Rankine cycle apparatus, combined heat and power system, and rankine cycle apparatus operation method
A Rankine cycle apparatus includes a pump, an evaporator, an expander, a condenser, and an internal heat exchanger. The internal heat exchanger allows heat exchange to take place between a working fluid discharged from the expander and a working fluid discharged from the pump. A temperature of the working fluid at an inlet of the expander is set so that a temperature of the working fluid at an outlet of the expander be higher than a saturation temperature on a high-pressure side of the cycle.
1. A Rankine cycle apparatus comprising:
a pump that pressurizes a working fluid;
an evaporator that heats the working fluid pressurized by the pump;
a positive-displacement expander that converts expansion energy of the working fluid heated in the evaporator into rotary power;
a condenser that cools the working fluid discharged from the positive-displacement expander; and
an internal heat exchanger that allows heat exchange to take place between the working fluid discharged from the positive-displacement expander and the working fluid discharged from the pump, wherein
the Rankine cycle apparatus is configured such that:
a temperature of the working fluid at an inlet of the positive-displacement expander is set so that a temperature of the working fluid at an outlet of the positive-displacement expander is higher than the saturation temperature on a high-pressure side of the cycle, and
the working fluid changes from a liquid phase to a gas-liquid two phase inside the internal heat exchanger after being discharged from the pump before being heated in the evaporator, and
the working fluid is a single organic working fluid.
2. The Rankine cycle apparatus according to claim 1 , wherein the temperature of the working fluid at the inlet of the positive-displacement expander is set so that a difference between the temperature of the working fluid at the outlet of the positive-displacement expander and a saturation temperature on a low-pressure side of the cycle is larger than a difference between the temperature of the working fluid at the inlet of the positive-displacement expander and the temperature of the working fluid at the outlet of the positive-displacement expander.
3. The Rankine cycle apparatus according to claim 1 , wherein a maximum temperature of the working fluid is lower than 300° C.
4. The Rankine cycle apparatus according to claim 1 , further comprising:
at least one selected from the group consisting of a pressure sensor that detects a pressure of the working fluid on the high-pressure side of the cycle and a temperature sensor that detects the saturation temperature on the high-pressure side of the cycle; and
at least one selected from the group consisting of a temperature sensor that detects the temperature of the working fluid at the inlet of the positive-displacement expander and a temperature sensor that detects the temperature of the working fluid at the outlet of the positive-displacement expander.
5. The Rankine cycle apparatus according to claim 1 , wherein
the internal heat exchanger comprises a low-temperature side flow path through which the working fluid discharged from the pump flows, and
the low-temperature side flow path has a larger cross-sectional area near an outlet thereof than near an inlet thereof.
6. The Rankine cycle apparatus according to claim 1 , wherein
the internal heat exchanger comprises a low-temperature side flow path through which the working fluid discharged from the pump flows and a high-temperature side flow path through which the working fluid discharged from the positive-displacement expander flows, and
the low-temperature side flow path has a cross-sectional area smaller than a cross-sectional area of the high-temperature side flow path.
7. The Rankine cycle apparatus according to claim 1 , wherein the positive-displacement expander is one of a scroll expander, a rotary expander, a screw expander, and a reciprocating expander.
8. A combined heat and power system comprising:
the Rankine cycle apparatus according to claim 1 ; and
a heat medium circuit in which a heat medium for use as a low-temperature heat source flows through the condenser of the Rankine cycle apparatus to cool the working fluid.
9. The combined heat and power system according to claim 8 , wherein
the heat medium is water, and
hot water produced in the condenser is used for at least one selected from hot water supply and space heating.
10. The combined heat and power system according to claim 8 , wherein the heat medium is air, and hot air produced in the condenser is used for indoor heating.