Coal and Its Environment

Though coal is cheap and plentiful, it is a dirty fuel which contaminates our environment and contributes to the CO2 imbalance in our atmosphere as well as oxides of nitrogen from the combustion process. The principal contaminant in coal is sulfur which bums to form sulfur dioxide (SO2) 

The SO2 can dissolve in water to form sulfurous acid (H2SO3). The SO2 is also catalytically converted to SO3 using V2O5 as a catalyst  

The SO3 is then treated with water or sulfuric acid solution to form H2SO4. 

Acid rain is not the only environmental contaminant fi-om coal burning. The average concentration of mercury in coal is about 0.3 pg/g (i.e., less than 1 ppm). A 755-MW steam turbine-driven power station bums approximately 7,100 t of coal per day. This corresponds to about 2.5 kg/day of mercury being sent up the stack. With present North America estimates of coal consumption at about lO t/year, about 3,0001 of mercury is put into the environment. This is about four times the natural source.  

The use of fly ash in concrete does not solve the disposal problem but only shifts it to another locale. If cement is composed of 30% fly ash, it has been estimated that the radon diffusing out of the concrete (porosity—5%) into a room (10 x 10 x 4 m) would be about 10 pCi/cm —100 times lower than the MFC. However, with higher porosity, concrete and lower ventilation rates the margin of safety decreases, and it means that concrete containing fly ash should not be used in structures for habitation though it would be permissible for use in foundations, bridges, and roads. 

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