Through risers and caps

Solution. Liquid head equivalent to pressure drop through riser and cap (hc ) By Eq. (9),... 

Pressure Drop through Risers and Cap, This loss is chiefly a kinetic velocity effect due to the changing cross-sectional areas. The pressure drop in inches of the liquid equivalent to the kinetic head is... 

Historically the most common gas disperser for cross-flow plates has been the bubble cap. This device has a built-in seal which prevents liquid drainage at low gas-flow rates. Typical bubble caps are shown in Fig. 14-20. Gas flows up through a center riser, reverses flow under the cap, passes downward through the annulus between riser and cap, and finally passes into the liquid through a series of openings, or slots, in the lower side of the cap. 

The liquid reflux flows across each tray and enters the downcomer by way of a weir, the height of which largely determines the amount of liquid on the tray. The downcomer extends beneath the liquid surface on the tray below, thus forming a vapour seal. The vapour flows upwards through risers into caps, or through simple perforations in the tray. 

Cu. ft. vapor per second per cap a. Pressure drop through risers and inside cap... 

Vapor rises up through risers or up-takes into bubble cap, out through slots as bubbles into surrounding liquid on tray. Bubbling action effects contact. Liquid flows over caps, outlet weir and downcomer to tray below. Figures 8-63-67, 79, and 81. 

The reversal area is the area of the cylindrical vertical plane between the top of the riser and the underside of the bubble cap through which the incoming vapor must pass. The vapor then moves into the annulus area between the inside diameter of the cap and the outside diameter of the riser before entering the slots in the cap. 

Cap assembly partial pressure drop, including drop through riser, reversal, annulus, slots, in. liquid Pressure drop through risers, in. liquid Pressure drop through reversal and annulus, in. liquid... 

Bubble-Cap Trays (Fig. 14-27a) These are flat perforated plates with risers (chimneylike pipes) around the holes, and caps in the form of inverted cups over the risers. The caps are usually (but not always) equipped with slots through which some of the gas comes out, and may be round or rectangular. Liquid and froth are trapped on the tray to a depth at least equal to the riser or weir height, giving the bubble-cap tray a unique ability to operate at very low gas and liquid rates. 

Cross-sectional areas for vapor flow through riser, direction-reversal space, annular cap space, and slots are equal. 

In this type of tray, each opening assembly consists of a cap, or inverted cup, with slots at its base, fixed above an opening. The opening consists of a hole and a riser through which vapor rises from the tray below. Its flow is reversed downward by the cap, after which the vapor flows down around the riser and bubbles out through the slots and into the liquid. Bubble cap diameters are usually about three to four inches. Because of the liquid seal created by the riser, bubble caps can operate at wide ranges of vapor and liquid flows with little loss in tray efficiency. 

When the liquid level is below the top of the recycle cup, the oil feed does not circulate through the cup, downcomer, risers, bubble caps, and the reaction zone, which can cause stagnation of the liquid and hot spots making the operation of the reactor dangerous. Using a floating recycle pan, the loss of liquid circulation, equipment... 

For bubble caps, Ki is the drop through the slots and Ko is the drop through the riser, reversal, and annular areas. Equations for evaluating these terms for various bubble-cap designs are given by BoUes (in chap. 14 of Smith, Equilibrium Stage Processes, McGraw-HiU, New York, 1963), or may be found in previous editions of this handbook. 

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