反应器流场测试技术进展

流体流动速度分布测试技术的发展对反应器内流体的传质、传热、传动的研究,进而对反应器的机理性数学模型建立及数学模拟起极大地推动作用。本文对反应器以及颇具特色的生化反应器的流场测试技术作了综述并展望了该技术的发展。     

Local,global, and elementary stoichiometry

Stoichiometry refers to conservation of atomic species. In this article, local refers to a point at the continuum level, global refers to the macroscopic balance level, and elementary refers to conservation of atomic species associated with distinct kinetic steps. The role of stoichiometry in the determination of the pivot matrix and the mechanistic matrix is presented. The elements of both these matrices are referred to as stoichiometric coefficients; however, both sets of coefficients are different and both play different roles in the analysis of chemical reactors. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

滴流床反应器流体力学的研究进展

系统综述了滴流床反应器的流体力学研究现状，分析了流型的转变、床层压降和持液量的关联结果，总结了主要的反应器模型和压力对床层压降及持液量的影响，并详细讨论了操作方式对滴流床反应器流体力学的影响。     

Modelling of catalytic reactors containing core–shell pellets with various morphologies for series reactions

Modelling of series reactions was performed for core–shell catalysts. Mathematical solutions of concentrations inside the pellets were derived from reaction–diffusion equations considering inert-core thickness (ξ_c) for first-order kinetics. Transient behaviours of catalytic reactors containing core–shell pellets were predicted, assuming pseudo-steady state approximation. In a batch reactor, the removal rate of reactants increased with increasing Thiele modulus and decreasing ξ_c in the order of sphere > cylinder > slab. The transient concentration of the intermediate product was maximum and affected by the distribution coefficient, diffusivity ratio, particle shape, and ξ_c. In a continuously stirred tank reactor, the concentration was affected by feed rate and catalyst loading, and conversion could be enhanced by a cascade connection. In a fixed-bed reactor, the concentration increased with increasing ξ_c due to an insufficient catalyst volume. Péclet number and particle shape also affected the concentration, implying that axial dispersion and interfacial area are important design parameters.     

Modeling studies of low‐temperature aerobic NOx reduction by a sequence of LNT‐SCR catalysts

The relationship between fuel penalty and precious metal loading in coupled LNT? SCR systems for NO_x reduction at low temperatures is determined. Simulations of adiabatic, aerobic NO_x reduction determine the impact of catalyst architecture, precious metal loading, cycle time, catalyst length and the support material. These revealed that (a) high NO_x conversion can be achieved for a given precious metal loading at low temperatures (510 K) with about 0.3% fuel penalty, (b) shortened cycle time and increased pulse duty reduce the overall NO_x slip from the coupled catalyst and lead to significant improvement in the NO_x conversion, (c) alternate arrangement of the LNT/SCR catalysts increases the NO_x conversion, (d) a monotonic decreasing PGM loading in LNT leads to higher NO_x conversion compared to uniform loading, (e) for a fixed catalyst volume, there is an optimal aspect ratio that maximizes the nonisothermal effect, and (f) metal based monolith supports improve NO_x conversion. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3421–3431, 2013     

丙烯氢氧环氧化动力学与反应器概念设计研究进展

环氧丙烷（PO）在全球产能最高的35种化学品中,是仅次于聚丙烯的第二大丙烯衍生物,主要用于生产聚醚多元醇、聚氨酯等。相比传统的氯醇法、共氧化法和双氧水直接氧化法（HPPO）等PO生产工艺,丙烯在氢氧混合气中一步环氧化制PO（HOPO）具有工艺简单、选择性高、产物易分离、能耗低等突出优势,是生产PO的理想工艺。重点介绍了丙烯氢氧环氧化反应动力学研究进展,包括主、副反应动力学模型以及催化剂失活模型。总结了基于该过程安全操作的反应器概念设计进展。分析了丙烯氢氧环氧化反应存在的挑战,从副产物生成途径、失活动力学及颗粒催化剂上的动力学等方面展望了可能的研究方向。     

