Abstract:
The invention relates to a method of operating a gas turbine installation ( 1 ), compressed fresh air ( 6, 19, 38 ) is branched off after a compressor ( 2 ) and supplied to an evaporator device ( 14 ), in the evaporator device ( 14 ) feed water ( 17, 26, 28 ) is evaporated, while heat is supplied, and is mixed with the fresh air ( 6, 19, 38 ) in order to generate a steam/air mixture ( 22, 37 ), the steam/air mixture ( 22, 37 ) is fed back upstream of a gas turbine ( 10 ), the heat required for the evaporation of the feed water ( 17, 26, 28 ) is at least partially extracted from an exhaust gas ( 12 ) of the gas turbine ( 10 ). In order to improve the efficiency of the gas turbine installation ( 1 ), the feed water ( 17, 26, 28 ) runs down along a wall arrangement ( 39 ) heated by the exhaust gas ( 12 ) and is subjected to the fresh air ( 6, 19, 38 ). The feed water ( 17, 26, 28 ) evaporates and mixes with the fresh air ( 6, 19, 38 ), by which means the steam/air mixture ( 22, 37 ) forms for the recirculation.

Description:
This application claims priority under 35 U.S.C. §§119 and/or 365 to Appln. No. 2001 1290/01 filed in Switzerland on Jul. 13, 2001; the entire content of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a method of operating a gas turbine installation with the features of the preamble to claim 1. The invention also relates to a gas turbine installation with the features of the preamble to claim 6. In addition, the method relates to a use of a trickling film or thin film evaporator. 
     BACKGROUND OF THE INVENTION 
     A gas turbine installation is known from WO 98/01658 which has a gas turbine with steam injection, a plurality of heat exchangers for heat recovery from the exhaust gas of the gas turbine, an evaporator and humidification device for generating the steam and a compressor for generating compressed fresh air. Fresh air is extracted from the compressor and supplied, via a plurality of heat exchangers, to the humidification device. Heated feed water, which evaporates and, together with the compressed fresh air, forms a steam/air mixture is additionally supplied to this humidification device. This steam/air mixture is recirculated via one or a plurality of heat exchangers and is injected upstream of the gas turbine, in particular upstream of the associated combustion chamber. In this arrangement, the heating of the feed water and the superheating of the steam/air mixture take place in heat exchangers to which the gas turbine exhaust gas is admitted. In this arrangement, these heat exchangers form a device for heat recovery from the exhaust gas. Furthermore, the exhaust gas can be additionally used for preheating the feed water in a further heat exchanger. The overall efficiency of such a gas turbine installation depends, in particular, on how much thermal energy is extracted from the exhaust gas emerging from the gas turbine. 
     An appliance is known from EP 0 843 083 by means of which a liquid fuel is treated by means of a scavenging gas in order to match the volumetric calorific value of the liquid fuel to that of a gaseous fuel. For this purpose, this appliance contains an evaporator tube, which consists of a good heat-conducting material and which interacts with a heating device. In this arrangement, the liquid fuel is introduced into the evaporator tube at the top in such a way that it runs down along the inner surface of the evaporator tube and, in the process, forms a relatively thin film. Because of the heating of the evaporator tube, the fuel film can evaporate easily. The scavenging gas is simultaneously introduced into the evaporator tube from below in such a way that it mixes with the fuel vapor; the fuel is simultaneously transported away by this means. In this way, the density of the fuel/scavenging gas mixture is adjusted in such a way that the desired volumetric calorific value results. Such an appliance can also be designated as a “trickling film or thin film evaporator”. 
     SUMMARY OF THE INVENTION 
     The invention, as characterized in the claims, deals with the problem of providing an embodiment for a gas turbine installation and for an associated operating method of the type mentioned at the beginning, which embodiment permits an increased overall efficiency for the gas turbine installation. 
