TECHNICAL FIELD
[0001] The present invention relates to a binary power generation system and a binary power
generation method.
BACKGROUND
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
SUMMARY
[0006] 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 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 the evaporator, 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.
[0007] 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, 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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
[0012]
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
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] A warm water line L1, 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.
[0020] 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 L1B 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
1. 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);
a stop means (16A-16C) that is 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 the evaporator (4A, 4B, or 4C); 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.
2. 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.
3. 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; and
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), 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.