EP1985946B1

EP1985946B1 - Heat pump system and method for operating a heat pump system

Info

Publication number: EP1985946B1
Application number: EP07001035.0A
Authority: EP
Inventors: Takanori Shibata; Shigeo Hatamiya; Toshihiko Fukushima
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2006-02-27
Filing date: 2007-01-18
Publication date: 2013-07-10
Anticipated expiration: 2027-01-18
Also published as: JP2007224868A; US20100089077A1; US20070201999A1; EP1985946A3; EP1985946A2; JP4923618B2

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat pump system and a method for operating a heat pump system.

2. Description of the Related Art

With regard to heat pump systems, a technique that uses water as an operating medium and water bearings as bearings, is disclosed in JP, A 2001-165514 (Patent Document 1), for example.
US 3,728,857 shows a turbo-compressor-pump unit utilizing a common working fluid in the turbine, compressor, pump, and as lubricant. A dynamic sealing and bearing means maintains separation of the working fluid at different energy or pressure levels within the turbo-compressor-pump unit.
US 5,050,389 describes a refrigeration system having a compressor rotor rotatably supported by a plurality of hydrodynamic bearings lubricated by oiless pressurized liquid refrigerant and pressurizing refrigerant which flows to a condenser providing liquid refrigerant which flows to an evaporator in fluid communication with the condenser and the compressor. A refrigeration circuit coupled to the compressor is included, for providing pressurized refrigerant to the hydrodynamic bearings from the compressor and to the evaporator; a bearing pump, coupled to the refrigerant circuit and to the condenser, for providing pressurized refrigerant to the refrigeration circuit and a controller, coupled to temperature sensors, for controlling activation of the compressor and bearing pump as a function of the temperature signals to provide for three modes of operation with the first mode of operation being activation of only the compressor, the second mode of operation being activation of the bearing pump and the compressor and the third mode of operation being activation of only the bearing pump.

SUMMARY OF THE INVENTION

In the technique described in Patent Document 1, the deterioration in reliability of the bearings due to boiling of lubricating water for the bearings are not considered.
An object of the present invention is to provide a heat pump system and a method for operating a heat pump system, which suppress boiling of lubricating water for bearings and thereby minimize the deterioration in reliability of the bearings.
The object is solved according to the independent claims. Dependent claims describe preferred embodiments of the present invention.
In order to achieve the above object, the present invention provides a heat pump system comprising an evaporator for generating steam and a plurality of compressing means for compressing the steam, having the features of claim 1 and a method for operating a heat pump system for adjusting a temperature of lubricating water in said heat pump system.
According to the present invention, it obtains the advantageous effect that the deterioration in reliability of the bearings can be minimized by suppression of boiling of the lubricating water for the bearings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a configuration diagram of a heat pump system according to an embodiment helpful to understand the present invention.
Fig. 2 shows a configuration diagram of a heat pump system according to an embodiment helpful to understand the present invention.
Fig. 3 shows a configuration diagram of a heat pump system according to an embodiment helpful to understand the present invention.
Fig. 4 shows a configuration diagram of a heat pump system according to an embodiment helpful to understand the present invention.
Fig. 5 shows an enlarged view of bearings in a heat pump system of the present invention.
Fig. 6 shows a configuration diagram of a heat pump system according to a embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Firstly, a system which uses water or steam as an operating fluid in the industrial heat pump, will be technically described below. There is a technique that employs hot water or cold water as an operating fluid in case of supplying energy to the heat-utilizing equipment by the industrial heat pump. The present inventors have repeatedly conducted studies under the technical trends of steam compressors being improved in performance at high pace. As a result, the inventors have found that if steam is used as the operating fluid for a heat pump system, the amount of energy transferable per weight of the medium can be remarkably increased. The inventors have also been able to obtain the knowledge that it makes possible to acquire heat from outside very efficiently if the operating fluid is made negative pressure in the above case.
However, since the atmosphere pressure of bearings in the compressor of the system is not more than an atmospheric pressure, when the operating fluid is made negative pressure and oil bearings are used as the compressor bearings, it may lead to a risk that lubricating oil for the bearings is mixed into the operating fluid.
Herein, when water is used as a bearings lubricant instead, i.e., water bearings are used as the compressor bearings, it makes possible to suppress the deterioration in reliability of the bearings, even if lubricating water for the bearings is mixed into the steam contained in the main stream of compressor fluid. In that case, it is desirable that both the atmosphere pressure of the bearings and the boiling temperature of water at this atmosphere pressure are considered. Otherwise, the reliability of the bearings will significantly deteriorate when the lubricating water boils in the bearings and air bubbles occur in large quantities in the lubricating water.
The present invention is made in consideration of an atmosphere pressure of bearings and a boiling temperature of water at the atmosphere pressure. Means for suppressing the deterioration in reliability of bearings due to the occurrence of air bubbles in lubricating water will be described below in detail with several embodiments.
In the following, a description of five embodiments is given, wherein the first to forth embodiments do not form part of the invention, but are helpful to understand the invention, whereas the fifth embodiment forms a part of the invention as claimed.

