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隔板式生物质内循环流化床的流动特性研究
其他题名Experimental Study on Particle Flow Characteristics in a Claboard-type Internal Circulating Fluidized Bed Reactor
黄立成
导师马隆龙
2007-06-08
学位授予单位中国科学院广州能源研究所
学位授予地点广州能源研究所
学位名称硕士
关键词内循环流化床 流动特性 生物质气化
摘要针对循环流化床(指外循环流化床)生物质气化炉燃气带出气化炉的飞灰含炭量较高,生物质炭在炉内停留时间较短,以及循环流化床结构复杂,被分离的飞灰难以正常循环,炭回流难以控制等问题,研究了一种隔板式生物质内循环流化床气化炉。在流化床中垂直设一隔板,将流化床分为高速区和低速区。隔板两侧的流化速度应控制高速区流化速度大,低速区流化速度小。物料在炉内实现绕隔板的内循环流动。低速区主要为生物质气化区,高速区主要为生物质气化后的焦炭燃烧区。 采用稻壳、石英砂和木粉三种原料,在隔板式内循环流化床气化炉冷态实验装置上对颗粒内循环流动特性进行了研究,考察了高速区和低速区的流化速度、床结构尺寸和侧风量大小等因素对颗粒内循环流动的影响。本文还研究了稻壳与石英砂的混合物料以及木粉与石英砂的混合物料分别在隔板式生物质内循环流化床中的混合现象和内循环流动特性。 通过对纯生物质颗粒和石英砂颗粒的冷态实验研究发现:(1)由于稻壳和木粉密度小,不易形成良好流化,在内循环流化床低速区很容易形成沟流和节涌现象,使流化恶化。要想在内循环流化床中形成良好稳定的内循环,操作气速必须满足如下条件:以稻壳为床料时,要求uL/umf>1.4,uH/umf>1.7;以石英砂为床料时,要求uL/umf>1.0,uH/umf>1.9;以木粉为床料时,要求uL/umf>1.2,uH/umf>2.1。(2)两床风速对颗粒循环量有较大的影响。在固定其他条件不变时,增大高速区风速,颗粒循环量和孔口压差随着高速区流化速度的增大先增大后减小,存在一个最大值。最大值范围出现在:以稻壳为床料时,要求uL/umf>1.4,uH/umf=2.2~2.4;以石英砂为床料时,要求uL/umf>1.0,uH/umf=3.5~4.5;以木粉为床料时,要求uL/umf>1.2,uH/umf=3.0~4.0。(3)隔板高度和孔口高度也是影响颗粒循环量的重要因素。当隔板高度逐渐增大时,颗粒循环量先增大后减小,隔板高度在初始床层高度附近时,颗粒循环量达到最大值。颗粒循环量随着孔口高度增加而增加,但增大趋势慢慢变缓。提出了合理的结构尺寸要求:孔口高度h在0.12~0.2Hmf之间;隔板高度L在0.9~1.2Hmf之间。(4)侧风的加入能明显改善低速区物料流动性。颗粒循环量随侧风量的增大而增大,当侧风量增大到一定值时,继续增大侧风量,颗粒循环量增大变缓。(5)通过实验数据回归分别得到采用石英砂、稻壳和木粉三种床料时的颗粒循环量关联式,计算值与实验值误差分别小于6%、14%和46%。石英砂属于流化性质较好的B类颗粒,稻壳属于平均粒径大的D类颗粒,经验公式计算结果误差较小。而木粉则属于密度小且平均颗粒粒径小的颗粒,可见对于木粉,需要采用其他更合适的经验公式进行计算。 通过对稻壳与石英砂的混合物料以及木粉与石英砂的混合物料分别在隔板式生物质内循环流化床中的混合现象和内循环流动特性的研究发现:(1)由于石英砂的包裹与覆盖,生物质颗粒与石英砂的混合物在隔板式内循环流化床中可以形成良好的混合和稳定的内循环。对于石英砂和稻壳的混合物,当uL/umf>1.2,uH/umf>2.0时,就可以形成良好的混合和稳定的混合物料内循环;对于石英砂和木粉的混合物容易形成分层现象,当uL/umf>1.3,uH/umf>1.8时,就可以形成良好的物料混合和稳定的混合物料内循环流动。(2)两种混合物料颗粒循环量和孔口处低速区与高速区压差随高速区风速增大的变化趋势相同,都是先增大后趋于不变。石英砂的加入能增大操作速度范围,使物料的流动阻力比纯生物质的流动阻力小且稳定,改善生物质颗粒在隔板式内循环流化床中的颗粒内循环特性。
其他摘要The fluidized bed, as an efficient and high production capacity reactor, has desirable characteristics on biomass gasification. However, some factors lead to its low gasification efficiency, including: the fly ash from the circulating fluidized bed gasifier containe too much carbon; the residence time of biomass carbon in the furnace is relatively short and it is difficult to make the ash circulating. A new Clapboard-type Internal Circulating Fluidized Bed (ICFB) was designed to solve these problems. The fluidized bed was divided into fast bed and slow bed by a clapboard set vertically. The internal circulating fluidization of particles around the clapboard was realized. The slow bed was mainly gasification area, and the fast bed is mainly chark combustion area. A cold-state test was performed on a small-scale clapboard-type internal circulating fluidized bed gasifier for three kinds of bed materials, namely rice husk, quartz sand and sawdust. The effects of gas velocities, structural parameters and the amount of side air on the solid circulation rate were investigated. Besides, the mixed characteristics and internal circulating fluidization characteristics for mixture of rice husk、quartz sand and mixture of sawdust、quartz sand were studied in the clapboard-type internal circulating fluidized bed. The fluidization hydrodynamics of pure biomass particles and quartz sand was investigated, the experimental results showed: (1) because of the low density of rice husk and sawdust, it was hard to form good fluidization, channel and slugging could be observed in the slow bed, which made the fluidization worse. The operation gas velocity to obtain stable and fine internal circulation in the fluidized