AT512271A2 - Process for the preparation of porous grains of water glass - Google Patents

Abstract

The invention relates to a process for the preparation of porous grains of water glass by drying dried particles of water glass by a heating process following melting and evaporation of trapped water. In the optimal procedure, a single particle is formed by hardening a single mass drop; In the heating step leading to foaming, the particles and the porous grains formed therefrom are heated by microwave radiation while at the same time being held above a fluidized bed and moved.

Description

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description

The invention relates to a method for producing porous grains of water glass.

For example, WO 2008010074 A2 describes the production of porous grains by foaming previously compact particles in a two-stage heating process. The particles consist of a material which becomes viscous at high temperature and in which a component which becomes gaseous at elevated temperature is enclosed. In the first heating process, the particles are only heated so much that the entrapped, gaseous component at elevated temperature partially volatilizes and only remains to a desired, reduced extent. In the second, hotter heating stage, the particles are heated to soften their solid material and to be foamed by the remainder of the gaseous component. The second heating stage takes place in a shaft furnace, in the shaft of which the particles are introduced at the top and are heated and blown down during the fall through the shaft. The method is widely used in practice and it can thus produce high quality products. Based on the plant costs and the installation space requirement, the yield of manufactured products per time is often perceived as low.

EP 1 033 354 B1 describes a production route for a mineral foam-like material. A liquid o-kneadable material, which in any case contains water glass (= alkali metal silicate) and / or ammonium silicate and water, water is removed in a drying step until only a desired residual water content is included. For a foaming stage, the material is introduced into a mold and heated to the extent that solid fractions melt and by the existing residual water, which evaporates, are bloated. After cooling it is

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HW-5 »* · · · · · · · the mass into a highly porous rigid body, such as a plate, solidifies. Microwaves as heating source can be used both in the drying stage, which preferably takes place at temperatures just below 100 ° C, as well as in the foaming stage, which then takes place at temperatures between 100 ° C and 250 ° C. The material thus formed is light and good heat insulating. With good heat insulating effect, however, the substance has very little mechanical stability. Often it is also annoying that the material can absorb and store a great deal of water. That the process of foaming whole components are made instead of a bulk material, which is used as a building material, while often an advantage, but also brings the disadvantage that flexibility is lost.

Based on this state of the art, the inventor has set itself the task of providing a production method for a bulk material of grains of a mineral material, in which the individual grains are highly porous inside and thus specifically very light and good heat insulating, but on the other hand as solid as possible and having a liquid-tight surface layer. Compared with the production process according to WO 2008010074 A2, a higher yield per time should be made possible in relation to the costs and space requirements of the required plants.

According to the invention, the object is achieved in an optimal manner by a process according to the following steps: a) solidifying a mixture containing water, liquid water glass and a hardener for water glass in such a way that even when solidifying individual, separate particles are formed. b) removing water from the particles by drying the particles, for example by heating and keeping the particles warm

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• * * * * • • • • • • • • HW-5 • · ·· kel until only the desired residual water content is contained. c) cooling the partially dewatered particles. d) foaming the particles into porous grains by heat while simultaneously moving the particles or granules on a fluidized bed and heating them by microwave radiation so that the mineral material softens and is inflated by contained, evaporating water. e) cooling the porous grains formed by puffing of particles

The invention combines several effects, which are certainly also advantageous in each case alone, so that an extremely advantageous overall result is achieved. The most valuable new single effect is likely to be microwave frothing while moving the particles on a fluidized bed. By this measure, the yield of foamed grains per time and system volume is drastically increased compared to other methods with good quality of the product obtained.

The following explains each of the listed steps:

Step a) " solidification and particle formation "

By forming the individual particles from which the grains are later to be puffed up, not by breaking a larger solid into smaller pieces, but by solidifying a liquid or mushy "drop of mass" whose mass equals the mass of the mass to be formed Particles, the quality of the surface of the finished grains {solid, dense) is improved and the shape of the grains is less jagged and rather ball-like, which is also an advantage in general.

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Preferably, the hardening of a mass drop to a particle takes place while the mass drop is surrounded only by air and does not abut any solid surface. For this you can spray the mass at the appropriate moment during its hardening or press through a sieve and let it fall freely under the sieve. Ideally, the spraying of the mass or the pressing through a sieve is controlled in such a way that the individual drops of mass have the same size and the most similar shape as possible.

The spraying can for example be done by allowing the mass to flow to an adjustable fast rotating disc, from which the mass is thrown by centrifugal force. About the rotational speed of the disc, the size of the resulting particles is controllable. With faster rotation, the thrown-away drops and thus the resulting particles are smaller.

