Abstract
Switzerland, such as most of the other countries which are part of the Paris agreement, decided to reduce GHG emissions to zero by 2050. The ambition of net-zero GHG emission across all industrial sectors can only be achieved by rapid decarbonization and the deployment of negative emission technologies to compensate residual emissions from for example agriculture. In the scope of this work, the proof of technology of a negative emission value chain at industrial scale in the concrete sector is presented. The core of the system is a mineralization technology, which fixes biogenic CO2 permanently as calcium carbonate in concrete aggregate. In addition, the net-negativity in terms of GHG emissions and environmental burdens beyond these are quantified in a Life Cycle Assessment (LCA). It could be shown that an industrial-scale mineral carbonation process can be seamlessly integrated in today's concrete recycling processes and that it can process relevant amounts of concrete aggregate while storing on average 7.2 kg CO2 per ton of concrete aggregate. Moreover, material tests revealed that the carbonated concrete aggregate fulfills the same service as the regular one—thus no significant effects on the concrete properties could be observed. The LCA shows that every processing step requires materials and energy, and thus generates associated emissions. However, from a cradle to gate perspective, the carbon removal efficiency is 93.6%. Thus, 1,000 kg of CO2 stored generate 64 kg of CO2-eq. emissions. Furthermore, it could be shown that biogas upgrading can supply sufficient amounts of CO2 until 2030 in Switzerland. From 2030 on, more and more CO2 from other emission sources, such as waste incineration, need to be utilized to exploit the full potential of the value chain, which is going to be 560 kt of negative CO2 emissions in Switzerland in 2050, corresponding to 30% of the projected demand within the national borders.
Highlights
Limiting global warming to 1.5–2 degrees requires substantial and fast reduction of greenhouse gas (GHG) emissions in basically all economic sectors (Tollefson, 2018; Allen et al, 2018)
The left y-axis indicates the emissions of greenhouse gases per kilogram of recycling concrete aggregate (RCA), the right y-axis the amount of GHG emissions per ton of CO2 stored
The right panel shows the results of the left panel in a cumulative way and the positive emissions associated with the four sub-processes in total compared to the corresponding amount of CO2 stored. This shows that the net effect, which is given by the difference between negative and positive emissions, is 936.2 kg CO2,eq of net negative emissions generated for every ton of CO2,eq mineralized and stored, or – in other terms – of 6.7 g CO2,eq for every kg of RCA carbonated
Summary
Limiting global warming to 1.5–2 degrees requires substantial and fast reduction of greenhouse gas (GHG) emissions in basically all economic sectors (Tollefson, 2018; Allen et al, 2018). -called “negative emission technologies” (NET) or “carbon dioxide removal” (CDR) options become important. Such NET or CDR options permanently remove carbon dioxide from the atmosphere they act as carbon sinks and allow for compensation of residual GHG emissions, enabling “net-zero” GHG emissions without reducing overall antrophogenic GHG emissions to zero (Van Vuuren et al, 2013; Rogelj et al, 2015; Geden and Schenuit, 2019; Geden et al, 2019; Kirchner, 2020). Without NET in place, drastic reductions of energy demand and consumption in general would be required (Grubler et al, 2018)
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