A high performance direct ammonia fuel cell using a mixed ionic and electronic conducting anode

A high performance direct ammonia fuel cell incorporating a doubly doped barium cerate electrolyte and a novel cermet anode consisting of europium doped barium cerate, a mixed ionic and electronic solid electrolyte, and Ni was studied. The catalytic activity of the cermet anodes was superior to that of Pt catalysts. The I–V and power density data suggest that the direct ammonia fuel cell could be operated at temperatures as low as 450 °C. The fuel cell was operated with ammonia as fuel in excess of 500 h without significant deterioration in performance.     

Parametric study of membrane reactors for hydrogen production via high-temperature water gas shift reaction

This study presents numerical studies of hydrogen production performance via water gas shift reaction in membrane reactor. The pre-exponential factor in describing the hydrogen permeation flux is used as the main parameter to account for the membrane permeance variation. The operating pressure, temperature and H₂O/CO molar ratio are chosen in the 1–20 atm, 400–600 °C and 1–3 ranges, respectively. Based on the numerical simulation results three distinct CO conversion regimes exist based on the pre-exponential factor value. For low pre-exponential factors corresponding to low membrane permeance, the CO conversion approaches to that obtained from a conventional reactor without hydrogen removal. For high pre-exponential factor, high CO conversion and H₂ recovery with constant values can be obtained. For intermediate pre-exponential factor range both CO conversion and H₂ recovery vary linearly with the pre-exponential factor. In the high membrane permeation case CO conversion and H₂ recovery approach limiting values as the operating pressure increases. Increasing the H₂O/CO molar ratio results in an increase in CO conversion but decrease in H₂ recovery due to hydrogen permeation driving force reduction. As the feed rate increases in the reaction side both the CO conversion and hydrogen recovery decrease because of decreased reactant residence time. The sweep gas flow rate has a significant effect on hydrogen recovery. Low sweep gas flow rate results in low CO conversion H₂ recovery while limiting CO conversion and hydrogen recovery can be reached for the high membrane permeance and high sweep gas flow rate cases.     

Syngas production from oxidative methane reforming and CO cleaning with water gas shift reaction

Fuel cell based heat and power cogeneration is considered to be well qualified for a distributed energy system for residential and small business applications. A fuel processing unit including an oxidative steam methane reformer, a high temperature shift reactor and a low temperature shift reactor is under development in South China University of Technology. Performance of the unit is experimentally investigated in a bench-scale experimental setup. Processor performance under typical operating conditions is tested. The influence of reaction temperature, methane space velocity in the oxidative steam methane reformer, and air to carbon molar ratio on unit performances is experimentally studied. It is found that under the typical operating conditions, the total energy efficiency reaches 88.3%. The efficiency can further be improved by utilizing the sensible heat of the reformate gas. The current study has been focused on the chemical performances such as methane conversion of the reformer and CO concentration in the synthesis gas downstream water gas shift reactors. Heat integration of the unit will be further implemented in future to improve energy efficiency.     

Three-dimensional numerical analysis of mixed ionic and electronic conducting cathode reconstructed by focused ion beam scanning electron microscope

Three-dimensional microstructure of mixed ionic and electronic conducting cathode, La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF6428), is obtained by a dual-beam focused ion beam-scanning electron microscope, and its overpotential is predicted by the lattice Boltzmann method. Gaseous, ionic and electronic transport equations coupled with electrochemical reaction at the gas/solid interface in the three-dimensional microstructure are solved with an assumption of local equilibrium in the solid oxide. The gas transport is modeled by the dusty gas model. The numerical simulation is conducted under the current density conditions of 0.01, 0.05, 0.1 and 0.2 A/cm². Predicted cathode overpotentials agreed well with the experimental results. However, predicted overpotential was very large at O₂ = 20%, T = 973 K and i = 0.2 A/cm² case due to the decline of ionic conductivity at low oxygen partial pressure. Three-dimensional chemical potential and current vector distributions inside LSCF microstructure are presented. Ionic and electronic current stream lines are uniform and smooth, which indicates good ionic and electronic conductions as well as wide electrochemically active areas inside the LSCF microstructure. Present method will be an effective tool for investigating local oxygen potential field which affects local reactions, diffusions and physical properties of the MIEC cathodes.     

