Emergy analysis on upgraded process systems of bio-oil from pinus sylvestris pyrolysis

Abstract: Fast pyrolysis of biomass and upgrading techniques for the high chemical value bio-oil production have been investigated widely in recent decades. A variety of upgrading techniques are applied in industrial manufacture process, while the production efficiency and sustainability of those techniques have their own merits and demerits, which emphasizes the importance of the evaluation systems for those techniques. Several evaluation methods, such as energy analysis, exergy analysis, and emergy analysis, have been developed to evaluate the fast pyrolysis of biomass and upgrading techniques. Based on different emergy flows, the methods chosen for the thermodynamic analysis lead to various outcomes. All the input and output energies in an industrial production system are considered in energy analysis, while exergy analysis takes the additional available energy into account. In emergy analysis, all kinds of emergy flows are taken into consideration, including monetary flow, information flow and energy flow. Emergy analysis is derived from the viewpoint that the sun provides the energy for everything on the earth so it is reasonable to convert all kinds of energy to the solar energy. It is so efficient and comprehensive that it has been applied to evaluate the fast pyrolysis of biomass and upgrading techniques. Based on the input-output framework and emergy indices, with the consideration of environment elements, emergy analysis method was applied to comprehensively evaluate two schemes in this paper, achieving upgraded bio-oil from pinus sylvestris by fast pyrolysis and catalytic hydrogenation (Scheme I) and supercritical ethanol upgrading technique (Scheme II), respectively. Meanwhile, the effects of different schemes were compared from three aspects, including production efficiency, environmental support and sustainability. As the results indicated, Scheme II consumed less solar energy and enjoyed higher efficiency when the same amount of fuel was produced. For the input of economic emergy and total emergy, Scheme I were 4.58×1020 and 4.64×1020 sej/a while Scheme II were 5.82×1020 and 5.88×1020 sej/a respectively, which showed that Scheme I needed less economic emergy input and total emergy input by contrast with Scheme II. For the renewable ratio, Scheme I was 49.57 while Scheme II was 39.12, which showed that renewable emergy input occupied higher percent of the total emergy input in Scheme I. For the environment sustainable index, Scheme I was 0.99 while Scheme II was 0.65, which showed that Scheme I had less stress on the environment and got more support from it. In brief, Scheme I achieves larger renewable ratio, less environment stress, better sustainability and greater environmental support. The optimal direction for both Scheme I and Scheme II is to reduce the emergy input. Scheme I focuses on improving the efficiency of emergy conversion, while Scheme II emphasizes on adjusting the process to reduce the dependency on external support. Compared with the results of energy analysis and exergy analysis, Scheme II needs more total inputs and total energy consumptions, while Scheme I has higher exergy efficiency. Scheme I and Scheme II shared the same emergy yield ratio, which indicated emergy analysis could provide a more comprehensive and deeper evaluation. In sum, theoretical foundations on improving the integrated performance of fast pyrolysis of biomass and upgrading techniques for the bio-oil production are achieved in this paper.