Orc power generation device

Abstract

There is provided a simple ORC power generation device that can efficiently generate power. The ORC power generation device includes a pump 2 configured to discharge a working medium that is condensed, an evaporator 3 configured to evaporate the working medium from the pump 2 through heat exchange with a heat source, an expander 4 configured to be driven by steam generated by evaporation at the evaporator 3, a condenser 5 configured to condense the steam expanded at the expander 4 to allow discharge from the pump 2, and a power generator 6, an input shaft of which is coupled to an output shaft of the expander 4. The power generator 6 is designed such that torque of the power generator during rated operation matches torque of the expander 4 during rated operation.

Description

Technical Field

[0001] The present invention relates to an ORC power generation device that uses an organic Rankine cycle.Background Art

[0002] Conventionally, there is known ORC power generation that uses an organic Rankine cycle where heat is recovered from a high-temperature heat source (such as geothermal heat, industrial waste heat, solar heat, or biomass), an organic medium is boiled, and a turbine (expander) is rotated by steam to generate power, and also, the steam is cooled by a heat exchanger to be returned to liquid, the liquid is fed to the heat exchanger again by a pump, and the liquid is heated by the heat exchanger to be returned to steam. For example, a power regeneration Rankine cycle system described in Patent Literature 1 may be cited.

[0003] With the system in Patent Literature 1, torque of an electric power generator is feedback-controlled using, as a target rotation speed of the electric power generator, a rotation speed that is obtained by inputting a calorie of a heating fluid input into an evaporator to a target rotation speed map indicating a relationship between the calorie of the heating fluid and a rotation speed of the electric power generator at which the electric power generator can stably and efficiently obtain power. An expander can thus be rotated at a rotation speed at which power can be stably and efficiently obtained.

[0004] Patent Literature 1: Japanese Patent Laid-Open No. 2022-152029Summary of InventionTechnical Problem

[0005] However, with the system in Patent Literature 1, torque of the electric power generator has to be feedback-controlled with the rotation speed obtained by inputting the calorie of a heating fluid input into the evaporator to the target rotation speed map as the target rotation speed of the electric power generator, and the system is complex.

[0006] In view of the problem of the conventional art, an object of the present invention is to provide a simple ORC power generation device that can efficiently generate power.Solution to Problem

[0007] (1) An ORC power generation device of the present invention is an ORC power generation device comprising: a pump configured to discharge a working medium that is condensed; an evaporator configured to evaporate the working medium from the pump through heat exchange with a heat source; an expander configured to be driven by steam generated by evaporation at the evaporator; a condenser configured to condense the steam expanded at the expander to allow discharge from the pump; and a power generator, an input shaft of which is coupled to an output shaft of the expander, where the power generator is designed such that torque of the power generator during rated operation matches torque of the expander during rated operation.

[0008] According to the present invention, because the input shaft of the power generator is coupled to the output shaft of the expander, and the torque of the power generator during rated operation matches the torque of the expander during rated operation, rotational torque generated by the expander can be maximally utilized. Accordingly, output of the power generator can be maximized, and high power generation efficiency can be achieved.

[0009] Furthermore, because the power generator and the expander are appropriately matched as described above, even in a situation where load changes, for example, stable operation of the power generator is maintained simply by adjusting torque (current) according to an output voltage of the power generator, and reliability of the device can be increased. Moreover, because torque matches between the power generator and the expander, a mechanical load can be minimized, and stability of the device can be increased. Moreover, due to appropriate matching between the power generator and the expander, a required size of the power generator can be minimized, and cost of the device can be reduced.

[0010] (2) In the present invention, the torque of the power generator during rated operation may be torque when efficiency of the power generator is highest. This allows efficiency of the power generator to be the highest during rated operation, and the power generator can generate maximum power, and energy loss can be minimized.

