DE694721C - Dehumidification of gases - Google Patents

Description

Dehumidification of gases The invention relates to the use of aqueous solutions of hygroscopic salts necessary for the absorption of water vapor, z. B. in the dehumidification of air or other gases are suitable.

If there is no aqueous solution of a hygroscopic salt for absorption of moisture from a gas is used, the solution becomes during use diluted by the water condensed and absorbed in it, and also its temperature gradually through the absorption of the latent heat of condensation of water vapor and increased by the heat of dilution of the saline solution. Usually it is necessary to cool the solution by artificial means to bring it to a sufficient temperature low point to allow the evacuation of the gas on lines suitable Dew point is effective. Furthermore, the solution must be used after it has been used has been diluted enough to be concentrated again by heating to remove excess Water to evaporate, and the hot, re-concentrated solution must then be added to a lower temperature to be cooled down before going back to dehumidifying the gas can be used.

The effectiveness of a hygroscopic salt for the above purposes depends on its property, in a dissolved state the water vapor pressure of it to depress aqueous solutions to a low value here. The lower the vapor pressure thus attainable at a given temperature, the more effective is the solution for absorbing moisture from a gas.

Salt solutions with a low vapor pressure can also be used for dehumidification are used at higher temperatures and require a lower one in use Cooling to keep them at a suitable working temperature.

It has been proposed to use an aqueous solution of calcium chloride and / or calcium bromide, magnesium chloride, magnesium bromide, lithium chloride or lithium bromide to be used as a dehumidifying solution.

For many purposes, however, it is desirable to have air on a lower level To dehumidify dew point or water vapor in a solution at a higher temperature to absorb, as it can be done with a concentrated lithium bromide solution is.

The present invention consists in the use of a lithium bromide and one or more of the salts lithium chloride, calcium chloride and calcium bromide aqueous solution containing oil in such proportions that the saturated solution the salt mixture has a lower vapor pressure than a saturated lithium bromide solution at the same temperature possesses as a means of absorbing moisture his gas.

The use of a solution as in the present invention used is particularly advantageous because it has a much lower Vapor pressure than previously suggested for use as dehumidifying solutions Has solutions. Such solutions have the advantage of being considerably larger in size To reduce surface contact between the solution and that to be dehumidified Gas is required so that the economy in terms of the size of the required system is guaranteed.

Due to the greater effectiveness of the present invention The solution used can be the volume of air or gas that is in an air freshener if desired, the circulation should be reduced considerably. According to The solution used in the invention has the further advantage that it is in a conventional Dampening system results in less corrosion than either a lithium bromide solution or a solution containing a mixture of calcium bromide and calcium chloride. By the use of the dehumidifying solution according to the invention, it is possible to use water vapor from air and other gases at practical working temperatures without absorbing that the use of cooling devices or similar accelerators is necessary would be to keep temperatures in a suitable working range.

It has been found that mixtures of lithium bromide with a or more of the salts lithium chloride, calcium bromide and calcium chloride in certain Portions of aqueous solutions can be used to dehumidify air and others Gases suitable for temperatures have a lower vapor pressure than a saturated one Lithium bromide solution at the appropriate temperature. Such solutions contain that Lithium cation and the bromine ion mixed with the calcium cation or chlorine anion or both. The effective proportions of cation and anion in the solutions can The easiest way to explain it is by means of the drawing, which is a square diagram or a map showing the proportions of the ions Li, Ca Br, Cl in the solutions as well the proportions of the various salts from which the solutions can be prepared, represents. The map is based on the Jänecke (journal for physical Chemie, Vol. 41, p. 132, and Vol. 71, p. I).

In the illustration, the four corners of the diagram represent the anhydrous Salts calcium chloride, calcium bromide, lithium chloride and lithium bromide, where the common-toned salts at adjacent corners of the square lie. The corner A represents 1 mole of calcium chloride, expressed as CaCl2 (110.99g) dar; B 1 mole of calcium bromide, expressed as CaBr2 (199.9g); C 1 equivalent mole of lithium chloride, expressed as Li2 Cl2 (84.8g) and D 1 molar equivalent of lithium bromide, expressed as Li2Br2 (173.7g).

The following description illustrates the reading procedure of the diagram.

