Valorización de biomasas residuales mediante el proceso de pirólisis para producción de biochar y biocombustibles

Résumé

Anthropogenic CO2 emissions have been duplicated in the past 50 years. These emissions have their origin in the population size, the economic activity, the life style, the use of new technologies, and the energy use. The promotion and development of environmental policies are key tools to change the current scenery and mitigate the climate change. Under the environmental vision of circular economy, sustainability and rational use of natural resources, this work presents the use of the pyrolysis process as an environmental technology to manage biomass residues, producing energy and biochar. The scope of this work is based on the positive effect that this technology generates when it is used for residues management, reducing CO2 emissions, creating new products and reducing cost derived from the use of this technology. The term of “pyrolysis” coming from the Greek alphabet points their own meaning, “pyro” (fire) and “lysis” (breaking into several parts), giving three main products that improve the CO2 cycle and having fuel features. These fractions are biochar, bio-oil and pyrolysis gases. Firstly, the treatment through fast pyrolysis is studied for bio-oil production taking into account the high difficulty in processing an agroresidual biomass (rape straw) in this process due to its inorganic matter. Thus, this study is focused on the changes in yields and bio-oil characteristics developed when the production conditions are modified. Secondly, the rape straw as well as a vine shoot biomasses are processed under slow pyrolysis to evaluate yields and characteristics of the charred fraction when the production conditions are modified, being also studied the effect of its inorganic matter content. The purpose is to compare the differences between slow and fast pyrolysis and to identify the use as biochar of this charred fraction. Thirdly, the measurement of the carbon fixed into the biochar structure is studied through indirect methods. The high recalcitrance index (R50) measures the structural strength named as “recalcitrance” and the accelerated ageing test measures the chemical degradation that it will show when it is applied to soils. When these methods are used for our samples some limitations were found, proposing some modifications in this work, especially in the R50 method. Afterwards, a correlation between both was found. Finally, a variety of biomasses were processed in a pilot scale reactor with 15-20 kg/h of maximum capacity. These biomasses were olive tree pruning, pine wood, almond shells and olive pits. The feasibility of processing them was evaluated as well as the chance of getting auto-thermal pyrolysis processes with the energy contained in the pyrolysis gas and bio-oil. Moreover, the physical features of the biochars and their carbon retention capacity were assessed as function of the feedstock and the pyrolysis temperature. Alternative application as fuel is proposed for this charred fraction in case that its use as biochar may not be advisable.