Production of synthesis gas from propane using thermal water vapor plasma

In this work, an experimental plasma-chemical reactor equipped with a water vapor plasma torch was used for catalyst-free thermal plasma reforming of propane to produce a synthesis gas. Thermal arc discharge plasma (a mixture of water vapor and argon) was generated at atmospheric pressure.     

Determination of effective water vapor diffusion coefficient in pemfc gas diffusion layers

The primary removal of product water in proton exchange membrane (PEM) fuel cells is through the cathode gas diffusion layer (GDL) which necessitates the understanding of vapor and liquid transport of water through porous media. In this investigation, the effect of microporous layer (MPL) coatings, GDL thickness, and polytetrafluorethylene (PTFE) loading on the effective water vapor diffusion coefficient is studied. MRC Grafil, SGL Sigracet, and Toray TGP-H GDL samples are tested experimentally with and without MPL coatings and varying PTFE loadings. A dynamic diffusion test cell is developed to produce a water vapor concentration gradient across the GDL and induce diffusion mass transfer. Tests are conducted at ambient temperature and flow rates of 500, 625, and 750 sccm. MPL coatings and increasing levels of PTFE content introduce significant resistance to diffusion while thickness has negligible effects.     

An experimental study on vapor condensation of wet flue gas in a plastic heat exchanger

An experimental system investigating condensation heat transfer of wet flue gas was set up, and the heat transfer performance of vapor‐gas mixture with vapor condensation was discussed. The experimental results of laminar flow in a plastic longitudinal spiral plate heat exchanger were obtained and are in good agreement with the modified classical film model. It is shown that the plastic air preheater can avoid acid corrosion in the low‐temperature field for the boiler using fuel containing sulfur and recover latent heat of the water vapor of the wet flue gas. Also some SO₂ was scrubbed during the vapor condensing process in the heat exchanger. © 2001 Scripta Technica, Heat Trans Asian Res, 30(7): 571–580, 2001     

褐煤焦吸附烟气中气态汞的实验研究

利用汞渗透管的汞蒸气发生装置和其他烟气成分模拟烟气条件,在小型固定床实验台上开展褐煤焦脱除Hg0的试验研究。结果表明:O2和HCl单独存在时均能够有效地促进单质汞在煤焦上的吸附,使煤焦的穿透率减少,吸附效率提高;SO2的存在会造成竞争吸附,抑制煤焦对Hg0的吸附;NO对煤焦吸附Hg0影响不大。随着入口汞浓度的增加,煤焦的穿透率增加;随着吸附反应温度的升高,煤焦的穿透增加,吸附效率降低。     

A reactor model for hydrogen generation from sodium borohydride and water vapor

This paper reports new data on the production of hydrogen from water vapor plus NaBH₄, or NaBH₄ + 10% CoCl₂. Data were collected with the aid of an isothermal semi-batch reactor with in-situ H₂ rate measurement. The reaction of NaBH₄ to generate H₂ proceeds via three steps: deliquescence, dissolution and reaction. The deliquescence regime of NaBH₄ in the presence of 10 weight percent CoCl₂ is defined. The H₂ yield is quantified at various reaction conditions (reaction temperature 70–120 °C, relative humidity 31–69%). CoCl₂ significantly accelerates the rate of H₂ production compared to deliquescence + reaction of pure NaBH₄. It is also found that a combination of high temperature and high relative humidity contributes to high H₂ rate and yield, and either of the two factors dominates the reaction at different conditions. A two-part reactor model accounting for the mechanism of the steam hydrolysis by NaBH₄ is developed. The model captures the dissolution + reaction step as well as reaction-only step and was validated by experimental data.     

