共查询到19条相似文献,搜索用时 78 毫秒
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汽液固三相循环流化床蒸发器已应用到盐化、烧碱、中药和造纸等工业中,表现出良好的防除垢性能。文中研究了这种新型流化床蒸发器的防、除垢机理。首先揭示出汽液固三相流剪应力对延长污垢的诱导期起主要作用,并对汽液固三相流剪应力和三相流剪应力增长率进行了定量计算,分析其影响因素。其次从污垢附着和剥蚀的角度,考察了固体颗粒的除垢作用。根据理论分析指出三相流剪应力对污垢附着需要的时间和污垢剥蚀比率的影响,从而计算了剥蚀比例和剥蚀速率及其影响因素。 相似文献
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In order to achieve high solids circulation rate (Gs),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. 相似文献
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0 前 言循环流化床锅炉 (后称 CFB锅炉 )与常规煤粉炉相比 ,汽水一侧的控制基本相同 ,但床温及床压的控制不同。CFB锅炉的炉膛类似于一个低温的化学反应器 ,一般将密相区物料温度控制在 850~ 90 0℃ ,这是最佳脱硫、脱硝温度 ,床温过低使锅炉燃烧效率下降 ,床温过高则会造成 NOx 及 SOx 排放增多 ,污染环境 ,甚至造成床料结焦 ,影响设备安全运行。1 床温影响因素1 .1 设计因素炉膛传热计算方法不准确 ,没有考虑宽筛分床料的特性 ,导致计算偏差大 ,炉内受热面配置不合理。1 .2 运行因素锅炉的实际运行条件往往同设计不一致 ,尤其是… 相似文献
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利用粒子图像测速技术在循环流化床烟气脱硫试验台上进行喷嘴角度布置的试验研究。选取喷嘴与脱硫塔径向呈30、45、-30、-45°的4种布置方式,通过粒子图像测速仪对雾化水流场进行测量、采集图像,利用测速仪自带的Insight 3G软件分析流场中的运动参数。研究表明:喷嘴与脱硫塔径向呈-45°布置时,雾化水轴向速度较小,轴向加速度较大,湍动能的平均值高于其他3种布置方式,有利于脱硫反应的充分进行。 相似文献
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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pd和提升段压降pr周期性波动且pd>pr和pd
r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。 相似文献
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循环流化床锅炉燃烧适应性广,燃烧效率高达97%-99%,负荷调节性能好,烟气中有害成份NOX的排放符合环保要求,并可热电联产,是节能新产品,有广阔的应用前景。 相似文献
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利用由高速数字摄影设备及大功率激光构成的测试系统在一截面为200 mm×200 mm、高为4 m的冷态循环流化床实验台上进行了床内颗粒旋转特性的实验研究.对在距布风板3.54 m高度的稀相区的1/4截面内13个测试点拍摄获得的图像序列利用Matlab、PhotoShop和ACDSee软件进行分析处理,采用人工直接判别获得颗粒转速,用双帧频验证法进行颗粒转速校验.结果表明:循环流化床气固两相流中固相颗粒普遍存在旋转现象,截面边壁区内的颗粒平均转速高于中心区域;粒径小或径向速度大的颗粒,其平均转速较大,反之亦然;不规则颗粒的平均转速明显高于球[JP2]形颗粒;当空截面气体速度Vg=5 m8226;s-1,固体质量循环流率Gs=1.5 kg8226;m-28226;s-1,玻璃珠颗粒平均粒径dp=0.5 mm时,颗粒转速最高可达2000 r8226;s-1,平均转速300 r8226;s-1. 相似文献
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<正> 一、引言煤是一种组成复杂、品质各异的固体矿物类燃料,其理化性质和燃烧特性随产地不同而千变万化。在燃烧高灰和(或)高硫煤以及粒度范围较宽、未经筛分的煤时,常常出现很多困难。中国煤炭资源丰富、品种繁多,煤炭的燃烧利用已有数千年的历史,因此在燃用各类煤种方面,积累了很多经验。但是中国目前燃煤设备的总体性能还很差。例如,耗煤量占全国年产总量约1/3的中小型工业锅炉的平均热效率只有60%左右,而电站的发电平均煤耗也超过400g标煤当量/kWh。此外,由于燃 相似文献
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Sansanee Kumthanasup Suchaya Nitivattananon 《Korean Journal of Chemical Engineering》2007,24(5):851-855
The research was conducted in a cold flow circulating fluidized bed (CFB). The diameter and height of riser are 5 and 200
cm, respectively. The objective is to study effect of gas velocity on hydrodynamic of glass beads having mean diameter of
547 micron and density of 2,400 kg/m3. The measurement of particle velocity profile was achieved by using a high-speed camera and an image processing software.
