A performance study of methanol steam reforming in an A-type microchannel reactor

The methanol steam reforming (MSR) performance in a microchannel reactor is directly related to the flow pattern design of the microchannel reactor. Hydrogen production improvements can be achieved by optimal design of the flow pattern. In this study, an A-type microchannel reactor with a flow pattern design of one inlet and two outlets was applied to conduct the MSR for hydrogen production. The MSR performance of the A-type microchannel reactor was investigated through numerical analysis by establishing a three-dimensional simulation model and compared with that of the conventional Z-type microchannel reactor. Experiments were also conducted to test the MSR performance and validate the accuracy of the simulation model. The results showed that compared with the conventional Z-type microchannel reactor, the species distributions in the A-type microchannel reactor were more homogeneous. In addition, compared with the Z-type microchannel reactor, the A-type microchannel reactor was shown to effectively increase the methanol conversion rate by up to 8% and decrease the pressure drop by about 20%, regardless of a slightly higher CO mole fraction. It was also noted that with various quantities of microchannels and microchannel cross sections, the A-type microchannel reactor was still more competitive in terms of a higher methanol conversion rate and a lower pressure drop.     

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.     

Multi-objective optimization of rotary regenerator using genetic algorithm

The rotary regenerator (heat wheel) is an important heat recovery equipment, which rotates between two cold and hot streams. The pressure drop and effectiveness of rotary regenerator are important parameters in optimal design of this equipment for industrial applications. For optimal design of such a system, it was thermally modeled using -NTU method to estimate its pressure drop and effectiveness. Frontal area, ratio of hot to cold frontal heat transfer area, matrix thickness, matrix rotational speed, matrix rod diameter and porosity were considered as design parameters. Then fast and elitist non-dominated sorting genetic algorithm (NSGA-II) method was applied to find the optimum values of design parameters. In the presented optimal design approach, the effectiveness and the total pressure drop are two objective functions. The results of optimal designs were a set of multiple optimum solutions, called ‘Pareto optimal solutions’. The sensitivity analysis of change in optimum effectiveness and pressure drop with change in design parameters of the regenerator was also performed and the results are reported.     

Application of response surface methodology in the parametric optimization of a pin-fin type heat sink

In this paper, an effective procedure of response surface methodology (RSM) has been successfully developed finding the optimal values of designing parameters of a pin-fin type heat sink (PFHS) under constrains of mass and space limitation to achieve the high thermal performance (or cooling efficiency). Various design parameters, such as height and diameter of pin-fin and width of pitch between fins are explored by experiment. The thermal resistance and pressure drop are considered as the multiple thermal performance characteristics. Experiments are performed by a standard RSM design called a central composite design (CCD). The results identify the significant influence factors to minimize thermal resistance and pressure drop. The obtained optimal designing parameters have been predicted and verified by conducting confirmation experiments.     

钠冷堆非能动余热排出系统建模研究

非能动余热排出系统是核电站堆芯安全性的重要保障,为优化钠冷堆余热排出系统的热工设计方法,明确环境温度及空气冷却器结构变化对余热排出系统的影响。在考虑拔风烟囱自然循环影响的情况下建立完整的钠冷堆非能动传热模型,得到通用的余热排出系统通风量方程,并基于流动平衡和能量平衡对一定设计传热量的余热排出系统进行流程优化并分析环境温度、烟囱高度及翅高变化对系统热力参数的影响规律。结果显示,系统的总驱动压和总传热系数随着环境温度升高逐渐减小,且环境温度对驱动压力的影响更为明显;拔风烟囱高度增加,系统总驱动压和总传热系数均增大,且增大趋势不断变缓,存在设计最优值;翅片管翅片高度减小,系统总传热系数及单位压降传热系数大幅增加,对系统的传热性能影响明显。     

