Patent Application
20140150447
1. Technical Field
The disclosure is related generally to a combined cycle power plant. More particularly, the disclosure is related to a load ramp and start-up system for a gas turbine and heat recovery steam generator (HRSG) of a combined cycle power plant and a method of increasing the load ramp rate and start-up rate processes of a combined cycle power plant.
2. Related Art
Conventional combined cycle power plants are used to generate power using a variety of power generation components. In its most basic form, conventional combined cycle power plants include a gas turbine, a heat recovery steam generator (HRSG) and a steam turbine. During operation of the combined cycle power plant, the gas turbine produces an exhaust gas while generating a portion of the power output for the combined cycle power plant. The HRSG, coupled to the gas turbine, receives the high-temperature exhaust gas from the gas turbine, and utilizes the energy in the high-temperature exhaust gas to convert water to steam. The steam generated by the HRSG is then utilized and expanded in the steam turbine for generating additional power for the combined cycle power plant.
In the conventional combined cycle power plant, the gas turbine is typically started first because the gas turbine may become fully operational in a very short amount of time. However, because the gas turbine is capable of starting so quickly, the HRSG of the combined cycle power plant is subject to a tremendous amount of thermal stress. More particularly, the gas turbine may produce high-temperature exhaust gas within seconds of being started. This high-temperature exhaust gas is then supplied to the HRSG, which typically has not been adequately warmed. As a result, the “cold” HRSG is subject to the high-temperatures of the exhaust gas generated by the gas turbine.
This thermal stress created by the exhaust gas may cause damage to the components of the HRSG. Although it may be beneficial to start the gas turbine for near-instantaneous power generation in the combine power cycle system, the negative effects caused by the thermal stress to the HRSG may outweigh any benefit. Particularly, repairing, or replacing HRSGs can be very expensive, time consuming and require the combined cycle power plant to be powered down.
A load ramp system for a heat recovery steam generator (HRSG) of a combined cycle power plant and a method of increasing the rate of a load ramp and a start-up process of a gas turbine system of the combined cycle power plant is disclosed. In one embodiment, the load ramp system includes: a conduit in fluid communication with a supercharger positioned upstream of a compressor of a gas turbine system in the combined cycle power plant, the conduit configured to direct a portion of supercharged air for use in cooling the HRSG in fluid communication with the gas turbine system during load ramp of the gas turbine system in the combined cycle power plant.
A first aspect of the invention includes a load ramp system for a heat recovery steam generator (HRSG) of a combined cycle power plant. The load ramp system includes: a conduit in fluid communication with a supercharger positioned upstream of a compressor of a gas turbine system in the combined cycle power plant, the conduit configured to direct a portion of supercharged air for use in cooling the HRSG in fluid communication with the gas turbine system during load ramp of the gas turbine system in the combined cycle power plant.
A second aspect of the invention includes a load ramp system for a heat recovery steam generator (HRSG) of a combined cycle power plant. The load ramp system includes: a conduit in fluid communication with a supercharger positioned upstream of a compressor of a gas turbine system in the combined cycle power plant, the conduit configured to direct a portion of supercharged air for use in cooling the HRSG in fluid communication with the gas turbine system during load ramp of the gas turbine system in the combined cycle power plant; and an airflow monitoring system operably connected to the supercharger, the airflow monitoring system including: an airflow sensor positioned within the conduit, the airflow sensor for sensing a flow rate of the directed portion of the supercharged air within the conduit; and a diagnostic system operably connected to the airflow sensor, the supercharger and an automated valve positioned within the conduit, the diagnostic system configured to: modify a position of the automated valve in response to the flow rate of the directed portion of the supercharged air differing from a predetermined flow rate.
A third aspect of the invention includes a method for increasing the load ramp rate of a gas turbine system of a combined cycle power plant. The method includes: providing a conduit in fluid communication with a supercharger positioned upstream of a compressor of the gas turbine system in the combined cycle power plant, the conduit configured to direct a portion of supercharged air for use in cooling an HRSG in fluid communication with the gas turbine system during load ramp of the gas turbine system in the combined cycle power plant; and modifying a position of an automated valve positioned within the conduit in response to a flow rate of the directed portion of the supercharged air differing from a predetermined flow rate.
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which:
It is noted that the drawings of the invention are not necessarily to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings.
As described herein, aspects of the invention relate to a combined cycle power plant. Specifically, aspects of the invention relate to the load ramp and start-up system for a heat recovery steam generator (HRSG) of a combined cycle power plant and a method of increasing the load ramp rate and start-up processes of a gas turbine system of the combined cycle power plant.
