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Uncovering the Secret of the Organic Rankine Cycle: How to Use Waste Heat to Generate Electricity?
In today's thermal engineering field, Organic Rankine Cycle (ORC) has gradually become an important thermal energy utilization technology. This system is mainly aimed at the recovery and conversion of waste heat from low-temperature heat sources, providing us with an effective way to convert waste heat into electricity. This article will explore how ORC works, its application areas and future prospects, and unveil how this technology can play an important role in sustainable development.
What is the Organic Rankine Cycle?
The organic Rankine cycle is a thermodynamic cycle that works in a similar way to the traditional Rankine cycle, but uses an organic polymer liquid as the working fluid. These liquids evaporate at lower temperatures than water, enabling ORC to recover heat from a variety of low-temperature heat sources, such as biomass combustion, industrial waste heat, geothermal energy, and solar energy.
How ORC works
The basic process of ORC can be divided into four main steps:
1. The working fluid is pumped into the boiler, heated and evaporated.
2. The steam is inserted into an expansion device (such as a turbine or other expander) where it does the mechanical work.
3. The vapor passes through the condenser heat exchanger, where it is cooled and condensed back into liquid.
4. Finally the liquid is pumped back to the boiler, completing the cycle.
An ideal ORC cycle will experience pressure drops and energy losses in the heat exchangers, but these conditions will affect the overall cycle efficiency.
ORC Application Areas
Organic Rankine cycle technology has a wide range of applications, with an installed capacity of more than 2.7GW currently in 698 different power plants worldwide. The most notable applications include the following areas:
Waste heat recovery
Waste heat recovery is one of the main areas of development for ORC. The technology can be used in combined heat and power systems, industrial processes or agricultural processes, making full use of the heat exhaust from water heaters, small combined heat and power equipment to furnaces.
Biomass power generation
With the abundance of biomass resources, the application of organic Rankine cycle in small and medium-sized power plants is becoming more and more important. Its efficient return on investment reduces equipment costs and extends the service life of the machine compared to traditional steam boilers.
Geothermal power
Organic Rankine cycle technology is well suited to the needs of geothermal power generation, especially in the case of low-temperature heat sources. For geothermal sources below 100°C, the efficiency is lower but still not negligible.
Solar thermal power generation
Compared to the conventional steam-type Rankine cycle, ORC can generate electricity at a lower collector temperature, making it a viable option for small-scale decentralized centralized power generation systems.
Choosing a working fluid is critical
In the cryogenic Rankine cycle, choosing the appropriate working fluid is crucial. Because the heat conduction efficiency in low temperature environment will directly affect the performance of the overall system, it is necessary to select a fluid with low evaporation temperature and high thermal stability.
Finally, the environmental impact, chemical stability and economy of the selected fluid are also important considerations in the screening process.
ORC system modeling
Simulating ORC cycles usually requires a numerical solver that takes into account factors such as mass and energy balance, heat transfer, and pressure losses. According to the requirements, ORC models can be divided into steady-state models and dynamic models. The former is mainly used for design and partial load simulation, while the latter is used to implement and simulate control strategies.
Future Outlook
The promotion and application of organic Rankine cycle technology can not only effectively utilize new energy, but also contribute to environmental protection. With the advancement of science and technology, ORC technology may be more widely used and become an important part of sustainable energy utilization. The report pointed out that this technology has potential in addressing global energy shortages and climate change. However, this also raises a question: how will future energy utilization patterns change the way we live?
