催化裂化汽提器在国内外研究进展

汽提器是催化裂化装置的一个重要组成部分,整个催化裂化装置的稳定性和经济效益是由催化裂化汽提性能的优劣决定的,开发效率更高的汽提器是现在一项比较急迫的任务。本文简单的介绍的催化裂化汽提器以及催化剂和蒸汽在汽提器内的运动状况,综述了汽提器的发展,对环形挡板汽提器、环流汽提器、填料汽提器进行的总结。     

催化裂化新型环流汽提器的大型冷模实验

采用氧气示踪的方法在φ486mm×8000mm的有机玻璃床内对三种不同结构的催化裂化用催化剂汽提器(空筒结构、盘环形挡板结构和两段环流结构)在不同的工况下进行了系统的汽提效率模拟冷态对比实验。最终发现在实验条件下,新型环流汽提器具有更高的汽提效率,和空筒结构相比,最多可减少82%的可汽提焦炭量;和现有工业装置最常用的盘环形汽提结构相比,最多也可以减少48%的可汽提焦炭量。同时该型汽提器还具有结构简单的优点,易于在现有工业装置上改造和推广。     

工业催化裂化汽提器内气固停留时间的数值模拟

在双流体模型以及团聚修正曳力模型的基础上,采用停留时间分布(RTD)模型,对工业催化裂化装置汽提器内气体和催化剂的停留时间进行了模拟计算,得到了人字型挡板、盘环型挡板和两段环流汽提器内气固两相的RTD特征。三种结构汽提器中气体的RTD曲线都呈现很不平滑的多峰分布,而催化剂颗粒的RTD曲线则呈现平滑的单峰分布,气体及催化剂颗粒的RTD曲线都出现了拖尾现象。模拟结果表明,三种汽提器内气体及颗粒的流动明显偏离平推流,催化剂的返混程度比气体强。与人字型挡板相比,盘环型挡板改善了汽提器内气固接触效果,从而提高汽提效率;与人字型挡板和盘环型挡板相比,两段环流汽提器不但改善了气固接触效果,还延长了催化剂颗粒的停留时间,并且降低催化剂的返混程度,模拟结果解释了工业两段环流汽提器汽提效率最高的原因。     

催化裂化汽提器技术研究进展

介绍了近年来催化裂化装置汽提器的研究现状,主要包括挡板汽提器的气固流态化行为,环流汽提器和填料型汽提器.叙述了气固两相在后两种汽提器内的流动特点,并指明了汽提效率优于挡板汽提器的原因.填料型汽提器在高催化剂循环通量条件下仍可有效降低再生器烧焦量,正适合原油重质化和利用催化裂化生产低碳烯烃的发展趋势.     

重油催化裂化装置汽提段及汽提工艺研究进展

重油催化裂化装置沉降器内汽提段的作用越来越受到重视,因为高效的汽提段可以降低焦炭的产率。国内外对汽提段的挡板型式、挡板倾角、裙板结构、蒸汽喷嘴分布等进行了改进,设计了预汽提及多段汽提,增加水蒸气和催化剂的接触面积。考察了汽提温度、时间、水蒸气量等汽提工艺条件对汽提效率的影响,认为汽提段存在重油液相分的化学反应,应对重油催化裂化汽提段结构和汽提工艺进行优化,以提高汽提效率,减少装置结焦。     

炼油厂催化裂化再生器中垂直挡板对混合特性影响研究

本文模拟炼油厂催化裂化第一再生器结构设计；在直径φ308／650mm；高2030mm冷模实验流化床中添加A、B、C三种形式的垂直挡板，用冷模示踪脉冲响应法考查了床内挡板对平衡催化剂流动的影响研究结果表明，在再生器内气体分布器上方平衡催化剂进出口之间加入B型垂直挡板，催化剂在床内流动短路情况可得到较明显的改善，从而可减少再生器内催化剂再生时烧焦不均匀的现象，此结论可作为炼油厂催化裂化装置技术改造的依据．     

