Chemical reactors

In recent years, much attention has been focused upon predictive control of nonlinear systems. The implementation of such a control strategy for real processes has greatly improved their performance. This paper deals with a model-based predictive control (MBPC) strategy using a generalised Hammerstein model and its application to the temperature control of a semibatch reactor. Both unconstrained and constrained adaptive control problems are considered. A simple identification method based on the weighted recursive least squares method (WRLS) is used to estimate the model parameters on-line. An indirect adaptive nonlinear controller is designed by combining the predictive controller with an indirect parameter estimation algorithm. This adaptive scheme has been applied for the control of a semi-batch chemical reactor. Experimental results show that the performance of the generalised Hammerstein MBPC (NLMBPC) was significantly better than that of a linear model predictive controller (LMBPC).

A hybrid in situ bioremediation/pulsed pumping strategy has been developed to cost effectively remediate a carbon tetrachloride plume in Schoolcraft, Michigan. The pulsed pumping system uses a line of alternating injection and extraction wells perpendicular to the direction of natural groundwater flow. The wells pump periodically to clean the recirculation zone between adjacent wells. During the pump-off phase, natural groundwater flow brings new contaminant into the recirculation zone. The wells are pumped again prior to breakthrough of contaminant from the recirculation zone.A computationally efficient reactor model has been developed, which conceptually divides the aquifer into injection, extraction, and recirculation zones, which are represented by a network of chemical reactors. Solute concentration histories from three-dimensional finite difference simulations and from field data confirm the reactor model predictions. The reactor model is used to investigate the optimal well c...

The use of software-intensive solutions for industrial automation and control systems has been a promising trend due to the flexibility, interoperability, and cost savings provided by such an approach. This paper presents a component-based framework for the development of industrial supervision and control systems, which provides reusable solutions for data acquisition, control, and supervision activities. Interoperability and real- time issues are handled by the implementation of the DAIS (Data Acquisition for Industrial Systems) standard, in conjunction with the use of CIAO, a real-time implementation of the CCM (CORBA Component Model) standard. We present the design and implementation of the proposed framework, as well as two application examples built atop our software platform: a chemical reactor supervisory and a cruise control system simulation.

Pentachlorophenol (PCP) was studied as a model recalcitrant compound for a sequential chemical oxidation and biodegradation treatment, in a continuous laboratory-scale system that combined a Fenton's chemical reactor and a packed-bed bioreactor.

A joint U.S./Federal Republic of Germany (FRG) project has successfully tested a unique solar-driven chemical reactor in the CAtalytically Enhanced Solar Absorption Receiver (CAESAR) experiment. The CAESAR test was a "proofof-concept" demonstration of carbon-dioxide reforming of methane in a commercial-scale, solar, volumetric receiver/reactor on a parabolic dish concentrator. The CAESAR design; test facility and instrumentation; thermal and chemical tests; and analysis of test results are presented in detail. Numerical models for the absorber and the receiver are developed and predicted performance is compared with test data. Post test analyses to assess the structural condition of the absorber and the effectiveness of the rhodium catalyst are presented. Unresolved technical issues are identified and future development efforts are recommended.

Many different reactor systems have been proposed and some of these have been developed to prototype and commercial scale. Six types of reactor (Magnox, AGR, PWR, BWR, CANDU and RBMK) have emerged as the designs used to produce commercial electricity around the world. A further reactor type, the so-called fast reactor, has been developed to full-scale demonstration stage. These various reactor types will now be described, together with current developments and some prototype designs.

Proportional-integral-derivative (PID) controllers are widely used in process control, and consequently they are described in most of the textbooks on automatic control. However, rather than presenting the overall design process, the examples given in such textbooks are intended to illuminate specific focused aspects of selection, tuning and implementation of the controller. This paper describes in detail the design of a PID controller for temperature control of a polymerase chain reaction (PCR) microreactor showing how different aspects, which necessarily are taught separately, interact in a real-world design. After setting the design targets by taking the hardware limitations into consideration, a continuous time controller, having two degrees of freedom, is designed by placing its dominant pair of poles using the root locus technique. Then, the integrator wind-up is addressed, the controller is translated into a discrete time version and, after implementation, the experimental performances are measured.

