System and process for active draft control of power plant

Abstract

To provide a process and system for active draft control through a combined cycle power plant (CCPP).SOLUTION: A CCPP has one turbomachine / heat recovery steam generator (HRSG) that is shut down (or offline), and a second turbomachine / HRSG that is online. The HRSG-supplied duct dampers can provide sealing air to ensure no back flow from the online turbomachine / HRSG to the shut-down turbomachine / HRSG of the CCPP. However, as a cooling flow is desired, a controlled flow may be implemented to allow a cooling flow to the shut-down turbomachine. This solution is useful in cooling CCPP configurations with multiple (e.g., 2) HRSGs discharging into a common exhaust stack without individual flues dedicated to the respective HRSGs, regardless of a turbomachine configuration.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to processes and systems for providing active draft control, and more particularly to processes and systems for controlling natural induced airflow through shut down combined cycle power plant (CCPP) equipment. [Background technology]

[0002] Combined cycle power plants, including turbomachinery and heat recovery steam generators (HRSGs), are often connected to power grids that require flexible operation to meet fluctuating power demands. Some power grids may require the turbomachinery to be shut down during periods of low power demand and then restarted to meet the power demands of the power grid. During operation, various components of the turbomachinery and HRSGs expand and contract. For example, there may be thermal expansion due to the relatively high temperatures associated with the operation of the turbines, and there may be mechanical expansion due to centripetal forces as internal components rotate.

[0003] Turbomachinery components expand and contract at different rates. The speed variations can be due to differences in material, shape, location, and purpose of each component. These differences are typically designed into the cooldown profiles of turbomachinery components and factored into the restart criteria for those components. To further accommodate the mismatch in expansion and contraction rates, turbomachinery is sometimes designed with clearances between the tips of the blades and the corresponding casing shrouds, commonly referred to as "tip clearances." Tip clearances allow the blades to expand without contacting the shroud, reducing the risk of damage to the turbine.

[0004] However, tip clearances significantly reduce the efficiency of the turbine during operation by allowing some of the heated gases to pass through the blades without doing useful work, wasting otherwise usable energy. A similar clearance can be designed into the compressor between the compressor blades and the compressor case, but it can also allow air to pass through the compressor blades.

[0005] During shutdown, ambient air infiltration may be naturally induced through the compressor and hot gas path of the turbomachine. The ambient air infiltration may be induced, for example, by natural convection of hot gases contained in the turbomachine, HRSG, and / or exhaust stack, and / or pressure differentials due to wind speed and direction at the turbomachine inlet. Such ambient air infiltration may cool the turbomachine and HRSG, which may be detrimental to a rapid restart due to thermal operating constraints imposed on the turbomachine and HRSG. If the HRSG and / or exhaust are not factored into the cool-down profile for the restart, this may raise concerns about whether the turbomachine can be restarted without undesirable friction.

[0006] If the turbomachine components are still in an "expanded" state, but the stator case cools and the clearances shrink to an unsuitable level for rotation of the turbomachine components, undesirable rubbing can occur due to expansion and restart attempts. Concerns such as rubbing and contraction / expansion can also be a consequence, for example, of retrofitting a turbomachine with a HRSG and / or exhaust, if the design and operating aspects of the retrofitted HRSG are not factored into the turbomachine cooling scheme.

[0007] Thus, the induced draft through the turbomachine and HRSG can be actively controlled to allow the turbomachine and HRSG to be restarted as quickly as possible. Traditionally, to counteract the induced draft, the turbomachine compressor's variable inlet guide vanes (i.e., vanes at the inlet of the compressor to control the flow of air through the turbomachine) have been closed, and / or intake dampers and louvers (e.g., in the inlet section upstream of the compressor) and / or stack dampers (e.g., in the exhaust stack) have been closed. Although the conventional approaches reduce the natural draft through the turbomachine and possibly the HRSG, due to leakage, a significant amount of induced natural draft may still exist. Summary of the Invention

[0008] All aspects, embodiments and features listed below may be combined in any manner technically possible.

