L12 - ORC, Kalina, Gas engines

Question 1

Organic rankine cycle (ORC) advantages

Answer 1

Less heat is required during evaporation of fluid
• Evaporation can take place at a lower temperature and pressure
• Exit from the expansion process is in the form of vapour (reducing risk of damage)
• Smaller temperature difference between evaporation and condensation, resulting in smaller pressure drops and simpler turbine configurationsORC Advantages

Question 2

Kalina cycle advantages

Answer 2

Temperatures of phase changes with varying concentrationallowbetter matching with heat sources
• Varying ammonia concentration in different parts of the cycle canfurther improve efficiency
• Regeneration or recuperation can reduce condenser and vaporiserthermal loads
• Power generation can be maximised by expanding ammonia vapourso that its condensing temperature is below the temperatureof thecooling medium. Absorption in the water rich stream produces a mixture which can be condensed by the cooling medium.

Question 3

Kalina cycle disadvantages

Answer 3

1. Higher thermal efficiency than ORC but equipment requirements higher so higher capital costs
2. Ammonia and water have high critical pressure compared to ORC= safety and cpaital costs
3. Ammonia/water mixes extremely corrosive = expensive materials
4. Turbines/expanders subjected to condensation and droplet corrosion