环流技术在石油炼制领域中的研究与应用

环流技术在生物工程、废水处理、有机化工、煤直接液化等领域得到了较多的研究和应用,这些研究多集中于气-液、液-固及气-液-固体系。近年来,环流技术的研究延伸到了气-固体系,应用范围也拓展到了石油炼制领域。本文重点概述了气-固环流技术在石油炼制领域中催化裂化装置的粗旋快分、汽提器、外取热器、降烯烃反应器及石油焦燃烧器等装备中的研究与应用进展,同时也对气-液环流技术在渣油悬浮床加氢、气-液-固环流技术在水合物法分离炼厂气中氢气技术上的研究与应用情况进行了综述。     

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.     

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。     

催化裂化待生剂汽提器大型冷模实验装置的设计

以研究催化裂化技术为背景,依据汽提器的相关技术,拟设计建立一套催化裂化待生剂汽提器大型冷模实验装置,利用该装置对汽提器的汽提效率以及气固流态化状况进行系统的研究。该实验装置主要包括提升管、旋风分离器、快速分离器、汽提器及气体分布器等部件。本论文详细论述了该套实验装置各操作单元的设计过程,主要完成了工艺计算和设备计算。本设计的核心装置是汽提器装置部分。     

工业RFCC汽提段内颗粒混合情况的CFD模拟

用计算流体力学方法对人字型挡板、盘环型挡板和两段环流3种工业重油催化裂化(Resid Fluid Catalytic Cracking,RFCC)汽提段内的气固两相流动进行了模拟研究,考察了汽提段内的颗粒体积分数分布情况;结合模拟示踪技术得到了催化剂出口处颗粒的停留时间分布(RTD),通过对RTD曲线进行分析,得到了表征汽提段内颗粒混合特性的参数,平均停留时间(tm)、无因次方差(σθ2)、Peclet准数(Pe),以及死区、活塞流区和全混流区的体积分数。模拟结果表明,环流汽提段外环区和内环区间存在密度差,是催化剂环流流动的推动力。人字形挡板汽提段内的tm最小,σθ2最大,Pe值最小,同时死区体积达到了汽提段体积的40%,而活塞流区体积仅占15.8%,说明其中颗粒的返混非常剧烈,汽提效率最低。相对于盘环型挡板汽提段,两段环流汽提段内颗粒的σθ2较大,Pe较小,颗粒的整体返混程度高于盘环型挡板汽提段。但从死区模型的分析看,活塞流流动的增强有利于促进气固间的传质,死区体积增大则是由于环流流动的增强所导致的,这些都有利于提高汽提效率。两段环流汽提段内活塞流区体积为26.8%,死区体积占32.3%,都大于盘环型挡板汽提段,使环流汽提段的汽提效率更高。     

两段气固环流反应器流体动力学行为和传质特性的研究

借鉴气液环流的理论,提出了气固多段环流的设想.以空气和FCC催化剂为介质,在内环表观气速为0.089～0.424 m/s、外环表观气速为0.04～0.08 m/s的范围内,在一套两段气固环流反应器内系统研究了两段环流反应器内颗粒的流体动力学行为和气固传质特性.发现反应器平均颗粒密度随着内环表观气速的增加而减小,随外环表观气速的增加变化不大.一段、二段环流速度随着内环表观气速的增加而增加,随外环表观气速的增加略有减小.环流反应器汽提效率随内环表观气速的增加而增加,随外环表观气速的增加略有减小,两段环流反应器的汽提效率大于单段环流反应器.     

高低并列式重油催化裂化汽提器挡板的结构优化

催化裂化汽提器的汽提效果对装置产品收率、能耗和长周期平稳高效运行有重要影响。高效的汽提器不仅可以提高轻质油品的收率、改善产品分布,更能降低再生器的烧焦负荷、减少催化剂的水热失活。当前常用的汽提器主要呈现两种结构形式,其一为填料结构汽提器,该汽提器空间利用率和汽提效率很高,但填料容易被焦块堵塞,不易清理,因而不适宜于重油催化裂化装置;另一种汽提器为挡板结构汽提器,该汽提器结构简单、汽提效率高、运行周期长,应用非常广泛。开孔挡板结构汽提器作为挡板结构汽提器中应用最广一种,其挡板区内气固流动特征及流场分布特点目前还研究较少,同时受实验条件和测量方法的限制,工业尺度开孔挡板结构汽提器更是鲜有研究报道。本研究将运用双流体模型结合分段曳力模型对一套工业规模催化裂化装置的锥环形挡板汽提器进行模拟,考察其流场特点和气固流体力学行为。发现模拟所得床层密度与工业实测值能较好吻合。模拟结果表明：挡板区内蒸汽并不严格呈“S”形穿过各块挡板向上流动,相邻环形挡板0.85相似文献   

