基于熔融盐加热的甲烷蒸汽重整制氢反应器的熵产生率和氢气产率分析

太阳能热化学储能能够有效解决太阳能时间和空间分布不均的问题。在工业甲烷蒸汽重整反应器模型的基础上,利用有限时间热力学理论建立了基于熔融盐加热的甲烷蒸汽重整反应器（steam methane reforming reactor heated by molten salt,MS-SMRR）模型,得到了MS-SMRR的设计参数,并分析了MS-SMRR的几何参数和操作参数对氢气产率和总熵产生率的影响规律。结果表明：在氢气产率一定时,逆流参考反应器比顺流参考反应器的总熵产生率低,且消耗的熔融盐少;增大熔融盐进口温度和减小反应混合物进口压力能够显著提高MS-SMRR的氢气产率。研究结果对实际MS-SMRR的优化设计具有一定的理论指导意义。     

Numerical study of hydrogen production by the sorption-enhanced steam methane reforming process with online CO<Subscript>2</Subscript> capture as operated in fluidized bed reactors

A three-dimensional (3D) Eulerian two-fluid model with an in-house code was developed to simulate the gas-particle two-phase flow in the fluidized bed reactors. The CO₂ capture with Ca-based sorbents in the steam methane reforming (SMR) process was studied with such model combined with the reaction kinetics. The sorption-enhanced steam methane reforming (SE-SMR) process, i.e., the integration of the process of SMR and the adsorption of CO₂, was carried out in a bubbling fluidized bed reactor. The very high production of hydrogen in SE-SMR was obtained compared with the standard SMR process. The hydrogen molar fraction in gas phase was near the equilibrium. The breakthrough of the sorbent and the variation of the composition in the breakthrough period were studied. The effects of inlet gas superficial velocity and steam-to-carbon ratio (mass ratio of steam to methane in the inlet gas phase) on the reactions were studied. The simulated results are in agreement with the experimental results presented by Johnsen et al. (2006a, Chem Eng Sci 61:1195–1202).     

Numerical simulation of gas-solid flows in fluidized bed gasification reactor

A numerical model for simulating a fluidized bed gasifier should include appropriate parameters to capture the dynamics of gas-solid flows, gasification kinetics and the interaction between these two. The focus of the present study is to analyze the effects of coal gasification chemistry models reported in literature on the prediction of product gas composition in a fluidized bed gasification reactor. Numerical results are validated against the experimental data available in literature. The validated model is used to examine the available chemical kinetics schemes for water gas shift reaction, steam methane reforming reaction and char heterogeneous reactions. It is also used to assess the effects of hydrodynamic models parameters such as drag model, particle-particle restitution coefficient and specularity coefficient on exit gas composition. Results show that the predictions of product gas composition are notably affected by the choices of the kinetics schemes for water gas shift and steam methane reforming reactions. Systematic analysis using the available choices to simulate initial processes such as moisture removal, volatile and tar cracking is reported. Drag models and the value of specularity coefficient are shown to have no effect on product gas composition, and the particle-particle restitution coefficient slightly influences the predicted gas composition.     

Optimization of an experimental membrane reactor for low-temperature methane steam reforming

The systematic and rigorous model-based optimization of the configuration and operating conditions of a methane membrane steam reforming reactor for hydrogen production is performed. A permeable membrane with Pd–Ru deposited on a ceramic dense support is used to selectively remove the produced hydrogen from the reaction zone. The shifted chemical equilibrium towards hydrogen production enables the achievement of high methane conversion at relatively low reactor temperature levels. Steam reforming takes place over a Ni–Pt/CeZnLa ceramic foam-supported catalyst that ensures better thermal distribution, at an operating temperature of 773 K and a pressure of 10⁶ Pa. A nonlinear, two-dimensional, and pseudo-homogeneous mathematical model of the membrane fixed-bed reactor is developed and subsequently validated using experimental data. For model validation purposes, two sets of experiments have been performed at the experimental reactor installed at CPERI/CERTH. The first set of experiments aims to investigate membrane permeability in order to estimate the parameters involved in the applied Sieverts law. The second set of experiments explores the performance of the membrane reactor at different steam to carbon ratios and total inlet volumetric flowrates. The derived mathematical model, consisted of mass, energy, and momentum balances that consider both axial and radial gradients of temperature and concentration, is then utilized within a model-based optimization framework that calculates the optimal operating conditions for the highly interactive reactor system. The optimal steam to carbon ratio and sweep gas flow rate that minimize the overall methane utilization (i.e., reformed methane and equivalent methane for heating purposes) are calculated for a range of hydrogen production rates. Τhe optimal reactor design configuration described by the length of the catalyst zone is also obtained for a given pure hydrogen production rate.     

