Method for mixing carbide slag to produce cement clinker

Abstract

The invention relates to a method for producing cement clinker, having the following method steps: preheating of lime- and silicate-containing raw meal in a preheater, deacidification of the preheated raw meal in a calciner, sintering of the deacidified raw meal in a rotary kiln, quenching of the sintered cement clinker in a cooler, wherein the preheated raw meal is fed into the foot of the calciner, where it is suspended in the ascending gas stream of the exhaust gas from the rotary kiln flowing into the calciner. According to the invention it is provided that carbide slag is fed as a raw meal substitute into the foot of the calciner (115).

Description

TECHNICAL FIELD

[0001] The invention relates to a method for producing cement clinker, having the following method steps: preheating of lime- and silicate-containing raw meal in a preheater, deacidification of the preheated raw meal in a calciner, sintering of the deacidified raw meal in a rotary kiln, quenching of the sintered cement clinker in a cooler, wherein the preheated raw meal is fed into the foot of the calciner, where it is suspended in the ascending gas stream of the exhaust gas from the rotary kiln flowing into the calciner. BACKGROUND

[0002] In order to produce cement clinker, from a mixture of calcite components and clay components, carbon dioxide (CO2) is formally removed from the calcium carbonate (CaCO3) contained in the aforementioned stages in a high heat input, in order to finally yield a raw material rich in calcium oxide (CaO), which is used to form the specific mineral phases of the cement clinker.

[0003] Cement, as the end product, is CO2-intensive in its manufacture, so that this production accounts for the highest percentage of eight percent of the global annual carbon dioxide emissions. A characteristic value often mentioned in this context is the specific carbon dioxide emission. It describes how many tons of CO2 are emitted when one ton of cement is produced. According to the German Emissions Trading Authority (DEHSt), this value was approximately 0.59 in 2018. From this it can be seen that 590 kilograms of CO2 are emitted per ton of cement. Germany produced approximately 337 million tons of building materials in 2018. The high CO2 emissions look like a lot, but are still bearable in the civil use of cement. However, efforts are being made to reduce CO2 emissions in cement production.

[0004] With regard to the production of cement clinker, it is advantageous in the process of the desired reduction of CO2 emissions to use alternative calcium sources as raw materials instead of limestone (CaCO3). In such raw materials, calcium should be present in oxidic form (CaO) and not in carbonate form (CO3 2-) is bound. In comparison with the combustion processes common today, this raw material likewise necessitates lower reaction temperatures in order to bring about combustion in the process in the furnace. Such a raw material for the production of cement clinker does not need to have carbon dioxide (CO2) removed from it by heat. The fuel necessary for the production process for the production of cement clinker can thus be less. A known alternative raw material as a natural raw material substitute is carbide residue (also called Baukalk), which occurs in the production of acetylene (C2H2) from carbide (CaC2) as a chemical base material in a chemical process that is considered to be outdated today. In modern oil chemical plants, acetylene can be obtained from the light fraction of oil by means of catalytic processes. In the 1980s and 1990s of the 20th century, carbide (CaC2) was still used to produce acetylene to the extent of 70% and calcium cyanamide (CaCN2), also called lime nitrogen, to the extent of 30%, which is a relatively inexpensive nitrogen fertilizer for plants. In order to control the transformation of carbide (CaC2) into calcium cyanamide (CaCN2) in a strongly exothermic reaction, calcium chloride (CaCl2) and calcium fluoride (CaF2) are added to the carbide (CaC2) according to known methods. This greatly reduces the reaction temperature and also reduces the undesired production of calcium cyanide (Ca(CN)2). The halogenated carbon compounds contained in the lime nitrogen and produced in the transformation into calcium cyanamide (CaCN2) were considered to be a desirable herbicidal effect of the lime nitrogen in the early 20th century. From today's perspective, the halogenated carbon compounds are no longer tolerable for the environment. The currently still very large amounts of carbide residue result from the industrial mixing waste of carbide production and lime nitrogen production. Carbide residue is not problem-free industrial waste, it contains halogenated hazardous substances. Therefore, from the perspective of environmental policy, the use of carbide residue as a raw material for the production of cement clinker as an intermediate product for cement production serves two desirable goals, namely on the one hand to avoid the physical surplus contained in the landfill of halogenated carbon compounds and on the other hand to reduce the formation of carbon dioxide (CO2) in cement production. It is even conceivable to reuse the carbide residue as a physical surplus landfill. In order to avoid the hazardous substances contained in the carbide residue from entering the atmosphere as volatile components when used as a raw material for the production of cement clinker, corresponding adaptations of the isolated production process for cement clinker must be made.

