Effect of elevated temperature and silica sand particle size on minimum fluidization velocity in an atmospheric bubbling fluidized bed

The impact of temperature and particle size on minimumfluidizing velocity was studied and analyzed in a small pilot scale of bubbling fluidized bed reactor.This study was devoted to providing some data about fluidization to the literature under high temperature conditions.The experiments were carried out to evaluate the minimum fluidizing velocity over a vast range of temperature levels from 20℃ to 850℃ using silica sand with a particle size of 300-425μm,425-500μm,500-600μm,and 600-710μm.Furthermore,the variation in the minimumfluidized voidage was determined experimentally at the same conditions.The experimental data revealed that the Umf directly varied with particle size and inversely with temperature,whileεmf increases slightly with temperature based on the measurements of height at incipient fluidization.However,for all particle sizes used in this test,temperatures above 700℃ has a marginal effect on Umf.The results were compared with many empirical equations,and it was found that the experimental result is still in an acceptable range of empirical equations used.In which,our findings are not well predicted by the widely accepted correlations reported in the literature.Therefore,a new predicted equation has been developed that also accounts for the affecting of mean particle size in addition to other parameters.A good mean relative deviation of 5.473% between the experimental data and the predicted values was estimated from the correlation of the effective dimensionless group.Furthermore,the experimental work revealed that the minimum fluidizing velocity was not affected by the height of the bed even at high temperature.

Prediction of Minimum Spouting Velocity at Elevated Pressures and Temperatures

Minimum spouting velocity （Ums） is one of the most important flow characteristics for proper design and operation of spouted bed reactors. Many correlations for Ums have been published since spouted bed technology was initiated in 1955. In this paper, a new correlation is developed for Ums based on 767 published experimental data covering both high pressure and high temperature conditions. The calculated and the measured results of Ums are in better agreement than other published correlations.

A new die-cast magnesium alloy for applications at higher elevated temperatures of 200-300℃

The development of lightweight magnesium(Mg)alloys capable of operating at elevated temperatures of 200-300℃and the ability of using high pressure die casting for high-volume manufacturing are the most advanced developments in manufacturing critical parts for internal combustion engines used in power tools.Here we report the microstructure and mechanical properties of a newly developed die-cast Mg-RE(La,Ce,Nd,Gd)-Al alloy capable of working at higher elevated temperatures of 200-300℃.The new alloy delivers the yield strength of 94 MPa at 300℃,which demonstrates a 42%increase over the benchmark AE44 high temperature die-cast Mg alloy.The new alloy also has good stiffness at elevated temperatures with its modulus only decreasing linearly by 13%from room temperature up to 300℃.Thermal analysis shows a minor peak at 364.7℃in the specific heat curve of the new alloy,indicating a good phase stability of the alloy up to 300℃.Nd and Gd have more affinity to Al for the formation of the minority of divorced Al-RE(Nd,Gd)based compounds,and the stable Al-poor Mg_(12)RE(La_(0.22)Ce_(0.13)Nd_(0.31)Gd_(0.31))Zn_(0.39)Al_(0.13)compound acts as the continuous inter-dendritic network,which contribute to the high mechanical performance and stability of the new die-cast Mg alloy at 200-300℃.

Oxidation Kinetics of Aluminum Powders in a Gas Fluidized Bed Reactor in the Potential Application of Surge Arresting Materials

In this technical paper, the oxidation mechanism and kinetics of aluminum powders are discussed in great details. The potential applications of spherical aluminum powders after oxidation to be part of the surging arresting materials are discussed. Theoretical calculations of oxidation of spherical aluminum powders in a typical gas fluidization bed are demonstrated. Computer software written by the author is used to carry out the basic calculations of important parameters of a gas fluidization bed at different temperatures. A mathematical model of the dynamic system in a gas fluidization bed is developed and the analytical solution is obtained. The mathematical model can be used to estimate aluminum oxide thickness at a defined temperature. The mathematical model created in this study is evaluated and confirmed consistently with the experimental results on a gas fluidization bed. Detail technical discussion of the oxidation mechanism of aluminum is carried out. The mathematical deviations of the mathematical modeling have demonstrated in great details. This mathematical model developed in this study and validated with experimental results can bring a great value for the quantitative analysis of a gas fluidization bed in general from a theoretical point of view. It can be applied for the oxidation not only for aluminum spherical powders, but also for other spherical metal powders. The mathematical model developed can further enhance the applications of gas fluidization technology. In addition to the development of mathematical modeling of a gas fluidization bed reactor, the formation of oxide film through diffusion on both planar and spherical aluminum surfaces is analyzed through a thorough mathematical deviation using diffusion theory and Laplace transformation. The dominant defects and their impact to oxidation of aluminum are also discussed in detail. The well-controlled oxidation film on spherical metal powders such as aluminum and other metal spherical powders can potentially become an important part of switch devices of surge arresting materials, in general.

