【作者】 毕荣山；

【导师】 马连湘；

【作者基本信息】 青岛科技大学 ， 化学工程， 2008， 博士

【摘要】 化工装置中的反应过程通常都是在湍流状态下进行的,反应物之间混合的好坏和混合速度的快慢对反应的收率和选择性具有重要的影响。喷射器作为一种新型的具有高强度混合效果的反应器型式,在石油、化工、环保、制药等领域发展迅速,已有广泛应用。然而,由于喷射器内湍流反应过程的复杂性和多尺度性,目前对其研究还很不充分,设计和放大都基本依靠实验来进行。本文对高Schmidt数下喷射器内湍流反应过程这一复杂问题进行了研究,通过尺度理论分析、面激光诱导荧光(Planar laser induced fluorescence,PLIF)实验和计算流体力学(Computed fluid dynamics,CFD)模拟相结合的方法,对湍流反应过程中涉及的宏观混合、微观混合、反应过程及其之间的相互作用对喷射反应器性能的影响进行了探讨。一、利用尺度理论对高Schmidt数下喷射器内湍流反应过程进行了分析,计算了通常情况下湍流反应所涉及的宏观混合、介观混合、微观混合和反应过程的特征时间尺度,初步获得了湍流反应过程各特征时间之间的相互关系,为反应器的初步设计和详细计算提供依据。二、利用PLIF技术对不同操作条件下喷射器内物料的宏观混合情况进行了实验研究,利用离析度的概念对混合状态进行了分析,结果表明喷嘴速度和引射流速度对混合效果作用相反,而二者流速比越大,混合效果越好,同一流速比下,绝对速度越大,混合效果越好。利用PLIF实验数据对三种不同的湍流模型:标准k-ε模型、重整化k-ε模型和可实现k-ε模型进行了比较,结果显示重整化k-ε模型与实验数据相差较大,而标准k-ε模型和可实现k-ε模型均能获得较好的结果。三、借助于涡破碎(Eddy break-up,EBU)模型,利用酸碱反应的转化率来表征宏观混合情况,在避免了EBU模型模拟反应过程不准确缺点的同时,考虑了反应对混合过程的反作用。利用此模型对不同操作参数、不同结构尺寸下喷射反应器内的宏观混合进行了分析,并进一步讨论了喷射器的放大规律。结果表明:1.扩散角度越小,喷射反应器内流体混合越好,相同截面上转化率越高,但是同时喷射器的阻力也越大;喷嘴/混合段直径比存在一个最优值,大于该值则喷射反应器相同截面上转化率变低,而小于该值则会消耗更多的能量但转化率不会再提高;喷嘴出口离混合段距离越远,反应越快完成,喷嘴出口位置与吸入口流体管中心在同一平面时反应效果最好。2.根据速度相似原则和雷诺数相似原则放大的喷射反应器不能满足要求,而同时提高入口速度和改变结构尺寸可以得到满足放大要求的喷射反应器。喷射反应器最佳的速度比随着基准情况下流速的增加和喷嘴直径的增加而增大,并利用模拟数据回归出了放大前后的喷射器入口流速比与基准反应器结构尺寸和流速的关系。四、利用宏观混合分数方差和微观混合分数方差来定量的表征宏观混合和微观混合状态,对喷射器内的湍流混合进行了多尺度模拟和研究,并计算出了达到完全混合所需要的特征混合时间。对不同操作条件下的多尺度混合情况进行了模拟计算和分析。结果表明,在引射流速度不变的情况下,增加喷嘴速度,可以降低达到完全混合所需要的时间;在喷嘴速度不变的情况下,增加引射流速度,可以增加达到完全混合所需要的时间;在喷嘴和引射流速度比不变的情况下,增加两者绝对速度,可以降低达到完全混合所需要的时间;在本文所研究的情况下,喷射反应器内湍流混合过程由微观混合控制。五、通过矩直接积分(Direct quadrature method of moments,DQMOM)模型对典型的平行—竞争反应体系在喷射反应器内湍流反应过程进行了模拟研究,结果显示:1.DQMOM模型可以正确的对喷射器内湍流混合与反应之间的相互关系进行模拟,可以直观的给出喷射器内不同位置的反应混合情况,为反应器的优化设计提供依据。2.在引射流速不变的情况下,喷射反应器随着喷嘴速度的增加混合效果越来越好,达到完全混合所需要的时间越来越短,平行—竞争反应的选择性越来越高,副反应的转化率越来越低;在固定喷嘴流速的情况下,喷射反应器随着引射流体速度的增加混合效果越来越差,达到完全混合所需要的时间越来越长,平行—竞争反应的选择性越来越低,副反应的转化率越来越高;喷射反应器随着喷嘴与引射流体流速比的增加混合效果越来越好,在流速比一定的情况下,达到完全混合的时间随着绝对速度的增加而逐渐降低。3.在喷嘴速度一定的情况下,反应转化率与Da数成线性关系,而直线的斜率由喷嘴速度确定。更多还原

