SYSTEM AND METHOD FOR MANAGING HEAT RECOVERY STEAM GENERATOR INLET TEMPERATURE

A system may include a gas turbine system. The gas turbine system may include a compressor, such that the gas turbine system may produce exhaust gas in an exhaust outlet when generating electricity. The system may also include a heat recovery steam generator (HRSG) that may use the exhaust gas to create steam, a manifold system configured to couple compressed air in the compressor to the exhaust outlet, and a controller configured to send a command to the manifold system to couple the compressed air to the exhaust outlet when a temperature of the exhaust gas is above a threshold.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to operating heat exchangers, and more specifically, to systems and methods for managing temperatures within a heat recovery steam generator.

Heat exchangers are used to transfer heat from one medium to another in a variety of industries. A heat recovery steam generator (HRSG) is an example of a heat exchanger, which may be used in combined cycle power plants and similar plants. An HRSG may use gas turbine engine exhaust to heat a fluid flowing through heat exchangers in the HRSG, for example, to convert water into steam. In some configurations, the fluid may be steam used for high-pressure, intermediate-pressure, and/or low-pressure sections of a steam turbine. Generally, the HSRG may be rated to receive mass flows of gases within a particular range of temperatures. As such, improved systems and methods for managing the temperature within the HRSG are desirable.

BRIEF DESCRIPTION OF THE INVENTION

Certain embodiments commensurate in scope with the originally claimed embodiments are summarized below. These embodiments are not intended to limit the scope of the claims, but rather these embodiments are intended only to provide a brief summary of possible forms of the presently disclosed systems and techniques. Indeed, the presently disclosed systems and techniques may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

In one embodiment, a system may include a gas turbine system. The gas turbine system may include a compressor, such that the gas turbine system may produce exhaust gas in an exhaust outlet when generating electricity. The system may also include a heat recovery steam generator (HRSG) that may use the exhaust gas to create steam, a manifold system configured to couple compressed air in the compressor to the exhaust outlet, and a controller configured to send a command to the manifold system to couple the compressed air to the exhaust outlet when a temperature of the exhaust gas is above a threshold.

A non-transitory machine readable medium may include computer-executable instructions that may cause a processor to monitor a temperature of exhaust gas provided to a heat recovery steam generator (HSRG) via an exhaust outlet. The processor may then send a command to a manifold system when the temperature exceeds a threshold, such that the command may cause the manifold system to couple compressed air to the exhaust outlet.

A manifold system may include one or more valves configured to couple compressed air from a compressor of a gas-turbine system to an exhaust outlet of the gas-turbine system, such that the exhaust outlet is configured to provide exhaust gas to a heat recovery steam generator (HSRG). The manifold system may also include a control system that may adjust the one or more valves to couple the compressed air to the exhaust outlet when a temperature of the exhaust gas is above a threshold.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure is generally directed to systems and methods for controlling the inlet temperature of a heat recovery steam generator (HRSG). For example, a system may include a gas turbine that may be coupled to an HRSG, such that the exhaust gas from the gas turbine may be provided to the HRSG. Generally, the HRSG may use the heat from the exhaust gas to produce steam that may then be used to drive a steam turbine. As such, the HRSG enables the gas turbine to efficiently use the heat provided in exhaust gas to produce additional power.

The HRSG may be rated or designed to receive exhaust gas at or below a certain temperature. With this in mind, in one embodiment, a gas turbine system may employ a valve within a compressor of the gas turbine system to bleed compressed air from the compressor into an exhaust frame that may be provided to the HRSG. By bleeding the compressed air into the exhaust frame, the gas turbine system may decrease the temperature of the exhaust gas provided to the HRSG. As a result, the gas turbine system may ensure that the HRSG may operate at or below its rated temperature, thereby enabling the HRSG to operate efficiently and improve its operating lifespan. Additional details with regard to how the gas turbine system may control the temperature of the exhaust gas provided to the HRSG is provided below with reference toFIGS. 1-3.

By way of introduction,FIG. 1is a block diagram of an embodiment of a combine cycle power plant10with a controller12that may control the temperature of the exhaust flow sent to a heat recovery steam generator. Moreover, the controller12may also enable the combined cycle power plant10to rapidly increase electrical output (i.e., loading) from an inactive state (i.e., no electrical output) to an active state (i.e., electrical output requested for grid), or in other words a starting load to a base load/dispatch power load. More specifically, the controller12may enable the combined cycle power plant10to increase power output from a gas turbine system14and a steam turbine system16through increased/accelerated steam production. In some embodiments, the increased/accelerated steam production may be used for a boiler, enabling a boiler to rapidly start.

