Patent Application
20150322822
One or more aspects of the present invention relate to water injection and liquid fuel heating for a power plant. In particular, one or more aspects of the present invention relate to using boiler feedwater for liquid fuel heating and water injection during liquid fuel operation.
A gas turbine may be incorporated in a combined cycle power plant. As the name suggests, a typical combined cycle power plant combines two or more thermal cycles within a single power plant. There are normally two cycles in a combined cycle power plant classified as “topping” and “bottoming” cycles. Most or all heat is supplied in the topping cycle. The waste heat produced in the topping cycle is utilized in the bottoming cycle, which operates at a lower temperature level than the topping cycle.
In a typical combined cycle power plant, gas turbines are the prime movers to generate power. These gas turbine engines typically have high exhaust flows and relatively high exhaust temperatures. Steam is produced by directing the exhaust gases to a heat recovery steam generator. The produced steam is directed to a steam turbine to produce additional power. In this manner, a gas turbine produces work via the Brayton Cycle, and the steam turbine produces work via the Rankine Cycle.
It is assumed that the combustor 120 is capable of both gas fuel and liquid fuel operation. For the gas fuel operation, gas fuel can be heated before combustion to increase thermal efficiency. In the conventional power plant 100, hot water extracted from an exit of an intermediate pressure economizer 172 (i.e., the water entering an intermediate pressure evaporator) of the heat recovery steam generator 170 is used for heating the gas fuel in the performance heater 150.
Liquid fuel can also be heated prior to combustion to increase efficiency during the liquid fuel operation (e.g., during startup, part load). In
Additionally, water may be injected during the liquid fuel operation to reduce emissions (NOx, CO). In
A non-limiting aspect of the present invention relates to a liquid fuel heating and water injection system of a power plant. The system may include a boiler feedwater pump, a heat recovery steam generator, a liquid fuel heater, and a water injector. The boiler feedwater pump may be configured to provide feedwater at its output. The heat recovery steam generator may be configured to heat water received at its input and to output some or all heated water at its output. The liquid fuel heater may be configured to receive hot water at its input, heat liquid fuel prior to the liquid fuel being combusted in a combustor, and output the used hot water at its output. The water injector may be configured to receive water at its input and inject the received water into the combustor. The output of the boiler feedwater pump may fluidly communicate with the input of the heat recovery steam generator and with the input of the water injector. The output of the heat recovery steam generator fluidly may communicate with the input of the liquid fuel heater and with the input of the water injector. The output of the liquid fuel heater may fluidly communicate with the input of the water injector.
Another non-limiting aspect of the present invention relates to a power plant. The power plant may include a compressor, a combustor, and a gas turbine. The combustor may be configured to combust a fuel-air mixture to drive the gas turbine, in which the fuel-air includes a mixture of compressed air from the compressor and fuel. The fuel being gaseous and/or liquid. The power plant may also include a boiler feedwater pump, a heat recovery steam generator, a liquid fuel heater, a water injector, and a controller. The controller may be configured to control one or more operations of the power plant. The boiler feedwater pump may be configured to provide feedwater at its output. The heat recovery steam generator, whose input may fluidly communicate with the output of the boiler feedwater pump, may be configured to heat the feedwater received at its input and output at least some of the heated feedwater its output. The liquid fuel heater, whose input may fluidly communicates with the output of the heat recovery steam generator, may be configured to heat the liquid fuel prior to the liquid fuel being combusted in the combustor using the received heated feedwater at its input and output the used heated feedwater at its output. The water injector, whose input may fluidly communicates with the output of the BFP 280 and with the output of the heat recovery steam generator, may be configured to receive the feedwater at its input and inject the received feedwater into the combustor.
Yet another non-limiting aspect of the present invention relates to a method of operating a power plant which comprises a boiler feedwater pump, a heat recovery steam generator downstream of the BFP in a fluid path, a liquid fuel heater downstream of the heat recovery steam generator in the fluid path, and a water injector downstream of the LF heater in the fluid path. The method may include providing feedwater to the fluid path towards the heat recovery steam generator and the liquid fuel heater using the boiler feedwater pump. The method may also include determining whether liquid fuel supplied to a combustor should or should not be heated. When it is determined that the liquid fuel should be heated, the method may proceed to heating the liquid fuel. The step of heating the liquid fuel may include directing the feedwater from the boiler feedwater pump to the heat recovery steam generator, heating the directed feedwater in the heat recovery steam generator, providing the heated feedwater to the liquid fuel heater, and heating the liquid fuel in the liquid fuel heater using the heated feedwater from the heat recovery steam generator. The method may further include determining whether water injection into the combustor should or should not take place. When it is determined that the water injection should take place, the method may proceed to injecting the feedwater into the combustor. The step of injecting the feedwater may include directing the feedwater from the boiler feedwater pump to the water injector, and injecting the feedwater into the combustor using the water injector.
The invention will now be described in greater detail in connection with the drawings identified below.