[0009] One aspect of the disclosure provides a method for active ventilation control in a system including an operating turbomachine including a turbine and a heat recovery steam generator (HRSG) and an idle turbomachine including a turbine and a HRSG, the method including measuring a rotational speed of a turbine of the idle turbomachine, measuring an exhaust pressure of the idle turbomachine, measuring an idle time of the idle turbomachine, and increasing an exhaust gas temperature of the operating turbomachine to increase an idle flow rate from the HRSG of the operating turbomachine to equal a pressure drop across the turbine of the idle turbomachine based on at least one of the measured rotational speed, the measured exhaust pressure, and the measured idle time.

[0010] Another aspect of the present disclosure includes the above-mentioned aspects and adjusts the ventilated flow temperature of an operating turbomachine to provide sub-atmospheric pressure to a turbine of the shut-down turbomachine based on at least one of a measured rotational speed, a measured exhaust pressure, and a measured shut-down time.

[0011] Another aspect of the disclosure includes any of the aspects described above, wherein increasing the exhaust gas temperature of the operating turbomachine and adjusting the air flow temperature of the operating turbomachine are determined by comparing a measured rotational speed of a turbine of the shut-down turbomachine to a first threshold, comparing a measured exhaust pressure of the shut-down turbomachine to a second threshold, and comparing a measured shut-down time of the shut-down turbomachine to a third threshold.

[0012] Another embodiment of the present disclosure includes any of the above embodiments, wherein the first threshold is about 150 rpm, the second threshold is about -0.1 barg, and the third threshold is about 60 minutes.

[0013] Another aspect of the disclosure provides a system including: an idle turbomachine including a turbine and a heat recovery steam generator (HRSG); an operating turbomachine including the turbine and the HRSG; a common exhaust stack shared by the HRSG of the idle turbomachine and the HRSG of the operating turbomachine; and a control system configured to increase an exhaust gas temperature of the operating turbomachine to increase a ventilated flow rate from the HRSG of the operating turbomachine to equal a pressure drop across the turbine of the idle turbomachine based on at least one of a rotational speed of a turbine of the idle turbomachine, an exhaust pressure of the idle turbomachine, and an idle time of the idle turbomachine.

[0014] Another aspect of the present disclosure includes the above aspect, wherein the control system is further configured to adjust the airflow temperature of the operating turbomachine to provide subatmospheric pressure to a turbine of the shut-down turbomachine based on at least one of the measured rotational speed, the measured exhaust pressure, and the measured shut-down time.

[0015] Another aspect of the present disclosure includes any of the aspects described above, wherein the system further includes a sensor for measuring a rotational speed of a turbine of the turbomachine during shutdown, a sensor for measuring an exhaust pressure of the turbomachine during shutdown, and a timer for measuring a shutdown time of the turbomachine.

[0016] Another aspect of the disclosure includes any of the aspects described above, wherein the control system is further configured to increase an exhaust gas temperature of the operating turbomachine and regulate an airflow temperature of the operating turbomachine by comparing a measured rotational speed of a turbine of the shut-down turbomachine to a first threshold, comparing a measured exhaust pressure of the shut-down turbomachine to a second threshold, and comparing a measured shut-down time of the shut-down turbomachine to a third threshold.

[0017] Another aspect of the disclosure includes any of the aspects described above, wherein the control system is further configured to increase an exhaust gas temperature of the operating turbomachine and regulate a ventilated flow temperature of the operating turbomachine when a rotational speed of the turbine of the shut-down turbomachine is less than a first threshold, an exhaust pressure of the shut-down turbomachine exceeds a second threshold, and a shut-down time of the shut-down turbomachine exceeds a third threshold.

[0018] Another embodiment of the present disclosure includes any of the above embodiments, wherein the first threshold is about 150 rpm, the second threshold is about -0.1 barg, and the third threshold is about 60 minutes.

[0019] Another aspect of the disclosure includes any of the aspects described above, wherein the system further includes a first exhaust duct for connecting the HRSGs of the operating turbomachinery to the common exhaust stack, and a second exhaust duct for connecting the HRSGs of the shut-down turbomachinery to the common exhaust stack.

[0020] Another aspect of the present disclosure includes any of the above aspects, wherein at least one of the first exhaust duct and the second exhaust duct are directly connected to a common exhaust duct.

[0021] Another aspect of the present disclosure includes any of the aspects described above, wherein at least one of the first exhaust duct and the second exhaust duct includes a damper.

