Equipment Design Basis
Equipment Design Basis
Equipment Design Basis
Factors like pumps shut-off conditions, pressure drops in recycle loop etc. should be
considered for fixing design pressure. Pump shut-off shall be calculated at 1.25 x rated
head + max. suction pressure.
Equipment which could have to bear the shut-off pressure of a pump in case of a valve
closing (either control valve or block valve) is designed for the following pressure:
Design pressure = Design pressure of the suction vessel + liquid height at vessel HLL at
pump suction + 125 % of pump differential pressure.
When operating pressure is less than or equal to 100 kg/cm, design pressure shall be
equal to normal operating pressure plus 10 % (min. 2.0 kg/cm). When operating pressure
is more than 100 kg/cm, design pressure shall be equal to normal operating pressure plus
5 % (min 10 kg/cm).
All steam handling / condensate vessels shall be designed for full vacuum conditions also.
Minimum design pressure for equipment connected with flare header should be
3.5 kg/cmg.
Special consideration should be given (for vacuum design) to the design of vessel
normally subject to internal pressure and connected to a compressor suction or ejectors.
Full vacuum will be specified for isolable equipment containing fluid having a vapour
pressure lower than atmospheric pressure at ambient temperature.
For equipment subject to pressure and temperature swings, the magnitude and frequency
of these swings will be given on the specification sheet.
When several pieces of equipment are protected by the same relief valve, each piece of
equipment will be designed, at least for the pressure imposed by the discharge conditions
of the relief valve in case of emergency.
For fractionation columns, the reference design pressure is taken as that at the bottom of
the column.
Design temperature for unfired pressure vessels and interconnecting piping will in
general be equal to maximum anticipated operating temperature plus 30C if vessel
operates between zero to 400C and 28C if vessel operates above 400C.
If it operates below zero degree C temp. LICENSOR should follow his own philosophy.
Conditions like steam-out (for handing out vessel to maintenance) will be considered
while specifying design temperature.
For vessels operating at ambient temperature, 65C will be used for mechanical design.
Note:
When different metal temperature can be predicted to occur for different zones of a
vessel during operation then different temperature should be indicated on the sketch
and different temperature should be taken into account for designing the vessel.
The column internals can be trays or packing. Preferred type of trays shall be a valve tray
(stainless steel).
For operating temperatures below 0C, minimum operating temperature 5C or
minimum ambient temperature.
The effect of autorefrigeration due to depressurization to atmospheric pressure will be
taken into consideration (LPG systems for example).
For feed/effluent exchangers of reaction sections + 25C to be added to max. operating
temperature to take into account the temperature profile modification at low capacity.
Residence time
Reflux
: 10 minutes
Column feed
Reboiling by heater
Reboiling by thermosiphon
: 10 to 30 seconds
Product to storage
: 5 minutes
In the case of pumps ensuring several services such as reflux and liquid distillate to storage,
the residence time of the corresponding vessel will be whichever is greater from the above
list.
Vessels, exception done for reactors, will be provided with vent and drain nozzles.
Vent and drain sizes will not be indicated, unless required for process reasons.
Preferred diameters of columns and vessels : see attached table in the following page.
Where possible minimum column diameter to be 1000 mm.
4.5 Metre
For small diameter towers ( 800), tower internals should be removable from one end
and to be cartridge type. Provide flanges where necessary along tower.