Multi-stage clay calcination process for controlling product color

Abstract

This invention relates to a method for heat-treating clay, comprising the steps of: preheating clay suspended in a carrier gas in a heat exchanger (150); heat-treating the clay in a calcination stage (160) operating under chemical oxidation conditions; subsequently heat-treating the clay in a calcination stage (170) operating under chemical reduction conditions; cooling the clay in a cooling stage (180) operating under chemical reduction conditions; and cooling the clay in a cooling stage (190) operating under chemical oxidation conditions. The alternating sequence of the redox potentials in the environment results in black to gray products rather than reddish-brown products while minimizing harmful gas emissions. This guided method allows for stable operation.

Description

Technical Field

[0001] This invention relates to a method for heat-treating clay. Background Technology

[0002] Cement clinker, a composition of calcium silicate with varying stoichiometry, is a current building material used as a starting material for high-performance concrete. In the manufacture of cement clinker, CO2 is formally expelled from naturally occurring lime through heat treatment, resulting in high CO2 emissions. Given the anticipated greenhouse effect due to excessively high CO2 concentrations in the Earth's atmosphere, efforts are underway to find alternative building materials with lower CO2 concentrations. Calcined clay is increasingly being used as a building material alternative to cement clinker. While it does not possess the strength of high-performance concrete based on cement clinker, it is suitable for a wide range of building applications where such high strength requirements for building materials are not necessary. Activated, i.e., calcined clay, is also suitable as a concrete additive. This partial substitution of building materials is accompanied by a reduction in CO2 emissions related to the amount of building materials produced.

[0003] Activated clay is clay mined in mines through chemical / thermal activation. Clay is a naturally occurring material primarily composed of fine-grained minerals, which is generally plastically deformable in sufficient water content and becomes brittle when dried or burned. Although clay typically contains layered silicates, it can contain other materials that impart plasticity and harden when dried or burned. As a related phase, clay can contain materials that do not impart plasticity, such as quartz, calcite, dolomite, feldspar, and organic materials. The definition of clay is not uniformly defined. However, at the geological science level, clay particles are considered to be less than 2 μm, and in some cases less than 4 μm, according to the standard EN ISO 14688 system, and at the colloidal chemistry level, particles less than 1 μm are considered clay particles. The main clays to be studied within the scope of this patent application are kaolinite, illite, and montmorillonite, which possess the properties mentioned above. In order for the clay to affect the curing properties of concrete as an additive or to participate in concrete as a binder, the clay must be chemically / thermally activated, as mentioned at the beginning, so that it reacts with quicklime or cement clinker in the desired manner.

[0004] Naturally occurring clays contain inorganic impurities such as iron, titanium, and manganese, which determine the color of activated clay by altering its oxidation state. The reddish-brown color of Italian terracotta bricks, but also that of clay brick houses known in California, is attributed to the color of oxides of the aforementioned metals. Iron impurities in clay can exist as structured iron, such as as part of the structure of kaolinite or additional minerals, and as free iron as oxides, hydroxides, carbonates, and also as sulfides, and the list described is not exhaustive. The results of clay studies allow for a correlation between the red color saturation of clay and the content of titanium and iron oxides, which is directly related to the colorimetric parameters of the clay's external appearance. Manganese, when oxidized, is brown. So-called manganese dioxide is a typical manganese oxide, which also gives activated clay its color.

[0005] To date, no reliable studies exist regarding the color and strength of activated clay. However, modern building materials are expected to be color-neutral and not exhibit reddish to reddish-brown hues. The undesirable reddish color of activated clay occurs when it is industrially calcined or activated under oxidizing conditions and subsequently cooled with atmospheric air.

[0006] In the chemical / thermal activation of clay, the structurally contained water (H2O) in the clay is expelled by heat treatment. This “dehydration” of clay is also referred to as “dehydroxylation,” although the terms “dehydration” and “dehydroxylation” are used differently in chemistry and the cement industry. Dehydroxylation of clay typically occurs within a temperature window between 650°C and 800°C, where the optimal temperature window is related to the water content in the clay and the presence of accompanying materials.