[0022] Yet another aspect of the disclosure includes a computer readable medium including computer executable instructions that, when executed, perform a method of active ventilation control through a system including an operating turbomachine including a turbine and a heat recovery steam generator (HRSG) and an idle turbomachine including a turbine and a HRSG, the method including measuring a rotational speed of a turbine of the idle turbomachine, measuring an exhaust pressure of the idle turbomachine, measuring an idle time of the idle turbomachine, and increasing an exhaust gas temperature of the operating turbomachine to increase a ventilation flow rate from the HRSG of the operating turbomachine to equal a pressure drop across the turbine of the idle turbomachine based on at least one of the measured rotational speed, the measured exhaust pressure, and the measured idle time.

[0023] Another aspect of the present disclosure includes the above-mentioned aspects and adjusts the ventilated flow temperature of an operating turbomachine to provide sub-atmospheric pressure to a turbine of the shut-down turbomachine based on at least one of a measured rotational speed, a measured exhaust pressure, and a measured shut-down time.

[0024] Another aspect of the disclosure includes any of the aspects described above, wherein increasing the exhaust gas temperature of the operating turbomachine and adjusting the air flow temperature of the operating turbomachine are determined by comparing a measured rotational speed of a turbine of the shut-down turbomachine to a first threshold, comparing a measured exhaust pressure of the shut-down turbomachine to a second threshold, and comparing a measured shut-down time of the shut-down turbomachine to a third threshold.

[0025] Another aspect of the disclosure includes any of the aspects described above, wherein increasing the exhaust gas temperature of the operating turbomachine and adjusting the ventilated flow temperature of the operating turbomachine occurs when a rotational speed of a turbine of the shut-down turbomachine is less than a first threshold, an exhaust pressure of the shut-down turbomachine exceeds a second threshold, and a shut-down time of the shut-down turbomachine exceeds a third threshold.

[0026] Another embodiment of the present disclosure includes any of the above embodiments, wherein the first threshold is about 150 rpm, the second threshold is about -0.1 barg, and the third threshold is about 60 minutes.

[0027] Two or more aspects described in this disclosure, including aspects described in the Summary of the Invention, may be combined to form an embodiment not specifically described herein.

[0028] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will become apparent from the description, drawings, and claims.

[0029] These and other features of the present disclosure may be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings, which set forth various embodiments of the present disclosure. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a schematic diagram of a combined cycle power plant (CCPP) including two gas turbomachines each equipped with a heat recovery steam generator (HRSG) sharing a common exhaust stack and a system for active ventilation control according to an embodiment of the disclosed technique. [Diagram 2] FIG. 1 is a schematic diagram of a CCPP including two gas turbomachines each equipped with a HRSG sharing a common exhaust stack and a system for active draft control in accordance with another embodiment of the disclosed technique. [Diagram 3] 1 is a flow chart of a process for active ventilation control through a CCPP in accordance with an embodiment of the disclosed technique. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Cooling schemes for combined cycle power plants (CCPPs), including the use of fans / blowers (hereafter "fans") followed by natural cooling, typically rely on the periodic opening of exhaust stack dampers. Cooling schemes for CCPPs may also typically rely on thermal draft, e.g., at subatmospheric levels, at the inlet of the exhaust stack of a heat recovery steam generator (HRSG).

[0032] In an embodiment of the disclosed technology, the CCPP cooling scheme typically allows fan flow to continue for several hours (e.g., 4 hours) after shutdown. When the fan flow is shut off, the fan flow can induce natural cooling flow. During base load operation of the gas turbomachine / HRSG, the pressure at the inlet of the HRSG exhaust stack may be slightly above atmospheric pressure, for example, due to friction losses in the exhaust stack being greater than buoyancy gains. In a particular embodiment of the disclosure, the pressure may be about 0.34 mbar or about 0.14 inches H2O.

[0033] In an embodiment of the disclosed technology, in a CCPP where one turbomachine / HRSG is shut down (or offline) and a second turbomachine / HRSG is online, duct dampers supplying the HRSG can provide sealing air so that there is no backflow from the online turbomachine / HRSG to the shut down turbomachine / HRSG of the CCPP. However, if cooling flow is desired, controlled flow may be implemented to allow cooling flow to the shut down turbomachine. This solution is useful for cooling CCPP configurations that have multiple (e.g., two) HRSGs exhausting to a common exhaust stack without separate flues dedicated to each HRSG, regardless of turbomachine configuration.

