EP0213135A1

EP0213135A1 - Method and plant for producing highly porous ceramic form bodies

Info

Publication number: EP0213135A1
Application number: EP85902455A
Authority: EP
Inventors: Sigismund Kienow
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-05-14
Filing date: 1985-05-13
Publication date: 1987-03-11
Also published as: NO860097L; FI860038A0; DE3514141A1; AU4401685A; FI860038A; WO1985005353A1

Abstract

Procédé de fabrication de corps de moules céramiques très poreux à partir d'argiles plastiques gonflables, d'argiles schisteuses, de cendres volcaniques ou de matières brutes naturelles similaires et installation pour réaliser ce procédé. Conformément à la présente invention, les matières brutes granulées et séchées sont amenées dans des chambres capsulaires (1) séparées de l'atmosphère extérieure à une surpression de 2 à 10 mbar jusqu'à des processus exothermes survenant au-dessus de la température d'équilibre et jusqu'au moussage (gonflage) par les gaz libérés.Process for manufacturing bodies of highly porous ceramic molds from inflatable plastic clays, shale clays, volcanic ash or similar natural raw materials and installation for carrying out this process. In accordance with the present invention, the granulated and dried raw materials are brought into capsular chambers (1) separated from the external atmosphere at a pressure of 2 to 10 mbar up to exothermic processes occurring above the temperature. balance and until foaming (inflation) by the released gases.

Description

Method and device for the production of highly porous ceramic shaped bodies

The invention relates to a method for producing highly porous, ceramic moldings from plastic clays, shale clays, volcanic ashes or similar natural raw materials for the thermal insulation of buildings and a device for carrying out the method.

It is known to produce highly porous products from plastic clays, shale clays, volcanic ashes, tufts or similar natural raw materials, optionally after adding blowing aids, by heating, the pores being caused by gases which form when the raw materials are heated. Gases develop for the following reactions:

1. Fe ₃ 0 ₄ + G - 3 FeO + C0 in shades of blue

2. CaC0 ₃ - CaO + C0 ₂ in calcareous clays

3. 2 FeS0 ₄ - 2 FeO + 2 S0 ₂ + 0 ₂ in clays containing sulfate 4. chemically bound water - water vapor in pearlite.

In this way, it has so far only been possible to produce large amounts of blown granules with an average diameter of 10 mm. These granules have to be bound with chemical or hydraulic binders, especially cements, to form large-format structures, the binding effect being greatly reduced by the binders. There has therefore been no shortage of attempts to produce large moldings without binders by ceramic sintering in order to improve the insulating effect. Among other things, it has been proposed to fill already heated, highly heated granules into molds and to compress them by mechanical pressure so that the individual granules can deform until they touch intimately and sinter together. The moldings produced in this way had a higher bulk density than the more voluminous heap before pressing, moreover the moldings had an irregular structure and low strength.

To avoid these disadvantages, it was further proposed to completely fill molds with unexpanded granules, to close the molds and then to heat them from the outside to the blowing temperature. The swelling granules should fill the cavities in the pile and sinter together under the internal pressure that builds up. This attempt was also unsuccessful because the porous, poorly heat-conducting material heated up unevenly. The peripheral zones were overheated before the core reached the expansion temperature.

In order to achieve uniform and rapid heating, according to a further proposal, granules of the same size should be poured into a molding box which has a gas-permeable bottom consisting of grate bars. In such a molding box, hot gases were passed through the granules alternately from below and from above until the blowing temperature was reached. In this case, the granules are heated directly by the heating gases, for which only a fraction of the time required for heating from the outside via the forklift wall was required. This suggestion, which is obvious in itself, did not produce a satisfactory result. The granules expanded to a greater or lesser extent into the cavities in the pile, but the bond between them was inadequate or there was a condensed structure at the contact points of two granules.

The object of the invention consists in a method of the type mentioned at the beginning and in an apparatus for carrying it out of the process, whereby the highly porous ceramic moldings are to be manufactured with a uniform structure and improved strength.

This object is achieved in that the granulated and dried raw materials in capsule spaces sealed off from the outside atmosphere under excess pressure of 2 to. 10 mbar up to exothermic processes occurring above the equilibrium temperature and up to foaming (blowing) by released gases. The fire is preferably carried out at an overpressure of 2 to 4 mbar. The overpressure should be released at the start of foaming.

Surprisingly, the special design of the gas pressure gives shaped articles with a uniform structure and good strength.

The gas phase occurring in the reactions must therefore not be removed or mixed with other gases. It is not sufficient if only the swelling process itself takes place in an atmosphere free of oxygen, as was proposed in German Patent 1,940,358. The capsules must not have large openings which allow gas exchange with the surrounding atmosphere, as are provided, inter alia, in US Pat. No. 1,960571.