The impact of thermal conductivity and diffusion rates on water vapor transport through gas diffusion layers

Proper water management in a hydrogen-fueled polymer electrolyte membrane (PEM) fuel cell is critical for performance and durability. A mathematical model has been developed to elucidate the effect of thermal conductivity and water vapor diffusion coefficient in the gas diffusion layers (GDLs). The fraction of product water removed in the vapor phase through the GDL as a function of GDL properties/set of material and component parameters and operating conditions has been calculated. The current model enables identification of conditions wherein condensation occurs in each GDL component. The model predicts the temperature gradient across various components of a PEM fuel cell, providing insight into the overall mechanism of water transport in a given cell design. The water condensation conditions and transport mode in the GDL components depend on the combination of water vapor diffusion coefficients and thermal conductivities of the GDL components. Different types of GDLs and water transport scenarios are defined in this work, based on water condensation in the GDL and fraction of water that the GDL removes through the vapor phase, respectively.     

Graphene inclusion effect on anion-exchange membranes properties for alkaline water electrolyzers

The main issues facing the development of Anion Exchange Membranes (AEM) are the low hydroxide ion (OH⁻) conductivity compared to protons (H⁺), and the thermal and chemical stability. Based on the its unique two-dimensional structure, graphene is estimated to be one of the best solutions for the hydrogen ions (H⁺ and OH⁻) selectivity and conductivity improvement. This work presents the graphene-composite membranes (AEMGrs) preparation and characterization in comparison with commercial FAA3-20® and FAA3-30® membranes from Fumatech. Various amounts of commercial graphene were incorporated into the Fumion® FAA-3 in NMP (10%), solutions which were then used to fabricate new AEMs by the Doctor-Blade (DB) method. Commercial and graphene-composite AEMs were studied by infrared spectroscopy with Fourier Transformation (FTIR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), water uptake (WU), ion exchange capacity (IEC), and in plane four-points electrochemical impedance spectroscopy (4p-EIS). The results indicated that the composite membranes containing 50 mg of graphene exhibited an improved IEC (3.16 mmol g⁻¹) and OH⁻ conductivity (113.27 mS cm⁻¹) at 80 °C measured in 0.01 M KOH (pH = 12).     

The investigation of desulphurization and water recovery from flue gas using ceramic composite membrane

Using nanoporous ceramic composite membranes to remove sulphur dioxide and to recover water vapor in flue gas is a new method, and this paper studied the effects of sulphur dioxide on the water recovery process. In this study, the outer‐side coating of hollow nanoporous ceramic composite membrane is selected as the study object. In the membrane module for desulphurization, one end of membrane is closed to create the high‐pressure environment inside membrane to ensure that the cooling water in the membrane penetrates the outer surface of the membrane to form a stable water film which can absorb sulphur dioxide from flue gas. In the membrane module for recovering water, using a vacuum pump to create micro‐negative pressure environment inside membrane, and then water vapor and condensate can penetrate through the membrane under pressure difference. Based on the ceramic composite membrane module, an integrated experimental platform for desulphurization and water recovery is constructed, and the mathematical model for predicting water recovery performance is established. According to the experimental and theoretical results, the mathematical model can predict the water recovery performance of the ceramic composite membrane.     

An Experimental Study on Latent Heat Recovery of Exhaust Wet Flue Gas

The experiment was conducted to investigate the heat transfer performance of wet flue gas in a vertical tube. The factors influencing the convective condensation of wet flue gas were experimentally investigated. The measured results indicate that the convective heat transfer of bulk flow and condensation heat transfer of vapor have significant contribution to the total heat transfer and the dominant transport mechanism is dependent upon the vapor fraction in mixture.     

An experimental study and model validation of a membrane humidifier for PEM fuel cell humidification control

This paper presents an experimental study and model validation of an external membrane humidifier for PEM fuel cell humidification control. Membrane humidification behavior was investigated with steady-state and dynamic tests. Steady-state test results show that the membrane vapor transfer rate increases significantly with water channel temperature, air channel temperature, and air flow rate. Water channel pressure has little effect on the vapor transfer rate and thus can be neglected in the system modeling. Dynamic test results reveal that the membrane humidifier has a non-minimum phase (NMP) behavior, which presents extra challenges for control system design. Based on the test data, a new water vapor transfer coefficient for Nafion membrane was obtained. This coefficient increases exponentially with the membrane temperature. The test results were also used to validate a thermodynamic model for membrane humidification. It is shown that the model prediction agrees well with the experimental results. The validated model provides an important tool for external humidifier design and fuel cell humidification control.     

