# Appendix B - Industrial Sector Decarbonization Examples
# Cement Production
Currently, cement production accounts for about 6% of global CO2 emissions. Approximately 60% of these emissions are produced from the conversion of calcium carbonate into calcium oxide. The remaining 40% results from the combustion of fossil fuels to heat the kilns where the calcination takes place, requiring a temperature of up to 1600°C (Hasanbeigi 2019). Therefore, eliminating the emissions from cement requires two changes to the process—one that addresses the emissions from the chemical transformation that occurs and another that replaces the current source of heat with an emissions free option.
Options for decarbonizing the energy required for heat in cement production include:
Conversion from fossil fuels to biofuels or biomass, which would require only a modest retrofit of the kiln. However, differing biofuel or biomass sources would likely require differing modifications and these sources are likely to vary by location.
Conversion to hydrogen would require an extensive retrofit of the kiln due to the differences in combustion characteristics and heat transfer between hydrogen and fossil-fuel burners. Further research is required to develop a cement kiln capable of using hydrogen as a fuel.
CCS applied to the exhaust gases from cement kilns. This could also be used to capture the CO2 produced from the limestone calcination. However, this solution would require an increase in upfront capital cost and many locations may not have suitable CO2 storage or use locations nearby.
Options for decarbonizing the emissions from the chemical transformation that occurs in cement production include:
As highlighted above, applying CCS to capture CO2 from the limestone calcination.
Replacement of some of the components of cement, such as the calcium carbonate and/or binders, with alternate materials that do not release CO2. This solution may not be suitable to all applications, however, as changing the components may change the physical characteristics of the concrete in a way that is unacceptable for some applications.
In summation, the challenge of eliminating CO2 emissions from concrete production is that it requires solutions for the CO2 released in the chemical reaction that forms the cement as well as the energy used in the production of the cement. Further, while there are solutions for each source of emission, two separate solutions may be required and some solutions may ultimately impact the quality of the final product, which may make it unsuitable for certain applications. Finally, any of the solutions are unlikely to be a universal solution for all regions of the world. When combined together, these challenges present a very hard to decarbonize challenge for the source of 6% of worldwide emissions.
# Steel Production
Steel production accounted for between 7 and 9% of global GHG emissions (worldsteel 2020a). Currently, steel is typically produced by heating iron ore to around 1200°C in a coal fired blast furnace. The coal serves not only as an energy source for the heat, but its use is also critical in the formation of the steel as it acts as a reductant in the conversion of the iron ore into steel. Therefore, eliminating the CO2 emissions from steel is likely not as simple as supplying heat with a carbon-free energy source[1]; rather, if coal is to be replaced a new reducing agent must also be found.
Potential options for the decarbonization of steel include:
Use of biomass as a replacement for coal as a fuel and reductant. Some modification of the blast furnace would be required for the biomass and potential contaminants from biomass would have to be eliminated. However, the diversity of biomass types and availability may require differing solutions for different locations across the globe.
Utilization of CCS with the current steel-making process. This option would require some modification of the blast furnace to allow for the capture of emissions. It would also result in an increase in upfront capital cost and may not be suitable for locations without nearby CO2 storage or utilization options.
Use of an electric arc furnace (EAF) and hydrogen as the reductant, called the direct reduced iron (DRI) process. The electricity used for the EAF would have to be carbon free and the hydrogen would have to be sourced from sources without emissions or with any emissions captured for the steel to be carbon-free. There are currently numerous research programs and even some commercial production of steel utilizing this option, though currently steel produced using DRI is higher cost than steel produced using the traditional process.
Utilization of an electric arc furnace to melt scrap steel in order to produce new steel. It is estimated by 2030 that the entire global demand for new steel could theoretically be met by scrap alone (worldsteel 2020b). However, if scrap steel were to prove insufficient for demand this option would not fully decarbonize steel production.
Similar to cement, the decarbonization of steel requires not only the decarbonization of the energy source used to produce it but also the replacement of a key component of the physical transformation of the material. And the potential solutions may not be universal in nature, either. Therefore, the decarbonization of steel may require multiple solutions so that various regions have the option to choose a solution best matched to their resources.
Note there is a possible exception to this if scrap steel or CCUS were to be used, as noted in the decarbonization options for steel. ↩︎