Description:“METHOD TO REMOVE FLY ASH FROM REAR ARCH FLOOR TO SECOND PASS FOR TWO PASS DESIGN BOILER”

FIELD OF THE INVENTION:
[001] The present invention is related to fly ash removal in the high ash coal fired boilers. High ash coals while firing in boiler, commonly encounters the issue of ash accumulation, which increases during part load operation of boiler and sometime causes ash leakage. This invention discloses a method of removing such fly ash from deposit prone areas.

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 case of the two pass coal fired design of boiler, the flue gas flow takes a turn from the furnace outlet through a small horizontal pass, which is called as rear arch area, to the second pass. Through the rear arch, first pass and second pass of the boiler is connected. In the rear arch area, part of the Superheater (SH) and Reheater (RH) sections are accommodated.

[004] A large amount of ash accumulation in rear arch area of a boilers is a common problem in power plant and which leads to additional weight on rear arch panel & maintenance of boiler.

[005] According to the research of the parties concerned, the main causes for this ash accumulation issue are mentioned below:

- Prolonged operation of unit with Low Load
[006] Fly ash carrying capacity of flue gas is greatly affected by the velocity of the flue gas. Flue gas flow rate at rear arch area will influence the Ash settling possibility. During full load operation of unit, Flue gas flow rate will be more and higher gas velocity can be maintained @ Rear arch area zone. However, at Part load of boiler operation, Flue gas velocity will come down and the ability of the flue gas to carry fly ash is reduced, resulting in the deposition of ash at rear arch area.

- Higher Ash content in the Coal
[007] The amount of ash accumulation in the boiler is directly affected by the % ash present in the fired coal. Higher the ash content in the coal, the greater the ash accumulation amount in the boiler. The ash content of the designed coal is considered while designing the boiler. However, the coal used in the actual operation changes greatly, and the actual ash content of the coal is much higher than the designed coal ash content, so heavier ash accumulation is expected. Currently, number of plants are running with both design coal (Less Ash content %) and Worst Coal (More Ash content %). Unit operation with Worst cola is unavoidable.

PRIOR ART:
[008] Reference may be made to the following prior arts:
[009] Chinese patent No. CN104696975A describes the ash removal with the help of steam air cap soot blower system. The steam air cap soot blower system comprises blow-sweep steam pipes, steam air cap nozzles, a steam mother pipe and fins, etc. The superheated steam of the auxiliary steam header is used for blowing and sweeping each blow-sweep steam pipe in sequence. The deposited soot in the furnace arch or the horizontal flue secondarily flies is taken away by the flowing smoke.

[0010] Chinese patent No. CN204063079U describes ash removal with temperature measuring system. Temperature measuring system comprises of first hygrosensor on walling of flue and the second hygrosensor is arranged on the vertical direction of flue cross section, height is from any position between bottom to 1/3 section. This patent describes the soot blower system comprising of air supply pipe which is arranged on the magnetic valve on air supply pipe. Blast caps are distributed uniformly and Electromagnetic valve will open based on the feedback from first and second hygro sensor.

[0011] US patent No. 20180119952A1 describes ash removal with the help of compressed gas. The system includes a soot blower disposed within the boiler and a gas supply line in fluid communication with the soot blower and a gas source. The soot blower system is operating to inject compressed gas from the gas source into the boiler to remove the ash deposit on the surface of boiler. The compressed gas is carbon dioxide.

[0012] Indian patent application No.202011002783A dated 22/01/2020, describes ash removal method by mounting acoustic horns and rows of air blowing nozzles which flattens the ash heap and pushes the ash respectively. The placement and orientation of the air nozzles are governed by the effectiveness and vicinity of the boiler components.
None of the above prior arts can fulfill the requirements of the present invention, for which it is devised.

OBJECTS OF THE INVENTION:
[0013] An object of the invention is to provide a Method to remove fly ash from rear arch floor to second pass for two pass design boiler.

[0014] Another object of present invention to mitigate the ash accumulation at rear arch and reduce the boiler maintenance activity.

[0015] Yet another object of the invention is to provide a method of arrangement of gates to alleviate the ash accumulation in the rear arch of the boiler especially at part loads of the boiler operation.

[0016] 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:
[0017] 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.

