AT504051B1 - PROCESS FOR PRODUCTION OF SHEET GOODS - Google Patents

Description

2 AT 504 051 B1

The invention relates to a process for the production of bulk material from porous grains by foaming a granulate by heat, wherein the individual grains of the starting granules consist of a viscous at elevated temperature material, in which a gaseous at elevated temperature substance is included.

A very important application is the production of a bulk material with low density and high heat insulating capacity by foaming a granulate of a mineral material such as perlite or Pechstein. These have a high proportion of network-forming ("glass-forming") material - in the examples mentioned SiO 2 - and a significant proportion of trapped water of crystallization, which evaporates on heating.

Using the example of perlite or Pechstein, during the ideal process of foaming in the course of heating, first the surface water and then excess water of crystallization are evaporated from the individual, still solid particles. Then the temperature rises so that the mineral becomes viscous. By the still enclosed, further evaporating proportion of remaining water of crystallization, the mineral is foamed. Once the desired, low specific gravity of the particles is reached, it is cooled, and thus the mineral is re-solidified in a suitably porous state.

In industrially applied foaming process, this ideal process is achieved only with a very low reliability. The end product is rarely a homogeneous bed of similarly inflated particles. In most cases, the end product contains disturbingly low predictability on the one hand not or only slightly foamed particles, on the other hand, dust-like particles resulting from the breakage of larger particles, which were foamed too much. Another significant problem arises from the fact that particles stick together with one another during their viscous chamfer as well as with parts of the system. To reduce these disadvantages, several approaches are known:

For example, it is known from EP 0 431 112 B1 to supply the raw material in the form of particles in a specific size range. This reduces those problems that result from the fact that in the same hot environment, smaller particles heat up much faster than larger particles.

EP 0 225 074 B1 discloses rapidly cooling the particles after they have been inflated by blowing coolant, and also removing them from the heating zone.

Even with the application of all these methods, it is currently not possible for many potential industrial applications to produce a homogeneous, lightweight granulate of uniformly foamed mineral particles in sufficiently good and safe quality.

It is known from the documents US 4,931,211, FR 2529879 A1, WO 1986/06713 A1, JP 6247756 A and SU 1178728 A to subdivide the heating process of the particles into two stages. The primary effect of this is that in the first, not so hot stage water, which is contained in the particles, is withdrawn. The subsequent hotter second stage is then foamed in a better defined manner than in a one-stage heating process in which the water content is often indeterminate and / or too high.

The object underlying the invention is to improve the process of foaming over the achievable with the aforementioned methods measure extent to the extent that thus a much more homogeneous bulk material is obtained from similarly foamed particles.

To solve the problem, in addition to the consistent application of the previously described known methods from the frothing granules prior to that heating stage in which is foamed, and after that heating stage in which the frothy granules is preheated without melting, dust particles and particles whose size falls below a certain minimum size, sifted out.

The effect achieved as well as useful further developments of the method according to the invention will be explained with reference to a concrete embodiment with the aid of the flowchart shown in FIG.

Fig. 1: shows an exemplary flowchart for a concrete embodiment of the method according to the invention.

The raw material delivered to the chute 1 for processing is granules of 0.4 to 0.6 mm particle size of Pechstein. Chemically it consists of about 72% SiO 2, as well as about 12% Al 2 O 3; the rest is water and impurities.

With the bucket conveyor 2 about 2.5 kg of this material per minute are introduced into the processing process. On a first sieve 3 any existing grains larger than 0.6 mm or smaller than 0.4 mm are sorted out. Too large grains would froth too little, too small grains would foam too quickly and too much and subsequently lead to sticking with other grains, or with plant parts, or break after solidification and form dust.

