Effect Of Distributor Design Research Articles

Effect of distributor design on particle distribution in a binary fluidised bed

The influence of distributor design, including orifice size, number and positioning, on the behaviour of a gas-fluidised granular bed has been studied experimentally. The use of Positron Emission Particle Tracking (PEPT) to non-invasively probe the system's three-dimensional dynamics has allowed the extent of (de)fluidisation and the homogeneity of particle distribution to be quantitatively characterised. While increasing the number of orifices demonstrates a clear, positive influence on both fluidisation quality and homogeneity, the data obtained suggest that the orifice size and positioning play a more complex role.

Horizontal gas mixing in rectangular fluidized bed: A novel method for gas dispersion coefficients in various conditions and distributor designs

Abstract In a rectangular fluidized bed combustor, the tracer gas is injected continuously into the bed from a point source at the center of the distributor plate. In this study, a general governing equation is formulated for tracer gas dispersion in the bed. An analytical solution is derived to estimate the dispersion coefficients, D x and D y , in a horizontal plane. The concentration profiles at different sampling heights with various gas velocities are plotted. Subsequently, to estimate the dispersion coefficients, surface fitting of the obtained analytical solution to the experimental data is performed. The dispersion coefficients obtained from this model are compared with those of a conventional model. Additionally, the effect of walls, bed height and gas injection rate on the dispersion coefficients in a horizontal plane is investigated, and the effect of distributor design on the dispersion coefficients in a horizontal plane is investigated with different tracer positions. It is found that D x and D y are nearly equivalent at a lower tracer gas ratio of the injected gas to the total gas flow rate. It is also demonstrated that the effect of bed height on D x is minor. This model is also able to estimate the dispersion coefficients in the case of a multi-horizontal nozzle distributor.

Study of the Hydrodynamics and Mass Transfer Coefficient in a 2D Mimicked FT Slurry Bubble Columns for Alternative Clean Energy and Chemical Production

Abstract Bubble columns are widely used for contacting gas–liquid and gas–liquid–solid mass transfer/chemical reactions. Gas distributor is the most important accessory because it decides the bubble size/rise velocity and gas distribution. In this study, the effect of distributor design on hydrodynamics and mass transfer coefficient are studied at different operating conditions of height to diameter ratio, solid loading, and superficial gas velocity The overall gas holdup, is studied experimentally using a rectangular slurry bubble column operating at ambient temperature and pressure, using liquid paraffin (C9–C11), three heights to diameter ratios (6, 7.5 and 10) and silica as a solid phase (0 %, 9 % and 25 %) with oxygen as gas phase. Two types of distributor were used, perforated plate and ring type. The results showed that the overall gas holdup increased by increasing gas velocity and decreased by increasing height to diameter ratio and solid loading. Also, it is found that the perforated plate distributor gave a higher gas hold up than ring distributor at gas velocity higher than 0.03 m/sec. The following correlations are obtained: Plate distributor at presence of silica particles: ε g = 1.343 U g 0.0612 − 0.00891 ε s − 0.374 − 0.702 L D 0.041 4.904 − 0.0251 $$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} =& {\left({1.343{\rm{U}}_{\rm{g}}^{0.0612} - 0.00891{\rm{\varepsilon}}_{\rm{s}}^{- 0.374} - 0.702{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.041}}} \right)^{4.904}}\cr& - 0.0251}$$ Ring distributor at presence and absence of silica particles: ε g = 0.216 U g 0.297 − 0.354 ε s 1.4671 − 0.127 L D 0.147 1.1206 + 0.058 $$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} = &{\left({0.216{\rm{U}}_{\rm{g}}^{0.297} - 0.354{\rm{\varepsilon}}_{\rm{s}}^{1.4671} - 0.127{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.147}}} \right)^{1.1206}} \cr&+ 0.058}$$ There is a good agreement between experimental and predicted values with a percent of error less than 2 %. It has been found that the mass transfer coefficient is higher for ring distributor than the perforated plate and growing higher for heterogeneous flow regime and higher solid loading.

The impact of flow distribution on column performance: A computational fluid dynamics study

In this manuscript, the band broadening contribution of a generic flow distributor and collector has been calculated using computational fluid dynamics (CFD). The effects of distributor design and operating conditions on distributor performance have been studied. The non uniform flow fields in the distributor cause band deformation and an increase in volumetric band variance (σv2). This volumetric band variance was calculated to be about 0.2 μl2 at the inlet of a 4.6mm ID column and 0.3μl2 at the outlet for a flow rate of 2ml/min. For a 2.1mm column the volumetric band variance is about 0.002μl2 for a flow rate of 0.41ml/min. For current column performance the measured contributions are negligible in practice, probably because designs have been empirically improved together with improving column performance. None the less, the simulations show that bad distributor design can be detrimental for column performance.

