Can BECCS deliver sustainable and resource efficient negative emissions?

Abstract

Negative emissions technologies (NETs) in general and Bioenergy with CO2 Capture and Storage (BECCS) in particular are commonly regarded as vital yet controversial to meeting our climate goals. In this contribution we present a whole-systems analysis of the BECCS value chain associated with the cultivation, harvesting, transport and conversion in dedicated biomass power stations in conjunction with CCS, of a range of biomass resources – both dedicated energy crops (miscanthus, switchgrass, short rotation coppice willow), and agricultural residues (wheat straw). We explicitly consider the implications of sourcing the biomass from different regions, climates and land types. The water, carbon and energy footprints of each value chain were calculated, and their impact on the overall system water, carbon and power efficiencies were evaluated. An extensive literature review was performed and a statistical analysis of the available data is presented. In order to describe the dynamic greenhouse gas balance of such as system, a yearly accounting of the emissions was performed over the lifetime of a BECCS facility, and the carbon "breakeven time" and lifetime net CO2 removal from the atmosphere were determined. The effects of direct and indirect land use change were included, and were found to be a key determinant of the viability of a BECCS project. Overall we conclude that, depending on the conditions of its deployment, BECCS could lead to both carbon positive and negative results. The total quantity of CO2 removed from the atmosphere over the project lifetime and the carbon breakeven time were observed to be highly case specific. This has profound implications for the policy frameworks required to incentivise and regulate the widespread deployment of BECCS technology. The results of a sensitivity analysis on the model combined with the investigation of alternate supply chain scenarios elucidated key levers to improve the sustainability of BECCS: 1) measuring and limiting the impacts of direct and indirect land use change, 2) using carbon neutral power and organic fertilizer, 3) minimising biomass transport, and prioritising sea over road transport, 4) maximising the use of carbon negative fuels, and, 5) exploiting alternative biomass processing options, e.g., natural drying or torrefaction. A key conclusion is that, regardless of the biomass and region studied, the sustainability of BECCS relies heavily on intelligent management of the supply chain

The Global Food‐Energy‐Water Nexus

“…Likewise, the boom of oil palm plantations in Southeast Asia in response to biofuel and oil crop markets has come at the cost of high biodiversity old‐growth forests, including substantial emissions of GHGs from cleared forests and particularly drainage of carbon‐dense tropical peatlands (Carlson et al, , ). Depending on the previous land cover and its capacity for carbon storage, negative net GHG emissions, often touted as the potential advantage of biofuels over conventional fossil fuels, may not be realized for decades after the land conversion when the “carbon debt” from the increased GHG emissions caused by forest clearing has been paid off (Fajardy & Mac Dowell, ; Fargione et al, ). Using current agricultural lands for biofuel crops may offset the “carbon debt” of land use change but can lead to a displacement of food crops and substantial water use (Rulli et al, ).…”

Slicing the pie: how big could carbon dioxide removal be?

“…Considering a power generation efficiency of 45% HHV , this would translate into a limit on the biomass carbon footprint of 36 g CO 2 /MJ of biomass. It is important to note that biomass supply chain emissions could be drastically higher when including land use change, potentially leading to a negative capture potential per MJ of biomass . Now, if all of the CO 2 sequestered by the biomass is assumed to be released in the flue gas upon combustion, the amount of CO 2 sequestered per MJ of biomass would then depend on the postcombustion capture rate applied to the power facility, the biomass carbon content, the biomass heating value, and the biomass carbon footprint.…”

“…It is important to note that biomass supply chain emissions could be drastically higher when including land use change, potentially leading to a negative capture potential per MJ of biomass. 27 Now, if all of the CO 2 sequestered by the biomass is assumed to be released in the flue gas upon combustion, the amount of CO 2 sequestered per MJ of biomass would then depend on the postcombustion capture rate applied to the power facility, the biomass carbon content, the biomass heating value, and the biomass carbon footprint. Considering a capture rate of between 60 and 90%, biomass carbon content between 45 and 50% dry , an HHV dry between 18 and 20 MJ/kg, and a biomass carbon footprint between 0 and 36 g CO 2 / MJ, the amount of CO 2 sequestered would be between 14 and 92 g CO 2 /MJ.…”

Mitigation potential and environmental impact of centralized versus distributed BECCS with domestic biomass production in Great Britain

“…In addition, depending on the land‐use change (LUC) transition and nature of the feedstock, several studies showed significant GHG emission savings, soil carbon sequestration potentials (Hastings et al, ; Richards et al, ) and ecosystem service benefits such as flood protection, pest control, positive effects on water and soil quality and wildlife game cover (Milner et al, ). The large‐scale deployment of BECCS, however, involves a number of environmental, economic and social implementation challenges associated with the emissions from LUC to grow bioenergy crops, potential conflicts with food and feed production when bioenergy crops are grown on agricultural land and the building of BECCS infrastructure required for energy vectors that still rely on a fossil fuel supply chain (Fajardy & Mac Dowell, ; Hastings, ; Samsatli, Samsatli, & Shah, ).…”