木屑热解挥发物冷凝特性研究
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科技部农业科技成果转化资金项目(20150237)和广东省科技计划项目(20160221)


Condensation Characteristics of Volatile Matter from Sawdust Pyrolysis
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    摘要:

    在自行设计的生物质热解挥发物两级冷凝特性参数测试系统上,进行了木屑在450、550、650℃下热解挥发物冷凝特性研究,其中,一级冷凝采用空气作为冷凝介质,二级冷凝采用水作为冷凝介质,计算了表面局部冷凝换热系数,以及冷凝液膜热阻和厚度。结果表明:一级冷凝换热系数随着温度的升高而减小,在热解温度为450℃时达到最大值671.02W/(m2·K);二级换热系数随着温度的升高先增大后减小,在热解温度为550℃时达到最大值1.484×105W/(m2·K)。基于冷凝器内壁一维稳态冷凝换热特性,分析了冷凝液膜形成过程,存在3个阶段:液膜形成、液膜积累、液膜流动。在液膜形成和积累阶段,液膜厚度逐渐增大,热阻变大;液膜厚度达到一定程度后,冷凝液产生流动,在液膜流动初期,液膜厚度逐渐减小,热阻变小;在稳定流动期,热阻基本保持稳定。

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    Pyrolysis is a relatively simple, inexpensive, and robust thermochemical technology for transforming biomass into bio-oil, biochar and syngas. While the intention of slow pyrolysis is to produce mainly charcoal, fast pyrolysis is meant to convert biomass to a maximum quantity of liquids (bio-oil). Biochar can be used with existing infrastructure as a replacement for pulverized coal, bio-oil can be used as a fuel in existing industrial boilers. The pyrolysis of sawdust contains volatile bio-oil and non-condensing gas, so the condensation characteristics are different from those of other simple mixture. Based on the test system of biomass pyrolysis volatile matter condensation characteristic parameter, the experiment of condensation characteristics of pyrolysis volatile was carried out at 450℃, 550℃ and 650℃. The condensation characteristics of volatile matter produced at different pyrolysis temperatures were tested, and the heat transfer coefficient, the thermal resistance and thickness of condensation liquid film were calculated. Based on the one-dimensional heat transfer characteristics of liquid condensation, the condensate film formation process had three stages: formation, accumulation and flow of liquid film. The results showed that the first stage condensation heat transfer coefficient was decreased with the increase of temperature, biomass volatile surface heat transfer coefficient at 450℃ was the highest,which was 671.02W/(m2·K);with the increase of temperature, the heat transfer coefficient of the second stage was increased first and then decreased, biomass volatile surface heat transfer coefficient at 550℃ was the highest, which was 1.484×105W/(m2·K). According to the experimental value and the hypothesis of condensate film, in the film formation and accumulation stage, the film thickness was gradually increased and the thermal resistance was decreased;early in the liquid film flow stage, with the decrease of the film thickness, the thermal resistance was decreased;in the steady flow stage, resistance was remained stable. The research result can provide reference for the on-line collection of bio-oil and the design of bio-oil condenser in continuous pyrolysis equipment.

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王明峰,陈志文,蒋恩臣,任永志,韩平,孙焱.木屑热解挥发物冷凝特性研究[J].农业机械学报,2017,48(4):271-275,223.

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  • 收稿日期:2016-07-28
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  • 在线发布日期: 2017-04-10
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