Waste heat power generation system

Abstract

To provide a waste heat power generation system capable of suppressing accumulation of an oil in an evaporator.SOLUTION: A waste heat power generation system includes: an evaporator 11 for heating a refrigerant by waste heat to vaporize the same; an expander 12 for expanding the vaporized refrigerant; and power generator 18 connected to the expander 12 for generating electric power. The evaporator 11 includes a main evaporator 111 and a sub-evaporator 112 connected in parallel, in a refrigerant circuit for circulating the refrigerant of a cycle. The main evaporator 111 is constituted to allow the refrigerant to flow from a lower side to an upper side inside thereof so that the refrigerant is efficiently heated. The sub-evaporator is constituted to allow the refrigerant to flow from the upper side to the lower side inside thereof so that an oil is discharged with the refrigerant.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a waste heat power generation system that generates power by utilizing waste heat generated in a facility or the like. [Background technology]

[0002] In recent years, it has become common to generate electricity using waste heat at facilities that generate waste heat (such as hot springs and factories). Patent Document 1 discloses a waste heat power generation system that generates electricity using a Rankine cycle.

[0003] The waste heat power generation system of Patent Document 1 uses waste heat to heat a working fluid (refrigerant), and generates electricity by operating a generator using the working fluid circulating in a Rankine cycle. In such a waste heat power generation system using a heat cycle, an expander provided in the heat cycle rotates a turbine, and electricity is generated by a generator connected to the turbine. For this reason, the expander requires lubrication of the turbine bearings. A typical lubrication method is to fill the refrigerant circuit of the heat cycle with lubricating oil and circulate the oil together with the refrigerant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-143533 A Summary of the Invention [Problem to be solved by the invention]

[0005] The method of circulating oil in the refrigerant circuit of the heat cycle has a problem in that the oil accumulates in the evaporator in the heat cycle, reducing the amount of oil circulating.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a waste heat power generation system capable of suppressing oil retention in an evaporator. [Means for solving the problem]

[0007] In order to solve the above problems, the waste heat power generation system of the present invention is a waste heat power generation system that generates electricity using waste heat, and includes an evaporator that heats a refrigerant using the waste heat and vaporizes the refrigerant, an expander that expands the refrigerant vaporized by the evaporator, and a generator connected to the expander that generates power from the expanding refrigerant to generate electricity, and is characterized in that the evaporator has a main evaporator and a sub evaporator connected in parallel to each other within a refrigerant circuit that circulates the refrigerant.

[0008] According to the above configuration, the refrigerant can be efficiently heated in the main evaporator, while the sub-evaporator can recover oil together with the refrigerant from within the evaporator, thereby suppressing accumulation of oil in the evaporator.

[0009] In addition, in the above waste heat power generation system, the main evaporator can be configured to allow refrigerant to flow from bottom to top inside, and the sub-evaporator can be configured to allow refrigerant to flow from top to bottom inside.

[0010] According to the above configuration, in the sub-evaporator in which the refrigerant flows from top to bottom, both the refrigerant and the oil are easily discharged, and the oil does not accumulate inside the sub-evaporator.

[0011] According to the above configuration, the refrigerant can be efficiently heated in the main evaporator where the refrigerant flows from bottom to top, while the sub-evaporator where the refrigerant flows from top to bottom recovers oil together with the refrigerant from inside the evaporator and prevents oil from accumulating in the evaporator. That is, in the sub-evaporator where the refrigerant flows from top to bottom, both the refrigerant and oil are easily discharged, and oil does not accumulate inside the sub-evaporator.

[0012] In addition, in the above waste heat power generation system, the connecting pipe connecting the main evaporator and the sub-evaporator on the refrigerant inlet side can be configured to connect a lower part of the main evaporator and an upper part of the sub-evaporator.

[0013] According to the above configuration, the oil remaining in the lower part of the main evaporator can move to the sub-evaporator through the connecting pipe. The oil that moves from the main evaporator to the sub-evaporator does not remain inside the sub-evaporator and is easily returned to the refrigerant circuit.

[0014] The waste heat power generation system may be configured such that a first solenoid valve that can be opened and closed is provided on the connection pipe.

[0015] According to the above configuration, when oil can be returned to the refrigerant circuit without being retained in the main evaporator without using a sub-evaporator (for example, when the refrigerant flow rate is high), the heat exchange efficiency in the evaporator can be increased by closing the first solenoid valve and circulating the refrigerant only through the main evaporator.

