Simulation and thermodynamic analysis of chemical looping reforming and CO2 enhanced chemical looping reforming

The production of hydrogen from methane via two chemical looping reforming (CLR) processes was simulated and thermodynamically analysed, one process being the conventional CLR process, the other being a CO₂ sorption enhanced process. The aim of the work was to identify suitable operating conditions for obtaining an optimum hydrogen gas purity and yield, whilst operating auto-thermally, at atmospheric pressure and with no carbon formation. In both simulations, the reactors were simulated using the Gibbs minimisation technique. NiO was used as the oxygen storing species, whilst CaO was used as the CO₂ adsorbent.     

Design of a thermally integrated bioethanol-fueled solid oxide fuel cell system integrated with a distillation column

Solid oxide fuel cell systems integrated with a distillation column (SOFC-DIS) have been investigated in this study. The MER (maximum energy recovery) network for SOFC-DIS system under the base conditions (C_EtOH = 25%, EtOH recovery = 80%, V = 0.7 V, fuel utilization = 80%, T_SOFC = 1200 K) yields Q_Cmin = 73.4 and Q_Hmin = 0 kW. To enhance the performance of SOFC-DIS, utilization of internal useful heat sources from within the system (e.g. condenser duty and hot water from the bottom of the distillation column) and a cathode recirculation have been considered in this study. The utilization of condenser duty for preheating the incoming bioethanol and cathode recirculation for SOFC-DIS system were chosen and implemented to the SOFC-DIS (CondBio-CathRec). Different MER designs were investigated. The obtained MER network of CondBio-CathRec configuration shows the lower minimum cold utility (Q_Cmin) of 55.9 kW and total cost index than that of the base case. A heat exchanger loop and utility path were also investigated. It was found that eliminate the high temperature distillate heat exchanger can lower the total cost index. The recommended network is that the hot effluent gas is heat exchanged with the anode heat exchanger, the external reformer, the air heat exchanger, the distillate heat exchanger and the reboiler, respectively. The corresponding performances of this design are 40.8%, 54.3%, 0.221 W cm⁻² for overall electrical efficiency, Combine Heat and Power (CHP) efficiency and power density, respectively. The effect of operating conditions on composite curves on the design of heat exchanger network was investigated. The obtained composite curves can be divided into two groups: the threshold case and the pinch case. It was found that the pinch case which T_SOFC = 1173 K yields higher total cost index than the CondBio-CathRec at the base conditions. It was also found that the pinch case can become a threshold case by adjusting split fraction or operating at lower fuel utilization. The total cost index of the threshold cases is lower than that of the pinch case. Moreover, it was found that some conditions can give lower total cost index than that of the CondBio-CathRec at the base conditions.     

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.     

Surface segregation of siloxane containing component in polysiloxane‐block‐polyimide and s‐BPDA/ODA polyimide blends

Surface segregation in polymer blend systems between 3,3′,4,4′‐biphenyltetracarboxylic dianhydride/4,4′‐diaminodiphenyl ether (s‐BPDA/ODA) polyimide and block copolymer based on polysiloxane‐block‐polyimide (SPI) has been investigated. These polyimide blends, having various compositions of the SPI, were processed by a solution casting method. The glass substrate used in the film‐casting process shows significant effect on the migration of surface segregated species to enrich the air‐exposed surface, whereas the more polar s‐BPDA/ODA tends to remain close to the polar glass substrate. X‐ray photoelectron spectroscopy reveals that even at low SPI concentration, the siloxane moieties in the block copolymer tend to segregate into the air side surface. Contact angle measurement evidently indicates an enrichment of the hydrophobic siloxane fraction on the blend film surface. The average water contact angle of glass side surface is 77°C whereas that of the air side is about 102°C in every blend ratio. This behavior confirms the surface segregation phase separation in these polymer blends. Finally, the surface morphology observed by atomic force microscopy also suggests segregation type of phase separation in these blend systems. POLYM. ENG. SCI., 47:489–498, 2007. © 2007 Society of Plastics Engineers.     