Numerical simulations of high pressure carbon dioxide fluid fluidized beds

Hydrodynamics of carbon dioxide fluid-particle mixtures are predicted using a low density ratio-based kinetic theory of granular flow in high pressure carbon dioxide fluid fluidized beds.A coexistence of particle waves and particle aggregates exists along bed height.The threshold to identify the occurrence of particle aggregates is suggested based on standard deviation of solid volume fractions in aggregative fluidization.The existence time fractions and frequencies of particle aggregates are predicted along axial direction.The effect of carbon dioxide fluid temperature and pressure on volume fraction and velocity distributions are analyzed at different inlet carbon dioxide velocities and particle densities in high pressure carbon dioxide fluidized beds.Simulated results indicate that the carbon dioxide-particles fluidization transits from particulate to aggregative states with the increase of inlet carbon dioxide ve-locities.The computed fluid volume fractions and heterogeneity indexes are close to the measurements in a high pressure carbon dioxide fluidized bed.

高密度聚乙烯装置流化床运行周期短的原因分析及对策

对中国石油兰州石化公司榆林化工有限公司40万t/a高密度聚乙烯装置流化床出现分布板筛孔堵塞、通道粉料堆积、加热板粉料挂壁严重等问题造成流化床运行周期短的原因进行了分析,并采取了相应的优化措施。结果表明:上述问题是由聚合反应系统产生块状树脂,流化床进、出料流量波动大,通道设计缺陷以及循环N_(2)风机设计功率偏小等因素引起的;通过采取优化聚合反应、离心机、流化床等系统操作,消除气力输送系统运行故障等措施,将乙烯进料量由18~45 t/h提高到52 t/h,流化床1腔床层压差由5.5 kPa降低至4.5 kPa,流化床运行周期由90 d延长至288 d。

航天炉高硅铝烟煤煤灰熔融及黏温特性调控研究

具有高灰分、高硅铝、低硅铝比(质量比)煤灰特性的动力烟煤在气流床气化炉上鲜有应用,其煤质特性偏离气化用煤指标,且调控难度非常大。为将具有上述煤灰特性的动力烟煤应用于航天炉气化,开展煤质特性调控研究,利用灰熔融测试仪、高温旋转黏度仪以及热力学计算软件FactSage,研究了动力烟煤(HS)添加不同质量比的工业助熔剂(石灰石、铁矿石和二者复合助剂)以及配煤(白石湖煤)对煤灰熔融特性、黏温特性以及矿物质组成的影响。结果表明:HS灰硅铝比为1.32,酸碱比为12.82。热转化过程中煤灰矿物组成以莫来石为主要成分,是其四个灰熔融特征温度均高于1500℃的根本原因,黏温特性的调控难度大于一般晋城无烟煤黏温特性的调控难度;同等比例下工业助熔剂按调控效果由大到小依次为铁钙复合助剂、铁矿石、石灰石;单一石灰石助熔剂对HS的调控效果不佳,针对此类煤灰特性,宜选用铁钙复合助剂或与高碱金属煤灰特性的煤混配以降低灰熔融温度,改善黏温特性,即同时增加煤灰中CaO和Fe_(2)O_(3)等碱金属含量,使其在矿物质热转化过程形成如钙铁辉石、易变辉石、透辉石、堇青石和霞石等低熔点矿物质或多元低温共熔物,从而降低体系熔融温度。

HPB工艺用于污水厂扩容提标的中试实验

山东某水厂因进水超标而造成减产,拟用HPB(High concentration powder carrier bio-fluidized bed)工艺提高水厂产量,故进行中试实验验证该技术的可行性及低温下对北方高浓度工业废水的处理结果。实验期间,中试装置进水水质与原水厂相同,结果表明:工况Ⅰ,在水力停留时间为25.84 h时(模拟厂区3×10^(4) m^(3)/d),中试系统COD去除率为96.3%,TN去除率为91.1%,NH_(3)-N去除率为96.0%,TP去除率为98.8%;工况Ⅱ,在水力停留时间为20.0 h时(模拟厂区4×10^(4) m^(3)/d),中试系统COD去除率为94.3%,TN去除率为93.4%,NH_(3)-N去除率为96.4%,TP去除率为98.4%;极限工况下,水力停留时间15.6~20.0 h(模拟厂区4~5.33×10^(4) m^(3)/d),中试系统COD去除率为94.5%,TN去除率为92.0%,NH_(3)-N去除率为96.8%,TP去除率为98.3%。在水力停留时间减半的情况下,中试装置出水仍接近甚至优于原厂区,稳定达到二沉池设计出水水质(COD<100 mg/L,ρ(NH_(3)-N)<1.5 mg/L,ρ(TN)<10mg/L,ρ(TP)<0.3 mg/L)。中试实验验证了北方低温下HPB用于该水厂提标扩容的可能性,为日后的生产性实验奠定基础。

