Avoiding emissions during production of artificial pozzolana made of mineral material, in particular clay

Abstract

The invention relates to a plant for heat treatment, the plant comprising at least one preheater (10), a calciner (20) and a material cooler (30), a solid stream being introduced into the preheater (10), from the preheater (10) into the calciner (20), from the calciner (20) into the material cooler (30), and from the material cooler (30); wherein a gas stream is introduced into the material cooler (30), from the material cooler (30) into the calcining furnace (20), from the calcining furnace (20) into the preheater (10), and then from the preheater (10), and wherein the device comprises a combustion chamber (40), through which the gas stream from the material cooler (30) is at least partially introduced into the calcining furnace (20), characterized in that the gas stream is introduced into the calcining furnace (20) from the combustion chamber (40). A residence time device (50) is arranged between the combustion chamber (40) and the calcining furnace (20).

Description

[0001] The invention relates to an apparatus and method for achieving waste gas treatment in a process to convert pollutants without the need for downstream waste gas treatment, thereby reducing or avoiding energy consumption for waste gas treatment.

[0002] Alternative fuels are increasingly being used to replace primary raw materials such as pulverized coal, in particular to 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, such alternative fuels are often burned in a combustion chamber attached to the side of the actual process unit. The advantage of this is that a very direct connection can be achieved between the heat generation in the combustion chamber and the heat required for the reaction in the process unit.

[0003] The combustion of the heated fuel is accompanied by the formation of nitrogen oxides (NOx for short), and may also produce some unburned hydrocarbons and hydrocarbon-containing compounds. For the sake of simplicity (and ignoring other heteroatoms), these compounds are collectively referred to as CxHy in this article. NOx can be converted into nitrogen by non-catalytic reduction (SNCR) or catalytic reduction (SCR), especially using ammonia (NH3) or urea. The hydrocarbons CxHy can react with oxygen to produce water and carbon dioxide. Such conversions usually require a temperature window above 800°C. Therefore, it is usually necessary to reheat the relatively cold exhaust gas in exhaust gas treatment, which not only consumes energy but also often requires additional heat exchangers.

[0004] A method for producing a clinker substitute is known from DE 10 2011 014 498 A1.

[0005] US 9 458 059 B2 describes a process for producing synthetic pozzolanic materials.

[0006] WO 2012 / 082683 A1 describes a method for producing an artificial pozzolanic material.

[0007] WO 2005 / 108891 A1 describes an apparatus and a method for producing cement clinker.

[0008] EP 2 587 149 A1 discloses a method and a device for reducing nitrogen oxide-containing gases in the exhaust gas of a rotary kiln.

[0009] A method for controlling the temperature of a precalcining furnace is known from EP 1 898 171 A1.

[0010] The object of the invention is to save energy in the exhaust gas treatment process and thereby avoid additional CO2 emissions due to the combustion of fuel, for example as a heat source.

[0011] The invention is achieved by an apparatus having the features of claim 1 and a process having the features of claim 20. Advantageous features of the invention emerge from the dependent claims, the subsequent description and the drawings.

[0012] The device of the present invention is mainly used for thermal treatment of mineral materials, especially clay, to produce artificial pozzolanic materials as an additive to cement clinker. Clay is becoming an increasingly important raw material in the cement industry because, during its thermal treatment, the raw material itself releases less or almost no CO2 compared to limestone calcination. However, since the activation temperature of mineral materials, especially clay, is generally below 800°C, the temperature inside the calciner is not sufficient to reliably convert pollutants. The device includes at least one preheater, a calciner and a material cooler. The preheater can be configured as a co-flow heat exchanger with a cyclone separator, or a series of two to six co-flow heat exchangers with cyclones. Alternatively, the preheater can also be designed as a cross-flow heat exchanger. Similarly, the material cooler can preferably be configured as a co-flow heat exchanger with a cyclone separator, or a cascade of two to six co-flow heat exchangers with cyclones. Optionally, the material cooler can also be designed as a cross-flow heat exchanger. The solids stream is directed into a preheater, from the preheater into a calciner, from the calciner into a charge cooler and out of the charge cooler. Countercurrently thereto, a gas stream is directed into a charge cooler, from the charge cooler into a calciner, from the calciner into a preheater and out of the preheater. The device comprises a combustion chamber. The gas stream from the charge cooler at least partially passes through the combustion chamber into the calciner. In addition, there may be another part of the gas stream, for example directly from the charge cooler into the calciner, which means that a combustion chamber bypass is formed. In the combustion chamber, the heat energy required for the process is provided by the combustion of natural gas, hydrogen, coal, ammonia or alternative fuels such as biomass, waste tires or household waste. It is well known that such devices can be used for the thermal treatment of mineral substances, in particular clays.

