Ammonia is primarily used in Ocean Thermal Energy Conversion (OTEC) because it significantly reduces the required size of critical components like turbines and heat exchangers.
Ocean Thermal Energy Conversion (OTEC) is a process that generates electricity using the temperature difference between deep cold ocean water and shallow warm surface water. There are different types of OTEC systems, but the most common is the Closed Cycle system.
Ammonia as a Working Fluid in Closed Cycle OTEC
In a Closed Cycle OTEC system, a working fluid with a low boiling point is needed to turn a turbine using the heat from the warm surface water. This fluid is then condensed using the cold deep-sea water and the cycle repeats.
Key Advantage of Ammonia
Based on the provided reference, a major reason ammonia is favored as the working fluid in Closed Cycle OTEC is its thermodynamic properties. These properties allow the system to be designed more efficiently, leading to:
- Reduced Turbine Size: The characteristics of ammonia mean that a smaller turbine can generate the same amount of power compared to systems using other working fluids under similar temperature differences.
- Reduced Heat Exchanger Size: Similarly, the heat exchangers (evaporator and condenser) where heat is transferred between seawater and the working fluid can be smaller. This is crucial as heat exchangers are often the largest and most expensive components in an OTEC plant.
Using ammonia reduces the size of the turbines and heat exchangers required, which has substantial benefits for the overall system.
Implications of Smaller Components
Smaller components offer several practical advantages for OTEC power plants:
- Lower Manufacturing Costs: Smaller turbines and heat exchangers cost less to build.
- Easier Transportation and Installation: Compact equipment is simpler to move and set up, especially for offshore platforms or coastal plants.
- Reduced Footprint: A smaller plant occupies less space, which can be important for both land-based and floating OTEC systems.
Variations Using Ammonia
While Closed Cycle OTEC primarily uses pure ammonia, a variation called the Kalina Cycle uses a mixture of water and ammonia. This specific mixture can offer further thermodynamic efficiency improvements, although it still leverages ammonia's properties.
In summary, ammonia is a preferred working fluid in OTEC due to its efficiency in transferring thermal energy, which translates directly into a more compact and potentially more cost-effective plant design, primarily by reducing the size of the necessary turbines and heat exchangers.