[0007] Because of the similar methods guiding the process between calcination of raw material powders and activation of clay in the manufacture of cement clinker, the terms "calcination," "activation," and "dehydroxylation" overlap in professional literature. Within the scope of this patent application, the term "activation" should be used to refer to the chemical / thermal activation of clay.

[0008] German patent application DE 10 2016 005 285 B3 discloses a method for activating clay. The activated clay produced using the method learned therein is suitable as a concrete admixture. However, no specific measures for color control are used.

[0009] A method for heat-treating natural clay and / or zeolite is disclosed in German publication DE 10 2014 116 373 A1. Based on the concept described therein, the calcination, i.e., heat treatment of the clay and / or zeolite, is performed under reducing conditions. Here, the compounds exhibit a reddish-brown color as ferric iron (Fe(III)) is converted to ferrous iron (Fe(II),) and the compounds appear black. It is also important to note that during the cooling of activated clay, a continuously present reducing or at least oxygen-free condition is necessary. A reducing or oxygen-free method, guided by cooling conditions, cannot be easily controlled without other measures to prevent undesirable emissions.

[0010] In German publication DE 10 2015 106 417 A1, the previously mentioned DE 10 2014 116 373 A1 is improved by measures for maintaining the cleanliness of the exhaust gas. To this end, a tapered section is introduced into the calcination reactor, which causes different flow velocities of the clay suspension and enables the separation of the reheated clay from the gas of the calcination reactor. The reducing exhaust gas from the calcination reactor then oxidizes and removes reducing gases, especially CO, without oxidizing the clay. The tapered section should ensure strong mixing of the reducing calciner gas and the introduced oxidant. The oxidant can thus be precisely quantified so that the material is just about not re-oxidized. The separation of material and gas occurs in a connected cyclone separator. This operating mode requires precise dosing of the oxidant because, on the one hand, CO should be completely oxidized to avoid emissions, and on the other hand, the re-oxidation of the clay itself must be prevented. The separation of calcination gases from suspended, but still hot, clay requires a very good balance of flow and pressure relationships in the calcination reactor, which is not very easy when using secondary fuels with non-uniform ignition characteristics. Summary of the Invention

[0011] The object of the present invention is to provide a stable and well-controllable method for activating clay, wherein an undesirable red color does not appear due to the oxidation of iron and titanium components and possible other metallic impurities, such as manganese, for example.

[0012] The objective according to the invention is achieved by a method having the features according to Embodiment 1. Other advantageous designs are given in dependent embodiments of Embodiment 1.

[0013] Therefore, according to the concept of the invention, two consecutive activation and cooling steps guided under chemical reduction conditions are confined on both sides by activation and cooling steps guided under chemical oxidation conditions. This alternation of chemical reduction and chemical oxidation steps enables the production of gray to black clay instead of reddish-brown clay. On the other hand, the process gas from stoichiometric reduction is oxidized in the method stage of oxidation operation, allowing it to be released into the atmosphere without problems as an exhaust gas. The process guidance or method described herein can operate stably, reliably producing gray to black clay, with acceptable exhaust values ​​and no undesirable emissions such as carbon black or carbon monoxide.

[0014] In the specific design scheme of this method, it can be proposed that a cyclone heat exchanger be used to preheat the clay in the waste gas of the calcination stage operating under chemical oxidation conditions.

[0015] Furthermore, it is possible to propose introducing the exhaust gas from the heat exchanger into the cooling stage operating under chemical reduction conditions.

[0016] Alternatively, it can be proposed to introduce the exhaust gas from the circulating drying facility into a cooling stage operating under chemical reduction conditions to treat the clay.

[0017] The specific design scheme of this method proposes that the calcination stage operating under chemical oxidation conditions oxidizes the waste gas from the calcination stage operating under chemical reduction conditions.

[0018] In order to stabilize the gray to black color of clay by forming the main divalent iron compounds, it is proposed that the clay be cooled to a temperature below 250°C in a cooler operating under reducing conditions.

[0019] In an advantageous manner, clay activation occurs during heat treatment in a calcining stage at a temperature between 350°C and 1050°C, preferably in the temperature range between 600°C and 950°C.

