Cement Clinker Production Research Articles

Techno-economic assessment of calcium sulfoaluminate clinker production using elemental sulfur as raw material

The foreseen decarbonisation of the cement industry by 2050 will require a combination of different measures in the current manufacturing practices such as the improvement of the energy efficiency, the use of alternative fuels, the reduction of the clinker to cement ratio, and the integration of carbon capture, especially beyond the year 2030. The production of alternative binders, for the substitution of the current product families of cement, is under investigation due to its significant potential in emissions reduction, although robust and agreed life cycle assessment methodologies are still claimed by the industry in this field. Calcium sulfoaluminate (CSA) cements appear as a promising alternative to Portland cements due to the significant reduction of the direct emissions of carbon dioxide caused by the lower need of limestone and fuel. However, they require sulfate and higher inputs of aluminium oxide, sourced from bauxite. This study focuses on the techno-economic performance, in the geographical scope of Qatar, of a novel CSA production method consisting of the combustion of sulfur to supply SO3/SO2 to the clinkering reaction. This new approach is proven to reduce the associated greenhouse gases emissions of Portland cement clinker production, while, in general, CSA clinker production costs are higher than those for Portland cement clinker. Nevertheless, CSA has a competitive CO2 avoidance cost, provided that the economics of raw materials supply, such as bauxite, favours its production; an aspect that is further emphasised in a prospective analysis towards more restrictive climate policies.

Surface tension of melts of СаО – SiO<sub>2</sub> – Al<sub>2</sub>O<sub>3</sub> – В<sub>2</sub>O<sub>3</sub> system

Using the method of experiment planning by simplex, the surface tension of the melts of СаО – SiO 2 – Al 2 O 3 – В 2 O 3 system was researched. The local part of the system was explored which covered the process of ferrosilicon, silicochrome, cement clinker, ceramics, glass, and sittals production. The amount of oxides in it was (%): 9.8 – 52.0 CaO; 0 – 70.4 SiO 2 ; 0 – 51.5 Al 2 O 3 and 0 – 20 B 2 O 3 . A mathematical model of surface tension dependence on the melts composition has been created and diagrams in the form of tetrahedron sections in B 2 O 3 have been constructed. It was found that, in the CaO – SiO 2 – Al 2 O 3 system, which is basic for metallurgy, melts with a high surface tension adjoin the binary side of CaO – Al 2 O 3 in the area of calcium aluminates crystallization which have small sizes, high charge and due to this bond to melt volume. With the introduction of SiO 2 , σ of melts decreases due to the formation of large aluminosilicon formations of the [Al 2 Si 2 O 8 ] 2– type, rankinite groups Si 2 O 7 6- , and ring complex [Si 3 O 9 ] 6- pseudo-wollastonite anion. The complication of anions due to polymerization leads to a drop of surface tension because of a decrease in charge ratio of the latter to the radius and, consequently, the strength of bond with cations. Boron anhydride injection causes a decrease in surface tension of melts СаО – SiO 2 – Al 2 О 3 which can be explained by boron transition at high temperature from four oxygen-coordinated (BO 4 5- ) to three oxygen-coordinated state (BO 3 3- ). Formed flat triangles BO 3 3- or complexes with them are loosely related to the melt’s volume, they are forced out to the surface and reduce surface tension. Mostly this affects the main aluminate melts, rather than acid ones. The latter can be explained by the closeness of the capillary activity of boron – and silicon-oxygen anions. The surface phenomena between the products of blast-furnace smelting of titanomagnetite iron ores have been studied experimentally using the method of lying drop. It was noted that the highest adhesion forces (work of adhesion) take place between slag and grenal (cast iron with a high titanium and silicon content), which is the reason for the loss of metal at the outlet with slags during the processing of such ores. Boron loaded into the blast furnace (in the form of natural ores) is redistributed under reduction conditions between cast iron, grenal and slag. Experiments have shown that the presence of boron in slag at the level of microconcentrations reduces the work of adhesion from 688 to 436 MN/m (by 37 %). Industrial experiments have shown that this helped to reduce the loss of valuable vanadium-containing cast iron with slags by 1.2 – 1.5 times with a simultaneous improvement in smelting performance.

