Mechanical control of foaming in stirred‐tank reactors

The foam‐breaking characteristics of rotating‐disk mechanical foam‐breakers (MFRDs) fitted to stirred‐tank reactors (STRs) containing various foaming liquids were evaluated. The critical disk rotational speed, N_c, required for foam‐breaking and the liquid hold‐up, ?_L, in ascending foam reflected, respectively, the foam‐breaking behaviour of MFRDs and the foaming behaviour of STRs. Empirical equations for the prediction of N_c and ?_L, which can be applied independently of the type, concentration and temperature of foaming liquid, were obtained. The foam‐breaking power, P_kc, of MFRDs was also clarified in relation to the level of ?_L which is related to the difficulty or ease of mechanical foam‐breaking. © 2001 Society of Chemical Industry     

Performance characteristics of novel mechanical foam breakers in a stirred tank reactor

Unlimited foam formation and insufficient foam collapse can have serious effects in an aerated system such as a fermentation process. Mechanical foam breakers are used in foam control to avoid the drawbacks associated with the use of chemical antifoams and defoaming agents. In this paper, two new foam breakers consisting of a two‐blade paddle with three slits, and a two‐blade paddle with 168 thin needles have been tested. They gave significantly reduced critical speeds and power consumption for foam control in a stirred vessel, compared with some conventional foam breakers. The effects of various parameters, namely the physical properties of the foaming solution, type of gas sparger, surfactant concentration, and foam‐breaker clearance above liquid level, have been investigated. The degree of difficulty of controlling dynamic foams generated continuously in a stirred vessel is found to be a function of the nature of the foam, ie its bubble size, its liquid holdup, and the degree of foamability of the system. © 1999 Society of Chemical Industry     

Aldol condensation of n‐butyraldehyde in a biphasic stirred tank reactor: Experiments and models

To model a biphasic stirred tank reactor, intrinsic reaction kinetics and interfacial area are required. In this study, reactor modeling for n‐butyraldehyde aldol condensation was investigated under industrially relevent conditions. The interfacial area in the reactor was directly measured using a borescope system under appropriate temperature, NaOH concentration and rpm conditions. To estimate the interfacial area, a semiempirical correlation was developed, which provides good estimates within ±15% error. The reactor model based on two‐film theory was developed, combining the interfacial area and intrinsic reaction kinetics reported in our prior work. The model was verified by reaction experiments in the range 0.05–1.9 M NaOH, 80–130°C, and 600–1000 rpm. The prediction errors using the interfacial area from direct measurements and the correlation were ±8% and ±15%, respectively, suggesting that the model accuracy may be improved with better interfacial area estimation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2228–2239, 2015     

Gas hold‐up in stirred tank reactors

Based on a study of the gas hold‐up data for stirred tank reactor generated in the present work and the data available in the literature for large stirred tank reactors (T = 0.57 m to 2.7 m) equipped with disc turbines and pitched blade downflow turbines a correlation is presented which reliably predicts gas hold‐up data over wide range of system configurations and operating parameters. The parameter used, N/N_cd, relates gas hold‐up at impeller speed N with respect to the gas hold‐up at minimum impeller speed for complete dispersion of the gas, N_cd. It is shown that the gas hold‐up data of different workers when compared on the basis of N/N_cd, shows unanimity.     

Suspension of solid particles in multi‐impeller three‐phase stirred tank reactors

Solids suspension characteristics in gas—liquid–solid three‐phase stirred tanks with multi‐impellers were experimentally examined. Minimum impeller speeds for ultimately homogeneous solid suspension have been measured stirred tank reactors. Three impellers were installed: two four‐pitched blade downflow disk turbines and one Pfaudler type impeller chosen to provide good gas dispersion and to accomplish off‐bottom suspension of solid particles, respectively. Gas dispersion causes an increase in particle sedimentation associated with a decrease in power consumption and as a result, minimum impeller speeds for ultimately homogeneous solid suspension increase with increasing gas flow rates. A correlation was developed to predict minimum impeller speeds for ultimately homogeneous solid suspension. The proposed correlation, which agrees satisfactorily with the experimental results, is expected to be useful in design and scale‐up.     

