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首页> 外文期刊>Combustion and Flame >Measurement of the times for pyrolysis and the thermal diffusivity of a pyrolysing particle of wood and also of the resulting char
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Measurement of the times for pyrolysis and the thermal diffusivity of a pyrolysing particle of wood and also of the resulting char

机译：测量热解的次数和木材的热解体颗粒的热扩散率，也是由所得炭

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Cubes and spheres of spruce wood have been prepared, with a fine thermocouple inserted to measure the temperature at their centre. Individual particles were immersed rapidly in a bed of sand (mean size similar to 0.2 mm), which was fluidised by nitrogen and held at a fixed temperature up to 700 degrees C. The rising temperature measured at a particle's centre yielded the effective value of the particle's thermal diffusivity. The temperature response showed evidence of at least two endothermic decomposition reactions, which corresponded to the pyrolysis of fine particles of the wood in a thermogravimetric analyser (TGA). However, the wood undergoing thermal decomposition in a fluidised bed at 500 degrees C revealed at least one exothermic step at the very end of heating. After being heated this way in a hot bed fluidised by nitrogen, the particles of char formed by spruce wood had very much the same size and shape as the original piece of wood before being heated. These new particles of "char", formed whilst being heated in a hot fluidised bed, were cooled in a stream of nitrogen and returned to the fluidised bed for re-heating without any complications from pyrolysis. The rise in the char's central temperature with time gave an unambiguous value for the thermal diffusivity of the char. It is clear that volatile matter leaving a particle of wood reduced the rate of heat transfer between a hot fluidised bed and the centre of a devolatilising particle. Also, the time for complete pyrolysis was proportional to the square of the characteristic size (r(0)) of the spruce being heated. In addition, the time for pyrolysis was proportional to T-bed(3 +/- 1), so that for a cube of spruce t(pyr) = 2.9 + 0.3 x 10(15) r(0)(2)/T-bed(3), in seconds. Photographic evidence confirmed that devolatilisation of particles of spruce larger than approximate to 2 mm in a fluidised bed follows a shrinking core model and is accordingly controlled by internal heat transfer. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：已经准备好云杉木的立方体和球形，插入精细热电偶以测量其中心的温度。将个体颗粒迅速浸入砂床（平均尺寸类似于0.2mm），其通过氮气流体化，并在固定温度下保持高达700℃。在粒子中心测量的上升温度产生了有效值粒子的热扩散率。温度响应显示了至少两个吸热分解反应的证据，其对应于热量分析仪（TGA）中木材的细颗粒的热解。然而，在500摄氏度下在流化床中经历热分解的木材在加热的最终下显示至少一个放热步骤。在通过氮气流化的热床中被加热后，由云杉木形成的颗粒具有与在加热之前的原始木材的大小和形状非常相同。这些新的“焦炭”颗粒，在热流化床中加热的同时在氮气流中冷却，并返回流化床以再加热，而不会从热解中进行任何并发症。 Char的中央温度的上升随着时间的推移给出了炭的热扩散率的明确值。很明显，留下木材颗粒的挥发性物质降低了热流化床和脱挥发粒子的中心之间的传热速率。而且，完全热解的时间与被加热的云杉的特征尺寸（R（0））的正方形成比例。此外，热解的时间与T型床（3 +/-1）成比例，使云杉的立方体（Pyr）= 2.9 + 0.3×10（15）R（0）（2）/ t - （3），以秒为单位。摄影证据证实，在流化床中的云杉颗粒颗粒颗粒沿着收缩的核心模型，因此通过内部传热控制。 （c）2019燃烧研究所。由elsevier Inc.出版的所有权利保留。

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