Abstract:
A gas turbine combustion air cooling system includes an intake a duct having an inlet region and an outlet, the duct adapted to supply ambient air to an inlet of a compressor; a first set of nozzles for spraying atomized water into the ambient air at a location adjacent the duct inlet; a second set of nozzles for spraying atomized water into the ambient air to supersaturate the ambient air at a location proximate the compressor inlet; and a control system for apportioning water to the first and second sets of nozzles.

Description:
TECHNICAL FIELD 
     This invention relates to an integrated air saturation and supersaturation system for gas turbine combustion air. 
     BACKGROUND OF THE INVENTION 
     Known equipment to humidify gas turbine inlet (i.e., combustion) air for performance augmentation have included one or the other of the systems described below. These systems are generally used under high load conditions and relatively high ambient temperatures (over about 40° F.). 
     An evaporative cooler system includes an absorbtive media or other system located in a low velocity section of the air intake duct, and is supplied with water which is exposed to the air flowing through the media for evaporation of the water by energy in the air. The energy used for evaporating the water reduces the temperature of the air to near the saturation point, or wet bulb temperature. The reduced temperature of the air entering the gas turbine compressor increases the gas turbine temperature ratio and mass flow, thereby increasing gas turbine output and efficiency. This system does not have the ability to supersaturate the combustion air, however, without the potential for large water drop entrainment which potentially erodes the compressor blades. 
     An inlet fogging system includes a plurality of manifolds and nozzles that spray finely atomized water into the combustion air for the gas turbine. The fogging systems are located in the air intake duct and have the ability to humidify air to (or near) the saturation point and in most applications to supersaturate the air. Supersaturation of the air in the duct leads to the potential for the formation of large water drops that can erode compressor blades. Condensation of water in the intake duct also requires a drain system to dispose of the unwanted water. Water entrained in the air entering the compressor does cool the air being compressed to reduce compressor power consumption and thereby increase gas turbine power output. Inlet foggers are difficult to control, however, since measurement of supersaturation is impossible. 
     A compressor intercooling system involves cooling of air between sections of an air compressor, reducing the compressor power consumption and thereby increasing gas turbine power output. Cooling of the air by intercoolers have included (1) heat exchangers where energy removed from the air is rejected to an external media; and (2) evaporative intercoolers in which water is evaporated into the air being compressed. Heat exchanger type intercoolers remove energy from the gas turbine system which must be replaced by energy from fuel burned, so they significantly decrease efficiency, albeit they do increase power output. Evaporative intercoolers perform essentially the same function as inlet air supersaturation, but evaporative intercooling is performed in interstage pressure vessels, which are costly and which introduce pressure drops which degrade gas turbine performance. Moreover, intercooling systems typically must be used under all operating conditions. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention relates to an integrated air saturation and supersaturation system for gas turbine combustion air to provide maximum augmentation of power and efficiency during high load operation at ambient air temperature in excess of a practical minimum temperature of about 40° F. (4.44° C.). 
     In the exemplary embodiments, the integral system includes a spray type or media type evaporative cooler which introduces atomized water into the gas turbine inlet air in the inlet region of the intake duct (well upstream of the compressor inlet) which humidifies the air with water at or near the saturation point. At the same time, water spray nozzles are located in the gas turbine air intake duct in close proximity to the compressor inlet, at the outlet end of the intake duct, which introduce finely atomized water to the previously humidified combustion air to supersaturate it and thus cool the compressor as explained further herein. 
     The system also includes a control arrangement to deliver and manage the saturation and supersaturation water introduced into the gas turbine inlet or combustion air to optimize the gas turbine performance augmentation within the overall limits of the gas turbine components. 
     Accordingly, in its broader aspects, the present invention relates to a gas turbine combustion air cooling system comprising a duct having an inlet region and an outlet, said duct adapted to supply ambient air to an inlet of a compressor; a first set of nozzles for spraying atomized water into the ambient air at a location adjacent the duct inlet; a second set of nozzles for spraying atomized water into the ambient air to supersaturate the ambient air at a location proximate the compressor inlet; and control means for apportioning water to the first and second sets of nozzles. 
     In another aspect, the invention relates to a method of augmenting gas turbine power output in a system comprising a gas turbine, a combustor and a compressor comprising a) saturating combustion air upstream of an inlet to the compressor with water to cool the combustion air to a temperature at or near the wet bulb temperature; and b) supersaturating the combustion air at a location closely adjacent the inlet to the compressor to thereby permit liquid water entrained in the combustion air to enter the compressor where it is evaporated to cool the air being compressed in the compressor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic flow diagram illustrating a first exemplary embodiment of the invention; 
     FIG. 2 is a schematic flow diagram illustrating a second exemplary embodiment if the invention; and 
     FIG. 3 is a schematic flow diagram illustrating a third exemplary embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, the gas turbine  10  includes a compressor  12 , a combustor  14 , and the turbine  16 , with the compressor and turbine sharing a common rotor  18  connected to a load device (for example, a generator)  20 . 
     The integrated intake air humidification system in accordance with this first embodiment of the invention includes intake air duct work which supplies ambient air to the inlet of the compressor  12 . The duct work includes an ambient air flow inlet region  22  which may incorporate, in the direction of flow, weather louvers or a weather hood  24 , an air filter  26 , and a plurality of saturating water spray nozzles  28 ,  30  which are fixed within respective manifolds  32 ,  34 . The inlet region  22  tapers down to a duct  36  which may incorporate a conventional silencer  38 , an optional air heating system  40  (for use only at low or part load conditions in a low NOx mode) and a debris screen  42 . The duct  36  feeds the air into an inlet bell mouth  44  of the compressor  12  with flow arrows indicating the flow or air into the compressor. Closely adjacent the compressor inlet bell mouth  44  along one side of the duct  36 , there are a pair of supersaturation water manifolds  46  and  48 , each having sets of water spray nozzles  50  and  52 , respectively. 
