Search Results (141)

Cement production is a carbon-intensive process that contributes significantly to global greenhouse gas emissions. Approximately 50–60% of these emissions result from limestone calcination, while 30–40% result from fossil fuel combustion in kilns. This study presents a multi-objective optimization (MOO) framework that integrates raw mix design and alternative fuel blending to simultaneously reduce production costs and carbon dioxide (CO₂) emissions while maintaining clinker quality. A hybrid Genetic Algorithm–Linear Programming (GA-LP) model was developed to navigate the balance between economic and environmental objectives under stringent chemical and operational constraints. The approach models the impact of raw materials and fuel ash on critical clinker quality indices: the Lime Saturation Factor (LSF), Silica Modulus (SM), and Alumina Modulus (AM). It incorporates practical constraints such as maximum substitution rates and specific fuel compositions. A case study inspired by a medium-sized African cement plant demonstrates the utility of the model. The results reveal a Pareto front of optimal solutions, highlighting that a 20% reduction in CO₂ emissions from 928 to 740 kg/ton clinker is achievable with only a 24% cost increase. Optimal strategies include 10% fly ash and 30–50% alternative fuels, such as biomass, tire-derived fuel (TDF), and dynamic raw mix adjustments based on fuel ash contributions. Sensitivity analysis further illustrates how biomass cost and LSF targets affect clinker performance, emissions, and fuel shares. The GA-LP hybrid model is validated through process simulation and benchmarked against African case studies. Overall, the findings provide cement producers and policymakers with a robust decision-support tool to evaluate and adopt sustainable production strategies aligned with net-zero targets and emerging carbon regulations. Full article

The co-disposal of municipal solid waste incineration fly ash (MSWI-FA) in cement kilns is an effective method for managing incineration by-products in China. However, the presence of heavy metals in MSWI-FA raises environmental concerns. This study analyzed the Cu, Zn, Cd, Pb, Cr, and Ni concentrations in MSWI-FA from 11 representative facilities across China and assessed the efficacy of a three-stage water washing process for Cl and heavy metal removal. The results revealed significant regional variations in heavy metal content that were strongly correlated with surface soil levels, with Zn, Pb, and Cu exhibiting the highest concentrations. Elemental correlations, such as Cu-Pb and Zn-Cd synergies and Cd-Ni antagonism, suggest common waste sources and temperature-dependent volatilization during incineration. The washing process (solid–liquid ratio = 1:10) achieved 97.1 ± 2.0% Cl removal, reducing residual Cl to 0.45 ± 0.32%, but demonstrated limited heavy metal elimination (10.28–19.38% efficiency), resulting in elevated concentrations (32.5–60.8% increase) due to 43.4 ± 9.2% mass loss. Notably, the washing effluents exceeded municipal wastewater discharge limits by up to 52-fold for Pb and 38-fold for Cd, underscoring the need for advanced effluent treatment. To mitigate environmental risks, the addition of washed MSWI-FA in cement kilns should be restricted to ≤0.5%, with Cd content prioritized in pre-disposal assessments. This study provides actionable insights for optimizing MSWI-FA co-processing while ensuring compliance with ecological safety standards. Full article

With increasing traffic loads and the continuous deterioration of asphalt pavements, it has become necessary to explore alternative materials that enhance both performance and sustainability. This study aims to investigate the effect of using cement kiln dust (CKD) as a filler substitute in hot mix asphalt composites, focusing on the mechanical and durability properties of pavements. The results indicate that replacing conventional filler with CKD in different proportions (1.5%, 3%, 4.5%, and 6%) positively affects the properties of asphalt mixtures. Marshall stability values increased by 58.4% when using 100% CKD, indicating a significant improvement in the mixture’s ability to withstand traffic loads. Flow tests revealed that replacing CKD by up to 50% enhances the flexibility of the mixture, but exceeding this percentage makes the mixture stiffer, which may lead to premature cracking. In terms of moisture sensitivity, incorporating CKD by 25% improves the mixture’s resistance to water damage, while increasing it to 100% reduces this resistance, highlighting the need to improve the adhesion properties of asphalt. Indirect tensile strength tests have confirmed that CKD enhances the cohesion of the mixture, reducing the likelihood of cracking under pressure and contributing to longer pavement life. Based on these results, it is recommended that CKD be used for up to 50% to achieve a balanced combination of strength, flexibility, and moisture resistance, with further studies being needed to evaluate the long-term performance and potential improvements through additional material modifications. Full article