These and other features of the present invention will be better understood through the following detailed description of example embodiments in conjunction with the accompanying drawings, in which:
One or more aspects of a novel power plant are described. Among many advantages, the inventive aspects include simplified water injection and liquid fuel heating system which can reduce costs and foot print sizes. Also, the combined cycle efficiency may be increased through the inventive aspects.
In one or more aspects, an arrangement is provided in which boiler feedwater, e.g., from a bottoming cycle, can be used for both liquid fuel (LF) heating as well as for water injection during the LF operation in a power plant. For example, a tapping downstream of a feedwater pump maybe used for the liquid fuel heating. The same feedwater may be sent to a water injection skid that sends the water to the combustor nozzles. The water injection skid may also regulate the flow of the water.
The LF operation of the power plant may be viewed as when liquid fuel is combusted in the combustor of the gas turbine (GT) system. Also, gas fuel (GF) operation of the power plant may be viewed as when gaseous fuel is combusted in the combustor. Note that it is possible that both LF and GF may be combusted at the same time. That is, the GT system of the CCPC may be in both LF and GF operations.
In
The power plant 200 may include a GT system as the prime mover. In
The power plant 200 may further include a boiler feedwater pump (BFP) 280, a heat recovery steam generator (HRSG) 270 and a performance heater 250. The BFP 280 may fluidly communicate with the HRSG 270. Generally, two devices or elements may be said to be in fluid communication when there is a path for a fluid to flow from one device to the other. In this instance, it is seen that there is a path for a fluid (e.g., feedwater) to flow from the output of the BFP 280 to the input of the HRSG 270.
Note that two devices may be in fluid communication even if there are intervening elements. For example, it can be said that the BFP 280 fluidly communicates with the performance heater 250 even though the HRSG 270 may be in between. This is because there is a path for the feedwater to flow from the output of the BFP 280 to the input of the performance heater 250 via the HRSG 270.
The BFP 280 may be configured to provide feedwater at its output. As arranged in
The HRSG 270 may be configured to heat water received at its input and to output some or all heated water at its output. The output of the HSRG 270 may fluidly communicate with the input of the performance heater 250. As arranged, the HRSG 270 may be configured to heat the feedwater provided from the BFP 280. In one aspect, the exhaust from the gas turbine 230 may be the heat source used in the HRSG 270 to heat the feedwater. The heated feedwater from the HRSG 270 may be provided to the performance heater 250, and the performance heater 250 may be configured to heat the gas fuel using the heated feedwater from the HRSG 270 (e.g., from the economizer 272) during the GF operation. A heated feedwater valve 290 may be configured to regulate an amount of the heated feedwater exiting the HRSG 270.
The economizer 272 may be an intermediate pressure (IP) economizer or a high pressure (HP) economizer. Likewise, the BFP 280 may be either an IP BFP or a HP BFP. While not specifically illustrated, the heated feedwater used in the performance heater 250 may be from any combination one or both the IP and the HP economizers. In one instance, there may be two BFPs 280 and two heated feedwater valves 290 for the corresponding economizers 272. For the remainder of this description, one BFP 280 and one heated feedwater valve 290 will be assumed. But it should be recognized that the scope of the description readily encompasses multiple BFPs and/or multiple heated feedwater valves 290 corresponding to multiple economizers 272.
As previously mentioned, during the LF operation (e.g., during startup, part-load), the liquid fuel can be heated prior to combustion to increase efficiency. Also during the LF operation, water maybe injected into the combustor to reduce emissions. But in the conventional system (see
However, the power plant 200 addresses some or all deficiencies of the conventional system. The power plant 200 enables the use of the feedwater provided by the BFP 280 for the liquid fuel heating. The power plant 200 enables the use of the feedwater from the BFP 280 also for water injection into the combustor 220.
In an embodiment, the power plant 200 may include a LF heater 235. The output of the HRSG 270 may be in fluid communication with the input of the LF heater 235. Since the HRSG 270 is in fluid communication with the BFP 280, it can also be said that the output of the BFP 280 fluidly communicates with the input of the LF heater 235 via the HRSG 270. The LF heater 235 may be configured to receive hot water at its input, heat liquid fuel prior to the liquid fuel being combusted in the combustor 220, and output the used hot water at its output. In this instance, due to the fluid communication, the hot water used by the LF heater 235 is the feedwater from the BFP 280 heated by the HRSG 270.
This is advantageous in that a separate auxiliary heat source is not required to heat the liquid fuel. Thus in one embodiment, there is no auxiliary heat source for liquid fuel heating. But in another embodiment, an auxiliary heat source may be used in combination with the heated feedwater from the HRSG 270.
