Methods to control s ox emissions oxides of sulphur desulphurization gaseous pollutants air pollution and control

1. Methods to control SOx
emissions
Ravi Kumar GARRE

2. Contents covered
• Introduction
• Natural dispersion by dilution
• Use of alternate fuel
• Desulphurization before combustion
• Desulphurization during combustion
• Desulphurization after combustion
• Coal gasification
• Microbial method

3. Introduction
• SOx includes four different gaseous compounds
namely:
 SO – Sulphur monoxide
 SO2 – Sulphur dioxide
 SO3 – sulphur trioxide
 SO4 – Sulphur tetra oxide
• SO2 is primary and major pollutant. Almost 60 to
70% of world’s air pollution is caused by SO2.

4. Introduction
• SO2 is colourless, non-flammable and non-
explosive. It has pungent and unpleasant
odour.
• SO2 is highly soluble in water. Causes acid rain.
• Reacts photo-chemically to form SO3, H2SO4.
SO2+H2O H2SO3 (Sulphurous acid)
SO3+H2O H2SO4 (Sulphuric acid)

5. Introduction
• Natural sources of sulphur dioxide include
Volcanoes and hot springs.
• Man-made sources of sulphur dioxide include
gas processing, oil production, chemical
manufacturing and other fossil fuel processing
and burning.
• About 30% of SO2 in the atmosphere is
converted to sulphate aerosols.

6. Introduction
• SOx affect the health of human beings and cause
vegetation damage.
• SOx always move close to ground surface.
• Reduces lung function, create problems to
respiratory system.
• Causes irritation of eyes, throat and nose.
• Alone, SO2 will dissolve in the watery fluids of the
upper respiratory system and be absorbed into
the blood stream.
• Health effects attributed to SOx are due to
exposure to sulphur dioxide, sulphate aerosols
and SO2 adsorbed onto particulate matter.

7. Introduction
• The following various methods used to control
the emission of SOx into atmosphere:
 Natural dispersion by dilution
 Using alternate fuels
 Desulphurization before combustion
 Desulphurization during combustion
 Desulphurization after combustion
 Coal gasification
 Microbial method

8. Introduction
• The control methods of SOx involves in
extraction of sulphur in fuels.
• The sulphur either in organic or in inorganic
form in fuels.
• Inorganic sulphur – iron sulphide. It can be
readily reduced by washing.
• Organic sulphur – cystine, thiones and
sulphides, etc. It can be reduced by various
types of chemical processes.

9. Natural dispersion by dilution
• The control method is based on natural
dispersion at high elevation. So that the ground
level concentrations are acceptable.
• In India, minimum stack height recommended is
30m.
• Height of chimney H = 14XQ0.3, where Q is SOx
emission rate in kg/hr.
• Obsolete method/ very less used.
• People have now become more conscious about
the atmosphere, environment.

10. Using alternate fuel
• A switch to natural gas from the conventional
high sulphur fuels like coal and petroleum
reduces SOx emissions.
• LNG/ LPG are also quite effective.
• Low sulphur containing coals also an
alternative.

11. Using alternate fuel

12. Desulphurization before combustion
• Pre-combustion – (reducing sulphur content of
the fuel before combustion).
• Emissions of SO2 are proportional to the sulphur
content of the fuel.
• Although w. r. to coal proportions and usually less
than 10% is retained in the ash.
• This can be accomplished by:
 Usage of low sulphur fuel
 Hydrodesulphurization of coal
 Hydrodesulphurization of oil

13. Usage of low sulphur coal
• One of the simplest ways to reduce SO2
released from the combustion can be
achieved by switching to a fuel that has a low
sulphur content.
• That is burning low sulphur coal/ oil instead of
high sulphur coal/ oil.

14. Hydrodesulphurization of coal
• This process uses a solvent extraction process
for the removal of sulphur.
• By using this procedure, both the organic and
inorganic sulphurs can be removed.
• In this process, slurry is prepared with coal
and oil, and then the slurry is heated at high
temperature up to 4500C to dissolve the coal.
• Then the ash (contains sulphites and
sulphates) is eliminated by filtration process.

