Experimental Study of Internal Reforming on Large‐area Anode Supported Solid Oxide Fuel Cells

The effect of endothermic internal steam reformation of methane and exothermic fuel cell reaction on the temperature of a planar‐type anode‐supported solid oxide fuel cell was experimentally investigated as a function of current density and fuel utilization. We fabricated a large‐area (22 × 33 cm²) cell and compared temperature profiles along the cell using 30 thermocouples inserted through the cathode end plate at 750 °C under various conditions (Uf ∼50% at 0.4 A cm⁻²; Uf ∼70% at 0.4 A cm⁻²; Uf ∼50% at 0.2 A cm⁻²) with hydrogen fuel and methane‐steam internal reforming. The endothermic effect due to internal reforming mainly occurs at the gas inlet region, so this process is not very effective to cool down the hot spot created by the exothermic fuel cell reaction. This eventually results in a larger temperature difference on the cell. The most moderate condition with regards to thermal gradient on the cell corresponds to high fuel utilization (Uf ∼70%) and low current density (∼0.2 A cm⁻²). The electrochemical performance was also measured, and it was found that the current–voltage characteristics are comparable for the cell operated under hydrogen fuel and internal steam reforming of methane because of lower polarization resistance with high partial pressure of water vapor.     

Effect of Ethane and Propane in Simulated Natural Gas on the Operation of Ni–YSZ Anode Supported Solid Oxide Fuel Cells

Solid oxide fuel cells with Ni–yittria‐stabilised zirconia (YSZ) anode supports were tested on surrogate natural gas fuels (methane containing 2.5–10% ethane and 1.25–5% propane) and compared with results for pure methane. Inert anode‐side diffusion barriers were found to help suppress coking on the Ni–YSZ anodes. However, carbonaceous deposits were observed on anode compartment surfaces and the barrier layers for all of the natural gas compositions tested. The addition of air to the natural gas was shown to suppress this coking. For natural gas with 5% ethane and 2.5% propane, the addition of 33% air yielded stable, coke‐free operation at 750 °C and 800 mA cm^–2. Cell performance on this fuel was only slightly worse than for the same cell operated with dry hydrogen.     

Membrane‐assisted vapor stripping: energy efficient hybrid distillation–vapor permeation process for alcohol–water separation

BACKGROUND: Energy efficient alternatives to distillation for alcohol recovery from dilute solution are needed to improve biofuel sustainability. A process integrating steam stripping with a vapor compression step and a vapor permeation membrane separation step is proposed. The objective of this work is to estimate the energy and process costs required to make a fuel grade ethanol (0.5 wt% water) from 1 and 5 wt% ethanol aqueous streams using the proposed process. RESULTS: Using process simulation and spreadsheeting software, the proposed membrane‐assisted vapor stripping process was estimated to require as little as 8.9 MJ of fuel‐equivalent energy per kg of fuel grade ethanol recovered from a 1 wt% ethanol feed stream, 2.5 MJ kg^?1 for a 5 wt% ethanol solution. This represents an energy saving of at least 43% relative to standard distillation producing azeotropic ethanol (6 wt% water). Process costs were also found to be lower than for distillation at the 3.0 × 10⁶ kg‐ethanol year^?1 scale modeled. CONCLUSION: In this hybrid system, the stripping column provides high ethanol recoveries and low effluent concentrations while the vapor compression‐membrane component enables the efficient recovery of latent and sensible heat from both the retentate and permeate streams from the membrane system. Published in 2008 by John Wiley & Sons, Ltd.     

广州石化总厂乙烯厂燃料平衡及优化

在化工企业中，作为动力的燃料（ＦＧ）和燃料油（ＦＯ）起了关键的作用。充分回收丁二烯尾气，苯乙烯尾气和低压甲烷，多用自产的燃料油，以低成本的生产方式，为节能降耗。     

Combination of Sorption-Enhanced Steam Methane Reforming and Electricity Generation by MCFC: Concept and Numerical Simulation Analysis

