隔板式内循环流化床的流动特性研究

以石英砂和稻壳为实验床料,在隔板式内循环流化床气化炉冷态实验装置上对颗粒的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、结构尺寸和侧风量等对颗粒内循环流动的影响.结果表明:在保持低速区流化速度一定的条件下,随着高速区风速增大,颗粒循环量先增大后减小;流化速度不变的条件下,颗粒循环量随孔口和侧风量的增大而增加,但增加趋势逐渐变缓.实验给出了合理的运行设计参数.通过实验数据回归,得到了石英砂和稻壳通过隔板式内循环流化床孔口的颗粒循环量关联式,计算结果与实验值误差分别小于6%和14%,能较好地预测孔口颗粒流动.     

加压喷动流化床最小喷动速度的试验研究

在内径100 mm的有机玻璃冷模装置上进行了加压喷动流化床试验.床料直径为1.6 mm、2.3 mm的小米.研究了压力、静止床高及流化风对最小喷动速度的影响.试验结果表明:喷动流化床的最小喷动速度随压力的增大而减小,但减小幅度逐渐变小;静止床高增大,最小喷动速度增大,但床高的增加对最小喷动速度的影响随着压力的增大而减弱.流化风风量增加导致最小喷动速度降低.根据试验数据进行了线性回归,分别得出了uf=0和uf＞0(uf为流化风床内表观气速)时最小喷动速度的关联式,相关系数分别为0.964和0.920,关联式和试验值吻合较好.     

增压流化床最小流化速度的实验研究

在80mm的铸铁流化床实验台上,以窄筛分和宽筛分两类颗粒为实验物料,在压力(101kPa~6 000kPa)和温度(20℃~800℃)范围内,研究了两类颗粒的最小流化速度。实验结果表明:在相同的温度下,随压力的增大最小流化速度减小。然而,在压力不变的情况下,温度对最小流化速度的影响与床料的平均粒径有关。最后,根据上述实验结果和空气在不同压力和温度下的密度,研究了增压流化床在临界流化状态下,风机送风量随流化床压力和温度的变化规律。风机送风量在温度不变的情况下,随压力的增大而明显增加。然而,温度对其的影响随床料的平均粒径的不同而略有不同。     

高温流化床的流化特性及结焦非流化行为

在 8 0 mm× 30 mm和 80 mm× 10 mm石英流化床中 ,以低温粘结的高密度聚乙烯和聚丙烯 ,高温粘结的玻璃珠为实验物料 ,研究了高温流化床的流化特性及高温下物料结焦产生的非流化行为。结果表明 ,在本文实验条件下 ,Geldart A、B类高温表面粘结物料 ,床层温度小于其最小粘结温度时 ,床层温度增大 ,颗粒的最小流化速度减小 ;Geldart D类高温表面粘结物料的最小流化速度随温度增加而增大。得出了不同温度下颗粒最小流化速度预测式。床层温度大于最小粘结温度时 ,流化床需在较高的表观气速下才能保持流化 ,床层温度愈高床层流化所需的表观气速越大。研究同时发现 ,颗粒物料的粒径减小 ,流化颗粒的最小粘结温度减小。     

双循环流化床内稻壳-石英砂混合颗粒循环流率的实验研究与预测

混合颗粒循环流率是气化反应的双循环流化床系统稳定运行的关键。在自行搭建的双循环流化床冷态系统上,对气化室风速、提升管风速、初始物料质量和石英砂粒径等控制参数对不同稻壳质量比的稻壳-石英砂混合颗粒的循环流率的影响进行实验研究。研究表明:混合颗粒循环流率随着气化室和提升管风速的增加而增加;随着初始物料质量的增加,气化室侧返料管压力增加,混合颗粒循环流率增大;随着粒径增加,石英砂颗粒流化困难,循环流率减小;由于稻壳密度小,形状不规则,在一定程度上阻碍物料的流化,因此随着稻壳质量比的增加循环流率下降;基于以上各参数提出经验关联式,预测误差在-18. 04%～19. 8%间,能够很好地对双循环流化床系统中稻壳-石英砂双组份物料颗粒的循环流率进行预测。     

棉花杆成型颗粒循环流化床流化及气化特性

通过成型棉花杆颗粒冷态流化试验与床料混合试验,得到了关于成型棉花杆颗粒的流化特性,包含临界流化速度、与各种不同粒径石英砂的混合分布情况。在此基础上,开展了700～800℃下的1MW循环流化床气化试验,研究了该种棉花杆成型颗粒的气化特性,试验结果表明该种生物质成型颗粒在循环流化床中运行稳定,产生的燃气热值在4500 kJ/m~3左右,属于低热值燃气,燃气产量约为1.70 m~3/kg,焦油产率低于1.5 g/m~3。     