Optimal monolithic configuration for heat integrated ethanol steam reformer

A design concept for optimal design of monolith catalyst is presented through modeling of transport–kinetic interactions in a monolith catalyst. We argue that reactors employing monolithic catalysts should be based on its optimal choice of geometry. In line with that argument, we present a thorough analysis of the geometrical parameters influencing the performance of non-isothermal reactor operation. In this study, an optimal monolith configuration is estimated to be a combination (d_h, t_w) of (0.9 mm, 0.2 mm) for a compact ethanol reformer to produce hydrogen for portable applications where maximum volumetric reactor activity exists. A three-dimensional modeling framework is developed for the resulting optimal monolithic catalyst design that couples the reforming section with a suitable heat source in a recuperative way. As a result, greater ethanol conversion is obtained from the monolith channels near the periphery of the block. The coupling with combustion could predict the formation of cold and hot spots inside the reactor, their nature being dependent on the flow configuration. Further, the effect of altering the feed inlet operating conditions over the variation of ethanol conversion and temperature inside the reactor is also analyzed. The increase in reforming inlet velocity decreases the outlet conversion and shifts the cold spot, forward and deeper in co-flow configuration. The decreasing inlet feed temperature enhances the transfer of heat, eliminating the cold spot.     

Pressurized ultrasonic production of biodiesel from Jatropha oil: optimization and energy analysis

The present study deals with the development of a biodiesel production reactor based on pressurized ultrasonic cavitation technique. Transesterification of Jatropha oil takes place by passing low-frequency ultrasonic irradiation in the reaction mixture flowing at pressurized conditions in the sonochemical reactor. Reaction variables such as reaction time, molar ratio, catalyst concentration, and pressure of the reaction mixture were investigated to find the optimal parameters for biodiesel production. The energy requirement decreases with increase in pressure. Very low value of Specific Energy Consumption (0.018 kWh/kg) and significantly high value of Energy Use Index (598.83) are obtained when the pressure of reaction mixture is 15 bar. Increasing the pressure thereafter, leads to nominal gains. Ultrasonic irradiation at high-pressure condition has an additional advantage of rapid reaction and lower requirement of alcohol to oil molar ratio and catalyst concentration. Fifteen bar pressure is optimal for biodiesel production.     

Robust design of assembly parameters on membrane electrode assembly pressure distribution

The membrane electrode assembly (MEA) pressure distribution is an important factor that affects the performance of polymer membrane electrolyte fuel cell (PEMFC) stack. However, the general rules for assembly parameters that affect the MEA pressure distribution are hardly reported. In this study, a robust design analysis based on response surface methodology (RSM) was performed on a simplified fuel cell stack in order to identify the effect of assembly parameters on the MEA pressure distribution. The assembly pressure and bolt position were considered as randomly varying parameters with given probabilistic property and acted as the design variables. The max normal stress and normal stress uniformity of the MEA were determined in terms of the probabilistic design variables. The reliability of the robust design has been verified by comparing the robust solution with the optimal solution and an arbitrary solution.     

A correlation of optimal heat rejection pressures in transcritical carbon dioxide cycles

In this work, a cycle simulation model has been developed to optimize the coefficient of performance (COP) of transcritical carbon dioxide air-conditioning cycles. The analysis shows that the COP of the transcritical carbon dioxide cycle varies nonmonotonically with the heat rejection pressure; a maximum COP occurs at an optimal heat rejection pressure. It is further revealed that the values of the optimal heat rejection pressure mainly depend on the outlet temperature of the gas cooler, the evaporation temperature, and the performance of the compressor. Based on the cycle simulations, correlations of the optimal heat rejection pressure in terms of appropriate parameters are obtained for specific conditions. The results are of significance for the design and control of the transcritical carbon dioxide air-conditioning and heat pump systems     

Parametric analysis of the proton exchange membrane fuel cell performance using design of experiments

