EP3112622B1

EP3112622B1 - Binary power generation system and binary power generation method

Info

Publication number: EP3112622B1
Application number: EP16176833.8A
Authority: EP
Inventors: Tamotsu Fujioka; Atsushi Unami; Takaaki Izumi
Original assignee: Anest Iwata Corp
Current assignee: Anest Iwata Corp
Priority date: 2015-06-30
Filing date: 2016-06-29
Publication date: 2019-05-01
Anticipated expiration: 2036-06-29
Also published as: EP3112622A1; CN106321172A; CN106321172B; JP2017014986A

Description

TECHNICAL FIELD

The present invention relates to a binary power generation system and a binary power generation method.

BACKGROUND

Known as this type of technique in the related art is a device described in Japanese Unexamined Patent Publication No. 2008-175108 . This device is a Rankine cycle power recovery device, and includes a single vapor generator, a plurality of displacement type expanders, and a condenser. A passage of vapor generated by the vapor generator is branched and connected to each expander. Condensed water supplied to the vapor generator is heated and vaporized in the vapor generator by heat of exhaust gas generated from an internal combustion engine, and supplied to the expander. Vapor expanded at each expander is collected in one vapor passage, and cooled and condensed at the condenser. Expansion of the vapor at each expander rotates a power take-out shaft, and power is generated by an induction generator.
In this device, the number of expanders to be operated can be increased or decreased. The number of expanders to be operated is increased when the pressure of the vapor generated at the vapor generator is detected and exceeds an upper limit of an appropriate range, and decreased when the pressure of the vapor falls below a lower limit thereof. As a result, a constant level of Rankine cycle efficiency is maintained without wasting the vapor even when a heat amount of the vapor changes.
In the above-mentioned device, the vapor is vaporized by the heat of the exhaust gas generated from the internal combustion engine, and the number of expanders to be operated is changed in accordance with the pressure of the vapor. That is, the heat amount of the vapor generated by the single vapor generator and thus the pressure thereof fluctuate with the fluctuations in heat amount of the exhaust gas generated from the internal combustion engine. Therefore, the number of expanders to be operated is determined using these pressure fluctuations. However, despite the fluctuations in heat amount of the exhaust gas, the condensed water is vaporized by the single vapor generator, which results in substantial fluctuations in heat exchange amount (recovered heat amount) at the vapor generator. Then, the vapor generator has, for example, working and non-working parts. In addition, an operating efficiency of the expander may not be sufficient due to the substantial fluctuations in the pressure of the generated vapor. Therefore, in the Rankine cycle, an overall efficiency may be reduced. US 2014/102101 A1 relates to heat engine systems and methods for recovering energy, such as by generating electricity from thermal energy.
US 5 860 279 A relates to a method and an apparatus for cooling hot fluids wherein the cooling is effected using a heat exchanger, a turbine, and a condenser.
An object of the present invention is to provide a binary power generation system and a binary power generation method whereby sufficient power can be generated without reductions in the overall efficiency even when an input heat amount fluctuates.
The object is achieved by the features of the subject-matter of the independent claims. The dependent claim relates to a further aspect of the invention.
An aspect of the present invention is a binary power generation system including a plurality of displacement type expanders and a plurality of power generators connected to each of the displacement type expanders, and generating power by expansion of an operating medium, which has received heat from a heat source medium for vaporization, at least at one of the displacement type expanders, the binary power generation system including a plurality of evaporators that is connected to each of the corresponding displacement type expanders and vaporizes the operating medium using the heat from the heat source medium, a condenser that is connected to each of the displacement type expanders, and cools and condenses the operating medium expanded at least at one of the displacement type expanders, a plurality of branched lines branched from a line through which the heat source medium circulates, each of the branched lines passing through each of the plurality of evaporators, a stop means that is capable of stopping circulation of the operating medium for each set of the evaporators and the displacement type expanders and circulation of the heat source medium for each of the evaporators through the branched lines, and a control unit that controls the numbers of the evaporators and the displacement type expanders to be operated by controlling the stop means based on information on a heat amount of the heat source medium.
Another aspect of the present invention is a binary power generation method where power is generated, using a binary power generation system including a plurality of displacement type expanders and a plurality of power generators connected to each of the displacement type expanders, by expansion of an operating medium which has received heat from a heat source medium for vaporization at least at one of the displacement type expanders, wherein the binary power generation system includes a plurality of evaporators that is connected to each of the corresponding displacement type expanders and vaporizes the operating medium using the heat from the heat source medium, and a condenser that is connected to each of the displacement type expanders, and cools and condenses the operating medium expanded at least at one of the displacement type expanders, a plurality of branched lines branched from a line through which the heat source medium circulates, each of the branched lines passing through each of the plurality of evaporators, and the binary power generation system controls the numbers of the evaporators and the displacement type expanders to be operated based on information on a heat amount of the heat source medium.
With these binary power generation system and binary power generation method, a plurality of displacement type expanders, to each of which a power generator is connected, and a plurality of evaporators, which corresponds to these displacement type expanders on a one-on-one basis, are provided. On the other hand, only one condenser is provided to the displacement type expanders. The numbers of the evaporators and the displacement type expanders to be operated are controlled based on the information on the heat amount of the heat source medium. Therefore, the operating medium can be vaporized with a heat amount required and sufficient for one displacement type expander. As a result, even when the input heat amount fluctuates, an efficient Rankine cycle can be realized and sufficient power can be generated without reductions in the overall efficiency.
In the above binary power generation system, the numbers of the evaporators and the displacement type expanders are N units, respectively. The control unit stores at least (N - 1) different thresholds for the information on the heat amount of the heat source medium, and may put (a + 1) units of the evaporators and the displacement type expanders into operation when detecting the information on the heat amount of the heat source medium and evaluating that the detected information exceeds an a-th (a is any integer from 1 to (N - 1)) smallest threshold of the (N - 1) thresholds.
With this configuration, the number of units to be operated is changed gradually with (N - 1) different thresholds as boundaries. Therefore, more efficient power generation can be achieved by simplified determining processing.
According to the present invention, even when the input heat amount fluctuates, an efficient Rankine cycle can be realized and sufficient power can be generated without reductions in the overall efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a schematic configuration of a binary power generation system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating each power generator in operation in accordance with an input heat amount.

