Piping Layout: Drums And Vessel Layout Nozzle Orientation And Platform

The process vessels and drums are cylindrical hollow vessels used in process plants as intermediate containers. They are often used to provide surge volumes for liquid-vapourseparations on distillation columns or separating mixtures of immiscible liquids. Other usesare flash drums, condensate and other process liquid collectors and holding drums foradditives and chemicals.

The piping study on drums shall consider the general requirements for drum plant layoutand provide information required to locate nozzles, instruments, piping and controls for plat forming and operation / maintenance access.

In the first study of plot plan, platform levels and details of vessel elevations are set from process requirements (net positive suction head - NPSH, gravity feed, barometric legsetc.)

nd from considerations of access for safe and convenient operation and maintenance.

Methods of supporting vessels and operating platforms are detailed. Access for lifting equipment or overhead hoists and trolley beams is arranged for removal of motors, mixers and internal heat exchangers from process vessels. A platform should always be provided for the removal of such

heavy items of equipment and for access to manholes, sight glass, light glassetc.

In absence of any specific process requirement, the drum should be located at a minimumheight depending on the valves and fittings that are below the drum. Platforming should bekept to the minimum necessary to provide safe and suitable access to manholes and operating valves.

A typical vertical drum and horizontal drum are illustrated in sketches

Types Of Drum:

Drums are categorised as horizontal or vertical drums.  Drums internals are normally demisterpads, baffles, vortex breakers and distribution piping.

Steam drums and deaerators are usually proprietary items. Knock-out drums are used to separate condensate in the relieving discharges before going to the flare stack. Headers to flare stacks from relief and blow

down valves and vents are run first to knockout drum. It is recommended that the line

should run overhead to the top of the drum and must slope atminimum 1:400 so that all condensate drain into the drum.

The leg-supported drum is illustrated in sketch

The saddle supported drum is illustrated in sketch

The lug-supported drum is illustrated in sketch

Leg-supported drums should not be used in reciprocating compressor circuits

Location of Drums:

Drums are located within a process unit either adjacent to related equipment (e.g. the reflux drum) or as a standalone unit (e.g. a condensate collection drum)

When operating within process sequence of related items (e.g. pumps, condensers andtowers) the drum should be positioned to facilitate an orderly and economic pipinginterconnection between itself and those items.

Within a conventional inline process unit, drums and their related items are generally locatedon either side of a central Piperack serviced by auxiliary roads for maintenance access.

In certain cases (e.g. flash drums and deaerators), drums can be located above the piperack.In chemical plants, drums are located at all levels of enclosed or open structures.

Similar to towers, drum elevations are dictated by the NPSH

Drums for chemical collection systems are generally located below ground level insideconcrete pits.

To locate a drum, the following information to be collected so that the level of drum canbe finalised.

Drum  dimensions heads Support detail NPSH requirements of pump Bottom outlet size

Minimum clearances Location.