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A great quantity of thermal energy is consumed in ceramic tile manufacture, mainly in the firing stage. The most widely used facilities are roller kilns, fuelled by natural gas, in which more than 50% of the energy input is lost through the flue gas and cooling gas exhaust stacks. This paper presents a calculation methodology, based on certain kiln operating parameters, for quantifying the energy saving obtained in the kiln when part of the cooling gases are recovered in the firing chamber and are not exhausted into the atmosphere. Energy savings up to 17 % have been estimated in the studied case.Comparison of the theoretical results with the experimental data confirmed the validity of the proposed methodology. The study also evidenced the need to improve combustion process control, owing to the importance of the combustion process in kiln safety and energy efficiency. KEYWORDS: ceramic tile, roller kiln, heat recovery, energy efficiency HIGHLIGHTS:Some energy input (30 -35%) in ceramic roller kilns is lost through the cooling gas stack.Cooling air is directly recovered in the combustion chamber, providing oxygen. This energy recovery from the cooling gas stack has been quantified.It has been proven that the proposed methodology to estimate energy savings is valid.
España y Brasil son dos de los mayores productores de baldosas cerámicas en el mundo. El proceso de fabricación de baldosas consume gran cantidad de energía térmica, y en estos dos países se obtiene principalmente de la combustión de gas natural, lo que conlleva la emisión a la atmósfera de CO 2 , gas de efecto invernadero. El objetivo del trabajo presentado es mostrar comparativamente los consumos de energía térmica y las emisiones de CO 2 en el proceso de obtención de baldosas cerámicas en España y en Brasil, atendiendo a las diferentes tecnologías de producción y a los distintos productos fabricados. El consumo energético y las emisiones de CO 2 son muy parecidos en ambos países, en el proceso de obtención de baldosas por vía húmeda. En el proceso vía seca utilizado en Brasil, se consume menos energía térmica, y se emite menos CO 2 , que en el proceso vía húmeda, pero es un proceso que se utiliza únicamente en la obtención de un tipo de producto en particular, que presenta algunas limitaciones técnicas. En España, el uso de sistemas de cogeneración en la etapa de atomización incrementa notablemente la eficiencia energética global del proceso. Los consumos energéticos medios de las diferentes etapas del proceso se sitúan, en ambos países, dentro del intervalo indicado en el Documento de Referencia sobre las Mejores Técnicas Disponibles en la Industria Cerámica de la Unión Europea (BREF de la Industria Cerámica). Palabras clave: consumo energético, emisiones de CO 2 , baldosas cerámicas, España, Brasil Thermal energy consumption and carbon dioxide emissions in ceramic tile manufacture -Analysis of the Spanish and Brazilian industriesSpain and Brazil are two of the world's biggest ceramic tile producers. The tile manufacturing process consumes a great quantity of thermal energy that, in these two countries, is mainly obtained from natural gas combustion, which entails CO 2 emission, a greenhouse gas. This study presents a comparative analysis of the thermal energy consumption and CO 2 emissions in the ceramic tile manufacturing process in Spain and Brazil, in terms of the different production technologies and different products made. The energy consumption and CO 2 emissions in ceramic tile manufacture by the wet process are very similar in both countries. In the dry process used in Brazil, less thermal energy is consumed and less CO 2 is emitted than in the wet process, but it is a process that is only used in manufacturing one particular type of product, which exhibits certain technical limitations. While in Spain the use of cogeneration systems in spray-dryers improves significantly the global energy efficiency. The average energy consumption in the different process stages, in both countries, lies within the range indicated in the Reference Document on Best Available Techniques in the Ceramic Manufacturing Industry (BREF of the Ceramic Manufacturing Industry) of the European Union. Keywords INTRODUCCIÓNLa producción mundial de baldosas cerámicas prácticamente se ha duplicado en los últimos diez años, y país...
