Composite cycle power plant and method for controlling emissions therefrom

Abstract

To provide systems and methods of heating a reduction catalyst for use in a power plant.SOLUTION: A combined cycle power plant (100) includes a first gas turbine engine (102) including a first turbine section (112), a second gas turbine engine (104) including a second turbine section (112) having an aft outlet (120) configured to discharge an exhaust gas stream (122), an emissions reduction system (128) configured to receive the exhaust gas stream (122) discharged from the second gas turbine engine (104), and configured to remove oxides of nitrogen from the exhaust gas stream (122), and an interstage extraction system (140) communicatively coupled with the first turbine section (112). The interstage extraction system (140) is configured to selectively extract turbine extraction air (142) from the first turbine section (112) for providing heat to the emissions reduction system (128).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to selective catalytic reduction systems, and more specifically, to systems and methods for heating a reduction catalyst for use in a power plant.

Background Art

[0002] Rotating machines such as gas turbines are often used to generate power for generators. At least some known gas turbines have a gas path that includes, in flow order, an intake, a compressor, a combustor, a turbine, and a gas outlet. The compressor and turbine sections include multiple rows of circumferentially spaced rotating buckets or blades coupled within a housing. At least some known turbine engines are used in cogeneration facilities and power plants. Such engines may have a high specific work output and power per unit mass flow rate. To increase operating efficiency, at least some known gas turbine engines can be operated at elevated combustion temperatures since engine efficiency generally increases as the combustion gas temperature increases.

[0003] However, operating a turbine engine at high temperatures can also increase the production of pollutant emissions such as nitrogen oxides (NO x ). To facilitate reduction of NO x emissions, at least some known gas turbine plants inject a reducing agent throughout the catalyst to convert NO x to elemental nitrogen. More specifically, the use of ammonia with a selective catalytic reduction (“SCR”) catalyst is a common technique for reducing NO x emissions. However, such NO x reduction reactions are generally only effective within a given temperature range above ambient temperature.

Summary of the Invention

[0004] In one aspect, a combined cycle power plant is provided. The power plant includes a first gas turbine engine including a first turbine section, a second gas turbine engine including a second turbine section having a rear outlet configured to discharge an exhaust gas stream, an emissions reduction system configured to receive the exhaust gas stream discharged from the second gas turbine engine and configured to remove nitrogen oxides from the exhaust gas stream, and an interstage extraction system communicatively coupled to the first turbine section. The interstage extraction system is configured to selectively extract turbine extraction air from the first turbine section to supply heat to the emissions reduction system.

[0005] In another aspect, a combined cycle power plant is provided. The power plant includes a first gas turbine engine including a first turbine section having a rear outlet configured to discharge a first exhaust gas stream, a first emissions reduction system configured to receive the first exhaust gas stream and configured to remove nitrogen oxides from the first exhaust gas stream, a second gas turbine engine including a second turbine section having a rear outlet configured to discharge a second exhaust gas stream, a second emissions reduction system configured to receive the second exhaust gas stream and configured to remove nitrogen oxides from the second exhaust gas stream. The power plant also includes an interstage extraction system communicatively coupled to the first turbine section and configured to selectively extract turbine extraction air from the first turbine section to supply heat to the second emissions reduction system.

[0006] In yet another aspect, a method for controlling emissions in a combined cycle power plant having a first gas turbine engine and a second gas turbine engine is provided. The method includes determining an operating temperature of an emissions reduction system for removing nitrogen oxides from an exhaust gas stream received from the second gas turbine engine, monitoring the temperature of the emissions reduction system, and selectively extracting turbine bleed air from a turbine section of the first gas turbine engine to supply heat to the emissions reduction system. The selective extraction is based on a comparison of a monitored temperature to the operating temperature.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0008] The embodiments described herein relate to a system and method for heating a reduction catalyst for use in a power plant. Specifically, the systems and methods described herein use gas turbine interstage extraction gas to heat the selective catalytic reduction (SCR) catalyst of a chemical injection grid and / or a heat recovery steam generator (HRSG) associated with a different gas turbine engine within the same combined cycle block. Interstage extraction is performed to facilitate reduction of emissions during startup and shutdown of the gas turbine engine that are formed when the catalyst is not operating within its effective operable temperature range. More specifically, turbine extraction air extracted from a first gas turbine engine is sent to a second gas turbine engine to raise the temperature of the catalyst. The extraction is actively controlled by a controller to achieve a desired HRSG exhaust gas flow temperature with the AIG and catalyst associated with the second gas turbine engine. Thus, by extracting gas from the turbine section, not only is it easier to control emissions from the power plant, but it is also easier to reduce the load during turndown operation during periods of low power demand.

