Carbon capture, utilisation and storage
A critical tool in the climate energy toolbox
Carbon, capture utilisation and storage (CCUS) is one of the only technology solutions that can significantly reduce emissions from coal and gas power generation and deliver the deep emissions reductions needed across key industrial processes such as steel, cement and chemicals manufacturing, all of which will remain vital building blocks of modern society.
There is a growing interest in novel ways of using CO2 as a feedstock for products that have a market value in addition to their value in mitigating climate change. CO2 use may provide a number of other services to society, such as the substitution of fossil fuels as a feedstock for fuels and materials and the conversion of renewable electricity to hydrocarbons that are compatible with existing infrastructure.
The last ten years have seen a sharp rise in the amount of public and private spending on R&D programmes and projects using CO2 to make valuable products, mainly in North America and Europe.
Simple classification of CO2 uses
Source: modified from European Commission, 2013. Implications of the Reuse of Captured CO2 for European Climate Action Policies. Report to DG Climate Action by Ecofys and Carbon Counts.
The range of potential CO2 use applications is very large and includes the intermediate use by which the CO2 is not chemically altered, and the use of CO2 by conversion to a fuel, chemical or building materials. Most of today’s industrial applications are based on the former use of CO2, such as for food processing, carbonated beverages and enhanced oil recovery (CO2-EOR). A promising future application is in supercritical power cycles, where CO2 would act as a working fluid and increase the efficiency of electricity generation.
CO2-based fuels and chemicals can be manufactured through chemical or biological conversion of CO2, but require large amounts of low-carbon energy, either for direct use or to produce green hydrogen through water electrolysis. CO2-derived fuels and chemicals can be competitive in places where cheap and abundant low-carbon electricity and CO2 is jointly available; however, in most places, they are several times more expensive than their fossil counterparts and often other low-carbon energy carriers and products. Although energy-intensive, fuels manufactured from CO2 may eventually find an application in sectors for which few green alternatives are available, such as aviation and long-haul transport.
In building materials, CO2 can be used as an ingredient in concrete production, either as part of the binding material (cement), as a component of the filler (aggregate), such as sand, gravel or crushed stone, or by replacing water during the process of concrete curing. Aggregates can be produced from natural alkaline minerals (e.g. magnesium- and calcium-rich silicates) or from industrial by-products (e.g. iron slag and coal fly ash). The main challenges with the production of aggregates are the high amounts of energy and minerals required per tonne of CO2 used, resulting in high processing costs. Another challenge is the low market value of aggregates.
The use of CO2 to manufacture valuable products has the potential to reduce emissions by either permanently storing part of the carbon in the product (e.g. cement or carbonate materials) or by displacing a product with a higher CO2-footprint (such as fossil-based fuels). If the captured CO2 originates from the atmosphere or from sustainably produced biomass and is ultimately stored, for example in a carbonate material, the use of CO2 could potentially deliver “negative emissions”, i.e. remove CO2 from the atmosphere. The emissions reduction potential is dependent on several critical factors, including the permanence of the storage, the energy intensity of the conversion process, the source of the energy and the product or service it displaces. A robust life cycle assessment is required to assess the avoided CO2 emissions for each application.