Abstract:
A method and apparatus for filtering and cooling air used by a gas turbine. Heat conducting liquid is pumped from a reservoir pool, routed through a heat exchanger, and pumped through a plurality of spray nozzles and allowed to fall as a shower back into the pool. At least some of the heat is extracted from the liquid as it passes through the heat transducer. The energy to run the pump is provided by the transduction of waste heat from the heat conducting liquid and/or from the hot gasses passing through the gas turbine exhaust. The air intake for the turbine is routed through the shower, where foreign particles and contaminants are removed physically and/or chemically removed therefrom.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. Provisional Application Serial No. 60/135,064 filed May 20, 1999. 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0002]    The present invention generally relates to heat recovery devices and, more particularly, to a turbine inlet air cooler system.  
         BACKGROUND OF THE INVENTION  
         [0003]    Although electric power is utilized in diverse ways in the economy and demand remains high at all times, the demand for electric power nevertheless fluctuates markedly during the course of a day. Business demand is high throughout daylight hours in the operation of stores and offices, but diminishes significantly thereafter. Residential demand is highest in the evening hours. Industrial demand is relatively steady and high at all times. Other demands, such as for urban transportation, peak at differing times. Additionally, demand can vary greatly seasonally and with short-term changes in the weather. For example, electricity usage soars on abnormally hot days due to widespread use of air conditioning equipment.  
           [0004]    In an optimized power utilization system, all such demands would be complementary and thus provide a substantially constant power requirement which could be served readily by the various sources of electric power in a readily predictable manner. In reality, however, electric power demand is nowhere near constant.  
           [0005]    The uneven demand for electric power requires that power generation capacity be sufficiently great to accommodate the maximum instantaneous demand. This, in turn, leads to uneconomic operation of generally over-sized electric power generation facilities. One approach to this problem has been the encouragement of off-peak usage of electric power in an effort to restructure the demand pattern. Another approach has been the installation of additional generating facilities intended for use during the periods of peak power demand. For example, an electric utility may lease one or more gas turbine electric generators in order to bring on-line more power generation capacity during warmer months of the year.  
           [0006]    One such prior art gas turbine electric generator is illustrated in FIG. 1 and indicated generally at  10 . The turbine  10  is housed within a structure  12  having an air inlet  14  and an exhaust stack  16 . The gases exiting the top of the exhaust stack  16  are extremely hot, typically in the neighborhood of 900° F.  
           [0007]    This exhausted heat is energy that is not being utilized by the system, thus drastically lowering the efficiency of the turbine  10 . This heat represents energy that is consumed by the turbine  10  but not turned into useful generated electricity.  
           [0008]    Furthermore, the turbine  10  generally does not operate at peak efficiency due to the relatively high temperature of the ambient air entering the inlet  14 . This is because the air becomes less dense as its temperature increases, lowering the amount of energy per unit volume contained therein.  
           [0009]    Obviously, it would be desirable to recover the energy being lost as heat from the turbine  10  (or any other system that produces wasted heat exhaust) and convert this heat to a useful form. It would also be desirable to lower the temperature of the air entering the inlet  14  in order to improve the efficiency of the turbine  10 . The present invention is directed toward these goals.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention an air filtration and cooling system for treating air used by a gas turbine. One form of the present invention includes a reservoir pool of heat conducting liquid, from which heat conducting liquid is pumped through a plurality of spray nozzles and allowed to fall as a shower back into the pool. The energy to run the pump is provided by the transduction of waste heat from the turbine exhaust. The air intake for the turbine is routed through the shower, where foreign particles and contaminants are removed therefrom.  
           [0011]    Another form of the present invention includes a reservoir pool of heat conducting liquid, from which heat conducting liquid is pumped through a heat exchanger for cooling and then sprayed through a plurality of spray nozzles and allowed to fall as a shower back into the pool. The energy to run the pump is provided by the transduction of waste heat from the turbine exhaust. The air intake for the turbine is routed through the shower, where foreign particles and contaminants are removed therefrom while the air is cooled and densified.  
           [0012]    One object of the present invention is to provide an improved system for efficiently filtering and cooling gas turbine intake air. Related objects and advantages of the present invention will be apparent from the following description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a perspective view of a prior art gas turbine electric generator.  
         [0014]    [0014]FIG. 2 is a schematic diagram of a heat recovery system of the present invention.  
         [0015]    [0015]FIG. 3 is a plan view of a pair of heat recovery coil units of the present invention.  
         [0016]    FIGS.  4 A-B are schematic side elevational views of one of the heat recovery coil units of FIG. 3.  
