WO2021228430A1

WO2021228430A1 - Method and system for activating clay

Info

Publication number: WO2021228430A1
Application number: PCT/EP2021/000065
Authority: WO
Inventors: Marc FEISS; Hans-Peter Jeschinowski; York Reichardt; Norbert Streit
Original assignee: Khd Humboldt Wedag Gmbh
Priority date: 2020-05-13
Filing date: 2021-05-11
Publication date: 2021-11-18
Also published as: EP4149900A1; DE102020112894A1; CN115916722A

Abstract

The invention relates to a method and a system for activating clay. According to the invention, clay raw material is divided into a coarse product fraction and a fine product fraction; the fine product fraction is preheated in a preheater, and the fine product fraction is then activated in a fluidized bed reactor and/or entrained bed reactor; the activated and heated fine product fraction is combined with the separated and cooled coarse product fraction, whereby the thermally activated clay fraction is quenched; and the combined clay fractions are discharged out of the reactor. The aforementioned method is advantageous in that the activated clay is not oxidized and therefore the clay is not colored reddish. Additionally, the preceding separation process saves a considerable amount of thermal energy, and the quenching process of the thermally activated clay stabilizes the total product against an undesired red coloring.

Description

Process and system for activating clays

The invention relates to a method and system for activating clays.

As a substitute for cement clinker as a building material, it is known to use thermally activated clay. It is true that thermally activated clays do not achieve the strength of concrete based on cement clinker, but the properties of activated clays as a building material are sufficient for a large number of construction projects that do not depend on the particular performance of the building material, as is the case with prestressed concrete bridges Is the case, or as is the case with extremely tall skyscrapers far beyond the 100 m limit.

Buildings made of clays have been known since ancient times. Houses made of baked clays and loam show the typical reddish color, which can extend to the color of terracotta tiles.

Clay minerals, which are suitable for processing as building materials and which develop hydraulic properties through thermal treatment, can vary greatly in their chemical and mineralogical compositions and also in their physical properties. In addition to the clay minerals, natural occurrences of these clay minerals usually contain various components with regard to the hydraulic properties of inert components such as quartz, feldspar, flint. Clay minerals of purely natural origin of various origins usually differ in terms of various properties such as particle size, density and moisture. In addition to these external properties, clay minerals of various origins differ in the inorganic impurities they contain, such as iron, titanium and manganese.

CONFIRMATION COPY These chemically bound metallic accompanying substances determine the color of the activated clay by changing their oxidation state during thermal treatment of the clay minerals. Iron impurities can be present as structural iron (part of the kaolinite structure or the structure of additional minerals) and as free iron in the form of oxides, hydroxides, carbonates and sulfides. The titanium and iron oxide content correlates with colorimetric parameters and the color saturation of red. Manganese turns brown when oxidized with the formation of manganese dioxide. It is known that the red color is caused by iron (III) compounds. The content of impurities such as iron and titanium in naturally occurring clay minerals leads to the undesired red coloration of the clay mineral activated by heat treatment during calcination under oxidizing conditions and subsequent cooling with atmospheric air.

Clay is a naturally occurring material that consists mainly of clay mineral particles, is generally plastically deformable with sufficient water content and becomes brittle when dried or burned. Although clay usually contains layered silicates, it can contain other materials that give it plasticity and harden it when dried or fired. As associated phases, clay can contain materials that do not give it plasticity, e.g. B. quartz, calcite, dolomite, feldspar and organic substances.

Unlike earlier definitions, this definition by the AIPEA (Association Internationale Pour L’Etudes Des Argiles) and the CMS (Clay Minerals Society) does not specify the exact grain size of the clay components, as various disciplines have made their own specifications. In the geosciences, in accordance with the EN ISO 14688 standard, clay particles are considered to be particles <2 pm (sometimes also <4 pm [2]) and in colloid chemistry <1 pm.

In the context of this application, clays are understood to mean the naturally occurring material that either mainly consists of clay mineral particles, i.e. more than 50% clay mineral particles, but also those made of clay mineral depository degradable materials that have less than 50% clay mineral particles to as little as 10% to 20% clay mineral particles. The rest consists of sand, silt, quartz, calcite, dolomite, feldspar and possibly also gravel. The large proportions of material that are not clay mineral particles are almost chemically inert, abrasive and cannot be activated thermally. The latter clays are thus similar to clay.

The object of the invention is to provide a system and a method for the thermal activation of clays in which the undesired red coloration does not occur.

The object on which the invention is based is achieved by a system with the features according to claim 1 plus subclaims 2 to 4 and by a method with claims 6 to 10.