Proton exchange membrane fuel cell (PEMFC) performance depends on different fuel cell operating temperatures, humidification temperatures, operating pressures, flow rates, and various combinations of these parameters. This study employed the method of the design of experiments (DOE) to obtain the optimal combination of the six primary operating parameters (fuel cell operating temperatures, operating pressures, anode and cathode humidification temperatures, anode and cathode stoichiometric flow ratios). In the first stage, this study adopted a 2^k−2 fractional factorial design of the DOE to determine whether these factors have significant effects on a response and the interactions between various parameters. Second, the L₂₇(3¹³) orthogonal array of the Taguchi method is utilized to determine the optimal combination of factors for a fuel cell. Based on this study, the operating pressure, the operating temperature, and the interactions between operating temperature and operating pressure have a significant effect on the fuel cell performance. Among them, the operating pressure is the most important contributor. When the operating pressure increases, it should simultaneously lower the effects of other factors. While both the operating temperature and pressure increase simultaneously with that, the other factors are at appropriate conditions, it is possible to improve the fuel cell performance.     

The impact of ammonia feed distribution on the performance of a fixed bed membrane reactor for ammonia decomposition to ultra-pure hydrogen

In this study, the influence of distribution of ammonia feed along the height of a fixed bed membrane reactor (FBMR) for ammonia decomposition to hydrogen is investigated to understand the leverage of this approach. A rigorous heterogeneous model with verified kinetics is implemented to simulate the reactor. The simulation results indicate that the application of a distributed ammonia feed with equal distribution of injection points resulted in a 17.45% improvement in hydrogen production rate at a low temperature of 800.0 K over a FBMR without feed distribution. In the parameter space of this study, it has been shown that the ammonia conversion is sensitive to the number of distribution points and has an optimal value. It is found that the implication of the optimum number of injection points can substantially reduce the length of the reactor by 75.0% to achieve 100.0% ammonia conversion. The hydrogen reversal permeation phenomenon is observed at a low pressure and the upper part of the reactor. A novel configuration of a FBR and a FBMR with feed distribution is proposed for efficient production of ultra-pure hydrogen at a relatively low pressure. The critical reactor length ratio has been provided for this configuration.     

Optimum design parameters of Pin-Fin heat sink using the grey-fuzzy logic based on the orthogonal arrays

The effects of design parameters and the optimum design parameters for a Pin-Fin heat sink (PFHS) with the multiple thermal performance characteristics have been investigated by using the grey-fuzzy logic based on the orthogonal arrays. Various design parameters, such as height and diameter of pin-fin and width of pitch between fins are explored by experiment. The average convective heat transfer coefficient, thermal resistance and pressure drop are considered as the multiple thermal performance characteristics. Through the grey-fuzzy logic analysis, the optimization of complicated multiple performance characteristics can be converted into the optimization of a single grey-fuzzy reasoning grade. In addition, the analysis of variance (ANOVA) is applied to find the effect of each design parameter on the each or all thermal performance characteristics. Then the results of confirmation test with the optimal level constitution of design parameters have obviously shown that this logic approach can effective in optimizing the PFHS with the multiple thermal performance characteristics.     

Impact of the throat sizing on the operating parameters in an experimental fixed bed gasifier: Analysis,evaluation and testing

The aim of this research is to contribute into the diffusion of biomass power systems by analyzing and testing the throat sizing influence on the operation of a gasification plant coupled with an internal combustion engine. In order to do this, the assessment of the proper operation range for some of the driving process parameters has been carried out. The analysis has been focused on such parameters as pressure drop of the fixed bed reactor, the inlet air flow, the syngas production, electrical power production and efficiency, looking for improving the performance and guaranteeing the proper system operation. Two different campaigns of tests have been carried out for figuring out the best design on the reactor. Based on this analysis, the most convenient throat diameter has been determined (in this case, around 10 cm), producing an increment in the production of syngas of about 31%. This modification has demonstrated also an increment of the electrical power produced by the gasification plant of about 40%, which means an increment in the motor generator efficiency of 35%.     