[0013] According to the invention, a residence time device is provided between the combustion chamber and the calciner, so that the combustion chamber is arranged outside the solid material flow. Pollutants are formed in the combustion chamber, for example, NOx is formed at the combustion temperature. In addition, hydrocarbons and their hydrocarbon-containing compounds may also be released from the combustion material, which may be an important problem, especially when using alternative fuels. Generally, the combustion chamber can be arranged in the calciner (for example, when natural gas is used for combustion), or directly on the calciner (especially when using alternative fuels). This direct connection can prevent heat loss on the one hand, while also saving investment costs and construction space. Therefore, the heat generated is as close as possible to where the expected reaction is required. At the same time, this can also achieve higher temperature stability in the reaction area in a simple way. Therefore, it seems that it is not advantageous to separate the combustion chamber and the calciner in space and to provide a residence time device between the two, so that the combustion chamber is clearly separated from the solid material flow and the energy absorption position required for the reaction. However, this allows the exhaust gas of the combustion chamber to be treated at an ideal temperature level, thereby avoiding high energy consumption exhaust gas treatment downstream. Furthermore, the treatment of the exhaust gases can be carried out separately from the solid material flow and before the hot exhaust gases come into contact with the solid material flow. By means of a residence time device, the temperature of the exhaust gas treatment in the residence time device can be separated from the temperature of the heat treatment of the clay in, for example, the calciner, so that suitable temperature windows can be selected for the exhaust gas treatment and the heat treatment. In particular, the temperature in the residence time device can be selected to be higher than the temperature in the calciner, so that in this case CxHy can be burned, in particular with oxygen, or NOx can be generated into nitrogen (and water) by co-oxidation of NOx and NH3 in the presence of substances such as ammonia. The nature of the pollutants is usually closely related to the type of fuel used.

[0014] The residence time device is likewise preferably arranged completely outside the solids flow, although a certain degree of backmixing in the connection between the residence time device and the calciner cannot of course be completely excluded. However, the net gas flow is directed completely from the combustion chamber to the calciner.

[0015] In a further embodiment of the invention, an auxiliary combustion device is provided between the combustion chamber and the residence time device and / or in the residence time device. This embodiment is particularly preferred when the combustion chamber is used to burn alternative fuels. The calorific value of alternative fuels usually fluctuates greatly. The auxiliary combustion device is preferably designed to burn fuels that can achieve rapid and selectively adjustable combustion. The auxiliary combustion device is preferably used to burn fuels selected from the following fuel groups: pulverized coal, natural gas, hydrogen, biogas and ammonia. Thus, temperature changes caused by fluctuations in the fuel material in the combustion chamber can be quickly and accurately compensated, thereby ensuring a stable temperature in the residence time device and thus enabling a reliable pollutant removal process.

[0016] In a further embodiment of the present invention, the residence time device is a tubular structure. For example, the tubular residence time device can have a gooseneck structure. The tubular residence time device can also be designed as an expansion pipeline. In addition, the residence time device is optionally equipped with one or more flow internals to enhance the full mixing of gas in the device.

[0017] In another embodiment of the present invention, a first reactant supply device is provided between the combustion chamber and the residence time device. The reactant supply device is used to provide reactants for pollutant conversion. Since the pollutants to be treated are closely related to the fuel burned in the combustion chamber, appropriate reactants and corresponding first reactant supply devices should be selected according to the fuel used in the combustion chamber.

[0018] In another embodiment of the invention, the first reactant supply device is configured to supply oxygen, including for example in the form of air or air preheated in a charge cooler. Oxygen is necessary as a reaction partner for converting hydrocarbons CxHy into water and carbon dioxide.

[0019] In another embodiment of the present invention, the first reactant supply device is configured to supply various types of reducing agents, such as ammonia, urea, compounds thereof, or solutions of these substances, especially aqueous solutions. Ammonia or urea can selectively reduce nitrogen oxides NOx to generate nitrogen.

