Riser diameter

Radial 3 to 4 riser diameters above the point where the regenerated catalyst enters the riser... 

Slip factor is defined as the ratio of catalyst residence time in the riser to the hydrocarbon vapor residence time. Some of the factors affecting the slip factor are circulation rate, riser diameter/geometry, and riser velocity. 

Fig. 21. Computed and measured radial profiles of (a) solids concentration and (b) axial solids velocity in a CFB riser for three superficial gas velocities (U = 7.5 m/s, U = 10.0 m/s, and U = 15.0 m/s) at a constant mass flux of 300 kg/(m s). Riser diameter D = 0.0536 m, physical properties of the particles diameter, 126 pm density, 2540 kg/m. ...

THE TRANSPORT VELOCITY DETERMINES GAS VELOCITY AND RISER DIAMETER... 

To include a safety margin, the operating gas velocity will be chosen to exceed 1.2 Utr. As the minimum gas flow in the riser is determined by the reaction stoichiometry, the gas velocity and the riser diameter cannot be chosen independently. 

According to the acquired results, a pilot scale (approx. 100 kg maf biomass/h) CFB pyrolyser would have a riser diameter of approximately 0,16 m, while a demonstration scale one (aj rox. 1000 kg maf biomass/h), a riser diameter of 0.40 m. The specific feed rates for these two units correspond to specific feed rates of 1.3 and 2.6 kg/m s respectively, which are the highest for all units investigated so far in the literature (2). 

The influence of riser diameter on the predicted results is shown in Fig. 12.15. It can be seen that there are significant qualitative differences in the predicted radial... 

FIGURE 12.15 Influence of riser diameter (from Ranade, 1999). 

Weep hole area Weep hole diameter Riser-hat clearance Riser diameter Riser number Gaskets tightness cutting... 

Analysis could be skewed to favor riser versus downcomer data due to the riser cross-sectional area usually being larger than that of the downcomer. A better strategy would be to analyze each section separately. One approach is to assume a large degree of independence, which would work relatively well if the controlling factors in each section are independent of the other. A large effective riser diameter would... 

Furthermore, airlift bioreactor studies often use an effective riser diameter that is less than 0.15 m, which has been shown to influence the bubble size distribution in bubble columns (Kantarci et al., 2005). Not surprisingly, research work that compares ALR designs based on the bioreactor diameter uses smaller riser and downcomer columns and finds a strong bioreactor diameter dependence, noting... 

Pneumatic dryer pulverized, crystalline, fine products, products able to be pneumatically conveyed 25-500 kg/(m h) 4000-5000 Riser diameter 0.3-1.2 m Riser length 15-30 m Superficial gas velocity 10-40 m/s Particle size 0.01-10 mm Drying time 2-8 s Power consumption 15-KK) kW c... 

We regressed experimental data of a number of studies [66,83,90,91,94,96,98] and found that a varies most strongly with gas velocity, solids mass flux, and riser diameter and obtained the following expression... 

Solids hold-up increases with mass flux and decreasing gas velocity. The correlation predicts that density increases with increasing riser diameter. This effect can... 

In conclusion, a fundamental understanding of CFB hydrodynamics continues to lag behind commercial operating experience. Although CFB provides considerable advantages of operational flexibility, concerns about operational complexity and scale-up hinder commercialization of heterogeneous catalytic reactions. Concentrated research in the areas of gas-solid contact in the entry region, effect of internals, riser diameter, and solid fines content is required. The continued interaction between academia and industry, as seen in the four international conferences of CFB technology, will be necessary to further optimize commercial operations but also to further develop revolutionary industrial processes. 

D Riser diameter Axial dispersion Radial dispersion Diffusion... 

Figure 11 Pressure flucutations measured in a circulating fluidized bed between the windbox and at a height of 0.3 m above the distributor (riser diameter, 0.4 m superficial gas velocity, 3 m/s solids mass flux, 22 kg/m s).

Arena et al. (1988) measured the hydrodynamic behavior of two circulating fluidized beds with riser diameters of 0.041 and 0.12 m ID of roughly the same... 

Because of experimental limitations, it is uncommon in experimental CFB studies to vary the riser diameter, or even the H/D ratio, while keeping all other variables fixed. 

Fig. n.9. Heat release rate at flooding as a function of the vapor tube (riser) diameter for different solvents. 

The minimum velocities for risers are listed in Table 1. For a feed riser the lowest velocity is normally encountered at the bottom where the oil is first vaporized. In a vertical feed riser (e.g., Figure 6) it is important that the diameter of the riser at the feed injection point is sized to give at least 15 to 20 Ft/S (based on 100% vaporization of the feed). The riser diameter may be increased further up the riser as velocity picks up due to molar expansion. The bottom, narrow part of the riser is often referred to as the acceleration zone. Riser exit velocities are generally in the 60 Ft/S range. Riser velocities rarely exceed the limits of erosion resistant lining (90 Ft/S). 

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