Search Results (25)

The article presents the physico-mechanical properties of cement mortars modified with the addition of fly ash generated from municipal waste incineration (MSWI-FA) and dust from rotary kiln dedusting installations (CKD—cement kiln dust) produced during cement manufacturing. The waste materials were dosed separately and in combination—MSWI-FA in amounts of 10, 15, and 20% of the cement mass, with a volumetric adjustment of the standard sand mass, while CKD was used as a cement replacement in amounts of 10, 15, and 20% of the cement mass. Basic tests were conducted on the prepared mortars, including consistency and flexural and compressive strength after 7 and 28 days of curing, water absorption, bulk density, and resistance to freeze–thaw cycles. The results indicate that the addition of MSWI-FA and CKD reduces the strength of mortars compared to the control series, with CKD proving to be more effective and stable than MSWI-FA, especially over longer curing periods. The combination of MSWI-FA and CKD often resulted in the greatest decline in mechanical parameters, suggesting limited synergy between these materials. The best results were achieved using low additive concentrations, especially in the MSWI-FA-CKD/3–3 (i.e., after 3% of the MSWI-FA and CKD waste) combination. The research confirms the potential of utilizing MSWI-FA and CKD in sustainable cement compositions but highlights the need for further work on optimizing proportions and modification techniques. The importance of these efforts for reducing environmental impact and promoting a circular economy is emphasized. Full article

It is of great significance to effectively identify the flame-burning state of cement rotary kilns to optimize the calcination process and ensure the quality of cement. However, high-temperature and smoke-filled environments bring about difficulties with respect to accurate feature extraction and data acquisition. To address these challenges, this paper proposes a novel approach. First, an improved denoising diffusion probability model (RE-DDPM) is proposed. By applying a mask to the burning area and mixing it with the actual image in the denoising process, local diversity generation in the image was realized, and the problem of limited and uneven data was solved. Secondly, this article proposes the DAF-FasterNet model, which incorporates a deformable attention mechanism (DAS) and replaces the ReLU activation function with FReLU so that it can better focus on key flame features and extract finer spatial details. The RE-DDPM method exhibits faster convergence and lower FID scores, indicating that the generated images are more realistic. DAF-FasterNet achieves 98.9% training accuracy, 98.1% test accuracy, and a 22.3 ms delay, making it superior to existing methods in flame state recognition. Full article

The use of refuse-derived fuel (RDF) in cement kilns offers a multifaceted approach to sustainability, addressing environmental, economic, and social aspects. By converting waste into a valuable energy source, RDF reduces landfill use, conserves natural resources, lowers greenhouse gas emissions, and promotes a circular economy. This sustainable practice not only supports the cement industry in meeting regulatory requirements but also advances global efforts toward more sustainable waste management and energy production systems. This research promotes the integration of RDF as fuel in cement kilns to reduce the use of fossil fuels by improving the control of the combustion. Addressing the variable composition of RDF requires continuous monitoring to ensure operational stability and product quality, traditionally managed by operators through visual inspections. This study introduces a real-time, computer vision- and deep learning-based monitoring system to aid in decision-making, utilizing existing kiln imaging devices for a non-intrusive, cost-effective solution applicable across various facilities. The system generates two detailed datasets from the kiln environment, undergoing extensive preprocessing to enhance image quality. The YOLOv8 algorithm was chosen for its real-time accuracy, with the final model demonstrating strong performance and domain adaptation. In an industrial setting, the system identifies critical elements like flame and clinker with high precision, achieving 25 frames per second (FPS) and a mean average precision (${mAP}^{50}$) of 98.8%. The study also develops strategies to improve the adaptability of the model to changing operational conditions. This advancement marks a significant step towards more energy-efficient and quality-focused cement production practices. By leveraging technological innovations, this research contributes to the move of the industry towards sustainability and operational efficiency. Full article

