METHOD FOR ACTIVATING CLAYS WITH HIGH RESIDUAL MOISTURE CONTENT AND PLANT TO CARRY IT OUT

Abstract

The invention relates to a method for activating clays with high residual moisture, comprising the following steps: feeding the wet clay into a drying device (70), crushing the previously dried clay in a crushing device (130), thermally activating the crushed clay in an entrained flow reactor (160) or in a fluidized bed reactor, in which the crushed clay is suspended in a hot gas, separating the gas from the entrained flow reactor (160) or from the fluidized bed reactor in a separation device (170), and cooling the thermally activated clay in a cooling device (175) with a cooling gas, and a plant for carrying out the method.Inventively, the heated cooling gas after cooling the thermally activated clay is provided to mix with the gas from the entrained flow reactor (160) or the fluidized bed reactor, and to introduce the mixed gases into the drying device (70), and to filter the drying air after drying the clay in a dust filter (200), the filtered clay being mixed with the previously dried clay.

Description

The invention relates to a method for activating clays with high residual moisture, which method comprises the following steps: feeding wet clay into a drying device, crushing the previously dried clay in a crushing device, thermally activating the crushed clay in an entrained flow reactor or in a fluidized bed reactor, in which the crushed clay is suspended in a hot gas, separating the gas from the entrained flow reactor or the fluidized bed reactor in a separation device, and cooling the thermally activated clay in a cooling device by means of a cooling gas, and a corresponding plant for carrying out said method. The use of thermally activated clay as a substitute for cement clinker as a construction material is well known. Although thermally activated clays do not achieve the strength of cement clinker-based concrete, their properties are sufficient as a construction material for a variety of construction projects where the specific performance of the construction material is not important, such as prestressed concrete bridges or extremely tall skyscrapers exceeding the 100 m limit. 1995816 of 20 Buildings made of clay have been known since ancient times. Houses constructed of baked clay and marl display the typical reddish color, which can reach the shade of terracotta tiles. Clay minerals suitable for processing as building materials and which, through heat treatment (thermal activation), become hydraulic minerals that develop their own properties, can vary greatly in their chemical and mineralogical composition, as well as in their physical properties. Naturally occurring clay minerals often contain, in addition to clay minerals, varying proportions of components that are inert in terms of hydraulic properties, such as quartz, feldspar, and flint. Clay minerals of purely natural origin and from different sources often differ in several properties, such as particle size, density, and moisture content. In addition to these intrinsic properties, clay minerals from different sources are differentiated by the inorganic impurities they contain, such as iron, titanium, and manganese. Clay is a natural material consisting primarily of clay mineral particles. It is generally plastically deformable with sufficient water content and becomes brittle when dried or fired. Although clay generally contains silicates, 1995816 of 20 stratified, may contain other materials that impart plasticity and harden when dried or fired. As associated phases, clay may contain materials that do not impart plasticity, for example, quartz, calcite, dolomite, feldspar, and organic matter. Unlike the previous definitions, the AIPEA (Association Internationale Pour L'Etudes des Argües) and CMS (Clay Minerals Society) definitions do not specify an exact granulometry for clay constituents, as different disciplines have made their own determinations in this regard. In the geosciences, clay particles are defined, according to EN ISO 14688, as those particles with a granulometry less than 2 pm (sometimes also less than 4 pm), and in colloid chemistry, particles with a granulometry less than 1 pm are considered clay particles. In the context of the present application, clays are understood to be materials of natural origin which either consist mainly of clay mineral particles, i.e. contain more than 50% clay mineral particles, or are materials which can be extracted from clay deposits and contain less than 50% clay mineral particles up to a particle size range of 1 µm to only 10% to 20% clay mineral particles. The particle size range of the clay particles is 1995816 of 20, mostly less than 4 pm. The remainder is composed of sand, silt, quartz, calcite, dolomite, feldspar, and possibly gravel. The large portions of material that do not represent clay mineral particles are chemically almost inert, abrasive, and cannot be thermally activated. These latter clays are thus similar to mud. Clays typically occur in natural deposits with a high degree of moisture. Moisture gives clays a certain plasticity. Some clays have a pasty characteristic when mined from their deposits and also exhibit a certain stickiness. In the context of the present application, clays with high residual moisture are understood to be those that exhibit plastic properties when mined, forming a muddy to pasty mass and tending to form lumps. These clays lose these properties upon drying, becoming brittle and tending to agglomerate. In this state, when it dries into lumps, the clay has no or only a limited degree of hydraulic