稻壳成型颗粒化学链气化过程中机械强度演化特性

Mechanical Strength Evolution Characteristics of Rice Husk Pellets During Chemical Looping Gasification

生物质成型颗粒相对较小的比表面积和较大的颗粒尺寸使其在化学链气化过程中的破碎行为直接影响挥发分脱出速率和碳转化率。为研究稻壳成型颗粒在化学链气化过程中的机械强度演化,建立能够控制气化时间的鼓泡流化床反应器,分别在不同气化温度、流化风量等条件下收集到15~180 s气化后的稻壳焦炭样品,对其表面形貌及机械强度进行了表征。结果表明:稻壳焦炭样品表面形貌呈现由孔隙到不规则裂痕的演化趋势,剧烈传热传质下,稻壳成型颗粒内外因挥发分快速释放形成巨大压力差,载氧体由裂痕向颗粒内部渗透,显著促进了颗粒结构的破坏;此外,减小成型颗粒质量,热量传递和挥发分脱出速率得到改善,但体表面积的减小限制了成型颗粒与床料的碰撞和磨损,机械强度相应提高。

Due to the relative large volume and small specific surface area,the crushing behavior of biomass pellets in the chemical looping gasification(CLG)process has a direct influence on the devolatilization rate and carbon conversion rate.To investigate the mechanical strength evolution of rice husk pellet during CLG process,a bubbling fluidized bed reactor of controlling the gasification time was established.The coke samples gasified for 15 to 180 s were collected under different conditions such as,gasification temperature or fluidization wind speed,subsequently,their morphology and mechanical strength of samples were characterized.The results show that:the surface morphology of coke samples shows the evolution from pores to irregular cracks,under intense heat and mass transfer,the rapid release of volatiles forms a huge pressure difference between inside and outside of the rice husk pellet.The oxygen carrier penetrates into the particles from the cracks,which significantly promotes the destruction of the pellet structure.Moreover,reducing the pellet size could increase the heat transfer and devolatilization rate,but the reduction in body surface area limits the collision and wear of the shaped particles with the bed materials,and the mechanical strength is correspondingly improved.