         [0017]    [0017]FIG. 5 is a side elevational semi-schematic view of a first embodiment turbine inlet air cooler system of the present invention.  
         [0018]    [0018]FIG. 6 is a top plan semi-schematic view of a second embodiment turbine inlet air cooler system of the present invention.  
         [0019]    [0019]FIG. 7 is a top plan semi-schematic view of an evaporative cooler and turbine inlet of the present invention.  
         [0020]    [0020]FIG. 8 is a schematic diagram of the evaporative cooler of FIG. 7, detailing its filtering system.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and alterations and modifications in the illustrated device, and further applications of the principles of the invention as illustrated therein are herein contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0022]    The use of a heat recovery system of the present invention with a pair of gas turbine electric generators  10  is illustrated schematically in FIG. 2, and indicated generally at  20 . The heat recovery system  20  is illustrated in use with two turbines  10 , however it will be understood that the present invention may be used with any number of turbines  10 . In fact, the heat recovery system of the present invention may be used with any heat-producing device, and may be configured to work with any number of sources of such heat.  
         [0023]    [0023]FIG. 2 is a schematic top plan view, such that the tops of the heat exhaust stacks  16  are visible. In order to capture the heat emitted from the exhaust stacks  16 , a system of heat recovery coils  22  are positioned above the stack  16  on a superstructure supported by posts  24 . This allows the heat recovery coils  22  to be supported above the exhaust stacks  16  upon their own superstructure, thereby allowing the heat recovery system  20  to be installed without modification to the turbine  10 . The present invention also comprehends an embodiment in which the heat recovery coils  22  are attached to the top of the exhaust stack  16  or otherwise physically integrated with the turbine  10 .  
         [0024]    As is known in the art, the heat recovery coils work on a heat exchange principle, in which a heat conducting medium, such as water, is flowed through a series of coils in the path of the exhaust emitted by the exhaust stack  16 , such that the water within the coils is heated by the exhaust. If the water within the coils is caused to continuously flow, the heat captured from the exhaust is moved away from the exhaust stack  16  to a place where it can be recovered into useful energy. The use of water in the heat recovery coils  20  is a preferred embodiment of the present invention; however, any material may be used. For example, it is known in the art to use various oils for heat exchange (such as DOWTHERM manufactured by The Dow Corporation), in order to increase the temperature at which the heat recovery coils  22  may operate. It is also known in the art to pressurize the heat recovery medium, in order to allow it to absorb more heat. For example, water may be pressurized so that it may be heated to significantly higher temperatures before turning to steam than would be the case if the water were at normal atmospheric pressure. The present invention comprehends the use of any material for the heat exchange medium.  
         [0025]    In the preferred embodiment, the heat exchange water is pumped to the heat recovery coils  22  by means of a 16″ pipe  26  and is recovered from the heat recovery coils  22  by means of a 16″ return pipe  28 . In a preferred embodiment, the water entering the heat recovery coils  22  is at approximately 230° F., while the water exiting the heat recovery coils  22  is at approximately 270° F. This 40° F. increase in the temperature of the water represents energy that has been recovered from the exhaust of the stacks  16 . This heated water is pumped by a pumping package  29  into one or more chillers  30 , which maintains the flow of water through the system, and uses the chillers  30  for extracting the heat energy in the water, as is commonly known in the art. The number of chiller units  30  required for the application depends upon the quantity of heat being recovered from the turbines  10 . In a preferred embodiment, the pumping package  29  and chiller units  30  are contained within trailers in order to easily allow greater capacity to be added, or capacity to be taken away.  
         [0026]    As is known in the art, the chillers  30  extract heat energy from the water flowing through the heat recovery coils  22  and produce useful energy for any desirable purpose. For example, this transduced waste heat energy may be placed onto the electric grid that is being fed by the turbine generators  10 . As a further example, this transduced waste heat energy may be used to power air cooling devices  32  that are added to the air inlet  14  of each turbine  10 . The cooling devices  32  cool the inlet air to the turbine  10 , thereby increasing the efficiency of the turbine  10 . Use of the recovered energy for inlet air cooling is discussed in greater detail hereinbelow.  
         [0027]    One concern with the use of the heat recovery coils  22  in the path of exhaust gases as hot as those exiting the stack  16 , is that if the fluid within the coils  22  is allowed to heat to too high a temperature, an explosion is possible. For example, if water is flowing through the heat recovery coils  22 , and the temperature of the water is elevated above the boiling point of the water (at the pressure at which it is maintained), then the water will turn to steam, greatly expanding its volume and causing an explosion. Such a scenario may occur if the pumping package  29  fails and the water within the heat recovery coils  22  is not flowed at a high enough rate.  
