Abstract:
An airflow control system for a gas turbine system according to an embodiment includes: an airflow generation system for attachment to a rotatable expander shaft of a gas turbine system, downstream of the gas turbine system, for drawing in a flow of ambient air through an air intake section into a mixing area; and an eductor nozzle for attachment to a downstream end of the turbine component for receiving an exhaust gas stream produced by the gas turbine system and for drawing in a flow of ambient air through the air intake section into the mixing area, the exhaust gas stream passing through the eductor nozzle into the mixing area; wherein, in the mixing area, the exhaust gas stream mixes with the flow of ambient air drawn in by the airflow generation system and the flow of ambient air drawn in by the eductor nozzle to reduce a temperature of the exhaust gas stream.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to co-pending U.S. application Ser. No. ______, GE docket numbers 280650-1, 280685-1, 280687-1, 280688-1, 280692-1, 280707-1, 280714-1, 280730-1, 280731-1, 280815-1, 281003-1, 281005-1 and 281007-1 all filed on ______. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The disclosure relates generally to power generation systems, and more particularly, to systems and methods for cooling the exhaust gas of power generation systems. 
         [0003]    Exhaust gas from power generation systems, for example a simple cycle gas turbine power generation system, often must meet stringent regulatory requirements for the composition of the exhaust gas released into the atmosphere. One of the components typically found in the exhaust gas of a gas turbine power generation system and subject to regulation is nitrogen oxide (i.e., NO x ), which includes, for example, nitric oxide and nitrogen dioxide. To remove NO x  from the exhaust gas stream, technology such as selective catalytic reduction (SCR) is often utilized. In an SCR process, ammonia (NH 3 ) or the like reacts with the NO x  and produces nitrogen (N 2 ) and water (H 2 O). 
         [0004]    The effectiveness of the SCR process depends in part on the temperature of the exhaust gas that is processed. The temperature of the exhaust gas from a gas turbine power generation system is often higher than about 1100° F. However, SCR catalysts need to operate at less than about 900° F. to maintain effectiveness over a reasonable catalyst lifespan. To this extent, the exhaust gas from a simple cycle gas turbine power generation system is typically cooled prior to SCR. 
         [0005]    Large external blower systems have been used to reduce the exhaust gas temperature of a gas turbine power generation system below 900° F. by mixing a cooling gas, such as ambient air, with the exhaust gas. Because of the possibility of catalyst damage due to a failure of an external blower system, a redundant external blower system is typically utilized. These external blower systems include many components, such as blowers, motors, filters, air intake structures, and large ducts, which are expensive, bulky, and add to the operating cost of a gas turbine power generation system. Additionally, the external blower systems and the operation of the gas turbine power generation system are not inherently coupled, thus increasing the probability of SCR catalyst damage due to excess temperature during various modes of gas turbine operation. To prevent SCR catalyst damage due to excess temperature (e.g., if the external blower system(s) fail or cannot sufficiently cool the exhaust gas), the gas turbine may need to be shut down until the temperature issue can be rectified. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    A first aspect of the disclosure provides an airflow control system for a gas turbine system, including: an airflow generation system for attachment to a rotatable expander shaft of a gas turbine system, downstream of the gas turbine system, for drawing in a flow of ambient air through an air intake section into a mixing area; and an eductor nozzle for attachment to a downstream end of the turbine component for receiving an exhaust gas stream produced by the gas turbine system and for drawing in a flow of ambient air through the air intake section into the mixing area, the exhaust gas stream passing through the eductor nozzle into the mixing area; wherein, in the mixing area, the exhaust gas stream mixes with the flow of ambient air drawn in by the airflow generation system and the flow of ambient air drawn in by the eductor nozzle to reduce a temperature of the exhaust gas stream. 
