JP7615441B2 - Binary Power Generation System - Google Patents

Description

The present invention relates to a binary power generation system that uses thermal energy of a heat source fluid to heat and vaporize a low-boiling point working medium, and uses the pressure of the vapor to drive an expansion generator to generate power.

A binary power generation system is a system in which thermal energy from a heat source fluid, such as geothermal steam, hot water, or waste heat from factories with a heating process or incinerators, is used to heat and evaporate a low-boiling point working medium such as petroleum hydrocarbons, alternative fluorocarbons, or ammonia in an evaporator, and the high pressure of the steam is used to drive an expansion generator to generate electricity. The low-pressure steam that leaves the expansion generator is then cooled with a refrigerant in a condenser, condensing the working medium into a liquid, which is then circulated again through this power generation cycle by a low-boiling point working medium pump, thereby generating electricity continuously. Compared to typical steam expansion generators that use water vapor of about 300°C or higher, a binary power generation system is in practical use as a system that can generate electricity from low-temperature heat sources of less than 300°C (or less than 100°C in some cases), which are not widely used.

Considering the current situation of global warming caused by the excessive use of fossil fuels, and the increasing demand for electrical energy due to the expansion of the world's population and the electrification of mobility, binary power generation systems, which can generate electricity by making the most effective use of thermal energy that is currently wasted, are expected to be further put into practical use and applied in response to the needs of the times.

Furthermore, in order to strengthen the power system network in the event of a disaster, as Japan is prone to natural disasters such as typhoons and earthquakes, it is desirable to reduce risk by shifting from reliance on large-scale power plants to a smart grid of decentralized electricity.

Patent No. 4311982 Patent No. 5447677 Patent No. 6339908 JP 2016-61237 A JP 2019-22261 A

In this century, humanity is being forced to take urgent measures to combat global warming caused by the excessive use of fossil fuels. There are hopes for the practical application and application of binary power generation systems that can generate stable electricity by effectively utilizing discarded thermal energy. In prior art documents, there are several documents related to the lubrication of bearings in expansion generators in binary power generation systems.

In Patent Document 1, a pressure pump is not used to supply lubricating oil to the bearings of an expansion generator, but an ejector is used to inject a mixture of lubricating oil and a low-boiling point working medium to lubricate and cool the bearings.
Since a lubricating oil booster pump is not used, the system configuration is simplified and the energy consumption required for the booster pump is reduced, making it more economical.
However, in order to recover the lubricating oil that has entered the circulation path of the low-boiling point working medium, a gas-liquid separator and oil reservoir are provided inside the evaporator, and the oil is then piped to a lubricating oil tank for temporary storage, and from there it is piped again to pass through an ejector and then to the bearings, making it an extremely complicated mechanism.

In addition, in Patent Document 2, the lubrication mechanism for the bearings of the expansion generator is further simplified by providing a grease supply device and a control device that controls the same, and the grease supply device functions under the control of the control device, thereby providing a mechanism for supplying the appropriate amount of grease required for lubricating the bearings.

Patent Documents 3 and 4 improve the mechanism of Patent Document 2 to provide a mechanism for supplying a more appropriate amount of grease.

In Patent Document 5, a lack of grease in the bearings is detected based on the measurement values of a temperature sensor installed near the bearings of an expansion generator, and control is performed to supply grease to the bearings, thereby preventing problems such as bearing seizure and damage to the generator and contributing to the stable operation of the binary power generation system.

However, in the expansion generators of the power generation systems described in Patent Documents 1 to 5, the internal space of the turbine section where the high-pressure low-boiling point working medium gas expands is naturally an atmosphere of low-boiling point working medium gas, but the internal space of the power generation section, which contains the rotor that is directly connected to the shaft and rotates, the bearings that support the rotor, and the stator that is fixed to the casing, is also an atmosphere of low-boiling point working medium gas.

In binary power generation systems, the low-boiling point working medium is mainly made up of petroleum-based hydrocarbons or alternative fluorocarbons, which are organic compounds.
Lubricating oils and greases are also organic compounds, and organic compounds tend to blend and dissolve easily with each other.
Therefore, even if lubricating oil or grease is supplied to the bearings, because the bearings are in an atmosphere of a low-boiling point working medium, the lubricating oil or grease will dissolve into the low-boiling point working medium and be washed away, making it necessary to frequently replenish the lubricating oil or grease in the appropriate amount required for the bearings' lubricating function.
In addition, even if the lubricating oil and grease that have leaked into the circulation path of the low-boiling point working medium are recovered using a gas-liquid separator inside the evaporator, some of the lubricating oil and grease that cannot be recovered will become mist, mix with the low-boiling point working medium gas, and be introduced into the expander, where it will collide with the moving blades (impeller), and there is a risk of causing erosion.