[0005] The teaching of European patent application EP 3 670 468 A1 is to use carbide residue as an admixture for the production of a raw material for cement production, in which the hazardous substances are separated by a metallurgical method for the treatment of residue. SUMMARY

[0006] The task of the present invention is to design the use of organic trace amounts of residual material, i.e. the use of carbide residues, in a hot stove line for the production of cement clinker in such a way that no toxic emissions of volatile components occur in the heat exchange offgas.

[0007] The task underlying the present invention is solved by a method having the features according to claim 1. Further advantageous design options of the method are given in the dependent claims of claim 1.

[0008] According to the idea of the present invention, the carbide residues are fed into the foot of the calciner. The original function of the calciner is to deacidify preheated raw meal. Here, carbon dioxide (CO2) is formally removed from lime, calcium carbonate (CaCO3), so that raw lime (CaO) is produced. Carbide residues with a high residual humidity have Ca(OH)2 as the main component. It is no longer necessary to deacidify, so that feeding the carbide residues to the calciner initially appears superfluous and pointless. By feeding into the calciner, the carbide residues are heated up strongly in the hot offgas of the rotary kiln. Here, the organic components contained in the carbide residues are in certain cases volatilized. These organic components, which should not enter the atmosphere, will burn under the environmental conditions of the calciner. The raw meal, which is present in the calciner in addition to the carbide residues, catalyzes the decomposition of harmful substances. By means of the carbon monoxide (CO) component, which is retained in the calciner, the nitrogen oxides that can be produced when the organic components of the carbide residues burn are reduced. In order to produce cement clinker, the procedure of feeding into the calciner has proved to be advantageous in the search for the ideal use of the carbide residues as a replacement, since almost quantitatively the organic emissions into the atmosphere can be avoided thereby.

[0009] In this method embodiment, the percentage of the amount of raw meal and carbide residues in terms of weight can be 50:50. If other replacements for raw meal, the heat recovery from the offgas in the preheating stage of this plant for the production of cement is too small, so that measures must be taken in order to achieve better heat recovery.

[0010] When the replacement reaches the range of up to 50%, a significantly higher exhaust gas temperature of the preheater can be observed, less raw meal has to be preheated for deacidification. For the recovery of heat from the exhaust gas of the rotary kiln, the smaller amount of raw meal has a smaller heat capacity. But the increased exhaust gas temperature can be used for drying the carbide slag in a roller press drying device, which usually has a residual humidity of up to 25%. Here, the drying does not take place quantitatively, in order to avoid that volatile organic components ("volatile organic components, VOC") with the drying exhaust gas of the drying carbide slag enter the atmosphere. If the residual humidity of the dried carbide slag is 2% to 5%, the volatile organic components are bound in the carbide slag, until these organic components are safely burned in the calciner. However, in order to upgrade the drying quality, it can be provided that the exhaust gas of the dried carbide slag is fed into a cooler, so that the emissions produced in certain cases during the drying are fed back to the manufacturing process and burned. In the clinker cooler, the exhaust gas should be fed into the clinker cooler, so that the exhaust gas is fed into the rotary kiln together with the remaining cooler air as secondary air, or is brought into the calciner as tertiary air. By drying the carbide slag in the temperature of the exhaust gas of the preheater, most of the low-calorie heat in the manufacturing process is used for evaporating the humidity, which loses a large amount of heat when the moisture evaporates. If the humidity enters the steam chamber at once, the exhaust gas can also be mixed with the significantly hotter tertiary air or with the secondary air, without the humidity causing a drastic drop in temperature. BRIEF DESCRIPTION OF DRAWINGS

[0011] The application is further illustrated by the following drawings. In which:

[0012] Figure 1 An installation for carrying out the method according to the application is shown. DETAILED DESCRIPTION

[0013] The foregoing description of the solution according to the application thus includes, inter alia, various feature combinations defined by the subsequently consecutively numbered embodiments:

[0014] 1. A method for manufacturing cement clinker, with the following method steps:

[0015] - preheating of lime-containing and silicate-containing raw meal (R) in a preheater (110),

[0016] - deacidification of the preheated raw meal (R) in a calciner (115),

[0017] - sintering of the deacidified raw meal in a rotary kiln (140),

[0018] - quenching of the sintered raw meal (R) into cement clinker in a cooler (150),

[0019] wherein preheated raw meal (R) is fed into the foot of the calciner (115), where it is suspended in the rising gas stream of exhaust gas from the rotary kiln (140) flowing into the calciner (115),

[0020] wherein carbide slag is fed into the foot of the calciner (115).

[0021] 2. The method according to embodiment 1,

[0022] wherein the percentage of the amount of raw meal and carbide slag in terms of weight is 90:10 to 50:50.

