Explain supercritical boiler technology and its advantages over subcritical boilers.

Supercritical boilers operate above the critical point of water (374°C, 22.1 MPa) where distinct liquid and vapor phases cease to exist. Water transitions directly from liquid-like to gas-like state without boiling, eliminating the need for steam drums. Advantages include higher thermal efficiency (43-47% vs 35-40% for subcritical), lower fuel consumption and emissions per kWh, and better load-following capability. Challenges include more demanding metallurgy, precise water chemistry control, and higher capital costs. Ultra-supercritical plants operate at even higher parameters (600°C+) achieving efficiencies above 45%.