bed must satisfy conditions as follows: for rice husk, uL/umf>1.4,uH/umf>1.7;for quartz sand, uL/umf>1.0,uH/umf>1.9;for sawdust, uL/umf>1.2,uH/umf>2.1. (2) The solid circulation rate would be dramatically influenced by the gas velocities of two beds. When other conditions were kept constant, with the increasing of gas velocities of fast bed, the solid circulation rate and the pressure drops across the orifice increased first and then decreased, and there exited a maximum value which emerge at:for rice husk, uL/umf>1.4,uH/umf=2.2~2.4;for quartz sand, uL/umf>1.0,uH/umf=3.5~4.5;for sawdust, uL/umf>1.2,uH/umf=3.0~4.0. (3) The height of clapboard and the size of orifice also had great influence on the solid circulation rate. The circulation rate of solids first increased then decreased with increasing height of clapboard. The clapboard height should be nearly equal to the initial static bed height to obtain high solid circulation rate. The circulation rate of solids increased sharply first and then slowly with increasing the orifice height. The reasonable operation and design parameters were put forward to obtain high solid circulation rate: the height of orifice was between 0.12~0.2Hmf;the height of clapboard was between 0.9~1.2Hmf. (4) The side air could effectively improve the fluidization quality in slow bed. The solid circulation rate of solids increased sharply first and then slowly with increasing the amount of side air. (5) The correlation formulas to calculate the particle flow rate through the orifice for quartz sand、rice husk and sawdust were set up. The relative error between calculation results and experimental data were less than 6%、14% and 46% for quartz sand、rice husk and sawdust respectively. Quartz sand belongs to type-B particles which have desirable fluidization characteristics, and rice husk belongs to type-D particls, for these particles the empirical equation has showed good prediction ability. But for sawdust which is particle with low density and small average diameter, other more suitable empirical equation is required to achieve good prediction. Finally, the mixed characteristics and internal circulating fluidization characteristics for mixture of rice husk、quartz sand and mixture of sawdust、quartz sand were studied in the clapboard-type internal circulating fluidized bed. The results showed: (1) Due to the wrapping and covering of quartz sand, the mixture of biomass particle and quartz sand could form uniform mixing and stable internal circulating flow in the clapboard-type internal circulating fluidized bed. The operation gas velocity to obtain stable and fine internal circulation in the fluidized bed must satisfy conditions as follows: for the mixture of rice husk and quartz sand, uL/umf>1.2, uH/umf>2.0; for the mixture of sawdust and quartz sand, uL/umf>1.3, uH/umf>1.8. (2) The solid circulation rates of the two mixtures increased first then kept constant with increasing gas velocity of fast bed, which is similar to the trend of pressure drop across orifice. The addition of quartz sand could expand the operating specification of high solid circulation rate, and improve the internal circulating fluidization characteristics. The flow resisting force of the mixture is smaller and more stable than that of pure biomass particles.
页数71
语种中文
文献类型学位论文
条目标识符http://ir.giec.ac.cn/handle/344007/4019
专题中国科学院广州能源研究所
推荐引用方式
GB/T 7714
黄立成. 隔板式生物质内循环流化床的流动特性研究[D]. 广州能源研究所. 中国科学院广州能源研究所,2007.
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