Non-adiabatic Fixed Bed Reactor Research Articles

Evaluation of alternative processes of methanol production from CO2: Design, optimization, control, techno-economic, and environmental analysis

Converting carbon dioxide (CO2) to methanol via direct hydrogenation has been regarded as an essential part of the pursuit of a decarbonized energy economy. This study first explored and evaluated alternative processes for converting CO2 to methanol, in which six schemes based on adiabatic and/or non-adiabatic fixed-bed reactors were focused. The research scope includes rigorous process design, optimization, techno-economic and environmental assessment, and control. The generated results indicate that the two-reactor system (Scheme 5), which employs a non-adiabatic one as the first stage and a adiabatic one follows, has the lowest production cost. This process reveals great potential for decarbonization (i.e. CO2-e = −1.314 Ton-CO2/Ton-MeOH), whereas less economic attractiveness (i.e. minimum required selling price (MRSP) of methanol = 998 USD/Ton, average market price = 378 USD/Ton). Correspondingly, the maximum allowable CO2 emission from utilizing hydrogen (MACEH2) was found to be 6.554 Ton-CO2/Ton-H2. This indicated that using hydrogen produced from steam methane reforming (SMR) with carbon capture on both syngas and flue gas (i.e. 5.7 Ton-CO2/Ton-H2) leads to net decarbonization. Furthermore, if the emission associated with the CO2 feed (specific energy = 2.8 GJ/Ton-CO2) is also considered, net decarbonation would be achieved by using hydrogen produced from biomass gasification (i.e. 3.1 Ton-CO2/Ton-H2). A more comprehensive comparison between various CO2 utilization processes, in terms of the decarbonization ability and economics, was performed. Through this, it is concluded that there has been no existing CO2-based process that is attractive in both aspects. Finally, a suitable control strategy was proposed for the selected scheme, which suitably handles the throughput and composition disturbances.

Evaluation of alternative processes of CO2 methanation: Design, optimization, control, techno-economic and environmental analysis

Converting carbon dioxide (CO2) into substitute natural gas (SNG) has received renewed interests recently. It not only realizes large scale CO2 conversion, but also provides a synthetic source for those countries lacking natural gas. This study firstly attempts to explore and evaluate alternative processes for CO2 methanation, in which four schemes (six processes overall) based on adiabatic and/or non-adiabatic fixed-bed reactors are focused. Rigorous process design, optimization, waste heat recovery, economic and environmental evaluation, and control are covered. From this work, the most promising configuration (i.e. Scheme 4B) uses only two reactors. A counter-current cooling, non-adiabatic reactor equipped with internal recycle goes first, and an adiabatic reactor follows. This process reveals great CO2 reduction potential (i.e. CO2-e: −3.338 kg/kg), as compared with other previously developed processes converting CO2 to value-added chemicals (i.e. CO2-e: −0.154 to 2.242 kg/kg). More importantly, better operability of the first reactor is indicated by the generated temperature profile. Finally, a suitable control strategy is developed for this scheme, which results in satisfactory closed-loop responses under throughput and composition disturbances. For future work, clarifying how the feed impurities influence the reaction kinetics, and developing a less expensive hydrogen source, will be recommended.

Order reduction and control of hyperbolic, countercurrent distributed parameter systems using method of characteristics

The aim of this paper is to develop a model reduction technique based on method of characteristics (MOC) for control of counter-current distributed parameter systems that are modeled by semi-linear hyperbolic partial differential equations (PDEs). In our previous work, MOC was shown to be a suitable model reduction technique for a class of hyperbolic PDEs. This concept is extended to counter-current systems, wherein the so-called characteristic lines have slopes with opposite signs. Two different approximations are proposed that allow the use of MOC as a model reduction technique. The open-loop results from MOC are compared with a large dimensional model, based on the method of lines. The MOC-based models are used for closed loop simulations within the approximate dynamic programming (ADP) framework. Two case studies are considered: a non-adiabatic plug flow reactor (having characteristics with two different slopes) and a non-adiabatic fixed bed reactor (having characteristics with three different slopes). We demonstrate that using the MOC-based model in an ADP controller results in a significant improvement in computational time, along with a slight improvement in controller performance.