         [0007]    A second aspect of the disclosure provides a turbomachine system, including: a gas turbine system including a compressor component, a combustor component, and a turbine component; an airflow generation system coupled to a rotatable expander shaft of the gas turbine system, downstream of the gas turbine system, for drawing in a flow of ambient air through an air intake section into a mixing area; an eductor nozzle for attachment to a downstream end of the turbine component for receiving an exhaust gas stream produced by the gas turbine system and for drawing in a flow of ambient air through the air intake section into the mixing area, the exhaust gas stream passing through the eductor nozzle into the mixing area, wherein, in the mixing area, the exhaust gas stream mixes with the flow of ambient air drawn in by the airflow generation system and the flow of ambient air drawn in by the eductor nozzle to reduce a temperature of the exhaust gas stream; and a processing system for receiving the reduced temperature exhaust gas stream. 
         [0008]    A third aspect of the disclosure provides a gas turbine power generation system, including: a gas turbine system including a compressor component, a combustor component, a turbine component, and a shaft driven by the turbine component; an electrical generated coupled to the shaft to generated electricity; an airflow generation system coupled to a rotatable expander shaft of the gas turbine system, downstream of the gas turbine system, for drawing in a flow of ambient air through an air intake section into a mixing area; an eductor nozzle for attachment to a downstream end of the turbine component for receiving an exhaust gas stream produced by the gas turbine system and for drawing in a flow of ambient air through the air intake section into the mixing area, the exhaust gas stream passing through the eductor nozzle into the mixing area, wherein, in the mixing area, the exhaust gas stream mixes with the flow of ambient air drawn in by the airflow generation system and the flow of ambient air drawn in by the eductor nozzle to reduce a temperature of the exhaust gas stream; and a processing system for receiving the reduced temperature exhaust gas stream. 
         [0009]    The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawing that depicts various embodiments of the disclosure. 
           [0011]      FIG. 1  shows a schematic diagram of a simple cycle gas turbine power generation system according to embodiments. 
           [0012]      FIG. 2  depicts an enlarged view of a portion of the simple cycle gas turbine power generation system of  FIG. 1  according to embodiments. 
           [0013]      FIG. 3  is a schematic diagram of a simple cycle gas turbine power generation system according to other embodiments. 
       
    
    
       [0014]    It is noted that the drawing of the disclosure is not to scale. The drawing is intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawing, like numbering represents like elements between the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    As indicated above, the disclosure relates generally to power generation systems, and more particularly, to systems and methods for cooling the exhaust gas of power generation systems. 
         [0016]      FIG. 1  is a block diagram of a turbomachine system (e.g., a simple cycle gas turbine power generation system  10 ) that includes a gas turbine system  12  and an exhaust processing system  14 . The gas turbine system  12  may combust liquid or gas fuel, such as natural gas and/or a hydrogen-rich synthetic gas, to generate hot combustion gases to drive the gas turbine system  12 . 
         [0017]    The gas turbine system  12  includes an air intake section  16 , a compressor component  18 , a combustor component  20 , and a turbine component  22 . The turbine component  22  is drivingly coupled to the compressor component  18  via a shaft  24 . In operation, air (e.g., ambient air) enters the gas turbine system  12  through the air intake section  16  (indicated by arrow  26 ) and is pressurized in the compressor component  18 . The compressor component  18  includes at least one stage including a plurality of compressor blades coupled to the shaft  24 . Rotation of the shaft  24  causes a corresponding rotation of the compressor blades, thereby drawing air into the compressor component  18  via the air intake section  16  and compressing the air prior to entry into the combustor component  20 . 
         [0018]    The combustor component  20  may include one or more combustors. In embodiments, a plurality of combustors are disposed in the combustor component  20  at multiple circumferential positions in a generally circular or annular configuration about the shaft  24 . As compressed air exits the compressor component  18  and enters the combustor component  20 , the compressed air is mixed with fuel for combustion within the combustor(s). For example, the combustor(s) may include one or more fuel nozzles that are configured to inject a fuel-air mixture into the combustor(s) in a suitable ratio for combustion, emissions control, fuel consumption, power output, and so forth. Combustion of the fuel-air mixture generates hot pressurized exhaust gases, which may then be utilized to drive one or more turbine stages (each having a plurality of turbine blades) within the turbine component  22 . 
