Patent Application
20120297771
The invention relates generally to a feedwater heater cycle for a power plant. More particularly, the invention relates to a variable feedwater heater cycle allowing for active control of final feedwater temperature for optimal efficiency at a variety of operating conditions.
In power plants, the power output, temperature of exhausted flue gas, and efficiency are heavily impacted by adjusting a temperature of the feedwater system, i.e., the final feedwater temperature (FFWT), that enters the steam generating element, for example, a boiler in the plant. Where boilers are configured to accommodate combustion of different types of fuels, and/or operation at different loads, each set of operational conditions may require a unique final feedwater temperature (FFWT) in order to achieve maximum efficiency.
A first aspect of the disclosure provides a structure comprising: structure comprising a turbine having a plurality of valved steam extraction ports fluidly connected to a steam extraction line for delivering steam to a feedwater heater.
A second aspect of the disclosure provides system for controlling a power output of a power plant, comprising a variable feedwater heating system including: a turbine having a plurality of valved steam extraction ports fluidly connected to a steam extraction line for delivering steam to a feedwater heater; a control system for opening and closing each valve of the plurality of valved steam extraction ports in response to a desired final feedwater temperature; and a steam generator in circuitous fluid connection with the variable feedwater heating system.
A third aspect of the disclosure provides method for optimizing a final feedwater temperature comprising: providing a variable feedwater heating system including: a turbine having a plurality of valved steam extraction ports fluidly connected to a feedwater heater; and actively controlling an opening and a closing of each valve of the plurality of valved steam extraction ports in response to a desired final feedwater temperature.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.
At least one embodiment of the present invention is described below in reference to its application in connection with the operation of a power plant. Although embodiments of the invention are illustrated relative to a power plant including a boiler and a steam turbine, it is understood that the teachings are equally applicable to other types of power plants including, but not limited to, geothermal energy or solar energy plants, fossil fuel plants, biomass-fueled plants, combined cycle plants, nuclear plants and other types of power plants. Further, at least one embodiment of the present invention is described below in reference to a nominal size and including a set of nominal dimensions. However, it should be apparent to those skilled in the art that the present invention is likewise applicable to any suitable power plant. Further, it should be apparent to those skilled in the art that the present invention is likewise applicable to various scales of the nominal size and/or nominal dimensions.
As indicated above, aspects of the invention provide a feedwater heater cycle structure. Referring to
Feedwater heaters 20A-20n receive feedwater supplied by feedwater pump 23 via feedwater input line 25. It is noted that additional pumps may be present throughout the system to achieve and maintain the required maximum operating pressure.
As shown in
The extraction fraction of steam from HP turbine 50 is routed to at least one of feedwater heaters 20A-20n (in
Steam generator 30 may, in some embodiments, be a boiler which burns fossil fuels, biomass, or other fuels 15 in order to generate steam. In other embodiments, steam generator 30 may be a heat exchanger, as in a nuclear power plant, a geothermal energy source in a geothermal plant, waste heat, as in a combined cycle plant or other suitable steam source. In any event, steam is produced in steam generator 30, following which steam generator 30 releases high temperature steam via output steam line 70, and expels flue gas 35.
Output steam line 70 feeds high pressure, high temperature steam into the high pressure turbine 50, where the steam is used to generate power in high pressure turbine 50, which drives a shaft 51 to rotate a rotor within a stationary stator in generator 97. Subsequently, exhaust line 80 may feed steam into reheater 84 (in a case of a reheat cycle) or directly into the intermediate pressure turbine 90 through line 86 to generate intermediate pressure (IP) output. An extraction fraction is directed back to feedwater heater 20A as described above via steam extraction line 40. Similarly, steam used to generate power in IP turbine 90 is fed into low pressure (LP) turbine 95, less an extraction fraction which may be fed back into the feedwater heater cycle via second steam extraction line 41. In some embodiments, there may be more than one feedwater extraction in IP steam turbine 90 as described above relative to HP turbine 50. After passing through low pressure steam turbine 95, the steam is condensed in condenser 96 and recycled through the feedwater heater cycle via feedwater pump 23 and feedwater input line 25.
As discussed above, the final feedwater temperature is a parameter of operation of power plant 10 that ideally varies according to the type of fuel used to power steam generator 30 and power plant load requirements. FFWT has significant impact on performance of steam generator 30. Tailoring the FFWT according to the fuel source being used allows steam generator 30, and therefore plant 10, to operate at optimal efficiency. Similarly, tailoring the FFWT to accommodate part load operation also allows for improved efficiency.
As shown in
In order to vary a FFWT, HP steam turbine 50 may be provided with a plurality of steam extraction ports, or feedwater extraction ports.
