Ceramic Firing Process Research Articles

Optimizing industrial tunnel kiln operations for ceramic roof tile production: A bi-objective approach

The ceramic firing process constitutes a highly energy-intensive production step that significantly affects the quality and final properties of the ceramic product. This work presents a model-based, bi-objective optimization approach for an industrial-scale tunnel kiln used in ceramic roof tile production, focusing on the exploration of trade-offs between productivity and thermal energy consumption. Initially, sintering kinetics are established based on lab experiments and integrated within a novel physics-based tunnel kiln model, thus allowing sintering evolution to be considered for the derivation of the optimal kiln operation. Two bi-objective optimization studies are then conducted to explore trade-offs under steady-state and transient-state kiln operations, thus generating a set of non-dominated operating policies. The attained Pareto optimal solutions are then evaluated with respect to the values of Specific Energy Consumption (SEC), which is distinctly minimized. This results in optimal SEC values of 0.283 for the steady state and 0.277 kWh/kg for the transient state kiln operation.

Function optimization of ceramic firing process and reduction of energy consumption based on CFD simulation

Microwave sintering, as an efficient and energy-saving advanced sintering method, has advantages that traditional sintering methods cannot match, such as promoting ion diffusion and refining grains. This paper uses microwave heating equipment and solid-phase reaction method combined with microwave sintering technology to prepare ceramics. The treatment process of powders and the influence of microwave sintering parameters on the reduction of energy consumption in the ceramic firing process were studied, and the microwave sintering process was optimized. This article also uses computational fluid dynamics (CFD) as a tool to establish a numerical model of hydrodynamic sedimentation based on the Euler multiphase flow model, and it uses the established numerical model to conduct engineering scale research on the classification treatment process of processing waste. Finally, this article elaborates on the process of multi-process planning and optimizes relevant process parameters. This article builds on previous research by employing a BP neural network (BPNN) to determine the correlations between the many variables involved in the production of functional ceramics and their respective quality metrics. The experimental findings demonstrate the efficacy of the proposed methodology in performing intelligent tasks like process decision-making and optimizing process parameters.

Ceramic Firing Temperature Trajectory Monitoring System on IoT-Based Gas Furnace

This study introduces a novel system where a conventional ceramic furnace is upgraded with IoT capabilities, specifically utilizing NodeMCU and a thermocouple sensor. The integrated system enables real-time temperature monitoring, facilitating the correction of firing trajectory errors in the ceramic firing process. The sensors reading minimizes errors by detecting temperature changes with a maximum deviation of -2.5 °C and a minimum deviation of -1 °C. The average error ranges from 1.81% to 3.79%. The collected data is seamlessly transmitted to Google Spreadsheet for online monitoring. This comprehensive solution not only minimizes recording errors but also ensures the quality of final ceramic products by preventing issues such as cracks, breaks, black cores, and non-uniform sizes. The incorporation of NodeMCU, thermocouple sensors, and online monitoring represents a significant technological leap in optimizing ceramic firing processes for heightened precision and efficiency.

Crystalline Structure Assessment of Ceramic Veneered Co-Cr-W Dental Alloy Substructures Obtained by Selective Laser Melting—A Pilot Study

The aim of this work is to assess the crystalline structure modification of an SLM Co-Cr-W dental alloy, veneered with two different ceramics, by means of X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy, coupled with energy-dispersive spectroscopy (SEM-EDS). Ten identical plates were fabricated using SLM and were subsequently subjected to ceramic veneering. Following the repeated firing of the ceramic layers, carried out at temperatures exceeding 900 °C, new crystalline phases and variations in the crystallite sizes in the SLM Co-Cr-W dental alloy used for the substructure were detected via XRD. The two veneering ceramics showed significant differences in their behavior, beginning with the first firing, accompanied by structural changes. AFM micrographs and histograms of the surface heights over the whole scanned area of the samples showed that the surface of the Co-Cr-W dental alloy is strongly affected by the repeated firings necessitated by the ceramic firing process, a finding in accordance with the XRD results. The SEM investigation revealed that the different firing parameters had an impact on the alloy, the ceramic microstructure, and the surface quality. The differences in the chemical composition of the ceramics, highlighted by EDS, are reflected in their behavior. The crystalline alloy structure is influenced by the repeated firings of the ceramic layers.