Turning to
In embodiments, as shown in
As shown in
During the load ramp process of combined cycle power plant 100, gas turbine system 102 may drastically increase is power output in a very short period of time (e.g., under 10 seconds). That is, when combined cycle power plant 100 undergoes a load ramp process, combustor 110 of gas turbine system 102 ignites a flame and compressed air from compressor 108 is mixed with additional fuel to form an increased amount of combustion product, which is ignited by the flame of combustor 110 and increases the drive of gas turbine 112. After passing through gas turbine 112, the additional combustion product, now exhaust gas, passes through exhaust duct 120 and into HRSG 104 to aid in the conversion of water to steam for steam turbine 106. As a result of gas turbine system 102 generating exhaust gas having a high temperature in a short period of time, HRSG 104 may be subject to excessive thermal stresses during the load ramp process of combined cycle power plant 100. More specifically, HRSG 104 may undergo a change in temperature from 250 degrees Celsius to 650 degrees Celsius in less than 10 seconds, which may cause damage to HRSG 104 and may shorten the operational life of HRSG 104.
Also shown in
As shown in
A remaining portion of the supercharged air generated by supercharger 128 may be provided to compressor 108 of gas turbine system 102 for increasing an inlet air flow rate of compressor 108. More specifically, supercharger 128 may be configured to initially compress inlet air before it reaches compressor 108 of gas turbine system 102. By initially compressing the inlet air, supercharger 128 may increase the inlet air flow rate, which in part may increase the load ramp capabilities of gas turbine system 102 and/or combined cycle power plant 100 by providing compressor 108 with an increased amount of inlet air that may be already partially compressed. Moreover, by positioning supercharger 128 in series upstream of inlet air cooling system 118, a portion of supercharged air supplied to gas turbine system 102 may be cooled, and may result in an increase in the air mass flow rate prior to the supercharged air entering compressor 108. As discussed above, the increased mass air flow rate may result in increased load ramp time and increased power generation by gas turbine system 102 of combined cycle power plant 100. In addition, utilizing supercharger 128 may reduce the fuel discharged in combustor 110 during load ramp, which may minimize toxic emissions and/or pollutants (e.g., CO, NOx, etc.) during the load ramp process of combine power cycle 100.
As shown in
Airflow monitoring system 132 of combined cycle power plant 100 may also include a diagnostic system 136 operably connected to airflow sensor 134, supercharger 128 and an automated valve 138 positioned within conduit 127. As discussed herein, diagnostic system 136 may be configured to modify a position of automated valve 138 during the load ramp process of gas turbine system 102. As shown in
Turning to
Storage device 140 of diagnostic system 136, as shown in
Flow rate compare module 142 of diagnostic system 136, as shown in
Component adjustment module 144 of diagnostic system 136 may be configured to obtain an indicator from flow rate compare module 142 in response to determining that the flow rate data obtained from airflow sensor 134 differs from the predetermined flow rate data 146 of storage device 140, and may adjust an operational characteristic of at least one of automated valve 138, or supercharger 128. More specifically, component adjustment module 144 may receive an indicator from flow rate compare module 142, and may be configured to modify a position of automated valve 138 in conduit 127 and/or reduce the supercharged air output of supercharger 128. In an embodiment where a position of automated valve 138 may be modified, diagnostic system 136, and more specifically component adjustment module 144, may one of substantially open or substantially close automated valve 138 of conduit 127. By substantially opening or substantially closing automated valve 138 of conduit 127, an increased or decreased amount of the portion of supercharged air may be directed to exhaust duct 120, and/or HRSG 104. In an alternative embodiment, where the supercharged air output of supercharger 128 may be reduced, diagnostic system 136, and more specifically component adjustment module 144, may reduce the power output of auxiliary motor 130. By reducing the power output of auxiliary motor 130, supercharger 128 may produce less supercharged air for gas turbine system 102 of combined cycle power plant 100.
Diagnostic system 136, and its respective components (e.g., storage device 140, flow rate compare module 142, etc.), may be configured as any conventional data processing system (e.g., computer system) capable of receiving, temporarily storing and transmitting/forwarding data within the system and to external components coupled to the system (e.g., automated valve 138). More specifically, diagnostic system 138 may be configured as any conventional hardware device (computer system controller), and the components of diagnostic system 138 (e.g., storage device 140, flow rate compare module 142, etc.) may be configured as software components stored within said computer system forming diagnostic system 138. In an example embodiment, diagnostic system 138 may be configured as a General Electric™ Speedtronic circuit board implemented on a conventional computer system, and may including associated software for performing the operational functions discussed herein.
