催化裂化装置再生器的研究进展

介绍了近年来催化裂化再生器和再生工艺的研究现状。再生工艺主要包括单段再生、两段再生和快速流化床再生;比较了各类再生器的优缺点。简述了3种再生器的改进历程,根据现有再生器的优缺点提出了新的开发思路。     

催化裂化装置再生器检验

针对催化裂化装置的T-102再生器发生局部超温现象提出了具体的检验方法和检验重点.检验结果安全状况等级定为4级,监控使用.在监控使用过程中,必须密切监控简体壁温,严禁再次发生超温现象,这对确保再生器的安全运行具有重要意义.     

垂直内挡板对流态化流体动力学及谷物干燥特性之影响

The effect of vertical internal baffles on the particle mixing and grain drying characteristics in a batch fluidized bed column is investigated. Experimental work was carried out in a 3 m high rectangular fluidized bed dryer of cross sectional area of 0.15 mx0.61 m at different operating conditions using paddy, a group D particle, as the fluidizing material. The results of the study showed that the fluidized bed dryer system with vertical internal baffles gave better particle mixing effect in the bed of particles than that without vertical internal baffles. This is due to the fact that the vertical internal baffle act as gas bubble breakers by breaking up the large gas bubbles into smaller ones. The smaller bubbles cause a more vigorous mixing in the bed of particles before finally erupting at the bed surface. This improves the contacting efficiency and enhanced the heat and mass transfer of the fluidized bed system. Thus a higher drying rate was obtained in the falling rate period because the higher contactin efficiency increases the evaporation rate at the particle surface. However, the drying rate in the diffusion regiol shows little improvement because the moisture diffusivity does not depend on the contacting efficiency. The fluidized bed dryer with vertical internal baffles could therefore be used in the initial rapid drying stage in a two stage drying strategy for paddy. The insertion of vertical internal baffles into a fluidized bed system improves the processing of Group D particles in a fluidized bed system especially if the system is large in scale.     

催化裂化装置再生器开裂初探

近年来,随着原油的重质化和劣质化,我国一些炼油厂的重油催化裂化装置再生器时有设备开裂现象的发生,直接影响装置的长周期安全运转和炼厂的经济效益。本文对对再生器壳体产生裂纹的原因及腐蚀的机理进行了分析,并提出了防止裂纹产生的相关对策及建议。     

催化裂化再生器的安全评定

根据GB/T 19624—2004《在用含缺陷压力容器安全评定》标准,对在役的催化裂化再生器进行了缺陷检测,并通过缺陷表征、材料性能数据确定和评价计算等技术手段,完成了对所测定的压力容器的安全性评价。     

催化裂化装置反应器和再生器设计

通过本公司催化裂化装置反应器(沉降器)和再生器的设计,介绍了催化裂化装置两器结构设计(包括壳体、外集气室、分布管、衬里结构等的设计)及材料选择(包括壳体材料和内件材料)的特点,并对一些结构设计和材料选择问题进行了详细分析.     

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。     

带转动挡板的搅拌萃取塔连续相停留时间分布研究

为获取带转动挡板的搅拌萃取塔内部流体流动状况,采用脉冲示踪法对塔内连续相停留时间分布(RTD)进行研究,并结合轴向返混模型得到了连续相的返混系数。结果表明,随着连续相体积流量、总流量或连续相与分散相体积流量比值的增大,连续相RTD曲线收窄、峰值明显增大、连续相停留时间和返混系数均减小;改变分散相体积流量,连续相RTD以及返混系数基本不变。此外,改变搅拌转速对连续相RTD影响较小。将返混系数与操作条件和物性参数进行关联,关联式最大偏差为19.8%、平均偏差为7.7%,表明关联式可用于带转动挡板的搅拌萃取塔的连续相轴向返混程度的评估。     

