Abstract:
A method for preheating untreated water in a power plant having a water/steam circuit, the power plant has a steam producer, a steam turbine, and steam lines, of which at least some connect the steam producer to the steam turbine, wherein untreated water for producing deionized water is heated by means of wastewater from the water/steam circuit and the wastewater is added to the untreated water in order to heat the untreated water. A power plant is adapted for preheating untreated water by the method.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2015/079113 filed Dec. 9, 2015, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 102015201143.7 filed Jan. 23, 2015. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a procedure for preheating untreated water, in particular in a power plant. The invention further relates to a power plant having a water/steam circuit. 
       BACKGROUND OF INVENTION 
       [0003]    In the case of power plants that have steam extraction without, or with partial, return of the condensate, frequently there is a requirement for large quantities of deionate, i.e. demineralized (also: deionized) water, in order to compensate the circuit losses resulting from the steam extraction. At low outside temperatures, in particular, the untreated water does not have the temperature necessary for production of deionized water. Hitherto in this case, the untreated water was preheated by means of steam or electrically, resulting in a high requirement in respect of machinery or electrical equipment resources, in reduction of the efficiency or in an increased house load. 
       SUMMARY OF INVENTION 
       [0004]    An object is to further develop the said procedure and the said apparatus such that a considerable reduction of the resource requirement is achieved. 
         [0005]    These objects are achieved according to the invention by the procedure for preheating untreated water as claimed, and the power plant as claimed. Advantageous developments of the invention are defined in the respective dependent claims. In that, in the case of a procedure for preheating untreated water in a power plant having a water/steam circuit, the power plant comprising a steam generator, a steam turbine and steam lines, of which at least some connect the steam generator to the steam turbine, untreated water for production of deionized water is heated by waste water from the water/steam circuit, wherein the waste water is admixed with the untreated water for the purpose of heating the untreated water, it is achieved that residual heat in the waste water is utilized and the house load of the power plant is reduced, or the efficiency is increased. 
         [0006]    Waste water in this case is the water that leaves the water/steam circuit and that is usually discharged into the cooling water or discarded following appropriate recooling. Vessels for waste water, and associated pumps, and the pipeline to the cooling water are already present. It is necessary to add only a line branch to an untreated-water mixer having fittings. 
         [0007]    If the waste water is admixed with the untreated water for the purpose of heating the untreated water, no heat losses occur, as in the case of heating by means of low-pressure steam. Also, with appropriate selection of the waste water, the latter can be used again as untreated water. 
         [0008]    It is expedient in this case if the waste water is a blowdown water from the steam generator, in particular from steam drums. 
         [0009]    Alternatively or additionally, it may be advantageous if the waste water is a condensate from the steam lines that are automatically drained at low points. 
         [0010]    In respect of good intermixing of waste water and untreated water, it is advantageous if the waste water is distributed in the untreated water. 
         [0011]    Further, it is advantageous if an untreated water temperature is controlled, by closed-loop control, by alteration of a blowdown water quantity. 
         [0012]    In particular, it may be advantageous if, on the basis of a heat demand for the preheating, more water is blown down than is required on the basis of a water chemistry requirement. Only in this case, however, there is also only a comparatively small reduction in efficiency, since in this case additional heat is extracted from the steam generator. The electrical house load is not increased. In any case, closed-loop control of the untreated water temperature can be effected by variation of the boiler blowdown. It is thus also possible to set an optimal temperature for the production of deionized water. 
         [0013]    In the case of the power plant according to the invention having a water/steam circuit, the power plant comprising a steam generator, a steam turbine and steam lines, which at least in part connect the steam generator to the steam turbine, an untreated-water mixer and a vessel for waste water from the water/steam circuit, the untreated-water mixer and the vessel for waste water from the water/steam circuit are fluidically connected to each other, wherein an apparatus for distributing the waste water in the untreated water is provided in the untreated-water mixer. A distribution of the waste water in the untreated water improves the intermixing. 
         [0014]    It is expedient in this case if the vessel for waste water from the water/steam circuit is connected to the steam generator. In particular, blowdown water is produced regularly at the steam drums of the steam generator. 
         [0015]    Further, it is expedient if the vessel for waste water from the water/steam circuit is connected to steam lines. The latter are drained automatically at their low points, and the condensate produced is usually not contaminated. 
         [0016]    In a further advantageous embodiment of the power plant according to the invention, a closed-loop controller for closed-loop control of the untreated water temperature is provided. The optimal temperature for the production of deionized water can thus be set. 
         [0017]    It is expedient in this case if the closed-loop control for the untreated water temperature comprises an open-loop control of a blowdown water quantity. 