A novel pilot-scale production of fuel gas by allothermal biomass gasification using biomass micron fuel (BMF) as external heat source

A novel pilot-scale allothermal biomass gasification system integrating steam gasification, thermal cracking, and catalytic reforming aiming at fuel gas production was developed. Biomass micron fuel (BMF) was used as external heat source by combusting with air in the combustor. Biomass feedstock was gasified with steam, and then, tar in the produced gas was decomposed by thermal cracking and catalytic reforming. The waste heat of high-temperature flue gas and fuel gas was recovered and used for biomass feedstock pre-heating and steam generation, respectively. The fuel gas yield is 1.36 Nm³/kg with lower heating value of 11.61 MJ/Nm³. An overall energy analysis of the system was also investigated. The results showed that the cold gas efficiency and energy conversion efficiency in this system are 88.11 and 63.59 %, respectively. Meanwhile, combustion of BMF accounts for 25.66 % of the total energy input.     

Industrial wastewater treatment in a new gas-induced ozone reactor

The present work was to investigate industrial wastewater treatment by ozonation in a new gas-induced reactor in conjunction with chemical coagulation pretreatment. The reactor was specifically designed in a fashion that gas induction was created on the liquid surface by the high-speed action of an impeller turbine inside a draft tube to maximize the ozone gas utilization. A new design feature of the present reactor system was a fixed granular activated carbon (GAC) bed packed in a circular compartment between the reactor wall and the shaft tube. The fixed GAC bed provided additional adsorption and catalytic degradation of organic pollutants. Combination of the fixed GAC bed and ozonation results in enhanced oxidation of organic pollutants. In addition to enhanced pollutant oxidation, ozonation was found to provide in situ GAC regeneration that was considered crucial in the present reaction system. Kinetic investigations were also made using a proposed complex kinetic model to elucidate the possible oxidation reaction mechanisms of the present gas-induced ozonation system. As a complementary measure, chemical coagulation pretreatment was found able to achieve up to 50% COD and 85% ADMI removal. Experimental tests were conducted to identify its optimum operating conditions.     

Design and Fabrication of Ceramic Catalytic Membrane Reactors for Green Chemical Engineering Applications

Catalytic membrane reactors (CMRs), which synergistically carry out separations and reactions, are expected to become a green and sustainable technology in chemical engineering. The use of ceramic membranes in CMRs is being widely considered because it permits reactions and separations to be carried out under harsh conditions in terms of both temperature and the chemical environment. This article presents the two most important types of CMRs: those based on dense mixed-conducting membranes for gas separation, and those based on porous ceramic membranes for heterogeneous catalytic processes. New developments in and innovative uses of both types of CMRs over the last decade are presented, along with an overview of our recent work in this field. Membrane reactor design, fabrication, and applications related to energy and environmental areas are highlighted. First, the configuration of membranes and membrane reactors are introduced for each of type of membrane reactor. Next, taking typical catalytic reactions as model systems, the design and optimization of CMRs are illustrated. Finally, challenges and difficulties in the process of industrializing the two types of CMRs are addressed, and a view of the future is outlined.     

Modeling of the carbon nanotube chemical vapor deposition process using methane and acetylene precursor gases

Chemical vapor deposition of carbon nanotubes (CNTs) in a horizontal tube-flow reactor has been investigated with a fully coupled reactor-scale computational model. The model combined conservation of mass, momentum, and energy equations with gas-phase and surface chemical reactions to describe the evolution of a hydrogen and hydrocarbon feed-stream as it underwent heating and reactions throughout the reactor. Investigation was directed toward steady state deposition onto iron nanoparticles via methane and hydrogen as well as feed-streams consisting of acetylene and hydrogen. The model determines gas-phase velocity, temperature, and concentration profiles as well as surface concentrations of adsorbed species and CNT growth rate along the entire length of the reactor. The results of this work determine deposition limiting regimes for growth via methane and acetylene, demonstrate the need to tune reactor wall temperature to specific inlet molar ratios to achieve optimal CNT growth, and demonstrate the large effect that active site specification can have on calculated growth rate.     