[0020] In another embodiment of the present invention, the device includes at least one first NOx analyzer. The NOx analyzer is used to detect the NOx concentration. Typically, an infrared spectroscopy-based device is used as the NOx analyzer. In one embodiment, at least one first NOx analyzer is arranged in the residence time device or between the residence time device and the calciner. The advantage of this arrangement is that instant feedback and faster adjustment capabilities can be achieved. In addition or alternatively, at least one first or second NOx analyzer can be arranged in the preheater or downstream of the preheater. The advantage of this embodiment is that the gas temperature here is lower, thereby simplifying the measurement. At least one first or second NOx analyzer can also be arranged after the calciner, or even after the preheater, because the temperature at these locations should no longer be high enough to form NOx, so this value is also meaningful for the NOx content in the residence time device.

[0021] In another embodiment of the present invention, the device comprises at least one first NH3 analyzer. The NH3 analyzer is used to detect the NH3 concentration in the gas flow. Preferably, multiple NH3 analyzers are used to determine the concentration at different points in the exhaust gas path. One or at least two NH3 analyzers are located at different levels of, for example, the calciner and adjust / control the addition of reactants to determine the utilization rate of the reactants, thereby ensuring the effective utilization of the reactants. At least one NH3 analyzer, preferably at least two NH3 analyzers, are located, for example and preferably close to at least one NOx analyzer and / or at least one temperature sensor. The NH3 analyzer is connected to a corresponding container, preferably to at least one ammonia container, via at least one metering system. Thus, for example, ammonia can be injected into the gas stream in the same or different amounts and / or concentrations at different points and / or levels.

[0022] In another embodiment of the present invention, the device includes at least one first control device. At least one first control device is configured to read data from at least one first NH3 analyzer. At least one first control device is configured to start the first reactant supply device and / or at least one further reactant supply device according to the NH3 value detected by the at least one first NH3 analyzer, and adjust the first reactant supply device and / or at least one optional second reactant supply device according to the detected NH3 value, preferably at different levels and / or through multiple nozzles. In this way, reactants, such as ammonia, can be added in a targeted manner, thereby avoiding excessive reactants and related ammonia emissions.

[0023] In another embodiment of the invention, the device comprises a temperature sensor. In the present invention, the temperature sensor should be understood in a broad sense, covering any sensor system for temperature detection. The temperature sensor can be a thermocouple. Alternatively, the temperature sensor can also be an acoustic sensor, which determines the temperature over a spatial distance by the speed of sound. The temperature sensor is preferably 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 have a plurality of temperature sensors, in particular in the above-mentioned positions.

[0024] In another embodiment of the present invention, the apparatus comprises at least one first control device. The at least one first control device is used to read a temperature sensor. The at least one first control device is configured to start the first reactant supply device and / or at least one optional second reactant supply device and / or the auxiliary combustion device according to the temperature detected by the temperature sensor. In this way, fuel can be added in a targeted manner, so that the temperature can be accurately adjusted to the desired temperature window.

[0025] In another embodiment of the present invention, the first reactant supply device is designed to supply the reactant at a pressure of 0.5 bar to 5 bar.

[0026] In another embodiment of the present invention, the first water supply device is arranged near the first reactant supply device. Injecting water through the water supply device can be used to adjust the temperature in a targeted manner, thereby optimizing the temperature level to minimize pollutants. The water supply device is usually not only used to supply water; aqueous solutions, especially process wastewater, are usually used, which may also contain other substances. The calorific value of other substances is preferably not too high to offset the cooling effect caused by water evaporation. Therefore, for example, an aqueous solution containing a certain proportion of organic compounds can be used because these organic compounds can be reliably converted under existing conditions.

[0027] In another embodiment of the present invention, the device comprises at least one first control device. The at least one first control device is configured to read a temperature sensor. The at least one first control device is configured to drive the water supply device according to the temperature detected by the temperature sensor. This enables the temperature to be adjusted to a desired temperature window in a targeted manner.

[0028] In another embodiment of the invention, the residence time device has a certain length, so that the residence time in the residence time device is between 0.5 seconds and 10 seconds, more particularly between 1 second and 5 seconds, and particularly preferably between 1.5 seconds and 2.5 seconds. This provides a suitable window between sufficient reaction time and heat loss and flow resistance.

[0029] In another embodiment of the present invention, the reducing device is arranged between the calcining furnace and the material cooler. The reducing device is used to treat the heat-treated material in a reducing atmosphere, in particular for color optimization. In order to form a reducing atmosphere, gases, solids and / or liquids can be used, for example including carbon, hydrogen, nitrogen, carbon monoxide, etc. or their corresponding compounds, such as methane or ammonia or mixtures thereof, and inert gases, in particular nitrogen. The reducing atmosphere can also be produced by substoichiometric combustion (lack of oxygen). For example, FeIII can be reduced to FeII in this way, thereby reducing the color in the product, thereby improving market acceptance.

