Bioenergy with CCS and direct air CCS

Authors: Habiba Ahut Daggash and Mathilde Fajardy

This UKERC TPA working paper has been prepared to support the Committee on Climate Change’s advice to the UK government on the implications of the Paris Agreement on its long-term emissions reduction targets. In their recent reports, the Intergovernmental Panel on Climate Change have highlighted that large-scale carbon dioxide removal (CDR), defined as any anthropogenic activity that results in the net removal of CO2 from the atmosphere, is critical to meeting the Paris Agreement target.

This review addresses two technological CDR solutions that have been demonstrated: bioenergy with carbon capture and storage (BECCS) and direct air carbon capture and storage (DACCS). The overarching questions which this review addresses, for both BECCS and DACCS, are:

1. What is the potential contribution that these technologies could make to CO2 removal and potentially CO2 emissions reductions to achieve net zero emissions in the UK?
2. What are the current and projected costs, globally and in the UK, of these technologies and how plausible are projected cost reductions (including evidence for the benefits to be derived from economies of scale/technology learning)?

Summary of findings

Direct air carbon capture and storage

A systematic review resulted in an evidence base of 170 documents. Of these, only 20 documents assess DACCS technology explicitly. This highlighted the scarcity of literature on DACCS. Independent, bottom-up techno-economic assessments of DACCS technologies are particularly lacking. Only four of such assessments were found in the literature dating back to 1996; and several studies have taken these and sought to optimise the DACCS processes defined within them, so as to refine the energy and economic cost estimates. With the exception of one analysis, these assessments were published before 2012 so the cost estimates may be considered to be dated.

Five companies have been identified as commercial developers of DACCS. Two of these, Carbon Engineering and Climeworks, have provided cost estimates for their technologies. Recent studies seeking to evaluate the climate change mitigation potential of DACCS have assumed these values in their analyses. Owing to the proprietary nature of the underlying technologies used for DACCS, and their presentation of projected future costs (as opposed to current costs), it is difficult to independently verify capture costs and subsequent mitigation potential using DACCS.

Further work is needed to develop independent, bottom-up techno-economic assessments of DACCS, and demonstration to prove its commercial viability at scale. The potential implications of DACCS on the environment (as some archetypes of the technology consume water) also need further investigation.

Bioenergy with carbon capture and storage

The literature on BECCS is relatively large compared to DACCS. Out of the 170 documents reviewed, over 100 documents were specific to BECCS, with a majority of bottom-up assessments of BECCS potential and techno-economic studies.

BECCS technical potential is correlated with bioenergy technical potential, and can be therefore be determined in part through bioenergy resource assessments – whether at global or country scale. BECCS potential in the UK was assessed between 3 and 60 MtCO2/yr. These ranges are a function of the UK local bioenergy supply, on how this supply is distributed amongst the different bioenergy conversion routes to CDR, and on lifecycle emissions of each BECCS value chain. As the UK has considerable CO2 storage potential (80 GtCO2), it is possible that the UK could import biomass feedstock to extend BECCS deployment beyond this technical potential. When considering bioenergy imports, the maximum technical potential of BECCS increases to 100-160 MtCO2/yr. BECCS cost estimates in the literature span a wide range, with values as low as £12/tCO2 and as high as £314/tCO2.

The multiplicity of BECCS pathways (e.g. electricity, biofuel) and technologies (e.g. fermentation or gasification) is a first driver of variability. Additionally, differences in boundaries for both the cost and CO2 balance result in BECCS cost being provided alternatively as a cost per ton of CO2 avoided (i.e. as compared to a counterfactual), captured, or removed (i.e. CO2 captured minus life cycle GHG emissions). Based on UK specific CAPEX and feedstock cost data from the literature, BECCS removal cost in the UK was assessed as between £70 and £130/tCO2 when using local biomass, and between and £150 and £200/tCO2 when using imported biomass.

Two conflicting driving forces of BECCS cost were identified: 1) the potential decrease in capital cost from a “first of a kind” plant to an “nth of a kind plant” 2) the potential increase in feedstock cost, as sustainability criteria toughened and demand for biomass feedstock increases. A sensitivity analysis showed that overall, BECCS cost was more sensitive to feedstock cost. Whilst the “real cost” of BECCS can be determined by demonstration/real size BECCS projects, the uncertainty of the evolution of feedstock costs over time may therefore be one the main economic bottlenecks to BECCS deployment.

The financial viability of BECCS plant is still likely to rely on a revenue stream associated with the service of carbon dioxide removal, especially in the case of large scale bioelectricity plants. A review of the literature indicates that CO₂ prices between £25 and £190/tCO₂ are required for BECCS plants to be competitive with their unabated alternative. In the context of the UK, this assessment showed that a negative emission credit between £75 and £210/tCO₂ (depending on the feedstock cost) was required for a BECCS plant to breakeven (net present value is equal to zero). This is still much higher than the current value of the CO₂ price set by the EU ETS scheme, which suggests the need for the creation of a separate incentive scheme specific to CDR.

Contact

The project key contacts are Habiba Ahut Daggash and Mathilde Fajardy