To study the influence of particle concentration on the hydrodynamics of bubble-column slurry reactors operating in the heterogeneous flow regime, experiments were carried out in 0.10, 0.19, and 0.38-m-dia. columns using paraffinic oil as the liquid phase and slurry concentrations of up to 36 vol. %. To interpret experimental results a generalization of the “two-phase” model for gas–solid fluid beds was used to describe bubble hydrodynamics. The two phase identified are: a dilute phase consisting of fast-rising large bubbles that traverse the column virtually in plug flow and a dense phase that is identified with the liquid phase along with solid particles and entrained small bubbles. The dense phase suffers backmixing considerably. Dynamic gas disengagement was experimented in the heterogeneous flow regime to determine the gas voidage in dilute and dense phases. Experimental data show that increasing the solid concentration decreases the total gas holdup significantly, but the influence on the dilute-phase gas holdup is small. The dense-phase gas voidage significantly decreases gas holdup due to enhanced coalescene of small bubbles resulting from introduction of particles. The dense-phase gas voidage is practically independent of the column diameter. The dilute-phase gas holdup, on the other hand, decreases with increasing column diameter, and this dependence could be described adequately with a slight modification of the correlation of Krishna and Ellenberger developed for gas–liquid systems.

The problem in which a small parameter multiplies to the highest order derivative arises in various fields of science and engineering, for instance fluid mechanics, fluid dynamics, elasticity, quantum mechanics, optimal control, chemical reactor theory, hydrodynamics, convection–diffusion ...

This work proposes a simplified methodology for the analysis and design of reactive batch distillation columns based on the McCabe-Thiele method for reactive continuous columns and on the concept of a reactive difference point. To extend the application of the concept of a reactive difference point for reactive batch distillation columns, expressions for the McCabe-Thiele operating line and for the dynamics of the reboiler in the reactive case have been derived; two cases are considered depending upon the phase in which reactions occur (i.e., liquid or vapor). We also provide an approach to the derivation of an expression to calculate the molar turnover flow rate by considering each reactive distillation plate as a combined system of a conventional equilibrium stage linked to a chemical reactor (phenomena decomposition). Furthermore, we present our derivation of the Underwood equations (minimum reflux) for continuous and batch reactive distillation columns. Finally, five illustrative examples allow us to show that our results present reasonable agreement with those obtained through BatchFrac of AspenPlus.

A concise review of relevant experimental observations and modeling of high-pressure tricklebed reactors, based on recent studies, is presented. The following topics are considered: flow regime transitions, pressure drop, liquid holdup, gas-liquid interfacial area and mass-transfer coefficient, catalyst wetting efficiency, catalyst dilution with inert fines, and evaluation of tricklebed models for liquid-limited and gas-limited reactions. The effects of high-pressure operation, which is of industrial relevance, on the physicochemical and fluid dynamic parameters are discussed. Empirical and theoretical models developed to account for the effect of high pressure on the various parameters and phenomena pertinent to the topics discussed are briefly described.

Methods are given for the design of dump tanks to separate the liquid and vapour/gas phases from a two-phase emergency relief discharge from a runaway chemical reactor. A small-scale test apparatus is described which has been used to evaluate the design methods. Results and analysis are given for reacting and non-reacting systems, which give good agreement with the predictions from the design methods for water depressurization and a 'vapour-pressure' system. Results for a hybrid system indicate the problems associated with deciding whether the major component of the relief stream is the gas or the vapour.

Se resume las principales características de los reactores y se proporciona fotografías a nivel industrial de estos equipos. La información es una adaptación de la versión en inglés que se encuentra en: http://www.essentialchemicalindustry.org/processes/chemical-reactors.html

This critical review examines recent scientific and patent literature in the application of microwave reactors for catalytic transformation of biomass and biomass-derived molecules with a particular emphasis on heterogeneous catalysis. Several recent reports highlight dramatic reductions in reaction time and even superior selectivity when microwaves are used. However, there are still many controversies and unexplained effects in this area that deserve attention. We critically review the available sources attempting to establish trends and elucidate the actual status of this area of research. Additionally, where possible, we discuss the potential for scale-up and commercial utilization of microwaves and impediments that currently hold back their implementation. This critical review aims at highlighting the opportunity of combining catalysis with microwave technology for biomass conversion but also to stimulate the reader to generate future understanding of the influence of the microwaves in catalytic processes in general.