A plurality of pipes 56, 57, 58, 59 (labeled in
The opening and closing of valves 66, 67, 68, 69 may be controlled by control system 75, in response to a desired final feedwater temperature. Control system 75 is shown in greater detail in
As shown, control system 75 includes a processor 102, a memory 104, and input/output (I/O) interfaces 106 operably connected to one another. Further, control system 75 is shown in communication with display 108, external I/O devices/resources 110, and storage unit 112. I/O devices 110 may include any type of user input device such as a mouse, keyboard, joystick, or other selection device. In general, processor 102 executes computer program code which provides the functions of control system 75. Such program code may be in the form of modules, including fuel module 114, load module 116, ambient conditions module 118, and system degradation module 120, among other possible modules, and may be stored in memory 104 and/or storage unit 112, and perform the functions and/or steps of the present invention as described herein. Memory 104 and/or storage unit 112 can comprise any combination of various types of data storage media that reside at one or more physical locations. To this extent, storage unit 112 could include one or more storage devices, such as a magnetic disk drive or an optical disk drive. Still further, it is understood that one or more additional components not shown in
As noted, control system 75 may include one or more of a fuel module 114 for analyzing an input type of fuel 15, a load module 116 for analyzing a load at which the turbine is operating, typically in megawatts, an ambient conditions module 118, for analyzing ambient conditions in HP turbine 50 as may be detected by a sensor or sensors in the plant (not pictured), and a system degradation module 120 for analyzing any degradation to the system which may impact efficiency, performance and/or other aspects of operation over the lifespan of various components. Other modules for analyzing other system parameters are also contemplated, and may also be included.
Separately or collectively, modules 114, 116, 118, and 120 may include an algorithm for mapping operating conditions, including fuel, load, ambient conditions (e.g., temperature), and degree of degradation, to a particular steam extraction port 46, 47, 48, 49. In one embodiment, this logic may be embedded into each of the modules 114, 116, 118, 120. In another embodiment, this logic may reside in memory 104 on control system 75, which receives data from a variety of sources which may include, e.g. sensors in plant 10, operator input, etc. The particular steam extraction port 46, 47, 48, 49 to which conditions are mapped is the port which, when the respective valve 66, 67, 69, 69 is opened, an optimum FFWT is provided. Following the determination of which valve 66, 67, 68, 69 must be opened to achieve the optimum FFWT, a signal is transmitted via coupler 100, causing the opening (or closing) of the appropriate valve 66, 67, 68, 69. Following determination and execution of opening and/or closing the appropriate valve 66, 67, 68, 69, data may be archived, reported, and stored in memory 104 and/or in storage unit 112. In various embodiments, modules 114, 116, 118, 120 may be part of a standalone control system 75, or may be integrated with any other plant control system which may be used.
Returning to
As shown in
In addition to affecting efficiency of steam generator 30, the final feedwater temperature also impacts the temperature of flue gas 35 exhausted from power plant 10. Control of the temperature of flue gas 35 is important because of the chemicals present in flue gas 35 from the combustion process, particularly sulfur. Flue gas 35 must have a high enough temperature to prevent sulfuric acid condensation in the flue gas 35 pipes, to avoid corrosion damage. However, an unnecessarily high temperature of flue gas 35 results in dissipating energy to the atmosphere, which could be used to generate more steam. Balancing the objectives of avoiding corrosion and maximizing efficiency requires delicate balance, which is affected by the use of different fuels 15 and operation at part load conditions break that balance. These factors are included in those accounted for in control system 75.
As discussed above, steam is also returned to HP turbine 50 such that steam generator 30 is in circuitous fluid connection with the variable feedwater heating system, i.e., the steam flows fluidly through the cycle.
In addition to accommodating a variety of fuel 15 sources as detailed above, the use of a plurality of feedwater extraction ports 46, 47, 48, 49 as described above further allows for optimization of FFWT in accordance with turbine load in order to maximize efficiency for the given load condition. An optimized final feedwater temperature may be determined substantially in accordance with the function,
FFWT=T
sat(P)
where
FFWT=final feedwater temperature;
Tsat=saturation temperature of the steam at the extraction port pressure; and
P=extraction port pressure in feedwater heater 20A.
For example, where the load is about 50% of full load (i.e. maximum capacity), pressure drops by 50% compared to pressure under full load conditions, and the FFWT is decreased as well. But valves 66, 67, 68, 69 can be adjusted according to the above function in order to achieve maximum efficiency and flue gas 35 control at these operating conditions.
In the embodiment shown in
Also provided is a method for optimizing a final feedwater temperature. A variable feedwater heating system is provided, which includes a high pressure turbine 50 having a plurality of steam extraction ports 46, 47, 48, 49, with a plurality of pipes 56, 57, 58, 59 connecting each of the steam extraction ports 46, 47, 48, 49 with steam extraction line 40. Each of the plurality of pipes 56, 57, 58, 59 includes a valve 66, 67, 68, 69 disposed therein for opening and closing the respective pipe 56, 57, 58, 59 to the passage of steam. Steam extraction line 40 fluidly connects the plurality of pipes 56, 57, 58, 59 with a feedwater heater 20A-C. In response to a desired final feedwater temperature, the opening and closing of valves 66, 67, 68, 69 is actively controlled via control system 75. As described above, control system 75 allows an appropriate extraction pressure of steam to be conducted to feedwater heaters 20A . . . n to achieve maximum efficiency and/or control flue gas 35 temperature.
As used herein, the terms “first,” “second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of “up to about 25 mm, or, more specifically, about 5 mm to about 20 mm,” is inclusive of the endpoints and all intermediate values of the ranges of “about 5 mm to about 25 mm,” etc.).
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
