Abstract
Greenhouse gas removal technologies are needed to reach the targets of the UNFCCC Paris Agreement. Among existing technologies, the use of biochar is considered promising, particularly biochar derived from the large quantities of sugarcane residues available in South America and elsewhere. However, the net greenhouse gas removal potential of sugarcane biochar has not been assessed hitherto. We use a scenario-based anticipatory life cycle assessment to investigate the emissions associated with a change from the combustion of sugarcane residues in a combined heat and power plant to the pyrolysis of these residues for biochar production and field application in São Paulo State, Brazil. We define scenarios based on different mean marginal electricity production and biochar production share. The results indicate that emissions from covering the electricity deficit generated by partial combustion of biomass during biochar production is the main emitting process. Overall, the processes associated with biochar production lower the net greenhouse gas benefits of the biochar by around 25%. Our analysis suggests that allocating 100% of the available sugarcane residues to biochar production could sequester 6.3 ± 0.5 t CO2eq ha−1 yr−1 of sugarcane in São Paulo State. Scaled up to the entire State, the practice could lead to the removal of 23% of the total amount of GHGs emitted by the State in 2016.
Highlights
A global decrease of greenhouse gas (GHG) emissions of around 6% yearly is needed to reach the targets of the UNFCC Paris Agreement and limit global temperature increases to well below 2 ◦C above preindustrial levels (IPCC, 2018)
If 100% of these residues are used for biochar production, we calculated that conventional slow pyrolysis would produce up to 4.2 t of biochar, Lefebvre et al (2020)
These results show that the carbon sequestration of the practice increases as the emission factors (EF) of the marginal electricity mix decreases
Summary
A global decrease of greenhouse gas (GHG) emissions of around 6% yearly is needed to reach the targets of the UNFCC Paris Agreement and limit global temperature increases to well below 2 ◦C above preindustrial levels (IPCC, 2018). One of the promising technologies is based on biochar, the carbon-rich material produced in thermochemical conversion of biomass under restricted oxygen supply (IPCC, 2019; Schmidt et al, 2018). Sugarcane (Saccharum officinarum L.) cultivated for ethanol as well as human consumption is one of the largest sources of residual biomass globally, with 1.9 Gt of fresh sugarcane harvested in 2018 (FAO, 2019). It is grown in more than 90 countries, but most current production is in Brazil (Cardoso et al, 2019). Sugarcane cultivation generates large quantities of residues, with the increasingly widespread practise of “green harvesting” – mechanical harvest of cane without prior burning of leaves (Romero et al, 2007)
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