Patent Publication Number: US-2016230660-A1

Title: Gas turbine power generator with two-stage inlet air cooling

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to power generation, and particularly to a gas turbine power plant utilizing two-stage cooled air at the input thereof. 
     2. Description of the Related Art 
       FIG. 2  illustrates a conventional gas turbine system  100 . In such systems, ambient air enters a compressor  102 , where the ambient air is compressed to provide pressurized air to a combustion chamber  104 . Fuel is added to the compressed, pressurized air within combustion chamber  104  for combustion thereof, producing high temperature and high pressure combustion products (typically in the form of carbon dioxide, water vapor and air), which drive gas turbine  106 . Gas turbine  106 , driven by the high pressure and high temperature combustion products, drives a rotor  108  to partially power compressor  102 , as well as driving generator  110  for producing usable electrical power. In such systems, it is common for approximately ⅔ of the power generated by gas turbine  106  to be drawn by compressor  102 , with the remaining ⅓ of the power generated going to driving generator  110 . 
     The total capacity and efficiency of such gas-powered turbine systems are highly variable, particularly in light of variations in the inlet air temperature and density. In a relatively harsh climate, such as in the Kingdom of Saudi Arabia (KSA), turbine capacities can fluctuate as much as 20% between summer (i.e., the time of lowest output) and winter conditions (i.e., the time of highest output), primarily due to relatively high temperature and low density ambient air in the summer months. It has been found that the power output of a gas turbine can fall from 84.4 MW at 15° C. to 69.0 MW at an ambient temperature of 45° C. Thus, by cooling the incoming air, the power output typically can be increased by more than 20%. 
     In order to cool air at the inlet of the compressor, the two primary conventional approaches are evaporative cooling and refrigeration. Refrigeration can use either chilled water coils (i.e., indirect cooling) or direct contact with sprayed, chilled water (i.e., direct cooling). Refrigeration is commonly provided by mechanical or absorption systems and, in some cases, using a thermal storage medium, such as ice or chilled water. For a medium sized combustion turbine (typically in the output range of 20-60 MW), exhaust heat is suitable in quantities and temperatures to power absorption refrigeration cycle systems. 
     Evaporative cooling systems are generally desirable to conventional refrigeration techniques, as described above, due to lower costs and overall efficiency. Using either a wetted medium or a water spray system, the cooling effects in evaporative cooling depend solely on the difference between dry bulb temperature (i.e., the temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture) and wet bulb temperature (i.e., the temperature a parcel of air would have if it were cooled to saturation—with 100% humidity—by the evaporation of water into it, with the latent heat being supplied by the parcel). Examples of evaporative coolers for gas turbine inlets are shown in U.S. Pat. No. 8,360,711 B2; U.S. Pat. No. 7,428,819 B2; U.S. Pat. No. 6,820,430 B1 and U.S. Pat. No. 6,422,019 B1, each of which is hereby incorporated by reference in its entirety. 
     A conventional type of evaporative cooling system is the cooling tower, such as exemplary cooling tower  200 , shown in  FIG. 3 . Such cooling towers are well known in the art. Examples of such cooling towers are shown in U.S. Pat. No. 4,443,389; U.S. RE44,815 E and U.S. Pat. No. 6,615,585 B2, each of which is hereby incorporated by reference in its entirety. Returning to cooling tower  200  of  FIG. 3 , the cooling tower  200  includes a housing  211  having a cowl  212  at the upper end, in which is contained a blower  213  for causing movement of air in the direction indicated by the arrows  214  (outwardly, in this case), with air for the system being admitted through vents or louvers  216  in the lower end of housing  211 . A closed circuit cooling system includes a bank of coils  217 , inlet and outlet fittings  218  and  219 , respectively, a pump  220  and a storage receptacle  221 . The cooling tower  200  is associated with a device  222  to be cooled as described in greater detail below. 
     The pump  220  draws a cooling liquid or medium from the device  222  and forces it through helical coils  217 . The coils  217  have distributed thereover a cooling fluid, such as water, which is pumped by a pump  224  from a storage reservoir  226  in the lower end of cooling tower housing  211 , through a filter  227  to a nozzle  228 . A mounting bracket  254  carries an impeller of an impulse turbine  229 , which is coaxially mounted on shaft  230  of blower  213  so that the fluid ejected from nozzle  228  impacts on the blades of impeller  229  to rotate blower  213 . A float  231  controls a valve  232  for admitting make up water to replenish reservoir  226 . 