[0011] (3) In the present invention, there may be included a torque control unit configured to adjust an output current of the power generator based on an output voltage of the power generator. This allows the output voltage to correspond to a rotation speed and the output current to correspond to the torque, and thus, by monitoring the output voltage by the torque control unit and adjusting the output current as necessary, the power generator can be reliably prevented from deviating from a rated operation state, and stable operation of the power generator can be maintained, and reliability of the device can be increased.Brief Description of Drawing

[0012] FIG. 1 is a block diagram showing a configuration of an ORC power generation device according to an embodiment of the present invention.Description of Embodiment

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawing. FIG. 1 shows a configuration of an ORC power generation device according to the embodiment of the present invention.

[0014] As shown in FIG. 1, the ORC power generation device comprises a tank 1 configured to store a working medium, a pump 2 configured to discharge the medium stored in the tank 1, an evaporator 3 configured to evaporate the working medium discharged by the pump 2, through heat exchange with a heat source, an expander 4 configured to be driven by the working medium evaporated at the evaporator 3, a condenser 5 configured to condense the working medium expanded at the expander 4 and return the working medium to the tank 1, and a power generator 6, an input shaft of which is coupled to an output shaft of the expander 4.

[0015] As the working medium for the ORC power generation device, organic compounds such as organic fluorocarbons, cyclopentane, and cyclohexane are used. As a heat source 7 for the ORC power generation device, low-temperature heat sources such as waste heat from industrial processes, solar heat, geothermal heat, and biomass fuel can be used. The evaporator 3 has a function of transferring heat obtained from the heat source 7 to a liquid working medium, and converting the working medium from a liquid state to a steam state.

[0016] The expander 4 has a function of expanding the working medium in a high-pressure state to be in a low-pressure state, and causing a turbine to rotate by energy emitted by the working medium. There are several types of such a positive displacement expander, and a steam turbine is used in the case of large-scale power generation, and a screw expander is used in the case of medium-scale power generation of 20 to 50 kW, and in the case of small-scale power generation of less than 10 kW or power generation from a low-temperature heat source, a relatively small, high-efficiency, low-vibration scroll expander is desirably used.

[0017] The condenser 5 has a function of returning steam of a low-temperature working medium discharged by the turbine of the expander 4 to a liquid state. As the condenser 5, an air-cooling type is desirably used in the case of a small device, and a water-cooling type is desirably used in the case of a large device.

[0018] The power generator 6 is designed such that torque during rated operation matches torque of the expander 4 during rated operation. The torque of the power generator 6 during rated operation is torque when the efficiency of the power generator 6 is the highest.

[0019] Furthermore, the ORC power generation device comprises a torque control unit 8 configured to adjust an output current I of the power generator 6 based on an output voltage V of the power generator 6, a system control unit 9 configured to control a flow rate of the working medium, and a lithium-ion battery 10 configured to store power generated by the power generator 6. The torque control unit 8 adjusts a current value I flowing through the power generator 6 by changing a load connected to an output side of the power generator 6.

[0020] The flow rate of the working medium that is discharged by the pump 2 is proportional to a rotation speed of the pump 2, and the pump 2 is driven by a motor. The system control unit 9 controls a rotation speed of the motor through an inverter 11 such that the flow rate of the working medium is always maximum.

[0021] As described above, the power generator 6 is designed such that the torque of the power generator 6 matches the torque of the expander 4, and at this time, first, the expander 4 is driven without connecting the power generator 6. When a mass flow rate of the working medium that flows through the expander 4 is determined, a rotation speed of the expander 4 is determined. Then, a theoretical adiabatic heat drop of the working medium that can be used by the expander 4 is determined according to a pressure difference in the working medium between an inlet and an outlet of the expander 4.

[0022] By multiplying the theoretical adiabatic heat drop by the efficiency of the expander 4, a rotational energy, or in other words, an axial drive force, of the expander 4 that can be actually obtained is determined. The axial drive force is proportional to the rotation speed and the torque, and thus, the torque of the expander 4 can be obtained as a calculated value.

[0023] Accordingly, because the rotation speeds of the expander 4 and the power generator 6 match, the power generator 6 is designed such that the torque of the power generator 6 matches the calculated torque of the expander 4. Furthermore, the power generator 6 is designed such that the torque is constant torque in a period until rated operation.