Analytical solutions of reaction–diffusion phenomena by porous cylindrical pellets with finite length

Analytical solutions were derived to predict transient change of intra-particle concentration inside cylindrical pellets with finite length immersed in an infinitely large medium. After the derivation of steady-state concentration by eigenfunction expansion, a transient solution was obtained by the separation of variables. Effects of the Thiele modulus (Φ) and aspect ratio of the pellet (H/R) were studied by calculating the average intra-particle concentration at a stationary state. The effectiveness factor (η) was also affected by H/R and Φ, since irreversible first order kinetics was assumed. As Biot number (Bi) increased, both intra-particle concentration and η increased due to the decrease of the mass transfer resistance of the surrounding film. Good agreement between analytical and numerical solutions was confirmed for both steady-state and transient solution by comparing the analytical results with the numerical solutions by finite element method. To extend the results to a batch reactor with finite volume, Duhamel's theorem was applied by assuming time-dependent boundary conditions to reflect the change in bulk concentration as a function of time. A method was proposed to measure intra-particle diffusivity for batch adsorber by setting Φ = 0. To investigate the effect of H/R, η could be included in material balance of batch, continuously stirred tank reactor (CSTR), and fixed bed reactors to predict reactor performance assuming a pseudo-steady state. First-order reaction by egg-shell catalysts as well as nonlinear reaction with two reactants could be solved numerically assuming finite cylindrical pellets. By solving coupled differential equations of material and energy balances, dynamic catalysis was confirmed from the enhancement of conversion, assuming forced oscillation of inlet temperature in CSTR.     

固体颗粒对强化传递性质的多相气升式反应器流体力学影响

研究了加入机械搅拌和静态混合器后对多相气升式反应器流体力学性能的促进作用,重点考察固体颗粒的直径、固含率（固体质量分数,下同）对液体循环速度、气含率（气体体积分数,下同）等的影响。实验证明,对液体循环速度来说,在多相流中并非通气量、搅拌转速越大越好。对气含率而言,多相气升式反应器不但存在临界颗粒直径和临界固含率,还存在一个临界表观气速,在此气速以下,才能产生气含率随固含率增加而增加的现象。最后对气含率、固含率及能量耗散速率作了关联。     

超声波气升式内循环反应器流体力学性能研究

研究了超声波对气升式内循环反应器流体力学性能的促进作用,重点考察比较了有无超声波时气升式反应器性能及超声功率对反应器气含率、液体循环速度、混合时间等的影响。实验证明,超声波的加入对气含率未见影响,有使液体循环速度逐渐减小的趋势,而对混合时间的影响较复杂。在小气速下,小功率超声波促进流体的径向混合,随着超声功率的增加,超声振动阻碍流体的径向混合,因而存在一个最佳的超声功率,并且超声波对混合时间的影响随着表观气速的增加而逐渐减小。提出了该反应器流体力学关联式。     

Syngas chemical looping process: Dynamic modeling of a moving‐bed reducer

The syngas chemical looping process coproduces hydrogen and electricity with iron oxide based oxygen carriers in a circulating moving bed system. In this article, a one‐dimensional (1‐D) dynamic model is developed to simulate the countercurrent gas–solid reactive flow in the moving‐bed reducer. This model is validated by TGA and bench‐scale experiments. Both the steady state and dynamic composition profiles are obtained to help understand the reaction and reactor behaviors. Numerical simulation on the effects of reactor length is conducted to optimize the moving‐bed reducer design. It is also found that minor variations in the feed rate ratio near a critical point that is represented by the reaction equilibrium could yield a significant difference in the time required for the reactions to reach a steady‐state operation. Such a difference has an important practical implication in that the moving‐bed reducer should be designed and operated to circumvent the critical point. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3432–3443, 2013     

A dynamic analysis of chalcopyrite bioleaching in continuous flow reactor systems

