Reactor Inlet Temperature Research Articles

Simulation of Hydrodesulfurization Trickle Bed Reactor

The existence of sulfur in crude oil and petroleum fractions imposes plenty of harmful effects to the environment and process equipment. Therefore, elimination of these compounds from petroleum cuts has extensively been studied. In this research, the process of hydrodesulfurization of dibenzothiophene as one of the most stable sulfur components has been discussed and nonisothermal heterogeneous modeling and simulation of the three-stage trickle bed reactor has been performed. The catalyst, used in this operation, is CoMo/Al2O3. A kinetic equation, based on the Langmuir-Hingshelwood method of rate determination was incorporated into the model. The feed of the reactor was assumed to be gas oil and reactor inlet temperature and pressure were 354°C and of 70barg, respectively. The presence of stagnant liquid pockets between catalyst particles and the heat production due to highly exothermic HDS reactions have been considered in this model. The simulation results showed sulfur conversion of 99% in the final product and good agreement between the simulation results and the experimental data were achieved. In addition, two-dimensional modeling of the first bed of the reactor was conducted. The results indicated that maximum conversion rate occurred at the central axis of the reactor. The model has the ability of determining the position of the hot spots inside the reactor.

A fast hybrid start-up process for thermally self-sustained catalytic n-butane reforming in micro-SOFC power plants

This work aims at the investigation and optimization of a hybrid start-up process for a self-sustained reactor for n-butane to syngas conversion in intermediate temperature, micro-solid oxide fuel cell (micro-SOFC) power plants. The catalytic reaction is carried out in the presence of Rh-doped Ce0.5Zr0.5O2nanoparticles in a disk-shaped reactor. For the start-up, a resistance heater is embedded inside the catalytic bed and is activated until the exothermic oxidative reaction is initiated. The self-sustained temperature and reforming performance are demonstrated to be highly dependent on the fuel to oxygen (C/O) ratio and the catalytic activity at different space times. It is shown that a C/O ratio of 0.8 is a very good choice in terms of achieved steady-state temperature, syngas selectivity and start-up time. At a reactor inlet temperature of 809 °C for a C/O ratio of 0.8 and a space time as low as 8 ms, a syngas selectivity of 69.6% and a temperature of 529 °C at the simulated micro-SOFC membrane are demonstrated. After only 15 s from ignition, a temperature of 600 °C at the reactor inlet is reached. The hybrid start-up process is optimized with respect to a specific setup as an example, but is of general nature and utility to similar systems.

System Evaluation and Economic Analysis of a Nuclear Reactor Powered High-Temperature Electrolysis Hydrogen-Production Plant

A reference design for a commercial-scale high-temperature electrolysis (HTE) plant for hydrogen production was developed to provide a basis for comparing the HTE concept with other hydrogen-production concepts. The reference plant design is driven by a high-temperature helium-cooled nuclear reactor coupled to a direct Brayton power cycle. The reference design reactor power is 600 MWt, with a primary system pressure of 7.0 MPa, and reactor inlet and outlet fluid temperatures of 540°C and 900°C, respectively. The electrolysis unit used to produce hydrogen includes 4,009,177 cells with a per-cell active area of 225 cm2. The optimized design for the reference hydrogen-production plant operates at a system pressure of 5.0 MPa, and utilizes an air-sweep system to remove the excess oxygen that has evolved on the anode (oxygen) side of the electrolyzer. The inlet air for the air-sweep system is compressed to the system operating pressure of 5.0 MPa in a four-stage compressor with intercooling. The alternating current to direct current conversion efficiency is 96%. The overall system thermal-to-hydrogen-production efficiency (based on the lower heating value of the produced hydrogen) is 47.1% at a hydrogen-production rate of 2.356 kg/s. This hydrogen-production efficiency is considerably higher than can be achieved using current low-temperature electrolysis techniques. An economic analysis of this plant was performed using the standardized hydrogen analysis methodology developed by the Department of Energy Hydrogen Program, and using realistic financial and cost estimating assumptions. The results of the economic analysis demonstrated that the HTE hydrogen-production plant driven by a high-temperature helium-cooled nuclear power plant can deliver hydrogen at a competitive cost. A cost of $3.23/kg of hydrogen was calculated assuming an internal rate of return of 10%.

