共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Antony Raja Z. Robert KennedyAuthor VitaeB.C. PillaiAuthor Vitae C. Lindon Robert LeeAuthor Vitae 《Energy》2010
Fluidized bed flash pyrolysis experiments have been conducted on a sample of jatropha oil cake to determine particularly the effects of particle size, pyrolysis temperature and nitrogen gas flow rate on the pyrolysis yields. The particle size, nitrogen gas flow rate and temperature of jatropha oil cake were varied from 0.3 to 1.18 mm, 1.25 to 2.4 m3/h and 350 to 550 °C. The maximum oil yield of 64.25 wt% was obtained at a nitrogen gas flow rate of 1.75 m3/h, particle size of 0.7–1.0 mm and pyrolysis temperature of 500 °C. The calorific value of pyrolysis oil was found to be 19.66 MJ/kg. The pyrolysis gas can be used as a gaseous fuel. 相似文献
2.
This study, performed in the context of GAYA project, focuses on the development of a simple predictive model about steam gasification of char from woodchips fast pyrolysis. A semi-empirical model was developed through experiments in a macro thermogravimetric analyzer which owns the peculiar ability of fast heating, as well as to deal with macro-size particles and higher mass loads compared to conventional TGA. The experimental results show that gasification is controlled by chemical kinetics and internal transfer phenomena. During gasification, char particles can be considered as isothermal in a given range of temperatures and particle sizes, more likely for low values. The gasification model was based on the effectiveness factor, which involves the chemical kinetics and diffusion rate. The chemical kinetics were expressed by a classical Arrhenius law, whereas empirical expressions from mathematical fitting of the experimental data were established for the diffusion coefficient and surface function. The diffusion coefficient from this work is suspected to probably include supplementary rate limiting phenomena, apart from steam porous diffusion, such as H2 inhibition and/or the decrease of temperature within char particles because of the endothermic character of gasification. The model globally predicts with accuracy the gasification rate in typical operating conditions of a fluidized bed reactor. For its simplicity and reliability, this approach can be used for the modelling of char gasification in the conditions of interest. 相似文献
3.
Antonio Galgano Piero Salatino Silvestro Crescitelli Fabrizio Scala Pier Luca Maffettone 《Combustion and Flame》2005,140(4):371-384
A dynamical model of an atmospheric, bubbling, fluidized bed combustor of biomass is presented. The model, based on one previously developed for the steady combustion of high-volatile solids, accounts for the fragmentation and attrition of fuel particles, the segregation and postcombustion of volatile matter above the bed, as well as thermal feedback from the splashing region to the bed. The model was used to assess how the dynamic behavior of the combustor varies with some of the operating parameters. To this end, a bifurcation analysis was first used to study the influence of selected parameters on the number and quality of steady state solutions. Moreover, direct integration of the governing equations provided a simulation of the dynamic behavior of the combustor after perturbing the parameters. Results of the bifurcation analysis indicated that extinction may take place through limit point bifurcations when varying the moisture content of the biomass and the flow rates of feed or air. Dynamic simulations showed that the bed temperature changes slowly when a stepwise change is imposed on one of the parameters. Either a new steady state or extinction eventually results, depending on the stepwise change. While relaxation of the bed temperature occurs rather slowly, the dynamics of the splashing region and of the freeboard are much faster, due to the shorter time-scales associated with homogeneous oxidation reactions. The relaxation time of the bed is determined by the heat capacity of the fluidized solids and by the fraction of the heat released recycling to the bed as thermal feedback. 相似文献
4.
Mohammad A. Rakib John R. Grace Said S.E.H. Elnashaie 《Journal of power sources》2010,195(17):5749-3129
n-Heptane served as a model compound to study steam reforming of naphtha as an alternative feedstock to natural gas for production of pure hydrogen in a fluidized bed membrane reactor. Selective removal of hydrogen using Pd77Ag23 membrane panels shifted the equilibrium-limited reactions to greater conversion of the hydrocarbons and lower yields of methane, an intermediate product. Experiments were conducted with no membranes, with one membrane panel, and with six panels along the height of the reactor to understand the performance improvement due to hydrogen removal in a reactor where catalyst particles were fluidized. Results indicate that a fluidized bed membrane reactor (FBMR) can provide a compact reformer for pure hydrogen production from a liquid hydrocarbon feedstock at moderate temperatures (475-550 °C). Under the experimental conditions investigated, the maximum achieved yield of pure hydrogen was 14.7 moles of pure hydrogen per mole of heptane fed. 相似文献
5.
N. RangelC. Pinho 《Biomass & bioenergy》2011,35(10):4124-4133
In this work it is studied the combustion of batches of wood char particles in a shallow fluidized bed at laboratory scale. Commercial and recarbonized chars from nut pine and cork oak parent woods were burned for bed temperatures of 600-750 °C and particle sizes range of 1.8-3.6 mm. A combustion model based on the two-phase theory of fluidization is presented to evaluate the global combustion resistance. Sherwood numbers and kinetic constants for the heterogeneous phase reaction are also assessed. Through the comparison among theoretical and experimental results, conclusions are drawn on the combustion mechanism as well as on the combustion controlling resistance. The Arrhenius law is proposed to predict the kinetic constants for the studied chars. 相似文献
6.
Mohammad A. Rakib John R. Grace C. Jim Lim Said S.E.H. Elnashaie Bahman Ghiasi 《International Journal of Hydrogen Energy》2010
Steam reforming of propane was carried out in a fluidized bed membrane reactor to investigate a feedstock other than natural gas for production of pure hydrogen. Close to equilibrium conditions were achieved inside the reactor with fluidized catalyst due to the very fast steam reforming reactions. Use of hydrogen permselective Pd77Ag23 membrane panels to extract pure hydrogen shifted the reaction towards complete conversion of the hydrocarbons, including methane, the key intermediate product. Irreversible propane steam reforming is limited by the reversibility of the steam reforming of this methane. To assess the performance improvement due to pure hydrogen withdrawal, experiments were conducted with one and six membrane panels installed along the height of the reactor. The results indicate that a compact reformer can be achieved for pure hydrogen production for a light hydrocarbon feedstock like propane, at moderate operating temperatures of 475–550 °C, with increased hydrogen yield. 相似文献
7.
Yingshuang Shi Xiaoze DuLijun Yang Ying SunYongping Yang 《International Journal of Hydrogen Energy》2013
A novel approach for the hydrogen production which integrated methanol steam reforming and fluidized bed reactor (FBR) was proposed. The reaction was carried out over Cu/ZnO/Al2O3 catalysts. The critical fluidized velocities under different catalyst particle sizes and masses were obtained. The influences of the operating parameters, including that of H2O-to-CH3OH molar ratio, feed flow rate, reaction temperature, and catalyst mass on the performance of methanol steam reforming were investigated in FBR to obtain the optimum experimental conditions. More uniform temperature distribution, larger surface volume ratio and longer contacting time can be achieved in FBR than that in fixed bed reactor. The results indicate that the methanol conversion rate in FBR can be as high as 91.95% while the reaction temperatures is 330 °C, steam-to-carbon molar ratio is 1.3, and feed flow rate is 540 ml/h under the present experiments, which is much higher than that in the fixed bed. 相似文献
8.
Hydrogen production from steam reforming of glycerol in a fluidized bed reactor has been simulated using a CFD method by an additional transport equation with a kinetic term. The Eulerian–Eulerian two-fluid approach was adopted to simulate hydrodynamics of fluidization, and chemical reactions were modelled by laminar finite-rate model. The bed expansion and pressure drop were predicted for different inlet gas velocities. The results showed that the flow system exhibited a more heterogeneous structure, and the core-annulus structure of gas–solid flow led to back-mixing and internal circulation behaviour, and thus gave a poor velocity distribution. This suggests the bed should be agitated to maintain satisfactory fluidizing conditions. Glycerol conversion and H2 production were decreased with increasing inlet gas velocity. The increase in the value of steam to carbon molar ratio increases the conversion of glycerol and H2 selectivity. H2 concentrations in the bed were uneven and increased downstream and high concentrations of H2 production were also found on walls. The model demonstrated a relationship between hydrodynamics and hydrogen production, implying that the residence time and steam to carbon molar ratio are important parameters. The CFD simulation will provide helpful data to design and operate a bench scale catalytic fluidized bed reactor. 相似文献
9.