DETAILED DESCRIPTION

Embodiments of the present invention will be described below with reference to the drawings. In descriptions of the drawings, identical elements bear identical signs and overlapping descriptions will be eliminated.
First, a binary power generation system 1 of the present embodiment will be described with reference to FIG. 1. In FIG. 1, solid lines indicate electric circuits, while broken lines indicate warm water circuits. Two-dot chain lines indicate circuits of an operating medium. The broken lines illustrated so as to be connected to a control unit 30 indicate control circuits.
As illustrated in FIG. 1, the binary power generation system 1 is a power generation system that heats and vaporizes an operating medium with a low boiling point by a relatively low temperature (for example, approximately 80 - 90°C) heat source and generates power with the vapor. As a heat source, anything can be used such as hot spring water, geothermal heat, and factory exhaust heat. As an operating medium, hydrochlorofluorocarbon (HFC245fa) and ammonia, for example, are included. The binary power generation system 1 includes a heat exchanger 3 that heats the heat source medium by exchanging heat with the heat source. At the heat exchanger 3, heat is transmitted from the heat source to the heat source medium. The heat source medium is not limited to water. As a heat source medium, other heat media may be used.
The binary power generation system 1 includes a first evaporator 4A, a second evaporator 4B, and a third evaporator 4C that heat and vaporize the operating medium by heat exchange with the heat source medium. These three (that is, N = 3) evaporators 4A to 4C are provided so as to correspond to three series of binary power generating devices included in the binary power generation system 1 on a one-on-one basis. That is, the binary power generation system 1 includes three sets of a displacement type expander and a power generator. Specifically, the binary power generation system 1 includes a first scroll expander 6A, a second scroll expander 6B, and a third scroll expander 6C as well as a first power generator 7A, a second power generator 7B, and a third power generator 7C connected to each thereof.
The binary power generation system 1 further includes a condenser 10 provided to the first to third scroll expanders 6A to 6C. The condenser 10 is shared among three (that is, N = 3) expanders, the first to third scroll expanders 6A to 6C. Lines of cold water, which is a cold source, circulate to the condenser 10. The condenser 10 exchanges heat with the cold source such as groundwater and a cooling tower and cools and condenses the vapor of the operating medium expanded at the first to third scroll expanders 6A to 6C.
At the first scroll expander 6A and the first power generator 7A, expansion of the vapor of the operating medium vaporized at the first evaporator 4A at the first scroll expander 6A rotates an output shaft thereof, and power is generated by the first power generator 7A. At the second scroll expander 6B and the second power generator 7B, expansion of the vapor of the operating medium vaporized at the second evaporator 4B at the second scroll expander 6B rotates an output shaft thereof, and power is generated by the second power generator 7B. At the third scroll expander 6C and the third power generator 7C, expansion of the vapor of the operating medium vaporized at the third evaporator 4C at the third scroll expander 6C rotates an output shaft thereof, and power is generated by the third power generator 7C.
A warm water line LI, in which warm water, a heat source medium, circulates, passes through the heat exchanger 3. The warm water line L1 is provided with an inlet sensor 11 for detecting information on the heat amount of the warm water between an outlet of the heat exchanger 3 and inlets to the first to third evaporators 4A to 4C. The warm water line L1 is also provided with an outlet sensor 12 for detecting the information on the heat amount of the warm water between outlets of the first to third evaporators 4A to 4C and the inlet to the heat exchanger 3. The information on the heat amount of the warm water means any one, or two or more pieces of information on flow rates, temperatures, and pressures of the warm water. The inlet sensor 11 detects the information on the warm water before heat exchange at the first to third evaporators 4A to 4C. The outlet sensor 12 detects the information on the warm water after heat exchange at the first to third evaporators 4A to 4C. The "line" means a pipe through which a fluid flows.