[0009] Unless otherwise specified, words such as "generally", "substantially", and "approximately" used herein to represent approximations indicate that the terms so modified are not to the absolute or complete degree, but only to the approximate degree recognized by those skilled in the art. Thus, values modified by terms such as "approximately", "about", and "substantially" are not limited to the precisely stated values. In at least some instances, the words representing approximations can correspond to the accuracy of the instrument for measuring the value. In addition, unless otherwise specified, terms such as "first", "second", etc. are used herein merely as labels and are not intended to impose an order, position, or hierarchical requirement on the items referred to by these terms. Further, for example, a reference to a "second" item does not require, or exclude, the existence of a "first" or smaller numbered item, or a "third" or larger numbered item.

[0010] FIG. 1 is a schematic diagram of an exemplary combined cycle power plant 100. In an exemplary embodiment, the power plant 100 includes a first gas turbine engine 102, a second gas turbine engine 104, and a steam turbine 106. Each gas turbine engine 102 and 104 includes a compressor section 108, a combustor 110, and a turbine section 112 coupled together in flow sequence. During operation, the combustor 110 receives air 114 from the compressor section 108, receives fuel 116 from a fuel supply, and uses the fuel and air to produce a fuel-air mixture that is burned to produce combustion gas 118. The combustion gas 118 is conveyed through the turbine section 112 and discharged from a rear outlet 120 of the turbine section 112 as an exhaust gas stream 122.

[0011] In an exemplary embodiment, the power plant 100 also includes a first heat recovery system 124 associated with the first gas turbine engine 102 and a second heat recovery system 126 associated with the second gas turbine engine 104. Each heat recovery system 124 and 126 includes an emissions reduction system 128 and a heat recovery steam generator (HRSG) 130 coupled in fluid communication with the emissions reduction system 128. The emissions reduction system 128 includes a catalyst bed 131 and a chemical injection grid 132 in fluid communication with the catalyst bed 131.

[0012] During operation, the exhaust gas stream 122 is received in the emissions reduction system 128 to facilitate at least partial removal of nitrogen oxides (NO x ). For example, the chemical injection grid 132 injects a chemical such as ammonia into the exhaust gas stream 122 upstream of the catalyst bed 131. NO x reacts with the chemical across the surface of the catalyst bed 131 in the presence of oxygen to produce elemental nitrogen (N 2 ), water (H 2 O), and carbon dioxide (CO 2) is generated. Next, the reducing gas stream 134 is discharged from the emissions reduction system 128 due to its interaction with the feed water 136 within the HRSG 130. The reducing gas stream 134 heats the feed water 136 to generate steam 138, and the steam 138 is sent towards the steam turbine 106 to generate additional power.

[0013] As described above, the NO carried out within the emissions reduction system 128 x The reduction reaction may be effective only within a predetermined operating temperature range based on the catalyst material contained in the catalyst bed 131. Examples of catalyst materials include, but are not limited to, base metal oxides, platinum, and zeolite materials. In some embodiments, the temperature range can be between about 600°F and about 1000°F. Under steady-state operating conditions, the catalyst bed 131 can be heated to a predetermined operating temperature range through its interaction with the exhaust gas stream 122. Under other operating conditions, such as when the gas turbine engines 102 and 104 are in a temporary start-up or turn-down mode, the temperature of the exhaust gas stream 122 may be lower than that under steady-state operating conditions, and the temperature of the catalyst bed 131 may not be within the predetermined operating temperature range.