     Air, in this case, is drawn through the louvers  216  and upwardly through the cooling coils  217  in counter flow direction with respect to the flow of cooling water through a packing element, which removes the water from the air stream and the air exits through cowling  212  to the atmosphere. The coils  217  are designed to enhance the heat transfer between the cooling medium on the exterior surfaces of the coil  217  (a mixture of air and water) and the heat exchange medium flowing in the closed circuit to the device  222 . 
     In addition to conventional refrigeration and evaporative cooling, mechanical vapor compression refrigeration can also be used for cooling inlet air temperatures for the compressor. Such conventional mechanical vapor compression refrigeration is accomplished by passing relatively hot ambient air over a cooling coil which is fed with chilled water (or brine) coming from a chiller. A main advantage of such systems is that air can be cooled to temperatures well below the wet bulb temperature. Additionally, such refrigeration systems can potentially dehumidify the incoming air stream, thus minimizing the risk of damage to the compressor blades. However, mechanical chilling is typically characterized by a relatively high initial cost of usage, as well as relatively high power consumption in the various components of the system, such as the chiller, particularly when compared against evaporative cooling, which has a relatively low power consumption. Further, mechanical chilling can cause an appreciable and permanent pressure drop upstream of the compressor inlet which, in turn, can cause a relatively slight drop in power augmentation. 
     Hybrid turbine inlet cooling systems combining the benefits of evaporative cooling with those of mechanical vapor compression refrigeration are known. One such system is based on a two-step cooling process in which air is first cooled to an intermediate temperature by mechanical vapor compression and then further cooled by evaporative cooling. When compared to evaporative cooling, the two-stage system can have the advantage of achieving significantly lower air dry bulb temperatures, due to the air at the start of the evaporative cooling stage already having a wet bulb temperature well below that of the hot ambient air dry bulb temperatures. Further, such hybrid systems typically require significantly smaller amounts of make-up water compared to conventional evaporative cooling systems since the amount of water that needs to be added initially is significantly lower. When compared to mechanical vapor compression, the two-stage system cools the air to an intermediate temperature, making the required chilling/refrigerating capacity significantly lower. Thus, the required chillers can have smaller comparative capacities and consume relatively less power. 
     Given the benefits of the two-stage cooling cycle, as well as the advantages of evaporative cooling when compared against mechanical vapor compression refrigeration, it would be desirable to provide a two-stage evaporative cooling method for turbine inlet cooling to reduce the inlet air dry bulb temperature below the inlet air wet bulb temperature. Thus, a gas turbine power generator with two-stage inlet air cooling addressing the aforementioned problems is desired. 
     SUMMARY OF THE INVENTION 
     The gas turbine power generator with two-stage inlet air cooling is a gas turbine power plant for generating electrical power, where air fed into an inlet of a compressor thereof is cooled in a two-stage process. The gas turbine power generator with two-stage inlet air cooling includes a heat exchange cooler, the heat exchange cooler including a heat exchanger and as associated cooling tower to cool a cooling medium flowing through the heat exchanger, the heat exchanger adapted to receive ambient air and adapted to output cooled air at a first temperature lower than a temperature of the ambient air. An evaporative cooler for evaporative cooling is in fluid communication with the heat exchanger for receiving the cooled air at the first temperature and for evaporative cooling and outputting the evaporative cooled air at a second temperature lower than the first temperature. The cooled air at the second temperature is then delivered to a compressor, which is in fluid communication with a combustion chamber for combusting pressurized air output from the compressor with fuel. A gas turbine is in fluid communication with the combustion chamber for receiving heated combustion products therefrom, such that the heated combustion products drive the gas turbine. An electrical generator is in communication with, and is driven by, the gas turbine for producing usable electrical power. 
     These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  diagrammatically illustrates a gas turbine power generator with two-stage inlet air cooling according to the present invention. 
         FIG. 2  diagrammatically illustrates a conventional gas turbine system. 
         FIG. 3  diagrammatically illustrates a conventional cooling tower. 
         FIG. 4  is a graph illustrating a comparison of a humidity ratio of air versus temperature at differing stages in an embodiment of a process for two-stage evaporative cooling for gas turbine inlet cooling in a gas turbine power generator with two-stage inlet air cooling according to the present invention. 
     
