成果報告書詳細
管理番号20090000001109
タイトル*平成20年度中間年報 新エネルギー技術研究開発/バイオマスエネルギー等高効率転換技術開発(転換要素技術開発)/自己熱再生方式による革新的バイオマス乾燥技術の研究
公開日2009/12/5
報告書年度2008 - 2008
委託先名国立大学法人東京大学 三菱重工業株式会社
プロジェクト番号P07015
部署名新エネルギー技術開発部 バイオマスグループ
和文要約以下本編抜粋:1. 共同研究の内容及び成果等 1-1. 事業概要 カーボンニュートラルという特性を持つバイオマス資源のエネルギー利用は、化石資源由来のエネルギーの代替につながることから、地球温暖化防止に有効であるとともに、持続可能な循環型社会の形成に向けて重要な役割を担うものであり、その積極的な導入促進が強く期待されている。しかし、バイオマスは含水率が50%程度と高い為、(1)輸送効率が低く輸送費用が高い、(2)腐敗する為、数日でも保管が困難、(3)ガス化や直接燃焼での発熱量が低い、などのデメリットがある。そこで、バイオマスの発生地点で「オンサイト乾燥」を行えば、前述のデメリットは改善し、更に発生地点付近での分散型の保管も可能となる。そこで、本事業ではエタノール生産の事業化における重要な課題の一つとして、乾燥技術に着目する。このようなバイオマスの乾燥技術は、バイオエタノール生産に限らず、燃焼やガス化などの熱化学反応も含めて大変重要な技術である。
英文要約Title: Development of Innovative Energy-Efficient Biomass Drying Process based on Self-Heat recuperation Technology(FY2008-FY2009)FY2008 Annual Report Because biomass is one of the carbon neutral energy resources, its utilization has great potential to alleviate global environmental problems caused by the use of fossil fuels. However, biomass usually contains large amount of moisture, which results in extra fuel consumption for its transportation, decrease in thermal efficiency in combustion and gasification processes, and debasement during storage. Hence, it is necessary to develop the drying technology to establish efficient and dependable biomass utilization systems. In conventional drying technologies, only the sensible heat is usually used to elevate the temperature and the latent heat of water/steam is seldom recovered. Advanced utilization of the latent heat is desired to improve the overall thermal efficiency because the latent heat of water/steam is much larger than the sensible heat. In this project, we propose and develop a novel drying technology which is based on self-heat recuperation. In this technology, water in biomass is heated up to its boiling point and subsequently the evaporated steam is superheated. The superheated steam is compressed with a compressor to create a temperature difference required by the heat exchange step. The sensible heat of the compressed superheated steam is exchanged with that of evaporated steam. Then, the latent heat of the compressed steam is exchanged to evaporate steam from biomass. By applying this technology, not only the latent heat but also the sensible heat can be recuperated. In addition, the sensible heat of the dried biomass is also recovered by air and the obtained hot air is used as heat media to increase the overall thermal efficiency. In this work, we chose a fluidized bed type dryer because the heat transfer rate is large and the dryer is continuously stirred tank reactor which is considered to be effective for latent heat recuperation. Then, we calculated the mass and energy balance of the process using a commercial simulation software (PROII ver. 8.1, Invensys) under the following conditions; 1) carbon is used for biomass substitute, 2) flow rate of wet biomass (moisture content is 50wt% in wet basis) is 1000 kg/h (similar to commercial capacity), 3) dry biomass contains 20wt% of water (=75% of steam is evaporated), 4) minimum approach temperature for exchange in fluidized bed is 10 K and in other heat exchanger is 30 K, 5) air flow rate is 300 kg/h. The simulation results showed the net energy consumption of this process was 38.7 kW. Compared with the energy consumption in a conventional heater drying process with heat recovery (242.7 kW), it was found that the self-heat recuperation drying process could save greater amount of energy required to dry biomass. Based on the above results, a lab-scale fluidized bed was designed and fabricated. The dimension of the fluidized bed was 0.2 m×0.2 m square size and 1-2 m (adjustable) in height and its main body was made of stainless steel. Some inspection windows were located to observe the internal fluidization of particles. In this test dryer silica particles are fluidized by hot air blown from the bottom of the bed and the wet biomass sample is fed into the bed. The biomass sample is expected to be fluidized on the top of the fluidizing silica particles by utilizing segregation. The overflowing dry biomass can be collected and its moisture content is measured. The gas content in the effluent air and evaporated steam is also measured using a gas chromatograph. By using this fluidized bed, we are going to examine the following items next year; 1) fluidization property of the mixture of biomass and silica sand, 2) the relationship between residence time and moisture content of biomass, 3) biomass drying rate by heat exchange by utilizing heat tube (heat of condensation of superheated steam) and convection (hot air).
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