How a Thermal Power Station Works: From Fuel to Electrons

The Rankine Cycle in Action

A thermal power station converts chemical energy (coal, gas, oil) → thermal energy → mechanical energy → electrical energy. Most follow the **Rankine Cycle**.

Step-by-Step Process

1. Fuel Handling & Prep:
   • Coal: Crushed → pulverized (talcum fineness) → blown into boiler.
   • Gas: Piped in, metered.
   • Oil: Heated (reduce viscosity) → atomized.
2. Combustion (Boiler/Furnace): Fuel + preheated air → controlled burn (1300–1700°C). Radiant + convective heat transfer.
3. Steam Generation: Water circulates through boiler tubes (water-tube design). Absorbs heat → **High-pressure, high-temperature steam** (e.g., 170 bar, 540°C / 2400 psi, 1000°F). Superheated for efficiency.
4. Steam Turbine (Prime Mover): Steam expands through stages (HP → IP → LP). Blades on rotor convert pressure/velocity → **rotational mechanical energy** (3000/3600 RPM).
5. Generator: Rotor spins inside stator → **electromagnetic induction** → **AC electricity** (typically 13–25 kV).
6. Condensation (Condenser): Exhaust steam (vacuum ~0.05 bar) passes over tubes with cooling water → **condensate (liquid water)**. Vacuum maximizes turbine efficiency.
7. Cooling System:
   • Once-through (river/lake/sea).
   • Recirculating (cooling towers - evaporative).
   • Dry cooling (air-cooled condenser - water scarce areas).
8. Condensate → Feedwater Heating → Deaerator → Boiler Feed Pump (BFP) → High-Pressure Heaters → Boiler: Closed loop. Feedwater heaters (extraction steam) raise temp → efficiency. Deaerator removes O₂/CO₂ (corrosion prevention). BFP (huge pump) pushes to boiler pressure.
9. Emissions Control (Critical Modern Step):
   • ESP / Baghouse (particulates).
   • FGD / Scrubbers (SO₂).
   • SCR / SNCR (NOx).
   • Activated Carbon / Halide (Mercury).
   • CO₂ capture (emerging/CCS).
10. Step-Up Transformer → Switchyard → Transmission Grid (115–765 kV): Voltage raised for low-loss long-distance transport.

Efficiency & Evolution

• Subcritical: ~33–37%
• Supercritical (SC): ~40–42%
• Ultra-Supercritical (USC): ~44–47%
• Combined Cycle Gas Turbine (CCGT): ~60–63% (Gas turbine + steam bottoming cycle).

Modern plants integrate advanced controls, cycling capability (for renewables balancing), and stringent emissions compliance.