    
    
     Unless otherwise indicated, similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of a gas turbine power generator with a two-stage inlet air cooling system, such as a gas turbine power generator with a two-stage inlet air cooling system  10 , the “system  10 ”, is a gas turbine power plant for generating electrical power, where air fed into an inlet of a compressor  12  thereof is cooled in a two-stage process. As shown in  FIG. 1 , as to the gas turbine power generator portion of the system  10 , the gas turbine power generator portion is similar to the system  100  of  FIG. 2 . In this regard, the system  10  includes the compressor  12  for compressing air fed thereto to provide pressurized air to a combustion chamber  14 . Fuel is added to the compressed, pressurized air within the combustion chamber  14  for combustion thereof, producing high temperature and high pressure combustion products (typically including such combustion products in the form of carbon dioxide, water vapor and air), which drive a gas turbine  16 . 
     The gas turbine  16 , driven by the high pressure and high temperature combustion products, drive a rotor  18  to partially power the compressor  12 , as well as driving a generator  20  for producing usable electrical power. As opposed to a conventional gas turbine power plant, such as the system  100  of  FIG. 2 , ambient air entering the system  10 , on a flow path  25 , is first cooled in a first stage by a heat exchange cooler  22  including a heat exchanger  22   a  and an associated cooling tower  22   b . In the first stage heat exchange cooler  22 , the heat exchanger  22   a  can be integrated with the cooling tower  22   b , or can be separate therefrom and in fluid communication therewith, for example. 
     The heat exchanger  22   a  cools the ambient air by a cooling medium flowing through the heat exchanger  22   a . The cooling medium in the heat exchanger  22   a  is circulated to the cooling tower  22   b  to be cooled by the cooling tower  22   b . The heat exchanger  22   a  is adapted to receive the ambient air on the flow path  25  and adapted to output cooled air at a first temperature lower than a temperature of the ambient air entering the heat exchanger  22   a . The heat exchanger  22   a  and the cooling tower  22   b  can be any suitable type of heat exchanger and cooling tower, such as those described above, as can depend on the use or application, and should not be construed in a limiting sense. 
     The first stage cooled air is then delivered from the heat exchanger  22   a  on a flow path  26  to an evaporative cooler  24  for a second stage of evaporative cooling. The evaporative cooler  24  is in fluid communication with the heat exchanger  22   a  for receiving the cooled air at the first temperature and outputting the evaporative cooled air at a second temperature lower than the first temperature. The evaporative cooled air at the second temperature is then delivered on a flow path  27  from the evaporative cooler  24  to the compressor  12  as an input thereto. 
     The compressor  12  is in fluid communication with the combustion chamber  14  for combusting pressurized air output from the compressor  12  with fuel. The evaporative cooler  24  can be any suitable type of evaporative cooler, such as those described above, as can depend on the use or application, and should not be construed in a limiting sense. The gas turbine  16  is in fluid communication with the combustion chamber  14  for receiving heated combustion products therefrom, and the heated combustion products drive the gas turbine  16 . The gas turbine  16 , driven by the high pressure and high temperature combustion products, drive the rotor  18  to partially power the compressor  12 , as well as driving a generator  20  for producing or generating usable electrical power, as described. 
       FIG. 4  illustrates in a graph  400  an effectiveness of embodiments of the two-stage evaporative cooling by embodiments of the system  10 . In  FIG. 4 , the graph  400  compares temperature (T) in degrees centigrade (° C.) versus humidity ratio at a pressure 95.0 kilopascals (kPa). In the graph  400 , temperature  1  is the temperature of the initial ambient air which enters the heat exchanger  22   a  of the heat exchange cooler  22 , temperature  2  is the ambient air wet bulb temperature, temperature  3  is the temperature of the first stage cooled air; i.e., the air output from heat exchanger  22   a  and being input to the evaporative cooler  24 , and temperature  4  is the two-stage cooled air output from evaporative cooler  24  and being input to compressor  12 . 
     Additionally, Table 1 below shows the results of using an embodiment of the two-stage cooling system  10  with a conventional gas turbine power plant in Riyadh, Saudi Arabia, during the summer months of May through September. Table 1 also includes the weather conditions and assumes a 100% evaporative cooling effectiveness, a 5° C. temperature rise of water passing through the heat exchanger  22   a  of the heat exchange cooler  22 , a water flow rate in the cooling tower  22   b  per kilowatt (kW) cooling of the heat exchanger  22   a  of between 36×10 −6  meters 3 /second (m 3 /s) and 54×10 −6  (m 3 /s), and air exiting the cooling coil at a temperature of 3° C. higher than that of the cooling tower  22   b  water exit temperature T et . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Results of Two-Stage Cooling for a Gas Turbine Power Plant 
               
