Organic Rankine Cycle

 

“ORCs are the unrivalled technical solution for generating electricity from low-medium temperature heat sources of limited capacity”
cit. Organic Rankine Cycle(ORC) Power Systems – E.Macchi, M.Astolfi

Traditionally, in large-scale power generation, steam cycles are the preferred solution for heat recovery and external combustion of solid and heavy fuels, while internal combustion engines are the usual choice for clean and standard liquid or gas fuels.

Still there is a large variety of energy sources, with limited temperature and/or thermal power available, for which gas and steam cycles are not a convenient choice, Organic Rankine Cycles have proven to be the most technically and economically valuable solution available, offering higher performance, flexibility, and lower capital costs.

Organic Rankine Cycle (ORC) systems are used for power production from low to medium temperature heat sources in the range of 80 to 350 °C and for small-medium applications at any temperature level. This technology allows for exploitation of low-grade heat that otherwise would be wasted. The working principle of an Organic Rankine Cycle power plant is similar to the most widely used process for power generation, the Clausius-Rankine Cycle.

The main difference is the use of organic substances instead of water (steam) as working fluid. The organic working fluid has a lower boiling point and a higher vapour pressure than water and is therefore able to use low temperature heat sources to produce electricity. The organic fluid is chosen to best fit the heat source according to their differing thermodynamic properties, thus obtaining higher efficiencies of both cyle and expander.

The main components of an Organic Rankine Cycle power plant design are:

  • 1. The turbine

    it’s the key component of the entire ORC power plant, which determines the ORC system performance. It expands the working fluid producing mechanical energy that is converted into electricity by a generator coupled with the turbine shaft.

  • 2. The heat exchangers

    The working fluid flows through the heat exchangers, extracting the heat from the heat source. Shell and tube heat exchangers are usually applied but they can vary geometry and configuration depending on the energy source and the total thermal input.

  • 3. The condenser

    With the direct air to fluid heat exchanger, the organic fluid is cooled and liquefied before entering the pump. The use of air eliminates the requirement for water to treatment and make up. It is possible to use also a water cooled condenser.

  • 4. The feed pump

    Brings the organic fluid from the condensation pressure to the maximum pressure of the Organic Rankine Cycle. The pump is usually driven by an electric motor at variable rotating speed.
Exergy ORC 3D

By converting thermal energy to electricity at low temperature, ORCs are suitable for a wide range of applications, with plant size between 100 kW ad 50 MWe including:

Low-medium enthalpy geothermal sources exploitation (90 – 260 °C)
Low-medium enthalpy geothermal sources exploitation (90 – 260 °C)
BIOMASS
BIOMASS
CONCENTRATED SOLAR POWER (CSP)
CONCENTRATED SOLAR POWER (CSP)
Power generation from waste heat in industrial processes
Power generation from waste heat in industrial processes
Power generation increasing efficiency of systems based on diesel and gas turbines and reciprocating engines
Power generation increasing efficiency of systems based on diesel and gas turbines and reciprocating engines

The traditional choice of the expander for ORC cycles worldwide has been for decades to employ axial or radial inflow turbines. EXERGY introduced the innovative patented Radial Outflow Turbine (ROT) and is unique in applying this extremely efficient technology on a vast range of products.

ORC CYCLES:
SUITABLE FOR LOWER TEMPERATURE APPLICATIONS
SUITABLE FOR LOWER TEMPERATURE APPLICATIONS
  • Wider range of applications worldwide
NO LIQUID PHASE DURING EXPANSION
NO LIQUID PHASE DURING EXPANSION
  • Reliable and long-lasting expander
  • Simpler and lower maintenance cost
COMPACT AND AUTOMATED
COMPACT AND AUTOMATED
  • No need for operators
MODULAR CONFIGURATION
MODULAR CONFIGURATION
  • Ease of transportation and installation
  • Reduced environmental footprint
  • Few soil consumption
  • Low associated costs for foundation and assembly
DESIGN FLEXIBILITY TO USE THE MOST EFFICIENT WORKING FLUIDS
DESIGN FLEXIBILITY TO USE THE MOST EFFICIENT WORKING FLUIDS
  • Optimized efficiency
  • Customized solution on the resource characteristic
OPERATIONAL FLEXIBILITY
OPERATIONAL FLEXIBILITY
  • Superior off-design performances
NO-WATER CONSUMPTION OPTION
NO-WATER CONSUMPTION OPTION
  • Lower environmental impact with no waste of water
SIMPLE, FAST AND RELIABLE SYSTEM MAINTENANCE
SIMPLE, FAST AND RELIABLE SYSTEM MAINTENANCE
  • Long product life
  • Ideal for cycling environments and where fast start stops are required
HIGH MARKET AVAILABILITY OF CHEMICAL WITH FLUID REFILLING RARELY REQUIRED
HIGH MARKET AVAILABILITY OF CHEMICAL WITH FLUID REFILLING RARELY REQUIRED
  • Lower running costs

1990s

The use of ORC expands rapidly especially for biomass and geothermal applications, leaving a great margin of growth in WHR and solar thermodynamic applications.

1980s

THE FINNISH SCHOOL

Prof. J. Larjola guides the development of high-speed hermetic turbogenerators in the hundreds kWE range, in Finland. The generator and pump share the same shaft in this configuration. This new ORC turbogenerator configuration was at first used as charger for the batteries of a deep-see submersible in 1987

1970s

Prof. G. Angelino, together with Ennio Macchi and Mario Gaia start the Italian research activity in the ORC sector at Politecnico di Milano. They begin studying the possibility to use organic fluids instead of water to power the Rankine Cycle, for automotive, space and solar applications.

1945

Collaborating with Prof. d’Amelio who first designed a power plant using the ethyl chloride to power a turbine Società Anonima Forze Endogene Napoletane (SAFEN) installed a 300 kW geothermal plant on Ischia Island(Italy). This plant became operational in 1955 and was the forerunner, the first in the world, of a modern binary plant

1935

Prof. Luigi D'Amelio employs an organic fluid in a real turbine system. He is also the first to consider the advantages of high molecular mass fluids to reduce rpm and number of turbine stages

1883

Frank Ofeldt develops a power system engine that uses naphtha instead of water

1840s

Prof William John Macquorn Rankine develops a complete theory of the steam engine describing how power can be generated from temperature difference between a heat source and a cold source and idealizing the thermodynamic cycle that then took his name: Rankine Cycle.

1824

Nicolas Léonard Sadi Carnot publishes Reflections on the Motive Power of Fire, in which he expresses the first successful theory of the maximum efficiency of heat engines, laying the foundations of an entirely new discipline: thermodynamics

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