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Copy of Crude Oil Separation Unit

Design I - Oral Presentation

Usman Shahid

on 9 December 2012

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Transcript of Copy of Crude Oil Separation Unit

1. Scope/Mandate
2. Piping Design
3. Separation Design
4. Desalter Design
5. Cost Estimation Outline Why Desalt? Crude oils extracted contain:
May form salt cakes in equipments
Disturb flow pattern
Reduces rates of heat transfer
Heighten corrosion rate

Basic sediments and water (BS&W) (Water-in-Oil emulsions)
Reduce overall oil content
Increased downstream separation costs

Sellable crude oil must comply with product specifications; including the limits on BS&W and salt content Addition of demulsifiers (if needed);
Emulsion breakers are used to separate emulsions
Typically based on:
Acid (or base) catalysed phenol-formaldehyde resins
Polyamines, and Polyols
Ethylene/Propylene oxides added to adjust water/oil solubility

Addition of Fresh water
Allows salts to further dissolve in water Desalting Steps (1/3) Desalting Steps (2/3) After the addition of fresh water, flow is gently mixed to comingle the water with the oil and allow the BS&W and salts dissolve in the water
Flowing through a series of mixing valves for extreme mixing
Flowing through a series of bends in the pipes for gentle comingling This mixture is then sent to a settling vessel where the oil, having a lower density than water, floats upwards while the water emulsion droplets float downwards

Oil-water separation is thus achieved through gravity settling Desalting Steps (3/3) Gravity Desalter Separation solely based on gravity.
Denser water emulsions droplets fall to bottom of the tank, lighter oil droplets settle to the top of the vessel

Droplets reach a settling velocity of:

Larger water drops settle faster to the bottom of the vessel

The settling velocity also maximized by maximizing Δρ and minimizing μ Electrostatic Desalter (1/2) The crude oil-water mixture enters the settling vessel and is subject to electrostatic current

settling vessel contains two electrostatic plates
The top plate grounded to the vessel shell and ground
The bottom plate is alternatively charged and discharged with an alternative current 1) Current is increased at fast rate
2) Current is kept constant at that high voltage
3) Current is discharged back to zero
4) Current is stopped for a few seconds to allow settling Electrostatic Desalter (2/2) Salt content must be reduced from 50 PTB to max. 8 PTB
Final water content must be within 0.06 wt% to 0.1 wt% of the crude oil
Emulsion droplet diameter is to be calculated using:

Settling process residence time is 1 hour
Desalting vessel is of Carbon Steel
Vessel material minimum thickness is 1/16”
10 year life span with 2 mm/year of corrosion Desalter Design Criteria Desalter Recommendations Project Cost Estimation Separators What happens in a separator? Pipeline Diameters Assuming 4 inch pipelines, flow regimes were modeled using Aspen HYSYS
Diameters were modified to ensure acceptable flow regimes Total Pressure Drop (3/3) Pressure and temperature for the separation unit inlet was determined after the final length of pipeline was modeled on Aspen HYSYS Pipelines Preliminary Pipeline Design 1. Determine diameter of each pipeline
Based on two-phase flow patterns
2. Design for thermal expansion in pipelines
Adding expansion loops to design
3. Determine total pressure drop
Modeled on Aspen HYSYS Two-Phase Flow Patterns Slug or Plug Flow Under the influence of gravity, gas and liquid travel in increasingly long plugs or slugs through the pipeline
These slugs can overload the gas/liquid handling capacity of the plant at the outlet Expansion Loops (1/2) Steel will expand and contract due to thermal expansion with temperature fluctuations
Expansion loops provide piping in a perpendicular direction to absorb such effects Expansion Loops (2/2) The overall pipeline lengths used in design must include the added lengths due to expansion loops
This represents a 5 – 8 % increase in the pipeline lengths Total Pressure Drop (1/3) All 15 pipelines must merge at the same pressure to prevent backflow
This is done in two steps using Aspen HYSYS
Determine the pipeline with the lowest outlet pressure
Using choke valves, reduce the pressures of the other pipes to the lowest pressure found Total Pressure Drop (2/3) Pipelines in Design II Determining Material of Choice
Recalculating pipeline diameters based on industry regulations for gas and liquid velocities and friction gradients (ΔP/100 ft) Pipeline Assumptions (1/2) Pressure Calculations
No change in altitude
Heat Transfer Effects
Buried at a depth of 3 feet
No insulation
Calculated for three different ambient temperatures of 5, 30 and 50 °C Pipeline Assumptions (2/2) Expansion Loop Calculations
Expansion loops installed every 165 ft (50 m)
Temperature fluctuations of 45 °C
Pipes are made of low carbon steel (ASTM A106)
Modulus of elasticity of steel = 203.4 GPa
Maximum allowable stress of steel = 137.8 MPa Expansion Loop Calculations (1/3) Expansion Loop Calculations (2/3) Expansion Loop Results (3/3) Liquid Level Control Float and Displacement Sensor
No baffles or weirs
Weir Plate
To fix upper oil level
Oil and Water Weir
To fix oil and oil/water interface level Separator Design
Advantages Vertical Separators When plot space is limited
Ease of level control is desired
Small flow rates
Very low or very high GOR streams Horizontal Separators Larger volumes of gas and/or liquids
High-to-medium GOR streams
Foaming crudes
Three-phase separations Separator Design Selection procedure
Design a vertical separator
For L/D>5.0 horizontal separator is suitable

Design procedure
Calculate maximum gas velocity, vmax.
Use vmax to calculate cross-sectional area, A.
Calculate separator diameter using A.
Obtain height of the separator.
If L/D>5.0 D is recalculated by setting L/D=4.8 Choice of Separator Initial L/D ratio > 5.0
Large volume of liquid in feed
No limitation of plot space
No presence of sand, mud, paraffin or wax
Thus, Horizontal Separator chosen
Separator Dimensions
L=32.1 ft, D=6.68 ft, L/D=4.80 No. of Separators Series of Separator increase separation
How many separators to use?
3 cases = 3, 4, 5 Seps
Decision Criteria
Separation Ratio
Minimum C4 in gas phase
Max Liquid
Economical Feasibility Separator Design
Disadvantages Vertical Separators More expensive than
More difficult to ship
More difficult to reach and service
Require larger diameter for a given gas capacity Horizontal Separators Occupy more space unless “stack” mounted
Liquid-level control is more critical
More difficult to clean sand, mud, wax, paraffin, etc. Cases 3 Separators 4 Separators 5 Separators Recommendation Scope Department of Chemical Engineering McGill University Design Project Client: Heba Al-Ghouleh

Presented by

Faraz Rajput
Usman Bin Shahid conclude with learning outcomes
challenges etc
major hurdles
hardest part
interesting part
etc Flashing of a Gas-Liquid Mixture Overcoming Challenges
Pipeline Simulation
Desalting HYSYS Simulation
Project Management
Team Work Skills
Time Management
Written and Oral Communication Skills Learning Outcomes Questions?
Full transcript