            
           
           
               
               
               
               
            
               
                   
                 Ambient Conditions 
                   
                 ΔW/ 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 P atm   
                 T d   
                 T wet   
                 RH 
                 {dot over (m)} w   
                 T 4   
                 T ct   
                 W iso   
                 W with   
                 W without   
                 W without   
               
               
                 Month 
                 kPa 
                 ° C. 
                 ° C. 
                 % 
                 Ton/hr 
                 ° C. 
                 ° C. 
                 MW 
                 kW 
                 kW 
                 % 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 May 
                 94.2 
                 38.65 
                 21.45 
                 22 
                 12.87 
                 18.29 
                 24.98 
                 84.4 
                 82248 
                 71735 
                 14.7 
               
               
                 June 
                 94.2 
                 41.45 
                 20.35 
                 14 
                 16.17 
                 15.85 
                 24.22 
                 84.4 
                 83541 
                 70312 
                 18.8 
               
               
                 July 
                 94.2 
                 42.75 
                 21.55 
                 15 
                 16.28 
                 17.11 
                 25.05 
                 84.4 
                 82872 
                 69624 
                 19.0 
               
               
                 August 
                 94.2 
                 42.45 
                 20.95 
                 14 
                 16.53 
                 16.36 
                 24.64 
                 84.4 
                 83270 
                 69788 
                 19.3 
               
               
                 September 
                 94.2 
                 40.05 
                 21.05 
                 18 
                 14.39 
                 17.30 
                 24.71 
                 84.4 
                 82774 
                 71021 
                 16.5 
               
               
                   
               
            
           
         
       
     
     As can be seen in Table 1, the output power of the gas turbine without using the two-stage cooling system  10 , W without , falls down 15%-20% below the ISO power rating, W iso , for example. However, using the two-stage cooling system  10  and embodiments of the two stage cooling process can reduce for the cooled air the inlet air dry bulb temperatures to temperatures below the ambient wet bulb temperatures. Further, output power of the gas turbine power plant can be increased by 14.7%-19.3%, for example In Table 1, P atm  is atmospheric pressure, T d  is the dry bulb temperature, T wet  is the ambient wet bulb temperature, RH is relative humidity, rh w  is the rate of make-up water (in tons/hour), T 4  is the temperature of air being input to the compressor  12  (i.e., the twice-cooled air), W with  is the power output of the gas turbine using embodiments of the two-stage cooling system  10  and embodiments of the two-stage cooling process, and ΔW is the difference of W with −W without . 
     Also, embodiments of the two-stage cooling system can substantially reduce or substantially eliminate a need for use of mechanical vapor compression, which typically consumes relatively more power that evaporative cooling. Also, use of the evaporative cooler and evaporative cooling process can substantially reduce or can eliminate a need for use of environmentally hazardous refrigerants from the turbine inlet cooling system, thereby enhancing environmental friendliness of the cooling system. 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.