MTO装置急冷水系统降固措施分析与评价

针对甲醇制烯烃(MTO)装置急冷水系统运行的瓶颈问题,以某年处理180万t甲醇的MTO装置为研究对象,结合装置近三年运行数据,分析了急冷水系统固含量高的原因,并对瓶颈问题进行了定性、定量分析。通过试用急冷水高温萃取剂、采用分离技术、耦合沉降罐与地下污水池技术、应用沸腾床过滤技术,使急冷水含固质量浓度降至1 000 mg/L,实现了急冷水系统平稳运行。

CO2 residual concentration of potassium-promoted hydrotalcite for deep CO/CO2 purification in H2-rich gas

Elevated-temperature pressure swing adsorption is a promising technique for producing high purity hydrogen and controlling greenhouse gas emissions. Thermodynamic analysis indicated that the CO in H-rich gas could be controlled to trace levels of below 10 ppm by in situ reduction of the COconcentration to less than 100 ppm via the aforementioned process. The COadsorption capacity of potassiumpromoted hydrotalcite at elevated temperatures under different adsorption（mole fraction, working pressure） and desorption（flow rate, desorption time, steam effects） conditions was systematically investigated using a fixed bed reactor. It was found that the COresidual concentration before the breakthrough of COmainly depended on the total amount of purge gas and the COmole fraction in the inlet syngas.The residual COconcentration and uptake achieved for the inlet gas comprising CO（9.7 mL/min） and He（277.6 mL/min） at a working pressure of 3 MPa after 1 h of Ar purging at 300 mL/min were 12.3 ppm and0.341 mmol/g, respectively. Steam purge could greatly improve the cyclic adsorption working capacity, but had no obvious benefit for the recovery of the residual COconcentration compared to purging with an inert gas. The residual COconcentration obtained with the adsorbent could be reduced to 3.2 ppm after 12 h of temperature swing at 450 °C. A new concept based on an adsorption/desorption process, comprising adsorption, steam rinse, depressurization, steam purge, pressurization, and high-temperature steam purge, was proposed for reducing the steam consumption during CO/COpurification.

Analysis of the fluid-bed stability of FCC catalysts at high temperature in terms of bed elasticity

The effect of temperature on the fluid-bed stability of three FCC catalysts has been analyzed through considerations on fluid-bed elasticity. Experimental findings on the effect of temperature on the elasticity modulus at minimum bubbling conditions, （E）mb, were analyzed using the hydrodynamic fluid-bed stability model developed by Foscolo and Gibilaro （1984） and adopting the interparticle-forces-based stability criterion developed by Mutsers and Rietema （1977）. For both models, the parameters which control changes in （E）mb with temperature are discussed, in order to establish the origin of the fluid-bed elasticity and analyze the ability of these models to discriminate between the relative importance of the hydrodynamic and interoarticle forces on the stability of the fluidized catalysts.

350 MW超临界循环流化床锅炉床温偏高分析及优化

山西某电厂350 MW超临界循环流化床锅炉,在升负荷过程中炉膛下部平均床温为977℃,床温最高点为1017℃,床温过高将导致锅炉结焦,旋风分离器中心筒变形、分离效率下降,环保参数下降,锅炉效率下降,危及风帽和电袋除尘器安全,影响机组的安全稳定运行。针对该厂存在的问题开展了影响床温升高的因素分析,通过调整配煤掺烧、入炉煤粒径、一二次风配比、床压、运行过程中添加有效粒径床料等措施,机组可以顺利带至额定负荷,床温下降明显,平均床温下降11℃,最高床温下降24℃,提高了机组稳定运行的安全性,同时也为同类型循环流化床机组解决类似问题提供参考。

循环流化床锅炉高温屏式过热器变形原因分析

某型循环流化床锅炉内部检验时发现炉膛高温屏式过热器均产生严重弯曲变形,测量其最大挠度约为800 mm。经现场检测,管材厚度、材质均没有明显变化。查阅锅炉技术资料和运行数据分析得出不合理的设计及运行工况是其产生屈曲和塑性变形的主要原因,并通过材料力学理论推导和有限元数值模拟给出了最大变形量的计算公式以及最小失稳应力值,最后提出了几点解决措施方案。

