Partial CO2 capture to facilitate cost-efficient deployment of carbon capture and storage in process industries - Deliberations on process design, heat integration, and carbon allocation

Doktorsavhandling, 2022

It is now virtually certain that large-scale carbon dioxide removal (CDR) from the atmosphere will be required if we as humans are to commit seriously to limiting the warming of our planet to well below 2°C, as agreed upon in the Paris Agreement. Since natural mechanisms for CDR are limited, we will need to rely on technically removing the CO2 and storing it permanently in geologic formations at the gigatonne scale, i.e., at a scale similar to the size of the fossil fuel industry today. Since we won’t be able to conjure up this solution overnight, we need to initiate carbon capture and storage (CCS) today. However, CDR requires either vast amounts of scarce and sustainable biomass (which stores atmospheric CO2 during its growth) or the capture of CO2 from the air, which is capital- and energy-intensive due to its dilute state (0.04 vol.%).

We are still emitting vast flows of CO2 at much higher concentrations (~4–99 vol.%) at large industrial facilities, such as steel mills, cement kilns, and petroleum refineries, which often also have an excess of low-temperature heat. These are prerequisites for energy- and cost-effective capture of CO2 with a technology that is available at scale today, i.e., solvent-based CO2 separation from bulk gas flows. With the goal of incentivizing near-term investments in CO2 capture in industry, this thesis studies the concept of partial carbon capture, which aims to capture a certain fraction of the CO2 emissions from an industrial site, thereby lowering the absolute and specific costs (€/tCO2) for CO2 capture, as compared to a conventional full-capture process.

Specifically, the thesis identifies relevant aspects for the implementation of carbon capture at industrial sites in the immediate near-term. Numeric process modeling shows that energy- and cost-effective design of solvent-based processes for partial capture can lead to capture cost savings of up to 10% for CO2-rich gases. Techno-economic assessments of the efficient use of residual heat at industrial sites for partial capture reveal CCS costs savings of up to 24% compared to full capture. These cost savings can establish (partial) capture at a cost that is equal to or less than the current cost of emitting CO2 in the EU (EU ETS) of ~80 €/tCO2. The work further underlines the importance of incorporating site realities, such as temporal variations of available heat, into such assessments. In addition, it emphasizes the need for policies that incentivize investments in mitigation technologies and address how emissions savings from partial capture can be allocated to low-carbon products in a manner that rewards mitigation with respect to the level of ambition (partial vs. full capture) and defines product certificates, respectively. Finally, stakeholders in industry should recognize the –narrow window of opportunity that exists for partial capture with regards to the lifetime of the existing production infrastructure, alternative production and (co-) mitigation technologies, and regionally available infrastructure, such as renewable energy and CO2 transport and storage systems.

There are fewer than 30 years remaining until process industry needs to be decarbonized, implying full capture or carbon-free production processes. Unless immediate full mitigation is possible, partial capture represents an opportunity for process industry to start reducing emissions, so as to: 1) reach corporate and national climate targets for Year 2030; 2) contribute to the needed global reduction rates of 1–2 GtCO2/year; and 3) kick-off the ramping up of CCS activities that will be needed to form a CO2 transport and storage industry that is capable of also handling the gigatonnes of CO2 that we will need to remove from the atmosphere in the second half of this century.