Post on 16-Dec-2015
transcript
Sulfur oxidesSulfur oxides
authors: Dr. Bajnóczy Gábor
Kiss Bernadett
BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS
DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING
FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING
The pictures and drawings The pictures and drawings of this presentation can be of this presentation can be used only for education !used only for education !
Any commercial use is Any commercial use is prohibited !prohibited !
Physical properties of Physical properties of atmospheric sulfur oxidesatmospheric sulfur oxides
Sulfur dioxide
SO2
Sulfur trioxideSO3
Molecular mass 64 80
Melting point oC -75 16,8
Boiling point oC -10 43,7
density0 0C, 101.3 kPa
20 0C, 101.3 kPa
1.250 g/dm3
2.93 g/dm3
2.052 g/dm3
1,916 g/dm3
Solubility in water0 0C 101.3 kPa
80 dm3/ dm3 (97.7 ppmm)** decay
Conversion factors
0 0C, 101.3 kPa
1 mg/m3 = 2.663 ppmv***
1 ppmv = 0.376 mg/m3
Sulfur dioxide:• colorless• irritating odor (odor threshold 0,3-1 ppm)• soluble in water• natural background~1 ppb
Sulfur trioxide: • highly reactive => short lifetime in the atmosphere, sulfuric acid formation with water
Direct emission is mainly sulfur dioxide, only some percent of sulfur trioxide
Natural sources of sulfur Natural sources of sulfur
dioxidedioxide Volcanic action.
A volcanic gases: 90% water and
CO2, SO2 content 1-10 % .
Sulfur compounds from biological
activity
(CH3SCH3, H2S, CS2, COS) will be
oxidized in the atmosphere.
Sulfur emission in highest amount:
dimethyl-szulfide from the oceans →
biological activity of fitoplankton.
Sulfur dioxide from human activitySulfur dioxide from human activity
Main source: combustion of fossile fuels
Sulfur content of coal and crude oil differs.
Crude oil: mainly organic, (sulfides, mercaptenes, bisulfides,
tiofenes) => can be removed by simple technology.
Coal:
• pyritic (FeS), removable by physical method ,
• sulfates (CaSO4, FeSO4) removable by physical method (no decay at
combustion temperature to SO2)
• matrix sulfur a incorporated in polymer molecule
Atmospheric sulfur content is mainly anthropogenic origin.
Sulfur dioxide from human activitySulfur dioxide from human activityAnother significant source: smelter operation
Cu, Zn, Cd, Pb occur in the nature mainly in sulfide ore form. Can
not be reduced directly.
Roasting of sulfide ores on air produces oxides (ZnO, CdO, CuO….)
→ the oxides can be reduced
Cu, Ni:
roasting: only the metal content can be concentrated
Final sulfur elimination: air blowing through the melted sulfur
contaminated ore
Sulfur content is transformed to sulfur dioxide => the capture of SO2
depends on the level of technology.
Sulfur dioxide from human activitySulfur dioxide from human activity
smelter operation : far from built-up area.
Not a solution due to the global character of sulfur
oxide pollution !
Chemistry of sulfur oxide Chemistry of sulfur oxide
formationformation
O + S2 = SO + S
O + SO = SO2
Tüzelőanyag-S│
hő hatásra ▼ termikus bomlás┌─────────────────────┼─────────────────────┐
▼ ▼ ▼ H2S COS koksz-S
H2S + O = •OH + SH O + COS = SO + CO koksz-S + O → SO
SH + O = SO + H SO + O = SO2 koksz-S + CO2 → COS
SO + O = SO2 koksz-S + H2O → H2S
Burning of elemental sulfur: oxygen atom starts the reaction,
transition compound: sulfur monoxide.
Combustion of sulfur containing materials (fuel-S) :
thermal decay → char-S, (shrunken solid fuel) hydrogen sulfide (H2S) and carbonyl sulfide (COS) form.
All of the three products is oxidized to sulfur dioxideFuel-S
Heat effect Thermal decay
char-S
char-S
char-S
char-S
Chemistry of sulfur oxide Chemistry of sulfur oxide formationformation
O + SO2 <=> SO3
Further oxidation of sulfur dioxide → sulfur trioxide:
• oxygen atoms and hydroxyl radicals play a significant role.
• equilibrium shifts left with temperature increase
• the reaction rate is slow
• only 0.5-2.5% of SO2 is converted to SO3
• the time to reach the equilibrium depends of the catalytic effect of the metal content (W, Mo, V, Cr, Ni, Fe oxides) in ash
Chemistry of sulfur oxide Chemistry of sulfur oxide formationformation
The dew point of sulfuric acid depends on the SO3 and water content of the stack gas.
