Transcript Carbon monoxide

BUDAPEST
FACULTY
UNIVERSITY OF TECHNOLOGY AND ECONOMICS
OF CHEMICAL AND
BIOCHEMICAL ENGINEERING
DEPARTMENT
OF CHEMICAL AND
PROCESS
ENVIRONMENTAL
ENGINEERING
Carbon monoxide
Authors: Dr. Bajnóczy Gábor
Kiss Bernadett
The pictures and drawings of this
presentation can be used only for
education !
Any commercial use is prohibited !
Carbon monoxide
Some physical properties of CO
•colorless
•odorless
28.01
Moolecular mass
Melting point
-199 oC
Boiling point
-191.5 oC
•tasteless
•Burns with blue flame
density
Most abundant and widely
distributed pollutant in the
lower atmosphere
Solubility in water*
It has a density 96.5% that
of air
Reversible effect
in small
concentration
0 0C, 101.3 kPa
25 0C, 101.3 kPa
0C
0
20 0C
25 0C
Low and high flamability
limits
Conversion factors
0 0C, 101.3 kPa
25 0C, 101.3 kPa
*
volume of CO in STP
mass/mass
*** volume/volume
**
1.250 g/dm3
1.145 g/dm3
low
3.54 cm3/100 cm3 (44.3 ppmm)**
2.32 cm3/100 cm3 (29.0 ppmm)**
2.14 cm3/100 cm3 (26.8 ppmm)**
Wide range
12,5 – 74,2 tf %
1 mg/m3 = 0.800 ppmv***
1 ppm = 1.250 mg/m3
1 mg/m3 = 0.800 ppmv***
1 ppm = 1.250 mg/m3
Sources of carbon monoxide
Natural <=> Antropogenic ( 10-50% of the total)
Differences:

Distribution:

1.
Natural sources: distributed throughout the world
2.
Anthropogenic sources: concentrated in small area
Rates of formation:
1.
Natural conditions:
rate of formation ≈ rate of elimination
1.
In the vicinity of antropogenic sources (towns, industrial areas):
rate of formation > rate of elimination (accumulation)
Natural sources of carbon monoxide
Indirect sources:
mud, bogs
►anaerob
conditions
►methane
formation from the
decay of organic
materials
The surface of oceans is
supersaturated in carbon
monoxide:
Algae and other biological
sources.
Decay of chlorophyll in the
soil
Sources of natural carbon monoxide


Mud, oceans, chlorophyll…
The majority of CO is indirect origin:
oxidation of methan ► CO!
organic materials
Anaerob conditions
Biological decay
methane
OH *
CO
Formation CO from methane
1.
2.
3.
4.
5.
6.
CH4 + •OH = •CH3 + H2O
•CH3 + O2 + M = •CH3O2 + M * Strong oxidation character
•CH3O2 + NO = •CH3O + NO2
Lifetime: some hours
•CH3O + O2 = HCHO + •HO2 4-6 ppbv
λ<338nm
HCHO
•H + •HCO
•HCO + O2 = CO + •HO2
HCHO + •OH = CO + •HO2 + H2O
Reactions of the other formed radicals
•H + O2 + M = •HO2 + M *
•HO2 + NO = •OH + NO2
CO from anthropogenic sources
1.
2.
3.
4.
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
Chemistry of the CO formation
The formation of anthropogenic CO is generally the result
of the following chemical processes:
1.
Incomplete combustion of carbon or
carbon containing compounds
2.
High temperature reaction of
glowing carbon and carbon dioxide
3.
Dissociation of carbon dioxide at
high temperature
Incomplete combustion of carbon or carbon
containing compounds
ORIGIN OF THE RADICALS IN THE FLAME



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H2O → H + OH*
O2 → 2 O
CxHy → CxHy-1 + H
O + H2O → 2 OH*
thermal decay
thermal decay
thermal destruction
Stops under 650 °C
650ºC alatt leáll
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
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.
Reaction of glowing carbon with carbon
dioxide
CO2 + C = 2 CO


Reduction of iron ore:
reduction
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
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.)
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•
The fate of atmospheric CO

Condition:
nm
 O*+ O2*
O3 310
O* + H2O = 2 ∙OH
CO + • OH = CO2 + H

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.
The CO uptake by the soil types I.
~ 0 mg CO/m2hour
~ 100mg CO/m2hour
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
Effects of CO on plants


No detrimental effects have been detected.
Urban air : 50-60 ppm → no problem
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
CO2Hb + O2
O2Hb + CO2
In COHb the bond is 250 times stronger
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.
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.
Emission limits for different fuels in Hungary [mg/Nm3]
Output range 140 kW-50 MW regulation number: 23/2001 KöM
Carbon monoxide
Solid fuel
Liquid fuel
Gas fuel
250
175
100
Control of CO emission
Combustion devices, the CO depends on:


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
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)
Control of CO emission: boilers
Thermal afterburner
Min. temp: 850 °C
heat exchanger
Min. residence time: 2 sec
preheated
flue gas
flue gas with
high CO content
gas
burner
afterburner
Control of CO pollution:
transportation

Will be discussed later. ( See: hydrocarbons)