Step-by-step methodology of developing a solar reactor for emission-free generation of hydrogen

This study presents a methodology to develop a solar reactor based on the thermodynamics and kinetics of methane decomposition to produce hydrogen with no emissions. The kinetic parameters were obtained in the literature for two cases; methane laden with carbon particles and methane without carbon particles. Results show that there is significant difference in experimentally obtained and theoretically predicted methane conversion. The paper also presents a parametric study on the effects of temperature, pressure and the influence of inert gas composition, which is fed along with methane, on the thermodynamics of methane decomposition. Results show that there is significant effect of the inert gas presence in the feeding gas mixture on the equilibrium of methane conversion and product gas composition. Results also show that higher conversions are obtained when the carbon particles laden with methane. The step-by-step reactor design methodology for homogenous methane decomposition and the parametric study results presented in this paper can provide a very useful tool in guiding a solar reactor design and optimization of process operating conditions.     

Geometry optimization and pressure analysis of a proton exchange membrane fuel cell stack

For proton exchange membrane fuel cells (PEMFCs), the distribution of reactant streams in the reactor is critical to their efficiency. This study aims to investigate the optimal design of the inlet/outlet flow channel in the fuel cell stack with different geometric dimensions of the tube and intermediate zones (IZ). The tube-to-IZ length ratio, the IZ width, and the tube diameter are adjusted to optimize the geometric dimensions for the highest pressure uniformity. Four different methods, including the Taguchi method, analysis of variance (ANOVA), neural network (NN), and multiple adaptive regression splines (MARS), are used in the analyses. The results indicate the tube diameter is the most impactive one among the three factors to improve the pressure uniformity. The analysis suggests that the optimal geometric design is the tube-to-IZ length ratio of 9, the IZ width of 14 mm, and the tube diameter of 9 mm with the pressure uniformity of 0.529. The relative errors of the predicted pressure uniformity values by NN and MARS under the optimal design are 1.62% and 3.89%, respectively. This reveals that NN and MARS can accurately predict the pressure uniformity, and are promising tools for the design of PEMFCs.     

Analysis of design variables for water-gas-shift reactors by model-based optimization

This work analyzes the water-gas-shift reactor design as component of the CO clean-up system of the ethanol processor for H₂ production applied to PEM fuel cells. The WGS reactor constitutes the element of greater volume of the processor motivating its optimization. A model-based reactor optimization for different reactor configurations permits to obtain both designs for reducing volumes and optimal operating conditions. The heterogeneous model used allows computing the optimal reactor length and diameter, and the optimal catalyst particle diameter. The model computes the constraints required for catalyst, such as maximum and minimum operation temperature. The volume is sensitive to the CO outlet concentration. According to the required CO conversion it is necessary more than one reactor unit for the case study analyzed. When considering the insulating material, there exists an optimal thickness that affects the final volume and the design variables. These results are useful for estimating the minimum and relative sizes that allows conventional reactor technology.     

Multi-objective optimization design of condenser in an organic Rankine cycle for low grade waste heat recovery using evolutionary algorithm

The optimum design of a condenser is significant in an organic Rankine cycle to achieve higher waste heat utilization efficiency. Based on the mathematical model of a condenser using plate heat exchanger (PHE), some key geometric parameters on the total heat transfer surface area and pressure drop of the condenser are examined. In order to obtain geometric parameters of a plate heat exchanger, a multi-objective optimization of the condenser in organic Rankine cycle is conducted to achieve the optimal geometry design. The total heat transfer surface area and pressure drop are selected as two objective functions to minimize both total heat transfer surface area and pressure drop under the constant heat transfer rate and LMTD conditions. The plate width, plate length and plant distance are selected as the decision variables. Non-dominated sorting generic algorithm-II (NSGA-II) which is an effective multi-objective optimization method is employed to solve this multi-objective optimization design of PHE. The results show that an increase in channel distance or plate width increases the total heat transfer surface area and decreases pressure drop in the condenser. It is noted that the plate length of PHE has a positive effect on the optimization design of PHE. By multi-objective optimization design of the PHE, a Pareto optimal point curve is obtained, which shows that a decrease in total heat transfer surface area of a condenser can increase the pressure drop through the condenser.     

