Method for activating clays with secondary fuels

Abstract

The invention relates to a method for activating clays with secondary fuel, comprising the following steps: Drying and crushing (2) moist clay as raw material (1), thermally activating (7) the dried and crushed clay (100) in an entrained-flow reactor (230), wherein a first part of the clay (120, 132) is fluidized together with secondary fuel in a fluidized-bed reactor (200) and the secondary fuel is burned there in the presence of this first part of the clay (120, 132), introducing the offgas from the fluidized-bed reactor (200), which carries within it the first part of the clay (120, 132), into the entrained-flow reactor (230), where a second part of the clay (130) is thermally activated together with the first part of the clay (120, 132) in the entrained-flow reactor (230) to form thermally activated clay (131). The invention also relates to an installation for carrying out the method.

Description

[0001] KHD Humboldt Wedag GmbH

[0002] Process for activating clays with secondary fuels

[0003] The invention relates to a method for activating clays with secondary fuel.

[0004] Cement clinker as a basis for concrete requires production via the calcination of limestone (CaCO3), which formally drives carbon dioxide (CO2) out of the limestone to produce burnt lime (CaO), and subsequent sintering of the burnt lime with silicate rock (CaSiO3) at high temperatures. The generation of high temperatures requires a correspondingly high fuel input, which also produces carbon dioxide (CO2) from the fuel. The carbon dioxide footprint in the production of cement clinker is quite high and, considering the quantities used in civil building construction and the construction of municipal infrastructure, is now so high that efforts are being made to use other building materials as complete substitutes or as aggregates in order to reduce carbon dioxide emissions; these materials emit less carbon dioxide during production.

[0005] Thermally activated clay is a well-known alternative or additive to cement clinker as a building material. Thermally activated clay does not require the formal removal of carbon dioxide (CO2) from raw clay, and the activation temperature of 800°C is lower than the calcination temperature of cement clinker. The sintering temperature of 1,450°C required for the production of cement clinker is completely eliminated.

[0006] Although thermally activated clays do not achieve the strength of concrete based on cement clinker, the properties of activated clays as a building material are sufficient for a wide range of construction projects where special performance of the building material is not important, such as is the case with prestressed concrete bridges or extremely tall skyscrapers well beyond the 100 m limit.

[0007] To further improve the carbon dioxide balance of activated clay, also called "calcined clay," it is desirable to replace the fossil primary fuels gas, oil, and coal with biogenic or at least partially biogenic fuels as secondary fuels. In contrast to the classic clinker burning process, however, the lower temperature in this case is a decisive disadvantage: only very finely processed secondary fuels can be converted at 800 °C within 3 to 5 seconds in an entrained-flow reactor as a calciner or activation reactor. Since the process described here does not involve a rotary kiln for sintering, any unburned material cannot be burned out in the rotary kiln. However, the fine processing of lumpy alternative fuels as secondary fuels is very energy-intensive and in some cases even impossible to implement.The initially apparent advantage of a lower firing temperature for the calciner / activation reactor turns out to be energy-intensive upstream due to the necessary processing during conventional use of the calciner / activation reactor.

[0008] The object of the invention is therefore to propose a method for activating clays with secondary fuel, in which the energy-intensive processing for use of the fuel in a calciner / activation reactor can be avoided or at least in which a large part of the secondary fuel does not require energy-intensive processing.

