SE507887C2 - Humidity exchanger is mfd. from matrix of corrugated and flat sheets - Google Patents

Abstract

A humidity exchanger medium is made by a method comprising, (i) laminating, impregnating with sodium silicate water glass and partially drying a flat sheet and a corrugated sheet, each comprising paper of inorganic fibres, (ii) forming a honeycomb matrix from at least one sheet, (iii) soaking the matrix in an acid soln. contg. a titanium inorganic salt so as to form a Ti-contg. silicate hydrogel, and (iv) washing and drying the matrix to form a Ti-contg. silicate aerogel.

Description

507 887 use.

Consequently, in order to improve the efficiency of moisture exchangers, it has been desired to enhance the moisture absorption capacity of the airgel while at the same time reducing the energy required to regenerate the gel matrix after dehumidification.

SUMMARY OF THE INVENTION An object of the present invention is to provide a moisture exchanger which has increased absorbency and can be more easily regenerated after use.

One purpose is also to improve the process of manufacturing a moisture exchanger.

The above and other objects are achieved in a moisture exchanger element comprising: (a) a corrugated layer; (b) a planar layer laminated to the contact points on a raised surface of the corrugated layer, each of the corrugated and planar layers being a paper of inorganic fibers; and (c) an absorbent comprising an airgel bonded to the surfaces of each one of said layers and impregnated on the inorganic fibers, which airgel comprises a silicate of titanium or titanium-aluminum.

A moisture exchange medium is formed by a bonded cell structure matrix of wound or stacked layers of the moisture exchange element.

As used herein, the term "partially dried" refers to a laminate having a solids content of water glass between about 45-55% based on a total weight of impregnated water glass. The moisture exchange medium is manufactured by (a) formed by a laminate of (i) a corrugated layer and (ii) a flat layer bonded to contact points on a raised surface of the corrugated layer, which laminate has been impregnated with sodium silicate water glass and then partially dried , each of the corrugated and planar layers being a paper of inorganic fibers: (b) forming a cellular structure matrix of at least one laminate; (c) soaking the cell structure matrix in an acidic solution containing at least one inorganic titanium salt to convert the sodium silicate water glass to a titanium-containing silicate hydrogel; and (d) washing and drying the cell structure matrix to convert the titanium-containing silicate hydrogel to silicate silane hydrogel.

In another aspect, the oesophageal matrix is first soaked in an acidic solution to convert the sodium silicate water glass to a silicate hydrogel and then soaked in a titanium salt bath to form the titanium-containing silicate hydrogel.

In yet another embodiment, the matrix is soaked in an acidic solution of an inorganic titanium salt and an inorganic aluminum salt to form a titanium- and aluminum-containing airgel after washing and drying.

The finished moisture exchanger medium exhibits improved moisture absorption, improved mechanical strength and requires reduced energy to regenerate the moist absorbent matrix.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows in perspective a view of the layers of an element for a moisture exchanger; 507 887 Figure 2 shows in perspective a view of an element for a moisture exchanger formed into a cell structure matrix by spirally winding the element which is composed of a corrugated layer and a flat layer; Figure 3 shows in perspective a view of a moisture exchanger with a rotating type cell structure in which the helically wound element according to Figure 2 is used; and Figure 4 shows in perspective a view of moisture exchangers with cell structure blocks of the parallel flow type.

In the drawings, the same parts are denoted by the same reference numerals in the various views shown.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in Figure 1, an element 10 for a moisture exchanger comprises a flat layer 11 and a corrugated layer 12.

The corrugated layer generally has a corrugation height (or wave height) of about 1 to 2.6 mm, a corrugation length (or pitch length) of about 2.5 to 4.2 mm and a corrugation height / corrugation pitch ratio (or height / pitch ratio) of about 0.2 to 2.0.

The layers are each formed from porous paper made of from about 70-100%, preferably about 90%, heat-resistant inorganic fibers having a fiber diameter of about 3 to 15 microns. Typical heat-resistant fibers include ceramic fibers, slag fibers, carbon fibers and especially glass fibers. In addition, the paper may contain up to about 20% natural or synthetic binders, such as an organic pulp. Preferably less than about 11% pulp is used, such as wood pulp, vegetarian pulp, synthetic pulp or mixtures thereof.

