875 resultados para Gas-solid fluidized bed


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The conversion of biomass waste in the form of date seed into pyrolysis oil by fixed bed pyrolysis reactor has been taken into consideration in this study. A fixed bed pyrolysis has been designed and fabricated for obtaining liquid fuel from these date seeds. The major component of the system are fixed bed pyrolysis reactor, liquid condenser and liquid collector. The date seed in particle form is pyrolysed in an externally heated 7.6 cm diameter and 46 cm high fixed bed reactor with nitrogen as the carrier gas. The reactor is heated by means of a biomass source cylindrical heater from 4000C to 6000C. The products are oil, char and gas. The reactor bed temperature, running time and feed particle size are considered as process parameters. The parameters are found to influence the product yield significantly. A maximum liquid yield of 50 wt.% is obtained at a reactor bed temperature of 5000 C for a feed size volume of 0.11- 0.20 cm3 with a running time of 120 minutes. The pyrolysis oil obtained at this optimum process conditions are analyzed for some fuel properties and compared with some other biomass derived pyrolysis oils and also with conventional fuels. The oil is found to possess favorable flash point and reasonable density and viscosity. The higher calorific value is found to be 28.636 MJ/kg which is significantly higher than other biomass derived pyrolysis oils.

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Among various thermo-chemical conversion processes, pyrolysis is considered as an emerging technology for liquid oil production. The conversion of biomass waste in the form of plum seed into pyrolysis oil by fixed bed pyrolysis reactor has been taken into consideration in this study. A fixed bed pyrolysis has been designed and fabricated for obtaining liquid fuel from this plum seeds. The major component of the system are fixed bed pyrolysis reactor, liquid condenser and liquid collectors. The plum seed in particle form is pyrolysed in an externally heated 7.6 cm diameter and 46 cm high fixed bed reactor with nitrogen as the carrier gas. The reactor is heated by means of a biomass source cylindrical heater from 4000C to 6000C. The products are oil, char and gas. The reactor bed temperature, running time and feed particle size are considered as process parameters. The parameters are found to influence the product yield significantly. A maximum liquid yield of 39 wt% of biomass feed is obtained with particle size of 2.36-4.75 mm at a reactor bed temperature of 520oC with a running time of 120 minutes. The pyrolysis oil obtained at this optimum process conditions are analyzed for some fuel properties and compared with some other biomass derived pyrolysis oils and conventional fuels. The oil is found to possess favorable flash point and reasonable density and viscosity. The higher calorific value is found to be 22.39 MJ/kg which is higher than other biomass derived pyrolysis oils.

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Experiments on atmospheric two-stage fluidized bed drying of bovine intestines with heat pump were carried out. The investigation covers innovative fluidized bed heat pump drying of bovine intestines. The two-stage drying consists of atmospheric moisture sublimation immediately followed by evaporation. Studies were done to establish the influence of the drying condition on the drying characteristics and product quality of bovine intestines and properties focusing on kinetics, diffusion, and color. The investigation of the drying characteristics has been conducted during moisture removal by evaporation and combined sublimation and evaporation. The effect of drying temperature on the drying constants was determined by fitting the experimental data using regression analysis techniques. The investigation revealed that the drying kinetics is most significantly affected by temperature. Correlations expressing the drying constants and effective moisture diffusivity dependence on the drying conditions are reported.

