Abstract:
An expander circuit for a thermal expander, having a first pump arranged between a condenser and an evaporator, is proposed, the inlet of the expander being connected to the evaporator and the outlet to the condenser, and a separate lubricating circuit connecting the expander circuit to at least one bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit and priority of German Application No. DE 10 2013 200 413.3, filed on Jan. 14, 2013, the entire disclosure which is hereby incorporated by reference. 
       TECHNICAL FIELD 
       [0002]    The invention proceeds from an expander circuit having an additional lubricating circuit for a thermal expander in an organic rankine circuit. 
       BACKGROUND 
       [0003]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0004]    Expanders for the recovery of energy from waste heat are known from the prior art. A problem arising in this context is the mounting and the lubrication of the mounting of an expander shaft and the ventilation of the inner space of the expander, and also the pressure breakdown. 
         [0005]    In the prior art, permanently lubricated rolling bearings or hybrid bearings are used for mounting the expander shaft. However, the use of this type of bearing entails the risk that the expander suffers bearing problems, above all when the operating medium is steam at high temperature. 
         [0006]    The loads experienced by sealing washers are likewise very high. 
         [0007]    In order to address these problems, an expander was proposed in the prior art, DE 102006009211 A1, the circuit of which provides the lubrication of bearings by the operating medium. For this purpose, in the pump shaft or in the rotor, clearances and grooves are provided through which the operating medium can flow in the direction of the bearings. Water with an oil fraction is provided as the operating medium. 
         [0008]    The solution provided in the prior art lubricates the bearings with the aid of the rotor movement. The lubrication therefore cannot be decoupled from the rotation of the rotor. 
       SUMMARY 
       [0009]    This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its objectives and features. 
         [0010]    In contrast to conventional expanders of the type noted above, a solution in accordance with the invention provides a separate lubricating circuit for supplying the bearings with lubricant. 
         [0011]    In a further step, the operating-medium leakage stream is discharged inside the expander and the expander is scavenged in this way. 
         [0012]    It is in this case advantageous that, in the expander circuit for a thermal expander, with a first pump arranged between a condenser and an evaporator, the inlet of the expander being connected to the evaporator and the outlet to the condenser, a separate lubricating circuit connects the expander circuit to at least one bearing. By the use of a separate lubricant circuit, the pressure at the bearing can be set accurately. 
         [0013]    It is advantageous, furthermore, that the at least one bearing has a connection of the bearing to the outflow of the first pump. As a result, a constant pump pressure of the first pump, which transports the operating medium into the evaporator, prevails in the lubricating circuit. 
         [0014]    In another embodiment, it is advantageous that the at least one bearing has a connection of the bearing to the inflow of the first pump, and therefore a lower pressure, which corresponds to the intake pressure of the first pump, prevails. 
         [0015]    It is advantageous that the connection of the at least one bearing to the expander circuit has incorporated in it at least one throttle valve which allows fine adaptation of the pressure in the lubricating circuit to the lubricating demand of the bearing. 
         [0016]    A further version makes it possible that a leakage stream is discharged in the expander and the outlet of the leakage stream is converged with the outflow of the lubricating circuit. A simple possibility as to how the ventilation of internal leakages can take place has consequently been afforded. 
         [0017]    To optimize the ventilation of the leakage discharge, it is advantageous that a second pump is incorporated in the lubricating circuit. 
         [0018]    By the use of oil-free water as operating medium and lubricant, there is no need for any oil separators to be provided. 
         [0019]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0020]    The invention is described below by way of example, with reference to the accompanying drawings in which: 
           [0021]      FIG. 1  and  FIG. 2  illustrate a diagrammatic illustration of the set-up of an expander; 
           [0022]      FIG. 3  illustrates an advantageous embodiment; and 
           [0023]      FIG. 4  illustrates a second advantageous embodiment. 
       
    
    
     DESCRIPTION 
       [0024]    Example embodiments will now be described more fully with reference to the accompanying drawings. The example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and the neither should be constructed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
         [0025]    An expander  1  constructed in accordance with the present disclosure, as illustrated in  FIGS. 1 and 2 , includes a housing  2  which is closed by means of covers  3 , and a rotor assembly  5  formed from a shaft  6  and rotor  7 . The rotor assembly  5  is mounted in the covers  3  by means of a suitable bearing system  10 , a radial shaft bearing. Vanes  4  move in the rotors  7  in the radial direction. 
         [0026]    An expander chamber  8  is formed by two adjacent vanes  4  with the inside of the housing and with the rotor surface. An inlet  12  is formed on the housing  2 . The inlet  12  is connected to an inlet header  13  and to the inlet ducts  14 . The inlet ducts issue on the inside of the housing in the working space of the expander. An outlet header  15  connects outlet ducts  16  to the outlet  17 . 
