AVOIDING EMISSIONS IN THE PRODUCTION OF ARTIFICIAL PUZZOLANS FROM MINERAL MATERIAL, IN PARTICULAR CLAY

Description

[0001] The invention relates to a device and a method with which exhaust gas treatment for the conversion of pollutants is possible within the process itself and thus without downstream exhaust gas treatment, which in turn reduces or avoids the energy consumption for exhaust gas treatment.

[0002] Alternative fuels are increasingly being used to replace primary raw materials, such as pulverized coal, and thus contribute to climate neutrality. However, alternative fuels are often more difficult to ignite and, due to legal requirements, must meet minimum burning times and temperatures. Therefore, these alternative fuels are often combusted in combustion chambers attached laterally to the actual treatment device. This has the advantage of a direct connection between heat generation in the combustion chamber and heat consumption during the combustion process in the treatment device.

[0003] The combustion of fuels produces, for example, nitrogen oxides, collectively referred to as NOₓ, as well as partially unburned hydrocarbons and hydrocarbon-containing compounds, which, for simplicity (and neglecting other heteroatoms), are collectively referred to here and in the following as CₓH₅. NOₓ can be converted to nitrogen either non-catalytically (SNCR) or catalytically (SCR), particularly with ammonia (NH₃) or urea. Hydrocarbons (CₓH₅) can react with oxygen to form water and carbon dioxide. A temperature range above 800 °C is advantageous for this conversion. Therefore, exhaust gas treatment typically requires reheating the relatively cold exhaust gases, which consumes energy and often necessitates additional heat exchangers.

[0004] From DE 10 2011 014 498 A1 a process for the production of a clinker substitute is known.

[0005] A manufacturing process for synthetic pozzolans is known from US 9 458 059 B2.

[0006] A method for the production of artificial pozzolans is known from WO 2012 / 082 683 A1.

[0007] From WO 2005 / 108 891 A1 is a plant and a process for the production of cement clinker.

[0008] From EP 2 587 149 A1 a method and a device for reducing NO x-containing gases in exhaust gases of a rotary kiln are known.

[0009] The temperature control of a calcinator is known from EP 1 898 171 A1.

[0010] US 5,975,891 A discloses a furnace for the heat treatment of raw materials and is divided into at least three separate combustion zones. One of these zones is supplied with a quantity of fuel (c) together with oxygen-containing gas; a second zone is supplied with a quantity of fuel (b) together with nitrogen-containing gases from the other two zones, and the resulting exhaust gases are discharged from the system; the third zone is supplied with a quantity of fuel (a) together with oxygen-containing gas and at least a portion of the raw material.

[0011] The object of the invention is to save energy during exhaust gas treatment and thus avoid further CO2 emissions, for example from the combustion of fuels as a heat source.

[0012] This problem is solved by the device with the features specified in claim 1 and by the method with the features specified in claim 20. Advantageous embodiments are described in the dependent claims, the following description, and the drawing.

[0013] The device according to the invention is used for the thermal treatment of, for example, and in particular, mineral materials, especially clays, for the production of artificial pozzolans as an additive for cement clinker. Clays have become increasingly established as an important raw material in the cement industry, since their thermal treatment releases less or no CO₂ from the raw material, as occurs, for example, during the burning of limestone. However, since the temperature for the activation of mineral materials, especially clays, can often be below 800 °C, the temperature inside the calciner is insufficient to reliably convert pollutants. The device comprises at least one preheater, a calciner, and a material cooler. The preheater is designed, for example, as a direct-flow heat exchanger with a cyclone separator or as a cascade of two to six direct-flow heat exchangers with cyclone separators.Alternatively, the preheater can also be designed as a cross-flow heat exchanger. The material cooler is also preferably designed as a parallel-flow heat exchanger with a cyclone separator or as a cascade of two to six parallel-flow heat exchangers with cyclone separators. Alternatively, the material cooler can also be designed as a cross-flow heat exchanger. A solids stream is fed into the preheater, from the preheater into the calcinator, from the calcinator into the material cooler, and out of the material cooler. In counterflow, a gas stream is fed into the material cooler, from the material cooler into the calcinator, from the calcinator into the preheater, and out of the preheater. The device includes a combustion chamber. The gas stream from the material cooler is at least partially routed through the combustion chamber into the calcinator. There can be another partial stream, for example, which is fed directly from the material cooler into the calcinator, thus creating a combustion chamber bypass.In the combustion chamber, the thermal energy required for the process is provided by burning natural gas, hydrogen, coal, ammonia, or alternative fuels such as biomass, used tires, or household waste. Such systems are known for the thermal treatment of mineral materials, especially clays.