Lymphome et taches café-au lait

The aim of this paper is to develop a model reduction technique based on method of characteristics (MOC) for control of counter-current distributed parameter systems that are modeled by semi-linear hyperbolic partial differential equations (PDEs). In our previous work, MOC was shown to be a suitable model reduction technique for a class of hyperbolic PDEs. This concept is extended to counter-current systems, wherein the so-called characteristic lines have slopes with opposite signs. Two different approximations are proposed that allow the use of MOC as a model reduction technique. The open-loop results from MOC are compared with a large dimensional model, based on the method of lines. The MOC-based models are used for closed loop simulations within the approximate dynamic programming (ADP) framework. Two case studies are considered: a non-adiabatic plug flow reactor (having characteristics with two different slopes) and a non-adiabatic fixed bed reactor (having characteristics with three different slopes). We demonstrate that using the MOC-based model in an ADP controller results in a significant improvement in computational time, along with a slight improvement in controller performance.

Fixed-bed reactor modeling for methanol to dimethyl ether (DME) reaction over γ-Alumina using a new practical reaction rate model

Dimethyl ether (DME) synthesis reaction rate was studied over a commercial sample of γ-Alumina to investigate the accuracy of the most applicable rate models. Due to the deviation of the former proposed models especially at temperatures below 593K, a new simple empirical rate model was proposed. Besides, previous proposed correlations for methanol dehydration equilibrium constant were examined experimentally and a new equation was developed. Subsequently, one dimensional unsteady state heterogeneous model was applied to simulate adiabatic and non-adiabatic fixed-bed reactors. Temperature profile and methanol conversion along the reactors were predicted while varying feed rate and feed temperature.

Dynamic Cycling State of Nonadiabatic Catalytic Combustion of Propylene

An experimental study of nonadiabatic fixed-bed reactor for controlling propylene gas was made under flow reversal operation. Temperature measurements were made within the catalyst and packing beds. The influence of the operating parameters on the shape of temperature profiles, conversion, and heat removal were studied. The experiments showed that the maximum measured reactor temperature and heat removal were rather insensitive to changes in cycle duration and sensitive to feed flow rate and reactant concentration. The simulation results for the variation of concentration, flow rate, and cycle time showed the experimentally observed behavior Further simulations showed that runaway can occur when concentration was high.

Resolução de um modelo de reator de leito fixo não adiabático com dispersão axial utilizando redes neurais artificiais

The interpolation capabilities of multilayer perceptron networks (MLP) were used to solve a system of ordinary differential equations that models an axial dispersed non-adiabatic fixed bed reactor. The methodologies described in this paper follow the first ones proposed by Lagaris et al. (1998, 2000), but enlarge them to differential models with mix boundary conditions and by the use of the penalty method to convert the original constrained to unconstrained optimization problem in training the MLP networks. The results are in agreement on those in Luize e Biscaia (1991), which were obtained by well-established numerical techniques as finite element and orthogonal collocation methods. The neural interpolation method used in this paper is easier to handle than the classical methods for numerical solution of differential equations, particularly for non-linear differential systems, and defines a global approximation, in analytic form, for problems solution.

Model predictive control of a fixed-bed reactor with nonlinear quality inference

A generic model predictive control framework has been proposed for a fixed-bed reactor with exothermic reaction. The proposed framework can conduct nonlinear inferential control of a product concentration together with linear multivariable control of bed temperatures. In addition, the framework can accommodate the multi-rate sampling and analysis delay caused by the product measurement. Performance of the proposed technique has been demonstrated with a non-adiabatic fixed bed reactor model producing maleic anhydride under various operating scenarios.

A control-relevant model reduction technique for nonlinear systems

A novel control-relevant model reduction technique for nonlinear systems is proposed utilizing the idea of the balanced truncation. Unlike the widely-accepted Karhunen — Loeve method where the state basis for the reduced system is found from the state snapshots, the proposed technique takes into account the input, state, and output information together and provides a near-balanced reduced-order model that approximates the system map instead of the state snapshots. Performance of the technique is demonstrated for a linear system and a non-adiabatic fixed-bed reactor model.

Optimization of a nonisothermal nonadiabatic fixed-bed reactor using dirac-type silver catalysts for ethylene epoxidation

A heterogeneous, nonadiabatic, nonisothermal plug-flow reactor where ethylene epoxidation over silver catalyst occurs is studied theoretically. The catalyst distribution in the pellets is of a Dirac-delta type. The location of the Dirac distribution is optimized both the ethylene oxide yield and selectivity maximazation. Single-pellet results indicate that yield can be maximized either by surface or subsurface catalyst locations, depending on the operating conditions. However, for all practical purposes, selectivity is maximized only by surface catalysts. Significant improvements in reactor performance are found by using the appropriate Dirac catalyst, as compared to a uniform catalyst distribution. Further improvements can be achieved by using a two-zone reactor, with different catalyst location in each zone. Reactor runaway behavior can also be avoided by the use of Dirac catalysts.