First Embodiment

A first embodiment will be described below using Fig. 1. Fig. 1 is a configuration diagram of a heat pump system according to the first embodiment. In the present embodiment, a heat pump system comprising one steam compressor of a two-stage configuration as a plurality of compression devices will be described by way of example.
A heat pump apparatus shown in Fig. 1 primarily comprises an evaporator 42, a compressor 34, a motor 1 as a driving source, and a pipeline. Around the heat pump apparatus, heat-utilizing equipment 20 for consuming heat and an external heat source (not shown) for heating water supplied to a hot-water line 40 exist. The heat pump apparatus with these constituent elements added constitutes the heat pump system.
A flow of an operating fluid in the present embodiment will be described below. Liquid water as the operating fluid which has been supplied from a water supply line 31, flows through a branching point 30 and a valve 39 and is supplied to the evaporator 42. In the evaporator 42, the liquid water is heat-exchanged with hot water of the hot-water line 40 which has been heated to 80 °C by the external heat source, for example, and the water is evaporated and phase-changed to steam. A temperature and pressure of the steam as the operating fluid is increased in a first stage 33 and second stage 32 of the compressor 34. The steam of about 4 atmospheres and about 140 °C is supplied to the heat-utilizing equipment 20 through a pipeline 24. In the heat-utilizing equipment 20, the high-temperature high-pressure steam is used for purposes such as cleaning, boiling, and drying for industrial products, food, wood, and the like.
A part of the liquid water which has been supplied from the water supply line 31 is branched at the branching point 30, and is boosted to, for example, about 70 atmospheres by a pump 5. Then, the liquid water is regulated in flow rate by a valve 38, and is supplied to a mixer 36. The liquid water which has been supplied to the mixer 36 is mixed and evaporated with the compressed steam sent from the first stage 33 of the compressor. The resulting evaporation latent heat lowers a temperature of the steam flowing into the second stage 32 of the compressor. Generally, compressors have the character that when it is compared with the compressors of the same pressure ratio, a compression power decreases with decreasing a temperature of intake steam. Therefore, the evaporation of the liquid water which added in the mixer 36 contributes to an increase in mass flow rate and reduction in compression power, and thus resulting in improvement of efficiency of the entire system.
A rotor of the compressor is supported by bearings 51 and rotationally driven by the motor 1 connected to one shaft end of the rotor. A sealing mechanism 52 for preventing the fluid from leaking from a gap between a casing and a rotating shaft of the rotor is mounted at both shaft ends thereof. A part of the liquid water which has been supplied from the water supply line 31 is supplied to the bearings 51 through a water supply line 53. Then, the liquid water which has been performed a lubricating function is supplied to the evaporator 42 through a water drainage line 54.
Details of each constituent element will be described below.
The evaporator 42 includes the hot-water line 40 heated by the external heat source flowing therethrough. The hot water supplied to the hot-water line 40 is desirably one that has been heated by utilizing an unused heat source such as the waste heat discharged from a factory or a garbage disposal plant, or other unused energy resources such as river water, sewage, or atmospheric air. By utilizing either of these heat sources, it makes possible to reduce the costs required for installation and operation of the external heat source. Although Fig. 1 shows an example of an indirect type of heat exchanger, which does not contact the water of the hot-water line 40 and the liquid water in the evaporator 42 with each other directly, the heat exchanger may be of a direct-contact type in which the two fluids are mixed. Alternatively, the heat exchanger may be either a tube type of heat exchanger having flow path as a heat transfer surface disposed in the liquid water staying in the evaporator, or a two-phase flow type of plate heat exchanger.
A temperature of the liquid water in the evaporator 42 is equivalent to a boiling temperature, i.e., a saturation temperature, of this fluid at an internal pressure of the evaporator 42. Therefore, as the internal pressure of the evaporator decreases, the temperature of the liquid water correspondingly lowers. This increases the amount of heat which can be recovered from the external heat source. In addition, since exhaust heat of a lower temperature can be utilized as an effective heat source, it makes a broader range of selection of the heat sources usable as the external heat source.
The mixer 36 may be of, for example, a type in which the liquid water is sprayed into a flow of the steam, or a type in which the steam is passed through the container having the liquid water staying therein. Also, to accelerate mixing of fluids in a liquid phase and a gaseous phase, the mixer may be charged with a refiller to disturb the flows of the fluids therein. Since the mixing of the fluids in the liquid phase and gaseous phase is accelerated with increasing in contact areas of both fluids, the mixer can be made more compact by using a type in which minute liquid drops are sprayed into the steam.
In the present embodiment, the mixer 36 is installed between the first stage 33 and second stage 32 of the compressor. A Part or all of the water which has been supplied from the mixer 36 evaporates before entering the second stage 32 of the compressor. The steam discharged from the first stage 33 of the compressor is deprived of heat in the form of evaporation latent heat of the water, whereby the steam is lowered in temperature. Even if the water which has been supplied to the mixer 36 is left therein without evaporating before reaching an entrance of the second stage 32 of the compressor, a part or all of the water flows into the second stage 32 of the compressor with the flow of the steam. Then, the water in the compressor evaporates with temperature-increasing heat of the steam caused by compression work, thereby lowering the temperature of the steam being compressed.
While an example of using one compressor of a two-stage configuration is shown in the present embodiment, the heat pump system may use a multi-stage compressor of a configuration with three or more stages instead. Also, the heat pump system may use a plurality of single-stage compressors or a plurality of multi-stage compressors. In the case of increasing a number of compression devices, i.e., a number of compressors or stages, mixers 36 are installed respectively all or a part between the compression devices and cool the steam as the operating fluid for the compressor. Whereby, it can reduce the total amount of compression work and can enhance efficiency of the heat pump system.
The bearings in the heat pump system of the present embodiment will be described in detail below.