[0009] The object of the invention is achieved by a method having the features of claim 1. A plant for carrying out the method is specified in claim 9. Further advantageous embodiments of the method are specified in the subclaims to claim 1. According to the concept of the invention, a fluidized bed reactor is used in addition to the entrained flow reactor for calcining / activating the clay. This fluidized bed reactor is used to slowly burn the secondary fuels at a temperature of approximately 800°C. For this purpose, a fluidized bed is created in the fluidized bed reactor from preheated process air, a middle material from the clay crushing and / or a portion of already thermally activated clay, and secondary fuel is burned therein, the residence time of the fuel-clay mixture fluidized in the preheated process air being between 1 s and 20 s. Depending on the design of the method, the residence time is between 5 s and 15 s.The process is based on the following process steps: drying and crushing moist clay as raw material, thermally activating the dried and crushed clay in an entrained-flow reactor, whereby a first portion of the clay is fluidized in a fluidized-bed reactor together with secondary fuel, and the secondary fuel is combusted there in the presence of this first portion of clay, introducing the exhaust gas from the fluidized-bed reactor, which contains the first portion of clay, into the entrained-flow reactor, where a second portion of the clay is thermally activated together with the first portion of clay in the entrained-flow reactor to form thermally activated clay. Combusting the fuel together with the supplied clay in the fluidized-bed reactor enables slow burnout at temperatures around 800°C, whereby the clay in the fluidized bed is already activated there.The hot exhaust gases from the fluidized-bed reactor, together with the at least partially activated clay, are then fed into a conventional entrained-flow reactor, where a known type of calcination / activation takes place. For this purpose, a fine fraction of the crushed clay is fed to the entrained-flow reactor. Conversely, a mixture of a coarser fraction of the crushed clay and the fine fraction is fed to the fluidized-bed reactor. The stability of the fluidized bed can be controlled by adjusting the clay mixture of the clay fed into the fluidized-bed reactor. The unclassified exhaust gases from the fluidized-bed reactor are fed to the entrained-flow reactor in an adjustable amount, and the remaining portion is cooled and classified as thermally activated clay.

[0010] Depending on the temperature reached in the fluidized bed reactor, the exhaust gas from the fluidized bed reactor, which contains clay and fuel residues, may be combined with the already activated clay from the entrained-flow reactor for heat recuperation, transferring the heat from the activated clay to the exhaust gas. In this process, all of the clay is separated from the exhaust gas in a cyclone stage acting as a recuperator before the exhaust gas enters the entrained-flow reactor. The separated and activated clay can then be passed on to a cooling stage. There, the activated fine fraction can be cooled with a fresh gas. After cooling the activated fine fraction, the now heated fresh gas is passed under a nozzle plate of the fluidized bed reactor. This procedure enables maximum utilization of the heat present in the process.The fluidized-bed reactor may contain non-airborne particles from the fuel burned there, as well as oversized clay pieces in the crushed clay. To remove these non-airborne particles, a discharge of non-airborne contaminants from the secondary fuel and / or oversized ash particles from the fluidized bed can be provided at the level of a nozzle plate of the fluidized-bed reactor.

[0011] In the best possible implementation of the method according to the invention, the following process steps are provided: drying and comminuting moist clay as raw material in a drying and comminuting device, sifting the dried and comminuted clay in a sifter with an outlet for a middle fraction, a) wherein a sifted coarse fraction of the dried and comminuted clay is returned to the drying and comminution device, b) the sifted middle fraction of the dried and comminuted clay is fed to a fluidized bed reactor, and c) a sifted fine fraction of the dried and comminuted clay suspended in sifting air is fed to a dust collector, dedusting the sifting air in the dust collector, wherein a) the fine fraction from the sifting air is fed to a heat exchanger, b) a first portion of the dedusted sifting air is discarded as exhaust gas,and c) a second portion of the dedusted classifying air is returned to the drying and comminution device, preheating the fine fraction in the heat exchanger with exhaust gas from an entrained-flow reactor, classifying the preheated fine fraction and thermally activating the preheated fine fraction in the entrained-flow reactor to form activated clay, classifying the clay activated in the previous step and introducing a first portion of this activated clay as thermally activated clay into a recuperator, and introducing a second portion of this activated clay as thermally activated clay into the fluidized-bed reactor together with the middle fraction (the dried and crushed clay from the classifier), recuperating the heat from the thermally activated clay in a cyclone stage as a recuperator, whereby the heat from the thermally activated clay is transferred to an exhaust gas from the fluidized-bed reactor and cools the thermally activated clay,and wherein the aforementioned exhaust gas from the fluidized-bed reactor is fed into the entrained-flow reactor, cooling the thermally activated clay in a fresh-gas-operated cyclone stage, the exhaust gas of which is fed as heated fresh gas a) with a first part into the fluidized-bed reactor, b) with a second part into the entrained-flow reactor, c) with a third part into a heating device, and d) with a fourth part into the recuperator, wherein an exhaust gas from the heating device is fed back to the drying and comminution device, wherein the clay introduced therein is swirled together with secondary fuel in the fluidized-bed reactor, and the secondary fuel is ignited there, wherein the unclassified exhaust gas from the fluidized-bed reactor is fed a) with a first part into the entrained-flow reactor, and b) with a second part into the cyclone stage as a recuperator.