化学链气化串行流化床设计及试验研究

在生物质化学链气化反应基础上设计并搭建了一套串行流化床冷态模型。以石英砂为床料、空气为流化介质,在该冷态装置上开展了压力分布及控制规律试验研究。采用PY500型智能压力检测系统及PV-6型激光颗粒速度测量仪着重研究了循环流化床冷态装置的料层阻力特性及固体循环量,考察了空气反应器、燃料反应器、返料管部件的流化风量对循环状态和流化床内压力分布的影响,获得了串行流化床稳定运行的操作条件和控制规律。试验结果表明,最佳操作状态:燃料反应器流化气速为0.23~0.32 m/s,空气反应器气速为0.42~0.47 m/s,返料管气速为0.07~0.1 m/s,两反应器存料量为2.5~4.5 kg,为热态试验装置的设计、运行提供了参考依据。     

生物质热解液化反应塔中最小携带流速的可视化试验验证

生物质颗粒的最小流化速度是生物质快速热解液化工艺最重要的控制参数之一,准确掌握各种因素对最小携带流速的影响规律,对于保证充足的热解时间、提高生物质热解液化率是十分关键的,文章提出了生物质循环流化床快速热解反应塔中最小携带流速的预测方法;揭示了最小流化速度随生物质粒径和颗粒密度的变化规律,并通过可视化试验对预测结果进行了初步验证。     

鼓泡流化床风帽压力波动信号的小波局部奇异性检测

在冷态鼓泡流化床实验台上,针对不同流化数、静床高及床料颗粒粒径下测得的风帽压力波动信号,采用小波模极大值法获取信号的小波局部极大模线,分析了流化数、静床高及床料颗粒粒径对鼓泡流化床风帽压力波动信号奇异性的影响.结果表明:风帽压力波动信号的局部奇异性随着流化数的减小、静床高的增加和床料颗粒粒径的增大而有所增强,说明通过小波局部极大模线可以对风帽压力波动信号的局部奇异性进行描述,并且能够反映鼓泡流化床流化数、静床高和床料颗粒粒径变化时床内气固流动状态的变化.     

高温鼓泡流化床的流化行为

床层温度在20－1000℃范围内,以4种粒径的煤灰为实验物料,研究了不同表观气速下最小流化速度,床层平均空隙率,压力波动标准偏差和主频的变化规律,最小流化速度随床层温度升高而减小;相同床温下,平均空隙率随表观气速升高而增大,不同床温下,压力波动偏差随流化数增加而增大。相同流化数时,B类颗粒的压力波动标准偏差受床层温度变化影响较小,而D类粒子随床层温度升高压力波动标准偏差减小,胡着流化数增加,压力波动主频减小。     

Effect of Pressure on Minimum Fluidization Velocity

Minimum fluidization velocity of quartz sand and glass bead under different pressures of 0.5,1.0,1.5 and 2.0MPa were investigated.The minimum fluidization velocity decreases with the increasing of pressure.The influ-ence of pressure to the minimum fluidization velocities is stronger for larger particles than for smaller ones.Based on the test results and Ergun equation,an experience equation of minimum fluidization velocity is pro-posed and the calculation results are comparable to other researchers' results.     

生物质化学链气化串行流化床二元物系冷态实验研究

搭建了生物质化学链气化串行流化床冷态模型,考察了木粉与石英砂二元物系在不同工况下的流化特性,结果表明,木粉单独实现流化较为困难,稳定流态化操作范围也较小;石英砂木粉二元物系,随着石英砂含量的增加,流化状态持续改善,稳态流化操作范围增大,当石英砂含量超过70% 时,该二元体系流化状态接近石英砂;石英砂木粉二元混合体系物料循环量及颗粒平均速度随着表观气速的增加而持续增大。     

底饲进料循环喷动床进料与回料混合特性及影响因素

分别以石英砂和消石灰模拟进料和回料,对一台0.6m×15m底饲进料循环喷动床脱硫塔内颗粒混合特性进行了研究。利用石英砂和消石灰在水中溶解度的差异计算得到底饲进料与回料在不同位置的混合熵和不同高度上的混合指数,并分析不同操作参数对塔内颗粒混合行为的影响。研究结果表明:混合指数能够很好地反映塔内进料与回料颗粒的混合质量;随着流化速度的提高,塔内不同高度上的混合指数呈上升趋势;喷射速度和循环倍率对塔内尤其是反应塔底部的颗粒分布特性有明显影响,采用较高的喷射速度和循环倍率,混合指数随之上升,说明塔内颗粒的混合质量得到改善。     

