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循环流化床下料立管内气固两相流动状态与压力脉动的关系 总被引:2,自引:0,他引:2
在15 m高的大型气固循环流化床上对内径90和42 mm的下料立管内气固两相流的动态压力进行了测量. 实验结果表明,负压差下料立管内的气固两相流动存在着低频压力脉动,压力脉动的强度可以用动态压力的标准方差(Standard deviation, Sd)来表征,且与立管下料的流动状态密切相关. 立管下料的流动状态依据颗粒质量流量通量的大小有浓相输送状态和稀密两相共存两种状态. 浓相输送状态的压力脉动强度较大,是下行颗粒压缩其夹带气体引起气固两相强烈相互作用导致的;稀密两相共存状态的压力脉动强度较小,是密相段排料的不稳定性和稀相段较弱的气固相互作用共同引起的. 立管下料的压力脉动强度随颗粒质量流量通量的增加而增大,对于浓相输送状态,在实验操作范围内[Gs'=550~850 kg/(m2×s)],压力脉动的强度与立管下料质量流量通量近似成Sd=0.00875Gs'-4.77的线性关系. 相似文献
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负压差立管内的气固两相流 总被引:8,自引:3,他引:5
在φ800 mm×12000 mm流化床实验装置上对150 mm×11500 mm负压差立管内气固两相流的轴向压力、空隙率和气体流动特性进行了测量和分析.立管出口无约束淹没在密相流化床内,颗粒质量流率范围Gs<1200 kg8226;m-28226;s-1.立管内气固两相流态有两种存在形式,当颗粒质量流率Gs<200~250 kg8226;m-28226;s-1时,流态是稀密两相共存形式;当Gs>200~250 kg8226;m-28226;s-1时,流态是浓相输送流态.两种流态之间可以相互转换,主要取决于颗粒质量流率的变化.影响立管内气固两相流的轴向压力、空隙率分布、气相的流动特性和气固流态存在形式的主要参数是颗粒质量流率Gs、旋风分离器入口速度Vi、下端流化床流化速度uf,质量流率Gs是主要的影响因素. 相似文献
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在大型循环流化床装置上,通过改变负压差立管上的插板阀的开度,测定不同颗粒质量流率条件下插板阀上下的流态和脉动压力,以此分析插板阀对下料过程颗粒质量流率的调控机制。实验结果表明,对于立管的下料过程插板阀的开度存在一个临界开度,将插板阀的开度范围划分为非可控制区和可控制区。当插板阀的开度大于临界开度时,处于非可控制区,不能进行颗粒质量流率的调节,此时插板阀上下的流态一致,脉动压力曲线相似;当插板阀的开度小于临界开度时,处于可控制区,可以进行颗粒质量流率的调节,此时插板阀上的流态是移动床,阀下的流态是雨状下落流,上下的脉动压力曲线不同。 相似文献
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在无负压差的环境下,采用PV6D型颗粒速度测量仪,考察了垂直立管中FCC催化剂颗粒移动床的蠕动流动特性. 结果表明,颗粒质量流率较小时立管中颗粒流动具有明显的蠕动流动特性,可划分为两种流态,拟气固雷诺数Re<500时为间歇式蠕动流动,5004000时颗粒的蠕动流动转变为密相流化流动. 立管中颗粒的蠕动流动主要是出口区颗粒成拱与崩塌交替进行产生的,其次为颗粒与器壁滑动摩擦力的不稳定性变化起作用. 微观上颗粒流动的蠕动行为是颗粒之间力链作用变化的结果. 相似文献
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《过程工程学报》2017,(1)
测量了环流预汽提与带隔流筒的旋流快分系统(SVQS)相耦合的大型冷模实验装置的动态压力特性.结果表明,旋流快分系统轴向压力脉动曲线具有很强的相似性,脉动强度随旋流头喷出口气速、颗粒质量流率增大而增大,压力脉动标准偏差与喷出气速、颗粒质量流率存在对应关系.由实验结果关联获得的脉动标准偏差与喷出气速、颗粒质量流率经验公式,可用于预测特定工况下工业装置的颗粒质量流率.通过小波分析,装置主频范围为1.5~12.5 Hz,周期约为7~10 s,旋流快分头上部空间的压力脉动较大,存在不稳定的漩涡区,发现周向脉动基本一致,径向在r/R=0.4~0.7时漩涡区的压力脉动强度较低.为了使装置能稳定运行,建议快分头的喷出气速为18~24 m/s,颗粒质量流率在超过90 kg/(m2?s)范围内. 相似文献
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Experiments consisting of dense‐phase pneumatic conveying of pulverized coal using nitrogen were carried out in an experimental test facility, with a conveying pressure of up to 4 MPa. The influences of the conveying differential pressure, the coal moisture content, the gas volume flow rate and the superficial velocity, on the solid‐gas ratios, were investigated. The Shannon entropy analysis of the pressure fluctuation time series was developed to reveal the flow characteristics. By investigation of the distribution of the Shannon entropy at different conditions, the flow stability and the evolutional tendency of Shannon entropy, in different regimes and regime transition processes, were revealed, and the relationship between Shannon entropy and the flow regime was also established. The results indicate that the solid‐gas ratio and the Shannon entropy rise with increases in conveying differential pressure. The solid‐gas ratio and the Shannon entropy reveal preferable correlation with the superficial gas velocity. Shannon entropy is different for different flow regimes, and can be used to identify the flow regimes. Both the mass flow rate and the Shannon entropy, decrease with increases in moisture content. Shannon entropy analysis is a feasible approach to researching the characteristics of the flow regime, the flow stability and the flow regime transitions in dense‐phase pneumatic conveying systems, at high pressure. 相似文献