         [0028]    In order to guard against this problem, the present invention provides for heat recovery coils  22  as configured in FIG. 3. Visible in the view of FIG. 3 is the superstructure  34  which rests upon the posts  24  and which holds the components of the heat recovery coils  22 . The superstructure  34  includes a central crossbeam  36  which crosses substantially over the centerline of the exhaust stack  16 .  
         [0029]    The heat recovery coil  22  comprises two separate coil units  38  which are independently plumbed to the inlet water pipes  26  and the outlet water pipes  28 . In turn, each of the coil units  38  comprises three individual coils in the preferred embodiment. The number of coils or coil units is not critical to the present invention, and is considered to be a matter of design choice.  
         [0030]    Each of the coil units  38  rides upon wheels or other structures which allow it to be slid upon the side rails of the superstructure  34 . In this way the coil unit  38  may be moved into or out of the path of the exhaust flow exiting the stack  16 . Furthermore, the coil unit  38  may be moved partially into the exhaust flow, moved entirely into the exhaust flow, or moved completely out of the exhaust flow. Each of the two coil units  38  may be moved independently. In the view of FIG. 3, the upper coil unit  38  is shown positioned completely within the exhaust flow, while the lower coil unit  38  is shown positioned completely out of the exhaust flow. It can be seen with reference to FIG. 3 that when both coil units  38  are positioned completely within the exhaust flow, all of the exhaust produced by the stack  16  is forced to flow around the coils of the coil units  38 . In a preferred embodiment, the coil units  38  are moved by means of an electric motor  40  which drives a rack and pinion system attached to the superstructure  34 ; however, the present invention comprehends the use of any means for moving the coil units  38 , the particular choice of motive means not being critical to the present invention.  
         [0031]    Because the water inlet pipes  26  and outlet pipes  28  are fixed and because the coil units  38  are moveable, some means must be provided for connecting these structures for water flow therebetween. In a preferred embodiment to the present invention, these connections are made by lengths of 5″ braided stainless steel flexible hose that connect both to the inlet pipes  26 /outlet pipes  28  and to the individual coils of the coil unit  38 . For each coil, one flexible hose  42  is provided for the inlet and a second flexible hose  42  is provided for the outlet. Therefore, for the coil units  38  illustrated in FIG. 3, three pairs of flexible hose  42  are required for each coil unit  38  (as illustrated in relation to the lower coil unit  38 ); only one pair of the hoses  42  is illustrated in relation to the upper coil unit  38 . As an alternative, each of the coils within the coil unit  38  may be chained together in a series, so that only one inlet hose  42  and one outlet hose  42  is required to service the entire coil unit  38 .  
         [0032]    The hoses  42  are provided in a length sufficient to reach between the pipes  26 ,  28  and the coil unit  38  when the coil unit  38  is moved to a position representing its maximum distance from the pipes  26 ,  28 . In the embodiment FIG. 3, this position is the position illustrated by the lower coil unit  38 . Conversely, when the coil unit  38  is moved to be completely within the exhaust path of the stack  16 , the hose  42  connections to the coil unit  38  will be very near the hose  42  connections to the pipes  26 ,  28 . Therefore, the hoses  42  will assume a generally U-shaped configuration therebetween. The hoses  42  are supported by a series of trays  44  no matter what position the hoses  44  are placed in. This is illustrated schematically in FIGS.  4 A-B. In the view of FIG. 4A, the coil unit  38  is positioned entirely over the stack  16 , and the hose  42  assumes its shortest overall dimension. In the view of FIG. 4B, the coil unit  38  has been moved completely away from the stack  16 , extending the hose  42  to its longest dimension. In either position, the tray  44  supports a portion of the hose  42 , and the U-shaped configuration of the hose  42  allows it to transition between these two extreme positions without kinking.  
         [0033]    With the configuration of the heat recovery coil  22  illustrated in FIG. 3, it is possible to actively control the position of the coil units  38  in relation to the temperature of the coil units  38 . A control system (not shown) may be integrated with the heat recovery coil  22  in order to measure the temperature of the coil units  38  by means of an appropriate sensor. Such sensor may measure the temperature of the coils themselves, or may measure the temperature of the heat exchange fluid flowing through the coils. Based upon this temperature, the control system may determine whether the coil units  38  should be moved farther into the stack  16  exhaust or farther away therefrom. The control system may activate the motor  40  in order to achieve such movement. Such control of the position of the heat recovery coil units  38  would not only prevent catastrophic failure of the system in the case of extremely elevated temperatures, but would also allow the temperature of the coil units  38  to be maintained at the optimum temperature for heat recovery. The position of the coil units  38  could therefore be continuously controlled by the control system in order to achieve this optimum temperature. The implementation of such a control system may utilize any appropriate hardware known in the art, and preferably utilizes a PLC control system commercially available from the Allen-Bradley Company.  