In recent years, the variability in the composition of cement raw materials has increasingly impacted the quality of cement products. However, there has been relatively little research on the homogenization effects of equipment in the cement production process. Existing studies mainly focus on the primary functions of equipment, such as the grinding efficiency of ball mills, the thermal decomposition in cyclone preheaters, and the thermal decomposition in rotary kilns. This study selected four typical pieces of equipment with significant homogenization functions for an in-depth investigation: ball mills, pneumatic homogenizing silos, cyclone preheaters, and rotary kilns. To assess the homogenization efficacy of each apparatus, scaled-down models of these devices were constructed and subjected to simulated experiments. To improve experimental efficiency and realistically simulate actual production conditions in a laboratory setting, this study used the uniformity of the electrical capacitance of mixed powders instead of compositional uniformity to analyze homogenization effects. The test material in the experiment consisted of a mixture of raw meal from a cement factory with a high dielectric constant and Fe₃O₄ powder. The parallel plate capacitance method was employed to ascertain the capacitance value of the mixed powder prior to and subsequent to treatment by each equipment model. The fluctuation of the input and output curves was analyzed, and the standard deviation (S), coefficient of variation (R), and homogenization multiplier (H) were calculated in order to evaluate the homogenization effect of each equipment model on the raw meal. The findings of the study indicated that the pneumatic homogenizer exhibited an exemplary homogenization effect, followed by the ball mill. For the ball mill, a higher proportion of small balls in the gradation can significantly enhance the homogenization effect without considering the grinding efficiency. The five-stage cyclone preheater also has a better homogenization effect, while the rotary kiln has a less significant homogenization effect on raw meal. Finally, the raw meal processed by each equipment model was used for clinker calcination and the preparation of cement mortar samples. After curing for three days, the compressive and flexural strengths of the samples were tested, thereby indirectly verifying the homogenization effect of each equipment model on the raw meal. This study helps to understand the homogenization process of raw materials by equipment in cement production and provides certain reference and data support for equipment selection, operation optimization, and quality control in the cement production process. Full article

The cement industry is regarded as one of the primary producers of world carbon emissions; hence, lowering its carbon emissions is vital for fostering the development of a low-carbon economy. Carbon capture, utilization, and storage (CCUS) technologies play significant roles in sectors dominated by fossil energy. This study aimed to address issues such as high exhaust gas volume, low CO₂ concentration, high pollutant content, and difficulty in carbon capture during cement production by combining traditional cement production processes with cryogenic air separation technology and CO₂ purification and compression technology. Aspen Plus^® was used to create the production model in its entirety, and a sensitivity analysis was conducted on pertinent production parameters. The findings demonstrate that linking the oxygen-enriched combustion process with the cement manufacturing process may decrease the exhaust gas flow by 54.62%, raise the CO₂ mass fraction to 94.83%, cut coal usage by 30%, and considerably enhance energy utilization efficiency. An exergy analysis showed that the exergy efficiency of the complete kiln system was risen by 17.56% compared to typical manufacturing procedures. However, the cryogenic air separation system had a relatively low exergy efficiency in the subsidiary subsystems, while the clinker cooling system and flue gas circulation system suffered significant exergy efficiency losses. The rotary kiln system, which is the main source of the exergy losses, also had low exergy efficiency in the traditional production process. Full article

As the need to minimize environmental impacts continues to rise, it is essential to incorporate, advance, and adopt renewable energy sources and materials to attain climate neutrality in industrial operations. It is established that economic growth is built upon infrastructure, where the cement industry plays a crucial role. However, it is also known that this industry is actively looking for ways to transition toward low-carbon practices to encourage sustainable and environmentally conscious practices. To this end, the use of refuse-derived fuels to substitute fossil fuels is very appealing, as these have the potential to lower clinker production costs and CO₂ emissions. Bearing this in mind, the primary objective of this work is to gain insights into the combustion behavior in an industrial rotary kiln by studying real-life scenarios and to assess the potential of substituting alternative fuels for fossil fuels to reduce CO₂ emissions. A 3D CFD turbulent combustion model was formulated in Ansys^® considering a Pillard NOVAFLAM^® burner, where refuse-derived and petcoke fuels were used, and different secondary air mass flows were considered. From the obtained results, it was possible to conclude that the outcome of the combustion process is greatly influenced by the fuel-to-air ratio. Increasing the secondary air mass flow promotes the occurrence of a complete and efficient combustion process, leading to enhanced fuel conversion and the decreased formation of pollutants such as CO, soot, and unburned hydrocarbons. An increase in combustion efficiency from 93% to 96% was observed, coupled with a slight decrease in the pollutant mass fraction in the flue gas. Full article