[0018] During high ash coal firing in a two pass boiler, the flue gas velocity in the boiler is maintained much lower than the gas fired boiler. In the gas fired boiler, the flue gas velocity is maintained around 22 m/s, however such a high range of flue gas velocities are not possible in solid fuel fired boiler as the ash content in coal may erode the boiler tube, duct, burner component, etc. For a boiler designed with high ash content coal (Ash % around 30-40%), the flue gas velocity in the boiler is maintained between 8 – 10 m/s at full load of the boiler operation. However, when the boiler is operating at part load (Around 40 % to 60%), the velocity of the flue gas reduces significantly and prone for ash settlement. While lowering the load of the boiler, the flue gas velocity will fall in the range between 3 – 5 m/s. To avoid such low operating flue gas velocity at rear arch area, the invention describes a methodology which is simple, easy to manufacture, maintain and install in the boiler.
[0019] In this arrangement, two sliding gates are arranged on both sides (right and left side) of rear arch. This shall be operated intermittently to expel the ash accumulated on rear arch floor panel. During this process, free space availed for flue gas will reduce and lead to higher flue gas velocity across the rear arch bottom side at part load operation of boiler. Since these slide gates are to be operated intermittently, electrically operated slide gates are provided. Sufficient supporting arrangement is provided to hold these slide gates during operation and idle condition. Dust particle accumulation in rollers is expected over a period of operation and Compressed air cleaning mechanism in considered to clean these duct particles from roller frame to smoothen the gate operation.

[0020] Another aspect of the invention describes that the sliding gate system operates once in shift (within 8hrs) during part load operation. Due to this closure of Sliding gates, localized flue gas velocity will increase and ash particle will be carried over by flue gas.

[0021] Another aspect of the invention describes that the sliding gate system operation frequency can be varied based on coal quality, %ge of part load of boiler operation and boiler configuration.

[0022] Another aspect of the invention describes that the cross sectional area of the gate varies from 20% to 70% as per coal quality, %ge of part load of boiler operation and boiler configuration.

[0023] Another aspect of the invention describes the type of gate arrangement, wherein the gates can have perforations of various types to avoid overheating of the gate plates and supply minimal gas to the heating surface area immediately after the gate.

[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.

[0025] 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:
[0026] 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: Shows schematic diagram of two pass boiler along with heating
surface area.

Figure 2 shows: Sliding gate arrangement system along with guiding mechanism.

Figure 3 shows: Type of sliding gate with horizontal rectangular slot on plates.

Figure 4 shows: Type of sliding gate with vertical rectangular slot on plates.

Figure 5 shows: Type of sliding gate with Circular slot on plates.
[0027] 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.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:

[0028] 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.

[0029] The present invention makes a disclosure regarding a technology pertaining to an invention directing to method to remove fly ash from rear arch floor to second pass for two pass design boiler.

[0030] Now, reference may be made to Figure 1&2 illustrating the case of the two pass design boiler, the flue gas flow will flow vertically in first pass (1) and it will take a turn from the furnace outlet (2) through a small horizontal pass, which is called as rear arch area. From rear arch, again the flue gas will take a turn (3) and flow will be admitted to second pass. Through the rear arch, first pass and second pass of the boiler is connected. In the rear arch area, part of the Superheater (SH) and Reheater (RH) sections are accommodated. Due to the change in direction of flue gas combined with low gas velocities at part load, the ash particles segregate and lead to ash accumulation (6) at rear arch floor panel (7). There are two sliding gates on either side (Right (4) & Left (5)) and same will be moving inside flue gas path through rollers (9) perpendicular to flue gas direction from right side (10) and left side (11) wall of rear arch. Cross section area (8) at rear arch area will reduce for a short duration. Since these slide gates are to be operated in every shift or within two shift, electrically operated slide gates are provided. Sufficient supporting arrangement is provided to hold these slide gates during operation and idle condition. Dust particle accumulation in rollers is expected over a period of operation and compressed air cleaning mechanism is considered to clean these duct particles from roller frame to smoothen the gate operation.

[0031] Figure 3 illustrates the arrangement of sliding gate with like horizontal rectangular perforated slots (12) on right side (4) and left side(5) sliding gate to avoid overheating of the gate plates and supply minimal gas to the heating surface area immediately after the gate.

[0032] Figure 4 illustrates the arrangement of sliding gate with like vertical rectangular perforated slots (13) on right side(4) and left side(5) sliding gate to avoid overheating of the gate plates and supply minimal gas to the heating surface area immediately after the gate.