正弦波纹挡板式沉降器内流动特性

采用VOF模型对正弦波纹式入口挡板的重力非均相沉降器内流场进行数值模拟研究。对比了正弦波纹挡板与平挡板的平均流场分布情况,分析了沉降器的轴向流速均一程度(λ₁)随时间演化特性,探究了λ₁和面积加权平均湍流强度(I_a)在沉降器内空间分布特性;引入流场均稳指标USC,研究了冲击间距(L_b/D)对USC的影响。结果表明:正弦波纹挡板作为入口构件可以有效降低返混。在0.84b/D减小,平挡板沉降器内流场的λ₁基本不变,但正弦波纹挡板沉降器内流场的λ₁降低,且对I_a的影响不明显。对比平挡板,正弦波纹挡板可以有效降低轴向速度的梯度,使返混区面积减小,流场稳定性提高。随着L_b/D增加,USC值呈现多峰值趋势,L_b/D=2.17时正弦波纹板沉降器的USC取得极大值为14.68,较平挡板提高了...     

炉前干馏过程中煤与热载体混合方式的研究

在热解反应器的上部设置混合段 ,在混合段内安装几层特制的挡板 ,固体热载体与煤颗粒在进入热解反应器之前先进入混合段 ,在挡板的作用下依靠重力进行快速分散、混合 ,然后落入反应器内进行热解反应 .实验在 1 kg煤～ 1 0 kg热载体的间歇粉煤快速热解反应装置上进行 ,并与用螺旋搅拌桨进行搅拌混合的热解实验结果进行了比较 .结果表明 ,在混合段内设置几层挡板是一种非常有效的混合方式 ,可以被用于炉前低温干馏过程 .     

VK管内锥形挡板结构最优化的计算机辅助设计

采用有限差分法求解二维流动的控制方程，计算出二维流场的径向混合、速度分布及停留时间分布，从理论上阐明了消除死角的方法。对挡板倾斜角、相邻两挡板的间距及开孔率的最优化进行了具体讨论。     

THE EFFECT OF VORTICES INDUCED BY BAFFLES ON CONCENTRATION POLARIZATION

A numerical analysis was performed to investigate the effect of recirculations formed by rectangular or triangular baffles on depolarization of concentration in a flat sheet membrane module. The k- ? turbulent model was used to predict the flow field in the flat channel. Control-volume-based finite difference methods were employed to solve for the two-dimensional fluid velocity and solute concentration distributions. We examined rigorously the effect of various parameters including the velocity, diffusivity, permeate flux, baffle size, baffle shape, and interbaffle spacing in an effort to find optimum operating conditions which may provide enhanced mass transfer. The vortices induced by the baffles on the membrane are found to be extremely effective in depolarizing the retained solutes at the membrane surface. The predictions show that baffle configurations and flow conditions have a great influence on depolarization of concentration. To achieve effective concentration depolarization, the baffle height should be greater than 0·5 (h = half the channel height) and the interbaffle spacing around 2h to 3h for the Reynolds number from 1,250 to 25,000. The simulated results indicate that the optimal Reynolds number is around 5,000 to 8,000 in view of both concentration polarization and energy consumption.     

SALT EFFECT IN HEAT OF MIXING: EFFECT OF DISSOLVED SALTS ON THE HEAT OF MIXING OF 2-PROPANOL-BENZENE SYSTEM

The effect of three dissolved salts namely sodium chloride, calcium chloride and zinc chloride on the heat of mixing (endothermic) of the binary system 2-propanol-benzene has been experimentally investigated. The salts were dissolved in the component in which they were preferentially soluble to concentrations up to 15% by weight wherever possible. The experimentation was done at 30°C using a standard type calorimeter attached to a micro-processor based control unit M1PROC The established experimental procedure was followed. The salts sodium chloride and zinc chloride brought about an enhancement in the heat of mixing values. Calcium chloride on the other hand has been found to produce an opposite effect.     

THE EFFECT OF DISTRIBUTORS ON TWO-PHASE AND THREE-PHASE FLOWS IN VERTICAL COLUMNS

Two-phase air-water and three-phase air-water-solids flows have been investigated in a 0.152 m internal diameter vertical column. Pressure drop across the distributor and average phase hold-up were measured for two-phase and three-phase flows over flow ranges of superficial gas velocity from 0 to 259 m/s and superficial liquid velocity from 0 to 0.0346 m/s. Gas hold-up/pressure-drop ratios were obtained as a function of superficial gas velocity and liquid flow rate. It was found that the bubble cap was better at gas distribution than that of the Koch static mixer in two-phase and three-phase vertical flows. Drift flux to gas hold-up and drift flux to gas flow rate correlations were obtained for two-phase and three-phase vertical flows. Three flow patterns, churn-turbulent, transition and ideal bubble flows, were observed for vertical upflow.     