[0024] Furthermore, the torque of the power generator 6 is proportional to the current flowing through the power generator 6, but when the current increases, efficiency is reduced due to heat loss caused by heat generation. Furthermore, the number of turns of a coil contributes to voltage. Moreover, there is an optimum relationship between a diameter and the number of turns. The power generator 6 is designed in view of the above. Accordingly, a correlation between the torque and the rotation speed of the power generator 6 in which the efficiency of the power generator 6 is the maximum efficiency can be made to match the relationship between the torque and the rotation speed of the expander 4.

[0025] According to this configuration, at the time of operation of the ORC power generation device, the pump 2 feeds the working medium from the tank 1 to the evaporator 3 according to an instruction from the system control unit 9. The evaporator 3 converts the working medium in a liquid state that is fed into a state of steam through heat exchange with the heat source 7, and transmits the working medium to the expander 4.

[0026] The expander 4 receives the working medium in a high-temperature, high-pressure state, expands the working medium, converts an expansion force to a rotational force, and rotates the output shaft of the expander 4. The condenser 5 cools and condenses the working medium in a steam state that is expanded at the expander 4, and returns the working medium to the tank 1.

[0027] At the power generator 6, the input shaft of which is coupled to the output shaft of the expander 4, a rotor is rotated at a same rotational speed as the output shaft of the expander 4, and power is generated. At this time, in the case where the expander 4 and the power generator 6 are in a rated operation state, the torque of the expander 4 and the torque of the power generator 6 match, and thus, the power generator 6 maximally utilizes rotational torque generated by the expander 4, and generates power with high power generation efficiency.

[0028] During this time, the torque control unit 8 controls the current I corresponding to the torque of the power generator 6 based on the output voltage V corresponding to the rotation speed of the power generator 6, and prevents the power generator 6 from deviating from the rated operation state due to a change in load or the like. Power generation by the power generator 6 is thus constantly performed with high power generation efficiency. Power obtained by power generation by the power generator 6 is stored in the lithium-ion battery 10, and is also supplied to other loads.

[0029] As described above, according to the present embodiment, because the torque of the power generator 6 during rated operation matches the torque of the expander 4 during rated operation, the rotational torque generated by the expander 4 can be maximally utilized. Output of the power generator 6 can thus be maximized, and high power generation efficiency can be achieved.

[0030] Furthermore, the relationship between the rotation speed and the torque is appropriately matched between the power generator 6 and the expander 4, and thus, even in a situation where load changes, the rated operation state can be easily maintained by control, by the torque control unit 8, of the current I based on the voltage V of the power generator 6, and stable operation of the power generator can be maintained. Reliability of the ORC power generation device can thus be increased.

[0031] Furthermore, because the torque matches between the power generator 6 and the expander 4, a mechanical load can be minimized by simple control of monitoring the voltage V by the torque control unit 8, and stability of the device can be increased. Moreover, due to appropriate matching between the power generator 6 and the expander 4, a required size of the power generator 6 can be minimized, and cost of the ORC power generation device can be reduced.

[0032] Particularly, an estimated torque map, a target rotation speed map, and feedback control of torque of the power regeneration Rankine cycle system disclosed in Patent Literature 1, for example, become unnecessary, and a device configuration and a control method can be simplified.Reference Signs List

[0033] 1tank 2pump 3evaporator 4expander 5condenser 6power generator 7heat source 8torque control unit 9system control unit 10lithium-ion battery 11inverter

Claims

1. An ORC power generation device comprising: a pump configured to discharge a working medium that is condensed; an evaporator configured to evaporate the working medium from the pump through heat exchange with a heat source; an expander configured to be driven by steam generated by evaporation at the evaporator; a condenser configured to condense the steam expanded at the expander to allow discharge from the pump; and a power generator, an input shaft of which is coupled to an output shaft of the expander, wherein the power generator is designed such that torque of the power generator during rated operation matches torque of the expander during rated operation.

2. The ORC power generation device according to claim 1, wherein the torque of the power generator during the rated operation is torque when efficiency of the power generator is highest.

3. The ORC power generation device according to claim 1 or 2, comprising a torque control unit configured to adjust an output current of the power generator based on an output voltage of the power generator.

Images