Determining the Thermal Efficiency of Firing of a Cross Draft Kiln using Methane and Liquefied Petroleum Gas

Thermal efficiency in the ceramic firing process is crucial to reducing energy consumption, emissions of gaseous pollutants and the cost of production. This study, reports on the determination of thermal efficiencies of a traditional 3m x 28m x 2.7m cross draft kiln using the heat balance approach. Results of the study showed thermal efficiencies of 46.4% and 1.9% for methane and liquefied petroleum gas kiln to 1, 200 O C at ambient temperature of 26 O C. Findings from the study also showed that only 2.1%, and 32.3% of the thermal energy inputs from methane, and liquefied petroleum gas (LPG) were effectively utilized for the physio-chemical transformation of ceramic ware. Findings also revealed that thermal energy wastes, in the form of heat losses through radiation, and convection accounted for up to 280,1522.7 kcal/kg, and 102,338.592 kcal/kg for both methane, and LPG fired kilns respectively. Other sources of heat wastages identified included heat lost in the form of waste heat and combusted exhaust gas. It is hoped that findings from this study, will aid in addressing the gross thermal inefficiency of the traditional cross draft kiln. Keywords: Ceramic, Firing, Greenhouse gas, Methane, Thermal efficiency .

Biomass gasification in a fixed bed downdraft reactor with oxygen enriched air: a modified equilibrium modeling study

Biomass conversion by gasification process is increasingly becoming attractive, especially for ceramic making industry, to transform biomass materials into combustible fuel gas called producer gas. This producer gas can then be used to fully or partially substitute liquefied petroleum gas in ceramic firing process. However, air gasification is known to generate low calorific value of gaseous fuel (3-6 MJ/Nm3) which may not be able to generate sufficiently high temperature (> 1200 oC) flame required by ceramic firing process. Use of oxygen enriched air is therefore of great interest if medium to high calorific value producer gas is required. In this work, a modified equilibrium model of global gasification reactions is developed to predict the resultant distribution of combustible gas species in the producer gas and to study the effect of operating parameters (oxygen content in air, and equivalence ratio) in a gasification process of agro-residues in a fixed bed downdraft gasifier at a fixed temperature. The modified equilibrium model of global gasification reactions developed in this work is based on thermodynamically stoichiometric approach due to its simplicity and reduced computational time. Model predictions of reaction kinetic constants for gasification reactions and gas concentration are validated by comparing with available experimental data. Simulation of influence of oxygen content in air (21-50%) and equivalence ratio (0.15-0.35) on composition of combustible gas and its heating value is carried out. The preliminary model simulation is found to give good qualitative prediction of experimental results. For maximum calorific value of producer gas generated, oxygen content in air should be 50%, and the equivalence ratio should be 0.15, respectively. For better accuracy of this modified equilibrium model, unconverted char and tar should be further considered.

Simulation of Producer Gas Combustion in a Premixed Burner for Ceramic Firing Process

Producer gas from biomass may be used to substitute liquefied petroleum gas in ceramic firing process. Numerical simulation offers a powerful tool that can assist in ceramic kiln design, optimization and scale up of the process, saving expensive pilot works. This study aims to simulate combustion of producer gas in a premixed burner in ceramic kiln based on computational fluid dynamics. The steady-state governing equations were solved using the SIMPLE algorithm and the effect of turbulence on the mean flow field was accounted for using the RANS k–ω model. The reaction mechanism was used for combustion of producer gas as the intermediate species. For geometrical model, a 3D model for the burner was developed while an axis-symmetric model for a combustion chamber was implemented to reduce computational costs. The present model was validated and refined using results from experiments. It was found that simulated results of flow and temperature patterns were qualitatively in similar agreement to experiments. For temperature profiles, mean differences between experiments and simulation were within 1.0-7.4%.