[0014] According to the invention, a residence time device is arranged between the combustion chamber and the calcinator, thus positioning the combustion chamber outside the solids stream. Pollutants, such as NOₓ, are produced in the combustion chamber at combustion temperatures. Hydrocarbons and hydrocarbon-containing compounds can also escape from the fuel. This can be a particularly relevant issue when using alternative fuels. Typically, the combustion chamber is either located within the calcinator, for example, in the case of natural gas firing, or directly adjacent to the calcinator, especially for alternative fuels. The direct connection prevents heat loss and also saves on investment costs and installation space. This ensures that the heat is generated as close as possible to where it is needed for the intended conversion process.At the same time, this achieves a higher degree of temperature stability in the reaction zone in a simple manner. Therefore, it initially appears disadvantageous to spatially separate the combustion chamber and the calciner and to place a residence time device between them, thus clearly separating the combustion chamber from the solids stream and therefore from the energy sink of the reaction. However, this approach makes it possible to treat the exhaust gases from the combustion chamber at an ideal temperature level, thereby eliminating the need for subsequent and energy-intensive exhaust gas treatment. Furthermore, the exhaust gases are treated separately from the solids stream and before the hot exhaust gases come into contact with it.The residence time device allows for a separation of temperatures for exhaust gas treatment in the residence time device and for thermal treatment, for example of clay, in the calciner. This enables the selection of a suitable temperature range for both exhaust gas treatment and thermal treatment. In particular, the temperature in the residence time device can be set higher than in the calciner, allowing for the combustion of CxHy, especially with oxygen, or, in the presence of, for example, ammonia, NOx to be converted to nitrogen (and water) through synproportionation of NOx and NH3. The type of pollutants is typically highly dependent on the type of fuel used.

[0015] The residence time device is also preferably arranged completely outside the solids stream, although a certain degree of backmixing at the connection between the residence time device and the calcinator cannot naturally be ruled out. However, the net gas stream is directed entirely from the combustion chamber to the calcinator.

[0016] In a further embodiment of the invention, an auxiliary combustion device is arranged between the combustion chamber and the residence time device and / or within the residence time device. This embodiment is preferred when the combustion chamber is designed for the combustion of alternative fuels. Alternative fuels typically exhibit a greater variation in calorific value. The auxiliary combustion device is preferably designed for the combustion of a fuel that enables rapid and precisely adjustable combustion. The auxiliary combustion device is preferably designed to combust a fuel selected from the group consisting of pulverized coal, natural gas, hydrogen, biogas, and ammonia.This makes it possible to compensate for temperature fluctuations caused by variations in the fuel in the combustion chamber in a targeted and rapid manner, ensuring a stable temperature in the residence time device and thus guaranteeing a reliable pollutant degradation process.

[0017] In a further embodiment of the invention, the residence time device is tubular in shape. For example, the tubular residence time device can be swan-neck shaped. Likewise, the tubular residence time device can be designed as a flared pipe. The residence time device can optionally be equipped with one or more flow-enhancing elements to improve intensive mixing of the gas within the device.

[0018] In a further embodiment of the invention, a first reaction agent feed is arranged between the combustion chamber and the residence time device. The reaction agent feed serves to supply a reaction agent for pollutant conversion. Since the pollutants to be treated are highly dependent on the fuel burned in the combustion chamber, the reaction agent, and thus the first reaction agent feed, must be selected according to the fuel to be used in the combustion chamber.