According to the invented method, a separation of a clay raw material into a coarse fraction and a fine fraction, subsequent preheating of the fine fraction in a preheater, and subsequent activation of the fine fraction in a fluidized bed and / or entrained flow reactor is provided. A thermal treatment of the fine material fraction takes place in the fluidized bed and / or entrained flow reactor. Following the thermal activation, the still hot fine material fraction is combined with the separated and cold coarse material fraction and the combined clay fractions are discharged from the reactor.

Corresponding to the method, a system is proposed having at least one fluidized bed and / or entrained flow reactor and at least one cyclone heat exchanger, the cyclone heat exchanger following the fluidized bed and / or entrained flow reactor in the gas flow direction, and with a feed device for clay to be activated at the upper end of the cyclone heat. exchanger is arranged. The system is characterized in that a sifter is in flow connection with a coarse material discharge opening of the sifter in the material flow direction upstream with a gas feed device for the fluidized bed and / or entrained flow reactor, and the sifter with a Fine material discharge opening of the classifier is in flow connection upstream in the material flow direction with the feed device for clay to be activated. This system enables the clay to be treated in accordance with the aforementioned method.

The invention is based on the surprising finding that the red coloration of clays when activated by oxidation of the iron contained in the clay mineral to iron (III) in conjunction with other chemically bonded metallic components occurs exclusively in the fine-grained components of natural clays. The coarse-grained components of the natural clays, on the other hand, show no tendency to turn red. The invention is based on the knowledge that the fine components of the clay can be activated by thermal treatment. If this is carried out under chemically strongly reductive conditions, iron (III) is not formed in the clay, but iron (II), which appears chemically bonded in clay minerals rather greenish to colorless. The clay fraction activated under chemically reducing conditions therefore has a gray to anthracite color in conjunction with all accompanying substances. The fine fraction of natural clays activated by thermal treatment initially remains very sensitive to oxidation in atmospheric air. In order to avoid oxidation, the fine, thermally activated clay fraction is quenched from a temperature of 600 ° C to 1000 ° C at the end of a reactor for thermal activation to a temperature well below 600 ° C. This thermal quenching must not take place with atmospheric air, otherwise the undesired iron (III) would be formed. The quenching must be chemically neutral. The coarse fraction separated from the natural clay in the first process step is suitable for this purpose. This coarse fraction is almost chemically inert and can absorb a large amount of heat without oxidizing itself. The invention is based on a separation of clay minerals into a fine fraction, which is thermally activated, and a coarse fraction, which is not heated as an inert material. The surprising effect is that it is separated into a coarse fraction and in a fine material fraction leads to a clay-depleted and inert coarse material fraction and to a clay-enriched fine material fraction. After the thermal activation of the still warm and oxidation-sensitive fine material, the activated fine material is quenched with the previously separated coarse fraction, the coarse material fraction being significantly colder. In the quenched state, the chemically bound iron (II) is protected from oxidation. The clay mineral treated in this way has a gray to anthracite tint.

It is advantageous if the activated gray to anthracite-colored mineral is discharged from the reactor. For this purpose it can be provided that the material flow outlet of the cyclone heat exchanger at the lower end is in flow connection with a gas feed device for the entrained flow reactor, at which point the activated clay combines with the coarse material from the coarse material discharge opening of the classifier. The gas feed device can be in the form of a cyclone, from which the carrier gas escapes through a dip tube and the solid suspended in the carrier gas emerges as dust from a cone that is usually pointing downwards.

The temperature has an influence on the activated product not only during activation, but also after activation. Tests have shown that combining the thermally activated fine material fraction in a temperature window of 600 ° C to 1000 ° C with the coarse material fraction of the raw material leads to a final temperature of 350 ° C to 600 ° C. A temperature control that leads to a final temperature of below 500 ° C. is preferred. The fine material fraction of the activated clay quenched in this way shows itself to be insensitive to discoloration due to oxidation in atmospheric air with natural air humidity at these temperatures.

The separation of the natural clay into a fine material fraction and a coarse material fraction and the exclusive thermal activation of the separated fine material fraction and subsequent quenching with the previously separated coarse material fraction has several advantages. First, the activated Quench the fine fraction under chemically inert conditions, which stabilizes the activated clay component against red discolouration. Furthermore, due to the thermal activation, only a fraction of the heat is required, which saves fuel and resources. Yet another advantage is the equally surprising finding that the thermally activatable fine material fraction is significantly less abrasive than the coarse material fraction. The coarse fraction includes quartz, feldspar and flint. By separating the coarse fraction, the thermally loaded system is less exposed to abrasive dust, which extends the service life and operating time of the system. By using a wind sifter, especially a V-sifter, the exposure of moving machine parts to the abrasive clay content is reduced to a minimum.