     According to the invention, this problem is solved by a method with the features of claim 1 and by a gas turbine installation with the features of claim 6. The problem on which the invention is based is also solved by an employment with the features of claim 14. Advantageous embodiments are given in the sub-claims. 
     Due to the application, according to the invention, of trickling film or thin film evaporation during the evaporation of the feed water, more heat can be extracted from the gas turbine exhaust gas than in the case of conventional feed water evaporation. The overall efficiency of the installation can be increased in this way. The intensive cooling effect of the trickling film or thin film evaporation is based, in particular, on the high heat transfer between the wall arrangement and the feed water and on the direct contact between the wall arrangement and the feed water running down along it. 
     An improvement to the evaporation effect can be achieved by the fresh air and the exhaust gas being admitted to the wall arrangement, down which the feed water runs, according to the counterflow principle. 
     A further improvement to the evaporation performance can be achieved by the feed water being preheated before its evaporation. For this purpose, the feed water can, on the one hand, have a heat exchange relationship, in a first heat exchanger, with the fresh air compressed, and by this means heated, in the compressor. Alternatively or additionally, the feed water can, by means of a second heat exchanger, have a heat exchange association with the exhaust gas, which has already been cooled by the trickling film or thin film evaporation. In addition, it is expedient to carry out the superheating of the steam/air mixture, likewise by means of heat contained in the exhaust gas, which superheating can be realized by means of a third heat exchanger which is, on the one hand, arranged in the steam path downstream of the trickling film or thin film evaporation and, on the other, in the exhaust gas path upstream of the trickling film or thin film evaporation. 
     In a particularly advantageous embodiment, at least one of the heat exchangers mentioned can form an integral unit with the trickling film or thin film evaporator, by which means line losses can be avoided. 
     Further important features and advantages of the invention are provided by the sub-claims, from the drawing and from the associated description of the figures using the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred exemplary embodiment of the invention is shown in the drawing and is explained in more detail in the following description. The single FIG. 1 shows a greatly simplified representation, in principle, of a gas turbine installation according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A gas turbine installation  1  according to the invention has, corresponding to FIG. 1, a compressor  2 , whose inlet  3  is supplied with fresh air  4 , for example, from the surroundings. During operation of the gas turbine installation  1 , the compressor  2  compresses the fresh air, so that compressed fresh air  6  emerges at an outlet  5  from the compressor  2 . The main quantity of the compressed fresh air  6  is supplied to a combustion chamber  7  of the gas turbine installation  1  in which, in a conventional manner, combustion of a usual fuel  40 , in particular natural gas, takes place. Hot and highly compressed exhaust gases  8 , which are supplied to an inlet  9  of a gas turbine  10  of the gas turbine installation  1 , emerge correspondingly from the combustion chamber  7 . These exhaust gases are expanded in the gas turbine  10 , so that expanded, hot exhaust gases  12  emerge at an outlet  11  from the gas turbine  10 . In this arrangement, energy released from the gas turbine  10  is essentially used to drive the compressor  2  and to drive a consumption unit, in particular a generator  13  used for electricity generation. 
     The gas turbine installation  1  according to the invention is also equipped with a trickling film or thin film evaporator  14 , which forms an integral unit made up of an evaporation device and an exhaust gas heat recovery device. The trickling film or thin film evaporator  14  has a casing  15 , which has a water inlet  16  for feed water  17 , an air inlet  18  for compressed fresh air  6  or  19 , an exhaust gas inlet  20  for the hot exhaust gas  12 , a steam outlet  21  for superheated steam or for superheated steam/air mixture  22 , an exhaust gas outlet  23  for cooled exhaust gas  24 , an additional inlet  25  for feed water  26 , which has to be preheated, and an additional outlet  27  for preheated feed water  28 . In addition, the casing  15  contains an evaporation line arrangement  29 , which is, for example, formed from a multiplicity of tubes  30  extending parallel to one another, and is arranged in an evaporator section of the casing  15  designated by a curly bracket  31 . The evaporation line arrangement  29  is supplied at  32 , via the water inlet  16  and at the upper end of the individual tubes  30 , with the feed water  17  to be evaporated. In this arrangement, the feed water  17  is guided in such a way that it runs down within the tubes  30  on their wall surfaces and forms a film on them which can, in particular, be thinner than 1 mm. The tubes  30 , or the evaporation line arrangement  29 , therefore contain, in the evaporator section  31 , a wall arrangement  39 , which is designated symbolically with uninterrupted line and along which the feed water  17  to be evaporated runs down. 