Pore control using the nano structured powders on the fabrication of porous membrane and its application

In this study, a catalytic membrane with controlled pore size and structure was fabricated with nano sized particles and used in a steam and dry reforming reaction. The catalytic membrane was made using uniaxial-pressing and thermal treatment of the mixed powder. Nano sized yttria stabilized ZrO2 added to the nickel powder was determined to be a key factor in the preparation of the catalytic membrane. The membrane did not show the sintering effect due to the hindering of nickel agglomeration when subjected to heat treatment at high temperature. The optimum yttria stabilized ZrO2 content was below 1 wt% due to its strength and porosity. It was also unnecessary to deposit an additional reforming catalyst on the catalytic membrane, since the surface nickel site displayed excellent catalytic activity. When a mixture of methane and water/carbon dioxide was fed into the YSZ-Ni catalytic membrane reactor, the activity trended exceeded the performance of a conventional catalyst reactor, because of the difference in the flux of the gases.     

Seventeen-lump model for the simulation of an industrial fluid catalytic cracking unit (FCCU)

A 17-lump kinetic model has been developed for the riser–reactor cum regenerator of a fluid catalytic cracking unit (FCCU). This accounts for cracking, hydrogen transfer, aromatization, isomerization, alkylation and dimerization, as well as catalyst deactivation due to the coke deposition in its pores. A model for the industrial combustor–regenerator unit is also developed. The lumping scheme includes the detailed characterization in terms of the paraffins, naphthenes and aromatics (PNAs) for the VGO feed and also the detailed compositions of the two important products: gasoline and LPG. A total of 199 kinetic parameters for the riser–reactor cum regenerator have been fitted (tuned) using 192 sets of plant data (under different operating conditions) from an industrial FCC unit. The tuned model of the integrated FCCU was run for 15 additional operating conditions. The match was found to be quite good.     

Plasmagestützte Oberflächenfunktionalisierung komplex strukturierter,miniaturisierter Kunststoff‐Formteile. Plasma assisted surface functionalization of miniaturized plastic devices

Different methods can be used for chemical surface functionalization of devices made from plastics in order to prepare them for coating, joining and similar purposes. The methods exhibit different usage properties concerning achievable surface effects as well as processing conditions. Methods based on low pressure plasmas can be demonstrated to be favorable in both aspects for functionalization of geometrically complex devices. Especially, the gap penetration capability of plasma proves to be unique. Even extremely small sized and complex miniaturized devices can be treated this way. Investigations using gas phase grafting reactions revealed access to and homogenous treatment of very small gap structures which can not be treated otherwise.     

Supercritical fluid attachment of palladium nanoparticles on aligned carbon nanotubes

Nanocomposite materials consisting of Pd nanoparticles deposited on aligned multi-walled carbon nanotubes have been fabricated through hydrogen reduction of palladium-beta-diketone precursor in supercritical carbon dioxide. The supercritical fluid processing allowed deposition of high-density Pd nanoparticles (approximately 5-10 nm) on both as-grown (unfunctionalized) and functionalized (using HNO3 oxidation) nanotubes. However, the wet processing for functionalization results in pre-agglomerated, bundle-shaped nanotubes, thus significantly reducing the effective surface area for Pd particle deposition, although the bundling provides more secure, lock-in-place positioning of nanotubes and Pd catalyst particles. The nanotube bundling is substantially mitigated by Pd nanoparticle deposition on the unfunctionalized and geometrically separated nanotubes, which provides much higher catalyst surface area. Such nanocomposite materials utilizing geometrically secured and aligned nanotubes can be useful for providing much enhanced catalytic activities to chemical and electrochemical reactions (e.g., fuel cell reactions), and eliminate the need for tedious catalyst recovery process after the reaction is completed.     