Low-temperature Cu/Zn/SBA-16 integrating carbon membrane reactor for hydrogen production and high CO conversion through water-gas shift reaction

The increasing demand for H₂ energy has led to a great amount of research being conducted in a membrane reactor (MR), in which a membrane is applied during the water-gas shift (WGS) reaction. In this study, Cu/Zn/SBA-16 WGS catalysts and carbon molecular sieve (CMS) membranes were integrated into CMS MRs. To improve the CO conversion and H₂ yield, C MRs were investigated, and different steam/CO (S/C) ratios were used to evaluate the conversion performance. In this study, a tubular CMS membrane was used as the membrane material for a MR. The as-prepared CMS membrane exhibited excellent selectivity of 185.64 for H₂ and CO₂ mixed gas, and an ideal H₂ permeability of 9.7 × 10^?9 mol m^?2 s^?1 Pa^?1 when operated under low temperature/pressure conditions (300 °C/3 bar). The Cu/Zn/SBA-16 catalyst synthesized via coprecipitation was used in the WGS reaction. With a relatively low reaction temperature of 300 °C, 2500 h^?1 gas hourly space velocity, and S/C equal to 1.5, the CO conversion efficiency of MR could reach up to 99%, and the recovery of H₂ was approximately 76%. However, as the S/C increased to 2, the H₂ recovery increased to 99%, whereas the CO conversion decreased to 89% because of the water vapor adsorbed on the active site. The hydrophobic Si/C-modified membrane was further synthesized and showed outstanding performance in CO conversion of over 99% with S/C equal to 2.     

Detailed analysis of the operational characteristics of the steam reformer and water–gas shift reactors for 5 kW HT-PEMFCs

The reactors designed for 5-kW high-temperature polymer electrolyte fuel cells are able to evaluate the performance of the steam reformer and each water–gas shift reactor independently. The goal of the experiments is to obtain the best overall performance for steam reforming while minimizing the CO concentration and maximizing the hydrogen yield. For this purpose, the performance of the steam reforming reactor unit with two types of flow paths was evaluated while evaluating the performance of various series of component combinations of the high-, middle-, and low-temperature shifts. Via experiment, thermal control followed by the appropriate heating and cooling mechanism is key to successful reaction performance. In addition to an individual unit-based experiment, numerical analyses were executed to understand the local chemical performance inside a reactor unit. These numerical analyses show good agreement with the experimental data measured at the outlet and provide a comprehensive detailed internal reaction mechanism such as the thermal conditions and CO concentration effect. Both experiments and numerical analyses can fundamentally improve the reaction performance by finding the optimal values of many control parameters.     

The development and evaluation of microstructured reactors for the water gas shift and preferential oxidation reactions in the 5 kW range

5 kW_el One-Stage Water Gas Shift (WGS) and Preferential Oxidation (PROx) reactors were designed and evaluated for the clean-up of surrogate diesel reformate. For the WGS reactor, CO conversions of up to 95% were attained using typical surrogate synthetic diesel reformate. The PROx reactor was capable of converting a feed concentration of 1.0 mol% CO to 20 ppm. Load changes for both reactors could be carried out without significant overshoots of carbon monoxide.     

Process simulation and integration of IGCC systems for H2/syngas/electricity generation with control on CO2 emissions

IGCC is a pre-combustion technology that can be effectively used to produce both hydrogen and electricity while reducing the greenhouse gas (GHG) emissions. Two process models are developed in Aspen Plus^® software and are compared techno-economically. The conventional design of IGCC process is taken as case 1, whereas, case 2 represents the conceptual design of sequential integration of reforming model with the gasification unit to enhance the syngas yield. The case 2 utilizes the steam generated in the gasification process to sustain the methane reforming process which consequently enhances both the H₂ production capacity and cold gas efficiency. It has been analyzed from results that case 2 can enhance the process performance by 4.77% and economics in terms of cost of electricity by 5.9% compared to the conventional process. However, the utilization of natural gas in the case 2 is considered as a standalone fuel so the process performance of NGCC power plants has been also incorporated to ensure the realistic analysis. The results also showed that case 2 design offers 3.9% higher process performance than the cumulative (IGCC + NGCC) processes, respectively. Moreover, the CO₂ specific emissions and LCOE for the case 2 is also lower than the case.     

