FR2473489A1 - Recovery of atmospheric moisture - by passing cooled night air through silica adsorbent and desorbing water with hot day time air - Google Patents

Abstract

Process of recovering water from air involves alternate utilisation of the cool night air for cooling and dehumidifying the air by adsorption, and of the warm day-time air for desorption with condensation of the water removed by adsorption from the night air. The improvement comprises passing the night air first through a layer of a substantially non-absorbing material so as to cool the non-adsorbing material, and thereafter through a layer of coarsely grained, shaped slica gel so as to adsorb the moisture content of the night air, conducting the hot day-time air in reverse direction first through the layer of silica gel so as to remove the water adsorbed in the layer of silica gel, and thereafter through the layer of non-absorbing material cooled by the cooler night air so as to condense the water removed from the layer of silica gel on the cooled non-adsorbent material and draining off the condensed water from the non-adsorbent material. The silica gel permits water adsorption within the temp. range of 0-40 degrees C and water desorption within the temp. 30-70 degrees C.

Description

The subject of the present invention is a method and an installation for obtaining water from the air in tropical countries, especially in the subtropical desert zones, by taking advantage alternately of the fact that the air is cool at night for the dehumidify by adsorption and it is very hot during the day to extract, that is to say desorb, the water extracted from the air during the night and stored in an adsorbent. A process of this kind is already known, but it has never been able to be put into practice because there was not an appropriate adsorbent and either the amount of water obtained was much too low, or the expense too much energy was needed.

Furthermore, in total, the investment and operating costs were not acceptable in relation to the result obtained.

The object of the present invention is to create a process and an installation producing themselves, in a manner largely independent of external energy, the energy necessary for operation, and allowing, and at acceptable costs, obtain quantities of water such that it can be used not only as potable water, but also, on a large scale, for irrigation in deserts.

This task is accomplished thanks to numerous measures, the whole of which alone makes it possible to obtain water rationally, and which, therefore, taken as a whole, are an essential element of this invention. The solution to the problem is provided, in particular, by the use of new, formed silica gels, having particular new properties. These silica gels are distinguished by the fact that, because of the large dimensions of their pores, ranging for example up to 60 angstroms, they have a strong power of adsorption of water, for example, in all, 80 | of their own weight, in a range of temperatures from less than 0 to 20, 30 or 400 C. In addition, they have a wide range of temperatures for yielding water at an equally low temperature, namely 30 at 50, 40 to 60 or 50 to 700 C. These two temperature ranges are precisely the temperatures that we have, in the desert zones, for about ten hours for each of the cases, night and day. Because the terrestrial radiation is more important in the desert zones, going up to 90% whereas it reaches up to 50% only in other regions, we often have temperature differences going up to 40 degrees C between day and night.

The present invention also relates to a process for manufacturing these new gels, because they alone make it possible to obtain water in the desert, for the most part, only by taking advantage of the temperature differences between day and night. . To this is added the exploitation of the unevenness of the ground to produce, in places located lower, energy by means of the water obtained on mountains or on uplifts of the ground
This invention starts from the fact that a large quantity of water, in the form of vapor, is permanently in the terrestrial atmosphere. It is constantly subjected to condensation, precipitation and evaporation from the surface of the earth and the sea. This is done in cycles of twelve days each, and there are about thirty a year.

The present invention takes advantage of the fact that the winds always bring a large amount of fresh water to the deserts, so that, even in these renions, there are 10 to 20 g of water in a cubic meter of air, especially at night.

We consider that the invention resides first of all in the fact that, with a process which was mentioned at the beginning of this text, the air is passed, at night, first through stones which it must cool, then through a layer of silica gels formed with large pores, with large grains, in particular spherical and 8 to 12 min in diameter. These gels have an optimal adsorption range between zero and 20, 30 or 400 C and an optimal desorption range ranging from 30 to #oc C. In addition, the very hot air of the day passes, in the reverse region, from first through the now wet layer of silica gel, then through the stones, so that the water taken in by the layer of silica gel overnight is removed from it by the air of the day in the regeneration process and that it condenses on the stones cooled overnight; it is then evacuated.

The advantage of the new spherical gels used here is, on the one hand, that they have a high water adsorption capacity, up to 70% of their own weight, and, on the other hand, that, due to their structure and size, they undergo very little abrasion and therefore have a long service life, so that it is possible to use them for decades. In addition, they only offer a low resistance to the passage of air, so that in the adsorption layer 300 to 400 mm thick, there is only a pressure drop of 1 to 2 mm of water (pressure drop) and that, in total, the pressure drop in the installation does not exceed 3 to 8 mm of water depending on the conditions, the layer of stones having 3 to 5 m of thickness and the diameter of these stones being from 100 to 200 min.

To create the possibility of energy production, this invention provides for the installation of the water supply installation on a mountain or on an uplift. The water obtained and discharged will then be sent to a turbine with an alternator, located at least 200 m below, preferably more, up to 1000 m. Here, we therefore produce, with the resulting strip, the energy used in particular to run the fans, before this water is used for its proper role, which is irrigation or use as drinking or industrial water.