[0016] In addition, in the above waste heat power generation system, the sub-evaporator can be vertically oriented with the refrigerant piping inside arranged in the vertical direction, and the connecting piping can be configured so that the outlet side is higher than the inlet side.

[0017] According to the above configuration, it is possible to suppress a problem in which the refrigerant flow rate in the sub-evaporator increases and the refrigerant flow rate in the main evaporator decreases (the heat exchange efficiency in the evaporator decreases).

[0018] In addition, the waste heat power generation system can be configured such that the section between the evaporator and the expander is branched into a first path for sending refrigerant to rotate the turbine in the expander, and a second path for supplying oil to a bearing portion of the turbine in the expander, and the second path is provided with an orifice for adjusting the refrigerant flow rate.

[0019] According to the above configuration, by adjusting the refrigerant flow rate in the second path by the orifice, the refrigerant flow rate in the second path can be kept to a necessary minimum, and a decrease in the refrigerant flow rate in the first path (a decrease in power generation efficiency) can be suppressed.

[0020] In addition, the waste heat power generation system can be configured to include a bypass path that is arranged in parallel with the expander and allows the refrigerant to flow without passing through the expander, and a second solenoid valve that can be opened and closed and is provided in the bypass path, and to have an oil circulation mode in which the second solenoid valve is opened to allow some of the refrigerant to flow through the bypass path.

[0021] According to the above configuration, in the oil circulation mode, the temperatures of the refrigerant and oil can be increased while the rotation speed of the expander is suppressed, making it easier to circulate the oil within the refrigerant circuit. Effect of the Invention

[0022] The waste heat power generation system of the present invention has the advantage that the refrigerant can be efficiently heated in the main evaporator, while the sub-evaporator recovers oil together with the refrigerant from inside the evaporator, thereby suppressing the accumulation of oil in the evaporator. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a block diagram illustrating a schematic configuration of a waste heat power generation system according to an embodiment of the present invention. [Diagram 2] 1 is a perspective view showing an example of the appearance of a waste heat power generation system. [Diagram 3] FIG. 2 is a perspective view showing a sub-evaporator in the waste heat power generation system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] [First embodiment] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a block diagram showing a schematic configuration of a waste heat power generation system of the present invention (hereinafter, referred to as the present system). Fig. 2 is a perspective view showing an example of the appearance of the present system. The present system generates power using a thermal cycle such as a Rankine cycle.

[0025] 1, the system includes as its components an evaporator 11, an expander 12, a condenser 13, a receiver 14, a subcooling heat exchanger 15, a pump 16, an electric valve 17, and a generator 18. In the system, a refrigerant (working fluid) circulates through the pump 16, the electric valve 17, the evaporator 11, the expander 12, the condenser 13, the receiver 14, and the subcooling heat exchanger 15 in this order.

[0026] The evaporator 11 is composed of a main evaporator 111 and a sub-evaporator 112, which are connected in parallel in a refrigerant circuit of a heat cycle. The main evaporator 111 and the sub-evaporator 112 heat the refrigerant with waste heat generated in facilities such as hot springs and factories, and turn the refrigerant into a gas phase. In this system, the waste heat is supplied by a heat source medium such as hot water or high-temperature gas, and the refrigerant is heated by heat exchange between the refrigerant and the heat source medium.

[0027] The expander 12 expands the gas phase refrigerant. This system generates power from the expanding refrigerant and generates electricity using this power. Specifically, a turbine is rotated in the expander 12 by the expanding refrigerant, and electricity is generated by a generator 18 connected to this turbine.

[0028] The condenser 13 condenses the expanded refrigerant and turns it into a liquid phase. In the condenser 13, the temperature of the refrigerant is lowered by heat exchange with cooling water. However, in this system, not all of the refrigerant turns into a liquid phase in the condenser 13, and the refrigerant is in a gas-liquid mixed state at the outlet of the condenser 13.

[0029] The receiver 14 functions as a gas-liquid separator in the heat cycle. That is, the refrigerant in a gas-liquid mixed state at the inlet of the receiver 14 is separated into a liquid phase refrigerant and a gas phase refrigerant in the receiver 14, and only the liquid phase refrigerant is discharged from the outlet of the receiver 14. The subcooling heat exchanger 15 further cools the liquid phase refrigerant separated in the receiver 14 by heat exchange with cooling water, to produce a subcooled liquid.

