Construction and working principle of geothermal energy.

6.a) Describe the construction and working principle of geothermal energy with a schematic diagram.

Answer:

Construction of a Geothermal Power Plant

This diagram and explanation offer a comprehensive overview of geothermal plant construction and operation, especially for the increasingly used binary-cycle systems.

1. Production Well
   • Drilled deep into the Earth’s crust to tap into hot geofluid (natural steam or hot water).
   • In binary systems, this fluid transfers heat through a heat exchanger without mixing with turbine fluids.
2. Heat Exchanger
   • Transfers geothermal heat to a secondary working fluid (e.g., isobutane) with a lower boiling point.
   • Maintains closed-loop operation, preventing contamination of prime fluids.
3. Binary Cycle Turbine & Generator
   • The heated secondary fluid evaporates into vapor, driving the turbine.
   • The turbine turns a generator to produce electricity.
4. Condenser & Cooling System
   • After exiting the turbine, the vapor is cooled and condensed.
   • Waste heat is removed via cooling towers or for cascading uses (e.g., heating, desalination).
5. Reinjection Well
   • The cooled, spent geofluid is pumped back underground to sustain reservoir pressure and prevent subsidence.

Working Principle

1. Extract Heat
   Hot geothermal fluid is brought to the surface via the production well.
2. Heat Exchange
   Heat transfers in a closed heat exchanger to a working fluid, which vaporizes.
3. Power Generation
   Vapor expands in a turbine, generating mechanical energy to drive a generator and produce electricity.
4. Condensation & Cooling
   The vapor is cooled back into liquid form in a condenser; excess heat is rejected or repurposed.
5. Reinjection
   Both geothermal and working fluids are recycled: geothermal returns underground; working fluid returns to the heat exchanger.

Comparison: Types of Geothermal Plants

• Dry Steam Plants
  Use natural steam directly, oldest and simplest technology.
• Flash Steam Plants
  Extract high-pressure hot water, flash it into steam in flow valves/separators, then drive turbines.
• Binary Cycle Plants
  Use medium- to low-temperature fluids; rely on secondary working fluid—ideal for lower-temperature resources.