The energy consumption of the installation is particularly low because, according to the present invention, the passage of air through the stones and the layer of silica gel takes place, thanks to numerous low-power fans placed one to cdt8 of the other from the side of the air inlet and the catie of its outlet, in such a way that this air is divided into different currents and that one works with low air passage speeds. This increases the duration of its contact with the surfaces of the spherical gels. These only have a smaller area than the known gels, which are smaller. As the area is decisive for the water exchange, this is compensated by the increase in contact time.

To take advantage of the temperature differences in desert areas, the present invention provides for air to pass, alternately in one direction and in the other, through the stones and the layer of gels, in periods of ten hours each followed two hours of interruption.

There are then, during the humidification of the gels at night, average temperatures of: the outside air of 5 to 150 C and, during their dehumidification during the day, of 30 to 600 C.

It is precisely these low nocturnal temperatures that promote the cleanliness of the gels used here. The lower the adsorption temperature, the more water the gel will adsorb. During the night, the outside air temperature drops and its relative humidity increases; It reaches 70 to 95%, and sometimes even the dew point.

But even the daytime temperatures up to 600 C are sufficient for the dehumidification of the new gel with large pores, because it already reaches 95 to 98% of its desorbing effect at temperatures of 50 to 550 C, that is to say say that it is perfectly suited to the production of water at these temperatures.

As it is near the ground that the outside air temperature drops the lowest, the air is always brought, for the adsorption, from a point located near the ground Preferably, for the adsorption , the air is passed from bottom to top through the stones and the layer of silica gel and, for desorption, from top to bottom. The water which condenses on the cold stones can then flow downwards and be collected and discharged in a simple manner. Due to the drop in the temperature of the outside air during the night, the rise in temperature of the gel of 2.2 degrees C per g of adsorbed water, rise which occurs during this adsorption, is suppressed in a proportion up to about 90%, which also improves the water adsorption capacity.

An additional improvement can be obtained by dividing the layer of silica gel into elementary layers of gels of different pore sizes, so that their optimum absorption temperature increases in the direction of the air flow while the temperature optimal regeneration has decreasing values. Indeed, the air passes, during the day, for regeneration, in the opposite direction through the different elementary layers. In this way, the different kinds of gels have optimal activity at different temperatures. This is obtained, during their manufacture, by varying the pH of the washing liquid and bringing it up to 14. In addition, a very hot washing liquid is used. An gel with even larger pores is obtained. , up to the 60 angstrm range, which has optimal adsorption temperatures up to a little above 200 C and optimal desorption temperatures already starting a little below 25 * C. Therefore, it is already possible to carry out the inversion passing from adsorption to desorption even if the temperature differences between day and night are very small.

The use of extremely large pore gels for the production of water has another advantage, compared to their use for the drying of air or gas, which resides in the fact that, in the production of water, we can go beyond the breakthrough charge for which there are again traces of water vapor in the air which emerges. the silica gel is not yet saturated but can continue to adsorb water until equilibrium fixation is reached. This lengthens the possible duration of the subscription, bringing it to the rhythm of ten hours which we are talking about here
For equilibrium fixation, the partial pressure of the water vapor in the silica gel is equal to its partial pressure in the moving air. relative air to be dried is high. The latter is higher the fresher the air. It is also for this reason that, at night, the introduction of air takes place near the ground.

The use of the new large diameter large pore gels means that, at constant volume, the surface of the gel is smaller. This reduces abrasion and, thus, the risk of dirt. This means that the installation requires little maintenance and that its service life increases.

The installation for producing water extracted from the air will preferably consist of a structure, for example 100 to 200 m in width and up to 15 km in length. In this work, the layer of stones and, above it, the layer of silica gel will be placed on an intermediate floor permeable to air. Air passage openings located next to each other, overlooking the air inlet and outlet spaces under the stones and above the gel layer, are closed by t filters behind which are arranged the fans.

 In this way, the installation is protected from the fine dust of the desert, which is always in the air. For the layer of stones, we could use concrete spheres. As they are still too expensive, basalt or silicate are preferably used, for example flints having a density as high as possible and a porosity as low as possible. Their diameter is from 100 to 250 mm. If the stones are too porous, they can be coated with a thin layer of silicone To benefit more from the sun during regeneration, you can make the cover of the structure, above the layer of silica gel, under the shape of a roof letting through the solar radiation, for example glass, polyacrylic glass or polyester. Thanks to the additional solar radiation which reaches the layer of silica gel, we reach, for an average daytime temperature of the outdoor air of 400 C, & bring the temperature of the regeneration air up to 520 C. This makes it possible to obtain a desorption rate of the silica gel of almost 100%. By modifying the roof, for example by choosing domes or oblique surfaces instead of a shed / material roof allowing solar radiation to pass, the profit obtained from the sun's rays can be further increased. It is also possible to use solar collectors, for example aluminum sheets coated with aluminum oxide to blacken them.

