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ORC – Organic Rankin Cycle

The main ORC-plant equipment consists of a thermal oil boiler unit and a steam ORC-turbine, similarly to the conventional steam turbine cycle.

When ORC cycle implemented, organic coolant with a high boiling temperature is used as working fluid. Biofuel is supplied to thermal oil boiler to be combusted to produce heat in the form of high temperature organic fluid (generally, thermal oil) which circulates through heat exchanger and transfers heat to the cycle working fluid. The working fluid is converted into steam in evaporator heat exchanger which comes to a special ORC-steam turbine where it performs mechanical work by rotating turbine blades to produce electric energy in the generator. Heat energy extracted in the condenser as a result of plant cooling and further directed for hot water heating for technological purposes, district heating and ventilation.  Heat may be converted into cold energy in the form of chilled circulating water in absorption refrigerating machines. Since for cold generation in such case biomass energy is used, the chilled water energy is sometimes called “bio-cold”.

For the purpose of correct thermal oil boiler selection we apply different technological solutions in terms of fuel combustion technologies implemented: grate firing or bubbling fluidized bed (BFB). Burning technology selection is according to properties of biomass to be combusted. Important properties of fuel are as follows: volatile content, humidity, calorific value, ash content, chlorine and sulphur content, ash melting point temperature. We analyze solid fuel in laboratories before recommendation provision on the combustion technology selected.

Technical and economically feasible capacity of ORC-plants using biomass is within the range of 0.5-5 MW of electricity.

ORC cycles are often also used for electric energy generation from different heat energy discharge flows, such as gas turbine compression stations exhaust gases, furnaces exhaust gases, drying systems and as a combination with gas reciprocating engines as dissipated heat to electricity converters.