Regenerated magnesia-calcium brick samples with different aluminium oxide (Al₂O₃) contents were prepared using spent magnesia-calcium bricks and fused magnesia as the main raw materials and Al₂O₃ powders as the additive. The phase compositions, microstructures, room temperature, hot flexural strength, and kiln coating adherence of the regenerated samples were investigated. This indicates that the Al₂O₃ content increased, mainly resulting in the content of tetracalcium aluminoferrite (C₄AF) and tricalcium aluminate (C₃A) increasing in the regenerated samples. The bulk density, room temperature flexural strength, and kiln coating adherence all increased, whereas the hot flexural strength and corrosion resistance to cement clinker both deteriorated with an increase in the Al₂O₃ content. This was because, on the one hand, the low melting point phases of C₄AF and C₃A improved the sinterability of the regenerated samples during the burning stage, and on the other hand, they melted or existed in the liquid phase at the experimental temperature, which degraded the hot flexural strength and corrosion resistance but enhanced the kiln coating adherence as the wettability of the liquid phase. The content of Al₂O₃ in the regenerated magnesia-calcium brick should not be higher than 1.1 wt.%, considering its comprehensive performance for cement rotary kiln. Full article

This article presents the numerical modeling of the thermochemical conversion of biomass and tires as alternative fuels in kilns dedicated to the production of cement. The study seeks to understand and control the phenomena that occur when heavy fuel oil (traditional fuel) is partially replaced by biomass and tires. These are thoroughly mixed with meal at the entrance to the rotary kiln and form the bed of solids. The mathematical model developed takes into account both chemical reactions of meal and alternative fuels. At the entrance, the meal is made up of species such as CaCO₃, MgCO₃, Al₂O₃, SiO₂, Fe₂O₃, MgO, CaO, C₂S, C₃A, C₄AF and C₃S, some of which form along the kiln. The article focuses specifically on the influence of alternative fuels on the clinker or cement obtained. The properties (moisture, organic matter, composition, energy value, etc.) of the biomass and the tires, which are associated with the operating parameters of the kiln, greatly influence the production of clinker. In order to understand and control the behavior of each material and the operating parameters in the clinker (cement) production process, the mathematical model follows the evolution of each species and parameters step-by-step, until the clinker is obtained. The effect of alternative fuels on clinker production was found for the kiln’s operational parameters, the dynamic angle of the bed (30°), the angle of inclination of the kiln (2°), rotation (2 rpm), the length and the inside diameter, respectively (80 m) and (4 m); the chemical and physical properties (humidity, organic, inorganic matter, C, H, O, N, S, Cl); the lower calorific value, raw material); and the numerical parameters (spatial discretization 30 and 120). Despite the high energy content of tire fuels, the results of the use of biomass give better characteristics of clinker/cement (52.36% C3S and 3.83% CaO).The results found show that biomass pyrolysis is endothermic, with the heat of reaction found to be ${∆}_r{H}^{pyro}=184.9 \mathrm{kJ}/\mathrm{kg}$, whereas for tires, a heat of reaction of ${∆}_r{H}^{pyro}=-1296.3 \mathrm{kJ}/\mathrm{kg}$ was found, showing that the pyrolysis of this material is exothermic. Char production is higher in the case of tires than in the case of biomass, with rates of 0.261 kg/kgOrg.Mat. and 0.196 kg/kgOrg.Mat., respectively. In both cases, waste conversion was complete (100%). The cement obtained in the different cases meets the requirements of Portland cements (73.06% silicates and 18.76% aluminates), the conversion of alternative fuels is complete (100%), and the specific energy consumption is almost consistent with values from the literature. Full article

The cement industry includes energy-intensive processes, e.g., clinker rotary kilns and clinker grate coolers. Clinker is obtained through chemical and physical reactions in a rotary kiln from raw meal; these reactions also involve combustion processes. The grate cooler is located downstream of the clinker rotary kiln with the purpose of suitably cooling the clinker. The clinker is cooled through the action of multiple cold air fan units as it is transported within the grate cooler. The present work describes a project where Advanced Process Control techniques are applied to a clinker rotary kiln and a clinker grate cooler. Model Predictive Control was selected as the main control strategy. Linear models with delays are obtained through ad hoc plant experiments and suitably included in the controllers’ formulation. A cooperation and coordination policy is introduced between the kiln and the cooler controllers. The main objectives of the controllers are to control the rotary kiln and grate cooler critical process variables while minimizing the fuel/coal specific consumption of the kiln and the electric energy consumption of the cold air fan units within the cooler. The overall control system was installed on the real plant, obtaining significant results in terms of service factor and control and energy-saving performances. Full article

