Previous Year Question
Consider the following statements.
Coal ash contains arsenic, lead and mercury.
Coal-fired power plants release sulphur dioxide and oxides of nitrogen into the environment.
High ash content is observed in Indian coal.
Which of the statements given above is/are correct?
Only 1
2 and 3
Only 3
1, 2 and 3
Correct Answer: D
Detailed Solution
Coal combustion produces solid residues mainly in the form of fly ash and bottom ash.
Along with silica, alumina and iron oxides, coal ash may contain toxic metals such as arsenic, lead and mercury. Therefore, Statement 1 is correct.
It may also contain other trace pollutants such as cadmium, chromium and selenium.
Improper storage of ash may allow these pollutants to leach into soil, surface water and groundwater.
Fine particles of dry fly ash may also become airborne and cause respiratory problems.
Sulphur present in coal is oxidized during combustion to produce mainly sulphur dioxide.
Nitrogen oxides are formed through reactions between nitrogen and oxygen at high combustion temperatures.
Therefore, coal-fired power plants emit both sulphur dioxide and nitrogen oxides. Hence, Statement 2 is correct.
These plants may also emit carbon dioxide, particulate matter and other pollutants.
Indian coal generally has a high ash content, which may reach approximately 30–45% in many cases. Therefore, Statement 3 is correct.
Compared with imported coal, Indian coal often has higher ash content and lower calorific value.
High ash content may require more coal for the same energy output and the management of a larger quantity of ash.
Electrostatic precipitators can separate fly-ash particles from exhaust gases.
Fly ash may be used in cement, bricks, roads, embankments and mine filling, provided environmental safety standards are followed.