Which of the following statements about conventional sources of energy and their improvements is true?

Question

Which of the following statements about conventional sources of energy and their improvements is true?

1. A. Thermal power plants cannot exceed 35% efficiency, even with advanced boiler technology.
2. B. Supercritical and ultra-supercritical boilers allow coal power plants to achieve higher efficiency. (Correct answer)
3. C. Hydroelectric power plants cannot improve energy output once the dam is built.
4. D. Efficiency of petroleum refining is solely determined by the quality of crude oil, not technology.

Correct Answer

Option B — Supercritical and ultra-supercritical boilers allow coal power plants to achieve higher efficiency.

Detailed Solution & Explanation

The correct answer is Supercritical and ultra-supercritical boilers allow coal power plants to achieve higher efficiency.

Key Points

• Supercritical and ultra-supercritical technology raises steam above the critical point of water — approximately 221 bar and 374 °C — where liquid and vapour become indistinguishable. Operating at these higher temperatures and pressures raises thermal efficiency in accordance with the Carnot principle.
  • Subcritical plants operate at about 33–37% efficiency.
  • Supercritical plants reach roughly 40–42%.
  • Ultra-supercritical plants reach about 44–46%.
• Every percentage point of efficiency gained means less coal burnt and less CO₂ emitted for the same electricity generated.

Additional Information

• Why the other statements are wrong:
  • Option A is false precisely because supercritical technology already exceeds 35%. India's newer thermal units are mandated to be supercritical or better.
  • Option C is false — hydroelectric output can be improved after construction by turbine runner replacement, uprating of generators, refurbishment of penstocks and better reservoir operation. Renovation and Modernisation (R&M) programmes for old hydro stations exist for exactly this purpose.
  • Option D is false — refinery efficiency depends heavily on technology: catalytic cracking, hydrocracking, heat integration and process control all raise yields substantially from the same crude.
• Conventional sources of energy: coal, petroleum, natural gas, firewood, and large hydropower.
• Thermal efficiency is bounded by the Carnot limit $\eta = 1 - \dfrac{T_{cold}}{T_{hot}}$, which is why raising steam temperature is the principal route to improvement.