Online cement clinker quality monitoring: A soft sensor model based on multivariate time series analysis and CNN

The content of free calcium oxide (f-CaO) in cement clinker is an important index for cement quality. Aiming at the characteristics of strong coupling, time-varying delay and highly non-linearity in cement clinker production, a soft sensor model based on multivariate time series analysis and convolutional neural network (MVTS–CNN) is proposed for the online f-CaO content monitoring. Based on the process industry characteristics, the MVTS–CNN modeling involves the detailed analysis of coupling relationship and time-varying delay in cement production and the application of neural network in multivariate time-series feature extraction. The main researches and contributions are fourfold: First, the strong coupling in the production system is further analyzed, and the proposed model is focused on the data coupling between specific processes, not the control coupling. Second, a multivariate time series analysis method is designed to select the time series that may have direct impacts on the f-CaO content in different production conditions, which is founded on the information on time delay range and longest active duration. Third, a multivariate time series feature extraction method is designed and adopted in the MVTS–CNN model to extract the multivariate time series features, such as active duration difference features, coupling features, nonlinear features and key time series features. Fourth, a new timing matching method, which is combined the rough timing matching of multivariate time series and the detailed timing matching of key features, is proposed to deal with the time-varying delay in various production conditions. Compared with traditional CNN, support vector machines (SVM) and long-short term memory networks (LSTM), the results demonstrate that the MVTS–CNN model has higher accuracy, better generalization ability and superior robustness.

Combined Approach to Analysis and Regulation of Thermodynamic Processes in the Energy Technology Complex

The purpose of this work is to increase the theoretical and methodological approaches to value and regulate the dynamics of management processes. Application of these dynamics is implemented via methods of improving the quality of management of complex energy technology systems in the organization of recycling processes. As a result of the research, a technological model of a rotary kiln with a division into separate sections corresponding to the combustion zones for the production of cement clinker in recycling technology was developed. Mathematical modeling, analytical calculations of thermodynamic and gas-dynamic processes in the drums of rotating furnaces, and experimental studies were carried out. As a scientific novelty, an approximation of piecewise linear functions is obtained for modeling the processes of improving the quality of control by the criterion of reducing the error of data transmission for monitoring and regulating the thermodynamic parameters of the furnace via analog-to-digital methods. An algorithmic scheme of the method of in-depth analysis of management quality using data science tools in the concept of combining organizational, economic, technical, technological, and mathematical methods and methods of data collection, processing, and storage of big data is developed. This made it possible to apply the models in the formed energy technology complex using learning neural network algorithms. The possibilities of applying the methodology of combining methods for in-depth analysis and modeling of thermodynamic processes in an energy technological complex with any composition of equipment for the production of cement clinker are substantiated.

Using Cement Kiln Dust in Asphalt Concrete Mixes in Jordan

AbstractCement kiln dust (CKD) is produced in the kiln as a byproduct during the production of cement clinker. CKD is undesirable material for a clean environment. The main purpose of this study wa...

Evaluating Biomass Ash Properties as Influenced by Feedstock and Thermal Conversion Technology towards Cement Clinker Production with a Lower Carbon Footprint

Purpose: This study evaluates the potential of biomass ash as raw clinker material and the influence of biomass feedstock and thermal conversion technology on biomass ash properties. Methods: A set of criteria for biomass feedstock and ash properties (i.e. CaO/SiO2 ratio and burnability) are established. A large dataset was collected and the best combination of biomass feedstock and conversion technology regarding the desired ash quality was identified. Results: Wood biomass has the highest potential to provide the right CaO/SiO2 ratio which is needed to form clinker minerals. Bark content and exogenous Si inclusion in wood biomass have a large influence on the CaO/SiO2 ratio. Paper sludge is composed of Ca, Si and Al and can potentially serve as a source of cement elements. Wood fly ash from pulverized fuel combustion can substitute a considerable amount of raw clinker materials due to its similar burnability. The replacement ratio is determined by the content of adverse elements in the ash (i.e. MgO2 and P2O5). Conclusion: Using biomass ash to lower the CO2 emission from clinker production depends on the joint effort of bioenergy producers, by providing higher quality biomass ash, and cement makers, by adapting the kiln operation to enable a high level of raw material replacement by biomass ash.The presented evaluation of the ash production chain, from biomass selection through combustion technology and ash management, provides new insights and recommendations for both stakeholders to facilitate this sustainable development.Graphic