开孔形式对盘环形挡板汽提器特性影响的模拟分析

采用CFD方法对安置盘环挡板的汽提器进行了模拟计算,对比了盘环挡板上有无开孔情况下的颗粒流动分布。结果表明,在盘环挡板上进行开孔可有效减少“气垫”区域,使气体与颗粒更顺利地穿透挡板进行高效接触。此外,通过对比不同开孔形式下的催化剂颗粒流动与气泡分布特性,可以发现均匀开孔时,随着开孔尺寸的增加,气相流动阻力下降,可以携带颗粒更加均匀地穿过盘环挡板,使得挡板以下的“气垫”区域减小,颗粒在汽提器内分布更加均匀,有利于汽提蒸汽与催化剂颗粒之间的接触。但是,随着开孔尺寸增加,汽提器内气泡的平均尺寸有所增加,气泡数量减小,气泡所占的总体积及气泡所能提供的相界面积有所减少。对比均匀开孔与非均匀开孔的颗粒流动与气泡特性,结果表明,在盘形挡板顶部附近开孔12mm,其他区域均匀开孔9mm的非均匀开孔形式在确保催化剂颗粒流动的均匀性分布、汽提蒸汽与催化剂颗粒之间的接触效果的同时,容易产生更小的气泡,可以提供更高的气固相界面积,更加有利于汽提器性能的改善,因此是比较优选的开孔方式。本文关于挡板开孔形式影响的模拟分析对设计高性能的汽提器内构件具有重要意义。     

催化裂化填料式汽提器效率研究

针对新型导向板式填料汽提结构,实验考察了填料结构参数-导向板倾斜角、导向板间距、填料间距及填料组间距对汽提效率的影响。和改进的盘环形挡板结构相比,填料式汽提器在汽提效率、处理量、操作稳定性以及操作弹性等方面均具有明显的优势,在相同操作条件下汽提效率可提高约25％,处理量可提高约50％。     

原油催化裂化高效汽提技术的研究进展

随着生产能力的扩大及加工原油中重质油含量的提高,催化裂化装置汽提段引起了人们的重视.高效汽提技术可以有效降低焦炭产率,减轻再生器负荷,在节能降耗中有着重要的意义.国内外关于汽提设备技术方面专利有许多,多是对传统环形挡板进行了改造,并提出了一些新型汽提设备.汽提工艺参数的优化也是提高汽提效率的重要因素.预汽提和多段汽提技术强化了催化剂和水蒸气之间的接触,提高了汽提效率.     

催化剂汽提器内气固传质特性的研究

采用氧气示踪的方法在f 486×8000mm的有机玻璃床内对普通流化床汽提器和盘环形挡板汽提器进行了系统的气固相传质冷态模拟实验,得出了不同汽提线速和催化剂质量流率下上述两种催化剂汽提器内油气浓度轴向分布的变化规律。根据其油气浓度轴向分布的特点,结合鼓泡流化床两相理论以及一系列的假设,提出了针对这两种汽提器的一维传质模型。由实验结果待定了一维传质模型的模型参数,获得了计算两种汽提器轴向油气浓度分布的半经验的指数关联式。该关联式和实验数据比较吻合,相对误差均在10%以内。由该关联式可进一步计算出汽提器的汽提效率,可以为工业汽提器工艺参数的优化以及工程设计提供参考。     

CFD simulation of gas and solids mixing in FCC strippers

The gas and solid mixing in fluid catalytic cracking strippers with and without internals were investigated using computational fluid dynamics simulations. The Eulerian–Eulerian two‐fluid model coupled with the modified Gidaspow drag model was used to simulate the gas‐solid flow behavior. The grid independency study and the comparison of 2D and 3D simulations were carried out first. The residence time distribution model and axial dispersion model were utilized to obtain the parameters indicating the back‐mixing degree, such as mean residence time, dimensionless variance and Peclet number of gas and solids. Moreover, the influence of bubble size and gas/solid flow distribution on the mass transfer between the bubble and emulsion phase were also analyzed. The results show that the baffles in the V‐baffle stripper can efficiently enhance the gas and solids mixing, reduce the back‐mixing degree of gas and solids, strengthen the mass transfer between the bubble and emulsion phase, and hence improve the stripping efficiency. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Gas and solids mixing in a dynamically scaled fluid coker stripper

Gas mixing and solids mixing were studied in a geometrically and dynamically scaled cold model fluid coker stripper. Tracer gas (helium) was first injected into the stripper standpipe to quantify total gas entrainment into the underflow stream. Tracer gas was then injected into the upper reactor and lower stripper separately to investigate gas mixing in the stripper. The stripping efficiency was found to depend strongly on operating conditions (solids circulation rate, stripping gas velocity) as well as on the baffle configuration in the stripper. Unsteady state measurements were also obtained in an effort to understand gas dispersion in the stripper. The results show that gas mixing is most intensive in the stripper core. To study solids mixing and residence time distribution in the stripper, solid tracer particles impregnated with salt were injected into the reactor and detected at the top of the stripper and standpipe. The results indicate that axial dispersion of solids in the presence of the baffles could be represented by axially dispersed plug flow.     