binding properties. Only through thermal activation, during which the water of hydration also escapes from the clay minerals, do the hydraulic binding properties develop. Due to the above-described material properties of clays with high residual moisture, the 4 1995816 of 20 Direct further processing (storage, crushing, transport, dosing) without prior drying is only possible with great technical effort or is completely impossible. When handling this material, it is almost impossible to transport the material with conventional bulk material conveying devices, since the clays clog and block the devices. To keep the transport distances of freshly mined clay short and avoid material handling problems, the clay drying plant is usually located directly after the clay extraction site. From there, further processing is usually a longer distance.The utilization of process heat from a subsequent stage is hampered by the fact that, on the one hand, the process heat fluid has to be transported over long distances and, on the other hand, the appropriate heat sources necessary for drying clay with high residual moisture are often not available on site. A large amount of heat is required to dry clays with high residual moisture. The available process waste heat is divided in industry into high and low calorific value waste heat. High calorific value process waste heat has a high temperature, typically above 800°C. Low calorific value process waste heat usually has a temperature below 300°C. However, the terms high 5. 1995816 of 20 calorific value and low calorific value, however, reveal little about the amount of heat available. Waste heat from low-calorific value processes can have a large amount of heat, and waste heat from high-calorific value processes can also have a small amount of heat, albeit at an elevated temperature. Since the path of the drying gas from the source of waste heat from an available process to the clay extraction point often involves long distances, separate heating gas generators are often used to dry the supplied clay from soft to paste-like in a clay dryer.This is because low calorific value waste heat from processes cannot be easily transported over long distances because the temperature drops too rapidly when it reaches the point of exploitation and, therefore, the process waste heat is at too low a temperature for effective drying. As a rule, the high calorific value process heat from the calcination process cannot be used directly because the gas temperature is too high for, for example, an impact hammer mill. F, since the machine protection, the required strength, wear and the choice of material do not allow the high calorific value process heat to be used. Therefore, the gas temperature 6 1995816 of 20 waste would have to be conditioned for further use, either with a higher input during installation, in a multi-stage cyclone heat exchanger, and / or by increasing the gas volume (e.g., by injecting fresh air), but this has a negative impact on machine size and energy efficiency, for example, the need for electric power for fans. Since the pasty properties of clay generally collapse, and depending on the nature and composition, only at a residual moisture content of at least 10%, in favor of a dry, bulk-like property, drying to less than 10s of residual moisture is necessary. This significantly reduces the energy efficiency of producing an alternative building material with its own hot gas generator for drying the clay on-site. Therefore, the object of the present invention is to provide a method for activating clays with high residual moisture, in which handling is facilitated and the process heat necessary for drying and transport is available. The problem of the invention is solved by a method of the type initially described which is characterized by comprising the following additional steps: 1995816 of 20 - mixing the heated cooling gas after cooling of the thermally activated clay with the gas from the entrained flow reactor or the fluidized bed reactor, and - introduce the mixed gases into the drying device, and - filter the drying air after the clay has dried in a dust filter, the clay separated by filtration being mixed with the previously dried clay. Another advantageous embodiment for executing the method according to the present invention is characterized by using an impact hammer mill to crush the clay. Another advantageous embodiment for carrying out the method according to the present invention is characterized by introducing into the grinding device a part of the cooling gas heated after cooling the thermally activated clay. A final advantageous embodiment for carrying out the method according to the present invention is characterized by introducing a portion of the clay produced during the separation of the gas from the entrained flow reactor or the fluidized bed reactor into the grinding device. A plant for carrying out the inventive method comprises: _a drying device for drying wet clay, 1995816 of 20 a grinding device for grinding pre-dried clay, - an entrained flow reactor or a fluidized bed reactor for the thermal activation of crushed clay, in which the crushed clay is suspended in a hot gas, - a separation device for separating the gas from the entrained flow reactor or the fluidized bed reactor, and - a cooling device for cooling the thermally activated clay by means of a cooling gas, characterized by - a device for mixing the heated cooling gas after cooling of the thermally activated clay with the gas from the entrained flow reactor or the fluidized bed reactor, and - a duct for conducting the mixed gases to