The current manuscript presents a review on existing kiln burner technologies for the cement production process, in the context of the current climate of energy transition and environmental remediation. Environmental legislation has become ever stricter in response to global climate change, and cement plants need to adapt to this new reality in order to remain competitive in the market and ensure their longevity. The cement production process is a well-established technology with more than a century of existence. There are several plants in operation whose process is outdated by modern standards, particularly considering the current industry decarbonization needs. The cement process requires tremendous amounts of energy, mainly recovered from the combustion of solid, liquid or gaseous fuels, which yields massive emissions of greenhouse gases. Thus, an important onus is placed upon the minimization of pollutant emission in the combustion system, as well as a substitution of fossil fuels with more sustainable alternatives. One of the sustainable alternative fuels comes in the form of refuse derived fuels (RDF). These high caloric fractions of municipal solid waste present a double advantage by reducing the amount of fossil fuels used and reducing the landfilling fraction of waste. However, their use in rotary kiln burners comes with important limitations for burner operation, namely that a high degree of control over primary air supply is needed to ensure complete combustion with minimal pollutant emission. Full article

No alternatives are currently available to operate industrial furnaces, except for hydrocarbon fuels. Plant managers, therefore, face at least two challenges. First, environmental legislation demands emission reduction. Second, changes in the origin of the fuel might cause unforeseen changes in the heat release. This paper develops the hypothesis for the detailed control of the combustion process using computational fluid dynamic models. A full-scale mock-up of a rotary cement kiln is selected as a case study. The kiln is fired by the non-premixed combustion of Dutch natural gas. The gas is injected at Mach $0.6$ via a multi-nozzle burner located at the outlet of an axially mounted fuel pipe. The preheated combustion air is fed in (co-flow) through a rectangular inlet situated above the attachment of the fuel pipe. The multi-jet nozzle burner enhances the entrainment of the air in the fuel jet. A diffusion flame is formed by thin reaction zones where the fuel and oxidizer meet. The heat formed is transported through the freeboard, mainly via radiation in a participating medium. This turbulent combustion process is modeled using unsteady Favre-averaged compressible Navier–Stokes equations. The standard k-$ϵ$ equations and standard wall functions close the turbulent flow description. The eddy dissipation concept model is used to describe the combustion process. Here, only the presence of methane in the composition of the fuel is accounted for. Furthermore, the single-step reaction mechanism is chosen. The heat released radiates throughout the freeboard space. This process is described using a P1-radiation model with a constant thermal absorption coefficient. The flow, combustion, and radiative heat transfer are solved numerically using the OpenFoam simulation software. The equations for flow, combustion, and radiant heat transfer are discretized on a mesh locally refined near the burner outlet and solved numerically using the OpenFoam simulation software. The main results are as follows. The meticulously crafted mesh combined with the outlet condition that avoids pressure reflections cause the solver to converge in a stable manner. Predictions for velocity, pressure, temperature, and species distribution are now closer to manufacturing conditions. Computed temperate and species values are key to deducing the flame length and shape. The radiative heat flux to the wall peaks at the tip of the flame. This should allow us to measure the flame length indirectly from exterior wall temperature values. The amount of thermal nitric oxide formed in the flame is quantified. The main implication of this study is that the numerical model developed in this paper reveals valuable information on the combustion process in the kiln that otherwise would not be available. This information can be used to increase fuel efficiency, reduce spurious peak temperatures, and reduce pollutant emissions. The impact of the unsteady nature of the flow on the chemical species concentration and temperature distribution is illustrated in an accompanying video. Full article

A rotary kiln is a unique facility with widespread applications not only in the process industry, such as building-material production, but also in the energy sector. There is a lack of a more comprehensive review of this facility and its perspectives in the literature. This paper gives a semi-systematic review of current research. Main trends and solutions close to commercial applications are found and evaluated. The overlap between process and energy engineering brings the opportunity to find various uncommon applications. An example is a biogas plant digestate treatment using pyrolysis in the rotary kiln. Artificial intelligence also finds its role in rotary kiln control processes. The most significant trend within rotary kiln research is the waste-to-energy approach in terms of various waste utilization within the process industry or waste pyrolysis in terms of new alternative fuel production and material utilization. Results from this review could open new perspectives for further research, which should be focused on integrated solutions using a process approach. New, complex solutions consider both the operational (mass calculations) and the energy aspects (energy calculations) of the integration as a basis for the energy sustainability and low environmental impact of rotary kilns within industrial processes. Full article