Estimation of the environmental impact of a petrochemical process using coupled LCA and exergy analysis

Reduction of the environmental impact in the oil and gas industry is an ecological and financial issue for process development and design. Currently, the environmental impact of a process is often determined by life cycle assessment (LCA). But exergy analysis has also been proposed to assess process sustainability. To illustrate the potential of coupling LCA and exergy analysis in the petroleum industry, a naphtha catalytic reforming process has been selected and evaluated in terms of climate change, one of the classical environmental impacts used in LCA. LCA and exergy analysis are used together to show how greenhouse gas (GHG) emissions and a thermodynamic indicator ( I p ) related to exergy are modified when the process parameters are varied (feed characteristics, inlet reactor temperature, type of utilities). A positive relationship between GHG emissions and I p has been obtained. It does not depend upon the feed characteristics and can be used for process development without performing a full LCA. The methodology has been extended to take into account natural resources depletion, greenhouse gas emissions and quality of co-products during process development and design for a given product specification. Two catalytic reforming process variants (i.e. processing same inputs and producing same outputs with different internal unit operations arrangement; for this reason, these process variants have the same function) are compared from these previous different points of view. LCA and exergy analysis are shown to be complementary tools.

Dynamic optimization of a novel radial-flow, spherical-bed methanol synthesis reactor in the presence of catalyst deactivation using Differential Evolution (DE) algorithm

In this work, a novel radial-flow spherical-bed methanol synthesis reactor has been optimized using Differential Evolution (DE) algorithm. This reactor's configuration visualizes the concentration and temperature distribution inside a radial-flow packed bed with a novel design for improving reactor performance with lower pressure drop. The dynamic simulation of spherical multi-stage reactors has been studied in the presence of long-term catalyst deactivation. A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methanol production in radial-flow spherical-bed methanol synthesis reactor. The simulation results have been shown that there are optimum values of the reactor inlet temperatures, profiles of temperatures along the reactors and reactor radius ratio to maximize the overall methanol production. The optimization methods have enhanced additional yield throughout 4 years of catalyst lifetime, respectively.

Testing the impact of hydrodesulphurisation process parameters on diesel fuel properties

In this work the influence of changes in hydrodesulphurisation (HDS) process parameters (space velocity and temperature) on efficiency of sulphur compounds removal was tested. The feedstock, straight run gas oils (STGO) from Croatian crude oil used for diesel fuel production have been subject to the hydrodesulphurisation process with Co-Mo/Al2O3 commercial catalyst in a trickle bed reactor in high-pressure apparatus at the following conditions: total reactor pressure of 500 kPa, reactor inlet temperature in the range 330 - 355 °C, liquid hourly space velocity (LHSV) in the range 2.0, 2.5 and 3.0 h-1 and hydrogen/hydrocarbons ratio of 120. The laboratory high-pressure apparatus was upgraded by implementation of a modern computer-based control system. Control system supports experimentation aiming better process conditions monitoring and control with the purpose of improved repeatability and achievement of safe operation.

Benzene Reduction by Alkylation in a Solid Phosphoric Acid Catalyzed Olefin Oligomerization Process

A refinery with a solid phosphoric acid olefin oligomerization unit can reduce the benzene content of its motor-gasoline by co-feeding the benzene-containing material to that unit. It has been shown that benzene co-feeding has little disruptive impact on olefin oligomerization, and >80% benzene conversion to alkylated benzenes has been demonstrated during a commercial test run on an industrial unit. Benzene conversion is insensitive to reactor inlet temperature in the range of 160−180 °C and remains better than 80% at liquid hourly space velocities of up to 1.5 h−1. A high propene content in the olefinic feed promotes benzene alkylation, and although butene-rich feeds can be employed, benzene conversion is lower.