A very quick method of mass to small " drops " to singulate is to place them in recesses of a band of silicone or PTFE and push them out after hardening, for example by bending the band around a tight roller. Of course, instead of a band, one could also use a rigid body with many local depressions, from which the mass particles are moved out after they have solidified, for example by shaking them.

Step b) " Dry "

The removal of water from the solidified, not yet foamed particles is typically carried out at temperatures around 130 ° C. In addition to many other suitable devices probably a fluidized bed furnace is very well suited because with this comparatively a very high material throughput is possible and the enforced material mechanically hardly loaded. The comparatively high level of

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The material throughput is achieved primarily by the fact that in the fluidized bed furnace the particles to be treated are constantly exposed to air or gas be flowed through, so that water, which escapes from the particles escaped promptly and thus the water vapor content in the environment of the particles is kept far below the saturation content. As a result, the drying of the individual particles takes place particularly quickly.

In order to ensure consistently high quality of the final product, it is important to dry only those particles which have approximately the same size and shape, since otherwise the residual water content in the various particles is too different.

The aim of this step is to set a suitable residual water content in the particles for the subsequent foaming process. In fact, one will rather not measure the residual water content of the dried particles, but find empirical values for which particle sizes and materials at which drying times and temperatures, which maximum reduction of specific gravity by inflation under heat is possible.

The drying can also be carried out at ambient temperature, for example at 20 ° C. With good ventilation with low humidity air (less than 50%), the drying process typically takes about three days.

Step c) " Cool off in between "

Surprisingly, the surface area of the foamed grains is substantially better, namely, when the particles that are foamed into the grains are allowed to cool to normal ambient temperature after a drying process of elevated temperature in step b) than if they are further heated immediately for foaming. It appears that during the cooling of the particles at their near-surface layers to advantageous changes

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| REPLACED «· HW-5 material changes. These changes cause the grains formed from the particles by foaming according to the following step d) to become almost spherical and have a closed surface, almost independently of the original shape of the particles.

It appears that the surface of the particles has openings immediately after the drying process and that these openings close during the cooling process. When a dried particle is inflated by the action of heat without having previously cooled and thus having reached a closed surface layer, a significant proportion of the evaporating crystal water still remaining in the particles escapes from these openings. The particle is then foamed only in individual volume areas and it forms a shapeless fissured grain with uneven, but on average relatively high density.

If said openings of the particles are closed before foaming, there is a more uniform expansion of the volume and the dense outer skin of the particle spans like the envelope of a balloon around the forming of evaporating water of crystallization water vapor and the doughy crystalline material. So this explains why the shape of the grains is always approximately spherical regardless of the shape of the original particles.

Step d) " Inflate by heat "

Microwave heating for the foaming of the particles to grains with highly porous volume is advantageous over other heating methods, because it foaming takes place particularly quickly and because the warming inside the grain hardly hides the heating on the outer skin.

A " fluidized bed " For the purpose of this description, like the fluidized bed known from fluid bed furnaces, one with many solutions

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· • e e,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, At the top of the bottom surface are the foaming particles or the already foamed grains; they are raised slightly by the air blown up from the bottom surface and whirling confused.

Preferably, the bottom surface is slightly inclined, so that the overlying, slightly raised by the air flow Good slowly floats to the lower surface areas. By adding new material to the top and taking out the material below, this makes good continuous operation possible. Optionally, the bottom surface can also be moved in the manner of a vibrating conveyor to transport the particles or the foamed grains in the desired direction.

Among other advantageous effects, the blown-through air or the blown-through gas causes the temperature profile in the individual particles or grains to be smoothed over time and that all particles or the grains which form from them undergo the same temperature profile as far as possible. At the beginning of the treatment in the fluidized bed furnace, the blown-through air or the blown-through gas causes heating of the particles in addition to the microwave heating. Later, heat is also dissipated by the particles or grains, which was introduced to them by microwave heating.

In addition to the effects already described, the fluidized bed has the following further advantageous effects; - Grains do not stick together even if they touch each other in a doughy soft state. - Water, which comes to the surface of the grains, is transported away quickly by the air or gas flow. This has an advantageous effect on the distribution of the Wärmeein page 7

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♦ carry out the microwave radiation in the grains. This desired effect is significantly enhanced when the flowing medium (air or gas) is dried or constantly replaced by dry medium. (For example, you can replace used, hot, humid air with fresh air and heat the fresh air in a Gegenstromwärmetäuscher through the used air.) - Due to the fluidized bed without disturbing side effects, the number of foaming particles or grains per volume compared to other systems for the heat-induced foaming of particles or grains are greatly increased. - Due to the fluidized bed, the required heat input into the particles or grains to inflate them without much annoying side effects can be done much faster than would other systems for the heat-related foaming of particles or grains, for example, shaft furnaces, would be possible.

