Exhaust Gas Heat Exchange for Ammonia Evaporation Using a Heat Pipe

Abstract

A heat pipe has a first portion positioned within an exhaust path of a gas turbine exhaust processing system and a second portion positioned in a heat exchange relationship with a flow path of a heat exchange fluid. The flow path of the heat exchange fluid includes an ammonia evaporator configured to evaporate ammonia received from an ammonia source. The heat pipe is configured to transfer thermal energy from exhaust gas in the exhaust path to the heat exchange fluid to enable the heat exchange fluid to vaporize the ammonia while cooling the exhaust gas to enable the gas turbine exhaust processing system to more effectively process the exhaust gas.

Description

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to turbine systems and, more specifically, to systems and methods for injecting cooling air into exhaust gas flow(s) produced by turbine systems.

Gas turbine systems typically include at least one gas turbine engine having a compressor, a combustor, and a turbine. The combustor is configured to combust a mixture of fuel and compressed air to generate hot combustion gases, which, in turn, drive blades of the turbine. Exhaust gas produced by the gas turbine engine may include certain byproducts, such as nitrogen oxides (NO_x), sulfur oxides (SO_x), carbon oxides (CO_x), and unburned hydrocarbons.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a gas turbine system includes an exhaust processing system fluidly coupled to an outlet of a turbine of a gas turbine engine, the exhaust processing system being configured to receive an exhaust gas having products of combustion generated by the gas turbine engine, and to process the exhaust gas before the exhaust gas exits the gas turbine system; an exhaust path of the exhaust processing system configured to flow the exhaust gas through the exhaust processing system. The system also includes an ammonia injection system having a source of ammonia and configured to introduce vaporized ammonia into the exhaust path; and a heat pipe having a first portion positioned within the exhaust path and a second portion positioned in a heat exchange relationship with a flow path of a heat exchange fluid used in the ammonia injection system. The heat pipe is configured to transfer thermal energy from exhaust gas in the exhaust path to the heat exchange fluid to enable the heat exchange fluid to vaporize the ammonia while cooling the exhaust gas to enable the exhaust processing system to more effectively process the exhaust gas.

In another embodiment, a heat pipe has a first portion positioned within an exhaust path of a gas turbine exhaust processing system and a second portion positioned in a heat exchange relationship with a flow path of a heat exchange fluid. The flow path of the heat exchange fluid includes an ammonia evaporator configured to evaporate ammonia received from an ammonia source. The heat pipe is configured to transfer thermal energy from exhaust gas in the exhaust path to the heat exchange fluid to enable the heat exchange fluid to vaporize the ammonia while cooling the exhaust gas to enable the gas turbine exhaust processing system to more effectively process the exhaust gas.

In a further embodiment, a gas turbine system includes a gas turbine engine configured to combust a mixture of fuel and an oxidant and to release exhaust gas resulting from the combustion; an exhaust processing system having an exhaust duct fluidly coupled to an outlet of a turbine of the gas turbine engine, the exhaust duct being configured to receive the exhaust gas released by the gas turbine engine. The exhaust processing system is configured to process the exhaust gas using a selective catalytic reduction (SCR) catalyst to reduce NO_x in the exhaust gas before the exhaust gas exits the gas turbine system. An exhaust path of the exhaust processing system is configured to flow the exhaust gas through the exhaust processing system. An ammonia injection system has an ammonia evaporator configured to receive aqueous ammonia from an ammonia source and vaporizes ammonia in the aqueous ammonia to enable the ammonia injection system to introduce vaporized ammonia into the exhaust path. A plurality of heat pipes is configured to receive thermal energy from exhaust gas in the exhaust duct to cool the exhaust gas before the exhaust gas reaches the SCR catalyst, transfers the thermal energy to a heat exchange fluid used in the ammonia evaporator to vaporize the ammonia.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a diagrammatical overview of an embodiment of a gas turbine system having an exhaust processing system that uses heat pipes for exhaust gas cooling and ammonia evaporation;

FIG. 2 illustrates a side elevational view of an embodiment of the gas turbine system of FIG. 1 in which the heat pipes have a first portion positioned in an exhaust duct and a second portion positioned in an ambient air heat exchanger;

FIG. 3 illustrates a schematic side elevational view of an embodiment of the exhaust processing system of FIG. 1 in which an exhaust processing control system controls the flow of ambient air and the flow of aqueous ammonia to achieve levels of ammonia evaporation suitable for use in the exhaust processing system;

FIG. 4 illustrates a cross-sectional view of an embodiment of the heat exchange configuration of the heat pipes in accordance with various configurations of the present disclosure; and

FIG. 5 illustrates a schematic side elevational view of another embodiment of the exhaust processing system of FIG. 1 in which the heat pipes are used to directly vaporize ammonia.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

As set forth above, gas turbine engines may produce a number of products of combustion. These products may include nitrogen oxides (NO_x), sulfur oxides (SO_x), carbon oxides (CO_x), and unburned hydrocarbons. Generally, reducing the relative concentration of these products within an exhaust gas may include reacting such products with other reactants in the presence of a catalyst. The reaction between NO_x and a reductant such as ammonia (NH₃), for example, may occur within an exhaust duct in the presence of a metal oxide catalyst of a selective catalytic reduction (SCR) system. The catalyst lowers the activation energy of a reaction between the NO_x and ammonia to produce nitrogen gas (N₂) and water (H₂O), thereby reducing the amount of NO_x in the exhaust gas before the exhaust gas is released from the gas turbine system. Such catalyst systems may be referred to as “DeNO_x” systems.