     The evaporation line arrangement  29  is supplied, at  33 , with compressed fresh air  6  or  19  via the air inlet  18 , i.e. at the bottom, by which means the tubes  30  have fresh air admitted to them on the inside. The feed water running down the wall arrangement  39  mentioned is correspondingly also subjected to the fresh air. 
     In order to supply the trickling film or thin film evaporator  14  with compressed fresh air  6 , a partial flow  38  of the fresh air  6  is branched off after the compressor  2 . It is likewise possible to branch off the fresh air necessary for the evaporation at another location in the compressor  2 . 
     In the embodiment shown here, a first heat exchanger  34  is also provided which is arranged upstream of the air inlet  18  with respect to the branched-off, compressed fresh air  38  and upstream of the water inlet  16  with respect to the feed water. Feed water, on the one hand, and the compressed fresh air  38 , on the other, therefore flow through this first heat exchanger  34 . By this means, the feed water is preheated, whereas the compressed fresh air is cooled; the cooled fresh air is here designated by  19 . 
     Corresponding to the special embodiment shown here, a second heat exchanger  35  is integrated into the casing  15  of the trickling film or thin film evaporator  14 . Feed water flows through this second heat exchanger  35 , on the one hand, and exhaust gases from the gas turbine  10  are admitted to it, on the other. This second heat exchanger  35  is arranged, with respect to the exhaust gases, downstream of the trickling film or thin film evaporator  14  and, with respect to the feed water, upstream of the first heat exchanger  34  or upstream of the water inlet  16 . 
     In addition, a third heat exchanger  36  is arranged in the casing  15  of the trickling film or thin film evaporator  14  and, on the one hand, a steam/air mixture  37 , which emerges from the evaporator section  31  of the evaporation line arrangement  29 , flows through the third heat exchanger  36 . On the other hand, the hot exhaust gases  12  are admitted to this third heat exchanger  36 . With respect to the exhaust gases, this third heat exchanger  36  is therefore arranged upstream of the evaporator section  31  of the evaporation line arrangement  29  whereas, with respect to the steam/air mixture  37 , it is arranged between the evaporator section  31  and the steam/air mixture outlet  21 , i.e. upstream of the gas turbine  10 . By means of its evaporator section  31 , the evaporation line arrangement  29  forms an evaporation device on the inside whereas, on the outside, it forms an exhaust gas heat recovery device which can, in addition, be supplemented by the second heat exchanger  35  and/or the third heat exchanger  36 . 
     Due to the arrangement selected, the feed water  17  running down along the evaporator wall arrangement  39  formed by the inside of the tubes  30  is subjected to the fresh air  19  on the counterflow principle. In a corresponding manner, the tubes  30  are subjected to the fresh air  19  and the hot exhaust gas  12  in the casing  15  on the counterflow principle. Flow likewise occurs on the counterflow principle through the first heat exchanger  34 , the second heat exchanger  35  and the third heat exchanger  36 . 
     The gas turbine installation  1  is, according to the invention, operated as follows: 
     During operation of the gas turbine installation  1 , the compressor  2  compresses fresh air  6 , of which the proportion designated by  38  is supplied to the first heat exchanger  34 . After the first heat exchanger  34 , the compressed and cooled fresh air  19  is supplied via the air inlet  18  to the evaporation line arrangement  29 , in which it mixes with the feed water evaporating in the evaporation line arrangement  29 , the fresh air  19  also ensuring the transport of the steam/air mixture designated by  37  out of the evaporation line arrangement  29 . 
