Indian Patents. 250029:AN IMPROVED EROSION PROTECTION DEVICE FOR HANGER TUBES IN BUBBLING FLUIDIZING BED BOILERS(BFDC)

Title of Invention	AN IMPROVED EROSION PROTECTION DEVICE FOR HANGER TUBES IN BUBBLING FLUIDIZING BED BOILERS(BFDC)
Abstract	Erosion of bed tubes in BFBC boiler is a regular affair requiring periodical replacement of the tubes. Hence an alternate method of erosion protection is invented. The invention described herein with reference to drawing is not limitative, any modification and/or alteration of such will be well within the knowledge of person skilled in art.

Full Text	2 FIELD OF THE INVENTION The present invention relates to an improved method of erosion protection of hanger tubes in Bubbling fluidized bed combustion boilers. (BFBC). More particularly, the present invention relates to an improved erosion protection device for hanger tubes in BFBC boilers. BACKGROUND OF THE INVENTION The BFBC is an environment friendly and efficient system of burning various grades of fuels. The fuel burns between 700-900 deg C. This temperature ensures that Nox is not formed. Sorbent in the form of limestone is added to capture the sulphur in the fuel thereby preventing the formation of Sox. The principle heat transfer surfaces like evaporator and super heater are immersed in the fluidized bed. The primary air of combustion is directed through the bed at a pre determined velocity, at which the bed behaves like fluid and effective heat transfer takes place due to fluidization. Hanger tubes constituting evaporator tubes are used for supporting Super heater coils inside the furnace of the boiler. Typical arrangement is shown in Fig 1. During the course of the process of fluidization there is a continuous impingement of bed material particles on the hanger tubes supporting the super heater coils in the bed. Due to continuous impingement, the tubes are quickly eroded. 3 Conventionally to increase the tube life, welding of small (about 8 mm) diameter pin studs are used to prevent direct impingement of the particles on the tube.(Fig 2) These pin studs are electrical resistance welded on the tubes. Both carbon steel and stainless steel studs are adopted. The studs are welded in closed pitch on the tubes. They prevent direct impingement of bed material on the tubes The studs get eroded first and then only erosion starts in tubes. Thereby tube life is enhanced. Once the studs are fully eroded the tubes have to be replaced with a freshly studded tube OBJECTS OF THE INVENTION It is therefore an object of the present invention to propose an improved erosion protection device which protects the hanger tubes from erosion due to impingement of the bed material. An another object of the invention is to propose an improved erosion protection device which efficiently protects the hanger tubes from erosion due to impingement of the bed material thereby enhances the life of the hanger tubes. 4 A further object of the present invention is to propose an improved erosion protection device which efficiently protects the hanger tubes from erosion due to impingement of the bed material which enables routing of the hanger tubes close to coal nozzles and ash re injection nozzles, without subjecting the tubes to significant erosion. A still further object of the present invention is to propose an improved erosion protection device which efficiently protects the hanger tubes from erosion due to impingement of the bed material which makes the furnace further compact. SUMMARY OF THE INVENTION Accordingly, there is provided an improved erosion protection device for hanger tubes in BFBC boilers comprising a hot air distributor plate disposed at the bottom boundary of the combustor enclosed by a membrane, said plate having a plurality of air nozzles, a hot air source for continuous supply of hot air through said nozzles into the fluidized bed, a first super heater coil immersed in the bed of the boiler; a second super heater coil above the bed supported by a plurality of hanger tubes; and a tube assembly comprising a tube and a plurality of ceramic sleeves fitted over the tube. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1- shows a typical arrangement of hanger tubes in a BFBC boiler. 5 Figure 2 - shows a cross sectional view of a studded tube used in prior art Figure 3 - shows a ceramic ring fitted on to a hanger tube. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION With the above and other objectives in view, the present invention provides an alternative method of erosion protection. The present invention relates to a BFBC boiler to overcome the above said drawbacks. It has been the endeavor of the applicant to develop alternate ways employing ceramics to avoid erosion. The present invention provides an improved and cost effective device for erosion protection. According to present invention, ceramic rings are designed to form a ring over a tube (11) (both straight and bent portion) so that they form a protective layer. (Fig 3) The type of ceramic used has high erosion resistant properties. The ceramic material used is suitably selected with the right amount of alumina etc. to get the requisite hardness properties. Further it is tested with suitable erosion tests to determine the suitability for the intended working atmosphere. Having ensured so the ceramic material is selected. 6 Now the exact ring shapes required for covering the tubes (11) are determined. While doing so care has been taken to ensure that no exposed part of hanger tubes will be visible once the coating is done. The rings are then die cast in specially developed dies. They are then sintered at a predetermined temperature for a pre-determined time. The rings (6) are now assembled over the tubes to form a protective layer. Arrangements are provided to lock the rings in place. Actual tests at site have indicated that life of the hunger tubes with ceramic rings is much more than the pin studded tubes. A hot-air distributor plate (1) is arranged fixedly on the boundary wall of the BFBC boiler by a membrane (2). The plate (1) is having a number of air-injecting nozzles (7). Hot air form a source is continuously passed to the fluidized bed (8) of the boiler via the nozzles (7). One each heater coil (3,4) is placed inside the bed (8) and above the bed (8). The second heater coil (4) is supported by a plurality of hanger tubes (5). Instead of pin studs (9) as of the prior art, a number of ceramic sleeves (6) are arranged over a tube (11) to entirely cover the tube (11) thereby forming a tube assembly (10). The tube assembly (10) covers the hanger tubes (5) from getting impinged by the bed material thereby protecting the hanger tubes (5) from quick erosion. 7 WE CLAIM 1. An improved erosion protection device for hanger tubes in BFBC boilers comprising a hot air distributor plate (1) disposed at the bottom boundary of the combustor enclosed by a membrane (2), said plate (1) having a plurality of air nozzles (7); a hot air source for continuous supply of hot air through said nozzles into the fluidized bed (8); a first super heater coil (3) immersed in the bed (8) of the boiler; a second super heater coil (4) above the bed (8) supported by a plurality of hanger tubes (5); and a tube assembly (10) comprising a tube (11) and a plurality of ceramic sleeves (6) fitted over the tube (11). 2. The device as claimed in claim 1, wherein the ceramic sleeves (6) are die- cast using ceramic material having high erosion resistance properties. 3. The device as claimed in claim 1 or 2, wherein the ceramic sleeves (6) are subjected to sintering at a predetermined temperature for a predetermined time after die-casting. 4. An improved erosion protection device for hanger tubes in BFBC boilers as substantially described herein and illustrated with reference to the accompanying drawing. Erosion of bed tubes in BFBC boiler is a regular affair requiring periodical replacement of the tubes. Hence an alternate method of erosion protection is invented. The invention described herein with reference to drawing is not limitative, any modification and/or alteration of such will be well within the knowledge of person skilled in art.