3D simulation on pressurized oxy-fuel combustion of coal in fluidized bed

Pressurized oxy-fuel combustion technology is considered as a perspective carbon capture technology in industrial process. A computational fluid dynamics (CFD) model based on Multi-Phase Particle-In-Cell (MP–PIC) method was developed to predict pressurized oxy-coal combustion process in fluidized bed. The heterogeneous and homogeneous combustion reactions of coal were considered in this model. The predicted results were validated the accuracy of this model with experimental data from a 15 kW_th pressurized fluidized bed combustor in terms of the gas component and temperature characteristics. The characteristics of gas–solid flow and combustion under different pressure (0.1–2 MPa) and oxygen atmosphere were studied in this work. The predicted results show that the intensity of particle motion and the expansion degree in the fluidized bed was gradually decreased with an increase in pressure. A correlation was proposed based on the simulation results to maintain suitable fluidization conditions in pressurized circulating fluidized bed at different pressures. The temperature of particle phase region gradually increased with combustion pressure and inlet O₂ concentration increased. In addition, the CO₂ concentration in outlet increased while the emission of CO and NO_x decreased as the combustion pressure increased.     

Numerical study of SiC CVD in a vertical cold-wall reactor

The conventional heat and mass transport model is extended to describe silicon cluster formation in the gas phase and is employed for a numerical analysis of SiC chemical vapor deposition in a commercial vertical rotating disc reactor. The model is verified by comparing the computed growth rate with available experimental data. The growth rate is studied as a function of precursor flow rates varied in a wide range of values. It is found that the growth rate is limited by the gas mixture depletion in silicon atoms due to homogeneous nucleation. The secondary phase formation on the growing surface is analyzed. The SiC growth window depending on the precursor flow rates is calculated, and a significant influence of the homogeneous nucleation on the window width is shown. The model results predict that the Si/C ratio on the wafer can considerably differ from that at the reactor inlet.     

Modulation of Molecular Spatial Distribution and Chemisorption with Perforated Nanosheets for Ethanol Electro‐oxidation

Integrating thermodynamically favorable ethanol reforming reactions with hybrid water electrolysis will allow room‐temperature production of high‐value organic products and decoupled hydrogen evolution. However, electrochemical reforming of ethanol has not received adequate attention due to its low catalytic efficiency and poor selectivity, which are caused by the multiple groups and chemical bonds of ethanol. In addition to the thermodynamic properties affected by the electronic structure of the catalyst, the dynamics of molecule/ion dynamics in electrolytes also play a significant role in the efficiency of a catalyst. The relatively large size and viscosity of the ethanol molecule necessitates large channels for molecule/ion transport through catalysts. Perforated CoNi hydroxide nanosheets are proposed as a model catalyst to synergistically regulate the dynamics of molecules and electronic structures. Molecular dynamics simulations directly reveal that these nanosheets can act as a “dam” to enrich ethanol molecules and facilitate permeation through the nanopores. Additionally, the charge transfer behavior of heteroatoms modifies the local charge density to promote molecular chemisorption. As expected, the perforated nanosheets exhibit a small potential (1.39 V) and high Faradaic efficiency for the conversion of ethanol into acetic acid. Moreover, the concept in this work provides new perspectives for exploring other molecular catalysts.     

Modeling for plasma-enhanced catalytic reduction of nitrogen oxides

In this work, we simulated the whole processes of plasma-enhanced selective catalytic reduction for nitrogen oxides removal with hydrocarbon additive. The simulation model consists of plasma simulation and catalysis simulation. First, single filamentary microdischarge in dielectric barrier discharge was calculated to evaluate the radical production yield as a function of specific input energy. Second, the chemical reaction process in the discharge reactor was simulated to find the gas reforming property by the plasma. This plasma simulation was applied to NO oxidation process in atmospheric pressure N₂/O₂/NO/C₃H₆ mixtures under various discharge conditions. Finally, the catalytic reaction process was modeled using simple mass balance equations in gas-phase and on catalyst surface. The catalytic reaction simulation was tested for the reduction of nitrogen oxides on γ-Al₂O₃ catalyst in N₂/O₂/NO/C₃H₆ and in N₂/O₂/NO₂/C₃H₆.     

