高长径比气液固三相内环流反应器的流体动力学

在高径比为22的三相内环流反应器中,常温常压下,根据动量平衡原理建立了空气-水-石英砂三相物系的循环液速模型,并建立了上升区气含率、上升区固含率和底部换向区阻力系数模型;考察了在不同颗粒粒径下,表观气速对上升区固含率和液体循环速度的影响。结果表明:当粒径(ds)≤0.3mm时,上升区固含率随表观气速的增加变化呈平缓趋势,当0.3mmds≤1.2mm时,上升区固含率随表观气速的增加而呈先下降后增加的趋势;不同粒径下上升区循环液速均随表观气速的增加而增加;气含率、固含率和循环液速的计算值和实验值吻合较好,其平均相对误差分别为6.32%、4.56%和11.97%。     

三级环流反应器中气液流动与传质规律

针对级间安装导流筒的三级环流反应器的气液流动与传质过程开展实验研究。通过冷模实验获得不同表观气速下(0.015～0.1m/s)以及安装不同级间内构件时环流反应器内的气含率、混合时间、停留时间以及体积氧传质系数。结果表明,随着表观气速的增加,反应器各级内的气含率增加,混合时间减少,平均停留时间减小,同时氧传质系数增加。通过对反应器内气液流型的变化的观察,进一步分析了级间内构件对三级环流反应器性能的影响,发现内构件上截面较宽时(3^#内构件),反应器的混合效果更好,而内构件的上截面较小时(1^#内构件),反应器可以更好地抑制返混。     

级间隙高度和表观气速对多级环流反应器混合和传质的影响

针对应用广泛的简单多级环流反应器,研究了级间隙高度和表观气速对其混合和传质的影响规律。发现简单多级环流反应器的各级存在着非正常流动、过渡及正常流动三个典型流动状态,且流动状态的转变存在着受级间隙高度影响的两个临界表观气速,并提出了相应的预测模型。研究结果表明：级间隙高度越大,多级环流反应器内形成正常流型所需的表观气速越大;各级上升管和降液管的气含率会增高,且相同条件下第三级气含率最大,第二级次之,第一级气含率最小;各级的循环液速会增大,且第一级循环液速最大,第二级次之,第三级最小;混合时间会缩短,而传质系数会增大。本研究可为工业多级环流反应器的科学设计、放大和操作提供重要指导。     

气升式内循环反应器的数值模拟和结构参数

采用Euler-Euler双流体模型对内循环反应器(高1240 mm,直径165 mm,导流筒高590 mm)进行数值模拟,考察了表观气速、导流筒结构(导流筒内径比Dt/D,底隙高度)对反应器内上升区、下降区流体力学参数(气含率、液体速度)的影响. 结果显示,表观气速、导流筒内径、底隙高度对反应器气含率、液体速度有很大影响,随表观气速增加,反应器上升区、下降区气含率都增加,导流筒内径比为0.58时更易实现气液循环,底隙高度为30 mm时反应器内下降区气含率、气液速度都最小;气液分离器角度越大,进入下降区的气体越多,当气液分离器角度为45o时,能更好地实现气液循环.     

气液外环流反应器中气泡行为的实验研究

详细考察了气液外环流反应器中上升管、下降管的气泡行为随轴向、径向的变化规律. 由于外环流反应器的结构特点,发现在上升管底部存在偏流,并对分布板区气泡行为随角向的变化规律进行了研究. 分析实验结果得出,气含率和气泡速度均随表观气速的升高而升高;在上升管内,气含率和气泡速度自中心向边壁逐渐降低,而沿轴向变化很小;在分布板区,由于受分布器及下降管的影响,使气含率和气泡速度在不同角向存在不同的径向分布. 在下降管中,气含率自中心向边壁逐渐降低,而气泡速度则基本不变;且下降管中的气体循环率随表观气速的升高而升高.     

级间隙高度和表观气速对多级环流反应器混合和传质的影响

针对应用广泛的简单多级环流反应器,研究了级间隙高度和表观气速对其混合和传质的影响规律。发现简单多级环流反应器的各级存在着非正常流动、过渡及正常流动三个典型流动状态,且流动状态的转变存在着受级间隙高度影响的两个临界表观气速,并提出了相应的预测模型。研究结果表明:级间隙高度越大,多级环流反应器内形成正常流型所需的表观气速越大;各级上升管和降液管的气含率会增高,且相同条件下第三级气含率最大,第二级次之,第一级气含率最小;各级的循环液速会增大,且第一级循环液速最大,第二级次之,第三级最小;混合时间会缩短,而传质系数会增大。本研究可为工业多级环流反应器的科学设计、放大和操作提供重要指导。     

多室气升式环流反应器流动特性的数值模拟

在空气-水两相多室气升式环流反应器（MALR）中,采用欧拉欧拉两相流模型对扇形反应室内气液两相流动过程进行了数值模拟研究,考察了上升室的气含率、液体速度随表观气速的变化,最后用实验数据对模拟结果进行了验证.结果表明,某一上升室气含率受该室表观气速的影响较大,与另一上升室表观气速的影响较小;循环液体与上升室流体流动型式有关;气含率和循环液速的模拟值与实验值的平均相对误差分别为5.36％和8.28％;说明了应用数值模拟方法研究MALR流动特性的可行性.     