SCR systems may be used in a variety of different gas turbine systems, which range from relatively small scale systems to larger, heavy-duty gas turbine systems. Small scale systems produce exhaust gases having a relatively low temperature, while heavy-duty gas turbine systems produce exhaust gases with much higher temperatures. While exhaust gases from small scale systems (e.g., aero-derivative systems) have a temperature range that is generally amenable to the SCR process, the temperature of exhaust gases produced by heavy-duty systems is often much higher than acceptable operating ranges for the SCR process (e.g., temperatures suitable to maintain stability of the SCR catalyst). For example, in accordance with an embodiment of the present disclosure, the isotherm temperature of exhaust gases produced by a heavy-duty gas turbine engine may be greater than about 1000° F. (e.g., about 540° C.), such as between about 1100° F. and about 1300° F. (e.g., about 590° C. and about 705° C.), while an acceptable operating range of a “hot” SCR system (an SCR system having a relatively higher operating temperature range compared to other SCR systems) may be between about 800° F. and about 900° F. (e.g., about 425° C. and about 485° C.).

To reduce a temperature of these hot exhaust gases to the acceptable operating range for the SCR system, the exhaust gases may be mixed with tempering air to transfer heat from the exhaust gas to the tempering air and thereby cool the exhaust gas. Generally, the amount and temperature of tempering air therefore largely determines the amount of heat removed from the exhaust gas.

In an SCR system, as noted above, ammonia is reacted with NO_x in the exhaust gas to produce nitrogen and water. The SCR system may inject the ammonia into a stream of the exhaust gas, and the resulting mixture of ammonia and exhaust gas is directed to a catalyst of the SCR system. The source ammonia may include “wet” ammonia, which is an aqueous solution of ammonia, or “dry” ammonia, which is compressed or vapor ammonia that is substantially free of water. In embodiments where the source ammonia is wet ammonia, it may be desirable to separate the ammonia from the water in the aqueous solution. This may be accomplished by evaporating the ammonia away from the solution in an ammonia evaporator, which utilizes a feed of heated air to facilitate the evaporation process.

In accordance with aspects of the present disclosure, heat from the exhaust gas may be utilized to drive the ammonia evaporation process using one or more heat pipes. For example, it is now recognized that one or more heat pipes positioned along an exhaust path of the exhaust gas may conduct heat away from the exhaust gas and to one or more features used for ammonia evaporation. For instance, the one or more heat pipes may impart heat to an air flow to generate heated air for the ammonia evaporator. Additionally or alternatively, the one or more heat pipes may impart heat directly to an aqueous solution of ammonia to generate dry ammonia for injection by the SCR system. Accordingly, in general, the heat pipes of the present disclosure may be configured to transfer thermal energy from exhaust gas in an exhaust path to a heat exchange fluid (e.g., an air flow, or water within an aqueous ammonia solution) to enable the heat exchange fluid to vaporize the ammonia while cooling the exhaust gas. The cooling of the exhaust gas may enable the DeNOx catalyst to more effectively process the exhaust gas.

While the present disclosure may be applicable to a number of different gas turbine systems, such as combined cycle, the embodiments described herein may be particularly useful in simple cycle heavy-duty gas turbine systems that produce relatively high temperature exhaust gases (e.g., greater than 1000° F., about 540° C.). One example of a system having a configuration in accordance with certain aspects of the present disclosure is depicted in FIG. 1, which is a schematic view of an embodiment of a simple cycle gas turbine system 10. However, it should be noted that the embodiments set forth herein may also be applied to combined cycle systems.

As illustrated, the simple cycle gas turbine system 10 includes a gas turbine engine 12, which may include a heavy-duty gas turbine engine or an aero-derivative gas turbine engine. However, the present disclosure may be particularly applicable to embodiments where the gas turbine engine 12 is a heavy-duty gas turbine engine due to the much higher temperatures of exhaust gas 14 produced in such engines. Such aspects are discussed in further detail below.

The gas turbine system 10 may be part of a power plant, and may include a load 16 driven by the gas turbine engine 12 (e.g., a shaft 18 of the gas turbine engine 12 drivingly couples the gas turbine engine 12 to the load 16). By way of non-limiting example, the load 16 may include an electrical generator configured to output electrical power to an electric grid. The gas turbine engine 12 drives the load 16 by performing a combustion process, which produces the exhaust gas 14.

The simple cycle gas turbine system 10 also includes an exhaust processing system 20 configured to receive the exhaust gas 14 from the gas turbine engine 12, which may enable the exhaust gas 14 to be released from the simple cycle gas turbine system 10. More specifically, the exhaust processing system 20 may include features configured to reduce a temperature, and/or concentration of certain products of combustion in the exhaust gas 14 before releasing the exhaust gas 14 via a stack and/or to another process 22. Generally, the exhaust gas 14 flows along an exhaust path 24 from the gas turbine engine 12, through the exhaust processing system 20, and to the stack or other process 22.

The exhaust processing system 20 includes a selective catalytic reduction (SCR) catalyst 26, which may be a part of an SCR system configured to reduce a concentration of NO_x present within the exhaust gas 14. More particularly, the SCR catalyst 26 lowers the activation energy for a reaction between the NO_x and ammonia (NH₃), which is a reducing agent, to produce nitrogen (N₂) and water (H₂O). As noted above, while certain types of SCR catalysts are stable at relatively high temperatures, the exhaust gas 14 produced by the gas turbine engine 12 may still be much higher than is suitable for such catalysts.

