Susan M. Burke
Calculating the effect of pollutants “loaded” into the atmosphere
Computing the total mass of pollutants ‘loaded’ into the atmosphere requires calculating the percentage by volume of specific substances. The mass volume of the atmosphere without additional pollutants is computed from the atmospheric pressure, the earth’s mean radius and gravitational acceleration. This formula is 4 * ( ) * 1.013 * 10
5
N/m
2
/g and g equals 9.8 m/s
2
. The total mass of the atmosphere is 5.1 * 10
18
kg after the total mass of mountains has been deducted from the above formula which does not allow for irregularities of the earth’s surface.
Testing for pollutants in a specific volume of atmosphere requires finding a per cent by volume of the pollutants. This is expressed in parts per million (ppm). That is x number of pollutants per million of atmospheric air. To find the number of molecules of a substance the total weight is divided by the molecular weight. For instance, the normal unpolluted dry air has a total mass of nitrogen or 3,850,000,000 metric tons (78.09%) and 1,180,000,000 metric tons of oxygen (21%).
9
(Appendix 6).
Similarly, the pound-moles of input and output products in coal combustion can be calculated. In the coal-fired furnace where 2000 pounds of coal is burned, the percentage of carbon is converted to pounds and then to pound moles. The weight of gaseous emissions in flue gas can also be computed. Carbon is released in combinant form with oxygen as carbon monoxide or carbon dioxide. Sulfur and nitrogen are released in oxide forms. Or, minute particles called particulates enter the atmosphere in the form of ash.
Particulates are graded according to size, and the size is an indicator of the settling speed with which the matter is removed by gravitational pull. Particles are Aitken, large or giant according to increased size; and, the settling speed is determined by density. Smoke is a term used to describe a mixture of particulate material gases and mists. Dust refers to solid dispersion aerosols and mist to liquid aerosols.
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Even though the mass volume of pollutants can be determined by using the formulae below, it is not always easy to document the strength of pollutants or the exact location of particular emissions. An accumulation of materials over a long period of low concentration depositions called ‘loading’ results in the long-range transportation and long-term accumulations. Pollution often extends over several states. The environmental impact in any one specific region is assessed according to the variable factors specific to that region. Areas of great humidity, temperature inversion zones and frequent precipitations are more susceptible to smog and acid rain damage than arid areas. Further geological formations and soil composition can enhance an areas vulnerability to acid rain damage through changes to soil chemistry.
11
(Appendix 7).
The calculations below are completed to show the pound-moles of flue gas emissions released by a single coal-fired furnace.
MATERIAL 7 ENERGY BALANCE ON A COAL-FIRED FURNACE
(figure available in print form)
MATERIAL BALANCE
BASIS: 2000 LB. COAL
WEIGHT OF ASH PRODUCED
= (2000)(0.1671) 334.2
CARBON BALANCE
Lb.moles carbon in coal = lb.moles carbon in flue gas
(2000)(0.6593) = 109.88
____
12
OTHER COMPONENTS OF FLUE GAS (DRY BASIS)
Lb.moles 02
(figure available in print form)
Lb.moles N2
(figure available in print form)
Lb.moles SO2
(figure available in print form)
TOTAL MOLES DRY FLUE GAS
C0
|
109.88
|
02
|
29.91
|
N2
|
598.79
|
SO2
|
1.85
|
|
740.43
|
NITROGEN BALANCE
Lb.moles N2 in flue gas = lb.moles N2 in coal + lb.moles N2 in air
(figure available in print form)
Lb.moles N2 in air = 597.86
(figure available in print form)
HYDROGEN BALANCE
Lb.moles net hydrogen in coal + lb.moles water in coal
= lb.moles water in flue gas
(figure available in print form)
Lb.moles water in flue gas 46.88