Heterogeneous Plug-flow Model Research Articles

Development of a green process based on a novel tri-reforming reactor to produce syngas for methanol synthesis: Process Design, Modeling and Multi objective optimization

In this study, a clean and energy-efficient reforming process is introduced that can act as a promising alternative to the conventional reforming process for syngas production used in methanol synthesis process. In this proposed configuration, a pre-reformer is combined with a novel tri-reformer consisting of a combustion chamber and a catalytic bed. The combustion chamber was simulated using the CHEMKIN package incorporating GRI3.0 as a comprehensive mechanism and the catalytic bed was modeled by a heterogeneous plug flow model. A multi-objective optimization model was used to explore operational conditions of the proposed process to optimize CH4 conversion, H2 yield, and CO2 net production. Hence, the other aspect of novelty in this study deals with the use of a new methodology for multi-objective optimization of this process. This methodology is the first to integrate the CHEMKIN package and MATLAB software that leads to a higher degree of accuracy and comprehensiveness. The mathematical model of the conventional process was also developed and the favorable comparison between the performances of both processes was studied. The results indicate that eliminating a steam reformer in the novel configuration, not only reduces toxic emissions and the need for a large quantity of energy, but it also significantly decreases the required value of H2O/CH4 ratio. Therefore, the steam content of the process gas is reduced and energy efficiency is improved. Analyzing the characteristics of the synthesis gas produced by the studied cases results, that the proposed case produces a synthesis gas with higher quality (SN = 2 and a higher CO/CO2 ratio) while substantially reducing energy consumption as well as toxic emissions production.

Simulation of Reactors under Different Thermal Regimes and Study of the Internal Diffusional Limitation in a Fixed-Bed Reactor for the Direct Synthesis of Dimethyl Ether from a CO2-Rich Input Mixture and H2

This paper presents the simulation of reactors under different thermal regimes using the most used kinetic models for the simulation of the direct synthesis of DME with the objective of optimizing the coupling between heat and mass transfer. A pseudo-homogeneous and a heterogeneous plug-flow model are developed to simulate isothermal, adiabatic, and isoperibolic fixed-bed (shell-and-tube) reactors for the direct synthesis of DME from CO2 and H2, enabling the analysis of the limitations by the internal mass transfer. Concentrations, reaction rates, and temperature gradients within the catalyst are assessed. Catalytic efficiency factors are calculated and represented along the reactor tube. The results show that the choice of the kinetic model is crucial for optimal coupling of these functions since it strongly influences the design and sizing of the reactor for synthesis of DME from CO2-rich feedstocks. Therefore, this analysis demonstrates that the direct synthesis of DME can be limited by internal mass transfer, which promotes the DME synthesis at low conversions, therefore requiring particular attention for future reactor optimization.

Numerical and experimental investigation on the performance of lean burn catalytic combustion for gas turbine application

This manuscript presents our numerical and experimental results regarding the performance characteristics of lean burn catalytic combustion for gas turbine application. The reactant transport was assumed to be controlled by both bulk diffusion as well as surface kinetics, implemented by means of an approximate reaction rate equation and empirical coefficients to incorporate reaction mechanism. Experimental and numerical results were compared to examine the effects of methane mole fraction, inlet temperature, operating pressure, velocity and hydrogen species on combustion intensity. The results indicate that inlet temperature is the most significant parameter that impacts operation of the catalytic combustor and the most effective methods for improving the methane conversion are increasing the inlet temperature and increasing the methane mole fraction. Simulations from 1D heterogeneous plug flow model can capture the trend of catalytic combustion and describe the behavior of the catalytic monolith in detail. The addition of hydrogen will provide heat release by the exothermic combustion reaction so that the reactants reach a temperature at which methane oxidation can light-off.

Part-load performance characteristics of a lean burn catalytic combustion gas turbine system

The purpose of this study is to compare the part-load performance of a lean burn catalytic combustion gas turbine (LBCCGT) system in three different control modes: varying fuel, bleeding off the fuel mixture flow after the compressor and varying rotational speed. The conversions of methane species for chemical process are considered. A 1D heterogeneous plug flow model was utilized to analyze the system performance. The actual turbomachinery components were designed and predicted performance maps were applied to system performance research. The part-load characteristics under three control strategies were numerically investigated. The main results show that: the combustor inlet temperature is a significant factor that can significantly affect the part-load characteristics of the LBCCGT system; the rotational speed control mode can provide the best performance characteristics for part-load operations; the operation range of the bleed off mode is narrower than that of the speed control mode and wider than that of the fuel only mode; with reduced power, methane does not achieve full conversion over the reactor at the fuel only control mode, which will not warrant stable operation of the turbine system; the thermal efficiency of the LBCCGT system at fuel only control strategy is higher than that at bleed off control strategy within the operation range.