The present invention aims to provide a binary power generation system that simplifies or eliminates the mechanism for replenishing lubricating oil and grease to the bearings, in order to reduce or eliminate the burden of frequent replenishing lubricating oil and grease to the bearings and problems such as erosion of the rotor blades due to lubricating oil and grease mist.

The binary power generation system for solving the above problems is as follows.
The invention according to claim 1 of the present invention is a binary power generation system comprising an evaporator which evaporates a low boiling point working medium by thermal energy of a heat source fluid, an expansion generator which rotates and drives a rotor shaft by the low boiling point working medium evaporated in the evaporator and brought to a high pressure to generate power, a condenser which cools and condenses the low boiling point working medium which has left the expansion generator and brought to a low pressure by a refrigerant, and a low boiling point working medium pump which circulates the low boiling point working medium from the condenser to the evaporator, and a mechanism for isolating the internal atmosphere of the expansion generator between the expander of the expansion generator and the generator ,
A gas bearing is used to support the expander side of the rotor shaft that is driven to rotate, and a rolling bearing is used to support the generator side of the rotor shaft that is driven to rotate, and a spring is provided at the mounting portion of the rolling bearing to absorb elongation due to thermal expansion of the generator side of the rotor shaft,
Furthermore, the binary power generation system is characterized in that the expansion generator comprises a turbine section, a mechanical seal section, and a power generation section, the mechanical seal section comprises a seal ring liner fixed to the rotor shaft, a seal ring attached to the seal ring liner, and an insert attached to the seal flange of the mechanical seal section, oil is sealed in the internal space of the mechanical seal section, and a spring is provided in the insert to prevent the gap between the seal ring and the insert from opening too wide.

The invention described in claim 2 of the present invention is a binary power generation system as described in claim 1, characterized in that a water-cooled jacket structure is provided for cooling oil heated by frictional heat generated by the rotational motion of the seal ring liner and the seal ring.

The invention described in claim 3 of the present invention is a binary power generation system as described in claim 1 or 2, characterized in that a pipe leading from the evaporator to the expansion generator is branched off to obtain a portion of the high-pressure low-boiling point working medium as the gas to be supplied to the gas bearing.

According to a fourth aspect of the present invention, there is provided a binary power generation system as described in the first or second aspect, characterized in that a magnetic bearing is used to support the expander side of the rotor shaft that is rotated.

According to the invention described in claim 1 of the present invention, the generator side of the rotating rotor shaft is in an air atmosphere, and the mechanism for replenishing lubricating oil and grease to the bearings can be simplified to the same extent as that of a general motor, or can be made unnecessary by applying grease-sealed bearings.
In addition, it is possible to suppress vibration and wobble in the radial direction of the expander side of the rotating rotor shaft, and to stabilize the radial position of the expander side of the rotor shaft.
Furthermore, the spring provided at the mounting portion of the rolling bearing of the power generation unit absorbs the elongation caused by thermal expansion of the generator side of the rotating rotor shaft, and the spring provided in the insert of the mechanical seal unit prevents the gap between the seal ring and the insert from becoming too large, thereby preventing a deterioration in the sealing function due to the effects of thermal expansion and vibration of each component that makes up the expansion generator.

According to the second aspect of the present invention, the water-cooled jacket structure cools the oil sealed in the mechanical seal portion, preventing evaporation and performance deterioration, and maintaining the sealing function.

According to the third aspect of the present invention, the gas supply mechanism for realizing the second aspect of the present invention can be simplified.

According to the invention described in claim 4 of the present invention, vibration and wobble in the radial direction on the expander side of the rotating rotor shaft can be suppressed, and the radial position of the rotor shaft on the expander side can be stabilized.

As described above, the improved reliability of the continuous and stable operation of the binary power generation system according to the present invention will, overall, broaden the range of applications to which binary power generation systems can be applied, promote the spread and development of binary power generation systems, and help solve the problem of global warming.

