喷嘴对液固外循环流化床内颗粒循环特性的影响

液固外循环流化床换热器可以用来蒸发浓缩单基药提取硝化棉的提取液.设计了实现液固外循环流化床内颗粒正常循环的关键部件喷嘴,构建了以喷嘴作颗粒循环装置的液固外循环流化床换热器,研究了喷嘴的结构参数及操作参数对起始循环流体流量、全床压降、负压和最大颗粒循环流量等的影响.结果表明,喷嘴的口径比及安装位置对提高颗粒循环效果均存在一个最佳值,为外循环流化床换热器的设计计算提供了依据.     

液固外循环流化床起始外循环液体流量的实验研究

为外循环流化床换热器的设计计算提供依据,以喷嘴为颗粒循环装置的液固外循环流化床换热器为研究对象,考察了颗粒直径、口径比、喷嘴安装位置、颗粒初始加入量及流体粘度对起始外循环液体流量的影响;得出了稳定操作情况下,液固外循环流化床换热器起始外循环液体流量与上述因素之间的经验关联式.结果表明:计算值与实验值吻合较好.     

液固外循环流化床换热器主压降的实验研究

以喷嘴为颗粒循环装置的液固外循环流化床换热器为研究对象,考察颗粒直径、口径比、喷嘴安装位置、颗粒初始加入量及流体黏度对主压降的影响,得出了稳定操作情况下,液固外循环流化床换热器主压降与上述因素之间的经验关联式,计算值与实验值吻合较好,为外循环流化床换热器的设计计算提供依据。     

循环流化床锅炉一体化外置式换热器

大型循环流化床锅炉广泛采用各种形式的外置式换热器。传统的换热器只能实现换热器（EHE）和返料机构（loop seal）之间的物料流量的调节,此时进入EHE的物料将会全部顺次流过各个换热仓室,很难对外置床中的各种受热面的传热量进行单独调节。本文首次提出了一种全新的非机械阀式外置式换热器布置方式,通过控制流入各个换热仓室的固体物料流量,从而达到对各换热仓室中布置的受热面的换热情况进行单独调节。同时把EHE和loop seal结合在一起,保证向炉膛的返料。文中对这种一体化外置式换热器及其返料机构中的物料流动特性进行了冷态试验研究。试验结果表明,这种外置式换热器有很好的物料分流和流量控制特性。可以通过调节运行参数和结构参数来控制两个换热室、EHE和loop seal以及两个返料口之间的物料流量和比例。同时还得到了物料在换热室的流动特性。通过对可见输送分离高度的测量,提出了分配室和换热室相对隔板高度的设计方法。     

液固循环流化床换热器中固体颗粒分布

利用CCD图像测量与数据处理系统对多管液固循环流化床换热器中的两相流动特性进行了研究。探讨了下管箱中的分布板结构对固体粒子的体积分数分布、固体粒子的速度分布,以及液固两相流压降的影响。实验结果表明:在循环流化床换热器进口段安装适当结构的多孔板分布器,即多孔板的面积小于床层截面积,且床中心处的遮挡面积大于边缘处的遮挡面积,可以有效地提高固相速度的均匀程度,在较高流速下,能较好地改善固体颗粒在管束中的不均匀分布。     

循环流化床中颗粒振荡循环现象的实验研究

颗粒的循环特性是循环流化床研究的重点及热点之一,在建立颗粒循环时,颗粒循环由非稳态向稳态过渡。本文在循环流化床实验装置中,采用摄像法和压力检测法研究了不稳定颗粒循环条件下颗粒流动结构和各段压降的变化情况。首次发现了不稳定颗粒循环状态下的颗粒振荡循环现象及其具有的两个特征:下降段、提升段气固流动结构呈周期性变化;下降段压降p_d和提升段压降p_r周期性波动且p_d>p_r和p_dr交替出现。进一步对颗粒振荡循环过程进行受力分析,建立了颗粒振荡周期的计算公式。研究还发现在颗粒藏量一定的条件下,循环气流量或颗粒循环段阀门开度大于某一临界值时才能诱发颗粒振荡循环;颗粒振荡循环周期随着循环气流量的增大而增大,与阀门开度无关。研究结果为动态颗粒循环建立过程的研究奠定了基础,有助于快速地建立颗粒的稳定循环。     