For the roof, it is also possible to use, instead of glass or, in the case of solar collectors, instead of aluminum sheet blackened by anodization, a black polyester fabric coated with PVC on both sides. It is much more resistant to abrasion and it is much more resistant than glass, aluminum or polyester sheets, which are already scratched and made opaque, after a relatively short time, by the sand which is always stunned by the wind. The polyester fabric can be kept stretched by an internal overpressure of about 5 mm of water, as is done for inflatable halls. By inflating and reducing the tension alternately, at the intervals provided for the process, one can easily get rid the fabric of dust and sand. The use of fabric makes it possible to have a lighter load-bearing structure for the roof, constituted by steel or concrete purlins which support the strips of fabric with elastic anchoring and sealing.

To take account of the geological conditions in various regions, the installation can be carried out with ~ similar component elements between which, if necessary, passages are allowed for the movement of personnel and maintenance. But these constituent elements, which are autonomous, can also be installed far from each other, & from different places where water is needed. The costs of producing distribution buckets are therefore low.

As the filters must be cleaned often because of the sand conveyed by the air, and particularly because of the sand winds, it is necessary to provide for this simple mobile brushing devices equipped with rotary brushes which can cover the filtering surface. When they are needed, they can be moved from item to item. To facilitate cleaning, the filters, constituted by strips of filter cloth, can be arranged so as to be able to pivot. Cleaning is then done during breaks during which there is no air passage
As we said at the beginning, an essential foundation of the new water production process is the fact that large-pore gels, having the properties required here, exist and are available in sufficient quantity.

We already contact processes and installations for the production of silica gel from raw materials comprising silicic acid, for example solubilized glass, and hydrochloric or sulfuric acid. Precipitation is caused with an intermediate formation of an unstable soil containing silicic acid, followed by gelling, elimination of the salts by washing and drying the gels. In practice and also in the literature, solutions are used. 13-15% Aids soluble glass, which results in approximately 10% SiC2 sol. It would be desirable to obtain higher concentrations, since these would reduce the costs of spraying water and energy costs and, thus, would make the manufacturing process more profitable. Until now, they have not been able to be obtained in industrial exploitation because there is an absolutely undesirable precipitation of silicic acid or even a premature gelation which paralyzes the functioning of the installations or gives, with the flakes , a lower quality silica gel. In addition, the silica gels produced according to known methods do not have the hardness, and therefore the abrasion resistance, necessary for prolonged use, and
their adsorption power is limited.

This is why one of the aims of the present invention is to make the manufacture of gels more economical while producing dos gels having new and more advantageous properties, giving improved and new employment possibilities.

This invention is based on the fact that it has been found that the precipitation reaction of silicic acid can be avoided if the injection of water glass with a higher proportion of SiO2 than the usual proportion hitherto takes place. with such a rapid stirring effect, with one or more agitators in the precipitating vessel, with such an exit speed and, at the same time, with such a fine division, that the mixing reaction of the raw material. with about 20 8 acid is done in seconds or fractions of a second. In this way, there cannot be a preponderance of the alkaline component (water glass). With the new process, this preponderance can be avoided, for an increased concentration of SiO2, until the pH reaches 1, 8.

Thanks to the process according to this invention, it becomes possible to start, during precipitation, from soluble glasses comprising from 20 to 32 z de sic2 and, thus, giving soils having contents of 14 to 18 t of SiO2, that is to say, they save 40 to 80 t of subsequent water vaporization and energy costs. At the same time, the utilization rate of the production facility is improving to the same extent, and there is a considerable reduction in production costs, including wages.

 Thanks to the transformation of soluble glass with an increased SiO2 # content and thanks to other new features of the process, we obtain, in addition to an increase in hardness and abrasion resistance, and an increase in the power of adsorption, gels with different adsorption and desorption temperatures. These gels therefore have optimal activity at different temperatures, and they thus open up new applications.

This is why this invention also relates to a process for manufacturing silica gel from a raw material comprising silicic acid and an acid, by precipitation, with intermediate formation of an unstable sol comprising silicic acid, followed by gelation, removal of salts by washing and drying of the gel.

According to the invention, the precipitation is carried out in two stages so that, at least in the first stage, until a pH of 1.5 to 1.8 is reached for the initial mixture of acid and raw material, the raw material comprising from 20 to 32 8 of SiO2 is brought so finely divided, for example by spraying by means of nozzles placed at the bottom of the precipitation containers, and under such a high pressure and therefore at a speed of such a large flow, upon arrival in the initial mixture of acid and raw material, or there is constantly stirring at an appropriate speed, that the following results therefrom: a reaction of said acS6e immediately takes place , by avoiding the precipitation of silicic acid in flakes, at the second stage, the proportion of SiO2 in the raw material is lowered to 8 to 14% until a pH of 2.6 to 3.5 is obtained. After that, the soil having 14 to 18% of SiO2 is transferred to a gelling container which can be used at the same time for washing and drying, and the salts are removed before drying by washing with a liquid. washing with a pH between 1.8 and 12.

If we take as a base, during precipitation, a soluble glass containing up to 32% of Si02, we can dilute to the rate of 10 to 12% of H2SO4 the 95% sulfuric acid used for the mixture initial acid and raw material.

However, we take as a base a neighboring soluble glass
20% SiO2, no need to dilute sulfu acid
risk only 20 - 30% H2SO4 to obtain the concentration
high of SiO2 in the soil, up to 18%.

