Vapor-flow area

Vapor flow area, fr Specific heat of the quench fluid Cfl Specific heat of the reactants... 

Valve trays. Figure 6.216 illustrates the dry pressure drop of a typical valve tray as a function of vapor velocity. At low vapor velocities, all valves are closed (i.e., seated on the tray deck). Vapor rises through the crevices between the valves and the tray deck, and friction losses through these crevices constitute the dry pressure drop. Once the closed balance point (CBP) is reached, there is sufficient force in the rising vapor to open some valves. A further increase in vapor velocity opens more valves. Since vapor flow area increases as valves open, pressure drop remains constant until all valves open. This occurs at the open balance point (OBP). Further increases of vapor velocity cause the dry pressure drop to escalate in a similar manner to a sieve tray. When two weights of valves are used in alternate rows on the tray, a similar behavior applies to each valve type. The result is the pressure drop-vapor velocity relationship in Fig. 619e. 

Basically, the overall model for valve trays is similar to that for sieve trays with the exceptions that the vapor flow area in the contactor can vary for valve units depending on the extent of the valve opening, and the number of kinetic... 

The correlations for sieve (and bubblecap) trays have no provision for multipass flow of liquid. Their basic data may have been obtained on smaller towers with liquid flow equivalent to two-pass arrangement in towers 8 ft dia. The sieve tray correlation velocity should take into account the loss of vapor flow area due to downcomers. 

Step 4. Calculate the required vapor flow area. Qv... 

The perforated-pipe distributor is best suited where vapor mass velocities are high and where an open area in excess of 70 percent is needed to avoid localized flooding (305). Together with the spray type, the perforated-pipe distributor offers the highest vapor flow area. However, the maximum liquid flow recommended for this type of distributor is relatively low and should not exceed 10 gpm/ft of column area (305) with standard designs. 

For large vapor flow, it may be cheaper to use split flow design to reduce the required vapor flow area. Feed will enter the vessel at its midpoint and vapor exits from both ends of the vessel, or feed is split to half and enters the vessel from each end, and vapor exits fix>m vessel s midpoint. 

For a two-phase vapor-liquid separator, both vertical and horizontal separators are used, and the selection should be made on a case-by-case basis. In a horizontal separator, with an increase in liquid level, the area of the vapor space is reduced and the possibility of liquid entrainment increases. On the other hand, the vapor-flow area remains constant in the vertical separator, and liquid entrainment is not an issue at high liquid level. Vertical separators also have the advantage of lower space requirement and easy-to-install control systems. 

The vapor-flow area is calculated as tire area available above the high liquid-level shutdown. Once tire vapor-flow area is known, the vapor residence time can easily be calculated, using the actual vapor velocity. The required length of the KO drum is calculated by multiplying the droplet velocity and vapor residence time. This length is then checked with tire available length. 

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