【Abstract】 Reactions in chemical industry normally proceed in condition of turbulent flow. Mixing of reactive materials has an important effect on yield and selectivity of the reactions. As a new type of high-intensity-mixing reactor, jet reactors have been widely used in the field of petroleum, chemical, environment and pharmacy industries. However, turbulent reaction in jet reactors is a complex multi-scale process and studies on it are not enough. Up to now, design and scale-up of jet reactors are depend on experiments. The work in this thesis aims to study the complex process of turbulent reaction in jet reactors on high Schmidt. The effects of macro-, meso-, micro- mixing and reactions on reactors were studied by means of scale theory analysis, PLIF experiments and CFD simulations.1. The turbulent reaction in jet reactors on high Schmidt number was analyzed with scale theory. The characteristic time of micr-, meso-, macro-mixing process and reaction on normal conditions were calculated and the control step was obtained. These data could provide useful information for the incipient design and detail computation of jet reactor.2. The macro-mixing in jet reactor was studied through PLIF experiments and the mixing performance was analyzed by means of intensity of segregation (IOS). Results showed that the nozzle velocity and entrained flow velocity have opposite effects on the mixing performance. The larger of the ratio of nozzle and entrained flow velocities is, the better the mixing performance is; In the case of the constant ratio , the larger the velocities are, the better the mixing performance is. Three turbulent model were tested by the PLIF experiments, and the results showed that the RNG k-εmodel gave worst data compared with that of experiments, but both the standard and realizable k-εmodel gave satisfied results.3. EBU model was used to compute the conversion of the acid-base neutralization, and the conversion was used to measure the macro-mixing performance. This method avoids the shortcoming of the EBU model and at the same time, the effect of reaction to mixing process is allowed. Based on the method, the macro-mixing in jet reactors was studied on different operation condition and different configuration parameters, and the rule of scale-up was also considered:(1) The smaller the angle of diffuser section is, the better the macro-mixing and the higher conversion rate can be achieved, but at the same time more kinetic energy is consumed; An optimum value for the ratio of diameter between nozzle and mixing section existed. If the value is larger than the optimum value, the conversion rate in the jet reactor would decrease, while if the value is smaller than the optimum value, more kinetic energy would be consumed but could not improve conversion rate any more; The farther the distance between nozzle outlet and mixing section are, the faster the reaction completes. The best case was obtained when the nozzle outlet shares the same plane with the center of suction inlet.(2) The scaled up rules of the velocity similarity principle the Reynolds number similarity principle are not proper to jet reactor, however, improving velocity and changing geometry size simultaneously gave satisfied results. The CFD simulation results showed that the optimum value of velocity ratio was increased with the increasing of velocity and diameter in initial conditions. Two formulas of the velocity ratio and initial configuration of jet reactors with the velocity were regressed based the simulation results4. The variances of macro- and micro- mixture fraction were used to represent the performance of macro- and micro-mixing. Multi-scale simulation and study were made of jet reactor and the characteristic times of macro- and micro-mixing were obtained on different operation conditions. The results showed that in the case of constant entrained flow velocity, the mixing time to reach complete mixing was decreased when the nozzle velocity was increased; In the case of constant nozzle velocity, the mixing time to reach complete mixing was increased when the entrained flow velocity was increased; In the case of constant velocity ratio of nozzle and entrained flow, the mixing time to reach complete mixing was decreased when both the velocity were increased; All the cases studied in this thesis, the control step of the turbulent mixing in jet reactor was micro-mixing process.5. The turbulent reactions of typical parallel-competitive reactions were simulated and studied using DQMOM model. The results showed:(1) The DQMOM model can be used to simulate turbulent reactions in jet reactor appropriately and can give detailed information inside the reactor. This information can be used for optimized design of jet reactor.(2) In the case of constant entrained flow velocity, with the nozzle velocity increased, the mixing performance of jet reactor became better, the time needed to reach complete mixing was decreased, the selectivity and of parallel-competitive reactions was increased and the conversion of the side reaction was decreased. In the case of constant nozzle velocity, with the entrained flow velocity increased, the mixing performance of jet reactor became bad, the time needed to reach complete mixing was increased, the selectivity and of parallel-competitive reactions was decreased and the conversion of the side reaction was increased. In the case of constant velocity ratio of nozzle and entrained flow, with the nozzle and entrained flow velocity increased, the mixing performance of jet reactor became better, the time needed to reach complete mixing was decreased, the selectivity and of parallel-competitive reactions was increased and the conversion of the side reaction was decreased.(3) In the case of constant nozzle velocity, the conversion of the second reaction has a linear relationship with Damkoler number, and the slope of the line was connected with nozzle velocity.更多还原