Staged columns perforated plates

Pulsed columns Perforated plate packed Low HE IT No internal moving parts, but mechanicatly complex Many stages possible Karr column often less expensiw... 

Perforated-plate columns are semistage in operation. They are reasonably flexible and efficient. A 7-ft-diameter, 80-ft-high perforated-plate column used for extraction of aromatics was reported to have the equivalent of 10 theoretical stages. Because of the simplicity and low cost of packed and perforated-plate columns, they are widely used in industry despite their low efficiency, particularly for processes requiring few theoretical stages and for corrosive systems where absence of mechanical moving parts... 

A simplified empirical equation for finite-stage contactor columns operating on petroleum and similar hydrocarbons has been presented by Drickamer and Bradford Their results are based on plant tests with 54 refinery columns used for distillation or absorption of hydrocarbons. The columns were of the standard bubble-cap or perforated-plate type operated under typical refinery conditions. The results were correlated on the basis of the single variable, liquid viscosity, to give... 

The overall concentration distribution of solids in a multistage column depends upon the axial dispersion of the solids in each stage and the back flow of liquid (and solids) at the perforated plate. Kubota and Sekizawa69 proposed a model to describe the exchange of solid particles through the perforated partition plate. The model used a parameter K° which was defined as... 

Fig. 5. Three-stage thermostatted flotation column (25 mm diameter). P feed R liquid outlet with protein residue S foam liquid outlet gas inlet 1 glass frit 2 thermostat 3 perforated plates with overflow and down-comer 4 liquid level in the three stages 5 electrical conductivity probe and 6 foam breaker (3000 rpm) [70]...

Consider now the absorption extraction of heavy hydrocarbons under the conditions of counter-current flow in a column absorber presented schematically in Fig. 20.7. Gas of a given composition yo = (yoi, yo2, , yon), where yoi is the molar fraction of i-th component, with the flow rate Qgo enters the bottom part of the column. At the same time, an absorbent with composition xo = (xoi 5 02, , on) and flow rate qo enters the top part of the column. The number of contact stages is equal to N. Each stage is equipped with a perforated plate operating in the ablation regime. This means that the liquid is not collected on the plate, but exists in a dispersed state in the inter-plate space. Each contact stage contains a separation device, for example, a mesh droplet catcher, in which the exhausted absorbent is separated from the gas and directed toward the next plate. 

Two pailially miscible liquid phases may be contacted for extraction puiposes in a discontinuous or stage-wise manner in columns where the stages take the form of perforated plates, fitted with downcomers to facilitate flow of the continuous phase. Bubble-cap plates have been found ineffective in extraction, because of the lower density difference, lower interfacial tension, and higher viscosity of the disperse phase, compared to gas-liquid systems. 

Skelland and co-woikers have developed a procedure for the design of perforated plate extraction columns. This eliminates the need for experimentally measured stage efficiencies, which are usually costly and troublesome to obtain. Additionally, the validity of such efliciencies in scaled-up application is fir quently uncertain. Currently, the procedure involves use of rate equations for mass transfer during drop formation either at the perforations or at the end of jets issuing from the perforations, during ftee rise or fall of the drops, and during coalescence beneath Mcb i le, to locate a pseudoequilibtium curve. The latter is employed instead of the actual equilibrium curve on the - >a distribution diagram in a stepwise... 

Distillation column. In a patent by O Brien et al. [75], a distillation column with perforated plates and optional use of packing material and heating on the stage are described. In an experiment with a single tray, a DP 10 feed was fed to the top, and N2 was used to strip the... 

Sieve tray columns have also fotmd an application in staged countercurrent liquid extraction operations. The perforated plates, arranged in much the same way as in gas-liquid contact, act to break up accumulations of the dispersed phase and provide fresh surfaces for renewed mass transfer. Each of the plates, or rather the space between them, is a potential equilibrium stage, but the efficiency E is generally quite low. 

The absence of a concentration effect was also observed by Tohata et al. (1964A, B) for wetted wall and perforated plate columns. In the wetted wall column study, lithium chloride solutions in the range of 18.7 to 28.4% were employed. The results showed the gas-phase resistance to be controlling. Very high-stage efficiencies (up to 90%) were observed in the perforated plate column study, also indicative of a gas-phase resistance controlled absorption. 

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