Nickel and copper deposition on Al2O3 and SiC particulates by using the chemical vapour deposition–fluidized bed reactor technique

A chemical vapour deposition–fluidized bed reactor technique was developed to perform metal deposition on ceramic particulates. Experiments of nickel and copper deposition on Al₂O₃ and SiC particulates were conducted. Argon was used as the carrier gas to fluidize the ceramic particulates. The metal–H–Cl system was selected for the chemical vapour deposition. The volumetric ratios of the inlet gas were 3.5% HCl, 20.0% H₂, and 76.5% Ar. The deposition reactions were carried out at four different temperatures: 500, 600, 700 and 800 °C. Successful deposition of metallic nickel and copper on the ceramic particulates was observed. It was also noticed that the deposition rates varied with the types of substrates and deposited metals. This revised version was published online in November 2006 with corrections to the Cover Date.     

An investigation of the treatment of particulate matter from gasoline engine exhaust using non-thermal plasma

A plasma reactor with catalysts was used to treat exhaust gas from a gasoline engine in order to decrease particulate matter (PM) emissions. The effect of non-thermal plasma (NTP) of the dielectric discharges on the removal of PM from the exhaust gas was investigated experimentally. The removal efficiency of PM was based on the concentration difference in PM for particle diameters ranging from 0.3 to 5.0 microm as measured by a particle counter. Several factors affecting PM conversion, including the density of plasma energy, reaction temperature, flow rate of exhaust gas, were investigated in the experiment. The results indicate that PM removal efficiency ranged approximately from 25 to 57% and increased with increasing energy input in the reactor, reaction temperature and residence time of the exhaust gas in the reactor. Enhanced removal of the PM was achieved by filling the discharge gap of the reactor with Cu-ZSM-5 catalyst pellets. In addition, the removal of unburned hydrocarbons was studied. Finally, available approaches for PM conversion were analyzed involving the interactions between discharge and catalytic reactions.     

A study of gas and solid mixing behaviors in a three partitioned fluidized bed

A previously unknown partitioned fluidized bed gasifier (PtFBG) has been developed for improving coal gasification performance. The basic concept of the PtFBG is a fluidized bed divided into two parts, a gasifier and a combustor, by a partitioned wall. Char is burnt in the combustor and the generated heat is supplied to the gasifier along with the bed materials. During that time, highly concentrated CO₂ is inevitably generated in the combustor. Therefore, vigorous solid mixing is an essential precondition as well as minimizing horizontal gas mixing. In this study, gas and solid mixing behaviors were verified in a cold model three partitioned fluidized bed (3-PtFB). Glass beads with an average diameter of 150 μm and a particle density of 2500 kg/m³ were used as bed materials. For the gas mixing experiments, CO₂ and N₂ were introduced into the beds through each distributor. Then, outlet gas flow rates and concentrations were measured by gas flow meters and an IR gas analyzer respectively. The calculated gas exchange ratios ranged from 3% to 10% with varying gas flow rates. For the solid mixing experiments, 1000 μm polypropylene particles with a density of 883 kg/m³ were continuously fed into the reactor. Then, the polypropylene particles were distributed to the entire beds evenly. Solid mixing behaviors were very analogous to liquid mixing behaviors in a continuous stirred tank reactor (CSTR).     

Catalytic oxidation of gaseous reduced sulfur compounds using coal fly ash

Activated carbon has been shown to oxidize reduced sulfur compounds, but in many cases it is too costly for large-scale environmental remediation applications. Alternatively, we theorized that coal fly ash, given its high metal content and the presence of carbon could act as an inexpensive catalytic oxidizer of reduced sulfur compounds for "odor" removal. Initial results indicate that coal fly ash can catalyze the oxidization of H(2)S and ethanethiol, but not dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) at room temperature. In batch reactor systems, initial concentrations of 100-500 ppmv H(2)S or ethanethiol were reduced to 0-2 ppmv within 1-2 and 6-8 min, respectively. This was contrary to control systems without ash in which concentrations remained constant. Diethyl disulfide was formed from ethanethiol substantiating the claim that catalytic oxidation occurred. The presence of water increased the rate of adsorption/reaction of both H(2)S and ethanethiol for the room temperature reactions (23-25 degrees C). Additionally, in a continuous flow packed bed reactor, a gaseous stream containing an inlet H(2)S concentration of 400-500 ppmv was reduced to 200 ppmv at a 4.6s residence time. The removal efficiency remained at 50% for approximately 4.6h or 3500 reactor volumes. These results demonstrate the potential of using coal fly ash in reactors for removal of H(2)S and other reduced sulfur compounds.