Description:AN IMPROVED SOLUTION TO RETROFIT A 4-PASS VERTICAL CHANNEL-UP TYPE LOW PRESSURE HEATER HAVING CUPRO-NICKEL TUBES

FIELD OF INVENTION :
[001] Invention is related to retrofitting solutions for heat exchangers known as low pressure feed water heaters used in thermal power stations for preheating fed water.

BACK GROUND & PRIOR ART OF THE INVENTION :
[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] Low pressure Feed water heaters are part of regenerative cycle of thermal plants, deployed to improve the thermal efficiency of Rankine cycle by preheating in multiple stages -the condensate received from condenser through condensate extraction pump. The low pressure feed water heater uses steam extracted from turbines on shell side to heat the condensate flowing through U-tubes, of a shell and tube type heat exchanger. Normally the condition of heating steam is wet, implying heat is extracted by condensing the steam, followed by sub-cooling. Thus, in most of the cases, a typical low pressure feed water heater has two zones for steam extraction namely- condensing and sub-cooling zones. However, in some cases steam condition is superheated thereby necessitating heat extraction by de-superheating of steam followed by condensing of steam.

[004] Some of the old designs employed tubes made of Cupro-Nickel alloys, which was good thermally conductive material but has less corrosion and erosion resistance. Moreover, the usual installation method used was either horizontal or vertical channel-down position. However, very few plant layouts focussing on saving the amount of piping deployed and the space, preferred vertical channel-up type heaters, which had tube bundle hanging downwards from the tube sheet with ease of removability of tube bundles from fixed shells.

PRIOR ART:
[005] Previous design which is to be retrofitted has a 4-pass arrangement of tubes as shown in figure 1. Further, previous design is fitted with cupro-nickel U-tubes. The design is such that allows removal of tube bundle facilitated by opening a bolted joint between tubesheet and channel flange. The channel header has a flow arrangement for tubeside fluid that suits 4-pass arrangement of this design. Referring to Fig. 1, wherein fed water enters the channel cylinder 1 through nozzle 2, into a chamber 4 through a sector-shaped conduit 3. Chamber 4 is formed by walls created by dividing plate 10 and a semi-circular barrel 11. Chamber 4 enables entry of fed water to U-tubes through Pass-I (Leg 1 of U-tube 5). U-tubes are hanging vertically with legs pointing upwards. Feed water flowing through U-tube 5 gets heated by steam on shell side while flowing downwards i.e., Pass-I and also during return in upward direction called Pass-II. Feed water emerges in channel cylinder 1 in zone 7, from all the return legs of U-tubes comprising of Pass-I & II. Zone 7 has more tube holes on outer periphery to enable re-entry of feed water received from Pass II into Pass-III of U-tube 6. Feed water again gets heated by shell side steam, while flowing through downward Pass-III and upward return pass-IV to come back to channel cylinder 1 into the chamber 8 to finally flow out through nozzle 9.

OBJECTS OF THE INVENTION:

[006] An object of the invention is to provide Low pressure feed water heater used in thermal power stations for preheating feed water.

[007] Another object of the invention is to provide Low pressure feed water heater used in thermal power stations for preheating feed water, which uses better material i.e., stainless steel of tubes having proven better longevity but lesser thermal conductivity as compared to cupro-nickel of old heater without compromising on thermal performance.

[008] Still another object of the invention is to provide Low pressure feed water heater used in thermal power stations for preheating feed water, which simplifies the 4-pass arrangement and improvises on steam flow path for better utilization of steam superheat.

[009] Yet another object of the invention is to provide Low pressure feed water heater used in thermal power stations for preheating feed water, which accommodates the different design of tube bundle of new heater in a size that does not disturb existing piping and support interfaces.

[0010] One another object of the invention is to provide Low pressure feed water heater used in thermal power stations for preheating feed water, which retains the facility of old heater of having tube bundle removability from the fixed supported shell.

[0011] 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:

[0012] 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.

[0013] The present invention proposes an improved retrofit design using stainless steel tubes to replace old cupro-nickel tubed vertical channel up type low pressure feed water heater with improved and simplified 4-pass arrangement, a new split-flow design of de-superheating zone and a new three-quarter condensing zone having baffles displaced by 90-degree angle, while retaining the external interfacing of old design and ease of tube bundle removability to enable smooth retrofitting.