To enable cooling of the exhaust gas 14 for more effective treatment of the exhaust gas 14 by the SCR catalyst 26, a heat pipe 28 positioned in a heat exchange relationship with the exhaust path 24 transfers thermal energy from the exhaust gas 14 to ambient air 30. This heat transfer may be facilitated by an ambient air heat exchanger 32 configured to place a flow of the ambient air 30 in a heat exchange relationship with the heat pipe 28. More particular arrangements of the heat pipe 28, the exhaust path 24, and the ambient air heat exchanger 32 are described below. In addition, while the present disclosure refers to “ambient air,” such disclosures are intended to encompass treated (e.g., filtered) ambient air or untreated ambient air. Indeed, the use of untreated ambient air may provide the advantage of reduced capital and operating costs associated with the gas turbine system 10.

The flow of the ambient air 30 is controlled using, by way of non-limiting example, an air flow control system 34. The air flow control system 34 may include features configured to enable monitoring and control of a flow of the ambient air 30 into the ambient air heat exchanger 32. Controlling the flow of the ambient air 30 into the ambient air heat exchanger 32 may also control the temperature and pressure of heated ambient air 36 produced by heat exchange between the heat pipe 28 and the ambient air 30.

In accordance with an aspect of the present disclosure, the heated ambient air 36 facilitates ammonia vaporization in an ammonia injection system 38 to generate vaporized ammonia 40. The vaporized ammonia 40, in turn, reacts with the exhaust gas 14 in the exhaust processing system 20 as set forth above. The air flow control system 34 may control provision of the heated ambient air 36 to the ammonia injection system 38 within particular operating ranges. For example, the air flow control system 34 may adjust a flow rate, a temperature, a pressure, or any similar parameter of the heated ambient air 36 to within a particular operating range depending on characteristics of the heated ambient air 36 suitable to achieve a level of ammonia vaporization appropriate for the exhaust processing system 20. The air flow control system 34 may be a part of a larger control system that is centrally located or distributed, as described in further detail below.

In situations where the ammonia injection system 38 does not necessarily need the total amount of the heated ambient air 36 exiting the ambient air heat exchanger 32, the air flow control system 34 may direct at least a portion of the heated ambient air 36 to a vent or other process 42. In this regard, the air flow control system 34 may control a split of the heated ambient air 36 between a first heated air flow path 44 leading to the ammonia injection system 38 and a second heated air flow path 46 leading to the vent or other process 42.

A side elevational view of an embodiment of the simple cycle gas turbine system 10 is shown in FIG. 2. The gas turbine engine 12 may generally power the gas turbine system 10, and includes one or more combustors 50 in which a fuel 52 and compressed oxidant 54 (e.g., compressed air) are mixed and undergo combustion. Other streams may also be present in the combustor to adjust combustion parameters as appropriate (e.g., exhaust gas diluent). Combustion products 56 generated in the one or more combustors 50 flow to a turbine 58, which extracts work from the combustion products 56 to rotate the shaft 18 of the gas turbine engine 12. The turbine 58 drives compression stages of an oxidant compressor 60 via the rotation of the shaft 18. Staged compression within the oxidant compressor 60 creates a pressure gradient that draws in ambient air 30 to continue the compression and combustion cycle.

The combustion products 56 exit the turbine 58 as the exhaust gas 14, which is directed into an exhaust duct assembly 62 fluidly coupled to an outlet 64 of the turbine 58. The exhaust duct assembly 62 may include segments fluidly coupled to one another, or may include a single continuous duct. In certain embodiments, the exhaust duct assembly 62 may be segmented to allow for ready maintenance and replacement as appropriate.

The exhaust duct assembly 62 includes an exhaust inlet 66 configured to receive the exhaust gas 14 from the gas turbine engine 12, and an exhaust gas outlet 68 in the form of a stack 70. Generally, features of the exhaust processing system 20 are located within the exhaust duct assembly 62 along the exhaust path 24 and are configured to sequentially process the exhaust gas 14 as the exhaust gas flows from the exhaust inlet 66 to the exhaust outlet 68. The processing may include encouraging turbulent flow of the exhaust gas 14 (which facilitates heat exchange), direct or indirect heat exchange, and catalytic byproduct removal, among others.

In the illustrated embodiment, such features include, but are not limited to, an ammonia injection grid 72 configured to inject the vaporized ammonia 40 into the exhaust path 24, the SCR catalyst 26, and a plurality of heat pipes 74 having respective first portions 76 (e.g., first ends) positioned along the exhaust path 24 upstream of the SCR catalyst 26. The heat pipe 28 described above with respect to FIG. 1 may be one heat pipe of the plurality of heat pipes 74 or, in other embodiments, the heat pipe 28 may be the only heat pipe positioned along the exhaust path 24.

The respective first portions 76 of the plurality of heat pipes 74 are illustrated as being positioned between the ammonia injection grid 72 and the SCR catalyst 26. This configuration may facilitate mixing of the exhaust gas 14 and the vaporized ammonia 40 by encouraging turbulent flow. Facilitating mixing in this manner may encourage homogeneity of the vaporized ammonia 40 and the exhaust gas 14 from both a compositional and thermal standpoint. However, the plurality of heat pipes 74 may have their respective first portions 76 positioned in any one or a combination of different locations along the exhaust flow path 24, including upstream and/or downstream of the ammonia injection grid 72.

During operation of the simple cycle gas turbine system 10, the exhaust gas 14 flows along the exhaust path 24 in a bulk flow direction 78. The first portions 76 of the plurality of heat pipes 74, being oriented crosswise relative to the bulk flow direction 78, contact the exhaust gas 14 (and vaporized ammonia 40, in the illustrated embodiment) and receive thermal energy from (and cool) the exhaust gas 14. Accordingly, the first portions 76 of the plurality of heat pipes 74 correspond to a “hot” side or end of the plurality of heat pipes 74.