[0034] This application discloses a system and method for controlling naturally induced airflow drafts through power plant equipment (e.g., turbomachinery) during shutdown. Advantageously, by controlling the naturally induced airflow, heat loss from the turbomachinery stator casing and the HRSG outer casing during shutdown cycles is reduced. Drafting is induced either downstream (normal flow direction) or upstream (reverse or counter-flow direction) through the turbomachinery depending on the operating and environmental conditions. By reducing the heat loss during shutdown, the disclosed system and method can increase the clearance between the blade tips and the stator case during hot restart cycles to avoid tip rub during hot restart. In other words, by reducing the heat loss of the stator casing during shutdown cycles, a larger clearance can be achieved during hot restart cycles, thereby reducing the clearance during steady state cycles and increasing efficiency.

[0035] Referring now to the drawings, where like parts are numbered like, FIG. 1 shows a combined cycle power plant (CCPP) 10 including first and second gas turbomachines 12, 12'. The first gas turbomachine 12 includes a gas turbine 20, a heat recovery steam generator (HRSG) 14, and an exhaust system 28. The second gas turbomachine 12' also includes a gas turbine 20', a HRSG 14', and an exhaust system 28'. Each of the two gas turbomachines 12, 12' are substantially similar. In an embodiment of the disclosed technique, the two gas turbomachines 12, 12' share a common HRSG exhaust stack 36, as described below.

[0036] The first gas turbomachine 12 further includes a compressor 16 and a combustion chamber 18. Similarly, the second gas turbomachine 12' further includes a compressor 16' and a combustion chamber 18'. The gas turbine 20 and / or the gas turbine 20' are connected to one or more generators 22, 22', which are electrically connected to a power grid (not shown). In other applications, the gas turbine 20 and / or the gas turbine 20' may be connected to other machines depending on the need and design.

[0037] Upstream of the compressor 16, the first turbomachine 12 includes an inlet section 24 for the ambient air 40 supplied to the compressor 16. Additionally, the compressor 16 may typically be provided with variable inlet guide vanes 26 for controlling the amount of ambient air 40 supplied to the compressor 16. Similarly, upstream of the compressor 16', the second turbomachine 12' includes an inlet section 24' for the ambient air 40' supplied to the compressor 16'. The compressor 16' may also be provided with variable inlet guide vanes 26' for controlling the amount of ambient air 40' supplied to the compressor 16'.

[0038] An exhaust system 28 may be provided downstream of the gas turbine 20. The exhaust system 28 may be connected to the bypass stack 30 and / or the HRSG 14. A damper 32 may be provided for selectively connecting the exhaust system 28 to the bypass stack 30. An exhaust damper 34 may be provided for selectively connecting the exhaust system 28 to the HRSG 14. An exhaust system 28' may be provided downstream of the gas turbine 20' and may be connected to the bypass stack 30' and / or the HRSG 14'. A damper 32' and an exhaust damper 34' may be provided for selectively connecting the exhaust system 28' to the bypass stack 30' and the HRSG 14', respectively.

[0039] In some embodiments of the disclosed technology, a common HRSG exhaust stack 36 may be provided downstream of each HRSG 14, 14' to direct exhaust from each HRSG 14, 14' to the atmosphere. An exhaust duct 38 directly connects the HRSG 14 to the common HRSG exhaust stack 36. Similarly, an exhaust duct 38' directly connects the HRSG 14' to the common HRSG exhaust stack 36.

[0040] 2 illustrates an alternative configuration of the CCPP 10. In FIG. 2, the HRSG 14 includes an exhaust duct 42 that leads directly to the common exhaust stack 36. The HRSG 14' includes an exhaust duct 44 that connects to the exhaust duct 42, and the flow from the exhaust duct 44 can proceed through the exhaust duct 42 to the common HRSG exhaust stack 36. Thus, in accordance with an embodiment of the disclosed technology, exhaust from the HRSGs 14, 14' can flow to the common HRSG exhaust stack 36 either directly via the exhaust ducts 38, 38' (FIG. 1) and exhaust duct 42 (FIG. 2), or indirectly from one of the HRSGs 14' (FIG. 2) via the exhaust ducts 42 and 44. While FIG. 2 shows HRSG 14 directly connected to the common HRSG exhaust stack 36 by exhaust duct 42, aspects of the disclosed technology include connecting either HRSG 14 or HRSG 14' directly to the common HRSG exhaust stack 36 via its exhaust duct 42 or 44, and the other via the other's exhaust duct 44 or 42.

