Download review/theory of separation (mass transfer) unit-ops

Review of Separation Unit
Ops
Holly Barra
Simone Gelinas
Franklin Ning
Max Pereboom
Agenda
1. What is separations?
2. Types of separations?
3. Three separation operations present in Hydrocarbon Formation
What are separations processes?
Pure products are valuable!
Side reactions and excess reactants lead to impure products
Separations are used to separate unwanted components
These can be disposed of, sold, or used as recycle
Definitions
Split Fractions (i.e. recovery)
Separation Factor
Intro to Separations in Hydrocarbon Formation
http://www.orioninstruments.com/petroleum-refining#preflash drums
Liquid-Solid Separation Unit Ops
Considerations: Solids concentration, feed rate, nature of solid particles, and objective
(recovery, degree of dryness)
Filtration
Passing slurry through porous filter medium
Key Terms: Filtrate (Permeate) and Retentate
Cross-Flow Filtration
Batch
● Nutsche (Gravity and Vacuum)
● Plate and Frame Press (Pressure)
● Leaf Filters (Pressure and Vacuum)
● Rotary Drum Filters (Usually Vacuum)
Continuous
● Disc Filters (Pressure and Vacuum)
● Belt Filters (Vacuum)
● Horizontal Pan Filters (Vacuum)
● Centrifugal Filters
● Cross-Flow Filters
Source: LiqTech International
Common Types of Gas-Liquid Separation
Separations Process Principles (Textbook)
Phase Addition/Creation
Flash Drums (Liquid --> Vapor)
Absorption (Vapor --> Liquid)
Stripping (Liquid --> Vapor)
Distillation (Liquid and/or Vapor --> Liquid and/or Vapor)
Common Types of Gas-Liquid Separation (Cont’d)
Barrier
Osmosis (Liquid across
nonporous agent)
Gas Permeation (Vapor across
nonporous agent)
Solid Agent
Adsorption (Vapor or Liquid
separated by solid)
Chromatography
Ion Exchange
Force Field or Gradient
Centrifugation
Electrodialysis
Separations Process Principles (Textbook)
Flash Drums (or Knockout Drums)
Purpose: Separate entrained liquid
droplets from vapor streams
Method: Use gravity to settle the liquid
Types: Vertical & Horizontal Drums
Modifications: Demisters improve
separation performance (esp. for small
droplets)
https://en.wikipedia.org/wiki/Flash_evaporation
Designing Vertical Flash Drums
1. Solve for settling velocity ut
1. Solve for minimum vessel diameter Dv
1. Calculate liquid depth hL for holdup time of
10 minutes (ensure suitable vessel sizing)
Chemical Engineering Design, Principles, 2nd Edition (Textbook)
Designing Horizontal Flash Drums
Vessel diameter cannot be
determined independently
from length
Vapor residence time for liquid
settling
Liquid holdup time requirements
See pg. 772 Design Textbook for
calculation examples
Most economical Lv/Dv ratio
depends on operating
pressure
Chemical Engineering Design, Principles, 2nd Edition (Textbook)
Flash Drums in Diesel Production
http://www.orioninstruments.com/petroleum-refining#preflash drums
Flash Drums in Diesel Production
Separates out the vapors before
entering column etc.
Reduces vapor loading to avoid
flooding
Prevents higher heater firing and
pressure drops
http://www.orioninstruments.com/petroleum-refining#preflash drums
Distillation
Purpose: Separate components based on
volatility
Method: Selective evaporation and
condensation
Types: Batch & continuous
Applications: Alcohols, fossil fuels,
atmospheric gases
http://controlguru.com/distillation-introduction-to-control/
Designing Distillation Columns
1. Plot equilibrium data
2. Plot operating lines & q line
3. Count steps between operating line
and equilibrium data from xd to xb
4. This is the required number of stages
http://www.slideshare.net/alsyourih/design-of-packedcolumns
Sizing and Pricing Distillation Columns
Smaller is cheaper!
Fewer trays means less height
Diameter is determined by vapor velocity
and tray spacing
Spacing is usually around 2ft but can be
changed to minimize shell volume
Trays also cost money
http://www.wikiwand.com/en/Fractionating
_column
Useful Resources
Solid Liquid Separators: Towler Chapter 18.6
Liquid Vapor Separators: Towler Chapter 16.3
Liquid Liquid Separators: Towler Chapter 16.4
Distillation Columns: Towler Chapter 17