In one non-limiting example, a temperature of the exhaust gas 14 entering the exhaust duct assembly 62 from the gas turbine engine 12 is between about 1000° F. (about 540° C.) and about 1200° F. (about 650° C.). This temperature range may be higher than suitable for the SCR catalyst 26. The plurality of heat pipes 74 reduces the temperature of the exhaust gas 14 to between about 800° F. (about 430° C.) and about 900° F. (about 480° C.) before the exhaust gas 14 reaches the SCR catalyst 26, which may be more suitable for the SCR catalyst 26. That is, the SCR catalyst 26 may be more efficient in catalyzing the reaction between the vaporized ammonia 40 and the NO_x in the exhaust gas 14 at such temperatures.

By way of non-limiting example, the plurality of heat pipes 74 may be arranged in rows of individual heat pipes 28 (e.g., substantially aligned along the bulk flow direction 78), columns of individual heat pipes 28 (e.g., substantially aligned crosswise relative to the bulk flow direction 78), staggered rows and columns of individual heat pipes 28, or any combination thereof. Thus, any suitable arrangement of the plurality of heat pipes 74 may be utilized that enables the first portions 76 to contact the exhaust gas 14.

Each heat pipe 28 of the plurality of heat pipes 74 is configured to rapidly conduct thermal energy from its respective first portion 76 (hot side or hot end) to a respective second portion 80 or end, which is a “cold” side or end of the heat pipe 28. It is presently recognized that the second portions 80 of the plurality of heat pipes 74 may be placed in thermal communication (e.g., a heat exchange relationship) with one or more fluids (e.g., a heat exchange fluid) to integrate cooling and heating processes utilized in the exhaust processing system 20. In the illustrated embodiment of FIG. 2, the cooling process involves cooling of the exhaust gas 14 and vaporized ammonia 40, and the heating process involves heating a fluid to produce, either directly or indirectly, the vaporized ammonia 40. Further, the embodiment depicted in FIG. 2 is not limited to the specific heat exchange relationship shown.

For example, in one embodiment, a first set of the plurality of heat pipes 74 may have respective second portions 80 positioned in a heat exchange relationship with the ambient air 30 (e.g., a first flow path of a heat exchange fluid). Further, a second set of the plurality of heat pipes 74 may have respective second portions 80 in a separate heat exchange relationship with the ambient air 30 (e.g., a second flow path of the heat exchange fluid). The second flow path may be separate from and arranged in parallel with respect to the first flow path, and may lead to the same or different destinations (e.g., be used for the same or different purposes).

The one or more fluids may be capable of receiving thermal energy from the second portions 80 of the plurality of heat pipes 74 (e.g., rejecting heat from the second portions 80 of the plurality of heat pipes 74). In the illustrated embodiment, the heat exchange fluid is ambient air 30 taken into the ambient air heat exchanger 32. However, other heat exchange fluids may be utilized. For example, the heat exchange fluid may be water in the aqueous ammonia subject to vaporization.

The air flow control 34 described with respect to FIG. 1 may include, as illustrated, a heated air flow control device 82 configured to controllably close or open a heated air path 84 (e.g., a heated air conduit) coupling an outlet 86 of the ambient air heat exchanger 32 to a heated air motivator 88. That is, the heated air flow control device 82 is configured to at least partially control a flow of the heated ambient air 36 to the heated air motivator 88. By way of non-limiting example, the heated air flow control device 82 may include a damper 90 coupled to an actuation mechanism 92. The actuation mechanism 92 may be communicatively coupled to an exhaust processing control system 94 configured to control operation of the damper 90 via the actuation mechanism 92. In certain embodiments, the heated air flow control device 82 may include a plurality of flow control devices.

The exhaust processing control system 94 may also regulate other operational aspects of the exhaust processing system 20. For example, the exhaust processing control system 94 is communicatively coupled to a variety of components that facilitate regulation of a flow rate, temperature, pressure, and so forth, of various fluids used to achieve suitable processing of the exhaust gas 14.

The exhaust processing control system 94 may be implemented on any suitable programmable architecture, such as an architecture including one or more processors 96 and one or more memory 98. Once programmed, the exhaust processing control system 94 may be considered to constitute a specially-configured device that is configured to control specific aspects relating to the exhaust processing system 20 based at least on algorithmic structure associated with its programming. In this way, the exhaust processing control system 94 be configured to perform certain functions, and these functions should be considered to denote a specific algorithmic structure of the exhaust processing control system 94, for example a structure associated with the one or more processors 96 and one or more memory 98.

By way of non-limiting example, the exhaust processing control system 94 may include one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more general purpose processors, or any combination thereof. Additionally, the memory 98 storing instructions executed by processors 96 of the exhaust processing control system 94 may include, but are not limited to, volatile memory, such as random access memory (RAM), and/or non-volatile memory, such as read-only memory (ROM), optical drives, hard disc drives, or solid-state drives. Further, the exhaust processing control system 94 may be implemented as a part of a larger control system (e.g., a gas turbine control system), and/or as a variety of control devices and/or subsystems distributed throughout simple cycle gas turbine system 10 (e.g., a distributed control system). The control devices and/or subsystems, therefore, may include any one or a combination of the processing and memory circuitry configurations noted above. Additionally, the exhaust processing control system 94 will generally include various input devices, and may include a user interface in the form of a display, or in the form of a connector that is accessible through wired or wireless connection with a computing device of the user.

The exhaust processing control system 94 is also communicatively coupled to the heated air motivator 88. The heated air motivator 88 is configured to motivate the heated ambient air 36 to the ammonia injection system 38, and may include a blower, fan, pump, compressor, or similar device. The heated air motivator 88 may create a pressure gradient between the ambient air heat exchanger 32 and its outlet 96, which functions to draw the ambient air 30 into the ambient air heat exchanger 32. Accordingly, the operation of the heated air motivator 88 may be controlled to affect a residence time of ambient air 30 in the ambient air heat exchanger 32, which in turn affects a temperature and pressure of the heated ambient air 36.