This study explores the potential of using sustainable materials in brick manufacturing by designing a novel brick mix in the laboratory, incorporating sand, lime kiln dust (LKD) waste, tyre rubber, and ground granulated blast furnace slag (GGBFS) waste. These cementless bricks blended LKD–GGBFS wastes as the binder agent and fine crumb rubber from waste tyres as a partial replacement for sand in measured increments of 0%, 5%, and 10% by volume of sand. Ordinary Portland cement (OPC) and fired clay bricks were sourced from the industry, and their properties were compared to those of the laboratory bricks. Tests performed on the industry and laboratory bricks included compressive strength (CS), freeze-thaw (F-T), and water absorption (WA) tests for comparison purposes. Additionally, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were performed on the bricks to assess the morphological and mineralogical changes responsible for the observed strengths and durability. The CS and WA values of the engineered bricks were 12, 6, and 4 MPa, and 7, 12, and 15%, respectively, for 0, 5, and 10% crumb rubber replacements. The industry bricks’ average CS and WA values were 13 MPa and 8%, respectively. From the results obtained, the green laboratory bricks passed the minimum strength requirements for load-bearing and non-load-bearing bricks, which can be used to construct small houses. Lastly, the engineered bricks demonstrated strength and durability properties comparable to those of the industry-standard bricks, indicating their potential as a sustainable alternative to help divert waste from landfills, reduce the pressure on natural fine sand extraction, and support eco-conscious brick production for a sustainable environment. Full article

The cement industry faces increasing energy costs and environmental pressures, driving the adoption of alternative fuels derived from waste materials. In Togo, approximately 350,000 t of end-of-life tires (ELT) are generated annually, creating significant environmental and health hazards through uncontrolled disposal and burning practices. This study investigated the technical feasibility and economic viability of incorporating waste tires as an alternative fuel in cement manufacturing. Tire-derived fuel (TDF) performance was evaluated by comparing pre-processed industrial tires with unprocessed ones, focusing on clinker production loss, elemental composition, heating values, and bulk density. The results demonstrate that TDF exhibits superior performance characteristics, with the highest heating values, and meets all the required specifications for cement production. In contrast, whole tire incineration fails to satisfy the recommended criteria, necessitating blending with conventional fuels to maintain clinker quality and combustion efficiency. The investigation revealed no significant adverse effects on production processes or clinker quality while achieving substantial reductions in nitrogen and sulfur oxide emissions. The experimental results were compared with the theoretical burnout times to optimize the shredding operations and injection methods. However, several challenges remain unaddressed, including the absence of streamlined handling processes, limited understanding of long-term ecological and health impacts, and insufficient techno-economic assessments. Future research should prioritize identifying critical aging points, investigating self-rejuvenating behaviors, and quantifying long-term environmental implications. These findings provide a foundation for developing computational models to optimize the mixing ratios of alternative and fossil fuels in cement manufacturing, offering significant environmental, economic, and societal benefits for the cement industry. Full article

The use of tunnel kiln firing in clay brick production offers a promising approach for disposing of Cl-containing solid waste, with lower chlorine (Cl) and heavy metal volatilization compared to cement kiln processes. However, the effects of Cl salts on brick properties and the volatilization mechanisms remain unclear. This study investigates the behaviors of NaCl, KCl, and CaCl₂ during sintering. Adding 15 wt% Cl salts significantly alters pore structure, increasing water absorption by 80–100% and reducing compressive strength by 70–80%. At 1050 °C, 10.8–16.4% of Cl volatilizes mainly as HCl (g), 24.4–26.2% remains in original salt form, and over half is immobilized within the brick matrix. Thermodynamic and TG-MS analyses reveal Cl salts are stable below 800 °C but release HCl (g) at higher temperatures due to lower reaction energy barriers than Cl₂ (g). Density functional theory (DFT) calculations show that H⁺ for HCl (g) formation primarily originates from water vapor (H₂O), with organic decomposition having minimal effect. The presence of Cl salts promotes feldspar and silicate phase formation, enhancing densification but increasing porosity from HCl release. To reduce HCl emissions, a two-stage temperature control strategy is proposed: organic decomposition and moisture removal below 600 °C, followed by sintering at 800–1000 °C. This work clarifies the volatilization mechanisms of Cl salts and provides guidance for optimizing industrial brick production using Cl-containing waste. Full article