[0014] Accordingly, in an exemplary embodiment, the power plant 100 also includes an interstage extraction system 140 communicatively coupled to the turbine sections 112 of the gas turbine engines 102 and 104 to facilitate the supply of auxiliary heating to the emissions reduction system 128. The following description explains a scenario in which auxiliary heating is supplied from the first gas turbine engine 102 to the second heat recovery system 126 when the second gas turbine engine 104 is in a transient operating mode. However, it should be understood that the following description is also applicable to a scenario in which the first gas turbine engine 102 may be in a transient operating mode and the first heat recovery system 124 requires auxiliary heating.

[0015] In an exemplary embodiment, the inter-stage extraction system 140 selectively draws or extracts turbine extraction air 142 from the turbine section 112 of the first gas turbine engine 102 and routes it towards the second emissions reduction system 128 to supply heat thereto. The turbine section 112 includes a plurality of stages 144, and the turbine extraction air 142 can be drawn from any one or more of the stages 144. For example, in one embodiment, the stages 144 include a plurality of stages including at least a first stage 146 and a second stage 148 downstream of the first stage 146. The turbine extraction air 142 extracted from the first stage 146 is generally hotter than the turbine extraction air 142 extracted from the second stage 148. Thus, the turbine extraction air 142 can be extracted from one or both of the first stage 146 and / or the second stage 148 based on the desired amount of heat and extraction air to be supplied to the second heat recovery system 126.

[0016] The inter-stage extraction system 140 includes any number of valves associated with the plurality of stages 144 of the turbine 112. For example, the system 140 includes a first valve 150 in fluid communication with the first stage 146 and a second valve 152 in fluid communication with the second stage 148 to facilitate controlling the extraction of the turbine extraction air 142 from the turbine section 112. Further, a first temperature sensor 154 monitors the temperature of the catalyst bed 131, and a second temperature sensor 156 monitors the temperature of a quantity of chemical within the chemical injection grid 132. The valves 150 and 152, and the temperature sensors 154 and 156 are communicatively coupled to a controller 158 of the inter-stage extraction system 140. During operation, the controller 158 selectively opens and closes the valves 150 and 152 based on a comparison of the monitored temperatures to a predetermined operating temperature range.

[0017] For example, in one embodiment, the controller 158 receives feedback from the first temperature sensor 154 and compares the monitored temperature to a predetermined operating temperature range of the catalyst material within the catalyst bed 131. If the monitored temperature drops outside the predetermined operating temperature range, the controller 158 opens one or more of the valves 150 and 152 to supply heat directly or indirectly to the catalyst bed 131. In one embodiment, the turbine extraction air 142 is used to heat the catalyst bed 131 and is then sent to heat the feed water 136. The controller 158 continues to monitor the temperature of the catalyst bed 131 and selectively adjusts the positions of the valves 150 and 152 to maintain the temperature of the catalyst bed 131 within the predetermined operating temperature range, for example, while the load of the second gas turbine engine 104 continues to be adjusted.

[0018] In one embodiment, the controller 158 alternatively or additionally receives feedback from the second temperature sensor 156. As described above, the chemical injection grid 132 injects a chemical into the exhaust gas stream 122 upstream of the catalyst bed 131. The injected chemical contacts the catalyst bed 131. Thus, supplying heat to the chemical injection grid 132 facilitates raising the temperature of the chemical before it contacts the catalyst bed 131, and as a result, the turbine extraction air 142 is used to indirectly heat the catalyst bed 131 within the predetermined operating temperature range. Thus, if the monitored temperature of the catalyst material drops outside the predetermined operating temperature range, the controller 158 opens one or more of the valves 150 and 152 to supply heat to the chemical injection grid 132.

[0019] In some embodiments, the interstage extraction system 140 is operated when the power plant 100 is in a turndown mode. In the turndown mode, the output of one or both of the gas turbine engines 102 and 104 is reduced when the need for power is relatively low. In one embodiment, the output of both gas turbine engines 102 and 104 is reduced. In such a scenario, rather than holding the turbine extraction air 142 within the first turbine section 112 to generate power that may become unused, by operating the interstage extraction system 140, the first gas turbine engine 102 can be turndown in a more efficient manner by utilizing the energy obtained from the turbine extraction air 142.