Abstract

Reformed gas made by the steam methane reforming(SMR) process is used as fuel feed to MCFC, but it is not as good as pure hydrogen due to the presence of CO₂ and CO. The sorption-enhanced steam methane reforming(SE-SMR) process can reduce CO₂ and CO to a low level and produce high purity hydrogen. Considering the merits of similar operating temperatures (about 500°C) and carbon dioxide recycle, a novel concept of a six-step sorption-enhanced steam methane reforming (SE-SMR) combined with electricity generation by molten carbonate fuel cell (MCFC) is proposed. In the present paper, a cycle of the SE-SMR process, which include the steps of reaction/adsorption, depressurization, gas purges (nitrogen and reformed gas, respectively), and pressurization with reformed gas, is modeled and analyzed. The process stream in the SE-SMR process is used as anode feed in MCFC. According to the result of numerical simulation, a fuel cell grade hydrogen product (above 80% purity) at the SE-SMR temperature of 450°C can be obtained. A carbon dioxide recycle mechanism is developed for cathode feed of MCFC from flue gas by burning with excess air to achieve a proper CO₂/air ratio (about 30:70). The novel electricity generation system, which can operate at lower energy consumption and high purity hydrogen feed is helpful for the MCFC'S performance and life time.     

Anaerobic biogas generation from sugar industry wastewaters in three‐phase fluidized‐bed bioreactor

In the present study, attempts are made to optimize digestion time, initial feed pH, feed temperature, and feed flow rate (organic loading rate, OLR) for maximum yield of methane gas and maximum removal of chemical oxygen demand (COD) and biological oxygen demand (BOD) of sugar industry wastewaters in three‐phase fluidized‐bed bioreactor. Methane gas is analysed by using flame‐ionisation detector (FID). The optimum digestion time is 8 h and optimum initial pH of feed is observed as 7.5. The optimum temperature of feed is 40°C and optimum feed flow rate is 14 L/min with OLR 39.513 kg COD/m³ h. OLR is calculated on the basis of COD inlet in the bioreactor at different flow rates. The maximum methane gas concentration is 61.56% (v/v) of the total biogas generation at optimum biomethanation process parameters. The maximum biogas yield rate is 0.835 m³/kg COD/m³ h with maximum methane gas yield rate (61.56%, v/v) of 0.503 m³/kg COD/m³ h at optimum parameters. The maximum COD and BOD reduction of the sugar industry wastewaters are 76.82% (w/w) and 81.65% (w/w) at optimum biomethanation parameters, respectively.     

Modelling of multicomponent gas separation with asymmetric hollow fibre membranes—methane enrichment from biogas

A mathematical model for the dynamic performance of gas separation with high flux, asymmetric hollow fibre membranes was developed considering the permeate pressure build‐up inside the fibre bore and cross flow pattern with respect to the membrane skin. The solution technique provides reliable examination of pressure and concentration profiles along the permeator length (both residue/permeate streams) with minimal effort. The proposed simulation model and scheme were validated with experimental data of gas separation from literature. The model and solution technique were applied to investigate dynamic performance of several membrane module configurations for methane recovery from biogas (landfill gas or digester gas), considering biogas as a mixture of CO₂, N₂ and CH₄. Recycle ratio plays a crucial role, and optimum recycle ratio vital for the retentate recycle to permeate and permeate recycle to feed operation was found. From the concept of two recycle operations, complexities involved in the design and operation of continuous membrane column were simplified. Membrane permselectivity required for a targeted separation to produce pipeline quality natural gas by methane‐selective or nitrogen‐selective membranes was calculated. © 2012 Canadian Society for Chemical Engineering     

Teflon AF2400/Ultem composite hollow fiber membranes for alcohol dehydration by high‐temperature vapor permeation

High‐temperature vapor permeation has a stringent requirement of membrane stability under harsh feed environments. This work reports the design of Teflon AF2400/Ultem composite hollow fiber (HF) membranes for alcohol dehydration via vapor permeation. Fabrication parameters such as Teflon concentration and coating time were systematically investigated. Interestingly, the fabricated composite HF membranes possess an unusual surface with honeycomb‐like microstructure patterns. Owing to the Teflon protective layer, the newly developed composite HF shows a promising and stable separation performance with a flux of 4265 gm^?2 h^?1 and a separation factor of 383 for 95% isopropanol dehydration at 125°C. The composite HF also performs well under extreme vapor feed compositions from 87 to 99 wt % isopropanol. In addition, it exhibits impressive separation performance for the dehydration of ethanol and n‐butanol. This work may provide useful insights of designing thermal‐stable and high‐performance composite polymeric membranes for vapor permeation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1747–1757, 2016     