[0030] The pump 16 is a power source that circulates the refrigerant in the heat cycle, and is disposed downstream of the subcooling heat exchanger 15, thereby acting on the liquid phase refrigerant. The motor-operated valve 17 is an opening adjustment valve whose opening can be adjusted, and is used to control the flow rate of the refrigerant in the heat cycle. That is, by increasing the opening of the motor-operated valve 17, the flow rate of the refrigerant can be increased, and by decreasing the opening, the flow rate of the refrigerant can be decreased. Note that the pump 16 and the motor-operated valve 17 are preferably disposed at a low position in the system, at least lower than the evaporator 11, in order to act on the liquid phase refrigerant.

[0031] In addition, the system may include a dryer 19 for removing moisture from the refrigerant and a filter 20 for removing dust from the refrigerant. Furthermore, the system may include a temperature sensor and a pressure sensor for detecting the temperature and pressure of the refrigerant at a predetermined point in the heat cycle. For example, a thermometer T1 and a pressure gauge P1 are arranged downstream of the refrigerant flow direction in the evaporator 11, and the degree of superheat of the refrigerant in the heat cycle is calculated from the outputs of the thermometer T1 and the pressure gauge P1. In addition, a thermometer T2 and a pressure gauge P2 are arranged upstream of the refrigerant flow direction in the pump 16, and the degree of subcooling of the refrigerant in the heat cycle is calculated from the outputs of the thermometer T2 and the pressure gauge P2. Of course, the system may include temperature sensors and pressure sensors other than the thermometers T1 and T2 and the pressure gauges P1 and P2.

[0032] As described above, in this system, the expander 12 rotates the turbine, and the generator 18 connected to the turbine generates electricity. At this time, lubricating oil is circulated together with the refrigerant in the refrigerant circuit of the heat cycle to lubricate the turbine bearings.

[0033] In this system, the refrigerant circuit is branched into a first path 41 and a second path 42 between the evaporator 11 and the expander 12. The first path 41 is a path for sending refrigerant to rotate the turbine in the expander 12. On the other hand, the second path 42 is a path for supplying oil to a bearing part of the turbine in the expander 12. For this reason, the downstream side of the second path 42 is connected to the expander 12 at a location where oil can be supplied to the bearing part of the turbine in the expander 12. Furthermore, when there are multiple turbine bearing parts in the expander 12, the downstream side of the second path 42 may be branched into multiple paths according to the number of bearing parts.

[0034] If the refrigerant flow rate in the second path 42 increases and the refrigerant flow rate in the first path 41 decreases accordingly, the power generation efficiency of the present system decreases. For this reason, it is preferable to keep the refrigerant flow rate in the second path 42 to a minimum, and it is preferable that an orifice for adjusting the refrigerant flow rate is provided in the second path 42. For example, it is possible to provide an orifice at the connection point between the second path 42 and the expander 12 to adjust the refrigerant flow rate.

[0035] Further, the second path 42 is provided with a shutoff valve 31 and is connected to PORT1. PORT1 is a port for filling the refrigerant circuit with oil, and when filling PORT1 with oil, the shutoff valve 31 is closed to reliably send the oil to the expander 12 side. Further, in the refrigerant circuit of this system, PORT2 is connected via a shutoff valve 32 on the downstream side of the motor-operated valve 17. PORT2 is a port for recovering oil from the refrigerant circuit. Further, in the refrigerant circuit of this system, PORT3 is connected via a shutoff valve 33 to the receiver 14. PORT3 is a port for filling the refrigerant circuit with refrigerant.

[0036] This system is characterized by a configuration that can suppress the retention of oil in the evaporator 11. This characteristic configuration will be described in detail below.

[0037] As described above, the evaporator 11 in this system is composed of the main evaporator 111 and the sub-evaporator 112. The evaporator 11 heats the refrigerant and vaporizes it using waste heat, and this function is mainly performed by the main evaporator 111. On the other hand, the sub-evaporator 112 is provided for the purpose of recovering oil together with the refrigerant from the evaporator 11 and suppressing the accumulation of oil in the evaporator 11.

[0038] In the main evaporator 111, it is required to efficiently exchange heat between the refrigerant and the heat source medium. For this reason, in the main evaporator 111, as shown in Fig. 1, the refrigerant is supplied from below and discharged from above, and the heat source medium is supplied from above and discharged from below, in the opposite manner to the refrigerant. In this case, if the evaporator 11 is configured to consist of only the main evaporator 111 (without the sub-evaporator 112), the oil that is not vaporized tends to accumulate in the lower part of the main evaporator 111.