The AB side of the square represents all the molar proportions of calcium chloride and calcium bromide. Similarly, side CD illustrates all of the proportions of lithium chloride and lithium bromide, the side AC all proportions of calcium chloride and lithium chloride and the side BD all proportions of calcium bromide and lithium bromide. It then represents a point on the AB side, e.g. B E chosen for illustration is a Composition of the solute represents 0.3 moles of calcium chloride and 0.7 moles Contains calcium bromide. Similarly, point F on side CD illustrates a solution composition with 0.3 and 0.7 moles of lithium chloride and lithium bromide, respectively. Point E and F illustrate hence two solution compositions, each of which has the ratio of mole equivalents from chlorine (Cl2) to those of bromine (Br2) like 0.3 to 0.7 is and The line connecting the points E and F illustrates in the same way solution compositions, lead, all of which have chlorine and bromine in this same proportion. Generally Expressed, the position of E is relative to B and # A and the position @ of F is relative to D and C in such a way that the sides AB and CD are divided in the ratio of X to I-X, where X 1 is the equivalent mole part of chlorine lead solute and idaber I-X is the equivalent mole part of bromine in the solute.

Similarly, e.g. B. the points G and H, which are a distance of Y from C and D, respectively, where Y is the equivalent mole part of calcium in the solute Bodies is two solution compositions, each of which has the ratio of calcium (Ca) to lithium (Li2) Y is to r-Y. The G and H - connecting line illustrates the composition of dissolved bodies in all of which calcium and lithium are in this same relationship exist. For the particular chosen for illustration Points G and H, this ratio is 0.4 to 0.6. The point P, in which the both lines EF and GH intersect, then illustrates the composition of the solute of solution, 1 the X mole equivalents of chlorine (C12), d. H. 0.3, I-X mole equivalents of bromine (Br2), i.e. 0.7, Y mole equivalents of calcium (Ca), i.e. 0.4, and I-Y molar equivalents of lithium (Li2), i.e. 0.6 l. Thus can all the compositions of the solute bodies represented by the diagram Solution can be determined when the values of X and Y are given.

The composition represented by a point inside the square may in terms of the equivalent molar parts of the various salts in place of the different ions are expressed. To this end, the reference is made to the diagonal lines AD and BC intersecting at Q are expedient. As an illustration can be the composition represented by point P in molar equivalents one of the two groups of three salts at the corners of the triangles ABD and BDC, the include the point in their areas, expressed as CaCl2 0.3 Mol, CaBr2 0.1 mol and Li2Br2 0.6 mol or as CaBr2 0.4 mol, Li2Br2 0.3 mol and Li2Cl2 0.3 mol.

Solution compositions lying on the diagonal line AD can are made from 'the salt pair calcium chloride and lithium bromide, and the on The compositions lying on the line connecting B and C may be reciprocal of them Salt pair calcium bromide and lithium chloride are made because these salts contain the ends of the diagonals. The through point Q, the intersection of the diagonals, The solution composition shown can therefore be given in particulars of one or the other can be expressed as reciprocal salt pairs.

The amount of water in which the dissolved bodies dissolve is up not shown in the diagram. For the sake of convenience, the diagram can look like this be considered as if it represents the composition of solutions as it represents the Composition of the solute or 1 of the salt mixture from which the solutions shows.

In the diagram, the curve lines 11, I2, I3 and I4 are isobars, that are lines drawn from pure point of the compositions of the solved Cores of solutions in a saturated state at 32.2 ° C, being noted became that all points lying on the same curve are essentially the same Have vapor pressure. The saturated solutions, their composition of the dissolved Bodies on which isobar 11 is located have a vapor pressure of 1.8 mm, the solutions on isobaric 12 one of 1.6 mm, on isobaric 13 1.5 mm and on 14 1.3 irin. The vapor pressure of the saturated solutions of the individual salts Ca Cl2, Ca Br2, Li2Br2 and Li2Cl2 at 32.20 C is 8mm, 5.4mm, 2.1mm and 4.1mm, respectively. So became found that certain solution compositions containing the ion equivalents Ca, Li2 and Br2 and in certain cases also contain C12, have a lower vapor pressure have as saturated solutions of the individual salts from which the solutions are made are at the appropriate temperature. In particular, the proportions of the salts were determined the solutions dissolved in water with a lower vapor pressure than give a saturated lithium bromide solution at the same temperature. The compositions the solute in the area between the two isobars II of 1.8 mm and the parts of the end-cut pages of the diagram produce a total of Solutions that have a substantially lower vapor pressure than a saturated one Have lithium bromide solution at the same temperature.