Strength and durability of fiber reinforced concrete with partial replacement of cement by Ground Granulated Blast Furnace Slag

Concrete is a widely used construction material all over the world, with approximately six billion tons has been delivered every year. In the production of cement clinker, approximately one ton of CO2 has been released for one ton of cement. Cement use must be reduced by using substitute products to minimise CO2 emissions. To reduce the pollution and economy of construction industry cement is replaced by by-products to enhance its strength parameters. Our research work deals with the study of mechanical and durability properties of concrete. To assess the efficiency of Ground Granulated Blast Furnace Slag (GGBS) as a partial substitute for cement and to improve the tensile and flexural strengths and serviceability of concrete, all tests are carried out according to Indian standard codes. Various concrete mixes were planned with partial replacement of cement by GGBS in different proportions (0%, 20%, 40%, 60% and 80%) for a cement content of 400 kg/m3, with W/B ratio of 0.5, and steel fibers having an aspect ratio of 60 with three volume fractions (0.5%, 1% and 1.5%) .At the ages of 28, 90, and 180 days, concrete specimens were cast and investigations were carried out to determine the strength variations of concrete with and without fibers. Durability studies like water absorption, sorptivity, Rapid Chloride ion Penetration Test (RCPT) were done on GGBS concrete without fibers at 28 and 180 days. By replacing of cement with GGBS in concrete upto 40% increases the compressive strength of concrete by about 5–20%. Steel fibres increase the split tensile and flexural strength of concrete by considerable amount. A significant increase of split tensile flexural strengths of Steel Fiber Reinforced Concrete (SFRC) which ranged from 19 to 65% and 18–74% respectively, increase in strength was compared with conventional concrete without fibers of 28 to 180 days. A remarkable reduction has been observed in RCPT, sorptivity, and water absorption values when the cement was partially replaced by GGBS at 80% than conventional concrete.

The Effect of Addition Basalt Stone and Coal as Substitution Material for Producing Cement Clinker

National infrastructure development in Indonesia requires supporting materials, one of which is cement. This increases cement clinker production. The composition of limestone as the main raw material required in the manufacture of clinker is 81%. Basalt is used as an alternative raw material because it contains SiO2, Al2O3, and Fe2O3 with a total of >70%. It meets the chemical requirements of ASTM C618 as a substitute material for cement making. This study aims to determine the effect of adding 10% basalt rock and coal variations as a limestone substitution in cement clinker manufacture. Coal is obtained from the Tanggamus district with the variations used, namely 5, 10, 15, and 20% outside the total mass. Raw materials such as limestone, silica stone, clay, basalt stone, coal, and iron sand are ground with a ball mill and formed into pellets followed by burning at sintering temperatures of 1100, 1200, and 1300 oC with a holding time of 2 h. The clinker was analyzed using XRF (X-Ray Fluorescence), XRD (X-Ray Diffraction), and OM (Optical Microscope). This study aims to know the effect of coal on the cement clinker. The results showed that the manufacture of cement clinker at 15% substitution of coal at 1300 oC obtained a CaO compound of 66.384% and SiO2 of 22.747% with sample results close to ASTM requirements (C150-99). The phases formed are alite, belite, aluminate, and ferrite. From microanalysis with a 100 µm magnification, it can be seen that the phases alite and belite.

Evaluation and comparison of exergy-based resource consumption for fly ash utilisation in a cement clinker production system and landfill disposal

Evaluation and comparison of exergy-based resource consumption for fly ash utilisation in a cement clinker production system and landfill disposal

Evaluation and comparison of exergy-based resource consumption for fly ash utilisation in a cement clinker production system and landfill disposal

It is unclear whether the utilisation of fly ash as valuable resource is preferable to landfill disposal from the resource perspective. The objective of this study was to evaluate and compare the r...