The following processes are assumed in the capsule chamber when the fired material is heated:

1. Escape of the crystal water and, if the clay is calcareous, carbon dioxide through the still open pores, mixing these gases with air.

2. Formation of excess pressure of the gas phase above the bed of clay and limitation of the excess pressure due to the escape of excess amounts of gas through the leaky points of the capsule. 3. At approx. 700 ° G the equilibrium (equilibrium temperature) is established for the reaction. The CO vapor pressure reached

1 bar. CO passes through the open pores into the gas phase. Rise in CO partial pressure in the gas phase. The reaction is inhibited by the increased CO partial pressure.

4. The clay begins to soften at approx. 1100 ° C. The pores close. The reaction can continue because the resulting GO gas can push the softening clay aside. New pores arise.

5. At about 1150 ° C the clay is so soft that the CO gas under pressure suddenly foams the clay until it fills the entire interior of the capsule.

6. The rapid and even foaming suggests that the reaction is exothermic. The heat of reaction Δ H is positive, i.e. endothermic. Heat must be applied so that the

Reaction expires. However, since a gas phase arises during the reaction, the disorder of the system and thus the entropy Δ S increases.

As a result, the free enthalpy G = A H - T A S

(T = absolute temperature) decreases with increasing temperature and finally becomes negative. Then the reaction is exothermic, i.e. it releases heat. According to thermodynamic calculations, this is the case from approx. 750 ° C.

The course of reactions 2 to 4 can also be assumed accordingly. They differ from reaction 1 in that they have different temperature levels and gas composition.

According to the invention, a capsule made of sheet steel with the dimensions 25 x 10 x 12 cm was filled up to a third with dried fine-grained iron oxide and carbon-containing blue tone in a grain size of up to 5 mm in a laboratory test. The capsule was sealed with a sheet steel lid, but was not sealed gas-tight. The capsule with the firing material was placed in an oven heated to the blowing temperature of 1150 ° C. The kiln heated up developed significantly faster than expected and expanded quickly and evenly when the inflation temperature was reached. The CO atmosphere in the capsule during the experiment was demonstrated by the fact that a. Stick of wood stuck during the fire not burned but charred. After the capsule had cooled, it became a shaped body

3 mm should be obtained with 0.35 g / cm RRoohddiicchhttee, even structure and good strength.

It has now been found that in the case of illite-rich blue tones, the fact that the temperature required for foaming for 5 to 20 minutes, preferably 10 to 20 minutes, with the excess pressure being maintained until the end of the temperature required for foaming, gives shaped articles with an even more uniform and firmer structure be preserved.

The illite-rich blue shades used as raw material in the process are characterized by their content of iron oxide and organic substance, to which their swelling properties are attributed. A bulking aid can also be added to this raw material. Due to the holding time at the temperature required for foaming in the process in the case of illitic blue shades as the raw material, a highly porous molded body with a more uniform and firmer structure is obtained. This process is promoted by maintaining the pressure in the capsule. The pressure in the capsules rises sharply while the inflation temperature is maintained. According to thermodynamic calculations, e.g. 1200 ° C a pressure of 860 mbar occur. At the same time, there is an extensive reduction of the iron oxide, sometimes reaching as far as metallic iron.

The device for the method according to claim 6 of the invention is shown schematically in Figures 1 to 5.

Show it:

1 the furnace chamber with capsule chambers, combustion chambers and regenerators, 2 shows the furnace chamber according to section AA of FIG. 1,

3 the furnace ceiling with pressure regulator,

Fig. 4 shows a horizontal section through an oven with two capsules and

Fig. 5 shows a vertical section through a filling device.

The capsule spaces 1 are alternately arranged in the furnace system with combustion chambers 10. Both are separated by walls 7, which are made of a material with high thermal conductivity and fire resistance, preferably silicon carbide. The two end faces of the capsule space can be closed by hydraulically operated doors 2. The capsules are fed through tightly closable filler neck 3, which are guided through the furnace roof 5. In addition, the pressure regulators 4, shown enlarged in FIG. 3, are embedded in the furnace ceiling, by means of which the gas pressure in the capsule space can be checked and changed. They consist of a tube 12 which is led through the ceiling and which is preferably made of silicon carbide. This pipe directs the escaping gases to a hot wind pipe 13, at the end of which there is a burner 14 in which the gases are flared. However, they can also be fed into the fuel gas line. The tube 12 can be closed by a water-cooled hot wind valve 15, which is driven by the motor 16. The engine is advantageously controlled by a manometer, which measures the gas pressure.