15. Hydrodesulphurization of fuel oils
• Sulphur can be removed from fuel oil by
hydrodesulphurization process.
• In this process, fuel oil treated with hydrogen
over a catalyst (molybdenum) at temperature
higher than 3000C.
• Estimated casts for reducing sulphur content
from fuel by 50%.

16. Hydrodesulphurization plant

17. Desulphurization during combustion
• Sulphur removal in combustion chamber.
• It is applicable to conventional combustion
chamber.
• In this method, finely powdered lime stone is
injected directly into the combustion chamber.
• The lime stone, first is calcinated to CaO by
the heat in combustion chamber.
• And then it reacts with SO2 contained in the
flue gas to form sulphites and sulphates.

18. Desulphurization during combustion
• The formation of CaSO4 is favoured at and
above 10000C.
• CaCO3 CaO+CO2
• CaO+SO2 CaSO3
• CaO+SO2 1/2O2 CaSO4
• The formed CaSO4 is not stable above 12000C.
• The process is not efficient to remove more
than 50% of SO2 formed.

19. Desulphurization during combustion
• A number of technologies has been developed to
prevent production and release of SO2 during
combustion have been developed during fast
decades.
• the most developed are the fluidized bed
combustion (FBC) process and the integrated
gasification combined cycle (IGCC) system.
• The FBC process is most advanced and is
developed to over come the instability of forming
of CaSO4.

20. Fluidized bed combustion system
• In this process, both the coal and lime stone
are crushed together and formed the bed and
air is used as fluidized medium.
• The operating temperature lies between 700
to 1000˚C.
• This process have proved very effective as it
can remove 90 to 95% of SO2 formed.

21. Fluidized bed combustion system
C+CaSO4 2CaO+2SO2+CO2
• This regeneration will reduce the consumption
also.
• In this process, non-stability of forming is
avoided.
• This process prevents ash fusion, fouling and
corrosion of the boiler tubes.

22. Desulphurization after combustion
• Post combustion/ flue gas desulphurization.
• Flue gas desulphurization is employed to control from
industries or power plants.
• Classified as dry process and wet process.
Dry processes
Alkalized alumina
process
Manganese oxide
process
Adsorption by
activated carbon
Wet processes
Lime stone
scrubbing
Manganese oxide
process
Welman’s Lord
process

23. Dry process
• Adsorption of SO2 by metal oxides to form
stable sulphites or sulphates with subsequent
regeneration.
Alkalized alumina process
Manganese oxide process
• Adsorption on activated carbon followed by
regeneration and conversion of concentrated
to sulphuric acid or elemental sulphur.
The Reinluft process

24. Alkalized alumina process
• Also called as cyclic adsorption process.
• Developed by US Bureau of Mines.
• Adsorbent: Sodium aluminate (Na2O.Al2O3)
• This process uses Sodium aluminate
(Na2O.Al2O3) to remove SO2 in fluidized bed at
3150C.
• Na2O.Al2O3+SO2+1/2O2 Na2SO4+Al2SO3

25. Alkalized alumina process

26. Alkalized alumina process
• The product of above reaction is then
contacted with a reducing gas such as H2 in a
regenerator at 6800C to produce H2S.
Na2SO4+Al2O3+4H2 Na2O.Al2O3+H2S+3H2O
• Sodium aluminates is recycled back and H2S is
sent to Claus process for producing sulphur.

