Reactor Inlet Temperature Research Articles

Cooling Performance Analysis of ThePrimary Cooling System ReactorTRIGA-2000Bandung

The conversion of reactor fuel type will affect the heat transfer process resulting from the reactor core to the cooling system. This conversion resulted in changes to the cooling system performance and parameters of operation and design of key components of the reactor coolant system, especially the primary cooling system. The calculation of the operating parameters of the primary cooling system of the reactor TRIGA 2000 Bandung is done using ChemCad Package 6.1.4. The calculation of the operating parameters of the cooling system is based on mass and energy balance in each coolant flow path and unit components. Output calculation is the temperature, pressure and flow rate of the coolant used in the cooling process. The results of a simulation of the performance of the primary cooling system indicate that if the primary cooling system operates with a single pump or coolant mass flow rate of 60 kg/s, it will obtain the reactor inlet and outlet temperature respectively 32.2 °C and 40.2 °C. But if it operates with two pumps with a capacity of 75% or coolant mass flow rate of 90 kg/s, the obtained reactor inlet, and outlet temperature respectively 32.9 °C and 38.2 °C. Both models are qualified as a primary coolant for the primary coolant temperature is still below the permitted limit is 49.0 °C.

CFD coupled kinetic modeling and simulation of hot wall vertical tubular reactor for deposition of SiC crystal from MTS

Chemical Vapor Deposition (CVD) process is generally carried out in a hot wall reactor of vertical or horizontal type keeping the substrate inside the chamber on which deposition is targeted. Present study is focused to explain the role of hydrodynamics and temperature conditions on the overall coating rates inside a hot wall vertical tubular reactor. Deposition of β-Silicon Carbide crystals from Methytricholorosilane catalyzed by hydrogen is modeled here considering growth kinetics which can be successfully described – using only two steps. Finite Element Method based simulation is performed to obtain the flow and temperature profiles inside the hot wall reactor. Model equations for kinetics are derived in differential form based on mass balance considering transport of species. Kinetic parameters were approximated comparing the experimentally found coating rates as reported earlier. Present model is seen to fit reasonably well for the wide variation of gas flow rates as well as temperature. Apart from the flow rates of total fluid at inlet and initial wall temperature of reactor, sample position and the inlet diameter of the reactor are found to be key important parameters for the desired coating to take place. Model prediction thus can provide better knowledge in order to carefully choose process parameters in designing the reactor for achieving optimized deposition rates by CVD with desired properties.

A hybrid non-dominated sorting genetic algorithm and its application on multi-objective optimal design of nuclear power plant

The design of nuclear component can be optimized by seeking out the best combination of article operational and structural parameters. Through multi-objective optimization, the optimized scheme can not only meets the design requirements, but also satisfies the safety regulations. In this work, a hybrid non-dominated sorting genetic algorithm is proposed, and its performance is verified by comparing it with its prototype and immune memory clone constraint multi-objective algorithm through four test-functions; the designs of the steam generator and the primary loop of Qinshan I nuclear power plant are optimized by the proposed algorithm. The results show that the algorithm outperforms the other two through overall evaluation; the reactor inlet temperature is an important parameter which influences the distribution of the Pareto optimal front; through optimization, the weight of the steam generator can be reduced by 16.5%, and the primary flow-rate can be reduced by 17.0%, the weight of the primary loop can be reduced by 11.4%, and the volume can be reduced by 9.8%.