By modifying the pH of the washing liquid for ob
hold gels with different properties, process
which is certainly known, with the use of stepped pH here
much more strongly, we obtain, for example, the qua
gels indicated in the table below. The
abbreviations have the following meanings:
EE: very small pore E: narrow pore
W: with large pores M: with medium pores
WW: medium pore WWX: extremely pore
great.

Type Liquid Size of the Heat of Mass Tempera- Washing temperature for pore volume wetting adure ture
apparent desorptive sorption (pH) (angstroms) (cal / g) (g / cm) (C) tion
( VS)
EE 1.8-2.5 20-25 32-35 720-770 to 100 150-200
E 2.5-3.5 25-30 26-30 680-720 "80 120-150
M 5.0-6.0 30-40 18-22 560-680 "60 80-100
W 7.0-8.0 40-50 15-18 460-520 "40 50-70 WW 8.0-10.0 50-60 12-15 300-460" 30 40-60
WWX 10.0-12.0 60-70 10-12 250-350 "20 30-50
Additional improvement in properties is obtained
based on silica gel, during precipitation,
on a soluble glass having a molecular ratio between
Na20 and Si02 from 1 / 3.5 to 1/5.
of commercially soluble glasses are at most
1 / 3.33, but most often only 1 / 2.1 or less.

So we had to find a new way to produce a
water glass with the desired molecular ratio.

According to the present invention, the precipitation is,
therefore, preceded by treatment of the
raw material, in such a way that
reacting quartz sand with detergent
soda at least 50% takes place at a temperature of 130 to 180D C and under a pressure of 4 to 12 atm off. . This is done with such a proportion that a solution of water glass having a ratio of 1 / 3.5 to 1/5 between Na2O and SiO2 is obtained.

Here, the solution of water glass is obtained without detour by the water glass pieces, which was necessary until now. This is possible by a direct reaction of quartz, in the form of pure sand, with sodium hydroxide, giving Na2SiO3. The reaction takes place in rotary autoclaves in chromium-nickel steel with high resistance to alkaline products, equipped with an internal blade system. Instead of being steam heated as for dissolving water glass into pieces, the autoclave should be heated from the outside, as the initial concentration of soda should be maintained throughout the dissolving process.

The proportion of sand or quartz and lye is a decisive factor, as well as, in particular, the concentration of this lye. For 4 portions of sand, you must have 2 portions of sodium hydroxide solution at 50-60 8 if you want to obtain, for example, a molecular ratio of 1 / 3.8 to 1/4 between Na2H and SiO2. Temperatures of 130 to 1800 C and pressures of 4 to 12 atm off must be maintained for two to four hours.

 During the dissolution process, a mass is formed, the consistency of which ranges from semi-solid to semi-liquid. It loses its pasty form only by dilution with water or, which has proved to be an even better procedure, by dilution with the settling or filtering solutions coming from the mud of the solutions of soluble glass extracted from the autoclaves and to be clarified This gives the concentration necessary for precipitation. It is interesting to know that it has been realized that small amounts of aluminum or magnesium, or both, can cause variations in the quality of the gels, variations which have advantages.

By avoiding the glass melting process and the dissolving of the soluble glass into pieces which follows it, these operations consuming large amounts of heat and energy, in all, almost 70% of the heat and kinetic energy are saved. spent previously and more than 50% of the corresponding investment costs and other production costs. This gives a saving of around 10 Swiss cents per kg of silica gel, or around 200,000 Swiss francs for an annual production of 2,000 t.

To avoid with certainty a precipitation of salicic acid during the following precipitation and in order to obtain a gel of more solid structure, allowing a longer duration of use, the present invention makes it possible to carry out the second stage of the precipitation only up to pH 2.

After that, in a third stage, the proportion of SiO2 in the raw material can between reduced to a value between 5 and 80 until the desired pH is obtained, for example 3.2 in discontinuous operation. In the two axioms and third stages, the addition of raw material can be done, with a lower flow rate, by the same nozzles, or by nozzles of smaller section.

Cooling, necessary in continuous operation, of the initial mixture of acid and raw material to less than 200 C in the precipitation container, to avoid a premature start of gelation and, thus, solidification, can preferably be done by pumping the contents of the container so that it passes through a coolant. The new process achieves precipitation in 20 to 40 minutes, while it takes much longer with already known processes.

If the precipitation takes place in continuous operation, it is possible to dispense with cooling the precipitation container and obtain a significant acceleration of this precipitation if the latter, in accordance with the present invention, takes place continuously in channels mounted one on the other. following each other. The acid-raw material mixture does not remain more than one to three minutes in the first channel, for the first level of precipitation; there are no more than two minutes left in the second channel, for the second level.

With the present invention, it is also possible to reduce the gelation time by carrying out the gelation at the same time as a preliminary drying, for example continuously by passing the soil in a thin layer, and this for example in a belt dryer, preferably several bands.

According to the present invention, an installation is used for carrying out the new method in which a precipitation container is followed by another container divided into two compartments and provided with a valve mounted in an intermediate bottom. The upper compartment is designed as a gelation container, the lower compartment as a washing and drying container. The container can be a round container made of chromium-nickel steel or polyester, its convex upper part being provided with a centered opening having for example 200 to 500 mm in diameter. In the same way as a valve closure, this opening is controlled by a conical tube closed on all sides, provided with a rubber retaining gasket mounted by pressure. The conical tube also serves as a bottom valve for the intermediate bottom, as it enters its centered opening. When the tube is pulled upwards, the opening of the intermediate bottom is cleared and the passage of the gel in the lower compartment of the container can take place. Containers can be from i to 5 m in diameter.