Ensuring efficient long-term quality control of the raw mix remains a priority for the cement industry, supporting initiatives to lower the CO₂ footprint by incorporating significant amounts of alternative fuels and raw materials in clinker production. This study presents an effective method for creating a robust auto-tuner for proportional–integral–differential (PID) controller control of the lime saturation factor (LSF) of the raw mix using artificial neural networks (ANNs). This auto-tuner, combined with a previously studied robust PID controller, forms an integrated system that adapts to process changes and maintains low long-term variance in LSF. The ANN links each of the three PID gains to the process dynamic parameters, with the three ANNs also interconnected. We employed the Levenberg–Marquardt method to optimize the ANNs’ synaptic weights and applied the weight decay method to prevent overfitting. The industrial implementation of our control system, using the auto-tuner for 16,800 h of raw mill operation, shows an average LSF standard deviation of 2.5, with fewer than 10% of the datasets exceeding a standard deviation of 3.5. Considering that the measurement reproducibility is 1.44 and assuming a low mixing ratio of the raw meal in the silo equal to 2, the LSF standard deviation in the kiln feed approaches the analysis reproducibility, indicating that disturbances in the raw meal largely diminish in the kiln feed. In conclusion, integrating traditional, well-established tools like PID controllers with newer advanced techniques, such as ANNs, can yield innovative solutions. Full article

This study evaluates pistachio shell ash (PSA) as a sustainable cement substitute and investigates its effect on setting time, strength and microstructure. In this study, pistachio shell ash (PSA) obtained from the kiln flue gas filter of pistachio shells burnt at 300–350 °C in an industrial kiln was used. PSA was substituted for ordinary Portland cement (OPC) at 5, 10, 15, 20, 25 and 30%. PSA increased the SO₃ value in the cement mortars, so 5% PSA substitution delayed the cement setting time by up to 174%. However, it increased the water requirement of the cement mortar by about 2%. While it increased the early strength (22% on day 1, 15% on day 2, and 5% on day 7), the 28-day strength decreased slightly (about 4.5%) due to low pozzolanic activity. Microstructural analyses such as SEM-EDX and XRD showed that the calcite and gypsum phases of PSA provided early strength gains, but there were long-term losses. With a 5% replacement rate, PSA provides significant environmental benefits by reducing CO₂ emissions while maintaining optimum mechanical performance and supports the circular economy through the efficient use of agricultural waste. Full article

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

In the municipality of La Granja d’Escarp, for over thirty years, an important natural cement factory was in operation. In 1876, the Girona family, who were businessmen and bankers from Barcelona, opened the factory with modern industrial facilities. It included kilns, mills, and crushers, alongside warehouses, a small railway for internal transportation of the various materials used, and even a housing area for workers. The neighboring Ebro River allowed distribution by river transport at first. Later, with the use of railways, transport to consumption points was possible. This industrial complex became a center of significant importance in Catalonia in the production of cement, which was used for building hydraulic and civil works. During the first decade of the twentieth century, the factory stopped its activity and the facilities were abandoned. Nowadays, this industrial heritage site is in a state of neglect, without any kind of protection or maintenance. In turn, this has caused the collapse of some buildings in recent times and the loss of historical value of the architectural ensemble. We have carried out initial geomatic research, which has highlighted the constructive properties of the kilns. We have also tested five samples from different buildings using XRD and TGA/DSC, which showed the use of lime mortars in their construction. This is the first study to be carried out at this site, with the aim of showing the historical importance of the ensemble. The goal of the study was to highlight the value of this industrial heritage site and illustrate that it was once a pioneer in the production of natural cement and a driving force for Catalonia. Full article