Dew point of sulfuric acid in function of SO3 and water concentration in stack gas ..and the damage
• Sulfur trioxide at 482 oC transforms to sulfuric acid. Under the dew point sulfuric acid condensates on the structure materials (heat exchanger, stack wall ).
stack gas temperature
Dimethyl sulfide, hydrogen sulfide, carbonyl Dimethyl sulfide, hydrogen sulfide, carbonyl sulfide, carbon disulfide in the atmospheresulfide, carbon disulfide in the atmosphere
Oxidized to sulfur dioxide
Oxidizing agent: hydroxyl radicals
Oxidation of dimethyl-sulfide → methane sulfonic acid aerosol (CH3SO3H) → serves as nuclei for cloud formation
carbonyl-sulfide:
Slow oxidation by hydroxyl radicals => oxidation in the stratosphere by atomic oxygen
Lifetime in years.
Hydrogen sulfide, carbonyl disulfide quick oxidation to SO2 in the troposphere
Catalytic transformation of sulfur Catalytic transformation of sulfur dioxide to sulfuric aciddioxide to sulfuric acid
SO2 dissolution
O2 dissolution Ash particles
catalyst
Photochemical transformation of Photochemical transformation of sulfur dioxide to sulfuric acidsulfur dioxide to sulfuric acid
Hydroxyl radicals oxidize the sulfur dioxide to sulfur trioxide.
O3 + light = O + O2
O + H2O = 2 OH•
OH• + SO2 + M = HSO3• + M*
HSO3• + O2 = HO2• + SO3
Sulfur trioxide and water → quick reaction → sulfuric acid
SO3 + H2O = H2SO4
▼
Acidic rain
Effects of acidic rainEffects of acidic rain
pH of rain: adjusted by the rate of natural acidic and basic materials
Usually acidic: solution of carbon dioxide (pH=5.56)
Generally accepted: pH under 5 is due to human activity .
The acidity surplus :
60-70% sulfuric acid from sulfur dioxide
The rest comes from nitric acid formed from nitric oxide
Some percent hydrochloric acid
pH of rain > pH of fog particles
Effects of acidic rain on plantsEffects of acidic rain on plants
Three stages can be distinguished
1. Mobilization of soluble plant nutrients, e.g. nitrogen compounds
2. Nutrient wash out by the rain water → nutrient shortage
3. Al 3+ ion liberation from the clay minerals due to the decreasing pH in the soil.
The free aluminum ion is toxic to the roots, weakens the immunizing system → secondary infections
toxic Non toxic▐
Soil pH
Effect of acidic rain on natural Effect of acidic rain on natural water I.water I.
The excess of H+ ion in rain water shifts the hydro carbonate equilibrium towards the formation of free carbon dioxide.
H+ + HCO3 ─ <=> H2O + CO 2
• The physically dissolved CO2 inhibit the OO22 ↔↔ CO CO22 exchange in living organisms : e.g. fishexchange in living organisms : e.g. fish). ).
• occurs at spring when the melted acidic snow flows suddenly into the rivers of catchments area.
• If natural water is in contact with limestone, dolomite, the pH does not change → buffer effect. The living organisms are killed by the increased CO2 content
• In case of week buffer effect (small Ca- and Mg-hydro carbonate content) the living organisms are killed by the decreased pH
Effect of acidic rain on natural water Effect of acidic rain on natural water II.II.
pH tolerance of waterborne organisms
The lack of mussels in natural waters may indicate the change of pH, they can not change theirs position
quickly
Effect of acidic rain on calcium carbonate Effect of acidic rain on calcium carbonate containing materials I.containing materials I.
• calcium carbonate containing materials: marble, limestone, plaster, concrete → sensitive to acidic rain
• in the last fifty year the weathering of open air ancient monuments speeded up
Effect of acidic rain on calcium Effect of acidic rain on calcium carbonate containing materialscarbonate containing materials II. II.
Effect: The infiltrating acidic rainwater contaminated by sulfuric acid changes the crystals of calcium carbonate to calcium sulfate
The solubility of calcium sulfate > solubility of calcium carbonate.
Crystal volume of CaSO4 > crystal volume of CaCO3
stress in the material structure → crack
CaCO3 + H2SO4 = CaSO4 + H2O + CO2
Effect of acidic rain on metal constructions Effect of acidic rain on metal constructions
I.I. Preliminary conditions of the electrochemical corrosion:
1. two metallic material with different electrochemical potential in metallic contact.
2. electrolyte cover on the metallic contact, (e.g.. water solutions of acids, salts)
3. presence of electron uptake material (H+ O2 Cl2 )
Electrochemical corrosion of metal:
Oxidation: the metal transform to ion and free electrons release.
Fe = Fe 2+ + 2 e-
Reduction: uptake of free electrons by
2H+ + 2e- = H2
O2 + 4H+ + 4e- = 2 H2O
H2O + CO2 + e- = H + CO32-
Cl2 + 2e- = 2 Cl-
Effect of acidic rain on metal Effect of acidic rain on metal constructions II.constructions II.Fe ─────> Fe2+ + 2 e-
2H+ + 2e- = H2
Air pollution induced electrochemical corrosion resulted in the collapse of Silver bridge over Ohio river on 15-th. Dec. 1967.
Acid rain: electrolyte and the hydrogen ion serves the reduction (electron uptake)
Effect of atmospheric SOEffect of atmospheric SO22 on on paperspapers
Paper surface H2SO4 formation on the surface The result
The paper gets yellow and brittle.