Closed loop model reduction applied to a tank reactor process

The subject of this article is the direct assessment of model simplification from a feedback control perspective. Normally, dynamic systems are simplified dimensionally and structurally from an open loop perspective. In spite of the intentions, the resulting models still often tend to be unnecessary complex for controller design and synthesis. Here, a four step method is proposed that incorporates a feedback controller, and makes use of the closed loop sensitivity functions to indicate significant impact on the closed loop behaviour from a performed model simplification. The method is applied to a first order reaction in an ideally stirred tank reactor with a cooling system. For this system a general and detailed model is derived. The model includes temperature dependent parameters such as specific heat capacities and densities. This reference model is locally unstable in most operating points, making open loop simplification impractical. The proposed closed loop simplification method makes it possible to evaluate which approximations of the system that can be justified.     

R－X图解法计算多级串联理想混合反应器

论述Ｒ－Ｘ图解法计算多级串联理想混合反应器的基本原理，并结合实例，对Ｒ－Ｘ法的计算步骤予以详细介绍，为多级串联反应器的设计与计算，提供一种新颖适用的图解计算方法。     

Particle‐resolved PIV experiments of solid‐liquid mixing in a turbulent stirred tank

Particle Image Velocimetry (PIV) experiments on turbulent solid‐liquid stirred tank flow with careful refractive index matching of the two phases have been performed. The spatial resolution of the PIV data is finer than the size of the spherical, uniformly sized solid particles, thereby providing insight in the flow around individual particles. The impeller is a down‐pumping pitch‐blade turbine. The impeller‐based Reynolds number has been fixed to Re = 10⁴. Overall solids volume fractions up to 8% have been investigated. The PIV experiments are impeller‐angle resolved, that is, conditioned on the angular position of the impeller. The two‐phase systems are in partially suspended states with an inhomogeneous distribution of solids: high solids loadings near the bottom and near the outer walls of the tank, much less solids in the bulk of the tank. The liquid velocity fields show very strong phase coupling effects with the particles increasingly attenuating the overall circulation patterns as well as the liquid velocity fluctuation levels when the solids volume fraction is increased. © 2017 American Institute of Chemical Engineers AIChE J, 63: 389–402, 2018     

R－X图解法计算多级串联理想混合反应器

论述Ｒ－Ｘ图解法计算多级串联理想混合反应器的基本原理，并结合实例，对Ｒ－Ｘ法的计算步骤予以详细介绍，为多级串联反应器的设计与计算，提供一种新颖适用的图解计算方法。     

Synthesis of ZSM‐5 by hydrothermal method with pre‐mixing in a stirred‐tank reactor

This work proposed a synthesis route of ZSM‐5 via the hydrothermal method with premixing in a stirred tank reactor (STR). Effects of various operating conditions, including pre‐mixing time, molar ratio of SiO₂/Al₂O₃, TPAOH (organic template agents) concentration, NaCl (alkali metal cations) concentration, crystallization temperature, and crystallization reaction time, on the average particle size (PS) and particle size distribution (PSD) were investigated. It was found that the pre‐mixing time in the STR significantly affect the formation of proto‐nuclei in premixing process and crystal growth in hydrothermal reaction process, and consequently influence the PS and PSD of the prepared ZSM‐5. ZSM‐5 with good thermal stability, a PS of 380 nm, PSD of 0.17–0.9 µm, pore diameter of 2.31 nm, pore volume of 0.19 cm³ · g^?1 and specific surface area of 337.25 m² · g^?1 were obtained under the optimal conditions of a crystallization reaction time of 24 h, a crystallization temperature of 130 °C, a molar ratio of SiO₂/Al₂O₃ of 200, a TPAOH concentration of 3.5 mol · L^?1, NaCl concentration of 0.3 mol · L^?1, and a pre‐mixing time of 5 h. This work indicated that the operating conditions including premixing time have a significant effect on its PS and PSD.     

多级串联等体积全混流反应器与平推流反应器等效性研究——以二级可逆反应为例

在多级串联全混流反应器中,在等温等容条件下给出了二级可逆反应第Ⅳ级反应器的出口浓度表达式.讨论了在相同操作条件下,达到平推流反应器的转化率所需要的等体积串联全混流反应器的级数Ⅳ;主要考察了正反应速率常数k1、平衡常数K、反应物初始浓度之比M、停留时间τ等因素对N的影响,得出了N与正反应速率常数k1、相平衡常数K以及停留...     