The chemical reactions taking place in the chemical reactor form the heart of any chemical process. Reaction kinetics are the translation of our understanding of the chemical processes into a mathematical rate expression that can be used in reactor design and rating. Because of the importance of correct and safe design of chemical reactors, chemical reaction kinetics is a key aspect of research and development in chemical industries, in research institutes, and academic centers, as well as in industrial laboratories. There is, and there will always be, a strong need for knowledge and a skill base concerning the determination of reaction kinetics and their application in the form of a kinetic model. This paper is a result of cooperation within Eurokin, a consortium of over 10 European companies and 4 universities. An industrial questionnaire in 1995 highlighted that industry is not only a little conservative in the methods it uses to determine kinetics, but also that there was a wide awareness of the scope for improvement. Eurokin was thus founded in 1998 to try and establish the best practices and to facilitate development work in kinetics and associated areas. The paper briefly explains some underlying theory of heterogeneously catalyzed chemical reactions and their kinetics. It deals specifically with the acquisition of kinetic data, and gives recommendations for the selection of the experimental reactor and conditions. A primary aim of this paper is discuss kinetic experimentation and modeling through a series of case studies, attempting to illustrate good practice, methods in kinetic modeling, pitfalls, and recommendations. The paper closes with some recommendations and a perspective on the future needs of industrial reaction kinetics.

A simple calorimetric method to estimate both kinetics and heat transfer coefficients using temperature-versus-time data under non-adiabatic conditions is described for the reaction of hydrolysis of acetic anhydride. The methodology is applied to three simple laboratory-scale reactors in a very simple experimental setup that can be easily implemented. The quality of the experimental results was verified by comparing them with literature values and with predicted values obtained by energy balance. The comparison shows that the experimental kinetic parameters do not agree exactly with those reported in the literature, but provide a good agreement between predicted and experimental data of temperature and conversion. The differences observed between the activation energy obtained and the values reported in the literature can be ascribed to differences in anhydride-towater ratios (anhydride concentrations).

A novel photocatalytic reactor design for water treatment is characterized by the use of new extremely narrow diameter lamps, thus allowing for much higher surface area for catalyst coating per unit reactor volume and consequently for much higher specific reactor capacity. Experiments in a reactor containing 21 novel U-shaped lamps coated with catalyst showed a 695% increase in efficiency of the reactor performance in comparison with a classical annular reactor and 259% in comparison with a slurry reactor. Both a classical annular reactor and a slurry reactor cannot be scaled up for large-scale applications due to the low values of illuminated catalyst surface area per unit volume of liquid treated inside the reactor while this configuration is flexible enough for large-scale applications.

Because of more stringent regulations of aircraft particle emissions as well as strong uncertainties about their formation and their effects on the atmosphere, a better understanding of particle microphysical mechanisms and their interactions with the engine components is required.

This thesis focuses on the development of a 0D/1D combustion model with soot production in an aeronautical gas turbine. A major objective of this study is to assess the quality of soot
particle emission predictions for different flight configurations. The model should eventually allow performing parametric studies on current or future engines with a minimal computation time.

The model represents the combustor as well as turbines and nozzle with a chemical reactor network (CRN) that is coupled with a detailed combustion chemistry for kerosene (Jet A-1)
and a soot particle dynamics model using the method of moments. The CRN was applied to the CFM56-2C1 engine during flight configurations of the LTO cycle (Landing-Take-Off) as in the APEX-1 study on aircraft particle emissions. The model was mainly validated on gas turbine thermodynamic data and pollutant concentrations (H2O, COX, NOx, SOX) which were measured in the same study. Once the first validation completed, the model was subsequently used for the computation of mass and number-based emissions indices of the soot particulate population and average diameter.