The effect of specific surface area on the activity of nano-scale ceria catalysts for methanol decomposition with and without steam at SOFC operating temperatures

Nano-particulate high surface area CeO₂ was found to have a useful methanol decomposition activity producing H₂, CO, CO₂, and a small amount of CH₄ without the presence of steam being required under solid oxide fuel cell temperatures, 700-1000 °C. The catalyst provides high resistance toward carbon deposition even when no steam is present in the feed. It was observed that the conversion of methanol was close to 100% at 850 °C, and no carbon deposition was detected from the temperature programmed oxidation measurement.The reactivity toward methanol decomposition for CeO₂ is due to the redox property of this material. During the decomposition process, the gas-solid reactions between the gaseous components, which are homogeneously generated from the methanol decomposition (i.e., CH₄, CO₂, CO, H₂O, and H₂), and the lattice oxygen on ceria surface take place. The reactions of adsorbed surface hydrocarbons with the lattice oxygen ( can produce synthesis gas (CO and H₂) and also prevent the formation of carbon species from hydrocarbons decomposition reaction (C_nH_m⇔nC+m/2H₂). V_O^·· denotes an oxygen vacancy with an effective charge 2⁺. Moreover, the formation of carbon via Boudouard reaction (2CO⇔CO₂+C) is also reduced by the gas-solid reaction of carbon monoxide with the lattice oxygen .At steady state, the rate of methanol decomposition over high surface area CeO₂ was considerably higher than that over low surface area CeO₂ due to the significantly higher oxygen storage capacity of high surface area CeO₂, which also results in the high resistance toward carbon deposition for this material. In particular, it was observed that the methanol decomposition rate is proportional to the methanol partial pressure but independent of the steam partial pressure at 700-800 °C. The addition of hydrogen to the inlet stream was found to have a significant inhibitory effect on the rate of methanol decomposition.     

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.     

Active power filter for three-phase four-wire electric systems using neural networks

This paper presents the design of neural networks compared with the conventional technique, a hysteresis controller for active power filter for three-phase four-wire electric system. A particular three-layer neural network structure is studied in some detail. Simulation and experimental results of the active power filter with both controllers are also presented to verify the feasibility of such controller. The simulation and experimental result show that both controller techniques can reduce harmonics in three-phase four-wire electric systems drawn by nonlinear loads and can reduce neutral current. The advantage of the neural network controller technique over hysteresis controller technique are less voltage ripple of d.c. bus, and less switching loss. Furthermore, the neural networks controller has better fault tolerance than the hysteresis controller.     

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.     

Isosynthesis via CO hydrogenation over SO4–ZrO2 catalysts

Catalytic performances of sulfated zirconia catalysts with various contents of sulfur (from 0.1 to 0.75%) on isosynthesis were studied. It was firstly found that undoped-zirconia synthesized from zirconyl nitrate provided higher activity towards isosynthesis reaction (106 μmol kg-cat^?1 s^?1) compared to that synthesized from zirconyl chloride (84.9 μmol kg-cat^?1 s^?1). Nevertheless, the selectivity of isobutene in hydrocarbons was relatively lower. It was then observed that the catalytic reactivity and selectivity significantly improved by sulfur loading. The most suitable sulfur loading content seems to be at 0.1%, which gave the highest reaction rate and selectivity of isobutene. By applying several characterization techniques, i.e. BET, XRD, NH₃- and CO₂-TPD and SEM, it was revealed that the high reaction rate and selectivity towards isosynthesis reaction of sulfated zirconia catalysts are related to the acid–base properties, Zr³⁺ quantity and phase composition.     

Modeling of IT-SOFC with indirect internal reforming operation fueled by methane: Effect of oxygen adding as autothermal reforming

Mathematical models of an Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC) with indirect internal reforming operation (IIR-SOFC) fueled by methane were developed. The models were based on a steady-state heterogeneous two-dimensional tubular-design SOFC. The benefit in adding oxygen to methane and steam as the feed for autothermal reforming reaction on the thermal behavior and SOFC performance was simulated. The results indicated that smoother temperature gradient with lower local cooling at the entrance of the reformer channel can be achieved by adding a small amount of oxygen. However, the electrical efficiency noticeably decreased when too high oxygen content was added due to the loss of hydrogen generation from the oxidation reaction; hence, the inlet oxygen to carbon (O/C) molar ratio must be carefully controlled. Another benefit of adding oxygen is the reduction of excess steam requirement, which could reduce the quantity of heat required to generate the steam and eventually increases the overall system performance. It was also found that the operating temperature strongly affects the electrical efficiency achievement and temperature distribution along the SOFC system. By increasing the operating temperature, the system efficiency increases but a significant temperature gradient is also detected. The system with a counter-flow pattern was compared to that with a co-flow pattern. The co-flow pattern provided smoother temperature gradient along the system due to better matching between the heat supplied from the electrochemical reaction and the heat required for the steam reforming reaction. However, the electrical efficiency of the co-flow pattern is lower due to the higher cell polarization at a lower system temperature.