[0033] Figure 4 illustrates the arrangement of sliding gate with like circular perforated slots (14) on right side (4) and left side(5) sliding gate to avoid overheating of the gate plates and supply minimal gas to the heating surface area immediately after the gate.

[0034] Thus, the invention discloses a Sliding gate opening /closing system to remove ash from rear arch in high ash coal fired boilers when boiler is operating at part loads. Sliding gate system comprises of Guide channel/Rollers, supporting structure, electric motor for moving back & forth of Sliding gates, etc. There are two sliding gates on either side (Right (4) & Left (5)) of the flue gas duct and same will be moving inside flue gas path through rollers (9) perpendicular to flue gas direction from right side (10) and left side (11) wall of rear arch. Due to the reduction in cross section area (8) in rear arch after sliding gate closing, velocity of flue gas will increase at part load of boiler operation and deposit soot (6) will be carried by high velocity flue gas.

ADVANTAGES OF INVENTION:
[0035] This gate arrangement system is easy to manufacture, maintain, erect and operate in the coal fired boilers where the ash accumulation issues are frequent. Since these slide gates are to be operated intermittently, electrically operated slide gates are proposed. Sufficient supporting arrangement is provided to hold these slide gates during operation and idle condition. Sliding Gate with different perforated slots like horizontal rectangular slots (12), vertical rectangular slots (13) and circular slots (14) are provided to avoid overheating of the gate plates and supply minimal gas to the heating surface area immediately after the gate.

WORKING OF INVENTION:
[0036] Method to remove fly ash from rear arch floor (7) to second pass for two pass design boiler comprises below steps:

- The flue gas flows vertically in first pass (1) followed by taking a turn from furnace outlet (2) through a horizontal pass forming a rear arch area;
- The flue gas turns from rear arch followed by admission of flow to second pass, wherein the ash particles segregate and lead to ash accumulation (6) at rear arch floor panel (7) due to the change in direction of flue gas;
- Two Sliding gates on either side (Right (4) & Left (5)) move inside flue gas path through rollers (9) perpendicular to flue gas direction from right side (10) and left side (11) wall of rear arch, in which cross section area (8) at rear arch area reduces for a short duration.
[0037] 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.

[0038] 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.

[0039] 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”.

[0040] 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.
[0041] 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.

[0042] 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.

[0043] 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. Method to remove fly ash from rear arch floor (7) to second pass for two pass design boiler comprising steps of:

- flow of the flue gas vertically in first pass (1) followed by taking a turn from furnace outlet (2) through a horizontal pass forming a rear arch area;
- turning (3) of flue gas from rear arch and admission of flow to second pass, wherein the ash particles segregate and lead to ash accumulation (6) at rear arch floor panel (7) due to the change in direction of flue gas;
- movement of two Sliding gates on either side (Right (4) and Left (5)) inside flue gas path through rollers (9) perpendicular to flue gas direction from right side (10) and left side (11) wall of rear arch, in which cross section area (8) at rear arch area reduces for a short duration.

2. The Method to remove fly ash as claimed in claim 1 or 2, wherein localized flue gas velocity is increased in boiler part load operation and fly ash is carried by flue gas to the second pass.

3. The Method to remove ash as claimed in claims 1-2, wherein electrically operated slide gates are provided since these slide gates are to be operated intermittently.

4. The Method to remove ash as claimed in claims 1-3, wherein width of the sliding gate is based on the type of boiler, Steam generation capacity of boiler, coal specification, minimum flue gas velocity requirement at part load of boiler operation, platform location, Structural arrangement, etc.

5. The Method to remove ash as claimed in claims 1-4, wherein height of the sliding gate is based on the type of boiler, Steam generation capacity of boiler, coal specification, minimum flue gas velocity requirement at part load of boiler operation, platform location, Structural arrangement, etc.

6. The Method to remove ash as claimed in claims 1-5, wherein location of the sliding gate is based on the type of boiler, Steam generation capacity of boiler, coal specification, minimum flue gas velocity requirement at part load of boiler operation, platform location, Structural arrangement, heating surface area arrangement, etc.

7. The Method to remove ash as claimed in claims 1-6, wherein the gates are made with perforations of various type including horizontal rectangular slots (12), vertical rectangular slots (13) and circular slots (14).

8. The Method to remove ash as claimed in claims 1-7, wherein the area of slots is in the range of 5 to 20% of the gate cross sectional area.