Overview of the Rankine Cycle

The Rankine cycle is a thermodynamic cycle used in power stations to generate electricity.

It represents a practical implementation of the ideal Carnot cycle.

The main processes in the Rankine cycle involve the generation of superheated steam, its expansion in a turbine to produce work, and the condensation of the steam back into water for recycling in the system.

Working Fluid: The cycle typically uses water or steam as the working fluid, which undergoes Key Components of the Rankine Cycle:

1. Boiler (or Steam Generator): Converts water into superheated steam using heat, typically from burning fuel or other heat sources.
2. Turbine: The superheated steam expands in the turbine, causing it to spin. This mechanical energy is converted into electrical energy by a generator.
3. Condenser: After leaving the turbine, the steam is cooled and condensed back into liquid water by removing heat, typically using cooling water.
4. Pump: The condensed liquid water is pumped back into the boiler to complete the cycle, increasing its pressure.

Processes in the Rankine Cycle

1. State 1 to 2: Liquid water is pumped from low pressure (condenser pressure) to high pressure (boiler pressure). This is an isentropic process (adiabatic and reversible).
2. State 2 to 2′: The compressed liquid is preheated at constant pressure until it reaches the saturated liquid state.
3. State 2′ to 3′: The saturated liquid is heated at constant pressure until it becomes saturated vapor.
4. State 3′ to 3: The saturated vapor is superheated by adding heat at constant pressure, increasing its temperature.
5. State 3 to 4: The superheated steam expands in the turbine, doing work and losing temperature and pressure in an adiabatic process.
6. State 4 to 1: The low-pressure steam is condensed back into liquid water in the condenser, completing the cycle.

Organic Rankine Cycle (ORC)

The Organic Rankine Cycle is a variation of the traditional Rankine cycle that utilizes organic fluids with lower boiling points than water.

Advantages and Disadvantages

• Advantages:
  • Efficiency: The Rankine cycle is efficient for converting heat into work, especially when using superheated steam.
  • Flexibility: The cycle can operate on various fuels and heat sources, including fossil fuels, biomass, and solar energy.
  • Mature Technology: It is a well-established and widely used technology in power generation.
• Disadvantages:
  • Water Requirement: The cycle requires a constant supply of water for operation.
  • Complexity: The system’s complexity increases with the addition of components like reheaters or regenerative heaters.