[0014] According to the invention, there is provided Low pressure feed water heater used in thermal power stations for preheating feed water comprising of:
[0015] Four-pass arrangement in channel cylinder ensuring equal distribution of tubes in each pass with correct deployment of de-superheating zone on fourth pass;
[0016] Improved de-superheating zone including features of (i) split flow steam path leading to less pressure drop while meeting the heat duty requirements (ii) Entrance through an annular path to lead steam from nozzle placed at piping position to enter the fourth quarter of tube bundle enclosing tubes from pass-IV (iii) a unique shape of desuperheating zone owing its uniqueness to occupying a quarter of tube bundle for a design length having split- flow i.e., one entrance and two exits of steam;

[0017] A condensing zone is provided to employ the improved de-superheating zone, in which the zone occupies three-quarters of tube bundle for the length covered by one-quarter de-superheating zone and for the rest of length of tube bundle all four quarters of tube bundle are occupied by the condensing zone;

[0018] An arrangement of baffles in three- quarter portion of condensing is provided to have proper steam flow path in condensing zone, in which the arrangement comprises of semi-circular baffles displaced by 90-degree angle alternately.

[0019] 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.

[0020] 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.

[0021] 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 ACCOMPANYING DRAWINGS :

[0022] 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: Four-pass arrangement of tubes according to the Prior Art.

Figure 2 shows: De-superheating zone in Prior Art.

Figure 3 shows: A simplified four-pass arrangement in channel cylinder in accordance with the present invention

Figure 4 shows: A new design of de-superheating zone of the present invention.

Figure 5 shows: Condensing zone according to the Present Invention.

[0023] 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 PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS:

[0024] 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.

[0025] The present invention makes a disclosure regarding a technology pertaining to an invention directing to Low pressure feed water heater used in thermal power stations for preheating feed water.

[0026] The design objectives translated into a design with a unique combination of following features:

[0027] Improved 4-pass arrangement: A simplified 4-pass arrangement in channel cylinder while keeping existing nozzle (entrance and exit pipe piece attached to channel cylinder) arrangement, as shown in Figure-3. This arrangement ensures equal distribution of tubes in each pass. This arrangement also enables correct deployment of de-superheating zone on fourth pass only. Ideally, desuperheating zone should be deployed as the last heat addition phase for feed water flowing through U-tubes i.e., fourth pass of U-tubes. In previous design, de-superheating zone is adding heat to multiple tube passes, having feed water flowing at different temperatures and in different directions(figure-2).

[0028] Improved design of de-superheating zone: A new design of desuperhetaing zone is employed in new design (Figure-4) which includes features such as (i) split flow steam path leading to less pressure drop while meeting the heat duty requirements. (ii) Entrance through an annular path to lead steam from nozzle placed at existing piping position to enter the fourth quarter of tube bundle enclosing tubes exclusively from pass-IV. (iii) A unique shape as shown in figure 4 of desuperheating zone owing its uniqueness to occupying a quarter of tube bundle for a design length only having split- flow i.e., one entrance and two exits of steam. One exit is towards U-bend end of bundle, while other exit is towards tubesheet end of tube bundle. Both exits lead to different portions of condensing zone to enable further heat transfer from condensing steam over rest of the tube bundle. (Refer Figure-4)

[0029] New design of condensing zone: To employ improved design of de-superheating zone as mentioned above, a new design of condensing zone is provided which occupies three-quarters of tube bundle for the length covered by one-quarter de-superheating zone (Refer figure-4). For the rest of length of tube bundle all four quarters of tube bundle are occupied by condensing zone. To have proper steam flow path in condensing zone, a new arrangement of baffles in three- quarter portion of condensing zone has been employed which comprises of semi-circular baffles displaced by 90-degree angle alternately. (Refer Figure-5).

[0030] No change in interfaces and ease offered by existing design: While there is complete change in internals in new design over previous design, this retrofit solution maintains the nozzle terminal connections to existing piping and would match the existing support. Further, ease of tube bundle removal is retained in new design also by opening shell-skirt joint and unbolting the channel to tube sheet joint.

ADVANTAGES OF THE INVENTION:

- Uses better material i.e., stainless steel of tubes having proven better longevity but lesser thermal conductivity as compared to cupro-nickel of old heater without compromising on thermal performance;

- Simplifies the 4-pass arrangement and improvises on steam flow path for better utilization of steam superheat;
- Accommodates the different design of tube bundle of new heater in a size that does not disturb existing piping and support interfaces;

- Retains the facility of old heater of having tube bundle removability from the fixed supported shell;

- User Friendly;

- Serves the purpose effectively.

