PROJECT DESCRIPTION
BACKGROUND
Current firing techniques for ceramic tiles are having a negative impact on the environment, producing carbon dioxide emissions and having low energy-efficiency rates. Such emissions are especially problematic as they tend to concentrate in small regions. The amount of CO2 produced per unit mass of finished product ranges from 90 to 125 g per kilogramme of product 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, nitrous oxides are generated. Such emissions range from 6 mg per kilogramme of porcelainised stoneware to 413 mg/kg of single firing red body tiles. In spite of the use of modern insulation materials, pulsed burners and partial heat recovery from exhaust gases, it is clear that further improvements will not be achieved unless combustion behaviour is changed.
OBJECTIVES
The objective of the LIFE ZEF-tile project was 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, the exhaust gases would contain only CO2 and water vapour, which can be easily recovered. As a result, the heating requirement would be reduced along with the volume of exhaust gases. For this purpose, the project planned to set up a demonstrative roller kiln with modified burners in order to use pure oxygen. As part of the process, water vapour would be condensed in order to leave a stream of almost pure CO2, which will then be subjected to sequestration techniques.
The project team would assess the effect of using part of the CO2 flux to boost the growth of plants and vegetables in a greenhouse, while another part would be compressed and stored in liquid form to be used in different ways. As a practical demonstration moreover, one part would be immobilised in mineral to be further recycled as raw material in the manufacture of other ceramic products. Finally, the project aimed to speed up the firing curve of the emerging thin tiles and glass-based material through the use of higher flame temperatures.
RESULTS
The ZEF-tile project demonstrated the possibility of significantly reducing CO2, NOx and particulate emissions (PM) from the firing of ceramic tiles through the use of the oxy-fuel technology (oxygen instead of air as a combustive agent) and the recovery of CO2 and steam from the exhaust gases. A pilot plant consisting of improved refractory walls (higher emissivity of the flames) was set up to test the oxy-fuel technology. It had a daily production capacity of 120 m2 of ceramic tiles.
The plant also contained a CO2 capture system for recovering CO2 and steam from the kiln exhaust gases and recycling them in the production processes. This was achieved through CO2 fixation in carbonates and the condensation of water. The carbonates are a source material for re-use in the tile production process. Around 200 tile samples were produced with the new technology, and their technical and aesthetical properties were shown to be comparable with tiles produced by the conventional process.
A theoretical study of possible alternative uses of the recovered CO2 was also carried out. It concluded that the recovered material could be used in greenhouse fertilisers with increased carbon contents or compressed and used in other sectors. A simplified comparative LCA analysis further confirmed the benefits of the new firing process. The new firing process helps reduce emissions of CO2 by 90%, (equivalent to 100 000 kg of CO2 per year at pilot plant level), NOx by 80% (equivalent to 192 kg of per year at pilot plant level) and PM by 70%. The new process also consumes about 10% less energy mainly due to lower fuel consumption linked to the reduction in the volume of combustion gases. The recovered CO2 and steam were recycled in the production process, slightly lowering the requirements for raw materials.
Furthermore, the process offers economic advantages linked to lower fuel consumption and increased productivity – i.e. lower production times due to the higher emissivity of the flames. End-of-pipe technologies also reduce costs, as exhaust gases are easier to treat due to the reduced contents of CO2, NOx and particulates. Though the pilot plant had an external supply of oxygen, it was assessed that further cost reductions could be achieved for larger productions if oxygen is produced internally.
The project results are in line with the EU 2020 strategy, particularly the reduction of greenhouse gas emissions by implementing a flexible strategy comprising the immobilisation of CO2 in a solid state or in a compressed form, or as an aid for crop growth. The greater efficiency of the process is also in line with the energy end-use efficiency and energy services directive (2006/32/CE) while reducing NOx and particulate emissions demonstrates how pollution prevention legislation (e.g. Industrial Emissions Directive 2010/75/EU)) could be implemented.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).
