SO2

1
SO2
Reading Chap 15

• Strategies for SO2 removal
• Formation Prevention
• Low sulfur fuel, Fuel desulfurization,
• Flue Gas Treatment
• Wet scrubbing, Dry scrubbing, Spray drying, Dual
  Alkali, Wellman-Lord Process

2
Strategies for SO2 Removal
3
Fuel Desulfurization
Oil natural gas
Coal
Mineral sulfate --gt wash away Organic
sulfur ??? --gt SO2 removal IGCC
Integrated Gasification Combined Cycle
Claus process
(for sale a commodity, not a pollutant)
SO2 Removal
High concentration (e.g. smelting)
Absorbing SO2 to make H2SO4
Low concentration (lt 2000 ppm)
Flue gas desulfurization
4
Limestone (Wet) Scrubbing
(packed tower) (effluent hold tank)
Q Advantages and disadvantages compared to water?
Mass transfer in liquid film
f enhancement factor
Overall mass transfer coefficient
Q Does mass transfer increase as f increases?
Main reactions converting SO2 to bisulfite in the
liquid film
precipitate
5
Q Is it better to have a high pH?
6
Lime (Wet) Scrubbing
Q How does it compare to limestone scrubbing?
Dual Alkali
(recycled)
Q Advantages and disadvantages?
7
Lime-Spray Drying
Same as lime scrubbing except the water
evaporates before the droplets reach the bottom
of the tower
Dry scrubbing
Direct injection of pulverized lime or
limestone, also trona (natural Na2CO3) or
nahcolite (natural NaHCO3)
Q Advantage of dry methods over wet methods?
8
Wellman-Lord (W-L) process
(1) Flue gas pretreatment (venturi prescrubber)
to remove particulates, SO3 and HCl
(2) SO2 absorption by Na2SO3 solution
No further SO2 absorption
(3) Purge treatment centrifuge the slurry to
remove solids
(4) Na2SO3 regeneration
Claus process
(concentrated, 85)
(averagely, 1 mole Na2SO3 for 42 moles of SO2)
(make-up sodium)
Westvaco process
9
Quick Reflection