2. gaseous compounds SOx includes six different
namely:
SO – Sulfur Monoxide
SO2– SulfurDioxide
SO3– Sulfur Trioxide
SO4– Sulfur Tetroxide
S2O5– Sulfur Sesquioxide
S2O6– Sulfur Heptoxide
SOx Emissions
Most
Significant
3. SO2is
Colorless
Non Flammable
Non Explosive
Suffocating Odor (Threshold value 0.5 ppm)
Highly Soluble in water (70%Acid rain)
Reacts photo-chemically to form SO3, H2SO4
SO2+ H2O → H2SO3(Sulphurous Acid)
SO3+ H2O → H2SO4(SulphuricAcid)
SOx Emissions
4. Natural sources of sulphur dioxide include volcanoes
and hot springs.
Sulphur dioxide is also formed by the oxidation of
hydrogen sulphide (H2S), a toxic gas that smells like
rotten eggs. Hydrogen sulphide is frequently found with
natural gas.
Man-made sources of sulphur dioxide include sour gas
processing, oil production, coal combustion, ore
refining, chemical manufacturing and other fossil fuel
processing and burning.
Sources of SOx Emissions
5. There are six procedures for controlling of SOx emissions.
Natural dispersion by dilution.
UsingAlternate fuels.
Removal of Sulfur by desulphurization.
Control of SOxin the combustion process.
Treatment of flue gas→ Dry Methods &Wet Methods
Control of SOx Emissions
6. The control method is based on natural dispersion at
high elevation so that the ground level concentration
are acceptable.
In India, minimum stack height recommended is 30m.
Height of Chimney H = 14*Q0.3;for Q kg /hr of SOx
emission.
Obsolete method/very less used.
People have now become more conscious about the
atmosphere, environment.
Natural Dispersion by Dilution
7. A switch to natural gas from the conventional high
reduces SOxsulfur fuels like coal & petroleum
emissions.
LNG/PNG are also quiet effective.
Low sulfur containing coals is also an alternative.
Use Alternate Fuel
9. Removal of sulphur from fuels prior to combustion is
theoretically an attractive route.
Sulphur in coal is present in both inorganic and
organic forms. All inorganic sulphur is present in coal
as Iron Disulphide (FeS2).
Washing can reduce the pyritic sulphur content which
also results in the loss of combustible material and may
add 20% to the cost of coal. Organic sulphur is present
in forms of cystin, thiols, sulphides which is uniformly
bound with most of the carbonaceous material and can
be removed only by chemical processing.
Removal of Sulfur from Fuels
10. The term hydro treating is used to describe the process of
the removal of sulphur, nitrogen and metal impurities in
the feedstock by hydrogen in the presence of a catalyst.
Objectives:
Removing impurities, such as sulphur, nitrogen and
oxygen for the control of a final product specification or
for the preparation of feed for further processing.
Removal of metals, usually in a separate guard catalytic
reactor when the organo-metallic compounds are
hydrogenated and decomposed, resulting in metal
deposition on the catalyst pores (e.g. atmospheric residue
desulphurization (ARDS) guard reactor).
Hydro Treating
12. Process Explanation
The liquid feed is mixed with hydrogen and fed into a
heater and the mixture is brought to the reaction
temperature in a furnace and then fed into a fixed bed
catalytic reactor.
The effluent is cooled and hydrogen-rich gas is separated
from the liquid using a high pressure separator.
Before the hydrogen is recycled, hydrogen sulphide can be
removed using an Amine Scrubber.
Some of the recycle gas is also purged to prevent the
accumulation of light hydrocarbons (C1–C4).
The liquid effluent for the reactor is introduced to a
fractionators for product separation.
13. This process can remove both the organic & inorganic
sulfur from coal.
Steps :
Preparation of Slurry (Oil + Anthracene Coal)
Heating at high temperature (450°C)
Filtration of organic & inorganic form from ash.
Evaporation followed by Distillation
Solidification
Hydro-desulphurization of
Coal (Solvent Extraction)
15. In this process slurry of anthracene oil with finely
grounded coal is prepared to which a small amount of
hydrogen is added to prevent repolymerization.
The slurry is then heated at high temperature of 450°C
in order to dissolve coal.
The ash residue consisting of pyritic sulphur and
other minerals is eliminated by pressure filtration.
The coal solution filtrate is sent to flash evaporator
where the light fraction is removed which is followed
by distillation operation to recover solvent.