Separation of Pyridine/Water Solutions Using Pervaporation

Abstract

Studies were performed on the separation of pyridine/water solutions using pervaporation. Organic permeation experiments were performed using a ‘silicalite»-filled silicone composite membrane. Effects of feed concentration, feed temperature, and permeate side pressure were examined. Benchmark conditions of 5.0 wt% pyridine, 50°C, and 2 torr were chosen. At the benchmark conditions, an organic selectivity of 34 and a permeate flux of 0.428 kg/m²h was achieved. An increase in feed concentration caused an increase in both the permeate concentration and flux, but caused a decrease in the selectivity. Also, permeate compositions far exceeded standard vapor—liquid equilibrium. Temperature had an Arrhenius-type relationship with regard to flux, but had no effect on the selectivity. Increasing the permeate pressure caused a steady decrease in permeate flux and also decreased the permeate composition and selectivity.     

Recovery enhancement of liquid hydrocarbons in dew point control unit of natural gas processing plant

ABSTRACT

The low temperature absorption method is currently used in a gas-processing unit to control the natural gas dew point. The major problem of this unit is the simultaneous absorption of high amount of methane within heavier hydrocarbons, which leads to low purity of ethane and propane streams. Considering the operational conditions, the mentioned method used in second and third phases, will control the dew point at ?23° c at the best condition. This temperature is not proper for dew point and shows very high amount of hydrocarbons in product gas. In this study, a new process has been introduced in order to drop the gas liquid dew point (natural gas liquid) to ?85° c by self-refrigeration technology. Due to the advanced nature of absorption process, the problem of methane existence in the product of gas liquids is noticeably overcome. In this process, natural gas enters the turbo expander after passing through a refrigeration cycle at ?37° c and it is then expanded in an isotropic process to 2896 kPa pressure. Expander outlet with reflux and condensate produced from a cold separator are fed to an absorption tower with a reboiler and the separation will occur. The advantage of this method is controlling the concentration of methane in the product streams. Simulation results show that the process can daily produce 22,280 barrels of gas liquids with a concentration of 0.5 mole% of methane. In addition, the recovery efficiencies of propane and butane in the newly proposed method are 97.3% and 99.99%, respectively, which show a remarkable advantage over the current trend.     

Fabrication and operation of flow‐through tubular SOFCs for electric power and synthesis gas cogeneration from methane

Flow‐through type tubular solid oxide fuel cells were successfully fabricated and operated with a single‐chamber configuration for realizing the simultaneous generation of electric power and synthesis gas from methane by integrating a downstream catalyst into the fuel cell reactor. A new operation mode, which completely eliminated the gas diffusion between cathode side and anode side, is proposed. The cell showed high open‐circuit voltages of 1.02–1.08 V at the furnace temperature range of 650–800°C when operating on CH₄‐O₂ gas mixture at a molar ratio of 2:1. A peak power density of approximately 300 mW cm^?2 and a maximum power output of 1.5 W were achieved for a single cell with an effective cathode geometric surface area of 5.4 cm² at the furnace temperature of 750°C. The in‐situ initialization of the cell using CH₄‐O₂ gas mixture was also realized via applying an effective catalyst into the tubular cell. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1036–1044, 2014     

Methanol formation at high pressure by the catalyzed oxidation of natural gas and by the sensitized oxidation of methane

A three part study of the partial oxidation of natural gas or methane to methanol was carried out. In the first part, the effect of reactor wall composition on the homogeneous oxidation of natural gas was determined at a pressure of 30 atm (1 atm=1.01325·10⁵ Pa) and temperatures of 350–400°C. In the second part, the effect of solid catalysts on the oxidation of natural gas was determined in a heterogeneous system at 30 atm and various temperatures. Finally, the effect of various homogeneous 'sensitizers' on the oxidation of pure methane at 10 atm was evaluated.     