Full Text

2
FIELD OF THE INVENTION
The present invention relates to an improved method of erosion protection of hanger tubes in Bubbling fluidized bed combustion boilers. (BFBC). More particularly, the present invention relates to an improved erosion protection device for hanger tubes in BFBC boilers.
BACKGROUND OF THE INVENTION
The BFBC is an environment friendly and efficient system of burning various grades of fuels. The fuel burns between 700-900 deg C. This temperature ensures that Nox is not formed. Sorbent in the form of limestone is added to capture the sulphur in the fuel thereby preventing the formation of Sox. The principle heat transfer surfaces like evaporator and super heater are immersed in the fluidized bed. The primary air of combustion is directed through the bed at a pre determined velocity, at which the bed behaves like fluid and effective heat transfer takes place due to fluidization.
Hanger tubes constituting evaporator tubes are used for supporting Super heater coils inside the furnace of the boiler. Typical arrangement is shown in Fig 1.
During the course of the process of fluidization there is a continuous impingement of bed material particles on the hanger tubes supporting the super heater coils in the bed. Due to continuous impingement, the tubes are quickly eroded.

3
Conventionally to increase the tube life, welding of small (about 8 mm) diameter pin studs are used to prevent direct impingement of the particles on the tube.(Fig 2)
These pin studs are electrical resistance welded on the tubes. Both carbon steel and stainless steel studs are adopted. The studs are welded in closed pitch on the tubes. They prevent direct impingement of bed material on the tubes
The studs get eroded first and then only erosion starts in tubes. Thereby tube life is enhanced. Once the studs are fully eroded the tubes have to be replaced with a freshly studded tube
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an improved erosion protection device which protects the hanger tubes from erosion due to impingement of the bed material.
An another object of the invention is to propose an improved erosion protection device which efficiently protects the hanger tubes from erosion due to impingement of the bed material thereby enhances the life of the hanger tubes.

4
A further object of the present invention is to propose an improved erosion protection device which efficiently protects the hanger tubes from erosion due to impingement of the bed material which enables routing of the hanger tubes close to coal nozzles and ash re injection nozzles, without subjecting the tubes to significant erosion.
A still further object of the present invention is to propose an improved erosion protection device which efficiently protects the hanger tubes from erosion due to impingement of the bed material which makes the furnace further compact.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved erosion protection device for hanger tubes in BFBC boilers comprising a hot air distributor plate disposed at the bottom boundary of the combustor enclosed by a membrane, said plate having a plurality of air nozzles, a hot air source for continuous supply of hot air through said nozzles into the fluidized bed, a first super heater coil immersed in the bed of the boiler; a second super heater coil above the bed supported by a plurality of hanger tubes; and a tube assembly comprising a tube and a plurality of ceramic sleeves fitted over the tube.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1- shows a typical arrangement of hanger tubes in a BFBC boiler.

