報告書番号

V10025

タイトル（和文）

木質バイオマスのエネルギー利用における貯蔵・輸送行程での温室効果ｶﾞｽ排出量の再評価

タイトル（英文）

A re-evaluation of GHG emission from cellulosic biomasses during the storage/transport

概要 （図表や脚注は「報告書全文」に掲載しております）

バイオマスの石炭混焼による二酸化炭素排出量の削減効果を推測するためには、ＬＣＡを行うことが重要である。しかし、バイオマス貯蔵・輸送行程でのＧＨＧ発生についてはよく知られて居らず、ＬＣＡにも一部しか組み込まれていない。一方、バイオマスは微生物分解などによって損耗するとともに、条件によってはより温室効果の高いＧＨＧを多量に排出し、ＬＣＡに影響する可能性がある。そこで、バイオマスの貯蔵・輸送行程でのＧＨＧ発生について文献調査を行い、ＬＣＡに利用できるようにその可能性を試算・評価した｡その結果、貯蔵・輸送行程で発生するＧＨＧや量的損耗をＬＣＡ算出に考慮する必要があること、考慮してもなお石炭代替燃料としての利用が温室効果低減に有効であることが示された。しかし、その効果は貯蔵・輸送の形態・期間に大きく左右され、従来の試算とは相当程度異なる場合もあるため、個々のケース毎に判定を行う必要があると考えられた。

概要 （英文）

Biomasses are expected to be a renewable energy source to solve the problem of Greenhouse effective gas (GHG) emission by fossil fuel consumption. Biomass co-firing in a coal-combusting power plant is one good practice of the utilization, and the practice has been popularized in a couple of years. Then, life cycle assessment (LCA) is adopted to estimate the efficiency in the GHG cut-down than a case of coal-combusting power generation. However, GHG emission from cellulosic biomasses, especially during the storage/transport steps, is not well known, and only an effect of the direct energy consumption and related materials procuration is included in LCA for the steps. On the other hand, cellulosic biomasses can be degraded by a microbial activity and/or chemical oxidation. It could generate CH4 and N2O, which bearing much higher greenhouse effect than CO2. This may lead imprecise judgment of LCA.
Here, we conducted literature search-based investigation for GHG emission from cellulosic biomasses during the storage/transport steps and reevaluated the possible effect on LCA. Because no direct data showing GHG emission during these steps, some related observations, such as GHG emission from composting, landfilling, and accident of organic gaseous emission in cargo ship, were extrapolated to give a calculation basis for GHG emission in these steps. The estimation using the calculation basis clearly showed a potential that cellulosic biomasses arise a considerable level of CH4 emission during the storage/transport steps. Thus, the emission could induce at most 8% reduction in the co-firing effect on the GHG cut-down even though the co-firing effect could be still remained. Such reduction in the co-firing effect could be an attribute of the storage/transport condition, such as the humidity of materials, atmospheric oxide concentration, and temperature. Also, it could be dependent on the duration of the storage/transport. Hereafter, an observation-based accurate GHG emission data for these steps is necessary to determine LCA by case by case.

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