Abstract:
A method and an assembly for thermal water treatment for STIG power station concepts. The heat of an exhaust gas after a heat recovery steam generator stage is used for treating water in a water treatment system. The heat of the exhaust gas, the gas having a low-temperature level, is transported through a heating element to water that circulates between at least one evaporator and condenser in the water treatment system. The treated process water can then be used for steam injection into the gas turbine.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. national stage of International Application No. PCT/EP2014/057478, filed Apr. 14, 2014 and claims the benefit thereof. The International Application claims the benefit of German Application No. 102013208002.6 filed on May 2, 2013, both applications are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    Described below is a method for the thermal preparation of untreated water or condensation water to give process water. 
         [0003]    Also described below is a system of a gas turbine with steam injection, a waste heat steam generator, a heater and a water preparation plant. The system may further include at least one vaporizer and condenser. 
         [0004]    Gas turbines are used to drive generators in electric power plants but are also used to drive propellers in jet engines, or to drive compressors or pumps. In the field of combined heat and power, gas turbines are used in order that the hot exhaust gas thereof can be used to generate heat. Gas turbines are composed of a compressor-combustor-turbine arrangement, wherein turbine refers only to the expansion part of the gas turbine. Depending on the configuration and operating conditions of the gas turbine, the exhaust gas leaving the turbine is at a temperature of between 400° C. and 650° C. According to the related art, a waste heat steam generator is connected downstream of the gas turbine in order to use the thermal energy of the exhaust gas and generate steam. The steam can be injected back into the combustion chamber of the gas turbine so as to increase the power of the gas turbine by virtue of the increased mass flow. Furthermore, the injection of steam reduces the nitrogen oxide concentration in the exhaust gas. Overall, this increases the efficiency of the gas turbine. This method is known as the STIG concept or the Cheng process. Downstream of the waste heat steam generator, the exhaust gas is typically at a low temperature of 70° C. to 200° C. in the case of a two- or three-pressure connection of the waste heat steam generator and approximately 100° C. to 250° C. in the case of a one-pressure connection. For the injection of the water into the gas turbine, high-quality water is also necessary. For water preparation in STIG concepts, the related art offers various onerous methods, wherein the effort involved is dependent on the quality of the untreated water. The most prevalent of these possible methods are ion-exchange and reverse osmosis. However, both methods have limitations in the event of high levels of pollution in the untreated water. Thus, organic pollutants lead to irreversible adsorption processes in the case of ion-exchange and to reduced flux rate in the case of reverse osmosis. In certain circumstances, therefore, further costly steps are connected upstream of both methods. A further drawback of the STIG concept is the loss of the steam and thus of the water in the exhaust gas of the gas turbine. It is thus often necessary to provide process water of the quality required for the steam injection. The STIG process is therefore not used in long-term operation but only for short-term power increases in the case of briefly raised current demand. 
         [0005]    A method for operating a thermal water preparation in the context of STIG concepts, which makes use of the low thermal energy of an exhaust gas downstream of a waste heat steam generator, is described. A system which permits this use and avoids the above-mentioned drawbacks is also described. 
       SUMMARY 
       [0006]    In one aspect, a method for operating a thermal water preparation plant includes the following operations:
       generating a first exhaust gas using a gas turbine,   using a waste heat steam generator to cool the first exhaust gas to give a second exhaust gas at a temperature of 70° C. to 250° C.,   supplying a first warm water from a condenser to a vaporizer within the water preparation plant,   feeding the second exhaust gas to a heater to pass on the exhaust gas heat to the first warm water.       
