Description:STEAM COOLING SYSTEM FOR BALANCE PISTON OF SINGLE FLOW STEAM TURBINE AND A METHOD THEREOF”

FIELD OF THE INVENTION:
[001] The invention relates to steam cooling system for balance piston of single flow intermediate pressure steam turbine and a method thereof.

BACKGROUND OF THE INVENTION AND PRIOR ART:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[003] In the power generation industry, steam turbines are often used to generate electrical power. The steam turbines often are positioned in a series of varying steam pressures so that a high pressure (HP) turbine, an intermediate pressure (IP) turbine, and a low pressure (LP) turbine are respectively positioned one after the other. Steam Turbines are devices used to convert thermal energy of steam into mechanical energy and then into electrical energy by connecting rotor shaft to generator. The steam turbines are arranged by different module, each module helping to extract little more energy from steam before it’s exhausted. All three modules HP, IP & LP turbines are mounted on same rotor axle and all turning the generator at the same time.

[004] With reaction blading, the reaction of steam causes the blades of the rotor to turn. The reaction blading provides a very high pressure drop and, accordingly, the thrust across the rotor is quite high. Accordingly, an imbalance can arise between the HP turbine and the IP turbine and/or the LP turbine.
[005] In the current market scenario with emphasis on renewables, lower rating turbines apt for configuring with flexible operations are required to reduce carbon footprints/increase the efficiency of existing steam turbines. In pursuant of this, lower rating supercritical sets are required which shall take are of flexible operation and higher efficient turbine cylinder. For lower rating supercritical sets single flow IP turbine shall be more efficient and cost effective.

[006] Accordingly, for certain applications, turbine with reaction blading and a straight through or single flow configuration is desirable.

[007] Although a split flow turbine can be used in an attempt to reduce or eliminate the thrust, split flow turbine designs can be expensive and complex. Split flow designs are also often associated with thermal efficiency loss.

[008] In single flow IP turbine, therefore, a balance piston is positioned at the inlet to the IP in an attempt to balance the axial thrust emerging from steam for forces in blades. However, even with such a balance piston, the turbine system may still experience problems due to creep deformation of the balance piston.

[009] For example, at running or operational speeds, a large tangential stress in the rotor material can occur in a large diameter balance piston, and creep deformation can occur due to the balance piston's location near a hot inlet of the IP turbine. The elevated temperature lowers the allowable limit of creep rupture strength.

[0010] Referring to Patent EP1050666A2 provides a solution of using steam for balancing axial thrust as well as cooling of balance piston however provides a steam cooling system and associated methods having cooling steam routed between a HP turbine and a combined IP-LP turbine to reduce potential damage to the balance piston. For a turbine, incorporating the solution informed in the patent shall be costly and complex, and may not be feasible.

[0011] Thus, there exists a need of a steam cooling arrangement of balance piston to lower down the temperature of balance piston and limit the creep deformation/ creep rupture strength in balance piston area. A steam cooling arrangement is needed to maintain the temperature of the balance piston using colder steam extracted from the steam turbine flow path region. This shall enable to keep the balance piston diameter as required for thrust balance and creep deformation/rupture strength within allowable limit.

OBJECTS OF THE INVENTION:
[0012] An object of the present invention is to provide a steam cooling system and associated methods having cooling steam routed between a HP turbine and an IP turbine to reduce potential damage to the balance piston.

[0013] Another object of the present invention is to provide a steam cooling system and associated methods that works well in all design cases of differential thermal expansion of steam routing pipe and turbine casing.

[0014] Still another object of the present invention is to provide a steam cooling system and associated methods that allows uniform cooling of balance piston to lower down the operating temperature of the balancing piston.

[0015] Yet another object of the present invention is to provide a steam cooling system and associated methods having a straight through design for each of a series of turbines to thereby reduce the costs and complexity for the turbine system.

[0016] One another object of the present invention is to provide a steam cooling system and methods which significantly reduces or eliminates the efficiency losses of redirecting the steam that is found in a split flow IP design.