In some instances, it may not be necessary and/or not desirable for the feedwater to flow into the LF heater 235. For example, if only gas fuel is being combusted in the combustor 220, i.e., no LF operation is taking place, then there would be no need for the liquid fuel heating. As another example, during a startup, the HRSG 270 may be unable to sufficiently heat the feedwater from the BFP 280 for liquid fuel heating. In this instance, even if LF operation is taking place, it may be more desirable to bypass the liquid fuel heating. Indeed, it may be more beneficial to bypass the HRSG 270 as well so as to allow the HRSG 270 to reach operating temperature quicker.
To enable such flexibilities, the power plant 200 may include a HRSG bypass valve 215, which may be configured to regulate an amount of water received at its input to pass through its output. As seen, the HRSG bypass valve 215 may be in a parallel arrangement with the HRSG 270. That is, the input and output of the HRSG bypass valve 215 may fluidly communicate respectively with the output of the BFP 280, and with the input of the water injector 255. With the parallel arrangement, the amount of the feedwater not passing through the HRSG bypass valve 215 can be directed to the HRSG 270. The amount of the feedwater passing through the HRSG bypass valve 215 may range between a minimum (as low as zero) and a maximum (as much as all). This implies that the amount of the feedwater directed to the HRSG 270 can also range between some minimum and maximum.
The power plant 200 may include a LF heater bypass valve 225, which may also be configured to regulate an amount of water received at its input to pass through its output. The LF heater bypass valve 225 may be in a parallel arrangement with the LF heater 235. That is, the input and output of the LF heater bypass valve 225 may fluidly communicate respectively with the output of the HSRG 270, and with the input of the water injector 255. The input of the LF heater bypass valve 225 may fluidly communicate output of the HRSG bypass valve 215. With the parallel arrangement, the amount of the feedwater not passing through the LF heater bypass valve 225 can be directed to the LF heater 235. The amount of the feedwater passing through the LF heater bypass valve 225 may range between a minimum and maximum, which implies that the amount of the feedwater directed to the LF heater 235 can also range between some minimum and maximum.
In one aspect, when the controller 205 may determine whether the liquid fuel is to be heated. For example, during the LF operation, sensor information may indicate that the temperature of the liquid fuel is lower than a desired temperature. When it is determined that the liquid fuel should be heated, the controller 205 may control the HRSG bypass valve 215 such that at least some, i.e., a non-zero amount, of the feedwater from the BFP 280 is directed to the HRSG 270. In this way, heated feedwater should be available. The controller 205 may also control the LF heater bypass valve 225 such that a non-zero amount of the heated feedwater is directed to the LF heater 235.
Note that by controlling any one or more of the BFP 280, the HRSG 270, the HRSG bypass valve 215, the LF heater bypass valve 225, and the LF heater 235, the controller 205 can regulate the heat exchange occurring the LF heater 235 during the LF operation. For example, the controller 205 may control the temperature and/or the flow rate of the feedwater entering the LF heater 235.
The power plant 200 may further include a water injector 255, which may be configured to receive water at its input and inject the received water into the combustor 220. The input of the water injector 255 may fluidly communicate with the output of the BFP. In this instance, due to the fluid communications, the water injected into the combustor 220 by the water injector 255 is the feedwater from the BFP 280. That is, the same feedwater used for the liquid fuel heating may also be used for water injection. This is further evidenced by noting that the output of the LF heater 235 can be in fluid communication with the input of the water injector 255 as well. Note that the input of the water injector 255 may also fluidly communicate with the output of the HRSG 270.
Referring back to
Note that it is not necessary for the water injection to take place all the time. In one aspect, the controller 205 may determine whether the water injection should take place. For example, sensor information may indicate that the GT system is under a part load (e.g., 30% load or more). In which case, water injection may be useful for NOx abatement. When it is determined that the water injection should take place, the controller 205 may control the three-way valve 245 such that a non-zero amount of the feedwater is directed to the first output, i.e., towards the water injector 255. On the other hand, when it is determined that the water injection should not take place, the controller 205 may control the three-way valve 245 to direct all received feedwater to the second output.
Whenever water injection does take place, the amount of feedwater used for the water injection should be made up. In
Any combination of the heated and/or unheated feedwater may be injected into the combustor 220. Unheated water refers to the portion of the feedwater that is not heated by the HRSG 270. This may correspond to the amount of feedwater that passes through the HRSG bypass valve 215.
While not illustrated in
Of course, it is also possible for the all of the feedwater injected is unheated, e.g., when the HRSG bypass valve 215 and the LF heater bypass valve 225 are both in full bypass operation. This may occur, for example, during startup.
In
In step 820, the controller 205 may determine whether or the liquid fuel supplied to the combustor 220 should or should not be heated. When it is determined that the liquid fuel should be heated, the controller 205 may proceed to heating the liquid fuel in step 830.
Referring back to
In one or more of the inventive aspects, the feedwater provided from a boiler feedwater pump can be used for liquid fuel heating. This has the advantage in that no auxiliary heat source is required. The feedwater from the boiler feedwater pump can also be used for water injection into the combustor. This has the advantage in that overall liquid fuel heating and water injection may be simplified.
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 language of the claims.