         [0027]    The purpose of the expander  1  is to conduct a gas, which is under pressure and high temperature and serves as operating medium, via the inlet ducts  14  and the inlet header  13  into the interior of the expander or into the expander chambers  8 . This takes place as long as an opening is present between the respective expander chamber  8  and the inlet header  13 . As soon as the respective expander chamber  8  is closed with respect to the inlet  12  as a result of the rotation of the rotor  7 , the gas expands and at the same time causes the shaft  6  to work. This takes place until the respective chamber is opened with respect to the outlet header  15 . Expansion is then ended and the gas is simply expelled from the expander at an approximately constant pressure. 
         [0028]    During the expansion step, the expansion chamber is closed with respect to the inlet and outlet, and a lower pressure always prevails in the leading expansion chamber than in the expansion chamber which is just active. Torque is thereby generated in the depicted direction of rotation. 
         [0029]    Beyond a certain pressure difference between the inlet and outlet of the expander, the frictional losses are overcome and the expander runs automatically due to the transfer of torque to the shaft. 
         [0030]    Possible embodiments are illustrated below. 
         [0031]    The expander circuit  11  is illustrated diagrammatically in  FIG. 3 . The expander  1  is connected via its inlet  12  to an evaporator  19 . The outlet  17  is connected to a condenser  21  which is connected via a first pump  20  to the evaporator  19 . The expander circuit  11  requires the first pump  20  in order to bring the operating medium to pressure before evaporation. The operating medium is consequently available under pressure at the exit  2   p  of the pump  20 . 
         [0032]    At the exit  2   p  of the pump  20 , a volume flow is branched off, which is routed in lines as far as the bearing system  10  and from there further on to the entry side  1   p  of the pump  20 . This lubricating circuit is a circuit which is additional to the expander circuit, but in which a reduced pressure prevails. By the appropriate volume flow being branched off, this fraction of operating medium can be used for scavenging and lubricating the plain bearings. 
         [0033]    Lead-throughs through the bearing for feeding and discharging the operating medium are not given in the drawing, only the function of the bearing  10  as a throttle being depicted. 
         [0034]    With a suitable design, the unavoidable internal leakage  25  of the expander can therefore also be discharged. It is advantageous in this case that a pressure substantially lower in relation to the expander circuit prevails in the lubricating circuit  18  and therefore the low pressure in the leakage stream does not have the result that this fraction of the operating medium stream cannot flow out into the lubricating circuit. For this purpose, the leakage stream is routed suitably out of the housing of the expander and, together with the outflow from the seal of the bearing  10 , is connected on the entry side to the first pump  20 . The total volume flow is then returned to the low-pressure side  1   p  of the first pump  20 . 
         [0035]    A further variant of the solution in accordance with the invention is presented in  FIG. 4 . Here, the expander circuit is not given in full, but corresponds to the arrangement for  FIG. 3 . 
         [0036]    The volume flow necessary for the lubricating circuit is in this case diverted on the entry side upstream of the first pump  20  and is introduced into the expander circuit  11  again upstream of the condenser  21 . The lubricating circuit  18  contains a throttle valve  24  which reduces the pressure at the plain bearing. 
         [0037]    The operating medium is sucked through the plain bearings  10  directly from the low-pressure side of the first pump  20  by an additional leakage pump, the second pump  22 . Via the volume flow of the additional second pump  22 , the pressure drop across the plain bearings  10  and therefore also the pressure which acts upon a radial shaft sealing ring  23  contained in the bearing system can be set and influenced. Here, too, leakage discharge from inside the expander  1  is possible again. The operating medium conveyed by the second pump  22  is fed into the main circuit again. In  FIG. 4 , feed is carried out at the point  4   p  upstream of the condenser  21 . In a further advantageous solution, the feed is also possible directly upstream of the first pump  20  at  1   p.    
         [0038]    Water, to which no additives are added, is generally used as operating medium for the expander. If suitable materials are used for the expander, work and lubrication can be carried out with water as the operating medium. However, other coolants which can perform sufficiently lubricating functions are also used as operating medium. 
         [0039]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
         a. Expander 
         b. Housing 
         c. Cover 
         d. Vane 
         e. Rotor assembly 
         f. Shaft 
         g. Rotor 
         h. Expander chamber 
         i. Rotor surface 
         j. Bearing system 
         k. Expander circuit 
         l. Inlet 
         m. Inlet header 
         n. Inlet ducts 
         o. Outlet 
         p. Outlet ducts 
         q. Outlet 
         r. Lubricating circuit 
         s. Evaporator 
         t. First pump 
         u. Condenser 
         v. Second pump 
         w. Radial shaft sealing ring 
         x. Throttle valve