[0039] For this reason, this system is provided with a sub-evaporator 112 in parallel with the main evaporator 111, and oil is returned from the sub-evaporator 112 to the refrigerant circuit. Since the main purpose of the sub-evaporator 112 is not to exchange heat between the refrigerant and the heat source medium, as shown in Fig. 2, the sub-evaporator 112 has a smaller capacity than the main evaporator 111, and in particular, has a lower profile than the main evaporator 111.

[0040] The sub-evaporator 112 is vertically oriented with its internal refrigerant piping arranged vertically, and the refrigerant is supplied from above and discharged from below, as shown in Fig. 1. The heat source medium is supplied from below and discharged from above, in the opposite manner to the refrigerant. In the sub-evaporator 112, the refrigerant is discharged from below, so that oil is easily discharged together with the refrigerant, and oil does not accumulate inside the sub-evaporator 112.

[0041] 1, the main evaporator 111 and the sub-evaporator 112 are connected on the refrigerant inlet side via a connection pipe 43. The connection pipe 43 is installed to connect the lower part of the main evaporator 111 and the upper part of the sub-evaporator 112, and the outlet side (sub-evaporator 112 side) is higher than the inlet side (main evaporator 111 side) (see FIG. 3).

[0042] 2, the positions of the bottom surfaces of the main evaporator 111 and the sub-evaporator 112 are generally aligned. Therefore, the height between the inlet and the outlet of the connection pipe 43 generally coincides with the height of the sub-evaporator 112, and since the sub-evaporator 112 is made lower than the main evaporator 111, the height is significantly lower than the height between the inlet and the outlet of the main evaporator 111.

[0043] As a result, oil that accumulates in the lower part of the main evaporator 111 can move to the sub-evaporator 112 through the connecting pipe 43. That is, since the height between the inlet and the outlet of the main evaporator 111 is large, it is difficult to return the oil from the outlet of the main evaporator 111 to the refrigerant circuit, but since the height between the inlet and the outlet of the connecting pipe 43 is not so high, it is relatively easy to move the oil from the main evaporator 111 to the sub-evaporator 112. And, as described above, the oil that moves from the main evaporator 111 to the sub-evaporator 112 does not accumulate inside the sub-evaporator 112 and is easily returned to the refrigerant circuit.

[0044] If the sub-evaporator 112 is arranged horizontally (the refrigerant piping inside is arranged in a horizontal plane) to reduce the height between the inlet and the outlet of the connecting pipe 43, oil is more likely to move from the main evaporator 111 to the sub-evaporator 112. However, in that case, the refrigerant flow rate of the sub-evaporator 112 increases and the refrigerant flow rate of the main evaporator 111 decreases, which may reduce the heat exchange efficiency of the evaporator 11. For this reason, it is preferable to arrange the sub-evaporator 112 vertically and to provide a certain degree of height between the inlet and the outlet of the connecting pipe 43.

[0045] Although not shown in FIG. 1, a solenoid valve (first solenoid valve) may be provided in the connection pipe 43, and the opening and closing of the solenoid valve in the connection pipe 43 may be controlled based on the operating state of the system. That is, if the flow velocity of the refrigerant in the main evaporator 111 becomes large, the oil in the main evaporator 111 may be returned to the refrigerant circuit without accumulating in the main evaporator 111 without using the sub-evaporator 112. For this reason, if the flow velocity of the refrigerant in the main evaporator 111 is larger than a predetermined value, the solenoid valve in the connection pipe 43 may be closed, and the refrigerant in the evaporator 11 may be circulated only to the main evaporator 111. If the refrigerant is circulated only to the main evaporator 111, the heat exchange efficiency in the evaporator 11 is increased compared to the case where the refrigerant is circulated to both the main evaporator 111 and the sub-evaporator 112. The flow velocity of the refrigerant in the main evaporator 111 can be estimated, for example, from the degree of superheat of the refrigerant in the heat cycle.