Overall, the model is representative of the thermodynamic conditions and succeeds in predicting the emissions of major pollutants, particularly at high power. Concerning soot particulate emissions, the model's ability to predict simultaneously the emission indices as well as mean diameter has been partially validated. Indeed, the mass emission indices have remained higher than experimental results particularly at high power. These differences on particulate emission index may be the result of uncertainties on thermodynamic parameters of the CRN and mass air flow distribution in the combustion chamber. The analysis of the number-based emission index profile along the CRN also highlights the need to review the nucleation model that has been used and to consider in the future the implementation of a particle aggregation mechanism.

Many of the chemical reactor vessels used in the pharmaceuticals industries are glass-lined to provide corrosion prevention and to avoid product contamination. Typically these reactors contain retreat curve impellers, which may have been modified to fit into a conical-based vessel. The latter are designed for ease of product discharge and prevention of batch to batch contamination. Thus pharmaceutical processes often use non-standard impellers and unusual stirred tank reactor geometries, compared to those found in other chemical processes; these geometries are not covered by the standard correlations in the literature. In this work experiments and computational fluid dynamics calculations have been conducted for a retreat curve impeller in a 0.29 m diameter, conical-based vessel. Power numbers have been obtained experimentally and computationally for a range of impeller clearances and baffling arrangements and correction factors have been proposed to account for the effect of the conical base and partial baffles. Experimentally, liquid blending operations have been shown to occur rather quickly in these vessels, mainly due to the large D/T impellers used. Just-suspended impeller speeds for solids suspension have been measured experimentally and correlated using Zwietering's equation; values of the Zwietering's s parameter are proposed for a range of liquid fill levels, impeller clearances and baffle arrangements.

Singular perturbation problems are of common occurrence in all branches of applied mathematics and engineering. These problems are encountered in various fields such as solid mechanics, fluid dynamics, quantum mechanics, optimal control, chemical reactor theory, aerodynamics, reaction-diffusion processes, geophysics etc. In this paper, the basic methods and literature for solving the singular perturbation problems have been presented with their comparative study.

Options for the treatment or disposal of the two-phase discharge from a runaway reactor following emergency venting are discussed. Methods are given for the design of separation vessels and quench tanks. Different types of separation vessel and various design methods are compared. Examples are given for the different methods and systems.

This paper proposes and compares different steady-state models for the methanol synthesis fixed-bed reactor. The main goal is to indicate the pros and cons of these alternative models, to highlight their peculiarities in providing accurate and reliable estimations, and to warn the reader about possible risks involved in certain modeling assumptions. The Lurgi-type shell and tube boiler-reactor mathematical modeling is also laid out, before more complex issues and research, such as dynamic simulation or PDEbased predictive control, are broached.

The efficacy of steam reforming of the aqueous species in bio-oils produced from the fast pyrolysis of biomass is examined. A fractionating condenser system was used to collect a set of fractions of fast pyrolysis liquids with different chemical characteristics. The water-soluble components from the different fractions were steam-reformed using a nickel-based commercial catalyst in a fixed-bed reactor system. When reforming at 500°C, an overall positive effect in hydrogen yields was observed for the fractions with higher concentrations of lower molecular-weight oxygenates, such as acetic acid and acetol, while the heavier compounds, such as the carbohydrates, showed an opposite effect. In general, higher selectivity toward hydrogen correlated to a lower tendency toward carbon deposits. Overall, the bio-oil fraction corresponding to the light end performed the best with the highest activity toward hydrogen. A range of steam/carbon ratios was examined. Carbon accumulation in the reactor was clearly a main issue during steam reforming of all of the bio-oil fractions studied. Chemical changes caused by aging of aqueous bio-oil were found to have a detrimental effect on hydrogen production.