[0041] 1, in certain aspects of the disclosed technology, an HRSG stack damper 46, 46' may be provided to close and control the flow of exhaust gas from the HRSG 14, 14' to the common HRSG exhaust stack 36. The HRSG stack damper 46, 46' may be provided at the junction of the HRSG 14, 14' and the exhaust duct 38, 38' as shown in FIG. Another aspect of the disclosed technology involves locating the HRSG stack damper 46, 46' at any point along the exhaust duct 38, 38'.

[0042] As shown in FIG. 2, the HRSG 14 is directly connected to the common HRSG exhaust stack 36 by an exhaust duct 42. Also, the HRSG 14' is connected to an exhaust duct 44, which is connected to an exhaust duct 42, which is then connected to the common HRSG exhaust stack 36. To this extent, HRSG stack dampers 48, 48' may be located at any point along the exhaust ducts 42, 44, respectively, to control the flow of exhaust gas from the HRSGs 14, 14' to the common HRSG exhaust stack 36. Additionally, aspects of the disclosed technology include placing a separate HRSG stack damper 50 at the junction of the exhaust ducts 42, 44 to control the flow of exhaust gas therebetween.

[0043] In accordance with an embodiment of the disclosed technology, the use of a common HRSG exhaust stack (e.g., common HRSG exhaust stack 36) coupled to two HRSGs (e.g., HRSGs 14, 14') can prevent normal cool down after shutting down a gas turbine (e.g., gas turbine 20') while the other gas turbine and HRSG (e.g., gas turbine 20' and HRSG 14') remain in operation. In certain aspects of this embodiment, when the operating gas turbine (e.g., gas turbine 20') is operating at high load, the pressure drop across the common HRSG exhaust stack 36 may still be higher than the available draft of the common HRSG exhaust stack 36. This pressure difference may create back pressure on the shut down gas turbine (e.g., gas turbine 20). In accordance with an embodiment of the disclosed technology, the control system 60 may be used to provide sub-atmospheric pressure to the shut down gas turbine (e.g., gas turbine 20) with active draft control with minimal hardware modifications and limited power generation losses.

[0044] FIG. 3 is a flow chart of a method for active draft control through a CCPP including multiple HRSGs coupled to a common HRSG exhaust stack (such as CCPP 10 shown in FIGS. 1 and 2) according to an embodiment of the disclosed technique. In the following description, the CCPP includes at least a first gas turbomachine and a second gas turbomachine. The first gas turbomachine includes a gas turbine, a HRSG, and an exhaust system, and the second gas turbomachine includes a gas turbine, a HRSG, and an exhaust system. The method may be performed by / using a control system, such as control system 60 shown in FIGS. 1 and 2. Control system 60 may be part of an overall control system of CCPP 10 or may be in addition to the overall control system. A single control system 60 may be provided, or each gas turbomachine 12, 12′ may include its own control system that cooperates to provide the functionality of control system 60 described herein.

[0045] In process P1, a determination is made that one of the gas turbines of the first gas turbomachine or the gas turbine of the second gas turbomachine is shut down and the other of the first gas turbine or the second gas turbine is in operation. The shutdown determination can be provided, for example, automatically by the control system 60 or via an operator input to the control system 60. In process P2, the rotational speed of the turbine of the shut down gas turbomachine is measured. For example, as shown in Figures 1 and 2, a speed sensor 62, 62' may be coupled to the turbine 20, 20' of the turbomachine 12, 12' and used to determine the speed of the turbine 20, 20'. In process P3, the exhaust pressure of the shut down gas turbomachine is measured. The exhaust pressure can be measured, for example, by a pressure sensor 64, 64' coupled to the exhaust system 28, 28' of the turbomachine 12, 12' as shown in Figures 1 and 2. In process P4, the time until the shutting down gas turbine is shut down (e.g., provided by a shutdown timer 66, 66′) is measured by the control system 60. The speed of the turbine of the shutting down gas turbomachine and the exhaust pressure of the shutting down gas turbomachine are provided to the control system 60.