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。     

组合约束型提升管出口气固分布器的压降

在一套组合约束型提升管冷态实验装置上,通过实验研究了不同操作条件下提升管出口气固分布器的压降,并与常规气体分布器压降进行了对比。实验结果表明,在零床层及有床层的操作模式下,气固分布器压降均随提升管内表观气速和颗粒循环强度的增加而增大,在颗粒循环强度较低时,气固分布器压降曲线变化的斜率随着表观气速的增加而增大,在颗粒循环强度较高时,气固分布器压降曲线变化的斜率随着表观气速的增加而减小;随着开孔率及上部流化床层压降增加,气固分布器压降呈降低趋势,当流化床层压降达到一定程度后,分布器各孔方可实现有效布气,此后气固分布器压降趋于近似不变;在相同表观气速及开孔率下,气固分布器压降大于常规气体分布器压降。     

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.     

A study of the pressure balance around the loop of a circulating fluidized bed

Pressure measurements around the loop of a circulating fluidized bed with 152 mm ID riser and L-valve fecuer were analysed to determine the effect of operating parameters (superficial gas velocity in the range 2.2 - 4.0 m/s, solids circulation flux in the range 5 - 50 kg/m² · s and solids inventory, in the range 80 - 180 kg) on the components of the pressure balance. The riser pressure drop, and hence, riser solids holdup were not affected by changes in the inventory of solids in the system, provided riser superficial gas velocity and solid circulation flux were held constant. The mean suspension concentration in the riser was found to be directly proportional to the ratio of solids flux to superficial gas velocity (G / U) in the riser.     

Circulation liquid velocity in external-loop airlift reactors

In the tracer impulse method using only a conductivity probe, the more recommendable calculation method for the circulation liquid velocity was suggested, which decreased the errors resulted from the response time. The effects of the horizontal connection length (0.1≤L≤0.5 m), the cross-sectional area ratio of downcomer-to-riser (0.11≤A_d/A_r≤0.53), and the superficial gas velocity (0.02≤U_G≤0.18 m s¹) on the circulation liquid velocity were studied. The horizontal connection length as well as U_G, and A_d/A_r, had a significant effect on the circulation liquid velocity. The circulation liquid velocity increased with increasing L_c.     

Flow structure and thickness of annular downflow layer in a circulating fluidized bed riser

Flow structures were determined in a circulating fluidized bed (CFB) riser (0.203 m i.d.×5.9 m high) of FCC particles (d_p=70 μm, ρ_s=1700 kg/m³). A momentum probe was used to measure radial momentum flux profiles at several levels and to distinguish between upward and downward flow regions. Time-mean dynamic pressure (ΔP_m) decreases towards the wall in the range U_g=5-8 m/s, G_s=10-340 kg/m² s. The thickness of the annular downflow layer based on ΔP_m=0 reaches a maximum with increasing height. The annular downflow layer disappears locally with increasing solids mass flux (G_s) at a constant gas velocity, with achievement of the dense suspension upflow (DSU) regime. A new correlation is developed to predict the time-mean thickness of solids down-flowing layer based on solids mass flux and momentum flux. It successfully accounts for the variation of the annular layer thickness with height and G_s, and covers a wide G_s range right up to near the onset of the DSU regime.     

循环曝气生物反应器的流体力学和传质特性

循环曝气生物反应器是一种具有曝气筒的用于废水处理的生物反应器,曝气筒外为下降区,常常填充填料作为微生物生长的载体。从循环液量(V_l)、环流液速(U_ld)以及停留时间分布函数的量纲1方差(σ_θ²)等方面研究了循环曝气生物反应器的流体力学性能和传质特性。研究表明,在下降区内有或无填料以及不同曝气筒截面积与反应器截面积比值(A_r/A_re)的情况下,循环曝气生物反应器内的循环液量与气体流量之间均符合幂函数关系,A_r/A_re对循环液量或循环液速的影响是先增后减,极值点为0.11。下降区放置填料降低了循环液量、循环液速,但提高了σ_θ²,改善了液相传质性能。当A_r/A_re为0.11时,在液体进料为0.1 m³·h^-1、气体流为量0.5~3.1 m³·h^-1的情况下,循环曝气生物反应器内的液相循环量是液相进料的9~28倍、σ_θ²为0.9以上,循环曝气生物反应器具有较好的液相混合和稀释能力,可直接处理高浓度废水。     

