Plate dual-flow

The perforated plate, punched plate, or Dual-Flow plate are terms used to refer to a tray operating without downcomers, with rapor and liquid passing countercurrent through perforations in the tray. The Dual-Flow term has been coined by Fractionation Research, Inc., and its design know-how is restricted to contributing members, and cannot be presented in this book. 

Table 9.1 Calculation of Drop Diameter for Dual-Flow Plates... 

Structured packed columns with dual flow plates 57 284.5 0.494 35.0 0.406 0.847 18.7... 

The Karr reciprocating-plate column (Fig. 15-50) is a popular example. It uses dual-flow plates with 50 to 60 percent open area and has no downcomers [Karr, AlChE J., 5(4), pp. 446-452 (1959) Karr and Lo, Chem. Eng. Prog., 72(11), pp. 68-70 (1976) and Karr, AIChE J., 31(4), pp. 690-692 (1985)]. Because of the high open area, a Karr column may be operated with relatively high throughput compared to other types of agitated columns, up to about 1000 gaF(h ft ) [40 m /(h m )] depending upon the application. The plates are mounted... 

Plates are available in the following designs bubble-cap plates, plates with fixed or moving valves, sieve plates, and dual-flow plates. 

The disadvantage of limited loadability especially applies for dual-flow plates. These have no downcomers for the liquid, and gas and liquid pass together through the holes in the plate. The main application is separations that are prone to soiling, for example, substances that tend to polymerize. 

Dual-flow plates 2-3 plates per meter, plate efficiency 40-50%. 

Countercurrent plates are of perforated or slottea construction and require no downcomers. The vapor and the liquid use the same openings, alternating on an intermittent basis. Layout of such plates is extremely simple. Types of such plates used commercially are Perforated (dual-flow)... 

Perforated Plate Without Downcomers Dual-Flow, from FRI)... 

Columns 30 mm diameter, packed column 35 nun diameter, structured ordered packings, dual-flow columns 50 nun diameter, bubble-cap plates... 

In systems with a low surface tension, the hole size of the sieve tray with downcomer should be smaller than 2 mm to prevent the continuous phase percolating through. For the treatment of such systems, dual flow trays without downcomers are more suitable. On a dual flow tray, the disperse and continuous phases flow in turn through the base plate holes and between the trays, producing strongly circulating convection cells. 

Sivakumar and Pandit [13] reported the use of hydrodynamic cavitation for decolorization of dye effluent stream. It has been observed that for same flow area, plate with larger number of small diameter holes gives higher extent of color removal as compared to the plate with smaller number of larger diameter holes. The observed results have been explained on the basis of frequency of turbulence for the two cases. The hydrodynamic cavitation reactor using multiple hole orifice plates has been found to give cavitational yields, which are two times higher than the best acoustic cavitation device (Dual frequency flow cell with capacity of 1.5 L). 

This work was done with a Waters Model 244 liquid chromatograph having two Du Pont Blmodal IIS columns (29,000 plates/meter) and a Linear dual-pen recorder. Also used was a Waters Model 440 UV absorbance detector. Samples were run at 0.1% (w/v) using an Injection volume of 25-pL and a flow rate of 1 mL/mln. The system was calibrated with polystyrene standards from Pressure Chemical Co. according to the universal callbaratlon procedure. Data collection and computation were done with an Intel 80/30 microprocessor. 

Closure at the instant of flow reversal is most nearly attained with tilting-disk, dual-plate, and specialty axial-flow check valves. However, quick closure is not the solution to all noise, shock, and water hammer problems. External dashpots are available when a controlled rate of closure is desired. Nonmetallic seats are also available. 

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