         [0034]    As a fail-safe safety measure, the heat recovery coil  22  is preferably designed such that failure of the control system will result in the coil units  38  automatically moving out of the exhaust path of the stack  16 . It is therefore necessary for the control system to actively command the coil units  38  to be in the path of the exhaust of the stack  16  at all times. Failure of the control system  40  to send such control signals (for example, if there is a loss of power to the control system) will result in the coil units  38  automatically retracting away from the exhaust stack  16 . If such a fail-safe were not provided, failure of the control system would result in the coil units  38  remaining in the path of the exhaust indefinitely, and could result in a dangerous elevation of temperature.  
         [0035]    Several methods for implementing such fail-safe measures may be used. For example, a cable may be attached to the side of the coil unit  38  which is opposite to the stack  16 . This cable may be routed through a pulley suspended from the superstructure  34  and a large weight attached to the other end of the cable. Upon a loss of a command signal from the control system activating the motor  40 , there would be nothing counteracting the gravitational pull on the weight, and the weight would act to pull the coil unit  38  away from the stack  16 . In an alternative embodiment, the rails of the superstructure  34  upon which the coil unit  38  rolls may be slightly angled away from the stack  16 . Therefore, upon loss of a control system signal activating the motor  40 , gravitational action upon the coil unit  38  will cause it to roll down this inclined ramp and away from the stack  16 . Other methods for automatically moving the coil units  38  away from the stack  16  upon a loss of control signal to the motor  40  will be apparent to those having ordinary skill in the art, and are comprehended by the present invention.  
         [0036]    As discussed hereinabove, the energy recovered by the heat recovery coils  38  may be used to power a system for cooling the air presented to the air inlet  14  of the turbine  10 . Cooling this inlet air increases the density of the air and therefore its energy per unit volume, thereby increasing the efficiency of the turbine  10 . With the system of the present invention, it is possible to cool the inlet air to the turbine  10  using only power recovered from the exhaust exiting the stack  16  in a substantially closed system.  
         [0037]    With reference to FIG. 5, there is illustrated a side elevational view of a first embodiment turbine inlet air cooler system of the present invention, indicated generally at  50 . The system  50  is similar to the system  20  of FIG. 2, in that heated heat recovery fluid from the heat recovery coils  22  is pumped through the pipe  28  by the pumping package  29  to the chillers  30  (here comprising a chiller unit  30 A and an associated evaporative cooler  30 B). The heat of this fluid is used to power the chillers  30  and in the process the temperature of the fluid is lowered approximately 50°. This lower temperature fluid is then returned to the heat recovery coils  22  through the pipe  26 . In the system  50 , however, the chillers  30  are not used solely for reducing the temperature of the heat recovery medium used in the heat recovery coils  22 . The chillers  30  are also used in conjunction with an evaporative cooler  52  which is used to cool the air entering the turbine inlet  14 , thereby increasing the efficiency of the turbine  10 .  
         [0038]    In a preferred embodiment of the present invention, the cooler  52  is an evaporative cooler available from Baltimore Aircoil (BAC). As is known in the art, an evaporative cooler operates by pumping water (or other fluid) to the top of the cooler  52  and spraying it downward. The air entering the cooler  52  is passed through this spray of water and is substantially cooled in the process. The cool, dense air leaving the evaporative cooler  52  is fed to the turbine air inlet  14  by means of one or more conduits  54 . The turbine  10  provides the suction which causes the air to move through the evaporative cooler  52 . Air enters the evaporative cooler  52  at the air inlet  56 .  
         [0039]    In the process of cooling the air moving through the cooler  52 , the water used by the cooler  52  absorbs heat. This water may be pumped to the chillers  30  through a conduit  58 , cooled and then returned to the cooler  52  by means of the conduit  60  to be used in cooling inlet air. In a preferred embodiment of the present invention, the chilled water entering the cooler  52  is maintained at approximately 40° F. After being used to coil the inlet air, the water is elevated to a temperature of approximately 50° F. and is then pumped to the chillers  30 .  
         [0040]    A top plan view of a second embodiment turbine inlet air cooler system of the present invention is illustrated, and indicated generally at  70 . The system  70  is similar to the system  50 , with the exception that inlet air coolers  52  are provided for two separate turbines  10 . The energy recovered by heat recovery coils  22  which are placed over the stack  16  of only one of the two turbines  10 , is sufficient to power the chillers  30  which provide chilled water for both inlet air evaporative coolers  52 .  