A further examination of the diagram shows that: from a mixture solutions made from calcium bromide and lithium bromide in certain proportions are lower Have vapor pressures as a saturated lithium bromide solution.

If z. B. the proportions of CaBr2 0.12 to 0.76 mol and for Li2Br2, 0.88 to 0.24 moles, the vapor pressure of the solution is 1.8 mm or less Compared to 2.1 mm for a saturated lithium bromide solution 32.2% C. Between 0.40 to 0.72 moles of CaBr2 and 0.60 to 0.28 moles of Li2Br2 is the Solution I vapor pressure, 5 mm or less.

As already stated, certain compositions result in the dissolved Body within the diagram solutions with a lower vapor pressure than ler with a mixture of calcium bromide and lithium bromide even at their best proportions can be achieved that about 0.65 mol CaB½ to 0.35 mol Li2Br2 at 32.20C in saturated Conditions. with the last-mentioned solution having a vapor pressure of 1.4 mm. The preferred proportions of the four ion equivalents Ca, Li2, C12 and Br2 to achieve the lowest vapor pressures are within isobars 14, the vapor pressure of the solutions, their soluble fractions through points 15, 16 iunid I7 within isobars 14 are of particular interest. Their vapor pressures are less than Imm at 32.20 C.

The position of the above-mentioned isobar lines, the points of which, as indicated, Represent compositions of the dissolved bodies, their aqueous solutions in saturation have essentially the same vapor pressure at the same temperature, changes depends on the concentration of the solution, and the latter depends on the temperature. The lines shown in the drawing represent the composition for illustration purposes the solute for solutions saturated at 32.2 ° C, as indicated above became. Similar lines can be drawn for other temperatures.

The present invention also contemplates the use of unsaturated ones Aqueous solutions, the composition of which in the dissolved body is the calcium cations and lithium and the bromine anion with or without the chlorine anion in such proportions has that the vapor pressure of the solutions is lower than a corresponding concentrated solution of lithium bromide at the same temperatures.

Within this range of proportions, certain Unique compositions of the dissolved bodies found, their aqueous solutions the lowest vapor pressure of stable solutions with the four ion equivalents Ca, Li2, Show Br and C12. They are compositions of # dissolved bodies in such a way that in the case of a saturated solution the relative proportions of the four ion equivalents do not change significantly with different crystallization when water is removed therefrom by isothermal evaporation at the saturation temperature. A characteristic of these solutions is that they are in equilibrium with salt crystals three or more solid salt phases are present. According to the drawing are examples the composition of the dissolved bodies of saturated solutions of this type 32.20 C at points 15, I6 and I7 mentioned above. The proportions of the Ion equivalents and the salts from which the solute is made the proportion of water which results in a saturated solution thereof, and their vapor pressures at 32.20 C and 37.80 C are shown in Table 1.

Table I. Composition of the solute in mole equivalents Solution per mole of dissolved body, moles of H20 Vapor pressure Reference expressed in partial molar equivalents of mol- expressed in mm Hg sign of anhydrous salts equivalent in the in solved Sign-part mole equivalents dissolved from triangle ABD from triangle BDC body at temperature 32.2 ° C Ca Li2 Br2 Cl2 CaCl2 CaBr2 Li2Br2 CaBr2 LiBr2 LiCl2 32.2 ° C 37.8 ° C I5 0.65 0.35 o. 80 0.20 0.20 0.45 0.35 0.65 0.15 0.20 3.82 0.97 I, 38 I6 0.64 0.36 0.87 0.13 0.13 0.51 0.36 0.64 o, 23 0.13 3.87 o, g8 1.4 I7 0.60 0.40 0.80 0.20 0.20 0.40 0.40 o.60 0.20 0.20 3.55 0.98 1.4 In the preparation of the solutions used according to the invention, the anhydrous salts, salts containing water of crystallization, or mixtures thereof can be used, and water can be added or removed by evaporation in order to obtain the desired proportion of water.

Ordinary, commercially available pure salts can be used. in the Generally, such salts contain a small amount of impurities resulting from soluble and insoluble salt. The latter are preferably by filtering or Settling away before using the solution. The one to use Water content is based on the solubility of the mixtures of the salts. It was found that the salt mixtures used according to the invention are more soluble than the individual Salts from which the solution can be prepared. This attribute is extremely advantageous because it allows solutions to be made that are not only a relatively low vapor pressure, but also a relatively low one have a low crystallization temperature.