CO-PrOx reactor design by model-based optimization

This work analyzes the CO-PrOx reactor design as a component of the CO clean-up system of the ethanol processor for H₂ production applied to PEM fuel cells. The operating conditions of the processor require compact and lightweight pieces of equipment and efficient operation at different conditions. An egg-shell catalyst type of Pt/Al₂O₃ is considered. One-dimensional heterogeneous catalytic reactor model accounting for interfacial gradients is used to optimize the PrOx reactor. Different reactor components are added gradually to illustrate how the system dimensions and configuration change after optimization. The optimization problem determines the optimal reactor length, reactor diameter, catalyst particle diameter, inlet reactants temperature and insulating material thickness that minimize the total system volume. On these model-based results, the final reactor design is mainly governed by the presence of hemispherical heads (distributor and collector). Different inlet CO compositions and power generation targets are analyzed. According to the inlet CO level, more than one catalytic stage is required to meet design goals and fulfill process constraints. The model-based reactor optimization of the pseudo-adiabatic operation allows obtaining both designs for reducing volumes and optimal operating conditions that allows conventional reactor technology. Afterwards, simulation runs based on a rigorous one-dimensional heterogeneous catalytic reactor model accounting for intra-particle gradients are performed using data obtained from model-based optimization results. The aim of these simulations is to verify feasibility of the optimal design obtained from the proposed one-dimensional heterogeneous catalytic reactor model without intra-particle gradients, which is intended to approximate an egg-shell catalyst behavior. The present work reflects clearly the advantages of applying mathematical programming techniques to optimize both design and operation conditions of the PrOx reactor.     

Thermodynamic optimization of design variables and heat exchangers layout in HRSGs for CCGT,using genetic algorithm

The heat recovery steam generator (HRSG) is one of the few equipments that are custom made for combined cycle power plants, and any change in its design affects all performance parameters of a steam cycle directly. Thus providing an optimization tool to optimize its design parameters and the layout of its heat exchangers is of great importance. A new method is introduced for modeling a steam cycle in advanced combined cycles by organizing non-linear equations and their simultaneous solutions by use of the hybrid Newton methods in this article. Thereafter, optimal thermodynamic performance conditions for HRSGs are calculated with the help of the genetic algorithm. In the conclusion, the results obtained for different types of HRSGs are compared. The results show that the use of several pressure levels in HRSGs increases the power production in the steam cycle, and similarly, reheating is very beneficial in three pressure heat recovery steam generators.     

Differential evolution (DE) strategy for optimization of hydrogen production,cyclohexane dehydrogenation and methanol synthesis in a hydrogen-permselective membrane thermally coupled reactor

In this work a novel reactor configuration has been proposed for simultaneous methanol synthesis, cyclohexane dehydrogenation and hydrogen production. This reactor configuration is a membrane thermally coupled reactor which is composed of three sides for methanol synthesis, cyclohexane dehydrogenation and hydrogen production. Methanol synthesis takes place in the exothermic side that supplies the necessary heat for the endothermic dehydrogenation of cyclohexane reaction. Selective permeation of hydrogen through the Pd/Ag membrane is achieved by co-current flow of sweep gas through the permeation side. A steady-state heterogeneous model of the two fixed beds predicts the performance of this configuration. A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methanol, benzene and hydrogen production in a membrane thermally coupled reactor. The co-current mode is investigated and the optimization results are compared with corresponding predictions for a conventional (industrial) methanol fixed bed reactor operated at the same feed conditions. The differential evolution (DE), an exceptionally simple evolution strategy, is applied to optimize this reactor considering the mole fractions of methanol, benzene and hydrogen in permeation side as the main objectives. The simulation results have been shown that there are optimum values of initial molar flow rate of exothermic and endothermic stream, inlet temperature of exothermic, endothermic and permeation sides, and inlet pressure of exothermic side to maximize the objective function. The simulation results show that the methanol mole fraction in output of reactor is increased by 16.3% and hydrogen recovery in permeation side is 2.71 yields. The results suggest that optimal coupling of these reactions could be feasible and beneficial. Experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.