Fractionator sizing feed stage

In the cement industry, particle size classification by screening as part of the production operations is of less importance than, say, in the lime industry or in coal and ore preparation. Indeed, true classification procedures in the primary size reduction stage do not occur in cement manufacture, since the aim of the crushing treatment is to produce a feed material suitable for grinding to a fine powder, not the production of size fractions as required for crushed stone used in road construction, concrete production, etc. 

Acetonitrile serves to greatly enlarge the spread of relative volatilities so that reasonably sized distillation equipment can be used to separate butadiene from the other components in the C4 fraction. The polar ACN acts as a very heavy component and is separated from the product without much difficulty.The feed stream is carefully hydrogenated to reduce the acetylene level rerun, and then fed to the single stage extractive distillation unit. Feed enters near the middle of the extractive distillation tower, while (lean) aqueous ACN is added near but not at the top. Butenes and butanes go overhead as distillate, with some being refluxed to the tower and the rest water washed for removal of entrained ACN. 

If maximum product size is desired, the process stream flow is parallel, with a fresh feed and slurry discharge to product recovery equipment from each crystallizer. Cascaded product flow is avoided because flow through a series of tanks narrows the residence time distribution and the CSD and reduces the mass mean size by reducing the number of larger crystals in the distribution tail. This tail represents the major mass-weighted fraction. Population models have been solved to verify this effect, assuming an equal nucleation rate in each stage (Randolph and Larson 1988). The actual mean in industrial practice is lower because transfer of... 

If, instead of charging the still kettle with feed, the feed can be introduced some distance up the column with a heel of material (probably a portion of the residue from the previous batch) already being boiled up the column, the most volatile fraction can be stripped in the fractionating stages below the feed and taken off while the batch is being charged. This not only provides stripping plates but also increases the size of the batch because the volatile fraction never needs to be accommodated in the kettle. The latter can be a substantial increase in batch size in many solvent recovery operations. The feed rate should correspond to the rate of tops product. 

Once the scale of spray dryer is established, it is important to select an atomization nozzle appropriate to the scale. The purpose of the atomization stage is to produce a fine mist (spray) from a liquid feed to substantially increase the liquid surface area and improve the efficiency of heat and mass transfer. For example, 50 ml of a solvent atomized in 800 million droplets of 50 xm creates a surface area about 6 m. By the generation of such high surface area, droplets dry fast, in the order of seconds or fraction of a second depending on the drying conditions. Moreover, the control of the atomization process dictates droplet size and consequently the particle size. 

The classification performed at a single plate subdivides a given feed material into a fine and a coarse fraction. The coarse fraction is collected on the plate and therefore removed from the flow, the fine fraction is still entrained in it. If more points of a distribution cuiwe have to be determined, several im-pactor stages have to be arranged in series, with the cut sizes decreasing in the direction of the flow. One obtains a so-called cascade impactor. 

Use the data from Appendix 5.A the feed solids properties, the overall efficiency, the grade-efficiency curve and Eq. (16.1.1) to calculate the differential size distribution of the overflow fraction from the first-stage cyclone. 

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