BINARY POWER GENERATION SYSTEM

Abstract

 Provided is a compact binary power generation system with good power generation efficiency.
The binary power generation system includes an evaporator configured to heat a low-boiling medium and turn a liquid state into a vapor state; an expander configured to be activated by expansion of a vaporous low-boiling medium discharged from the evaporator; a generator configured to generate power by the expander being activated; a condenser configured to liquefy the vaporous low-boiling medium discharged from the expander; a pump for circulating the low-boiling medium; a closed-loop circulation pathway including the evaporator, the expander, the condenser, and the pump; and an intermediate heat exchanger configured to exchange heat between the vaporous low-boiling medium which is discharged from the expander and is still not flown into the condenser, and a liquid low-boiling medium which is discharged from the pump and is still not flown into the evaporator.

Description

[0001] The present invention relates to a binary power generation systems, which generate electricity with a low-temperature heat source such as hot spring water, and in particular, relates to a binary power generation system including an intermediate heat exchanger.

[0002] Conventionally, binary power generation systems use a low-temperature (100°C to 150°C, for example) heat source such as hot spring and industrial waste heat is known. In the binary power generation systems, heat of the heat source is imparted through a heat exchanger to a low-boiling medium which is a working medium, which brings the medium to a boil and creates vapor pressure. The binary power generation systems use this vapor pressure to rotate a turbine and thus generate power. Due to its structure, however, binary power generation is low in energy efficiency and requires a large number of heat sources to generate a small amount of electricity. The binary power generation therefore has difficulty in ensuring heat sources.

[0003] With an aim to solve the foregoing problem, for example, the binary power generation system disclosed in Patent Document 1 is suggested to improve a heat-energy use efficiency overall in the binary power generation system and enhance power-generation efficiency.

[0004] Patent Document 1: Japanese Patent Application Publication (Kokai) No. 2014-177922

[0005] The binary power generation system disclosed in Patent Document 1 requires two kinds of heat sources different in temperature, which makes the system complicated. The system therefore needs to be of large size, which incurs high manufacturing cost.

[0006] In light of the issues mentioned above, the present invention is directed to an object of providing a binary power generation system which is compact in size and improved in power-generation efficiency.

[0007] The invention solves the issues as described below. A first invention provides a binary power generation system. The binary power generation system includes an evaporator configured to heat a low-boiling medium and turn a liquid state into a vapor state; an expander configured to be activated by expansion of a vaporous low-boiling medium discharged from the evaporator; a generator configured to generate power by the expander being activated; a condenser configured to liquefy the vaporous low-boiling medium discharged from the expander; a pump for circulating the low-boiling medium; a closed-loop circulation pathway including the evaporator, the expander, the condenser, and the pump; and an intermediate heat exchanger configured to exchange heat between the vaporous low-boiling medium which is discharged from the expander and is still not flown into the condenser, and a liquid low-boiling medium which is discharged from the pump and is still not flown into the evaporator.

[0008] In a second invention according to the first invention, the circulation pathway includes bypasses connecting the expander to the condenser, and the pump to the evaporator, without passing through the intermediate heat exchanger. The binary power generation system further includes a first temperature measuring device configured to measure temperature T1 of the liquid low-boiling medium discharged from the pump; a second temperature measuring device configured to measure temperature T2 of the vaporous low-boiling medium discharged from the expander; and a medium flow-path switching device configured to switch a flow path of the low-boiling medium between a fist pathway passing through the intermediate heat exchanger and a second pathway which follows the bypass without passing though the intermediate heat exchanger. The medium flow-path switching device is configured to switch the flow path of the low-boiling medium from the first pathway to the second pathway when a difference between the temperature T1 and the temperature T2 is smaller than a predetermined temperature difference.

[0009] In a third invention, the expander is a scroll expander including a fixed scroll and an orbiting scroll. The vaporous low-boiling medium is introduced from a central portion into a gas pocket which is formed by spiral-shaped fixed and orbiting wraps provided in the fixed and orbiting scrolls being meshed with each other.

[0010] The binary power generation system of the present invention is capable of cooling the low-boiling medium which has not yet flown into the condenser and simultaneously heating the low-boiling medium which has not yet flown into the evaporator. This makes it possible to improve condensation and evaporation efficiencies and improve power-generation efficiency overall in the system. It is then further possible to downsize the binary power generation system and reduce manufacturing cost.

Fig. 1 illustrates a configuration of a binary power generation system according to an embodiment of the present invention.

Fig. 2 illustrates a configuration of a binary power generation system according to another embodiment of the present invention.