The simultaneous drying in the lower part of the containers provided with an intermediate bottom, starting at about 600 C and with a dry gas comprising at least 80 to 90 8 relative humidity, facilitates the penetration of the temperature as well for gelling as for washing. In addition, for layer thicknesses of 500 to 1,500 minutes, the washing can be done with battery mounting, so that one can obtain sulfate or sodium chloride.
According to this invention, the precipitation container can be made, for continuous operation, under. channel shape & two bearings. As a gelation container, a specially designed band dryer can be used, preferably with several bands. It is fitted with chrome-nickel steel strips provided with plastic transverse and lateral ribs. The soil is poured into the spaces between these ribs, which hold it in place.

The strip drier (s) can be followed by a sinilary tank, that of the discontinuous process, provided with a bottom valve in an intermediate bottom dividing it into two compartments. This tank is used for washing at its upper part and for drying at its lower part. You can also choose a variant with which washing and drying are done in the same container. The continuous process is preferably carried out in the following manner: there is a tank, as far as possible closed, or else open at the top and producing no projections. It is made of a material resistant to corrosion, preferably polyester, its diameter is 300 to 500 mm, its length 366 m, and it is equipped with an agitator shaft with energetic agitator. The agitator channel is slightly inclined. At the upper end, after a first quantity of acid has been poured in at low concentration, a metering pump continuously supplies the acid at the concentration necessary for precipitation. At the same time, nozzles placed on the bottom of the tank inject a solution of high concentration soluble glass, also sent by a dosing pump. This solution has the desired concentration to obtain the desired high concentration in the gel, for example 24% of SiO2. The duration of stay, and therefore reaction, of the soil in the tank must not exceed 20 & 180 seconds.

The pH to be reached during precipitation should not exceed 1.8 to 2. It is preferable to work with pH of 1.2 to 1.5. The mixture (soil) heated by the heat of reaction during precipitation flows continuously, at the lower end of the tank, into a second smaller reaction channel, also inclined Nozzles, also mounted in the bottom, inject a less concentrated solution of soluble glass, comprising approximately 8 to 10% of Six2. This injection is carried out under very high pressure, preferably by means of an autoclave giving an air pressure of 30 atm eff., Or by means of high pressure pumps. This is done until the desired pH, for example between 2.8 and 3, is reached. The reaction in the second channel must take place in such a way that the residence time does not exceed one to two minutes.

Indeed, a few minutes later, the soil, which flows at a high temperature, begins to gel.

The gelling, also continuous, is done in the dryer with several bands. The side ribs and the transverse ribs can be 50 to 100 mm high and come in elastic polyurethane or silicone rubber. When the bands pass over idler rollers having for example 300 mm in diameter, these ribs bend with the band and the solidified gel automatically falls on the next band, or from the last band on a conveyor belt or a chute which brings into the washing container next.

As the washing liquid, hydrochloric or sulfuric acid is used which is suitably diluted. To obtain a tighter structure of the pores, it is advisable to start, as of precipitation, of a molecular weight ratio, between Na2O and SiO2, of 1: 3.5 to 1: 5 possibly, while, until Now, ratios of up to 1: 3.33 were usual. A lower salt content is obtained from the start, which favors the formation of a tight pore gel of high hardness. To obtain large pore gels, it may be advisable to add salts from the precipitation stage, for example salts which form during the subsequent washing process or syneresis (i.e. volume reduction during drying), therefore, for example, sodium chloride or sulphate.

During the manufacture of tight-pore gels, the temperature of the washing liquid can rise up to 600 C during the last washing phase. Its pH, which should normally be maintained at 1.8-2.5, may temporarily drop to 5-7. During the manufacture of large-pore gels, the temperature of the washing liquid can pass in successive stages at 900 C.

It is advisable to carry out drying after washing in the same container so as not to modify the structure of the gel, which is in the form of gelatin. We preferably work for a first drying stage, with air circulation, at around 800 C and with a relative humidity of 70 & 80 5. For the second stage, we preferably work at a temperature of 120 to 1400 vs.

The different adsorption temperatures of the new types of gels allow a new use, for gas drying. According to the present invention, several linings are placed in the stream of gas to be dried, one behind the other, comprising gels having different pore diameters. Their optimal adsorption temperatures are increasing, while their optimal regeneration temperatures are decreasing. For regeneration, the gas is passed through these linings in the opposite direction to that of the gas drying.

By using the different types of gels in several packings placed one behind the other, with the adsorption temperatures indicated in the table on page 11, it is obtained that the drying of the gas can take place for longer than it was possible so far, with optimal gel activity, because the temperature of the gas to be dried increases from pad to pad. Conversely, the temperature of the regeneration gas which is passed through the linings in the reverse order decreases. The expenditure of heat for regeneration therefore also decreases, and the savings achieved reach up to 50% of expenditure on heat and energy. This means that, for desorption, only 750 to 800 kcal are needed instead of 1500.