[0046] In process P5, the control system 60 compares the speed of the turbine of the shut down gas turbomachinery to a threshold value of X revolutions per minute (rpm). For example, the X rpm threshold may be between about 50 RPM and about 300 RPM. In process P6, the control system 60 compares the exhaust pressure of the shut down gas turbomachinery to a Y threshold value (e.g., in bars (barg) above atmospheric pressure). For example, the Ybarg threshold may be between about -0.3 barg and about -0.1 barg. In process P7, the control system 60 compares the shut down time of the shut down turbomachinery assembly to a Z threshold value. For example, the Z threshold may be between about 30 minutes and about 90 minutes.

[0047] In process P8, the control system 60 receives a ventilation request signal 70 (FIGS. 1 and 2) from the shut down gas turbomachine regarding the cool down status of the shut down gas turbomachine. Once the shut down gas turbomachine has completed the cool down process (NO in process P8), the operating gas turbomachine returns to nominal operating conditions in process P9. If the shut down gas turbomachine has not completed the cool down process (YES in process P8), the flow proceeds to process P10.

[0048] If the control system 60 determines that the rotational speed of the shut-down gas turbomachine is less than the threshold value of X rpm (YES in process P5), determines that the exhaust pressure of the shut-down gas turbomachine is greater than the threshold value of Y (YES in process P6), determines that the shut-down time of the shut-down gas turbomachine is greater than the threshold value of Z (YES in process P7), and determines that the shut-down gas turbomachine has not completed the cool-down process (YES in process P8), then in process P10 the control system 60 sends appropriate control signals (e.g., control signals 68, 68' (FIGS. 1 and 2)) to the operating gas turbomachine. In some embodiments, the control signals instruct the operating turbomachine to increase the exhaust gas temperature of the operating turbomachine to increase the ventilated flow rate from the HRSG of the operating turbomachine to equal the pressure drop across the turbine of the shut-down turbomachine, and instruct the turbine of the shut-down turbomachine to adjust the ventilated flow rate from the HRSG of the operating turbomachine to adjust the subatmospheric pressure. The ventilation flow from the HRSG of an operating gas turbomachine can be adjusted, for example, by increasing the stack temperature or decreasing the total mass flow rate. The total mass flow rate can be decreased, for example, by unloading the operating gas turbomachine. The stack temperature can be increased, for example, by increasing the exhaust temperature of the operating gas turbomachine or by bypassing the HRSG water around an economizer (such as a tube heat exchanger) to reduce the HRSG-Rankine cycle efficiency.

[0049] In an additional embodiment, the control system 60 may further receive an adjusted ventilation signal 72 (FIGS. 1 and 2) from the shut-down gas turbomachine requesting an increase or decrease in ventilation flow rate in response to the adjustments performed in process P10. In response, the control system 60 provides appropriate instructions to the operating gas turbomachine to increase or decrease the ventilation flow rate.

[0050] As will be apparent to one skilled in the art, the present disclosure may be implemented as a system, method, or control that may utilize a computer program product. Accordingly, the present disclosure may include hardware embodiments, software embodiments (including firmware, resident software, microcode, etc.), or embodiments combining software and hardware aspects, all of which are collectively referred to herein as "circuits," "modules," or "systems." Furthermore, the present disclosure may take the form of a computer program compliant control embodied in a tangible medium having computer usable program code embodied in the medium.

[0051] Any combination of one or more computer usable or computer readable media (one or more) may be utilized. The computer usable or computer readable medium may be, for example, an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, device, apparatus or propagation medium. More specific examples of computer readable media include, but are not limited to, an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read only memory (ROM), an erasable programmable read only memory (EPROM or flash memory), an optical fiber, a portable compact disk read only memory (CD-ROM), an optical storage device, a transmission medium such as one supporting the Internet or an intranet, or a magnetic storage device. The computer usable or computer readable medium may be, for example, paper or another suitable medium on which the program is printed, so that it can be electronically captured via optical scanning of the paper or other medium, and then compiled, interpreted or otherwise processed in an appropriate manner as necessary, and then stored in a computer memory. In this application, a computer usable or computer readable medium may be any medium that can contain, store, communicate, transmit or propagate a program for use by or in connection with an instruction execution system, apparatus or device. The computer usable medium may include a data signal propagated with the computer usable program code, either in baseband or as part of a carrier wave. The computer usable program code may be transmitted using any suitable medium, including but not limited to wireless, wired, fiber optic cable, RF, etc.