[0011] An embodiment of the present invention will be described below with reference to the accompanying drawings. A binary power generation system 1 includes an evaporator 10, an expander 20, a generator 60, a condenser 30, a pump 40, a single intermediate heat exchanger 70, and a circulation pathway 50 including the foregoing elements. The evaporator 10 heats a low-boiling medium 90 and turns a liquid state into a vapor state by using hot water 100 drawn from a hot source. The hot water 100 serves as a heat source. Examples of the hot source include hot spring. The expander 20 expands the vaporous low-boiling medium 90 discharged from the evaporator 10 to generate rotational driving energy. The generator 60 uses rotational driving energy generated with the expander 20 to generate power. The condenser 30 condenses the vaporous low-boiling medium 90 discharged from the expander 20 in an expanded state into a liquid state. The pump 40 circulates the low-boiling medium 90 liquefied in and discharged from the condenser 30. The intermediate heat exchanger 70 cools the vaporous low-boiling medium 90 which has been discharged from the expander 20 and has not yet flown into the condenser 30. The intermediate heat exchanger 70 heats the liquid low-boiling medium 90 which has been discharged from the pump 40 and has not yet flown into the evaporator 10. The circulation pathway 50 has a closed-loop configuration wherein the low-boiling medium 90 flows through the evaporator 10, the expander 20, the intermediate heat exchanger 70, the condenser 30, and the pump 40 in the order named and returns to the evaporator 10 through the intermediate heat exchanger 70.

[0012] In the binary power generation system 1 illustrated in Fig. 1, examples of the low-boiling medium 90 includes an inert gas consisting mainly of chlorofluorocarbon having no global warming potential such as HFC-245fa and HFC-134A, hydrocarbon such as pentane, a mixture of water and ammonia. In particular, HFC-245fa is suitable for serving as the low-boiling medium 90. However, examples of the low-boiling medium 90 are not limited to the foregoing substances.

[0013] The evaporator 10 exchanges heat between the hot water 100 drawn from the hot source and the circulation pathway 50, heats the low-boiling medium 90, and turns the liquid state into the vapor state. The hot water 100 may be, for example, hot spring water. The hot water 100 may be fresh water which is heated by exchanging heat with hot spring water to prevent scale present in the hot spring water from depositing and negatively affecting the binary power generation system 1.

[0014] The vaporous low-boiling medium 90 which has been discharged from the evaporator 10 passes through the circulation pathway 50 and flows into the expander 20.

[0015] In one example, the expander 20 may be a displacement-type expander. Examples of the displacement-type expander include, but are not limited to, a scroll expander, a screw expander, a claw expander, a reciprocating expander, a Roots-type expander. In particular, the scroll expander including fixed and orbiting scrolls is suitable for serving as the displacement-type expander, which has been disclosed by Japanese Patent Application Publication (Kokai) No. 2012-007518 which is a publicly known document. The expander 20 converts expansion energy of the vaporous low-boiling medium 90 flown into the expander 20 into rotary motion. The generator 60 produces power with the rotary motion.

[0016] When the scroll expander is used, a hyperbaric vaporous low-boiling medium 90 is introduced from a central portion of the fixed scroll into a gas pocket. The gas pocket is formed by meshing a spiral shaped orbiting wrap provided in an orbiting scroll with a spiral shaped fixed wrap-provided in a fixed scroll. The orbiting scroll is then brought into orbital motion due to energy caused during the vapor expansion. An orbital force of the orbiting scroll is transmitted to the generator 60 mounted on a shaft of the expander to generate power. The scroll expander thus configured may provide high noise reduction. The size of the scroll expander may be small compared with that of a turbine expander, and further the energy needed to drive the scroll expander is low compared with the required energy in the turbine expander.

[0017] The vaporous low-boiling medium 90 discharged from the expander 20 passes through the circulation pathway 50 and flows into the intermediate heat exchanger 70, the details of which will be described below. The vaporous low-boiling medium 90 flown into the intermediate heat exchanger 70 is then cooled with the intermediate heat exchanger 70.

[0018] The condenser 30 exchanges heat between the vaporous low-boiling medium 90 which has been expanded in the expander 20 and then cooled with the intermediate heat exchanger 70 and cooling water 200 drawn from a cold source to further cool the vaporous low-boiling medium 90 and turn the vaporous state into the liquid state. Examples of the cooling water 200 include groundwater.

[0019] The low-boiling medium 90 which has been cooled in the condenser 30 is liquefied and then flows into the pump 40. The low-boiling medium 90 which has passed through the condenser 30 occasionally fails to be thoroughly liquefied and partially remains as vapor. When this happens, a receiver tank (not shown) may be disposed upstream from the pump 40 to store the liquid low-boiling medium 90 to prevent the vapor from flowing into the pump 40.