From the sieve 3, the granulate enters the rotary kiln 4. Its furnace interior has the shape of a circular cylinder with a length of about seven meters, a diameter of 480 mm, and one of the input side to the output side by about five degrees inclined axis. The outer surface of the furnace interior - essentially a tube made of steel - rotates at about 40 revolutions per minute about its longitudinal axis. Along its length, the rotary kiln is electrically heated in several successive temperature-controlled heating zones. In the first part of the pipe the temperature is 220 to 320 ° C, in the second part 280 to 360 ° C. In the first part of the furnace, especially the water accumulating on the surface of the grains is evaporated. In the second part of the furnace, water of crystallization, that is water, is evaporated from the interior of the grains. It is also some fresh air passed through the rotary kiln. This improves the drying of the granulate. The correct effect of the rotary kiln, namely dehydration to the right amount without damaging the grains, is to be judged by the experienced caretaker of the plant most directly by the color of the grains coming out of the rotary kiln.

It makes sense to use the waste heat of the flowing from the rotary kiln 4 air-water mixture. The proportion of water can also be condensed out of the exhaust air by conduction to correspondingly cool and large surfaces. For example, you can lead the exhaust air from the rotary kiln through the screened sieve 3 granules.

After the granules have passed the rotary kiln 4, it is sieved again on the screen 5 according to the invention. As a result, dust is removed, which was apparently insoluble part of the surface of these grains before drying the granules, and it will be the individual - for further treatment too small - parts of those grains of granules removed, which are broken during the run in the rotary kiln. Due to their small size, the sieved-out particles would foam up too quickly during the subsequent foaming process and lead to sticking of the plant as well as to disturbing dust as a result of breakage due to a lack of firmness. Experience has shown that 5 to 3 percent of the mass of the introduced granules are sieved on this sieve.

Both the sieve 5, as well as the subsequent parts of the promotion of the foamed granules should be operated largely isolated from the ambient air, so that in the 4 AT 504 051 B1

Rotary kiln 4 heated granules neither unnecessarily cools nor performs an uncontrolled moisture exchange with the ambient air.

After the sieve 5, the granules to be foamed are brought via a cup conveyor 6 to the filling opening 7 located at the upper end of the shaft furnace 8, the furnace interior has the shape of a slender circular cylinder standing. The filling opening 7 is formed as a cone distributor. That is, the upper end of the shaft furnace is completed on the one hand by an axially arranged downwardly widening, conical or frustoconical part, on the other hand by a part which on the one hand surrounds this first part on its lateral surface at a distance thereto, on the other hand on the inner surface of the Furnace interior is applied. The granules trickle down in the gap forming a truncated cone lateral surface between these two parts. It thus arrives at the upper end, close to the lateral surface, into the furnace interior of the shaft furnace 8.

The trickling of the granules through the filling opening 7 can be set very uniformly by adjusting the gap with a thickness which is only slightly greater than the size of the particles to be carried out, and by applying a vibration to the frusto-conical part of the cone distributor.

The shaft furnace 8 has a height of 7.3 meters and an inner diameter of 30 cm. It is electrically heated over its height in seven individual temperature-controlled heating zones. With decreasing height, the temperature rises from 800 ° C to 1100 ° C. The foaming grains of the above introduced granules fall down in the shaft furnace. They are heated in the temperature range in which their state is doughy, and froth them as a result of the evaporation of remaining residual water of crystallization. Close to the lower end of the shaft furnace 8, a closable opening for sampling should be attached. Down arriving, foamed but still doughy particles can be removed there with an inserted spoon-like device, and their degree of foaming in a subsequent consequence, be assessed visually and by weight and volume measurement. If the removed grains are too light, ie foamed too much, then either the temperature is reduced or the amount of granules introduced increases per time. If the extracted grains are too heavy, the temperature must be increased or the amount of granules introduced per unit of time must be reduced.

At the lower end, the lateral surface of the shaft furnace 8 ends in a downwardly narrowing, externally water-cooled truncated cone lateral surface 9. Impacted, foamed grains are first cooled on this surface. The temperature of this surface should be as cool as possible, in any case below the vitrification temperature of the material of the granules.