[0046] Furthermore, even if the refrigerant flow rate in the main evaporator 111 is high and the solenoid valve in the connecting pipe 43 is closed, if the solenoid valve is left closed for a long period of time, the flow of refrigerant and oil in the sub-evaporator 112 may remain stopped, causing the oil to stagnate in the sub-evaporator 112. To prevent this, the solenoid valve in the connecting pipe 43 may be opened for a fixed time (e.g., 30 seconds) every predetermined time (e.g., 1 hour) so that the flow of refrigerant and oil in the sub-evaporator 112 is not stopped for a long period of time.

[0047] [Embodiment 2] This system may have an oil circulation mode for promoting oil circulation in the refrigerant circuit, in addition to a normal operation mode in which power is generated by the generator 18. In the second embodiment, this oil circulation mode will be described.

[0048] 1 as a configuration for implementing the oil circulation mode. The bypass path 44 is provided in parallel with the expander 12, and is a path for allowing the refrigerant to flow without passing through the expander 12. In addition, the bypass path 44 is provided with a solenoid valve (second solenoid valve) 34.

[0049] In the normal operation mode of the present system, the solenoid valve 34 is closed and the refrigerant does not flow through the bypass path 44. In this case, all of the refrigerant flowing through the refrigerant circuit passes through the expander 12 and contributes to power generation in the generator 18.

[0050] On the other hand, in the oil circulation mode of the present system, the solenoid valve 34 is opened and some of the refrigerant flows through the bypass path 44 without passing through the expander 12. As a result, in the oil circulation mode, the temperature of the refrigerant and the oil can be increased while suppressing the rotation speed of the expander 12. If the oil temperature increases, the viscosity of the oil decreases accordingly, making it easier to circulate the oil in the refrigerant circuit. The oil circulation mode is preferably implemented as a warm-up operation mode when the present system is started up.

[0051] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention is not interpreted solely by the above-described embodiments, but is defined by the claims. Also, all modifications within the scope and meaning equivalent to the claims are included. [Explanation of symbols]

[0052] 11 Evaporator 111 Main evaporator 112 Sub-evaporator 12 Expander 13 Condenser 14 Receiver 15 Supercooling heat exchanger 16 Pump 17 Motor-operated valve 18. Generator 34 Solenoid valve (second solenoid valve) 41 Route 1 42 Route 2 43 Connection piping 44 Bypass Route

Claims

1. A waste heat power generation system that generates electricity using waste heat and circulates lubricating oil together with a refrigerant in a refrigerant circuit that circulates the refrigerant, an evaporator that heats a refrigerant using waste heat and vaporizes the refrigerant; an expander that expands the refrigerant vaporized in the evaporator; a generator connected to the expander and generating power from the expanding refrigerant to generate electricity, The evaporator includes a main evaporator and a sub evaporator connected in parallel to each other in the refrigerant circuit, A waste heat power generation system characterized in that a refrigerant piping connecting the expander and the main evaporator and a refrigerant piping connecting the refrigerant inlet side of the main evaporator and the refrigerant inlet side of the sub-evaporator are connected in parallel.

2. The waste heat power generation system according to claim 1, The main evaporator allows the refrigerant to flow from bottom to top therein, A waste heat power generation system, wherein the sub-evaporator allows a refrigerant to flow from top to bottom inside the sub-evaporator.

3. The waste heat power generation system according to claim 1 or 2, A waste heat power generation system, characterized in that a connecting pipe that connects the main evaporator and the sub-evaporator at a refrigerant inlet side connects a lower part of the main evaporator and an upper part of the sub-evaporator.

4. The waste heat power generation system according to claim 3, A waste heat power generation system, characterized in that a first solenoid valve that can be opened and closed is provided in the connecting pipe.

5. The waste heat power generation system according to claim 3 or 4, The sub-evaporator is vertically oriented, with the refrigerant piping therein arranged along the up-down direction, A waste heat power generation system, wherein the connecting pipe is higher on the outlet side than on the inlet side.

6. The waste heat power generation system according to any one of claims 1 to 5, A section between the evaporator and the expander is branched into a first path for feeding refrigerant to rotate a turbine in the expander and a second path for supplying oil to a bearing portion of the turbine in the expander, A waste heat power generation system, wherein the second passage is provided with an orifice for adjusting a flow rate of the refrigerant.

7. The waste heat power generation system according to any one of claims 1 to 6, a bypass path provided in parallel with the expander for allowing the refrigerant to flow without passing through the expander; a second solenoid valve provided in the bypass path and capable of opening and closing; a waste heat power generation system having an oil circulation mode in which the second solenoid valve is opened to allow a portion of the refrigerant to flow through the bypass path;

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