Charring reactor in a plant for producing cement clinker
By carbonizing secondary fuels in a separate reactor and adding ash post-sintering, the process addresses clinker quality issues and ash utilization, achieving efficient energy use and improved cement strength.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- KHD HUMBOLDT WEDAG GMBH
- Filing Date
- 2026-01-15
- Publication Date
- 2026-07-23
AI Technical Summary
The use of secondary fuels with high ash content in cement clinker production can impair clinker quality and lead to the incorporation of unwanted free lime, while the removal of ash is costly and inefficient, and the pozzolanic properties of ash are not utilized.
A process where secondary fuels are carbonized and/or burned in a separate reactor, with the resulting ash being added to the cement clinker manufacturing process after sintering, allowing it to burn off and act as a pozzolanic additive, and the gases are used for heat recovery.
This process maintains clinker quality by preventing ash incorporation into the matrix and utilizes ash as a valuable additive, enhancing cement strength development while achieving high energy efficiency and resource conservation.
Smart Images
Figure EP2026050897_23072026_PF_FP_ABST
Abstract
Description
[0001] KHD Humboldt Wedag GmbH
[0002] EM2025001 14.01.2026
[0003] H 25 / 001 PCT
[0004] Carbonization reactor in a plant for the production of cement clinker
[0005] The invention relates to a process for the production of cement clinker, comprising the following steps: preheating raw meal, and subsequent calcining of the preheated raw meal in a calcining stage using a fuel, followed by sintering of the calcined raw meal in a kiln to form cement clinker using further fuel, and subsequent cooling of the cement clinker in a clinker cooler with cooling air, recuperation of hot cooling air from the clinker cooler into the calcining stage via a tertiary air line and a corresponding plant for the production of cement clinker for carrying out this process.
[0006] The production of cement clinker requires the use of specific raw materials, particularly limestone as well as silicate, aluminate, and ferritic components. These materials contain the chemical compounds necessary to produce the desired clinker phases. The most important phases are alite (tricalcium silicate, chemical formula Ca3SiO5) and belite (dicalcium silicate, chemical formula Ca2SiO4). Alite is the main component that provides the initial strength of cement during hardening, while belite supports longer-term strength development.
[0007] The optimal composition of the four main oxides – calcium oxide (CaO), silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3) – is determined by the so-called Lime Saturation Factor (LSF). KHD Humboldt Wedag GmbH
[0008] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0009] LSF describes the ratio of calcium oxide (CaO) to the other main oxides and is calculated according to the following formula:
[0010] LSF = CaO / (2.8 x SiO2+ 1.2 x AI2O3+ 0.65 x Fe2O3)
[0011] The values for the oxides in the formula are expressed as mass fractions (weight percent). Typical LSF values for modern cement clinker range between 92% and 98%, indicating that the composition of the raw mix must be precisely tailored to the requirements of cement production. An LSF value of 100% means that the calcium oxide present can theoretically react completely with the other oxides. In practice, however, a small amount of free lime often remains. An LSF value above the optimal range (e.g., above 98%) may indicate an excess of lime, leading to the formation of free lime. A value below the range indicates that there is not enough lime present to react completely with the other oxides. Controlling the LSF is crucial for the quality of the clinker and the cement produced from it.
[0012] Another important parameter is the silicon dioxide modulus (SM), which describes the ratio of silicon dioxide (SiO2) to the other relevant oxides. It is calculated using the following formula:
[0013] SM = SiO2 / (Al2O3+ Fe2O3)
[0014] Here too, the values are expressed in mass fractions (weight percent). The SM indicates how much silicon dioxide is present relative to the alumina and ferrite phases and influences the formation of calcium silicate phases such as alite and belite. Typical SM values range between 2.0 and 3.0. A low SM indicates that the alumina and ferrite phases dominate, while a high SM indicates a higher proportion of silicon dioxide, which favors the calcium silicate phases. KHD Humboldt Wedag GmbH
[0015] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0016] The alumina modulus (TM) is another essential parameter that describes the ratio of aluminum oxide (Al₂O₃) to iron oxide (Fe₂O₃). The formula is:
[0017] TM = Al2O3 / Fe2O3
[0018] Here too, the calculation is based on mass fractions in percent. The TM (total mass) influences the relative proportions of the alumina and ferrite phases in the clinker. Typical TM values range between 1.0 and 4.0. A higher TM indicates that aluminum oxide dominates over iron oxide, which promotes the formation of tricalcium-containing phases such as C3A (tricalcium aluminate). A lower TM signifies a higher proportion of ferrite phases, which affects the heat generated during the hydration process.
