CA1328787C - Method and apparatus for protecting screen tubes in boilers - Google Patents
Method and apparatus for protecting screen tubes in boilersInfo
- Publication number
- CA1328787C CA1328787C CA 589797 CA589797A CA1328787C CA 1328787 C CA1328787 C CA 1328787C CA 589797 CA589797 CA 589797 CA 589797 A CA589797 A CA 589797A CA 1328787 C CA1328787 C CA 1328787C
- Authority
- CA
- Canada
- Prior art keywords
- screen
- tubes
- tube
- boiler
- screenguard
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
- F22B37/00—Component parts or details of steam boilers
- F22B37/02—Component parts or details of steam boilers applicable to more than one kind or type of steam boiler
- F22B37/10—Water tubes; Accessories therefor
- F22B37/107—Protection of water tubes
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22G—SUPERHEATING OF STEAM
- F22G3/00—Steam superheaters characterised by constructional features; Details of component parts thereof
- F22G3/008—Protection of superheater elements, e.g. cooling superheater tubes during starting-up periods, water tube screens
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Paper (AREA)
Abstract
METHOD AND APPARATUS FOR PROTECTING SCREEN TUBES IN BOILERS
ABSTRACT OF THE INVENTION
This invention is directed to a method and apparatus for minimizing the risk to screen tubes in boilers from damage from falling lumps of deposits. More particularly, this invention pertains to a method and apparatus for protecting the screen tubes at the furnace exit in boilers which are subject to heavy deposits of some of the products of combustion on the heating surfaces; such boilers as kraft recovery boilers which burn liquor from the pulping process in paper manufacture. In a boiler in which solid fire-side deposits may occur, a method of protecting sloping sections of boiler screen tubes, from falling deposits which comprises positioning screenguards above the screen tubes.
ABSTRACT OF THE INVENTION
This invention is directed to a method and apparatus for minimizing the risk to screen tubes in boilers from damage from falling lumps of deposits. More particularly, this invention pertains to a method and apparatus for protecting the screen tubes at the furnace exit in boilers which are subject to heavy deposits of some of the products of combustion on the heating surfaces; such boilers as kraft recovery boilers which burn liquor from the pulping process in paper manufacture. In a boiler in which solid fire-side deposits may occur, a method of protecting sloping sections of boiler screen tubes, from falling deposits which comprises positioning screenguards above the screen tubes.
Description
METHOD AND APPARATU~ FOR PROTECTING BCREEN TUBES IN BOI~ER8 FIELD OF THE INVENTION
This invention is directed to a method and apparatus for minimizing the risk to screen tubes in boilers from damage from falling lumps of deposits. More particularly, this invention pertains to a method and apparatus for protecting the screen tubes at the furnace exit in boilers which are subject to heavy deposits of some of the products of combustion on the heating surfaces; such boilers as kraft recovery boilers which burn liquor from the pulping process in paper manufacture.
BACKGROUND OF THE INVENTION
Boilers are widely used to generate steam for numerous applications. In the pulp and paper industry, recovery boilers are used to burn the waste liquor produced in a kraft pulp making process. In such boilers, the combustion gases pass upwards through the furnace and over the tubes of the various heating surfaces of the boiler.
Some of the products of combustion, and liquor droplets and unburned liquor particles are carried upwards in the furnace by combustion gases and are subsequently deposited on the heating surfaces in the upper region of the furnace.
Kraft recovery boilers usuall~ include superheaters which are generally constructed of a series of continuous vertical in-line loops of tubes, arranged in elements, each consisting of several of these loops. A superheater bank consists of several flat elements, which are arranged parallel to each other across the width of the boiler. These elements are often called platens if the adjacent tubes within each element are very close together, or touching one another. The inlet and outlet ends of the tubes of each loop pass upwards between the ~328787 roof tubes of the furnace and then are connected to the super-heater collecting tubes, or headers. These collecting headers are arranged with their longitudinal axes at right angles to the planes of the superheater elements and generally across the full width of the boiler. The superheater tubes are generally arranged such that the steam flows in parallel thr~ugh the elements of each bank. Steam from a previous superheater bank or the inlet header of each superheater bank passes up and down through the successive tube loops of each superheater element, in parallel to the other elements of the same superheater bank, to the outlet header or to the next superheater bank and is superheated for process or power generation.