上流式反应器气液相间传质特性的实验研究

上流式反应器设置在固定床渣油加氢反应器前有利于提高渣油原料适用性,延长装置运行时间。实验研究了上流式反应器气液相间传质,采用五齿柱形氧化铝催化剂模拟工业催化剂颗粒,水溶液模拟渣油,空气模拟氢气,采用无氧水物理吸收和亚硫酸钠化学吸收的方法,测定了在高气液比的条件下上流式反应器床层气液相间传质特性实验。考察了表观气速、表观液速、填料粒径、内构件、催化剂级配和床层高径比对液相体积传质系数和气液相界比表面积的影响规律。实验数据表明,液相体积传质系数随着气、液速的增大而增大;随填料颗粒增大而减小;在床层内安装合适的内构件或增大反应器高径比,能够促进气液相间传质。基于实验数据拟合了适合上流式反应器液相体积传质系数和气液相界比表面积的经验关联式,拟合误差最大分别为12%和24%;表明所建气液相间传质的经验关联式能更好地预测上流式反应器中的气液相间传质特性。     

高长径比三相内环流反应器中细颗粒相含率和循环液速的分布研究

在高径比为22的三相内环流反应器中,在常温常压下以空气-水-石英砂为物系,研究了在不同粒径下上升区固含率、下降区固含率和上升区循环液速随表观气速的变化规律和不同粒径下轴向固含率的分布情况,以及在固体体积分数不同的条件下,平均气含率和上升区气含率随表观气速的变化情况。结果表明:当粒径(ds)≤0.3 mm时,上升区固含率随表观气速的增加呈平缓变化趋势,下降区固含率随表观气速的增加而增加;当0.3 mm相似文献   

三相气升式环流反应器内上升区相含率轴向分布与循环液速的研究

常温常压下,在三相气升式内环流反应器中,将硅铝球、石英砂和瓷球分别与空气、水组成三相物系,考察了细颗粒与大颗粒物系中上升区相含率轴向分布规律、固体装载率和颗粒粒径对该规律的影响,以及各物系中上升区循环液速随表观气速的变化规律。结果表明:随轴向高度的增加,瓷球物系中上升区固含率εsr先增大后减小;硅铝球物系中εsr减小;石英砂物系中εsr均匀分布。随轴向高度的增加,瓷球物系中上升区气含率εgr增大;硅铝球物系中εgr减小;石英砂物系中εgr先增大后减小。固定表观气速,各轴向位置处的上升区气含率随固体装载率、颗粒粒径的增大而增大。当固体装载率相同时,各物系中上升区循环液速随表观气速的增大而增大。     

Axial hydrodynamic studies in a gas-liquid-solid circulating fluidized bed riser

Axial distribution of phase holdups was studied in the riser of a gas-liquid-solid circulating fluidized bed (GLSCFB). The effects of gas and liquid superficial velocities as well as solids circulation rate on radial distribution of phase holdups at different axial locations were investigated. Electrical resistance tomography (ERT) and optical fiber probe were employed online in the experiments for a precise determination of phase holdups. An empirical model was developed for the determination of gas bubbles in analysis of data obtained by fiber optic sensor. Gas holdup was higher at the central region of the riser and increased axially due to coalescence of small bubbles and decrease of hydrostatic pressure at higher levels in the riser. This led to an increase in solids holdup in regions close to the wall which was slightly higher than the solids holdup at the wall. Both solids and liquid holdups were lower in the central region and increased radially towards the wall. Gas holdup decreased with increasing solids circulation rate but opposite trend was observed for solids holdup. Solids circulation rate had negligible effect on liquid holdup at lower axial locations compared to top of the riser. Cross-sectional average of solids, gas and liquid holdups did not change significantly at higher liquid superficial velocities.     

EFFECTS OF AERATED LIQUID LEVEL ABOVE DOWNCOMER ON HYDRODYNAMIC CHARACTERISTICS OF AN EXTERNAL-LOOP AIRLIFT REACTOR

Effects of the aerated liquid level above the downcomer on riser superficial liquid velocity, gas flow rates, and gas holdups in individual sections were investigated in an external-loop airlift reactor. The aerated liquid level is an important operating parameter, and the valve connected to the extension tube could adjust it. As the aerated liquid level was increased up to 0.158 m, which was slightly larger than the diameter of the riser, both the liquid circulation velocity and the gas flow rate in the extension tube increased, whereas the riser gas holdup, the downcomer gas holdup, and the gas flow rate in other individual sections except the extension tube decreased. A combination of the gas-liquid separation ability and hydraulic resistance of the head region and the surface aeration could explain the impact of the aerated liquid level on the hydrodynamic characteristics. However, the effect was negligible when the aerated liquid level was higher than 0.158 m.     