Additional features may be present upstream of the heated air motivator 88 to process the ambient air 30 and/or the heated ambient air 36. For example, one or more filters, silencers, and so forth, may be positioned upstream of an inlet 100 of the ambient air heat exchanger 32, within the ambient air heat exchanger 32, or along the heated air flow path 84, or any combination.

Again, the heated air motivator 88 directs the heated ambient air 36 to the ammonia injection system 38 for ammonia vaporization. More particularly, in the illustrated embodiment, the heated ambient air 36 is directed into an ammonia evaporator 102 of the ammonia injection system 38 through a heated air inlet 104. The ammonia evaporator 102 also includes an ammonia inlet 106 configured to receive ammonia (e.g., aqueous ammonia 107) from an ammonia source 108, and a vaporized ammonia outlet 110 fluidly coupled to the ammonia injection grid 72 by a vaporized ammonia flow path 111 (e.g., a vaporized ammonia conduit).

In accordance with present embodiments, vaporization of the aqueous ammonia 107 (ammonium hydroxide) generates the vaporized ammonia 40. The aqueous ammonia 107 may be held in a storage vessel 110 configured to store the aqueous ammonia 107 under controlled conditions (e.g., closed to the ambient environment). The storage vessel 110 may include a tank or similar vessel that allows the aqueous ammonia 107 to be controllably withdrawn.

To allow for such control, the ammonia injection system 38 may include various flow control and motivation features positioned along an aqueous ammonia flow path 112 coupling an outlet 114 of the storage vessel 110 to the aqueous ammonia inlet 106 of the ammonia evaporator 102. In the illustrated embodiment, an ammonia motivator 116 positioned along the aqueous ammonia flow path 112 is configured to create a pressure gradient between the ammonia source 108 and the ammonia evaporator 102. The pressure gradient causes the aqueous ammonia 107 to be withdrawn from the storage vessel 110 and motivated toward the ammonia evaporator 102. The ammonia motivator 116 may include a pump or similar feature capable of motivating a fluid having properties of the aqueous ammonia 107 in a suitable manner. As an example, the aqueous ammonia 107 held in the storage vessel 110 may include between about 15% and about 20% by volume or by weight ammonia (NH₃), with the remainder being water. In one embodiment, the aqueous ammonia 107 is a 19% by weight solution of ammonia in water.

An ammonia flow control unit 118 positioned along the aqueous ammonia flow path 112 may further adjust the flow of the aqueous ammonia 107, for example by controllably restricting the size of the flow path 112 (e.g., controllably closing or opening an orifice). The ammonia flow control unit 118 may be positioned downstream of the ammonia motivator 116 as shown, or may be positioned upstream of it (between the ammonia source 108 and the ammonia motivator 116).

The exhaust processing control system 94 is shown as being communicatively coupled to the ammonia motivator 116 and the ammonia flow control unit 118. In accordance with the illustrated embodiment, the exhaust processing control system 94 may control one or more operating parameters of the ammonia motivator 116 and/or the ammonia flow control unit 118 to control the amount of aqueous ammonia 107 provided to the ammonia evaporator 102 over time.

The ammonia evaporator 102 is schematically depicted as having an injection nozzle 120 fluidly coupled to the aqueous ammonia flow path 112. The injection nozzle 120 may be configured to inject a spray of the aqueous ammonia 107 into the ammonia evaporator 102 to encourage atomization. The aqueous ammonia 107 is also brought into heat exchange with the heated ambient air 36, which further encourages evaporation of the aqueous ammonia 107 to produce the vaporized ammonia 40. The heat exchange between the aqueous ammonia 107 and the heated ambient air 36 may be through direct contact of their associated flows, or indirect by way of heat exchange features within the ammonia evaporator 102. The vaporized ammonia 40 may be discharged as an overhead vapor through the vaporized ammonia outlet 110.

In the illustrated embodiment, the vaporized ammonia 40 is provided to the ammonia injection grid 72 via the vaporized ammonia flow path 111. The ammonia injection grid 72 includes a plurality of spray injectors 122 configured to introduce the vaporized ammonia 40 into the exhaust path 24. The plurality of spray injectors 122, as shown, may have the same axial position along the flow direction 78 but different radial positions with respect to the exhaust duct assembly 62.

The amount of vaporized ammonia 40 introduced into the exhaust path 24 may be controlled by the exhaust processing control system 94 to achieve a particular objective. For example, the amount of vaporized ammonia 40 introduced into the exhaust path 24 may be controlled over time to achieve a desired amount of NO_x reduction within the exhaust gas 14 (e.g., maximum NO_x reduction, reduction of NO_x to a mandated level). By way of non-limiting example, the amount of vaporized ammonia 40 introduced into the exhaust path 24 may be determined or otherwise controlled by the exhaust processing control system 94 a function of various parameters, such as the amount of exhaust gas 14 flowing through the exhaust path 24, a composition of the exhaust gas 14 (e.g., the level of NO_x in the exhaust gas 14), activity of the SCR catalyst 26, and so forth.

The amount of vaporized ammonia 40 used for NO_x reduction may, in turn, determine how the exhaust processing control system 94 controls intake and heating of the ambient air 30 in the ambient air heat exchanger 32. By way of non-limiting example, the exhaust processing control system 94 may control a temperature of the heated ambient air 36 and a flow rate of the heated ambient air 36 to respective levels that are appropriate to produce suitable amounts of the vaporized ammonia 40 (e.g., as a function of time, as a function of exhaust gas composition, or a combination).

