Emergy-based Evaluation Research On Plant Bioenergy

As one kind of renewable energy, bioenergy is of great amount, and is favorable to replace fossil fuels and ease energy crisis. Energy plants can absorb carbon dioxide through photosynthesis, which is helpful to improve the environment quality. However, the production and use of bioenergy consume energy and pollute the environment. Therefore, scientific and rational evaluation of plant bioenergy has great significance for sustainable development.Economic analysis and energy analysis were offen used to evaluate the system. In the economic analysis, only purchased flows can be evaluated. The value of environmental resources were not reflected. In the energy analysis, only energy flows were considered. And different kinds of energy were sumed by the unit of Joule. The different kinds of energy has the different potential ability to do work. Energy analysis did not consider the grade difference of energy. Emergy analysis was used to evaluate the bioenergy system in this paper. In emergy analysis, all the inputs (material, energy, money, labor, etc.) of the system are converted into a unified solar energy to be measured and analyzed. Emergy analysis takes into account the contribution of environmental resources to the system. Emergy analysis opened up a new method for quantitative analysis of the system, and provide the unified unit to measure and compare the different inputs.In order to make emergy analysis more suitable for evaluating plant bioenergy, emergy analysis was improved in this paper.?Emergy input of environmental resources were counted considering the growth cycle of plant;?The emergy sub-indices were put forward for evaluating the impact and contribution of subsystem to the whole system;?The emergy of by-product should be calculated by multiplying the transformity as the product and the quantity;?Emergy of waste was given a new definition, that is total solar energy directly or indirectly input in the process of the waste treatment. And the emergy of waste is negative;?Cr (emergy consumption ratio) was proposed, which is corresponding to the transformity. It is used to measure the impact of waste treatment processes on the environment from the perspective of emergy consumption;?ERCF (emergy ratio of carbon footprint) were proposed to evaluate the environmental impact of the system.Plant bioenergy was evaluated by emergy analysis taking the system of CFE (cassava-based fuel ethanol) as an example.?Through emergy analysis of cassava chips, emergy indices of cassava chip were obtained. And the indices of cassava chips, corn, sugar cane, and wheat were compared and discussed;?Emergy indices of CFE were obtained through emergy analysis. And the indices of CFE and other fuels (such as fossil fuel, biodiesel, etc.) were compared and discussed;?The subsystem of cassava chips and industrial production of CFE were evaluated by emergy analysis, and the sub-indicators and their weights were obtained to measure the impact of subsystems to the whole system;?ERCF of CFE were calculated and compared with ERCF of the gasoline;?Cr of cassava-alcohol vinasses was obtained through emergy analysis, and the emergy indices of cassava-alcohol vinasses treatment were compared and discussed with other waste disposal systems.Indices system for emergy evaluation of plant bioenergy was set up through emergy analysis of CFE system. The guidances of emergy analysis on the sustainable development of plant bioenergy were pointed out, embodied in three aspects: the cultivation of energy plants, the industrial production of plant bioenergy, and the treatment of waste.?The planting of energy plants: the input of environmental resources can be evaluated by emergy analysis scientificly; the contribution of different types of flows to the growth of plant could be measured; energy plants can be evaluated objectively by emergy indices.?The production of plant bioenergy: the proportion of each flow to the total emergy inputs can be analyzed to reduce the main emergy input; different kinds of energy can be compared according to emergy indices; the optimal production process of plant bioenergy can be obtained by emergy analysis; environmental impacts of plant bioenergy can be evaluated.?Treatment of waste: the impact of waste on the environment can be evaluated; different treatment process of waste can be compared by emergy analysis.Through emergy analysis of plant bioenergy, the contribution of natural environment can be measured. And the energy plants can be evaluated reasonably. The environmental impact of bioenergy production and the waste treatment can be evaluated from the perspective of emergy. Emergy analysis played a positive role in promoting sustainable development of plant bioenergy.