In the present embodiment, a lubricant for the bearings in the heat pump system is water as same kind of fluid as the operating fluid for the compressor. Accordingly, even if the lubricant leaks into the main stream of compressor fluid for reasons such as performance deterioration of the sealing mechanisms 52, the operating fluid is kept free from any adverse effects due to entraining a dissimilar kind of substance, because of the same kind of fluid. The water as the lubricant may be supplied from the outside of the system or from the inside thereof. In the present embodiment, however, normal-temperature water from the system exterior is used. Regardless of what kind of water is used, since foreign substances such as rust of the piping may be mixed in the water, these foreign substances are desirably removed via a filter before the water is supplied to the bearings.
Fig. 5 is an enlarged peripheral view showing the bearings 51 of the compressor 34 according to the present embodiment. Rotor shaft 80 to which a impeller 81 is connected is supported by the bearings 51. Lubricating water which has been supplied from the water supply line 53 absorbs frictional heat while performing a lubricating function near the bearings 51, and then the lubricating water is collected into the evaporator 42 through the water drainage line 54. While, in the present embodiment, the lubricating water which has performed the intended function as a lubricant is supplied to the evaporator 42, the water may be drained to outside the system without being supplied to the evaporator 42 or may be cooled and reused as supply water for the bearings.
The bearings 51 may be adapted for exposure to an ambient air pressure atmosphere, or may be installed in an enclosed casing of the compressor and exposed to an atmosphere pressure of the main stream of the steam. In both cases, it is important to focus attention on a relationship between the temperature of the lubricating water supplied to the bearings 51, and the saturation temperature (at an atmospheric pressure, approx. 100 °C) at the atmosphere pressure of the bearings (i.e., the atmospheric pressure if the bearings are exposed to the atmosphere). The present embodiment assumes that each bearing 51 is exposed to an atmospheric pressure.
If even a temperature of a part of the lubricating water locally exceeds the saturation temperature, air bubbles may occur since the water makes an attempt to evaporate. The occurrence of the bubbles causes breaks in a fluid film on the surface of the bearing and could result in increased friction loss. Also, the metallic surfaces of the bearing and the rotor shaft are directly contacted with each other, and it could result in the bearing being abruptly damaged. In addition, it could present the problem that the evaporation of the lubricating water precipitates scales in the bearing system. For these reasons, reliability of the bearing 51 deteriorates if there is even one part of the lubricating water which causes the local temperature thereof to exceed the saturation temperature. Conversely, when any part of the lubricating water is sampled, if the temperature of the sampled part is lower than a saturation temperature associated with the particular part, the problems discussed above are unlikely to occur.
If any parts of the lubricating water can be controlled below the saturation temperatures associated with the particular parts, that is an ideal method of controlling a temperature of the lubricating water. To realize this method, it is desirable that local temperatures be measured and confirmed over the entire lubricating water line. However, it is very difficult, for the structural reasons, to install a great number of thermometers and to measure local temperatures minutely in the heat pump system. A streamlined method assumed is by measuring the temperature of the lubricating water in at least one position and controlling the temperature of the entire lubricating water according to the measured value. Only from the perspective of temperature control of the lubricating water, by conducting temperature measurements at a larger number of positions, it naturally makes appropriate control of the temperature possible. However, in terms of, for example, decreases in efficiency, increases in costs, and structural restrictions on installation of a temperature-measuring device, it is considered that actual measurements need to be conducted at up to only about several positions.
Firstly, it considers a case in which a temperature-measuring device is installed on the lubricating water supply line 53, on the lubricating water drainage line 54, or at the bearing section (hereinafter, these sections are collectively termed the lubricating water line). The lubricating water for the bearings performs the function of a coolant to cool the bearing section, as well as the function of a lubricant. In the bearing section, heat equivalent to bearing loss occurs and thus the temperature of the lubricating water increases by about 30 °C to 50 °C, compared with the temperature of the lubricating water when supplied to the bearings.
The temperature of the lubricating water is measured for the support of suppressing the occurrence of air bubbles due to excessive increases in the temperature of the lubricating water. Therefore, it is actually considered to supply the lubricating water of which the temperature is based on the saturation temperature at the pressure of the main stream of the fluid in the compression device, allows for the bearings lubricating temperature rise about 30 °C to 50 °C, and does not exceed the temperature obtained by subtracting that value from the saturation temperature. Further, it is customary to design and control operations with a required margin on temperature in consideration of local variations in water temperature, changes in water temperature during the operation, measurement errors of thermometer, and other factors. This required margin depends on accuracy of the design, the number of temperature-measuring positions, and others. Therefore, the margin is independently assigned to each system. Hereinafter, the temperature obtained by subtracting the margin from the saturation temperature is termed the preset lubricating water temperature.
The margin is taken as 15 °C in the present embodiment. Unless the measured temperature exceeds the temperature obtained by first subtracting 15 °C from the saturation temperature and then further subtracting the bearings lubricating temperature rise of 30°C to 50 °C (in the present embodiment, 30 °C) from the subtracted temperature (i.e., the preset lubricating water temperature), an impact of air bubbling upon the reliability of the bearings can be regarded as sufficiently insignificant. That is to say, the deterioration in reliability of the bearings can be suppressed by installing the lubricating water temperature-measuring device in at least one place on the bearings lubricating water line and setting the supply temperature of the lubricating water to a value equal to or less than the temperature value obtained by subtracting the bearings lubricating temperature rise from the preset lubricating water temperature. Additionally, if the temperature of the lubricating water is set in this manner, it is possible to suppress the likely occurrence of the problem that during supplying and draining, the lubricating water may evaporate to precipitate scales on the water supply line and the water drainage line. In other words, deterioration in reliability of the entire lubricating water system including the supply and drainage lines can be suppressed by installing the temperature-measuring device on the bearings lubricating water line and controlling the lubricating water-draining temperature below the temperature obtained by subtracting the bearings lubricating temperature rise from the preset lubricating water temperature.