Simulation of supercritical water oxidation reactor in transitory state: Application to time-dependent processes

Supercritical Water Oxidation (SCWO) is a powerful process for the treatment of organic wastewater. It has already been studied for decades and, nowadays there are several demonstration and industrial plants under construction worldwide. Simulation tools play an important role, both to predict and optimize the operating conditions during the process and to evaluate its economic viability. In the case of SCWO, transitory state models are sparse in the literature. In order to exhaustively know the behavior of the SCWO process during time-dependent applications, a transitory tubular reactor model has been built. That model has been developed by the finite difference method in two dimensions. It takes into account the reaction of wastewater along the reactor and the heat loss from the fluid to the atmosphere in a radial way, both along the pipe and through the isolation material.In order to validate the model, a set of experiments under different operating conditions were carried out in a pilot plant. Their aim was to characterize the heat loss in the system to fit both simulated and experimental data in steady state. Then, the transitory model is tested and typically time-dependent applications at industrial scale are analysed under different operating conditions (varying feed concentrations, reactor inlet temperature or amount of cooling water injection). In each case, the model results are collected and they show the time variation according to the changes in operating parameters such as temperature, feed concentration or heat loss along the reactor. The model developed can also be used for other technologies based on supercritical water, such as supercritical water gasification.

Effects of heterogeneous–homogeneous interaction on the homogeneous ignition in hydrogen-fueled catalytic microreactors

The effects of heterogeneous–homogeneous interaction on the homogeneous ignition behavior in hydrogen-fueled catalytic microreactors in the submillimeter to millimeter range were investigated numerically. A two-dimensional CFD (computational fluid dynamics) model that includes detailed hetero-/homogeneous chemistry and transport was employed to study the effect of mechanistic interactions between heterogeneous and homogeneous reaction pathways on the homogeneous ignition behavior of hydrogen-air mixtures over platinum in parallel-plate microreactors. Parametric studies were carried out to identify the effect of various operating parameters (inlet temperature, reactor size, inlet pressure, and feed composition) on the homogeneous ignition behavior. Comparisons with purely homogeneous cases were made. Heterogeneous–homogeneous interaction diagrams delineating the regions of the different homogeneous ignition types were constructed in terms of microreactor dimension and inlet temperature. An inflection point temperature of homogeneous ignition mode transition was found. The catalyst promotes the homogeneous ignition at lower temperatures but inhibits the homogeneous ignition at higher temperatures. The homogeneous inhibition is mainly induced by heterogeneous reactions; decreasing the reactor size enhances this inhibiting effect and moves the inflection point toward higher temperatures. Microreactor dimension has a strong impact on the homogeneous ignition behavior at lower temperatures, but has little effect at higher temperatures. Three homogeneous ignition regions can be observed in heterogeneous–homogeneous interaction diagrams, and a transition from completely heterogeneously- to heterogeneously-, and eventually homogeneously-controlled ignition occurs with increasing reactor size and inlet temperature. The diverging ignition behavior occurs with increasing pressure. The homogeneous ignition location at higher temperatures is found to be nearly independent of feed compositions that has an important effect at lower temperatures.

Performance comparison and optimization of two configurations of (Very) high temperature gas-cooled reactors combined cycles

(Very) high temperature gas-cooled reactors have a reactor outlet temperature of 900–1000°C, which provides a base for higher cycle efficiency by adopting closed nuclear gas-turbine combined cycles (NGTCCs) instead of direct regenerative cycles (RCs). Typical NGTCCs (TCCs) usually only adopt precoolers and do not include recuperators. The analysis of precoolers in the TCC indicates that a simplified TCC (SCC), a TCC without precoolers, has higher cycle efficiency because of a higher reactor inlet temperature. Moreover, a criterion whether a TCC adopts precoolers is derived. If NGTCCs includes recuperators, it becomes a typical compound combined cycle (TCCC). The analysis of recuperators in the TCCC indicates that recuperator’s effectiveness should be above 0.7 for high efficiency, otherwise recuperators can only be used to adjust the inlet temperatures of reactors and steam generators. Based on the discussion of precoolers and recuperators in NGTCCs, a simplified TCCC (SCCC) that only including recuperator is proposed. The further parametric calculations show that the optimum cycle efficiency is 50.0–57.8% for RC, 51.5–59.2% for SCC and 53.3–61.5% for SCCC, with a reactor outlet temperature of 900–1200°C. Once the reactor inlet temperature is limited to 400–750°C, a threshold value (500–600°C) of reactor inlet temperature that separates the working condition of SCC and SCCC is obtained. The SCC is most favorable when the limit temperature is below the threshold value; otherwise, the SCCC has the highest efficiency.

