Flash Drum: Equipment Tab

Variable Definitions, Ranges and Default Values

The following table shows the meaning of the variables appearing in this tab, as well as their default values and their generally acceptable range. Note that due to the manner by which the variables are used by the sizing and costing equations, the range of acceptable values may be further reduced.

Variable	Default Value	Range

◙ Volume The total vessel volume.	0.0 L	Positive
◙ Max Volume The maximum volume that a unit of this type is available for purchase in the market.	2000.0 L	Positive
○ Min Allowable Working/Vessel Volume The minimum ratio of working (liquid) volume of material to total vessel volume allowed.	0%	(0,100]
○ Max Allowable Working/Vessel Volume The maximum ratio of working (liquid) volume of material to total vessel volume allowed.	90%	(0,100]
● Height The internal height of the vessel.	0 m	Positive
● Diameter The internal diameter (or diameter equivalent) of the vessel.	0 m	Positive
○ Height/Diameter The ratio of height to diameter (aka aspect ratio) of the vessel.	4.0	Positive
○ Is ASME Vessel? ASME standards of vessel construction will increase the cost of the vessel.	Yes	Yes/No

Symbol Key: ○ User-specified value (always input); ● Calculated value (always output); ◙ Sometimes input, sometimes output

Sizing: Design Mode

In Calculate (Design Mode), the user specifies the Maximum Volume and the system computes the Number of Units and the Volume. The volume of the drum is calculated by multiplying the outlet liquid phase flowrate by the residence time of the liquid phase in the drum and then by dividing by the operation’s working to vessel volume ratio (see Continuous Vessel Operations (Design Mode): Volumes Tab). By default, an optimum height to diameter ratio of 4.0 is assumed (Henley and Seader, 1981). From the drum volume and the height-diameter aspect ratio, the actual dimensions of each drum (height and diameter) are calculated. The equipment’s min and max allowable working to vessel volume ratio limits act as constraints on the operation’s working to vessel volume ratio (i.e., the operation’s working to vessel volume ratio must be within the range defined by the equipment’s min and max working to vessel volume ratio limits).

Sizing: Rating Mode

In rating mode, the volume of the drum and the number of units are provided by the user. As in the design mode case, the actual dimensions of each drum (height and diameter) are calculated from the drum volume and the height-diameter aspect ratio. The program also calculates exactly as in the design mode case the demand on drum volume by the operation carried out as part of the unit procedure hosted by the equipment resource, and if the operation’s drum volume demand of exceeds the drum vessel volume, it generates a warning.

Costing

The equipment purchase cost is based on the diameter and the height of the drum. It is supplied by the built-in model assuming as material of construction CS. Other factors that affect the cost are:

● Conforming to ASME Specification; if checked, then the vessel is assumed to have been constructed according to standards published by the American Society of Mechanical Engineers (ASME) and it is assumed to withstand pressure up to 35psig. Checking this option penalizes the cost by about 20% over the base cost.

For more information on this equipment, see Flash Drum.

For information on the left-hand side variables and options, see Equipment Data Dialog: Equipment tab.