In an advantageous embodiment, the surface is formed by a heat-resistant, for example ceramic textile. This is a particularly fine grid of openings through which air or gas can flow, bildbar and it can also be very fine particles can be lifted in a fluidized bed without accumulating between openings of the fluidized bed at the surface of the fluidized bed.

Step e) During cooling, the bloated grains solidify. Cooling can be done, for example, by dropping the grains through the air over a short height distance at normal ambient temperature. It is particularly advantageous to guide the foamed grains over a surface area of the fluidized bed, at which no microwave radiation is more

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occurs and at which the air flowing through the surface of the fluidized bed (or gas) is at least a few degrees cooler than the solidification temperature of the grains. &Quot; water glass " For the purposes of this description are amorphous sodium and potassium silicates and their aqueous solutions.

From the prior art, a variety of Hartem and additives to these for water glass is known. As hardeners, metal phosphates, in particular aluminum phosphates, as well as organic acids and their esters, in particular carboxylic acid esters, acetic acid and their esters, are likely to be the most widespread. The advantages and disadvantages of these hardeners (dynamic process of hardening, chemical resistance of the final product, final strength) as well as meaningful mixing ratios are known to those working with water glass experts, so here only - further down - exemplified. Incidentally, many material compositions and suitable process parameters such as drying temperatures, drying times, heating rates, etc., which are also strongly dependent on the particle size, can and must be optimized by trial and error in the context of expert action on the respective systems used.

The liquid or pasty mass to be hardened to solid water glass according to step a) above can, in addition to water glass, water and hardener, also fillers, such as e.g. Quartz sand, glass dust, fly ash, volcanic dust (Pechstein, Perlite, Obsidian, Vermiculite). Such especially mineral, glassy or ceramic admixtures can facilitate the processability and also increase the strength. With the exception of volcanic dust, they also often increase volume weight and thermal conductivity.

Of particular importance are fillers made from dust of heat-inflatable volcanic rocks such as pitchstone, perlite, obsidian or vermiculite. These materials have a high silicate content and contain water of crystallization. If they

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FALLING HW-5, the solid portion becomes viscous and the water of crystallization vaporizes and expands the viscous mass. Dust from these rocks accumulates in the usual processing methods for these rocks in bulk and there are otherwise hardly useful applications for it. As a filler according to the present application, the dust, due to the fact that it is inflatable itself, can cause a reduction in the density and the thermal conductivity of the granules formed.

The invention provides a bulk material made of extremely lightweight and therefore good heat insulating and at the same time extremely solid grains, which due to the tightness of their outer shell hardly tend to water absorption and water storage. The bulk material, like sand, can be used as a filler for the formation of bricks, walls, plasters, cement- or lime-bound prefabricated parts and as an admixture to ceramic materials. It can bring about a very low specific weight and a very low specific thermal conductivity of the articles produced accordingly, without significantly reducing the mechanical strength or making it difficult to produce. In addition to ceramic masses, the bulk material can even improve the strength, as it reduces shrinkage.

The raw materials required for the preparation of the grains according to the invention are available inexpensively and the systems required for the production according to the invention are cost-effective in relation to the amount per time and in absolute terms. Thus, the bulk material formed from grains produced according to the invention is economically very competitive.

Finally, for reasons of clarity, the method according to the invention is described by a number of examples:

Example 1:

Liquid waterglass consisting of 30 weight percent S1O2, 10 weight percent Na20 and 60 weight percent water

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After one hour, the formed from the hardened water glass, located in said wells particles are shaken out of the wells, sprinkled on a fine screen surface made of stainless steel wire and dried for 72 hours, the surrounding air has a temperature of 20 ° C and a relative humidity of 30% having.

After the 72 hours dust particles are first removed from the bulk of the particles and then the particles are fed as bulk material to a fluidized bed furnace, whereby the fluid blown through the bulk material, which causes a basic heating and fluidization (ie "floating") of the particles a temperature of 250 ° C is. At the same time, a microwave emitter radiates onto the fluidized bed, that is to say the bulk material, the radiation power being about 150 W per dm 2 of fluidized bed. The heating zone of the fluidized bed is inclined at 2 ° (the inclination should be adjustable) and three meters long. Particles are continuously added at the top of the surface and flow through the heating zone. After exiting the heating zone, the particles are moved one meter further in a fluidized bed in which air having ambient temperature is used as the fluidizing medium and no microwave radiation acts on the particles. Finally, there are foamed, solid particles, which a

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Have bulk density of about 250 kg / m3. (The bulk density is best influenced by the water content of the particles entering the fluidized bed furnace.) The degree of previous drying of the particle particles allows bulk densities of fully expanded particles to be set between 80 and 600 kg / m3.)

