needs to be less stable the amount of foaming chemical may be reduced. A third method is to produce the foam without the foaming chemical by bubbling such an amount of air at a high speed to the liquid that it behaves like a foam. However, as this kind of foam has no stability at all, the use thereof sets high demands for the headbox and the formation section.

[00125] While the invention has been described herein by way of exam ples in connection with what are, at present, considered to be the most particular embodiments, it is to be understood that the invention is not limited to the dis closed embodiments, but is intended to cover various combinations or modifica- tions of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in con nection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.

Claims

1. A process of producing a heat storage material by means of a fiber web machine (10), characterized by the steps of:

b) bringing a reactive substance in contact with the at least one fibrous suspension,

c) introducing the reactive substance and the at least one fibrous suspension on a forming wire (18) or between forming wires (38’, 38”) of the fiber web machine (10), and d) removing liquid through the wire(s) (18; 38’, 38”) and allowing a heat storage material web (26) to be formed.

2. The process as recited in claim 1 , characterized by in step a) the amount of the at least one fibrous component is comprised between 5 and 50% of the bone dry weight of the heat storage material.

3. The process as recited in any one of the previous claims, characterized by in step b), the amount of the reactive substance is comprised between 50 and 95% of the bone cry weight of the heat storage material.

4. The process as recited in any one of the previous claims , characterized by, in step a) preparing a first and a second fibrous suspension of at least one fibrous component and a suspending medium, the first and the second fibrous suspensions being either similar or different.

5. The process as recited in any one of claims 1 to 3, characterized by, prior to step b), mixing the reactive substance with a suspending medium.

6. The process as recited in any one of the preceding claims, characterized by using a headbox having two separate chambers, the chambers being delim ited by means of an intermediate wall to a first chamber and a second chamber such that, prior to step b), the fibrous suspension is brought to the first chamber and the reactive substance to the second chamber.

7. The process as recited in claim 1 or 5, characterized by using a headbox (42) having three chambers (44, 46, 48), the chambers (44, 46, 48) comprising two outer chambers (44, 48) and an inner chamber (46), said inner chamber (46) being disposed between the outer chambers (44, 48), and the chambers (44, 46, 48) being delimited by means of intermediate walls (50, 52), and, before step b), bringing the at least one fibrous suspension to one outer chamber (44) and the reactive substance to the inner chamber (46) and the other outer chamber (48).

8. The process as recited in claims 4 or 5, characterized by using a head- box (42) having three separate chambers (44, 46, 48), said separate chambers (44, 46, 48) comprising two outer chambers (44, 48) and an inner chamber (46), said inner chamber (46) being disposed between the outer chambers (44, 48), and the separate chambers (44, 46, 48) being delimited by means of intermediate walls (50, 52), and by in step b), the fibrous suspension is brought to the outer chambers (44, 48) and the reactive substance to the inner chamber (46).

9. The process as recited in claim 1 , 2, 3, 4, 5, or 6, characterized by, in step c),

· using at least a first headbox (42’) and a second headbox (42”) arranged at a distance from one another,

• forming a fibrous layer by using the first headbox (42’), and forming a reactive substance-containing layer on the fibrous layer by using the second headbox (42”).

10. The process as recited in claim 6 or 9, characterized by, in step c), form ing, on the forming wire (18) or between forming wires (38’, 38”), a two layer heat storage material web (26) having a fibrous layer and a reactive substance-con taining layer thereon.

11. The process as recited in claim 7, 8 or 9, characterized by, in step c), forming, on the forming wire (18) or between forming wires (38’, 38”), a three layer heat storage material web (26) having outer fibrous layers and an inner reactive substance-containing layer.

12. The process as recited in any one of the preceding claims, characterized by adding at least one heat tolerant component to the suspending medium.

13. The process as recited in claim 12, characterized in that the heat tolerant component comprising at least one of aramid fibers, ceramic fibers (such as glass, glass microfiber), silica -or alumina.

14. The process as recited in any one of the preceding claims 1 - 11 , characterized by the at least one fibrous component added in step a) being a heat tolerant component.

15. The process as recited in any one of the preceding claims, characterized by, in step a), adding at least one organic fibrous component to the at least one fibrous suspension.

16. The process as recited in claim 15, characterized by the organic fibrous component added in step a) to the at least one fibrous suspension being chosen from at least one of cellulose pulp, highly refined cellulose, microfibrillated cellu- lose (MFC), nanocellulose (NFC) and short cut synthetic cellulose, such as lyocell and viscose.

17. The process as recited in any one of the preceding claims, characterized by performing steps a) and b) simultaneously.

18. The process as recited in any one of the preceding claims, characterized by performing steps b) and c) simultaneously.

19. The process as recited in any one of the preceding claims, characterized by performing steps b), c) and d) simultaneously.

