Organic Rankine Cycle (ORC)

Date of publication: 2025-10-17 / Reading time: 8 minutes / Author: Karolina Kozak

The Organic Rankine Cycle is a heat recovery method that allows for the efficient use of waste heat and low-temperature energy sources to generate electricity. ORC installations enhance energy efficiency, reduce energy costs, and contribute to the reduction of CO₂ emissions. The Rankine Cycle is a classic thermodynamic process used in steam power plants, in which water is heated to steam and then drives a turbine. In the Organic Rankine Cycle, however, organic fluids with a lower boiling point are used instead of water. This makes it possible to utilize heat sources with much lower temperatures - even in the range of 80–350°C - which would be insufficient for conventional steam power plants.

What is the Organic Rankine Cycle?

The Organic Rankine Cycle (ORC) is a technology for generating electricity based on the classical Rankine Cycle, but with one key difference: instead of water as the working fluid, it uses organic compounds such as siloxanes, refrigerants (HFCs, HFOs), or hydrocarbons. These fluids have a lower boiling point and favorable thermodynamic properties, allowing for the recovery of energy even from low-temperature heat sources.

A typical ORC process consists of four stages:

heating and evaporating the working fluid in a heat exchanger,
expanding the organic vapor in a turbine coupled with a generator,
condensing the fluid in a condenser,
and compressing the fluid in a pump.

This enables the conversion of thermal energy at temperatures between 80°C and 350°C into electrical energy in a stable and safe manner. Importantly, ORC systems operate similarly to traditional steam power plants but with much lower temperature requirements, making the technology flexible and widely applicable in industrial and renewable energy sectors.

Where is ORC technology used?

The applications of ORC systems are extensive, and the technology is used wherever waste heat or low-temperature energy sources are available. The most common examples include:

heavy industry – steelworks, cement plants, chemical plants, and refineries, where production processes generate large amounts of waste heat,
geothermal energy – harnessing low-temperature geothermal resources unsuitable for conventional steam power plants,
biomass and biogas plants – converting residual heat from biomass boilers into additional electricity,
waste incineration plants – recovering energy from municipal waste combustion,
engines and gas turbines – using exhaust heat from engines and turbines to generate electricity through ORC.

Due to its flexibility, ORC technology is applicable across various sectors - from renewable energy to energy-intensive industrial facilities.

How does ORC support energy efficiency?

In many industrial facilities, a significant portion of energy is lost as waste heat. ORC technology enables the recovery of this energy and its conversion into electricity, which can be used to power the plant’s own operations. From an economic perspective, ORC installations can lower electricity purchase costs, especially when combined with other modernization measures such as cogeneration or process heat recovery. As a result, they form an important component of strategies aimed at improving energy efficiency and reducing CO₂ emissions.

Advantages of ORC technology

Do głównych korzyści wynikających ze stosowania ORC zalicza się:

ability to utilize low-temperature heat sources – organic fluids allow ORC systems to be much more flexible than conventional steam systems,
improved energy efficiency – recovering energy from waste heat reduces primary energy consumption,
CO₂ emission reduction – lower demand for external energy translates into reduced greenhouse gas emissions,
high reliability – ORC systems are simple to operate, work at lower pressures, have a long lifespan, and entail lower maintenance costs,
integration with existing processes – ORC units can be relatively easily added to existing industrial installations,
support for renewable energy – ORC enhances the economic viability of renewable sources such as biomass and geothermal energy.

Where ORC is not suitable

As for its limitations, the efficiency of ORC systems is generally lower than that of conventional steam power plants, typically ranging from 10% to 20%. This means that only a portion of the available thermal energy can be converted into electricity, which limits efficiency in very high-power applications.

Moreover, for stable operation, a constant and predictable heat source is necessary - fluctuations in temperature or flow can significantly reduce overall system performance. Another critical aspect is the selection of an appropriate working fluid, whose thermodynamic properties must be precisely matched to the heat source parameters. An unsuitable fluid may lead to lower efficiency or operational issues.

ORC systems are best suited for capacities ranging from several tens of kilowatts to a few megawatts of electricity, which makes them less competitive for large-scale power generation. Therefore, the technology is primarily applied in industrial facilities and decentralized energy projects rather than in conventional grid-scale power plants.

It is also worth noting that HFC gases are being gradually phased out under EU regulations, requiring the use of alternative working fluids - usually more expensive and necessitating system adaptations.

How to implement ORC in industrial processes

ORC systems are most effective in locations where low- or medium-temperature waste heat is available, and where other conventional heat recovery technologies - such as waste heat boilers, steam turbines, or absorption systems - cannot be used efficiently.

Low-temperature process heat

In many industrial sectors - such as food processing, aluminum smelting, or chemical production - part of the waste heat has a temperature between 80°C and 250°C. For traditional steam turbines, this temperature is too low to operate efficiently, but ORC systems make it possible to recover this energy and convert it into electricity, which would otherwise be lost.

Processes with distributed heat sources

In plants with numerous small furnaces, dryers, or heating processes - where heat sources are scattered - it is difficult to install a large, conventional heat recovery system. Due to their modularity, ORC systems can be adapted to multiple smaller sources and operate over a wide range of conditions.

Processes requiring compact installations

In facilities where space is limited or modernization of existing heating systems is difficult, ORC systems can be installed as standalone modules, unlike traditional large turbines or waste heat boilers.

Summary

The Organic Rankine Cycle (ORC) technology enables efficient recovery of energy from waste heat and low-temperature sources that would otherwise remain unused in traditional systems. By using organic fluids with lower boiling points, ORC systems make it possible to generate electricity in a stable and safe manner, improving industrial energy efficiency and supporting CO₂ emission reduction. ORC systems can operate in installations ranging from several tens of kilowatts to a few megawatts, allowing for the utilization of energy that cannot be recovered through other heat recovery methods. These installations are successfully applied across various sectors — from heavy industry and biogas plants to waste incineration facilities and geothermal energy — and can be easily integrated into existing industrial processes.