         [0041]    The use of the evaporative cooler  52  to cool the inlet air to the turbine  10  represents a significant advancement over prior art turbine inlet air coolers which utilized heat exchanging coils. A typical turbine  10  will be located outdoors, often in a rural area, and will be ingesting on the order of 250,000 cubic feet per minute of inlet air. In order to prevent airborne debris, that are sucked in along with the inlet air, from fouling the turbine  10  as well as the prior art heat exchange coil, large and expensive media filters must be placed on the inlet side of the coolers. Not only are such filters expensive, but they represent a continuous and expensive maintenance cost in cleaning and/or replacing the filter material.  
         [0042]    The evaporative cooler  52  of the present invention passes the inlet air stream through a shower of falling water, which acts as a scrubber to remove even very fine particulate matter from the inlet air stream. The droplets of falling water interact with the incoming airborne particulate matter and force this matter out of the air stream and into a collecting pool at the bottom of the cooler  52 . As a result, the air exiting the cooler  52  into the conduits  54  is not only chilled, but is extremely clean.  
         [0043]    [0043]FIG. 7 illustrates a top plan view of a preferred embodiment evaporative cooler  52  of the present invention. FIG. 8 illustrates a side cross-sectional view of the evaporative cooler  52 . The cooler  52  contains several filters which are operative to clean the water collected in the bottom of the cooler, thereby removing any particulate matter which has been filtered from the incoming air stream. As shown in FIG. 8, the cooler  52  allows inlet air to enter the cooler through the air inlet  56 . This air is transferred to the conduit  54  by means of suction generated by the turbine  10 . Internal to the cooler  52  is a media structure or manifold  72 , which is preferably formed from polyvinyl chloride (PVC) formed into a shape to cause turbulent flow of the air therethrough. Cooling water is sprayed into the top of the media structure  72  by means of a plurality of nozzles  74 . This water falls through the media structure  72  by the force of gravity. Interaction within the media structure  72  between the falling water and the rising air causes the water droplets to interact with the incoming airborne particulate matter and to cause this matter to be deposited in the pool  76  formed in the bottom of the cooler  52 .  
         [0044]    Large scale debris, such as leaves, insects, seed hulls, etc., will float on the surface of the water collected in the pool  76  and may be removed by means of a top surface skimming device  78 . Water and debris within the top surface skimmer  78  is routed through a pump  80  to a basket strainer  82 , which removes the large scale particulate matter and returns the filtered water to the top of the pool  76 . By control of the valves  84 , the water coming from the pump  80  may be used to blow out the trapped debris in the basket strainer  82  to the drain  86 .  
         [0045]    Non-floating particulate matter will sink to the bottom of the pool  76 , where a bottom skimming system acts to keep the particulate matter suspended in the water and off of the bottom of the cooler  52 . This bottom skimming system removes water from the pool  76  by means of a pump  88  and routes this water to a series of water jets  90  aimed at the bottom surface of the cooler  52 . High velocity water exiting these water jets  90  acts to blast the particulate matter off of the bottom of the cooler  52  and suspend the matter into the water in the pool  76 .  
         [0046]    The main filtering of the water in the pool  76  is performed by a centrifugal filter  92  which is fed by a pump  94 . The centrifugal filter  92 , which is preferably of the type manufactured by LAKOS, is able to remove particulate matter from the water down to the 75 micron size. This particulate matter is deposited into a drain  96 . The clean water exits the centrifugal filter  92  into the conduit  98  which is controlled by a three-way valve  100 . In one position, the three-way valve  100  returns this filtered water to the chillers  30  in order to lower the temperature thereof prior to returning the chilled water to the cooler  52  supply line  60 . Alternatively, the three-way valve may be positioned so that the filtered water exiting the centrifugal filter  92  is routed directly to the evaporative cooler  52  supply line  60  without being returned to the chillers  30 . In this mode, the cooler  52  may be used strictly as a filter for the inlet air without cooling the air. This may be desirable in situations where the ambient air surrounding the turbine  10  is of a low enough temperature that cooling of this inlet air is not desirable.  
         [0047]    In one alternate embodiment, the pool  76  may be filled with another heat conducting liquid, such as ammonia. In this embodiment, ammonia is circulated through the turbine inlet air cooler system  50  as indicated above to produce an ammonia shower capable of cooling and cleaning the turbine inlet air. It should be noted that by varying the composition of the heat conducting liquid, chemical as well as physical air scrubbing and purifying effects may be enjoyed.  
         [0048]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.