The temperature of the lubricating water becomes a maximum after the bearings have been lubricated, i.e., when the lubricating water is drained. If the temperature is to be measured in one place only, the most effective measuring position is on the drainage line 54 of the lubricating water. In this case, the temperature of the lubricating water in the drainage line 54 is desirably controlled below the preset lubricating water temperature. This is because control based on the temperature of the water in the lubricating water drainage line 54 keeps the water temperature from exceeding the preset lubricating water temperature while the lubricating water is flowing from the water supply line 53 through the bearings lubricating water line into the drainage line 54. More specifically, it does not need to allow for the temperature rise at the bearings in advance, and it can conduct temperature control in a better-suited manner and in a wider operating range than by using the temperature-measuring device installed on the lubricating water supply line 53 and/or at the bearings.
While an example of installing the lubricating water temperature-measuring device in at least one place has been presented in the present embodiment. A plurality of temperature-measuring devices may be provided where it is considered to be preferable that temperature be measured in further detail with total system efficiency and other factors being taken into account.
In cases such as during rated operation of the heat pump system, when the rotor is rotating at high speed, water films are formed between the surface of the fast-rotating rotor and the bearings. This water-film section assumes a very high pressure and during rated operation, a region in which the pressure reaches a level as high as several tens of thousands atmospheres appears locally. During a period of rated operation, therefore, unless the bearings-lubricating water supplied exceeds the saturation temperature, the lubricating water is extremely unlikely to boil in the bearings while lubricating the bearings. Accordingly, at least the deterioration in reliability of the bearings 51 can be suppressed by installing the lubricating water temperature-measuring device in at least one place on the lubricating water line and setting the supply temperature of the lubricating water to be equal to the preset lubricating water temperature.
The heat pump apparatus according to the present embodiment uses water as an operating medium, and the temperature of the operating medium during the apparatus shutdown is about 15 °C, which is essentially of the same level as that of the atmosphere at normal temperature. The internal pressure of the apparatus is about 0.02 atmospheres that is equal to the pressure of the steam at 15 °C, and thus the inside of the apparatus is maintained in nearly a vacuum state. At this time, if hot water of 80 °C, for example, is supplied to the hot-water line 40 and the water temperature in the evaporator 42 consequently reaches about 60 °C, the internal pressure of the apparatus increases to about 0.2 atmospheres that is equal to the pressure of the steam at that water temperature. Even in this state, since the pressure itself is very low, if an atmosphere pressure of the bearings is equal to, for example, an atmospheric pressure, it is most likely that air will leak into the compressor through the sealing mechanisms 52 of the bearings and thus that the lubricant will be entrained in the compressor. If oil bearings commonly used as bearings in a compressor are used in a heat pump apparatus which employs steam as an operating fluid, oil is most likely to leak from the bearings into the main stream of the fluid within the compressor. If this actually happens, steam that is the main fluid flowing inside the compressor will be contaminated with lubricating oil and become a mixture of the oil and the steam. In the present embodiment, however, since water is used as the lubricant for the bearings, even if this lubricant leaks from the bearings into the main stream of the fluid within the compressor, components of this fluid are water and air. This means that lubricant leakage does not result in the main stream of the steam being contaminated with oil. Thus, the steam, which of temperature and pressure has been increased inside the compressor, can be directly used as a heat source for the heat-utilizing equipment required to be kept clean such as dryness of food.
In the present embodiment, external supply water of about 15 °C which is as low as an atmospheric air temperature is supplied to the bearings 51. The atmosphere pressure of the bearing section is an atmospheric pressure, and the saturation temperature of the lubricating water is about 100 °C. The supply water temperature of 15 °C is less than the preset lubricating water temperature (85 °C) applied in that case, so the lubricating water does not boil when supplied to the bearings. Additionally in the present embodiment, the lubricating water temperature, even if increased by about 30 °C by bearing loss, is about 45 °C, which is lower than the preset lubricating water temperature of 85 °C. Therefore, the lubricating water is essentially unlikely to bubble, even when drained from the bearings 51. The lubricating water temperature, even if increased by bearing loss under an atmospheric air temperature of about 40 °C as in the middle of the summer, is about 70 °C, which is lower than the preset lubricating water temperature of 85 °C. Therefore, the lubricating water is most unlikely to bubble, even in that case. That is to say, when the atmosphere pressure of the bearings is an atmospheric pressure, provided external supply water of a temperature as low as an atmospheric air temperature is supplied as lubricating water to the bearings 51, since air bubbling is most unlikely, the deterioration of the bearings in reliability can be suppressed without regulating the temperature of the lubricating water.
In the heat pump system of the present embodiment, the deterioration in reliability of the bearings is suppressed because the atmosphere pressure of the bearing section is an atmospheric pressure and because external supply water of normal temperature is used. Therefore, it is expected to obtain desired effects, even without controlling the temperature of the lubricating water in an attempt to prevent the reliability of the bearings from deteriorating as above described. If any preventives against unusual increases in the lubricating water temperature for whatever reasons are to be taken as the best possible measures to ensure the above, these preventive measures would be to supply a high-pressure fluid to the sealing mechanisms 52 to make the atmosphere pressure of the bearings increasable, for example.
In the present embodiment, the lubricating water which has been supplied to the bearings 51 is further supplied to the evaporator 42 through the water drainage line 54. Thus, heat due to bearing loss can be effectively used as the evaporation heat required for the evaporator 42, and an even greater deal of steam can be generated. Additionally in the present embodiment, since the external supply water 31 originally of a low normal temperature, acquired from the system exterior, is supplied to the bearings 51, there is no need to provide a cooling tower, a chiller, or other cooling devices for reducing the temperature of the supply water, and thus it is possible to simplify equipment and to reduce the cost.