Effect of Distributor Design on Gas-Liquid Distribution in Monolithic Bed at High Gas/Liquid Ratios

Experiments were carried out to investigate the liquid flow distribution at high gas/liquid ratios in a cold model monolith bed of a 0.048 m diameter with 62 cells per cm2. Three types of distributor for the liquid distribution were used to evaluate their distribution performance. Local liquid saturation in individual channels was measured using 16 single-point optical fiber probes mounted inside the channels. The results indicate that 1) The optical fiber probe technique can measure phase distribution in the monolith bed; 2) Liquid saturation distribution along the radial direction of the monolith bed is not uniform and the extent of non-uniformity depends on the distributor design and phase velocities; and 3) The tube array distributor provides superior liquid distribution performance over the showerhead and nozzle distributors.

Pressure drop and liquid hold-up in multiphase monolithic reactor with different distributors

Total pressure drop and liquid hold-up in two different monolith packings have been investigated experimentally in the co-current downward flow mode with a reactor diameter of 0.1 m and 0.6 m high monolith packing operating in the Taylor flow regime. The effect of distributor design on the flow distribution was investigated using two different types of distributor (nozzle distributor and packed bed distributor with 1 mm glass beads). A close relation of the distributor design to the hydrodynamics in monolith beds was observed to exist, evidenced by the larger pressure drop and liquid hold-up values for the monolith packings with an accompanying use of the packed bed distributor, as compared with the use of the nozzle distributor. An explanation for this phenomenon is the better gas and liquid distribution capability the packed bed has. By taking account of the effect of the liquid slug lengths, correlations were derived for predicting the two-phase friction factor and liquid hold-up and satisfactorily describe the experimental data. Finally an analysis of the unstable flow phenomenon characterized by negative pressure drops within bed shows that the unstable region is not only dependent on the operating conditions and properties of monolith but also on the distributor design.

Effect of Distributor Design on the Bottom Zone Hydrodynamics in a Fluidized Bed Dryer Using 1-D X-ray Densitometry Imaging

The hydrodynamics near the base of a 15 cm i.d. fluidized-bed dryer having perforated, punched, and porous plate distributors have been studied using one-dimensional X-ray densitometry imaging. The time-averaged solids concentration profiles of dry pharmaceutical granule and wet granule undergoing drying were compared. The porous plate creates good gas distribution over the bed cross section with dry granule but results in defluidization at the distributor level when the granule is wet. The perforated and punched plates exhibit different solids concentration profiles with dry granule; however, the presence of moisture results in similar hydrodynamics between the plates during drying. Standard deviation analysis of the high-frequency solids concentration data was used to corroborate the results of the time-averaged solids concentration measurements.

The effect of distributor design on gas dispersion in a bubbling fluidized bed

In this study, the behavior of gas dispersion in a bubbling fluidized bed was investigated. Carbon dioxide was used as the tracer gas. Most of the gas jets from tuyeres are towards the same direction, parallel with the longitudinal axis. The movement of particles in the lateral direction was enhanced by the momentum of horizontal gas jets within the bed. The experimental results show that the effect of superficial gas velocity on the gas mixing depends on the distributor type. Comparing with perforated distributor, a better performance of gas mixing was observed while the bed was equipped with horizontal nozzle distributor.

Axial flow structure in the entrance region of downer fluidized bed: Effects of the distributor design

Compared to riser reactors, downer reactors have reduced gas and solids segregation and more uniform flow structure which enhance the gas–solids contacting efficiency and eventually result in more uniform product distributions within shorter residence times. However, little research has been reported on the entrance region and/or on the effect of distributor design, although this is a very important issue. In this study, a cold model downer unit (9.3 m tall and 0.10 m i.d.) with three distributor designs was used to test the gas–solids flow conditions in the entrance region. Pressure gauges were employed to measure the pressure gradient profiles, while fibre-optic probes were used to measure particle velocity and solids holdup. The development of the axial gas–solids flow is found to be highly dependent on distributor type. Pre-acceleration of the particles inside the solids distributor tubes and high-velocity gas nozzles that provide significant momentum can effectively shorten the particle acceleration length. Increased wall friction can increase the acceleration length. For higher superficial gas velocity, the rate of acceleration increases given the increased gas drag, but the acceleration length is also extended because the equilibrium particle velocity is higher.

Enzyme and protein mass transfer coefficient in aqueous two-phase systems—I. Spray extraction columns

Fractional dispersed phase hold-up and dispersed side mass transfer coefficients for bovine serum albumin (BSA) and amyloglucosidase were measured in 22, 34, 50, 56, 70 and 95 mm i.d. spray columns using salt-polyethylene glycol (potassium phosphate-PEG and sodium sulphate-PEG) systems. The effect of distributor design and column height were investigated. The effect of phase compositions of the aqueous phase system was also studied. Empirical and semi-empirical correlations have been developed for fractional dispersed phase hold-up and dispersed side mass transfer coefficients.