Simulation of biomass char gasification in a downdraft reactor for syngas production

A steady state, one‐dimensional computational fluid dynamics model of wood char gasification in a downdraft reactor is presented. The model is not only based on reaction kinetics and fluid flow in the porous char bed but also on equations of heat and mass conservation. An original OpenFOAM solver is used to simulate the model and the results are found to be in good agreement with published experimental data. Next, a sensitivity analysis is performed to study the influence of reactor inlet temperature and gas composition on char conversion, bed temperature profile and syngas composition. In addition, the evolution of the complex reaction mechanisms involved in mixed atmosphere gasification is investigated, and the most suitable operating parameters for controlling syngas composition are evaluated. Our simulation results provide essential knowledge for optimizing the design and operation of downdraft gasifiers to produce syngas that meets the requirements of various biofuel applications. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1079–1091, 2016

Optimizing an Industrial Scale Naphtha Catalytic Reforming Plant Using a Hybrid Artificial Neural Network and Genetic Algorithm Technique

In this paper, a hybrid model for estimating the activity of a commercial Pt-Re/Al2O3 catalyst in an industrial scale heavy naphtha catalytic-reforming unit (CRU) is presented. This model is also capable of predicting research octane number (RON) and yield of gasoline. In the proposed model, called DANN, the decay function of heterogeneous catalysts is combined with a recurrent-layer artificial neural network. During a life cycle (919 days), fifty-eight points are selected for building and training the DANN (60%), nineteen data points for testing (20%), and the remained ones for validating steps. Results show that DANN can acceptably estimate the activity of catalyst during its life in consideration of all process variables. Moreover, it is confirmed that the proposed model is capable of predicting RON and yield of gasoline for unseen (validating) data with AAD% (average absolute deviation) of 0.272% and 0.755%, respectively. After validating the model, the octane barrel level (OCB) of the plant is maximized by manipulating the inlet temperature of reactors, and hydrogen to hydrocarbon molar ratio whilst all process limitations are taken into account. During a complete life cycle results show that the decision variables, generated by the optimization program, can increase the RON, process yield and OCB of CRU to about 1.15%, 3.21%, and 4.56%, respectively. © 2015 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Effects of reactor pressure and inlet temperature on n‐butane/dimethyl ether oxidation and the formation pathways of the aromatic species

Oxidation of n‐butane/dimethyl ether (DME)/O2/Ar system was studied by chemical kinetic modeling in a tubular reactor operated adiabatically and at constant pressure. Effects of the reactor pressure on the formation of various major, minor, and trace oxidation products were investigated for two different pressures (1 and 5 atm) and at six different inlet temperature values (700, 800, 900, 1100, 1300, and 1500 K). The analysis was carried out for two different concentrations of dimethyl ether in the inlet fuel mixture (20 and 50 mol %). Higher pressure (5 atm) resulted in higher mole fractions of methane, vinylacetylene, and cyclopentadiene; and lower mole fractions of formaldehyde, acetylene, acetaldehyde, ethane, propargyl, and propane. The mole fractions of CO and CO2 were not affected considerably by the pressure change. The main formation routes of benzene were developed at two different inlet temperature values (1100 and 1300 K), and the main precursors participating in these routes were found to be propargyl, propene, and diacetylene. A skeletal mechanism was developed for the oxidation of n‐butane/DME mixture from the detailed mechanism by reduction of the elementary reactions by 79%, and it was tested for accuracy by comparison with the data from the literature. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 230–240, 2016

Thermoelectric generation coupling methanol steam reforming characteristic in microreactor