         [0019]    In operation, the combustion gases flowing into and through the turbine component  22  flow against and between the turbine blades, thereby driving the turbine blades and, thus, the shaft  24  into rotation. In the turbine component  22 , the energy of the combustion gases is converted into work, some of which is used to drive the compressor component  18  through the rotating shaft  24 , with the remainder available for useful work to drive a load such as, but not limited to, an electrical generator  28  for producing electricity, and/or another turbine. An expander shaft  124  may be coupled to the shaft  24  (or may comprise an extended portion of the shaft  24 ). The expander shaft  124  extends in a downstream direction  34  beyond the downstream end  30  of the turbine component  22 . The expander shaft  124  may rotate at the same rotational speed as the shaft  24 , or may be configured (e.g., with appropriate gearing) to rotate at a different rotational speed than the shaft  24 . 
         [0020]    The combustion gases that flow through the turbine component  22  exit the downstream end  30  of the turbine component  22  as a stream of exhaust gas  32 . The exhaust gas stream  32  may continue to flow in the downstream direction  34  towards the exhaust processing system  14 . The downstream end  30  of the turbine component  22  may be fluidly coupled via a mixing area  35  to a carbon monoxide (CO) removal system (including, e.g., a CO catalyst  36 ) and an SCR system (including, e.g., an SCR catalyst  38 ) of the exhaust processing system  14 . As discussed above, as a result of the combustion process, the exhaust gas stream  32  may include certain byproducts, such as nitrogen oxides (NO x ), sulfur oxides (SO x ), carbon oxides (CO x ), and unburned hydrocarbons. Due to certain regulatory requirements, an exhaust processing system  14  may be employed to reduce or substantially minimize the concentration of such byproducts prior to atmospheric release. 
         [0021]    One technique for removing or reducing the amount of NO x  in the exhaust gas stream  32  is by using a selective catalytic reduction (SCR) process. For example, in an SCR process for removing NO x  from the exhaust gas stream  32 , ammonia (NH 3 ) or other suitable reductant may be injected into the exhaust gas stream  32 . The ammonia reacts with the NO x  to produce nitrogen (N 2 ) and water (H 2 O). 
         [0022]    As shown in  FIG. 1 , an ammonia evaporator system  40  and an ammonia injection grid  42  may be used to vaporize and inject an ammonia solution (e.g., stored in a tank  46 ) into the exhaust gas stream  32  upstream of the SCR catalyst  38 . The ammonia injection grid  42  may include, for example, a network of pipes with openings/nozzles for injecting vaporized ammonia into the exhaust gas stream  32 . As will be appreciated, the ammonia and NO x  in the exhaust gas stream  32  react as they pass through the SCR catalyst  38  to produce nitrogen (N 2 ) and water (H 2 O), thus removing NO x  from the exhaust gas stream  32 . The resulting emissions may be released into the atmosphere through a stack  44  of the gas turbine system  12 . 
         [0023]    The ammonia evaporator system  40  may further include, for example, a blower system  48 , one or more heaters  50  (e.g., electric heaters), and an ammonia vaporizer  52 , for providing vaporized ammonia that is injected into the exhaust gas stream  32  via the ammonia injection grid  42 . The ammonia may be pumped from the tank  46  to the ammonia vaporizer  52  using a pump system  54 . The blower system  48  may include redundant blowers, while the pump system  54  may include redundant pumps to ensure continued operation of the ammonia evaporator system  40  in case of individual blower/pump failure. 
         [0024]    The effectiveness of the SCR process depends in part on the temperature of the exhaust gas stream  32  that is processed. The temperature of the exhaust gas stream  32  generated by the gas turbine system  12  is often higher than about 1100° F. However, the SCR catalyst  38  typically needs to operate at temperatures less than about 900° F. 