Modularization strategy for syngas generation in chemical looping methane reforming systems with CO2 as feedstock

This study considers a CO₂ feedstock in conventional methane reforming processes and metal oxide lattice oxygen based chemical looping reforming. Lattice oxygen from iron‐titanium composite metal oxide provides the most efficient co‐utilization of CO₂ with CH₄. A modularization chemical looping strategy is developed to further improve process efficiencies using a thermodynamic rationale. Modularization leverages the ability of two or more reactors operating in parallel to produce a higher quality syngas than a single reactor operating alone while offering a direct solution to scale up of multiple parallel reactor processes. Experiments conducted validate the thermodynamic simulation results. Simulation and experimental results ascertain that a cocurrent moving bed in a modularization system can operate under CO₂ neutral or negative conditions. The results for a modularization process system for 7950 m³ per day (50,000 barrels per day) of liquid fuel indicate a ～23% reduction of natural gas usage over baseline‐case. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3343–3360, 2017     

A Novel Cell‐Array Design for Single Chamber SOFC Microstack

A novel design of single chamber solid oxide fuel cell (SC‐SOFC) microstack with cell‐array arrangement is fabricated and operated successfully in a methane–oxygen–nitrogen mixture. The small stack, consisting of five anode‐supported single cells connected in series, exhibits an open circuit voltage (OCV) of 4.74 V at the furnace temperature of 600 °C and a maximum power output of 420 mW (total active electrode area is 1.4 cm²) at the furnace temperature of 700 °C. A gas mixture of CH₄/O₂ = 1 leads to best performance and stability.     

Experimental validation of hybrid distillation‐vapor permeation process for energy efficient ethanol–water separation

BACKGROUND: The energy demand of distillation‐based systems for ethanol recovery and dehydration can be significant, particularly for dilute solutions. An alternative separation process integrating vapor stripping with a vapor compression step and a vapor permeation membrane separation step, termed membrane assisted vapor stripping (MAVS), has been proposed. The hydrophilic membrane separates the ethanol–water vapor into water‐rich permeate and ethanol‐enriched retentate vapor streams from which latent and sensible heat can be recovered. The objective of this work was to demonstrate experimentally the performance of a MAVS system and to compare the observed performance with chemical process simulation results using a 5 wt% ethanol aqueous feed stream as the benchmark. RESULTS: Performance of the steam stripping column alone was consistent with chemical process simulations of a stripping tower with six stages of vapor liquid equilibria (VLE). The overhead vapor from the stripper contained about 40 wt% ethanol and required 6.0 MJ of fuel‐equivalent energy per kg of ethanol recovered in the concentrate. Introduction of the vapor compressor and membrane separation unit and recovery of heat from both membrane permeate and retentate streams resulted in a retentate ethanol concentrate containing ca 80 wt% ethanol, but requiring only 2.2 MJ fuel kg^?1 ethanol, significantly less than steam stripping alone. CONCLUSION: Performance of the experimental unit with a 5 wt% ethanol feed liquid corroborated chemical process simulation predictions for the energy requirement of the MAVS system, demonstrating a 63% reduction in the fuel‐equivalent energy requirement for MAVS compared with conventional steam stripping or distillation. Published 2009 by John Wiley & Sons, Ltd.     

Improving electrochemical performance of (Cu,Sm)CeO2 anode with anchored Cu nanoparticles for direct utilization of natural gas in solid oxide fuel cells

Development of solid oxide fuel cell (SOFC) anode with high resistance to coking and sulfur poisoning is highly desirable for the direct application of natural gas in SOFC. Herein, a (Cu, Sm)CeO₂ anode with anchored Cu nanoparticles has been prepared. Most of Cu nanoparticles particle size ranges from 20 to 50 nm, which can increase the conductivity and catalytic activity of the anode. The Cu/CSCO10 supported cell exhibits a maximum power density of 404.6 mW/cm² at 600 °C when dry methane is used as fuel while its ohmic resistance is only 0.39 Ω cm². The single SOFC shows good stability when H₂S content in the fuel is less than 150 ppm. Up to 900 h of continuous stable operation with simulated natural gas and commercial natural gas as fuel prove the advantages and application potential of this anode.     

Catalytic Partial Oxidation. Part I. Catalytic Processes to Convert Methane: Partial or Total Oxidation

The presence of large reserves of natural gas has stimulated research to utilize methane, its principal component, as an alternative energy source and to convert it to other fuels and industrially important chemicals. The reserves of natural gas in the world are estimated to be 1.4 × 10¹⁴ Nm³, while new gas fields are being discovered every year. Although this natural gas is available under pressure for piping and transport, extensive research efforts have been directed to develop gas-to-liquid (GTL) technology for the conversion of remote natural gas reserves into high-added-value liquid products, such as methanol and synthetic fuels, that can be more easily transported. A further incentive for natural gas utilization originates from environmental concerns that drive the search for cleaner energy sources. Catalytic combustion of methane offers an attractive alternative to gas-phase homogeneous combustion since it can stabilize flames at lower fuel-to-air ratios, thereby lowering flame temperatures and reducing NO_x emission. Another alternative can be found in the conversion of natural gas into hydrogen, which can be used to generate electricity in fuel cells. Fuel cells have a much higher energy efficiency compared to current combustion-based power plants. Also, hydrogen is a much cleaner fuel than hydrocarbon feedstocks since the only product from hydrogen fuel cells is water.     

