Thermodynamic analysis of a proton conducting SOFC integrated system fuelled by different renewable fuels

This work proposes a power generation system consisting of steam reformer and SOFC–H⁺ fuelled by different types of fuel, i.e., ethanol, glycerol and biogas. The performance analysis of integrated system is performed based on thermodynamic calculation through Aspen Plus simulator. The total of the Gibbs free energy minimization is used to determine product composition at equilibrium. The electrochemical model not only considers all voltage losses but also includes the effect of current leakage as a result from the electrolyte used. Considering the operating condition of steam reformer, it is found that the gas product contains the highest amount of hydrogen without the carbon formation when reformer is operated at 973 K with steam to carbon ratio of 1. In addition, the simulation results show that the SOFC–H⁺ operated at 973 K and 1 A/cm² can provide a suitable compromise between system performances and exhaust gas composition. The use of glycerol reformate has the highest cell and system efficiencies and fuel utilization compared to the others. In addition, the integrated system fuelled by glycerol can release low CO amount whereas there is more heat provided to the surrounding. Therefore, it can be concluded that glycerol is suitable renewable fuel for SOFC–H⁺ integrated system.     

An experimental study for optimizing the energy efficiency of a proton exchange membrane fuel cell with an open-cathode

To develop an operating strategy for maximizing the energy efficiency of open-cathode proton exchange membrane fuel cells (OCPEMFCs), the present study investigates the effect of the fan speed on the stack performance and energy efficiency using a commercially available OCPEMFC system. The temperature, voltage, and current of the stack are monitored, and the energy efficiency is calculated at various stack power levels. The results of the system with a lab-developed controller are compared with the commercial system with a built-in controller. It is found that the fan speed should be minimum to reduce the auxiliary power consumption and that the stack should be efficiently heated to enhance the electrochemical reaction. In addition, it is noticed that the stack performance dramatically drops when the stack temperature is above 75 °C, due to the membrane dehydration. Overall, the results show that the stack temperature is an important indicator for controlling the fan speed for optimization of energy efficiency, and for stack powers of 50, 60, 70, and 80 W, the peak values of energy efficiencies are 38.0%, 38.3%, 38.5%, and 38.3% at the duty cycles of 0.2, 0.2, 0.25, and 0.3, respectively, which are 28–38% higher than the commercially available OCPEMFC system.     

Studies on optimal control approach in a fed-batch fermentation

Fed-batch operation of fermentation processes has been receiving a great deal of interest as it offers the possibility to control a substrate concentration at a desired condition. However, control of a fed-batch fermentation reactor has been known to be a difficult task due to its highly nonlinear and complicated behavior. This work addresses an optimization-based control strategy for a fed-batch bioreactor where an ethanol fermentation process is chosen as a case study. The optimal control problem is formulated to determine the optimal feeding rate policy giving the highest product yield. The resulting optimization problem is solved by using an efficient sequential approach with a piecewise constant control parameterization. Due to the limitation of the sequential approach to cope with inequality path constraints, comparative studies of the methods for handling such constraints are carried out. Furthermore, the impact of time interval and switching time on the solution of the optimal control is investigated.     

Hydrogen production from glycerol steam reforming for low- and high-temperature PEMFCs

This paper presents a thermodynamic study of a glycerol steam reforming process, with the aim of determining the optimal hydrogen production conditions for low- and high-temperature proton exchange membrane fuel cells (LT-PEMFCs and HT-PEMFCs). The results show that for LT-PEMFCs, the optimal temperature and steam to glycerol molar ratio of the glycerol reforming process (consisting of a steam reformer and a water gas shift reactor) are 1000 K and 6, respectively; under these conditions, the maximum hydrogen yield was obtained. Increasing the steam to glycerol ratio over its optimal value insignificantly enhanced the performance of the fuel processor. For HT-PEMFCs, to keep the CO content of the reformate gas within a desired range, the steam reformer can be operated at lower temperatures; however, a high steam to glycerol ratio is required. This requirement results in an increase in the energy consumption for steam generation. To determine the optimal conditions of glycerol steam reforming for HT-PEMFC, both the hydrogen yield and energy requirements were taken into consideration. The operational boundary of the glycerol steam reformer was also explored as a basic tool to design the reforming process for HT-PEMFC.     

Production of ethyltert-butyl ether fromtert-butyl alcohol and ethanol catalyzed byβ-zeolite in reactive distillation

The synthesis of ethyl tert-butyl ether (ETBE) from a liquid phase reaction between tert-butyl alcohol (TBA) and ethanol (EtOH) in reactive distillation has been studied.β-Zeolite catalysts with three compositions (Si/Al ratio=13, 36 and 55) were compared by testing the reaction in a semi-batch reactor. Although they showed almost the same performance, the one with Si/Al ratio of 55 was selected for the kinetic and reactive distillation studies because it is commercially available and present in a ready-to-use form. The kinetic parameters of the reaction determined by fitting parameters with the experimental results at temperature in the range of 343–363 K were used in an ASPEN PLUS simulator. Experimental results of the reactive distillation at a standard condition were used to validate a rigorous reactive distillation model of the ASPEN PLUS used in a simulation study. The effects of various operating parameters such as condenser temperature, feed molar flow rate, reflux ratio, heat duty and mole ratio of H₂O : EtOH on the reactive distillation performance were then investigated via simulation using the ASPEN PLUS program. The results were compared between two reactive distillation columns: one packed withβ-zeolite and the other with conventional Amberlyst-15. It was found that the effect of various operating parameters for both types of catalysts follows the same trend; however, the column packed withΒ-zeolite outperforms that with Amberlyst-15 catalyst due to the higher selectivity of the catalyst.     

