Wetting velocity, minimum

Space Velocity. Most of our experimental data were developed with operation at a wet outlet space velocity of approximately 10,000 vol/vol hour. However, we do have data at space velocities of up to 25,000/hr. The pilot plant will operate at a space velocity of 5,000/hr while processing 1 million scf raw syngas/day. With operation on a once-through basis without recycle and at the indicated space velocities, catalyst volumes are minimum compared with other processes when identical over-design factors are used. 

In order to tailor the physical properties of nano-particles, wet granulation was conducted. Hydroxypropylecellulose (HPC-L) 5% aqueous solution was sprayed onto nano-sized Ti02 particles through a binary nozzle. Fluidization air velocity was set at approximately 1.5 times as large as the minimum fluidization air velocity. 

At low liquid rates, the onset of instability occurs at a constant value of the total superficial velocity, and is predictable from holdup and flooding data for wetted wall columns. As liquid flow rates increase, Nicklin and Davidson predict that unstable flow begins at lower values of the gas flow rate. For high liquid flow rates, however, the slug length becomes important, and the unstable flow will begin at higher values of gas flow rate. Therefore, a definite liquid flow rate exists at which an unstable flow pattern appears with a minimum gas flow rate. 

In Figure 3.49, the minimum liquid superficial velocity versus particle size in order to have a wetting efficiency higher than 90% for water as liquid phase at 25 °C is presented. 

For the typical case of water systems used in environmental applications, e.g. removal of S02 from gas streams, the minimum superficial velocity of water for a wetting efficiency higher than 90% v.s. can be correlated to particle size as follows ... 

Thus, for a vapor of p,.-0.2 Ibn/Tt at an apparent velocity of l, 3 ft/s carrying an entrained liquid of density p,>45 Ibm/fl, with the interfacial tension 0.066 Ibm/s, the minimum size at which coalesced droplets will start to disengage is D >0.0I7 ft (5.000 Sim). The actual disengagement size may be smaller, due to the droplets smaller wetted perimeter (smaller surface-tension force) and droplet deformation (smaller projected area receiving the vapor momentum). 

A cylindrical extractor, 1-m long, is filled with crushed-vegetable-oil seeds. The oil is to be extracted with pumping supercritical carbon dioxide at a density of 500 kg/m3 through the packed bed. The estimated solubility of the oil in the dense gas at this density is 3.425 kg/m3. The superficial velocity of the carbon dioxide in the bed will be 1 mra/s. This fluid velocity is sufficiently small for the fluid to become saturated with oil. We are required to estimate the minimum time of operation for complete extraction of the oil from the bed. The initial oil fraction is 12% (wt/wt) based on wet seeds, the void fraction of the bed is 40%, and the density of the particles is 900 kg/m3. 

Schmidt (102) observed that flooding and minimum wetting are caused by two different mechanisms. A low-liquid-rate column may therefore flood even when it operates below the MWR. This is most likely to occur in vacuum systems (where liquid rates are low and vapor velocities are high) and in high-surface-tension, low-viscosity systems. 

The power required to move flue gas through the scrubber, from the absorber inlet to the mist eliminator outlet, was calculated from pressure drop and gas flow-rate data reported in the literature for a range of superficial velocities, liquid/gas ratios, and internal scrubber packings. A fan of the wet induced-draft type was assumed for each case, operating on saturated flue gas at 125°F. The gas-side power input was added to the power delivered through the slurry recirculation pumps which was calculated from the volumetric flow rates and the minimum discharge pressures required for the given scrubbers. The total power input for SO2 absorption was thus determined as ... 

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