Ceramic is considered to be one of the earliest, greatest and most successful inventions of mankind. However, from the extraction of raw materials to waste treatment, ceramics will have an impact on the natural and social system in its whole life cycle. In order to reduce the climate impact of ceramic products and processes and ensure the sustainable development of the industry, this paper intends to introduce the comprehensive research article "decarbonization of ceramic industry: a systematic and critical review of policy selection, development and social technology system" published by Dylan D. furszyfer del Rio and other authors in the Journal renewable and sustainable energy reviews. The original text traces back 324 relevant studies, The main determinants of energy and carbon emissions in the ceramic industry are determined, and the possible benefits and obstacles to be overcome by adopting relevant low-carbon processes are combed. Finally, the author proposes that the environmental and energy challenges related to the ceramic industry are not only limited to the manufacturing stage, but also should focus on the energy consumption and emissions of the whole life cycle of products (including raw material extraction, waste treatment and landfill).
As a traditional energy intensive industry, ceramic industry consumes about 30% of the total production cost. The International Energy Agency estimates that globally, the emissions from the ceramic industry exceed 400 MT CO2 / year, mainly from the emissions from the ceramic preparation process and energy use. For example, in the European Union, the ceramic manufacturing industry (refractory materials, wall and floor tiles, and bricks and roof tiles) emits 19 million tons of carbon dioxide per year. Of these emissions, 66% came from fuel combustion,while electric power emissions and process emissions accounted for 18% and 16% of the total emissions, respectively.
The emissions of the ceramic industry depend on two factors, namely, the chemical conversion of raw materials used in the preparation process and the use of fossil fuels. CO2 emissions may also come from the combustion of organic substances present in raw materials or organic mixtures during the preparation process. There are also indirect CO2 emissions in the power and raw material preparation stages. In addition to CO2 emissions, chlorine, fluorine, sulfur and nitrogen oxide emissions will also be released during the preparation process. In the past few years, the emissions of the ceramic industry have been reduced, for example, the emissions of fluorine have been reduced by more than 80%. Similarly, in countries with a high degree of industrialization, due to the use of natural gas and the adoption of new technologies (e.g., cogeneration system, single combustion and roller kiln), CO2 emissions have also been reduced.
In general, the ceramic industry is a natural gas intensive industry. In the energy structure, natural gas accounts for 85-92%, and electricity accounts for 8-15%. The intensive use of natural gas is well illustrated in Türkiye, which accounts for more than 12% of the total industrial natural gas consumption. In addition, in Brazil, in 2014, the ceramic industry accounted for about 5.8% of all energy consumed by the national industrial sector, most of which came from renewable energy and natural gas. In the preparation process, the main energy end use is for drying, sintering and cooling stages. The sintering stage accounts for about 75% of the total energy cost and more than 50% of the energy required for the preparation process. A study shows that the annual final energy consumption of ceramics sintered by using natural gas in the world is estimated to be 182 TWH, and about 265 kgco2 / T is generated during the process of firing ceramic tiles. Another study showed that more than 80% of greenhouse gas emissions occurred in the sintering and drying stages.
In addition, in the process of ceramic preparation, the factory needs a lot of heat to dry and remove the moisture in the materials. In most cases, producers rely on fossil fuels to evaporate water. The process is complex and expensive, and the process variables need to be strictly controlled to ensure the quality of the final product. Although the drying system develops with the deployment of new technologies, the final energy consumption at this stage is still very high.
The energy intensity of the ceramic industry is reflected in its energy end use and carbon footprint. The production of each ton of ceramic floor tiles requires 940 kwh of electricity, and the average consumption of bricks and roof tiles per ton of products is 380 to 1250 kwh. The carbon footprint of ceramic products weighing 0.417 kg is 1.22 kg CO2e, and 90% of the total greenhouse gas emissions come from the end use of energy. At the same time, due to the high consumption of resources (including energy and water) and problems related to noise and waste, ceramic products will have a negative impact on the environment throughout their life cycle. In the process of ceramic tile preparation, three stages require thermal energy: drying the newly formed ceramic tile body, ceramic tile firing and ceramic slurry preparation.
Another study conducted a full life cycle assessment of ceramic tiles. The researchers investigated the environmental impact from the mining of raw materials and transportation to the tiling and waste removal in the construction process. The results show that the ceramic tile preparation process has the greatest environmental impact, followed by product transportation and distribution. The explanation can be found in the thermodynamic analysis. Some analysis shows that the kiln efficiency is very low, because only 5-20% of the energy input is used for firing ceramic tiles. The rest is lost through cooling chimneys (30 – 35%), flue gas chimneys (20 – 25%), kiln walls and vaults (10 – 15%) and fired tiles (5 – 10%). This conclusion has also been confirmed in similar research centers. The research of Ferrer et al. Shows that the single-layer roller kiln in the world shows low energy performance, in which more than 61% of the total energy input in the kiln is lost through the exhaust stack.
For decades, the ceramic industry has been striving to improve energy efficiency. Since 1990, the European ceramic tile industry has adopted many new technologies and implemented energy-saving actions to reduce carbon dioxide emissions and reduce final energy use. The core of low-carbon technology in the ceramic industry is to reduce the final consumption of energy in the ceramic industry by improving furnace design, improving firing efficiency and optimizing preparation.