What is the Organic Rankine Cycle?

The Organic Rankine Cycle (ORC) is a technology that converts waste heat or low-temperature heat sources into electricity.

ORC operates in a similar way to the classic steam cycle known from conventional power generation. The difference is that, instead of water, it uses an organic working fluid that evaporates at a lower temperature.

As a result, an ORC installation can operate with heat sources that would be too low-temperature or economically unviable for a traditional steam cycle.

Such sources include, among others: industrial processes, flue gases, hot process water, heat from combined heat and power plants, cogeneration systems, biomass, geothermal energy, and other sources of waste heat. Modern waste heat recovery heat exchangers make it possible to capture and utilize this otherwise lost energy.

How does ORC work?

The operating principle of the Organic Rankine Cycle is relatively simple.

Heat from the waste source is transferred to a heat exchanger. There, the energy is transferred to the organic working fluid, which evaporates. The resulting vapor drives a turbine or expander, which in turn drives a generator that produces electricity.

After passing through the turbine, the vapor is condensed and returns to the cycle. The entire process takes place in a closed loop.

In simplified terms:

waste heat → heat exchanger → evaporation of the working fluid → turbine → generator → electricity

This is why ORC is often seen as a technology that makes it possible to “recover” energy from processes where it was previously lost.

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Why is the heat exchanger crucial in an ORC installation?

In an ORC installation, the heat exchanger performs one of the most important functions. It is responsible for efficiently transferring energy from the heat source to the working fluid.

Depending on the operating conditions, ORC systems can use shell-and-tube, plate, or specialized heat exchangers designed for high temperatures and demanding industrial environments. Learn more about heat exchangers for ORC power stations.

If heat exchange is not effective, the entire process loses efficiency. Even the best turbine or generator will not use the full potential of the installation if the energy is not properly transferred during the evaporation stage of the working fluid.

That is why ORC projects place such great importance on:

• selecting the appropriate type of heat exchanger,
• material resistance,
• compact design,
• low pressure drops,
• stable operation under variable parameters,
• adaptation to the specific medium and heat source.

Depending on the application, engineers may choose shell-and-tube heat exchangers  or plate and shell heat exchangers to optimize thermal performance and reliability.

In practice, the heat exchanger is the bridge between the waste heat source and electricity generation.

Example application: working fluid evaporator in an ORC system

A good example of the use of a heat exchanger in an Organic Rankine Cycle installation is a working fluid evaporator for ORC systems designed for the power industry.

In this case, the unit operates in a system based on the Organic Rankine Cycle, in which energy from flue gases is transferred to the medium on the tube side and then used to evaporate the working fluid on the shell side.

In ORC applications, heat exchangers must withstand demanding operating conditions while ensuring efficient heat transfer. The example below presents a working fluid evaporator designed for an Organic Rankine Cycle power generation system, where energy from high-temperature flue gases is used to evaporate the working fluid and generate electricity.

Parameters of an Example ORC Heat Exchanger

This example demonstrates the engineering requirements of heat exchangers used in ORC installations. High operating temperatures, aggressive process media, and the need for reliable long-term performance require carefully selected materials and optimized thermal design. Solutions such as shell-and-tube heat exchangers  are often used in waste heat recovery applications where durability and thermal efficiency are critical for maximizing electricity generation.

Where can ORC technology be used?

The Organic Rankine Cycle can be used wherever there is available heat that cannot easily be used directly.

The most common areas of ORC application include:

• the chemical industry,
• food processing,
• paper mills,
• cement plants,
• metallurgical facilities,
• cogeneration installations,
• combined heat and power plants,
• biogas plants,
• waste incineration plants,
• biomass processing plants,
• geothermal installations.

Many of these sectors already use application-specific heat exchanger solutions to improve heat recovery and energy efficiency.

ORC is particularly useful where electricity is more valuable than heat itself. Electricity can be more easily used locally, transmitted, balanced, or used to partially reduce a plant’s dependence on rising energy costs.

ORC and industrial energy efficiency

Rising energy prices, emission reduction requirements, and pressure to improve energy efficiency mean that companies are increasingly analyzing not only where they obtain energy from, but also how to reduce energy losses.

ORC fits into this trend because it allows the overall efficiency of a plant to be increased without the need to build a completely new energy source.

Instead of treating waste heat as a problem, it can be treated as a resource. Modern heat recovery systems help businesses recover thermal energy that would otherwise be wasted and convert it into useful energy.

This represents an important shift in thinking: energy that was previously a cost or a loss can become an additional source of value.

Why is ORC becoming more important?

The importance of ORC technology is growing because it combines several important directions in industrial development:

• improving energy efficiency,
• recovering waste heat,
• reducing CO₂ emissions,
• lowering energy costs,
• increasing energy independence,
• making better use of existing infrastructure.

In the context of the energy transition, ORC does not compete with renewable energy sources. Rather, it complements them.

Photovoltaics, heat pumps, and geothermal energy answer the question of how to produce energy in a more sustainable way. ORC answers another, equally important question: how not to waste the energy we already have.

Summary

The Organic Rankine Cycle is a technology that makes it possible to convert waste heat into electricity. By using an organic working fluid, ORC can operate at lower temperatures than a classic steam cycle.

The most important element of the entire process is the heat exchanger because it enables effective energy transfer from the heat source to the working fluid. Learn more about Hexonic heat exchangers for ORC systems and waste heat recovery.

The example of a working fluid evaporator for an ORC system shows that effective heat recovery requires precise design: an appropriate heat transfer area, suitable materials, resistance to high temperatures, and adaptation of the unit to specific process media.

At a time of rising energy costs and growing importance of energy efficiency, ORC is becoming a practical tool for industry, the power sector, and installations that use waste heat.

The energy transition is not only about producing new energy.

It is also about the intelligent use of energy that has already been produced.