引入大颗粒助剂对径向移动床流动特性的影响

针对错流移动床存在的空腔和颗粒流动偏离平推流的不正常操作问题。在一套φ600 mm×1300 mm半圆锥形和柱形错流移动床大型冷模实验装置上,借助于大颗粒助剂的引入有效提高了错流移动床出现空腔的临界速度,解决了错流移动床操作弹性低的问题。理论分析和实验结果表明,混入适量的大颗粒助剂可使颗粒流动不均匀性得到明显改善。     

Optimal conditions of isobutane dehydrogenation in radial flow moving bed hydrogen-permselective membrane reactors to enhance isobutene and hydrogen production

In the isobutane dehydrogenation process, coupling reaction and separation and optimization of the intensified process can improve the isobutane conversion and selectivity, reduce operational costs and lets to produce pure hydrogen. In this research, the radial flow moving bed reactors in the Olefex technology have been supported by Pd–Ag membrane plate to remove hydrogen from the reaction zone. The reactions occur in the tube side and the hydrogen is permeated from the reaction zone to the sweep gas stream. The proposed configuration has been modeled heterogeneously based on the mass and energy conservation laws considering reaction networks. To prove the accuracy of the considered model, the simulation results of the conventional process have been compared against available plant data. The Genetic algorithm as an effective method in the global optimization has been considered to optimize the operating condition of membrane reactors to enhance isobutene productivity. In this optimal configuration, the isobutene production has been enhanced about 3.7%.     

Steady state behavior of moving bed reactors

A relatively simple model for a moving bed reactor in which ignition takes place is presented and the steady state problem is solved analytically and numerically. The dependence of multiplicity and the nature of the solution on the parameters of the system are investigated. Some similarities in the analyses between fixed bed reactor theory and moving bed reactor theory are shown.     

Comparison between simulated moving bed and reverse flow chromatographic reactors for equilibrium limited reactions

A staged linear model, containing five parameters, is developed to compare equivalent simulated moving bed chromatographic reactors (SMBCR) and reverse flow chromatographic reactors (RFCR). A first order reversible reaction and linear adsorption equilibrium, with preferential adsorption of the reactant is assumed. The analysis uses simple, easily computable analytical solutions that rigorously represents the transients in the cyclic steady state for both the RFCR and the SMBR. A comparison between the two types of reactors is carried out to determine the maximum conversion attainable and the range of operation where these systems have advantages over conventional steady state reactors. It is found that the maximum conversion of both reactors is similar. The range of operation in terms of amount of catalyst and range of switching times favors the RFCR, while the conversion at low separation factors favors the SMBCR.     

Simulation of petcoke gasification in slagging moving bed reactors

A mathematical model for simulation of moving bed petcoke gasifiers was developed. The model introduces a new feed characterization method, gas-phase resistance and volatilization models. The model is validated using reported data for a slagging gasifier. Effect of feed oxygen-to-coke and steam-to-coke ratios and feed coke rates on gasification performance was examined. Slagging zone moving bed gasifier operation with very high petcoke fluxes of over 4000 kg/m²/h was possible with high petcoke conversion. Peak gas temperatures exceeded 1500 °C. Fluxes higher than 5000 kg/m²/h are limited by an approach to fluidization of small particles in the combustion zone. The moving bed gasifier performance was found superior to performance of an entrained flow gasifier (EFG) with respect to energy efficiency and oxygen consumption.     

Selectivity of aging catalyst in static,moving and fluidized bed reactors

The catalyst decay theory of Wojciechowski is applied to a simplified mechanism of catalytic gas oil cracking. The resulting patterns of selectivity predicted for a static bed reactor are presented in detail and general conclusions are drawn. It is shown that selectivity in gas oil cracking is bounded by optimum and minimum performance envelopes which confine the range of possible product distributions. For the simple cases considered, moving and fluidized bed reactors show selectivity patterns which invariably fall on the optimum performance envelope.     

Trickle bed reactors: Effect of liquid flow modulation on catalytic activity

The effect of slow ON-OFF liquid flow modulation on the oxidation of aqueous solutions of ethanol using a 0.5% Pd/Al₂O₃ commercial egg-shell catalyst was investigated in a laboratory trickle bed reactor (TBR). In this mode of operation, the catalyst was cyclically exposed to oxidative and reductive environments.The study was carried out under different gas and liquid flow rates, cycle periods and splits. Cycling results have been compared with the steady-state experiments performed at the corresponding average liquid flow rate. Significant improvements over the continuous operation were obtained when the catalyst was exposed to a short surplus of oxygen (to minimize deactivation by overoxidation in the kinetic regime) after a longer time of working in the mass transfer limited regime. According to the results presented here, it is recommended to work with high liquid flow rates and moderate gas flow rates to ensure complete wetting of the catalyst during the ON cycle and to minimize the overoxidation process during the OFF cycle.     