1 illustrates a schematic diagram of a binary power generation system according to a first embodiment of the present invention. 2 shows a schematic diagram of the "expansion generator" shown in FIG. 1. 3 is a schematic diagram showing a sealing mechanism of the "mechanical seal portion" shown in FIG. 2. 3 is a schematic diagram showing a hydrostatic gas bearing portion of the "turbine section" shown in FIG. 2. 3 is a cross-sectional view taken along line AA in FIG. 2.

Hereinafter, an embodiment of a binary power generation system of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of a binary power generation system G according to a first embodiment.
The binary power generation system G includes an evaporator 1 that evaporates a low-boiling point working medium LM using the thermal energy of a heat source fluid HW, an expansion generator 2 that is driven to rotate by the low-boiling point working medium LM gas that has evaporated in the evaporator 1 and become high pressure, a condenser 3 that cools and condenses the low-boiling point working medium LM gas that has left the expansion generator 2 and become low pressure using a refrigerant CW, and a low-boiling point working medium pump 4 that circulates the low-boiling point working medium LM from the condenser 3 to the evaporator 1. The low-boiling point working medium LM is made of a petroleum-based hydrocarbon, an alternative fluorocarbon, ammonia, or the like, and the system includes a heat source fluid pump 5 that pumps the heat source fluid HW, a refrigerant pump 6 that pumps the refrigerant CW, and a cooling tower fan 7 that cools the refrigerant CW by using outside air as necessary.

FIG. 2 is a schematic diagram illustrating the expansion generator 2 of the binary power generation system G of the first embodiment.
The expansion generator 2 is composed of a turbine section, a mechanical seal section, and a power generation section, and contains the rotor blades 11, rotor shaft 12, and permanent magnets 13, which are integrated into a rotating body inside. The turbine section, mechanical seal section, and power generation section are fixed together with bolts to form an integrated unit and function as a module (component) for generating electricity.

The principle is that in the evaporator 1, the low boiling point working medium LM gas, which has received thermal energy from the heat source fluid HW and has been vaporized to a high pressure, is introduced through the medium gas inlet 16a in the turbine casing 14, and the pressure energy generated when the low boiling point working medium LM gas is released from high pressure to low pressure is received by the moving blades 11 attached to the turbine section of the rotor shaft 12 and converted into rotational kinetic energy of the rotor shaft 12, and the permanent magnets 13 attached to the power generation section of the rotor shaft 12 cause a change in the magnetic field inside the stator core 17 of the power generation section, which generates an electromotive force in the coil 18 wound around the stator core 17, thereby generating electricity.

In the first embodiment of the binary power generation system G of the present invention, a mechanical seal is provided between the turbine section, which converts the pressure energy of the high-pressure low boiling point working medium LM gas into rotational kinetic energy of the rotor shaft 12, and the power generation section, which converts the rotational kinetic energy of the rotor shaft 12 into electrical energy, making it possible to separate the internal space of the turbine section into an atmosphere of the low boiling point working medium LM gas, and the internal space of the power generation section into an air atmosphere.

The internal space of the mechanical seal is an oil atmosphere, and oil penetrates into the small gap between the sliding surfaces of the seal ring 22 attached to the seal ring liner 21 fixed to the rotor shaft 12 and the insert 23 attached to the seal flange 20, thereby providing a sealing function.
In addition, the oil is heated by frictional heat generated by the rotational motion of the seal ring liner 21 and the seal ring 22, which may cause evaporation or performance degradation. Therefore, a water-cooled jacket structure is provided on the seal flange 20 and cooling water is circulated to cool the oil, prevent evaporation and performance degradation, and maintain the sealing function.
The oil is sealed and its properties are checked during regular inspections every six months to one year, and it is replaced with new oil as appropriate and necessary.

The power generation section side of the rotor shaft 12 is supported by angular ball bearings 29 attached to a power generation section flange 25 and a power generation section bottom flange 27 of the power generation section, respectively, and the position of the rotor shaft 12 in the thrust direction and radial direction is fixed.
In addition, since there is a concern that elongation due to thermal expansion of the power generation section of the rotor shaft 12 may occur, a damping structure using a spring 30 is provided at the mounting portion of the angular ball bearing 29b to the power generation section bottom flange 27 to absorb the elongation due to thermal expansion of the power generation section of the rotor shaft 12.

The turbine side of the rotor shaft 12 has a moving blade 11 attached to its tip, and the moving blade 11 is the part that receives the force of the pressure energy of the low-boiling point working medium LM gas that has been vaporized and become high pressure. However, due to the structure having a mechanical seal, there is a distance between the moving blade 11 and the angular ball bearing 29a attached to the power generation section flange 25, so the turbine side of the rotor shaft 12 may vibrate in the radial direction and become displaced.

