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Carbon monoxide

BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS. DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING. FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING. Carbon monoxide. Authors: Dr. Bajnóczy Gábor Kiss Bernadett.

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Carbon monoxide

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  1. BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS • DEPARTMENT OF CHEMICAL AND • ENVIRONMENTAL PROCESS ENGINEERING • FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING Carbon monoxide Authors: Dr. Bajnóczy Gábor Kiss Bernadett

  2. The pictures and drawings of this presentation can be used only for education !Any commercial use is prohibited !

  3. Carbon monoxide • colorless • odorless • tasteless • Burns with blue flame • Most abundant and widely distributed pollutant in the lower atmosphere • It has a density 96.5% that of air low Wide range Reversible effect in small concentration

  4. Sources of carbon monoxide Natural <=> Antropogenic( 10-50% of the total) Differences: • Distribution: • Natural sources: distributed throughout the world • Anthropogenic sources: concentrated in small area • Rates of formation: • Natural conditions:rate of formation ≈ rate of elimination • In the vicinity of antropogenic sources (towns, industrial areas): rate of formation > rate of elimination (accumulation)

  5. Natural sources of carbon monoxide The surface of oceans is supersaturated in carbon monoxide: Algae and other biological sources. Indirect sources: mud, bogs ►anaerob conditions ►methane formation from the decay of organic materials Decay of chlorophyll in the soil

  6. Sources of natural carbon monoxide • Mud, oceans, chlorophyll… • The majority of CO is indirect origin: oxidation of methan ► CO! organic materials methane Anaerob conditions Biological decay OH* CO

  7. λ<338nm Formation CO from methane • CH4 + •OH = •CH3 + H2O • •CH3 + O2 + M = •CH3O2 + M * • •CH3O2 + NO = •CH3O + NO2 • •CH3O + O2 = HCHO + •HO2 • HCHO •H + •HCO • •HCO + O2 = CO + •HO2HCHO + •OH = CO + •HO2 + H2O Strong oxidation character Lifetime: some hours 4-6 ppbv Reactions of the other formed radicals •H + O2 + M = •HO2 + M * •HO2 + NO = •OH + NO2

  8. CO from anthropogenic sources • Transportation: Internal combustion engines (~75%) • Agricultural burning: (~ 10%) • Industrial process losses: Steal industry, carbon black production, petroleum refineries (~ 10%) • Fuel combustion – stationary sources: coal, fuel oil, natural gas, wood(~ 1%) • Low CO → greater efficiency

  9. Chemistry of the CO formation The formation of anthropogenic CO is generally the result of the following chemical processes: • Incomplete combustion of carbon or carbon containing compounds • High temperature reaction of glowing carbon and carbon dioxide • Dissociation of carbon dioxide at high temperature

  10. Incomplete combustion of carbon or carbon containing compounds ORIGIN OF THE RADICALS IN THE FLAME • H2O → H + OH* thermal decay • O2 → 2 O thermal decay • CxHy → CxHy-1 + H thermal destruction • O + H2O → 2 OH* Stops under 650 °C 650ºC alatt leáll

  11. Incomplete combustion of carbon or carbon containing compounds Fuel and air are poorly mixed Localized areas of oxygen deficiency Accumulation of CO • Optimized combustion conditions: air excess ratio (n) = Actual input of air ▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬ Theoretical need of air input for the perfect combustion

  12. Incomplete combustion of carbon or carbon containing compounds • n = 1 : In case of perfect mixing the available lowest CO content • n < 1 : the amount of oxygen is not enough for the CO → CO2 transformation • n > 1 : too much air cools down the combustion chamber and residence time is decreasing. There is not enough time for the slow CO → CO2 reaction.

  13. Reaction of glowing carbon with carbon dioxide CO2 + C = 2 CO • Reduction of iron ore: CO + iron oxide iron a part of it escapes into the atmosphere • Coal in the fire box: Air input is limited suddenly CO accumulation CO concentration is above the low flamability limit CO & air is exploded from the glowing carbon reduction

  14. Dissociation of carbon dioxide • In spite of the perfect burning conditions carbon monoxide is present because of the dissociation of carbon dioxide: CO2 <=> CO + O • The temperature increase shifts the equilibrium towards the CO Eg. 1745 ºC 1% , 1940 ºC 5 % • The quick cooling of the hot gases results in untransformed CO. (There is no time to be transformed. At low temperature the rate of the reaction is very slow, can be neglected.)

  15. The fate of atmospheric CO • The CO concentration should be doubled within 4-5 years • The CO concentration is nearly constant in the troposphere ► effective elimination reaction must exist. • A hydroxyl radicals ~ 40% CO is oxidized CO + OH• → CO2 + H•

  16. The fate of atmospheric CO • Condition: • CO uptake by the soil • Different microscopic fungi CO → CO2 • CO uptake 0 – 100 mg CO/(hour m2 ) • The rate of uptake depends on the organic content of the soil. CO + • OH = CO2 + H

  17. The CO uptake by the soil types I. ~ 0 mg CO/m2hour ~ 100mg CO/m2hour

  18. The CO uptake by the soil types II. CO uptake is low significant CO uptake The CO uptake is restricted in the town. The soil is covered or severely polluted

  19. Effects of CO on plants • No detrimental effects have been detected. • Urban air : 50-60 ppm → no problem

  20. Effects of CO on Humans The oxygen uptake is restricted • Hemoglobin (Hb): O2 and CO2 transport. • CO2Hb in the lung, CO2 is exchanged to O2, • O2Hb in the tissue, O2 is exchanged to CO2 In COHb the bond is 250 times stronger

  21. Effects of CO on Humans • The COHb content of the blood depends on the CO concentration of the air, the physical activity and the residence time in the polluted area.

  22. Control of CO pollution • Transportation is mainly responsible Solutions: • Perfect mixing of air and fuel. The maximum has been reached. • Slow cooling of the exhaust gases. It is not possible • Quick oxidation to CO2: catalytic transformation of carbon monoxide to carbon dioxide • Combustion of coal, oil, gas and biomass: • The emission is restricted officially.

  23. Control of CO emission Combustion devices, the CO depends on: • Particle size of the fuel (greater the size, higher the CO emission) • Structure of the solid fuel (airy, loose structure eg. straw, local oxygen deficiency in the bulk) • Mixing of air and fuel (perfect mixing results in low CO emission) • Air excess ratio (lack of oxygen or low temperature and residence time) • Residence time at high temperature (longer residence time at high temperature decreases the CO emission)

  24. Control of CO emission: boilers Thermal afterburner heat exchanger Min. temp: 850 °C Min. residence time: 2 sec preheated flue gas flue gas with high CO content gas burner afterburner

  25. Control of CO pollution: transportation • Will be discussed later. ( See: hydrocarbons)

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