Drums are located within a process unit either adjacent to related equipment (e.g. the reflux drum) or as a standalone operation (e.g. a condensate collection drum).
When operating within the process sequence of related items (e.g. pumps, condensers and towers), the drum should be positioned to facilitate an orderly and economic piping interconnection between itself and those items.
Within the conventional inline process unit, drums and their related items are generally located on either side of a central pipe rack serviced by auxiliary roads for maintenance access.
In certain cases (e.g. for flash drums and deaerators), drums can be located above the pipe rack. In chemical plants, drums are generally located at all levels of enclosed or open sided structures.
Elevation and Support
Similar to towers, drum elevations are dictated by the NPSH, as illustrated below, minimum clearance, common platforming and maintenance and operator access.
Withing structures, especially chemical facilities, drums could be elevated above the minimum requirements of accommodate floor space availbility .
Drums for chemical collection systems are generally located below ground in concrete pits as shown below. Methods of support are influenced by the size and location of the drum.
Similar to towers, large vertical drums are supported by skirts. If size permits, small vertical drums may be supported by legs as shown below, or by lugs if elevated within the structure as shown below.
Horizontal drums are usually supported by saddles from concrete piers or steel frames if elevated within a structure as shown below.
Leg supported drums should not be used in reciprocatin compressor circuits. The first step in drum layout is setting the height of the drum.
To do this, the plant layout designer requires the following information:
- Drum dimensions.
- Type of heads.
- Support details.
- NPSH requirements of pump.
- Bottom outlet size.
- Minimum clearances.
The centreline elevtion of the drum, as illustrated below, was set using the following listed information.
a. Drum dimensions : 4 ft by 10 ft length.
b. Support details : saddles and concrete piers.
c. NPSH – 9 ft
d. Bottom outlet – 4 in
e. Location : Free standing
f. Minimum Clearance – 7 ft. 2100 mm