Oxidation Bed Research Articles

Research and Application of Digital Emergency Decontamination System

With the development of nuclear energy, tritium is extensively used in fusion reactors, nuclear power plants, and tritium-related systems. A digital Emergency Detritiation System (EDS) was developed by combining an ionization chamber, a dew point meter, a circulating pump, a drying bed, a liquid nitrogen condenser, etc. to monitor the system and the tritium gas in the industrial exhaust in real time as well as recover and remove the tritium gas in the exhaust. In the work of a factory, the online monitoring of tritium-containing gas in industrial tail gas was realized. A large amount of tritium gas in industrial tail gas was treated by catalytic oxidation of precious metal oxidation bed to form HTO, and finally, HTO was recovered by a liquid nitrogen cold trap. The complex process flow is visualized and automated by the system integration software to improve the efficiency of scientific research. The results demonstrate that the system can monitor the amount of tritium in tail gas instantaneously and accurately. The removal efficiency of tritium from the industrial exhaust can be up to 99%. After repeated regeneration and activation, the working efficiency of the molecular sieve can still reach 99%, ensuring that the composite emission standards of tritiation-related sites or fusion reactors and other plants are met.

Experimental validation of bed depth service time model using vapor adsorption bed for coolant purification system of fusion research

A breeding blanket system breeds tritium for fuel, and the system heat is removed by a helium cooling system in the fusion reactor. A Coolant Purification System (CPS) is an ancillary system that removes tritium and impurities from the coolant so that the levels of tritium and impurity in a helium cooling system remain within design requirements. The CPS consists of an oxidation bed that oxidizes Q2 (H, D, T) to Q2O, respectively, an Ambient Molecular Sieve Bed (AMSB) that adsorbs oxidized Q2O, a reduction bed that reduces Q2O back to Q2, and a heated getter bed that removes other impurities. An AMSB filled with zeolite has excellent vapor adsorption at room temperature, and is used semi-permanently by repeating adsorption and regeneration through a pressure–temperature swing adsorption process. In this work, an experimental study on the vapor adsorption and desorption of AMSB was conducted with research apparatus for vapor adsorption and desorption. The purpose of this study was to identify the adsorption and desorption characteristics of an AMSB with various geometries and operation conditions of vapor concentration and flow rate, and to verify its performance. The experimental results were analyzed by applying the bed depth service time model. Through such analysis, real-scale operating conditions could be predicted from the scaled-down test results, and this could be used for code validation of CPS in the future.

Mathematical Model of Maximum Commutation Half Cycle for Thermal Countercurrent Oxidation of Low‐Concentration Gas in Coal Mine Ventilation

The Fluent computational fluid dynamics software was used to study the relevant factors affecting the maximum commutation half cycle for thermal countercurrent oxidation of low‐concentration gas in coal mine ventilation. Based on orthogonal experiments, the maximum commutation half cycle for thermal countercurrent oxidation of the exhaust gas in the coal mine ventilation under 25 working conditions with the combination of different methane concentrations, inlet speeds, porosities, and oxidation bed filling lengths is investigated. SPSS data processing software was used to perform regression analysis on the numerical simulation data, and a mathematical model for predicting the maximum commutation half cycle under the influence of four factors was obtained. Through experiments, the mathematical model of the maximum commutation half cycle by the numerical simulation was verified. After introducing the wall heat loss correction coefficient, the complete prediction model of the maximum commutation half cycle was obtained. Comparing the experimental test value with the calculated value using the corrected model, the relative error was not more than 3%. The complete mathematical model corrected can be applied to the design calculation of the maximum commutation half cycle for thermal countercurrent oxidation of low‐concentration gas in actual coal mine ventilation.