[0012] The invention is explained in more detail with reference to the following figures. They show:

[0013] Fig. 1 is a diagram of a plant for calcining / activating clay to carry out the process according to the invention, Fig. 2 is a flow diagram of the plant shown in Figure 1 with individual process steps.

[0014] Figure 1 shows a diagram of a plant for calcining / activating clay to carry out the process according to the invention. In this diagram, the material flow is shown as line arrows, whereas the gas flow is shown as bar arrows with a black border, as shown in the legend. Fuel is shown as a black bar arrow. Raw material 1 is fed via a bunker 150 via a conveyor system into a circuit of a device 270 for drying and comminution. There, the raw material 1, moist clay, is dried and comminuted. A line for pneumatic transport of dried and comminuted clay 100 leads from the device 270 for drying and comminution and leads to a cyclone classifier 250 with an outlet for medium material 120.The cyclone 250 directs the separated fine fraction 130 via a pneumatic transport line to a dust collector 210, the separated medium fraction 120 via a line to a fluidized-bed reactor 200, and the separated coarse fraction 110 back to the drying and comminution device 270. The fines 130 are separated from the separating air in the dust collector 210 and directed to a heat exchanger 220. The separating air is directed from the dust collector 220 to an exhaust gas line, which branches off and returns a portion of the separating air, instead of exhaust gas, to the drying and comminution device 270.The fine material 130 enters the heat exchanger 220, where it is preheated by exhaust gas 231 from an entrained-flow reactor 230. It is separated by a cyclone at reference numeral (6), which represents the "separating" process step, and then conveyed to the lower inlet of the entrained-flow reactor 230, where the fine material 130 is thermally treated to form thermally activated clay 131. The thermally activated clay 131 is then separated by a cyclone at reference numeral (8), which also represents the "separating" process step, and fed to a recuperator 240, where the thermally activated clay, with a first portion as thermally activated clay 133, releases its heat to process gas through recuperation. A further part of the thermally activated clay 131 is passed in the material flow direction behind the cyclone at reference number (8) as thermally activated clay 132 to the fluidized bed reactor 200.The first portion of the thermally activated clay 133 is then cooled with fresh gas in a further cyclone stage 260 and leaves the plant as activated clay. The fresh gas heated by cooling the activated clay is fed via a compressor with a first portion to the fluidized-bed reactor. Another portion of the heated fresh gas is fed to a heating device 280, which further heats the fresh gas and feeds it to the drying and comminution device 270. A third portion of the heated fresh gas, however, is fed to the lower inlet of the entrained-flow reactor. In the fluidized-bed reactor 220, the combined clay from the middle fraction 120 and the thermally activated clay 132 is fluidized together with fuel—here, biogenic fuel as a secondary fuel in contrast to high-quality primary fuels such as oil, coal, and gas—where the secondary fuel is combusted.The residence time of the fluidized bed in the fluidized bed reactor 220 is between 1 s and 20 s, preferably between 5 s and 15 s. The unclassified exhaust gas from the fluidized bed reactor is split and fed, on the one hand, into the recuperator 240 and, on the other hand, directly into the lower inlet of the entrained-flow reactor 230. The relative quantities of the unclassified exhaust gas from the fluidized bed reactor 220 can be adjusted using appropriate control elements. Figure 2 shows a flow diagram of the plant shown in Figure 1 with individual process steps. In this diagram, the material flow is shown as line arrows, whereas the gas flow is shown as black-bordered bar arrows, as shown in the legend. Fuel is shown as a black-filled bar arrow. Raw material 1 is dried and comminuted in a combined drying and comminution device 270 as process step 2.From there, gas is fed as a carrier gas together with the dried and crushed clay for classification in process step 3. From the classification stage in process step 3, a coarse fraction is fed back to device 270 for drying and crushing. A medium fraction is fed to a fluidized bed reactor 200 in process step 12. The fine material from process step 3, on the other hand, is passed on for dedusting in process step 4. The dedusted exhaust gas is discarded on the one hand and fed back to device 270 for drying and crushing. The fine material is passed from dedusting in process step 4 on to preheating. The gas from process step 5, preheating, is passed on to recuperation in process step 9 on the one hand and back to heating in process step 11 on the other.After preheating, the fines are classified in the counterflowing gas in process step 6 and fed for thermal activation in process step 7. After thermal activation in process step 7, classification follows in process step 8. Thermally activated clay is then fed to fluidized bed reactor 200 and recuperation in process step 9. From recuperation in process step 9, the thermally activated clay is fed to process step 10 for cooling and then leaves the process as activated clay. In process step 10, fresh gas enters the process, with the heated fresh gas being fed to fluidized bed reactor 220 and to process step 11 for heating the fresh gas. The heated gas is fed to device 270 for drying and heating. Gas from process step 9, recuperation, is fed to the entrained flow reactor, process step 7.Gas from the preceding process step 8 in the direction of material flow is fed to the classifier in process step 6. Finally, unclassified exhaust gas from the fluidized-bed reactor 200 enters the entrained-flow reactor in process step 7 and then enters process step 9, the recuperation process. In this material-flow-centered process diagram, the gas paths take convoluted paths to return as much heat as possible to the process and to lose as little heat as possible with the exhaust gas leaving the plant in process step 4.