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Using a combination of multivariate statistical techniques and the graphical assessment of major ion ratios, the influences on hydrochemical variability of coal seam gas (or coal bed methane) groundwaters from several sites in the Surat and Clarence-Moreton basins in Queensland, Australia, were investigated. Several characteristic relationships between major ions were observed: 1) strong positive linear correlation between the Na/Cl and alkalinity/Cl ratios; 2) an exponentially decaying trend between the Na/Cl and Na/alkalinity ratios; 3) inverse linear relationships between increasing chloride concentrations and decreasing pH for high salinity groundwaters, and; 4) high residual alkalinity for lower salinity waters, and an inverse relationship between decreasing residual alkalinity and increasing chloride concentrations for more saline waters. The interpretation of the hydrochemical data provides invaluable insights into the hydrochemical evolution of coal seam gas (CSG) groundwaters that considers both the source of major ions in coals and the influence of microbial activity. Elevated chloride and sodium concentrations in more saline groundwaters appear to be influenced by organic-bound chlorine held in the coal matrix; a sodium and chloride ion source that has largely been neglected in previous CSG groundwater studies. However, contrastingly high concentrations of bicarbonate in low salinity waters could not be explained, and are possibly associated with a number of different factors such as coal degradation, methanogenic processes, the evolution of high-bicarbonate NaHCO3 water types earlier on in the evolutionary pathway, and variability in gas reservoir characteristics. Using recently published data for CSG groundwaters in different basins, the characteristic major ion relationships identified for new data presented in this study were also observed in other CSG groundwaters from Australia, as well as for those in the Illinois Basin in the USA. This observation suggests that where coal maceral content and the dominant methanogenic pathway are similar, and where organic-bound chlorine is relatively abundant, distinct hydrochemical responses may be observed. Comparisons with published data of other NaHCO3 water types in non-CSG environments suggest that these characteristic major ion relationships described here can: i) serve as an indicator of potential CSG groundwaters in certain coal-bearing aquifers that contain methane; and ii) help in the development of strategic sampling programmes for CSG exploration and to monitor potential impacts of CSG activities on groundwater resources.

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The COREX melter gasifier is a countercurrent reactor to produce liquid iron. Directly reduced iron (DRI), noncoking coal, and other additives are charged to the melter gasifier at their respective temperatures, and O-2 is blown through the tuyeres. Functionally, a melter gasifier is divided into three zones: a moving bed, fluidized bed, and free board. A model has been developed for the moving bed, where the tuyere region is two-dimensional (2-D) and the rest is one-dimensional (1-D). It is based on multiphase conservation of mass, momentum, and heat. The fluidized bed has been treated as 1-D. Partial equilibrium is calculated for the free board. The calculated temperature of the hot metal, the top gas, and the chemistry of the top gas agree with the reported plant data. The model has been used to study the effects of bed height, injection of impure O-2, coal chemistry, and reactivity on the process performance.

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It is important to know and to quantify the liquid holdups both dynamic and static at local levels as it will lead to understand various blast furnace phenomena properly such as slag/metal.gas.solid reactions, gas flow behaviour and interfacial area between the gas/solid/liquid. In the present study, considering the importance of local liquid holdup and non-availability of holdup data in these systems, an attempt has been made to quantify the local holdups in the dropping and around raceway zones in a cold model study using a non-wetting packing for liquid. In order to quantify the liquid holdups at microscopic level, a previously developed technique, X-ray radiography, has been used. It is observed that the liquid flows in preferred paths or channels which carry droplets/rivulets. It has been found that local holdup in some regions of the packed bed is much higher than average at a particular flow rate and this can have important consequences for the correct modelling of such systems.

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A solid oxide galvanic cell and a gas-solid (View the MathML source) equilibration technique have been used to measure the activities of the solutes in the α-solid solutions of silver with indium and tin. The results are consistent with the information now available for the corresponding liquid alloys, the phase diagram and the heats of mixing of the solid alloy. When the results of this study are taken together with published data for the α-solid solutions in Ag + Cd system, it is found that the variation of the excess partial free energy of the solute with mole fraction can be correlated to the electron/atom ratio. The significant thennodynamic parameter that explains the Hume-Rothery findings in these alloys appears to be the rate of change of the excess partial free energy with composition near the phase boundary, and this in turn reflects the value of the solute-solute interaction energy.

