Drainage drain layouts

Fig. 8.5 Drain layouts (a) drainage of wet areas (b) intercepting springs (rushy areas) (c) herringbone system in valley (note separation of junctions) (d) grid system.

Holes for drainage must be adequate to drain the column in a reasonable time, yet not too large to interfere with tray action. Draining of the column through the trays is necessary before any internal maintenance can be started or before fluid services can be changed, when mixing is not desirable. The majority of holes are placed adjacent to the outlet or downcomer weir of the tray. However, some holes are placed in the downcomer inlet area or any suspected low point in the mechanical layout of the column. 

Before piping is installed, the layout should be analyzed to eliminate low points where liquid could collect and to provide drains where low points cannot be eliminated. A regular part of the operating procedure must be the periodic drainage of low points in the piping and separators, as well as inspection of automatic drain traps. 

Flow diagrams. Drain hubs (see Figure 8-4) collecting drainage from equipment above grade or from paving, which were previously added to the sewer layout, should also be run to the proper classified sewer. Flow diagrams should be consulted to make sure that no drain connection has been omitted, especially those located at the upper levels. Drain hubs need not consist of an... 

The loop may be drained into a vessel which can be either the fill tank or a separate drain tank. Piping lines should be sloped to facilitate drainage undrainable pockets should be provided with separate drain lines or, if possible, eliminated. A typical liquid-bismuth loop layout is shown in Fig. 23-6. 

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