Regenerators 8 are provided under the combustion chambers 10, in which the heat of the exhaust gases can be stored and used to heat the combustion air. The lines 6a required for this and for the gas supply are installed in the regenerator ceiling 6 and are indicated schematically in the drawing. The regenerators 8 are separated by walls 9 and built on the thermally insulated foundation 11. According to the invention, the capsules filled with firing material can also be fired in a tunnel kiln. However, this method is less advantageous because the processes in the capsules cannot be controlled or influenced during the passage through the quencher. • Apart from that, the large capsule park required represents a considerable cost factor.

When the furnace system is in operation, the combustion chambers 10 provided with gas flues are heated until the capsule chamber 1 has reached a temperature of approximately 700 ° C. The firing material should have a grain size in the range of 3 to 15 mm with a possibly small grain fraction below 3 mm. After preheating from 250 to 300 ° C., it is introduced through the nozzle 3 that the capsule space 1 is filled to a third to a half, depending on the desired bulk density of the shaped body. Then continue to heat until the fired material has reached the blowing temperature. During this time, the gas pressure in the capsule chamber should not exceed 10 and preferably 4 mbar.

As soon as the foaming process begins, the hot wind valve 15 can be opened in order to produce the greatest possible difference between gas pressure in the closed pores of the material to be burned and that in the surrounding atmosphere. As a result, the foam process is accelerated particularly advantageously and a uniformly fine-pored structure of the molded body is achieved. When the foam has filled the entire capsule space, no more fuel is supplied and only the hot air from the regenerators 8 is passed through the trains of the combustion chambers. The molded body cools slowly and the foam structure is frozen. When the surface temperature of the molded body has dropped to approx. 700 ° G, it is pressed out of the capsule space after opening the doors 2 with the aid of a slotting machine and transferred to a cooling channel for further cooling.

In order to facilitate the pressing out of the molded body, the capsule space 1 can be sprayed out with a mass before the heating, which has such a low surface tension that the material to be burned on you are not liable. The mass consists of a material, optionally based on graphite or boron nitride.

Finally, the surfaces of the shaped bodies are smoothed in a grinding machine or the shaped bodies are divided into smaller formats in a sawing line.

The high internal pressure that arises during the process, in particular when illiterate blue raw material is used, is advantageously achieved by designing the end walls of the capsule as an upwardly movable slide 2 a and as a pressure plate 20, and also by the binder walls 17 supporting the partition walls 7 in the combustion chambers 10 and met by the outer walls 18, 19. The slides 2a can be guided in recesses in the outer walls 19 or rear wall. The outer wall 18 or front wall, through the openings of which the pressure plates 20 are moved with the aid of a linkage 27, is continuous. The walls at the ends of a battery must be made so stable that they are practically not deformed by the pressure created.

Insulated feed silos 22 are to be provided above the capsule spaces 1, each of which is fed through the filling opening 25 with a weighed batch of dried and preheated raw materials in the form of pellets. The capsule spaces 1 are filled with the pellets from the loading silos 22 via conical closures 23 in the furnace roof 5 and actuation of the closing device 24. The filling of the capsules with pellets on the one hand and the emptying of the capsules by pushing out the highly porous ceramic molded body on the other hand is expediently carried out economically in each battery containing several capsules. When the capsule chamber 1 is emptied, the slide 2a is first extended upwards after the ceramic shaped body has cooled down and the molded body with the pressure plate 20 is then pushed out of the capsule. The capsule spaces combined in batteries are advantageously operated periodically staggered in time. The regenerators shown after the main application under the combustion chambers can be replaced by a central regenerator system for one battery each.

In the process for producing the highly porous ceramic moldings, the dried and preheated illite-rich blue clay in the form of pellets from the silos, which is preheated to 250 to 300 ° G, is initially filled into the capsule spaces 1 of a battery by opening the closures 23 in the furnace roof 5. Then the closing devices 24 are raised and the battery is heated by supplying 750 ° C. of hot air from the regenerator into the combustion chambers 10. With the supply of natural gas and preheated combustion air, the capsules are heated up as quickly as possible within 15 to 20 minutes through the combustion chambers. At the temperature for the foaming of about 1150 ° C, the temperature over a period of e.g. Held for 15 minutes. An exothermic process creates a fine, porous ceramic body with a uniform structure from the raw material. Subsequently, drop cooling is introduced through the combustion chambers until the moldings have cooled to approximately 750 ° C. The shaped bodies shrink by 0.6 mm in width and detach from the silicon carbide plates. The hot molded bodies are pressed out of the capsules by the linkage 21 and the pressure plates 20 and transferred to the cooling system.

in blowing aids there is, for example, iron oxide with sulfite waste liquor.