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The chemical potentials of tin in its α-solid solutions with Cu, Au and Cu + Au alloys have been measured using a gas-solid equilibration technique. The variation of the excess chemical potential of tin with its composition in the alloy is related to the solute-solute repulsive interaction, while the excess chemical potential at infinite dilution of the solute is a measure of solvent-solute interaction energies. It is shown that solute-solute interaction is primarily determined by the concentration of (s + p) electrons in the conduction band, although the interaction energies are smaller than those predicted by either the rigid band model or calculation based on Friedel oscillations in the potential function. Finally, the variation of the solvent-solute interaction with solvent composition in the ternary system can be accounted for in terms of a quasi-chemical treatment which takes into account the clustering of the solvent atoms around the solute.

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Surface coatings and treatments have been used to reduce material loss of components in bubbling fluidized bed combustors (FBCs). The performance of protective coatings in FBC boilers and laboratory simulations is reviewed. Important coating properties to minimize wastage appear to be high hardness, low oxidation rate, low porosity, high adhesion and sufficient thickness to maintain protection for a long period. Economic considerations and criteria for choosing a suitable coating or treatment are discussed for the different types of bubbling FBC. © 1995.

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Chemical looping combustion (CLC) is a means of combusting carbonaceous fuels, which inherently separates the greenhouse gas carbon dioxide from the remaining combustion products, and has the potential to be used for the production of high-purity hydrogen. Iron-based oxygen carriers for CLC have been subject to considerable work; however, there are issues regarding the lifespan of iron-based oxygen carriers over repeated cycles. In this work, haematite (Fe2O3) was reduced in an N2+CO+CO2 mixture within a fluidised bed at 850°C, and oxidised back to magnetite (Fe3O4) in a H2O+N2 mixture, with the subsequent yield of hydrogen during oxidation being of interest. Subsequent cycles started from Fe3O4 and two transition regimes were studied; Fe3O4↔Fe0.947O and Fe 3O4↔Fe. Particles were produced by mechanical mixing and co-precipitation. In the case of co-precipitated particles, Al was added such that the ratio of Fe:Al by weight was 9:1, and the final pH of the particles during precipitation was investigated for its subsequent effect on reactivity. This paper shows that co-precipitated particles containing additives such as Al may be able to achieve consistently high H2 yields when cycling between Fe3O4 and Fe, and that these yields are a function of the ratio of [CO2] to [CO] during reduction, where thermodynamic arguments suggest that the yield should be independent of this ratio. A striking feature with our materials was that particles made by mechanical mixing performed much better than those made by co-precipitation when cycling between Fe3O4 and Fe0.947O, but much worse than co-precipitated particles when cycling between Fe3O 4 and Fe.

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On the basis of the two-continuum model of dilute gas-solid suspensions, the dynamic behavior of inertial particles in supersonic dusty-gas flows past a blunt body is studied for moderate Reynolds numbers, when the Knudsen effect in the interphase momentum exchange is significant. The limits of the inertial particle deposition regime in the space of governing parameters are found numerically under the assumption of the slip and free-molecule flow regimes around particles. As a model problem, the flow structure is obtained for a supersonic dusty-gas point-source flow colliding with a hypersonic flow of pure gas. The calculations performed using the full Lagrangian approach for the near-symmetry-axis region and the free-molecular flow regime around the particles reveal a multi-layer structure of the dispersed-phase density with a sharp accumulation of the particles in some thin regions between the bow and termination shock waves.