The layers are each generally from about 0.1 to 0.4 507 887 mm, preferably 0.17 to 0.18 mm, in thickness. Each layer typically has a bulk density of usually not more than 100g / m 2, preferably not more than 35g / m 2. The corrugated and planar layers are alternately bonded with an adhesive, preferably partially dried water glass, so that the axes of the corrugated paper 12 adhere to the planar the kraft paper 11 to obtain one-sided corrugated paper 10, as shown in Figures 1 and 2, about 50 to 600 mm wide. As shown in Figure 2, the one-sided corrugated paper 10 is wound around an axis or the like to form a cylindrical cell structure matrix 14, as shown in Figure 3. Alternatively, corrugated paper elements 10 may be stacked to form a block matrix with cell structure curve shown in Figure 4.

It is preferred to impregnate the paper with a sodium silicate water glass as a binder and to use a paper having an organic content of less than about 11%.

The water glass is transformed into a titanium silicate or titanium-aluminum silicate airgel as the active absorbent material for the moisture exchanger.

It is not necessary to heat the cell structure matrix at elevated temperatures (on the order of 400-600 ° C) to remove the organic material (eg binder and / or pulp) before use. By using less than about 10% organic matter in the paper fibers and no organic binders, it is possible to use the cell structure as a moisture exchanger without burning off the remaining organic matter. The moisture exchange medium of the present invention can be regenerated at relatively low temperatures, usually from 60 ° to 175% L using less energy than with typical moisture exchange materials. Due to the low final content of organic substances in the present moisture exchanger material and the low regeneration temperatures, there is no real risk of either self-supporting combustion or excessive smoke formation as is the case with conventional 507 887 moisture exchanger materials.

The impregnated paper is then partially dried to increase the adhesion between the layers and reduce the shrinkage size of the well during the subsequent gel formation and to finally give the structure greater uniformity as a moisture exchanger element.

The cellular structure matrix of layers containing partially dried water glass can be transformed into a highly effective absorbent by soaking the cellular structure in an acidic solution of soluble titanium salts to form a titanium silicate hydrogel which is then washed and dried to form a titanium silica agar.

Alternatively, the cell structure is soaked in an oxygen bath to form a silicon hydrogel. The gel matrix is then soaked in a bath of titanium salts to cause titanium to penetrate into the hydrogel.

The hydrogel is washed and then dried to form an airgel.

Aluminum salts may be present either in the acidic solution of titanium salts or in the bath of titanium salts to incorporate aluminum into the airgel.

The dried titanium silicate aerogel preferably contains from about 1 to 3% titanium, as titanium dioxide, and from 95 to 97% silica. In another embodiment, the airgel is preferably formed from about 1 to 3% titanium, as titanium dioxide, 2 to 5% aluminum, as alumina, and 92 to 96% silica.

The dried cell structure matrix is machined to desired dimensions. A tough coating of melamine, latex, nylon, Teflon®, colloidal silicon, phenolic resins or the like can be applied to the surfaces of the cell structure matrix and cured to effectively increase abrasion resistance and give the structure additional strength. 507 887 7 The presence of titanium in the silicate or aluminosilicate gel matrix has been found to improve moisture absorption and reduce the energy required to regenerate the matrix after use. In general, the moisture absorption of the gel matrix can be increased in the order of up to about 20% by using titanium in the gel. The energy required to regenerate the matrix can also be reduced in the order of 5 to 10% by using titanium in the matrix.

In addition, the introduction of titanium into the matrix serves to increase the mechanical strength of the moisture exchanger. Experiments have shown that the mechanical strength, in the form of compressive strength, can be increased in the order of 38%.

In one embodiment, a moisture exchanger element is made by impregnating paper of substantially inorganic fibers, preferably more than 89% inorganic fibers, and especially fiberglass fibers, continuously with sodium silicate water glass (37.6% solids, 3.22 SiOL / NaqO). The paper can be passed through a water glass bath to impregnate the layers.

The water glass binder has a high chemical affinity for the fiberglass paper and moistens the surface of the composite layers and also the openings between the fibers. If desired, the water glass is transferred to the paper via a pressure roller.

