Observer-based nonlinear control law for a continuous stirred tank reactor with recycle

This paper proposes new results concerning the problem of the control of a continuous stirred tank reactor with recycle. The novelty of the proposed results consists of a new nonlinear observer-based controller which is found by means of recent results of differential geometry for time-delay nonlinear systems, without using linear approximations of the model. Local convergence of the system state to the arbitrarily chosen operating point is theoretically proved. The significance of the proposed control law is shown by many simulations, which show high performances with any initial conditions, even at the start-up, and with critical cases of mismatched parameter values.     

Steady‐state multiplicity in an adiabatic continuous stirred tank reactor with vapor recycle

The multiplicity features of a continuous stirred tank reactor with vapor recycle have been studied for a dimerization reaction with second‐order kinetics. Such reaction systems are common in the polymer industry. The aim of the analysis is to provide a simple design methodology that will ensure safe operation of the reactor. It is shown that solutions with and without vapor recycle exist. The bifurcation set for the system is calculated, and 11 different bifurcation diagrams arise. A linear relationship exists between the system parameter values, when these are normalized by their values at the ignition point. This leads to a simple method for defining a safe operating point for the system under a defined disturbance. © 2012 American Institute of Chemical Engineers AIChE J, 59: 553–559, 2013     

Cultivation of spirulina maxima in an annular photochemical reactor

An 8-L annular photochemical reactor has been designed and built for the cultivation of micro- or semi-microalgae at the laboratory scale. It may be operated in batch or continuous mode and is controlled for pH, temperature, gas mixture ratio (CO₂ and air), flow rate, light intensity and also illumination type (daylight or plant growth light) and mode (continuous or intermittent). It behaves as a perfect mixed reactor for all concentrations of algal cells. The reactor was used for the cultivation of the blue-green alga Spirulina maxima in a synthetic medium in both batch and continuous operations. At the dilution rate of 0.24 day^?1, the optimal productivity was 0.91 g/L-day for biomass or 0.55 g/L-day for protein. This is equivalent to 14.5 g/m²-day for biomass or 8.7 g/m²-day for protein. The optimal productivity as well as the chemical composition of the algal biomass were comparable to results obtained from pilot plant studies and reported in the current literature.     

Comparison of photobioreactors for cultivation of the red microalga Porphyridium sp

The growth of the red microalga it Porphyridium sp was studied in three bench‐scale bioreactors of 13 dm³ volume: a bubble column, an airlift reactor and a modified airlift reactor with helical flow promoters in the top of the downcomer. Most of the experiments reported were run with a photon flux density of 250 µE m⁻² s⁻¹, but other illuminances were studied as well. Superficial gas velocities were in the range of 5.4 × 10⁻⁴ to 82 × 10⁻⁴ m s⁻¹ (0.033–0.5 vvm). Algal growth in the airlift reactor with helical flow promoters had lower gas requirements than in the other reactor configurations. This implies lower costs in air compression and in air and CO₂ requirements. It was concluded that the advantages found are related to the particular fluid dynamic characteristics of the reactor. © 2000 Society of Chemical Industry     

Bifurcation analysis of two continuous bioreactors operated in series with recycle

In this paper, bifurcation analysis has been carried out for two continuous bioreactors operated in series with recycle from the second reactor. The existence of multiplicity of steady states is analyzed by considering Contois growth kinetics in the process model. It was observed that there exist two possible steady states of which one is trivial (wash out condition). Stability analysis is carried out to determine the stability of these steady states and it was observed that both these steady states are unstable in nature. Bifurcation analysis has been carried out for substrate and biomass concentration with dilution rate as the bifurcation parameter. Effect of recycle ratio, substrate separation factor and biomass separation factor is studied and analyzed. It was observed that Hopf bifurcation occurs at a dilution rate of 1.0208 with purely imaginary Eigen values which showed that sustained oscillatory behavior exists in the substrate concentration of the second reactor. The significance of different bifurcation points and the operating conditions by considering biomass and substrate concentrations in each reactor is studied and it was observed that the bioreactors need to be operated at intermediate dilution rates to obtain improved conversion and yield.     

大型平底储罐失稳后的修复

介绍了大型化工装置中,平底储罐失稳后的修复技术。重点介绍了一种利用水压进行修复的办法。     

The occurrence and biosynthesis of gamma-linolenic acid in a blue-green alga,Spirulina platensis

The acyl-lipid and fatty acid composition of six blue-green algae, namely,Spirulina platensis, Myxosarcina chroococcoides, Chlorogloea fritschii, Anabaena cylindrica, Anabaena flos-aquae, and Mastigocladus laminosus is reported. All contain major proportions of mono-and digalactosyl diglyceride, sulfoquinovosyl diglyceride, and phosphatidyl glycerol, but none possess lecithin, phophatidyl ethanolamine, or phosphatidyl inositol. Trans-3-hexadecenoic acid was absent from all extracts. The analyses provide further evidence that there is no general chemical or physical requirement for any specific fatty acid in photosynthesis. S. platensis is unique among photoautotrophic organisms so far studied, containing major quantities of γ-linolenic acid (6,9,12-octadecatrienoic acid). This acid is synthesized by the alga by direct desaturation of linoleic acid and is primarily located in the mono- and digalactosyl diglyceride fractions. The possible phylogenetic relationship betweenS. platensis and other plant forms is discussed.     