Catalytic steam reforming of bio-oil is a promising process for producing hydrogen in a sustainable environmentally friendly way that can improve the utilization of local resources (natural sources or wastes). However, there remain drawbacks such as coke formation that produce operational problems and deactivation of the catalysts. Coprecipitated Ni/Al catalysts are here used in a fluidized bed for reforming at 650 °C of acetic acid as a model compound of bio-oil–aqueous fraction. Different strategies are applied in order to study their effects on the catalytic steam reforming process: modification of the catalyst by increasing the calcination temperature or adding promoters such as calcium. The addition of small quantities of oxygen is also tested resulting in an optimum percentage to achieve a high carbon conversion process with less coke and without a hydrogen yield penalty production. The results for catalytic steam reforming are compared with other ones from literature. 相似文献
10.
A model for the oxidative pyrolysis of wood 总被引:1,自引:0,他引:1
A generalized pyrolysis model (Gpyro) is applied to simulate the oxidative pyrolysis of white pine slabs irradiated under nonflaming conditions. Conservation equations for gaseous and solid mass, energy, species, and gaseous momentum (Darcy’s law approximation) inside the decomposing solid are solved to calculate profiles of temperature, mass fractions, and pressure inside the decomposing wood. The condensed phase consists of four species, and the gas that fills the voids inside the decomposing solid consists of seven species. Four heterogeneous (gas/solid) reactions and two homogeneous (gas/gas) reactions are included. Diffusion of oxygen from the ambient into the decomposing solid and its effect on local reactions occurring therein is explicitly modeled. A genetic algorithm is used to extract the required material properties from experimental data at 25 kW/m2 and 40 kW/m2 irradiance and ambient oxygen concentrations of 0%, 10.5% and 21% by volume. Optimized model calculations for mass loss rate, surface temperature, and in-depth temperatures reproduce well the experimental data, including the experimentally observed increase in temperature and mass loss rate with increasing oxygen concentration. 相似文献
11.
Genyin Ye Donglai Xie Weiyan Qiao John R. Grace C. Jim Lim 《International Journal of Hydrogen Energy》2009
Hydrogen production via steam methane reforming with in situ hydrogen separation in fluidized bed membrane reactors was simulated with Aspen Plus. The fluidized bed membrane reactor was divided into several successive steam methane sub-reformers and membrane sub-separators. The Gibbs minimum free energy sub-model in Aspen Plus was employed to simulate the steam methane reforming process in the sub-reformers. A FORTRAN sub-routine was integrated into Aspen Plus to simulate hydrogen permeation through membranes in the sub-separator based on Sieverts' law. Model predictions show satisfactory agreement with experimental data in the literature. The influences of reactor pressure, temperature, steam-to-carbon ratio, and permeate side hydrogen partial pressure on reactor performances were investigated with the model. Extracting hydrogen in situ is shown to shift the equilibrium of steam methane reactions forward, removing the thermodynamic bottleneck, and improving hydrogen yield while neutralizing, or even reversing, the adverse effect of pressure. 相似文献
12.
Ragnar Warnecke 《Biomass & bioenergy》2000,18(6):489-497
Gasification as a thermochemical process is defined and limited to combustion and pyrolysis. A systematic overview of reactor designs categorizes fixed bed and fluidized bed reactors. Criteria for a comparison of these reactors are worked out, i.e. technology, use of material, use of energy, environment and economy. A utility analysis for thermochemical processes is suggested. It shows that the advantages of one of the reactor types are marginal. An advantage mainly depends on the physical consistency of the input. As a result there is no significant advantage for the fixed bed or the fluidized bed reactor. 相似文献
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In this work, we model a countercurrent tubular reactor where an automotive shredder residue (ASR) is subject to pyrolysis. An inert gas is adopted to convey the pyrolysis products; the solid entering the reactor undergoes an endothermic chemical process which is very sensitive with respect to the temperature. Pressure effects and friction loss of the gas phase are taken into account to better match the real operative conditions. The reaction is modelled by a system of boundary-value differential-algebraic equations (DAEs) where the thermodynamic variables of both phases are investigated with respect to the axial coordinate of the tube. This algorithmic strategy has shown a greater robustness and reliability in comparison with a more traditional approach relying upon well-known ODE solver codes. In particular, the effects of different gas-solid ratios on conversion and the relevant configurations in the inner phase geometries have been investigated. 相似文献
16.
