Decarbonization of the Cement Production

Technologies for industry and agriculture

Cement is the most used material produced by man on the planet in terms of volume, in fact it is used to build buildings, roads and several types of infrastructures and there are no materials that can totally replace its use due to the abundant availability of the raw materials of which it is made. According to the data reported by the United States Geological Survey (USG) in  [1], in 2020 4.1 billion cubic meters of cement were produced, keeping a constant value since 2018 [2]. In Italy cement production in 2020 was about 18 million tons.  The production of cement requires an initial stage for grinding, mixing and calcination of the base materials (calcareous and clay minerals added with various other elements) and the subsequent sintering in high-temperature furnaces (about 1450 °C) for the production of clinker, the main constituent of cement. The clinker is mixed with different elements depending on the type of the cement. The initial phase take place with wet processes or with dry processes. The choice between the two process depends on the degree of humidity of the base materials. The wet process is typically more expensive than the dry process. In addition, it requires more energy because the slurry (mixture of material and water) requires a drying process before calcination.  Cement is therefore an energy-intensive process, in fact the average global thermal energy intensity is between 3.4-3.5 GJ/t clinker, and it has remained stable in the last five years [3]. The use of fossil fuels to feed high-temperature furnaces obviously implies a significant amount of CO₂ emissions which, however, represent less than 40% of the CO₂ emissions of the cement production process. In fact, more than 60% of total emissions result from the decomposition of basic minerals in the calcination phase [4], [5]. The cement sector is responsible for 5 to 8% of the global CO₂ emissions [6] and according to the data from the International Energy Agency (IEA) its carbon intensity in 2020 was 0.59 tCO₂ per ton of cement, a 1.8% increase compared to 2014 and in contrast to the needed 3% annual reduction fundamental to reach the global climate objectives [3]. In 2020 According to the International Energy Agency (IEA) the pillars to reduce emissions of this sector are: energy efficiency, fuel-switching, material efficiency strategies to reduce the clinker-cement ratio and total demand, the adoption of new innovative process technologies and carbon capture and utilization technologies (CCS) [1] [3]. Among the various CCS technologies applicable to the cement production process (oxy-combustion, post-combustion), capture from combustion exhaust gases (post-combustion) or from gaseous effluxes with a high CO₂ content by means of solid sorbents or liquid solvents seems to be the most suitable. The CCS technologies, although expensive, are applicable to all combustion processes but their application to cement production is particularly efficient because this process produces high amounts of CO₂ with high concentrations. Moreover, about 60 to 65% of those emissions due to the decomposition of calcium carbonate at temperatures above 550°C is not avoidable using non-fossil fuels because they were not generated by combustion.

29-07-2022

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