The warm water line L1 is provided with a circulating pump 15 for circulating the warm water. The warm water line L1 is branched into three lines. A first warm water branch line L1A passes through the first evaporator 4A, a second warm water branch line LIB passes through the second evaporator 4B, and a third warm water branch line L1C passes through the third evaporator 4C. The first to third warm water branch lines L1A to L1C are provided with a first to third electromagnetic valves 14A to 14C for stopping (blocking) circulation of the warm water in each line.
A first vapor supply line L2A, through which the vapor vaporized through heat exchange with the warm water at the first evaporator 4A flows, is connected to the first scroll expander 6A. A second vapor supply line L2B, through which the vapor vaporized through heat exchange with the warm water at the second evaporator 4B flows, is connected to the second scroll expander 6B. A third vapor supply line L2C, through which the vapor vaporized through heat exchange with the warm water at the third evaporator 4C flows, is connected to the third scroll expander 6C. These first to third vapor supply lines L2A to L2C are provided with a fourth to sixth electromagnetic valves 16A to 16C for stopping (blocking) the circulation of the vapor in each line.
A first vapor recovery line L3A connected to a vapor outlet of the first scroll expander 6A, a second vapor recovery line L3B connected to a vapor outlet of the second scroll expander 6B, and a third vapor recovery line L3C connected to a vapor outlet of the third scroll expander 6C are joined into one line for passing through the common condenser 10. A condensate supply line L4 through which the operating medium condensed through heat exchange with the cold source at the condenser 10 is branched into three lines and connected to each of the first to third evaporators 4A to 4C. The condensate supply line L4 is provided with a circulating pump 20 for circulating the operating medium. An inverter 19 for adjusting a circulating flow rate by the circulating pump 20 is connected thereto.
In this way, the warm water line L1 and the first to third warm water branch lines L1A to L1C constitute a circulation route of the warm water that supplies heat. The first to third vapor supply lines L2A to L2C, the first to third vapor recovery lines L3A to L3C, and the condensate supply line L4 constitute a circulation route of the operating medium that receives heat from the warm water. Both circulation routes are branched therealong, but shapes and lengths of pipes of respective branch lines are set equally, for example, and thus pressure losses thereof are substantially equal. Substantially equal flow rates of a liquid flow through respective branch lines.
The above first to third evaporators 4A to 4C, the first to third scroll expanders 6A to 6C, and the first to third power generators 7A to 7C are relatively small binary power generation devices adopting an organic Rankine cycle system. Each rated rotation speed of the first to third scroll expanders 6A to 6C is, for example, 3,000 rpm, while each transmission end output of the first to third power generators 7A to 7C is, for example, 5.5 kW.
Each of the first to third power generators 7A to 7C is connected to an inverter 17 via a ground detector, an electromagnetic contactor, and the like. The inverter 17 is connected to a three-phase alternate current (for example, 200 V) commercial power source 21. A load 18 such as an electric motor is connected to the inverter 17.
In the binary power generation system 1, the first to third electromagnetic valves 14A to 14C and the fourth to sixth electromagnetic valves 16A to 16C are equivalent to a stop means capable of stopping circulation of the operating medium for each set of the first to third evaporators 4A to 4C and the first to third scroll expanders 6A to 6C and circulation of the warm water for the first to third evaporators 4A to 4C.
The binary power generation system 1 includes the control unit 30 that controls the numbers of the first to third evaporators 4A to 4C and the first to third scroll expanders 6A to 6C to be operated by controlling this stop means based on the information on the heat amount of the warm water. The control unit 30 is a computer including hardware such as a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM) and software such as programs stored in the ROM. Once detecting the information on the heat amount of the warm water, the inlet sensor 11 and the outlet sensor 12 sequentially transmit the detected information to the control unit 30. The control unit 30 acquires the information on the heat amount of the warm water, and controls, based on the