EFFECTS OF AERATED LIQUID LEVEL ABOVE DOWNCOMER ON HYDRODYNAMIC CHARACTERISTICS OF AN EXTERNAL-LOOP AIRLIFT REACTOR

Effects of the aerated liquid level above the downcomer on riser superficial liquid velocity, gas flow rates, and gas holdups in individual sections were investigated in an external-loop airlift reactor. The aerated liquid level is an important operating parameter, and the valve connected to the extension tube could adjust it. As the aerated liquid level was increased up to 0.158 m, which was slightly larger than the diameter of the riser, both the liquid circulation velocity and the gas flow rate in the extension tube increased, whereas the riser gas holdup, the downcomer gas holdup, and the gas flow rate in other individual sections except the extension tube decreased. A combination of the gas-liquid separation ability and hydraulic resistance of the head region and the surface aeration could explain the impact of the aerated liquid level on the hydrodynamic characteristics. However, the effect was negligible when the aerated liquid level was higher than 0.158 m.     

Phase distributions in a gas–liquid–solid circulating fluidized bed riser

The distributions of the three phases in gas–liquid–solid circulating fluidized beds (GLSCFB) were studied using a novel measurement technique that combines electrical resistance tomography (ERT) and optical fibre probe. The introduction of gas into a liquid–solid circulating fluidized bed (LSCFB), thus forming a GLSCFB, caused the increase of solids holdup due to the significantly decreased available buoyancy with the lower density of the gas, even with a somewhat increased liquid velocity due to the decreased liquid holdup giving space for the gas holdup. The gas passed through the riser in the form of bubbles, which tended to flow more through the central region of the riser, leading to more radial non‐uniformity in radial holdup of the phases. The gas velocity has the most significant effect on the gas phase holdup. While the gas velocity also has an obvious effect to the solids holdups, the liquid flow rate had a much more considerable effect on the phase holdups. The solids circulation rate also had a significant effect on the phase holdups, with increasing solids circulation rate causing much more increased solids holdup in the central region than close to the wall. A correlation was developed for the relative radial distributions of solids holdup in GLSCFB, as such radial profiles were found similar over a wide range of operating conditions, like those in a typical gas–solid circulating fluidized beds (GSCFB). Finally, the axial solids profiles in a GLSCFB was found to be much closer to those in an LSCFB which are very uniform, than those found in a GSCFB which are less uniform and sometime having a S shape. Water was used as the continuous and conductive phase, air was the gas phase and glass bead and lava rock particles were used as the solid and non‐conductive phase.     

三相多室气升式环流反应器气含率的研究

在1个4流道的三相多室气升式环流反应器中,以空气-水-K树脂为体系,采用压差法测量气含率,考察了上升室气体表观速率、固体装载量对上升室与下降室气含率的影响.结果表明:上升室的气含率随着该室气体表观速率增加而增加,而随着另一上升室气体表观速率增加而略有降低;下降室的气含率随着该室气体表观速率增加呈现3种变化趋势,而随着另...     

高长径比环流反应器中气、固含率的轴向分布研究

在高长径比(H/D=22.2)内环流反应器中,常温常压下,以空气-水-石英砂为物系,研究了表观气速和固体装载量对平均气含率、下降区气含率、上升区固含率、下降区固含率的影响,以及上升区气含率、固含率随轴向高度的分布规律.结果表明:平均气含率、下降区气含率随着表观气速的增加而增加,随ω(固体)增大而下降,ω(固体)≤2.6...     

Circulation liquid velocity,gas holdup and volumetric oxygen transfer coefficient in external-loop airlift reactors

The effects of the horizontal connection length (0.1 ± L_e ± 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 on gas phase holdups in the riser and downcomer were studied. The circulation liquid velocity, the mixing performance and the volumetric mass transfer coefficient in the external-loop airlift reactors were also measured. The horizontal connection length and A_d/A_r were major parameters which strongly affected the performance of external-loop airlift reactors. Useful correlations in the external-loop airlift reactors were obtained for gas holdups, the volumetric mass transfer coefficient, the circulation liquid velocity, and the mixing time.     

Hydrodynamic and mass transfer characteristics of external-loop airlift reactors without an extension tube above the downcomer

The effects of the horizontal connection length (0.1≤L_c≤0.5 m), the downcomer-to-riser cross-sectional area ratio (0.11≤A_d/A_r≤0.53) and the superficial gas velocity (0.02≤U_G≤0.18 ms^-1) on gas holdups in the riser and downcomer, the circulation liquid velocity, the mixing time, and the overall volumetric mass transfer coefficient were determined in external-loop airlift reactors without an extension tube above the downcomer [configuration (a)]. For otherwise fixed conditions, the absence of the extension tube strongly affected the hydrodynamic and mass transfer characteristics of external-loop airlift reactors. In contrast with the external-loop airlift reactor with the extension tube [configuration (b)], a large air pocket formed in the top horizontal connection and the surface aeration took place in the external-loop airlift reactor without the extension tube [configuration (a)]. As a result, the riser circulation liquid velocity in configuration (a) was slower than that in configuration (b). The riser and downcomer gas holdups, the mixing time and the overall volumetric mass transfer coefficient in configuration (a) were larger than those in configuration (b), respectively.