Abstract:
In a thermodynamic cycle with at least one first heat exchanger for creating a first heated or partially evaporated working medium flow by heating or partially evaporating a liquid working medium flow by heat transmission from an expanded working medium flow; a second heat exchanger for creating a second at least partially evaporated working medium flow; a separator for separating a liquid from a vaporous phase of the second flow; and an expansion device for creating an expanded vaporous phase, pressure pulsations are prevented during the start-up of the cycle in that the vaporous phase separated by the separator is conducted past the expansion device and the first heat exchanger. The liquid phase separated by the separator is cooled in the first heat exchanger by heat transfer to the liquid flow. After the first heat exchanger, the cooled, separated, liquid phase and the separated vaporous phase are brought together.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/EP2008/066673 filed Dec. 3, 2008, which designates the United States of America, and claims priority to DE Application No. 10 2008 007 249.4 filed Feb. 1, 2008 and DE Application No. 10 2008 045 450.8 filed Sep. 2, 2008. The contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a method for operating a thermodynamic circuit, and to a thermodynamic circuit 
       BACKGROUND 
       [0003]    A circuit such as this is disclosed, for example, in EP 1 613 841 B1. 
         [0004]    Thermal power stations use thermodynamic cycles to convert heat to mechanical and/or electrical energy. Conventional thermal power stations produce the heat by combustion of fuels, in particular the fossil energy sources coal, oil and gas. In this case, the cycles are operated, for example, on the basis of the classical Rankine cycle, with water as the working medium. However, the high boiling point of water makes water unattractive in particular when using heat sources at temperatures between 100 and 200° C., for example geothermal liquids or waste heat from combustion processes, because it is not economic. 
         [0005]    In recent years, widely different technologies have been developed for heat sources with a temperature as low as this, which allow their heat to be converted to mechanical and/or electrical energy with high efficiency. In addition to the Rankine process with an organic working medium (organic Rankine cycle, ORC), the so-called Kalina cycle is, in particular, distinguished by considerably higher efficiencies than the classical Rankine process. 
         [0006]    Various circuits have been developed for widely differing applications based on the Kalina cycle. These circuits use a two-substance mixture (for example ammonia and water) instead of water as the working medium, with the non-isothermal boiling and condensation process of the mixture is used to increase the efficiency of the circuit, in comparison to the Rankine circuit. 
         [0007]    EP 1 613 841 B1 discloses a Kalina circuit of this type, which is particularly suitable for temperatures from 100 to 200° C., in particular from 100 to 140° C. EP 1 070 830 A1 discloses a further known circuit such as this. 
         [0008]    It is already known from conventional water-steam circuits for the steam that is produced to first of all bypass the turbine, in order to start a circuit such as this, until a pressure has built up in the circuit which is sufficient to operate the turbine. However, if this principle is applied to a Kalina circuit mentioned above, then pressure pulsations can occur in the circuit during the starting of the circuit, which can become sufficiently great that an emergency shut-down of the circuit is required. 
       SUMMARY 
       [0009]    According to various embodiments, a method for operating a circuit can be specified, in which such pulsations during starting can be prevented. According to other embodiments, a circuit, in particular for carrying out the above method, can be specified by means of which such pulsations can be prevented. 
         [0010]    According to an embodiment, in a method for operating a thermodynamic circuit with at least the following components: —a first heat exchanger for producing a first heated or partially vaporized working medium flow by heating or partially vaporizing a liquid working medium flow by heat transfer from an expanded working medium flow; —a second heat exchanger for producing a second at least partially vaporized working medium flow by at least partially vaporizing or further vaporizing the first working medium flow with heat which is transferred from an external heat source; —a third heat exchanger for completely condensing the expanded working medium flow; —a separator for separating a liquid phase from a vapor phase of the second working medium flow; —an expansion device, in particular a turbine, for expanding the vapor phase, converting its energy to a usable form, and producing an expanded vapor phase; —a combination point for producing the expanded working medium flow by combining the liquid phase and the expanded vapor phase; in order to start the circuit, —the vapor phase which has been separated by the separator bypasses the expansion device and the first heat exchanger, —the liquid phase which has been separated by the separator is supplied via the combination point to the first heat exchanger, where it is cooled down by heat transfer to the liquid working medium flow, and —after the first heat exchanger, the cooled-down separated liquid phase and the separated vapor phase are combined to form a cooled-down working medium flow. 