Most energy studies on the traditional ceramic manufacturing process focus on the firing stage because this is the process stage that consumes the greatest amount of thermal energy. At present in Europe, using typical technologies, about 50% of the energy input in the firing stage is still lost through the kiln stacks. A key issue in energy studies is the accurate determination of the energy efficiency of the process, an issue that may become crucial in coming years to enable the energy management of different facilities and products to be compared. To reliably determine energy efficiency, accurate determination is required of the energy needed for the necessary physico-chemical transformations to develop in the material in the firing stage. This energy is also the only strictly unrecoverable energy, as the energy contained in other streams could, potentially at least, be partly recoverable. The present study was undertaken to develop an analytical methodology for estimating the heat of reaction of seven different traditional ceramic products, involving a broad spectrum of compositions, with peak firing temperatures ranging from 850 ºC to 1200 ºC. The following industrial ceramic compositions were studied: four ceramic tile compositions (red-body stoneware tile, porcelain tile, red-body earthenware wall tile, and white-body earthenware wall tile); two structural ceramics compositions (white brick and roof tile), and a porcelain tableware composition. To estimate the energy involved in the physico-chemical reactions in the firing stage, an analytical methodology was developed, based on the mineralogy data of the unfired body composition and on the enthalpy of formation of the minerals in the fired tiles. The methodology was validated by comparing the results with experimental data.
The ceramic tile manufacturing process consumes large amounts of energy, mainly in the firing stage. Firing usually takes place in natural gas-fuelled continuous roller kilns, the most widely used tile firing facilities worldwide, which typically exhibit low energy efficiency (generally 5 to 20%). This paper investigates the application of energy and exergy balances to an industrial roller kiln firing porcelain tiles in order to identify the most critical parameters affecting kiln energy efficiency and propose ways of improving kiln energy performance. The experimental kiln measurements and thermodynamic calculations confirmed the kiln's low energy performance (15%). Exergy analysis showed that 83% of the total exergy input into the kiln was destroyed, only 10% of the exergy input being kept in the physico-chemical transformations of the ceramic tile composition. The main sources of irreversibilities: natural gas combustion, heat transfer in the fired tile cooling process, and heat transfer through the kiln surfaces, were identified and quantified. The study shows that waste heat (over 61%) recovery could be expected to significantly increase kiln energy performance. Finally, further measures are proposed for optimising kiln energy efficiency.
The most important ceramic subsector (in turnover) is the floor and wall ceramic tiles. According to European data, production is around 1304 million m 2 , consumption amounts to 964 million m 2 and total sales were close to €9
El proceso de fabricación de baldosas cerámicas consume gran cantidad de energía, mayoritariamente energía térmica, que se obtiene de la combustión de gas natural. El incremento del coste de este combustible, así como la situación económica actual, hace que este coste sea crítico para las empresas y pueda mermar su competitividad. El proceso de cocción de las baldosas cerámicas en hornos de rodillos no destaca precisamente por el aprovechamiento de la energía utilizada, pues aproximadamente el 50 % se pierde a través de las chimeneas de humos y de enfriamiento del horno. Con el objetivo de mejorar el aprovechamiento de la energía consumida durante la operación de cocción se han instalado, en las chimeneas de un horno, dos intercambiadores de calor, en los cuales los gases procedentes del horno ceden su calor sensible a un aceite térmico, que posteriormente lo transfiere a través de otros dos intercambiadores a los gases de secado en las conducciones de recirculación de un secadero vertical. En este trabajo se presenta una planta industrial experimental en la que los resultados obtenidos de ahorro energético se sitúan en un valor medio de 650 kW, dependiendo de las condiciones de funcionamiento y materiales procesados. Palabras clave: eficiencia energética, recuperación de calor, intercambio de calor, aceite térmico. Energy optimization in ceramic tile manufacture by using thermal oilThe ceramic tile manufacturing process consumes a great amount of energy, mainly thermal energy, which is obtained from natural gas combustion. The increased cost of this fuel and the current economic situation make cost a critical issue that can hurt company competitiveness. The ceramic tile firing process in roller kilns does not exactly stand out for its energy efficiency, because about 50% of the energy input is lost through the kiln combustion flue gas and cooling gas stacks. With a view to improving the reuse of the energy consumed in the firing operation, two heat exchangers were installed in the stacks of a kiln. In these heat exchangers, the kiln gases transfer their sensible heat to a thermal oil that then passes this on, through two other exchangers, to the drying gases in the recirculation ducts of a vertical dryer. This study presents an experimental industrial plant in a fine-tuning test phase, in which the preliminary results indicate an energy efficiency improvement in a range of 60-90%, depending on the operating conditions and processed materials.
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