The reduction of emissions from large industrial furnaces critically relies on insights gained from numerical models of turbulent non-premixed combustion. In the article Mitigating Thermal NOx by Changing the Secondary Air Injection Channel: A Case Study in the Cement Industry, the authors present the use of the open-source OpenFoam software environment for the modeling of the combustion of Dutch natural gas in a cement kiln operated by our industrial partner. In this paper, various model enhancements are discussed. The steady-state Reynolds-Averaged Navier-Stokes formulation is replaced by an unsteady variant to capture the time variation of the averaged quantities. The infinitely fast eddy-dissipation combustion model is exchanged with the eddy-dissipation concept for combustion to account for the finite-rate chemistry of the combustion reactions. The injection of the gaseous fuel through the nozzles occurs at such a high velocity that a comprehensive flow formulation is required. Unlike in Mitigating Thermal NOx by Changing the Secondary Air Injection Channel: A Case Study in the Cement Industry, wave transmissive boundary conditions are imposed to avoid spurious reflections from the outlet patch. These model enhancements result in stable convergence of the time-stepping iteration. This in turn increases the resolution of the flow, combustion, and radiative heat transfer in the kiln. This resolution allows for a more accurate assessment of the thermal NO-formation in the kiln. Results of a test case of academic interest are presented. In this test case, the combustion air is injected at a low-mass flow rate. Numerical results show that the flow in the vicinity of the hot end of the kiln is unsteady. A vortex intermittently transports a fraction of methane into the air stream and a spurious reaction front is formed. This front causes a transient peak in the top wall temperature. The simulated combustion process is fuel-rich. All the oxygen is depleted after traveling a few diameters into the kiln. The thermal nitric oxide is formed near the burner and diluted before reaching the outlet. At the outlet, the simulated thermal NO concentration is equal to 1 ppm. The model is shown to be sufficiently mature to capture a more realistic mass inflow rate in the next stage of the work. Full article

Worldwide, in the rotary kilns of cement plants, various amounts of combustible waste are burned, which would otherwise end up in municipal landfills. The paper first analyzes the literature on the co-processing of waste in cement manufacture and its influence on the environment and human health. Then, it shows how the combustion components of co-processed waste can influence the final characteristics of clinker and cement. The main objective of the paper is to determine the level of emissions of the resulting pollutants (total dust and flue gases: NOx, SO₂, and CO) at the outlet of the chimney of the clinker kiln and flour mill to meet the requirements of the Integrated Environmental Permit (EIA) from Romania and present an estimation of the level of atmospheric air pollution using the climatological model of pollutant dispersion. Following these assessments (data shown), the cement factories will establish measures to reduce the pollution, if necessary, to comply with the regulations in force for the cement industry. Full article

To realize the efficient and comprehensive utilization of specularite resources, combined with the cement clinker production technology of rotary kilns, the coupling process of the direct reduction of specularite by lignite and the preparation of cementitious material was proposed, with the additional aim of achieving the reduction of iron oxide and transforming the gangue component into cementitious material. Thermodynamic software was used to calculate the product composition when the reaction reached equilibrium under the set conditions. By analyzing the influence of the ratio of C/O, basicity, temperature, and other parameters on the reduction of iron oxide and cementitious material generation, the feasibility of the process was judged and experimentally verified. The results showed that the coupling process of the direct reduction of specularite and the preparation of cementitious material was thermodynamically feasible when using highly volatile lignite with added calcium oxide. The optimal C/O ratio of the reducing agent was 1.2 for the complete reduction of iron oxide (Fe₂O₃, Fe₃O₄, FeO) without the gangue fraction; reduced iron could stably coexist with the cementitious material components, but the unreduced FeO would result in a substantial reduction in tricalcium silicate generation. Using lignite as a reducing agent, the hydrogen-rich volatiles in coal created a good reducing atmosphere, strengthened the reduction process of iron oxide, and provided favorable conditions for the generation of cementitious material. A two-stage heating system must be adopted to realize the reduction of iron oxide and the generation of cementitious material. The process parameters conducive to the reduction of specularite and cementitious materials were determined, the basicity range of the system was regulated to 2.4–3.3, the reasonable reduction temperature was close to and not higher than 1137 °C, and the optimal temperature of cementitious material generation was 1450 °C. Full article