Performance analysis of crude terephthalic acid hydropurification in an industrial trickle-bed reactor experiencing catalyst deactivation

In this work, a dynamic model of an industrial trickle-bed reactor for hydrogenation reactions of 4-carboxybenzaldehyde has been developed. In this case, a heterogeneous plug-flow model has been considered to predict the dynamic behavior of the catalytic hydropurification reactor of Purified Terephthalic Acid production plant. Furthermore, deactivation model of carbon coated palladium catalyst of the reactor (0.5wt.% Pd/C, type D3065, supplied by Chimet SpA) has been devised based on the actual plant data. The catalyst of the proposed industrial reactor is deactivated after 360days. The simulation results indicate that the concentration of 4-carboxybenzaldehyde is very influential. In addition, concentration of para-toluic is not as destructive as that of 4-carboxybenzaldehyde so that it lessens the lifetime of catalyst about 40days if its concentration in normal operation builds up more than 1.6 times. Besides, the concentration of reactor feed should not be increased to boost the rate of production since this makes the lifetime of the catalyst shorter. If the production rate enhances about 18%, the lifetime of the catalyst drops more than 6months. The hydropurification reactor control is the most crucial part of the purification unit operation. Thus, in addition to the reactor operation assessment, this dynamic model can be used to evaluate the purification section performance at any time to continue producing on-spec product. Also, it might be used in future in the formulation of model based control strategies for the reactor control.

Modeling and simulation of catalytic partial oxidation of methane to synthesis gas by using a plasma-assisted gliding arc reactor

In the present study, a numerical investigation of the catalytic partial oxidation (CPO) of methane to synthesis gas (syngas) using a gliding arc (GlidArc) reactor is presented. A 2D heterogeneous plug-flow model with radial dispersion and no gradients inside the catalyst pellet are used, including the transport equations for the gas and solid phase and reaction rate equations. The governing equations of this model formed a set of stationary differential algebraic equations coupled with the non-linear algebraic equations, and were solved numerically using in-house MATLAB® code. Model results of CPO of methane were compared to previous experimental data with the GlidArc reactor found in the literature. A close match between the calculated and experimental results for temperature, reactant (CH4 and O2) conversion, H2 and CO yields and species mole-fraction was obtained. The developed model was extended to predict and quantify the influence of the gas hour space velocity (GHSV) as well as determine the influence of the reactor energy density (RED), the O2/CH4 molar ratio and the O2/N2 molar ratio. The predicted behaviors for the species mole-fraction, reactants conversion, H2 and CO yields and temperature along the length of the reactor have been analyzed.

Investigation of combustion and thermodynamic performance of a lean burn catalytic combustion gas turbine system

The goals of this research were to investigate the combustion and thermodynamic performance of a lean burn catalytic combustion gas turbine. The characteristics of lean burn catalytic combustion were investigated by utilising 1D heterogeneous plug flow model which was validated by experiments. The effects of operating parameters on catalytic combustion were numerically analysed. The system models were built in ASPEN Plus and three independent design variables, i.e. compressor pressure ratio (PR), regenerator effectiveness (RE) and turbine inlet temperature (TIT) were selected to analyse the thermodynamic performance of the thermal cycle. The main results show that: simulations from 1D heterogeneous plug flow model can capture the trend of catalytic combustion and describe the behavior of the catalytic monolith in detail. Inlet temperature is the most significant parameter that impacts operation of the catalytic combustor. When TIT and RE are constant, the increase of PR results in lowering the inlet temperature of the catalytic combustor, which results in decreasing methane conversion. The peak thermal efficiency and the optimal PR at a constant TIT increase with the increase of TIT; and at the constant PR, the thermal efficiency increases with the increase of TIT. However, with lower TIT conditions, the optimal PR and the peak efficiency at a constant TIT of the LBCCGT cycle are relative low to that of the conventional cycle. When TIT and PR are constant, the decrease of RE may result in lower methane conversion. The influences of RE on the methane conversion and the thermal efficiency are more significant at higher PRs. The higher thermal efficiency for the lower RE is achieved at lower PR.