A probe of 0.5 cm in diameter was inserted into the riser at the height of 110 cm from gas distributor and was set at 3 positions
along the radius of the riser; 0, 0.6, and 1.8 cm from center. Transport velocity (U
tr
), core-annulus velocity (V
CA
) and minimum pneumatic velocity (V
mp
) were employed in determining solid flow pattern in the riser. It was observed that the flow regimes changed from fast fluidization
to core-annulus and to homogeneous dilute bed when the gas velocities increased from 7, 8 and 9 m/s, respectively. The results
from high-speed camera showed that glass beads velocity existed a maximum value at the center of the riser and gradually decreased
toward the wall for all three gas velocities. It was also found that most of solid traveled upward in the core of the riser,
however, solid traveled downward was identified at the wall layer. 相似文献
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A common hydrodynamic feature in heavily loaded circulating fluidized beds is the presence of clusters. The continuous formation and destruction of clusters strongly influences particle hold-up, pressure drop, heat transfer at the wall, and mixing. In this paper fiber optic data is analyzed using discrete wavelet analysis to characterize the dynamic behavior of clusters. Five radial positions at three different axial locations under five different operating conditions spanning three different flow regimes were analyzed using discrete wavelets. Results are summarized with respect to cluster size and frequency. 相似文献
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The effects of particle properties (particle density, size and sphericity) on solids concentration in a 2-D riser were comprehensively investigated by measuring the axial and lateral solids concentration with an optical fiber probe. In this study, solids concentration of different types of particles shows that heavier particles have higher solids concentration laterally and axially than lighter particles; larger particles result in more compact solids distribution and such size effect is more evident at the riser bottom; more spherical particles lead to higher solids concentration. Various forces acting on particles and the change in the slip velocity between gas and particles were used to explain the effects of particle properties on solids distribution. 相似文献
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Coal combustion under the elevated partial pressure of oxygen in a circulating fluidized bed environment was investigated. The fuel used was bituminous coal. The concentration of oxygen in the air was increased to 35% per volume. Excess oxygen ranged from 1.1 to 1.3 and the temperature ranged from ca. 1073 K to 1273 K. A 0.1 MWth CFB combustor was adapted for oxy-combustion. The conversion ratios respectively studied were: carbon, sulfur and nitrogen to CO, SO2 and NOX. An increase of nitrogen and sulfur conversion ratios and a strong decrease of incomplete combustion losses were found under the oxygen-enriched conditions. Moreover, a strong increase in temperature was noticed during oxy-combustion. 相似文献
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Zhe Wang Author Vitae Author Vitae Zhiwei Yang Author Vitae Author Vitae Zheng Li Author Vitae 《Powder Technology》2011,214(3):469-476
A numerical model was established to investigate the lateral mass transfer as well as the mechanism of bed-inventory overturn inside a pant-leg circulating fluidized bed (CFB), which is of great importance to maintain safe and efficient operation of the CFB. Results show that the solid loading along the central line of the pant-leg CFB is promotional to the lateral mass transfer across the central line as well as the bed-inventory overturn. Although the lateral pressure difference generated from lateral mass transfer inhibits continuing lateral mass transfer, providing the pant-leg CFB with self-balancing ability to some extent, the primary flow rate change due to the outlet pressure change often disable the self-balancing ability by continually enhancing the flow rate difference. As the flow rate of the primary air fan is more sensitive to its outlet pressure, it is easier to lead to bed inventory overturn. While when the solid particle is easier to follow the surrounding air flow, the self-balancing ability can be more active. 相似文献
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Satoru Matsuda 《Powder Technology》2008,187(2):200-204
A method using an optical mouse sensor was developed to monitor the moving velocity of a solid mass. Calibration was carried out using a rotating plate. Results clarified that the developed method is useful to monitor the velocity up to some limit (v < 0.3 m/s), which depends on the optical mouse sensor used. A solid circulation rate in a circulating fluidized bed (CFB) was measured using this method. Results obtained using this method show agreement with those of visual observations. 相似文献