[0020] FIG. 2 is a flow diagram showing an exemplary method 200 for controlling emissions in a combined cycle power plant. The method 200 includes a step 202 of determining an operating temperature of an emissions reduction system for use in removing nitrogen oxides from an exhaust gas stream received from a second gas turbine engine, a step 204 of monitoring the temperature of the emissions reduction system, and a step 206 of selectively withdrawing turbine extraction air from a turbine section of the first gas turbine engine to supply heat to the emissions reduction system, wherein the step of selectively withdrawing is based on the monitored temperature relative to the operating temperature.

[0021] The embodiments described herein relate to a system and method for heating a catalyst bed of a heat recovery steam generator (HRSG) associated with a different gas turbine engine coupled to the same combined cycle block using gas turbine interstage gas from a first gas turbine engine. The interstage extraction is performed to reduce emissions during startup and shutdown of different gas turbine engines formed when the catalyst is not operating within its effective operable temperature range. The extraction is actively controlled by a microprocessor-based controller with a predetermined sequence logarithm, particularly to control the extraction of the gas. The extracted gas is extracted from one or more different stages of the turbine section to achieve a desired HRSG exhaust gas flow temperature at the location of the AIG and catalyst associated with the second gas turbine engine. Thus, by extracting the gas from the turbine section, it becomes easier to control the emissions from the power plant.

[0022] The above description is intended to be illustrative only, and those skilled in the art will recognize that modifications can be made to the described embodiments without departing from the scope of the disclosed invention. For example, the process steps described herein may be modified, for example, in terms of duration, temperature, or time between cycles. Further other modifications within the scope of the invention will be apparent to those skilled in the art upon consideration of this disclosure, and such modifications are intended to be within the scope of the appended claims.

[0023] Exemplary embodiments of a combined cycle power plant have been described in detail above. The method of controlling emissions is not limited to the specific embodiments described herein. Rather, the steps of the method can be utilized separately and independently of the other steps described herein. For example, the method described herein is not limited to implementation in the combined cycle power plant described herein. Rather, the exemplary embodiments can be implemented and utilized in connection with many other applications.

[0024] Certain features of various embodiments of the present invention are shown in some drawings and may not be shown in others, but this is merely for convenience. Further, the reference to "one embodiment" in the above description is not intended to exclude the existence of additional embodiments incorporating the described features. According to the principles of the present invention, any feature in a drawing can be referenced and / or claimed in combination with any feature in any other drawing.

[0025] Although the present invention has been described with respect to various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the claims.

Explanation of Reference Numerals

[0026] 100 Combined cycle power plant 102 First gas turbine engine 104 Second gas turbine engine 106 Steam turbine 108 Compressor section 110 Combustor 112 First turbine section 114 Air 116 Fuel 118 Combustion gas 120 Rear exit 122 Exhaust gas flow 124 First heat recovery system 126 Second heat recovery system 128 Second emission reduction system 130 Heat recovery steam generator (HRSG) 131 Catalyst bed 132 Chemical injection grid 134 Reduction gas flow 136 Feed water 138 Steam 140 Inter-stage extraction system 142 Turbine extraction air 144 Stage 146 First stage 148 Second stage 150 First valve 152 Second valve 154 First temperature sensor 156 Second temperature sensor 158 Controller 200 Method

Claims

1. A combined cycle power plant (100), wherein the combined cycle power plant (100) comprises a first gas turbine engine (102) including a first turbine section (112); a second gas turbine engine (104) including a second turbine section (112) having a rear outlet (120) configured to discharge an exhaust gas stream (122); an emissions reduction system (128) configured to receive the exhaust gas stream (122) discharged from the second gas turbine engine (104) and configured to remove nitrogen oxides from the exhaust gas stream (122); an interstage extraction system (140) communicatively coupled to the first turbine section (112), the interstage extraction system (140) being configured to selectively extract turbine extraction air (142) from the first turbine section (112) to directly supply heat to the emissions reduction system (128); A combined cycle power plant (100) comprising the above.

2. The interstage extraction system (140) comprises at least one valve (150, 152) in fluid communication with one of a plurality of stages of the first turbine section (112); at least one temperature sensor (154, 156) configured to monitor the temperature of the emissions reduction system (128); a controller (158) communicatively coupled to the at least one valve (150, 152) and the at least one temperature sensor (154, 156), the controller (158) being configured to selectively open and close the at least one valve based on the monitored temperature; The combined cycle power plant (100) according to Claim 1, comprising the above.