The screen tubes at the furnace exit, on the other hand, like the tubes which form the furnace envelope, generally contain water which is heated by the combustion gases on the outside of the tubes. For ease of circulation, this water generally is introduced into the lower end of the screen tubes which are generally arranged in several vertical rows, which are generally in line with and upstream of the superheater elements relative to the direction of gas flow. The water passes upwards through all the screen tubes in parallel, in what is commonly referred to as one water pass. The lower end of the screen tubes is bent out of the vertical and slopes downwards, at an angle of approximately 20 degrees to the horizontal. At this point the tubes pass through either the front or rear wall of the furnace, or through a so-called nose baffle which is, in a modern boiler, a fully-welded gas-tight wall formed by the continuation of the tubes of the rear wall of the furnace. Outside the furnace, the screen tubes are connected to collecting headers at the upper and lower ends of the tubes. The screen tubes forming the sloping portion of the screen are also in vertical line with the superheater elements.
The screen tubes and the superheater tubes and the other pressure parts of the boiler, which include the generating bank and the economiæer, are generally suspended from a steel framework above the boiler. The screen tubes and the superheater tubes comprise the so-called pendent heating surfaces of the boiler.
All the heating surfaces are generally provided with sootblowers which are intended to remove the deposits from the outside of the tubes. Unfortunately, the deposits are often difficult to remove and in some regions can accumulate and grow into large, heavy, masses of material. The size of such heavy deposit masses can range from several inches to several feet in thickness. This heavy material, or portions thereof, can be dislodged by the sootblowers, or vibration, or simply by its own weight. Lumps of this material then may fall from the roof, furnace walls, or elements of the screen and superheater. If large lumps strike the sloping tubes at the lower end of the screen tubes, the screen tubes may be damaged. Damage may range from small dents, tube deflection, broken tubes, or tubes ripped from the upper headers of the screen. If a tube leak is the result, the water from the ruptured tubes, if in sufficient quan-tities, may, in the case of a kraft recovery boiler, fall to the molten bed of smelt in the bottom of the furnace and cause a smelt-water explosion. Such explosions have occurred not infrequently and have caused loss of life and major economic losses due to extended downtime of the boiler, and often extended downtime of the entire pulp mill.
As the capacity of boilers has increased, their size has increased proportionately. The fall-height from the roof and the upper part of the superheater to the sloping portion of the screen tubes at the furnace exit has commensurately increased.
The height from the furnace roof to the sloping tubes at the lower end of these screen tubes can be 15 m or more in a large boiler. The momentum energy inherent in a very large lump of falling fire-side deposits, which may range from football size to cabin-trunk size, is considerable and, as explained, can cause considerable tube damage. It is important for reasons explained to minimize the likelihood of damage to the sloping screen tubes.
132~787 ~.
This can be done by reducing the size of the lumps and/or by deflecting them from the sloping tubes.
SUMMARY OF THE INVENTION
The invention pertains to a boiler in which solid fire-side deposits may occur, a method of protecting sloping sections of boiler screen tubes at the furnace exit, from falling deposits which comprises positioning devices which, for purposes of this discussion will be called screenguards, above the screen tubes.
The boiler can be a kraft recovery boiler.
In the method wherein the sloping portion of the screen tubes at the furnace exit can be protected from falling lumps of fire-side deposits by positioning the screenguards so that the falling lumps hit the screenguards and can be deflected from their initial direct line of fall, and may also be broken into smaller pieces. The falling lumps of fire-side deposits can be deflected from their initial line of fall by hitting a series of tubes, screenguards, positioned in their fall path, above and in line with the sloping portion of the screen tubes which can be protected. The falling lumps can be broken into smaller lumps when they impact with the screenguards.
