Patent Publication Number: US-8529234-B2

Title: Water injection type screw fluid machine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to water injection type screw fluid machines. 
     2. Description of the Related Art 
     In a screw fluid machine, such as a screw compressor for compressing a target gas by means of intermeshing male and female screw rotors housed in a rotor chamber, or a screw expander (an expansion apparatus), in which the target gas is expanded to rotate the intermeshing male and female screw rotors in the rotor chamber, a shaft sealing structure is provided between a rotor shaft of the screw rotor and a bearing to seal the target gas in a system or prevent the target gas from being mixed with outside air or the like. 
     In conventional screw compressors as described in Japan Patent No. 4559343, a lip seal is used as a shaft sealing device on the intake side, while a mechanical seal is used as a shaft sealing device on the discharge side. 
     Although the lip seal is an inexpensive and space saving shaft sealing device, the maximum pressure which can be sealed by the lip seal is typically around 0.3 kgf/cm 2 . For this reason, since the lip seal could have an insufficient shaft sealing effect or tend to be significantly inferior in durability when used on the high pressure side, the lip seal can be only used to seat a shaft on the low pressure side. On the other hand, the mechanical seal, which is capable of sealing a shaft under on the high pressure side, is problematic in terms of its extremely high cost and large footprint. 
     In the screw compressor disclosed in the above noted Japan Patent No. 4559343, the lip seal is used for sealing a shaft on the intake side and also used for sealing the shaft on the discharge side. In order to prevent application of an excessive pressure on the lip seal, which is used for sealing the shaft on the discharge side, the screw compressor is equipped with a labyrinth seal disposed between a screw rotor and the lip seal, and a communicating channel for allowing a space between the labyrinth seal and the lip seal to be communicated with an intake channel or an intermediate pressure section located close to the intake side in the rotor chamber. 
     On the other hand, as described in JP 2000-45948-A, for example, some screw fluid machines are of a water injection type that water is injected into a rotor chamber for the purposes of lubrication and cooling. When the lip seal is used as the shaft sealing device in such a screw fluid machine of the water injection type, it is necessary for the lip seal to have a water sealing function. However, because lubrication property of water is poor as contrasted to oil, the lip seal becomes more vulnerable to abrasion when it is used for sealing water. Therefore, such a water injection type screw fluid machine suffers from a problem that the lip seal has a short service life, necessitating frequent maintenance. 
     SUMMARY OF THE INVENTION 
     In view of the problems set forth above, the present invention advantageously provides a water lubrication type screw fluid machine, in which a shaft sealing device has a long life. 
     In order to overcome the above problems, a water injection type screw fluid machine according to the present invention, in which a target gas is compressed or expansion force of the target gas is converted into turning force by intermeshing male and female screw rotors housed in a rotor chamber formed in a casing, while water is injected inside the rotor chamber to lubricate the screw rotors, the screw fluid machine comprising: a first non-contact seal, a second non-contact seal, and a lip seal, which are disposed between the rotor chamber and a bearing for a rotor shaft of the screw rotor and in this order from the rotor chamber side; a pressurized communicating channel for introducing the target gas which is at high pressure into a pressurized space formed between the first non-contact seal and the second non-contact seal; and an open communicating channel, through which an open space, which is formed between the second non-contact seal and the lip seal, opens to an outside of the casing. 
     According to the above-described structure, a pressure of the pressurized space is increased by introducing the target gas whose pressure is increased through the high pressure communicating channel. In this way, because the pressure of the pressurized space is maintained at high pressure, water that leaks out of the rotor chamber into an outflow space is not allowed to flow into the pressurized space. In addition, even if water could leak into the pressurized space and thus the open space, the leaked water is released from the open space through the open communicating channel to the outside, which can prevent the leaked water from arriving at the lip seal without increasing the pressure of a sealed space. As a result, the lip seal is protected against damage, and a leak of a lubricating oil for the bearing caused by the entry of water into the lip seal can be avoided. 
     Further, the bearing may be a bearing on the high pressure side, and the water injection type screw fluid machine may further include a low pressure communicating channel for allowing an outflow space, which is formed on the rotor chamber side with respect to the first non-contact seal, to be communicated with a low pressure space inside the rotor chamber or a low pressure channel for the target gas, which is in communication with the rotor chamber. 