A dynamic analysis of chalcopyrite bioleaching was performed in continuous flow systems. In contrast to a previous batch analysis¹ in which the influence of particle surface area on reaction rate was not accounted for, the unsteady‐state change in particle surface area was integrated into the dynamic analysis by application of the modified PBM.² The current study extends the analysis to include the influence of convective flow on the system. It is demonstrated that the analysis can be used to determine feasible control strategies for operating near the steady‐state maximum rate that is stable. Two strategies were evaluated for the purpose of increasing the leaching rates, showing that an increased rate of 56% is feasible. Analysis on experimental data showed that increased rates can be achieved by controlling the biomass concentration and ferric:ferrous ion ratio at an optimum by increasing the solids loading [m/v] in the reactor. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2428–2440, 2012     

An investigation into the dynamics of chalcopyrite bioleaching

A study was undertaken to investigate the dynamics of chalcopyrite bioleaching. The analysis revealed significant dynamics features because the chemical leaching rate of chalcopyrite does not vary monotonically with solution redox potential but undergoes a maximum followed by a minimum as potential increases. The analysis does account for reaction passivation, an effect that has consistently been reported in the literature. The existence and stability of steady states were determined as functions of the solution redox potential, reactor temperature, and biomass concentration. It was found that the rate of bioleaching increased with temperature at lower overall solution potentials with competitive rates observed at high ferric/ferrous ion ratios. Both high and low overall bioleaching rates were observed with increasing biomass concentration, indicating an upper concentration limit before passivation. These results indicate that the frequently observed inhibiting rates may simply be artifacts of the system dynamics rather than due to physical phenomena. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Determination of mass transfer resistances of fast reactions in three‐phase mechanically agitated slurry reactors

A methodology for the determination of mass transfer resistances of fast reactions in three‐phase mechanically agitated slurry reactors under the reaction conditions is presented. The mass transfer resistances affect significantly the overall mass transfer rate, the design equation and consequently the scale up of the reactor. There is not established methodology to separate the mass transfer resistances under reaction conditions by changing catalyst loading and manipulating the process variables, pressure and agitation speed. This allows to avoid the use of different catalyst particles and give the chance to calculate the mass transfer resistances without caring about the type of catalyst. We calculate each mass transfer resistance under conditions which do not allow to neglect any of the resistances. It is shown that the level off of mass transfer rate which is developed in the plot of mass transfer rate against agitation speed plots is not enough to determine the limiting regime. The hydrogenation of styrene over Pd/C (5% catalyst content) is used as case study to demonstrate the methodology. © 2016 American Institute of Chemical Engineers AIChE J, 63: 273–282, 2017     

Chemical‐looping combustion process: Kinetics and mathematical modeling

Chemical Looping Combustion technology involves circulating a metal oxide between a fuel zone where methane reacts under anaerobic conditions to produce a concentrated stream of CO₂ and water and an oxygen rich environment where the metal is reoxidized. Although the needs for electrical power generation drive the process to high temperatures, lower temperatures (600–800°C) are sufficient for industrial processes such as refineries. In this paper, we investigate the transient kinetics of NiO carriers in the temperature range of 600 to 900°C in both a fixed bed microreactor (WHSV = 2‐4 g CH₄/h/g oxygen carrier) and a fluid bed reactor (WHSV = 0.014‐0.14 g CH₄/h per g oxygen carrier). Complete methane conversion is achieved in the fluid bed for several minutes. In the microreactor, the methane conversion reaches a maximum after an initial induction period of less than 10 s. Both CO₂ and H₂O yields are highest during this induction period. As the oxygen is consumed, methane conversion drops and both CO and H₂ yields increase, whereas the CO₂ and H₂O concentrations decrease. The kinetics parameter of the gas–solids reactions (reduction of NiO with CH₄, H₂, and CO) together with catalytic reactions (methane reforming, methanation, shift, and gasification) were estimated using experimental data obtained on the fixed bed microreactor. Then, the kinetic expressions were combined with a detailed hydrodynamic model to successfully simulate the comportment of the fluidized bed reactor. © 2010 American Institute of Chemical Engineers AIChE J, 2010