     A water storage tank  54  receives water from a supply source (not shown), and supplies water via pump P to the supersaturating water manifolds  46  and  48  by means of conduits  56 ,  58  and  60 , as well as to the saturating water manifolds  32  and  34  by means of conduits  56 ,  62  and  64 . 
     A control system generally indicated at  66  (including a microprocessor and appropriate software) controls the flow of water to the supersaturating water manifolds  46 ,  48  as well as to the saturating water manifolds  32 ,  34 . Included in the control system is a water flow sensor  68  which monitors water exiting the pump P, as well as water flow sensors  70  and  72  which monitor the flow of water to the manifolds  46 ,  48 , respectively. 
     A dry bulb temperature sensor  74  monitors the temperature of the inlet air between the filter  26  and the manifolds  32 ,  34 , and additional water flow sensors  76  and  78  monitor the flow of water to the saturating water spray manifolds  32 ,  34 . An ambient air dew point temperature or humidity sensor  80  forwards temperature or humidity information to the control system  66  from a position just outside the inlet region  22 . A second dry bulb temperature sensor  82  provides temperature information to the control system  66  from a location beyond the debris screen  42  but upstream of the compressor inlet bell mouth  44 . A water saturated air flow sensor  84  monitors the air flow upstream of the compressor inlet  44 . 
     Conventional valves are utilized in conjunction with the control system  66  to control the flow of water. For example, a minimum flow control valve  86  controls the water flow in conduit  56  from pump P. Similarly, flow control valves  88  and  90  control the flow of water to supersaturation manifolds  46 ,  48  through conduits  58  and  60 . Control valves  92 ,  94  control the flow of water to saturation manifolds  32 ,  34  through conduits  62  and  64 . 
     Turning to FIG. 2, reference numerals are used which are similar to those used in FIG. 1 for corresponding components, and except where appropriate, only the structural and functional differences are discussed in detail. In this second embodiment, the integrated gas turbine intake air humidification system which eliminates the saturating water spray manifolds  32  and  34  and associated saturating water spray nozzles  28  and  30  in the inlet region  22  of the intake duct in favor of a media type saturator  96  and mist eliminator  98 , located just downstream of the air filter  26 . In this embodiment, potable water is supplied to a holding tank  100  from a supply conduit  102 . This water is in turn supplied via pump  104  to the media type saturator  96  by means of a conduit  106 . The water flow to the media saturator  96  is determined by a blow down control valve  108  controlled by the control system  66 , with excess water drained via line  110 . A drain sump level transmitter  112  monitors the level of the potable water within the holding tank  100 , with the information transmitted to the control system  66 . Water for the supersaturating water manifolds  46 ,  48  and respective spray nozzles  50 ,  52  continues to be supplied from the water storage tank  50  as in the previously described embodiment. 
     In the FIG. 3 embodiment, where identical reference numerals are again used to indicate corresponding components, the supersaturating water manifolds  46 ,  48  and respective water spray nozzles  50 ,  52  utilized in the previously described embodiments are eliminated in favor of a supersaturating water manifold system located about the conduit  36  at a location immediately upstream of the compressor inlet bell mouth  44  (as opposed to across from the inlet). More specifically, water from the water storage tank  50  is supplied via conduits  58  and  60  to a pair of supersaturating water manifolds  114 ,  116 , respectively. These manifolds have supersaturation water spray nozzles  118 ,  120  which spray atomized water into the duct  36  in a direction transverse to the air flow. The system is otherwise similar to the system described in connection with FIG.  1 . 
     Common to all three embodiments are a number of key elements. First, the spray type evaporative nozzles  28 ,  30  (or media type saturator  96 ) are able to introduce atomized water into the gas turbine combustion air in the duct  36  well upstream of the compressor inlet bell mouth  44 , and thus humidify all of the air entering the duct. The air velocity here is low, so that evaporation of the water can be achieved with minimum entrainment of water. Governed by control system  66 , the saturating spray nozzles  28  and  30  apportion water to the inlet or combustion air to reduce the total air flow down to or near the wet bulb temperature to thereby humidify and cool all of the inlet air. This arrangement provides the lowest possible temperature for the air entering the compressor  12  to thereby achieve maximum gas turbine cycle temperature ratio and maximum flow of humidified air. Second, water spray nozzles  50 ,  52  (or  118 ,  120 ) in the gas turbine air intake duct immediately adjacent or immediately upstream of the compressor inlet bell mouth  44 , also governed by the control system  66 , introduce finely atomized water (or fog) to the now humidified inlet air to supersaturate it. The close proximity of nozzles  50  and  52  (or  118 ,  120 ) to the compressor minimizes the agglomeration of large droplets which could otherwise erode the compressor blades. The liquid water entrained in the humidified air at the compressor inlet bell mouth  44  is carried into the compressor blade path where it is evaporated to cool the air being compressed. This decreases the compressor power consumption and thereby increases the gas turbine power consumption and thereby increases the gas turbine power output. Third, the integrated control system optimizes the water supplied to the saturating section and supersaturating sections to achieve maximum gas turbine performance and efficiency, within the overall limits and operating parameters of the gas turbine and related components. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.