Ecological Thermodynamics Assessment Of Biomass Pyrolytic Polygeneration System

The world is confronting tough challenges of climate change and energy crisis. Biomass, as an important renewable energy, has received great attention in world. Biomass pyrolytic polygeneration, a kind of pyrolysis, is one of the most promising technologies of biomass utilization offering the advantages of three products, liquid oil, solid char and biogas that can be stored and transported. However, the system based on biomass pyrolytic polygeneration technology would consume nonrenewable energy and release greenhouse gas during the construction of buildings, the manufacture of equipment, the operation of system and so on. With the development of biomass pyrolytic polygeneration technology, it is urgent to evaluate the environmental and ecological effects. This research analyzed the greenhouse gas emission, nonrenewable energy cost, renewability, ecological footprints and environmental effects of biomass pyrolytic polygeneration system based on ecological thermodynamics theory and methods.Firstly, the research advance of ecological thermodynamics theory is summarized in this study. Methods to calculate the greenhouse gas emission, fossil energy consumption, ecological footprints and environmental effects are summed up. A general systems model of biomass pyrolytic polygeneration is presented based on the ecological thermodynamics theory to show the energy flows, material flows and information flows in and through the system. Meanwhile, concrete evaluation procedures of nonrenewable energy cost, greenhouse gas emission, emergy, emergy-based ecological footprint and a set of indicators are brought forward for the system analysis of biomass pyrolytic polygeneration system in the light of the ecological thermodynamics theory.An integrated systems ecological thermodynamical evaluation is presented for two typical pyrolysis system in China, biomass-based fixed-bed pyrolytic polygeneration(syngas, bio-oil and biochar) system and moving-bed pyrolytic polygeneration(syngas, bio-oil, biochar, heat and electricity) system. A system model of each case is established based on an ecological input-output framework, which covers all steps of biomass conversion processes, including agricultural cultivation, plant construction, equipment installation, operation and maintenance. Systems accountings of greenhouse gas emissions, nonrenewable energy cost, emergy cost, emergy-based ecological footprint are conducted for each ease.(1) Systems accounting on nonrenewable energy cost for the biomass fixed-bed and moving-bed pyrolytic polygeneration system are conducted in this research. The renewability or nonrenewability of these systems is identified. Comparison between different biomass-based technologies and conventional fossil energy systems are also conducted. Results show that both systems are renewable and the biomass moving-bed pyrolytic polygeneration system shows higher renewability.(2) Systems accounting on greenhouse gas emission for the biomass fixed-bed and moving-bed pyrolytic polygeneration system are conducted. The greenhouse gas emission intensity is also calculated. The model of carbon cycle are developed to analysis the potential of greenhouse gas reduction. Results reflect that compared with fixed-bed system, moving-bed system can significantly reduce greenhouse gas emissions and biochar returning to field could offset greenhouse gas emission of the system.(3) The ecological effects of the biomass fixed-bed and moving-bed pyrolytic polygeneration system are demonstrated with indicators referred to emergy and emergy-based ecological footprints. Dominant elements which affect the final results are identified. Results imply that moving-bed system shows better sustainability and high electricity consumption is the main factor which influence the sustainability of fixed-bed system.