Experimental Study and Modeling of an Adiabatic Fixed-bed Reactor for Methanol Dehydration to Dimethyl Ether

One-dimensional heterogeneous plug flow model was employed to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether. Longitudinal temperature and conversion profiles predicted by this model were compared to those experimentally measured in a bench scale reactor. The reactor was packed with 1.5 mm γ-Al 2O 3 pellets as dehydration catalyst and operated in a temperature range of 543-603 K at an atmospheric pressure. Also, the effects of weight hourly space velocity (WHSV) and temperature on methanol conversion were investigated. According to the results, the maximum conversion is obtained at 603.15 K with WHSV of 72.87 h −1.

Simulation and Optimization of an Adiabatic Multi‐Bed Catalytic Reactor for the Oxidation of SO2

AbstractA software package was developed for the simulation and optimization of a multi‐bed adiabatic reactor for the catalytic oxidation of SO2, using a heterogeneous plug flow model. The orthogonal collocation (OC) technique with up to eight collocation points was used for the solution of a nonlinear, two‐point boundary value differential equation for the catalyst particle, and it was shown that the use of the OC technique with two collocation points can describe the system well. Because of the nonlinear behavior of the effectiveness factor along the bed, optimal catalyst distribution between the beds and corresponding inlet temperatures were determined by two methods, including: the use of (1) intrinsic or (2) actual rate of reaction in the optimization criteria. The results showed that for the second case, the minimum amount of the catalyst can be reached at lower temperatures, the amount of catalyst required is always less, and the number of beds is greater than or equal to that of the first case.

Optimization of the Decoking Procedure of an Ethane Cracker with a Steam/Air Mixture

Using a heterogeneous plug flow model for the reactor tubes and a general gas−solid reaction/diffusion model with intrinsic reaction kinetics for coke combustion and coke gasification, an in-depth study on the influence of seven operating parameters of the decoking procedure of an ethane cracking furnace is performed. On the basis of the results of this study, the air and steam flow to the reactor tubes during the decoking procedure are adapted to propose an optimized decoking procedure that allows reducing the required decoking time of an industrial ethane cracking furnace by a factor of 3. In the new decoking conditions for the ethane cracker, the air flow rate is raised by a factor of 3, while the steam dilution is lowered by a factor of 4.5.

Fixed-bed reactor for gasoline sweetening: Kinetics of mercaptan oxidation and simulation of the Merox reactor unit

The kinetic study of mercaptans oxidation was extended to the oxidation of n-hexyl mercaptan in n-heptane and to the sweetening of a typical light gasoline. The simulation of a typical industrial Merox reactor was then performed. The fixed-bed reactor was modelled by using a one-dimensional heterogeneous plug-flow model. Both the steady-state and transient behaviour were studied, as well as the influence of the real distribution of Merox catalyst inside particles and along the bed on the simulation results.

Determination of kinetic parameters from dynamic investigations of heterogeneously catalyzed reactions

The problem of evaluating kinetic parameters from dynamic experiments is considered. An instationary isothermal heterogeneous plug-flow model is applied to determine parameters from experimental data on the heterogeneously catalyzed oxidative dehydrogenation of isobutyric aldehyde to methacrolein. Numerical integration of the model equations is performed by an explicit finite-difference scheme. Parameter estimates are obtained by a modified Gauss-Newton method. Two different reaction models for the main reactions, i.e. the reaction of isobutyric aldehyde with the oxidized catalyst and the reoxidation of the reduced catalyst, are proposed and compared with respect to their suitability. The activation energies for the various reaction steps are determined for both models.

Dynamic modelling of heterogeneous catalytic reactions—I. Theoretical considerations

The problem of modelling heterogeneous catalytic reactions by dynamic methods is considered, using a one-dimensional heterogeneous plug-flow model. Assuming constant reactor inlet temperature, uniform initial temperature profile, reactor inlet concentration step changes and absence of part of the reactants, it is shown that the reactor outlet concentration transients may be used to determine individual steps of the reaction scheme and to estimate kinetic parameters. Reaction steps can be determined by comparison of measured transients with classified transients for typical model reactions. Estimation of kinetic parameters is carried out by using the concentration transients and their time derivatives.