Patent Application
20180195392
The present disclosure relates generally to a turbomachine system, and more particularly, to a steam turbine system with an impulse stage having a plurality of nozzle groups individually controlled.
With the rise of renewable energies available, steam power plants operate in low or minimal load in order to react to fluctuations in the power generation of these renewable energies, such as solar and wind. However, steam power plants that operate in sliding pressure mode still have to maintain a certain fixed minimum pressure mode during part load in order to protect the boiler from overheating. State of the art steam power plants operating in sliding pressure mode maintain this fixed minimum pressure mode at low and minimum loads by throttling the live steam via the high pressure (HP) turbine entry valve. The lower the plant load, the higher the throttling losses and the lower the cycle efficiency.
A first aspect of the disclosure provides a steam turbine system including a plurality of blade stages arranged axially along a first shaft, an impulse stage configured upstream of the plurality of blade stages, the impulse stage having an impulse wheel and a casing, the casing including a plurality of inlet sections with each of the plurality of inlet sections having a corresponding nozzle group and operatively connected to a corresponding control valve controlling a first steam flow through the corresponding nozzle group, a first inlet configured to provide the first steam flow through the impulse stage and the plurality of blade stages, and, a second inlet configured to provide a second steam flow to the plurality of blade stages and bypassing the impulse stage.
A second aspect of the disclosure provides a power plant including a steam source for generating a steam flow, a high pressure turbine system having a plurality of blade stages arranged axially along a first shaft, an impulse stage configured upstream of the plurality of blade stages, the impulse stage having an impulse wheel and a casing, the casing including a plurality of inlet sections with each of the plurality of inlet sections having a corresponding nozzle group and operatively connected to a corresponding control valve controlling a first steam flow through the corresponding nozzle group, a first inlet configured to provide the first steam flow through the impulse stage and the plurality of blade stages, and, a second inlet configured to provide a second steam flow to the plurality of blade stages and bypassing the impulse stage, an intermediate turbine system and low pressure turbine system fluidly coupled to the high pressure turbine system, and, a first generator driven by the first shaft.
A third aspect of the disclosure provides an impulse stage system for a steam turbine system, the impulse stage system including an impulse wheel arranged on a first shaft, and, a casing including a plurality of inlet sections, wherein each of the plurality of inlet sections has a corresponding nozzle group and is operatively connected to a corresponding control valve controlling a first steam flow through the corresponding nozzle group, a first inlet configured to feed the first steam flow through the impulse stage.
The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed.
These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which:
It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.
As an initial matter, in order to clearly describe the current disclosure it will become necessary to select certain terminology when referring to and describing relevant machine components within a steam turbine. When doing this, if possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. Unless otherwise stated, such terminology should be given a broad interpretation consistent with the context of the present application and the scope of the appended claims. Those of ordinary skill in the art will appreciate that often a particular component may be referred to using several different or overlapping terms. What may be described herein as being a single part may include and be referenced in another context as consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single part.
In addition, several descriptive terms may be used regularly herein, and it should prove helpful to define these terms at the onset of this inlet section. These terms and their definitions, unless stated otherwise, are as follows. As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through the turbine engine or, for example, the flow of air through the combustor or coolant through one of the turbine's component systems. The term “downstream” corresponds to the direction of flow of the fluid, and the term “upstream” refers to the direction opposite to the flow. The terms “forward” and “aft,” without any further specificity, refer to directions, with “forward” referring to the front or compressor end of the engine, and “aft” referring to the rearward or turbine end of the engine. It is often required to describe parts that are at differing radial positions with regard to a center axis. The term “radial” refers to movement or position perpendicular to an axis. In cases such as this, if a first component resides closer to the axis than a second component, it will be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. It will be appreciated that such terms may be applied in relation to the center axis of the turbine.
As used herein, “approximately” indicates+/−10% of the value, or if a range, of the values stated.