Impact of flow-corrective insert on flow patterns in two-dimensional moving bed

This paper presents the study of the flow patterns inside a granular moving bed in a quasi-two-dimensional (2D) model of a granular moving bed filter (GMBF) vessel with vertical walls and a mass flow hopper. Fine quartz sand was chosen as the granular filter media in experiments. The related flow properties were measured by a Jenike Shear Tester. According to the flow properties of fine silica sand and Johanson's theory, a 2D moving-bed apparatus was built, with transparent walls and the flow-corrective insert to diminish the quasi-stagnant zones along the side walls. The flow patterns and velocity profiles of silica sand in the system with flow-corrective insert were studied experimentally, and the effect of the location of the flow-corrective insert on the internal flow patterns was investigated. The optimal placement of flow-corrective insert according to Johansson's theory was demonstrated to efficiently diminish the quasi-stagnant zones near the side walls. Little vertical shift of the flow-corrective insert from optimal position changed the stable and uniform mass flow pattern of moving bed into the funnel flow.     

Laminar radial flow electrochemical reactors. III. Electroorganic sysnthesis

This paper investigates the performance and design of three laminar radial flow electrochemical cells (the capillary gap cell, stationary discs; the rotating electrolyzer, co-rotational discs; the pump cell, one disc rotating and the other stationary). Modeling of a competing electrosynthesis pathway is described — the methoxylation of furan. The model developed incorporates convective, diffusive and migrative influences with three homogeneous and two electrodic reactions. Two sizes of reactors are considered and the performance of the different reactor types analyzed as a function of size. The superiority of the rotational cells is illustrated for this reaction scheme compared to both the capillary gap cell (CG) and a parallel plate reactor (PPER). Scale-up criteria are scrutinized and two approaches to laminar radial flow reactor scale-up are investigated. The one suggested herein shows that Taylor number, residence time,IR drop and rotational Reynolds number must all be accounted for even with a fairly simple electrosynthesis pathway. A quantitative evaluation of this scale-up procedure is included.Nomenclature a gap width (m) - C dimensionless concentration - D diffusion coefficient (m² s^-1) - Pe Peclet number ( _c a/D) - Q volumetric flow rate (m³ s^-1) - r dimensionless radius - R radius (m) - Re Reynolds number ( _c a/v) - Re rotational Reynolds number (R ₀ ² /v) - t time (s) - residence time of reactor - _r dimensionless radial velocity - _z dimensionless axial velocity - V volume (m³), velocity (m s^-1) and voltage - z dimensionless axial distance Greek symbols Taylor number ((a ² )/4v)^1/2 - ratio of characteristic lengths (a/R ₀) - constant - v kinematic viscosity (m² s^-1) - angular velocity (rad s^-1) - reference value - Thiele moduli      

Laminar radial flow electrochemical reactors. I. Flow fields

The velocity fields of three laminar radial flow electrochemical reactors are modeled using numerical and semi-analytical techniques. The capillary gap cell configuration is modeled using Galerkin finite element (GFEM) analysis and the asymptotic form of its velocities presented. An approximate asymptotic expression for entry length is also derived and compared to predicted entry lengths from the GFEM. Qualitative agreement is achieved. Two areas of flow separation are observed, their location being a function of gap width, flow Reynolds number (Re) and inlet pipe diameter. The rotating electrolyzer (REL) flow field is also simulated with the GFEM model. The insensitivity of the REL radial velocity profiles as a function of flow rate is shown. The shape of the radial velocity profiles and the degree of separation of the radial velocity jets are shown to be determined by the Taylor number (being the ratio of half-gap width over the theoretical boundary layer thickness). The asymptotic entry length solution is shown to provide a better estimate for this cell than for the capillary gap cell. Unlike the previous cells the pump cell shows less asymptotic behavior and is therefore more difficult to simulate. The GFEM approach is usually too costly for this cell and therefore perturbation techniques are applied. The resulting semi-analytical solution adequately represents laminar pump cell velocity profiles over a broad range of parameter values and is very short and easy to implement. One high Taylor number simulation is performed using the GFEM and the previously reported decoupling of electrodic mass transfer is interpreted via velocity profiles.Nomenclature a gap width - Q volumetric flow rate (m³ s^–1) - r dimensionless radius - R radius (m) - Re Reynolds number (v _c a/v) - Re _gap gap Reynolds number (a ²/v) - Re rotational Reynolds number (R ₀ ² /v) - Sc Schmidt number (v/D) - spin dimensionless group (Equation 8) - t time (s) - v _c characteristic velocity (m s^–1) two defined: for FEM analysis it wasQ/b ² for Perturbation analysis 6Q/(2R _in a) - v _r dimensionless radial velocity - v _z dimensionless axial velocity - v dimensionless azimuthal velocity - V velocity (m s^–1) - z dimensionless axial distance Greek symbols Taylor number (Equation 7) - ratio of characteristic lengths (a/R _o ) - viscosity (kg m^–1 s) - constant - density (kg m^–3) - azimuthal direction - kinematic viscosity (m² s^–1) - angular velocity (rad s^–1)     