Reducing the mean size of API crystals by continuous manufacturing with product classification and recycle

A continuous crystallization process is proposed that can produce active pharmaceutical ingredients with a small mean size and narrow distribution. The process flowsheet consists of a new product classifier configuration where the large crystals from the classifier are recycled to a dissolver along with the mother liquor from the filter. Crystallizer stability is explored and regions of sustained limit cycles are identified for the proposed kinetic models. Most industrial crystallizers are operated at low supersaturation; however, with this methodology the continuous crystallizer must be operated at high levels of supersaturation to promote nucleation and increase the number of small crystals in order to maintain a fixed desired production rate. The design and operating strategies presented can be implemented by simple modifications to most conventional continuous crystallization processes. This particle micronization technique may offer significant cost savings over other size reduction methods that utilize mechanical means.     

On the dynamic behavior of continuous stirred tank reactors

The types of dynamic behavior possible for a single first order reaction carried out in a stirred tank reaction are classified according to values of the parameters and plots in parameter space used to define the various possibilites. Analytic criteria are developed which predict the existence and stability character of limit cycles as a function of the system parameters. The types of dynamic behavior predicted are illustrated by numerical computation of the temperature and concentration trajectories. Several kinds of new jump phenomena for this problem are observed and explained in terms of the parameter space plots. The theory and analysis methods can be easily generalized to other types of reaction systems.     

Simulation of nonequimolecular polycondensation in continuous flow-stirred tank reactors

Conversion and molecular weight distribution are computed and compared for uncatalyzed and catalyzed nonequimolecular polycondensation in continuous flow-stirred tank reactors (CSTRs) using two different kinetic schemes proposed by Flory and Lin, respectively. The contrast between the two schemes is also remarkable as found in the batch reactors. The polydispersity indices in the CSTRs are substantially larger than those obtained in the batch reactors. Also, the molecular weight distribution splits into two curves for odd and even homologues regardless of the two different schemes. An extremely long rersidence time is needed to obtain the higher conversion accompanying a large polydispersity index as compared to the batch reactors. The polydispersity can be expressed in CSTR as x?_w/x?_n = 2 Σn²N_n(R+1?2P)/(1+R)²[A]₀.     

Modeling the continuous melt transesterification of bisphenol-A and diphenyl carbonate in a continuous stirred tank reactor

A model of continuous melt transesterification of bisphenol-A and diphenyl carbonate in a continuous stirred tank reactor is developed using phase equilibria assumption and the method of molecular weight moments. The model equations can be simplified into a polynomial system that has 17 equations and 17 unknowns. Solution of the polynomial system gives out almost every aspects of the continuous transesterification process. Molecular weight and polydispersity index, end group ratio of hydroxyl to phenyl carbonate, contents of molecular species, and lost diphenyl carbonate fractions are studied in different operation parameters.     

On the detailed dynamics of coupled continuous stirred tank reactors

The dynamic behaviour of coupled parallel and serial arrays of cells is analysed. Phenomena such as synchrnization of oscillations at a common frequency, rhythm splitting, amplitude amplification, jump between oscillatory regimes and quasi-periodic oscillations of a torus type have been observed for an autocatalytic reaction with product inhibition. The possibility of steady-state operation driven by the coupling of two cells, each of which is oscillatory by itself, has been detected. The configuration of the cell arrays does not change the bifurcation pattern drastically.     

并联连续再生/再循环的多杂质间歇用水系统优化方法

为了有效地减少多杂质间歇用水系统的新鲜水消耗量和再生处理量,针对多杂质间歇过程用水网络提出连续操作并联再生处理单元水网络结构模型及其优化设计方法。通过在用水网络中设置中间储罐和再生单元以实现对不同水质废水并联分质处理,建立了减少用水系统的新鲜水用量和再生水量以及废水排放量的数学规划模型,采用GAMS软件对一个实例进行求解。计算和分析表明：提出的水网络结构与优化设计方法可有效地解决按水质对废水进行并联处理的间歇用水系统,使系统的新鲜水用量和再生水流率同时达到最小。     

Forced oscillations in continuous flow stirred tank reactors with nonlinear step growth polymerization

The self-step growth polymerization of RA_f monomers in homogeneous, continuous flow stirred tank reactors (HCSTRs) is simulated under conditions of periodic feed concentration (with frequency ω and amplitude α). By having periodic operation, the polydispersity index of the polymer is found to increase by about 35% over the values at steady state. Periodic operation of HCSTRs is found to lead to gelation only for certain values of the frequency and the dimensionless residence time τ^*. Gelling envelopes have been obtained to give conditions under which HCSTRs should be operated. These envelopes can be described in terms of two critical dimensionless residence times, τ and τ such that nongelling operation is always ensured when τ^* < τ. For τ^* > τ, periodic operation always leads to gelation, and HCSTRs cannot be used. For τ < τ^* < τ, the gelling behavior is found to depend on the functionality f, amplitude α, and the dimensionless residence time τ^*.