A screenguard for protecting the sloping part of a screen tube at the furnace exit in a boiler which comprises a protrusion extending above the sloping part of the screen tube and in vertical line with the screen tube and wherein the protrusion can be formed by screen tube, superheater tube, or furnace wall tube bent in a zig-zag pattern to form a series of protrusions.
The screenguard tube can be a furnace wall tube, screen tube, or superheater tube.
DRAWINGS
In drawings which illustrate specific embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way:
Figure 1 is a schematic side elevation of part of a typical boiler;
Figure 2a is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes at the furnace exit protected by screenguards.
Figure 2b is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes at the furnace exit protected with a first alternative design of screenguard.
Figure 2c is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes at the furnace exit protected with a second alternative design of screenguard.
Figure 2d is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes at the furnace exit protected with a third alternative design of screenguard.
DETAILED DESCRIPTION OF SPECIFIC
EMBODIMENTS OF THE INVENTION
The heating surfaces of a furnace of a boiler are shown in Figure 1, which is a schematic side elevation of part of a typical boiler. These surfaces comprise the water-cooled tube walls 2, the nose baffle 4 and the roof 6 of the furnace.
Pendent heating surfaces of screen tubes 10 are located at the furnace exit 12. Superheater tubes 14 are located in the superheater cavity downstream of the screen tubes 10 relative to the direction of combustion gas flow 8. The superheater cavity is the entire region between the rear tubes of the screen and the water-cooled heating surfaces downstream of the superheater. The superheater cavity thus contains the pendent superheater. The screen tube bank 10 is separated from the adjacent bank of superheater tubes 14 by a cavity 15.
The invention pertains to a method of and apparatus for deflecting falling lumps of fire-side deposits, such that they will not directly strike the sloping portion of the screen tubes at the furnace exit, or will miss the screen tubes entirely by falling past either side of the screen tubes. In some cases, the falling lumps will be broken into smaller less dangerous lumps by impacting the apparatus.
According to the invention, tubes of either the furnace wall, or of the screen or of the adjacent superheater bank are bent in any number of configurations, but typically as shown in Figures 2a, 2b, 2c or 2d. Figure 2a is a schematic enlarged sectional side elevation of the screen and superheater of a boiler with the sloping portion of the screen tubes protected by screenguards. Figure 2b is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes protected with a first alternative design of screenguard. Figure 2c is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes protected with a second alternative design of screenguard.
Figure 2d is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with a sloping portion of the screen tubes protected with a third alternative design of screenguard.
132~7~7 The tubes are bent across the cavity above the sloping portion of the screen tubes and in line with the screen and superheater elements and sloping portion of the screen tubes.
The wall tubes, screen tubes or superheater tubes which are thus bent across the cavity above the sloping screen tubes according to the invention are called "screenguards" 18. Sootblowers 16 would generally be located in the spaces between the screenguards (as shown by + in the drawings).
These screenguards 18 do not have the same function as so-called tie tubes, which may be employed to tie the lower ends of superheater elements of one bank of superheater to the screen or to an adjacent superheater bank. There would be, as shown in Figures 2a, 2b, 2c and 2d, several screenguards in the cavity above the sloping screen tubes.
Figure 2a shows in detail the use of front wall tubes 10 to form the screenguard 18, such that the front wall tubes 10 span the cavity between the screen tubes 1 and the front wall 2.
Figure 2b shows the screen tubes 10 being used to form the screenguard 18 between the front wall 2 and the water-cooled screen 10. Figure 2c shows the screen tubes 10 being used to form the screenguard 18 in the cavity between the screen 10 and the superheater 14. Figure 2d shows the superheater tubes 14 from the bank adjacent to the screen tubes 10 being used to form the screenguard 18.
A screenguard can be formed by one or more screen tubes. It may be formed by manipulating the outer tube(s) of a screen tube element or platen, on the same side of the platen as the sloping tubes at the bottom of the screen, such that, considering the direction of fall from top to bottom of the tube, the tube is bent out from the vertical in the plane of the platen and angled downwards at a suitable angle to minimize deposit accumulation on the screenguard itself, for example, at 55 degrees to the horizontal, across the depth of the adjoining cavity between the screen tube bank and the adjoining front wall 132~787 (or bank of heating surface downstream of the screen) then bent into the vertical again, still in the plane of the platen, such that the new vertical portion is adjacent to the closest adjoining tube of the adjacent tube bank or furnace front wall.