A process dynamic modeling and control framework for performance assessment of Pd/alloy-based membrane reactors used in hydrogen production

In the present study a comprehensive, insightful and practical process dynamic modeling framework is developed in order to analyze and characterize the transient behavior of a Pd/alloy-based (Pd/Au or Pd/Cu) water-gas shift (WGS) membrane reactor. Furthermore, simple process control ideas are proposed aiming at enhancing process system performance by inducing the desirable dynamic characteristics in the response of the controlled process during start-up as well as in the presence of unexpected adverse disturbances (process upset episodes) or operationally favorable set-point changes that reflect new hydrogen production requirements. Finally, the proposed methods are evaluated through detailed simulation studies in an illustrative example involving a Pd/alloy-based WGS membrane reactor that exhibits complex dynamic behavior and is currently used for lab-scale pure hydrogen production and separation.     

Production of hydrogen with low COx-content for PEM fuel cells by cyclic water gas shift reactor

Hydrogen gas with low CO content was produced by cyclic water gas shift (CWGS) reactor based on the periodic reduction and re-oxidation of Fe₂O₃–CeO₂–ZrO₂. The process was operated with CO/H₂ mixtures produced by e.g. auto-thermal reforming of hydrocarbons. During the reduction phase of the cyclic process, the incoming CO/H₂ mixture converted Fe₂O₃–CeO₂–ZrO₂ into a reduced form. Subsequently, steam was fed into the reactor for re-oxidation of the reduced material. Thereby, H₂ was released which can be used for a proton exchange membrane fuel cell (PEMFC) without any further purification. As side product, some coke can be formed on the solid surface by Bouduard reaction. This coke is removed in the re-oxidation step with steam leading to the formation of carbon monoxide. The extent of coke formation is controllable by keeping the oxygen conversion of the material below a certain degree. The feasibility of the novel process was demonstrated by combining the CWGS reactor with a 5-cell PEMFC stack.     

Preparation of highly dispersed Cu/SiO2 doped with CeO2 and its application for high temperature water gas shift reaction

Highly dispersed Cu/SiO₂ catalysts doped with CeO₂ have been successfully prepared via in-situ self-assembled core-shell precursor route. The prepared catalysts were characterized by XRD, SEM, TPR, chemisorption and XPS techniques. The results showed that our newly developed method could not only prepare highly dispersed supported metal catalysts but also highly dispersed supported CeO₂ on silica. The highly dispersed CeO₂ showed strong interaction with highly dispersed Cu. The synergy between the highly dispersed CeO₂ and the highly dispersed Cu exhibited high catalytic activity for high temperature water gas shift reaction compared to the catalysts prepared with the routine method of incipient impregnation.     

Techno-economic assessment of the novel gas switching reforming (GSR) concept for gas-fired power production with integrated CO2 capture

The focus of this study is to carry out techno-economic analysis of a pre-combustion capture method in Natural Gas based power plants with a novel reactor concept, Gas Switching Reforming (GSR). This reactor concept enables auto thermal natural gas reforming with integrated CO₂ capture. The process analysed integrates GSR, Water Gas Shift (WGS), and Pressure Swing Adsorption (PSA) into a Natural Gas based combined cycle power plant. The overall process is defined as GSR-CC. Sensitivity studies have been carried out to understand the performance of the GSR-CC process by changing the oxygen carrier utilization and Steam/Carbon ratio in GSR. The net electrical efficiency of the GSR-CC lies between 45.1% and 46.2% and the levelised cost of electricity lies between 124.4 and 128.1 $/MWh (at European natural gas prices) for the parameter space assumed in this study. By eliminating the WGS step from the process, the net electrical efficiency improves to 47.4% and the levelised cost of electricity reduces to 120.7 $/MWh. Significant scope exists for further efficiency improvements and cost reductions from the GSR-CC system. In addition, the GSR-CC process achieves high CO₂ avoidance rates (>95%) and offers the possibility to produce pure H₂ during times of low electricity demands.     

Hydrogen-rich gas production with CO2 capture from steam gasification of pine needle using calcium oxide: Experimental and modeling study

A research-scale bubbling fluidized bed reactor (BFBR) has been assembled and used to study the steam gasification of pine needles with calcium oxide (CaO) as sorbent and catalyst. The output parameters such as syngas composition, higher heating value, lower heating value, and cold gas efficiency, have been analyzed at the operating conditions of a temperature of 650°C to 850°C, steam/biomass (S/B) ratio of 0.4 to 1.6, and CaO/biomass ratio of 0.3 to 1.5. Furthermore, an ASPEN PLUS model of BFBR has been developed using Gibbs free energy minimization technique and model values have been compared with experimental values. From the experimental results, it is analyzed that the concentration of H₂ is increased from 37.02 vol% to 68.36 vol% with an increase in temperature from 650°C to 750°C at the S/B ratio of 1 and CaO/biomass ratio of 0.9 and after that, it decreased slightly. Furthermore, the concentration of CO₂ in syngas captured from 5.49 vol% to 0 vol%, when the CaO/biomass ratio is varied from 0.3 to 1.5. From the result analysis, it is concluded that higher temperature and higher CaO/biomass ratio has a significant impact on H₂ production while excess S/B ratio has a negative impact.     