The manner in which the exhaust processing control system 94 may monitor and control elements of the system 10 may be further appreciated with respect to FIG. 3, which is a schematic side view of an embodiment of the gas turbine system 10. More specifically, the embodiment of the gas turbine system 10 includes one or more exhaust sensors 130 positioned along the exhaust duct 62 at various positions in the exhaust flow direction 72. The one or more exhaust sensors 130 may be communicatively coupled to the exhaust processing control system 94 to enable monitoring of one or more parameters of the exhaust gas 14 as it flows through the exhaust duct 62. By way of non-limiting example, the exhaust sensors 130 may enable monitoring of temperature, pressure, oxygen levels, NO_x levels, CO levels, and/or similar parameters.

In the illustrated embodiment, for example, the exhaust sensors 130 may be configured to monitor one or more parameters of the exhaust gas 14 upstream of the ammonia injection grid 72, between the ammonia injection grid 72 and the plurality of heat pipes 74, between the plurality of heat pipes 74 and the SCR catalyst 26, and/or downstream of the SCR catalyst 26. As a more specific example, the exhaust gas 14 temperature may be monitored upstream of the SCR catalyst 26 to enable the exhaust processing control system 94 to determine appropriate flows and temperatures for the vaporized ammonia 40, the ambient air 30, the heated ambient air 36, and so forth. A first of the exhaust sensors 130 positioned upstream of the ammonia injection grid 72 may monitor a temperature of the exhaust gas 14 before mixing with the vaporized ammonia 40, while a second of the exhaust sensors 130 positioned between the ammonia injection grid 72 and the plurality of heat pipes 74 may monitor a temperature of a mixture of the exhaust gas 14 and the vaporized ammonia 40. Feedback relating to cooling of this mixture by the plurality of heat pipes 74 may be obtained by a third of the exhaust sensors 130 positioned between the plurality of heat pipes 74 and the SCR catalyst 26. Additionally or alternatively, the exhaust gas composition (e.g., NO_x levels) of treated exhaust gas 132 downstream of the SCR catalyst 26 may be monitored to determine appropriate flow rates and temperatures for the vaporized ammonia 40, the ambient air 30, the heated ambient air 36, and so forth.

The exhaust processing control system 94 is also communicatively coupled to features that enable the exhaust processing control system 94 to monitor and control such flows and temperatures. For instance, an ambient air sensor 134 may be a temperature sensor configured to enable the exhaust processing control system 94 to monitor a temperature of the ambient air 30. Based at least on this information, the exhaust processing control system 94 may determine the extent to which the ambient air 30 should be heated within the ambient air heat exchanger 32. This may be at least partially accomplished by controlling a flow rate of the ambient air 30 using one or more ambient air flow control devices 136 (e.g., including a fan and/or baffle) positioned upstream of the ambient air heat exchanger 32 via associated actuators 138 and/or using the flow control devices 88, 90 downstream of the ambient air heat exchanger 32.

The ambient air sensor 134 is positioned upstream of the ambient air heat exchanger 32 (e.g., upstream along a flow path of a heat exchange fluid), which may provide feed forward information to the exhaust processing control system 94. Indeed, the exhaust processing control system 94 may include one or more air flow control modules 140 (e.g., code implemented in software) configured to provide air flow control using the feed forward information and, additionally or alternatively, feedback information from a heated ambient air sensor 142 positioned downstream of the ambient air heat exchanger 32.

The exhaust processing control system 94 may also be communicatively coupled to features of the ammonia injection system 38, and may include one or more ammonia injection control modules 144 (e.g., code implemented in software) configured to provide control over operational aspects of the ammonia injection system 38. For example, the one or more ammonia injection control modules 144 may control the rate at which the ammonia injection system 38 produces the vaporized ammonia 40, a temperature of the vaporized ammonia 40, or similar parameters. As an example, the control may be performed based on a target NO_x level for the treated exhaust gas 132, which may be a feed forward input, as well as feedback obtained from the one or more exhaust sensors 130, such as a fourth of the exhaust sensors positioned downstream of the SCR catalyst 26. The feedback information may include, as one example, a measured level of NO_x within the treated exhaust gas 132.

The exhaust processing control system 94 may monitor parameters relating to the ammonia injection system 38, such as a temperature of the aqueous ammonia 107, flow rates of the aqueous ammonia 107 through the ammonia injection system 38, and so forth, via communication with one or more ammonia sensors 146. The exhaust processing control system 94 may use feedback generated by the one or more ammonia sensors 146 as a control input for the overall control of the injection of vaporized ammonia 40 into the exhaust duct 62.

Again, embodiments of the present disclosure may utilize one or more heat pipes 28 (e.g., the plurality of heat pipes 74) to cool the exhaust gas 14 within the exhaust duct 62. In this regard, while the illustrated embodiments of FIGS. 2 and 3 depict the heat pipe 28 (or plurality thereof) as being positioned between the ammonia injection grid 72 and the SCR catalyst 26, the present disclosure is not necessarily limited to this configuration. Indeed, embodiments of the present disclosure may use one or more heat pipes 28 positioned at any point along the exhaust flow direction 78 upstream of the SCR catalyst 26. Thus, certain embodiments of the gas turbine system 10 may include one or more heat pipes 28 positioned upstream of the ammonia injection grid 72, either in addition to or as an alternative to one or more heat pipes 28 positioned between the ammonia injection grid 72 and the SCR catalyst 26.