     According to the above-described structure, the pressure of the outflow space is reduced by connecting the outflow space through the low pressure communicating channel to the rotor chamber or an intake channel whose pressure is lower than a discharge pressure, while the pressure of the pressurized space is increased by introducing the target gas whose pressure is increased through the pressurized communicating channel. In this way, because the pressure of the pressurized space is maintained at the pressure higher than that of the outflow space, the water leaked out of the rotor chamber into the outflow space is not allowed to flow into the pressurized space, and the water is circulated through the low pressure communicating channel into the rotor chamber. Further, even if the water would be leaked into the pressurized space and thus the open space, the leaked water is released from the open space through the open communicating channel to the outside. In this way, it can be prevented without increasing the pressure of the sealed space that the leaked water arrives at the lip seal. This contributes to remarkably enhanced effects of protecting the lip seal against damage and preventing a leak of the lubricating oil for the bearing resulting from entry of the water into the lip seal. 
     Still further, the water injection type screw fluid machine of the present invention may be a water injection type screw compressor for compressing the target gas; further include a water recovery unit for separating the water from the target gas that is discharged; and supply the target gas, from which the water is separated in the water recovery unit, through a pressure reducing means to the pressurized communicating channel. 
     According to the above structure, a part of the target gas discharged from the water injection type screw compressor can be reused as the target gas to be introduced into the pressurized space, which can eliminate the necessity to provide an additionally attached facility for supplying the target gas to the pressurized communicating channel. 
     Moreover, the water injection type screw fluid machine of the present invention may supply the target gas, from which the water is separated in the water recovery unit, through a dryer to the pressurized communicating channel. 
     According to the above structure, after the water recovery unit removes water from the target gas to be introduced into the pressurized space, the target gas can be further dehumidified by means of the dryer, to ensure that there is no possibility of supplying water through the pressurized communicating channel to each shaft sealing means. 
     In addition, in the water injection type screw fluid machine of this invention, an on-off valve, which is closed when operation of the water injection type screw fluid machine is stopped, may be installed in the pressurized communicating channel or in a flow path between the water recovery unit and the pressurized communicating channel. 
     According to the above structure, when a plurality of the screw fluid machines are connected at their discharge side (at positions in the discharge channels located downstream of the water recovery units) to each other, for example, it can be avoided that the pressurized communicating channel of one of the screw fluid machines which has been stopped is supplied with a part of the target gas discharged from other screw fluid machines in operation. Thus, the target gas can be effectively utilized. 
     Further, the water injection type screw fluid machine of the present invention may further include a sleeve member fittingly mounted around the rotor shaft, the sleeve member located in the open space and equipped with a flange projected toward a radial outside. 
     According to the above-described structure (the flange), because water leaked out of the rotor chamber and penetrated into the open space can be dispersed toward the radial outside by centrifugal force created by the flange, and consequently released through the open communicating channel to the outside, a risk of penetration of leaked water into the lip seal can be further reduced. 
     Still further, in the water injection type screw fluid machine of the present invention, each of the first and second non-contact seals may include: a fit member having opposed surfaces formed so as to be opposed to each other across an interval along an axial direction; two seal rings, which are respectively contacted with the opposed surfaces; and an elastic member disposed between the two seal rings to push the seal rings against the opposed surfaces. 
     According to this structure, even if the seal ring in the non-contact seal is brought into contact with the rotor shaft, the seal ring can be shifted along a radial direction, to thereby prevent the possibility that the non-contact seal or the rotor would be severely damaged. Therefore, a clearance between the non-contact seal (the seal ring) and the rotor shaft can be reduced to a minimum, which can lead to further improvement in the effect of sealing the shaft. Thus, a risk that the leaked water reaches the lip seal can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified cross sectional diagram of a screw compressor according to a first embodiment of the present invention; 
         FIG. 2  is a simplified cross sectional diagram of a screw compressor according to a second embodiment of the present invention; 
         FIG. 3  is an enlarged cross sectional diagram of a first non-contact seal depicted in  FIG. 2 ; 
         FIG. 4  is a simplified cross sectional diagram of a screw compressor according to a third embodiment of the present invention, and 
         FIG. 5  is a simplified cross sectional diagram of a screw compressor according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings.  FIG. 1  schematically shows a water injection type screw compressor  1  which is a first embodiment of a water injection type screw fluid machine according to this invention. The screw compressor  1  functions to discharge a target gas (such as, for example, air) compressed by means of a pair of intermeshing male and female screw rotors  4  housed in a rotor chamber  3 , which is formed inside a casing  2 . Further, in the screw compressor  1 , water is introduced into the rotor chamber  3  for cooling, sealing, and lubrication. 