Predicting Separation of Lower Hydrocarbon from Natural Gas by a Nano‐Porous Membrane using Capillary Condensation

In the present work, the potential of a nano‐porous membrane for predicting the separation of lower hydrocarbons from natural gas by capillary condensation was explored. While a gas permeates through a capillary at a suitable pressure, the adsorbed layer may attain a thickness enough to fill the entire membrane pore. Poiseuille flow of the condensed phase follows. Our computed results have established that for a passage through a nano‐porous membrane, gas having lower condensation pressure condenses in the pores at a pressure which is about an order of magnitude lower than its vapor pressure at the concerned temperature. In the case of propane/methane and butane/methane binary mixtures, propane and butane are preferentially condensed and permeation rates up to 700 g mol/m² s bar for propane and 600 g mol/m² s bar for butane have been achieved at a temperature lower than the critical temperature of the permeating species and higher than the critical temperature of the non‐permeating species. Since methane has a much lower critical temperature than both propane and butane, it gets physically dissolved in the condensed phase of propane, butane in the case of propane/methane and butane/methane binary mixtures, respectively. An equation of state (EOS) approach has been adopted to calculate the fugacity of methane in the gas, as well as in the condensed phase, in order to estimate its solubility. The Peng‐Robinson equation of state was used. Computation of the separation factor for methane/propane and methane/butane was performed over a wide range of temperature, pressure, and gas composition. The separation factor which is expectedly a function of these variables ranged from 0.3–75 for methane/propane and 0.7–140 for methane/butane binary mixtures. It has been established that an acceptable degree of separation is achievable at moderate pressure and at low temperature for the removal of propane and butane from natural gas. The results have the potential to be used for further refinement and optimization of the process conditions so that this strategy can be exploited for large‐scale removal of lower hydrocarbon from natural gas at a low cost.     

Carbon dioxide separation and dry reforming of methane for synthesis of syngas by a dual‐phase membrane reactor

High‐temperature CO₂ selective membranes offer potential for use to separate flue gas and produce a warm, pure CO₂ stream as a chemical feedstock. The coupling of separation of CO₂ by a ceramic–carbonate dual‐phase membrane with dry reforming of CH₄ to produce syngas is reported. CO₂ permeation and the dry reforming reaction performance of the membrane reactor were experimentally studied with a CO₂–N₂ mixture as the feed and CH₄ as the sweep gas passing through either an empty permeation chamber or one that was packed with a solid catalyst. CO₂ permeation flux through the membrane matches the rate of dry reforming of methane using a 10% Ni/γ‐alumina catalyst at temperatures above 750°C. At 850°C under the reaction conditions, the membrane reactor gives a CO₂ permeation flux of 0.17 mL min^?1 cm^?2, hydrogen production rate of 0.3 mL min^?1 cm^?2 with a H₂ to CO formation ratio of about 1, and conversion of CO₂ and CH₄, respectively, of 88.5 and 8.1%. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2207–2218, 2013     

Upgrading of Simulated Syngas by Using a Nanoporous Silica Membrane Reactor

The permeance properties of a nanoporous silica membrane were first evaluated in a laboratory‐scale porous silica membrane reactor (MR). The results indicated that CO, CO₂, and N₂ inhibited H₂ permeation. Increased H₂ permeability and selectivity were obtained when gas was transferred from the lumen side to the shell side. This was therefore selected as a suitable permeation direction. On this basis, upgrading of simulated syngas was experimentally investigated as a function of temperature (150 – 300 °C), feed pressure (up to 0.4 MPa), and gas hourly space velocity (GHSV), by using a nanoporous silica MR in the presence of a Cu/ZnO/Al₂O₃ catalyst. The CO conversion obtained with the MR was significantly higher than that with a packed‐bed reactor (PBR) and broke the thermodynamic equilibrium of a PBR at 275 – 300 °C and a GHSV of 2665 h^–1. The use of a low GHSV and high feed pressure improved the CO conversion and led to the recovery of more H₂.