[0020] The intermediate heat exchanger 70 exchanges heat between the vaporous low-boiling medium 90 which has been discharged from the expander 20 and has not yet flown into the condenser 30 and the liquid low-boiling medium 90 which has been discharged from the pump 40 and has not yet flown into the evaporator 10. As discussed previously, the vaporous low-boiling medium 90 discharged from the expander 20 is cooled in the intermediate heat exchanger 70 with the liquid low-boiling medium 90 which has been discharged from the pump 40 and has not yet flown into the evaporator 10. Furthermore, the liquid low-boiling medium 90 discharged from the pump 40 is heated in the intermediate heat exchanger 70 with the vaporous low-boiling medium 90 discharged from the expander 20.

[0021] Heat exchangers that have been known in the art may use as the intermediate heat exchanger 70. In particular, a plate-type heat exchanger is suitable for serving as the intermediate heat exchanger 70.

[0022] The plate heat exchanger is produced by attaching a predetermined number of heat-transfer plates to guide bars perpendicularly to guide bars, the plates being formed by stamping convex-concave wave patterns on thin panels made of corrosion-resistant metal, such as stainless and titanium, and sealing margins of the panels with synthetic rubber gaskets, sandwiching the heat-transfer plates between stationary and movable frames made of steel sheets, and fastening the stationary and mobile frames and the heat-transfer plates together with bolts. Heat is exchanged between a high-temperature vaporous low-boiling medium 90 which has been discharged from the expander 20 and flows through flow paths formed between the plates, and a low-temperature liquid low-boiling medium 90 which has been discharged from the pump 40 and flows through flow paths formed between the plates before being flown into the evaporator 10.

[0023] With a structure described above, the vaporous low-boiling medium 90 which has been discharged from the expander 20 and has not yet flown into the condenser 30 is cooled with the intermediate heat exchanger 70 to a temperature immediately before the vapor starts being liquefied. This optimizes efficiency of the condenser 30. At the same time, the liquid low-boiling medium 90 which has been discharged from the pump 40 and has not yet flown into the evaporator 10 is heated to a temperature immediately before the liquid starts being evaporated. It is therefore possible to optimize a heat source use efficiency of the binary power generation system 1 as a whole.

[0024] The low-boiling medium 90 which has been discharged from the pump 40 and has not yet flown into the evaporator 10 is heated with the intermediate heat exchanger 70 to a temperature immediately before the low-boiling medium 90 starts being evaporated, which is inherent to the low-boiling medium 90. The efficiency of the evaporator 10 then becomes maximum, which optimizes power generation efficiency.

[0025] Since the power generation efficiency is fully improved simply by employing the single intermediate heat exchanger 70, the binary power generation system 1 may be downsized and is easily installed even in a relatively small space, such as a site of a hot spring facility. Furthermore, the binary power generation system 1 needs not be complicated in structure, thus reducing manufacturing cost.

[0026] Fig. 2 illustrates a configuration of a binary power generation system 1a according to another embodiment of the present invention. In the description of the present embodiment, components having the same functions as those of the previous embodiment will be provided with the same reference numerals as those used in the previous embodiment, and the description thereof will be omitted.

[0027] Referring to Fig. 2, a circulation pathway 50 of the binary power generation system 1a includes bypasses 51 and 52. The bypass 51 connects an expander 20 to a condenser 30 without passing through an intermediate heat exchanger 70. The bypass 52 connects the pump 40 to an evaporator 10 without passing through the intermediate heat exchanger 70.

[0028] The binary power generation system 1a further includes medium flow-path switching devices 81 to 84. The medium flow-path switching devices 81 and 82 are disposed in both end portions of the bypass 51. The circulation pathway 50 includes a divergent pathway extending from the medium flow-path switching device 81 through the intermediate heat exchanger 70 to the medium flow-path switching device 82. The medium flow-path switching devices 83 and 84 are disposed in both end portions of the bypass 52. The circulation pathway 50 includes a divergent pathway extending from the medium flow-path switching device 83 through the intermediate heat exchanger 70 to the medium flow-path switching device 84. The medium flow-path switching devices 81 and 82 are capable of switching the flow path of the low-boiling medium 90 between a first pathway which passes through the intermediate heat exchanger 70 and does not pass through the bypass 51, and a second pathway which bypasses the intermediate heat exchanger 70 and passes the bypass 51. Likewise, the medium flow-path switching devices 83 and 84 are capable of switching the flow path of the low-boiling medium 90 between a first pathway which passes through the intermediate heat exchanger 70 and does not pass through the bypass 52, and a second pathway which bypasses the intermediate heat exchanger 70 and passes through the bypass 52.