Case Study on Tubular Reactor Hot-Spot Temperature Control for Throughput Maximization

Auctioneering hot-spot temperature control of a highly exothermic cooled tubular reactor (constant coolant temperature) for cumene production via the irreversible gas-phase alkylation of benzene with propylene (A + B → C) is studied. Specifically, three control configurations are quantitatively evaluated for tightness of hot-spot temperature control and maximum achievable process throughput with reactor cooling duty as the bottleneck constraint. The configurations manipulate respectively the reactor cooling duty (CS1), the reactor inlet temperature (CS2), and the fresh propylene feed (CS3) for regulating the hot-spot temperature. Plantwide dynamic simulation results show that tightest hot-spot temperature control is achieved by the direct manipulation of the reactor cooling duty (CS1). Use of reactor inlet temperature as the manipulation handle (CS2) is not recommended due to large deviations in the reactor temperature profile for a throughput increase. Manipulating the fresh propylene feed rate (limiting reactant) as in CS3 provides loose but acceptable hot-spot temperature control. CS3 is most preferred for throughput maximization as the reactor is operated at the bottleneck constraint of maximum heat removal capacity. For the sample case study, the maximum achievable throughput increases by more than 7% by use of CS3 (over CS1).

Simulation of methane conversion to syngas in a membrane reactor. Part II: Model predictions

A one-dimensional non-isothermal model was employed in the simulation of partial oxidation of methane to syngas in a dense oxygen permeation membrane reactor. The model predicts that if methane is consumed completely in the reactor, a temperature runaway occurs. The reactor inlet temperature is chosen as a major factor to demonstrate the correlativity of the reactor performance and this phenomenon. A borderline inlet temperature (BIT) is defined. Simulation results showed that when the reactor inlet temperature approaches this value, an optimized reactor performance is achieved. This temperature increases with the increase of the air flow rate and carbon space velocity. The surface exchange kinetics at the oxygen-rich side has a small effect on this temperature, while that at the oxygen-lean side has a significant effect.

The Application of System CFD to the Design and Optimization of High-Temperature Gas-Cooled Nuclear Power Plants

Abstract The objective of this paper is to model the steady-state and dynamic operation of a pebble-bed-type high temperature gas-cooled reactor power plant using a system computational fluid dynamics (CFD) approach. System CFD codes are 1D network codes with embedded 2D or even 3D discretized component models that provide a good balance between accuracy and speed. In the method presented in this paper, valves, orifices, compressors, and turbines are modeled as lumped or 0D components, whereas pipes and heat exchangers are modeled as 1D discretized components. The reactor is modeled as 2D discretized system. A point kinetics neutronic model will predict the heat release in the reactor. Firstly, the layout of the power conversion system is discussed together with the major plant parameters. This is followed by a high level description of the system CFD approach together with a description of the various component models. The code is used to model the steady-state operation of the system. The results are verified by comparing them with detailed cycle analysis calculations performed with another code. The model is then used to predict the net power delivered to the shaft over a wide range of speeds from zero to full speed. This information is used to specify parameters for a proportional-integral-derivative controller that senses the speed of the power turbine and adjusts the generator power during the startup of the plant. The generator initially acts as a motor that drives the shaft and then changes over to a generator load that approaches the design point value as the speed of the shaft approaches the design speed. A full startup simulation is done to demonstrate the behavior of the plant during startup. This example demonstrates the application of a system CFD code to test control strategies. A load rejection example is considered where the generator load is suddenly dropped to zero from a full load condition. A controller senses the speed of the low pressure compressor/low pressure turbine shaft and then adjusts the opening of a bypass valve to keep the speed of the shaft constant at 60rps. The example demonstrates how detailed information on critical parameters such as turbine and reactor inlet temperatures, maximum fuel temperature, and compressor surge margin can be obtained during operating transients. System CFD codes is a powerful design tool that is indispensable in the design of complex power systems such as gas-cooled nuclear power plants.