Two-dimensional Numerical Simulation of Continuous Reverse-flow Oxidation of Ultralow Heating Value Coalbed Methane

In order to investigate the continuous reverse-flow oxidation of ultralow heating value coalbed methane, a two-dimensional mathematical mode for the continuous reverse-flow oxidation of ultralow heating value coalbed methane was set up. The software FLUENT was used to simulate the thermal structure of the oxidation bed and the effect of operating conditional parameters. The result indicates that: the temperature field of oxidation bed presents trapezium. There exists obvious difference in temperature at the both ends of oxidation bed, and it is helpful to preheat the fresh gas and recover the flue gas heat. Comparing with the conventional porous media combustion, the continuous reverse-flow oxidation has lower peak temperature and outlet temperature, and the methane conversion rate remains high. With the increase of methane concentration, the high-temperature zone widens, the both of temperature and outlet temperature rise, and the reaction area moves to inlet continuously. As the inlet velocity increases, the peak of temperature and outlet temperature both rises significantly, and the reaction area shifts toward to outlet continuously. With the increase of wall heat loss, the peak of temperature and the whole temperature of oxidation bed both reduce, the high-temperature zone becomes narrow obviously, and the reaction area is far away from the inlet.

Novel carbon fiber cathode membrane with Fe/Mn/C/F/O elements in bio-electrochemical system (BES) to enhance wastewater treatment

A novel conductive membrane with Fe/Mn/C/F/O elements is developed, it functions as the catalytic cathode of MFC and the antifouling filter of MBR simultaneously, in a newly designed integrated wastewater treatment system, without proton exchange membrane (PEM). The optimal conductive membrane is characterized using SEM-EDX, XRD and XPS. BET and porous structure analysis of the grounded membrane material indicate a narrow and small pore size (2–7 nm). The membrane surface is rich in Fe species (Fe - Fe2O3- Fe3O4) and manganese oxide (MnO2). Its characteristics such as excellent electro-chemical oxygen reduction reaction (ORR) activity, high clear water flux (>240 L/(m2·h)) and better antifouling filtration performance are further confirmed. The new system features bio-electrochemical system (BES) and integrates bio-filtration (trickling filter and air contact oxidation bed) and proton transfer through quartz sand chamber (QSC) which eliminates the use of expensive proton exchange membrane. The system removes chemical oxygen demand (>97.4%), ammonia nitrogen (>96.7%), total phosphorus (>98.0%) effectively, and it simultaneously generates electricity (446 mW/m3). The low cost and high performances, economic and advantageous system has good compatibility with existing wastewater treatment facilities and a wide application prospect.

A novel bio-electrochemical system with sand/activated carbon separator, Al anode and bio-anode integrated micro-electrolysis/electro-flocculation cost effectively treated high load wastewater with energy recovery

A novel bio-electrochemical system (BES) was developed by integrating micro-electrolysis/electro-flocculation from attaching a sacrificing Al anode to the bio-anode, it effectively treated high load wastewater with energy recovery (maximum power density of 365.1 mW/m3 and a maximum cell voltage of 0.97 V), and achieving high removals of COD (>99.4%), NH4+-N (>98.7%) and TP (>98.6%). The anode chamber contains microbes, activated carbon (AC)/graphite granules and Al anode. It was separated from the cathode chamber containing bifunctional catalytic and filtration membrane cathode (loaded with Fe/Mn/C/F/O catalyst) by a multi-medium chamber (MMC) filled with manganese sand and activated carbon granules, which replaced expensive PEM and reduced cost. An air contact oxidation bed for aeration was still adopted before liquid entering the cathode chamber. micro-electrolysis/electro-flocculation helps in achieving high removal efficiencies and contributes to membrane fouling migration. The increase of activated carbon in the separator MMC increased power generation and reduced system electric resistance.

Oxidation of lean methane in a two-chamber preheat catalytic reactor

This paper presents the results of lean methane oxidation in a two-chamber preheat catalytic reactor. A preheat catalytic reactor was built, and the effects of the space velocity (3800 h−1 to 8100 h−1), the inlet methane concentration (0.6 vol.% to 0.8 vol.%) and the inlet temperature of catalytic oxidation bed (420 °C–540 °C) were experimentally investigated. The results showed that when the space velocity is low, the methane conversion rate maintains a high value. But when the space velocity is higher than 7100 h−1, the methane conversion rate decreases dramatically. With the increases of the inlet methane concentration and the inlet temperature, the overall temperature of the oxidation bed increases rapidly, the temperature increment of the first catalytic ceramic layer increases, the methane conversion rate increases.

