Green Economy in the Cement Industry Part 8 : A Comprehensive Approach and the Role of Biomass

Efforts to reduce or lower CO2 in the cement industry continue to develop with various methods to achieve adequate targets. The global target is to achieve Net-Zero Emissions by 2050 while intermediate targets depend more specifically on the cement industry itself, for example, there is a cement industry that targets to reduce its emissions by 35% with a 1990 baseline in 2025 and then to more than 40% in 2030. This can practically be translated into a reduction in CO2 emissions in cement production from around 800 kg CO2/ton of cement, to 520 kg/ton of cement in 2025 and less than 475 kg/ton of cement in 2030. To achieve this target, the industry must create a roadmap that refers to the latest climate solutions in the cement industry, so that it is easier to achieve based on science (Science-Based Targets / SBT).

While the motivations for reducing CO2 emissions are similar across the world, progress is not uniform across regions. Europe is the fastest region to move forward due to its readiness, supported by a number of factors, including:
• Regulations that prioritize efficient resource use and promote a circular economy.
• Economic incentives to switch to cleaner fuels, which in many cases result in negative energy costs.
• Greater market acceptance of blended cement and consumer demand for low-carbon products.
• Significant government support for research and testing of cleaner technologies.
• Carbon emissions regulations, which result in a predictable carbon price.

Efforts to reduce CO2 emissions in cement plants directly or directly related to cement production are focused on three things, namely the use of alternative fuels or renewable energy or low-carbon fuels, reducing emissions from the calcination process and the use of cement additives (supplementary cementious material / SCM) or lowering clinker factor. While indirect efforts can be done by using electricity from renewable energy for the operation of the cement plants.

Technically or technologically in achieving the target of reducing CO2 emissions in the cement industry, the alternative energy sector or more specifically biomass fuel is in third place. This is because the largest source of emissions in cement plants or around 60% comes from the calcination process (clinker production), while combustion or related to fuel is only around 40%. This is so that carbon capture or CCS (Carbon Capture and Storage) in an effort to achieve emission targets is ranked first, then clinker substitution with additives or SCM (Supplementary Cementious Material) is in second place, and the use of alternative fuels including biomass is in third place. CCS technology is still expensive so that its implementation is still constrained, so that in practice it has not been done much but clinker substitution and the use of alternative energy including biomass are easier to do, so many cement plants have done it.

If efforts to become net zero emissions in coal-fired power plants can be done by converting their fuel to 100% biomass, then in cement plants it cannot be done by simply replacing the fuel with biomass because the main source of carbon emissions in cement plants is in their clinker production. So if a cement plant does this, the percentage of CO2 that can be reduced is only a maximum of 40%, meaning that CO2 emissions from the calcination process (clinker production) of 60% still occur. The use of clinker for cement production can be reduced so that CO2 emissions from clinker production can be reduced. That is why in cement plants the use of SCM for clinker substitution, the ratio or portion must also be increased. But of course it is impossible to reduce clinker production to zero or eliminate the calcination process and replace it entirely with SCM (lowering clinker factor) to reduce the 60% CO2 emissions.

This is so that the higher the ratio of clinker to cement produced (C/S), the greater the CO2 emissions produced and vice versa. China has the lowest ratio of clinker to cement (C/S) in the world today, which is 0.58, while a number of areas in other countries have the highest C/S ratio of up to 0.89, namely in the United States. While in Europe 0.77, then in India 0.68, in Latin America 0.71 and the global average is 0.76. It can also be understood that China uses SCM with the highest portion compared to countries in the world. That is why to achieve net zero emissions in cement plants, CCS (carbon capture and storage) equipment need to be added.

About CCS (carbon capture and storage) a number of innovations are being developed so that this technology is cheaper and easier to apply to cement plants. This also includes increasing the efficiency of CO2 capture, the use of new generation non-aqueous solvents, and cheaper modular technology. The transformation of captured CO2 into new marketable products is also the next focus.

The use of alternative fuels with high biomass content is highly recommended for cement plants to reduce CO2. But in reality, there are usually still a number of obstacles during its implementation so that it is even difficult to increase the ratio. These obstacles include the availability, quality and quantity of biomass waste, logistics and supporting infrastructure, market dynamics, the economics of the price of biomass waste-based fuels and a number of limiting technical factors related to the characteristics of the biomass fuel. A number of agricultural or plantation biomass wastes such as rice husks, palm kernel shells, cashew nut shells and olive seeds have also been used as biomass fuels in cement plants. Obtaining a supply of biomass fuel in sufficient volume, standard quality and continuous / sustainable is very important for cement plants to support the reduction of CO2 emissions. And basically there is no choice for cement plants to avoid climate problems, so what must be done is to respond to it with real action.  