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Solid concentration and particle velocity distributions in the transition section of a?200 mm turbulent fluidized bed (TFB) and a?200 mm annulus turbulent fluidized bed (A-TFB) with a?50 mm central standpipe were mea-sured using a PV6D optical probe. It is concluded that in turbulent regime, the axial distribution of solid concen-tration in A-TFB was similar to that in TFB, but the former had a shorter transition section. The axial solid concentration distribution, probability density, and power spectral distributions revealed that the standpipe hin-dered the turbulence of gas–solid two-phase flow at a low superficial gas velocity. Consequently, the bottom flow of A-TFB approached the bubbling fluidization pattern. By contrast, the standpipe facilitated the turbulence at a high superficial gas velocity, thus making the bottom flow of A-TFB approach the fast fluidization pattern. Both the particle velocity and solid concentration distribution presented a unimodal distribution in A-TFB and TFB. However, the standpipe at a high gas velocity and in the transition or dilute phase section significantly affected the radial distribution of flow parameters, presenting a bimodal distribution with particle concentration higher near the internal and external wal s and in downward flow. Conversely, particle concentration in the middle an-nulus area was lower, and particles flowed upward. This result indicated that the standpipe destroyed the core-annular structure of TFB in the transition and dilute phase sections at a high gas velocity and also improved the particle distribution of TFB. In conclusion, the standpipe improved the fluidization quality and flow homogeneity at high gas velocity and in the transition or dilute phase section, but caused opposite phenomena at low gas ve-locity and in the dense-phase section. 相似文献
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The transition between dense and dilute flow in vertical conveying of Geldart D particles were investigated for risers of different diameters using a spouted bed as a solid feeding system. The transition and choking velocities were identified by combining analyses of pressure gradient versus air velocity diagrams, pressure fluctuation signals and voidage values. Experimental data were used to evaluate the effect of particle and riser diameters on the pressure gradient, mean mixture voidage, the regime transition and choking velocities. The transition velocity from dilute to dense phase could be identified, as well as the onset of the choking condition, which appeared as the air velocity was further reduced. Data obtained in the same experimental apparatus facility using a screw conveyor and a gravitational system as solid feeding devices have been used as a reference to be compared to those obtained using the spouted bed feeder. 相似文献