[0015] Raw material 131 activated sound

[0016] Crushing / Drying 132 Ton

[0017] Views 133 Ton

[0018] Dust removal from 150 bunkers

[0019] Preheating 200 fluidized bed reactor

[0020] Viewing 205 Nozzle base thermal activation 210 Dust collector

[0021] View 220 heat exchangers

[0022] Recuperation 230 entrained flow reactor

[0023] Cooling 231 Exhaust

[0024] Heating 240 Recuperator

[0025] Swirling / 250 Classifier thermal treatment 260 Cyclone stage

[0026] 270 Device for crushing crushed clay 280 Heating device

[0027] Coarse fraction 290 classifiers

[0028] Middle fraction

[0029] Fine fraction

Claims

PATENT CLAIMS 1. A method for activating clays with secondary fuel, comprising the following steps: Drying and crushing (2) moist clay as raw material (1), thermally activating (7) the dried and crushed clay (100) in an entrained flow reactor (230), wherein a first portion of the clay (120, 132) is fluidized in a fluidized bed reactor (200) together with secondary fuel and the secondary fuel is burned there in the presence of this first portion of the clay (120, 132), Introducing the exhaust gas from the fluidized bed reactor (200), which carries the first part of the clay (120, 132), into the entrained flow reactor (230), where a second part of the clay (130) is thermally activated together with the first part of the clay (120, 132) in the entrained flow reactor (230) to thermally activated clay (131).

2. Method according to claim 1, characterized by Removing the first part of the clay (132) from a classifier (290) which is arranged downstream of the entrained flow reactor (230) in the direction of material flow.

3. Method according to claim 1, characterized by Removing the first part of the clay (120) from a sifter (250) which is arranged in the material flow direction downstream of a device (270) for drying and crushing.

4. Process according to one of claims 1 to 3, characterized by a residence time of the secondary fuel in the fluidized bed reactor (200) between 1 s and 20 s, preferably between 5 s and 15 s.

5. Method according to one of claims 1 to 4, characterized by Recovering the heat from a portion of the thermally activated clay (131) as thermally activated clay (133) in a cyclone stage as a recuperator (240).