[0019] The main raw material for cement clinker production is limestone, which must have a sufficiently high calcium oxide (CaO) content. In addition to limestone, other raw materials such as marl, chalk, claystone, gypsum, sand, and small amounts of iron ore can also be used to optimize the chemical composition of the raw mixture. The chemical composition of these raw materials essentially comprises:
[0020] • Marl: Consists mainly of calcium carbonate (CaCO3) and clay minerals containing silicon dioxide (SiO2), aluminum oxide (Al2O3) and iron oxide (Fe2O3).
[0021] • Chalk: A form of calcium carbonate (CaCO3) with a very high degree of purity.
[0022] • Claystone: Contains high proportions of silicon dioxide (SiO2) as well as aluminum oxide (Al2O3) and smaller amounts of iron oxide (Fe2O3).
[0023] • Gypsum: Consists mainly of calcium sulfate (CaSO4) and is used as a regulator for the setting time of cement. KHD Humboldt Wedag GmbH
[0024] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0025] • Sand: Consists mainly of quartz (SiO2) and serves to increase the silicon dioxide content.
[0026] • Iron ore: Mainly iron oxides (Fe2O3), which increase the iron content in the crude mixture and promote ferrite phase formation.
[0027] The availability of high-quality limestone is a crucial factor in the location selection of cement plants.
[0028] In some countries, such as India, deposits of high-quality limestone are limited. Most available deposits contain a relatively low calcium oxide content, which complicates the production of Ordinary Portland Cement (OPC). However, these limestone deposits often exhibit high concentrations of silicon dioxide (SiO2) and aluminum oxide (Al2O3), which just barely meets the minimum requirements for OPC.
[0029] The use of fuels in rotary kilns leads to the introduction of fuel ash and residues into the clinker firing process. These ashes typically contain high proportions of silicates and aluminates, but little to no calcium oxide. Depending on the calorific value and ash content of the fuel, these components can influence the chemical composition of the clinker, particularly the values for lime saturation (LSF), silicon dioxide modulus (SM), and alumina modulus (TM). To ensure the quality of the clinker, the raw material mixture must be adjusted with high-quality corrective materials such as particularly pure limestone.
[0030] In India, there is growing interest in the use of secondary fuels from waste processing. These fuels are generally characterized by a low calorific value and a high ash content. The resulting ash and residues pass directly into the clinker firing process via the calciner and are incorporated into the clinker matrix. This can be achieved by KHD Humboldt Wedag GmbH.
[0031] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0032] This can impair the quality of the clinker, especially in combination with inferior raw materials.
[0033] Technical approaches to improvement include methods for removing the ash from secondary fuels during the clinker process. This prevents the ash from being incorporated into the clinker matrix. However, this has disadvantages: Firstly, thermal energy released during combustion is lost. Secondly, the separate cooling, treatment, and further processing of the ash and slag is quite costly. At the same time, these ashes, being pozzolanically active, can potentially contribute to cement production. Pozzolans are materials that chemically react with calcium hydroxide (Ca(OH)₂) to form additional calcium silicate hydrates (CSH phases), which contribute to the strength development of cement.
[0034] The object of the invention is therefore to provide a process for the production of cement clinker using secondary fuels with a high ash content. This object is achieved by a process according to claim 1. Further advantageous embodiments are specified in the dependent claims to claim 1.
[0035] According to the invention, secondary fuels are carbonized and / or burned in a separate reactor. The resulting hot carbonization and / or combustion gases serve as an additional heat source and are introduced into the cement clinker manufacturing process. Crucially, the ash produced during carbonization and / or combustion is directed to a cooling stage of the process, where it mixes with the hot cement clinker. During this process, the ash burns off in the heat of the clinker without sintering, thus preventing the ash components from being incorporated into the clinker matrix. Due to its pozzolanic properties, namely setting in moisture through reaction with calcium hydroxide (Ca(OH)2) and the additional formation of KHD Humboldt Wedag GmbH
[0036] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0037] Calcium silicate hydrates (CSH phases) are available as an additive or admixture to cement clinker. Due to the late addition of the ash to the cement clinker manufacturing process, the resulting cement clinker contains no additional source of unwanted free lime.