         [0018]    Unlike condensate from the steam lines, the blowdown water quantity is easily set. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention is explained exemplarily in greater detail on the basis of the drawings. There are shown schematically, and not true to scale: 
           [0020]      FIG. 1  a power plant, and 
           [0021]      FIG. 2  the procedure for preheating untreated water according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0022]      FIG. 1  shows a power plant  1  according to the invention. The power plant  1  according to  FIG. 1  is designed as a gas and steam turbine plant, and comprises a gas turbine installation  11  and a steam turbine installation  12 . The gas turbine installation  11  comprises a gas turbine  13  that has a coupled air compressor  14 , and, upstream from the gas turbine  13 , a combustion chamber  15 , which is connected to a compressed-air line  16  of the compressor  14 . The gas turbine  13  and the air compressor  14 , and a generator  17 , are arranged on a common shaft  18 . The fuel supply is effected via a fuel line  40 . 
         [0023]    The steam turbine installation  12  comprises a steam turbine  4  having a coupled generator  19 , and, in a water/steam circuit  2 , a condenser  20  downstream from the steam turbine  4 , and a waste-heat steam generator  3 . In  FIG. 1  the steam turbine  4  is represented in a highly simplified form, and in the case of large plants is usually composed of a plurality of pressure stages, not shown in  FIG. 1 , which typically drive the generator  19  via a common shaft  21 . 
         [0024]    The waste-heat steam generator  3  is also represented in a highly simplified form. For the purpose of supplying working fluid, expanded in the gas turbine  13 , into the waste-heat steam generator  3 , there is a waste-gas line  22  connected to an input  23  of the waste-heat steam generator  3 . The expanded working fluid from the gas turbine  13  leaves the waste-heat steam generator  3 , via the output  24  thereof, in the direction of a flue, not represented in greater detail. 
         [0025]    A feed-water vessel/deaerator  25  can be fed with condensate from the condenser  20 , via a condensate line  26 , connected into which there is a condensate pump unit  27 . The arrangement of the feed-water vessel/deaerator  25  in the water/steam circuit  2  of  FIG. 1  is represented merely as an example. A feed-water pump  28  brings the feed water, flowing out from the feed-water vessel/deaerator  25 , to an appropriate pressure level. The feed water is supplied to a corresponding pressure stage in the waste-heat steam generator  3  via a feed-water preheater  29 , which is connected on the output side to a steam drum  30 . The steam drum  30  is connected to an evaporator  31 , arranged in the waste-heat steam generator  3 , for the purpose of forming a water/steam circuit. For the purpose of removing live steam, the steam drum  30  is connected to a superheater  32  that is arranged in the waste-heat steam generator  3  and that on the output side is connected, via steam lines  5 , to a steam inlet  33  of the steam turbine  4 . 
         [0026]    Shown exemplarily on the steam turbine  4  is a steam extraction  34  for a steam supply system. In principle, steam extractions may be provided at various points on the steam turbine, but also in the region of the waste-heat steam generator  3 . Exemplarily, a condensate return  35  goes into the condensate line  26 . 
         [0027]    The power plant  1  additionally comprises an untreated-water mixer  6 , and a vessel  7  for waste water from the water/steam circuit  2 , which, according to the invention, are fluidically connected to each other. An apparatus  8  for distributing the waste water in the untreated water is provided in the untreated-water mixer  6 . 
         [0028]    The vessel  7  for waste water from the water/steam circuit  2  is connected both to the steam generator  3  and there, in particular, to the steam drum  30 , and to the steam lines  5 . 
         [0029]    Provided for the purpose of closed-loop control of the untreated water temperature there is a closed-loop controller  9  that, on the one hand, senses a current untreated water temperature by means of a temperature sensor  36 , and on the other hand, by means of the pump  37  connected into the water line  41  between the vessel  7  and the untreated-water mixer  6 , conveys an appropriate quantity of waste water from the vessel  7  into the untreated-water mixer  6 . If the heat demand for the preheating of the untreated water in the untreated-water mixer  6  exceeds that which can be achieved by the quantity of water present in the vessel  7 , the blown-off water quantity is increased, by means of a corresponding open-loop control  10 , even if this were not necessary on the basis of a water chemistry requirement. 
         [0030]    Finally,  FIG. 1  shows an apparatus  38  for water conditioning, including demineralization, that is arranged between the untreated-water mixer  6  and the feed-water vessel/deaerator  25 , with corresponding pumps  39 . Here, also, the infeed of deionized water into the water/steam circuit  2  is represented merely exemplarily. 
         [0031]      FIG. 2  shows the procedure for preheating untreated water in a power plant  1 , in which untreated water for production of deionized water is heated by waste water from the water/steam circuit  2 . In a first step  42  it is checked whether the temperature of the untreated water need be raised at all. If this is not the case, the procedure is terminated  43 . If the temperature of the untreated water is to be raised, it is checked in a second step  44  whether the quantity of waste water present would be sufficient for this purpose. If it is, in a third step  45  waste water is routed, out of the vessel  7  for waste water from the water/steam circuit  2 , into the untreated-water mixer  6 . If the quantity is insufficient, in addition to the third step  45  a fourth step  46  is performed, in which a further blowdown is effected, as a result of which the water inflow to the vessel  7  is increased.