According to the most recent report from the Intergovernmental Panel on Climate Change (IPCC) humans are causing climate change by releasing greenhouse gases, such as carbon dioxide (CO2), into the atmosphere. The IPCC states that both emissions reductions and emissions removals will be necessary to meet our climate goals of keeping warming below 2 ºC to prevent the most disastrous impacts of climate change [1]. There are many sources of CO2 emissions, that include electricity production, agriculture, and industrial activity.
The annual emissions generated by human activity each year totals to around 36 gigatonnes (billions of tonnes) of CO2 (GtCO2). Cement production, used in concrete for building material accounts for nearly 5-8% of these emissions. In addition, these emissions are expected to rise to 2.3 GtCO2/yr in 2050 [2]. Industries like cement production face a particular challenge of decarbonization because the process requires high-grade heat, which is usually provided through fossil fuels, and also because the process itself produces CO2 as a byproduct. Cement is produced by heating limestone (CaCO3) in a high-temperature, calcination step, that causes thermal degradation, leaving calcium oxide (CaO) and CO2. The CO2 that is produced from the limestone is referred to as process emissions, since it stems from the chemical reaction of the process as opposed to the fuels used to heat the kiln.
One of the only ways to address process emissions from cement production is by use of carbon capture and storage (CCS) technologies or by changing the fundamentals of the cement process. CCS technologies are fed the flue gas from the kiln and separate out the CO2 from the other species. This CO2 can then be compressed so it is ready for transportation and storage. The flue gas that exits the cement kiln ranges between 14 – 33%, making the capture process less energy intensive than those for other more dilute streams containing CO2 [3]. However, performing this separation can still be energy intensive.
One emerging opportunity to ease the process of carbon capture and reduce its energy consumption is to replace the atmosphere in the cement kiln with an oxygen-rich environment. When coal or natural gas are burned in an oxygen-rich environment, the main products are CO2 and steam. When this is the case, the separation of CO2 from this mixture is simplified because the steam can be condensed into liquid water at temperatures that would still result in CO2 remaining in the gas phase. A configuration such as this is called oxycombustion. In 2009, LafargeHolcim, Air Liquide, and FLSmidth collaborated to design an oxycombustion calciner for cement production. They deployed this pilot calciner for 7 campaigns from 2011 through 2012 [4]. From these trials, it was determined that there are no safety concerns with the further implementation of this technology. One factor that may limit the scalability of this solution would be the availability of pure oxygen. Today, oxygen is produced by use of an air separation unit (ASU). A cement facility could consider investing in an ASU to be used onsite, but this may be cost prohibitive for adopting this technology. However, there are many industrial ASUs located throughout the world, that cement facilities could be co-located with for mutual benefit. Overall, oxycombustion poses an opportunity to decarbonize cement as a crucial building material and be an example of forging industrial partnerships between co-located resources, setting the stage for similar collaborations in the future.
References
1. IPCC. Summary for Policymakers. in Climate Change 2021: The Physical Science Basis. Contribution of Working Group I in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (2021).
2. Energy Transitions Commission. Mission Possible: Reaching Net-Zero Carbon Emissions from Harder-to-Abate Sectors by Mid-Century. Sectoral Focus: Cement (2018).
3. Bains, P., Psarras, P. & Wilcox, J. CO2 capture from the industry sector. Prog. Energy Combust. Sci. 63, 146–172 (2017).
4. Gimenez, M. & Workshop, E. C. CCUS Projects at LafargeHolcim Focus on Oxycombustion. (2015).
The annual emissions generated by human activity each year totals to around 36 gigatonnes (billions of tonnes) of CO2 (GtCO2). Cement production, used in concrete for building material accounts for nearly 5-8% of these emissions. In addition, these emissions are expected to rise to 2.3 GtCO2/yr in 2050 [2]. Industries like cement production face a particular challenge of decarbonization because the process requires high-grade heat, which is usually provided through fossil fuels, and also because the process itself produces CO2 as a byproduct. Cement is produced by heating limestone (CaCO3) in a high-temperature, calcination step, that causes thermal degradation, leaving calcium oxide (CaO) and CO2. The CO2 that is produced from the limestone is referred to as process emissions, since it stems from the chemical reaction of the process as opposed to the fuels used to heat the kiln.
One of the only ways to address process emissions from cement production is by use of carbon capture and storage (CCS) technologies or by changing the fundamentals of the cement process. CCS technologies are fed the flue gas from the kiln and separate out the CO2 from the other species. This CO2 can then be compressed so it is ready for transportation and storage. The flue gas that exits the cement kiln ranges between 14 – 33%, making the capture process less energy intensive than those for other more dilute streams containing CO2 [3]. However, performing this separation can still be energy intensive.
One emerging opportunity to ease the process of carbon capture and reduce its energy consumption is to replace the atmosphere in the cement kiln with an oxygen-rich environment. When coal or natural gas are burned in an oxygen-rich environment, the main products are CO2 and steam. When this is the case, the separation of CO2 from this mixture is simplified because the steam can be condensed into liquid water at temperatures that would still result in CO2 remaining in the gas phase. A configuration such as this is called oxycombustion. In 2009, LafargeHolcim, Air Liquide, and FLSmidth collaborated to design an oxycombustion calciner for cement production. They deployed this pilot calciner for 7 campaigns from 2011 through 2012 [4]. From these trials, it was determined that there are no safety concerns with the further implementation of this technology. One factor that may limit the scalability of this solution would be the availability of pure oxygen. Today, oxygen is produced by use of an air separation unit (ASU). A cement facility could consider investing in an ASU to be used onsite, but this may be cost prohibitive for adopting this technology. However, there are many industrial ASUs located throughout the world, that cement facilities could be co-located with for mutual benefit. Overall, oxycombustion poses an opportunity to decarbonize cement as a crucial building material and be an example of forging industrial partnerships between co-located resources, setting the stage for similar collaborations in the future.
References
1. IPCC. Summary for Policymakers. in Climate Change 2021: The Physical Science Basis. Contribution of Working Group I in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (2021).
2. Energy Transitions Commission. Mission Possible: Reaching Net-Zero Carbon Emissions from Harder-to-Abate Sectors by Mid-Century. Sectoral Focus: Cement (2018).
3. Bains, P., Psarras, P. & Wilcox, J. CO2 capture from the industry sector. Prog. Energy Combust. Sci. 63, 146–172 (2017).
4. Gimenez, M. & Workshop, E. C. CCUS Projects at LafargeHolcim Focus on Oxycombustion. (2015).
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Maxwell Pisciotta is a doctoral candidate in the Department of Chemical Engineering at the University of Pennsylvania. Pisciotta’s research focuses on the feasibility and implications of decarbonization pathways, specifically those that employ carbon capture and storage and carbon removal. Max also holds a B.S. and M.S. in Mechanical Engineering, which he earned at the Colorado School of Mines, with a research focus in energy storage via fuel cell technology.
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