Preferably, the paper is impregnated with water glass to a content of solid particles in the order of 180 g / m2 dry weight (480 g / m2 wet weight). Thereafter, two coated layers are partially dried in a pair of drying tunnels to the desired solids content. A layer is passed through a pair of corrugating rollers with teeth that produce wellers with a height of about 2 mm, a pitch of about 3.3 mm and a height / pitch ratio of about 0.61. The welded layer is attached to the planar layer to form the layer into a composite material. 507 887 A series of corrugated composite layers are stacked to form a block 15 as shown in Figure 4. Alternatively, a corrugated composite layer is wound around an axis in the form of a wheel 14 as shown in Figure 3.

To form the aerogel absorbent from water glass, the composite welded layer structure 14 or 15 is dipped in an oxygen bath containing titanium salts at an elevated temperature. In general, concentrated sulfuric acid and titanium sulfate salts were used to form the acidic bath. The water glass and the acidified titanium salts react to form a titanium silicate hydrogel on the layers. Sodium sulfate, a by-product, excess titanium sulfate and titanium silicate hydrogel not supported by the paper are then removed by washing. By heating and drying the cell structure matrix, its main constituent, a titanium silicate airgel, is obtained.

It has been found that in order to form a satisfactory gel matrix of the water glass impregnated matrix, the temperature of the oxygen bath and the pH of the bath are important interrelated factors which must be considered simultaneously. For the above and other purposes, the temperature of the bath is generally controlled to be from 20 to 60 ° C, preferably from 35 to 45 ° C. Generally, the reaction time is from 20 minutes to 90 minutes. The pH is generally adjusted from about 0.5 to 3, preferably from about 1.5 to 2.5, during the reaction.

During the gelling reaction, the pH of the oxygen bath tends to rise as the acidity is neutralized by the high pH water glass. To maintain a constant pH, additional concentrated acid can be added.

The particular temperature of the bath and the pH of the bath are selected due to the water content of the layers, the desired gel pore size, the gel pore volume distribution and the desired gel matrix strength.

The presence of the concentrated acid causes the pores to form in the gel matrix and causes their distribution. 507 88-7 9 If aluminum salts are used, their presence tends to stabilize the walls of the pores and increase the long-term stability of the gel. Although the literature indicates that the presence of aluminum may increase the efficiency or performance of the gel, this has not been unequivocally demonstrated.

The concentration of titanium salts in the bath can be preferably varied from more than about 1 wt. % to the soluble limit.

It has been found useful to circulate the acidic solution through the gel matrix for at least about 15 minutes by steadily raising and lowering the cell structure matrix from the bath. If desired, the acidic solution can be pumped through the cell structure matrix instead of lifting and lowering the matrix.

Instead of using an oxygen bath, an acidic solution can be circulated through the cell structure. Alternatively, the cell structure can be passed under an acidic waterfall to form the hydrogel.

If desired, the hydrogel can be formed by first dipping the cell structure in concentrated sulfuric acid. Thereafter, the cell structure can be dipped in a titanium sulfate solution to incorporate titanium into the hydrogel.

In general, concentrated sulfuric acid is preferred as the acid.

However, nitric, phosphoric or hydrochloric acid can be used.

Depending on the acid selected, titanium and aluminum sulfates, nitrates, phosphates or chlorides were used to incorporate titanium or titanium and aluminum into the gel.

Aluminum can be incorporated into the gel structure by adding an aluminum salt to the acidified titanium salt bath or by dipping the hydrogel in a solution of titanium and aluminum salts. 507 887 10 The pore size of the gel matrix is selected depending on the particular condition to be met by the moisture exchanger medium. If a uniform pore size is desired, the pH of the oxygen bath is maintained at a constant value. If a variation in pore size is desired, the pH is adjusted accordingly. For example, at a gas inlet side of the moisture exchanger medium, the size of the pores can be tailored to absorb water under cold steam conditions. Larger pores are effective for this purpose. At the outlet side of the moisture exchanger, the size of the pores can be tailored to effectively remove water from a hot and dry environment by designing smaller size pores.

As stated above, the pore size is regulated, in part, by the pH of the oxygen bath as well as by the temperature of the bath. Consequently, by varying the pH of the bath, the pore size can be made larger or smaller as needed. The pore size distribution in the airgel can be adjusted by keeping the pH of the acidic solution from 0.5 to 1.5 on one side of the matrix to obtain smaller pores and by keeping the pH on the other side of the matrix from 1.5 to 3.0. to obtain larger pores.