Second Embodiment

A second embodiment will be described below using Fig. 2. Fig. 2 is a configuration diagram of a heat pump system according to the second embodiment. In the present embodiment, internal water of the system is used as a supply source of lubricating water. A chiller 60 is further installed to cool the lubricating water. The chiller 60 cools the water supplied from an evaporator 42, and then supplies the water to bearings 51 via a pump 5 installed downstream. The bearings 51 are hermetically enclosed in a casing 35. Description of other sections having essentially the same functions as those of the first embodiment and as shown in Fig. 1 is omitted.
In the present embodiment, after heat of the steam supplied to heat-utilizing equipment 20 at, for example, 140 °C and 4 atmospheres has been utilized in the heat-utilizing equipment 20, the steam is recovered through a water recovery path 22 as hot water of 60 °C and 1 atmosphere, for example. The hot water which of the heat has been utilized in the heat-utilizing equipment 20 is reused as a heat medium to minimize consumption of the water as a heat medium. In addition, remaining heat of the recovered water is effectively used as a heat source, so it obtains a significant energy-saving effect.
The temperature and pressure of the evaporator 42 are limited by a temperature of a hot-water pipeline 40. For example, when hot water of 80 °C can be supplied to the hot-water pipeline 40, the temperature inside the evaporator 42 is preferably set to maintain a slightly lower temperature of 60 °C, and the pressure inside the evaporator 42 is preferably a saturated steam pressure of 0.2 atmospheres associated with that setting temperature. Since the evaporator 42 is always maintained in a saturated steam state, a temperature of the water therein, i.e., a saturation temperature of the water, lowers with reducing the internal pressure of the evaporator 42 by a relationship between pressure and saturation temperature. Therefore, even when the temperature of the hot water supplied to the hot-water pipeline 40 is lower, the water can be evaporated by recovering the heat thereof. This means that as the internal pressure of the evaporator is lowered, the temperature of the heat source usable for exhaust heat recovery can be lower. A selection range of usable heat sources also becomes wider. The present embodiment assumes 0.1 atmospheres as the internal pressure of the evaporator 42 at an intake air pressure lower than in the first embodiment, and based on this assumption, a description will be described in detail below.
When the present embodiment is considered with the first embodiment as its basis, since the internal pressure of the evaporator 42 is reduced from 0.2 atmospheres to 0.1 atmosphere, the internal water temperature of the evaporator 42 decreases from 60 °C to 45 °C and the temperature required of the hot water supplied to the hot-water pipeline 40 can also be lowered from a minimum of 80 °C to a minimum of 60 °C. This means a wider selection range of the heat sources usable to heat the hot water to be supplied to the hot-water pipeline 40. At the same time, however, an intake steam pressure of a compressor goes down, so the amount of external fluid leaking from sealing mechanism 52 is likely to increase. In the present embodiment, therefore, the bearing section is accommodated in the enclosed casing 35 integrated with the compressor. This accommodation form alleviates any effects of air leakage from the sealing mechanism due to reduction of the intake steam pressure.
When the bearing section is accommodated in the enclosed casing 35, an atmosphere pressure of the bearing section becomes as low as the intake steam pressure of the compressor. In the present embodiment, in order to prevent such reduction in the atmosphere pressure of the bearings, portions of main streams of steam at exits in a first stage 33 and second stage 32 of the compressor 34 are supplied as shaft-sealing steam to the sealing mechanisms 52 located at upstream and downstream sides, respectively. This part of the sealing steam contributes to enhancing the atmosphere pressure of the bearing section. For example, if the first stage 33 of the compressor 34 has a pressure ratio of 8, the atmosphere pressure of the bearings at the upstream side is 0.8 atmospheres. The saturation temperature at this pressure is about 94 °C, which is about 50 °C higher than a saturation temperature of about 45 °C at 0.1 atmospheres. Since steam of a pressure even higher than that at the upstream side is supplied to the bearings 51 located downstream, the atmosphere pressure of the downstream bearings 51 increases above that of the upstream bearings, so that the saturation temperature also increases. The sealing steam in the bearing secton also contributes to keeping the lubricating water from passing through the sealing mechanisms 52 and becoming entrained in the main stream of the steam.
In the present embodiment, liquid water of about 45 °C that is stored within the evaporator 42 is used as the lubricating water supplied to the bearing section. The liquid water which has been retrieved from a section near the bottom of the evaporator 42 is supplied to the chiller 60 through a pipeline. The liquid water is cooled to 10°C in the chiller, and then boosted in pressure by a pump 5 and supplied to the bearings 51. The chiller 60 is used as a cooler because water needs to be cooled down to an atmospheric air temperature or less. An atmospheric air release type of radiator or a cooling tower, because of their cooling principles, cannot cool the lubricating water to an atmospheric air temperature or below. Thus, even after cooling by these devices, the lubricating water may reach a temperature as high as about 40 °C in summer. In the present embodiment, since the temperature of the lubricating water supplied to the bearings 51 is maintained at about 10 °C by cooling with the chiller 60, the temperature of the lubricating water is sufficiently lower than a saturation temperature of about 94 °C associated with the atmosphere pressure of 0.8 atmospheres of the bearings. Furthermore, the lubricating water temperature is sufficiently lower than the preset lubricating water temperature of about 79 °C applied in that case. Even if there is a temperature rise of about 30 °C to 50 °C at the bearing section, air bubbling of the lubricating water is most unlikely. Accordingly, there is no need to consider the problems of bearing wear or thermal damage due to air bubbling, and deterioration of reliability is suppressed.
The lubricating water which has been performed the intended function in the bearing section is returned to the evaporator 42 as the hot water of 40 °C to 60 °C. The lubricating water which has been returned to the evaporator 42 is reused as the main stream of steam or as lubricating water. Therefore, it is possible to avoid a waste of water. In addition, it is possible to obtain a significant energy-saving effect since heat equivalent to bearing loss is effectively used as a heat source to aid the evaporator 42 in evaporating water.