Performance evaluation of fixed‐bed,millistructured, and metallic foam reactor channels for CO2 methanation

Power‐to‐gas technologies, combining hydrogen produced by water electrolysis with carbon dioxide to produce substitute natural gas (SNG), can support the increased penetration of renewable electricity sources. However, the technical and economic feasibility of these technologies requires the conversion efficiency of the whole process, including the methanation step. This paper provides an experimental performance comparison of three catalytic methanation reactor concepts, a fixed‐bed reactor, a millistructured reactor, and a metallic foam reactor with the same nickel‐alumina catalyst. The response of each reactor was analyzed in light of five performance criteria, representing the methane yield, the reactor compactness, and the maximum temperature elevation. The millistructured reactor channel showed a higher methane space‐time yield and volumetric productivity than the other reactors, but a significant catalyst temperature elevation. The metallic foam reactor showed a much lower space‐time yield and volumetric productivity, but very good thermal management.

     

Gas—liauid mass transfer in three-phase stirred tank reagors: Newtonian and non-newtonian fluids

Gas—liquid mass transfer has been investigated in gas—liquid-solid three-phase stirred tank reactors with Newtonian and non-Newtonian liquids. Volumetric mass transfer coefficients and gas hold-ups were measured in a 0.2 m i.d. stirred tank reactor and the effects of low-density polymeric particles (ρ_s, =1030 and 1200 kg/m³; up to 15 vol%) on gas—liquid mass transfer were examined. The volumetric mass transfer coefficients in water were found to decrease due to the presence of solid particles at constant impeller speed and superficial gas velocity. On the other hand, solids loading led to higher mass transfer rates in non-Newtonian carboxymethyl cellulose aqueous solutions. Our previously proposed model for mass transfer in gas—liquid two-phase systems was extended to gas—liquid—solid three-phase systems. Reasonable agreement was found between the predictions of the proposed model and the experimental data.     

基于MLD模型的CSTR建模和控制

A novel control strategy for a continuous stirred tank reactor （CSTR） system, which has the typical characteristic of strongly pronounced nonlinearity, multiple operating points, and a wide operating range, is initiated from the point of hybrid systems. The proposed scheme makes full use of the modeling power of mixed logical dynamical （MLD） systems to describe the highly nonlinear dynamics and multiple operating points in a unified framework as a hybrid system, and takes advantage of the good control quality of model predictive control （MPC） to design a controller. Thus, this approach avoids oscillation during switching between sub-systems, helps to relieve shaking in transition, and augments the stability robustness of the whole system, and finally achieves optimal （i.e. fast and smooth） transition between operating points. The simulation results demonstrate that the presented approach has a satisfactory performance.     

Continuous emulsion polymerization of vinyl acetate. I. Operation in a single continuous stirred tank reactor using sodium lauryl sulfate as emulsifier

Continuous emulsion polymerizations of vinyl acetate were carried out at 50 °C in a single continuous stirred‐tank reactor using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator. It was found that (1) the so‐called limit cycles could take place in monomer conversion, the number of polymer particles and the molecular weight of polymers produced under certain operating conditions, (2) the time‐average steady‐state monomer conversion was proportional to the 0.31 power of the emulsifier concentration in the feed, to the 0.50 power of the initiator concentration, to the ?1.0 power of the monomer concentration, and to the 0.90 power of the mean residence time, and (3) the time‐average steady‐state number of polymer particles produced was proportional to the 2.1 power of the emulsifier concentration in the feed, to the ?0.80 power of the initiator concentration, to the 0 power of the monomer concentration, and to the ?0.92 power of mean residence time. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2748–2754, 2002     

Experimental and theoretical investigation of parametric sensitivity and dynamics of a continuous stirred tank reactor for acid catalyzed hydrolysis of acetic anhydride

The continuous stirred tank reactor is a dynamic system exhibiting nonlinear behavior such as multiplicity and oscillations and, in certain range of operating conditions, may exhibit a parametric sensitivity where small changes in one or more of the input parameters lead to large changes in the output variable. In the present work, hydrolysis of acetic anhydride reaction system was used to demonstrate the existence of parametric sensitivity with respect to the input parameter, the cooling water flow rate. The applications of parametric sensitivity analysis were used for detection of parametric sensitivity in a continuous stirred tank reactor using catalyses hydrolysis of acetic anhydride reaction system. Also, theoretical investigation revealed that the effect of wall capacitance has definite influence on the dynamics of continuous stirred tank reactor. The continuous stirred tank reactor showed parametric sensitivity both in the regions of uniqueness and multiplicity, and a mathematical model was developed for the reactor. The numerically simulated results are in satisfactory agreement with the experimental data.