3. The emissions reduction system (128) includes a catalyst bed (131), and the interstage extraction system (140) is in fluid communication with the catalyst bed (131) to selectively heat the catalyst bed (131) with the turbine extraction air (142). The combined cycle power plant (100) according to Claim 2.

4. The exhaust reduction system (128) further includes a chemical injection grid (132) in fluid communication with the catalyst bed (131), and the inter-stage extraction system (140) is in fluid communication with the chemical injection grid (132) to selectively heat the chemical injection grid (132) with the turbine extraction air (142). The combined cycle power plant (100) according to claim 3.

5. The combined cycle power plant (100) according to claim 2, wherein the controller (158) is configured to selectively open and close the at least one valve (150, 152) to maintain a temperature within a predetermined temperature range.

6. The combined cycle power plant (100) according to claim 2, wherein the at least one valve (150, 152) includes a first valve (150) in fluid communication with a first stage (146) of the plurality of stages and a second valve (152) in fluid communication with a second stage (148) of the plurality of stages.

7. The combined cycle power plant (100) according to claim 1, wherein the inter-stage extraction system (140) is operable only when the second gas turbine engine (104) is in a transient operating state.

8. The exhaust reduction system (128) is further configured to form a reducing gas stream (134) from the exhaust gas stream (122), and the combined cycle power plant (100) further includes a heat recovery steam generator (130) configured to receive the reducing gas stream (134) from the exhaust reduction system (128). The combined cycle power plant (100) according to claim 1.

9. A combined cycle power plant (100), wherein the combined cycle power plant (100) includes a first gas turbine engine (102) including a first turbine section (112) having a rear outlet (120) configured to discharge a first exhaust gas stream (122); a first exhaust reduction system (128) configured to receive the first exhaust gas stream (122) and configured to remove nitrogen oxides from the first exhaust gas stream (122); a second gas turbine engine (104) including a second turbine section (112) having a rear outlet (120) configured to discharge a second exhaust gas stream (122); A second emissions reduction system (128) configured to receive the second exhaust gas stream (122) and configured to remove nitrogen oxides from the second exhaust gas stream (122); An interstage extraction system (140) communicably coupled to the first turbine section (112), the interstage extraction system (140) being configured to selectively extract turbine extraction air (142) from the first turbine section (112) to directly supply heat to the second emissions reduction system (128); A combined cycle power plant (100) including the same. **Claim 10** The combined cycle power plant (100) according to claim 9, wherein the interstage extraction system (140) is further communicably coupled to the second turbine section (112), and the interstage extraction system (140) is configured to selectively extract turbine extraction air (142) from the second turbine section (112) to supply heat to the first emissions reduction system (128). **Claim 11** The interstage extraction system (140) At least one valve (150, 152) in flow communication with one of a plurality of stages of the first turbine section (112); At least one temperature sensor (154, 156) configured to monitor the temperature of the second emissions reduction system (128); A controller (158) communicably coupled to the at least one valve (150, 152) and the at least one temperature sensor (154, 156), the controller (158) being configured to selectively open and close the at least one valve (150, 152) based on the monitored temperature; The combined cycle power plant (100) according to claim 9, including the same. **Claim 12** The combined cycle power plant (100) according to claim 11, wherein the first and second emissions reduction systems (128) each include a catalyst bed (131) and a chemical injection grid (132) in flow communication with the catalyst bed (131), and the at least one temperature sensor (154, 156) is configured to monitor the temperature of the catalyst bed (131) or the temperature of the chemical in the chemical injection grid (132). **Claim 13** The combined cycle power plant (100) according to claim 11, wherein the controller (158) is configured to selectively open and close the at least one valve (150, 152) to maintain a temperature within a predetermined temperature range.

14. The combined cycle power plant (100) according to claim 11, wherein the at least one valve (150, 152) includes a first valve (150) in fluid communication with a first stage (146) of the plurality of stages and a second valve (152) in fluid communication with a second stage (148) of the plurality of stages.

15. The combined cycle power plant (100) according to claim 9, wherein the inter-stage extraction system (140) is operable only when the second gas turbine engine (104) is in a transient operating state.

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