Third Embodiment

A third embodiment will be described below using Fig. 3. Fig. 3 is a configuration diagram of a heat pump system according to the third embodiment. In the present embodiment, the heat pump system uses a steam turbine 2 instead of a motor as a driving device. The heat pump system also uses an evaporator 43 which is a plate type of two-phase flow heat changer, instead of an evaporator 42 which is a tube-type heat exchanger. Bearings 51 are hermetically enclosed in a casing. Other sections of this heat pump system are basically the same as those of the first and second embodiments and as shown in Figs. 1, 2, and description of these sections is omitted.
High-pressure steam of about 70 atmospheres, for example, is supplied from an external high-pressure steam source (not shown) to the steam turbine 2 as a driving source through a supply line 4. The supplied high-pressure steam has its thermal power recovered by the steam turbine 2, then flows as low-pressure steam of about 4 atmospheres through a converger 28 and a pipeline 24, and is supplied as a heat source of about 140 °C to heat-utilizing equipment 20. The power that has been recovered by the steam turbine 2 is used as compression power of a compressor 34 in order to increase a pressure and temperature of moisture which has evaporated in the evaporator 43. Although a valve 29 for controlling a flow rate of the steam is present on the supply line 4, by installing a movable stator blade at an entrance of the turbine instead of the valve 29, it can obtain a similar effect.
The evaporator 43, a plate heat exchanger, is a structure with a multilayered stack of plates for separating a hot fluid and a cold fluid. Hot water which has been heated by an external heat source flows through a hot-water line 40 disposed at a high-temperature side, and water which is an operating fluid for heat pumps flows at a low-temperature side. The fluid at the low-temperature side is liquid water during an initial phase of inflow, and this fluid gradually evaporates by depriving heat of the water at the high-temperature side. All the liquid water evaporates at much the same time it reaches an exit at the low-temperature side, and the resulting fluid is supplied to the compressor 34 as dry steam of which a temperature is slightly higher than a saturation temperature of the fluid.
Water stored within a lubricating water tank 72 is boosted in pressure by a pump 5 and then supplied to the bearings 51 through a water supply line 53. The lubricating water which has been performed functions of lubricating and cooling in the bearing section is increased in temperature by bearing loss, and then is collected into the tank 72 through a water drainage line 54 and an expansion valve 79.
Since the tank 72 is coupled with a low-pressure section of an ejector 71 via a pipeline 73, an internal pressure of the tank 72 is maintained in a low-pressure state of 0.02 atmospheres, for example. The saturation temperature of the liquid water in the tank 72 at this time is about 15 °C. The bearings drainage water which has been supplied through the water drainage line 54 at a temperature above about 15 °C is depressurized and boils in the tank 72, and a part of the water which has boiled evaporates to generate steam. The evaporation is continued until the temperature of the bearings drainage water has decreased below the saturation temperature of the liquid water, and the generated steam is discharged by the ejector 71.
To a central section of the ejector 71, High-temperature high-pressure hot water 77 which has been produced by a condenser 70 by condensing the high-temperature high-pressure steam extracted from the steam turbine 2 is supplied. When the high-pressure hot water flows through the central section of the ejector 71 and is discharged to a discharge tank 74, suction force generated by the flow of the hot water reduces the internal pressure of the lubricating water tank 72. The temperature of the steam flowing through the condenser 70 is sufficiently high and thus the steam can be easily condensed by heat release to the atmosphere or supply of cooling water. The liquid water which has been collected into the discharge tank 74 is supplied to the evaporator 43 through a pipeline 76, and the heat of the water is effectively used as evaporation latent heat of water.