[0038] In one embodiment of the invention, the process begins with the preheating of raw meal, followed by calcination using a fuel that can be either primary or secondary. After calcination, the raw meal is sintered in a kiln, preferably a rotary kiln. The kiln exhaust gases are used to optimize energy consumption in the calcination stage. Subsequently, the cement clinker is cooled in a clinker cooler with cooling air, the hot cooling air being returned to the calcination stage via a tertiary air line. Simultaneously, heat is recovered in a separate carbonization and / or combustion reactor, in which secondary fuels are used. The gases produced are introduced into the tertiary air line or into the calciner, while the ash enters the clinker cooler and mixes with the cement clinker.Unlike conventional processes, the ash is added to the cement clinker only after sintering, resulting in a two-phase product: cement clinker and a separate ash phase with pozzolanic properties.
[0039] In the process according to the invention, secondary fuels are integrated into the production process of cement clinker. The raw meal is first heated in a preheating stage and then calcined in a calcining stage using fuels, thus preparing it for the sintering process. In a rotary kiln, the calcined raw meal is sintered at high temperatures to form the individual clinker phases, and the exhaust gases are recycled back into the calcining stage for further energy efficiency. The sintered clinker is then cooled in the clinker cooler with cooling air, some of which is directed as secondary air into the separate reactor for carbonization and / or combustion. The resulting ash is selectively fed into the clinker cooler, where KHD Humboldt Wedag GmbH
[0040] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0041] it burns out completely with the hot clinker without affecting the clinker matrix.
[0042] By adding the ash to the sintered cement clinker at a later stage, it remains as a separate phase, retaining its pozzolanic properties and thus serving as a valuable additive for cement production. At the same time, the quality of the cement clinker is not compromised. The plant designed for this process includes a preheating and calcining stage, a rotary kiln, a clinker cooler with a tertiary air supply, and a separate reactor for the carbonization and / or combustion of secondary fuels. The ash is discharged directly into the clinker cooler. This configuration enables high energy efficiency, resource conservation, and product quality, as secondary fuels such as shredded household waste, waste paper, or plastic waste can also be used efficiently.
[0043] The invention is explained in more detail with reference to the following figures. They show:
[0044] Fig. 1 is a process diagram to illustrate the process according to the invention,
[0045] Fig. 2 is a sketch of a plant according to the invention for the production of cement clinker.
[0046] Figure 1 shows a process diagram illustrating the inventive process for producing cement clinker Z. The process comprises the following steps: First, preheating 100 of raw meal R and subsequent calcination 200 of the preheated raw meal R in a calcining stage 1020 using fuel B1. The raw meal R, as a fine-grained fraction suspended in a gas, flows towards an exhaust gas AG from the sintering stage, kiln 1030, and calcining stage 1020. This is followed by sintering 300 of the calcined raw meal in the kiln 1030 to produce cement clinker Z using further fuel B2. The cement clinker Z is then cooled 400 in a clinker cooler 1040 with cooling air K. Hot air is released from the clinker cooler 1040.
[0047] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0048] Cooling air is fed into the calcining stage 1020. This is the step of recuperating hot cooling air K from the clinker cooler 1040 into the calcining stage 1020 via a tertiary air line 1050.
[0049] According to the invention, heat 600 is generated in a separate carbonization and / or combustion reactor 1070 using secondary fuels SB. These secondary fuels are typically low-grade and waste-rich residues such as shredded household and / or industrial waste, low-grade coal, car tires, chemical industry waste, animal carcasses, shredded wood waste, shredded bulky waste, waste paper, or plastic waste. The carbonization and / or combustion gases produced during the carbonization and / or combustion of the secondary fuels SB are introduced into the tertiary air line 1050 or into the calcining stage 1020. The ash A produced during the carbonization and / or combustion of the secondary fuels SB is introduced into the clinker cooler 1040, where it mixes with the cement clinker Z to be cooled.Atmospheric air L flows into the clinker cooler 1040 as a cooling gas for cooling purposes. This atmospheric air then flows as secondary air into the furnace 103 for sintering 300, into the tertiary air line 1050 for energy recuperation 500, and into the carbonization and / or combustion reactor 1070 for heat generation 600. A slide valve 1055 is provided in the tertiary air line 1050 to adjust the relative pressure between the tertiary air line 1050 and a line 1060 leading to the carbonization and / or combustion reactor 1070.