Example 2: (Percentages are by weight)

Liquid waterglass consisting of 42% S1O2, 12% NaaO and 46% water is mixed with a liquid hardener consisting of 90% water, 6% sodium bicarbonate (edible soda) and 4% glyoxal (= ethanedial). It comes to one kilogram of liquid water glass 900 grams of liquid hardener.

Mixing is carried out in a continuous mixer, wherein between the filling of the two liquids in the mixer and the outlet of the mixture about 40 seconds pass. The liquid is taught from above onto a rotating surface at several hundred revolutions per minute about a vertical axis and sprayed by centrifugal force into droplets, which are hurled horizontally up to 4 meters away from the surface and 8 meters below the surface on a soil , where they are solidified by the fast-acting hardener - and the ambient temperature of 50 ° C - already solid particles. The particles are dried on a fluid bed dryer at 130 ° C for one hour, then allowed to cool, then divided by several sieving operations with different mesh sizes in four particle fractions with particles of the same size as possible.

The particle fractions are individually heated as the particles in Example 1 by the simultaneous action of a fluid bed furnace and microwave radiation and thereby foamed. In the fractions with the smaller particles, the fluid flow in the fluidized bed furnace should be set more gently than in the fractions with larger particles. The slope of the fluidized bed surface should be

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POSSIBLE for the smaller particles to be set higher than for the larger particles, so that the smaller particles, which are foamed faster, are not so long in the heating zone.

Example 3:

The liquid glass used is liquid waterglass, which is called " T90 " from Wöllner GmbH & Co. KG is available (2012); the hardener used is a liquid hardener known as " Betol HC " from Wöllner GmbH & Co. KG is available (2012). The liquid water glass is mixed with 30 percent by weight volcanic dust. This mixture is further processed into foamed particles using nine percent by weight of said hardener as in Example 2.

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Claims (9)

··· «« «HW-5 ··· ·· · • fc ·« 1. Method for producing porous grains from water glass by - particles of solid water glass are first dried so that they evaporate without melting the trapped water, then the particles are heated in a heating stage to the extent that they melt and are inflated by evaporation of the remaining residue of trapped water to porous grains, - whereby the particles are heated in the heating stage by microwave radiation in that - the particles in the heating stage are held and moved over a fluidized bed during the time in which microwave radiation is applied to them. 2. The method according to claim 1, characterized in that a single particle is formed by hardening a single drop of ground, which contains liquid water glass and a hardener for water glass and wherein apart from the water content, the mass of the mass drop is equal to the mass of the Par-tikels. 3. The method according to claim 2, characterized in that the mass from which the mass drops are formed, in addition fillers are added. 4. The method according to claim 3, characterized in that as a filler dust is inflated by heat inflatable volcanic rocks. 5. The method according to any one of claims 2 to 4, characterized in that the hardening of the drop of mass to a Parti- Page 14 REPLACED * · V ····· · «* · HW-5 • f * · • * · • »·· * • * · • * · 4« »Kel occurs during a throwing or falling movement of the mass drop in air, without the drop of mass thereby rests against a solid. 6. The method according to any one of claims 1 to 5, wherein the particles are heated to dry, characterized in that are allowed to cool after drying before being fed to the heating stage for foaming. 7. The method according to any one of claims 1 to 6, characterized in that during the foaming causing the heating stage flowing from the bottom surface of the fluidized bed gaseous medium is maintained in a temperature range which is warmer than the ambient temperature of the fluidized bed furnace but cooler than the maximum temperature which the particles and the grains forming therefrom can reach the microwave radiation. 8. The method according to any one of claims 1 to 7, characterized in that the gaseous medium flowing from the bottom surface of the fluidized bed is continuously dried or replaced by a drier gaseous medium. 9. The method according to any one of claims 1 to 8, characterized in that the grains are moved during the inflation over the bottom surface of the fluidized bed along and reach after completion of inflation to an area above the bottom surface of the fluidized bed, where no microwave radiation acts on them and they are cooled below the solidification temperature of the water glass by a gaseous medium flowing from the bottom surface of the fluidized bed. Page 15 SUBSEQUENT i i