We therefore have an effect analogous to that obtained with multiple vacuum evaporation.

In accordance with the present invention, we therefore also seek patent protection for new types of gels having pores of different sizes and different adsorption powers and having, compared to already known gels, hardness, resistance to increased abrasion and wear resistance (see table on page 11>.

In summary, the following can be said about the new process: the fact that not only the pore size of the gels, but also their other properties, depend to a large extent on the pH of the washing solutions, is known per se. Despite its importance, it is not so much the variation brought to this fact known by the present invention, which gave the silica gels offering a surprising improvement in their qualities, as the combined action of a whole series of new characteristic features. of the process, such as precipitation at high concentration, the modification of the ratio between the molecular weights, the acceleration of gelling with pre-drying and the practical execution, in terms of process and equipment, of the drying operation with layer thicknesses of 500 to 1,500 mm, which also gives, at the start of drying, the high rates of air saturation with humidity which are important for drying which is gentle on the product. This applies to the formed gel as well as to the untrained gel.

With this new process, we therefore start by forming an unstable soil containing 11 silicic acid, and in which the proportion of SiO 2 is from 14 to 18%. the gel which then forms is brought to SiO 2 contents from 16 to 24 8 by rapid continuous or discontinuous gelation - on band dryers or in round containers according to the embodiment. # Here, only one occurs synereus, but also a pre-drying which, up to these limits, does not yet present any disadvantages due to the higher concentration of salts and, thus, does not present either the risk of rupture, and this same without taking account of the fact that the shift in molecular weight in favor of Si02 practically does not allow this risk to arise. A dryer with several bands in chromium-nickel steel or in normalized rubberized steel of the two cavities, provided with lateral covers of silicone rubber or polyurethane fixedly fixed to the bands but which are elastic, has proved to be ideal as a tool for accelerated, continuous or discontinuous gelation. The ideal height for these covers is 5 to 8 cm. For the simultaneous forming, also in the transverse direction, a system of glued silicone, polyester or polyurethane bands has been produced, the height of which is less than a few millimeters than that of the lateral overlaps, thus ensuring a uniform distribution during the pouring of the soil solution.

The transverse partitions in question provide vertical forming into bars having not only the same thickness, but also the same width, at any desired thickness. The rounded lower corners further facilitate demolding and give an even smoother surface.

When passing over the deflection rollers, the gel bars, which have already undergone a contraction of 10 to 20% depending on the degree of pre-drying, fall on a chute and in a tank containing or not water, or else are brought directly to the washing and drying battery by conveyor belts. To prevent the production of irregular pieces of these bars until the end, transverse ribs mounted inside the tanks can allow the formation of different pieces of gel.

An essential step on the way to obtain hemispheres or pieces in the form of two thirds of spheres can be accomplished by placing on the chrome-nickel steel strips, or directly on a rubber strip (silicone rubber or polyurethane) hemispherical shells or in the form of three quarters of spheres, with a diameter of at least 20 min and from 30 to 35 mm maximum. After the washing and contraction process, the gel is in the form of hemispheres and three-quarters of spheres with a diameter reduced by 20%. After drying, the diameter has decreased by about 80% and is therefore about 12 to 12 mm.

For the three-quarter-sphere shape, demolding when passing over the deflection rollers is made possible, in addition to the contraction of the gel, by the use of projections on the deflection rollers, in the case where rubber bands. These projections allow a certain separation from the upper edge and the exit of the hemispherical or spheroidal product,
Spherical gels can be obtained by adding to each conveyor belt of the multi-band dryer a covering band, preferably offset laterally with respect to the conveyor belt. The conveyor belt has hemispherical cavities from 22 to 25 mm in diameter open, on its upper face, the cover belt has identical cavities, open downwards, on its lower face. The bands are made of rubber or rigid or semi-rigid polyethylene or made of other plastics, for example elastomers which are not attacked by water or by acids. The bands are placed in such a way that the openings of the two bands situated in transverse rows lie one above the other, so that two cavities placed one above the other form a spherical cavity. conveyor belt pos welds lateral guide bands which, on the one hand, hold the ground, and, on the other hand, can also be used to guide the covering band So that the spherical cavities can be filled during the continuous pouring of the ground , the cavities of the cover strip have, at the top, small holes for the air to escape. If necessary, the bands can be held in place by load-bearing bands which absorb the tensile and elongation forces.

The rapid gelation with pre-drying in the belt drier can be controlled in such a way, between 50 and 700 C, that the syneresis (that is to say the contraction of the pieces of gel) begins at the end of the conveyor belt. When the conveyor belt and the cover band separate at the point of return, the gel spheres fall automatically, due to the change in direction of the belts, in water tanks placed at this end of the dryer. From these tanks, they are floated to the following washing and drying devices.

The gel blocks thus formed, the structure of which is not more granulated, have a whole series of advantages compared to the so-called spherical gels, but, reaching dew points of up to -800 ° C., they approach the molecular sieves more than normal and spherical gels do. As regards the adsorption isotherms, these are 10 8 better than those of normal silica gels. They therefore have higher optimal adsorption temperatures and lower theoretical optimal desorption temperatures.

