Monday, 22 February 2021
Gasworld contributer Stephen Harrison authored a thought provoking piece on the cement industry in the context of carbon emissions. We summarise and offer our comments below.
Heavy industry has often proved difficult to decarbonise. While energy usage often has solutions in the way of renewable sources and energy efficiency drives, industrial processes often necessitate the release of carbon dioxide and more often than not, from fossil sources.
The steel industry is given as a comparison - fossil coke is used in a chemical process to remove oxides, releasing CO2 in the process. However, a process called Direct Reduction of Iron (DRI) is being developed which essentially substitutes hydrogen in place of coke. The by-product is water and if the hydrogen source is green, the process has net zero emissions.
Greenfact: This is the premise of Swedish steel maker SSAB's HYBRIT technology.
However, the lime used to produce cement comes from heating limestone - there appears to be no suitable alternate method for producing the large volumes of lime required for the cement industry. Net carbon dioxide emissions from the cement manufacture process appear unavoidable.
Nevertheless, there are steps the industry could take to reduce their carbon footprint.
The first step involves a reduction in indirect emissions; 10% of the industry's emissions stem from electricity usage and transport vehicle emissions. Energy efficiency schemes improve the productivity per unit emission, and overall lead to a reduction in carbon.
Greenfact: Electricity usage can be made green via renewable sources backed by the appropriate green certificates (GOs for electricity in Europe). Vehicle emissions can be cut down by transition to fleets capable of operating on renewable fuels such as green hydrogen or biomethane.
Direct emissions also stem from the fuel burnt to provide the heat required for the cement making process. The associated emissions have been estimated to account for 30-35% of the total cement industry emissions. If renewable fuels can be sourced such as biomethane or certain types of waste, this can reduce the net emissions.
While biomethane can be more expensive (cost per unit energy) than other forms of biomass and waste, it offers efficient combustion and is easier to transport and store than biomass, particularly if the plant is already configured to run using natural gas.
Greenfact: Green gas usage should be back by the appropriate green certificate (for example RGGOs or BMCs in the UK) to verify the sustainability of the product and supply chain.
For the remaining CO2 emissions, released during the heating of limestone, carbon capture and storage (CCS) appears the only solution. While still a nascent technology, much time and effort have been put into developing the field given the high decarbonisation potential.
Greenfact: Norwegian cement manufacturer Norcem has plans to trial CCS on its Brevik facilities, with approval to come from the Norwegian government (who are providing financial support) and if approved, operations are slated for 2023/24.
Greenfact: It is also possible to use carbon offsets according to the GHG Protocol, although these are usually reserved for lower volume and difficult to abate emissions.
Puro earth (who Greenfact interviewed in 2020) operate a carbon removal market place, based on CO2 removal certificates, or CORCs which have similarities to other green certificates.
Greenfact: Interestingly, one of the technologies promoted by Puro earth is related to the cement industry - one of the methods of carbon removal involves using concrete (of which cement is an ingredient) to capture and bind CO2 as the concrete sets, effectively mineralising the CO2.
Furthermore, there are substitute binding materials to cement which can be used to make concrete. For example steel slag, waste from steelmaking processes, has been used as a concrete binder and is less carbon intensive to produce than cement. Binders based upon fly ash (waste from thermal power plants) have also been considered as an alternative to traditional cement.
However, such binders have yet to see the same widespread acceptance as cement.