A non-limiting example embodiment of the thermal configuration the heat pipe 28 or plurality of heat pipes 74 is depicted in FIG. 4. More specifically, a cross-sectional elevation view of the heat pipe 28 is shown in FIG. 4. The heat pipe 28 includes an exterior casing 160 defining an outer surface of the heat pipe 28. An absorbent wick 162 is disposed inside of the exterior casing 160 and surrounds a vapor cavity 164. A working fluid 166 such as a metal (e.g., sodium), a hydrocarbon, ammonia, or water, is disposed in the vapor cavity 164. The first portion 76 of the heat pipe 28 (the hot side or hot end) is disposed such that the exhaust gas 14 flows across the first portion 76, while the second portion 80 (the cool side or cool end) is positioned in a heat exchange relationship with a heat exchange fluid along a flow path of the heat exchange fluid. As illustrated, the heat exchange fluid may include the ambient air 30 as shown in FIGS. 2 and 3, or may include water present within the aqueous ammonia 107, which his described in further detail below with respect to FIG. 5.

At the first portion 76, thermal energy from the exhaust gas 14 transfers to the heat pipe 28, causing the working fluid 166 in the wick 162 at the first portion 76 to evaporate and migrate into the vapor cavity 164. This evaporation may also cause some evaporative cooling of the first portion 76 to thereby additionally cool the exhaust gas 14 and produce a cooled exhaust gas 168.

The vapor migrates to the second portion 80 along the vapor cavity 164. The vapor condenses at the second portion 80 and is absorbed by the wick 162, releasing the thermal energy to the heat exchange fluid in a heat exchanger (e.g., the ambient air heat exchanger 32 or the ammonia evaporator 102). The working fluid 166 migrates via the wick 162 to the first portion 76.

Additionally or alternatively, one or more of the heat pipes 28 may have other configurations. By way of non-limiting example, one or more of the heat pipes 28 may be a solid state heat pipe in which thermal energy of the exhaust gas 14 is absorbed by a highly thermally conductive solid medium disposed within the casing 160. In such embodiments, the temperature difference between the first and second portions 76, 80 may cause thermal energy migration to enable the heat pipe 28 to heat the ambient air 30 or directly vaporize the ammonia.

As set forth above, in addition to or in lieu of heating air, the heat pipes 28 may be configured to directly heat and vaporize the aqueous ammonia 107. FIG. 5 is a schematic elevational view of an example embodiment having this configuration. In the illustrated embodiment, the heat pipe 28 or the plurality of heat pipes 74 have their respective second portions 80 positioned in the ammonia evaporator 102. In this embodiment, the heat exchange fluid that is heated to effect ammonia vaporization may include water within the aqueous ammonia 107. Similar to the embodiment in FIG. 2, the exhaust processing control system 94 may control the flow of the aqueous ammonia 107 to the ammonia evaporator 102 using one or more ammonia flow control devices such as the ammonia motivator 116 and/or the ammonia flow control unit 118 and associated actuators 180.

While the ammonia motivator 116 and/or the ammonia flow control unit 118 may be positioned upstream of the ammonia evaporator 102, one or more evaporated ammonia flow control devices 182 and associated actuators 184 may be positioned along the evaporated ammonia flow path 111 downstream of the ammonia evaporator 102. The exhaust processing control system 94 may be in communication with the one or more evaporated ammonia flow control devices 182 and associated actuators 184 to enable additional control of evaporated ammonia injection via the ammonia injection grid 72. The exhaust processing control system 94 of FIG. 5 may have substantially the same configuration as set forth above with respect to FIG. 3, but may adjust ammonia flow as the primary and/or sole control parameter in response to feedback from the exhaust sensors 130, the ammonia sensors 146, and so forth.

Additional or alternative configurations for the system 10 of FIG. 5 are also possible. For example, rather than causing direct and total vaporization of the aqueous ammonia 107, the heat pipe 28 may be used to pre-heat the aqueous ammonia 107 to reduce reliance on other sources of heat. For example, the heat pipe 28 may be used to pre-heat the aqueous ammonia 107 to enable easier ammonia evaporation using heated ambient air generated by electric air heating of ambient air. This may reduce reliance on electrical energy to drive electric heaters while enabling tunable control of the final evaporated ammonia temperature using additional control mechanisms (e.g., electric heaters).

Indeed, any of the embodiments described herein may be used in lieu of or in addition to other independent heat exchange fluid flow paths, which may be independent and parallel to the flow paths described herein. As a more specific example, certain embodiments, such as the embodiment of FIG. 3, may also utilize an additional independent and parallel flow path for the ambient air 30 that flows the ambient air 30 over electric heaters to enable the use of an additional temperature control mechanism for ammonia evaporation.

Technical effects of the invention include the heat integration of exhaust gas release from a gas turbine engine with ammonia evaporation in an exhaust processing system that reduces NO_x in the exhaust gas. The heat integration may be accomplished using one or more heat pipes, where the one or more heat pipes are transfer thermal energy from the gas turbine flue gas (the exhaust gas) and to a heat exchange medium that is ultimately used for ammonia vaporization. This may reduce reliance on other forms of energy that would otherwise be required for ammonia evaporation, thereby enhancing efficiency of the exhaust gas treatment process.

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.

Claims

1. A gas turbine system, comprising:

an exhaust processing system fluidly coupled to an outlet of a turbine of a gas turbine engine, the exhaust processing system being configured to receive an exhaust gas having products of combustion generated by the gas turbine engine, and to process the exhaust gas before the exhaust gas exits the gas turbine system;

an exhaust path of the exhaust processing system configured to flow the exhaust gas through the exhaust processing system;

an ammonia injection system having a source of ammonia and configured to introduce vaporized ammonia into the exhaust path; and

a heat pipe having a first portion positioned within the exhaust path and a second portion positioned in a heat exchange relationship with a flow path of a heat exchange fluid used in the ammonia injection system, and wherein the heat pipe is configured to transfer thermal energy from exhaust gas in the exhaust path to the heat exchange fluid to enable the heat exchange fluid to vaporize the ammonia while cooling the exhaust gas to enable the exhaust processing system to more effectively process the exhaust gas.