循环流化床内颗粒运动的预测与测量

本文提出了一种二维气固流动的数值计算模型，它考虑了循环流化床中颗粒的脉动和颗粒间磁撞等因素。该模型将颗粒运动的脉动考虑成一种基于气流脉动频谱的随机Fourier级数，称为脉动频谱随机轨道模型（FSRT）。这一模型可用于预测循环床中颗粒相的速度、颗粒轨迹和颗粒相浓度。对循环床中颗粒相速度和浓度进行了测量，并与FSRT模型的计算结果进行对比，同时对循环床中颗粒运动的一些行为也进行了预测。     

大型循环流化床锅炉外置式换热器关键技术研究

外置式换热器对于大型循环流化床锅炉的高效运行有重要意义。为全面掌握CFB锅炉外置式换热器运行特性,消除现阶段制约超超临界CFB锅炉外置式换热器管屏壁温偏差问题,系统总结了外置式换热器的研究现状和关键技术研究进展,并介绍了超超临界循环流化床锅炉外置式换热器的设计方案。研究发现,600 MW超临界CFB锅炉外置式换热器壁温偏差十分明显,壁温分布呈现马鞍形分布(中心区域管屏壁温高,边壁区域管屏壁温低),这是由气泡不均匀性分布决定。外置式换热器内传热系数与受热面布置的空间位置密切相关,外置式换热器流化风速Ug=0.4 m/s时,床中央至x/Xw≈0.6处传热系数基本一致,而靠近壁面区域,传热系数显著降低,边壁流动区占床面宽度的25%～30%。将管束远离边壁区布置可以改善传热系数空间分布的不均匀性,传热系数极值偏差从15%降至6%。660 MW超超临界CFB锅炉外置式换热器的设计计算表明,外置式换热器布置高温再热器受热面时,高温再热器管子中径壁温与汽温差可达到58℃,显著制约外置式换热器的安全运行。因此,在660 MW超超临界CFB锅炉的外置式换热器中全部布置汽温相对较低的中温过热器,受热面采用TP347H和TP347HFG材料即可满足要求,仍可保证一定的余量。将外置式换热器管排布置选择与灰流动的方向平行的方式,同时为消除边壁流造成的局部换热不均问题,设计时考虑避免管屏布置在边壁区内,管屏距离边壁的距离应由传统设计的250 mm增至500 mm以上,可改善外置式换热器内的气固流动及传热行为,以减小颗粒侧传热偏差。该设计在保证外置式换热器安全运行的同时,还可有效调控炉膛温度和蒸汽温度。     

循环流化床内固体颗粒对受热面的磨损及降磨措施

<正> 一、概述循环流化床锅炉中,固体颗粒对受热面的磨损是一个十分重要的问题。目前国外投运的循环流化床锅炉,由于设计不合理,有些锅炉产生了非常严重的磨损,大大降低了锅炉的运行安全性。因为在高循环倍率的循环流化床锅炉中,特别是在其固体颗粒循环回路中,固体颗粒浓度很高,如果不采取措施,会带来严重的磨损。在对循环流化床锅炉进行研究开发的同时,我们也对循环流化床内的受热面磨损以及防磨措施进行了研究。本文报告的是这方面的部分研究结果。     

高颗粒通量循环流化床的构型作用

In order to achieve high solids circulation rate (G_s),an idea of coupling a moving bed to the bottom section of the riser of a circulating fluidized bed (CFB) was proposed and tested.The results from the preliminary study demonstrated that the solids circulation rate in the new-structure bed approached 370 kg·m^-2·s^-1 at superficial gas velocities around 10.5 m·s^-1 for sand particles with an average Sauter mean size of 378 μm.This study was devoted to further justifying the effects of the coupled moving bed by performing comparative studies in two CFBs with conventional configurations.It was shown that the pressure at the riser bottom and the realized solid circulation rate were only about 15 kPa and 230 kg·m^-2·s^-1 in the two conventionally configured CFBs,obviously lower than 25 kPa and 370 kg·m^-2·s^-1 in the moving bed coupled CFB.These verified that the coupled moving bed increased the force driving particles form the particle recycling side into the riser.The study further tested the effect of a few specially designed riser exit configurations,revealing that a smooth riser exit could facilitate solids circulation to increase the solids circulation rate.     