[0020] Chemical reduction conditions are preferably obtained by introducing a reducing environment into a calciner operating in chemical reduction mode using a superstoichiometric amount of fuel with respect to the presence of oxygen.

[0021] To implement the method as simply and cost-effectively as possible, in contrast to the more expensive operation of known grid-type coolers, the method may be characterized by cooling clay in an airflow cooler, in a vortex bed, or in a fluidized bed. Attached Figure Description

[0022] The invention is described in more detail with reference to the following drawings. The drawings show:

[0023] Figure 1The facility for activating gray to black clay according to the first embodiment is shown, performing a variation of the first method.

[0024] Figure 2 A facility for activating gray to black clay according to a second embodiment is shown, performing a variation of the second method. Detailed Implementation

[0025] The foregoing description of the solution according to the invention thus includes, in particular, various combinations of features defined by the subsequently numbered embodiments:

[0026] 1. A method for heat-treating clay, comprising the steps of: - preheating clay suspended in a carrier gas in a heat exchanger (150), - heat-treating clay in a calcination stage (160) operating under chemical oxidation conditions, subsequently - heat-treating clay in a calcination stage (170) operating under chemical reduction conditions, - cooling clay in a cooling stage (180) operating under chemical reduction conditions, and - cooling clay in a cooling stage (190) operating under chemical oxidation conditions.

[0027] 2. The method according to embodiment 1, wherein a cyclone heat exchanger (150) is used to preheat clay in the exhaust gas of a calcination stage (160) operating under chemical oxidation conditions.

[0028] 3. The method according to embodiment 1 or 2, wherein the exhaust gas from the heat exchanger (150) is introduced into the cooling stage (180) operating under chemical reduction conditions.

[0029] 4. The method according to embodiment 1 or 2, wherein waste gas from the circulating drying facility (101) is introduced into a cooling stage (180) operating under chemical reduction conditions to treat clay.

[0030] 5. The method according to any one of embodiments 1 to 4, wherein the waste gas from the calcination stage (170) operating under chemical reduction conditions is oxidized in the calcination stage (160) operating under chemical oxidation conditions.

[0031] 6. The method according to any one of embodiments 1 to 5, wherein the clay is cooled to a temperature significantly below 600°C in a cooler operating under reducing conditions and subsequently cooled to a product temperature below 250°C in a cooler operating under oxidizing conditions.

[0032] 7. The method according to any one of embodiments 1 to 6, wherein the clay is heat-treated in a calcination stage (160, 170) at a temperature between 350°C and 1050°C, preferably in a temperature range between 600°C and 950°C.

[0033] 8. The method according to any one of embodiments 1 to 7, wherein a reducing environment is created by introducing a superstoichiometric amount of fuel (B) with respect to the presence of oxygen into a calciner (170) operating in a chemical reduction manner.

[0034] 9. The method according to any one of embodiments 1 to 8, wherein the clay is cooled in an airflow cooler, in a vortex bed, or in a fluidized bed.