2. The system of claim 1, wherein the second portion of the heat pipe is positioned along an ambient air flow path leading to an ammonia evaporator of the ammonia injection system.

3. The system of claim 2, wherein the ammonia evaporator is configured to receive a flow of heated ambient air and place the heated ambient air in heat exchange with aqueous ammonia to generate vaporized ammonia.

4. The system of claim 3, comprising a flow control device positioned along the ambient air flow path and configured to control a flow of ambient air over the second portion of the heat pipe.

5. The system of claim 4, comprising a controller communicatively coupled to the flow control device configured to adjust the flow control device to adjust a temperature of the heated ambient air.

6. The system of claim 3, comprising an ammonia injection grid positioned along the exhaust path and fluidly coupled to the ammonia evaporator, wherein the ammonia injection grid is configured to receive the vaporized ammonia from the ammonia evaporator and to inject the vaporized ammonia into the exhaust path.

7. The system of claim 6, wherein the first portion of the heat pipe is positioned downstream of the ammonia injection grid.

8. The system of claim 1, wherein the first portion of the heat pipe is positioned upstream a selective catalytic reduction (SCR) catalyst of the exhaust processing system configured to reduce a concentration of nitrogen oxides (NOx) in the exhaust gas.

9. The system of claim 1, wherein the heat pipe is one of a plurality of heat pipes having respective first portions positioned within the exhaust path.

10. The system of claim 9, wherein less than all the heat pipes of the plurality of heat pipes have respective second portions positioned in the heat exchange relationship with the flow path of the heat exchange fluid.

11. The system of claim 9, wherein a first set of the plurality of heat pipes have respective second portions positioned in the heat exchange relationship with the flow path of the heat exchange fluid, and wherein a second set of the plurality of heat pipes have respective second portions in a separate heat exchange relationship with an additional flow path of the heat exchange fluid, wherein the additional flow path is separate from and arranged in parallel with respect to the flow path.

12. The system of claim 9, wherein all heat pipes of the plurality of heat pipes have respective second portions positioned in the heat exchange relationship with the flow path of the heat exchange fluid.

13. The system of claim 1, wherein the heat pipe is configured to transfer the thermal energy from the exhaust gas and to the heat exchange fluid using phase change of a fluid contained within the heat pipe.

14. The system of claim 1, wherein the heat pipe has a vapor cavity, a wick surrounding the vapor cavity, and a fluid, and wherein the heat pipe is configured to receive thermal energy from the exhaust gas at the first portion and to use the thermal energy to evaporate the fluid to cause the fluid to move from the wick and into the vapor cavity to thereby evaporatively cool the first portion, and wherein the heat pipe is configured to transfer thermal energy to the heat exchange fluid at the second portion to cause the fluid to cool and be re-absorbed by the wick.

15. The system of claim 1, wherein the source of ammonia is a storage tank holding aqueous ammonia, and wherein the flow path of the heat exchange fluid is configured to flow the aqueous ammonia, the heat exchange fluid being water in the aqueous ammonia such that the heat pipe is configured to directly evaporate the ammonia.

16. A system, comprising:

a heat pipe having a first portion positioned within an exhaust path of a gas turbine exhaust processing system and a second portion positioned in a heat exchange relationship with a flow path of a heat exchange fluid; and

wherein the flow path of the heat exchange fluid includes an ammonia evaporator configured to evaporate ammonia received from an ammonia source, and wherein the heat pipe is configured to transfer thermal energy from exhaust gas in the exhaust path to the heat exchange fluid to enable the heat exchange fluid to vaporize the ammonia while cooling the exhaust gas to enable the gas turbine exhaust processing system to more effectively process the exhaust gas.

17. The system of claim 16, wherein the heat pipe is configured to transfer the thermal energy from the exhaust gas and to the heat exchange fluid using phase change of a fluid contained within the heat pipe.

18. The system of claim 16, comprising a plurality of heat pipes including the heat pipe, wherein the gas turbine exhaust processing system includes a selective catalytic reduction (SCR) catalyst configured to reduce a concentration of NOx within the exhaust gas, and the plurality of heat pipes is configured to reduce a temperature of the exhaust gas from a first temperature to a second temperature, wherein the SCR catalyst has a better catalytic activity at the second temperature compared to the first temperature.

19. The system of claim 16, wherein the ammonia source includes a source of aqueous ammonia, and the heat exchange fluid is air, or is water of the aqueous ammonia.

20. A gas turbine system, comprising:

a gas turbine engine configured to combust a mixture of fuel and an oxidant and to release exhaust gas resulting from the combustion;

an exhaust processing system having an exhaust duct fluidly coupled to an outlet of a turbine of the gas turbine engine, the exhaust duct being configured to receive the exhaust gas released by the gas turbine engine, wherein the exhaust processing system is configured to process the exhaust gas using a selective catalytic reduction (SCR) catalyst to reduce NOx in the exhaust gas before the exhaust gas exits the gas turbine system;

an exhaust path of the exhaust processing system configured to flow the exhaust gas through the exhaust processing system;

an ammonia injection system having an ammonia evaporator configured to receive aqueous ammonia from an ammonia source and to vaporize ammonia in the aqueous ammonia and to enable the ammonia injection system to introduce vaporized ammonia into the exhaust path; and

a plurality of heat pipes configured to receive thermal energy from exhaust gas in the exhaust duct to cool the exhaust gas before the exhaust gas reaches the SCR catalyst and to transfer the thermal energy to a heat exchange fluid used in the ammonia evaporator to vaporize the ammonia.