Determining the Optimized Controller Parameters Using a Hybrid GA-SQP Technique

Dynamic simulation and optimization of a hydrogenation reactor system were developed and investigated in the present work. The process mainly consists of three adiabatic fixed bed hydrogenation reactors in series in addition to one heater before the first reactor and three coolers after each reactor for interstage cooling. The feed flow rate to the unit, the feed temperature or the carbon monoxide content of the feed may change and cause variations of the outlet temperature of reactors. Therefore, it is essential to control the inlet temperature of each reactor. There is a temperature controller before each reactor and also one after the third reactor. The tuning parameters of the controllers were optimized in three different cases, taking into account the process constraints. In each case, a special disturbance was forced to the process. Because of catalyst deactivation, the inlet temperature of reactors must be increased during the running period in order to have the desired conversion. Therefore, the optimal inlet temperature profile was determined based on SOR, MOR and EOR data. Optimization of the process was done by the use of a hybrid GA-SQP method. The new hybrid method was developed to overcome the difficulties of both methods. The genetic algorithm (GA) which is a stochastic method, is relatively slow, but is not sensitive to the initial point. In contrast, sequential quadratic programming (SQP) method is a deterministic method which is fast, but very sensitive to the initial point and gets trapped in local optima. In the newly developed hybrid method, the SQP method speeds the solving procedure, while the GA enables the algorithm to escape from local optima. An industrial acetylene hydrogenation system was used to provide the necessary data to adjust kinetics and to validate the approach.

Operability of an Industrial Catalytic Naphtha Reformer in the Presence of Catalyst Deactivation

AbstractBifunctional naphtha reforming catalysts are deactivated by side reactions such as coking, sintering, and poisoning in the course of industrial operation. This results in a reduction of the octane number of the product in a commercial naphtha reforming unit. Catalyst deactivation is compensated for by increasing the operating temperature so that the primary product yields are kept constant during an operating cycle. In the present study, a deactivation model has been developed for industrial catalytic naphtha reformers. The parameters for the deactivation model have been estimated using plant data. The results of the model show that increasing the reactor weighted average inlet temperature (WAIT) can offset the decrease in aromatic yield. Concentration and temperature profiles have been obtained to provide information about the extent of conversion in the individual reactors. Reactor inlet temperature is an important parameter, which can significantly affect reformer performance, the aromatic yield increasing with an increase in temperature.

Experimental and numerical investigation of the catalytic partial oxidation of [formula omitted] mixtures diluted with [formula omitted] and [formula omitted] in a short contact time reactor

The catalytic partial oxidation (CPO) of fuel-rich CH 4 / O 2 mixtures, heavily diluted with H 2 O and CO 2 (46.3% and 23.1% volumetric feed composition, respectively), was investigated experimentally and numerically at 5 bar. Experiments were carried out in an ∼ 8 ms residence time prototype gas-turbine honeycomb reactor coated with a Rh/ ZrO 2 catalyst and included temperature measurements along the reactor and exhaust gas analysis. Simulations with detailed hetero-/homogeneous chemical reaction schemes were performed using a steady, full elliptic 2D code for both the gas and solid phases. The employed catalytic reaction scheme overpredicted mildly the impact of the total over the partial oxidation route and this effect was more pronounced at lower reactor inlet temperatures ( < 523 K ). The contribution of the various chemical pathways to the synthesis gas yields and selectivities has been elucidated. It was shown that the addition of water provided a source of surface oxygen and hydroxyl radicals, which in turn enhanced the CH 4 conversion and H 2 selectivity and reduced the CO selectivity. On the other hand, the addition of CO 2 had a minor impact on the aforementioned parameters. The increase in the H 2 / CO product ratio with water dilution is highly desirable in new power generation processes with large exhaust gas recycle, which utilize the “catalytic rich combustion” methodology (the partial oxidation products stabilize a post-catalyst flame). At steady operation the catalyst surface temperatures exceeded by 200 K the adiabatic equilibrium temperature and standard (passive) heat transfer mechanisms in the solid were shown to be ineffective in providing proper reactor thermal management. Catalytic ignition was achieved at 670 K, however, the strong ignition/extinction hysterisis allowed for sustained steady CPO at inlet temperatures as low as 473 K.