After travelling downwards in a short straight length, the tube is then bent again out from the vertical in the plane of the platen, back towards the original screen tube platen at the same angle to the horizontal as before and then bent back into the original vertical axis of travel, close up against its original neighbouring tube. This procedure is repeated several times down the length of the same tube.
The screenguards function in the following manner. A
lump of fire-side deposits falling from the roof or from the cavity-bounding tubes of the scxeen or superheater can fall only a short distance before it strikes a screenguard and is deflected into the lane between the screen elements. Freefall is therefore limited. Usually the lump is deflected by the screenguard sideways into the space between adjoining screen or superheater elements. The falling lump is therefore deflected from the vulnerable sloping portion of the screen tubes. The falling lump may also be broken into smaller, less damaging, pieces by the impact with the screenguards.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifica-tions are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
This invention is directed to a method and apparatus for minimizing the risk to screen tubes in boilers from damage from falling lumps of deposits. More particularly, this invention pertains to a method and apparatus for protecting the screen tubes at the furnace exit in boilers which are subject to heavy deposits of some of the products of combustion on the heating surfaces; such boilers as kraft recovery boilers which burn liquor from the pulping process in paper manufacture.
BACKGROUND OF THE INVENTION
Boilers are widely used to generate steam for numerous applications. In the pulp and paper industry, recovery boilers are used to burn the waste liquor produced in a kraft pulp making process. In such boilers, the combustion gases pass upwards through the furnace and over the tubes of the various heating surfaces of the boiler.
Some of the products of combustion, and liquor droplets and unburned liquor particles are carried upwards in the furnace by combustion gases and are subsequently deposited on the heating surfaces in the upper region of the furnace.
Kraft recovery boilers usuall~ include superheaters which are generally constructed of a series of continuous vertical in-line loops of tubes, arranged in elements, each consisting of several of these loops. A superheater bank consists of several flat elements, which are arranged parallel to each other across the width of the boiler. These elements are often called platens if the adjacent tubes within each element are very close together, or touching one another. The inlet and outlet ends of the tubes of each loop pass upwards between the ~328787 roof tubes of the furnace and then are connected to the super-heater collecting tubes, or headers. These collecting headers are arranged with their longitudinal axes at right angles to the planes of the superheater elements and generally across the full width of the boiler. The superheater tubes are generally arranged such that the steam flows in parallel thr~ugh the elements of each bank. Steam from a previous superheater bank or the inlet header of each superheater bank passes up and down through the successive tube loops of each superheater element, in parallel to the other elements of the same superheater bank, to the outlet header or to the next superheater bank and is superheated for process or power generation.
The screen tubes at the furnace exit, on the other hand, like the tubes which form the furnace envelope, generally contain water which is heated by the combustion gases on the outside of the tubes. For ease of circulation, this water generally is introduced into the lower end of the screen tubes which are generally arranged in several vertical rows, which are generally in line with and upstream of the superheater elements relative to the direction of gas flow. The water passes upwards through all the screen tubes in parallel, in what is commonly referred to as one water pass. The lower end of the screen tubes is bent out of the vertical and slopes downwards, at an angle of approximately 20 degrees to the horizontal. At this point the tubes pass through either the front or rear wall of the furnace, or through a so-called nose baffle which is, in a modern boiler, a fully-welded gas-tight wall formed by the continuation of the tubes of the rear wall of the furnace. Outside the furnace, the screen tubes are connected to collecting headers at the upper and lower ends of the tubes. The screen tubes forming the sloping portion of the screen are also in vertical line with the superheater elements.
The screen tubes and the superheater tubes and the other pressure parts of the boiler, which include the generating bank and the economiæer, are generally suspended from a steel framework above the boiler. The screen tubes and the superheater tubes comprise the so-called pendent heating surfaces of the boiler.