[0023] 3. The method according to embodiment 1 or 2,

[0024] wherein exhaust gas is directed from the preheater (110) into a roller drying device for carbide slag.

[0025] 4. The method according to embodiment 3,

[0026] wherein the carbide slag is dried from 20% to 25% residual humidity to 2% to 5% residual humidity.

[0027] 5. The method according to embodiment 3 or 4,

[0028] wherein dry exhaust gas (T) is directed from the roller drying device into the cooler (150), so that the dry exhaust gas (T) arrives in the rotary kiln (140) as secondary air or in a tertiary air line (160).

[0029] Figure 1A sketch shows a plant 100 for manufacturing cement clinker. The plant 100 has a preheater 110 in which raw meal R is fed into the uppermost heat exchanger cyclone 111. Thereafter, the raw meal R passes through the heat exchanger cyclones 112, 113 from top to bottom. The raw meal R leaving the heat exchanger cyclone 113 and having been preheated falls via a downcomer 113' into the foot of a calciner 115. There, the preheated raw meal R is entrained and suspended by the exhaust gas stream flowing into the calciner 115 from a rotary kiln entry chamber 120 via a rotary kiln 140. The raw meal ascending with the exhaust gas is deacidified in the heat of the exhaust gas and in the heat of burners B at the foot of the calciner 115. The deacidified raw meal suspension flows via a descending branch 131 of the calciner 115 into the lowermost heat exchanger cyclone 114, where the deacidified raw meal is separated and falls via a downcomer 114' into the rotary kiln entry chamber 120 and there reaches the rotary kiln 140 under the ascending exhaust gas. According to the inventive concept, carbide slag is fed together with the raw meal into the foot of the calciner 115 and there suspended together with the deacidified raw meal. The path of the carbide slag as raw meal replacement starts here and is the same as the path of the raw meal. Since the carbide slag has no endothermic deacidification reaction but only a less endothermic dehydration step, more heat is available in the preheater, which can be exploited by the higher exhaust gas temperature at the uppermost heat exchanger cyclone 111. In order to advantageously exploit the changed heat balance situation of the plant 100 when adding carbide slag as raw meal replacement, it can be provided that at least a portion of the exhaust gas A from the uppermost heat exchanger cyclone 111 is conducted to a roller press drying device, here to a raw meal roller press. Here, the agglomerated carbide slag is comminuted and dried. Depending on the degree of drying, it can be advantageous to introduce the dried exhaust gas T into the cooler 150, so that in certain cases volatile organic components present in the dried exhaust gas T are combusted in the heat of the rotary kiln 140. Here, the dried exhaust gas can also be conducted via the cooler 150 to a tertiary air line 160, wherein the tertiary air line is at a higher temperature, so that organic volatile components already start to pyrolyze in the tertiary air line 160.

[0030] List of reference signs

[0031] 100 plant

[0032] 110 preheater

[0033] 111 heat exchanger cyclone

[0034] 112 heat exchanger cyclone

[0035] 113 heat exchanger cyclone

[0036] 113' downcomer

[0037] 114 heat exchanger cyclone

[0038] 114' downcomer

[0039] 115 calciner

[0040] 120 rotary kiln entry chamber

[0041] 131 descending branch

[0042] 140 rotary kiln

[0043] 150 cooler

[0044] 151 cooler head

[0045] 160 tertiary air line

[0046] A exhaust gas

[0047] B burner

[0048] L air

[0049] R raw meal

[0050] T drying air

[0051] Z cement clinker

Claims

1. A method for manufacturing cement clinker, comprising the following steps: - The raw meal (R) containing lime and silicates is preheated in the preheater (110). - The preheated raw material (R) is deacidified in the calciner (115). - The deacidified raw materials are sintered in a rotary kiln (140). - The raw meal (R) that has been sintered into cement clinker is quenched in a cooler (150). in, Preheated raw material (R) is fed into the foot of the calciner (115), where it is suspended in the rising gas stream from the rotary kiln (140) flowing into the calciner (115). Its features are, The carbide slag is fed into the foot of the calciner (115). The exhaust gas is guided from the preheater (110) into the crushing and drying device for carbide slag. The dry exhaust gas (T) is guided from the rolling dryer into the cooler (150), so that the dry exhaust gas (T) arrives as secondary air into the rotary kiln (140) or the tertiary air pipeline (160).

2. The method according to claim 1, Its features are, The weight percentage of raw meal and carbide slag is 90:10 to 50:

50.

3. The method according to claim 1, Its features are, The carbide slag is dried from a residual moisture content of 20% to 25% to a residual moisture content of 2% to 5%.

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