Flow through packed bed reactors: 1. Single-phase flow

Single-phase pressure drop was studied in a region of flow rates that is of particular interest to trickle bed reactors . Bed packings were made of uniformly sized spherical and non-spherical particles (cylinders, rings, trilobes, and quadralobes). Particles were packed by means of two methods: random close or dense packing (RCP) and random loose packing (RLP) obtaining bed porosities in the range of 0.37–0.52. It is shown that wall effects on pressure drop are negligible as long as the column-to-particle diameter ratio is above 10. Furthermore, the capillary model approach such as the Ergun equation is proven to be a sufficient approximation for typical values of bed porosities encountered in packed bed reactors. However, it is demonstrated that the original Ergun equation is only able to accurately predict the pressure drop of single-phase flow over spherical particles, whereas it systematically under predicts the pressure drop of single-phase flow over non-spherical particles. Special features of differently shaped non-spherical particles have been taken into account through phenomenological and empirical analyses in order to correct/upgrade the original Ergun equation. With the proposed upgraded Ergun equation one is able to predict single-phase pressure drop in a packed bed of arbitrary shaped particles to within ±10% on average. This approach has been shown to be far superior to any other available at this time.     

大型径向流反应器中流体均布参数的研究

文中研究了工业规模径向反应器中流体的变质量流动规律,在直径3 m,高7 m的大型径向反应器冷模装置中测定了流道静压变化和穿孔阻力,通过数学拟合获得了动量交换系数和侧流穿孔阻力系数。实验结果表明,大型径向反应器冷模装置测得分流和集流动量交换系数Kd和Kc与前人众多的实验室小试单管结果十分相近;而大型冷模的分流和集流侧流穿孔阻力系数dξ和cξ在穿孔流速与主流道流速之比大于2之后分别比实验室小试结果提高了35%和16%左右。上述大型冷模实验研究结果对工业径向流反应器的开发有参考价值。     

Heterogeneity analysis of gas-solid flow hydrodynamics in a pilot-scale fluidized bed reactor

Mesoscale drag model is of crucial significance for the reliability and accuracy in coarse-grid EulerianEulerian two-fluid model(TFM) simulations of gas-solid flow hydrodynamics in fluidized bed reactors.Although numerous mesoscale drag models have been reported in the literature,a systematic comparison of their prediction capability from the perspective of heterogeneity analysis is still lacking.In this study,in order to investigate the effect of several typical drag models on the hydrodynamic ...     

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。     

Investigations on heat transfer and hydrodynamics under pyrolysis conditions of a pilot-plant draft tube conical spouted bed reactor

This paper describes the hydrodynamic and heat transfer performance of a pilot-plant scale conical spouted bed reactor designed for the pyrolysis of biomass wastes. The spouted bed reactor is the core of a fast pyrolysis pilot plant with continuous biomass feed of up to 25 kg/h, located at the Ikerlan-IK4 facilities.The aim of this paper is to obtain a deeper understanding of the spouted bed reactor performance at pyrolysis temperatures, in order to operate under stable conditions, improve the heat transfer rate in the reactor and minimize energy requirements. The influence of temperature on conical spouted bed hydrodynamics has been studied and wall-to-bed and bed-to-surface heat transfer coefficients have been determined.     

CFD simulation of hydrodynamics of gas–solid multiphase flow in downer reactors: revisited

In the present work, a k₁–ε₁–k₂–k₁₂ two-fluid model based on the kinetic theory of granular flow (KTGF) was employed to predict the flow behavior of gas and solids in downers, where the particles of small size as 70 μm in diameter apparently interact with the gas turbulence. The turbulence energy interaction between gas and solids was described by different k₁₂ transport equations, while the particle dissipation by the large-scale gas turbulent motion was taken into account through a drift velocity. Johnson–Jackson boundary condition was adopted to describe the influence of the wall on the hydrodynamics. The simulation results by current CFD model were compared with the experimental data and simulation results reported by Cheng et al. (1999. Chem. Eng. Sci. 54, 2019) and Zhang and Zhu (1999. Chem. Eng. Sci. 54, 5461). Good agreement was obtained based on the PDE-type k₁₂ transport equation. The results demonstrated that the proposed model could provide good physical understanding on the hydrodynamics of gas–solid multiphase flow in downers. Using the current model, the mechanism for formation and disappearance of the dense-ring flow structure and the scale-up characteristics of downers were discussed.     

立式径向流吸附器中流体均布的理论分析

为提高空分用吸附器吸附效率,通常在内分布流道布置一锥体使内外分布流道沿轴向压降梯度相等以保证空气在吸附剂中流场均匀。通过对立式径向Z型吸附器内的压降分析,推导出一个可表征当空气在吸附剂中均匀分配时吸附器各参数应满足的量纲1微分控制方程。同时对一个实验径向吸附器进行设计,利用该量纲1微分控制方程获得了锥体截面半径随轴向高度的变化规律,为该类径向吸附器的设计提供了理论依据。