The following steps must be taken to manufacture silica gels with extremely large pore diameters, which are able to fix an amount of water up to 80 3 of their own weight at temperatures from + 20 to less than 0 C, while adsorption begins at temperatures close to 300 C, and which have a desorption yield of 95 to 98 8 from a temperature of 50 to 550 Cl (1) The starting materials of the reaction must have a very high concentration of soil, obtained thanks to a high concentration of sodium silicate and acid. I preferably add 1 to 5% sodium sulfate if sulfuric acid is used for precipitation, and the same percentage of sodium chloride if hydrochloric acid is used.

 (2) The formation of the gel is accelerated by such a simultaneous heating, and the pre-drying of the gels increases. This gel formation with simultaneous pre-drying should be done until the remaining weight is 15% of the wet gel.

(3) Washing is carried out at a pH between 7.0 and 11.0, 141 The temperature of the washing liquid must be at least 150 C and rise to 500.

 (5) By adding iron, magnesium and / or aluminum salts to the washing water, the water adsorption capacity can be further increased. Naturally, such additions should not be made if gels with small pores are made.

(6) The gel is dried by a multi-stage process, in layers up to 1.5 m thick, with an initial temperature not exceeding 600 C and a relative air humidity of at least 80 to 90 8.

Preferably the countercurrent battery system is applied to the drying operation.

A large installation that must produce 100,000 m3, therefore 108 kg of water in 24 hours, needs a base area of twice 10 m2. It is slightly inclined towards one of the sides due to the flow of water, and has side walls 6 n high in reinforced concrete. The total height is 11 m on one side, 8 m on the other side. The base surface can be between 20,000 x 100 m, 15,000 x 135 in or 10 G00 x 200 m. At about 2 m in height, the structure has a reinforced concrete grid, which must receive 8 times 106m3 of stones. This stone lining absorbs, with the concrete masses of the structure which act as heat exchangers , 6 times 1010 kcal for cooling. These calories are needed in the daily cycle for desorption, 108 times 600 kcal.

Depending on the water content of the air during the night, care should be taken to take 7 to 10 times 10 m of air in about 10 hours at night. The weight of the top layer of silica gel should be 15 to 16 times 107 kgp.

The applications and advantages of the present invention appear, for persons having experience in the art, from the accompanying drawings.

We have:
Fig. 1: diagram of the new water production process.

Fig. 2: section of the water production installation.

Fig. 3: section of a silica gel manufacturing container, serving either as a gelling, washing and drying container, or only as a washing and drying container.

Fig. 4: section of a gelling installation for spherical gels.

Fig. 5 and 6: section of a portion of the conveyor belt and of the covering band of the gelling installation of FIG. 4, on a smaller scale.

The operating diagram in FIG. 1 schematically represents the adsorbent layer 2 of the new process, for example silica gel, the regenerative heat exchanger 1 made of non-adsorbent material, for example stone, the fans 3 and a collector 4 of solar rays. The arrows on the left represent the flow of fresh night air, entering at the temperature of 50 C and leaving at 80 C.

The arrows on the right represent the passage of the hot air of the day, which enters at 450 C and leaves at 100 C. Thus, at night, the air sucked close to the ground passes, under the action of the fans 3, through the lining of stones 1, then through to the layer of silica gel 2. The stones are therefore cooled and the silica gel collects. humidity.

During the day, hot air is passed from above, first through the layer of silica gel 2, where it is charged with moisture. Then, this air is sucked through the layer of stones 2, on which the water in the air condenses.

It flows through the outlet pipe 5.

Figure 2 shows the installation with side walls, for example 6 meters high on one side and 8 meters on the other side. The bottom 18 of the installation is made in the form of a flat tank, so that the water which collects therein can be evacuated by the drain pipe 16. The installation is carried out according to the diagram of the Figure 1. The packing Se stones 15 rests on a concrete grid 9, the layer of silica gel 14 rests on a grid 10 located above. The fans 7 and 19 pass the air alternately in one direction and in the other, as the arrows show, through the layer of silica gel 14 and the lining of stones 15, and this at the rate of ten hours which has been described. Filters 8 and 13 are placed in front of the fans 7 and 19. The roof consists of a collector of solar rays 17, exposed to said rays, represented here by the arrows 11.

The container 51 of Figure 1 is divided into two separate compartments 63 and 64 by the partition 52. In the upper compartment, there is a valve for pipe 53, which forms the openings 65 and 70 made in the middle of the intermediate bottom 52 and from above. If this container is used for gelation, washing and drying, the soil 54 is located above the intermediate bottom 52, the gel 55 is located in the lower compartment. If the container is used for washing and drying, gel is placed in the upper compartment 63, or it is washed. Then it is passed into the lower compartment 64 to dry it.

The gelification installation 56 of FIGS. 4 to 6 has a conveyor belt 57 and a cover band 58 which moves over it. These two strips have cavities 61 and 62 in the form of hemispherical shells which, when the strips move, are one above the other, so that, between the shells 61 open towards the bottom of the covering strip 58 and the shells 62 open towards the top of the conveyor belt 57, spherical cavities are obtained in which the soil is introduced through the channel 59. So that the soil can penetrate into the shells from the top, these have holes 69 for air exhaust. In addition, as shown in Figure 6, the conveyor belt 57 has partitions 67 so that the shells 61 and 62 placed one above the other and constituting spheres can be filled to the top.