[0052] Computer program code for carrying out the operations of the present disclosure may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as the "C" programming language or similar. The program code may run entirely on the user's computer, partly on the user's computer and partly on the user's computer and partly on a remote computer, or entirely on a remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be to an external computer (e.g., via the Internet using an Internet Service Provider).

[0053] The present disclosure is described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. Each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, may be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine such that the instructions, executed by the processor of the computer or other programmable data processing apparatus, create means for implementing the function / act specified in the flowchart and / or block diagram block or blocks.

[0054] These computer program instructions may be stored on a computer-readable medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored on the computer-readable medium produce an article of manufacture that includes instruction means that implement the functions / acts specified in the flowchart and / or block diagram blocks or blocks.

[0055] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowcharts or block diagrams may represent a module, segment, or portion of code, which includes one or more executable instructions for implementing a given logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may in fact be executed substantially simultaneously, or the blocks may be executed in the reverse order, depending on the functionality involved. It should also be noted that each block of the block diagrams and / or flowchart diagrams, and combinations of blocks in the block diagrams and / or flowchart diagrams, may be implemented by a special purpose hardware-based system that performs a given function or operation, or a combination of special purpose hardware and computer instructions.

[0056] As described herein, various systems and components are described as "determining" or "obtaining" data. It is understood that the corresponding data can be obtained using any solution. For example, the corresponding systems / components can generate the data and / or be used to generate the data, obtain the data from one or more data stores (e.g., databases), receive the data from another system / component, and / or the like. If the data is not generated by a particular system / component, it is understood that another system / component can be implemented aside from the illustrated system / component that generates and provides the data to the system / component and / or stores the data for access by the system / component.

[0057] Approximate expressions used in the present specification and claims are applied to describe a quantity that can vary within a tolerance range without causing a change in the basic function to which the quantity relates. Thus, values ​​modified with terms such as "about", "approximately" and "substantially" are not limited to their exact numerical values. In at least some instances, approximation language may correspond to the precision of a measuring instrument for measuring the value. In the present specification and claims, ranges of numerical limitations may be combined and / or exchanged with each other. Such ranges specify and include all subranges contained within the range, unless otherwise clear from the context. The term "about" used in conjunction with a particular value of a range applies to the upper and lower limits and may indicate ±10% of the stated numerical value, except where it depends on the precision of the instrument for measuring the value. [Explanation of symbols]

[0058] 10 Combined Cycle Power Plants (CCPPs) 12,12' Gas Turbo Machinery 14,14' Heat recovery steam generator (HRSG) 16,16' Compressor 18,18' Combustion chamber 20,20' Gas Turbine 22,22' Generator 28,28' Exhaust System 30,30' bypass stack 32,32' Damper 34,34' Exhaust damper 36 Exhaust stack 38,38' Exhaust duct 40,40' Ambient air 42,44 Exhaust duct

Claims

1. 1. A method of active draft control through a system including an operating turbomachine (12') including a turbine (20') and a heat recovery steam generator (HRSG) (14'), an idle turbomachine (12) including a turbine (20) and a HRSG (14), and a common exhaust stack (36) shared by the operating turbomachine's HRSG and the idle turbomachine's HRSG, the method comprising: measuring the rotational speed of a turbine of said turbomachine during said shutdown; measuring an exhaust pressure of the turbomachine during said shutdown; measuring the shutdown time of the turbomachine during said shutdown; and increasing an exhaust gas temperature of the operating turbomachine to increase a ventilation flow rate from the HRSG of the operating turbomachine to equal a pressure drop across a turbine of the shut-down turbomachine based on at least one of the measured speed, the measured exhaust pressure, and the measured shut-down time. The method includes:

2. 10. The method of claim 1, further comprising adjusting a vent flow temperature of the operating turbomachine to provide subatmospheric pressure to a turbine of the shut-down turbomachine based on at least one of a measured rotational speed, a measured exhaust pressure, and a measured shut-down time.