20. The process as recited in any one of the preceding claims 1 - 16, characterized by, after step a), bringing the at least one fibrous suspension to a head- box (12) of the fiber web machine (10), and in step b) adding the reactive sub stance to the at least one fibrous suspension.

21. The process as recited in claim 20 taken in combination with claim 5 or 14, characterized by, in step c), the reactive substance is added inside the head- box (12) or on or between the wire/s (18; 38’, 38”) of the fiber web machine.

22. The process as recited in any one of the preceding claims, characterized by providing heat conductive medium to or on the heat storage material web (26).

23. The process as recited in claim 22, characterized by the heat conductive medium being provided on the heat storage material web (26) by applying, by means of a coating or printing device (60), a layer of the heat conductive medium on the heat storage material web (26).

24. The process as recited in claim 22, characterized by the heat conductive medium being provided on the heat storage material web by means of laminating a web-like support (64) containing the heat conductive medium on the heat stor age material web (26).

25. The process as recited in claim 22, characterized by the heat conductive medium being provided on the heat storage material web by means of applying a layer of the heat conductive medium on the heat storage material web (26) by using a web-like heat conductive medium-coated transfer support (70).

26. The process as recited in any one of the preceding claims, characterized by removing the suspending medium from the heat storage material web (26) to be formed by means of foil tables or suction boxes, and suction means.

27. The process as recited in any one of the preceding claims, characterized by the heat storage material web (26) being wet-pressed after step c).

28. The process as recited in any one of the preceding claims, characterized by the reactive substance added in step b) being in particle or powder form.

29. The process as recited in any one of the preceding claims, characterized by the heat storage material web (26) being dried and calendered after step c) or after wet-pressing.

30. The process as recited in claim 29, characterized by the heat storage material web (26) being cut into sheets after calendering.

31. The process as recited in claim 29, characterized by the heat storage material web (26) being reeled after calendering.

32. The process as recited in any one of the preceding claims, characterized by the reactive substance brought into contact with the suspension in step c) being selected from at least one of the following compounds:

• chlorides, chlorates, perchlorates, bromides, iodides, carbonates and ni trates of lithium, magnesium, calcium, strontium, barium, cobalt, nickel, iron, zinc, manganese, potassium, and aluminum;

• sulphides and hydroxides of calcium, lithium, sodium, and potassium, in- eluding both anhydrous and hydrated forms;

• compounds forming a redox system.

33. The process as recited in any one of the preceding claims 4 - 32, char- acterized by the first and the second suspensions being produced simultane ously.

34. The process as recited in any one of the preceding claims, characterized by applying heat conductive medium to the at least one fibrous suspension in step a) to provide the heat storage material web (26) with the heat conductive medium.

35. The process as recited in any one of the preceding claims, characterized by adding chemical binder in step a) to the at least one fibrous suspension.

36. The process as recited in any one of the preceding claims, characterized by applying chemical binder on the heat storage material web (26) between the steps of forming of the web and drying of the web.

37. The process as recited in any one of the preceding claims, characterized by the suspending medium being a foam or a liquid.

38. The process as recited in any one of the preceding claims 9 - 1 1 , characterized by the fibrous suspensions used for producing the fibrous layers being either similar or different.

39. The process as recited in any one of the preceding claims 5 - 38, characterized by the suspending medium with which the reactive substance is mixed being the same suspending medium by means of which the at least one fibrous component forms a fibrous suspension.

40. A heat storage material for use in an energy storage system comprising a web formed of:

• a fibrous component for an amount comprising between 5 and 50 wt% of the bone dry weight of the heat storage material web (26).

41. The heat storage material as recited in claim 40, wherein the heat stor age material web (26) further comprises a heat tolerant component for an amount comprised between 0,1 wt% and 20 wt%.

42. The heat storage material as recited in claim 41 , wherein the heat toler- ant component comprises at least one of inorganic fibers, ceramic fibers, aramid fibers, carbon fibers

43. The heat storage material as recited in any one of claims 40 to 42, wherein the heat storage material web (26) comprises at least one of cellulose pulp, highly refined cellulose, microfibrillated cellulose (MFC), nanocellulose (NFC), synthetic pulp, binder and short cut synthetic cellulose, such as lyocell and viscose for an amount comprised between 0 and 50 wt%.

44. The heat storage material as recited in any one of the preceding claims 40 to 43, wherein the heat storage material web (26) comprises a reactive sub- stance-containing layer provided on top of a fibrous layer.

45. The heat storage material as recited in any one of the preceding claims

40 to 44, wherein the heat storage material web (26) comprises a central reactive substance-containing layer and two fibrous layers on both sides of the reactive substance-containing layer.

46. The heat storage material as recited in any one of the preceding claims 40 to 45, wherein the heat storage material web (26) is provided with a heat conductive medium.