Experimental study of high-density gas-solids flow in a new coupled circulating fluidized bed

Experiments were carried out in a specially designed high-density coupled circulating fluidized bed system. Fluidized catalytic cracking (FCC) particles (ρ_p=1300 kg/m³, d_p=69 μm) were used. When the solids circulation flux is 400 kg/m²·s, the apparent solids holdup exceeds 20% near the top of the riser A, and the volumetric solids fraction (apparent solids holdup) is larger than 5.2% in the fully developed region of the downer. Hence, a high particle suspension density covers the entire coupled CFB system. Under the high-density conditions, the primary air rate had a small influence on the solids circulation flux, while the secondary air rate had an important effect on it. The results indicate a particle acceleration region and a fully developed region were identified along the downer from the pressure gradient profiles. In the fully developed region of the downer, the volumetric solids fraction increases with increasing solids circulation flux or decreasing superficial gas velocity U₁.     

Estimate of solid flow rate from pressure measurement in circulating fluidized bed

A method is described to estimate solid mass flow rate based on measurement of pressure drop in horizontal section of circulating fluid bed (CFB). A theoretical model was derived based on momentum balance equation and used to predict the solids flow rate. Several approaches for formulating such models are compared and contrasted. A correlation was developed that predicts the solids flow rate as a function of pressure drop measured in the horizontal section of piping leading from the top of the riser to the cyclone, often referred to as the cross-over. Model validation data was taken from literature data and from steady state, cold flow, CFB tests results of five granular materials with various sizes and densities in which the riser was operated in core-annular and dilute flow regimes. Experimental data were taken from a 0.20 m ID cross-over piping and compared to literature data generated in a 0.10 m ID cross-over pipe. The solids mass flow rate data were taken from statistically designed experiments over a wide range of Froude number , load ratio , Euler number , density ratio , Reynolds number , and Archimedes number . Several correlations were developed and tested to predict the solids mass flux based on measuring pressure drop in the horizontal section of CFB. It was found that load ratio is a linear function of the Euler number and that each of these expressions all worked quite well (R² > 95%) for the data within the range of conditions from which the coefficients were estimated.     

Experimental study of the effect of internals on optimizing gas-solid flow in a circulating fluidized bed

The solids concentration in a circulating fluidized bed of flue gas desulfurization (CFB-FGD) is low, and the gas-solid mixing needs to be strengthened to improve the reaction efficiency. The addition of internals in a square CFB-FGD is studied here. Different sizes of wedge-shaped internals were set in the middle of the riser on opposite sides of the bed, at same height or at different heights. By comparing the concentration distributions, we found that positioning the internals at different heights is more effective in increasing the density of the center region. By observing the radial distribution of the fractal dimension, we found that a strong degree of turbulence can improve the gas-solid mixing. A larger upper/smaller lower arrangement of the internals with a moderate apparent gas velocity provided the best flow field, with increased concentration gradients and improved gas-solid mixing.     

气液固循环流化床颗粒分布板实验研究

设计了用于气液固三相循环流化床换热器的固体颗粒分布板。采用功能强大的CCD图像采集分析系统,获得颗粒的分布和运动规律,考察了安装高度、运行参数等对分布板颗粒分布性能的影响。研究表明,分布板的安装高度、液体和气体流量、颗粒体积分数等对颗粒的速度和固含率分布有较大影响,得到了使固体颗粒在管束中分布效果较好的设计参数,以指导工程应用。     

水平液固循环流化床颗粒分布状况的实验研究

为使水平液固循环流化床换热器更好地强化传热和防垢、除垢,管中颗粒的分布是关键,因此对卧式换热器前管箱进行改造,采用双进料口并在前管箱加入挡板,使得颗粒在管路中分布均匀。在实验中自行设计了一套水平多管液固循环流化床实验装置。采用CCD图像采集系统,获得了颗粒的运动及分布状况。研究表明:挡板的角度、颗粒密度等对颗粒分布性能都有较大影响。通过对实验结果的分析,得到了使固体颗粒在管束中分布效果较好的挡板角度以及较适宜颗粒分布的运行参数,以指导工程放大应用。     

Improvement of continuous solid circulation rate measurement in a cold flow circulating fluidized bed

A method is described to independently estimate the solids velocity and voidage in the moving bed portion of the NETL circulating fluidized bed (CFB). These quantities are used by a device that continuously measures the solids circulation rate. The device is based on the use of a rotating Spiral vane installed in the standpipe of a circulating fluid bed (CFB). Correlations were developed from transient experiments and steady state mass balance data to correct the solids velocity and solids fraction in the standpipe as a function of standpipe aeration rate. A set of statistically-designed experiments was used to establish the need for these corrections and to verify the accuracy of solid circulation rate measurements after correction. The differences between the original and corrected measurements were quantitatively compared.