acquired information, opening and closing of the first to third electromagnetic valves 14A to 14C and the fourth to sixth electromagnetic valves 16A to 16C. By the opening and closing control of the first to third electromagnetic valves 14A to 14C and the fourth to sixth electromagnetic valves 16A to 16C, the numbers of the first to third evaporators 4A to 4C and the first to third scroll expanders 6A to 6C to be operated can be controlled. Thus, in the binary power generation system 1, the condenser 10 is shared, while a one to one relation is maintained between the evaporator and the displacement type expander. Furthermore, it is possible to switch among the numbers of sets (the numbers of series) of the evaporator and the displacement type expander to be operated.
The control unit 30 stores at least two (N - 1) different thresholds for the information on the heat amount of the warm water. The control unit 30 stores, for example, two thresholds (here, for example, a first threshold of 40% and a second threshold of 70%) for the input heat amount (%) calculated based on the detection results at the inlet sensor 11. The input heat amount (%) means a ratio of the actual heat amount of the warm water to a rated heat amount of three series as a whole. The control unit 30 uses these thresholds for switching control of the numbers of the first to third evaporators 4A to 4C and the first to third scroll expanders 6A to 6C to be operated.
Next, a method for operating the binary power generation system 1 (a binary power generation method using the binary power generation system 1) will be described with reference to FIG. 2. The control unit 30 calculates values corresponding to the above thresholds (values at the same level as the thresholds) based on the information on the heat amount of the warm water sent from the inlet sensor 11 while the binary power generation system 1 is in operation. Here, the control unit 30 calculates a present input heat amount based on the information from the inlet sensor 11.
The control unit 30 determines whether the calculated input heat amount exceeds the first and second thresholds described above. Once determining that the input heat amount is equal to or less than the first threshold, the control unit 30 opens the first electromagnetic valve 14A and the fourth electromagnetic valve 16A, and closes other electromagnetic valves. This puts the first evaporator 4A and the first scroll expander 6A that form a first series into operation. Once determining that the input heat amount exceeds the first threshold, the control unit 30 further opens the second electromagnetic valve 14B and the fifth electromagnetic valve 16B. This puts the second evaporator 4B and the second scroll expander 6B that form a second series also into operation, resulting in a total of two series put into operation. Once determining that the input heat amount exceeds even the second threshold, the control unit 30 further opens the third electromagnetic valve 14C and the sixth electromagnetic valve 16C. This puts the third evaporator 4C and the third scroll expander 6C that form a third series into operation, resulting in a total of three series put into operation.
In controlling opening and closing of the first electromagnetic valve 14A and the fourth electromagnetic valve 16A, the control unit 30 controls opening and closing of an electromagnetic contactor connected to the first power generator 7A. In controlling opening and closing of the second electromagnetic valve 14B and the fifth electromagnetic valve 16B, the control unit 30 controls opening and closing of an electromagnetic contactor connected to the second power generator 7B. In controlling opening and closing of the third electromagnetic valve 14C and the sixth electromagnetic valve 16C, the control unit 30 controls opening and closing of an electromagnetic contactor connected to the third power generator 7C.
As illustrated in FIG. 2, the number of units to be operated is switched with the first threshold of 40% and the second threshold of 70% as boundaries. The heat amounts of the vapor distributed to a plurality of scroll expanders simultaneously in operation are set equal. Therefore, rotation speeds at the scroll expanders are equal. (The figure shows that the rotation speeds at the scroll expanders are equal (lines are overlapped) by differentiating line types.) In the operating system illustrated in FIG. 2, the rotation speed at each scroll expander is changed gradually with each change by 10% in input heat amount.