the drying device, and - a device for filtering the drying air after drying the clay, where a conveying device mixes the clay separated by filtration in said device with the previously dried clay. Another way of making the plant is characterized by 1995816 of 20 The crushing device is an impact hammer mill for crushing clay. Another embodiment of the plant is characterized in that a duct for heated cooling air leads from the cooling device for cooling the thermally activated clay to the crushing device. The inventive concept includes the combination of two process circuits. On the one hand, it is provided to mix the waste gases from clay cooling after thermal activation of the clays as low-calorific process waste heat with the waste gases from thermal activation as high-calorific process waste heat, and to use this combined process waste heat to dry the clay at the clay mining site. Since a lot of dust is generated during clay drying because the clay already has a very fine particle size, the clay separated during filtration of the drying off gases is mixed with dried clay. The dried clay has the consistency of coarser bulk material, which can be easily transported by belt conveyors and bucket elevators.The fine fraction produced during drying is mixed or blended with the coarse fraction and these are fed together to a grinding device before the crushed fractions. 1995816 of 20 are sent together for thermal activation. The fine material fraction has a high proportion of thermally activatable layered silicates, while the coarse material fraction contains the aforementioned components, such as sand, silt, quartz, calcite, dolomite, feldspar, and possibly also gravel. The separation of materials, which is actually undesirable during drying, is made unnecessary by combining them before crushing. During co-crushing, the fractions are thoroughly mixed again at the same time. The invention will be explained in more detail with reference to the following figures, in which: Fig. 1 illustrates a flow diagram of a plant for carrying out the activation process of clays with high residual moisture in a first embodiment. Fig. 2 illustrates a simplified flow diagram showing the process carried out in the plant according to Fig. 1. Figure 1 shows a flow diagram of a plant A for carrying out the clay activation method with high residual moisture in a first embodiment. In this illustration, a linear arrow shows the solids path, while a cross-hatched arrow shows the gases path, as shown by the inscribed legends. The raw material in the form of clay 1995816 from 20 pasty, plastically deformable, to sticky, is fed from a feed hopper 10 to a conveyor belt 20, if necessary with the aid of conveying screws not illustrated here. The raw material subsequently falls onto a second conveyor belt 30, controlled by a conveyor belt scale 40. The high-moisture clay first passes through a magnetic separator 50 to remove any metallic pieces, typically machine parts, lost hammer points, broken excavator teeth and scrap metal, which may inadvertently enter the clay during extraction. In a subsequent stage, the freshly supplied clay passes through a coarse material separator 60, in which coarse stones, small boulders and other non-metallic parts, also wood and plant components, are classified and separated.After this initial coarse preparation, the freshly supplied and pre-cleaned clay falls into a clay dryer 70, through which a hot gas flows, which will be described in more detail below. During the drying of the clay, a large amount of dust is generated, which is discharged with the drying gas from the clay dryer 70 through an exhaust air duct 190. The dried clay is discharged through a cellular wheel sluice 71 onto a conveyor belt 90 and lifted by a bucket elevator 100. After the elevator 12 1995816 of 20 buckets 100, another conveyor belt 110 continues to a cellular wheel sluice 120 to an impact hammer mill 130. The material transport mentioned here takes place from the delivery of the fresh clay to the thermal line of the plant. The distances traveled can be several hundred meters. After passing through the cellular wheel sluice 120, the dried clay falls into the impact hammer mill 130, which rotates in the indicated direction. In the process, the hammers of the impact hammer mill 130 throw the crushed clay into an ascending branch 140 of an entrained flow reactor 160, in which the clay is thermally activated. For this purpose, the clay suspended in the ascending air of the entrained flow reactor 160 is heated by a burner supplied with fuel supply 150.The clay rising in the air from the ascending branch 140 is swirled in the hot gas in a swirl chamber 162, and in this process the remaining activation of the clay takes place. Following the swirl chamber 162 is a descending branch 163 of the entrained flow reactor 160, where the clay / gas slurry encounters a cyclone separator 170. In this cyclone separator 170, the thermally activated clay is separated from the off-gas from the entrained flow reactor 160. The solids, i.e. the thermally activated clay, fall through a solids line 250 to a cooler. 