Crude Oil Desalting and Distillation Flashcards
(29 cards)
Why is desalting of crude oil necessary?
Desalting minimizes corrosion caused by salt deposition and acids formed by decomposition of chloride salts.
It also prevents catalyst deactivation in catalytic processing units.
What are common suspended solids found in crude oil that need to be removed?
- Fine sand
- Clay
- Soil particles
- Iron oxide
- Iron sulfide
- Other contaminants picked up in transit or production
Total suspended solids removal should be 60% or better.
What is the minimum salt content that necessitates two-stage desalting?
More than 20 lb/1000 bbl
In some cases, three-stage desalting is used for certain crudes processed catalytically.
What challenges are associated with desalting crude oil?
- Efficient and economic water/oil mixing
- Water-wetting of suspended solids
- Separation of wash water from oil
The pH, gravity, viscosity, and volume of wash water affect separation efficiency.
At what temperature and water volume percentage is desalting typically carried out?
90-150 °C with 3-10 vol.% water
The ratio of water to oil and temperature are functions of the oil density.
What is the efficiency range for single-stage desalting units?
90 to 95%
Two-stage desalting units can achieve 99% or better efficiency.
What factors affect oil and water separation efficiency?
- Number of stages
- Electrical field
- Gravity of the crude oil
- Volume of wash water used
- Temperature of operation
- pH of the mixture
What is the purpose of atmospheric distillation in crude oil processing?
To separate crude oils by distillation into fractions according to boiling point
Higher efficiencies and lower costs are achieved through two steps: atmospheric and vacuum distillations.
What is the effect of reducing pressure in vacuum distillation?
Boiling points of hydrocarbons are reduced substantially
Distillation is carried out at absolute pressures of 25 to 40 mmHg.
What is the typical furnace outlet temperature range used in vacuum distillation?
730 to 850 °F (388 to 454 °C)
This range minimizes coke formation.
What are the three types of operations in vacuum distillation?
- Dry
- Damp
- Wet
What type of operation in vacuum distillation results in the lowest furnace outlet temperatures?
Wet operation
This involves adding steam both to the furnace inlet and the bottom of the vacuum tower.
What is the main product of a typical crude distillation unit in order of increasing boiling points?
- Fuel gas (dry gas)
- Wet gas
- Straight-run naphtha
Fuel gas consists mainly of methane and ethane.
What does wet gas contain?
Propane, butanes, methane, and ethane
Wet gas is a mixture of hydrocarbons that includes heavier components like propane and butanes.
What are propane and butanes used for?
Used for LPG and gasoline blending
Butanes can be further processed for various applications.
What is straight-run naphtha?
A product from distillation used in gasoline blending
It includes light straight-run (LSR) and heavy straight-run (HSR) naphtha.
What is the purpose of further processing heavy straight-run naphtha?
To improve octane before blending into gasoline
What is kerosene used for?
Jet fuel, gasoline operation, and heating applications
What are gas oils used for?
Produce gasoline, jet, and diesel fuels
What can heavier vacuum gas oils be used for?
Feedstocks for lubricating oil processing units
What is residuum?
The vacuum still bottoms that can produce heavy fuel oil or lube stocks
What can residuum from asphalt crude oils produce?
Road or roofing asphalts
At what pressure are boiling points reported during distillation?
760 mm pressure
What is the typical fraction cut point for distillation?
Reported boiling ranges for atmospheric and vacuum still fractions