Development of a novel proton exchange membrane-free integrated MFC system with electric membrane bioreactor and air contact oxidation bed for efficient and energy-saving wastewater treatment

A novel combined system integrating MFC and electric membrane bioreactor (EMBR) was developed, in which a quartz sand chamber (QSC) was used, replacing expensive proton exchange membrane (PEM). An air contact oxidation bed (ACOB) and embedded trickling filter (TF) with filled volcano rock, was designed to increase dissolved oxygen (DO) in cathodic EMBR to save aeration cost. Membrane fouling in EMBR was successful inhibited/reduced by the generated bioelectricity of the system. The combined system demonstrated superior effluent quality in removing chemical oxygen demand (>97%) and ammonia nitrogen (>93%) during the stable operation, and the phosphorus removal was about 50%. Dominant bacteria (Nitrosomonas sp.; Comamonas sp.; Candidatus Kuenenia) played important roles in the removal of organic matter and ammonia nitrogen. The system has good application prospects in the efficient use of water and the development of sustainable wastewater recycling technology.

Energy Balance Analysis on a Preheating Catalytic Oxidation Device of Coal Mine Ventilation Air Methane

Energy balance analysis was carried out during the operation process of a preheating catalytic oxidation device of coal mine ventilation air methane. The effects of space velocity, inlet gas temperature and methane volume concentration on each energy balance term were studied. The experimental results show that: the exothermic oxidation power and the surface heat dissipation power loss rise with the increase of methane volume concentration and the oxidation bed inlet temperature, and yet fall when space velocity achieves a high enough value; the exhaust heat power loss is enhanced significantly with the growth of the inlet temperature and space velocity, but the change of methane volume concentration has very little influence on the exhaust heat loss power; the fraction of the exhaust heat loss descends significantly with the increase of methane volume concentration and inlet temperature, and yet rises obviously with the improvement of space velocity. The above results provide a theoretical guidance on the stable self-heating maintenance operation of the preheating catalytic oxidation device.

Thermal Fatigue Life Prediction of Ventilation Air Methane Oxidation Bed

Thermal flow-reversal oxidation is the main technology that can effectively reduce emissions of ventilation air methane. As the core component of coal mine ventilation oxidation devices, honeycomb ceramic oxidation beds play a decisive role in the functionality of these devices. The thermal fatigue properties of mullite ceramic, which is commonly used in oxidation beds, were tested in the present research. Then, the service life of the oxidation bed was predicted according to the intensity attenuation law and the thermal fatigue experimental data. The results of the fatigue experiment indicated that in general, the bending strength of mullite ceramics decreases as thermal shocks increase. At higher temperature differences, the bending strength decreased at higher rates. At the temperature differences between 600 and 800°C, the bending strength initially declined. Then, after reaching a certain value, it remained unchanged for a while before declining again. The calculation results via the proposed equation based on the intensity attenuation theory and the thermal fatigue experimental data indicate that the thermal fatigue life of an oxidation bed is about 1–8 months. The predicted result is consistent with actual working conditions.

Numerical Study on Heat Distribution and Transfer Characteristics of a Manifold in a Coal Mine VAM TFRR Oxidation Bed

A thermal flow-reversal reactor is candidate for utilizing low concentration ventilation air methane. In this paper, a numerical study is performed by using the FLUENT software to explore the details of the transient preheating and starting process of the thermal flow-reversal reactor oxidation bed. The bed was heated by hot gas, which was transported and distributed through the holes of manifolds to the middle of the bed. The homogeneous porous media and coupled heat transfer models were chosen; and the mass and heat flow distributions passing through the holes, the heat transfer on the outer surface of the manifold and the temperature distribution of the bed were calculated. The results indicate that the heat of the hot gas passing through the holes decreases gradually along the direction of the hot gas flowing in the manifold, causing the temperature of the bed decrease accordingly. The calculated temperatures of the oxidation bed are compared with the tested results. The maximum error between the calculation and the test was 8.9%.