Use of catalytic reforming to aid natural gas HCCI combustion in engines: experimental and modelling results of open-loop fuel reforming

The potential of the homogeneous charge compression ignition (HCCI) combustion process to deliver drastically reduced emissions of NO x and improved fuel economy from internal combustion engines is well known. The process is, however, difficult to initiate and control, especially when methane or natural gas are used as fuel. To aid the HCCI combustion of natural gas, hydrogen addition has been successfully used in this study. This hydrogen can be obtained from on-line reforming of natural gas. Methane reforming is achieved here by reaction with engine exhaust gas and air in a small scale monolith catalytic reactor. The benchmark quantity of H 2 required to enhance the feasibility and engine load range of HCCI combustion is 10%. For low temperature engine exhaust gas, typical for HCCI engine operating conditions, experiments show that additional air is needed to produce this quantity. Experimental results from an open-loop fuel exhaust gas reforming system are compared with two different models of basic thermodynamic equilibria calculations. At the low reactor inlet temperatures needed for the HCCI application (approx. 400 ∘ C ) the simplified three-reaction thermodynamic equilibrium model is in broad agreement with experimental results, while for medium ( 550 – 650 ∘ C ) inlet temperature reforming with extra air added, the high hydrogen yields predicted from the multi-component equilibrium model are difficult to achieve in a practical reformer.

Exhaust gas assisted reforming of rapeseed methyl ester for reduced exhaust emissions of CI engines

The nitrogen oxides (NOx) emissions of compression ignition (CI) engines fueled with biodiesel are generally higher compared to conventional diesel fuelling. Previous research work in CI engines has shown that the partial replacement of hydrocarbon fuels by hydrogen combined with exhaust gas recirculation (EGR) can reduce NOx and smoke emissions without significant changes to the engine efficiency. In the present study, the production of hydrogen-rich gas by catalytic exhaust gas assisted fuel reforming of rapeseed methyl ester (RME) has been investigated experimentally as a way to provide the required hydrogen for the reduction of biodiesel emissions. For comparison, tests with ultra low sulphur diesel (ULSD) were also performed. The reforming experiments were carried out in a mini reactor supplied with exhaust gas from a single cylinder CI engine. In all cases, the reactor inlet temperature was kept at 290∘C which was chosen as a typical low exhaust gas temperature of diesel engines operating at part load. The engine operating condition (speed, load) was the same in all the tests and the reactor product gas was examined as a function of the reactor fuel flow rate and the composition of fuel and engine exhaust gas. Up to 17% hydrogen content of the reformer product was achieved and the results indicated that the main reactions in the reformer were the exothermic complete oxidation of part of the fuel and the endothermic steam reforming reaction. Reforming of RME produced more hydrogen with higher fuel conversion efficiency compared to ULSD reforming.

Low temperature exhaust gas fuel reforming of diesel fuel

The application of exhaust gas assisted fuel reforming in diesel engines has been investigated. The process involves hydrogen generation by direct catalytic interaction of diesel fuel with engine exhaust gas. Using a laboratory reforming mini reactor incorporated in the exhaust system of a diesel engine, up to 16% hydrogen in the reactor product gas was achieved at a reactor inlet temperature of 290 °C. The results showed that such levels of hydrogen can be produced with appropriate control of the reaction parameters at temperatures typical of exhaust gas temperatures of diesel engines operating at part load without any requirement for external heat source or air and steam supply. The use of simulated reformed fuel was shown to be beneficial in terms of engine exhaust emissions and resulted in reduction of NO X and smoke emissions.