Typically, steam power plants generate power while operating in either a constant pressure mode or a sliding pressure mode. While operating in the constant pressure mode, steam turbine control valves are throttled in order to control the pressure of the steam at the steam turbine inlet. While operating a steam power plant in the sliding pressure mode, the control valves are maintained in a constant position, and the steam pressure is controlled by boiler control loops. State of the art steam power plants operating in sliding pressure mode maintain a minimum pressure at low and minimum loads by throttling the live steam via the HP turbine entry valve. Throttling is used to shed load by reducing the valve area. When steam passes through a narrow area, it acquires kinetic energy at the expense of heat (enthalpy). The expansion of the steam beyond the valve causes some of the generated kinetic energy to be converted to frictional heat. The result is the retention of some enthalpy, but a loss in pressure and an increase in entropy (loss in availability of energy). The pressure drop produced at the valves of the turbine inlet and all subsequent fixed blades restricts the mass flow through the turbine system and hence the power output. The lower the plant load, the higher the throttling losses and the lower the cycle efficiency.
In contrast to the state of the art where impulse wheels are used for fixed pressure steam power plants for the total range of load cases, embodiments of the present disclosure provide an impulse wheel used in sliding pressure power plants during low load and minimum load during fixed minimum pressure operation.
Referring to the drawings,
In operation, steam 26 enters an inlet 28 of turbine 10 and is channeled through stationary vanes 22. Vanes 22 direct steam 26 downstream against blades 20. Steam 26 passes through the remaining stages imparting a force on blades 20 causing shaft 14 to rotate. At least one end of turbine system 10 may extend axially away from rotor 12 and may be attached to a load or machinery (not shown) such as, but not limited to, a generator, and/or another turbine. Steam 26 exits turbine 10 as exhaust 29 through outlet 30.
In
In general, embodiments of the present disclosure integrate an impulse stage with a high pressure (HP) turbine in order to reduce the resulting throttling losses during low load operation of a steam power plant. The impulse stage, in general, is configured upstream of the blade stages of the HP turbine and includes an impulse wheel and a casing having nozzle groups.
In the exemplary embodiment shown in
Nozzle groups 110, 112, 114 and 116 each may have a plurality of individual nozzles, e.g., nozzle 128 and nozzle 130. In an exemplary embodiment, each nozzle group 110, 112, 114, and 116, may have a different number of individual nozzles included in the nozzle group. For example, inlet section 102 may have nozzle group 110 with eight individual nozzles, while inlet section 104 may have nozzle group 112 with eleven individual nozzles. Further, in an exemplary embodiment, nozzle groups 110, 112, 114, and 116 may vary in the size of individual nozzles. For example, inlet section 108 may have nozzle group 116 with various individual nozzles 130 that may be larger than nozzles 128 in nozzle group 114 of inlet section 106.
Still referring to
For clarity, the operation of steam turbine system 200 in
This is in contrast to state of the art steam power plants throttling the live steam via the main HP turbine control valve (what would be labelled as inlet 226 in
Control valves 120, 122, 124 and 126 are controlled by a control module (not shown). In an embodiment, inlet sections 102, 104, 106, and 108 are designed such that all control valves 120, 122, 124 and 126 are open when the steam power plant load decreases to a load small enough that the minimum pressure mode should be maintained in order to protect the boiler. Usually, the fixed minimum pressure mode in sliding pressure power plants is maintained, e.g., starting at approximately 30-40% load. Further, in an embodiment, the inlet sections are designed such that only one of control valves 120, 122, 124 or 126 is fully open during minimum plant load operation. For the remaining decreasing load points between the start of maintaining the minimum pressure mode and the minimum plant load operation, the available control valves are opened or closed sequentially. As such, throttle losses can be reduced because control valves 120, 122, 124 and 126 are throttled one at a time.
In an embodiment, inlet sections 102, 104, 106, and 108 are designed such that diametrically opposing inlet sections have their corresponding control valves fully open during minimum plant load operation. For example: inlet section 102 having control valve 120 is diametrically opposed to inlet section 106 having control valve 124; and, inlet section 104 having control valve 122 is diametrically opposed to inlet section 108 having control valve 126.
Thus, in contrast to state of the art steam turbine systems, embodiments of the present disclosure throttle control valves 120, 122, 124 and 126 in the impulse stage inlets during fixed minimum pressure mode instead of throttling a valve controlling steam through inlet 226 (shown in
Plant 500 has steam turbine system 502 as HP turbine 524 that is fluidly coupled to IP turbine 522 and low pressure (LP) turbine 526 in a manner known in the art.
In example embodiments, HP turbine 524 of plant 500 may be any of steam turbine systems 200, 300, and 400 shown in
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