 
         [0011]    The method permits use of the heat of a second exhaust gas downstream of the waste heat steam generator in a water preparation plant, for example for the preparation of untreated water or condensation water to give process water. The water preparation plant may be operated according to the principle of convection-supported vaporization of water in a vaporizer in counter-flowing air combined with water-cooled condensers for condensing out the clean process water while at the same time recovering the vaporization heat. Therefore, the water preparation plant has at least one condenser and vaporizer. The water preparation plant is operated in combination with a gas turbine which generates a first exhaust gas at a temperature in the range from 400° C. to 650° C. In this context, the gas turbine can be a gas turbine with steam injection. Then, the first exhaust gas generated by the gas turbine is cooled using the waste heat steam generator to a low temperature of 70° C. to 250° C. The waste heat steam generator generates steam in the process. A second exhaust gas, which corresponds to the first exhaust gas cooled in the waste heat steam generator and is at a low temperature in the range from 70° C. to 250° C., is then fed to a heater in the water preparation plant. Use of the waste heat of the second exhaust gas is achieved using the heater, which passes on the heat of the exhaust gas to a first warm water in a circuit between the vaporizer and the condenser. The heater can in particular take the form of a heat exchanger. 
         [0012]    The low waste heat of the second exhaust gas may be sufficient for the operation of a water preparation plant of the type mentioned. It is possible for several of such water preparation plants to be connected in series or for these to be of multi-stage design. This reduces the temperature differences, which leads to higher efficiency. 
         [0013]    The system includes a gas turbine with steam injection, a waste heat steam generator, a heater and a water preparation plant having at least one condenser and vaporizer. It is designed for carrying out the above-described method. 
         [0014]    In one embodiment, the water preparation plant is operated according to the principle of convection-supported vaporization of water in a vaporizer in counter-flowing air combined with water-cooled condensers for condensing out the clean process water while at the same time recovering the vaporization heat. 
         [0015]    Advantageous embodiments and refinements of the water preparation for STIG power plant concepts are presented in the subclaims. According to these, the method can have the following additional operations: 
         [0016]    The water preparation plant can include a cooler which is operated with a first coolant, in particular with cooling water. If the water preparation plant is operated according to the principle of convection-supported vaporization of water in a vaporizer in counter-flowing air combined with water-cooled condensers for condensing out process water, it is expedient to cool the water circuit of the water preparation plant. This makes it possible for the water preparation plant to be in permanent operation since a second warm water must be cooled for use as cooling water in the condenser. The vaporization heat may be recovered simultaneously. 
         [0017]    In one embodiment, the second coolant which is used for cooling in the exhaust gas condenser is subsequently used as coolant in the cooler. In other words, the first and second coolants are one and the same. This keeps the construction of the plant as a whole simple since the number of components is reduced. The temperature spread of the coolant is also increased, thus increasing the specific heat content per unit of flow-through quantity. 
         [0018]    In an embodiment, it is possible for a third exhaust gas to be further cooled downstream of the heater in at least one exhaust gas condenser, using a second coolant such as cooling water. This causes steam in the third exhaust gas to condense to give a second condensation water. For example, cooling as far as 5° C. is expedient. The third exhaust gas may be cooled to below its saturation temperature. 
         [0019]    In one embodiment, the first coolant which is used for cooling in the cooler is subsequently used as coolant in the exhaust gas condenser. This reduces the number of components. The resulting temperature spread of the coolant also causes an increase in the specific heat content per unit of flow-through quantity. 
         [0020]    Untreated water or first condensation water from the heater or second condensation water from the exhaust gas condenser is prepared in the water preparation plant to give process water. Using the waste heat of the second exhaust gas downstream of the waste heat steam generator by the heater for operating the water preparation plant reduces the temperature of the second exhaust gas and condensation of water can take place. It is expedient to prepare this first condensation water in the water preparation plant. This recovers water which is for example injected as steam into the gas turbine. It is also possible to obtain water produced during combustion of the fuel in the gas turbine. A second condensation water can be obtained using the exhaust gas condenser. A third exhaust gas, which corresponds to the second exhaust gas cooled in the heater, is directed to the exhaust gas condenser in which condensation of at least part of the remaining steam present in the exhaust gas takes place. The second condensation water obtained using the exhaust gas condenser can subsequently be prepared in the water preparation plant to give more process water. It is also possible to use a plurality of exhaust gas condensers. 
         [0021]    In an embodiment, the waste heat steam generator can be used to generate steam from part of the process water. When demand for current is low, the steam may be used as a heat delivery medium to supply buildings or as process steam in industry. This increases the efficiency of the plant as a whole. 
