Device and method for reliably starting ORC systems

A thermodynamic cycle apparatus, in particular an organic Rankine cycle apparatus, comprising:

• a working medium;
• an evaporator for evaporating and additionally superheating the working medium;
• an expansion machine for generating mechanical energy while expanding the evaporated working medium;
• a condenser for condensing and additionally subcooling the working medium expanded in the expansion machine;
• and
• a pump for pumping the condensed working medium to the condenser when the thermodynamic cycle apparatus is in operation;
• a recuperator for transferring thermal energy from the expanded working medium to the working medium pumped between the pump and the evaporator when the thermodynamic cycle apparatus is in operation, the recuperator being arranged between the expansion machine and the condenser;
• and
• a bypass valve for bridging the recuperator in the circuit and for bypassing the pump,
• wherein the evaporator is located on a lower level than the condenser such that, prior to starting the pump, the condensed working medium can flow from the condenser to the evaporator by force of gravity and the working medium can circulate in a closed circuit via the evaporator and the condenser, to provide at least a predetermined minimum head height of the liquid working medium at the pump.

A method of starting a thermodynamic cycle apparatus, the thermodynamic cycle apparatus comprising:

• a working medium;
• an evaporator for evaporating and additionally superheating the working medium;
• an expansion machine for generating mechanical energy while expanding the evaporated working medium;
• a condenser for condensing and additionally subcooling the working medium, in particular the working medium expanded in the expansion machine, wherein the evaporator is located on a lower level than the condenser;
• and
• a pump for pumping the condensed working medium to the condenser when the thermodynamic cycle apparatus is in operation;
• the method comprising the following steps:
• applying heat to the evaporator and evaporating the working medium in the evaporator,
• superheating the working medium in the evaporator, wherein the working medium is caused to flow to the condenser;
• adjusting a condensation temperature to a first temperature value;
• adjusting the condensation temperature to a second temperature value, when the condensed working medium having the first temperature value has reached the pump, wherein the second temperature value is higher than the first temperature value;
• condensing the working medium in the condenser;
• and
• starting the pump when a predetermined head height of the working medium at the pump is reached or exceeded.