都市ごみ中の厨芥類および紙類の利用システムによる温室効果ガスの削減効果

Abstract

国内都市部の一例として京都市を対象に, 都市ごみ中のバイオマスである厨芥類および紙類の賦存量を推定した. 厨芥類の発生量は22.2万ton-wet/年, 紙類は22.3万ton-wet/年であり, ほぼ全量が焼却処理されている. これらを対象に利用システムの温室効果ガス (GHG) 削減効果およびエネルギー回収率を評価した結果, 「バイオガス化 (高温乾式メタン発酵)+ガスエンジン発電 (GE)」は既存の「直接燃焼+蒸気発電」, 「直接燃焼+堆肥化」よりも有利であった. また, バイオガス発電時の廃熱を利用する超高温可溶化技術を組み込んだ可溶化システムでは, 現状の乾式方式に対してエネルギー回収率およびGHG削減効果で27%の向上が見込まれた. さらに, バイオガスの燃料電池利用により, GE利用の最大1.7倍まで効果向上が期待された. 国内温室効果ガスの削減に向けて都市ごみ中バイオマスの高度なエネルギー変換技術の普及が望まれる.

Kyoto City was taken as an example of a domestic urban area in order to estimate the actual amount of food and paper biomass found in municipal solid waste. The annual amounts of food and paper waste were measured at 222 kt-wet and 223 kt-wet, respectively. At present, most of this is processed through incineration. After evaluation of the greenhouse gas (GHG) reduction effect and energy recovery ratio of the utilization system for this biomass, a biogasification (high-temperature and dry-type methane fermentation) system with gas engine (GE) power generation was found to be more beneficial than the existing system, which uses direct combustion with steam power generation and direct combustion with composting. In addition, biogasification with hydrolysis is expected to give a 27% improvement in GHG reduction effect and energy recovery ratio over the present system of combined biogasification with hyperthermal (80 ℃) hydrolysis technology operated by exhaust heat from a GE power plant. Futhermore, the use of biogas in fuel cells can reduce GHG emissions by up to 1.7 times compared to GE use. Diffusion of energy conversion technology with high efficiency is therefore being recommended for the reduction of GHG in Japan.