In order to prevent this radial vibration, a hydrostatic gas bearing structure is provided on the turbine flange 15, and the pressure of the low-boiling point working medium LM gas flowing out from the gas throttling nozzle 31 of this hydrostatic gas bearing keeps the vibration of the rotor shaft 12 minor and stabilizes the radial position of the rotor shaft 12 on the turbine side.

The low boiling point working medium LM gas flowing out from the gas throttling nozzle 31 of the hydrostatic gas bearing is supplied from a bearing gas pipe 8 which is a branch of the pipe leading from the outlet side of the evaporator 1 to the expansion generator 2, and only the minimum required flow rate is used to function as a hydrostatic gas bearing.
There is also a concern that contact between the rotor blades 11 and the turbine casing 14 may occur on the turbine side of the rotor shaft 12 due to elongation caused by thermal expansion, but by setting the gap between the rotor blades 11 and the turbine casing 14 to a design value that fully takes into account the elongation due to thermal expansion on the turbine side of the rotor shaft 12, contact between the rotor blades 11 and the turbine casing 14 can be avoided.

These mechanisms allow the rotor shaft 12 to rotate in a stable manner, reducing the risk of deterioration or failure of the expansion generator 2 and contributing to improving the efficiency of energy conversion from heat to electricity.

FIG. 3 is a schematic diagram showing the sealing mechanism of the mechanical seal portion shown in FIG.
The mechanical seal portion of the expansion generator 2 is provided between the turbine portion and the power generation portion, and separates the internal atmosphere of the turbine portion from that of the power generation portion.
As a result, the mechanical seal portion also plays a role in containing the low-boiling point working medium LM inside the binary power generation system G and preventing it from escaping into the atmosphere.

The angular ball bearings 29 that support the rotational motion of the rotor shaft 12 are lubricated with lubricating oil or grease, which are organic compounds. In an atmosphere containing the low-boiling point working medium LM, which is also an organic compound, there is a problem that these dissolve and are easily washed away. However, by providing a mechanical seal, the power generation section containing the angular ball bearings 29 can be placed in an air atmosphere, thereby solving this problem.

Oil is sealed in the internal space of the mechanical seal, and the oil penetrates into the small gap between the sliding surface, which is the seal ring 22 attached to the seal ring liner 21 fixed to the rotor shaft 12, and the insert 23 attached to the seal flange 20, thereby providing a sealing function.

To prevent the gap between the seal ring 22 and the insert 23 from becoming too large, the insert 23 is pushed toward the seal ring 22 by the force of a spring 40, thereby preventing a deterioration in the sealing function due to the effects of thermal expansion and vibration of each component that makes up the expansion generator 2.

However, the sealing mechanism of the mechanical seal does not play the role of supporting the rotor shaft 12 like a bearing, and due to the structure in which the mechanical seal is located between the turbine section and power generation section of the expansion generator 2, a distance is created between the rotor blades 11 and the angular ball bearing 29a attached to the power generation section flange 25, and the turbine section side of the rotor shaft 12 may vibrate in the radial direction and become displaced.
Therefore, in order to prevent this vibration in the radial direction, a hydrostatic gas bearing structure is provided on the turbine flange 15 .

FIG. 4 is a schematic diagram showing the hydrostatic gas bearing portion of the turbine section in FIG.
A gas throttling nozzle 31, which is a main component of the hydrostatic gas bearing, is attached to the turbine flange 15. When high-pressure low-boiling point working medium LM gas is introduced into this gas throttling nozzle 31, static gas pressure is generated in the surface throttling space 33, which is a groove provided on the circumference of the rotor shaft 12, passing through the air holes 32, and a force is generated that pushes the rotor shaft 12 towards the center of the rotation axis, stabilizing the radial position of the rotor shaft 12.

The high-pressure low-boiling point working medium LM gas supplied to the gas throttling nozzle 31 is obtained from a bearing gas pipe 8 which is a branch of the pipe leading from the outlet side of the evaporator to the expansion generator. However, in a hydrostatic gas bearing, the high-pressure low-boiling point working medium LM gas flows slowly, so the amount consumed for the bearing function is small compared to the amount supplied to the expansion generator 2 for power generation.

