Heat exchange system, cooling system and cooling method of gas turbine, and gas turbine system

A heat exchange system, comprising:

• a gas line through which a gas to be cooled is to flow;
• a heat exchanger disposed in the gas line and configured to cool the gas through heat exchange with a refrigerant;
• a refrigerant introduction line for introducing the refrigerant into the heat exchanger;
• a refrigerant discharge line for discharging the refrigerant after cooling the gas from the heat exchanger;
• a recirculation line for recirculating at least a part of the refrigerant flowing through the refrigerant discharge line into the refrigerant introduction line;
• and a flow-rate adjustment unit programmed to adjust a flow rate of the refrigerant flowing through the recirculation line so that a temperature of the refrigerant introduced into the heat exchanger from the refrigerant introduction line is not lower than a threshold, wherein the gas line is configured to supply compressed air to a cooling target part of a gas turbine from a compressor of the gas turbine, wherein the refrigerant introduction line is configured to be supplied with a part of condensate water as the refrigerant from a condenser of a steam turbine which constitutes a gas turbine combined cycle (GTCC) together with the gas turbine, the refrigerant introduction line is branched from a condensate main flow line disposed between the condenser and a boiler constituting the GTCC, the refrigerant discharge line joins the condensate main flow line, wherein the refrigerant discharge line joins the condensate main flow line at a joining position disposed downstream of a branching position at which the refrigerant introduction line branches, and the heat exchange system further comprises a valve which is capable of adjusting a flow rate of the condensate water flowing through a part of the condensate main flow line, the part of the condensate main flow line being disposed downstream of the branching position of the refrigerant introduction line and upstream of the joining position of the refrigerant discharge line.