Compressing device

A compressing device comprising:

• a compressor for compressing a gas;
• and
• a heat energy recovery unit for recovering heat energy of a compressed gas discharged from the compressor by employing a Rankine cycle using a working medium,
• wherein the heat energy recovery unit includes:
• a heat exchanger for recovering heat of the compressed gas by exchanging heat between the compressed gas and the working medium;
• an expander for expanding the working medium that is heat-exchanged with the compressed gas in the heat exchanger;
• a power recovery unit for recovering a power from the expander;
• a condenser for condensing the working medium flowing out of the expander;
• a circulation flow passage for connecting the heat exchanger, the expander, the condenser, and the pump;
• a bypass flow passage for bypassing the expander, the bypass flow passage being connected to the circulation flow passage between the heat exchanger and the expander, and also being connected to the circulation flow passage between the expander and the condenser, whereby the working medium can bypass the expander by flowing in the bypass flow passage;
• a bypass valve for opening and closing the bypass flow passage;
• a shut-off valve for shutting off an inflow of the working medium into the expander, wherein the shut-off valve is provided in the circulation flow passage at a location between the expander and the point of connection of the bypass flow passage to the circulation flow passage between the heat exchanger and the expander;
• a control unit for switching the bypass valve and shut-off valve between a state where the working medium is circulated in the circulation flow passage through the expander and a state where the working medium is circulated in the circulation flow passage through the bypass flow passage;
• a temperature sensor for detecting a temperature of the working medium, arranged between the heat exchanger and the expander in the circulation flow passage;
• and
• a pressure sensor for detecting a pressure of the working medium, arranged between the heat exchanger and the expander in the circulation flow passage,
• wherein the control unit:
• calculates a superheat degree of the working medium between the heat exchanger and the expander using the temperature obtained by the temperature sensor and the pressure obtained by the pressure sensor;
• and
• adjusts an inflow amount of the working medium into the heat exchanger so that the superheat degree becomes a predetermined lower limit value or more, the predetermined lower limit value being greater than or equal to zero, and also becomes a predetermined upper limit value or less, by controlling a rotation speed of the pump during the state where the working medium is circulated in the circulation flow passage through the bypass flow passage.