流动方向对循环流化床中颗粒混合行为的影响

对循环流化床提升管及下行床两种不同气固流动方式对颗粒混合行为的影响进行了较为深入的对比分析，发现在影响循环流化床颗粒混合的众多因素（如操作条件、床层直径、颗粒性质及床层内构件等）中，气固流动方向是影响颗粒轴向混合的最主要因素．当气固流动为顺重力场时（下行床），颗粒的轴向混合很小，流型接近平推流；当气固流动为逆重力场的提升管时，轴向颗粒混合将成倍增大，颗粒流动远离平推流流动．分析表明，下行床中颗粒混合仅为单一的弥散颗粒扩散，而提升管中则存在着两种颗粒混合机制：弥散颗粒扩散及颗粒团扩散．弥散颗粒的扩散基本以平推流的形式通过循环流化床，提升管中大量的颗粒轴向返混归因于颗粒团的严重返混并由此形成了提升管中颗粒停留时间的双峰分布．     

TRANSITION OF FLOW REGIME IN FLUIDIZED BEDS WITH SLANTING BLADE BAFFLES

A flow model is proposed to investigate the transition of flow regime from bubbling to turbulent fluidization postulating that the flow in the emulsion phase follows the Richardson-Zaki equation.

Void fraction of the whole bed ε_f and the mean velocity of bubbles U_b were measured in fluidized beds of 0.3 and 0.5 m ID, in which slanting blade baffles were positioned. Mo-catalyst, silica gel, sand and glass beads with size between 135-443 μm were fluidized by air.

Void fraction of the emulsion phase ε _e was calculated on the basis of the above model. Correlating ε _e with superficial gas velocity U_ƒ, we found that ε _e was very close to ε _mƒ in the bubbling regime and that e, increased with increasing U_ƒ in the turbulent regime.

Calculated values of the volume fraction of bubble phase δ were correlated with U_ƒ, from which apparent transition point from bubbling to turbulent regime was estimated. Combining information obtained, transition of flow regime in the above type of fluidized beds is discussed     

THE EFFECT OF IMPERFECT MIXING ON POLYMER QUALITY IN LOW DENSITY POLYETHYLENE VESSEL REACTORS

A mathematical model is developed for the calculation of polymer quality in low density polyethylene vessel reactors, taking into account mixing limitations at the initiator feed point. Model predictions show that imperfect mixing in the reactor can produce considerable variations in polymer molecular weight distribution. The effect of the most important process conditions, input feed temperature, solvent concentration, monomer flow rate and initiator type, on the final polymer quality is analyzed. The advantages of the design solution which divides the reactor in more compartments in series are also discussed.     

THE EFFECT OF IMPERFECT MIXING ON POLYMER QUALITY IN LOW DENSITY POLYETHYLENE VESSEL REACTORS

A mathematical model is developed for the calculation of polymer quality in low density polyethylene vessel reactors, taking into account mixing limitations at the initiator feed point. Model predictions show that imperfect mixing in the reactor can produce considerable variations in polymer molecular weight distribution. The effect of the most important process conditions, input feed temperature, solvent concentration, monomer flow rate and initiator type, on the final polymer quality is analyzed. The advantages of the design solution which divides the reactor in more compartments in series are also discussed.     

THE EFFECT OF DRAFT TUBES ON CIRCULATION AND MIXING TIMES

Low circulation times do not necessarily imply good mixing. Data on circulation and mixing times plus their various standard deviations should be obtained and reported in any mixing study. The standard deviation in circulation times inversely measures the uniformity of momentum transfer in an agitated tank but should not be used as a measurement of mixing. The standard deviations of the mixing times obtained were substantially different from those obtained from circulation time data. The use of draft tubes and cone bottoms will improve the mixing in a processing vessel.