5
Figure 2 - shows a cross sectional view of a studded tube used in prior art Figure 3 - shows a ceramic ring fitted on to a hanger tube.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
With the above and other objectives in view, the present invention provides an alternative method of erosion protection. The present invention relates to a BFBC boiler to overcome the above said drawbacks. It has been the endeavor of the applicant to develop alternate ways employing ceramics to avoid erosion.
The present invention provides an improved and cost effective device for erosion protection. According to present invention, ceramic rings are designed to form a ring over a tube (11) (both straight and bent portion) so that they form a protective layer. (Fig 3)
The type of ceramic used has high erosion resistant properties. The ceramic material used is suitably selected with the right amount of alumina etc. to get the requisite hardness properties. Further it is tested with suitable erosion tests to determine the suitability for the intended working atmosphere. Having ensured so the ceramic material is selected.

6
Now the exact ring shapes required for covering the tubes (11) are determined. While doing so care has been taken to ensure that no exposed part of hanger tubes will be visible once the coating is done. The rings are then die cast in specially developed dies. They are then sintered at a predetermined temperature for a pre-determined time.
The rings (6) are now assembled over the tubes to form a protective layer. Arrangements are provided to lock the rings in place. Actual tests at site have indicated that life of the hunger tubes with ceramic rings is much more than the pin studded tubes.
A hot-air distributor plate (1) is arranged fixedly on the boundary wall of the BFBC boiler by a membrane (2). The plate (1) is having a number of air-injecting nozzles (7). Hot air form a source is continuously passed to the fluidized bed (8) of the boiler via the nozzles (7). One each heater coil (3,4) is placed inside the bed (8) and above the bed (8). The second heater coil (4) is supported by a plurality of hanger tubes (5). Instead of pin studs (9) as of the prior art, a number of ceramic sleeves (6) are arranged over a tube (11) to entirely cover the tube (11) thereby forming a tube assembly (10). The tube assembly (10) covers the hanger tubes (5) from getting impinged by the bed material thereby protecting the hanger tubes (5) from quick erosion.

7 WE CLAIM
1. An improved erosion protection device for hanger tubes in BFBC boilers
comprising a hot air distributor plate (1) disposed at the bottom boundary
of the combustor enclosed by a membrane (2), said plate (1) having a
plurality of air nozzles (7); a hot air source for continuous supply of hot air
through said nozzles into the fluidized bed (8); a first super heater coil (3)
immersed in the bed (8) of the boiler; a second super heater coil (4)
above the bed (8) supported by a plurality of hanger tubes (5); and a
tube assembly (10) comprising a tube (11) and a plurality of ceramic
sleeves (6) fitted over the tube (11).
2. The device as claimed in claim 1, wherein the ceramic sleeves (6) are die-
cast using ceramic material having high erosion resistance properties.
3. The device as claimed in claim 1 or 2, wherein the ceramic sleeves (6) are
subjected to sintering at a predetermined temperature for a
predetermined time after die-casting.
4. An improved erosion protection device for hanger tubes in BFBC boilers as
substantially described herein and illustrated with reference to the
accompanying drawing.

Erosion of bed tubes in BFBC boiler is a regular affair requiring periodical
replacement of the tubes. Hence an alternate method of erosion protection is
invented.
The invention described herein with reference to drawing is not limitative, any
modification and/or alteration of such will be well within the knowledge of person
skilled in art.

Documents:

00079-kol-2007-correspondence-1.1.pdf

00079-kol-2007-form-18.pdf

0079-kol-2007 abstract.pdf

0079-kol-2007 assignment.pdf

0079-kol-2007 claims.pdf

0079-kol-2007 correspondence others.pdf

0079-kol-2007 description(complete).pdf

0079-kol-2007 drawings.pdf

0079-kol-2007 form-1.pdf

0079-kol-2007 form-2.pdf

0079-kol-2007 form-3.pdf

79-KOL-2007-(07-09-2011)-ABSTRACT.pdf

79-KOL-2007-(07-09-2011)-AMANDED CLAIMS.pdf

79-KOL-2007-(07-09-2011)-DESCRIPTION (COMPLETE).pdf

79-KOL-2007-(07-09-2011)-DRAWINGS.pdf

79-KOL-2007-(07-09-2011)-EXAMINATION REPORT REPLY RECEIVED.pdf

79-KOL-2007-(07-09-2011)-FORM 1.pdf

79-KOL-2007-(07-09-2011)-FORM 2.pdf

79-KOL-2007-(07-09-2011)-FORM 3.pdf

79-KOL-2007-(07-09-2011)-OTHERS.pdf

79-KOL-2007-(07-09-2011)-PA.pdf

79-KOL-2007-FORM-27.pdf

abstract-00079-kol-2007.jpg

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Patent Number

250029

Indian Patent Application Number

79/KOL/2007

PG Journal Number

48/2011

Publication Date

02-Dec-2011

Grant Date

30-Nov-2011

Date of Filing

22-Jan-2007

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OFFICES- REGIONAL OPERATIONS DIVISION (ROD), PLOT NO:9/1, DJ BLOCK, 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091. REGISTERED OFFICE- BHEL HOUSE, SIRI FORT, NEW DELHI-110049

Inventors:

#	Inventor's Name	Inventor's Address
1	SUNDARRAJAN PRABHAKAR	REGIONAL OPERATIONS DIVISION (ROD), PLOT NO:9/1, DJ BLOCK, 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091.

PCT International Classification Number

F24H1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA