Effect of moisture content on conveying characteristics of pulverized coal for pressurized entrained flow gasification

During the pneumatic conveying, pulverized coal with different moisture contents may develop substantial difference in flow characteristics, whose cause is not fully understood. This study focused on influence of moisture content on conveying characteristics in an experimental test facility with the conveying pressure up to 4 MPa. The experiments included soft coal and lignite with similar density and particle size. With the increase in moisture content, the mass flow rate decreased for lignite (3.24% < M < 8.18%) but increased at first and then decreased for soft coal (0.4% < M < 6.18%) at same operating parameters. The flowability of soft coal was worse than that of lignite at similar operating parameters and external moisture content. The extremal conveying moisture contents of two coal types were obtained. The particle charge and surface moisture content were investigated to indicate influence mechanism of moisture content on mass flow rate in pneumatic conveying at high pressure. Pressure drop of soft coal was greater than that of lignite for same test section. The conveying phase diagram of dense-phase pulverized coal at high pressure was obtained and the pressure drops through different test sections were compared and analyzed. The bend loss factor rose with the increase in moisture content and was independent of conveying velocity and solid-gas ratio in dense-phase pneumatic conveying at high pressure.     

Thermoacoustically driven flame motion and heat release variation in a swirl-stabilized gas turbine burner investigated by LIF and chemiluminescence

Laser-induced fluorescence and chemiluminescence, both phase-locked to the dominant acoustic oscillation, are used to investigate phenomena related to thermoacoustic instability in a swirl-stabilized industrial scale gas turbine burner. The observed sinusoidal phase-averaged flame motion in axial (main flow) direction is analyzed using different schemes for defining the flame position. Qualitative agreement between experimental data and theoretical analysis of the observed flame motion is obtained, interpreted as originating primarily from variation of the burning velocity. The heat release variation during an acoustic cycle is determined from the sinusoidally varying total OH* chemiluminescence intensity.

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Consecutive chemical reactions in an annular reactor with non-newtonian flow

The purpose of this paper is to analyze the homogeneous consecutive chemical reactions carried out in an annular reactor with non-Newtonian laminar flow. The fluids are assumed to be characterized by a Ostwald-de Waele (powerlaw) model and the reaction kinetics is considered of general order. Effects of flow pseudoplasticity, dimensionless reaction rate constants, order of reaction kinetics and ratio of inner to outer radii of reactor on the reactor performances are examined in detail.Nomenclature c _A concentration of reactant A, g.mole/cm³ - c _B concentration of reactant B, g.mole/cm³ - c _A0 inlet concentration of reactant A, g.mole/cm³ - C ₁ dimensionless concentration of A, c _A/c _A0 - C ₂ dimensionless concentration of B, c _B/c _A0 - C ₁ dimensionless bulk concentration of A - C ₂ dimensionless bulk concentration of B - D _A molecular diffusivity of A, cm²/sec - D _B molecular diffusivity of B, cm²/sec - k _A first reaction rate constant, (g.mole/cm³)^1–m /sec - k _B second reaction rate constant, (g.mole/cm³)^1–n /sec - K ₁ dimensionless first reaction rate constant, k _A r ₀ ² c _A0 ^m–1 /D _A - K ₂ dimensionless second reaction rate constant, k _B r ₀ ² c _A0 ^n–1 /D _B - K apparent viscosity, dyne(sec) ^m /cm² - m order of reaction kinetics - n order of reaction kinetics - P pressure, dyne/cm² - r radial coordinate, cm - r _i radius of inner tube, cm - r _max radius at maximum velocity, cm - r _o radius of outer tube, cm - R dimensionless radial coordinate, r/r _o - s reciprocal of rheological parameter for power-law model - u local velocity, cm/sec - u _max maximum velocity, cm/sec - u bulk velocity, cm/sec - U dimensionless velocity, u/u - z axial coordinate, cm - Z dimensionless axial coordinate, zD _A/r ₀ ² /u - ratio of molecular diffusivity, D _B/D _A - ratio of inner to outer radius of reactor, r _i/r _o - ratio of radius at maximum velocity to outer radius, r _max/r _o     

Liquid fuel droplets entrained in the transient unidimensional gas flow in a pipe

Studies of fuel droplets entrained in air flow are deemed to be important in the understanding of fuel transportation and evaporation in the induction system of spark-ignition engines. So far the studies by other authors were restricted to steady air flow, however, the air flow in the induction system is pulsative unsteady air flow. This paper presents a theoretical model and the computational solution for the fuel liquid droplets entrained in the transient unidimensional air flow in a pipe.     

Consecutive chemical reactions in a turbular reactor with turbulent flow

Homogeneous consecutive chemical reactions in turbulent flow system is analyzed in this paper. Arbitrary chemical reaction order is considered. The governing nonlinear material balance equations are solved numerically on a digital computer. It is seen from the preliminary numerical results that high Reynolds and Schmidt numbers significantly increase both reaction velocities.Nomenclature c _i concentration of i species, g. mole/cm³ - C _i dimensionless concentration of i species, c _i /c _A0 - c _A0 inlet concentration of A, g. mole/cm³ - D _i molecular diffusivity of i species, cm²/sec. - f Fanning friction factor - k ₁ first reaction rate coefficient, (g. mole/cm³)^1–m /sec. - k ₂ second reaction rate coefficient, (g. mole/cm³)^1–n /sec. - K ₁ dimensionless first reaction rate coefficient, k ₁ r ₀ ² c _A0 ^–1 /D _A - K ₂ dimensionless second reaction rate coefficient, k ₂ r ₀ ² c _A0 ^–1 /D _A - m order of the first chemical reaction - n order of the second chemical reaction - r radial distance, cm - r ₀ reactor radius, cm - R dimensionless radial distance, r/r ₀ - Re Reynolds number, r ₀ / - Sc Schmidt number, D/ - u local velocity, cm - bulk velocity, cm - U dimensionless local velocity, u/ - X, Y dimensionless concentrations of A and B, c _i /c _A 0 - xxx0058;, xxx0059; dimensionless bulk concentrations of A and B - z axial distance, cm - Z dimensionless axial distance, zD _A /r ₀ ² - ratio of eddy mass diffusivity to eddy viscosity, / - eddy mass diffusivity, cm²/sec. - kinematic viscosity, cm²/sec.     

Characteristics of flow from an oxy-fuel burner with separated jets: influence of jet injection angle

This paper presents an experimental study of flow development and structure on a separated jet burner in reacting and non-reacting flows. Effects of deflection jets in an aligned configuration of three round jets are emphasized. The idea is based on the confinement of a central jet of fuel by two side jets of oxygen to improve mixing, to control flame stability, and to reduce pollutant emissions. The fields of mean velocity and fluctuation intensity were measured using Particle Image Velocimetry. The deflection of jets has a considerable effect on the dynamic behavior and on the flame characteristics. Results showed that the deflection of jets favors mixing and accelerates merging and combining of jets to a single one. Measurements in reacting flow showed a high influence of combustion on dynamic fields. Compared to non-reactive case, in combustion, larger radial expansion and higher velocity were observed, particularly, above the stabilization point of the flame.     

Euler-Lagrange/DEM simulation of wood gasification in a bubbling fluidized bed reactor

We present an Euler–Lagrange method for the simulation of wood gasification in a bubbling fluidized bed. The gas phase is modeled as a continuum using the 2D Navier–Stokes equations and the solid phase is modeled by a Discrete Element Method(DEM)using a soft-sphere approach for the particle collision dynamic. Turbulence is included via a Large-Eddy approach using the Smagorinsky sub-grid model.The model takes into account detailed gas phase chemistry,zero-dimensional modeling of the pyrolysis and gasification of each individual particle,particle shrinkage,and heat and mass transfer between the gas phase and the particulate phase.We investigate the influence of wood feeding rate and compare exhaust gas compositions and temperature results obtained with the model against experimental data of a laboratory scale bubbling fluidized bed reactor.     

High-intensity turbulence measurements in a Taylor-Couette flow reactor

Turbulence-intensity measurements were made in a Taylor-Couette flow reactor consisting of two counter-rotating concentric cylinders designed for the purpose of studying turbulent premixed-flame propagation. In the annulus separating the two cylinders, a nearly homogeneous turbulent flow is generated. The intensities of turbulent velocity fluctuations in the annulus in both axial and circumferential directions were measured by using laser-Doppler velocimetry for a wide range of cylinder rotation rates, corresponding to low through high (120 cm/s) intensities relative to typical laminar flame speeds for lean methane-air mixtures. The experimental measurements indicate a linear relation between turbulence intensities and average cylinder surface speed and demonstrate the usefulness of the Taylor-Couette apparatus for studies of premixed-flame propagation in high-intensity turbulent flow.     

The stability of steady regimes in an isothermal chemical flow reactor

One of the fundamental problems in the theory of chemical reactors is the determination of the number of steady regimes and their stability. The problem of the number of steady regimes has been considered in many studies, for example, in [1–4]. The stability of a steady regime is usually established from an analysis of the behavior of small perturbations. The corresponding linear boundary-value problem for perturbations has been studied mainly in the limiting cases of ideal mixing and ideal displacement. When account was taken of longitudinal mixing, the only criteria obtained were ones which imposed fairly severe restrictions on the parameters [5]. In the present study numerical analysis is used in order to investigate the stability of steady concentration distributions in an isothermal chemical flow reactor with longitudinal mixing in the case of a single chemical reaction. The eigenvalues were obtained for the Sturm-Liouville problem, which fully characterize the stability for several laws of variation of the chemical reaction rate as a function of the concentration. A knowledge of the eigenvalues is essential, for example, in order to construct the stabilization system proposed in [6] for the unsteady regime.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 179–182, March–April, 1985.     