某循环流化床锅炉高温过热器爆管原因分析

某循环流化床锅炉高温过热器出现了爆管的现象,爆口附近其他受热面也被吹损。通过宏观检查、化学成分分析、金相检验、力学性能试验、断口分析及能谱分析等方法,对发生爆漏的高过鳍片管样品进行了失效原因的分析,结果表明:样品的角焊缝外观质量有缺陷,焊缝的边缘圆滑过渡不佳,局部存在凹陷,角焊缝其他检验结果及换热管母材与鳍片母材的其它检验结果未见明显异常;样品的爆管类型为应力腐蚀,主要是管屏在运行过程中由于不同位置温度差异大,由于热胀不同产生了应力,此外,角焊缝残留了部分焊接应力。角焊缝外观成形缺陷也加速了爆管的发生。建议对该循环流化床锅炉的高过管屏角焊缝部位进行探伤,若发现焊接缺陷,应及时消除。同时,应采取降低管屏热胀应力的措施,如可将管屏沿中部鳍片纵向切开等。研究结果可为国内其他锅炉同类问题解决提供参考。

高压流化床投料启炉过程问题分析及优化措施

分析了高压流化床气化炉投料启炉过程出现的点火失败、爆燃、炉顶温度低、副产重质焦油堵塞设备等问题,认为烘炉温度及恒温时间、投煤量、蒸汽量、氧气量、气化炉温度是主要的影响因素,针对存在问题提出了优化措施,并经过运行效果进行了验证,为高压流化床气化炉投料启炉操作提供参考。

“三高”煤性质分析及其在KSY技术中的应用研究

为了拓展双流化床超大型粉煤气化技术(KSY技术)原料用煤范围,通过工业分析、元素分析、热失重实验、CO_(2)反应活性分析,探讨了山西晋阳某矿区煤(SXJYM)应用于KSY技术的可行性。分析结果表明:SXJYM灰分为24.11%,硫质量分数为3.55%,灰熔融性温度在1500℃左右,属于典型的“三高”煤,且其CO_(2)反应活性较低、热失重效果较差,单独作为KSY技术的原料用煤可能气化效果不佳;适量添加CaO可在一定程度上降低SXJYM灰熔融性温度;可通过将SXJYM与灰分较低、CO_(2)活性较好的新疆某矿区煤(XJM)进行级配,既能获得较好的气化效果,又可降低原料成本。

Fluidization behavior of graphitized glassy particles in a fluidized carbon bed cooling process for investment casting

Fluidized Carbon Bed Cooling(FCBC)is an innovative investment casting process for directional solidification of superalloy components.It takes advantage of a fluidized bed with a base of small glassy carbon beads for cooling and other low-density particles that form an insulating layer by floating to the bed surface.This so-called“Dynamic Baffle”protects the fluidized bed from the direct heat input from the high-temperature heating zone and provides the basis for an improved bed microstructure.The prerequisites for a stable casting process are stable fluidization conditions where neither collapse of the bed nor particle blow out at excessive bubble formation occur.This work aimed to investigate the fluidization behavior of spherical carbon bed material in argon and air at temperatures between 20 to 350℃.Systematic studies at reduced pressures using the FCBC prototype device were performed to understand the stable fluidization conditions at all stages of the investment casting process.The particle shape factor and size distribution characterization and the measurement of the powder’s minimum fluidization velocity and bed voidage show that this material can be fully utilized as a cooling and buoyancy medium during the FCBC process.

超临界循环流化床锅炉氧化皮清理的实践研究

研究了超临界循环流化床锅炉氧化皮脱落位置,并测试了压缩空气吹扫及水冲洗两种清理方法,在此基础上设计了一套闭式水冲洗系统,实现了氧化皮的水冲洗清理,大大降低了检修工作量,提高了机组启动的安全性,为同类机组的冲洗清理提供了参考。

300MW循环流化床锅炉负荷、床温和床压的动态特性分析

基于300 MW循环流化床锅炉现场试验数据,采用最小二乘法进行拟合推导,提出了较为完整的锅炉负荷、床温和床压在不同工况下的阶跃响应模型.在此基础上分析了锅炉负荷、床温和床压的动态响应特性,阐述了相应的控制难点.分析结果为300 MW循环流化床锅炉的运行和优化控制提供了参考.

增压流化床热态临界流化速度的实验研究

在内径80 mm的加压热态流化床实验台上,测量不同粒径的石英砂和陶粒砂两类实验物料在压力(0.1～0.6 MPa)和温度(20～800℃)范围内的最小流化速度umf。实验结果表明:在相同的温度下,最小流化速度随压力的增加而减小,而在相同的压力下,温度对最小流化速度的影响随床料种类的不同而有明显的差别。较全面地总结了文献中已有的umf经验关联式,发现umf计算值与本实验值偏差较大。基于厄贡方程和文献中已有的关于最小流化空隙率的实验结论,给出了确定增压流化床热态最小流化速度的合理计算步骤。该方法的预测值和实验值的相对误差在10%以内,为增压流化床反应器的设计和运行提供较可靠的参考依据。