Keeping this in mind, the combined cycle power plant (CCPP)10includes the controller12, gas turbine system14, the steam turbine system16, and a heat recovery steam generator (HRSG)18. In operation, the gas turbine system14combusts a fuel-air mixture to create torque that drives a load, e.g., an electrical generator. In order to reduce energy waste, the combined cycle power plant10uses the thermal energy in the exhaust gases to heat a fluid and create steam in the HRSG18. The steam travels from the HRSG18through a steam turbine system16creating torque that drives a load, e.g., an electrical generator. Accordingly, the CCPP10combines the gas turbine system14with steam turbine system16to increase power production while reducing energy waste (e.g., thermal energy in the exhaust gas).

The gas turbine system14includes an airflow control module20, compressor22, combustor24, and turbine26. In operation, an oxidant28(e.g., air, oxygen, oxygen enriched air, or oxygen reduced air) enters the turbine system14through the airflow control module20, which controls the amount of oxidant flow (e.g., airflow). The airflow control module20may control airflow by heating the oxidant flow, cooling the oxidant flow, extracting airflow from the compressor22, using an inlet restriction, using an inlet guide vane, or a combination thereof. As the air passes through the airflow control module20, the air enters the compressor22. The compressor22pressurizes the air28in a series of compressor stages (e.g., rotor disks30) with compressor blades. After the air28is pressurized, the pressurized air may reside in a compressor discharge chamber29before the compressed air exits the compressor22.

As the compressed air exits the compressor22, the air enters the combustor24and mixes with fuel32. The turbine system14may use liquid or gas fuel, such as natural gas and/or a hydrogen rich synthetic gas, to run the turbine system14. For example, the fuel nozzles34may inject a fuel-air mixture into the combustor24in a suitable ratio for optimal combustion, emissions, fuel consumption, and power output. As depicted, a plurality of fuel nozzles34intakes the fuel32, mixes the fuel32with air, and distributes the air-fuel mixture into the combustor24. The air-fuel mixture combusts in a combustion chamber within combustor24, thereby creating hot pressurized exhaust gases. The combustor24directs the exhaust gases through a turbine26toward an exhaust outlet36. As the exhaust gases pass through the turbine26, the gases contact turbine blades attached to turbine rotor disks38(e.g., turbine stages). As the exhaust gases travel through the turbine26, the exhaust gases may force turbine blades to rotate the rotor disks38. The rotation of the rotor disks38induces rotation of shaft40and the rotor disks32in the compressor26. A load42(e.g., electrical generator) connects to the shaft40and uses the rotation energy of the shaft40to generate electricity for use by the power grid.

As explained above, the combined cycle power plant10harvests energy from the hot exhaust gases exiting the gas turbine system14for use by the steam turbine system16or a boiler. Specifically, the CCPP10channels hot exhaust gases44from the turbine system14into the heat recovery steam generator (HRSG)18. In the HRSG18, the thermal energy in the combustion exhaust gases converts water into hot pressurized steam46. The HRSG18releases the steam in line46for use in the steam turbine system16.

The steam turbine system16includes a turbine48, shaft50, and load52(e.g., electrical generator). As the hot pressurized steam in line46enters the steam turbine48, the steam contacts turbine blades attached to turbine rotor disks54(e.g., turbine stages). As the steam passes through the turbine stages in the turbine48, the steam induces the turbine blades to rotate the rotor disks54. The rotation of the rotor disks54induces rotation of the shaft50. As illustrated, the load52(e.g., electrical generator) connects to the shaft50. Accordingly, as the shaft50rotates, the load52(e.g., electrical generator) uses the rotation energy to generate electricity for the power grid. As the pressurized steam in line46passes through the turbine48, the steam loses energy (i.e., expands and cools). After exiting the steam turbine48, the steam enters a condenser49before being routed back to the HRSG18, where the steam is reheated for reuse in the steam turbine system16.

As explained above, the controller12enables the combined cycle power plant10to flexibly load the gas turbine system14, which may enable increased steam production in the HRSG18. The controller12may also be employed to control the temperature of the exhaust gas provided to the HRSG18. As mentioned above, the HRSG18may be associated with a temperature rating or threshold that described its preferred operating temperature. In some cases, the threshold may be associated with an upper limit (e.g., 10%) of the operating range of the HSRG18to enable the controller12to react and change the operation of the CCPP10. If the controller12detects that the exhaust temperature provided to the HRSG18is above this threshold, the controller12may decrease the firing temperature of the air-fuel mixture combusted in the combustor24to ensure that the HRSG18operates efficiently. However, in decreasing the firing temperature, the controller12may decrease the operating efficiency of the CCPP10.

