Life Cycle Assessment of Wheat Straw Pyrolysis with Volatile Fractions Chemical Looping Combustion

Teresa Mendiara, Alberto Navajas (), Alberto Abad, Tobias Pröll, Mikel Munárriz, Luis M. Gandía, Francisco García-Labiano and Luis F. de Diego
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Teresa Mendiara: Department of Energy and Environment, Instituto de Carboquímica-ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza, Spain
Alberto Navajas: Department of Science, Public University of Navarre, Arrosadía Campus s/n, 31006 Pamplona, Spain
Alberto Abad: Department of Energy and Environment, Instituto de Carboquímica-ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza, Spain
Tobias Pröll: Institute for Chemical and Energy Engineering, University of Natural Resources and Life Sciences, 1190 Vienna, Austria
Mikel Munárriz: Department of Science, Public University of Navarre, Arrosadía Campus s/n, 31006 Pamplona, Spain
Luis M. Gandía: Department of Science, Public University of Navarre, Arrosadía Campus s/n, 31006 Pamplona, Spain
Francisco García-Labiano: Department of Energy and Environment, Instituto de Carboquímica-ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza, Spain
Luis F. de Diego: Department of Energy and Environment, Instituto de Carboquímica-ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza, Spain

Sustainability, 2024, vol. 16, issue 10, 1-14

Abstract: Among the approaches to facilitating negative CO 2 emissions is biochar production. Biochar is generated in the pyrolysis of certain biomasses. In the pyrolysis process, carbon in the biomass is turned into a solid, porous, carbon-rich, and stable material that can be captured from the soil after a period of from a few decades to several centuries. In addition to this long-term carbon sequestration role, biochar is also beneficial for soil performance as it helps to restore soil fertility and improves the retention and diffusion of water and nutrients. This work presents a Life Cycle Assessment of different pyrolysis approaches for biochar production. Biomass pyrolysis is performed in a fixed-bed reactor, which operates at a mild temperature (550 ° C). Biochar is obtained as solid product of the pyrolysis, but there are also liquid (bio-oil) and gaseous products (syngas). The pyrolysis gas is partly used to fulfil the energy demand of the pyrolysis process, which is highly endothermic. In the conventional approach, CO 2 is produced during the combustion of syngas and emitted to the atmosphere. Another approach to facilitate CO 2 capture and thus obtain more negative CO 2 emissions in the pyrolysis process is burning syngas and bio-oil in a Chemical Looping Combustion unit. Life Cycle Assessment was performed of these approaches toward biomass pyrolysis to evaluate their environmental impact. The Chemical Looping Combustion approach significantly reduced the values of 7 of the 16 environmental impact indicators studied, along with the Global Warming Potential among them, it slightly increased the value of one indicator related to the use of fossil resources, and it maintained the values of the remaining 8 indicators. Environmental impact reduction occurs due to the avoidance of CO 2 and NO x emissions with Chemical Looping Combustion. The CO 2 balances of the different pyrolysis approaches with Chemical Looping Combustion configurations were compared with a base case, which constituted the direct combustion of wheat straw to obtain thermal energy. Direct biomass combustion for the production of 17.1 MJ of thermal energy had CO 2 positive emissions of 0.165 kg. If the gaseous fraction was burned by Chemical Looping Combustion, CO 2 was captured and the emissions became increasingly negative, until a value of −3.30 kg/17.1 MJ was generated. If bio-oil was also burned by this technology, the negative trend of CO 2 emissions continued, until they reached a value of −3.66 kg.

Keywords: biomass pyrolysis; Chemical Looping Combustion; Life Cycle Assessment; environmental impacts; carbon footprint (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2024
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