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In this paper, we study the issues of modeling, numerical methods, and simulation with comparison to experimental data for the particle-fluid two-phase flow problem involving a solid-liquid mixed medium. The physical situation being considered is a pulsed liquid fluidized bed. The mathematical model is based on the assumption of one-dimensional flows, incompressible in both particle and fluid phases, equal particle diameters, and the wall friction force on both phases being ignored. The model consists of a set of coupled differential equations describing the conservation of mass and momentum in both phases with coupling and interaction between the two phases. We demonstrate conditions under which the system is either mathematically well posed or ill posed. We consider the general model with additional physical viscosities and/or additional virtual mass forces, both of which stabilize the system. Two numerical methods, one of them is first-order accurate and the other fifth-order accurate, are used to solve the models. A change of variable technique effectively handles the changing domain and boundary conditions. The numerical methods are demonstrated to be stable and convergent through careful numerical experiments. Simulation results for realistic pulsed liquid fluidized bed are provided and compared with experimental data. (C) 2004 Elsevier Ltd. All rights reserved.

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The influence of HCl on CO and NO emissions was experimentally investigated in an entrained flow reactor (EFR) and an internally circulating fluidized bed (ICFB). The results in EFR show the addition of HCl inhibits CO oxidation and NO formation at 1073 K and 1123 K. At the lower temperature (1073 K) the inhibition of HCl becomes more obvious. In ICFB, chlorine-containing plastic (PVC) was added to increase the concentration of HCl during the combustion of coal or coke. Results show that HCl is likely to enhance the reduction of NO and N2O. HCl greatly increases CO and CH4 emission in the flue gas. A detailed mechanism of CO/NO/HCl/SO2 system was used to model the effect of HCl in combustion. The results indicate that HCl not only promotes the recombination of radicals O, H, and OH, but also accelerates the chemical equilibration of radicals. The influence of HCl on the radicals mainly occurs at 800-1200 K. (C) 2009 Elsevier Ltd. All rights reserved.

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Part I

Studies of vibrational relaxation in excited electronic states of simple diatomic molecules trapped in solid rare-gas matrices at low temperatures are reported. The relaxation is investigated by monitoring the emission intensity from vibrational levels of the excited electronic state to vibrational levels of the ground electronic state. The emission was in all cases excited by bombardment of the doped rare-gas solid with X-rays.

The diatomics studied and the band systems seen are: N2, Vegard-Kaplan and Second Positive systems; O2, Herzberg system; OH and OD, A 2Σ+ - X2IIi system. The latter has been investigated only in solid Ne, where both emission and absorption spectra were recorded; observed fine structure has been partly interpreted in terms of slightly perturbed rotational motion in the solid. For N2, OH, and OD emission occurred from v' > 0, establishing a vibrational relaxation time in the excited electronic state of the order, of longer than, the electronic radiative lifetime. The relative emission intensity and decay times for different v' progressions in the Vegard-Kaplan system are found to depend on the rare-gas host and the N2 concentration, but are independent of temperature in the range 1.7°K to 30°K.

Part II

Static crystal field effects on the absorption, fluorescence, and phosphorescence spectra of isotopically mixed benzene crystals were investigated. Evidence is presented which demonstrate that in the crystal the ground, lowest excited singlet, and lowest triplet states of the guest deviate from hexagonal symmetry. The deviation appears largest in the lowest triplet state and may be due to an intrinsic instability of the 3B1u state. High resolution absorption and phospho- rescence spectra are reported and analyzed in terms of site-splitting of degenerate vibrations and orientational effects. The guest phosphorescence lifetime for various benzene isotopes in C6D6 and sym-C6H3D3 hosts is presented and discussed.

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基于BP人工神经网络原理,利用MATLAB神经网络工具箱,以实验得到的57组气化实验数据作为样本,建立了一个以加料量和送风量为输入变量,以燃气热值、产气率、碳转化率和气化效率为输出变量,用于描述连续稳定气化过程的内循环流化床生物质气化模型。对模型的隐层节点数和训练周期改变对模拟结果的影响进行了分析,发现当隐层节点数为20,训练步骤为50步,模型的4个输出变量的模拟结果与实验结果相关系数均超过0.95;同时对该模型的预测能力进行了考察,模型预测结果与实验结果吻合良好,证明了该模型具有较强的泛化能力,为生物质内循环流化床气化系统的优化设计和自动控制提供新思路。