Claims

Patent claims

1.) Process for the production of highly porous, ceramic moldings from plastic clays, shale clays, volcanic ash or similar natural raw materials, characterized in that the granular and dried raw materials in capsule spaces sealed off from the outside atmosphere under excess pressure of 2 to 10 mbar up to above the exothermic processes occurring at the equilibrium temperature and are burned by released gases until they expand (expand).

2.) Method according to claim 1, characterized in that the excess pressure is released at the beginning of the foaming.

3.) Method according to claim 1, characterized gekennzeicnnet that the dried raw materials are burned under an excess pressure of 2 to 4 mbar.

4. The method according to claim 1, characterized in that when illiterate blue as the raw material, the temperature required for foaming (blowing temperature) is maintained for 5 to 20 minutes.

5.) Method according to claim 4, characterized in that the temperature required for foaming is held for 10 to 20 minutes.

6.) Method according to claim 4 or 5, characterized in that the excess pressure is maintained until the end of the holding time of the temperature required for foaming.

7.) Device for performing the method according to claims 1 to 6, characterized in that the capsules are arranged in a stationary manner and on both sides of the capsule spaces (1) there are combustion chambers (10) so that capsules and combustion chambers alternate with one another. 0

8.) Device according to claim 4, characterized in that the partition walls (7) between the capsule spaces (1) and the combustion chambers (10) consist of silicon carbide or silicon nitride.

5 9 Device according to claim 4, characterized in that the narrow end walls (2) of the capsule spaces (1) are designed as pneumatically closable doors.

10.) Device according to claim 7, characterized in that ⁰ the ceiling (5) of the capsule spaces (1) are provided with tightly closable filler neck (3).

11.) Device according to claim 7, characterized in that on the ceiling (5) of the capsule spaces (1) pressure regulators (4) ^ are attached, by means of which the gas pressure in the capsule space (1) can be checked and regulated.

12.) Device according to claim 11, characterized in that the pressure regulators (4) consist of silicon carbide tubes (12) through which the gases from the capsule chamber (1) are guided to a hot wind pipe (13), at the end of which they are passed through a burner (14) can be flared.

13.) Device according to claims 11 and 12, characterized in that the tube (12) can be closed by a water-cooled, from the motor (16) driven hot wind valve (15).

14.) Device according to claims 11 and 12, characterized in that a manometer is installed in the ceiling (5), which measures the gas pressure in the capsule chamber (1) and controls the motor (16).

15.) Device according to claim 7, characterized in that two regenerators (8) are arranged below the combustion chamber (10), which serve to preheat the combustion air.

16.) Device according to claim 7 for carrying out the method according to claims 1 to 6, characterized in that a mass based on graphite or boron nitride with a very low surface tension is applied to the walls of the capsule space (1).

17.) Device according to claims 6 to 16 for carrying out the method according to claims 1 to 6 with fixed capsules and on both sides of the capsule spaces (1) provided combustion chambers (10) and partition walls (7) made of silicon carbide or silicon nitride between the capsule spaces and the combustion chambers, characterized in that a narrow end wall of the capsule serves as an upwardly movable slide (2a) and the opposite other end wall fills the cross section of the capsule

Pressure plate (20) is formed.

18.) Device according to claim 17, characterized in that the slide (2a) consists of silicon carbide plates with an outer insulation of ceramic fiber molded bodies or fiber mats and the pressure plate consists of silicon carbide plates.

19.) Device according to claim 17, characterized in that in the combustion chambers (10) between the partition walls (7) are binder walls (17), between which gas flues are formed.

20.) Device according to claim 19, characterized in that the truss walls (17) consist of temperature change-resistant refractory stones, such as cordierite-containing refractory stones.

21.) Device according to claim 17, characterized in that the partition walls (7) are held by the outer walls (18 and 19).

22.) Apparatus according to claim 17 and 21, characterized gekenn¬ characterized in that the furnace floor (6), the furnace roof (5) and the outer walls (18 and 19) made of alumina-rich refractory concrete and an outer insulating layer made of ceramic fiber bodies or fiber ¬ mats exist.

23.) Device according to claim 4, characterized in that the pressure plate (20) in the capsule is moved by a linkage (21).

24.) Device according to claim 10, characterized in that the linkage (21) through openings in the outer wall (front wall) (18) is guided.

25.) Device according to claims 17 to 24, characterized in that several capsule spaces (1) and associated combustion chambers (10) are combined to form at least three batteries.

26.) Device according to claim 25, characterized in that five to fifteen capsule spaces (1) and associated combustion chambers (10) are combined to form a battery.