Particle fluidization experiments

In RANS codes, the weak numerical coupling of the phases makes the EL method well suited for gas turbine computations, but RANS with the EE approach may also be found for example in simulations of fluidized beds [277 335] or chemical reactors [284 272 289], two examples of two-phase flows with a high load of particles. The experience gained in the development of RANS has led to the conclusions that both approaches are useful and they are both found today in most commercial codes. Moreover, coupling strategies between EE and EL methods within the same application are considered for certain cases. In the framework of LES of gas turbines, it is interesting to compare again EL with EE formulations. 

It establishes a link between the head variation and the reduced weight of the particles. In a way, a fluidization experiment could be used as seales, since the pressure measurements allow the determination of the mass of the bed using the plateau measured on a plot such as in Figure 15.8. 

Avedesian and Davidson [62] have recently described an investigation in which carbon particles were burned in a bed of ash particles fluidized by air. The conclusion was reached that under the conditions of the experiments, chemical kinetics played no part in controlling the rate of combustion. The rate was determined by two diffusional steps ... 

Water-fluidization experiments are discussed in more detail in Chapter 12, after the derivation of a stability eriterion in Chapter 11 that is based on the full, two-phase model whieh is more appropriate for liquid-fluidized systems for which particle and fluid densities are relatively close. It will be seen, however, that the kinematic-wave velocity expression emerging from this more complete description is identical to that of the simplified, one-phase treatment considered here, eqn (9.3). 

Dry dense medium (pneumatic fluidized-bed) separation has been used, but has not received wide attention by the industry. An area of promise for future development is the use of magnetically stabilized dense medium beds by using ferro or magnetic fluids (2,10). Laboratory and pilot-scale units such as Magstream are available. In this unit, material is fed into a rotating column of water-based magnetic fluid. Particles experience centtifugal forces and... 

When heavier refractories are required because of operating conditions, insulating brick is installed next to the shell and firebrick is installed to protect the insulating brick. Industrial experience in many fields of application has demonstrated that such a hning will success-billy withstand the abrasive conditions for many years without replacement. Most serious refractory wear occurs with coarse particles at high gas velocities and is usually most pronounced near the operating level of the fluidized bed. 

In vertical disc-stirred mills the media should be in a fluidized condition (White, Media Milling, Premier Mill Co., 1991). Particles can pack in the bottom if there is not enough stirring action or feed flow or in the top if flow is too high. These conditions are usually detected by experiment. 

In wet granulation experiments, dried Ti02 particles were fed into the cylindrical air distributor (vessel), then the air distributor rotated and fluidization air was supplied. After a predetermined amount of binder liquid was sprayed, drying of products was conducted. 

CO2 adsorption capacities with dry sorbents before and after attrition were shown in Fig.3. We found variation of CO2 adsorption capacity during operation by examining effect of attrition on adsorption capacity. So, adsorption experiments for each sorbent fluidized for 30hours were carried out. As a result, percentage losses of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but those of activated carbon and activated alumina were 8.3% and 8.1% respectively. This is because retention time of molecular sieve 5A and molecular 13X decreased due to elutriation of particle generated from attrition. 

Experiments were carried out in a conical shape gas fluidized bed (0.1 m-i.d. x 0.6 m-high) that made of a transparent acryl column with an apex angle of 20°. The details of the conical fluidized beds can be found elsewhere [3]. Air velocity (Ug = 0-1.4 m/s) were measured by a flowmeter. The particle used in this study was 1.0 mm glass beads with a density of 2,500... 

Glicksman and McAndrews (1985) determined the effect of bed width on the hydrodynamics of large particle bubbling beds. Sand particles with a mean diameter of 1 mm were fluidized by air at ambient conditions. The bed width ranged from 7.6 cm to 122 cm while the other cross sectional dimension remained constant at 122 cm. Most experiments were carried out with an open bed. The bubble rise velocity increased with the bed width, in the representation of bubble velocity as... 

A mathematical model for solid entrainment into a permanent flamelike jet in a fluidized bed was proposed by Yang and Keaims (1982). The model was supplemented by particle velocity data obtained by following movies frame by frame in a motion analyzer. The experiments were performed at three nominal jet velocities (35, 48, and 63 m/s) and with solid loadings ranging from 0 to 2.75. The particle entrainment velocity into the jet was found to increase with increases in distance from the jet nozzle, to increase with increases in jet velocity, and to decrease with increases in solid loading in the gas-solid, two-phase jet. 

In fluidized bed experiments, most authors assume that all attrition products are elutriated. Consequently, they measure either the decrease in bed mass and use Eq. (2) (e.g.,Kono, 1981 Kokkoris etal., 1991, 1995) or the elutriated mass (e.g., Seville et al., 1992, Werther and Xi, 1993). It should be noted that all these authors used a certain particle size as a threshold below which all particles are assigned to be attrition products provided that all initial particles are clearly larger. Breakage events, which lead to particle sizes above the threshold level are, therefore, not considered. The choice of this threshold is very arbitrary and differs between the various research groups. 

Catalyst powders with carefully specified particle size distribution have been known to possess good fluidization characteristics. Generally, addition of fine particles to coarse particles tends to improve the latter s fluidization characteristics. Experiments were thus conducted on binary particle mixtures, each consisting of a fairly close particle size distribution. 

Testing of the catalyst was performed in the dual-fluidized bed reactor, where in the first reactor pyrolysis of the biomass and in the second upgrading of the pyrolysis vapours through catalytic de-oxygenation occurred. The bed material in the pyrolysis section was 40 g of quartz sand with a particle size distribution of 100 - 150 pm. The particle size of the catalyst was 250 - 355 pm. The amount of zeolite used in each experiment was 1.75 g. The biomass raw material used in the experiments was pine... 

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