         [0022]    At least part of the steam generated in the waste heat steam generator can be injected into the gas turbine. This has the effect of increasing the power and also the efficiency of the gas turbine with respect to the quantity of fuel used. The water or steam requirement which arises as a consequence of operating the gas turbine with steam injection can be entirely satisfied since the water in the exhaust gas is recovered. 
         [0023]    In one embodiment, the first or second condensation water is cleaned of volatile materials or further contaminants prior to preparation in the water preparation plant, or is prepared in a treatment plant. Treatment after the preparation in the water preparation plant can also be expedient. In particular, the condensation water which is obtained from the exhaust gas of the gas turbine can contain nitric acid or sulphuric acid, with the result that these chemical materials accumulate in the process water. Contamination with organic acids, in particular with ethanoic acid or carbonic acid, is also possible. This can lead to corrosion in downstream components, in particular in the gas turbine. 
         [0024]    Condensation in the condenser or vaporization in the vaporizer of the water preparation plant can be carried out in a plurality of operations. This reduces the temperature differences, which leads to higher efficiency. A multi-stage embodiment with a common water circuit can also be realized. 
         [0025]    The system for carrying out the method can have the following elements: 
         [0026]    The system for carrying out the method can include a cooler. The cooler cools a second warm water in a circuit within the water preparation plant. 
         [0027]    The system for carrying out the method can include an exhaust gas condenser. In one configuration, the exhaust gas condenser is used to cool a third exhaust gas downstream of the heater. This results in condensation of steam from the third exhaust gas and water being recovered. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
           [0029]      FIG. 1  is a schematic of a first embodiment of a thermal water preparation plant; 
           [0030]      FIG. 2  is a block diagram of second embodiment of a thermal water preparation plant; 
           [0031]      FIG. 3  is a schematic of a water preparation plant. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0033]      FIG. 1  shows a first exemplary embodiment for the operation of a thermal water preparation plant  2  for STIG concepts. A gas turbine  28  generates first exhaust gas  3  which is directed to a waste heat steam generator  4 . Steam  22  generated using the waste heat steam generator  4  can then for example be used as heat  25  or given off directly as end product. The waste heat steam generator  4  uses process water  20  from the water preparation plant  2 , which is for example stored in a tank  21 , to obtain the steam  22 . Second exhaust gas  6 , which after the waste heat steam generator  4  is at a low temperature in the range from 70° C. to 250° C., is transported to a heater  14 . In particular, the heater  14  can take the form of a heat exchanger. In this exemplary embodiment, the heater  14  is used in particular to prepare untreated water  16  in the water preparation plant  2  to give process water  20 . In particular, this can involve de-ionizing the process water  20 . By cooling the second exhaust gas  6  in the heater  14  to give the third exhaust gas  7 , steam can be condensed to give a first condensation water  18 . In this example, the first condensation water  18  is prepared in the water preparation plant  2  to give additional process water  20 . After the heater  14 , the cooled third exhaust gas  7  can still contain some steam. In order to also recover this water, the third exhaust gas  7  is directed to an exhaust gas condenser  30 . In the exhaust gas condenser  30 , more water then condenses to give a second condensation water  19 , which is in turn prepared in the water preparation plant  2  to give process water  20 . The process water  20  is then for example stored on-site in a tank  21  for later use. The third exhaust gas  7  then leaves the exhaust gas condenser  30  as further cooled and dried fourth exhaust gas  15 . 