Experiments and simulations of gas-solid flow in an airlift loop reactor

The hydrodynamics in a gas-solid airlift loop reactor was investigated systematically using experimental measurements and CFD simulation.In the experiments,the time averaged parameters,such as solid fraction and particle velocity,were measured by optical fiber probe.In the simulation,the modified Gidaspow drag model accounting for the interparticles clustering was incorporated into the Eulerian-Eulerian CFD model with particulate-phase kinetic theory.Predicted values of solid fraction and particle velocity ...     

Wall effects on close-to-equilibrium flow in a tubular reactor

The deviation from local homogeneous chemical equilibrium flow due to non-catalytic heterogeneous reactions in a tubular reactor is analysed by an asymptotic expansion for large Damköhler numbers. Close to the reacting surface a boundary layer is shown to exist where the effects of the homogeneous and the heterogeneous reaction have an influence of the same order of magnitude. The extension of this boundary layer into the equilibrium flow is proportional to the inverse of the square root of the Damköhler number. The boundary layer equation is derived and solved for a particular example.     

Euler–Lagrange/DEM simulation of wood gasification in a bubbling fluidized bed reactor

We present an Euler–Lagrange method for the simulation of wood gasification in a bubbling fluidized bed. The gas phase is modeled as a continuum using the 2D Navier–Stokes equations and the solid phase is modeled by a Discrete Element Method (DEM) using a soft-sphere approach for the particle collision dynamic. Turbulence is included via a Large-Eddy approach using the Smagorinsky sub-grid model. The model takes into account detailed gas phase chemistry, zero-dimensional modeling of the pyrolysis and gasification of each individual particle, particle shrinkage, and heat and mass transfer between the gas phase and the particulate phase. We investigate the influence of wood feeding rate and compare exhaust gas compositions and temperature results obtained with the model against experimental data of a laboratory scale bubbling fluidized bed reactor.     

Investigation of the optimum longitudinal mixing regime in an isothermal chemical flow reactor

A one-dimensional isothermal flow reactor with longitudinal mixing is examined. The known asymptotic results are analyzed and used as a basis for formulating the conditions and initial values of the parameters for a numerical investigation by the parameter mapping method. The object of the investigation is to construct the exact boundaries of the regions of variation of the characteristic parameters in which the maximum extent of reaction is achieved in one of the limiting (Pe=0 and Pe=) or intermediate (0相似文献   

Numerical simulation of the flow field in a thermal plasma reactor

A numerical simulation is presented for a thermal plasma reactor with particle-trajectory model in this paper.Turbulance is considered by using simple SGS model.Thegoverning equations are solved by means of the algorithm of SIMPLER.The calculatedresults give the velocity and the temperature fields within plasma reactor,and thetrajectories of the injected particles.     

Development of a high performance flexible porous burner(FPMB) with an adjustable cooling effect

A high performance flexible porous medium burner that can burn gaseous and liquid fuel with different type of flames(premixed and non-premixed) is proposed. The merit of the combustion within porous medium is that heat is recirculated from the combustion gas to porous medium at upstream wherein vaporization is taken place(in case of liquid fuel) or preheated(in case of gaseous fuel) before mixing with the combustion air followed by combustion within another porous medium at downstream. In a former version of the high performance flexible porous medium burner, the upstream porous medium is incorporated with a cooling system using the combustion air as a coolants to prevent thermal decomposition of fuels and thus the burner clogging caused by carbon deposit within the porous medium can be avoided. However, the cooling effect cannot be properly controlled such that the boiling point of the liquid fuel is maintained at suitable value irrespective of the volume flow rate of the combustion air,which is linearly varied with the firing rate of the burner. In particular at the lean burn condition, where high air flow rate is required with high cooling effect with porous medium. This can result in the porous medium temperature lower than the corresponding boiling point of the liquid fuel and thus evaporation of the fuel is failed and the combustion is ceased. Therefore, method of controlling the cooling air flow rate in the porous medium is proposed and studied in order to appropriately control the porous medium temperature and maintain it at above the boiling point irrespective of the combustion conditions. In this research, experimental and computation analysis are used to design the flexible porous burner(FPMB),with adjustable cooling effect. The result shows that, the new design of FPMB which has temperature in the upstream porous medium is higher than boiling point and lower than thermal decomposition temperature of fuel(kerosene) at all conditions and can be operated at a wide range of equivalence ratio without fuel decomposition and fuel non-vaporization problem.     

Fuel-oil concentration in a gas turbine burner measured with laser-induced fluorescence

We applied the technique of two-dimensional laser-induced fluorescence to measure relative local concentrations of the evaporated fuel oil in a premixed gas turbine burner. The dependence of the fuel-oil fluorescence in the burner on the air inlet temperature, on the total fuel mass flow, and on the residence time of the fuel was investigated. A Mie scattering experiment was performed in order to observe non-evaporated fuel oil. We conclude that the fuel-oil concentrations can be determined from the fluorescence intensity within an error of about 25% in regions of complete evaporation of the fuel oil. Received: 29 March 1999/Accepted: 5 January 2000