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After the supercharged air is compressed, mixed with fuel, combusted and passed through gas turbine 112 to generate power in generator 115, the exhaust gas is moved through exhaust duct 120 to HRSG 104 of combined cycle power plant 100. In response to directing the portion of the supercharged air to exhaust duct 120, as shown in
In response to supplying the portion of the supercharged air to HRSG 104, as shown in
Following process P100, and the load ramp of gas turbine system 102 of combined cycle power plant 100, in process P102 a flow rate of the directed portion of the supercharged air is measured using airflow sensor 134 positioned within conduit 127. The flow rate data measured by airflow sensor 134 may be received or obtained by diagnostic system 136, as shown in
Following process P102, in process P104, the flow rate data of the directed portion of the supercharged air measured by airflow sensor 134 may be compared with predetermined flow rate data 146 stored on storage device 140. Process P104 may be executed by flow rate compare module 142 (
Continuing the example in process P102, flow rate compare module 142 may receive or obtain from airflow sensor 134 a measured flow rate of 100 m3/s. Simultaneously, flow rate compare module 142 may also receive or obtain from storage device 140 a predetermined flow rate of 100 m3/s. The predetermined flow rate of 100 m3/s may be based upon the operational characteristics of gas turbine system 102 and/or combined cycle power plant 100. More specifically, predetermined flow rate data 146 may require a 100 m3/s flow rate as a result of the exhaust gas generated by gas turbine system 102 having an above average temperature, and an ambient temperature surrounding gas turbine system 102 and HRSG 104 being below average. The predetermined flow rate may compensate for the exhaust gas having an above average temperature entering HRSG 104 having a below average operational temperature just prior to the load ramp process. That is, an increased desired flow rate may mitigate the thermal stresses that HRSG 104 may undergo due to the increased exhaust temperature and decreased ambient temperature. After obtaining or receiving each respective flow rate data (e.g., 100 m3/s, 100 m3/s), flow rate compare module 142 may then compare the flow rates and determine that the measured air flow of the supercharged air within conduit 127 is less than the predetermined flow rate (e.g., 100 m3/s<100 m3/s). Finally, flow rate compare module 142 may transmit an indicator to component adjustment module 144 indicating that the measured air flow of the supercharged air within conduit 127 is less than the desired flow rat of predetermined flow rate data 146.
After comparing the flow rate data in process P104, in process P106, a position of automated valve 138 positioned within conduit 127 may be modified in response to the flow rate of the directed portion of the supercharged air differs from predetermined flow rate data 146. More specifically, once component adjustment module 144 receives the indicator from flow rate compare module 142 that the flow rate data from airflow sensor 134 is greater than, or less than the predetermined flow rate data 146 from storage device 140, component adjustment module 144 may modify the position of automated valve 138 to adjust the flow rate of the supercharged air within conduit 127. In response to determining the measured flow rate is less that the desired flow rate of predetermined flow rate data 146, the position of automated valve 138 may be modified to allow more air to flow through conduit 127 (e.g., open valve). In response to determining the measured flow rate is greater that the desired flow rate of predetermined flow rate data 146, the position of automated valve 138 may be modified to allow less air to flow through conduit 127 (e.g., close valve).
Continuing the example in process P104, component adjustment module 144 may receive an indicator from flow rate compare module indicating that the measured air flow of the supercharged air within conduit 127 is less than the desired flow rate of predetermined flow rate data 146 (e.g., 100 m3/s<100 m3/s). As a result, component adjustment module 144 of diagnostic system 136 may communicate with automated valve 138 in order to modify the position of automated valve 138. More specifically, component adjustment module 144 may modify the position of automated valve 138 such that the automated valve 138 may be substantially opened to allow more supercharged air to flow through conduit 127.
By substantially opening automated valve 138, the measured flow rate within conduit 127 may equal the desired flow rate of predetermined flow rate data 146, and may direct the necessary supercharged air to exhaust duct 120 and/or HRSG 104 to substantially mitigate the thermal stress placed on HRSG 104 during the load ramp of gas turbine system 102. Additionally, once gas turbine system 102 and HRSG 104 generate the desired amount of power output for the load ramp process, and the thermal stress on HRSG 104 is substantially mitigated by providing the portion of supercharged air through conduit 127 to initially cool the exhaust gas, automated valve 138 may be substantially closed. By substantially closing automated valve 138, the majority of the supercharged air generated by supercharger 128 may be provided to compressor 108 of gas turbine system 102 to increase the power output of gas turbine system 102, and in conjunction, combined cycle power plant 100. A small portion of the supercharged air may still be directed to conduit 127 in order to continue to mitigate the thermal stress placed on HRSG 104 during operation of combined cycle power plant 100. However, the supercharged air directed to exhaust duct 120 and/or HRSG 104 via conduit 127 may be most beneficial during the load ramp process of gas turbine system 102 when HRSG 104 may undergo dramatic thermal stresses due to the high temperature exhaust gas entering HRSG 104.
Although the system and method described herein may be directed to a load ramp process of gas turbine system 102 of combined cycle power plant 100, it is understood the system may also be used during a start-up process of combined cycle power plant 100. More specifically, load ramp system 126 may be used in a substantially identical method as described herein for increasing a start-up rate for gas turbine system 102 and HRSG 104 of combined cycle power plant 100. Load ramp system 126 may also substantially preventing thermal stresses to HRSG 104 during the start-up process of combined cycle power plant 100, which may be caused by high temperature exhaust gas entering a “cold” HRSG 104.
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.
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.