[0017] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION:
[0018] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0019] The invention relates to cooling the balance piston by extracting steam from the flow path and lowering the operating temperature, thereby increasing the allowable limit of creep deformation/creep rupture and, as a result, maintaining the desired diameter for thrust balance.
[0020] According to the invention, there is provided a steam cooling system for balance piston of a single flow intermediate pressure steam turbine, the said cooling system involves below steps:
- at least one cooling steam extraction chamber [11] adjacent to initial blade stages of the turbine and along the main steam axial flow path in the turbine and at an axial location where the temperature of the main steam is sufficient to maintain the cooling of the balance piston and pressure of the main steam is suitable to create the siphoning of cooling steam in multiple cooling conduits [40,41];
- at least one cooling steam upstream conduit [40] having its inlet connected to extraction chamber [11] and an outlet adjacent balance piston [31];
- at least one cooling steam downstream the conduit [41] receiving the cooling steam from the balance piston [31] and having its outlet connected to re-entry chamber [12];
- at least one cooling steam re-entry chamber [12] located beyond the extraction chamber [11] and along the main steam axial flow path in the turbine and at an axial location where the pressure of the main steam is suitable to create the negative pressure enough to siphon cooling steam in the cooling conduits [40,41];
wherein cooling steam pressure is maintained and controlled through a siphoned flow using the extraction chamber [11] and re-entry chamber [12] that the cooling steam conduit pressure is operationally maintained at a predetermined level greater than the inlet pressure of the Intermediate Pressure steam turbine without the need of external devices and sensors.

[0021] The conduits [40,41] are connected at their inlet and outlet ends through expansion joints [42].

[0022] The interaction of cooling steam with balance piston [31] ensures uniform cooling of balance piston and keeps the creep deformation/rupture strength of balance piston within allowable limit.

[0023] The cooling steam re-enters the turbine and mixes with the main steam.

[0024] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0025] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0026] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANAYING DRAWING:
[0027] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:
Figure 1 shows: longitudinal cross sectional view of a steam cooling system for a balance piston positioned in IP turbine according to the present invention.

[0028] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAIL DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPNAYING DRAWING:
[0029] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0030] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these illustrated embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime and double prime notation if used indicate similar elements in alternative embodiments.

[0031] The instant invention pertains to technology involving an invention directing to steam cooling for balance piston of single flow intermediate pressure steam turbine and a method thereof.

[0032] Reference may be made to Figure 1 showing the major components of single flow IP turbine namely inner casing [10], outer casing [20] and rotor [30], as understood by those skilled in the art. The inner casing [10] of IP Turbine comprises of separate chambers [11,12] for extraction and re-entry of steam respectively as shown in Figure 1. The steam upstream conduit [40] e.g., piping, tubing, or line, having an inlet connected to the extraction chamber [11] and an outlet at the balance piston [31], is connected through expansion joints [42]. The expansion joints [42] are provided at the steam conduit connections with extraction chamber and balance piston to take care of any differential thermal expansion and inner casing [10] deformation.

[0033] As the working main steam enters the IP turbine, it interacts with the first stage blades in rotor area and rotary work of turbine is extracted from the steam resulting in a relative drop of steam enthalpy i.e. lowered temperature and pressure of the working steam. This lower temperature, pressure steam (or cooling steam hereinafter) is drawn after certain blade stages wherein from through the extraction chamber [11] temperature and pressure of the working main steam is low enough to be extracted as cooling steam for balance piston cooling. Once the cooling steam exits from the outlet end of the steam upstream conduit [40], it is communicated to the balance piston [31].

[0034] By virtue of the stream travel over the various turbine blade stages and subsequent pressure and temperature drop and described hereinabove, a negative pressure is maintained during the entire stream travel from the steam upstream conduit [40] and steam downstream conduit [41] in order to maintain or regulate the cooling steam conduit pressure at a predetermined level greater than the inlet pressure. This is because the re-entry chamber [12] is preferably located at a distal location furtherer with respect to the extraction chamber [11] in the steam flow path within the turbine and therefore have to interact with a lot more number of blade stages resulting in a further drop in main stream pressure and temperature. The steam pressure and temperature at the location of the re-entry chamber [12] will always be lower relative to the steam pressure and temperature at the extraction chamber [11].

[0035] Upon interaction of this lower temperature pressure steam with balance piston [31], the cooling steam experiences a slight increase in temperature while the temperature of the balance piston drops to a controlled level. The cooling steam, upon cooling the balancing piston [31], is siphoned to the steam downstream conduit [41] travelling in which the cooling steam enters and mixes with the main steam through the re-entry chamber [12].

[0036] This proposed solution enables the uniform cooling of balance piston which results in keeping the creep deformation/rupture strength within allowable limit balance piston diameter and subsequently required diameter of thrust balance piston.

