Can bioenergy with carbon capture and storage deliver negative emissions? A critical review of life cycle assessment

The Value of Bioenergy Sequestration

Most mitigation scenarios compatible with a likely change of holding global warming well below 2 °C rely on negative emissions technologies (NETs). According to the integrated assessment models (IAMs) used to produce mitigation scenarios for the IPCC reports, the NET with the greatest potential to achieve negative emissions is bioenergy with carbon capture and storage (BECCS). Crucial questions arise about where the enormous quantities of biomass needed according to the IAM scenarios could feasibly be produced in a sustainable manner. Africa is attractive in the context of BECCS because of large areas that could contribute biomass energy and indications of substantial underground CO2 storage capacities. However, estimates of large biomass availability in Africa are usually based on highly aggregated datasets, and only a few studies explore future challenges or barriers for BECCS in any detail. Based on previous research and literature, this paper analyses the pre-conditions for BECCS in Tanzania by studying what we argue are the applications of BECCS, or the components of the BECCS chain, that are most feasible in the country, namely (1) as applied to domestic sugarcane-based energy production (bioethanol), and (2) with Tanzania in a producer and re-growth role in an international BECCS chain, supplying biomass or biofuels for export to developed countries. The review reveals that a prerequisite for both options is either the existence of a functional market for emissions trading and selling, making negative emissions a viable commercial investment, or sustained investment through aid programmes. Also, historically, an important barrier to the development of production capacity of liquid biofuels for export purposes has been given by ethical dilemmas following in the wake of demand for land to facilitate production of biomass, such as sugarcane and jatropha. In these cases, conflicts over access to land and mismanagement have been more of a rule than an exception. Increased production volumes of solid biomass for export to operations that demand bioenergy, be it with or without a CCS component, is likely to give rise to similar conflicts. While BECCS may well play an important role in reducing emissions in countries with high capacity to act combined with existing large point sources of biogenic CO2 emissions, it seems prudent to proceed with utmost caution when implicating BECCS deployment in least developed countries, like Tanzania.The paper argues that negative BECCS-related emissions from Tanzania should not be assumed in global climate mitigation scenarios.

ABSTRACTStudies show that the ‘well below 2°C’ target from the Paris Agreement will be hard to meet without large negative emissions from mid-century onwards, which means removing CO2 from the atmosphere and storing the carbon dioxide in biomass, soil, suitable geological formations, deep ocean sediments, or chemically bound to certain minerals. Biomass energy combined with Carbon Capture and Storage (BECCS) is the negative emission technology (NET) given most attention in a number of integrated assessment model studies and in the latest IPCC reports. However, less attention has been given to governance aspects of NETs. This study aims to identify pragmatic ways forward for BECCS, through synthesizing the literature relevant to accounting and rewarding BECCS, and its relation to the Paris Agreement. BECCS is divided into its two elements: biomass and CCS. Calculating net negative emissions requires accounting for sustainability and resource use related to biomass energy production, processing and use, and interactions with the global carbon cycle. Accounting for the CCS element of BECCS foremost relates to the carbon dioxide capture rate and safe underground storage. Rewarding BECCS as a NET depends on the efficiency of biomass production, transport and processing for energy use, global carbon cycle feedbacks, and safe storage of carbon dioxide, which together determine net carbon dioxide removal from the atmosphere. Sustainable biomass production is essential, especially with regard to trade-offs with competing land use. Negative emissions have an added value compared to avoided emissions, which should be reflected in the price of negative emission ‘credits’, but must be discounted due to global carbon cycle feedbacks. BECCS development will depend on linkages to carbon trading mechanisms and biomass trading.Key policy insightsA standardized framework for sustainable biomass should be adopted.Countries should agree on a standardized framework for accounting and rewarding BECCS and other negative emission technologies.Early government support is indispensable to enable BECCS development, scale-up and business engagement.BECCS projects should be designed to maximize learning across various applications and across other NETs.BECCS development should be aligned with modalities of the Paris Agreement and market mechanisms.

Coal-fired power plants are a major source of the anthropogenic CO2 emissions that drive climate change and associated environmental impacts. Bio-Energy with Carbon Capture and Storage (BECCS) has been identified as a renewable technology with the potential to remove CO2 from the atmosphere, as it refers to power generation through combusting biomass and capturing CO2 in the flue-gas using carbon capture storage (CCS). Wood and paper wastes have gained popularity as biofuels, due in part to their potential benefits as they do not directly compete with other industries for agricultural land and can significantly reduce the quantity of waste diverted to landfills. This study assesses the greenhouse gas (GHG) emissions reduction capability of retrofitting biomass co-firing and CCS technologies to an existing coal-fired power plant, using a Life Cycle Assessment (LCA) approach. The biomass considered in this study is wood-based waste, including paper, cardboard, palletised wood, chipboard, and furniture. The LCA utilises a “cradle-to-grave” approach, incorporating emissions associated with coal mining, procurement, treatment, combustion, and ash disposal. The system boundary excludes upstream emissions from the manufacture of the waste products, as these were considered “avoided products”. Thus, avoided landfill emissions from the disposal of wood-wastes were included as negative emissions. The life cycle GHG emissions of six different scenarios are considered (co-firing ratios of 0%, 5%, and 10%, each with and without CCS). Power-plant characteristics, waste transportation and pipeline transportation distances were based on existing coal-fired power plants at Mt. Piper, Bayswater, and Eraring, in NSW, Australia. Without CCS, co-firing waste at 5% and 10% without CCS only slightly reduced overall emissions (around 1% and 2% respectively) relative to the current coal-fired power arrangement (no co-firing without CCS). On the other hand, implementing BECCS with 10% co-firing can reduce life cycle CO2 emissions by around 80%, and negative life-cycle CO2 emissions are achievable at co-firing ratios above 30%. The life cycle GHG emissions are most sensitive to the energy penalty imposed by CCS on the power plant. At co-firing ratios of 15%, life-cycle CO2 emissions of BECCS are comparable to those of solar PV energy generation. Moreover, at co-firing ratios around 25%, BECCS life-cycle CO2 emissions are competitive with those of nuclear, wind and hydroelectric generation. This highlights how CCS has the ability to make biomass co-firing compare favourably with other renewable or low-emissions alternatives. Although those technologies possess a lower emission intensity than BECCS at co-firing ratios below 15%, if improvements in boiler efficiency and resource recovery continue then this will allow operation at higher co-firing ratios, lowering emissions intensity further. To determine if BECCS should form part of future plans to meet emissions reduction targets, further research into additional sources of suitable waste biomass is recommended.

Cutting through the noise on negative emissions

Bioenergy with carbon capture and storage (BECCS) based on purpose‐grown lignocellulosic crops can provide negative CO2 emissions to mitigate climate change, but its land requirements present a threat to biodiversity. Here, we analyse the implications of crop‐based BECCS for global terrestrial vertebrate species richness, considering both the land‐use change (LUC) required for BECCS and the climate change prevented by BECCS. LUC impacts are determined using global‐equivalent, species–area relationship‐based loss factors. We find that sequestering 0.5–5 Gtonne of CO2 per year with lignocellulosic crop‐based BECCS would require hundreds of Mha of land, and commit tens of terrestrial vertebrate species to extinction. Species loss per unit of negative emissions decreases with: (i) longer lifetimes of BECCS systems, (ii) less overall deployment of crop‐based BECCS and (iii) optimal land allocation, that is prioritizing locations with the lowest species loss per negative emission potential, rather than minimizing overall land use or prioritizing locations with the lowest biodiversity. The consequences of prevented climate change for biodiversity are based on existing climate response relationships. Our tentative comparison shows that for crop‐based BECCS considered over 30 years, LUC impacts on vertebrate species richness may outweigh the positive effects of prevented climate change. Conversely, for BECCS considered over 80 years, the positive effects of climate change mitigation on biodiversity may outweigh the negative effects of LUC. However, both effects and their interaction are highly uncertain and require further understanding, along with the analysis of additional species groups and biodiversity metrics. We conclude that factoring in biodiversity means lignocellulosic crop‐based BECCS should be used early to achieve the required mitigation over longer time periods, on optimal biomass cultivation locations, and most importantly, as little as possible where conversion of natural land is involved, looking instead to sustainably grown or residual biomass‐based feedstocks and alternative strategies for carbon dioxide removal.