If water overflows from the conveyor belt, it is discharged through an opening 65 (fig. 4). To combine the gelation with a pre-drying, hot air is introduced at around 55 to 600 ° C. in the zone 66 of FIG. 4. A tube 70 leads the gel from the gelation container 56 to the dryer.

Claims (15)

1. Process for the manufacture of silica gels from a  raw material containing silicic acid (for  example of water glass) and an acid, (e.g.  1 sulfuric or hydrochloric acid), by precipitation  with intermediate formation of an unstable soil comprising silicic acid, followed by gelation,  salt mining by washing and gel drying, pro  yielded characterized by the fact that the precipitation takes place in two steps so that at least the first level until a fold of the mixture is reached  starting acid-raw material between 1.5 and 1.8, the raw material, with a proportion of SiO2 included between 20 and 32 Z, either brought into the acid-matter mixture  first if finely divided (pulverized) and with a arrival speed so high, said mixture being perma stirred at an appropriate speed, if it occurs  immediately a reaction between the acid and the material first while avoiding precipitation of silicic acid  and that, at the second level, the proportion of SiO2 in the  raw material is lowered to a value between  8 and 14%, until a pH of 2.6 to 3.5 is reached,  after which the soil is transferred to a container of gelatin cation which can be at the same time the washing container and  drying. 2. Method according to claim 1, characterized in that that the precipitation is preceded by a treatment of the raw material so that a sand reaction of  quartz with at least 50% sodium hydroxide solution takes place at  a temperature between 130 and 1800C and under pressure  between 4 and 12 atm eff., with a proportion such that  a solution of soluble glass is formed, comprising NaO2 and  Si02 in ratios ranging from 1: 3.5 to 1: 5. 3. Method according to claim 1 or 2, characterized in that the second level of precipitation ## is exe cut only up to pH 2 and then in a troi  fifth step, the proportion of Si02 in the pre matter  mine is reduced to a value between 5 and 8%. 4. Method according to one of claims 1 to 3, characterized by the fact that the precipitation is done in a discon way kept in a container, the temperature of the contents of this  container being kept below 200C by pumping  passing it through a refrigerant.  second chute, for the second level. not exceeding three minutes, and two minutes in the  first chute, for this first level of precipitation,  of the mixture of acid and soluble glass in the in chutes mounted one behind the other, time by the fact that the precipitation is done continuously  5. Method according to one of claims 1 to 3, characterized 6. Method according to one of claims-l to 5, characterized by the fact that the gelling following the precipitation  takes place at the same time as drying, for example continuously, by passing the soil in a thin layer in a belt dryer. 7. Method according to one of claims 1 to 6, characterized  by the fact that washing after gelation so removing salts is done with a washing liquid of which  the pH is stepped between 1.8 and 12, so that we obtain  gels with pores of different sizes depending on the gels and different properties. 8. Installation for manufacturing silica gel according to the process  from one of claims 1 to 7, by precipitation followed gelling, washing and drying, characterized by the fact that the precipitation container is followed by a container divided into two compartments by an interior bottom with a bottom valve, the upper compartment  laughing serving as a gelling container, the compartment  washing and drying container bottom. 9. Installation according to claim 8, characterized by the  that the precipitation container, made under the  shape of a two-stage chute is followed by a  strips acting as a gelling container and equipped a chrome-nickel steel strip provided with ribs lateral and transverse plastic, this dryer  being itself followed by a container provided with a valve  from bottom to bottom 'intermediate, and divided into two compar  timents, the top one being the washing container, the one  from the bottom the dryer. 10. Installation according to claim 8, characterized by the fact that the belt of the belt dryer has such a surface  that the gelling product is preformed, receiving so the shape of a sphere or whatever. 11. Installation according to claim 9 or 10, characterized  by the fact that each conveyor belt has a corresponding  cover strip, that the two strips are rubber  plastic or plastic and the conveyor belt  has hemispherical cavities on its upper surface open upwards, the cover strip having the same cavities on its underside, open downwards,  these cavities preferably having a diameter of 22 to 25 mm,  where appropriate from 15 to 28 mm. 12. Method according to one of claims 1 to 6 characterized by the fact that the initial mixture of raw material and acid is added sodium sulfate if the  precipitation takes place with B2S04, and sodium chloride  if the precipitation is done with 1phi1, this addition  being from 1 to 5%. 13. Method according to one of claims 1 to 6, characterized by the fact that the elimination of the salts by washing is done with a washing liquid having an initial temperature  of 150C, which goes up to 50 C.  14. Method according to one of claims 1 to 6, characterized by  the fact that, to make gels with large pores, therefore for a washing liquid having a pH between 7 and 12, a washing liquid containing iron, magnesium is used  or aluminum. 15. Silica gels with pores of different sizes and  different adsorption powers and presenting, compared with known gels, greater hardness, greater  abrasion resistance and greater resistance to  wear, insofar as they are manufactured according to the process claimed above.