Cu/Fe3O4 catalyst for water gas shift reaction: Insight into the effect of Fe2+ and Fe3+ distribution in Fe3O4

Two precursors, namely, p-CFO-T (tetragonal) and p-CFO-C (cubic), were fabricated by a sol-gel method via citric acid and poly(vinyl alcohol) complexation, respectively. After H₂-reduction, the two were converted to Cu/Fe₃O₄ catalysts of different complexions, which are named as CFO-CA and CFO-PVA, respectively. The distribution of Fe²⁺ and Fe³⁺ in the Cu/Fe₃O₄ catalysts was studied by Raman and XPS techniques. It was disclosed that the distribution of Fe²⁺ and Fe³⁺ in Fe₃O₄ has an effect on Cu–Fe₃O₄ interaction and catalyst surface basicity. Compared to CFO-PVA, CFO-CA has a larger amount of Fe³⁺, which mostly sits at the octahedral sites, leading to stronger Cu–Fe₃O₄ interaction, and a larger amount of catalyst surface sites that are of weak basicity. As a result, the critical elementary steps of WGS reaction, viz. water dissociation, –COOH decomposition and CO₂ desorption are promoted as reflected in the lower E_a and higher catalytic activity of CFO-CA.     

DFT calculations of double vacancies MoS2 catalyzing water gas shift reaction: S vacancies as electron bridge promote electron transfer to H2O and CO molecules

The poor activity of molybdenum disulfide (MoS₂) basal plane is the key scientific problem to limit efficient hydrogen production. In this paper, MoS₂ with single (V_S-MoS₂) and double sulfur vacancy (V_{S, S}-MoS₂) have been constructed and used for water gas shift reaction (WGSR). Results show that the adsorption energy of V_{S, S}-MoS₂ for CO molecule is −1.43 eV, which is 28.6 times and 1.1 times than original MoS₂ and V_{S, S}-MoS₂, respectively. The energy barrier of the rate-determining step in the association mechanism of V_{S, S}-MoS₂ is 1.78 eV, which is 21% lower than pristine MoS₂. S vacancies are active sites for CO and H₂O adsorption. The delocalized electrons enrichment in S vacancies break the electron transfer barrier between the surface and molecules. Sulfur vacancies as medium make electrons continuously transferred to CO and H₂O molecules.     

A new application of the commercial high temperature water gas shift catalyst for reduction of CO2 emissions in the iron and steel industry: Lab-scale catalyst evaluation

In this study, we present a detailed investigation of a commercial iron-based high temperature water gas shift (HTWGS) catalyst (Johnson Matthey KATALCO^TM 71-6) in a new application: the production of hydrogen from blast furnace gas (BFG), which originates from iron and steel manufacturing. During the lab-scale catalytic testing under BFG conditions the catalyst demonstrated: 1) high water gas shift activity and stability; 2) minimal methanation at reduced steam to CO ratios; 3) high resistance towards H₂S impurities present in the feed. The results of post-characterization of the discharged samples confirm the robustness of KATALCO 71-6 towards BFG process conditions: no over-reduction of the catalytically active Fe₃O₄ phase and no formation of a less active FeS phase. An in situ X-ray absorption spectroscopy study revealed no over-reduction of the iron phase under BFG conditions and the stabilization of the iron phase by diffusion of chromium into the iron oxide matrix. The findings of this study demonstrate the suitability of the iron-based HTWGS catalyst KATALCO 71-6 for the production of hydrogen from BFG streams. Knowledge gained in this study is an essential step in the development and scale up of carbon capture and storage as well as carbon capture and utilization technologies, such as the sorption enhanced water gas shift (SEWGS) technology, aimed at reducing the CO₂ footprint during steel manufacturing.     