[0019] In a further embodiment of the invention, the first reaction medium supply is configured to supply oxygen, for example also in the form of air or air preheated in the material cooler. Oxygen is required as a reactant for the conversion of hydrocarbon C₆H₅ to water and carbon dioxide.

[0020] In a further embodiment of the invention, the first reaction agent feed is designed to supply various types of reducing agents, for example ammonia, urea, their compounds or solutions, in particular aqueous solutions. Ammonia or urea can synproportionate with nitrogen oxides (NOx) to form nitrogen.

[0021] In a further embodiment of the invention, the device comprises at least one first NOₓ analyzer. The NOₓ analyzer serves to determine the NOₓ concentration. Typically, a device utilizing infrared spectroscopy is used as the NOₓ analyzer. In one embodiment, the at least one first NOₓ analyzer is arranged in the residence time device or between the residence time device and the calciner. This has the advantage of immediate feedback and faster controllability. Additionally or alternatively, the at least one first or a second NOₓ analyzer can be arranged in or downstream of the preheater. The advantage of this embodiment is that the gases are significantly cooler here, which simplifies the measurement.At least one first or second NO x analyzer can also be located after the calcinator or even after the preheater, since the temperature in these should no longer be high enough for the formation of NO x, so that this value is also meaningful for the NO x content in the residence time device.

[0022] In a further embodiment of the invention, the device comprises at least one NH3 analyzer. The NH3 analyzer serves to detect the NH3 concentration in the gas stream. Preferably, several NH3 analyzers are used to determine the concentration at different points along the exhaust gas stream. The NH3 analyzer, or at least two NH3 analyzers, are located, for example, on different levels of the calciner and regulate / control the addition of the reactant to determine its utilization and thus ensure its effective use. The at least one NH3 analyzer, preferably the at least two NH3 analyzers, are located, for example, and preferably, in close proximity to the at least one NOx analyzer and / or at least one temperature sensor.The NH3 analyzer(s) are connected via at least one metering system to corresponding containers, preferably to at least one container for ammonia. This allows, for example, ammonia to be injected into the gas stream at different locations and / or levels in the same or different quantities and / or concentrations.

[0023] In a further embodiment of the invention, the device comprises at least one first control device. This first control device is configured to read the at least one first NOₓ analyzer. The first control device is configured to control the first reagent feed and / or an optional second reagent feed depending on the NOₓ value detected by the at least one first NOₓ analyzer. It regulates the first reagent feed and / or the optional at least one further reagent feed, preferably at different levels and / or with multiple nozzles, depending on the detected NOₓ value. This enables the targeted addition of the reagent, for example, ammonia, thereby preventing overdosing of the reagent and the associated emission of, for example, ammonia.

[0024] In a further embodiment of the invention, the device comprises at least one first control device. This first control device is configured to read the at least one first NH3 analyzer. The first control device is configured to control the first reagent feed and / or at least one further reagent feed depending on the NH3 value detected by the at least one first NH3 analyzer, and regulates the first reagent feed and / or the at least one optional second reagent feed depending on the detected NH3 value. This enables the targeted addition of the reagent, for example, ammonia, thereby preventing overdosing of the reagent and the associated emission of, for example, ammonia.

[0025] In a further embodiment of the invention, the device includes a temperature sensor. For the purposes of this invention, "temperature sensor" is to be understood broadly and encompasses any sensor system for temperature detection. The temperature sensor can be a thermocouple. Alternatively, a temperature sensor can also be an acoustic sensor that determines the temperature over a spatial distance using the speed of sound. Preferably, the temperature sensor is arranged in the first combustion chamber, in the residence time device, or between the combustion chamber and the residence time device. The device can also include several temperature sensors, particularly at the aforementioned positions.

[0026] In a further embodiment of the invention, the device comprises at least one first control device. This first control device is configured to read the temperature sensor(s). It is designed to control the first reaction agent feed and / or an at least optional second reaction agent feed and / or the auxiliary combustion device depending on the temperature detected by the temperature sensor. This enables the targeted addition of fuel, which in turn allows for precise temperature adjustment to the desired temperature range.