     The casing  2  includes an intake channel (a low pressure channel)  5 , which is in communication with the rotor chamber  3  to supply the rotor chamber  3  with the target gas to be compressed, a discharge channel  6 , which is in communication with the rotor chamber  3  to discharge the target gas compressed in the rotor chamber  3  by the screw rotors  4 , and shaft supporting and sealing spaces  8  and  9 , which are formed to respectively install structures for supporting and sealing a rotor shaft  7  of the screw rotor  4  on both an intake side and a discharge side. 
     The rotor shaft  7  is rotatably supported by both a roller bearing  10  installed in the shaft supporting and sealing space  8  on the intake side and two ball bearings  11  installed in the shaft supporting and sealing space  9  on the discharge side, and extended through the shaft supporting and sealing space  8  on the intake side so as to be connected to a motor, which is not illustrated. 
     In an area on the motor side with respect to the roller bearing  10 , a lip seal  12  is installed to block foreign matter (such as a lubricating oil for the roller bearing  10 ) from penetrating the motor side. On the other hand, in an area on the screw rotor  4  side with respect to the roller bearing  10 , a lip seal  13  is installed for sealing the area to block the lubricating oil for the roller bearing  10  from flowing toward a rotor chamber  3  side, while a lip seal  14  is installed for sealing the area to block the target gas or a lubricating fluid from penetrating a roller bearing  10  side from the intake channel  5 . 
     A partitioning wall section  15  defining an end surface of the rotor chamber  3  on the discharge side (a high pressure side) is formed in the casing  2  to separate the rotor chamber  3  from the shaft supporting and sealing space  9  on the discharge side. Between the partitioning wall section  15  and the ball bearings  11  in the shaft supporting and sealing space  9  on the discharge side, a first non-contact seal  16 , a second non-contact seal  17 , and a lip seal  18  are installed in this order from the rotor chamber  3  side. 
     The first and second non-contact seals  16  and  17  are commonly known labyrinth seals, in which passage of a fluid is suppressed by creating a small clearance of approximately 0.02 mm around the rotor shaft  7  with the intention of causing a high pressure loss of the fluid that is to pass through the clearance. The lip seal  18  is placed in an orientation in which the lubricating oil for the ball bearings  11  can be prevented from flowing out toward the rotor chamber  3  side. 
     The first non-contact seal  16 , the second non-contact seal  17 , and the lip seal  18  divide the shaft supporting and sealing space  9  into respective spaces to create an outflow space  19  between the partitioning wall section  15  and the first non-contact seal  16 , a pressurized space  20  between the first non-contact seal  16  and the second non-contact seal  17 , and an open space  21  between the second non-contact seal  17  and the lip seal  18 . 
     The casing  2  further includes a low pressure communicating channel  23  for allowing the outflow space  19  to communicate with a low pressure space  22 , which is a space, isolated from the intake channel  5  of the rotor chamber  3 , in the midstream of compression, a pressurized communicating channel  24  for introducing the target gas at high pressure into the pressurized space  20 , and open communicating channels  25 ,  26  that communicate with the open space  21  and the outside of the casing  2  so that the open space  21  opens to the atmosphere. 
     In addition, the water injection type screw compressor  1  is further equipped with a water recovery unit  27 , which separates water from the target gas discharged from the discharge channel  6 , a water supply pipe  28 , which re-supplies the water separated and recovered by the water recovery unit  27  into the intake channel  5 , and a pressurized pipe  31 , which introduces a part of the target gas from which water is removed by the water recovery unit  27  into the pressurized communicating channel  24  through a filter  29  and a regulator  30 . The regulator  30  is adjusted to reduce a pressure of the target gas almost to a pressure slightly higher than that of the low pressure space  22 . For example, when the pressure of the low pressure space  22  is approximately 0.03 MPa, the pressurized space  20  is adjusted to be almost at a pressure (of 0.13 MPa) which is higher by approximately 0.1 MPa than the pressure of the low pressure space  22 . It should be noted that, in addition to the regulator  30 , another pressure reducing means, such as, for example, an orifice, may be installed in the pressurized pipe  31  between the regulator  30  and the pressurized space  20 . 