Reactive distillation (RD), a promising multifunctional reactor, can be used to improve the selectivity of the desired product by manipulating the concentration profiles in the reactive zone of the column. In this work, a new approach has been proposed to obtain the feasible regions of RD for the reactive systems involving single reactants, e.g. dimerization, aldol condensation, etc. Two new models namely the reactive condenser and the reactive re-boiler have been proposed. These models indicate the best location of the reactive zone in a column. Multistage versions of these models namely, reactive rectification and reactive stripping further expand the feasible region and are capable of representing the performance offered by a conventional RD unit. Several hypothetical non-azeotropic ideal systems have been extensively studied using these models and it has been shown that selectivity close to 100% is attainable over the entire range of conversion for a series as well as a combination of series and parallel reactions with positive reaction orders. Two industrially important cases of aldol condensation of acetone and dimerization of isobutylene have also been addressed using this approach. For porous catalysts, the presence of intra-particle diffusion resistance may limit the feasible region and even in the case of ideal non-azeotropic systems it may not be possible to obtain 100% selectivity. A methodology to incorporate pore diffusion effects is also illustrated.

Optimization of the whole plant instead of important individual units is essential for maximizing savings and operational efficiency. Often, there are conflicting objectives for optimizing industrial processes. Many previous studies on multi-objective optimization involved a few critical units (and not complete plants) using models and simulation programs specifically developed for the respective application. Developing rigorous models and a separate code for simulating a complete plant, for the sake of multi-objective optimization is difficult and time consuming. There is potential to make this task easier by employing available process simulators such as Aspen Plus and Hysys. But these simulators do not currently have multi-objective optimization tools. Hence, an interface has been developed between Non-dominated Sorted Genetic Algorithm (NSGA-II) and Hysys. Plant-wide optimization using this interface involves three main steps: (a) development and testing of Hysys model for steady simulation of the process under study; (b) sensitivity analysis and selection of objectives, decision variables and constraints; and (c) optimization of the process for multiple objectives using NSGA-II. This paper describes optimization of a styrene unit/plant for multiple objectives using the interface and compares the obtained results with those obtained using an independently developed simulation program.

Pervaporation is one of the developing membrane technologies that can be used for various industrial applications but for a prede®ned task, the optimal process design is unlikely to consist solely of pervaporation. Often the optimised solution becomes a hybrid process combining pervaporation with one or more other separation technologies. A distinction will be made between hybrid and integrated processes. Hybrid processes are important and consequently need to be considered in process design. This paper focuses on pervaporation±based hybrid processes that have been realised on an industrial scale. Both present and future prospects of applying these process combinations will be reviewed. The emphasis of this paper is, therefore, on pervaporation combined with distillation and with chemical reactors. The economic potential of these hybrid processes is evaluated, for various applications, by cost comparisons between the pervaporation-based hybrid processes and alternative separation processes. Pervaporation-based processes for waste water treatment and biotechnology applications involve other types of pervaporation based hybrid processes and have been excluded from this review. #

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.

A strategy for adaptive control and energetic optimization of aerobic fermentors was implemented, with both air flow and agitation speed as manipulated variables. This strategy is separable in its components: control, optimization, estimation. We optimized parameter’s estimation (from the usual KLa correlation) using sinusoidal excitation of air flow and agitation speed. We have implemented parameter’s estimation trough recursive least squares algorithm with forgetting factor. We carried separate essays on control, optimization and estimation algorithms. We carried our essays using an original computational simulation environment, with noise and delay generating facilities for data sampling and filtering.

Our results show the convergence and robustness of the estimation algorithm used, improved with use of both forgetting factor and KLa dead-band facilities. Control algorithm used in our work compares favorably with PID using the integrated area criteria for deviation between oxygen molarity and critical molarity (set point). Optimization algorithm clearly reduces energetic consumption, respecting critical molarity. Integration of control, optimization and adaptive algorithms was implemented, but future work is needed for stability. Methods were defined and implemented for stability improvement. We have implemented data acquisition and computer manipulation of air flow and agitation speed for actual fermentors.

This paper deals with actuator fault diagnosis for chemical batch reactors. Two different nonlinear modelbased approaches have been developed in order to detect incipient and abrupt faults. Two residual generators were built by using an adaptive observer and a H∞ approach. Both approaches are well used for sensor fault detection due to their capability to estimate uncertain parameters and to guarantee robustness against modeling errors and disturbances. Here, the approaches have been extended to achieve actuator fault detection and a comparison of both techniques has been done by simulating the whole system in-design and off-design operating conditions.