Thus, the control unit 30 puts two units of evaporators and displacement type expanders into operation when detecting the information on the heat amount of the warm water and evaluating that the detected information has exceeded the first threshold (first smallest threshold) of two (N - 1) thresholds. The control unit 30 puts three units of evaporators and displacement type expanders into operation when evaluating that the detected information on the heat amount has exceeded the second threshold (second smallest threshold) of two thresholds.
With the binary power generation system 1 and the binary power generation method described above, a plurality of displacement type expanders 6A to 6C, to which the power generators 7A to 7C are connected respectively, and a plurality of evaporators 4A to 4C, which corresponds to these displacement type expanders 6A to 6C on a one-on-one basis, are provided. On the other hand, only one condenser 10 is provided to the displacement type expanders 6A to 6C. Opening and closing of the first to third electromagnetic valves 14A to 14C and the fourth to sixth electromagnetic valves 16A to 16C are controlled by the control unit 30 based on the information on the heat amount of the heat source medium. This controls the numbers of the evaporators 4A to 4C and the displacement type expanders 6A to 6C to be operated. Therefore, the operating medium can be vaporized with a heat amount required and sufficient for one displacement type expander, and the efficient Rankine cycle can be realized even when the input heat amount fluctuates. As a result, sufficient power is generated without reduces in the overall efficiency of the binary power generation system 1.
Particularly in a case where a heat source derived from nature such as hot spring water and geothermal heat is used, it is assumed that the heat amount significantly fluctuates in time. The binary power generation system 1 can respond to a wide range of heat amounts from a smaller amount to a larger amount, and offer efficient operations of the evaporators. Therefore, when the heat amount fluctuates substantially, particularly beneficial effects are exerted. As for the condenser 10, the disadvantages of excessively cooling the operating medium are insignificant and outweighed by the advantages of sharing the condenser 10.
The control unit 30 puts (a + 1) units of evaporators and displacement type expanders into operation when detecting the information on the heat amount of the heat source medium and evaluating that the detected information has exceeded an a-th (a is any integer between 1 and 2) smallest threshold of two thresholds. With this configuration, the number of units to be operated is changed gradually with two different thresholds as boundaries. Therefore, more efficient power generation can be achieved by simplified determining processing.
The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. For example, the number of series (number of units) of the evaporator and the displacement type expander may be four or more. Even when a number of series are provided, the switching control of the present invention can generate power simply and efficiently with the most appropriate number of units to be operated in accordance with the heat amount of the heat source medium.
The number of thresholds stored by the control unit 30 is not limited to that less than the number of series by 1. The number of thresholds may be more or less than that. The stop means is not limited to blocking by the electromagnetic valves. A pump may be provided independently to each series, and circulation and stoppage thereof may be carried out by on-off operation of the pump. A three-way valve may be used at a branch point.
In the above embodiments, a case has been described where heat exchange between the heat source and the warm water is carried out by the heat exchanger 3. However, in a case where a heat source such as hot spring water, geothermal heat, and factory exhaust heat can be made directly flow into the first to third evaporators 4A to 4C, the heat exchanger 3 may be omitted. In that case, the heat source such as hot spring water, geothermal heat, and factory exhaust heat is equivalent to a heat source medium providing heat to the operating medium, and vaporizes the operating medium at the evaporators. The control unit 30 acquires the information on the heat amount of the heat source (heat source medium) and provides control similar to the above.
The displacement type expanders are not limited to the scroll expanders. Instead of the first to third scroll expanders 6A to 6C, other displacement type expanders may be used. For example, various types of expanders such as screw expanders, claw expanders, reciprocating expanders, and root expanders may be used.