[0050] Depending on the chosen process, such as an oxyfuel process, it is also possible to use recirculated gas as a cooling gas. In this case, oxygen would be fed as a combustion gas into furnace 1030 as well as into the carbon dioxide and / or combustion reactor 1070, and exhaust gas AG from plant 1000 would be returned to the clinker cooler 1040, where the carbon dioxide-rich exhaust gas is used as cooling gas K and also flows as a secondary gas into furnace 1030 and into the carbon dioxide and / or combustion reactor 1070. KHD Humboldt Wedag GmbH
[0051] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0052] Figure 2 shows a sketch of a plant 1000 according to the invention for the production of cement clinker Z. In the direction of material flow from the raw material meal R to the product cement clinker Z, this plant comprises the following components: First, a preheating stage 1010 and a calcining stage 1020. In these stages, the raw material meal R is preheated, and in the calcining stage 1020, the raw material meal R is calcined, i.e., formally, carbon dioxide is driven off using heat and converted to quicklime. In a kiln 1030 following the calcining stage 1020, the calcined raw material meal is sintered into the individual cement clinker phases, so that cement clinker Z is produced. The kiln 1030 can be a rotary kiln, as shown here. This is followed by a clinker cooler 1040, in which the still-hot cement clinker Z is quenched, and crystalline cement clinker phases are formed during quenching. For this purpose, the clinker cooler 1040 is circulated with air.Depending on the type of process, for example an oxyfuel process, it is also possible to use recirculated gas instead of atmospheric air L to quench the hot cement clinker Z. In an oxyfuel process, oxygen is then fed into the kiln 1030 and also into the carbonization and / or combustion reactor 1070, where it is absorbed by the recirculated gas and provides the necessary combustion oxygen. Hot cooler exhaust air K, or recirculated gas from the clinker cooler 1040, is fed to the calcining stage 1020 via a tertiary air line 1050.
[0053] A further line 1060 between the clinker cooler 1040 and a carbonization and / or combustion reactor 1070 conveys hot cooler exhaust air K from the clinker cooler 1040 to the carbonization and / or combustion reactor 1070, in which secondary fuels SB are carbonized and / or burned. This carbonization and / or combustion reactor 1070 can be a rotary kiln or a fluidized bed reactor. An auxiliary burner may be provided to continuously reignite the secondary fuel, which is operated with further, but more readily combustible, fuel B. A further connecting line 1080 between the clinker cooler 1040 and KHD Humboldt Wedag GmbH
[0054] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0055] Ash A is directed from the pyrolysis and / or combustion reactor 1070 into the clinker cooler 1040, where the ash falls into the area of the opening 1035 of the furnace 1030 into the clinker cooler 1040.
[0056] A hot gas line 1075 directs the hot gas produced during carbonization and / or combustion into the tertiary air line 1050 or, as shown here with dashed lines, directly into the calcineration stage 1020. To adjust the relative pressure between line 1060 and the hot air line 1075, a slide valve 1055 is provided, allowing hot cooler exhaust air K to flow in through both the carbonization and / or combustion reactor 1070 and the tertiary air line 1050. This design enables both the utilization of heat from the combustion of low-grade fuels and the utilization of the ash produced during the combustion of low-grade fuels as a pozzolanic substance. KHD Humboldt Wedag GmbH
[0057] 01 / 14 / 2026 EM2025001 H 25 / 001 PCT
[0058] REFERENCE MARK LIST
[0059] 100 Preheating 1075 Hot gas line
[0060] 200 Calcining 1080 Connecting line
[0061] 300 sintering
[0062] 400 Cooling A Ash
[0063] 500 Recuperation AG Exhaust
[0064] 600 Generating heat B Fuel
[0065] B1 fuel
[0066] 1000 Plant B2 Fuel
[0067] 1010 Preheating stage G Hot gas
[0068] 1020 Calcining stage K Cooling air
[0069] 1030 Oven L Air
[0070] 1040 Clinker cooler R Raw meal
[0071] 1050 Tertiary air duct SB Secondary fuel 1055 Slide valve Z Cement clinker
[0072] 1060 Line
[0073] 1070 Charring and / or
[0074] combustion reactor
Claims
