ORC general information

Organic Rankine Cycle (ORC) plants enable the utilization of numerous, previously unused waste heat sources and lead to an additional energy gain from already used primary energy sources without added input costs. Moreover, ORC plants are not dependent on climatic conditions such as sun or wind. Therefore, they can guarantee a high security of supply both independent of external conditions and based on the plant’s system itself.

ORC systems are highly resilient, reliable systems capable of counteracting the effects of climate change in this time of global warming. Potential areas of use are an increased efficiency in power plants as well as energy production from waste heat and solar thermal energy.

The basic concept of an entire Micro ORC system is always the same and consists of the following components:

  • Evaporator with heat removal from a thermal process
  • Working medium
  • Expander with generator
  • Condenser with heat sink
  • Concept of network adaptation
  • Pump
  • Recuperate (see example 1)/additional heat input (see example 2)
  • Regulation/control

Origin

The Organic Rankine Cycle theory is based on the work of the Scottish scientist and engineer William John Macquorn Rankine (1820-1872). He described the thermodynamic steam turbine process. Put simply, this is a reverse cooling process. The basic principle of the ORC process differs from a normal power plant process (Rankine Cycle) only in the fact that an “organic” medium is used as a working medium instead of water. Compared to water, this working medium possesses more optimal evaporation characteristics at lower temperatures and lower pressure. Chemicals used may be carbohydrates or silicone oils. The correct selection of working media is of crucial importance for the optimal operation of the ORC process.

Function

In an ORC plant, previously unused heat energy is used for the evaporation of the working medium. The gaseous working medium is relaxed over an expander and thus creates torque used to drive a generator. The relaxed working medium is condensed during the recooling process and pumped back into the evaporator.

ORC plants can convert waste heat into a universally usable form of energy (electricity). This energy can be fed into the public power grid, if it is not needed for personal use. It can also be used as mechanical energy to operate air compressors, pumps, ventilators, etc.

Recooling Principle

The ORC modules work at full operating level, due to the relatively high condensation temperature during the recooling process with dry coolers. Since a recuperator is used (not included in the schematic images), measures aimed at the seasonal lowering of the condensation temperature are only moderately effective and of no economic relevance.  Due to the relatively high condensation temperature of ca. 50°C in the ORC cycle, the temperature level in the recooling cycle lies at 64°C. In some applications, this high temperature level can be sold as additional usable heat under application of the KWK bonus.

But even without an additional heat level increase there are applications that allow a sensible use of the 500 kW:

  • Heating of buildings or generation of warm water

  • Heating of fermenter and mash/hydrolysis

 
After running through the evaporator, the recooling heat level can be raised to 80°C through the use of engine heat or/and heat from thermal oil cycles. This heat can also be used for the following:
  • Feed of remote heat grids
  • Operation of hygienization
  • Cleaning processes


 

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