Since the present embodiment employs a steam turbine as the driving device for the compressor, the heat pump apparatus can be operated even at a location without electric power supply equipment if high-pressure steam can be supplied by using a high-pressure boiler or the like. In addition to a heat quantity of the high-pressure steam which has been supplied from the high-pressure steam source via the supply line 4, a heat quantity that has been absorbed from the external heat source by the heat pump is added to increase a heat quantity usable for a supply rate of steam. Thus, the present embodiment is particularly effective for increasing the amount of heat to be generated from an existing boiler. In addition, since the discharge steam in the steam turbine 2 is used as a heat source for supply to the heat-utilizing equipment 20, this heat pump scheme can create steam in great quantities, compared with a motorized heat pump scheme using the same compressor. Furthermore, by constructing that the discharge steam in the ejector 71 is mixed with the steam of the heat pump system and this mixture is supplied to the heat-utilizing equipment 20, it is possible to increase the supply rate of the steam and to improve total system efficiency.
The present embodiment uses a two-phase flow type of plate heat exchanger as the evaporator. The plate type, compared with the tube type, makes it possible to increase a heat transfer area per unit volume and thus to reduce dimensions of the heat exchanger to a fraction of the original ones. The dimensions of the heat exchanger are a main factor to determine those of the entire heat pump apparatus, and downsizing of the heat exchanger yields great advantages in terms of installation space requirement and manufacturing costs.
Additionally in the present embodiment, the ejector 71 is used, instead of the chiller 60 in the second embodiment, to cool the lubricating water. The chiller 60 needs to internally have a compressor for compressing a refrigerant, and requires compression power for compressing the refrigerant. In the present embodiment, the ejector 71 draws in the internal steam of the lubricating water tank 72 by using a pressure source present inside the system, then boosts the steam, and thus it obtains a compression effect. Hence, it is unnecessary to supply external electric power for compression power. Accordingly, the external electric power required for system operation can be reduced, compared with that using chiller.

Fourth Embodiment

A fourth embodiment will be described below using Fig. 4. Fig. 4 is a configuration diagram of a heat pump system according to the fourth embodiment. The present embodiment uses a vacuum pump 6 in stead of the ejector 71 in the third embodiment.
An internal pressure of a lubricating water tank 72 is always maintained at a low pressure of 0.02 atmospheres, for example, by the vacuum pump 6. When a temperature of liquid water in the tank exceeds a saturation temperature of about 15 °C at 0.02 atmospheres, the fluid boils to generate steam. The resulting evaporation latent heat is used to cool the internal lubricating water of the tank. The lubricating water is boosted in pressure by a pump 5, and then is supplied to bearings 51 through a water supply line 53. The lubricating water which has been performed a lubricating lubricating function is supplied to the lubricating water tank 72 through a drainage line 54. At this time, the temperature of the lubricating water is increased to about 45 °C by bearing loss, the lubricating water flows through an expansion valve 79 and is exposed to the internal low pressure of the tank 72. As a result, the lubricating water boils and evaporates. At the same time, a surrounding fluid is deprived of heat in the form of evaporation latent heat of the water, so a part of bearings drainage water is cooled and its temperature returns to the original value of about 15 °C.
For example, when an atmosphere pressure of the bearings equals an atmospheric pressure, the lubricating water does not boil before its temperature reaches about 100 °C, a saturation temperature of the lubricating water at that atmospheric pressure. Therefore, there is no problem, even if a temperature of the lubricating water which supplied to the bearings is increased above 15 °C. If a temperature-increasing effect obtained by bearing loss is estimated at 30 °C and the supply temperature of the lubricating water is set so that the water will not boil even at the drainage temperature of the bearings, the preset lubricating water temperature may be 55 °C, that is, a saturation temperature may be 55 °C. Since a saturated steam pressure for 55 °C is about 0.16 atmospheres, by maintaining the internal pressure of the lubricating water tank 72, as a cooler for the lubricating water, at 0.16 atmospheres or less, it is possible to maintain a lubricating water temperature not to deteriorate in reliability of the bearings under an atmospheric-pressure atmosphere.
The present embodiment is common to the above-described second embodiment and third embodiment in terms of basic configuration. In the present embodiment, therefore, it can obtain advantageous effects equivalent to those of the second and third embodiments. In addition, even where a chiller or high-pressure steam is absent, it is possible to cool the lubricating water by using the vacuum pump absolutely necessary for heat pump startup. Accordingly, it is possible to reduce installation costs in total system, compared with the other embodiments described above.