Producción de cerámicas griegas arcaicas en Huelva

A fines de la década de los 80 del siglo pasado fue diferenciado en Huelva un conjunto de cerámicas griegas arcaicas caracterizadas por una pasta de coloración verdosa amarillenta. La procedencia de estas cerámicas, desconocidas hasta la fecha en otros yacimientos, había permanecido sin determinar. El presente trabajo demuestra una producción in situ fundamentada en la exclusividad de la localización, las particularidades formales y decorativas de los tipos documentados, las anomalías malformativas de un ejemplar anfórico y, definitivamente, los resultados de los análisis de arcillas mediante difracción de rayos X y activación neutrónica. El primer método evidenció la formación durante la cocción de fases cristalinas compatibles con la composición de los materiales arcillosos ricos en carbonatos de los depósitos locales; el segundo, una estrecha similitud entre la composición química de las cerámicas y dichas arcillas locales. Un hallazgo particularmente llamativo lo constituye la detección de oro y plata en las pastas cerámicas. Las mismas determinaciones analíticas en dos muestras de otro grupo mal delimitado de cerámicas griegas arcaicas, caracterizadas por pastas de coloraciones variables entre anaranjadas, rojizas y amarillentas, engobes rojizos y escasa calidad, señalan que una parte de estas cerámicas, o quizás la mayoría, también fueron producidas localmente.

Development and Performance Evaluation of a Biomass Gasification System for Ceramic Firing Process

Abstract Ceramic products are manufactured in many countries worldwide. Ceramic manufacturing industry is vital in terms of employment and economics. The industry is very energy intensive, consuming large amount of fuels. Liquefied petroleum gas (LPG) and natural gas are usually used, representing a significant portion of the total production cost. Switching to alternative gaseous fuel such as biomass derived producer gas may result in lower energy cost. Producer gas generated from biomass gasification process contains H 2 , CO and CH 4 which are combustible. Under carefully controlled conditions, burning of producer gas can provide suitable firing atmospheres for manufacture of ceramic products. In this work, attempt has been made to develop a 600 kW th biomass gasification system for ceramic firing. Woodchips were used as fuel. Product gas was generated and analyzed for its composition and energetic content. Firing of this fuel gas in place of LPG with modified gas burners in a firing chamber and preliminary testing at a local ceramic factory were carried out and demonstrated. It was found that required heat outputs and high temperature conditions were realized. Acceptable quality of the ceramic products was obtained. A simple economic analysis yielded an attractive return on investment. This proved to be a very promising energy option for substitution of fossil based gaseous fuels in ceramic industry.

Performance evaluation of premixed burner fueled with biomass derived producer gas

Energy consumption of liquefied petroleum gas (LPG) in ceramic firing process accounts for about 15–40% of production cost. Biomass derived producer gas may be used to replace LPG. In this work, a premixed burner originally designed for LPG was modified for producer gas. Its thermal performance in terms of axial and radial flame temperature distribution, thermal efficiency and emissions was investigated. The experiment was conducted at various gas production rates with equivalence ratios between 0.8 and 1.2. Flame temperatures of over 1200°C can be achieved, with maximum value of 1260°C. It was also shown that the burner can be operated at 30.5–39.4kWth with thermal efficiency in the range of 84 – 91%. The maximum efficiency of this burner was obtained at producer gas flow rate of 24.3 Nm3/h and equivalence ratio of 0.84.

Nanoparticle emissions from traditional pottery manufacturing.

Traditional pottery manufacturing involves firing of the ceramics in kilns, a process that leads to high concentrations of airborne particles that are harmful to human health. In order to assess the associated exposure levels and the involved risks, here, for the first time, we investigate the size, the concentration and the elemental composition of the particles emitted during the different stages of the ceramic firing process. Number size distributions of the emitted particles, having diameters in the range from 10 nm to 20 μm, were measured in a traditional small-sized pottery studio using a Scanning Mobility Particle Sizer (SMPS) and an Optical Particle Counter (OPC). The measurements showed dominance of the nanoparticle mode (i.e., particles smaller than 100 nm) when the kiln reached temperatures above 600 °C. The mean size of the particles ranged from 30 to 70 nm and their peak number concentration was 6.5 × 10(5) cm(-3) during the first stage of the firing process where the ceramics were unpainted and unglazed. During the second stage of the firing process, where the ceramics were painted and glazed, the mean particle size ranged from 15 to 40 nm and their number concentration peaked at 1.2 × 10(6) cm(-3). Elemental analysis of individual particles collected during the two firing stages and studied by Energy-Dispersive X-ray (EDX) spectroscopy showed that the emitted nanoparticles contain significant amounts of lead. These findings provide new information for understanding the health impacts of traditional pottery manufacturing, and underline the need for adopting adequate measures to control nanoparticle emissions at the source.