Augmented Multidimensional Convolutional Neural Network for Industrial Soft Sensing

In the era of industrial big data, data-driven soft-sensor models have become an important method to guide production and optimize control. However, due to the limitation of data acquisition methods, the industrial data obtained in practice have unavoidable defects that affect the performance of soft sensors. Aiming at the unbalanced sampling, inaccurate matching, and partial missing of industrial process data, this article proposes an augmented multidimensional convolutional neural network (CNN) for industrial soft sensing. For complete process data information, we stitch the fine-grained data to obtain coarse-grained data and then use a CNN to extract deep features. On the basis of analyzing the physical meaning of data, the structure of multidimensional convolution is designed to focus on different details of process information. In this framework, the problem of partial missing data is emphasized. Then, mix-grained data augmentation strategies are invented to solve this problem and improve the performance of multidimensional CNN (MDCNN) soft sensors. The proposed augmented MDCNN is applied to the f-CaO prediction of the cement clinker production process, results of which show superiority compared to existing methods.

Benefits of using steel slag in cement clinker production for environmental conservation and economic revenue generation

Steel slag, the most discharged metallurgical slag in China, is rarely applied in the production of clinkers. The aim of this study is to analyze the maximum substitution amount of steel slag in raw meal and calculate the resources required as well as the environmental and economic benefits of the addition. Numerical studies show that 14.30% was the maximum amount of steel slag added to the raw meal, and this was mainly determined by its Fe2O3 content. Pilot runs revealed that the quality indices of the currently used iron ore-based raw meal cannot be transferred to steel-slag-based feeds because the physical properties of the latter induce several technical problems during the production process. However, by implementing optimized quality indices and operational processes, the plant was able to produce a steel slag clinker with excellent performance, whose indicators all met the national standard requirements. It is possible to substitute all the iron ore (26.35–125.42 kg/t) and part of the limestone (34.40–160.02 kg/t) with increasing amounts of steel slag (from 43.04 to 202.26 kg/t). Using steel slag also led to an additional reduction in energy consumption (2.32–11.38 kg/t). Lessened limestone dissociation and lowered sintering temperatures can also help decrease the process and fuel emissions by up to 72.28 kg/t and 24.16 kg/t, respectively. Moreover, the use of steel slag can decrease raw meal cost by up to 0.82 USD/t compared to using iron ore and potentially increase annual earnings up to 2.37 MUSD/a for a 2500 t/d cement plant.

Impact of emission reductions and meteorology changes on atmospheric mercury concentrations during the COVID-19 lockdown

Controlling anthropogenic mercury emissions is an ongoing effort and the effect of atmospheric mercury mitigation is expected to be impacted by accelerating climate change. The lockdown measures to restrict the spread of Coronavirus Disease 2019 (COVID-19) and the following unfavorable meteorology in Beijing provided a natural experiment to examine how air mercury responds to strict control measures when the climate becomes humid and warm. Based on a high-time resolution emission inventory and generalized additive model, we found that air mercury concentration responded almost linearly to the changes in mercury emissions when excluding the impact of other factors. Existing pollution control and additional lockdown measures reduced mercury emissions by 16.7 and 12.5 kg/d during lockdown, respectively, which correspondingly reduced the concentrations of atmospheric mercury by 0.10 and 0.07 ng/m3. Emission reductions from cement clinker production contributed to the largest decrease in atmospheric mercury, implying potential mitigation effects in this sector since it is currently the number one emitter in China. However, changes in meteorology raised atmospheric mercury by 0.41 ng/m3. The increases in relative humidity (9.5%) and temperature (1.2 °C) significantly offset the effect of emission reduction by 0.17 and 0.09 ng/m3, respectively, which highlights the challenge of air mercury control in humid and warm weather and the significance of understanding mercury behavior in the atmosphere and at atmospheric interfaces, especially the impact from relative humidity.

