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Process Vessels application and design
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Process Vessels
• Types and Functions• Design Considerations• Sizing Criteria• Calculation Method• Specification Data Sheet
Process Vessels
• Separation• Vapor/Liquid Separators• Liquid/Liquid Settlers• Fracrionators
• Accumulation• Liquid Surge• Liquid Storage
• Reaction• Reactors• Mixers
Types and Functions
Process VesselsVapor Liquid Separation
Process VesselsVapor Liquid Separation
Process Vessels
• Orientation• Sizing• Internals• Design Temp• Design Press
Design Considerations
Process Vessels
Usually Horizontal for:• A vessel handling large amounts of liquid or a large liquid
surge volume• Large amounts of dissolved gas in liquid• Where water must be separated from hydrocarbon liquid
Usually Vertical for:• Gas-Liquid ratio high• Total gas volumes low• Vessel with small surge volume such as a compressor
knock out drum
Design Considerations
Orientation
Process Vessels
• Vapor Velocity
Sizing Criteria
Va = Allowable Design VelocityVc = Critical Entrainment Velocity, ft/s (a)dl = Density of liquid. lb/cu.ftdg = Density of Vapor, lb/cu.ftF = Factor for Shape, Size and Internals
• F FactorsVertical/no internals 1.0 /with internals 1.5 – 2.0Horizontal 1.7Flash/Sharp Press Reduction 0.8
(a) Vc is based on Newton’s Law for velocity of spherical particle falling through motionless fluid
Process Vessels
• Liquid Hold-up Time
Sizing Criteria
Minutes (a)Feed to Heaters or Columns 10 (b)Reflux to Column 5Product Rundown 3 (c)
(a) Liquid volume between low and high levels(b) For vessels 1.5 m and larger
Provide more surge for hot fractionator bottoms to multistage pumps
(c) Higher for hot vessel bottoms on flow control
Process Vessels
• Liquid Settling Velocity
Sizing: Liquid Settling Space
cP Phase, Continuous ofViscocity Liquid of DifferenceGravity Specific
inch/min Droplets, ofVelocity Settling
8.20
S V
SV
Settling Velocity, inch/minWater-Light Oils 12 – 6Water-Heavy Oils 6 - 1
• Wash Drums (Typical)
Process VesselsSizing: Liquid Settling
Hydrocarbon
InterfaceWash Liquid
HydrocarbonOutlet
Mix valve
HydrocarbonIntlet
Wash Liquid
Settling drum
Interfacelevel control
valveCirculation pump
Fresh wash liquid
Spent wash liquid
LC
Process Vessels
Process Vessels
Process VesselsDesign Temperature and Pressure
•Max/Min Operating•Design Pressure•Design Temperature•Wall Thickness
Process Vessels
Process Vessels
Process VesselsDesign Temperature and Pressure
Process VesselsDesign Temperature and Pressure
Process VesselsVessel Calculation
• Define liquid & gas rates, properties, conditions• Establish liquid residence and water settling criteria• Calculate liquid volume & water settling space, and
establish total liquid space 1
• Assume L/D, and determine trail vessel dimensions• Calculate vapor flow cross section area based on
allowable vapor velocity equation: Va = F Vc and compare with available area 2
• Calculate water settling volume based on settling rate criteria, or provide separate pot for water
• Establish liquid and interface levels (max/min)• Repeat calc, as needed, for optimal vessel design
1 Increase by 10-15% for vapor flow space2 Revise vessel size to match required/available vapor areas
Process VesselsGeneral Tips
• Be sure to leave sufficient disengagement height above demisters
• For liquid/liquid separators, avoid severe piping geometry that can produce turbulence and homogenization. Provide an inlet diffuser and avoid shear producing items, such as slots and holes
• Avoid vapor entry close to a liquid level. Reboiler vapor should enter the bottom of the fractionator at least one tray spacing above high liquid level. Tray damage can result if liquid is disturbed
Process VesselsGeneral Tips
• Avoid extended nozzles or internal piping that the operator can not see, if at all possible
• Make sure items such as gauge glasses, level controls, or pressure taps do nor receive an impact head from an incoming stream
• Check gravity decanters for liquid seal and vapor equalizing line (syphon breaker)
• For gauge glasses it is good to have a vent at the top as well s a drain at the bottom. These should be inline for straight-through cleaning.
Process VesselsTypical Operating Problems
• Liquid Level• Entrainment• Demisters• Vortexing• Foaming• Carryover