Airblast atomization of micronized coal slurries using a twin-fluid jet atomizer

Airblast atomization of micronized coal water slurries was carried out at low atomizing air pressures (< 270k Pa) using twin-fluid jet atomizers of various distributor designs. Drop size and size distribution were measured using the laser diffraction technique. It was found that the atomized drop sizes of micronized coal water slurries substantially decrease as the atomizing air pressure exceeds a threshold value. In addition, the atomized drop size, represented by the mass median diameter scaled to a characteristic atomizer length ( MMD L c ), can be described by wave mechanism based models in terms of three non-dimensional groups, the slurry to air mass ratio ( s A ), the Weber number (We) and the Ohnesorge number (Z): MMD L c = (1 + S A )(x 2We −x 1 + x 3Z jx 1 ) where j = 1 and 2, We equals the ratio of aerodynamic force to surface tension and Z represents the viscous effect. The linear dependency on ( 1 + S A ) is based on momentum balance and energy considerations. The three parameters ( x i , i = 1−3) are determined by the best least-squares fit of the equation to the experimental results using the iterative generalized inverse method. Excellent agreement with coefficients of correlation of 0.97–0.98 has been obtained. The presence of coal particles causes a broader drop size distribution curve compared to pure viscous liquids. Nevertheless, the effects of coal volume fraction and liquid composition on slurry atomization can be accounted for by their effects on slurry rheology. Whereas the slurry pseudoplasticity plays a significant role in slurry atomization, the high shear slurry viscosity based on the free stream slurry velocity during atomization dictates the atomized drop sizes. The effects of distributor design on airblast atomization can be accounted for by its effects on the Weber number and the air mass flow rate.

THE EFFECTS OF DISTRIBUTOR DESIGN ON FLUIDIZED-BED HYDRODYNAMIC BEHAVIOR

should be addressed. The distributor was investigated for the purpose of design and scale up of large fluidized-bed combustors. Four orifice plates with different configurations were used to study the effect of distributor design on bubble formation and solid mixing. Experiments were carried out on a three-dimensional fluidized bed of 27.94 cm diameter and a two-dimensional bed with dimensions of 30.48cm ×1.27 cm. Motion pictures were used to study bubble formation and coalescence. Pressure profiles inside the three-dimensional bed were measured for several distributors to study bubble flow patterns, and tracer particles were used to study mixing patterns at various superficial velocities and particle sizes. The results show that the distributor plate with two-size orifices causes a non-uniform gas bubble flow inside the bed. This non-uniform gas bubble flow is associated with variations in local bed density and local voidage. Horizontal or radial solid circulation is also caused by this non-uniform gas b...

Effect of distributor design on heat transfer from an immersed horizontal tube in a fluidized bed

Experiments have been carried out to examine the effect of distributor design on the total heat transfer coefficient between a 12.7 mm diameter electrically heated copper tube and a square fluidized bed (0.305 m × 0.305 m) of glass beads ( d p = 265, 357 and 427 μm). The distributors are two perforated plates of different open area with a cloth sandwiched between them. The effect of distributor design on the total heat transfer coefficient is explained on the basis of its effect on the initial bubble size and frequency.

Effect of distributor design on heat transfer from an immersed horizontal tube in a fluidized bed

Experiments have been carried out to examine the effect of distributor design on the total heat transfer coefficient between a 12.7 mm diameter electrically heated copper tube and a square fluidized bed (0.305 m × 0.305 m) of glass beads ( d p = 265, 357 and 427 μm). The distributors are two perforated plates of different open area with a cloth sandwiched between them. The effect of distributor design on the total heat transfer coefficient is explained on the basis of its effect on the initial bubble size and frequency.

Design of gas distributors and prediction of bubble size in large gas—solids fluidized beds

Current methods for the process design of gas distributors for fluidized beds are based on empirical “rules of thumb” and do not take into consideration the effect of distributor design on bubble size in the bed. A method for designing the distributor plate in a large fluidized bed to give a specified bubble size-range is presented here. For a given distributor in a fluidized bed the method may also be used to estimate bubble size. The present predictions are in good agreement with observed bubble size in a 1.22 m × 1.22 m square fluidized bed reported by Whitehead and Young.

Fluidisation studies in large gas-solid systems Part II: The effect of distributor design and solid properties on fluidisation quality

The effects of change in solid properties and distributor design on fluidisation character have been measured using an array of void sensors arranged in a square pattern. The investigation covered two types of multituyered gas distributor and two silica sands with different size distributions and different incipient fluidising velocities, in beds 4ft. square and up to 9ft. deep. The more complex gas distributor did not produce a significantly better dispersion of gas in the upper region of a bed. For both types of sand the volume of void recorded by the probe was the same function of the gas flow in excess of incipient fluidising velocity. A new measure of fluidisation character, the mean continuous horizontal void length, is discussed and a relatively simple method of measurement is suggested.