Synthesis and characterization of cement clinker using recycled pulverized oyster and scallop shell as limestone substitutes

Developments in the aquaculture industry have increased the production of shellfish. However, the lack of a proper recycling method for discarded shells is resulting in marine environmental pollution. For the sustainable management of shellfish byproducts, pulverized oyster and scallop shell powder were used as major raw materials in cement-clinker production, replacing 100 wt% of limestone. The characteristics of the synthesized cement clinkers and hydrated cement pastes were analyzed via scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), strength tests, thermogravimetric analysis, isothermal calorimetry, and X-ray diffraction (XRD) with Rietveld refinement. The analysis results for the synthesized oyster-shell cement (OSC) and scallop-shell cement (SSC) were compared with those of limestone-based cement and commercial ordinary Portland cement (OPC). Anhydrous cement-clinker phases such as C3S, C2S, C3A, and C4AF were successfully formed in all the synthesized clinkers, similar to the OPC. Additionally, the OSC and SSC yielded the same main hydration products (C–S–H and portlandite) as the OPC, and the morphology of the hydration products in the OSC and SSC was very similar to that in the OPC. The results indicate that oyster and scallop shells are suitable substitutes for limestone as a raw material for cement.

Numerical investigation of the impact of coating layers on RDF combustion and clinker properties in rotary cement kilns

The formation of regions of solid coating, where agglomerated clinker material adheres to the refractory lining of the kiln wall, is very common during cement clinker production. While a thin coating layer protects the refractory lining, strong deposit formation can impair the material flow through the kiln. In this study, the impact of these coating layers on the clinker production process within a rotary kiln is investigated with CFD simulations. The fuel injected at the main burner is a mixture of pulverized coal and refuse derived fuel (RDF). Advanced models were developed to accurately describe the trajectories and thermal conversion of non-spherical RDF particles in the gas phase. These models are based on a detailed fuel analysis of major RDF fractions. A blocked-off region approach is used to consider different coating profiles within the simulation domain. The thermochemical processes in the clinker bed of the kiln are approximated with a one-dimensional model that calculates heat and mass exchange with the gas phase, the incorporation of fuel ashes into the bed and the chemical-mineralogical reactions of the clinker. The blocked-off region approach is also employed to account for the clinker bed geometry in the kiln, which greatly depends on the considered coating profile. Two cases, one with a thin and evenly distributed coating profile and one with a thick and locally concentrated coating, are simulated. The resulting impact on RDF conversion, gas phase properties and clinker phase formation are assessed and compared to a reference case without any coating. Results show that the insulation effect of a thin coating profile increases the gas phase temperature in the kiln and helps to reduce the free lime content of the final clinker product. In the case of heavy coating, a temperature shift towards the solid material inlet of the kiln occurs, which outweighs the beneficial insulation effect of the coating in the sintering zone and leads to lower local gas phase temperatures. In combination with reduced clinker residence times, this results in a slight increase of the free lime content in the clinker.

Granulated Blast-Furnace Slag and Coal Fly Ash Ternary Portland Cements Optimization

Granulated blast-furnace slag (GBFS) and coal fly ash (CFA) are two well-known constituents in Portland cements. Ternary Portland cements (GBFS-CFA-K) provide environmental advantages by reducing Portland cement clinker (K) production and, therefore, promote lower CO2 emissions. Nevertheless, both of them cause a delay in the compressive strength gain. Given that, the early compressive strength for both constituents is low, but they improve the compressive strength at medium and later ages as consequence of the pozzolanic reaction. In this paper, a full factorial design with two levels was developed for the mortar compressive strength estimation at 2, 7 and 28 days. Mortar prisms made with 25% and 40% of granulated blast-furnace slag (GBFS) and/or coal fly ash (CFA) were tested. The effects of the interaction between GBFS and CFA on the compressive strength development of ternary Portland cement mortars were reported. Results show that the contribution of both cement constituents to the ternary mortar mix reduces the compressive strength for all the tested ages. Nevertheless, the finer the GBFS, the better ternary cement performance was achieved, showing that the synergistic effect is more effective when the finer GBFS is used, probably due to a more adequate particle size distribution. Finally, a relationship between compressive strength, fineness, GBFS content and CFA content was found for each age.

