internal cycle efficiency
GreelTech’s solution is a redesign of the traditional ORC-cycle allowing a higher efficiency and power output. By using thermal energy to create a pressure in a closed vessel the need of electricity consuming pressure pump is eliminated. The total need of heat for driving the process is often less than 1 % of the thermal input and no produced electricity is used to run the process. Typical energy consumption for ORC under the same conditions would be 5-15 % of the produced electricity.
The refrigerant in the right high pressure tank is fed to an evaporator. The evaporated refrigerant is expanded in an expander and condensed in the condenser. The condensate flows to a low pressure tank which collects the condensated refrigerant.
Then the left low pressure tank which is receiving condensate is full and the tank containing high pressure gas is empty it is time to change the function of the two tanks. This is done by shifting the four valves.
Now the refrigerant in the full left tank is fed to the evaporator and the right tank is receiving condensate.
When the left tank is empty and the right tank is full it is once again time to shift the valves.
After shifting the valves the system is back at step 1 again.
Advantages over ORC
Greeltech’s solution is only using thermal energy to push the refrigerant through the system. The thermal energy put into the system is cheap compared to produced electricity and in a typical installation is less than 1 % of the thermal energy used for running the system.
Below is a comparison between GreelTech’s solution and an existing ORC for waste heat recovery on a pulp mill.
- Heat source temperature: 80 °C
- Heat source flow: 340 m3/h
- Coolant inlet temperature: 2 °C
- Coolant flow: 720 m3/h
- Avaliable heat: 20 000 kW
- Thermal power: 11 700 kW
- Thermal leakage: 50 kW (0.4 %)
- Produced electrical power: 1000 kW (8.5 %)
- Consumed electrical power: 0 kW
- Delivered power: 1 000 kW (5.0 % of heat source)
Utilized heat from source
Increased power output
- Thermal power: 7 800 kW
- Thermal leakage: 0 kW
- Produced electrical power: 675 kW (8.6 %)
- Consumed electrical power: 95 kW (14 %)
- Delivered power: 580 kW (2.9 % of heat source)