With this in mind, in one embodiment, the controller12may monitor the temperature of the exhaust gas provided to the HRSG18and bleed off compressed air from the compressor discharge chamber29, such that the temperature of the resulting exhaust/air mixture within the exhaust outlet36is reduced. As a result, the combustor24may maintain its firing temperature while the controller12ensures that the HRSG18operates at a desired temperature range. Additional details regarding how the controller12may adjust the temperature of the exhaust gas will be described below with reference toFIGS. 2 and 3.

Generally, the controller12may include a memory56and a processor58. The memory56stores instructions and steps written in software code. The processor58executes the stored instructions in response to feedback from the CCPP10. More specifically, the controller12controls and communicates with various components in the CCPP10in order to flexibly control the loading of the gas turbine system14, and thus the loading of the steam turbine system16. As illustrated, the controller12controls the airflow control module20, the intake of fuel32, and valve(s)47; and communicates with load42, exhaust gas temperature sensor60, HRSG steam temperature sensor62, and steam turbine metal temperature sensor64, in order to load the CCPP10along different load paths.

In operation, the controller12controls the airflow control module20and the consumption of fuel32to change the loading of the gas turbine system14and thereby the loading of CCPP10(i.e., how the CCPP10increases electrical power output to the grid). Specifically, the controller12adjusts the mass flow rate and temperature of the exhaust gas44, which controls how rapidly the HRSG18produces steam for the steam turbine system16, and therefore, how quickly the CCPP10produces electrical power using loads42and52. For example, when the controller12increases the airflow with the airflow control module20, it increases the amount of airflow flowing through the compressor22, flow through the combustor24, and flow through the turbine26. The increase in airflow increases the mass flow rate of the exhaust gas, and thus the torque of the shaft40. Moreover, the increase in the mass flow rate of the exhaust gas44increases the amount of thermal energy available for the HRSG18to produce steam (i.e., more exhaust gas is flowing through the HRSG18). An increase in steam production by the HRSG18reduces startup time for the steam turbine system16and thus increases electrical output from the load52.

As explained above, the controller12controls fuel consumption by the gas turbine system14. Control of the fuel32affects the mass flow rate through the gas turbine system14and the thermal energy available for the HRSG18. For example, when the controller12increases fuel consumption the temperature of the exhaust gas44increases. The increase in the exhaust gas temperature44enables the HRSG18to produce steam at higher temperatures and pressures, which translates into more power production by the steam turbine system16. However, when the controller12decreases fuel consumption there is a reduction in the temperature of the exhaust gas. Accordingly, there is less mechanical energy available to drive load42and less thermal energy available to produce steam for the steam turbine system16to drive load52.

Although the controller12has been described as having the memory56and the processor58, it should be noted that the controller12may include a number of other computer system components to enable the controller12to control the operations of the CCPP10and the related components. For example, the controller12may include a communication component that enables the controller12to communicate with other computing systems. The controller12may also include an input/output component that enables the controller12to interface with users via a graphical user interface or the like.

FIG. 2is a block diagram of an air extraction system70for controlling the temperature of exhaust gas provided to the HRSG18. As illustrated inFIG. 2, the air extraction system70may include an air extraction manifold system72coupled to the compressor discharge chamber29via piping74. In one embodiment, the piping74may be a 10-inch expansion joint that couples the compressor discharge chamber29to the air extraction manifold system72.

The air extraction manifold system72may include a chamber of one or more valves that may direct air or gases received by the air extraction manifold system72to various destinations. For example, the air extraction manifold system72may be coupled to an inlet bleed heat system and to the exhaust outlet36(e.g., overboard bleed system). As such, the air extraction manifold system72may direct the compressed air from the compressor discharge chamber29to the inlet bleed heat system, the exhaust outlet36, or a variety of proportions between the two.

In one embodiment, the air extraction manifold system72may include a control system that is capable of controlling the valves within the air extraction manifold system72. Moreover, the control system may be capable of sending and receiving data similar to the functions described herein with regard to the controller12.

The inlet bleed heat system may reduce the flow of air through the combustor24by recirculating a portion of the compressed air via the compressor discharge chamber29to an inlet air duct that is coupled to the compressor22. As such, the compressed air may heat inlet air provided to the compressor22, thereby making the inlet air less dense and increasing the operating range of the compressor22.