         [0011]    According to a further embodiment, a liquid phase and a vapor phase of the cooled-down working medium flow can be separated from one another, and are then combined again. According to a further embodiment, a multiple-substance mixture can be used as the working medium. According to a further embodiment, a two-substance mixture, in particular an ammonia-water mixture, can be used as the multiple-substance mixture. According to a further embodiment, a geothermal liquid, in particular thermal water, can be used as the external heat source. According to a further embodiment, the heat source can be at a temperature of 100° C. to 200° C., in particular from 100° C. to 140° C. 
         [0012]    According to another embodiment, a thermodynamic circuit, in particular for carrying out the method as described above, may comprise at least—a first heat exchanger for producing a first heated or partially vaporized working medium flow by heating or partially vaporizing a liquid working medium flow by heat transfer from an expanded working medium flow;—a second heat exchanger for producing a second at least partially vaporized working medium flow by at least partially vaporizing or further vaporizing the first working medium flow with heat which is transferred from an external heat source;—a third heat exchanger for completely condensing the expanded working medium flow;—a separator for separating a liquid phase from a vapor phase of the second working medium flow;—an expansion device, in particular a turbine, for expanding the vapor phase, converting its energy to a usable form, and producing an expanded vapor phase;—a combination point for producing the expanded working medium flow by combining the liquid phase and the expanded vapor phase; and a bypass line for bypassing the expansion device and the first heat exchanger, which branches off from a line between the separator and the expansion device and opens into a line between the first heat exchanger and the third heat exchanger. 
         [0013]    According to a further embodiment of the thermodynamic circuit, a further separator for separating a liquid phase from a vapor phase, and a mixer for mixing the liquid and vapor phases which have been separated by the further separator, can be connected in the line between the first heat exchanger and the third heat exchanger between the opening of the bypass line and the third heat exchanger. According to a further embodiment of the thermodynamic circuit, the working medium may consist of a multiple-substance mixture. According to a further embodiment of the thermodynamic circuit, the multiple-substance mixture may be a two-substance mixture, in particular an ammonia-water mixture. According to a further embodiment of the thermodynamic circuit, the thermodynamic circuit may have a geothermal liquid, in particular thermal water, as the external heat source. According to a further embodiment of the thermodynamic circuit, the external heat source can be at a temperature of 100° C. to 200° C., in particular from 100° C. to 140° C. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention as well as further advantageous refinements will be explained in more detail in the following text with reference to one exemplary embodiment in the FIGURE. 
           [0015]      FIG. 1  shows a thermodynamic circuit according to various embodiments, illustrated in a simplified, schematic form. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    According to various embodiments, during starting, a very large amount of energy is supplied to the first heat exchanger when the liquid phase, which has been separated by the separator, and the vapor phase are combined before the first heat exchanger. This means that all of the energy in these flows is passed into the first heat exchanger, thus resulting in a high degree of vaporization of the liquid working medium as a result of the heat transfer on the primary side of the heat exchanger. This results in major changes in the pressure ratios between the inlet to the first heat exchanger and the outlet from the second heat exchanger, particularly when the pressure of the working medium is measured at the outlet from the second heat exchanger or behind the separator, and is used as a controlled variable for the circuit. Because of the changing pressure ratios and the control actions that they result in, vaporization processes can be caused which can also suddenly collapse again, thus producing pressure pulsations in the circuit. 
         [0017]    If the separated vapor phase bypasses both the expansion device and the first heat exchanger, this prevents an excessive amount of heat being introduced into the first heat exchanger, and therefore an excessive amount of heat being transferred to the liquid working medium. This makes it possible to prevent excessive vaporization of the liquid working medium in the first heat exchanger, and thus reliably to suppress the pulsations. 
         [0018]    In the case of the cooled-down working medium flow, a liquid phase and a vapor phase are advantageously separated from one another, and are then combined again. This allows the working medium to be homogenized before it is supplied to the third heat exchanger, thus improving the efficiency of the circuit. 
         [0019]    The circuit according to various embodiments is distinguished by a bypass line which branches off from a line between the separator and the expansion device and opens after the first heat exchanger into a line between the first heat exchanger and the third heat exchanger. The advantages and considerations stated for the method according to various embodiments apply correspondingly to the circuit. 