TEST RESULT:

Parameter/feature Prior Art Invention Remarks
Total heating surface area, sq.m. 352 346.5 Redesigning of tube bundles and flow pass arrangement helped reduced surface area in spite of lesser thermal conductivity of tube material in invention as compared to prior art
Tube material Cupro Nickel Stainless steel Stainless steel has lesser thermal conductivity as compared to cupro-nickel but superior mechanical properties, erosion and corrosion resistance, implying longevity.
Tube bundle removability Exists Exists Although tube bundle is of different configuration and method to remove tube bundle has also changed, ease of bundle removability still remains.
User friendliness Maintained Complete internal details of equipment changed through invention, yet matching of new design with existing interfaces(piping and supports) remain unchanged ensuring user-friendliness.

WORKING OF THE INVENTION:

[0031] The Present invention is for developing a retrofit solution using stainless steel tubes, for an old cupro-nickel tubed low pressure feed water heater. The invention is designed to meet the design thermal performance expected by new version of previous heater. The invention shall fit into existing space (after removal of old cupro-nickel tube equipment), shall be seated on existing supporting arrangement and all the nozzles shall match existing pipelines. From the user point-of-view the retrofitting solution will be seamless, without occupying any extra space. Once the connections of nozzles with existing pipelines are made and process started, functional performance will be delivered. The thermal performance shall be for expected long life of stainless steel tubed heaters (30-40 years). The ease of removability of tube bundle shall be similar to old (prior art) heater, although bundle removal method shall be different. In prior art heater, bundle is removed by opening a bolted joint between part 22,23,24 in figure-2. Tube bundle is attached to tubeplate part 22 in figure-2. Once channel is removed, tubeplate(22) can be pulled out to remove tube bundle. In present invention, design is such that bundle is attached to skirt ( a shell extension welded to tubeplate) and can be removed by cutting shell-skirt joint and opening channel to tubeplate bolted joint. There is no bolted joint in present invention, between shell and tubeplate.

[0032] 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.

[0033] 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.

[0034] 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”.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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. Low pressure feed water heater used in thermal power stations for preheating feed water comprising of:
four-pass arrangement in channel cylinder ensuring equal distribution of tubes in each pass with correct deployment of de-superheating zone on fourth pass;
Improved de-superheating zone including features of (i) split flow steam path leading to less pressure drop while meeting the heat duty requirements (ii) Entrance through an annular path to lead steam from nozzle placed at piping position to enter the fourth quarter of tube bundle enclosing tubes from pass-IV (iii) a unique shape of desuperheating zone occupying a quarter of tube bundle for a design length having one entrance and two exits of steam;
a condensing zone is provided to employ the improved de-superheating zone, in which the zone occupies three-quarters of tube bundle for the length covered by one-quarter de-superheating zone and for the rest of length of tube bundle all four quarters of tube bundle are occupied by the condensing zone;
an arrangement of baffles in three- quarter portion of condensing is provided to have proper steam flow path in condensing zone, in which the arrangement comprises of semi-circular baffles displaced by 90-degree angle alternately.

2. The Low pressure feed water heater used in thermal power stations for preheating fed water as claimed in claim 1, wherein one exit is towards U-bend end of bundle, while other exit is towards tube sheet end of tube bundle.

3. The Low pressure feed water heater used in thermal power stations for preheating fed water as claimed in claim 2, wherein both exits lead to different portions of condensing zone to enable heat transfer from condensing steam over rest of the tube bundle.
4. The Low pressure feed water heater used in thermal power stations for preheating fed water as claimed in claims 1-3, which maintains the nozzle terminal connections to existing piping and would match the existing support, in which ease of tube bundle removal is retained in new design by opening shell-skirt joint and unbolting the channel to tube sheet joint.

5. The Low pressure feed water heater used in thermal power stations for preheating fed water as claimed in claims 1-4, wherein the unique shape of desuperheating zone owing its uniqueness to occupying a quarter of tube bundle for a design length having split- flow i.e., one entrance and two exits of steam.

6. The Low pressure feed water heater used in thermal power stations for preheating fed water as claimed in claims 5, wherein said one exit is towards U-bend end of bundle, while other exit is towards tubesheet end of tube bundle, in which Both exits lead to different portions of condensing zone to enable heat transfer from condensing steam over rest of the tube bundle.