Capacity, trays

Tower Internals and Equipment Modification. Tower capacity expansion can be achieved through the use of random or stmctured packing, or through the use of higher capacity trays such as the UOP multiple downcomer tray. Packing has been used in the gasoline fractionator, water quench tower, caustic and amine towers, demethanizer, the upper zone of the deethanizer, debutanizer, and condensate strippers. Packing reduces the pressure drop and increases the capacity. 

Revamp the tower internals with high-capacity trays or packing. 

High-capacity trays evolved from conventional trays by including one or more capacity enhancement features such as those discussed below. These features enhance not only the capacity but usually also the complexity and cost. These features have varying impact on the efficiency turndown, plugging resistance, pressure drop, and reliability of the trays. 

Sloley, A.W. Should you switch to high-capacity trays Chem. Eng. Prog. 1999, 95 (1), 23-35. 

The trays that carry the pumparound liquid are the heaviest loaded in the tower. Sometimes extra vertical spacing is provided at these trays, or high-capacity trays or packing may be used. 

FIGURE 12.70 Generalize(f comparison of capacities, structure(f packings vs. high-capacity trays. [J. L. Bravo, 1998. Chem. Eng. 105 (2) 77.]... 

If all droplets were of the same size (the maximum size that can exist), the vapor velocity at which the droplets would become suspended but would not rupture is given by Eq. (12-31). Above any actual tray, a range of droplet sizes exists, and the maximum vapor velocity which can actually be reached is well below the values predicted by Eq. (12-31). Figure 12-13, taken from Manning,13 shows a comparison of the theoretical maximum vapor velocity given by Eq. (12-31) and the actual maximum vapor velocity for several high-capacity trays. 

The lifeblood of engineering fabricators is their proprietary design manual, which contains formulas and graphs for calculating column parameters such as flooding, capacity, downcomer velocities, vapor capacity, tray diameters, column diameters, downcomer area, pressure drop, flow path width, tray layout, and cap, valve, or perforation size. Of key importance also are some of the other column internals such as ... 

The hydraulic capacity of trayed distillation columns is always limited by either a high liquid entrainment, or by an overload of downcomers. The technology of high capacity trays deals with these two fundamental limits by reducing the entrainment or by releasing the loads of downcomers. Both are generally connected (HUls, 2001). 

Replacement of tower internals in CDU distillation using high-capacity trays... 

All vendors now market a high capacity tray. These trays have a 5 to 15 percent capacity advantage over conventional trays. Basically, the idea behind these high capacity trays is the same. The area underneath the downcomer is converted to bubble area. This increase in area devoted to vapor flow reduces the percent of jet flood. 

High capacity tray with downcomer seai piate. 

For these reasons, high capacity trays using dynamic downcomer seals are best avoided on new columns. They should be reserved for use on retrofit tower expansion projects. 

The design I m most familiar with is the NorPro high capacity tray shown in Fig. 4.6. The head loss through the orifice holes in the downcomer seal plate shown is sufficiently high to prevent loss of the downcomer seal. These trays flood rather easily when their design downcomer liquid rates are exceeded. However, when operated at... 

---