[0035] exist Figure 1The diagram shows a facility 100 for activating black to gray clay, by which a first variant of the method according to the invention can be performed. Facility 100 consists of a processing facility 101 and a thermal pipeline 102. The construction of the thermal pipeline 102 and the method guidance derived therefrom are of inventive importance to the method described herein. Raw material from a feed hopper 103 is supplied to a conveying device 104. The conveying device transports the unprocessed clay to a magnetic separator 105 and a weighing scale 105' to regulate the transport of the unprocessed clay. After passing through the magnetic separator 105, the unprocessed clay is transported to a feeding device 106, where it falls into a hammer crusher 107 and is crushed. The hammer crusher 7 is circulated by air / exhaust gas. The crushed material is pneumatically conveyed upwards through an ascending pipe 108 to a cyclone screen 109, where the fine particles of the crushed unprocessed clay are separated from the coarse particles. The fine particles are further ascended via a fine particle pipe 110. The coarse material 111 separated from the hydrocyclone separator 109 falls back into the feed unit 106 via a corresponding pipe with a swing valve 112 and an impeller valve 113. Prior to this, the coarse material 111 still passes through a mass flow sensor 114 to regulate the flow of unprocessed clay. The feed unit 106 is connected to a vent line 115, through which the processing facility 101 can be vented. Dry air 120 flows into the processing facility 101, and is further heated via an afterburner 121 and fuel B. The dry air 120 is here heated into hot air 122 and then flows into the hammer crusher 107, where the hot air 122 dries the unprocessed clay immediately upon crushing. A pressure balancing pipe 123 also exists between the riser pipe 108 and the hot air pipe. The fine material exiting the hydrocyclone separator continues to the filter unit, where the dried and pulverized unprocessed clay 140 is filtered out. The fine material exits the hydrocyclone separator via the fine material conduit 110. Here, air is retained and discarded as exhaust gas via a fan 132 downstream of the filter unit 130, and is at least partially directed into the thermal line 102. The unprocessed clay 140 is then directed to the feed unit 141, where it reaches the heat exchanger 150. Two heat exchange cyclones 151 and 152 are present in the heat exchanger 150, through which exhaust gas from the subsequent calcination stages 160 and 170 flows. After passing through the heat exchange cyclones 151 and 152, the unprocessed clay is heated and enters the chemically oxidizing calcination stage 160. There, the clay heats up very rapidly. Water is expelled from the clay, dehumidifying it. Here, iron contained in clay can also be formed. ), Fe( This process produces a reddish-brown color. To prevent the red color from manifesting in the clay, a reduction-running calcination stage 170 is immediately followed by an oxidation-running calcination stage 160. The incoming clay has been heated and pre-dried. The red to brown color of the clay is formed only when it is completely dry. In the method described here, however, black to gray clay is formed because the clay is completely dehydrated in the oxidation-running calcination stage, allowing the solid-state reaction in iron (FE), titanium (Ti), and manganese (Mn) to begin. The oxidation and reduction conditions are derived from the different gas supplies of the two calcination stages 160 and 170. The oxidation-running calcination stage 160 obtains air from an oxidation-running cooler 190, which operates with fresh air from the atmosphere. Conversely, the chemical reduction-running calcination stage 170 operates with exhaust gas from a circulating mill, i.e., treatment facility 101. Here, air from the oxidizing cooler 190 flows through a conduit that directs cooler exhaust gas 193 into the oxidizing calcining stage 160. The chemically reducing calcining stage 170 obtains air from the reducing cooler 180, which operates via a return conduit 182 with the aid of exhaust gas from the filter assembly 130.

[0036] Solid clay exits the calcination stage 170 of the chemical reduction operation via a solids pipeline and falls into a cooler 180 of the chemical reduction operation, which is configured as an airflow cooler. In cooler 180, the clay is rapidly cooled to significantly below 600°C and raised to a cooling cyclone 181. The solids in cooling cyclone 181 then travel via a solids pipeline to a cooler 190 of the chemical oxidation operation, which operates with the aid of fresh air. Cooling cyclone 191 cools the clay to below 250°C and separates the activated, black to gray clay, causing the activated clay to exit the thermal line 102. The oxygen-rich exhaust gas from cooler 190 then rises via a pipeline as cooler exhaust gas 193 to the calcination stage 170 of the chemical oxidation operation. This variation of the method has the advantage that the filter exhaust gas from filter device 130 has a low temperature and a low oxygen concentration. These conditions allow for a reducing environment. Specific temperature and humidity control of the returned gas is not necessary.

[0037] exist Figure 2 The diagram shows a facility 200 for activating black to gray clay, by which a second variation of the method according to the invention can be performed. Herein lies... Figure 2 The facilities shown in the image are Figure 1 The difference in the facilities lies in the return pipe 182 surrounding the thermal pipeline 202. Here, in this embodiment of facility 200, instead of... Figure 1The return pipes 181 and 282 are led from the output end of the heat exchanger 150 back to the cooler 180 in the chemical reduction operation.