Global warming is a critical issue driven largely by the extensive release of greenhouse gases, with the cement industry being one of the biggest contributors to CO₂ emissions. A sustainable solution involves the integration of supplementary cementitious materials (SCMs) into cement production, which can mitigate environmental impacts. This study focuses on the effects of binary SCMs, composed of calcined expanded clay kiln dust and opoka, on the hardening and hydration behavior of Portland cement. The analysis used methods such as X-ray diffraction, thermal analysis, calorimetry, and compressive strength testing. The tested dust was thermally activated at 600 °C and the opoka was dried and milled to evaluate its combined influence on the cement properties. Portland cement was substituted with a combination of these two additives. The findings revealed that the two-component mixture exerts a multifaceted impact on the hydration process of Portland cement. The activated expanded clay kiln dust triggers a pozzolanic reaction because of its high reactivity, while the opoka component promotes the development of monocarboaluminates. This binary supplementary cementitious material, derived from opoka and expanded clay kiln dust, proves to be a highly effective substitute, allowing up to 25 wt.% replacement of Portland cement without reducing its compressive strength. Full article

Sustainable energy consumption in cement production involves practises and strategies aimed at reducing energy use and minimising environmental impact. The efficiency of a cement kiln is dependent on the kiln design, fuel type, and operating temperature. In this study, a dynamic simulation analysis is used to investigate heat losses and distribution within kilns with the aim of improving energy efficiency in cement production. This study used Computational Fluid Dynamics (CFD) with Conjugate Heat Transfer, Turbulent Flow, and the Realisable k−ϵ turbulence model to simulate heat transfer within the refractory and wall systems of the kiln, evaluate the effectiveness of these systems in managing heat losses, and establish the relationship between the heat transfer coefficient (HTC) and the velocities of solid and gas phases. The simulation results indicate that a temperature gradient from the kiln’s interior to its exterior is highly dependent on the effectiveness of refractory lining in absorbing and reducing heat transfer to the outer walls. The results also confirm that different thermal profiles exist for clinker and fuel gases, with clinker temperatures consistently peaking at approximately 1450 °C, an essential condition for optimal cement-phase formation. The results also indicate that phase velocities significantly influence heat absorption and transfer. Lower velocities, such as 0.2 m/s, lead to increased heat absorption, but also elevate heat losses due to prolonged exposure. The relationship between the heat transfer coefficient (HTC) and the velocities of solid and gas phases also indicates that higher velocities improve HTC and enhance overall heat transfer efficiency, reducing energy demand. Full article

This study compares the logistics of decommissioning wind turbine blades for energy recovery in a cement kiln (proposed scenario) to industrial landfill site disposal and coke fuel in a cement kiln combined (base scenario) to check the financial cost of the operation in each scenario. The wind farm coordinates, wind turbine blade mass, and logistics costs of the 760 wind farms in Northeast Brazil were used to determine the location of a material processing center (MPC) for wind turbine blade waste. The findings showed that the cost of the proposed scenario was higher than that of the base scenario when a single MPC was considered to serve the Northeast region. However, the proposed scenario was preferable when installing decentralized MPCs to serve the Northeast region. The installation of four additional decentralized MPCs shows that energy recovery is a more favorable technological route in the economic performance for disposing of 96% of the wind turbine blades in operation in the Northeast region, which represents 210,188 tonnes. Therefore, the gradual implementation of MPCs should consider a wind turbine blade decommissioning plan to support the energy recovery potential. Full article

Cement kiln dust (CKD), a by-product of cement manufacturing, has been largely underutilized despite its potential as an eco-friendly adsorbent for wastewater treatment. This study addresses the knowledge gap regarding CKD’s effectiveness in removing heavy metals from wastewater residuals. A comprehensive experimental program was conducted to optimize key parameters such as the pH (6–9), contact time, sorbent dosage, and initial heavy metal concentrations using a batch equilibrium technique. The results demonstrated that CKD can effectively remove heavy metals, achieving removal efficiencies of 98% for Pb, 94% for Zn, 92% for Cu, and 90% for Cd within just 4 h of treatment. Importantly, CKD not only provided high adsorption efficiency but also resulted in a significant reduction in the formation of hazardous solid sludge, a major concern in traditional wastewater treatment methods. The adsorption data closely matched the Langmuir isotherm model, further validating CKD’s potential as a sustainable, cost-effective solution for reducing heavy metal contamination in wastewater while minimizing the environmental impact. 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