P. Ammendola R. Chirone G. Ruoppolo G. Russo R. Solimene 《International Journal of Hydrogen Energy》2008
This paper reports a model of fluidized bed thermo-catalytic decomposition (TCD) of methane. The novelty of the model consists of taking into account the occurrence of different competitive phenomena: methane catalytic decomposition, catalyst deactivation due to carbon deposition on the catalyst particles and their reactivation by means of carbon attrition. Comparison between theoretical and experimental data shows the capability of the present model to predict methane conversion and deactivation time during the process. The model demonstrates to be also a useful tool to investigate the role played by operative parameters such as fluidizing gas velocity, temperature, size and type of the catalyst. In particular, the model results have been finalized to characterize the attrition phenomena as a novel strategy in catalyst regeneration. 相似文献
17.
The work described relates to the development of a coal-fired fluidized bed furnace for the generation of hot gases for industrial heating processes. Following a programme of coal model studies of the internal solids circulation rates between adjacent beds, a furnace test facility was developed in the form of two interconnected fluidized beds. One bed is operated as a partial gasifier/pyrolyser and the other as a char combustor. The gas produced by pyrolysis is mixed above the bed with the oxygen-rich gas from the char combustor and burns to give hot gas at temperatures of up to 1600°C. The use of low ash washed singles grade coal (13–25 mm size range) gives an overall combustion efficiency better than 98 per cent. 相似文献
18.
A two phase biomass char steam gasification kinetic model is developed in a bubbling fluidized bed with nuclear heat as source of energy. The model is capable of predicting the temperature and concentration profiles of gases in the bubble, emulsion gas and solid phases. The robust model calculates the dynamic and steady state profiles, as well as the complex parameters of fluidized bed. Three pilot scale gasifiers were simulated in order to see the effect of the H/D ratio and the bed heating dynamics in the gasification kinetics, these parameters are found to be really important in order to enhance the water-gas shift reaction, and consequently, the hydrogen production. For the system modeled, hydrogen is the principal product of the steam-only gasification, as reported in the literature data. The carbon dioxide yield seems to be smaller than the ones in other works, but these differences are due principally to the energy source (no combustion is conducted) and that char (no oxygen in the solids) was used as the carbon source. 相似文献
19.
J.L. Pinilla I. Suelves M.J. Lázaro R. Moliner J.M. Palacios 《International Journal of Hydrogen Energy》2010
CO2-free production of hydrogen via catalytic decomposition of methane (CDM) was studied in a fluidized bed reactor (FBR) using a NiCu/Al2O3 catalyst. A parametric study of the effects of some process variables, including catalyst particle size, reaction temperature, space velocity and the ratio of gas flow velocity to the minimum fluidization velocity (uo/umf), was undertaken. A mean particle size of 150 μm allows optimization of results in terms of hydrogen production without agglomeration problems. The operating conditions strongly affect the catalyst performance: hydrogen production was enhanced by increasing operating temperature and lowering space velocity. However, increases in operating temperature, space velocity and the ratio uo/umf provoked increases in the catalyst deactivation rate. At 700 °C, carbon was deposited as carbon nanofibers, while higher temperatures promoted the formation of encapsulating carbon, which led to rapid catalyst deactivation. 相似文献
20.
An auxiliary start-up system is required in fluidized bed combustors in order to heat the bed to a temperature at which coal fed to the bed will ignite and burn without producing excessive smoke. Four methods are used by the U.K. National Coal Board, the one selected for a particular application being dependent on the type of solid fuel used and the type of appliance. To illustrate the nature of the design calculations associated with start-up, the paper describes the principles of a mathematical model developed to determine the rating of burner required for the hot gas start-up approach. 相似文献