Life cycle assessment of co-firing coal and wood waste for bio-energy with carbon capture and storage – New South Wales study

Bioenergy with carbon capture and storage (BECCS) technology is expected to support net-zero targets by supplying low carbon energy while providing carbon dioxide removal (CDR). BECCS is estimated to deliver 20 to 70 MtCO2 annual negative emissions by 2050 in the UK, despite there are currently no BECCS operating facility. This research is modelling and demonstrating the flexibility, scalability and attainable immediate application of BECCS. The CDR potential for two out of three BECCS pathways considered by the Intergovernmental Panel on Climate Change (IPCC) scenarios were quantified (i) modular-scale CHP process with post-combustion CCS utilising wheat straw and (ii) hydrogen production in a small-scale gasifier with pre-combustion CCS utilising locally sourced waste wood. Process modelling and lifecycle assessment were used, including a whole supply chain analysis. The investigated BECCS pathways could annually remove between −0.8 and −1.4 tCO2e tbiomass−1 depending on operational decisions. Using all the available wheat straw and waste wood in the UK, a joint CDR capacity for both systems could reach about 23% of the UK's CDR minimum target set for BECCS. Policy frameworks prioritising carbon efficiencies can shape those operational decisions and strongly impact on the overall energy and CDR performance of a BECCS system, but not necessarily maximising the trade-offs between biomass use, energy performance and CDR. A combination of different BECCS pathways will be necessary to reach net-zero targets. Decentralised BECCS deployment could support flexible approaches allowing to maximise positive system trade-offs, enable regional biomass utilisation and provide local energy supply to remote areas.

Bioenergy with carbon capture and storage (BECCS) can act as a negative emission technology and is considered crucial in many climate change mitigation pathways that limit global warming to 1.5–2 °C; however, the negative emission potential of BECCS has not been rigorously assessed. Here we perform a global spatially explicit analysis of life-cycle GHG emissions for lignocellulosic crop-based BECCS. We show that negative emissions greatly depend on biomass cultivation location, treatment of original vegetation, the final energy carrier produced and the evaluation period considered. We find a global potential of 28 EJ per year for electricity with negative emissions, sequestering 2.5 GtCO2 per year when accounting emissions over 30 years, which increases to 220 EJ per year and 40 GtCO2 per year over 80 years. We show that BECCS sequestration projected in IPCC SR1.5 °C pathways can be approached biophysically; however, considering its potentially very large land requirements, we suggest substantially limited and earlier deployment. Negative emissions technologies are a cornerstone of many mitigation scenarios that limit global warming under 2 °C. Depending on the conditions, bioenergy with carbon capture and storage can provide negative emissions but requires large amounts of land and should be deployed early and with limits.

Bioenergy with Carbon Capture and Storage (BECCS) features heavily in the energy scenarios designed to meet the Paris Agreement targets, but the models used to generate these scenarios do not address environmental and social implications of BECCS at the regional scale. We integrate ecosystem service values into a land‐use optimization tool to determine the favourability of six potential UK locations for a 500 MW BECCS power plant operating on local biomass resources. Annually, each BECCS plant requires 2.33 Mt of biomass and generates 2.99 Mt CO2of negative emissions and 3.72 TWh of electricity. We make three important discoveries: (a) the impacts of BECCS on ecosystem services are spatially discrete, with the most favourable locations for UK BECCS identified at Drax and Easington, where net annual welfare values (from the basket of ecosystems services quantified) of £39 and £25 million were generated, respectively, with notably lower annual welfare values at Barrow (−£6 million) and Thames (£2 million); (b) larger BECCS deployment beyond 500 MW reduces net social welfare values, with a 1 GW BECCS plant at Drax generating a net annual welfare value of £19 million (a 50% decline compared with the 500 MW deployment), and a welfare loss at all other sites; (c) BECCS can be deployed to generate net welfare gains, but trade‐offs and co‐benefits between ecosystem services are highly site and context specific, and these landscape‐scale, site‐specific impacts should be central to future BECCS policy developments. For the United Kingdom, meeting the Paris Agreement targets through reliance on BECCS requires over 1 GW at each of the six locations considered here and is likely, therefore, to result in a significant welfare loss. This implies that an increased number of smaller BECCS deployments will be needed to ensure a win–win for energy, negative emissions and ecosystem services.