Claims

A binary power generation system (1) comprising a plurality of displacement type expanders (6A-6C) and a plurality of power generators (7A-7C) connected to each of the displacement type expanders (6A-6C), and generating power by expansion of an operating medium, which has received heat from a heat source medium for vaporization, at least at one of the displacement type expanders (6A-6C), the system comprising:
a plurality of evaporators (4A-4C) that is connected to each of the corresponding displacement type expanders (6A-6C) and vaporizes the operating medium using the heat from the heat source medium;

a condenser (10) that is connected to each of the displacement type expanders (6A-6C), and cools and condenses the operating medium expanded at least at one of the displacement type expanders (6A-6C);

characterized in that the system further comprises:
a plurality of branched lines (L1A-L1C) branched from a line (L1) through which the heat source medium circulates, each of the branched lines (L1A-L1C) passing through each of the plurality of evaporators (4A-4C);

a stop means (14A - 14C, 16A - 16C) capable of stopping circulation of the operating medium for each set of the evaporators (4A-4C) and the displacement type expanders (6A-6C) and circulation of the heat source medium for each of the evaporators (4A, 4B, or 4C) through the branched lines (L1A-L1C); and

a control unit (30) that controls the numbers of the evaporators (4A-4C) and the displacement type expanders (6A-6C) to be operated by controlling the stop means (16A-16C) based on information on a heat amount of the heat source medium.
The binary power generation system (1) according to claim 1,
wherein the numbers of the evaporators (4A-4C) and the displacement type expanders (6A-6C) are N units, respectively,

the control unit (30) stores at least (N - 1) different thresholds for the information on the heat amount of the heat source medium, and

the control unit (30) puts (a + 1) units of the evaporators (4A-4C) and the displacement type expanders (6A-6C) into operation when detecting the information on the heat amount of the heat source medium and evaluating that the detected information has exceeded an a-th (a is any integer from 1 to (N - 1)) smallest threshold of the (N - 1) thresholds.
A binary power generation method where power is generated, using a binary power generation system (1) comprising a plurality of displacement type expanders (6A-6C) and a plurality of power generators (7A-7C) connected to each of the displacement type expanders (6A-6C), by expansion of an operating medium which has received heat from a heat source medium for vaporization at least at one of the displacement type expanders (6A-6C),
wherein the binary power generation system (1) comprises:
a plurality of evaporators (4A-4C) that is connected to each of the corresponding displacement type expanders (6A-6C) and vaporizes the operating medium using the heat from the heat source medium;

a condenser (10) that is connected to each of the displacement type expanders (6A-6C), and cools and condenses the operating medium expanded at least at one of the displacement type expanders (6A-6C);

a plurality of branched lines (L1A-L1C) branched from a line (L1) through which the heat source medium circulates, each of the branched lines (L1A-L1C) passing through each of the plurality of evaporators (4A-4C), and

the binary power generation system (1) controls the numbers of the evaporators (4A-4C) and the displacement type expanders (6A-6C) to be operated based on information on a heat amount of the heat source medium.