Organic Rankine cycle (ORC) generator set principle

What is the Organic Rankine Cycle? Most power plants, captive power stations, and waste heat power stations use Rankine cycle with water as the working fluid, and the core engine is a steam turbine. When the working fluid is refrigerant, we call it an organic Rankine cycle. In principle, it is to directly apply the cycle of the steam generator set. The difference is that the physical properties of the working fluid have changed, and it can adapt to a lower temperature heat source for power generation.

Speaking of Rankine cycle, it is actually similar to the principle of differential pressure power generation. No matter how high the temperature of the working fluid is, if there is no pressure difference between the inlet and outlet of the expander (steam power generation is a steam turbine), work cannot be done. Therefore, in the industry, especially thermal power plants, many used temperature reducing and pressure reducing devices for heating in the early days. Later, they were replaced with a back-pressure steam turbine, which not only achieved the purpose of reducing temperature and pressure, but also generated more electricity. For low-temperature heat sources of 90-150°C, when water is used as the working fluid, its evaporation temperature under standard atmospheric pressure is 100°C. Not only is the heat obtained within the temperature difference range small, but when a steam turbine is used to generate electricity, due to the inlet and exhaust steam The steam pressure difference is small, the working capacity is low, and the thermal efficiency is also very low. However, it is different for organic working fluids. For example, R245fa has an evaporation temperature of only 15°C under standard atmospheric pressure. In actual use, if the evaporation temperature reaches above 90°C, the pressure can reach above 1Mpa. In this way, the intake and exhaust steam The pressure difference is relatively large, and the working ability is stronger than that of steam.