Moving toward Net-Zero Emissions Requires New Alliances for Carbon Dioxide Removal

Carbon dioxide removal (CDR) from the atmosphere is likely to be needed to limit global warming to 1.5 or 2°C and thereby for meeting the Paris Agreement. There is a debate which methods are most suitable and cost-effective for this goal and thus deeper understanding of system effects related to CDR are needed for effective governance of these technologies. Bio-Energy with Carbon Capture and Storage (BECCS) and Direct Air Carbon Capture and Storage (DACCS) are two CDR methods, that have a direct relation to the electricity system—BECCS via producing it and DACCS via consuming. In this work, we investigate how BECCS and DACCS interact with an intermittent electricity system to achieve net negative emissions in the sector using an energy system model and two regions with different wind and solar resource conditions. The analysis shows that DACCS has a higher levelized cost of carbon (LCOC) than BECCS, implying that it is less costly to capture CO2 using BECCS under the assumptions made in this study. However, due to a high levelized cost of electricity (LCOE) produced by BECCS, the total system cost is lower using DACCS as negative emission provider as it is more flexible and enables cheaper electricity production from wind and solar PV. We also find that the replacement effect outweighs the flexibility effect. Since variations in solar-based systems are more regular and shorter (daily cycles), one could assume that DACCS is better suited for such systems, whereas our results point in the opposite direction showing that DACCS is more competitive in the wind-based systems. The result is sensitive to the price of biomass and to the amount of negative emissions required from the electricity sector. Our results show that the use of the LCOC as often presented in the literature as a main indicator for choosing between different CDR options might be misleading and that broader system effects need to be considered for well-grounded decisions.

Quantifying the global warming potential of carbon dioxide emissions from bioenergy with carbon capture and storage

In this study, the economic and environmental feasibility of a process configuration based on the Bioenergy and Carbon Capture and Storage (BECCS) concept is assessed. The research analyses the production of jet fuel from forestry residues-derived syngas via the Fischer-Tropsch (FT) technology. Further, the CO2 removed in the syngas cleaning section is not released to the environment, instead it is permanently sequestrated. The produced Sustainable Aviation Fuel (SAF) has the potential to achieve negative emissions. The present research is a one-of-a-kind study for the jet fuel production within the BECCS concept. The process has been modelled within the Aspen Plus and Matlab software to obtain detailed and realistic mass and energy balances. Based on these balances, the technical, economic and environmental parameters have been calculated. Based on a plant that treats 20 dry-t/h of forest residues, 1.91 t/h of jet fuel are produced, while 11.26 t/h of CO2 are permanently stored. The inclusion of the CCS chain in the biorefinery increase the minimum jet fuel selling price from 3.03 £/kg to 3.27 £/kg. The LCA results for global warming show a favourable reduction in the BECCS case, in which negative emissions of −121.83 gCO2eq/MJ of jet fuel are achieved, while without CCS case exhibits GHG emissions equal to 15.51 gCO2eq/MJ; in both cases, the multi-functionality is faced with an energy allocation approach. It is, then, evident the significant environmental advantages of the BECCS process configuration. Nevertheless, financial feasibility can only be attained through the implementation of existing policy schemes and the formulation of new strategies that would reward negative emissions. The application of the UK’s policy “Renewable Transport Fuel Obligation” and a hypothetical scheme that rewards negative CO2 emissions, breaks-even the Minimum Jet fuel Selling Price (MJSP) at 1.49 £/kg for a certificate and carbon price of 0.20 £/certificate and 246.64 £/tonne of CO2.

Limiting climate change to 2 °C with a high probability requires reducing cumulative emissions to about 1600 GtCO2 over the 2000–2100 period. This requires unprecedented rates of decarbonization even in the short-run. The availability of the option of net negative emissions, such as bio-energy with carbon capture and storage (BECCS) or reforestation/afforestation, allows to delay some of these emission reductions. In the paper, we assess the demand and potential for negative emissions in particular from BECCS. Both stylized calculations and model runs show that without the possibility of negative emissions, pathways meeting the 2 °C target with high probability need almost immediate emission reductions or simply become infeasible. The potential for negative emissions is uncertain. We show that negative emissions from BECCS are probably limited to around 0 to 10 GtCO2/year in 2050 and 0 to 20 GtCO2/year in 2100. Estimates on the potential of afforestation options are in the order of 0–4 GtCO2/year. Given the importance and the uncertainty concerning BECCS, we stress the importance of near-term assessments of its availability as today’s decisions has important consequences for climate change mitigation in the long run.