         [0025]    According to embodiments, an airflow generation system comprising, for example, a fan  56 , may be provided. As depicted in  FIG. 1 , the fan  56  may be coupled to the expander shaft  124  downstream of the turbine component  22  of the gas turbine system  12 . The fan  56  is configured to draw in cooling air (e.g., ambient air) through an air intake section  116  (indicated by arrows  126 ) that may be used to lower the temperature of the exhaust gas stream  32  to a level suitable for use with the SCR catalyst  38 . The fan  56  may be fixedly mounted (e.g. bolted, welded, etc.) to the expander shaft  124  of the gas turbine system  12 . To this extent, the fan  56  may be configured to rotate at the same rotational speed as the expander shaft  124 . The fan  56  may also be selectively coupled/decoupled to the expander shaft  124  using a clutch mechanism (e.g., an on-off clutch, a variable clutch, etc.). In embodiments, a pitch adjustment system may be provided to vary the angle of the blades of the fan  56  to adjust the flow of air generated by the fan  56 . 
         [0026]    The airflow generation system may further include a converging-diverging eductor nozzle  58  attached to the downstream end  30  of the turbine component  22 . As the exhaust gas stream  32  passes through the eductor nozzle  58 , a low pressure zone is created at the end of the eductor nozzle  58  within the mixing area  35 . This causes ambient air to be sucked into the mixing area  35  from the air intake section  116 . The ambient air mixes with and cools the exhaust gas stream  32 . In combination, the eductor nozzle  58  and the fan  56  are configured to draw in sufficient ambient air via the air intake section  116  to cool the exhaust gas stream  32  from about 1100° F. to about 900° F. in the mixing area  35 . 
         [0027]    Based on the temperature of the ambient air, the temperature of the exhaust gas stream  32  exiting the turbine component  22 , and/or other factors, the eductor nozzle  58  may provide a sufficient amount of cooling air to the mixing area  35 . In this case, the fan  56  may not be needed and may be decoupled from the expander shaft  124 . Alternatively, the pitch of the blades of the fan  56  may be adjusted to vary the flow of air drawn into the mixing area  35  by the fan  56 . 
         [0028]    An illustrative flow regulation system  60  is shown in  FIG. 2 . In this example, the flow regulation system  60  includes a plurality of guide vanes  64 . Each guide vane  64  may be selectively controlled (e.g., rotated) by an actuator  66 . Actuators  66  according to various embodiments are shown schematically in  FIG. 2 , but any known actuator may be utilized. For example, the actuators  66  may comprise an electro-mechanical motor, or any other type of suitable actuator. The actuators  66  may be independently and/or collectively controlled in response to commands from the airflow controller  100  to selectively vary the positioning of the guide vanes  64 . That is, the guide vanes  64  may be selectively rotated about a pivot axis by the actuators  66 . In embodiments, each guide vane  64  may be individually pivoted independently of any other guide vane  64 . In other embodiments, groups of guide vanes  64  may be pivoted independently of other groups of guide vanes  64  (i.e., pivoted in groups of two or more such that every guide vane  64  in a group rotates together the same amount). Position information (e.g., as sensed by electro-mechanical sensors or the like) for each of the guide vanes  64  may be provided to the airflow controller  100 . The airflow controller  100  may adjust the rotational angle of one or more of the guide vanes  64  to vary the amount of ambient air allowed to flow from the air intake section  116  into the mixing area  35 . 
         [0029]    A supplemental mixing system  68  ( FIG. 1 ) may be positioned within the mixing area  35  to enhance the mixing process. The supplemental mixing system  68  may comprise, for example, a static mixer, baffles, and/or the like. 
         [0030]    The airflow controller  100  ( FIG. 1 ) may be used to regulate the amount of ambient air drawn in by the eductor nozzle  58  and the fan  56  through the air intake section  116  in order to maintain a suitable temperature at the SCR catalyst  38  under varying operating conditions. That is, the amount of ambient air drawn in by the eductor nozzle  58  and the fan  56  and directed into the mixing area  35  may be varied (e.g., by adjusting the guide vanes  64  of the flow regulation system  60  under control of the airflow controller  100 , coupling/decoupling the fan  56  to/from the expander shaft  124 , etc.) as the temperature of the exhaust gas stream  32  changes, in order to regulate the temperature at the SCR catalyst  38 . 