FIG. 5 is a cross-sectional view taken along line AA in FIG.
A groove is also provided on the outside of the gas throttling nozzle 31 on the circumference, and high-pressure low-boiling point working medium LM gas is introduced from there through four air holes 32 into a surface throttling space 33 provided on the circumference of the rotor shaft 12.
By using such a mechanism, a force is applied uniformly from the circumference of the rotor shaft 12 toward the center of the rotation shaft, thereby stabilizing the radial position of the rotor shaft.

The present invention has been described above using one embodiment as an example, in which the mechanism for replenishing lubricating oil and grease to bearings in a binary power generation system is simplified or eliminated. However, the rolling bearings supporting the rotor shaft of the present invention are not limited to the above embodiment, and each bearing does not have to be singular, and multiple bearings may be connected together.
Furthermore, the gas bearing of the present invention is not limited to the above embodiment, and may be configured not only in a single stage but also in multiple stages.

In a binary power generation system, the mechanism for supplying lubricating oil and grease to the bearings that support the rotor shaft of the expansion generator, which is the core driving module (component), is an important element in ensuring the continuous and stable operation of the system.
The present invention makes it possible to install bearings, which require frequent replenishment of lubricating oil and grease, in an air atmosphere, and therefore the mechanism for replenishing lubricating oil and grease to the bearings can be simplified to the same extent as that of a general motor, or can be made unnecessary by applying grease-sealed bearings.
Improving the reliability of the continuous, stable operation of binary power generation systems will, overall, expand the range of applications for which binary power generation systems can be used, promote the spread and development of binary power generation systems, and potentially help solve the problem of global warming.

1 Evaporator 2 Expansion generator 3 Condenser 4 Low boiling point working medium pump 5 Heat source fluid pump 6 Refrigerant pump 7 Cooling tower fan 8 Bearing gas piping 11 Rotor blade 12 Rotor shaft 13 Permanent magnet 14 Turbine section casing 15 Turbine section flange 16a Medium gas inlet 16b Medium gas outlet 17 Stator core 18 Coil 19 Power output connector 20a, b, c Seal flange 21 Seal ring liner 22 Seal ring 23 Insert 24a Cooling water inlet 24b Cooling water outlet 25 Power generation section flange 26 Power generation section casing 27 Power generation section bottom flange 28 Power generation section bottom casing 29a, b Angular ball bearing 30 Spring 31 Gas throttling nozzle 32 Air hole 33 Surface throttling space 34a, b Bearing medium gas inlet 40 Spring
G Binary power generation system
HW Heat source fluid
LM Low boiling point working fluid
CW Refrigerant
M Cooling tower fan drive motor

Claims (4)

A binary power generation system comprising an evaporator which evaporates a low boiling point working medium by thermal energy of a heat source fluid, an expansion generator which rotates and drives a rotor shaft by the low boiling point working medium evaporated in the evaporator and brought to a high pressure to generate power, a condenser which cools and condenses the low boiling point working medium which has left the expansion generator and brought to a low pressure by a refrigerant, and a low boiling point working medium pump which circulates the low boiling point working medium from the condenser to the evaporator , wherein a mechanism is provided between an expander of the expansion generator and a generator to separate an internal atmosphere of the expansion generator ,
A gas bearing is used to support the expander side of the rotor shaft that is driven to rotate, and a rolling bearing is used to support the generator side of the rotor shaft that is driven to rotate, and a spring is provided at the mounting portion of the rolling bearing to absorb elongation due to thermal expansion of the generator side of the rotor shaft,
Furthermore, the binary power generation system is characterized in that the expansion generator comprises a turbine section, a mechanical seal section, and a power generation section, the mechanical seal section comprises a seal ring liner fixed to the rotor shaft, a seal ring attached to the seal ring liner, and an insert attached to the seal flange of the mechanical seal section, oil is sealed in the internal space of the mechanical seal section, and a spring is provided in the insert to prevent the gap between the seal ring and the insert from opening too wide. 2. The binary power generation system according to claim 1, further comprising a water-cooled jacket structure for cooling oil heated by frictional heat generated by the rotational motion of the seal ring liner and the seal ring. 3. The binary power generation system according to claim 1, wherein a portion of the high-pressure low-boiling point working medium is obtained by branching a pipe leading from the evaporator to the expansion generator as the gas to be supplied to the gas bearing. 3. The binary power generation system according to claim 1, wherein a magnetic bearing is used to support the rotor shaft on the expander side when the rotor shaft is rotated.