6. Method according to claim 5, characterized by Cooling the thermally activated clay (133) with a fresh gas which, after cooling the thermally activated clay (133), is passed under a nozzle base (205) of the fluidized bed reactor (200).

7. Method according to one of claims 1 to 6, characterized by Removal of non-airborne contaminants from the secondary fuel and / or oversized ash particles from the fluidized bed at the level of a nozzle bottom (205) of the fluidized bed reactor (200).

8. Method according to one of claims 1 to 7, characterized by Drying and crushing (2) moist clay as raw material (1) in a device (270) for drying and crushing, Classifying (3) the dried and crushed clay (100) in a classifier (250) having an outlet for a middle fraction (120), wherein a) a classified coarse fraction (110) of the dried and crushed clay (100) is returned to the device (270) for drying and crushing, b) the sifted middle fraction (120) of the dried and crushed clay (100) is passed to a fluidized bed reactor (200), and c) a sifted fine fraction (130) of the dried and crushed clay (100) suspended in sifting air is passed to a dust collector (210), Dedusting (4) the classifying air in the deduster (210), wherein a) the fine fraction (130) from the classifying air is passed to a heat exchanger (220), b) a first part of the dedusted classifying air is discarded as exhaust gas, and c) a second part of the dedusted classifying air is passed back to the device (270) for drying and comminution, Preheating (5) the fine fraction (130) in the heat exchanger (220) with exhaust gas (231) of an entrained flow reactor (230), Classifying (6) the preheated fine fraction (130) and thermally activating (7) the preheated fine fraction (130) in the entrained flow reactor (230) to form activated clay (131), Viewing (8) the tone (131) activated in the previous step and Introducing a first part of this activated clay (131) as thermally activated clay (133) into a recuperator (240), and Introducing a second part of this activated clay (131) as thermally activated clay (132) into the fluidized bed reactor (200) together with the middle fraction (120) of the dried and crushed clay (100) from the sifter (250), Recuperating (9) the heat from the thermally activated clay (133) in a cyclone stage as a recuperator (240), wherein the heat from the thermally activated clay (133) is transferred to an exhaust gas from the fluidized bed reactor (200) and cools the thermally activated clay (133), and wherein the aforementioned exhaust gas from the fluidized bed reactor (200) is passed into the entrained flow reactor (230), Cooling (10) of the thermally activated clay (133) in a cyclone stage (260) operated with fresh gas, the exhaust gas of which is fed as heated fresh gas a) with a first part into the fluidized bed reactor (200), b) with a second part into the entrained flow reactor (230), c) with a third part into a heating device (280) and d) with a fourth part into the recuperator (240), wherein an exhaust gas from the heating device (280) is fed back to the device (270) for drying and comminution, wherein in the fluidized bed reactor (200) the clay (120, 132) introduced there is swirled together with secondary fuel and the secondary fuel is ignited there, wherein the unclassified exhaust gas from the fluidized bed reactor (200) a) with a first part into the entrained flow reactor (230), and b) with a second part into the cyclone stage as a recuperator (240).

9. Plant for carrying out the process for thermally activating clays with secondary fuel according to claims 1 to 8, comprising: a device (270) for drying and comminuting moist clay as raw material (1), an entrained-flow reactor (230) for thermally activating the dried and comminuted clay (100), a fluidized-bed reactor (200) for burning secondary fuel in the presence of clay, wherein the device (270) for drying and comminuting is connected in the material flow direction a) via a heat exchanger (220) to the entrained-flow reactor (230), and b) via a line for a middle fraction (120) to the fluidized-bed reactor (200), and the fluidized-bed reactor (200) a) is connected to the entrained-flow reactor (230) via a line for exhaust gas, and b) is connected to a line for exhaust gas with a recuperator (240) which returns heat from thermally activated clay (133) from the entrained-flow reactor (230) to the entrained-flow reactor (230) with a gas, and c) is connected to a cyclone of the heat exchanger (220) with a line for supplying clay.

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