Process Explanation
16. The hot liquid evaporator residue is cooled to a brittle
solid fuel which can be pulverized.
The product can be liquefied at 250°C which has a
higher heating value than raw coal and contains less
than 1% sulphur.
Process Explanation
17. Flue gas desulfurization aims to reduce sulfur oxides
emissions from the stack gases of the refineries and
power plants to 150-1500 ppm range, for pollution
control.
Classified as Dry Process and Wet Process.
Wet scrubbing processes are effective but the cost of
equipment is very high and difficult to install at
various plants.
Thus Dry Process are much preferred.
Desulphurization of Flue Gas
18. Adsorption of SO2 by metal oxides to from stable
sulphites or sulphates with subsequent regeneration.
Alkalized Alumina Process
Manganese Oxide Process
Adsorption on activated carbon followed by
regeneration and conversion of concentrated SO2 to
sulphuric acid or elemental sulphur.
The Reinluft Process
Dry Process
19. Also called as Cyclic Adsorption Process.
Developed by U.S Bureau of Mines.
Adsorbent :SodiumAluminate (Na2O.Al2O3)
This process uses Sodium Aluminate (Na2O.Al2O3) to
remove SO2in fluidized bed at 315°C.
Na2O.Al2O3+ SO2+ ½ O2→ Na2SO4+ Al2SO3
Alkalized Alumina Process
21. The product of above reaction is then contacted with a
reducing gas such as H2 in a regenerator at 680°C to
produce H2S.
Na2SO4+ Al2O3+ 4H2→ Na2O.Al2O3+ H2S+ 3H2O
SodiumAluminate is recycled back and H2S is sent to
Claus Process for producing Sulphur.
22. Developed by Mitsuibishi Heavy Industries, Japan.
The powdered adsorbent is fed into the reactor
wherein the Manganese Oxide reacts with SO2 to
produce Manganese Sulphate (MnSO4):
MnOx.yH2O + SO2+ ½ (2-x) O2 → MnSO4+ yH2O
Where x ranges from 1.5 to 1.8, and yranges from 0.1
to 1.0.
Manganese Oxide Process
23. The spent adsorbent is regenerated by reacting with
Manganese Sulphate with Air and Ammonia to
produce Ammonium Sulphate:
MnSO4+ 2NH3 + 2H2O + (y-1) H2O + ½ (x-1) O2→
(NH4)2SO4+ MnOx.yH2O
The activated manganese oxide is filtered from the
Ammonium Sulphate (NH4)2SO4 Solution and the
filtrate is passed through a crystallizer where
Ammonium Sulphate (NH4)2SO4is Recovered.
25. Reinluft Process (activated
charcoal)
Uses cheap semicoke of peat, carbonized under vacuum at 600°C
as a adsorbent.
The flue gas enters the lower section of the adsorber at 150-
200°C and after partial adsorption of the SO2gas it is withdrawn
and then passed through the cooler where it is cooled to about
110°C.After cooling it is returned to the
upper section of the adsorber and leaves the top of adsorber at
temperature 100°C.
The spent carbon is dropped into a regenerator where it is heated
upto 380-450°C by an inert gas stream which removes the
adsorbed acidic materials and produces SO2 of 10 – 15%
concentration which can be used as a feed gas for contact acid
plant.
26.
27. Absorption of SO2 by 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)
Wet Process
28. Lime Stone Scrubbing (Calsox)
Uses slurry of Lime orLime 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 5 to 15% 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 liquor of pH 6 to 8 is recycled back to the
scrubbing tower after fresh lime or limestone has been added.
29. Lime Stone Scrubbing (Calsox)
Removal Efficiency:
Generally can remove 80-90% of SO2. However if designed
properly can remove upto 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+ 2H O
31. Mg Oxide Process (Chemico)
Also known as Chemico Process.
Uses Slurry of Magnesium Oxide to scrub the flue gas in a
Venturi Scrubber.
The flue gas is scrubbed with a slurry of magnesium
oxide in venture scrubber which absorbs SO2and yields
Magnesium Sulphite and Sulphate according to the
following reaction:
MgO + SO2 →MgSO3
MgSO3+ SO2+ H2O → Mg(HSO3)2
Mg(HSO3)2+ MgO → 2MgSO3+ H2O
MgSO3+ ½ O2→MgSO4
32. 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 liquor (The liquid remaining
after a substance has crystallized out) 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
34. 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
35. 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 Na2SO3 crystals and
the rich SO2gas is processed.
36. 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.