Fifth Embodiment

A method of controlling a temperature of lubricating water in a heat pump system of the present invention will be described below using Fig. 6. Fig. 6 is a configuration diagram of the heat pump system according to a fifth embodiment which form a part of the present invention. The heat pump system of the present embodiment includes temperature-measuring devices 61, 62, a controller 90, and control lines 91, 92, 93, 94, in addition to the constituent elements of the fourth embodiment.
In the heat pump system of the present embodiment, the temperature-measuring devices 61, 62 are provided on a bearings lubricating water drainage line 54, and temperature information on lubricating water is transmitted to the controller 90 through the control lines 91, 92. The controller 90 uses obtained temperature information to control an internal pressure of a tank 72 by controlling an output of a vacuum pump 6 so that an appropriate temperature is assigned as a supply temperature of the lubricating water. When the internal pressure of the tank 72 is increased, a saturation temperature of a fluid in the tank 72, i.e., the temperature of the lubricating water supplied is increased in response to the pressure increase. Conversely, when the pressure is reduced, the supply temperature of the lubricating water correspondingly decreases. By controlling in this way, it is possible to supply the lubricating water at an appropriate temperature and to suppress the occurrence of the foregoing problems associated with steam bubbling of the lubricating water. Also, it is possible to perform the system operation that does not reduce the internal pressure of the tank 72 too much, and thus to save the electric power required for operation of the vacuum pump 6.
Application of this control method is not limited to the heat pump system of the fifth embodiment. The temperature of the lubricating water can likewise be adjusted in the heat pump system of the second, or fourth third embodiment by controlling or regulating the chiller 60 or the ejector 71 through a control line by using of a controller 90, as with the heat pump system of the present embodiment.

Claims

A heat pump system comprising an evaporator (42) for generating steam and a plurality of compression means (32-34) for compressing the steam,
wherein said plurality of compression means (32-34)are adapted for an operating fluid being at negative pressure,
wherein bearings (51) for supporting said plurality of compression means are water bearings, and
and a controller (90) is provided for controlling the lubricating water in each of said water bearings (51) to be at a temperature less than a saturation temperature associated with an internal pressure of each water bearing (51),
wherein a temperature-measuring device (61, 62) for measuring a temperature of lubricating water for each of said water bearings (51) is provided on a lubricating water line (53), and the temperature measured by said temperature-measuring device is controllable by said controller (90) below a preset temperature for the lubricating water,
wherein said water bearings (51) and said plurality of compression means (32-34) are hermetically enclosed in a casing (35), and
wherein means are provided for controlling the pressure of each of said water bearings (51) to be sufficiently higher than a pressure of main streams of the steam compressed by a compressor (32-34) in the vicinity of each of said water bearings (51).
The heat pump system according to claim 1, wherein the heat pump system comprises a cooling device (60) for cooling the lubricating water before supplying to said water bearings (51), wherein said cooling device (60) is an ejector, and steam ejected from said ejector is supplied to a heat-utilizing equipment (20).
The heat pump system according to claim 1, further comprising a cooling device (60) for cooling the lubricating water before supplying to said water bearings (51), and
wherein the water bearings (51) are adapted for the pressure of each of said water bearings (51) being atmospheric pressure, said cooling device (60) being adapted for utilizing depressurization boiling of water, and being further adapted for, during a rated operation of said plurality of compression means (32-34), the internal pressure of said cooling device (60) being equal to or less than 0.16 atmospheres absolute pressure.
A method for operating a heat pump system comprising
an evaporator (42) for generating steam,
a plurality of compression means (32-34) for compressing steam, and water bearings (51) for supporting said plurality of compression means, said compression means being adapted for operating fluid at negative pressure, said water bearings (51) and said plurality of compression means (32-34) being hermetically enclosed in a casing (35);
the method comprising the steps of
- controlling the lubricating water in each of said water bearings (51) to be at a temperature less than a saturation temperature associated with an internal pressure of each water bearing (51),

- measuring a temperature of lubricating water for each of said water bearings (51) on a lubricating water line (53) by a temperature-measuring device (61,62),

- controlling the temperature measured by said temperature-measuring device below a preset temperature for the lubricating water, and

- controlling the pressure of each of said water bearings (51) to be sufficiently higher than a pressure of main streams of the steam compressed by a compressor (32-34) in the vicinity of each of said water bearings (51).