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Zero Emission Firing strategies for ceramic tiles by oxy-fuel burners and CO2 sequestration with recycling of byproducts (LIFE ZEF-tile)
Start date: Jul 1, 2013, End date: Dec 31, 2015 PROJECT  FINISHED 

Background Carbon dioxide emissions and the low energy efficiency of current firing techniques for ceramic tiles have a negative impact on the environment. A recent study conducted in Sassuolo, the largest ceramic tiles manufacturing area in Europe, accounting for more than 90% of Italian production, showed that gas emissions are a major problem, especially as they tend to concentrate in very small regions. When firing tiles, CO2 is released due to the oxidation of natural gas. The amount of CO2 produced per unit mass of finished product ranges from 90 to 125 g/kg in the case of single firing, and up to 140 g/kg in the case of ‘porcelainised’ stoneware. Moreover, since air is used as a source of oxygen in the burners, large quantities of nitrogen are introduced to the firing kiln and NOx are generated. Such emissions range from 6 mg/kg of porcelainised stoneware to 413 mg/kg of single firing red body tiles. The firing of ceramic tiles is also responsible for another environmental problem, which is related to the energy efficiency of the firing kilns. The introduction of roller kilns helped to reduce specific energy consumption from 4.79 m3 of natural gas per m2 of tile in 1971 to 2.50 m3 in 1991, but it has remained at this level ever since. It is evident that despite the use of modern isol-refractory materials, pulsed burners and partial heat recovery from exhaust gases, unless combustion behaviour is changed, further improvements will not be achieved. Objectives The objective of the LIFE ZEF-tile project is to demonstrate the feasibility of applying oxy-fuel technologies to the firing stage of ceramic tile production in order facilitate CO2 sequestration. By using pure oxygen, instead of air, to burn hydrocarbons such as methane, the exhaust gases will contain only CO2 and water vapour. As a result, it will no longer be necessary to heat the inert gases contained in air and thus waste energy in continuously heating and cooling gases not directly involved in the combustion process. Moreover, it will lead to a proportional reduction in the volume of exhaust gas, which can then be processed easily due to its simple composition. For this purpose, the project will set up a demonstrative roller kiln with burners modified in order to use pure oxygen. As part of the process, water vapour will be condensed in order to leave a stream of almost pure CO2, which will then be subjected to sequestration techniques. The project team will assess the effect of using part of the CO2 flux to boost plants and vegetables growth in a greenhouse, and will compress and store another part in liquid form to be used in different ways. For example, one part will be immobilised in mineral to be further recycled as raw material in the manufacture of other ceramic products. A further objective will be to speed up the firing curve of the emerging thin tiles and glass-based materials through the use of higher flame temperatures, which are particularly suitable for processing materials with thickness of less than 2-3 mm. Expected results: An innovative zero emission firing process for ceramic tiles; Direct recycling of 100% of the gas processing byproducts of ceramic tile production as milling or glazing water, and as carbonates for ceramic body composition; Zero particulate emissions, due to the ideal combustion conditions in the oxy-fuel burners and to the installation of ash filters; A 75% reduction in the circulating mass and volume of the flue gas; Reduced heat losses from exhaust gases due to the use of heat exchangers and the reduction in gas volume; Condensable flue gases (CO2 and H2O), making compression separation possible; A 95% reduction in the production of NOx by using technically pure oxygen; An evaluation of the investment costs (expected to be 50% higher), and energy and running costs (expected to be 20% higher due to the need of oxygen supply and energy for CO2 compression), and a comparison with the environmental benefits in order to asses the cost of CO2 sequestration.

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