Physical and mechanical properties of Portland cement clinkers from raw materials of Karakalpakstan

In this article, the development of a technology for the production of clinkers and cements based on them using previously unexplored alternative sources of local raw materials in Karakalpakstan is studied, is an effective solution to the problem of covering the cement industry’s construction industry needs. Development of practical recommendations on the technology for obtaining Portland cement clinkers and cements based on the raw materials of Karakalpakstan. The study of the chemical and mineralogical composition of the raw materials of Karakalpakstan with the aim of their application to obtain high-quality clinkers and cements based on them. For raw mixes, which include limestone from the Dzhamansay-2 deposit, the clay component of the Berkuttau site, an iron-containing cinder from Almalyk mining-and-metallurgical integrated works, and gypsum stone from the Northern Dzhamansay deposit, the optimal firing temperature is 1450 ° C, which corresponds to the classical temperature index Portland cement clinker production. Raw mixtures based on the tested raw materials are highly reactive. When firing two-component feed mixtures using limestone of the Dzhamansay-2 deposit and basalt rock of the Berkuttau section, the optimum clinker sintering interval is 1400-1420 ° C;. Physical and mechanical tests have established that, on the basis of the tested raw materials (limestone of the Dzhamansay-2 deposit, the clay component of the Northern Dzhamansay deposit, the basaltic rock of the Berkuttau site and iron-containing additives), clinkers can be produced for general construction and sulfate-resistant cement grades of at least “400”, according to technological indicators fully meeting the requirements of State standard 10178; State standard 30515 and State standard 222 66.

Utilization of oil-based mud drilling cuttings wastes from shale gas extraction for cement clinker production.

A large amount of oil-based mud drilling cuttings (OBMDC) are generated during shale gas extraction, which adversely affects the environment. In order to realize the resource utilization of waste, the object of this paper is to study the feasibility of OBMDC to produce cement clinker. The results showed that at relatively low calcination temperature, adding a certain amount of OBMDC can produce cement clinker successfully and reduce fuel consumption. The compressive strength, hydration performance, and physical characteristics of clinker with 0, 3, 6, and 9% OBMDC were investigated by chemical analysis methods, X-ray diffraction, isothermal calorimetry, mercury intrusion, and energy dispersive spectroscopy. The results showed that the formulated cement has good hydration performance and the compressive strength also meets relevant standards. The heavy metal ions leaching test showed that the preparation of cement clinker by a low amount of OBMDC could effectively reduce the toxicity of OBMDC. In general, the preparation of cement clinker by OBMDC can realize the resource utilization of waste, effectively reduce its toxicity, and play a positive role in environmental protection.

Environmental Analysis on Co-Processing of Domestic Waste in Cement Kiln

The annual output of domestic waste has exceeded 400 million tons in China since 2016, which causes an urgent demand on harmless disposal in the current rapid process of urbanization. Compared with traditional disposal means (e.g. incineration and landfill), co-processing with cement production seems to be a better chose to meet the requirements of domestic waste treatment (i.e. harmless, volume reduction, waste utilization). However, co-processing technology also has some negative impact (e.g. extra energy consumption for pretreatment of domestic waste), so the environmental feasibility of domestic waste co-processing in cement kiln should be verified. In this paper, the influences caused by domestic waste co-processing on the cement clinker products including resource/energy consumption, as well as the pollutant emissions were quantify based on the investigation of typical plants in China. Moreover, the environment impact between landfill treatment and co-processing scenario were compared using life cycle assessment (LCA) method. The result shows that the energy consumption and CO2 emission per ton cement clinker production increased by 3.6% and 0.8% after co-process domestic waste, respectively. Furthermore, compared with sanitary landfill treatment, the co-processing in cement kiln will increase the impact of FFP, but reduce GWP and HTP impacts, especially significantly decrease the impact of LOP and SOP, bring in a good beneficial on material saving and energy saving.

Thermodynamic data for cement clinkering

The proportions of cement clinker phases produced by the pyro-processing of a raw-material mix are often predicted through the Bogue equations, established in the 1930s; however, the Bogue approach is limited in its applicability. This presents a challenge as the cement industry is seeking innovative and more environmentally friendly cement clinker formulations and production processes. These often go beyond the limitations of the Bogue equations and more flexible approaches are required. Modern thermodynamic calculations allow this flexibility but rely on databases not freely available and often specialised for other applications. The title paper reviews the thermodynamic data for stoichiometric clinker phases and presents a new dataset. The dataset is validated and its application demonstrated by case studies. Electronic CSV files containing the data which can be parsed for use with existing Gibbs energy minimisation solvers/software is distributed with this article as supplementary material.