1995816 of 20 clay 175, which consists of a dust separator 260 and a cyclone separator 280. The path of the exhaust gases from the entrained flow reactor 160 separated in the cyclone separator 170 continues through the hot gas duct 171, which leads to a coupling point 180, where the separated combustion gases from the entrained flow reactor 160 mix with the exhaust gases from the aforementioned clay cooler 175. The mixed exhaust gases flow to the aforementioned clay dryer 70 to dry the fresh clay with high residual moisture. The exhaust gases used for drying absorb a large amount of dust. The dust-laden drying air is conducted through an exhaust gas duct 190 to a dust filter 200, where the fine, dry clay is separated.The separated fine clay passes through rotating cellular wheel locks 210 to a conveyor belt 220, which transports the fine, dry clay to the conveyor belt 90. There the dry fine clay is mixed with the dry coarse clay from the clay dryer 70. The exhaust air from the dust filter 200 is then discharged as exhaust air at a temperature of approximately 150°C to 200°C with the aid of a blower 240. The thermally activated clay separated in the cyclone separator 170 falls through a solids chute 250 to the clay cooler 175, composed of a dust separator 260 and a cyclone separator 280. The clay cooler 14 1995816 of 20 175 is supplied with atmospheric air, which is heated during the cooling of the thermally activated clay and flows as a low-calorific heat carrier through a blower 300, a cooling gas outlet gas duct 310 and a gas duct 311 into the impact hammer mill 130, where it is available as preheated carrier air for the entrained flow reactor 160. On the other hand, another part of the outlet air from the clay cooler 175 flows to the coupling point 180, where this outlet air mixes as a low-calorific heat carrier with the outlet gas of the hot gas duct 171, which carries the separated exhaust gas from the entrained flow reactor 160.The mixing of the clay cooler 175 outlet air with the high calorific value waste heat of the separated off-gas from the entrained flow reactor results in a considerable cooling of the separated off-gas from the entrained flow reactor to a temperature of between 600°C and 900°C. However, the combined off-gases carry sufficient heat to a sufficient, but not too high, temperature. The thermally activated clay discharged from the clay cooler 175 exits the latter via a cellular wheel lock 290. The advantage of the process proposed here lies in the fact that by dividing it into drying and grinding, the need for further reduction / conditioning of the clay is eliminated. 1995816 of 20 temperature. On the exhaust gas side, gas inlet temperatures into the dryer of up to 900°C are realistic and technically feasible. The result is lower technical input, smaller system component dimensions, and greater energy efficiency. Figure 2 shows a simplified flow diagram illustrating the process carried out in the plant according to Figure 1. The loading of the raw material begins at the top of the flow diagram. This is followed by a drying stage. Following the path of the solids (straight arrows), a crushing stage follows. Following the crushing stage, the solid material continues toward thermal activation. Following the path of the solids, thermal activation is followed by separation of the off-gas from the thermal activation stage. The solids then pass through a cooling stage and are discharged from the process in the separation stage in the form of finished, thermally activated clay. In accordance with the inventive idea, it is provided that the air, which enters the process in the cooling stage, is separated after the thermally activated clay has cooled.Part of the separated air is recycled for thermal activation. Another part is mixed with the separated exhaust gases from thermal activation and is recirculated. 1995816 of 20 drying. The dust produced during drying is filtered and mixed with the freshly dried clay. Having described the nature of the present invention and the manner of putting it into practice, it is declared that what is claimed as an invention and exclusive property is yes THE CLAIMS CONTINUE ON PAGE 1 --------17 1995816 of 20 OF REFERENCES Plant Feed hopper Conveyor belt Conveyor belt Conveyor belt scale Magnetic separator Coarse material separator Clay separator Cellular wheel lock Bucket Elevator Conveyor Belt Cellular wheel lock Impact Hammer Mill Entrained Flow Reactor Fuel Supply Drag-flow reactor Upstream branch Swirl chamber Descending branch Cyclone separator Hot gas duct Clay cooler Docking point 1995816 of 20 Conduit Exhaust air duct Flapper valve Dust filter Cellular wheel lock Conveyor belt Exhaust air duct Flap control valve Blower Solids duct Dust separator Solids duct Cyclone separator Cellular wheel lock Blower Cooling gas outlet duct Gas duct Flapper valve 1995816 of 20 MUCHALL SRL - 30679678961 Digitally signed by PORTALTRAMITES - INPI Date: 2022.10.12 13:33:16 -03:00 Reason: Digitally signed by the INPI Location: Buenos Aires, Argentina 1995816

Claims

1. A method for activating clays with high residual moisture, in particular clays with a residual moisture content of at least 10%, comprising the following steps: - feeding wet clay into a drying device (70), - crushing the previously dried clay in a crushing device (130), - thermally activating the crushed clay in an entrained flow reactor (160) or in a fluidized bed reactor, in which the crushed clay is suspended in a hot gas, - separating the gas from the entrained flow reactor (160) or from the fluidized bed reactor in a separation device (170), and - cooling the thermally activated clay in a cooling device (175) using a cooling gas, characterized by - mixing the cooling gas heated after cooling the thermally activated clay with the gas from the entrained flow reactor (160) or from the fluidized bed reactor,- introducing the mixed gases into the drying device (70), and - filtering the drying air after the clay has been dried in a dust filter (200), the clay separated by filtration being mixed with the previously dried clay. Six claims follow.