Catalytic oxidation of coal mine ventilation air methane in a preheat catalytic reaction reactor

The results of experimental investigations on catalytic oxidation of coal mine ventilation air methane in a preheat catalytic reaction reactor is presented in this paper. The experimental system was located in the Energy Research Institute of Shandong University of Technology, which has been applied to investigate the effects of startup conditions such as the startup flow coefficient (0.3–0.5) and the startup power (10 kW–20 kW) on the startup process within the preheat catalytic reaction reactor. The average temperature distribution of catalytic oxidation bed and the minimal startup power were measured and the effects of operating conditions such as the space velocity (2600h−1 to 11,500 h−1) and the methane concentration (0.8%–1.2%) were experimentally investigated. Moreover, the methane conversion rate and the average temperature of the catalytic oxidation bed were discussed and the critical space velocity value and the critical methane concentration value were determined.

Experimental Investigation of Flow Resistance in a Coal Mine Ventilation Air Methane Preheated Catalytic Oxidation Reactor

This paper reports the results of experimental investigation of flow resistance in a coal mine ventilation air methane preheated catalytic oxidation reactor. The experimental system was installed at the Energy Research Institute of Shandong University of Technology. The system has been used to investigate the effects of flow rate (200 Nm3/h to 1000 Nm3/h) and catalytic oxidation bed average temperature (20°C to 560°C) within the preheated catalytic oxidation reactor. The pressure drop and resistance proportion of catalytic oxidation bed, the heat exchanger preheating section, and the heat exchanger flue gas section were measured. In addition, based on a large number of experimental data, the empirical equations of flow resistance are obtained by the least square method. It can also be used in deriving much needed data for preheated catalytic oxidation designs when employed in industry.

Modeling Thermal Oxidation of Coal Mine Methane in a Non-Catalytic Reverse-Flow Reactor

Inspired by detailed designs of industrial porous burners, the combustion of methane–air mixtures in a non-catalytic reverse-flow reactor was studied numerically. The governing equations are the unsteady state equations of conservation of mass and chemical species, with separate energy equations for the solid and gas phases. These equations were solved using the commercial CFD code Fluent. In order to reveal the actual thermal oxidation in porous media, the user defined function (UDF) is used to extend the ability of FLUENT. The model has been used to investigate the effects of operating conditions such as the mixture inlet approach velocity (0.15 to 0.8 m/s) and methane concentration (0.3 to 0.7%) on the oxidation of methane within non-catalytic reactors packed with ceramic monolith blocks under adiabatic conditions. The calculated values of methane conversion showed good agreement with the corresponding available experimental data. Moreover temperature distribution characteristics in the oxidation bed were studied in order to maintain the autothermicity of TFRR with a high enough temperature in the hot zone.

Direct conversion of glycerol to acrylic acid via integrated dehydration–oxidation bed system

Acrylic acid can be successfully produced in a single reactor via subsequent oxidation of the glycerol-dehydrated products. Selective dehydration of glycerol to acrolein was studied at 275–400 °C over HZSM-5, HBeta, HMordenite and HY. The V–Mo oxides (15–70 mol%V) on silicic acid support (20–100 wt% mixed oxides loading) were then included as a second bed for subsequent oxidation of the dehydrated products. Over the acid zeolites, acrolein and acetol are mainly generated, together with acetaldehyde, propionaldehyde, pyruvaldehyde and other oxygenates as secondary products. A complete conversion of glycerol with high selectivity to acrolein (up to 81 mol%) can be obtained when medium pore zeolites (HZSM-5) and low glycerol concentration (10–30 wt%) was used at 300 °C. A separated-sequential bed system provides high selectivity for acrylic acid with small amount of acetic acid and acetaldehyde (∼15 mol%). The catalyst with high V content promotes total oxidation of the dehydrated products to CO while that with highly dispersed V–Mo–O phases affords 98% selectivity to acrylic acid with 48% acrolein conversion.

Numerical Study on the Effect of Dislocation Relationship on Resistance Characters of the Ceramic Oxidation Bed Based on Fluent Software

As ceramic oxidation bed has high heat transfer efficiency, now, great attention has been given on it. In the oxidation bed, between the honeycomb holes of the fore-and-aft blocks of ceramic honeycombs, there are dislocation relationships. The effect of dislocation relationship on the pressure drop of the oxidation bed was numerically simulated by Fluent software. The results show that, between the two blocks of closely adjacent ceramic honeycombs, when a gap distance of 1mm was left, compared to the situation the gap distance is 0, the overall resistance loss of the oxidation bed reduced vast.