The invention is explained in more detail with reference to the following figures. It shows:

1 shows a sketch of a system according to the invention for activating clays

FIG. 1 shows a sketch of a system according to the invention for activating clays. Moist raw material runs through the system in the sketch from a feed hopper 10 at the top left in the sketch to the finished, activated product, which leaves the system shown here via a conveying device 240 at the bottom right in the sketch. Fresh air enters the system via a separator cyclone 230 in the sketch at the bottom right and leaves the system as exhaust air in this sketch via a compressor 180 at the top right in this sketch.

The raw material is fed from the feed hopper 10 via a conveyor device 20 to a regulated conveyor device 30, where it is combined with raw material that is in the sifter circulation. From the regulated conveying device 30 the raw material falls into a sifter 40, here a vertical sifter, in which the raw material rolls over cascades of stairs, deagglomerated and freed from the fine material fraction by sifting gas entering the sifter 40 from the left in this sketch. At this point, the coarse fraction and the fine fraction separate. In the following, the route of the coarse fraction on described. The coarse material of the classifier 40 falls from the classifier 40 onto a regulated conveying device 50 and is conveyed by this conveying device 50 to the left in this sketch. On the left side of the conveyor device 50, the coarse material falls into a regulated material switch 60. A first part of the coarse material is transported through the material switch 60 to a further conveyor device 70 to a bucket elevator 80, which throws the circulating material back onto the conveyor device 30 described above where the sifting material in circulation is combined with the raw material. A second part of the coarse material from the sifter 40 is transported as inert material to the right in this sketch via a conveying device 90, where it combines with the activated fine material of the raw material. On the transport route along the conveyor 90, a processing device 92, for example in the form of a sieving device 92 or a grinding device, can be arranged, which can be reached via the bucket elevator 91 in order to sift out the coarser components of the natural clays and also to the relative proportions of the activated clay and the inert material in the end product. Furthermore, an optional soaking device 93 can be present which moisten the coarse material before combining with the activated clay in order to increase the heat absorption capacity of the coarse material. At this point, the coarse material has a temperature of atmospheric temperature up to a maximum of below 150 ° C. due to the temperature of the separator gas in the separator 40. The route of the fine material from the raw material out of the sifter 40 leads into the gas line 160 into which it is carried by the sifting gas. The fine material is separated from the classifying gas in a dust separator 170. The classifying gas leaves the system to the top right via the compressor 180 as exhaust air, as was already described at the beginning. Below the dust separator 170 there is a conveying device 190 which conveys the fine material fraction into a feeding device 200. From the feed device 200, the fine material falls into the uppermost gas supply line to the uppermost heat exchanger cyclone 123 of the heat exchanger 120 shown here with three cyclones. It is also possible to use this system with a different number of cyclones in the heat to operate the exchanger strand. Suspended in the gas of the gas supply line to cyclone 123, the fine material fraction is heated in the warm gas of heat exchanger 120. In the uppermost heat exchanger cyclone 123, the fine material fraction is fed into the gas inlet to the penultimate cyclone 122, where the heating and subsequent separation are repeated. At the exit of the penultimate cyclone 122, the preheated fines fraction falls into the lower area of an entrained flow reactor shown here, which is constructed similarly to a calciner of a plant for the production of cement clinker. A fluidized bed reactor can also be located at this point. In the rising hot gas of the entrained flow reactor 110, which can be heated with a combustion point, or can also be heated with the hot process gas of another industrial process, the fine material fraction of the clay is thermally activated to a hydraulic binder that sets when mixed with water. After the hot gas in the entrained flow reactor 110 has reached the upper reversal point, the fuel from the entrained flow reactor burns out. The free oxygen concentration in the entrained flow reactor should not rise above 4%. The flame of the burner in entrained flow reactor 110 is therefore operated in a strongly reductive manner, which can take place through a substoichiometric oxygen supply or a superstoichiometric fuel supply. The descending branch of the entrained flow reactor 110 is followed by the heat exchanger 120. The thermally activated fines fraction of the clay suspended in the hot gas is separated by the lowest cyclone 121 of the heat exchanger 120 and has a temperature between 600 ° C and 1000 ° C at this point. The hot gas flows in the heat exchanger 120 towards the fresh fine material. In contrast, the freshly thermally activated clay fraction leaves the heat exchanger via the solids line of the lowermost cyclone 121 and combines there with the inert, cold coarse material of the clay which was separated in the classifier 40.

