UPPSC 2021 Prelims GS Paper-I · Question 11 of 150

Correct — C, Thermal power plant. Fly ash is the fine, glassy residue produced when pulverised coal is burnt in coal-fired thermal power stations; it is carried upward with the flue gases and captured by electrostatic precipitators (ESPs) before the gas leaves the chimney. Because coal-based thermal plants burn enormous quantities of coal, they are the dominant source of fly-ash pollution in India — the ash carries silica, alumina and toxic trace elements (arsenic, mercury, cadmium) and, if unmanaged, contaminates air, land and water.

• (a)Oil refining — Refineries process crude oil, not coal; their characteristic wastes are petroleum coke, oily sludge, spent catalysts and gaseous emissions (SO2, VOCs) — not fly ash, which comes from coal combustion.
• (b)Fertilizer industry — Fertilizer plants generate effluents, phosphogypsum and gaseous emissions (ammonia, fluorides); they do not burn pulverised coal to produce fly ash.
• (d)Mining — Mining generates overburden, tailings, dust and acid mine drainage. Coal mining moves and extracts coal but does not combust it — and fly ash is a product of burning coal, not of mining it.

Coal combustion in a thermal power plant leaves two ash fractions — the light 'fly' ash that rises with the flue gas (trapped by electrostatic precipitators) and the heavier 'bottom ash' that settles in the furnace. Fly ash is a major solid-waste and air-pollution challenge, but it is also a resource: it is used to make fly-ash bricks and to partially replace Portland cement in concrete, and its handling is governed by MoEFCC fly-ash utilisation notifications.

The trap is to associate 'ash / heavy pollution' with any big industry. The one keyword that fixes the answer is coal combustion — only a process that burns coal produces fly ash, and among the four options only the thermal power plant does. Oil refining, fertilizer plants and mining pollute, but in other ways.

• Fly ash = fine residue from burning pulverised coal in thermal power plants; captured by electrostatic precipitators.
• Composition: mainly silica, alumina and iron oxide, plus toxic trace elements (arsenic, mercury, cadmium).
• Reused productively in fly-ash bricks and as partial replacement for cement in concrete.
• Coal-based thermal power is India's single largest source of fly ash.

• Confusing fly ash with bottom ash
• Assuming mining (which only moves coal) makes fly ash, rather than combustion

UPPSC and UPSC ask either 'what causes fly-ash pollution' (source = coal thermal plants) or the uses / composition of fly ash (bricks, cement, toxic elements).

• practice — not a real PYQ

  Fly ash carried up with the flue gases of a thermal power plant is captured mainly by:

  • (a)Cyclone separators alone
  • (b)Electrostatic precipitators
  • (c)Wet scrubbers for CO2
  • (d)Catalytic converters

  Answer(b) Electrostatic precipitators — they electrically charge and collect the fine ash before the gas exits the chimney.

• practice — not a real PYQ

  Which of the following is a recognised productive use of fly ash?

  • (a)Making fly-ash bricks and partially replacing cement in concrete
  • (b)As a nitrogen fertilizer
  • (c)As a drinking-water coagulant
  • (d)As a vehicle fuel

  Answer(a) Making fly-ash bricks and partially replacing Portland cement in concrete.