Numerical Study on the Transient Preheating Process of a Regenerative Oxidation Bed

The transient preheating process of a regenerative oxidation bed placed in a coal mine methane thermal reverse-flow reactor is numerically investigated in this paper. The regenerative oxidation bed is heated by the burned gas which is generated from a burner and is distributed through manifolds, which is modeled in a three-dimensional, unsteady state and laminar flow system, and is assumed as a semitransparent porous media. Non-local thermal equilibrium between gas and solid is accounted for introducing separate energy equations for two phases in porous media, and the finite volume method is used to solve the radiative transfer equation of the solid phase to calculate the local radiation source term. The calculating results indicate that the regenerative oxidation bed is preheated mainly by the hot gas passing through the manifold, and increasing the inlet mass flow could shorten the time of preheating, specific heat and porosity have a great influence on the heat storage capacity of the regenerative oxidation bed, and the contribution of the solid phase radiation to heat transfer can not be ignored, the temperature is highest in the middle of the regenerative oxidation bed, and it decreases gradually along the direction of height of the regenerative oxidation bed. All these work can help to understand the transient preheating process of a regenerative oxidation bed and the heat transfer phenomena and mechanism during the process.

Model‐based optimization of hydrogen generation by methane steam reforming in autothermal packed‐bed membrane reformer

AbstractAn autothermal membrane reformer comprising two separated compartments, a methane oxidation catalytic bed and a methane steam reforming bed, which hosts hydrogen separation membranes, is optimized for hydrogen production by steam reforming of methane to power a polymer electrolyte membrane fuel cell (PEMFC) stack. Capitalizing on recent experimental demonstrations of hydrogen production in such a reactor, we develop here an appropriate model, validate it with experimental data and then use it for the hydrogen generation optimization in terms of the reformer efficiency and power output. The optimized reformer, with adequate hydrogen separation area, optimized exothermic‐to‐endothermic feed ratio and reduced heat losses, is shown to be capable to fuel kW‐range PEMFC stacks, with a methane‐to‐hydrogen conversion efficiency of up to 0.8. This is expected to provide an overall methane‐to‐electric power efficiency of a combined reformer‐fuel cell unit of ∼0.5. Recycling of steam reforming effluent to the oxidation bed for combustion of unreacted and unseparated compounds is expected to provide an additional efficiency gain. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Numerical Study on Transient Heat Transfer in a Regenerative Oxidation Bed during the Preheating Process

The transient heat transfer characteristics of a regenerative oxidation bed placed in a coal mine methane thermal reverse-flow reactor during preheating process are numerically investigated in this paper. The regenerative oxidation bed is modeled in a three-dimensional, unsteady state and laminar flow system, and is assumed as a semitransparent porous media. The calculating results indicate that increasing the inlet mass flow could shorten the time of preheating, specific heat and porosity have a great influence on the heat storage capacity of the regenerative oxidation bed, and the contribution of the solid phase radiation to heat transfer can not be ignored. All these work can help to understand the heat transfer phenomena and mechanism in a regenerative oxidation bed during the preheating process.

Hydrocarbon reformer for electrochemical cells

An apparatus for and a method of continuously supplying a conditioned fuel, such as CO and H 2 , to an electrochemical generator such as a high temperature solid oxide electrolyte, fuel cell generator (SOFC), for electrochemical reactions and continually regenerating a hydrocarbon reformation catalyst by providing at least two iron metal/iron oxide beds. At least one bed, a reformation bed, is mainly in the iron oxide (FeO) condition and incoming hydrocarbon feed fuel gas, such as natural gas, will be reformed or conditioned at a temperature of about 600° C. to 800° C. on the iron oxide to CO and H 2 which represents the fuel to be fed to the fuel cells of the electrochemical generator, thereby reducing iron oxide to iron metal (Fe). While the FeO reformer bed is being reduced to Fe, the at least one other bed, an oxidation bed, which previously served as a reformer bed mainly in the iron metal condition (Fe) is oxidized at a temperature of about 600° C. to 800° C. to mainly FeO form with generator spent fuel gases, thereby oxidizing iron to iron oxide and also producing some additional conditioned fuel gas. The beds can be operated concurrently or sequentially, and when each bed becomes substantially exhausted, it is switched over in function to the other mode of operation.