循环型高通量输送床的建立与控制

密相输送床气化和双流化床气化是基于循环型流化床反应器发展起来的两种新型煤和生物质气化技术,根据这两种技术对流动的要求,提出了在循环流化床的下行床底部耦合一段移动床,为输送床内的流动提供足够高的驱动压力而提高颗粒循环量的技术思想。在根据该思想而建立的直径90 mm的输送床实验装置上的实验研究表明,利用所提出的床型构造可在表观气速9.6 m•s^-1下实现400 kg•m^-2•s^-1的颗粒循环量。输送床的一次风速和移动床松动风速是影响颗粒循环量和输送床内颗粒浓度的主要因素,但循环量随输送床一次风速的增大而增加的走势弱于普通循环流化床。移动床松动风速在小于颗粒最小流化速度的范围内轻微变动即可显著改变颗粒循环量和输送床内颗粒浓度。在保持输送床总气速不变的前提下,通过二次风可在40%的比例范围内调节颗粒循环量,且调节作用随二次风位置的增高而减弱。     

Particle motion in the CFB riser with special emphasis on PEPT-imaging of the bottom section

The riser is the key-part of a circulating fluidized bed (CFB) and its hydrodynamics are determined mainly by the combined operating superficial gas velocity, U, and solids circulation flux, G. The bottom part of the riser contributes to the total pressure drop of the riser and affects the solids residence time in the riser, due to the possible existence of a dense bed and to the presence of an acceleration zone. Positron Emission Particle Tracking (PEPT) is applied to study these phenomena by measuring the real-time particle motion in a riser of 0.09 m diameter, defining (i) the extent of the acceleration zone, including acceleration length and acceleration time; (ii) the occurrence of a bubbling/turbulent bed under specific conditions of U and G; (iii) the establishment of a fully developed flow immediately after the acceleration zone; (iv) the occurrence of core-annulus flow under specific combinations of U and G; and (v) the disappearance of the intermediate core-annulus region at high values of U and G, where riser hydrodynamics will be either dilute or dense solid up-flow.The particle upflow velocity, U_pf, after acceleration was measured and compared with the situation of dilute transport. When the solids circulation flux increases, the dilute transport mode no longer prevails, and U_pf should be calculated using an appropriate slip factor, itself a combined factor of U and G. The acceleration length and time are nearly constant, at an approximate average of 0.26 m and 0.21 s respectively, independent of U and G. The acceleration length can be modelled fairly accurately, using a C_D-factor of approximately 3.2, which is about half the value predicted by empirical equations established for dilute transport.Dense Suspension Upflow (DSU) is achieved when G exceeds ~ 130 kg m⁻ ² s^− 1.     

Characteristics of solid hold up and circulation rate in the CFB reactor with 3-loops

The effects of the U_o, PA/[PA+SA] ratio, total solid inventory and fluidizing velocity of loopseal on the axial solid holdup and the solid circulation rate have been determined with different particle sizes (174, 199, 281, 377 μm) and particle types (silica sand: narrow PSD, coal ash: wide PSD) in a CFB reactor with 3-loops. A simple model for solid hold-up based on the previous works was in agreement with the experimental data. With increasing U_o, G_s increased exponentially, and in the center-loop, G_s was 1.5 times larger than that found in the other side-loops. As the PA/[PA+SA] ratio increased, and as SA injection port was placed at a lower part in the riser, the axial solid holdup and G_s increased. With increasing fluidizing velocity of loopseal to about 1.5u_mf, G_s somewhat increased, but above the gas velocity of 1.5u_mf, the loopseal lost the ability of the control ofGs. The following correlation for the solid circulation rate in the CFB was developed with good accuracy; G, = ϕ,[PA/TA]²⁺[H _l /H _l ]^0.5[Ar]^-188[Fr]^2k+[KU₁/U _l ]^3-45     

循环流化床中颗粒旋转特性

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V_g=5 m•s^-1,固体质量循环流率G_s=1.5 kg•m^-2•s^-1,玻璃珠颗粒平均粒径d_p=0.5 mm时,颗粒转速最高可达2000 r•s^-1,平均转速300 r•s^-1.