         [0034]      FIG. 2  shows a second exemplary embodiment which, in particular in the case of high demand for current, leads to a rapid increase in the power of the gas turbine  28 . The setup shown in  FIG. 2  also has the water preparation plant  2 , the gas turbine  28 , the waste heat steam generator  4 , the heater  14 , the exhaust gas condenser  30  and the tank  21 . Here, steam  22  from the waste heat steam generator  4  is used for steam injection  26  into the gas turbine  28 . In this case, the steam  22  is generated by the waste heat steam generator  4  from the process water  20  which is stored in the tank  21  and, according to the embodiment shown in  FIG. 1 , was obtained during low demand for current. The steam injection  26  causes an increase in the power of the gas turbine  28  and thus more current is generated. Furthermore, the steam injection  26  increases the water fraction in the first exhaust gas  3  downstream of the gas turbine  28  and consequently also in the second exhaust gas  6 , and possibly also in the third exhaust gas  7 . This leads to a significantly increased generation of first and possibly also of second condensation water  18 ,  19 , which can be prepared in the water preparation plant  2  to give process water  20 . Operation of the water preparation plant  2  uses the heat of the heater  14  which in turn uses the heat of the second exhaust gas  6  downstream of the waste heat steam generator  4 . By recovering, from the second and third exhaust gas  6 ,  7 , the process water  20  injected in the steam injection  26 , and by preparing it in the water preparation plant  2 , it is possible to fully cover the water requirements of the steam injection  26 . In addition, the heat requirements of the water preparation plant  2  are covered by the heat supplied to the water preparation plant  2  by the heater  14 . In addition to  FIG. 1 ,  FIG. 2  shows a treatment plant  34  for cleaning or preparing or treating the first or second condensation water  18 ,  19  of volatile or other materials. This can be necessary to clean the steam, injected into the gas turbine  28  by the steam injection  26 , of for example inorganic and organic acids. A further possibility (not shown) is to treat the process water  20  in a treatment plant, which takes place before this water is fed into the waste heat steam generator  4 . In addition, simultaneous treatment before and after the water preparation plant  2  may be used. 
         [0035]      FIG. 3  shows a schematic representation of the water preparation plant  2  in which untreated water  16  or first or second condensation water  18 ,  19  is prepared to give process water  20 . A first warm water  13 , which is heated by the heater  14 , wherein the heater  14  uses the heat of the second exhaust gas  6 , is in a circuit between the condenser  10  and the vaporizer  12 . In this exemplary embodiment, the water preparation plant  2  is operated according to the principle of convection-supported vaporization of water in a vaporizer  12  in counter-flowing air  11  combined with water-cooled condensers  10  for condensing out the clean process water  20 . In addition, it is possible for the vaporization heat to be recovered. The air  11  circulates with the support of a fan  36 . In the water preparation plant  2 , cold water  8  is used as cooling water in the condenser  10 , wherein process water  20  condenses out and the cooling water heats up. The heated cooling water, which now corresponds to the first warm water  13 , is then further heated by the heater  14  to give heated water  27 , and is then trickled in the vaporizer  12 . The temperature of the downward-flowing water drops from the top to the bottom of the vaporizer  12  because heat is extracted by vaporization and by transfer of heat to the air  11 . By contrast, the temperature of the counter-flowing air  11  increases from the bottom to the top of the vaporizer  12 . First warm water  13 , heated by the heater  14 , and counter-flowing air  11  thus form in this exemplary embodiment a counter-flow heat exchanger, in that the heat of the second exhaust gas  6  and the low temperature of the latter, in the range between 70° C. and 250° C., can be used optimally. In order to permit permanent operation, the heated water  9  which collects at the bottom of the vaporizer  12  and which can in turn be mixed with untreated water  16 , first condensation water  18  or second condensation water  19  to give a second warm water  17 , can be cooled to give a cold water  8  prior to further use in the condenser  10 . The second warm water  17  is cooled by a cooler  32  which uses cooling water  23 . In addition, the cooling water  23  can be used as coolant  24  in the exhaust gas condenser  30 . In the exhaust gas condenser  30 , the third exhaust gas  7  further cooled after the heater  14  is brought to the point of condensing out second condensation water  19 . The third exhaust gas  7  and the coolant  24  then leave the exhaust gas condenser  30  as further cooled and dried fourth exhaust gas  15  and third coolant  31 . The exhaust gas condenser  30  can also be operated with a further coolant source (not shown here), in particular with a second cooling water. It is also possible for the cooling water  23  to be first used in the exhaust gas condenser  30 , for condensing the second condensation water  19 , before it is directed for cooling in the cooler  32 . 
         [0036]    A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV,  358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).