[0027] In a further embodiment of the invention, the first reaction agent supply is designed for a supply with a pressure of 0.5 bar to 5 bar.

[0028] In a further embodiment of the invention, a first water supply is arranged adjacent to the first reagent supply. The water injection through the water supply can be used for targeted temperature control to optimally adjust the temperature level for pollutant minimization. The water supply is not typically used solely for water; aqueous solutions, particularly process wastewater, are usually employed, which may also contain other substances. Preferably, the calorific value of these other substances is not so high as to compensate for the cooling effect resulting from the evaporation of the water. For example, aqueous solutions containing organic compounds can be used here, as the organic compounds are reliably converted under the prevailing conditions.

[0029] In a further embodiment of the invention, the device comprises at least one first control device. This first control device is configured to read the temperature sensor(s). It is designed to control the water supply based on the temperature detected by the temperature sensor. This allows for targeted adjustment of the temperature to the desired temperature range.

[0030] In a further embodiment of the invention, the residence time device has a length such that the residence time in the residence time device lies between 0.5 s and 10 s, in particular between 1 s and 5 s, and most preferably between 1.5 s and 2.5 s. This achieves a suitable window between sufficient reaction time and heat loss and flow resistance.

[0031] In a further embodiment of the invention, a reduction device is arranged between the calcinator and the material cooler. A reduction device serves to treat the thermally treated material in a reducing atmosphere, particularly for color optimization. For example, gases, solids, and / or liquids can be used to create the reducing atmosphere, containing, for example, carbon, hydrogen, nitrogen, carbon monoxide, or the like, or corresponding compounds thereof, such as methane or ammonia, or mixtures thereof, as well as inert gases, particularly nitrogen. The reducing atmosphere can also be generated by substoichiometric combustion (a deficiency of oxygen). For example, this can reduce Fe III to Fe II, resulting in a reduction in the product's color and thus increased market acceptance.

[0032] In a further embodiment of the invention, the residence time device includes a catalyst. The catalyst is, for example, a platinum-rhodium catalyst suitable for the conversion of NOₓ and NH₃ to nitrogen.

[0033] In a further embodiment of the invention, the residence time device has at least one deflection. Alternatively or additionally, the residence time device has flow elements for gas mixing. In particular, the residence time device can be designed in a swan-neck shape. In addition to the compact spatial arrangement, the deflections lead to mixing. Furthermore, this allows for the compensation of height differences, which facilitates a compact design.

[0034] In a further embodiment of the invention, the residence time device has at least one second reagent feed. The at least second reagent feed is arranged between the combustion chamber and the residence time device or on the residence time device and is preferably connected to an optional control device. In a first case, the first reagent feed and the at least second reagent feed are configured to supply the same reagent. For example, both can be configured to supply ammonia. In particular, the first reagent feed and the at least second reagent feed are thus spaced apart from each other. This allows the concentration, for example of ammonia for NOₓ reduction, to be kept more constant.In a second case, the first reaction agent supply serves to supply a first reaction agent, for example NH 3 for the NO x degradation, and the at least second reaction agent supply serves to supply at least one second reaction agent, for example O 2 or air for the C x H y degradation.

[0035] In a further embodiment of the invention, the device includes an SCR reactor, the SCR reactor being arranged in the gas stream downstream of the preheater. The SCR reactor can be used, in particular, as a backup solution. As long as the NOₓ reduction according to the invention is sufficient, the SCR reactor is not operated, for example, thus saving the necessary energy.

[0036] In a further embodiment of the invention, the device has a bypass, the bypass being arranged between the combustion chamber and the calciner. The bypass is arranged parallel to the residence time device in terms of flow direction. Thus, a first partial flow is routed through the residence time device and a second partial flow is routed through the bypass. This enables optimal utilization of the permissible emissions.

[0037] In a further aspect, the invention relates to a method for operating a device according to the invention. The temperature in the residence time device is selected between 750 °C and 1300 °C. In particular, the temperature in the residence time device is selected between 800 °C and 1100 °C, and more preferably between 900 °C and 1050 °C.

[0038] In a further embodiment of the invention, a thermal treatment of mineral material, in particular clays or clay-like substances, is carried out.