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.     

Photoacoustic dual-gas sensor for simultaneous detection of hydrogen and water vapor

Hydrogen (H₂) is an important energy carrier, however, it can be hazardous owing to the risks involved with boring and explosion with colorless flames. By detecting the concentrations of H₂ and vapor water (H₂O) in real time, such risks can be prevented in advanced. In this study, a sensor system is developed based on photoacoustic spectroscopy using an H-type photoacoustic cell (PAC). Further, the time division multiplexing technique is used in a specific scanning period to realize dual-gas simultaneous detection. The dimensions of the PAC are optimized (inner volume: 1.8 cm³) and N-th characteristic frequencies are simulated through multiphysics simulation in COMSOL software. The optimized PAC is applied in the system and experiments of simultaneous dual gases detection are performed. The detection results show that the sensor's response time is 0.51 s and the recovery time is 0.38 s, and the minimal detection limit of H₂ is 138.69 ppm and H₂O can reach 3.70 ppm.     

Aerosol-assisted chemical vapor deposition of nickel sulfide nanowires for electrochemical water oxidation

Slow kinetics and emotive design of electrocatalysts are the main barriers to effective oxygen evolution and hydrogen production from water. To overcome these challenges, nickel sulfide impregnated electrocatalysts with auxiliary structural features have recently attracted attention as effective alternatives for the oxygen evolution reaction (OER). Herein, nickel sulfide (NiS) nanowires are developed directly on nickel foam (NF), which have proven to be a highly efficient electrocatalyst for OER in an alkaline medium. For this, NiS nanowires were grown on NF for short intervals of 30, 60, 90 and 120 min through an aerosol-assisted chemical vapor deposition (AACVD) process using nickel diethyldithiocarbamate as a precursor. The as-developed NiS electrode showed excellent OER activity in 1.0 M KOH solution. It is noteworthy that the NiS electrode produced after 90 min provides a reference current density of 10 mA cm^?2 at an overpotential (η) of 210 mV and achieves a higher current density of 500 mA cm^?2 at an overpotential of 340 mV. Moreover, the nanocatalyst has observed a low Tafel value (60 mV dec^?1) and good OER stability. After the electrolysis, it was found that the surface of the NiS catalyst was partially modified into nickel oxide. The S atom in the NiS catalyst can provide an activator function that first converts the sulfide to a hydroxide and then eventually becomes an oxyhydroxide species. The more active nickel hydroxide/oxyhydroxide phase raises the water oxidation performance to a new level. The facile synthesis of NiS nanowire films by AACVD tends to be used as an anodic material in various other power generation and energy conversion devices such as batteries, fuel cells, and supercapacitors.     

火电厂湿法烟气脱硫中“石膏雨”问题分析

取消烟气换热器装置后,采用石灰石-石膏湿法脱硫工艺的火电厂在运行中会出现“石膏雨”问题.分析了“石膏雨”现象的形成原因,讨论了解决方法.     

Numerical simulation of novel axial impeller patterns to compress water vapor as refrigerant

Through means of 3-D CFD (Computational Fluid Dynamics) method, a novel axial compressor with different impeller shapes compressing water vapor as refrigerant was investigated. The numerical simulation focuses on the fluid flow from compressor impeller inlet to outlet. The overall performance level and range are predicted. Different blade patterns with different hub sizes were compared regarding the aerodynamic performance. Independent of the blade pattern, in this numerical investigation the largest hub diameter shows the highest pressure ratio and efficiency at narrowest operating range.     