The freshly activated clay with a temperature of 600 ° C to 1000 ° C and is mixed together with the cold coarse fraction Quenched to a temperature of approx. 350 ° C to a maximum of 600 ° C and separated in the separating cyclone 100 from the thermal line of the plant. In order to bring about an increased temperature reduction, water can be added to the cold coarse material fraction before it is combined with the hot, activated clay fraction. The combined clay fractions flow into the gas feed line of the separation cyclone 230 where these fractions flow against fresh atmospheric air. The fractions cooled to approx. 80 ° C. to 120 ° C. leave the system via the solids line of the separating cyclone 230 via the conveying device 240 as a finished product. The fresh air entering the system, on the other hand, flows conveyed through a compressor 210 to a gas line 220 and as a gas feed line to the separating cyclone 100, the fresh air taking up the clay fractions quenched and combined in the gas space. The fish air that gets there serves as combustion air for a burner in entrained flow reactor 110 and as carrier air. Another portion of the fresh air flows to a T-junction with the gas discharge line 130, which guides the warm heat exchanger exhaust gas from the heat exchanger 120 to a hot gas generator 140. The combined gas fractions are heated in the hot gas generator 140 and, after the hot gas generator 140, a gas line 150 leads the heated gas as sifting and drying gas to the sifter 40, where all gas and material cycles and / or flows are now closed.

B E Z U G S Z E I C H E N L I S T E Feed bunker conveyor device 123 uppermost

Heat exchanger cyclone conveyor

13 Gas line classifier 0

14 Hot gas generator conveyor device 0

Gas line material switch 150 direction 16 Gas line conveyor 0

Dust collector bucket elevator 170

180 compressor conveyor

190 Conveyor device, bucket elevator, device 2 Feed device, processing unit 00

Compression device 2nd water 10

Gas line separating cyclone 220

Separation cyclone entrained flow reactor 230 uscher 2 conveyor device Wärmeta 40 second lowest heat exchanger cyclone lowest

Heat exchanger cyclone

Claims

PATENT CLAIMS

1. Plant for activating clays, having at least one fluidized bed and / or entrained flow reactor (110), at least one cyclone heat exchanger (120), the cyclone heat exchanger (120) following the fluidized bed and / or entrained flow reactor (110) in the gas flow direction, with a Feed device (200) for clay to be activated is arranged at the upper end of the cyclone heat exchanger (120), characterized in that a sifter (40) with a coarse material discharge opening of the sifter (40) in the material flow direction upstream with a gas feed device, preferably in the form of a separating cyclone (100) ), for the fluidized bed and / or entrained flow reactor (110) is in flow connection, and wherein the sifter (40) is in flow connection with a fine material discharge opening of the sifter (40) in the material flow direction upstream with the feed device (200) for clay to be activated.

2. Plant according to claim 1, characterized in that the material flow outlet of the cyclone heat exchanger (120) is in flow connection at the lower end with a gas feed device, preferably in the form of a cyclone separator (100), for the fluidized bed and / or entrained flow reactor (110), wherein At this point the activated clay is combined with the coarse material from the coarse material discharge opening of the classifier (40).

3. Plant according to one of claims 1 or 2, characterized in that a gas line (220) from the gas feed device, preferably in the form of a cyclone separator (100), for the fluidized bed and / or entrained flow reactor (110) is connected to a gas line (130) which serves as a gas discharge line from the cyclone heat exchanger (120), the combined gas line opening into a hot gas generator (140), and the hot gas generator (140) being connected downstream of the gas to a gas inlet of the classifier (40)

4. Plant according to one of claims 1 to 3, characterized in that the coarse material discharge opening of the sifter (40) is connected to a raw material inlet of the sifter (40) via a material switch (60).

5. Plant according to one of claims 1 to 4, characterized in that the sifter (40) is a vertical sifter.

6. Method for activating clays, characterized by

Separation of a clay raw material into a coarse fraction and a fine fraction,

Preheating of the fine material fraction in a preheater, and then

Activation of the fine material fraction in a fluidized bed and / or entrained flow reactor (110),

Combining the activated and hot fine material fraction with the separated and cold coarse material fraction,

Removal of the combined clay fractions from the reactor.

7. The method for activating clays according to claim 6, characterized by,

Combining the activated and hot fine material fraction with a temperature of 600 ° C to 1000 ° C with the separated and cold coarse material fraction, which is significantly colder.

8. The method according to any one of claims 6 or 7, characterized by

Activation of the fine material fraction in the fluidized bed and / or entrained flow reactor (110) under chemically reductive conditions with an oxygen content of the carrier gas of less than 4%.

9. The method according to any one of claims 6 to 8, characterized by

The combined clay fractions are discharged from the reactor via a cyclone.

10. The method according to claim 9, characterized by

The combined clay fractions are discharged from the reactor at a temperature of 50.degree. C. to a maximum of 200.degree. C., preferably at a temperature of 90.degree. C. to 120.degree.

11. The method according to any one of claims 6 to 10, characterized by

Preparation of the cold coarse fraction by sieving, sifting and / or crushing / grinding before it is combined with the activated fine fraction for quenching.

12. The method according to any one of claims 6 to 10, characterized by

Adjustment of the relative proportions of coarse material and activated fine material in the combined clay fractions.