[0039] The device according to the invention is explained in more detail below with reference to an embodiment shown in the drawing. Fig. 1 Device

[0040] In Fig. 1An exemplary apparatus is shown schematically. The material to be treated, for example, clay, is fed to the preheater 10 via a material feeder 110, preheated, and introduced into the calciner 20, where it undergoes thermal treatment. From the calciner 20, the material enters an optional reduction unit 100, where it is, in particular, color-optimized, and then enters the material cooler 30, from which the finished product is then removed via a product outlet 120. In a countercurrent flow, the gas is first introduced into the material cooler 30 via a gas supply 130 and heated there by the product being cooled. The heated gas then enters the combustion chamber 40. There, for example, a substitute fuel, such as waste, is burned. During combustion, nitrogen oxides can be formed simply due to the temperature and the presence of nitrogen and oxygen. The combustion chamber (40) and residence time device (50) are preferably equipped with temperature sensors.Furthermore, the gases are hottest when they leave the combustion chamber 40, making this point ideal for decomposing the nitrogen oxides. To compensate for fluctuations in the calorific value of the secondary fuel, the device includes an auxiliary combustion unit 60 (optionally several auxiliary combustion units 60), which is operated, for example, with gas, liquid fuel, or pulverized coal and is thus able to reliably regulate the temperature. The system also features a water inlet 62, which allows water to be added and the temperature to be easily lowered. The combination of the auxiliary combustion unit 60 and the water inlet 62 thus enables particularly precise temperature control. Additionally, an ammonia solution is injected via a first reaction agent inlet 70.This allows a reaction between NOₓ and NH₃ to take place in the residence time device 50 at, for example, 1000 °C. To complete the reaction and avoid producing an excess of ammonia (and thus introducing a new source of pollutants), the device has a second reaction agent feed 72, into which ammonia solution is injected again at a later point in the residence time device 50. Additionally, an NOₓ analyzer 80 and an NH₃ analyzer (82) are arranged in the residence time device. Furthermore, an NOₓ analyzer 80 and an NH₃ analyzer (82) are arranged downstream of the preheater.The NOₓ analyzers 80 and the NH₃ analyzers (82) are connected to a first control device 90, which regulates the injection of ammonia solution through the first reaction agent feed 70 and the second reaction agent feed 72 based on the NOₓ content detected by the NOₓ analyzer 80 and the NH₃ content detected by the NH₃ analyzer, as well as the temperature level detected by temperature sensors. From there, the warm gas, free of NOₓ and containing only small amounts of NH₃, enters the calcinator 20. For certain products, the calcinator can be operated at, for example, 750 °C, which would be too low to convert NOₓ within the calcinator 20. From the calcinator 20, the gas is fed into the preheater 10, where it transfers its heat to the material being fed into the calciner. The exhaust gas from the preheater 10 is then released via a gas outlet 140 and can, for example, be subjected to further treatment, such as dust removal. Reference sign

[0041] 10 Preheater 20 Calcinator 30 Material Cooler 40 Combustion Chamber 50 Residence Time Device 60 Auxiliary Combustion Device 62 Water Supply 70 First Reaction Medium Supply 72 Second Reaction Medium Supply 80 NOx Analyzer 82 NH3 Analyzer 90 Control Device 100 Reduction Device 110 Material Supply 120 Product Discharge 130 Gas Supply 140 Gas Discharge

Claims

1. A device for the thermal treatment of mineral materials, wherein the device comprises at least a preheater (10), a calciner (20) and a materials cooler (30), wherein a solids stream is guided into the preheater (10), from the preheater (10) into the calciner (20), from the calciner (20) into the materials cooler (30), and out of the materials cooler (30), wherein a gas stream is guided into the materials cooler (30), from the materials cooler (30) into the calciner (20), from the calciner (20) into the preheater (10), and out of the preheater (10), wherein the device comprises a combustion chamber (40), wherein the gas stream from the materials cooler (30) is guided at least partially through the combustion chamber (40) into the calciner (20), characterized in that a residence time device (50) is arranged between the combustion chamber (40) and the calciner (20), and so the combustion chamber (40) is arranged outside the solids stream.