The maximum concentration of sodium salt formed from the water glasses as a by-product in the acid bath is preferably controlled to allow at least several cell structure matrices to be treated in a single oxygen bath.

After the cell structure matrix has been transformed into a hydrogel, it is washed to remove by-products and excess reagents. Thereafter, the cell structure is dried with air at appropriate flow rates and air temperatures to form an airgel. The temperatures and flow rates used for this purpose are not critical. In general, an air temperature of about 175 ° C and a flow rate of 200 feet per minute are satisfactory.

It has been noted that during gel formation, wave heights can decrease on the order of up to about 15% from about 2,507,887 ll mm to about 1.7 mm. The step of partially drying the coated layers after impregnation with water glass and before gel formation reduces the net amount of this corrugation and gives a more uniform structure to the moisture exchanger element.

The following examples illustrate a preferred embodiment of the present invention but do not limit its scope.

EXAMPLE 1 To illustrate the improved moisture absorption and mechanical strength of an element according to the invention, samples of fiberglass absorbent were formed with a bulk density of 35 g / m 2 and an organic content of <11%. The samples were impregnated with water glass (37.6% solids, 3.22 sioz / Nazo) to 1000 g / m2 tar weight, partially dried to ss wt. % solids, and was reacted with a solution of titanium sulphate, sulfuric acid or aluminum sulphate at a pH of 1.5 for 30 minutes at a bath temperature of 43 ° C. The samples were washed and dried to form a titanium silicate airgel (hereinafter TiGe1).

For comparison purposes, samples of an aluminosilicate airgel (3-5% Al 2 O 3, 95-97% SiO 2) were prepared from an identical water glass impregnated fiberglass which was reacted at 45 ° C at a pH of 1.5 for one hour with aluminum sulfate and sulfuric acid solution. The samples were then washed (hereinafter referred to as SiGel). All samples were then introduced into dehumidifier wheels.

Test wheels of the absorbent (TiGel) according to the invention and of the comparable aluminosilicate absorbent (SiGel) were first regenerated to equilibrium at 220 ° F, 80 g / lb. and exposed to an air stream at standard temperature (20 ° C) and humidity (50% RH) for the same periods of time.

The net weight gain of the samples was measured. Moisture uptake was measured 507 887 12 at 3, 4, 5, 6, 10 and 15 minute intervals. The results are found in Table 1 below: Table 1 TiGel (Invention) (Prior Art) SiGel Sample Volume 24.75 25.97 (cu. In.) Desiccant 12.6 11.1 (ib./cu. Ft.) Minutes Minutes Moisture absorption 3 5.1 3 4.6 (% desiccant wt.) 4 6.6 4 6.0 5 8.0 5 7.2 6 9.3 6 8.5 10 14.2 10 13.3 15 19, 0 15 17.0 Moisture uptake 3 0.62 3 0.51 (ib.H, O / cu.ft.) 4 0.79 4 0.66 5 0.95 5 0.81 6 1.11 6 0.94 1.70 10 1.48 15 2.27 15 1.89 The dehumidifier wheels according to the invention of titanium silicate airgel showed greater moisture absorption than conventional aluminum silicate airgel wheels.

Samples from each absorbent were tested for mechanical strength. The force required to press a corrugated layer flat applied by a piston was measured at five locations on the same sample.

The TiGel samples exhibited a compressive strength of 36 at 4 psi, while the SiGel specimens exhibited a compressive strength of only 26 + 3 psi. The reason for the improved strength of the titanium silicate elements is not clear so far. Other embodiments will be apparent to those skilled in the art. The invention is not limited more than to what appears from the following claims.