KHD Humboldt Wedag GmbH EM2025001 14.01.2026 H 25 / 001 PCT Carbonization reactor in a plant for the production of cement clinker PATENT CLAIMS 1. A process for the production of cement clinker (Z), comprising the following steps: - Preheating (100) of raw flour (R), and subsequent - Calcining (200) of the preheated raw meal (R) in a calcining stage (1020) using a fuel (B1), subsequently Sintering (300) of the calcined raw meal in a kiln (1030) to cement clinker (Z) using further fuel (B2), and subsequent, - Cooling (400) of the cement clinker (Z) in a clinker cooler (1040) with cooling air, (K) - Recuperation (500) of hot cooling air (K) from the clinker cooler (1040) into the calcining stage (1020) via a tertiary air line (1050), characterized by KHD Humboldt Wedag GmbH EM2025001 14.01.2026 H 25 / 001 PCT - Generating heat (600) in a separate pyrolysis and / or combustion reactor (1070) using secondary fuels (SB), - Introduction of the pyrolysis and / or combustion gases produced during the pyrolysis and / or combustion of the secondary materials (SB) into the tertiary air line (1050) or into the calcining stage (1020), and - Introduction of the ash (A) produced during the pyrolysis and / or combustion of the secondary materials (SB) into the clinker cooler (1040), where the ash (A) mixes with the cement clinker (Z).
2. Method according to claim 1 , characterized by Introducing the ash (A) produced during the pyrolysis and / or combustion of the secondary materials (SB) into the clinker cooler (1040) in the area of the kiln opening (1035).
3. Method according to claim 2, characterized by Burning out the ash (A) in the area of the kiln opening (1035) into the clinker cooler (1040). KHD Humboldt Wedag GmbH EM2025001 14.01.2026 H 25 / 001 PCT 4. Method according to any one of claims 1 to 3, characterized by Introducing hot cooling air (K) from the clinker cooler (1040) into the separate carbonization and / or combustion reactor (1070) as secondary air.
5. Method according to any one of claims 1 to 3, characterized by Use of secondary fuels (SB) selected from the group consisting of: shredded household and / or industrial waste, low-grade coal, car tires, waste from the chemical industry, animal carcasses, shredded wood waste, shredded bulky waste, waste paper, plastic waste.
6. Plant (1000) for the production of cement clinker according to one of claims 1 to 5, comprising in the material flow direction a preheating (1010) and calcining stage (1020), an oven (1030), a clinker cooler (1040), wherein a tertiary air line (1050) directs hot cooler exhaust air (K) from the clinker cooler (1040) to the calcining stage (1020), KHD Humboldt Wedag GmbH EM2025001 14.01.2026 H 25 / 001 PCT characterized by the fact that a further line (1060) between the clinker cooler (1040) and a carbonization and / or combustion reactor (1070) directs hot cooler exhaust air (K) from the clinker cooler (1040) to the carbonization and / or combustion reactor (1070), which carbonizes and / or burns secondary fuels (SB), wherein a further connecting line (1080) between the clinker cooler (1040) and the carbonization and / or combustion reactor (1070) directs ash (A) from the carbonization and / or combustion reactor (1070) into the clinker cooler (1040), and another hot gas line (1075) directs hot pyrolysis and / or combustion gas as hot gas (G) into the tertiary air line (1050) or into the calcining stage (1020).
7. Plant for the production of cement clinker according to claim 6, characterized by the fact that the further connecting line (1080) directs hot cooler exhaust air (K) from the clinker cooler (1040) from the area of the kiln outlet (1035) into the clinker cooler (1040) to the carbonization and / or combustion reactor (1070) as secondary air (SL).
8. Plant for the production of cement clinker according to claim 6 or 7, characterized in that KHD Humboldt Wedag GmbH EM2025001 14.01.2026 H 25 / 001 PCT the further connecting line (1080) directs ash (A) into the area of the furnace opening (1035) into the clinker cooler (1040).
9. Plant for the production of cement clinker according to one of claims 6 to 8, characterized by the fact that the pyrolysis and / or combustion reactor (1070) is a rotary kiln.
10. Plant for the production of cement clinker according to one of claims 6 to 9, characterized by the fact that the pyrolysis and / or combustion reactor (1070) is a fluidized bed reactor.