Thermoelectric (TE) generator converts heat to electric energy by thermoelectric material. However, heat removal on the cold side of the generator represents a serious challenge. To address this problem and for improved energy conversion, a thermoelectric generation process coupled with methanol steam reforming (SR) for hydrogen production is designed and analyzed in this paper. Experimental study on the cold spot character in a micro-reactor with monolayer catalyst bed is first carried out to understand the endothermic nature of the reforming as the thermoelectric cold side. A novel methanol steam reforming micro-reactor heated by waste heat or methanol catalytic combustion for hydrogen production coupled with a thermoelectric generation module is then simulated. Results show that the cold spot effect exists in the catalyst bed under all conditions, and the associated temperature difference first increases and then decreases with the inlet temperature. In the micro-reactor, the temperature difference between the reforming and heating channel outlets decreases rapidly with an increase in thermoelectric material's conductivity coefficient. However, methanol conversion at the reforming outlet is mainly affected by the reactor inlet temperature; while at the combustion outlet, it is mainly affected by the reactor inlet velocity. Due to the strong endothermic effect of the methanol steam reforming, heat supply of both kinds cannot balance the heat needed at reactor local areas, resulting in the cold spot at the reactor inlet. When the temperature difference between the thermoelectric module's hot and cold sides is 22 K, the generator can achieve an output voltage of 55 mV. The corresponding molar fraction of hydrogen can reach about 62.6%, which corresponds to methanol conversion rate of 72.6%.

Dynamic Simulation of Adiabatic Catalytic Fixed-Bed Tubular Reactors: A Simple Approximate Modeling Approach

Fixed-bed tubular reactors are used widely in chemical process industries, for example, selective hydrogenation of acetylene to ethylene in a naphtha cracking plant. A dynamic model is required when the effect of large fluctuations with time in influent stream (temperature, pressure, flow rate, and/or composition) on the reactor performance is to be investigated or automatically controlled. To predict approximate dynamic behavior of adiabatic selective acetylene hydrogenation reactors, we proposed a simple 1-dimensional model based on residence time distribution (RTD) effect to represent the cases of plug flow without/with axial dispersion. By modeling the nonideal flow regimes as a number of CSTRs (completely stirred tank reactors) in series to give not only equivalent RTD effect but also theoretically the same dynamic behavior in the case of isothermal first-order reactions, the obtained simple dynamic model consists of a set of nonlinear ODEs (ordinary differential equations), which can simultaneously be integrated using Excel VBA (Visual BASIC Applications) and 4th-order Runge-Kutta algorithm. The effects of reactor inlet temperature, axial dispersion, and flow rate deviation on the dynamic behavior of the system were investigated. In addition, comparison of the simulated effects of flow rate deviation was made between two industrial-size reactors.Keywords: Dynamic simulation, 1-D model, Adiabatic reactor, Acetylene hydrogenation, Fixed-bed reactor, Axial dispersion effect

Multi-objective optimal design of vertical natural circulation steam generator

In this work, a hybrid non-dominated sorting genetic algorithm was proposed and utilized to perform the multi-objective optimization design of a natural circulation steam generator, which included minimizing of the weight, the volume and the reactor coolant flow-rate. Sensitivity analysis of the design variables was carried out to study the relationships between the optimization variables and the objective functions, which was also helpful for the explanation of the optimization results. The mathematical model of the steam generator was validated by the RELAP5 code. The results show that the mathematical model has a good agreement with the RELAP5 model after modifying the boiling correlation in the secondary side; the proposed hybrid non-dominated sorting genetic algorithm is able to find much better spread of solutions and better convergence near the true Pareto optimal front compared to the non-dominated sorting genetic algorithm; reactor inlet temperature is the most important variable which influences the distribution of Pareto optimal solutions.