Claims (1)

A heat exchanger element comprising: (a) a corrugated layer; (b) a planar layer laminated to contact points on a raised surface of the corrugated layer, each of the corrugated and planar layers being a paper of inorganic fibers, and (c) an absorbent comprising an airgel bonded to the surfaces of each and one of the layers and impregnated on the inorganic fibers, which airgel comprises a silicate of titanium or titanium-aluminum. An element according to claim 1, in which said airgel is a titanium silicate airgel. An element according to claim 1, in which said airgel is a titanium-aluminum silicate. Elements according to claim 1, in which said airgel contains from about 1 to 3% by weight of titanium. An element according to claim 1, in which the paper is a fiberglass paper. Elements according to claim 1, in which each of the corrugated and planar layers has from 0.1 to 0.4 mm thickness. Elements according to claim 1, in which said corrugated layer has a corrugation height between 1 and 2.6 mm, a corrugation pitch between 2.5 and 4.2 mm and a corrugation height and corrugation pitch ratio of 0.2 to 2.0. Moisture exchange medium comprising a cell structure matrix of a wound element or a plurality of stacked elements, each element comprising; 10. ll. 12. 13. 14. 15. 507 887 15 (a) a corrugated or corrugated layer; (b) a planar layer laminated to contact points on a raised surface of the corrugated layer, each of the corrugated and planar layers being a paper of inorganic fibers, and (c) an absorbent comprising an airgel bonded to the surface of each and one of the layers and impregnated on the inorganic fibers, which airgel comprises a silicate of titanium or titanium-aluminum. A moisture exchange medium according to claim 8, in which the airgel is a titanium silicate airgel. Moisture exchange medium according to claim 8, in which the airgel is a titanium-aluminum silicate. A moisture exchange medium according to claim 8, in which the airgel contains from about 1 to 3% by weight of titanium. Moisture exchange medium according to claim 8, in which the paper is a fiberglass paper. Moisture exchange medium according to claim 8, in which each of the corrugated and planar layers is from 0.1 to 0.4 mm in thickness. Moisture exchange medium according to claim 8, in which the corrugated layer has a corrugation height between 1 and 2.6 mm, a corrugation pitch between 2.5 and 4.2 mm and a corrugation height and corrugation pitch ratio of 0.2 to 2.0. A method of making a moisture exchange medium comprising: (a) forming a laminate of (i) a corrugated layer and (ii) a planar layer bonded to contact points on a raised surface of the corrugated layer, which laminate has been impregnated with sodium silicate water glass and then 507 887 16. 17. l8I 19. 20. 21. 16 partially dried, each of the corrugated and planar layers being a paper of inorganic fibers: (b) forming a cellular structure matrix from at least one laminate. (c) soaking the cell structure matrix in an acidic solution comprising at least one inorganic titanium salt to convert the sodium silicate water glass to a titanium-containing silicate hydrogel; and (d) washing and drying the cell structure matrix to convert the titanium-containing silicate silane hydrogel to the titanium-containing silicate hydrogel. The method of claim 15, wherein the cell structure matrix is first soaked in an acidic solution to transform the sodium silicate water glass into a silicate hydrogel and then soaking in a titanium salt bath to form the titanium-containing silicate hydrogel. A method according to claim 15, in which the cell structure matrix is soaked in an acidic solution of an inorganic titanium salt and an inorganic aluminum salt to form, after the washing and drying steps, a titanium- and aluminum-containing silicate aerogel. according to claim 15, in which the acidic solution has a temperature of from 20 ° to 60 ° C. The process according to claim 18, in which the acidic solution has a temperature of from 35 ° to 45 ° C. The process is maintained at 15, in which the acidic solution is about 0.5 to 3. According to claim 1, the pH of The process is maintained according to claim 1, wherein the acidic solution has a pH of 15, about 1.5 to 2.5. A process according to claim 20, wherein the pH is maintained at a constant value to form a moisture exchange medium having uniform pore sizes. The method of claim 20, wherein the pore size distribution in the airgel is varied by pouring the pH of the acidic solution at a value of from about 0.5 to 1.5 on a first side of the cell structure matrix and at a value of from about 1.5 to 3 , 0 on a second side of the cell structure matrix to provide a moisture exchange medium with different pore sizes at opposite sides. The method of claim 15, wherein the matrix is immersed in said acidic solution to convert the water glass to the titanium-containing silicate hydrogel from about 20 to 90 minutes. The method of claim 15, comprising circulating said acidic solution through the matrix for at least about 15 minutes. The method of claim 25, wherein the acidic solution is circulated by raising and lowering the cell structure matrix from a bath containing the acidic solution. A method according to claim 25, in which the acidic solution is circulated by pumping the solution through the cell structure matrix. A method according to claim 15, in which said paper is passed through a water glass bath to impregnate the paper with the water glass.