         [0020]    In order to homogenize the working medium before it is supplied to the third heat exchanger, and therefore to improve the efficiency of the circuit, a further separator for separating a liquid phase from a vapor phase, and a mixer for mixing the liquid and vapor phases which have been separated by the further separator, are advantageously connected in the line between the first heat exchanger and the third heat exchanger between the opening of the bypass line and the third heat exchanger. 
         [0021]    According to an embodiment, a multiple-substance mixture is used as the working medium. The multiple-substance mixture is preferably a two-substance mixture, in particular an ammonia-water mixture. A particularly high circuit efficiency can be achieved by the non-isothermal vaporization and condensation of a mixture such as this. 
         [0022]    Energy can be obtained in a particularly environmentally friendly manner by the use of a geothermal liquid, in particular thermal water, from a geothermal source as a heat source. However, exhaust gases (flue gases) from gas and/or steam turbine installations, or the heat produced in industrial production processes (for example during steel production) can also be used as a heat source. 
         [0023]    In this case, a high circuit efficiency can also be achieved if the heat source is at a temperature from 100° C. to 200° C., in particular 100° C. to 140° C. 
         [0024]    A thermodynamic circuit  1 , as illustrated in the FIGURE, comprises a first heat exchanger (preheater) W 1 , a second heat exchanger (vaporizer) W 2  and a third heat exchanger (condenser) W 3 . 
         [0025]    The second heat exchanger W 2  makes thermal contact on the primary side with an external heat source, and in the illustrated exemplary embodiment hot thermal water  20  from a geothermal source, which is not illustrated in any more detail, flows through its primary side, and its secondary side is connected on the one hand to the first heat exchanger W 1  and on the other hand to a separator  4 . The separator  4  is used to separate a vapor phase from a liquid phase of a partially vaporized working medium. A vapor-side outlet of the separator  4  is connected to a turbine  2 , as an expansion device. The output side of the turbine  2  is connected to a combination point in the form of a mixer  5 . The mixer  5  is additionally connected to a liquid output of the separator  4 . On the output side, the mixer  5  is connected to the secondary side of the first heat exchanger W 1 . This is in turn connected on the secondary side via a line  30  to the primary side of the third heat exchanger (condenser) W 3 , through whose secondary side cooling water  25  flows. 
         [0026]    A bypass line  31  is used for the vapor phase, which has been separated in the separator  4 , to bypass the turbine  2  and the first heat exchanger W 1 . The bypass line  31  branches off from a line  32  between the separator  4  and the turbine  2 , and opens after the first heat exchanger W 1  into the line  30  between the first heat exchanger W 1  and the third heat exchanger W 3 . Valves  3 ,  34  are used to control and/or regulate the supply of vapor phase  10  into the bypass line  31  or into the turbine  2 . 
         [0027]    A further separator  40  for separating a liquid phase from a vapor phase, and a further mixer  41  for mixing the liquid phase which has been separated by the separator  40  with the separated vapor phase, are connected in the line  30  between the first heat exchanger W 1  and the third heat exchanger W 3 , between the opening  35  of the bypass line  31  and the third heat exchanger W 3 . 
         [0028]    The third heat exchanger (condenser) W 3  is connected by its outlet on the primary side, possibly via a condensate tank which is not illustrated in any more detail, via a pump  3  to the primary side of the first heat exchanger W 1 . The primary side of the first heat exchanger W 1  is in turn connected to the secondary side of the second heat exchanger W 2 , which has already been mentioned. 
         [0029]    A two-substance mixture, comprising water and ammonia, is used as the working medium in the circuit  1 , and therefore exhibits non-isothermal vaporization and condensation. 
         [0030]    During normal operation of the circuit  1 , the working medium after the third heat exchanger (condenser) W 3  is in a liquid state as a liquid working medium flow  13 . The pump  3  is used to pump the liquid working medium flow  13  to an increased pressure by producing a pressurized, liquid working medium flow  14 . In this case, of course, it is also possible to first of all supply the liquid working medium flow  13  after the third heat exchanger (condenser) W 3  to a condensate tank, where it is temporarily stored, and from where it is taken and raised to an increased pressure by means of the pump  3 . 