     In the thus-configured water injection type screw compressor  1 , because the outflow space  19  is in communication with the low pressure space  22  inside the rotor chamber  3 , and the target gas at a pressure higher than that of the low pressure space  22  is introduced into the pressurized space  20 , the pressure of the outflow space  19  becomes lower than that of the pressurized space  20 . This generates, in the clearance between the first non-contact seal  16  and the rotor shaft  7 , a tiny stream of the target gas flowing from the pressurized space  20  to the outflow space  19 . Due to the stream, the water discharged from the rotor chamber  3  into the outflow space  19  along with the target gas is prevented from entering the pressurized space  20 . In this way, the lip seal  18  can be protected against damage caused by water that reaches the lip seal  18 , to thereby block the lubricating oil for the ball bearings  11  from being leaked out. 
     Meanwhile, the target gas is gradually introduced from the pressurized space  20  through the clearance between the second non-contact seal  17  and the rotor shaft  7  into the open space  21 . Because the target gas introduced into the open space  21  is released through the open communicating channels  25  and  26  into the atmosphere, the pressure of the open space  21  is maintained at an atmospheric pressure. Thus, even if water is introduced into the open space  21 , for example, while the water injection type screw compressor  1  is stopped, damage which will be inflicted on the lip seal  18  can be kept to a minimum, because the introduced water is released through the open communicating channels  25 ,  26  into the atmosphere. 
     Next, referring to  FIG. 2 , a water injection type screw compressor la according to a second embodiment of this invention is shown. It should be noted that, in the embodiments described later, the same components as those in the previous embodiment are designated by the same reference numerals as those of the previous embodiment, and the descriptions related to these components will not be repeated. 
     The water injection type screw compressor  1   a  of this embodiment includes a sleeve member  32 , which is fittingly mounted on the rotor shaft  7  while being slidably contacted with the lip seal  18 . On the sleeve member  32  extended in the open space  21 , a flange  33  is formed so as to be annularly projected toward a radial outside at a location between the open communicating channel  25  and the open communicating channel  26 . 
     Even when water is allowed to enter the open space  21  while flowing on the rotor shaft  7 , the flange  33  disperses the water toward the radial outside due to centrifugal force since the sleeve member  32  is rotated together with the rotor shaft  7 . In this way, it is ensured that the water is released into the atmosphere through the open communicating channels  25 ,  26 , to thereby prevent the water from reaching the lip seal  18 . 
     Further, in the thus-configured water injection type screw compressor  1   a,  the low pressure communicating channel  23   a  is in communication with the intake channel  5 . Therefore, the regulator  30  is adjusted so as to reduce the pressure of the target gas to a pressure slightly higher than the pressure of the intake channel  5 . In addition, a first non-contact seal  16   a  and a second non-contact seal  17   a  of this embodiment have a self aligning function. 
       FIG. 3  shows the structure of the first non-contact seal  16   a  of this embodiment in detail. It should be noted that the second non-contact seal  17   a , which is not shown, has a structure identical to the first non-contact seal  16   a . The first non-contact seal  16   a  is configured by a fit member  37 , which is fitted in a fit groove  34  formed in the casing  2  and equipped with two opposed wall sections  36  defining two axially opposed surfaces  35 , two seal rings  38 , which are respectively brought into contact with the opposed surfaces  35  and located, at their inner circumferences, close to the rotor shaft  7 , and an elastic member  39 , which is disposed between the two seal rings  38  to push the sealing rings  38  against the opposed surfaces  35 . 
     Although outer diameters of the seal rings  38  are defined to be smaller than an inner diameter of the fit member  37  in order to make the seal rings  38  radially movable inside the fit member  37 , the seal rings  38  are usually maintained at fixed positions due to friction force between the opposed surfaces  35  and the seal rings  38 . Upon coming into contact with the rotor shaft  7 , however, the seal rings  38  are pushed by the rotor shaft  7  and slidingly moved along a radial direction inside the fit member  37 . As a result, the seal rings  38  are self-aligned with respect to the rotor shaft  7 . 