2. The device as claimed in claim 1, characterized in that at least one auxiliary combustion device (60) is arranged between the combustion chamber (40) and the residence time device (50) and / or in the residence time device (50).

3. The device as claimed in either of the preceding claims, characterized in that a first reactant feed (70) is arranged between the combustion chamber (40) and the residence time device (50).

4. The device as claimed in claim 3, characterized in that at least the first reactant feed (70) is configured for the supply of ammonia, urea, compounds thereof or solutions of these.

5. The device as claimed in any of the preceding claims, characterized in that the device comprises at least one first NOx analyzer (80).

6. The device as claimed in claim 4 in combination with claim 5, characterized in that the device comprises at least one control device (90), wherein the at least one first control device (90) is configured for reading the at least one first NOx analyzer (80), wherein the at least one first control device (90) is configured for actuating at least one first reactant feed (70) in dependence on the NOx value detected by at least one first NOx analyzer (80) by adapting the type and / or amount and / or concentration of the reactant.

7. The device as claimed in any of the preceding claims, characterized in that the device comprises at least one temperature sensor.

8. The device as claimed in any of claims 3 to 6 in combination with claim 7, characterized in that the device comprises at least one first control device (90), wherein the at least one first control device (90) is configured for reading the temperature sensor, wherein the at least one first control device (90) is configured for actuating at least one first reactant feed (70) and / or at least one auxiliary combustion device (60) and / or at least one water feed (62) in dependence on the temperature detected by the temperature sensor by adapting the type and / or amount and / or concentration of the reactant.

9. The device as claimed in any of the preceding claims, characterized in that the device comprises at least one NH3 analyzer.

10. The device as claimed in any of claims 3 to 8 in combination with claim 9, characterized in that the device comprises at least one control device (90), wherein the at least one first control device (90) is configured for reading the at least one first NH3 analyzer (82), wherein the at least one first control device (90) is configured for actuating at least one first reactant feed (70) in dependence on the NH3 value detected by at least one first NH3 analyzer (82) by adapting the type and / or amount and / or concentration of the reactant.

11. The device as claimed in claim 10, characterized in that the reactant feed is mounted at at least one addition point, preferably at least two addition points, in at least one height plane, preferably in at least two different height planes.

12. The device as claimed in any of claims 3 to 8, characterized in that the first reactant feed (70) is designed for a feed with a pressure of 0.5 bar to 5 bar.

13. The device as claimed in any of claims 3 to 12, characterized in that at least one first water feed (62) is arranged adjacent to the first reactant feed (70).

14. The device as claimed in any of the preceding claims, characterized in that the residence time device (50) has a length, so that the residence time in the residence time device (50) is between 0.5 s and 10 s, more particularly between 1 s and 5 s, particularly preferably from 1.5 s to 2.5 s.

15. The device as claimed in any of the preceding claims, characterized in that a reduction device (100) is arranged between the calciner (20) and the materials cooler (30).

16. The device as claimed in any of the preceding claims, characterized in that the residence time device (50) comprises a catalyst.

17. The device as claimed in any of the preceding claims, characterized in that the residence time device (50) comprises at least one diversion and / or flow internals for the gas mixture.

18. The device as claimed in any of the preceding claims, characterized in that the residence time device (50) comprises at least one second reactant feed (72), wherein the second reactant feed (72) is arranged between the combustion chamber (40) and the residence time device (50) or at the residence time device (50).

19. The device as claimed in any of the preceding claims, characterized in that the device comprises a catalytic reactor, wherein the catalytic reactor is arranged in the gas stream downstream of the preheater (10).

20. A method for operating a device as claimed in any of the preceding claims, characterized in that the selected temperature in the residence time device (50) is between 750°C and 1300°C.

21. The method as claimed in claim 20, characterized in that the selected temperature in the residence time device (50) is between 900°C and 1050°C.

22. The method as claimed in any of claims 20 to 21, characterized in that a thermal treatment of clays or claylike substances takes place.