RFCC化学汽提过程的模拟研究

采用欧拉模型耦合反应模型对重油催化裂化环流汽提段内的化学汽提过程进行了模拟研究,考察了汽提段内的颗粒体积分数分布、油气组分分布以及高温再生剂的加入对汽提效果的影响,并与实验值进行了对比。结果表明模拟结果与实验数据基本吻合。模拟得到的汽提段底部颗粒体积分数约为0.3～0.45,而在上部迅速降低至0.2左右。由汽提段底部向上,气体组分和汽油组分含量（质量分数）显著增加,在床层上部达到了20%左右,重组分含量显著降低至床层上部的约30%,而柴油组分含量保持在30%左右变化不大。随着再生剂的加入,汽提段顶部气体组分和汽油组分的含量增加,重组分和柴油组分的含量减小,当再生剂加入量为60%时,重组分含量降至18%。     

CSC快分系统特点与应用及防焦措施探讨

提升管出口CSC(Circulating-Stripping Cyclone)快分系统具有高分离效率、良好的操作弹性及稳定性而在催化裂化装置上得到广泛的应用。其设计的工作原理是在粗旋下部设置一个密相环流式预汽提器,通过改变内外环的汽提蒸汽量来调整内外环的密度差,使催化剂在内外环之间形成密相环流动,以实现降低蒸汽用量、提高汽提效率的目的。工业应用中影响CSC系统性能的因素主要有内外环蒸汽流量、结焦及磨损等。其中,结焦问题是一个大问题,总结认为通过优化原料、选择合适的雾化喷嘴、采用预提升技术、加注反应终止剂、减小汽提蒸汽与油气的温差、停电事故处理时及时将沉降器中的催化剂转出等措施,可以有效防止(或减少)CSC系统结焦问题。     

Longitudinal dispersion of solid particles in fluid beds with horizontal baffles

The axial pressure profiles, allowable gas velocities and temperature distributions are measured for the fluidization of air—FCC cracking catalyst systems in 12- and 19-cm-diam. eight-stage fluid beds equipped with seven horizontal baffles. From these measurements, gas bubble holdup, apparent longitudinal dispersion and intermixing velocity of solid particles through the baffles are studied as functions of baffle design. It is shown that the gas bubble holdup increases, the operational range of gas flow decreases and the flow pattern of solid particles approaches plug flow with decreasing free area of baffles.     

催化裂化汽提技术的发展

催化裂化汽提设备(汽提器)是催化裂化装置的重要组成部分,高效汽提技术对催化裂化装置的经济效益和稳定操作都具有重要意义,能够有效地降低焦炭产率,节能降耗。随着FCC原料的重质化和劣质化以及装置大型化,对汽提器的要求也更加苛刻。对国内外汽提技术研究发现,这些技术均是通过不同途径,有效改善了汽提器内气固接触效率、增加气固接触时间和多段汽提技术,以提高汽提器效率。通过总结这些专利和技术,提出了今后汽提器的发展趋势。     

Effect of louver baffles on hydrodynamics and gas mixing in a fluidized bed of FCC particles

The effect of louver baffles on the particle concentration profiles, pressure fluctuations, bed expansion, and gas mixing of a fluidized bed was investigated in a transparent 2-D column of cross-section 500×30 mm and height 6 m over a broad range of operating conditions covering both the bubbling and turbulent flow regimes. Visual observations, pressure fluctuations and steady gas tracer experiments showed that louver baffles can break bubbles, as indicted by the lower amplitudes and higher mean frequencies of differential pressure fluctuations, but they were only effective for superficial gas velocities <∼0.7 m/s for the FCC particles considered in this study. The ability of louver baffles to break bubbles reached a maximum near the onset of the turbulent flow regime. A gas cushion of low particle concentration appeared below the louver baffle, and its height increased with increasing superficial gas velocity, indicating increasing suppression of solids backmixing. Internal emulsion circulation was promoted above the louver baffle, causing an uneven distribution of gas flow. The addition of louver baffles reduced the upstream tracer gas concentrations by 80-90%, indicating a significant decrease in the backmixing fluxes of both gas and solids across the baffle layer. The tracer gas concentrations above the louver baffles increased resulting from the promoted emulsion circulation by louver baffles.