Preliminary Tray Layout

As stated in the introduction to Chapter 6, detailed tray layout is performed in the sscondary phase of tray design. A preliminary layout, however, is needed at the primary phase, because the layout influences column size. In the present example, the preliminary layout will be based on tray layout guidelines detailed in a companion book (1). 

Number of tray passes. Set this eo that the liquid flow rate does not exceed 7 to 13 gpm/in of outlet weir (1). At this preliminary point in the calculation, assume that the weir length is 0.8 times the tower diameter, Le-, 

The weir load is satisfactory for a one-pass design for the top section, but a two-pass tray is needed for the bottom section. 

Tray spacing. For the bottom section, 24 in is appropriate (1). For the top section, there may be some spare capacity available, so that a smaller tray spacing (18 in) is preferred. Assume 

Hole diameter. A good choice of size for clean services is Vie in, while Vi in is preferred for fouling services (1). Assuming that the depropanizer is a mildly fouling service, Vis-in holes are appropriate. 

---

During the column-sizing phase, a preliminary tray layout is prepared by setting the following ... 

Tray layout. The preliminary tray and downcomer layout is prepared in the column-sizing phase and refined during the hydraulic design phase. In addition to the parameters previously set, such parameters as hole diameter or the type of valve unit are determined. 

Others. Based on Kister s guidelines (1), the following are appropriate preliminary choices for other tray layout parameters. 

The downcomer layout is listed in Table 12.6. Until now, we have conducted a preliminary column design, which provides the colunm geometry and tray layout. 

The hardware design proceeds In two phases primary (basic) and secondary (detailed layout). The primary phase sets column diameter, type of tray, and split of tray area Into bubbling and downcomer areas. This phase also provides a preliminary (and usually close) estimate of tray spacing, number of passes, and other features of tray and downcomer layout such as weir height, fractional hole area, hole diameter, and clearance under the downcomer. These estimates are later firmed up in the secondary phase. 

---