Green Economy in the Cement Industry Part 6: Clinker Substitution in Cement Plants

Substituting clinker with additives or SCM (Supplementary Cementious Material) plays a major role in efforts to reduce CO2 emissions in cement plants. This clinker substitution is ranked second after carbon capture or CCS (Carbon Capture and Storage) in efforts to reduce CO2 emissions or decarbonization in the cement industry. This is because the largest CO2 emissions in cement plants are not from combustion or related to fuel but in the calcination process. CCS technology is still expensive so its implementation still faces many obstacles, but clinker substitution is easier to do, so many cement plants are already doing it. 

In the cement industry, all fuel use and around 60% of electricity use is used for clinker production starting from grinding raw materials, fuel preparation and cement kilns. The higher the clinker to cement ratio, the higher the electricity and fuel used for each ton of cement produced. The clinker to cement ratio can be reduced if less clinker is used in cement production or more additional materials or SCM are added to the clinker. This also means that substituting clinker with SCM can significantly reduce energy use (electricity and fuel) for each ton of cement produced. 

China currently has the lowest clinker to cement ratio in the world, namely 0.58, while a number of areas in other countries have the highest ratio, up to 0.9. It can also be understood that China uses the highest portion of SCM compared to countries in the world. The most commonly used SCMs today are fly ash, ground granulated blast-furnace slag (GGBFS) and ground limestone. Meanwhile, other SCMs such as pozzolan and calcined clay have the potential to be used in the future.

Fly ash comes from by-products or waste from coal-fired power plants. Decarbonization of coal power plants is also continuing to be carried out, namely by cofiring coal with biomass, but this is being done in stages so that fly ash production will still be large for a while. Fly ash from coal-fired power plant waste is very useful in cement production because it reduces the clinker to cement ratio, thereby reducing energy requirements for cement production or in other words reducing the carbon footprint of cement products. Meanwhile, GGBFS comes from iron and steel plant waste. Not all iron and steel plants produce GGBFS waste, this is because it depends on the type of furnace used. Only plants that use blast furnaces - basic oxygen furnaces (BF - BOF) can produce GGBFS, while those that use electric arc furnaces (EAF) cannot. Around 70% of iron and steel plants in the world currently use the BF – BOF process so as to produce quite a lot of GGBFS, even in China more than 90% use this BF – BOF process. Decarbonization in the iron and steel industry is marked by the switch from BF – BOF to EAF which results in the availability of GGBFS. However, the process is running slowly and gradually, so that for a while the amount of GGBFS will be available and can reduce the carbon footprint of cement production.

The use of fly ash in cement production is usually limited to 25-35% for technical performance reasons. Meanwhile, GGBFS can be used in larger portions than fly ash or other SCM. Even European standards allow the use of GGBFS up to 95% but in practice it is lower. Other SCMs commonly used are pozzolan and calcined clay. Pozzolan comes from mining, namely from deposits in nature. Pozzolan requires drying and grinding before being used in cement production. The electricity used for crushing (grinding) pozzolan is also almost the same as crushing clinker. Calcined clay can also be used as a substitute for clinker. The initial use of calcined clay with a higher portion causes a decrease in the compressive strength of the cement product produced. However, further developments using a combination or mixture of calcined clay with limestone powder have the potential to substitute up to 50% clinker without affecting the quality of the cement. Calcined clay is produced from the clay calcination process which requires energy, but the energy required is much less than the energy for clinker production. It is predicted that in 2050 by the IEA (International Energy Agency) / WBCSD (World Business Council for Sustainable Development) cement production with the above combination of materials will reach more than 25% worldwide.

It turns out that the use of SCM is not only a substitute for clinker in cement production but also in concrete production. The use of SCM in concrete production is also no less than a substitute for clinker, even in the United States SCM is mostly added during concrete production and not during cement production. A study in the United States estimated that only 5% of SCM was added to cement production and around 13% to concrete production. But basically the addition of SCM to both cement production and concrete production has reduced the carbon footprint or is in line with decarbonization. The problem is that the lack of education regarding the benefits of SCM, especially in concrete production, is a barrier to increasing the use of SCM. Other factors such as the availability of SCM, price and its relation to cement and building quality are also similar barriers. The creation of new standards and codes related to increasing the use of blended cement with SCM and concrete production needs to be developed to transform the current market.