Cleaning up “dirty” ceramic tile production

Energy efficiency in kilns and other process stages of ceramics production are quite low and pollutants are currently emitted at unsustainable levels. But as costs for fossil fuels rise and governments impose ever tighter carbon emission regulations, ceramics companies are increasingly turning to creative solutions to reduce their climate footprint.


“Carbon dioxide emissions are a common issue for many intensive-energy industries, and any primary measure or secondary measures you implement that can reduce carbon dioxide emissions are good,” said Dra Irina Celades Lopez, who is responsible of the Sustainability Area in the Ceramic Technological Institute located in Castellón, a city in Spain.


Luca Manzini, in charge of energy management for the Ceramiche Atlas Concorde Spa, part of Gruppo Concorde in Italy and partner within the EU funded project ETEKINA, agrees: “All ceramic groups here in Italy are making huge investments in energy efficiency. You need a lot of thermal energy in order to make ceramics. We try to recover waste heat to cut down our main expense, which is natural gas.”


With kilns that can reach 1250 degrees Celsius, pollutants like carbon dioxide and sulphur dioxide being released, and litres of drinking water turned into waste water, the ceramic tile manufacturing industry does not have a reputation for being exactly environmentally friendly.


Gabriele Frignani, who works for Gruppo SACMI, a multinational that supplies advanced technologies for the ceramics and other sectors, noted that no one should expect industrialists to suddenly become eco-warriors unless there is a financial incentive.


“Industry, in general, is not interested at all in environmental issues unless they can transform this topic into higher turnover,” he said. “The idea that a new renaissance in environmental terms can be generated from the industrial sector is not only romantic but completely detached from reality.”


For example, as part of ceramic tile production, water is added to raw clay and materials, resulting in a clay/water mixture called slip characterized by a water content of 32-38%. The slip is dried in a spray drier, the water evaporates and humidity is reduced to about 6-7%. Finally, the ceramic tiles are pressed.


The ceramics industry sources drinking water for use in this process simply because it is cheaper than purifying waste water, according to Frignani. Although water is also expelled by this process, no measures have yet been put in place to recover it, though some prospective studies have been carried out. However, in Spain water scarcity issues have driven the industry to use part recycled water and part drinking water, and this is an example other countries could follow. In reality, drinking water is only a requirement for the preparation of glazes and inks, due to high quality requirements.


But there are savings to be made by implementing more energy efficient processes, and the European ceramics industry is experimenting with heat pipe heat exchangers (HPHEs) to recapture energy lost from piping hot kilns and transferring that energy to another point in the production chain.


Rather than dispose of the heat, Ceramiche Atlas Concorde Spa wants to collect it and then use it within other processes inside the plant. The HPHEs being developed as part of ETEKINA project will help with this.


“We will save some natural gas in this way. The idea is not a breakout in technology, it’s not like going to the moon. It’s something that we already do to some extent. But up until now we didn’t have the technology in order to recover the kiln exhaust energy,” said Manzini.


ETEKINA HPHEs will be tested on two kilns present within the new pilot plant at Ceramiche Atlas Concorde Spa. Luca Manzini expects that the initiative will result in savings of between €120,000-180,000 for the plant. That corresponds to 400,000 cubic metres of natural gas, which represents 2% of the overall heat produced.


“Actually, it will be slightly more, due to the fact that the plant has a lot of autoproduction, because of the presence of a generation plant inside the plant itself,” he said.


Within the Ceramics Technical Institute in Spain, Celades Lopez is also looking at heat pipes as a potential vehicle for heat transfer within ceramics plants. For her, a main advantage of heat pipes is that they are resistant to changing atmospheric conditions and are fast and effective no matter what the surrounding temperature or pressure may be.


“Sometimes in industry you can find environments that are very corrosive, with a lot of pollutants, and [the heat pipes] are still working properly,” she said.


Her department is also involved in the DREAM project, which is developing a simulation model to catalogue the thermal behaviour of ceramic products during the firing stage.


“[Our aim is to] try to install these heat pipes within the cooling area of the firing stage in order to harmonize the temperature during the cooling state, which is [a] tricky stage in the manufacturing of ceramic tiles,” she said. The cooling phase of the production of ceramic tiles is particularly delicate because stress within the ceramic pieces could cause breakages.


Gabriele Frignani is also involved in the DREAM project. He’s a big fan of how heat pipes can be used to transport heat away from heat emitters and towards heat consumers.


“One of the advantages in using heat pipe technology is that we are always sure that the air that we move to other thermal machines of the process is clean. There is no mixing between the air that we heat and the air that could potentially be contaminated from the firing area of the kiln, for example,” he said.


The efficiency of heat pipes is also a little higher compared to standard heat exchangers that are used for similar applications.


Another method that can be used to make ceramic tile production “greener” is to use the existing machinery in a more energy efficient way. Manzini is in the process of training and informing his co-workers about small tweaks and adjustments that can be made within the tile production process to increase efficiency.


“If you find a better way to run your machinery, it’s cheaper but you have to factor in people too. People are often not really willing to change their habits!” he laughed. “It’s long work but it has to be done, in terms of awareness.”


But, such tweaks are sometimes incompatible with the results that a client may want for a particular tile. That’s why innovations like ETEKINA’s heat pipes can provide value.


“If the market is asking you for tiles with certain specific characteristics, that are only obtained through high energy waste [methods], at least with ETEKINA you will be able to retrieve the heat that normally would be wasted, and take it back into the plant,” Manzini said.