间歇结晶过程的分批优化

It is the fact that several process parameters are either unknown or uncertain. Therefore, an optimal control, profile calculated with developed process models with respect to such process parameters may not give an optimal performance when implemented to real processes. This study proposes a batch-to-batch optimization strategy for the estimation of uncertain kinetic.par.ameters in a batch crystallization process of potassium sulfate production. The knowledge of a crystal size distribution of the product at the end of batch operation is used in the proposed methodology. The updated kinetic parameters are applied for determining an optimal operating temperature policy for the next batch run.     

Product quality improvement of batch crystallizers by a batch-to-batch optimization and nonlinear control approach

Batch crystallization is one of the widely used processes for separation and purification in many chemical industries. Dynamic optimization of such a process has recently shown the improvement of final product quality in term of a crystal size distribution (CSD) by determining an optimal operating policy. However, under the presence of unknown or uncertain model parameters, the desired product quality may not be achieved when the calculated optimal control profile is implemented. In this study, a batch-to-batch optimization strategy is proposed for the estimation of uncertain kinetic parameters in the batch crystallization process, choosing the seeded batch crystallizer of potassium sulfate as a case study. The information of the CSD obtained at the end of batch run is employed in such an optimization-based estimation. The updated kinetic parameters are used to modify an optimal operating temperature policy of a crystallizer for a subsequent operation. This optimal temperature policy is then employed as new reference for a temperature controller which is based on a generic model control algorithm to control the crystallizer in a new batch run.     

Hydrogen and power generation from supercritical water reforming of glycerol and pressurized SOFC integrated system: Use of different CO2 adsorption process

The performance analysis of an integrated system of glycerol supercritical water reforming and pressurized SOFC was presented. The use of different CO₂ adsorption processes that include in situ and ex situ processes was compared to determine the suitable process for hydrogen and power generations. The influence of operating condition, e.g., temperature and pressure of reformer, supercritical water to glycerol (S/G) molar ratio, and calcium oxide to glycerol (CaO/G) molar ratio was examined. Then, the electrical performance of each integrated process was considered with respect to the SOFC conditions comprising temperature, pressure, and current density. The simulation results revealed that both processes have same favourable conditions for temperature and pressure operated at 800 °C and 240 atm, respectively. The suitable S/G and CaO/G molar ratios for in situ process are 10 and 2 whereas those for ex situ process are 20 and 1. Under these conditions, maximum hydrogen can be achieved as 87% and 75% for in situ and ex situ processes, respectively. When both integrated processes are operated at the optimal SOFC conditions as 900 °C, 4 atm, and current density of 10,000 A/m², the SOFC efficiency of 71.56% and 62.12% can provide for in situ and ex situ processes, respectively.     

Maximizing the efficiency of a HT-PEMFC system integrated with glycerol reformer

The efficiency and output power density of an integrated high temperature polymer electrolyte fuel cell system and glycerol reformer are studied. The effects of reformer temperature, steam to carbon ratio (S/C), fuel cell temperature, and anode stoichiometric ratio are examined. An increase in anode stoichiometric ratio will reduce CO poisoning effect at cell’s anode but cause lower fuel utilization towards energy generation. High S/C operation requires large amount of the energy available, however, it will increase anode tolerance to CO poisoning and therefore will lead to enhanced cell performance. Consequently, the optimum gas composition and flow rate is very dependent on cell operating current density and temperature. For example, at low current densities, similar efficiencies were obtained for all the S/C ratio studied range at cell temperature of 423.15 K, however, at cell temperature of 448.15 K, low S/C ratio provided higher efficiency in comparison to high S/C ratio. High S/C is essential when operating the cells at high current densities where CO has considerable impact on cell performance. Optimal conditions that provide the maximum power density at a given efficiency are reported.     

Analysis of a pressurized solid oxide fuel cell–gas turbine hybrid power system with cathode gas recirculation

A pressurized solid oxide fuel cell–gas turbine hybrid system (SOFC–GT system) has been received much attention for a distributed power generation due to its high efficiency. When considering an energy management of the system, it is found that a heat input is highly required to preheat air before being fed to the SOFC stack. The recirculation of a high-temperature cathode exhaust gas is probably an interesting option to reduce the requirement of an external heat for the SOFC–GT system. This study aims to analyze the pressurized SOFC–GT hybrid system fed by ethanol with the recycle of a cathode exhaust gas via a simulation study. Effect of important operating parameters on the electrical efficiency and heat management of the system is investigated. The results indicate that an increase in the operating pressure dramatically improves the system electrical efficiency. The suitable pressure is in a range of 4–6 bar, achieving the highest system electrical efficiency and the lowest recuperation energy from the waste heat of the GT exhaust gas. In addition, it is found that the waste heat obtained from the GT is higher than the heat required for the system, leading to a possibility of the SOFC–GT system to be operated at a self-sustainable condition. Under a high pressure operation, the SOFC–GT system requires a high recirculation of the cathode exhaust gas to maintain the system without supplying the external heat; however, the increased recirculation ratio of the cathode exhaust gas reduces the system electrical efficiency.