No damag
e
Destroyed surface
adsorption
desorption
Fe catalyst
Anthropogenic effects of SOAnthropogenic effects of SO22
Good solubility in water → the effect on the upper part of the respiratory system.
Irritating effect over 10 ppm
Nonstop irritation of mucous lining in urban air results in frequent colds, flu
Control of sulfur dioxide Control of sulfur dioxide emissionemission
Power plants based on fossil fuels produce sulfur oxide emission
Transportation is based on fossil fuel but the emission is not so serious
The sulfur can be removed easily from liquid material
The anthropogenic emission decreased half of the original one since.
Sulfur dioxide easily can be eliminated from the stack gas
Problems to be solved: fate of the sulfur containing product
SO2 emission controls are divided into two categories:
Reduction of the sulfur content of the fuel,
The sulfur dioxide is removed from the exhaust gas.
Power plantsPower plants Simplest way: replacement of high sulfur content
fuel with low sulfur content fuel
e.g. coal fired power station → gas fired power plant.
Not a final solution: the available gas resources are restricted
Coal might be the fuel of future again
Sulfur content reduction of solid Sulfur content reduction of solid
fuelfuel Sulfur content of the coal: <1% . . . 10-12%
Form of sulfur:
1. pyritic sulfur (FeS2)
2. sulfate sulfur (e.g.. iron- and calcium sulfate)
3. matrix sulfur. (sulfur in organic bond ) Extraction of sulfur:
1.and 2. by simple technology (e.g.. flotation) , based on density difference of coal and pyrite, sulfate
3. chemically bonded => physical methods can not be applied.
Direct chemical treatment e.g. NaOH is not economical
Gasification of coal by air and/or water. Removal of the formed hydrogen sulfide H2S from the gas.
Sulfur content reduction of liquid and Sulfur content reduction of liquid and gas fuelgas fuel
Desulphurization:
Hydro processing: evaporated fractions of crude oil and hydrogen is in contact with catalyst Co/Mo to transform organic sulfur to hydrogen sulfide at high pressure.
Hydro processing might be
Destructive: carbon chain crack and sulfur transformation
Nondestructive: to improve the quality of oil fractions
Sulfur content → hydrogen sulfide
Nitrogen content → ammonia
Hydrogen sulfide removalHydrogen sulfide removal
Physical absorption at low temperature minus 30-120 °C (methanol, dimethyl ether)
Chemical adsorption (organic amines, metal oxides)
Reversible processes → the absorbed and adsorbed hydrogen sulfide can be recovered in concentrated form
The concentrated hydrogen sulfide → Claus plant
Hidrogen sulfide treatment by Claus Hidrogen sulfide treatment by Claus
processprocess Concentrated gas (> 50..60 vol % H2S) is partially
oxidized to sulfur and water2 H2S + O2 = S + 2
H2O• 2/3 part of the H2S concentrated gas is oxidized and combined with the rest
2 H2S + 2 O2 = SO2 + 2 H2O
2 H2S + SO2 = 2 S + 2 H2O
After cooling the gas mixture is feed into the Claus reactor at 200-350 0C(catalist: aluminum oxide) to increase the conversion.
→ 1000-1400 0C
→ after cooling the sulfur can be separated
Sulfur dioxide removal from the flue Sulfur dioxide removal from the flue gas gas
by wet processby wet process
Füstgázkezelés vizes mész szuszpenzióvalCaO + H2O = Ca(OH)2
SO2 + Ca(OH)2 + H2O = CaSO3∙2H2O
CaSO3∙2H2O + ½ O2 = CaSO4∙2H2O
-----------------------------------------------------------Füstgázkezelés vizes mészkő szuszpenzióval
CaCO3 + H2O + 2 SO2 = Ca(HSO3)2 + CO2
CaCO3 + Ca(HSO3)2 + H2O = CaSO3∙2H2O + CO2
CaSO3∙2H2O + ½ O2 = CaSO4∙2H2O
reactant: lime CaO / limestone CaCO3 → product: CaSO4 (gypsum)
Cheap raw material → 80 % of SO2 cleaning technologies are based on this one Wet scrubbers, at 70 – 90
0C
efficiency 90-95%
Flue gas treatment by lime suspension in water
Flue gas treatment by limestone suspension in water
Wet scrubber for SOWet scrubber for SO22 removal removal
Flue gas desulphurization (FGD) Flue gas desulphurization (FGD) regenerable regenerable adsorbentadsorbent
ScrubberNa2SO3 + SO2 + H2O = 2 NaHSO3
Na2SO3 + ½ O2 = Na2SO4
-------------------------------------------Regenerator
2 NaHSO3 = Na2SO3 + SO2 + H2O
-------------------------------------------Solution from the make up in the
scrubberNa2CO3 + SO2 = 2 Na2SO3 + CO2
2 NaOH + SO2 = 2 Na2SO3 + H2O
Wellman-Lord technology, advantages: Not too much byproduct Extracted sulfur dioxide in concentrated form