     This self aligning function prevents, even when the first and second non-contact seals  16   a  and  17   a  are brought into contact with the rotor shaft  7  due to vibration or other factors, excessively high stress from being applied to the first and second non-contact seals  16   a  and  17   a . It is therefore possible to minimize the clearance between the rotor shaft  7  and the seals  16   a  and  17   a  to approximately 0.1 mm. Thus, the first non-contact seal  16   a  and the second non-contact seal  17   a  can exert their superior capabilities of sealing the shaft, to thereby block water from flowing through the first and second non-contact seals  16   a  and  17   a.    
     Next, a water injection type screw compressor  1   b  according to a third embodiment of this invention is shown in  FIG. 4 . In the water injection type screw compressor  1   b  of the third embodiment, a first non-contact seal  40  and a second non-contact seal  41  are disposed in sequence from the rotor chamber side between the rotor chamber  3  and the lip seal  13  for the rotor shaft  7  on the intake side (low pressure side), as in the case of the discharge side (high pressure side). Both the first non-contact seal  40  and the second non-contact seal  41  are also labyrinth seals having the structure similar to those of the first and second non-contact seals  16  and  17  on the high pressure side. 
     Thus, inside the shaft supporting and sealing space  8  on the low pressure side, a pressurized space  42  is formed between the first non-contact seal  40  and the second non-contact seal  41 , while an open space  43  is formed between the second non-contact seal  41  and the lip seal  13 . The casing  2  includes a pressurized communicating channel  44  for introducing the target gas at high pressure into the pressurized space  42  and an open communicating channel  45  that communicates with the open space  43  and the outside of the casing  2  so that the open space  43  opens to the atmosphere. The pressurized communicating channel  44  is connected to a pressurized pipe  46 , which is branched from the pressurized pipe  31 , located downstream of the regulator  30 , so as to be provided with the target gas. 
     According to this embodiment, because the pressurized space  42 , into which the target gas is introduced to thereby maintain the pressurized space  42  at high pressure, is additionally formed in the shaft supporting and sealing space  8  on the intake side, no target gas is allowed to enter the pressurized space  42  even when the pressure of the target gas sucked by the water injection type screw compressor  1   b , i.e. the pressure of the intake channel  5  is higher than the atmospheric pressure. In this way, water entrained in the target gas is not allowed to enter and reach the lip seal  13 , thereby preventing the lip seal  13  from getting damaged or preventing the lubricating oil for the bearings from leaking. 
     Further, a water injection type screw compressor  1   c  according to a fourth embodiment of this invention is shown in  FIG. 5 . The water injection type screw compressor  1   c  of this embodiment includes a dryer  47 , which is disposed downstream of the water recovery unit  27  to supply the target gas dehumidified in the dryer  47  through the pressurized pipes  31 ,  46  and the pressurized communicating channels  24 ,  44  to the pressurized spaces  20 ,  42 . Still further, an on-off valve  48  to be closed when the water injection type screw compressor  1   c  is stopped is installed in the pressurized pipe  31 . 
     In the fourth embodiment, the dry target air, from which even moisture is removed by the dryer  48 , is supplied to the pressurized spaces  20 ,  42 , to thereby block moisture from penetrating into the open spaces  21 ,  43 , to which the lip seals  18 ,  13  are exposed. Thus, the lip seals  18 ,  13  can be maintained in a completely dried condition. 
     Moreover, even in a situation of using a plurality of the water injection type screw compressors  1   c  of this embodiment connected in parallel, the target gas is not introduced into the pressurized space  20 ,  42  in a stopped water injection type screw compressors  1   c  from another water injection type screw compressors  1   c  because the on-off valve  48  is installed in each of the water injection type screw compressors  1   c . This can eliminate wasteful consumption of the target gas, leading to high operation efficiency increased by controlling the number of the water injection type screw compressors  1   c.    
     Preferably, the on-off valve  48  may be configured, to ensure its reliable operation, for example, as a single acting electromagnetic on-off valve of a normally closed type that the valve is opened only while power is being supplied. In addition, it is also preferable that a so-called pressure keeping check valve is inserted between the water recovery unit  27  and the dryer  47 .