3. Increasing the exhaust gas temperature of the operating turbomachine and regulating the ventilated flow temperature of the operating turbomachine comparing a measured rotational speed of a turbine of the shut down turbomachine to a first threshold value; comparing the measured exhaust pressure of the shut down turbomachine to a second threshold; and comparing the measured downtime of the shut down turbomachine with a third threshold value; The method of claim 2, wherein the value is determined by

4. Increasing the exhaust gas temperature of the operating turbomachine and regulating the ventilated flow temperature of the operating turbomachine if a rotational speed of a turbine of the shut-down turbomachine is less than a first threshold; if an exhaust pressure of the shut down turbomachine exceeds a second threshold; and When the stop time of the stopped turbomachine exceeds a third threshold value. The method of claim 3, wherein the method is carried out on

5. monitoring a status of a cool-down process of the shut down turbomachine; and returning the operating turbomachine to its nominal operating condition once the cool-down process of the shut-down turbomachine is complete. The method of claim 4 further comprising:

6. an out-of-service turbomachinery (12) including a turbine (20) and a heat recovery steam generator (HRSG) (14); an operating turbomachine (12') including a turbine (20') and a HRSG (14'); a common exhaust stack (36) shared by the HRSG of the shut-down turbomachine and the HRSG of the operating turbomachine; a control system configured to increase an exhaust gas temperature of the operating turbomachine to increase a ventilation flow rate from the HRSG of the operating turbomachine to equal a pressure drop across the turbine of the shut down turbomachine based on at least one of a rotational speed of a turbine of the shut down turbomachine, an exhaust pressure of the shut down turbomachine, and a shut down time of the shut down turbomachine; A system comprising:

7. 7. The system of claim 6, wherein the control system is further configured to adjust a vent flow temperature of the operating turbomachine to provide subatmospheric pressure to a turbine of the shut-down turbomachine based on at least one of a measured rotational speed, a measured exhaust pressure, and a measured shut-down time.

8. a sensor for measuring the rotational speed of a turbine of the turbomachine during shutdown; a sensor for measuring an exhaust pressure of the turbomachine during shutdown; A timer for measuring a stop time of the turbomachine; The system of claim 7 further comprising:

9. The control system comprises: comparing the measured rotational speed of the turbine of the shut down turbomachine to a first threshold; comparing the measured exhaust pressure of the shut down turbomachine to a second threshold; and Comparing the measured downtime of the shut down turbomachine to a third threshold.

8. The system of claim 7, further configured to increase an exhaust gas temperature of the operating turbomachine and regulate an airflow temperature of the operating turbomachine by:

10. The control system comprises: a rotational speed of a turbine of the shut-down turbomachine is less than a first threshold; the exhaust pressure of the shut down turbomachine exceeds a second threshold; and The shutdown time of the turbomachine during shutdown exceeds a third threshold. The system of claim 9 , further configured at times to increase an exhaust gas temperature of the operating turbomachine and to regulate an airflow temperature of the operating turbomachine.

11. the first threshold is between about 50 rpm and about 300 rpm; the second threshold is from about −0.03 to about −0.1 barg; and The system of claim 10 , wherein the third threshold is between about 30 minutes and about 90 minutes.

12. a first exhaust duct for connecting the HRSGs of the operational turbomachines to the common exhaust stack; a second exhaust duct for connecting the HRSG of the shut-down turbomachine to the common exhaust stack; The system of claim 6 further comprising:

13. The system of claim 12 , wherein at least one of the first exhaust duct or the second exhaust duct is directly connected to a common exhaust duct.

14. The system of claim 13 , wherein at least one of the first exhaust duct or the second exhaust duct includes a damper.

15. 11. A computer-readable medium comprising computer-executable instructions that, when executed, perform a method of active draft control through a system including an operating turbomachine (12′) including a turbine (20′) and a heat recovery steam generator (HRSG) (14′), an idle turbomachine (12) including the turbine (20) and the HRSG (14), and a common exhaust stack (36) shared by the HRSG of the operating turbomachine and the HRSG of the idle turbomachine, the method of any one of claims 1 to 5.

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