A kinetic study of the methanol steam reforming reaction was performed over a commercial CuO/ZnO/ Al 2 O 3 catalyst (Süd-Chemie, G66 MR), in the temperature range of 200-300 1C. The reactions considered in this work were methanol steam reforming (MSR) and reverse water gas shift (rWGS). Several MSR kinetic rate models developed by different authors were compared and the one was determined that best fitted the experimental data. A kinetic Langmuir-Hinshelwood model was proposed based on the work by . The kinetic expressions that presented the best fit were used to simulate the packed bed reactor with a one-dimensional model. A good agreement between the mathematical model and the experimental data was observed.

During the Hadean to early Archean period (4.5-3.5 Ga), the surface of the Earth's crust was predominantly composed of basalt and komatiite lavas. The conditions imposed by the chemical composition of these rocks favoured the crystallization of Fe-Mg clays rather than that of Al-rich ones (montmorillonite). Fe-Mg clays were formed inside chemical microsystems through sea weathering or hydrothermal alteration, and for the most part, through post-magmatic processes. Indeed, at the end of the cooling stage, Fe-Mg clays precipitated directly from the residual liquid which concentrated in the voids remaining in the crystal framework of the mafic-ultramafic lavas. Nontronite-celadonite and chlorite-saponite covered all the solid surfaces (crystals, glass) and are associated with tiny pyroxene and apatite crystals forming the so-called "mesostasis". The mesostasis was scattered in the lava body as micro-settings tens of micrometres wide. Thus, every square metre of basalt or komatiite rocks was punctuated by myriads of clay-rich patches, each of them potentially behaving as a single chemical reactor which could concentrate the organics diluted in the ocean water. Considering the high catalytic potentiality of clays, and particularly those of the Fe-rich ones (electron exchangers), it is probable that large parts of the surface of the young Earth participated in the synthesis of prebiotic molecules during the Hadean to early Archean period through innumerable clay-rich micro-settings in the massive parts and the altered surfaces of komatiite and basaltic lavas. This leads us to suggest that Fe,Mg-clays should be preferred to Al-rich ones (montmorillonite) to conduct experiments for the synthesis and the polymerisation of prebiotic molecules.

A three dimensional transient model is developed to simulate the local hydrodynamics of a gas–liquid–solid three-phase fluidised bed reactor using the computational fluid dynamics (CFD) method. The CFD simulation predictions are compared with the experimental data of Kiared et al. [1999. Mean and turbulent particle velocity in the fully developed region of a three-phase fluidized bed. Chemical Engineering & Technology 22, 683–689] for solid phase hydrodynamics in terms of mean and turbulent velocities and with the results of Yu and Kim [1988. Bubble characteristics in the racial direction of three-phase fludised beds. A.I.Ch.E. Journal 34, 2069–2072; 2001. Bubble-wake model for radial velocity profiles of liquid and solid phases in three-phase fluidised beds. Industrial and Engineering Chemistry Research 40, 4463–4469] for the gas and liquid phase hydrodynamics in terms of phase velocities and holdup. The flow field predicted by CFD simulation shows a good agreement with the experimental data. From the validated CFD model, the computation of the solid mass balance and various energy flows in fluidised bed reactors are carried out. The influence of different interphase drag models for gas–liquid interaction on gas holdup are studied in this work.

The numerical prediction of NOx emissions from gas turbines is addressed in this paper. Generated from Computational Fluid Dynamics (CFD), a Reactor Network (RN) is defined to model the NOx formation with a detailed chemistry. An optimized procedure is proposed to split the reactive flow field into homogeneous zones considered as Perfectly Stirred Reactors (PSR). Once connected together, they result in a Chemical Reactor Network (CRN) that yields a detailed composition regarding species and temperature in the combustion chamber. Sensitivity studies are then performed to estimate the influence of air humidity and gas turbine load on NOx predictions. The NOx emissions predicted are in good agreement with the measured data in terms of levels and trends for the case studied (a gas turbine flame tube fed with natural gas and functioning at a pressure of 15 bar). Finally, the RN methodology has shown to be efficient estimating accurately NOx emissions with a short response time (few minutes) and small CPU requirements.