Effects of dimethyl ether on n-butane oxidation

Dimethyl ether (DME) is the simplest ether and it is used as an alternative fuel or fuel additive to reduce toxic emissions from combustion processes. The effects of DME on n-butane oxidation were investigated for two different concentrations of DME in the fuel mixture (i.e., 20% and 50%) and two different fuel-rich equivalence ratios (i.e., 2.6 and 3.0) using detailed chemical kinetic modeling. Reactor model was selected as atmospheric-pressure, adiabatic, tubular reactor, operated under laminar flow conditions. The concentration profiles of major, minor, and trace species were obtained for n-butane/DME/oxygen/argon at six different reactor inlet temperatures, and the results were compared with those attained for pure n-butane oxidation case (n-butane/oxygen/argon). Dimethyl ether addition decreased formations of various toxic species such as carbon monoxide, aromatic species, and polycyclic aromatic hydrocarbons, while it increased the formations of formaldehyde and acetaldehyde. Increasing equivalence ratio increased the formations of carbon monoxide, methane, aromatic species, and polycyclic aromatic hydrocarbons, while its effects on formaldehyde and acetaldehyde were not pronounced under the conditions studied.

Hydrogen Production by Sorption‐Enhanced Steam Glycerol Reforming: Sorption Kinetics and Reactor Simulation

Sorption‐enhanced glycerol reforming, an integrated process involving glycerol catalytic steam reforming and in situ CO2 removal, offers a promising alternative for single‐stage hydrogen production with high purity, reducing the abundant glycerol by‐product streams. This work investigates this process in a fixed‐bed reactor, via a two‐scale, nonisothermal, unsteady‐state model, highlighting the effect of key operating parameters on the process performance. CO2 adsorption kinetics was investigated experimentally and described by a mathematical reaction‐rate model. The integrated process presents an opportunity to improve the economics of green hydrogen production via an enhanced thermal efficiency process, the exothermic CO2 adsorption providing the heat to endothermic steam glycerol reforming, while reducing the capital cost by removing the processing steps required for subsequently CO2 separation. The operational time of producing high‐purity hydrogen can be enhanced by increasing the adsorbent/catalyst volume ratio, by adding steam to the reaction system and by increasing the inlet reactor temperature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2105–2118, 2013

Hydrotreating of straight-run gas oil blended with FCC naphtha and light cycle oil

In order to expand diesel fuel processing capacity an option to co-hydrotreat straight run gas oil blended with fraction containing FCC naphtha and light cycle oil was investigated. Industrial test run was performed under pressure of 40bar in the catalytic reactor with two layers of conventional Co-Mo/γ-Al2O3 catalyst, by increasing volume content of FCC naphtha and light cycle oil fraction in the reactor inlet to 20%vol. Reactor inlet temperature was also increased during the test run from 327 to 334°C. Liquid hourly space velocities between 1.05 and 1.32h−1 have been used with H2/oil ratios of 908–1135Nm3 hydrogen/m3 oil.Sulphur inlet concentrations of 6500–8200ppm were reduced to 36–72ppm in the hydrotreated oil. GC–MS analysis of the sulphur compound's sub-families has shown that most of the sulphur was present in more reactive classes like alkyl substituted benzothiophenes. High conversion of sulphur was achieved by a combination of the following process parameters: high reaction temperature, low space velocity, presence of FCC naphtha in the feed and distribution of inlet sulphur dominantly concentrated in more reactive benzothiophenes.The activation energy of 33.2kcal/mol was determined for this type of feedstock using power law kinetic expression.