     The hot exhaust gases  12  enter the casing  15  at the exhaust gas inlet  20  and are admitted first to the third heat exchanger  36 , superheating within it the steam/air mixture  37  so that the desired superheated steam/air mixture  22  appears. After the third heat exchanger  36 , the still hot exhaust gases flow around the outside of the tubes  30 . This means that the evaporation wall arrangement  39  mentioned above and along which the feed water flows on the inside, is subjected on the outside to the still hot exhaust gas. Because the tubes  30  are preferably manufactured from a relatively good heat-conducting material, for example steel, there is a relatively intense heat transfer in which, on the one hand, the exhaust gases cool relatively strongly whereas, on the other hand, intensive evaporation of the feed water is achieved. Downstream of this evaporator section  31 , the still relatively warm exhaust gases are admitted to the second heat exchanger  35  and effect, within it, an initial preheating of the feed water. The relatively substantially cooled exhaust gases  24  then emerge from the casing  15  at the exhaust gas outlet  23 . 
     At the additional inlet  25 , relatively cool feed water  26  is introduced into the casing  15  or into the second heat exchanger  35 , in which the first preheating, already mentioned above, of the feed water takes place. The feed water  28 , preheated to this extent, emerges again at the additional outlet  27  from the casing  15  and reaches the first heat exchanger  34 . A second preheating of the feed water takes place there before the feed water enters, at the water inlet  16 , the casing  15  or the evaporator section  31  of the evaporation line arrangement  29 . The trickling film or thin film evaporation then takes place in this evaporation section  31 , the evaporated feed water mixing with the fresh air introduced at  33 . In order to obtain intensive through-mixing, turbulators or the like (not described in any more detail) can be employed. It can likewise be advantageous to introduce the feed water tangentially into the individual tubes  30  in order to obtain a helical flow, for example. 
     The feed water steam/fresh air mixture  37  formed in the evaporator section  31  then passes into the third heat exchanger  36 , in which the superheating of the steam/air mixture described above takes place. The superheated steam/air mixture  22  can then be returned to the main flow of the compressed fresh air  6  upstream of the combustion chamber  7 . 
     An intensive heat recovery from the turbine exhaust gases is achieved by means of the trickling film or thin film evaporation in the evaporator section  31 , by which means the efficiency of the overall installation  1  is increased. In addition, the integration of the second heat exchanger  35  and of the third heat exchanger  36  into the casing  15  of the trickling film or thin film evaporator  14  also leads to an increase in the overall efficiency, a particularly compact design being also achieved. 
     List of Designations 
       1  gas turbine plant 
       2  compressor 
       3  inlet to  2   
       4  uncompressed fresh air 
       5  outlet from  2   
       6  compressed fresh air 
       7  combustion chamber 
       8  compressed, hot exhaust gas 
       9  inlet to  10   
       10  gas turbine 
       11  outlet from  10   
       12  expanded, hot exhaust gas 
       13  generator 
       14  trickling film or thin film evaporator 
       15  casing of  14   
       16  water inlet to  15   
       17  feed water, preheated twice 
       18  air inlet to  15   
       19  cooled, compressed fresh air 
       20  exhaust gas inlet to  15   
       21  steam/air mixture outlet from  15   
       22  superheated steam/air mixture 
       23  exhaust gas outlet from  15   
       24  cooled exhaust gas 
       25  additional inlet to  15   
       26  unheated feed water 
       27  additional outlet from  15   
       28  feed water, preheated once 
       29  evaporation line arrangement 
       30  tube 
       31  evaporator section 
       32  inlet to  29  for  17   
       33  inlet to  29  for  19   
       34  first heat exchanger 
       35  second heat exchanger 
       36  third heat exchanger 
       37  steam/air mixture 
       38  branched-off, compressed fresh air 
       39  evaporator wall arrangement 
       40  fuel supply