27. Manganese oxide process
MnO2 + SO2 MnSO4

28. Manganese oxide process

29. Reinluft process (Activated carbon)

30. Wet processes
Absorption of SO2 by liquids to from stable
sulphites or sulphates with subsequent regeneration.
• Lime Stone Scrubbing Process (Calsox Process)
• Magnesium Oxide Scrubbing Process
(Chemico Process)
• Welman Lord Process (Single Alkali Process)

31. Lime Stone Scrubbing (Calsox)
• Uses slurry of Lime or Lime stone as scrubbing liquid.
• Waste gases are first made free from any objectionable
materials like ash in a ash collector and then introduced into
Scrubber.
• The flue gas is scrubbed within slurry of Lime and Limes
stone through which SO2 is absorbed forming Calcium
Sulphate & Sulphite. (CaSO4 , CaSO3)
• The solids are continuously separated from the slurry and
are discharges into settling pond.
• The remaining liquid of pH 6 to 8 is recycled back to the
scrubbing tower after fresh lime or limestone has been
added.

32. Lime Stone Scrubbing (Calsox)
• Removal Efficiency:
Generally can remove 80-90% of SO2. However if designed
properly can remove up to 99% of SO2.
• Removal Efficiency
CaO + H2O → Ca (OH)2
Ca (OH)2 + CO2→ CaCO3 + H2O
CaCO3 + CO2 + H2O → Ca(HCO3)2
Ca (HCO3)2+ SO2+ H2O → CaSO3.2H2O + 2CO2
CaSO3.2H2O + ½ O2→ CaSO4.2H2O
2CaCO3 + 2SO2 + ½ O2 → CaSO3 + CaSO4+ 2CO2
2CaOH + 2SO + ½ O → CaSO + CaSO+ 2HO

33. Lime Stone Scrubbing (Calsox)

34. Mg Oxide Process (Chemico)

35. Mg Oxide Process (Chemico)
• The mixed sulphite/sulphate slurry along with
unreacted MgO is separated from the liquid phase in a
Centrifuge and the mother liquid is recycled to the
absorber.
• The centrifuged wet cake is dried and regenerated
in a calciner.
• Carbon is added in the calcining step to reduce any
MgSO4 to MgO and SO2:
MgSO4 + ½ C → MgO + SO2+ ½ CO2
• MgO is returned to the process, while the concentrated
SO2 can be reprocessed into H2SO4 or elemental
sulphur.

36. Mg Oxide Process (Chemico)

37. Welman-Lord (Single Alkali)
• Also known as Single Alkali Process.
• Uses Slurry of aqueous solution of sodium
sulphite
• to scrub the flue gas in a Absorber.
• In this process sulphite is converted into
bisulphite as the SO2 from the flue gases is
absorbed by saturated solution of sodium
sulphite according to the following reaction:
• Na2SO3+ SO2+ H2O →2NaHSO3

38. Welman Lord (Single Alkali)
• The sodium bisulphite formed is led to a double effect
evaporator cum crystallizer where it decomposed
into sodium sulphite at a temperature 100°C. This
results in ejection of SO2and steam.
2NaHSO3 → 100°C → Na2SO3+ SO2+H2O
• Fly ash is removed before the SO2scrubbing to keep the
rate of its accumulation in the scrubbing liquid low. SO2
and water vapour released from the evaporators are
passed into a condenser and the product goes to the
dissolving tank for dissolution of Na2SO3crystals and
the rich SO2gas is processed.

39. Welman-Lord (Single Alkali)
• Sodium sulphate is produced in this reaction
which is removed and substituted by an
equivalent amount of NaOH.
• Clear solutions of either sodium or ammonia
are excellent absorbers of SO2. The
regeneration step can be carried out a low
temperature in liquid system.

40. Welman Lord (Single Alkali)

41. Coal gasification
• This produces better quality gas other than
the oxides of sulphur.
• This remove both organic and inorganic oxides
of sulphur.
• The process is affected with partial oxidation
of coal in presence of oxygen and steam.
• This process yields carbon monoxide and
hydrogen.

42. Microbial method
• In this method a sulphur deficient bacteria is
utilized.
• Sulphur deficient bacteria is first culture in
medium which contains all the nutrients
except sulphur.
• When they passed through air containing
sulphur they utilize it for their growth.
• Example of such bacteria is IGT57.

43. Thank you