         [0031]    The airflow controller  100  may receive data  102  associated with the operation of the gas turbine power generation system  10 . Such data may include, for example, the temperature of the exhaust gas stream  32  as it enters the mixing area  35 , the temperature of the exhaust gas stream  32  at the SCR catalyst  38  after mixing/cooling has occurred in the mixing area  35 , the temperature of the air drawn into the air intake section  16  by the compressor component  18  of the gas turbine system  12 , the temperature of the air drawn into the air intake section  116  by the eductor nozzle  58  and fan  56 , and other temperature data obtained at various locations within the gas turbine power generation system  10 . The data  102  may further include airflow and pressure data obtained, for example, within the air intake sections  16 ,  116 , at the flow regulation system  60 , at the fan  56 , at the inlet, outlet, or other locations of the eductor nozzle  58 , at the entrance of the compressor component  18 , at the downstream end  30  of the turbine component  22 , and at various other locations within the gas turbine power generation system  10 . Load data, fuel consumption data, and other information associated with the operation of the gas turbine system  12  may also be provided to the airflow controller  100 . The airflow controller  100  may further receive positional information associated with the guide vanes  64  or other system components. It should be readily apparent to those skilled in the art how such data may be obtained (e.g., using appropriate sensors, feedback data, etc.), and further details regarding the obtaining of such data will not be provided herein. 
         [0032]    Based on the received data  102 , the airflow controller  100  is configured to vary as needed the amount of ambient air drawn into the mixing area  35  to maintain the temperature at the SCR catalyst  38  at a suitable level. This may be achieved, for example, by varying the flow of ambient air drawn into the mixing area  35  by the eductor nozzle  58  and the fan  56  (this flow may be controlled, for example, by adjusting the position of one or more of the guide vanes  64  of the flow regulation system  60 , by increasing the rotational speed of the expander shaft  124 , by coupling/decoupling the fan  56  to/from the expander shaft  124 , etc.). 
         [0033]    The airflow controller  100  may include a computer system having at least one processor that executes program code configured to control the flow of ambient air into the mixing area  35  using, for example, data  102  and/or instructions from human operators. The commands generated by the airflow controller  100  may be used to control the operation of various components (e.g., such as actuators  66  and/or the like) in the gas turbine power generation system  10 . For example, the commands generated by the airflow controller  100  may be used to control the operation of the actuators  66  to control the rotational position of the guide vanes  64  of the flow regulation system  60 . Commands generated by the airflow controller  100  may also be used to activate other control settings in the gas turbine power generation system  10 . 
         [0034]    The use of an airflow generation system including an eductor nozzle  58  and fan  56  in lieu of conventional large external blower systems and/or other conventional cooling structures provides many advantages. For example, the need for redundant external blower systems and associated components (e.g., blowers, motors and associated air intake structures, filters, ducts, etc.) is eliminated. This reduces manufacturing and operating costs, as well as the overall footprint, of the simple cycle gas turbine power generation system  10 , while increasing reliability. 
         [0035]    Power requirements of the simple cycle gas turbine power generation system  10  are reduced because the eductor nozzle  58  required no moving parts and the fan  56  is coupled to, and driven by, the expander shaft  124  of the gas turbine system  12 . This configuration eliminates the need for large blower motors commonly used in conventional external blower cooling systems. 
         [0036]      FIG. 3  is a schematic diagram of the simple cycle gas turbine power generation system  10  according to other embodiments. In this embodiment, the air intake section  116  is fluidly coupled to the air intake section  16 . The flow regulation system  60   
         [0037]    may be used to control the amount of cooling air (e.g., ambient air) drawn in through the air intake section  116  by the eductor nozzle  58  and the fan  56 . 
         [0038]    In various embodiments, components described as being “coupled” to one another can be joined along one or more interfaces. In some embodiments, these interfaces can include junctions between distinct components, and in other cases, these interfaces can include a solidly and/or integrally formed interconnection. That is, in some cases, components that are “coupled” to one another can be simultaneously formed to define a single continuous member. However, in other embodiments, these coupled components can be formed as separate members and be subsequently joined through known processes (e.g., fastening, ultrasonic welding, bonding). 
         [0039]    When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element, it may be directly on, engaged, connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0040]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0041]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.