Combined generation and separation of hydrogen in an electrochemical water gas shift reactor (EWGSR)

Hydrogen rich gas, originating from fossil fuel reforming processes or biomass gasification, contains a significant amount of CO. Typically, the yield of H₂ is increased with subsequent water gas shift units, converting CO to CO₂ and additional H₂. This study describes a new reactor concept enabling the water gas shift reaction and the separation of the generated hydrogen in one process step by using electrical energy. This electrochemical water gas shift reactor applies a H₃PO₄-doped Poly(2,5-benzimidazole) membrane as electrolyte and carbon supported Pt or PtRu as anode catalyst. The reactor operation was investigated at 130 °C and 150 °C with a H₂ free anode feed stream of humidified CO and N₂. The experimental results show the feasibility of the reactor concept, as H₂ was generated at the cathode according to Faradays Law. Anodic PtRu led to lower power demands than Pt. The operation at the two temperatures showed that 130 °C results in a lower electrical power demand while generating an equal amount of H₂. The feasibility of the reactor was assessed using exergy efficiency analysis.     

Hydrogen production from methane under the interaction of catalytic partial oxidation,water gas shift reaction and heat recovery

Hydrogen production from the combination of catalytic partial oxidation of methane (CPOM) and water gas shift reaction (WGSR), viz. the two-stage reaction, in a Swiss-roll reactor is investigated numerically. Particular emphasis is placed on the interaction among the reaction of CPOM, the cooling effect due to steam injection and the excess enthalpy recovery with heat recirculation. A rhodium (Rh) catalyst bed sitting at the center of the reactor is used to trigger CPOM, and two different WGSRs, with the aids of a high-temperature (Fe–Cr-based) shift catalyst and a low-temperature (Cu–Zn-based) shift catalyst, are excited. Two important parameters, including the oxygen/methane (O/C) ratio and the steam/methane (S/C) ratio, affecting the efficiencies of methane conversion and hydrogen production are taken into account. The predictions indicate that the O/C ratio of 1.2 provides the best production of H₂ from the two-stage reaction. For a fixed O/C ratio, the H₂ yield is relatively low at a lower S/C ratio, stemming from the lower performance of WGSR, even though the cooling effect of steam is lower. On the contrary, the cooling effect becomes pronounced as the S/C ratio is high to a certain extent and the lessened CPOM leads to a lower H₂ yield. As a result, with the condition of gas hourly space velocity (GHSV) of 10,000 h⁻¹, the optimal operation for hydrogen production in the Swiss-roll reactor is suggested at O/C = 1.2 and S/C = 4–6.     

Commercial process for mass production of synthetic natural gas through the adiabatic reactors: operational characteristics of a 50‐kW pilot‐plant,influence of steam,and CO2

In synthetic natural gas (SNG) reaction process, the water gas shift (WGS) reaction and methanation reaction take place simultaneously, and an insufficient supply of steam might deactivate the catalyst. In this study, the characteristics of the methanation reaction with a commercial catalyst and using a low [H₂]/[CO] mole ratio in SNG synthesis are evaluated. The reaction characteristics at various possible process parameters are evaluated varying different process parameters such as the [H₂O]/[CO] mole ratio, [H₂]/[CO] mole ratio, flow of different % CO₂, and reaction temperature. Temperature profiles on catalyst bed are monitored as a function of the [H₂O]/[CO] mole ratio, [H₂]/[CO] mole ratio, and flow of different % CO₂. Through a lab‐scale optimization process, suitable optimum conditions are selected and in the same condition a 50‐kW pilot‐scale SNG production process through adiabatic reactors is carried out. The pilot scale SNG reaction is stable through overnight and the CO conversion efficiency and CH₄ selectivity are 100% and 97.3%, respectively, while the maximum CH₄ productivity is 0.654 m³/kg_cat · h. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterisation of the electrochemical water gas shift reactor (EWGSR) operated with hydrogen and carbon monoxide rich feed gas

Water gas shift units are used to raise the H₂ yield of reforming processes by converting CO to CO₂ and additional H₂. Additional subsequent processes are required to separate H₂ from the product gas stream to obtain pure H₂. This study investigates a novel electrochemical membrane reactor, where the water gas shift reaction occurs electrochemically. The reactor is operated at 393 K and 403 K with electrical energy to enable hydrogen purification in terms of electrochemical pumping, as well as a simultaneous electrochemical CO oxidation to increase the yield of purified H₂. The experimental results show the influence of several operation parameters upon its operation characteristics (e.g. cell voltage, electrochemical CO oxidation, the energy demand, etc.). The process yielded high overall exergy efficiencies of, e.g. 78.3%, whereas the anodic outlet stream contributed with 35%-units, and the purified hydrogen with 43.3%-units.