Influence of water vapor on long-term performance and accelerated degradation of solid oxide fuel cell cathodes

The influence of water vapor in the air on the performance and durability of solid oxide fuel cell (SOFC) has been investigated for the-state-of-the-art cathodes, (La_0.8Sr_0.2)_0.98MnO₃ (LSM) and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF). Durability experiments were carried out at 800 °C up to 1000 h with various water vapor containing-air fed to the cathode side. Both types of cathode materials were basically stable under typical water vapor concentrations in the ambient air. Degradations could be accelerated at much higher water vapor concentrations, which could be associated with the decomposition of the cathode materials. Temperature dependence of this degradation was analyzed between 700 °C and 900 °C under 10 vol% water vapor concentration, which showed that the effect of water vapor depends strongly on the temperature and led to a severe degradation at 700 °C within a short time period for both cathode materials.     

水汽增强温室效应的探讨

从研究水汽的热力学特性出发,通过定性分析和定量计算,着重探讨水汽对全球气候变暖的影响。通过研究,推测水蒸气凝结是通过辐射放热的,其凝结过程中向地面的辐射可能是大气温室效应的一个主要原因。     

LNG电厂烟气排放品质分析

分析了LNG电厂机组启动初期、低负荷及高负荷运行时烟气排放品质,对启动初期烟囱冒黄烟现象进行了分析,提出了降低机组运行过程中NOx排放的建议。     

High performance ZIF-8/PBI nano-composite membranes for high temperature hydrogen separation consisting of carbon monoxide and water vapor

Two types of advanced nano-composite materials have been formed by incorporating as-synthesized wet-state zeolitic imidazolate frameworks-8 (ZIF-8) nano-particles into a polybenzimidazole (PBI) polymer. The loadings of ZIF-8 particles in the two membranes (i.e., 30/70 (w/w) ZIF-8/PBI and 60/40 (w/w) ZIF-8/PBI) are 38.2 vol % and 63.6 vol %, respectively. Due to different ZIF-8 loadings, variations in particle dispersion, membrane morphology and gas separation properties are observed. Gas permeation results suggest that intercalation occurs when the ZIF-8 loading reaches 63.6 vol %. The incorporation of ZIF-8 particles significantly enhances both solubility and diffusion coefficients but the enhancement in diffusion coefficient is much greater. Mixed gas tests for H₂/CO₂ separation were conducted from 35 to 230 °C, and both membranes exhibit remarkably high H₂ permeability and H₂/CO₂ selectivity. The 30/70 (w/w) ZIF-8/PBI membrane has an H₂/CO₂ selectivity of 26.3 with an H₂ permeability of 470.5 Barrer, while the 60/40 (w/w) ZIF-8/PBI membrane has an H₂/CO₂ selectivity of 12.3 with an H₂ permeability of 2014.8 Barrer. Mixed gas data show that the presence of CO or water vapor impurity in the feed gas stream does not significantly influence the membrane performance at 230 °C. Thus, the newly developed H₂-selective membranes may have bright prospects for hydrogen purification and CO₂ capture in realistic industrial applications such as syngas processing, integrated gasification combined cycle (IGCC) power plant and hydrogen recovery.     

Influence of water vapor on performance of co-planar single chamber solid oxide fuel cells

Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxide fuel cells (SC-SOFCs) are investigated with emphasis on the role of water vapor. The maximum open circuit voltage (OCV) and peak power density are obtained at a methane-to-oxygen ratio of 3.5 under the wet gas condition, and a stoichiometric ratio of 2.0 for methane partial oxidation under the dry gas condition. In addition to the partial oxidation of methane on the anode and electrocatalytic reactions, both steam reforming and methane combustion occur on the anode and cathode, respectively, in the presence of water vapor. Local volume expansion and a rise in temperature associated with these parasitic reactions intensify inter-mixing of the reactant and product gases by which the OCV and power density drastically deteriorate with decreasing anode-to-cathode gap distance, as confirmed by impedance analysis for the LSM-YSZ|YSZ|LSM-YSZ symmetrical cell.