微細藻類を利用したCO_2再資源化のエネルギー・環境評価

摘要

微細藻類の一種であるクロレラを培養し、これを石炭火力混焼向け燃料とすることを前提に、エネルギー収支およびCO_2排出量を評価した。クロレラ燃料化では乾燥工程のエネルギー負荷が非常に高く、エネルギー収支比は0.9と求められた。乾燥工程にDME脱水を適用することでEPRは2.0まで改善するが、他のバイオ燃料、さらには石炭調達に対する優位性は低く、さらなる改善が必要と考えられた。%Microalgae biomass are expected as the next generation energy resources taking the place of fossil fuel because they produce hydrocarbon fuel as by-products and their CO_2 absorption ability is higher than terrestrial plants. We evaluated the possibility of CO_2 recycling using Chlorella which is a representative of algae biomass with early growth by energy balance and CO_2 emission. The boundary condition of evaluation was defined as Chlorella cultivation, dewatering, and drying. A breakdown of the energy consumption indicated that the amount of energy consumption for the drying process is remarkably high. It accounted for 80% of the total energy consumption. The energy profit ratio (EPR), which is calculated as the ratio of output energy to consumed energy (output energy /input energy) was estimated to be 0.9, and it advanced to be 2.0 if drying technology using liquefied DME gas was introduced. On the other hand, the amount of energy production (calorific value conversion) per hectare of Chlorella achieved ten times higher than that of Jatropha, which is an inedible oilseed plant. Energy density of Chlorella is high and the productive efficiency per hectare is high. However, it was suggested that CO_2 absorption ability of Chlorella was extremely limited.