[0038] The modified method has the advantage that the heat exchanger exhaust gas already has a low oxygen concentration. It is transported via a booster fan in an ascending channel to the oxidizing cooler 190. For temperature and humidity regulation of the exhaust gas, heat can be extracted from the gas by means of water injection or by mixing in fresh air / preheated cooling air, or from a combination thereof.

[0039] List of reference numerals in the attached diagram:

[0040] 100 facilities

[0041] 101 treatment facility

[0042] 102 Thermal Pipeline

[0043] 103 Feed Hopper

[0044] 104 transport device

[0045] 105 Magnetic Separator

[0046] 105' Measuring Scale

[0047] 106 Feeding Equipment

[0048] 107 hammer crusher

[0049] 108 riser pipe

[0050] 109 Hydrocyclone Screen

[0051] 110 fine material pipeline

[0052] 111 Coarse Material

[0053] 112 Swing Valve

[0054] 113 Impeller Valve

[0055] 114 mass flow sensor

[0056] 115 vent pipe

[0057] 120 dry air

[0058] 121 Afterburner

[0059] 122 Hot Air Pipe

[0060] 123 Pressure Balance Piping

[0061] 130 filter unit

[0062] 131 Fresh Air Delivery Unit

[0063] 132 ventilation fan

[0064] 133 exhaust pipe

[0065] 140 Unprocessed clay

[0066] 141 Feeding Equipment

[0067] 150 heat exchanger

[0068] 151 heat exchanger cyclone

[0069] 152 heat exchanger cyclone

[0070] 160 calcined grade, oxidation

[0071] 170 calcined grade, reduction

[0072] 180 cooler, restore

[0073] 181 Cooling Cyclone

[0074] 182 return pipelines

[0075] 190 cooler, oxidation

[0076] 191 Cooling Cyclone

[0077] 192 Fresh Air Delivery Unit

[0078] 193 Cooler Exhaust Gas

Claims

1. A method for heat-treating clay, comprising the following steps: - The clay suspended in the carrier gas is preheated in the heat exchanger (150). - The clay was heat-treated in the first calcination stage (160) under chemical oxidation conditions, subsequently - heat treating the clay in a second calcination stage (170) operating under chemical reduction conditions, wherein, The second calcination stage (170) is carried out in a separate calciner, wherein the first calcination stage (160) is not carried out in said calciner. - The clay is cooled in the first cooler (180) operating under chemical reduction conditions. - The clay is cooled in a second cooler (190) operating under chemical oxidation conditions. The exhaust gas from the second calcination stage (170) operating under chemical reduction conditions is introduced into the first calcination stage (160) operating under chemical oxidation conditions and oxidized there. The clay was heat-treated in the first calcination stage (160) and the second calcination stage (170) at a temperature range between 600°C and 950°C.

2. The method according to claim 1, Its features are, The heat exchanger (150) is used to preheat the clay in the exhaust gas of the first calcination stage (160) operating under chemical oxidation conditions.

3. The method according to claim 1, Its features are, The exhaust gas from the heat exchanger (150) is introduced into the first cooler (180) which operates under chemical reduction conditions.

4. The method according to claim 2, Its features are, The exhaust gas from the heat exchanger (150) is introduced into the first cooler (180) which operates under chemical reduction conditions.

5. The method according to claim 1, Its features are, Waste gas from the treatment facility (101) is introduced into a first cooler (180) operating under chemical reduction conditions to treat the clay.

6. The method according to claim 2, Its features are, Waste gas from the treatment facility (101) is introduced into a first cooler (180) operating under chemical reduction conditions to treat the clay.

7. The method according to any one of claims 1 to 6, Its features are, The clay is cooled to a temperature significantly below 600°C in a first cooler (180) operating under reducing conditions and then cooled to a product temperature below 250°C in a second cooler (190) operating under oxidizing conditions.

8. The method according to any one of claims 1 to 6, Its features are, A reducing environment is created by introducing a superstoichiometric amount of fuel (B) with respect to the presence of oxygen into a calciner operating in a chemical reduction manner.

9. The method according to any one of claims 1 to 6, Its features are, Clay is cooled in an airflow cooler, in a vortex bed, or in a fluidized bed.

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