[0029] The binary power generation system 1a further includes a first temperature measuring device 53 and a second temperature measuring device 54. The first temperature measuring device 53 measures temperature T1 of the liquid low-boiling medium 90 at a point after the liquid is discharged from the pump 40 and before the flow path of the low-boiling medium 90 diverges toward the intermediate heat exchanger 70. The second temperature measuring device 54 measures temperature T2 of the vaporous low-boiling medium 90 at a point after the vapor is discharged from the expander 20 and before the flow path of the low-boiling medium 90 diverges toward the intermediate heat exchanger 70.

[0030] Normally, the temperature T1 of the liquid low-boiling medium 90 at the point after the liquid is discharged from the pump 40 and before the flow path of the low-boiling medium 90 diverges is sufficiently lower than the temperature T2 of the low-boiling medium 90 which has been discharged from the expander 20. However, due to a change in source temperature of the hot source and external air conditions, there is a chance that temperature difference ΔT is not sufficient between the temperature T2 of the low-boiling medium 90 discharged from the expander 20, and the temperature T1 of the liquid low-boiling medium 90 at a point after the liquid is discharged from the pump 40 and before the flow path of the low-boiling medium 90 diverges. In this case, it might not be efficient to use the intermediate heat exchanger 70 for exchanging heat between the low-boiling medium 90 discharged from the expander 20 and the low-boiling medium 90 discharged from the pump 40.

[0031] In this light, the binary power generation system 1a is configured to compare the temperature T1 measured by the first temperature measuring device 53 with the temperature T2 measured by the second temperature measuring device 54. If the difference ΔT is equal to or smaller than a predetermined value, the binary power generation system 1a switches the medium flow-path switching devices 81 to 84 to allow the low-boiling medium 90 to flow through the bypasses 51 and 52, instead of passing through the intermediate heat exchanger 70.

[0032] Because of the constitution described above, there is less chance that the binary power generation system 1a is affected by changes in heat source temperature and external air environment.

1, 1a

binary power generation system

10

evaporator

20

expander

30

condenser

40

pump

50

circulation pathway

51, 52

bypass

53

first temperature measuring device

54

second temperature measuring device

60

generator

70

intermediate heat exchanger

81 to 84

medium flow-path switching device

90

low-boiling medium

100

hot water

200

cooling water

Claims

1. A binary power generation system (1, 1a) comprising:

an evaporator (10) configured to heat a low-boiling medium (90) and turn a liquid state into a vapor state;

an expander (20) configured to be activated by expansion of a vaporous low-boiling medium (90) discharged from the evaporator (10);

a generator (60) configured to generate power by the expander (20) being activated;

a condenser (30) configured to liquefy the vaporous low-boiling medium (90) discharged from the expander (20);

a pump (40) for circulating the low-boiling medium (90);

a closed-loop circulation pathway (50) including the evaporator (10), the expander (20), the condenser (30), and the pump (40); and

an intermediate heat exchanger (70) configured to exchange heat between the vaporous low-boiling medium (90) which is discharged from the expander (20) and is still not flown into the condenser (30), and a liquid low-boiling medium (90) which is discharged from the pump (40) and is still not flown into the evaporator (10).

2. The binary power generation system (1a) of claim 1,
wherein the circulation pathway (50) includes bypasses (51, 52) connecting the expander (20) to the condenser (30), and the pump (40) to the evaporator (10), without passing through the intermediate heat exchanger (70),
wherein the binary power generation system (1a) further comprises:

a first temperature measuring device (53) configured to measure temperature T1 of the liquid low-boiling medium (90) discharged from the pump (40);

a second temperature measuring device (54) configured to measure temperature T2 of the vaporous low-boiling medium (90) discharged from the expander (20); and

a medium flow-path switching device (81, 82, 83, 84) configured to switch a flow path of the low-boiling medium (90) between a fist pathway passing through the intermediate heat exchanger (70) and a second pathway which follows the bypass (51, 52) without passing through the intermediate heat exchanger (70), and

wherein the medium flow-path switching device (81, 82, 83, 84) is configured to switch the flow path of the low-boiling medium (90) from the first pathway to the second pathway when a temperature difference between the temperature T1 and the temperature T2 is smaller than a predetermined temperature difference.

3. The binary power generation system (1, 1a) of claim 1 or 2,
wherein the expander (20) is a scroll expander including a fixed scroll and an orbiting scroll, and
wherein the vaporous low-boiling medium (90) is introduced from a central portion into a gas pocket which is formed by spiral-shaped fixed and orbiting wraps provided in the fixed and orbiting scrolls being meshed with each other.

Drawing