[0030] In another embodiment of the present invention, the residence time device comprises a catalyst, such as a platinum-rhodium catalyst, suitable for converting NOx and NH3 into nitrogen.

[0031] In another embodiment of the invention, the residence time device comprises at least one flow splitter. Alternatively, or in addition, the residence time device further comprises a fluid internal device for gas mixing. In particular, the residence time device can be designed in a gooseneck shape. In addition to a compact spatial arrangement, the flow splitter also enables mixing. In addition, this also allows compensation of height differences, thereby promoting a compact design.

[0032] In another embodiment of the invention, the residence time device comprises at least one second reactant supply device. At least the second reactant supply device is arranged between the combustion chamber and the residence time device or on the residence time device, preferably connected to an optional control device. In a first case, the first reactant supply device and the at least second reactant supply device are configured to supply the same reactant. For example, both can be configured to supply ammonia. In particular, the first reactant supply device and the at least second reactant supply device are spaced apart from each other. In this way, the NO x The concentration of the removed ammonia can be kept stable. In the second case, the first reactant supply device is used to supply a first reactant, such as NH3 for removing nitrogen oxides, and at least the second reactant supply device is used to supply at least one second reactant, such as O2 or air for removing CxHy.

[0033] In another embodiment of the invention, the apparatus comprises an SCR reactor, wherein the SCR reactor is arranged in the gas stream downstream of the preheater. The SCR reactor can be used in particular as a backup solution. x If it is high enough, the SCR reactor will not be operated, thus saving the required energy.

[0034] In another embodiment of the invention, the apparatus has a bypass, wherein the bypass is arranged between the combustion chamber and the calciner. The bypass is arranged fluidically parallel to the residence time device. Thus, a first part of the gas flow is guided through the residence time device and a second part of the gas flow is guided through the bypass. This achieves an optimal utilization of the permitted emissions.

[0035] In another aspect, the invention relates to a method for operating the apparatus according to the invention. The temperature selected in the residence time device is between 750° C. and 1300° C. In particular, the temperature selected in the residence time device is between 800° C. and 1100° C., particularly preferably between 900° C. and 1050° C.

[0036] In another embodiment of the invention, the mineral material, in particular clay or clay-like substances, is subjected to a heat treatment.

[0037] The device of the present invention will be described in more detail below with reference to an exemplary embodiment in the drawings.

[0038] Figure 1 equipment

[0039] Figure 1A schematic diagram of an exemplary device is provided. The material to be treated (e.g. clay) enters the preheater 10 through the material feed inlet 110 and, after preheating, enters the calciner 20 where it is heat treated. From the calciner 20, the material enters the optional reduction device 100, where the color is optimized, and then enters the material cooler 30, and finally the finished product is extracted from the material cooler 30 through the product receiving device 120. In countercurrent, the gas first enters the material cooler 30 through the gas supply device 130 and is heated there by the product to be cooled. The heated gas enters the combustion chamber 40. Here, alternative fuels such as garbage are burned. During the combustion process, nitrogen oxides are produced due to the temperature and the presence of nitrogen and oxygen. The combustion chamber (40) and the residence time device (50) are preferably equipped with temperature sensors. In addition, the gas is at its highest temperature when it leaves the combustion chamber 40, so it is very suitable for decomposing nitrogen oxides again at this time. In order to compensate for fluctuations in the calorific value of the secondary fuel, the device comprises an auxiliary combustion device 60 (which may be a plurality of auxiliary combustion devices 60), which can be operated using gas, liquid fuel or pulverized coal, etc., and thus can reliably regulate the temperature. In addition, the device also comprises a water supply device 62, through which water can be supplied, thereby reducing the temperature in a simple manner. The combination of the auxiliary combustion device 60 and the water supply device 62 thus allows particularly selective temperature regulation. In addition, an ammonia solution is injected through the first reactant supply device 70. Thus, NO x and NH3 can react in the residence time device 50 at, for example, 1000°C. In order to complete the reaction without producing excessive ammonia (thus introducing a new source of pollution), the device also includes a second reactant supply device 72, which injects ammonia solution again at a later position of the residence time device 50. In addition, a NO x Analyzer 80 and NH3 analyzer (82). In addition, NO x The analyzer 80 and the NH3 analyzer (82) are arranged after the preheater. x The analyzer 80 and the NH3 analyzer (82) are connected to a first control device 90 which controls the NO x NO detected by analyzer 80 x The ammonia solution injected through the first reactant supply 70 and the second reactant supply 72 is regulated based on the NH3 content detected by the NH3 analyzer and the temperature level detected by the temperature sensor. From there, the hot gases enter the calciner 20 with NOx removed and only a small amount of NH3. For some products, the calciner can be operated at a temperature of 750°C, but this temperature is too low to convert NOx in the calciner 20. From the calciner 20, the gases enter the preheater 10, where they transfer heat to the supplied material. The exhaust gases from the preheater 10 are then discharged through the gas discharge port 140 and can be used for further treatment, such as dust removal, for example.