In one embodiment, the air extraction manifold system72may direct the compressed air from the compressor discharge chamber29to the exhaust outlet36, thereby adding a certain amount of compressed air that has not been through the combustor24to the exhaust gas output via the turbine26. As a result, the compressed air may cool or lower the overall temperature of the exhaust gas present in the exhaust outlet36. In this way, the gas provided to the HRSG18may have a lower temperature, as compared to receiving the exhaust gas without the added compressed air via the air extraction manifold system72.

To control when the compressed air will be provided to the exhaust outlet36, the controller12may monitor the temperature of the exhaust gas in the exhaust outlet36, determine whether the temperature is greater than a threshold, and send a command to the air extraction manifold system72to direct compressed air to the exhaust outlet36when the temperature is greater than the threshold. As a result, the temperature of the exhaust gas provided to the HSRG18may start to decrease.

By way of example,FIG. 3illustrates a flow chart of a method90employed by the controller12to control the temperature of the gas within the exhaust outlet36. Although the following description of the method90will be described as being performed by the controller12, it should be noted that the method90may be performed by any suitable computing device including a computing device that is remotely positioned with respect to the CCIP10.

Referring now toFIG. 3, at block92, the controller12may monitor the temperature of the exhaust gas mixture within the exhaust outlet36. In one embodiment, the controller12may model the temperature of the exhaust gas mixture in the exhaust outlet based on a mixing mass flow of the compressed air via the piping74, the mass flow of the exhaust gas in the exhaust outlet36, the temperature of the compressed air in the piping74, and the temperature of the exhaust gas in the exhaust outlet36. In one embodiment, the mass flow of the compressed air in the piping74may be determined based on known gas turbine system parameters, such as a differential pressure sensor associated with the piping74and fluid mechanics. Moreover, the mass flow of the exhaust gas, as well as the temperature of the compressed air and the exhaust gas may be modeled based on known baseline parameters regarding the air28, the compressor22, the combustor24, the fuel32, the turbine26, and the like. Using the data described above, the controller12may model an expected temperature of the exhaust gas mixture present in the exhaust outlet36.

In some embodiments, the piping74and the exhaust outlet36may each include a temperature sensor (e.g., thermocouple) that may indicate the respective temperatures of the compressed air in the piping74and the exhaust gas in the exhaust outlet36. As such, the controller12may use the temperature data from the temperature sensors to determine the temperature of the exhaust gas mixture in the exhaust outlet36.

After receiving the expected temperature associated with the exhaust outlet36, at block94, the controller12may determine whether the expected temperature is greater than a threshold. The threshold may be defined by the user or automatically determined based on the operating parameters (e.g., operating temperature range) associated with the HRSG18. As mentioned above, the threshold may be related to an upper limit (e.g., 10%) of the operating range of the HSRG18. As such, the controller12may have a sufficient amount of time to divert the compressed air to the exhaust outlet36before the temperature of the exhaust gas provided to the HSRG18exceeds the operating range of the HSRG18.

If the temperature is not greater than the threshold, the controller12may return to block92and continue monitoring the temperature of the exhaust gas in the exhaust outlet36. If, however, the temperature is greater than the threshold, the controller12may proceed to block96.

At block96, the controller12may send a command to the air extraction manifold system72to open one or more valves within the air extraction manifold system72to provide a portion of the compressed air within the compressor discharge chamber29to the exhaust outlet36via the piping74. In one embodiment, the controller12may specify a valve setting in order to bleed a sufficient amount of compressed air to the exhaust outlet36based on a difference between the monitored temperature of the exhaust outlet36and the threshold.

After sending the command to provide compressed air to the exhaust outlet36, the controller12may return to block92and monitor the new temperature of the exhaust gas in the exhaust outlet36based on the provided compressed air. The controller12may then perform the method90continuously until the temperature of the exhaust outlet36is at or below the threshold.

Technical effects of the presently disclosed systems and techniques include improving the operating efficiency of the HSRG18by adjusting the temperature of the exhaust gas provided to the HSRG18. Moreover, by preventing exhaust gas that is above a temperature threshold from being input into the HSRG18, the controller12may prevent overloading the CCPP10, powering down the CCPP10, or the like.

In addition, by controlling the temperature of the exhaust gas provided to the HSRG18, the controller12may provide an enhanced turn down mode for the operation of the CCPP10. That is, the CCPP10may continue to operate by providing power to loads during off-peak hours, which may involve producing exhaust gas having temperatures above the threshold. However, by diverting the compressed air to the exhaust outlet36during off-peak hours, the CCPP10may continue to provide power to the loads even with the high exhaust temperatures by using the compressed air to cool the high exhaust temperatures.

This written description uses examples to disclose various embodiments of the presently disclosed systems and techniques, including the best mode, and to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the presently disclosed systems and techniques 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.