Managing the firing process of ceramics tiles to reduce convexity defect: design of experiment approach

Ceramics industry is an integral part of any country’s economic growth. Because of its competitive nature and wide range availability of ceramics, for both industrial and domestic consumers, it is important to have consistency in the quality of ceramics tiles. There are many defects identified in ceramics such as flatness, cracks, orthogonality, wrinkles etc. In this paper, many factors were identified during the firing process of production, which results in the convexity defect in tiles. A full factorial experiment that requires a total of 23 experimental runs (treatment combinations) for a complete replicate was carried out to determine the factors that affect the convexity occurrence. Minitab software was used to carry out regression analysis, analysis of variance, and residual analysis. The results show that the main factors below roll and above roll temperatures along with their respective interactions with the direct air blowing significantly affect the convexity of the tiles. Model implementation shows 41% reduction in convexity defects.

Crystal growth of tin oxide nano-sheets in aqueous solutions and time variation of N2 adsorption characteristics

Nucleation and crystal growth of tin oxide were realized in aqueous solutions. Nano-sheet structures grew in the solutions containing SnF2 at 90 °C to develop in-plane size and thickness gradually. Their color, size, morphology, crystal structure and N2 adsorption property varied with progress of crystal growth. Color of powder changed from white to light yellow, light blown to light green particles with growth. XRD analyses clarified that single phase of SnO2 was synthesized in the aqueous solutions without high temperature annealing. It is an advantage to conventional ceramic firing process. Growth curves of crystallite size were consistent with morphological observations using Field Emission Scanning Electron Microscopy FE-SEM. Development of sheet structure was caused by crystal growth of SnO2. Large crystallite size perpendicular to (200) planes indicated that growth along c-axis was suppressed compared to a-axis. Anisotropic crystal growth resulted anisotropic shape of nano-sheets. Chemical composition of fluorine-doped SnO2 nano-sheets was estimated to Sn : F = 1 : 0.06–0.12. BET surface area increased with crystal growth and reached to 85 m2/g. It gradually decreased with synthesis period. Growth of sheet structure along in-plane direction related to increase of surface area. Further growth in thickness increased volume of the sheets to cause decrease of surface area per weight. N2 adsorption property strongly related to crystal growth and shape change of the nano-structures. The system has the advantage of morphology controllability of tin oxide nano-structure and low environmental load.

Characterization and Inventory of PCDD/F Emissions from the Ceramic Industry in China

The ceramic industry is considered to be a potential source of dioxins (polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), considering the widespread distribution of dioxins in kaolinitic clays. Nevertheless, studies on the emission of dioxins from the ceramic industry are still very scarce. In this study, raw clays and stack gases from six typical ceramic plants in China were collected and analyzed to estimate the emission of dioxins from the ceramic industry. Dioxin profiles in raw clays were characterized by the domination of the congener octachlorodibenzo-p-dioxin (OCDD), and the contents of other congeners declined with the decreasing degree of chlorination. During the ceramic firing process, a considerable amount (16.5-25.1 wt % of the initial quantity in raw clays) of the dioxins was not destroyed and was released to the atmosphere. Dechlorination of OCDD generated a broad distribution within the PCDD congeners including a variety of non-2,3,7,8-substituted ones with the mass abundance of 0.4-3.6%. Based on the mean concentrations measured in this study, the inventory of PCDD/Fs from the manufacturing of ceramics on the Chinese scale was estimated to be 7.94 kg/year; the corresponding value on the I-TEQ basis is 133.6 g I-TEQ/year. This accounts for about 1.34% (I-TEQ basis) of the total emission of dioxins to the environment in China. The results suggest that the ceramic industry is a significant source of dioxins in the environment.

Selection of the composition of the reducing atmosphere for firing ceramics

The possible heterogeneous reactions between the oxides of the ceramic body in which iron oxides can participate were studied. The range of compositions for the reducing atmosphere required for such reactions during the firing process of ceramics was established by thermodynamic analysis. Gradual intensification of the reducing atmosphere led to gradual intensification of the sintering process of the ceramic. It was shown that when firing ceramic materials the oxidation-reduction reactions involving iron oxides and having a positive effect on the quality parameters can occur in the atmospheres consisting of fuel combustion products at an insignificant concentration of the reducing gases. Highly frost-resistant materials based on hydromicaceous-kaolinitic clays were obtained by maintaining a reducing atmosphere consisting of the products of fuel combustion with an air consumption coefficient of 0.92-0.97.