New Control Structure for Feed-Effluent Heat Exchanger/Reactor Systems

Feed-effluent heat exchangers (FEHEs) are widely used in high-temperature exothermic adiabatic tubular reactor systems to conserve energy. The hot reactor effluent is recycled back to a feed preheater to provide all or a portion of the energy required to preheat the reactor feed to the optimum reactor inlet temperature. Several alternative flowsheets have been presented in the literature for this type of configuration. Some use bypassing of cold material around the FEHE, some use a furnace after the FEHE and before the reactor, and some use a cooler (steam generator) after the reactor. A number of control structures have been proposed to control the reactor inlet temperature, which is critical for the steady-state performance (achieving the desired conversion and staying below some maximum temperature). It is also critical for dynamic performance since these systems can be openloop unstable as a result of the positive feedback of energy from the reactor back to the preheat system. The control structure must prevent quenching to low temperatures (“blowout”) and temperature runaways (“blowup”). The most commonly suggested control structure recommends controlling the temperature of the mixed stream after the FEHE by manipulating the bypass flow and controlling the reactor inlet temperature by manipulating fuel to the furnace. This paper presents an alternative process and control configuration that reduces furnace energy consumption while maintaining good dynamic control in the face of very large disturbances.

Core Temperature Monitoring System for Prototype Fast Breeder Reactor

The 500-MW(electric) Prototype Fast Breeder Reactor (PFBR) is currently under construction at Kalpakkam, India. A core temperature monitoring system is provided to monitor adequacy of core cooling and protect the reactor against design-basis events. Triplicated real-time computer systems and hardwired systems are used for monitoring subassembly outlet sodium temperature and reactor inlet temperature. This paper describes the core temperature monitoring system provided in PFBR.

Optimization of Inlet Temperature of Methanol Synthesis Reactor of LURGI Type

This paper presents an optimization study of inlet temperature of methanol synthesis reactor of LURGI type by using commercial simulator Aspen Plus and Aspen Energy Analyzer. The optimization routine is coupled to a steady-state model of the methanol synthesis reactor. By investigating the influences on methanol production and heat exchanger network synthesis, the inlet temperature of the reactor is optimized. when the inlet temperature is 230°C, the economic benefits of the methanol plant is maximized which could be increased by $ 44883.28/ year.

Steam Reforming of Ethanol in a Microchannel Reactor: Kinetic Study and Reactor Simulation

The kinetics of steam reforming of ethanol (SRE) was determined at atmospheric pressure in the temperature range of 450–550 °C over 2% Rh/20% CeO2/Al2O3 in a microchannel reactor. The product distribution could be explained by a reaction scheme consisting of four reactions: reaction of steam with ethanol, decomposition of ethanol, methane steam reforming, and the water-gas shift reaction. The kinetic expression based on Langmuir–Hinshelwood kinetics could explain the experimental data satisfactorily. A two-dimensional simulation was also carried out to predict the performance of a microchannel SRE reactor in which the endothermic heat of reaction was supplied by the co-current flow of a hot gas in the adjacent channel. The performance of the coupled reactor/heat exchange system was evaluated by varying several parameters such as heating side gas velocity and temperature, width of the channel, weight of the catalyst, reactor inlet temperature, and inlet flow rate.

Reacting flow simulations of supercritical water oxidation of PCB-contaminated transformer oil in a pilot plant reactor

The scale-up of a supercritical water oxidation process, based on recent advancements in kinetic aspects, reactor configuration and optimal operational conditions, depends on the research and development of simulation tools, which allow the designer not only to understand the complex multiphysics phenomena that describe the system, but also to optimize the operational parameters to attain the best profit for the process and guarantee its safe operation. Accordingly, this paper reports a multiphysics simulation with the CFD software Comsol Multiphysics 3.3 of a pilot plant reactor for the supercritical water oxidation of a heavily PCB-contaminated mineral transformer oil. The proposed model was based on available information for the kinetic aspects of the complex mixture and the optimal operational conditions obtained in a lab-scale continuous supercritical water oxidation unit. The pilot plant simulation results indicate that it is not feasible to scale-up directly the optimal operational conditions obtained in the isothermal lab-scale experiments, due to the excess heat released by the exothermic oxidation reactions that result in outlet temperatures higher than 600°C, even at reactor inlet temperatures as low as 400°C. Consequently, different alternatives such as decreasing organic flowrates or a new reactor set-up with multiple oxidant injections should be considered to guarantee a safe operation.