All the heating surfaces are generally provided with sootblowers which are intended to remove the deposits from the outside of the tubes. Unfortunately, the deposits are often difficult to remove and in some regions can accumulate and grow into large, heavy, masses of material. The size of such heavy deposit masses can range from several inches to several feet in thickness. This heavy material, or portions thereof, can be dislodged by the sootblowers, or vibration, or simply by its own weight. Lumps of this material then may fall from the roof, furnace walls, or elements of the screen and superheater. If large lumps strike the sloping tubes at the lower end of the screen tubes, the screen tubes may be damaged. Damage may range from small dents, tube deflection, broken tubes, or tubes ripped from the upper headers of the screen. If a tube leak is the result, the water from the ruptured tubes, if in sufficient quan-tities, may, in the case of a kraft recovery boiler, fall to the molten bed of smelt in the bottom of the furnace and cause a smelt-water explosion. Such explosions have occurred not infrequently and have caused loss of life and major economic losses due to extended downtime of the boiler, and often extended downtime of the entire pulp mill.
As the capacity of boilers has increased, their size has increased proportionately. The fall-height from the roof and the upper part of the superheater to the sloping portion of the screen tubes at the furnace exit has commensurately increased.
The height from the furnace roof to the sloping tubes at the lower end of these screen tubes can be 15 m or more in a large boiler. The momentum energy inherent in a very large lump of falling fire-side deposits, which may range from football size to cabin-trunk size, is considerable and, as explained, can cause considerable tube damage. It is important for reasons explained to minimize the likelihood of damage to the sloping screen tubes.
132~787 ~.
This can be done by reducing the size of the lumps and/or by deflecting them from the sloping tubes.
SUMMARY OF THE INVENTION
The invention pertains to a boiler in which solid fire-side deposits may occur, a method of protecting sloping sections of boiler screen tubes at the furnace exit, from falling deposits which comprises positioning devices which, for purposes of this discussion will be called screenguards, above the screen tubes.
The boiler can be a kraft recovery boiler.
In the method wherein the sloping portion of the screen tubes at the furnace exit can be protected from falling lumps of fire-side deposits by positioning the screenguards so that the falling lumps hit the screenguards and can be deflected from their initial direct line of fall, and may also be broken into smaller pieces. The falling lumps of fire-side deposits can be deflected from their initial line of fall by hitting a series of tubes, screenguards, positioned in their fall path, above and in line with the sloping portion of the screen tubes which can be protected. The falling lumps can be broken into smaller lumps when they impact with the screenguards.
A screenguard for protecting the sloping part of a screen tube at the furnace exit in a boiler which comprises a protrusion extending above the sloping part of the screen tube and in vertical line with the screen tube and wherein the protrusion can be formed by screen tube, superheater tube, or furnace wall tube bent in a zig-zag pattern to form a series of protrusions.
The screenguard tube can be a furnace wall tube, screen tube, or superheater tube.
DRAWINGS
In drawings which illustrate specific embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way:
Figure 1 is a schematic side elevation of part of a typical boiler;
Figure 2a is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes at the furnace exit protected by screenguards.
Figure 2b is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes at the furnace exit protected with a first alternative design of screenguard.
Figure 2c is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes at the furnace exit protected with a second alternative design of screenguard.
Figure 2d is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes at the furnace exit protected with a third alternative design of screenguard.
DETAILED DESCRIPTION OF SPECIFIC
EMBODIMENTS OF THE INVENTION
The heating surfaces of a furnace of a boiler are shown in Figure 1, which is a schematic side elevation of part of a typical boiler. These surfaces comprise the water-cooled tube walls 2, the nose baffle 4 and the roof 6 of the furnace.
Pendent heating surfaces of screen tubes 10 are located at the furnace exit 12. Superheater tubes 14 are located in the superheater cavity downstream of the screen tubes 10 relative to the direction of combustion gas flow 8. The superheater cavity is the entire region between the rear tubes of the screen and the water-cooled heating surfaces downstream of the superheater. The superheater cavity thus contains the pendent superheater. The screen tube bank 10 is separated from the adjacent bank of superheater tubes 14 by a cavity 15.
