Partial carbon capture – an opportunity to decarbonize primary steelmaking

Licentiate thesis, 2019

Climate change requires that all energy-related sectors drastically reduce their greenhouse gas emissions (GHG). To have a high likelihood of limiting global warming to 1.5°C, large-scale mitigation of GHG has to start being implemented and cause emissions to fall well before Year 2030. The process industry, including the iron and steel industry, is inherently carbon-intensive and carbon capture and storage (CCS) is one of the few options available to achieve the required reductions in carbon dioxide (CO2) emissions. Despite its high technological maturity, CCS is not being implemented at the expected rates due inter alia to the low value creation of CCS for process industries, which is often attributed to uncertainties related to carbon pricing and the considerable investments required in CO2 capture.

This thesis deals with the concept of partial carbon capture, which is governed by market or site conditions and aims to capture a smaller fraction of the CO2 emissions from an industrial site, thereby lowering the absolute and specific costs (€ per tonne CO2) for CO2 capture, as compared to a conventional full-capture process. Depending on the scale and market conditions these savings hold true especially for a process industry that has large gas flows with concentrations of CO2 ≥20 vol.% and access to low-value heat. Integrated steel mills typically fulfill these conditions.

The value of partial capture for the steel industry is assessed in a techno-economic study on the separation of CO2 from the most carbon-intensive steel mill off-gases. The design for partial carbon capture using a 30 wt.% aqueous monoethanolamine (MEA) solvent is optimized for lower cost. Powering the capture process exclusively with excess heat entails a cost of 28–35 (±4) €/tonne CO2-captured and a reduction in CO2 emissions of 19%– 43% onsite, depending on design and CO2 source. In contrast, full capture requires external energy to reduce the CO2 site emissions by 76%, entailing costs in the range of 39–54 (±5) €/tonne CO2-captured. Furthermore, the use of excess heat has impacts on the cost structure of partial carbon capture, i.e., increasing the ratio of capital expenditures to operational expenditures, as well as on the relationship between carbon and energy intensity for primary steel as an industrial product.

The present work concludes that near-term implementation of partial carbon capture in the 2020s will be economically sustainable if average carbon prices are in the range of 40–60 €/tonne CO2 over the entire economic life-time of the partial capture unit (ca. 25 years). Once implemented, partial capture could evolve to full capture over time through either co-mitigation (e.g., with biomass utilization or electrification) or efficiency improvements. Alternatively, partial capture could act as a bridging-technology for new, carbon-free production. In summary, partial carbon capture is found to be readily available and potentially economically viable to initiate large-scale mitigation before Year 2030. Partial capture may represent a starting point for the transition to the carbon-constrained economies of the future in line with the 1.5°C target.