Such mixtures of soluble substances lower the vapor pressure of water so strong that they can be used in more dilute solutions than saturation is equivalent to. So z. B. the salt mixtures, which in the saturated state a condruent Mass result in being dissolved in considerably more water than it was used to produce a saturated solution is necessary, and yet 1 becomes the restrained unsaturated one Solution have a lower vapor pressure than a correspondingly concentrated one Lithium bromide solution.

Such solutions have their advantage that they cool down afterwards a sufficient concentration for re-use, do not deposit solid salts, which would clog the apparatus. The appropriately diluted solutions can at relatively low temperatures, e.g. B. at 4.40 C or below, without Crystallization can be used and thereby have the advantage that a precipitation of salt crystals from the solution does not occur if z. B. the Entteuchtungsvorrichtung is switched off and the solution can cool below the usual working temperature.

The effect of dilution as well as # temperature on the vapor pressure is in the following numbers (Table II) for a composition of the solute Body shown in which X has a value of about o, z and Y has a value of letwa 0.65, so les is point 15 of the diagram. In the table is given or proportion of water to the dissolved bodies, the temperature which salt crystals begin to crystallize out of the solution, i.e. the crystallization temperature and the vapor pressure at different temperatures. The vapor pressure one at 32.20 C saturated lithium bromide solution at corresponding temperatures is for comparison issued.

Table II Vapor pressure in mm Hg at various temperatures O C Mole H2O Crystalline per mol sation released temperature 21.10 26.70 32.20 37.80 43.30 48.90 54.40 600 body 3.82 32.2 # 0.98 1.38 2.0 2.9 4.0 5.5 3.845 26.7 - - 0.68 1.04 1.52 2.2 3.06 4.4 6.2 3.90 21.1 0.50 0.77 1.2 I, 75 2.5 3.55 5, I 7.0 4.07 I7.8 0.86 I, I8 I, 8 2.6 3.8 5.2 7.0 9.8 4.29 I4.4 I, 35 2.0 # 2.85 3.95 5.74 7.88 Io, 8 # # 14.8 4.68 11.7 2.6 3.8 5.4 7.6 10.4 - 14.2 19.2 26.2 Moles H2O 32.2 - - 2.1 3.0 4.1 6.0 8.0 11.3 per mole Li2Br 4.98 Although a number of solute compositions have been given as illustrative examples in which the solutes consist essentially of calcium and lithium combined with bromine or chlorine and bromine, the invention is not limited to the solute compositions according to these figures lungs restricted or limited to the use of the dissolved bodies, which consist exclusively of the specified salts, since the dissolved bodies can contain calcium bromide in four bonds with lithium bromide in the given proportions together with one or more other salts, as stated above, without that one thereby deviates from the invention.

The new solutions according to the invention have various advantages compared to the solutions previously available for gas and air treatment. So has z. B. the solution with a through the point 15- im diagram at saturation at 21.1 ° C, the composition of the solute is the same Provides dehumidification power even at a temperature of 49.40 C like ice at 0 ° C the contact surface of the ice and gas is the same as the lead of the solution.

Furthermore, the solutions can be used at far higher temperatures than before be used to dehumidify air etc. to a much lower dew point, than those available with those that work at lower temperatures Solutions is possible for which additional cooling is necessary. Consequently is a relatively small interface between the improved solutions of the invention and the gas are effective to produce dehumidification. In the Removal of a relatively large amount of moisture is therefore only a relative one small volume of gas required. The solution also does not need to be artificially cooled will.

The above solutions can also be used to advantage when cooling water Find seduction by submitting them to a negative pressure, creating a cooling effect as a result of the resulting partial evaporation. By using a solution as used in the present invention for absorption of the developed water vapor z. B. by directing the evaporation in the presence of the solution, the water can be easily cooled without a relatively large amount of water Having to pump a lot of water vapor. Instead, you can get your steam out of the Water directly to an absorber. chamber flow in which the solution circulated or otherwise brought into contact with the water vapor and then removed, if desired continuously concentrated again and thoroughly atmospheric or air radiation cooled and then to the absorption device for reuse is returned. So water can be relatively deep Temperatures can be cooled without mechanical cooling.

Claims (1)

PATENT CLAIM: Use of a lithium bromide and one or more of the salts lithium chloride, calcium chloride and calcium bromide in such proportions containing aqueous solution that the saturated solution of the salt mixture zeine smaller Has vapor pressure as a saturated lithium bromide solution at the same temperature as a means of absorbing moisture from a gas.