[0040] List of reference numerals:

[0041] 10 Preheater

[0042] 20 Calcination furnace

[0043] 30 Material Cooler

[0044] 40 Combustion Chamber

[0045] 50 Dwell time device

[0046] 60 Auxiliary combustion device

[0047] 62 Water supply device

[0048] 70 first reactant supply device

[0049] 72. Second reactant supply device

[0050] 80NO x Analyzer

[0051] 82NH3 Analyzer

[0052] 90 Control Device

[0053] 100 Restore Device

[0054] 110 Material inlet

[0055] 120 Product receiving device

[0056] 130 Gas supply device

[0057] 140 Gas exhaust port.

Claims

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

2. The device according to 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 within the residence time device (50).

3. A device as claimed in any preceding claim, characterised in that The first reactant supply device (70) is arranged between the combustion chamber (40) and the residence time device (50).

4. The device according to claim 3, characterized in that At least the first reactant supply device (70) is configured to supply ammonia, urea, compounds thereof, or solutions of these substances.

5. A device as claimed in any preceding claim, characterised in that The device comprises at least one first NO x Analyzer (80).

6. The device according to 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 to read the at least one NO x A first analyzer (80), wherein at least one first control device (90) is configured to x The NO detected by the analyzer (80) x The at least one first reactant supply device (70) is driven by adjusting the type and / or amount and / or concentration of the reactant.

7. A device as claimed in any preceding claim, characterised in that The device comprises at least one temperature sensor.

8. The device according to any one 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 to read a temperature sensor, wherein the at least one first control device (90) is configured to drive at least one first reactant supply device (70) and / or at least one auxiliary combustion device (60) and / or at least one water supply device (62) by adjusting the type and / or amount and / or concentration of the reactant according to the temperature detected by the temperature sensor.

9. Apparatus according to any preceding claim, characterised in that The apparatus comprises at least one NH3 analyser.

10. The device according to any one 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 to read at least one first NH3 analyzer (82), wherein the at least one first control device (90) is configured to drive at least one first reactant supply device (70) by adjusting the type and / or quantity and / or concentration of the reactant according to the NH3 value detected by the at least one first NH3 analyzer (82).

11. The device according to claim 10, characterized in that The reactant supply device is installed at at least one feeding point, preferably at least two feeding points, and at least one height plane, preferably at least two different height planes.

12. The device according to any one of claims 3 to 8, characterized in that The first reactant supply device (70) is designed to have a feed pressure of 0.5 bar to 5 bar.

13. The device according to any one of claims 3 to 12, characterized in that At least one first water supply device (62) is arranged adjacent to the first reactant supply device (70).

14. Apparatus according to any preceding claim, characterised in that The residence time device (50) has a certain length, so that the residence time in the residence time device (50) is between 0.5 seconds and 10 seconds, more particularly between 1 second and 5 seconds, particularly preferably between 1.5 seconds and 2.5 seconds.

15. Apparatus according to any preceding claim, characterised in that A reduction device (100) is provided between the calcining furnace (20) and the material cooler (30).

16. Apparatus as claimed in any preceding claim, characterised in that The residence time device (50) includes a catalyst.

17. Apparatus as claimed in any preceding claim, characterised in that The residence time device (50) comprises at least one flow splitting and / or flow internals for the gas mixture.

18. Apparatus according to any preceding claim, characterised in that The residence time device (50) comprises at least one second reactant supply device (72), wherein the second reactant supply device (72) is arranged between the combustion chamber (40) and the residence time device (50) or on the residence time device (50).

19. Apparatus according to any preceding claim, characterised in that The apparatus comprises a catalytic reactor, wherein the catalytic reactor is arranged downstream of a preheater (10) in the gas flow.

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

21. The method of claim 20, wherein: The temperature selected in the residence time device (50) is between 900°C and 1050°C.

22. The method according to any one of claims 20 to 21, characterized in that Heat treatment of clay or clay-like substances.

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