High nozzles

Continuous discharge of solids, as a slurry, is achieved by sloping the inner walls of the bowl toward a peripheral zone containing between 8—24 orifices, commonly called nozzles, as shown in Figure 14g—i. The nozzles must be spaced closely enough so that the natural angle of repose of the solids deposited between the nozzles does not cause a buildup of cake to reach into the disk stack and interfere with clarification. The size of the nozzles is limited because the fluid pressure at the wall, which can be 6.9—13.8 MPa (1000—2000 psi), produces high nozzle velocities (see eq. 30). On the other hand,... 

The liquid injection is realized using a two-fluid nozzle (Co. Schlick, type 943, form 3, ring-shaped beam 20°-40°, dnozzie = 2.3 mm). A adjustable hose pump conveys the liquid from a store tank, and compressed air is used for the better spreading of the liquid. The investigations of Henneberg et al. [38, 39] in an industrial fluidized-bed plant showed that high nozzle injection rates may lead to low particle concentrations near the nozzle, and to overspray. 

However, a slight decrease in So by 10-20% is observed at high nozzle temperature (Tn) which is thought to be due to rotational excitation of D2 molecules [86]. Microscopic reversibility would lead one to predict that rotational cooling should occur on Pt(l 11) upon associative desorption, although no such measurement has been made. Note that a small rotational cooling has been observed for desorption not only from Cu surfaces [98], but also from Pd(l 0 0) surface where hydrogen dissociation is un-activated [99]. 

The reported study on gas-liquid interphase mass transfer for upward cocurrent gas-liquid flow is fairly extensive. Mashelkar and Sharma19 examined the gas-liquid mass-transfer coefficient (both gas side and liquid side) and effective interfacial area for cocurrent upflow through 6.6-, 10-, and 20-cm columns packed with a variety of packings. The absorption of carbon dioxide in a variety of electrolytic and ronelectrolytic solutions was measured. The results showed that the introduction of gas at high nozzle velocities (>20,000 cm s ) resulted in a substantial increase in the overall mass-transfer coefficient. Packed bubble-columns gave some improvement in the mass-transfer characteristics over those in an unpacked bubble-column, particularly at lower superficial gas velocities. The value of the effective interfacial area decreased very significantly when there was a substantial decrease in the superficial gas velocity as the gas traversed the column. The volumetric gas-liquid mass-transfer coefficient increased with the superficial gas velocity. 

Figure 9. Effect of high nozzle velocity on carbon oxides yield group for Pittsburgh seam coal...

Figure 9 presents the results of the high nozzle velocity tests for Pittsburgh seam coal. The carbon oxide yields are indeed higher than expected. The methane yields for these tests correlated in the same way as did those for the lower nozzle-velocity tests and are included in Figure 4. This is expected because the reactivity of char to direct metha-nation by hydrogen is considerably less than the active form of carbon produced in the initial heat-up of coal. Consequently, a higher char inventory, even in the high temperature region, would not produce higher methane yields.

Pipi7ig layouts. In laying out the piping system for an aqueous-fuel homogeneous reaetor, sufficient flexibility must be incorporated in the system to absorb thermal expansions without creating excessive stresses in the pipe wall, and to avoid high nozzle reaction loads at the equipment. 

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