[0037] As illustrated in Figure 1, the present invention includes a method of steam cooling a turbine system [10]. The method preferably includes positioning a balance piston [31] adjacent the inlet [17] of an intermediate pressure (IP) steam turbine, providing a steam cooling path upstream and downstream paths [40, 41] and in communication with the balance piston [31], and controlling cooling steam pressure during cooling steam flow using extraction chamber and re-entry chamber so that the cooling steam conduit pressure is operationally maintained at a predetermined level greater than the circulating steam at balance piston [31].
[0038] From the above, working of invention can be understood particularly by a person skilled in the art.

ADVANTAGES :
[0039] Since the said methodology works on the differential pressure-based siphoning of the cooling steam in the steam upstream and downstream conduits, it completely eliminates the need of control valves being positioned in the steam cooling flow path, sensors to record pressure in between steam conduits, electronic communicators, opening or closing mechanisms responsive to the sensed pressure or the delay in these mechanisms. Not only it reduces the construction and operational cost of the turbine but also reduces the associated operator’s dexterity and supervising needs to be engaged during the emergency situations or during malfunctioning.

[0040] Also by virtue of the siphon based design, the proposed solution works well in all designed cases of differential thermal expansion of pipe and casing while ensuring uniform cooling of balance piston to lower down the operating temperature of balance piston and in turn limit the creep deformation and creep rupture strength.

Reference Numerals

101 Flange connection at casing outer surface and Expansion joints to take care of differential thermal expansion
102 Cooling steam after 4th stage
103 After cooling of BP, steam entry after 5th stage
104 Cooling steam (Entry)
105 Chamber for extraction of steam
106 Chamber for entering of steam in flow path
107 Steam (exit)
11, 12 Chamber
40 Upstream Conduit
41 Downstream Conduit
31 Balance Piston
10 Inner casing
20 Outer casing
30 Rotor
42 Expansion joint
17 Inlet

[0041] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0042] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0043] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0044] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[0045] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0046] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0047] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
, Claims:We Claim:

1. A steam cooling system for balance piston of a single flow intermediate pressure steam turbine, the said cooling system comprising:
 at least one cooling steam extraction chamber [11] adjacent to initial blade stages of the turbine and along the main steam axial flow path in the turbine and at an axial location where the temperature of the main steam is sufficient to maintain the cooling of the balance piston and pressure of the main steam is suitable to create the siphoning of cooling steam in multiple cooling conduits [40,41];
 at least one cooling steam upstream conduit [40] having its inlet connected to extraction chamber [11] and an outlet adjacent balance piston [31];
 at least one cooling steam downstream the conduit [41] receiving the cooling steam from the balance piston [31] and having its outlet connected to re-entry chamber [12];
 at least one cooling steam re-entry chamber [12] located beyond the extraction chamber [11] and along the main steam axial flow path in the turbine and at an axial location where the pressure of the main steam is suitable to create the negative pressure enough to siphon cooling steam in the cooling conduits [40,41];
wherein cooling steam pressure is maintained and controlled through a siphoned flow using the extraction chamber [11] and re-entry chamber [12] that the cooling steam conduit pressure is operationally maintained at a predetermined level greater than the inlet pressure of the Intermediate Pressure steam turbine without the need of external devices and sensors.

2. The steam cooling system for balance piston of a single flow steam turbine as claimed in claim 1, wherein the conduits [40,41] are connected at their inlet and outlet ends through expansion joints [42].
3. The steam cooling system for balance piston of a single flow steam turbine as claimed in claim 1 or 2, wherein the interaction of cooling steam with balance piston [31] ensures uniform cooling of balance piston and keeps the creep deformation/rupture strength of balance piston within allowable limit.

4. The steam cooling system for balance piston of a single flow steam turbine as claimed in claims 1-3, wherein the cooling steam re-enters the turbine and mixes with the main steam.

5. A method of steam cooling a turbine system 10 comprises steps of: positioning a balance piston [31] adjacent inlet [17] of an intermediate pressure (IP) steam turbine, providing a steam cooling path upstream and downstream paths [40, 41] and in communication with the balance piston [31] , and controlling cooling steam pressure during cooling steam flow using extraction chamber [11] and re-entry chamber[12] that the cooling steam conduit pressure is operationally maintained at a predetermined level greater than the circulating steam at the balance piston [31].