At its lower edge line, this surface passes into a tubular removal line 11, which at its other end opens into a pipeline 12 serving for the transport and further cooling of the foamed grains. The junction of the line 11 in the pipe 12 should be formed at an acute angle to the transport direction in the pipe 12.

In the pipe 12 fresh air flows, which is blown at one end by a blower 10 via an injector. This injector tube is coaxial with the pipe 12, its outer diameter is smaller than the inner diameter of the pipe 12 and its end should protrude beyond the junction of the extraction line 11. This ensures that air flows from the open space of the shaft furnace 8 into the pipe 11 and not vice versa.

The reaching into the pipe 12 foamed granules is further cooled there and solidifies. The flow rate in the pipeline 12 should be sufficiently high so that there is no deposition. The pipe 12 may also have a few curvatures.

Claims (2)

5 AT 504 051 B1 gene have; Thus, a sticking of individual grains against a straight and thus more laminar flow is better avoided. With a tube diameter of 20 cm, a flow rate of 17 m / sec and a length of about 10 m, very good results are achieved. At the end of the pipeline 12, the foamed granules are thrown into - ideally funnel-shaped - collecting containers 14 with sacks 16 connected beneath them. By formed as a screen surfaces walls of the bags 14, the air flowing out of the pipe 12 is discharged. It is very advantageous to arrange a plurality of collecting containers 14 adjacent to one another in the flow direction of the outflowing air. Since specifically lighter grains are better carried by the flowing air than specific heavier grains whose movement is determined more by their mass, this results in a weight sorting of the foamed grains. At the end of the pipe 13 also a kind of trap 13 can be formed for poorly or not at all foamed grains. Due to their density, these grains are moved closer to the lower cross-sectional area of the pipeline 12, and can be sorted out well by a lower jacket opening and an adjoining insert part projecting from below into the pipeline 12. Of course, many modifications, such as other furnace principles, as well as other transport feeding and discharging methods for the granules are possible within the inventive concept. Of course, it is also not absolutely necessary to filter the delivered granules directly before entering the rotary kiln 4. The operating parameters described relate to a granulate of Pechstein. They are at least approximately true for the foaming of many silicate-rich minerals of volcanic origin with a high proportion of glazing and trapped water of crystallization. With appropriate adjustment of the operating parameters such as amount per time, temperatures and speeds, the method described for the foaming of a wealth of other materials can be modified. Of course, the medium that becomes gaseous under the action of heat does not necessarily need to be water. It is also possible to provide other substances acting as propellants, such as C02 or titanium hydride bound at normal temperature. The foamed material does not necessarily have to be a mineral material. It can also be, for example, a metal in which propellant particles have been incorporated in an earlier step. It may also be an organic material, which is foamed by means of the described method into flakes or beads. It is relatively difficult to control the shaft furnace 8 used for the specific foaming process with respect to the production amount per time in very different operating conditions. On the other hand, it is very straightforward to properly control the rotary kiln 4 responsible for the predrying in a wide capacity range. Therefore, in order to be able to adapt a frothing system well to changing workloads, it therefore makes sense to provide a single more powerful rotary kiln 4 for a plurality of shaft kilns 8, of which then a smaller or larger number is put into operation as required or not. Claims: 1. A method of foaming bulk material particles from a mineral material by heating the material to a temperature at which it becomes viscous and vaporizes trapped water of crystallization, wherein the heating process of the particles occurs in two stages, wherein a first stage, the particles are heated to a temperature which is above the evaporation temperature of the water but below the melting temperature of the mineral material, so that water is removed from the particles by evaporation from the particles and wherein in a second stage, the particles on a heated to a higher temperature compared to the first stage, in which the mineral material is viscous and is inflated due to the evaporation of residual water contained, characterized in that between the two heating stages, a screening of the bulk material, through which particles whose Size falls below a lower limit, excluded from the second heating level. 2. The method according to claim 1, characterized in that the material of the particles is a mineral of volcanic origin containing at least fifty percent by weight SiO 2. For this purpose 1 sheet of drawings