CIRCULATING MAGNETICALLY STABILIZED BED REACTORS

Circulating magnetically stabilized bed reactors (CMSBR's) operate in nearly plug flow for both the catalyst and fluid phases. Computer simulations show that they allow programming of temperature profiles without using either internal heat exchangers or interstage cooling of reactant. For highly exothermic, irreversible reactions, co-current CMSBR's are far less sensitive to temperature runaway than cbnventional nonadiabatic fixed-bed reactors. Thus, significant increases in conversion can be achieved without encountering catalyst-damaging hot spots and reduced selectivity. For equilibrium-limited, exothermic reactions, counter-current CMSBR's can give temperature profiles that nearly optimize conversion rates. Thus, smaller reaction zones are required in these reactors than in staged, adiabatic fixed-bed systems.

Simple method for the modelling of the behaviour of a non-isothermal, non-adiabatic fixed-bed catalytic reactor

The behaviour of a non-isothermal, non-adiabatic fixed-bed reactor used for the hydrogenation of toluene has been investigated. Although large radial temperature gradients existed in the reactor, a simple pseudo-homogeneous one-dimensional model was found to be suitable to describe the reactor behaviour. The model is based on the application of a mean cross section temperature which is derived from radial temperature profiles measured at two axial positions in the catalyst bed. Measured radial temperature profiles exhibited a parabolic shape. The mean cross section temperature applied corresponds to the temperature at the radial position (r/R) 2 = 0.5. The model equations were solved by means of the orthogonal collocation method and Gear's variable step integration algorithm. Measured radial toluene concentrations indicated that no significant radial toluene concentration gradients existed in the catalyst bed. Axial temperature and toluene concentration profiles measured during steady-state operation are compared with the corresponding profiles calculated with the reactor model.

On‐line optimizing control of a nonadiabatic fixed bed reactor

AbstractA scheme of on‐line optimizing control is presented for a nonadiabatic fixed bed reactor which experiences a highly exothermic reaction. The control scheme has been devised to perform adaptive control of bed temperature and on‐line steady state optimization simultaneously.Experiments were conducted with a pilot scale fixed bed reactor where partial oxidation of n‐butane to maleic anhydride occurs. The reactor system was interfaced with a microcomputer for real‐time control and optimization. With an objective function consisting of a net profit by producing maleic anhydride plus a penalty term on high bed temperature, it was clearly shown that the reaction conditions were driven to the expected optimum region.

Experimental study of ignition and extinction waves and oscillatory behavior of a tubular nonadiabatic fixed bed reactor for the oxidation of carbon monoxide

An experimental study of axial temperature profiles in a nonadiabatic tubular fixed bed reactor has been made under the transient operation. The catalytic carbon monoxide oxidation occurring on a Pt/alumina catalyst has been used. Ignition and extinction waves have been studied both in a short and a long catalyst bed. It is shown that in a short bed ignition and extinction occur at the reactor outlet while for a long bed the ignition and extinction process takes place inside the reactor and is not influenced by the outlet part of the reactor. A systematic measurement indicates that in a narrow range of inlet parameters the integral nonadiabatic nonisothermal reactor may operate in an oscillatory state. These oscillations can be periodic or aperiodic.

Experimental study of traveling waves in nonadiabatic fixed bed reactors for the oxidation of carbon monoxide

An experimental study of axial temperature profiles in a nonadiabatic tubular fixed bed reactor has been made under the transient operation. The catalytic carbon monoxide oxidation occuring on a Pt/alumina catalyst has been used. Unlike the adiabatic conditions the velocity of a traveling temperature wave in a nonadiabatical arrangement depends on its axial position. In certain regions of inlet concentration multiple temperature fronts have been observed. For low inlet CO concentration a downstream temperature wave results and the lower (kinetic) steady state is dominant. For high inlet CO concentration an upstream propagating front results and the upper steady state is dominant. For a downstream moving wave oscillations of wave velocity, hot spot temperature and exit conversion have been measured. For certain operating conditions periodic behavior of temperature profiles in the reactor has been observed.

Regeneration of coked zeolite catalyst in non-adiabatic fixed beds.

Regeneration of coked zeolite catalyst is carried out in a non-adiabatic fixed bed reactor and the experimental results are simulated with a one-dimensional model. Reactor behavior which shows a relatively small temperature rise can be simulated well. With greater temperature rise, the agreement between experimental and calculated results becomes unsatisfactory. The comparison of simulation is discussed in terms of stability criterion. A measure of stable conditions in catalyst regeneration is derived from Inoue''s criterion for the formation of hot spot. It is shown that the one-dimensional model is usable to simulate reactor behavior in catalyst regeneration if the experimental conditions satisfy Inoue''s criterion.