Studies on the operation of loop-seal in circulating fluidized bed boilers

Loop-seal, considered heart of a circulating fluidized bed (CFB), returns solids captured by cyclone to the base of the riser while preventing direct flow of gas from high pressure riser to the low-pressure cyclone. This non-mechanical valve is used in thousands of CFB systems yet only a limited information is available on its working. Present research studies the flow of solids through a loop-seal and the effect of several design and operating parameters on it. This experimental study was conducted in a loop-seal 110 mm × 448 mm × 400 mm high connected to a riser 152 mm diameter and 5180 mm high. Majority of the experiments was done with 171 μm sand though several other size and type of solids were studied for their flowability. It was found that for the solids to flow through the loop-seal a minimum level of aeration, in excess of that required for minimum fluidization was required. The length of the horizontal passage connecting the supply and recycle chambers of the loop-seal had an important effect on the solids flow. For example, the minimum aeration for the onset of solids flow increases with increase in this length. The pressure drop per unit length across the passage also increased with the passage length. The air fed into the supply chamber is split such that the superficial air velocity in the supply chamber (or the standpipe) remained below the minimum fluidization velocity of the particles while the remaining air conveys solids through the horizontal passage. Present study showed that the solids flowing through the horizontal passage are neither fully fluidized nor moving packed or suspended solids. It moves as a segregated flow of solids driven by hydrostatic pressure and fluid drag.     

Fluidization characteristics of two- and three-dimensional fluidized beds

Experiments have been conducted with particles of sand (d_p = 1,421 μm, silica sand (d_p = 171 μm), glass beads (d_p = 2,745 μm) and wax pellets (d_p = 5,476 μm) in two- and three-dimensional fluidized beds. In both beds, measurement of pressure drop as a function of superficial air velocity are taken and employed to determine the minimum fluidization velocity and the variation of bed voidage with superficial air velocity. Data analysis has made it possible to understand the nature of frictional forces that the front and back bounding walls of two-dimensional fluidized beds caused on bed particles, as well as their dependence on particle shape. Information useful in the design of fluidized beds has been generated.     

Heat transfer characteristics in a pulsating fluidized bed in relation to bubble characteristics

A pulsating fluidized bed is operated with two sequential durations designated as an on‐period with injecting fluidization gas and an off‐period without it. The heat transfer coefficient between a vertically immersed heater and bed in a pulsating fluidized bed is measured under various pulse cycles and fluidized particles. The obtained results are compared with those in a normal fluidized bed with continuous fluidization air injection. The relationship between heat transfer coefficients and bubble characteristics, evaluated using a digital video camera, has also been investigated. For certain fluidized particles and operating pulse cycles, the fluidization of particles and the increment of heat transfer coefficients can be obtained under a mean air velocity based on a pulse cycle duration smaller than the minimum fluidization air velocity in a normal fluidized bed. Under the pulse cycles where a static bed through the whole bed is formed in the off‐period duration, the improved heat transfer rate over that in a normal fluidized bed can be measured. This may be attributed to large bubble formation. As heat transfer in the pulsating fluidized bed is obstructed with increasing time to keep a static bed due to the excessive off‐period duration, it is indicated that there is an optimum off‐period duration based on the heat transfer rate. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 307–319, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10038     

Steam gasification of coal cokes in an internally circulating fluidized bed of thermal storage material for solar thermochemical processes

A laboratory-scale prototype windowed internally circulating fluidized-bed reactor made of quartz sand and coal coke particles was investigated for steam gasification using concentrated Xe-light radiation as the energy source. The quartz sand was used as a chemically inert bed material for the fluidized bed, while the coal coke particles functioned as the reacting particles for the endothermic gasification reaction. The advantages of using quartz sand as the bed material for the directly irradiated gasification reactor are as follows: (1) The bed height is maintained at a constant level during the gasification. (2) The quartz sand functions as a thermal transfer/storage medium inside the reactor. The gasification performances such as the production rates of CO, H₂, and CO₂; carbon conversion; and light-to-chemical energy conversion were evaluated for the fluidized-bed reactor with a thermal transfer/storage medium (quartz sand). The effects of using the bed material (quartz sand) on the gasification performance are described in this paper.     

Fundamental design of a continuous biomass gasification process using a supercritical water fluidized bed

A novel biomass gasification (first stage of hydrogen production from biomass) process using a supercritical water fluidized bed was proposed and the fundamental design of the process was conducted. The flow rate was determined by evaluating the minimum fluidization velocity and terminal velocity of alumina particles enabling fluidization with the thermodynamic properties of supercritical water. Three cases were examined: a bubbling fluidized bed in which water was used mainly as the fluidized medium and biomass were added for gasification, a bubbling fluidized bed fluidized by biomass slurry feed alone, and a fast fluidized bed fluidized by biomass slurry feed alone. According to calculations of the residence time and thermal efficiency assuming heat recovery with a heat exchanger efficiency of 0.75, the bubbling fluidized bed fluidized by biomass slurry alone was appropriate for continuous biomass gasification using a fluidized bed.