Presentation on theme: "Sulfur oxides authors: Dr. Bajnóczy Gábor Kiss Bernadett BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS."— Presentation transcript:
Sulfur 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 of this presentation can be used only for education ! Any commercial use is prohibited !
Physical properties of atmospheric sulfur oxides Sulfur dioxide SO 2 Sulfur trioxide SO 3 Molecular mass6480 Melting point o C-7516,8 Boiling point o C-1043,7 density 0 0 C, 101.3 kPa 20 0 C, 101.3 kPa 1.250 g/dm 3 2.93 g/dm 3 2.052 g/dm 3 1,916 g/dm 3 Solubility in water 0 0 C 101.3 kPa 80 dm 3 / dm 3 (97.7 ppmm) ** decay Conversion factors 0 0 C, 101.3 kPa 1 mg/m 3 = 2.663 ppmv *** 1 ppmv = 0.376 mg/m 3 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 dioxide Volcanic action. A volcanic gases: 90% water and CO 2, SO 2 content 1-10 %. Sulfur compounds from biological activity (CH 3 SCH 3, H 2 S, CS 2, 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 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 (CaSO 4, FeSO 4 ) removable by physical method (no decay at combustion temperature to SO 2 ) matrix sulfur a incorporated in polymer molecule Atmospheric sulfur content is mainly anthropogenic origin.
Sulfur dioxide from human activity Another 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 SO 2 depends on the level of technology.
Sulfur 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 formation O + S 2 = SO + S O + SO = SO 2 Tüzelőanyag-S │ hő hatásra ▼ termikus bomlás ┌─────────────────────┼─────────────────────┐ ▼ ▼ ▼ H 2 S COS koksz-S H 2 S + O = OH + SH O + COS = SO + CO koksz-S + O → SO SH + O = SO + H SO + O = SO 2 koksz-S + CO 2 → COS SO + O = SO 2 koksz-S + H 2 O → H 2 S 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 (H 2 S) and carbonyl sulfide (COS) form. All of the three products is oxidized to sulfur dioxide Fuel-S Heat effectThermal decay char-S
Chemistry of sulfur oxide formation O + SO 2 SO 3 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 SO 2 is converted to SO 3 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 formation The dew point of sulfuric acid depends on the SO 3 and water content of the stack gas. Dew point of sulfuric acid in function of SO 3 and water concentration in stack gas..and the damage Sulfur trioxide at 482 o C 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 sulfide, carbon disulfide in the atmosphere Oxidized to sulfur dioxide Oxidizing agent: hydroxyl radicals Oxidation of dimethyl-sulfide → methane sulfonic acid aerosol (CH 3 SO 3 H) → 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 SO 2 in the troposphere
Catalytic transformation of sulfur dioxide to sulfuric acid SO 2 dissolution O 2 dissolution Ash particles catalyst
Photochemical transformation of sulfur dioxide to sulfuric acid Hydroxyl radicals oxidize the sulfur dioxide to sulfur trioxide. O 3 + light = O + O 2 O + H 2 O = 2 OH OH + SO 2 + M = HSO 3 + M * HSO 3 + O 2 = HO 2 + SO 3 Sulfur trioxide and water → quick reaction → sulfuric acid SO 3 + H 2 O = H 2 SO 4 ▼ Acidic rain
Effects 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 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 water I. The excess of H + ion in rain water shifts the hydro carbonate equilibrium towards the formation of free carbon dioxide. H + + HCO 3 ─ H 2 O + CO 2 O 2 ↔ CO 2 exchange in living organisms : e.g. fish). The physically dissolved CO 2 inhibit the O 2 ↔ CO 2 exchange 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 CO 2 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 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 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 carbonate containing materials 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 CaSO 4 > crystal volume of CaCO 3 stress in the material structure → crack CaCO 3 + H 2 SO 4 = CaSO 4 + H 2 O + CO 2
Effect of acidic rain on metal constructions 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 + O 2 Cl 2 ) 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 - = H 2 O 2 + 4H + + 4e - = 2 H 2 O H 2 O + CO 2 + e - = H + CO 3 2- Cl 2 + 2e - = 2 Cl -
Effect of acidic rain on metal constructions II. Fe ─────> Fe 2+ + 2 e - 2H + + 2e - = H 2 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 SO 2 on papers Paper surface H 2 SO 4 formation on the surface The result The paper gets yellow and brittle. No damage Destroyed surface adsorption desorption Fe catalyst
Anthropogenic effects of SO 2 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 emission 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 SO 2 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 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 fuel Sulfur content of the coal: <1%... 10-12% Form of sulfur: 1. pyritic sulfur (FeS 2 ) 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 H 2 S from the gas.
Sulfur content reduction of liquid and gas 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 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 process Concentrated gas (> 50..60 vol % H 2 S) is partially oxidized to sulfur and water 2 H 2 S + O 2 = S + 2 H 2 O 2/3 part of the H 2 S concentrated gas is oxidized and combined with the rest 2 H 2 S + 2 O 2 = SO 2 + 2 H 2 O 2 H 2 S + SO 2 = 2 S + 2 H 2 O After cooling the gas mixture is feed into the Claus reactor at 200-350 0 C(catalist: aluminum oxide) to increase the conversion. → 1000-1400 0 C → after cooling the sulfur can be separated
Sulfur dioxide removal from the flue gas by wet process Füstgázkezelés vizes mész szuszpenzióval CaO + H 2 O = Ca(OH) 2 SO 2 + Ca(OH) 2 + H 2 O = CaSO 3 ∙2H 2 O CaSO 3 ∙2H 2 O + ½ O 2 = CaSO 4 ∙2H 2 O ----------------------------------------------------------- Füstgázkezelés vizes mészkő szuszpenzióval CaCO 3 + H 2 O + 2 SO 2 = Ca(HSO 3 ) 2 + CO 2 CaCO 3 + Ca(HSO 3 ) 2 + H 2 O = CaSO 3 ∙2H 2 O + CO 2 CaSO 3 ∙2H 2 O + ½ O 2 = CaSO 4 ∙2H 2 O reactant: lime CaO / limestone CaCO 3 → product: CaSO 4 (gypsum) Cheap raw material → 80 % of SO 2 cleaning technologies are based on this one Wet scrubbers, at 70 – 90 0 C efficiency 90-95% Flue gas treatment by lime suspension in water Flue gas treatment by limestone suspension in water
Flue gas desulphurization (FGD) regenerable adsorbent Scrubber Na 2 SO 3 + SO 2 + H 2 O = 2 NaHSO 3 Na 2 SO 3 + ½ O 2 = Na 2 SO 4 ------------------------------------------- Regenerator 2 NaHSO 3 = Na 2 SO 3 + SO 2 + H 2 O ------------------------------------------- Solution from the make up in the scrubber Na 2 CO 3 + SO 2 = 2 Na 2 SO 3 + CO 2 2 NaOH + SO 2 = 2 Na 2 SO 3 + H 2 O Wellman-Lord technology, advantages: Not too much byproduct Extracted sulfur dioxide in concentrated form