         [0031]    The pressurized, liquid working medium flow  14  is supplied to the primary side of the first heat exchanger W 1 , and is heated by partial condensation of an expanded working medium flow  12 , which has been passed through the secondary side of the first heat exchanger W 1 , and has even been partially vaporized, thus resulting, on the primary side after the first heat exchanger W 1 , in a first partially vaporized working medium flow  15  and, on the secondary side, a partially condensed, expanded working medium flow  12   a . The steam component in the first partially vaporized working medium flow  15  is, for example, 15%. 
         [0032]    The first partially vaporized working medium flow  15  is then supplied to the secondary side of the second heat exchanger W 2 . 
         [0033]    The hot thermal water  20  leaving the second heat exchanger W 2  as cooled-down thermal water  22  flows through the primary side of the second heat exchanger W 2 . In the second heat exchanger W 2 , the first partially vaporized working medium flow  15  is vaporized by heat transfer from the hot thermal water  20 , therefore cooling the thermal water  20  down even further, and producing a second at least partially vaporized working medium flow  18 . The second partially vaporized working medium flow  18  is supplied to the separator  4 , in which the vapor phase  10  is separated from the liquid phase  19 . The vapor phase  10  is then expanded in the turbine  2 , and its energy is converted to a usable form, for example to electricity via a generator that is not illustrated, with an expanded vapor phase  11  being produced. For this purpose, the valve  34  is opened, and the valve  33  is closed. 
         [0034]    The expanded vapor phase  11  and the liquid phase  19  which has been separated in the separator  4  are combined again in the mixer  5 , forming an expanded working medium flow  12 . 
         [0035]    The expanded working medium flow  12  is partially condensed in the first heat exchanger W 1 , and the partially condensed, expanded working medium flow  12   a  is produced. The partially condensed, expanded working medium flow  12   a  is then condensed in the third heat exchanger (condenser) W 3  with the aid of the (running) cooling water flow  25  producing the liquid working medium flow  13 . The heat which is transferred to the cooling water flow  25  by the condensation of the expanded working medium flow  12   a  is dissipated through the cooling water flow  26  as it runs out. 
         [0036]    In a modification of the circuit  1 , instead of partial vaporization of the working medium at this stage, it is also possible only for the working medium to be heated on the primary side, in the first heat exchanger W 1 . The at least partial vaporization of the working medium can then be carried out completely in the second heat exchanger W 2 . 
         [0037]    In a further modification of the circuit  1 , an additional, fourth heat exchanger can be connected in the circuit  1  between the first heat exchanger W 1  and the second heat exchanger W 2 , in order to transfer heat from the liquid phase  19 , which has been separated in the separator  4 , to the heated or already partially vaporized second working medium flow  15 , before it is supplied to the second heat exchanger W 2 . 
         [0038]    In order to start the circuit, the supply of vapor phase  10  to the turbine  2  is first of all suppressed by closing the valve  34 . Instead of this, the valve  33  is opened, and the vapor phase  10 , which has been separated by the separator  4 , bypasses the turbine  2  and the first heat exchanger W 1  through the bypass line  31 . The liquid phase, which has been separated by the separator  4 , is supplied—as during normal operation of the circuit  1  as well—via the mixer  5  to the first heat exchanger W 1 , where it is cooled down by heat transfer to the liquid working medium flow  14 . After the first heat exchanger W 1 , the cooled-down separated liquid phase and the separated vapor phase  10  are combined to form a cooled-down working medium flow. 
         [0039]    Before the combined phases are supplied to the third heat exchanger W 3 , a liquid phase and a vapor phase of the cooled-down working medium flow are separated from one another, and are then combined again via the mixer  41 , in order to homogenize the cooled-down working medium flow in the separator  40 . 
         [0040]    Because the vapor phase bypasses the first heat exchanger W 1  during starting of the circuit, this prevents excessive heat transfer to the liquid working medium flow on the primary side of the first heat exchanger W 1 , and therefore excessive vaporization, leading to pressure pulsations in the circuit, of the liquid working medium flow  14  in the first heat exchanger W 1 . 
         [0041]    The invention has been described above with reference to exemplary embodiments, but in general should not be considered to be restricted to these exemplary embodiments. In fact, there are a multiplicity of possible variations and modifications of the invention, and of these exemplary embodiments. For example, valves can additionally be connected in the circuit.