Life cycle analysis of energy production from Spartina argentinensis

EMILIANO JOZAMI; FERNANDO MELE; ROXANA PIASTRELLINI; BÁRBARA CIVIT; SUSANA FELDMAN

Evento virtual

Conferencia; CILCA 2021; 2021

RICV. RACV

The production of biofuels has grown steadily in recent decades given the recognition of biofuels in mitigating climate change. However, the fact that a fuel is derived from renewable sources does not necessarily mean that it is an environmentally friendly product. The reason is that in their production chain, the generation of emissions to air, soil and water could undermine the environmental benefits of being a renewable source. Life cycle analysis (LCA) is positioned globally as the tool to be used to assess the sustainability of biofuels. There are some barriers for their importation in many countries that establish thresholds for reducing greenhouse gas (GHG) emissions, with respect to the emissions of the fossil fuels to be replaced, that need to be surpassed in order not to be rejected. These emissions must be calculated using LCA. The Submeridional Lowlands located north of the province of Santa Fe (Argentina), cover an area of more than 2 million hectares, where there is a renewable resource that is currently underutilized. It is the espartillo, Spartina argentinensis Parodi. It is a perennial grass with C4 photosynthetic metabolism, which shows high growth rates, even under unfavorable conditions for most plants (frequent droughts and flooding, salinity, etc.). Therefore, it is the dominant species within a high proportion of the region. The productive systems that prevail there are cattle raising systems with low animal load and, consequently, low profitability. Fire management in these systems is a frequent practice usedto remove the abundant biomass of grass and promote the growth of more digestible shoots for livestock. This field combustion releases GHG into the atmosphere (although much of the carbon is biogenic CO2, there are other combustion non-biogenic gases with global warming potential) without taking advantage of the energy released. Likewise, particulate material is generated which is harmful for the respiratory tract of the populations surrounding the burnt area. Our proposal is based on finding energetic alternative uses for this material, maintaining the current state of these livestock systems, replacing burning with biomass harvesting. The objective of this work is to assess the global warming potential (GWP) of the use of this biomass as an energy source(electricity via synthesis gas produced by gasification of the wire) and its comparison with current systems to fulfill the same function. To do this, we carried out the life cycle analysis following the ISO 14040 and 14044standards. The proposed system ?production of synthesis gas to generate electricity? was evaluated and compared with the current reference system (Argentine electricity mix). The functional unit is to deliver 1 MWh ofelectricity to the grid. The Global Warming Potential impact category of the IPCC methodology was evaluated over a 100-year time horizon. The scope of the system, from cradle to gate, includes the field stage, which comprise the conditioning of the field, cutting with a mower, windrowing, rotary banding and transporting the rolls to the processing plant. It was decided to expand the limits of the system, including the functions of the co-products that were accounted as avoided products. In the field stage, burning was included as an avoided process, considering biogenic and non-biogenic carbon emissions as proposed by the IPCC for ?Savanna and grassland?. The system-product produces heat that is accounted, both from the combustion of synthesis gas and biochar, as an avoided process. For gasification, it is considered that all those stages of the industrial plant, which consume electrical energy, are supplied by the same plant. Based on this, to deliver 1 MWh of electricity to the grid, it is necessary to produce 1.22 MWh (0.22 MWh to supply the plant and the rest to deliver to the grid). The stages that consume electricity are the chopping and grinding of the grass, pelletizing and auxiliary equipment (transport, pumps, fans, etc.). The proposed system emits 203 kg of CO2eq into the atmosphere perMWh of electricity delivered to the grid. Moreover, it avoids emissions of 301, 273 and 583 kg of CO2eq, for avoided rangeland burn and heat of combustion of biochar and synthesis gas, respectively. The result is promising when compared with the value published for Argentina in Ecoinvent ?market for electricity, low voltage - AR? equivalente a 454 kg de CO2eq.