Catalytic exhaust gas fuel reforming for diesel engines—effects of water addition on hydrogen production and fuel conversion efficiency

Previous work in our laboratory has shown that the exhaust gas assisted fuel reforming process has the potential to provide a solution to the diesel engine exhaust emission problems. When simulated reformer product gas rich in hydrogen is fed to the engine, a reduction of both NO x and smoke emissions can be achieved. In this paper, the optimisation of the reforming process by water addition in the reactor is presented. Using a prototype catalyst at 290°C reactor inlet temperature, up to 15% more hydrogen in the reformer product was obtained compared to operation without water. The process has been found to be mainly a combination of the fuel oxidation, steam reforming and water gas shift reactions. The reforming process efficiency has been shown to improve considerably with water addition up to a certain level after which the adverse effects of the exothermic water gas shift reaction become significant.

Design and Control for Recycle Process with Tubular Reactor

Interaction between design and control for gas-phase adiabatic tubular reactor with liquid recycle is studied. This generic bimolecular reaction, A+B→C, has two important features: (1) stoichimoetiric balance has to be maintained and (2) reactor temperature plays an important role in design and operability. More importantly, it represents a large class of important industrial processes. Optimal reactant distribution can be obtained directly form the simplified TAC equation and effects of kinetics parameters and relative volatilities on this optimality are also explored. The results show that an increased reactor exit temperature leads to a more controllable optimal design while a high activation energy results in a less controllable one. For the operability analysis, two control structures are proposed with three different combinations of TPM. The control structure using the reactor inlet temperature as TPM gives good control performance when the reactant distribution is held constant. However, potential problem may arise as the result of high reactor exit temperature (T out ). For the case of biased reactant distribution, the reactant redistribution provides an extra degree of freedom and this alleviates the high T out problem. The results presented in this work clearly indicate that simple material and energy balances provide useful insights in the design and control of recycle processes.

Design of tubular reactors in recycle systems

The article presents an approach to design tubular reactors in recycle systems, based on non-linear analysis. A pseudo-homogeneous plug-flow reactor model is used. It is assumed that the separation unit delivers product and recycle streams with fixed composition. The stand-alone reactor has a unique stable steady state. The coupled reactor–separation–recycle system shows four types of conversion versus plant Damköhler number bifurcation diagrams. A feasible steady state exists only if the reactor volume exceeds a critical value. For isothermal reactor, the steady state is unique and stable. For non-isothermal reactor, one or two steady states are possible. In the second situation the low-conversion state is unstable. In some parameter regions, the unique state is unstable. The design should ensure state unicity and stability, which are favoured by large heat-transfer capacity, low coolant temperature and high reactor-inlet temperature. A case study demonstrates that these phenomena can be easily found in real plants.

Incorporation of Flexibility in the Design of a Methanol Synthesis Loop in the Presence of Catalyst Deactivation

AbstractThis paper presents the incorporation of process flexibility into a methanol synthesis loop operating under catalyst deactivation. A design methodology is discussed with regard to catalyst deactivation, and some limitations are identified. In the current flexibility study the size of the reactor and recycle ratio have been fixed. Attempts to maintain methanol production at the rates observed with fresh catalyst included increased pressure, increased make up gas flow rate, and the injection of carbon dioxide into the make up gas at optimized inlet temperature. In order to provide flexibility and produce a design compatible with increased production rates, the effect of interrelating equipment had to be considered. As a result of catalyst deactivation, an increased flow rate is necessary and the altered process streams entering the preheater disturb the reactor inlet temperature. These issues should be considered in the design stage and may be resolved by the flexible designs presented.