The invention pertains to a method of and apparatus for deflecting falling lumps of fire-side deposits, such that they will not directly strike the sloping portion of the screen tubes at the furnace exit, or will miss the screen tubes entirely by falling past either side of the screen tubes. In some cases, the falling lumps will be broken into smaller less dangerous lumps by impacting the apparatus.
According to the invention, tubes of either the furnace wall, or of the screen or of the adjacent superheater bank are bent in any number of configurations, but typically as shown in Figures 2a, 2b, 2c or 2d. Figure 2a is a schematic enlarged sectional side elevation of the screen and superheater of a boiler with the sloping portion of the screen tubes protected by screenguards. Figure 2b is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes protected with a first alternative design of screenguard. Figure 2c is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with the sloping portion of the screen tubes protected with a second alternative design of screenguard.
Figure 2d is a schematic enlarged sectional side elevation of the screens and superheater of a boiler with a sloping portion of the screen tubes protected with a third alternative design of screenguard.
132~7~7 The tubes are bent across the cavity above the sloping portion of the screen tubes and in line with the screen and superheater elements and sloping portion of the screen tubes.
The wall tubes, screen tubes or superheater tubes which are thus bent across the cavity above the sloping screen tubes according to the invention are called "screenguards" 18. Sootblowers 16 would generally be located in the spaces between the screenguards (as shown by + in the drawings).
These screenguards 18 do not have the same function as so-called tie tubes, which may be employed to tie the lower ends of superheater elements of one bank of superheater to the screen or to an adjacent superheater bank. There would be, as shown in Figures 2a, 2b, 2c and 2d, several screenguards in the cavity above the sloping screen tubes.
Figure 2a shows in detail the use of front wall tubes 10 to form the screenguard 18, such that the front wall tubes 10 span the cavity between the screen tubes 1 and the front wall 2.
Figure 2b shows the screen tubes 10 being used to form the screenguard 18 between the front wall 2 and the water-cooled screen 10. Figure 2c shows the screen tubes 10 being used to form the screenguard 18 in the cavity between the screen 10 and the superheater 14. Figure 2d shows the superheater tubes 14 from the bank adjacent to the screen tubes 10 being used to form the screenguard 18.
A screenguard can be formed by one or more screen tubes. It may be formed by manipulating the outer tube(s) of a screen tube element or platen, on the same side of the platen as the sloping tubes at the bottom of the screen, such that, considering the direction of fall from top to bottom of the tube, the tube is bent out from the vertical in the plane of the platen and angled downwards at a suitable angle to minimize deposit accumulation on the screenguard itself, for example, at 55 degrees to the horizontal, across the depth of the adjoining cavity between the screen tube bank and the adjoining front wall 132~787 (or bank of heating surface downstream of the screen) then bent into the vertical again, still in the plane of the platen, such that the new vertical portion is adjacent to the closest adjoining tube of the adjacent tube bank or furnace front wall.
After travelling downwards in a short straight length, the tube is then bent again out from the vertical in the plane of the platen, back towards the original screen tube platen at the same angle to the horizontal as before and then bent back into the original vertical axis of travel, close up against its original neighbouring tube. This procedure is repeated several times down the length of the same tube.
The screenguards function in the following manner. A
lump of fire-side deposits falling from the roof or from the cavity-bounding tubes of the scxeen or superheater can fall only a short distance before it strikes a screenguard and is deflected into the lane between the screen elements. Freefall is therefore limited. Usually the lump is deflected by the screenguard sideways into the space between adjoining screen or superheater elements. The falling lump is therefore deflected from the vulnerable sloping portion of the screen tubes. The falling lump may also be broken into smaller, less damaging, pieces by the impact with the screenguards.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifica-tions are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
Claims (9)
1. In a boiler in which solid fire-side deposits may occur, a method of protecting sloping sections of boiler screen tubes at the furnace exit, from falling deposits which comprises positioning screenguards above the screen tubes.
2. A method according to claim 1 wherein the boiler is a kraft recovery boiler.
3. A method according to claim 2 wherein the sloping portion of the screen tubes at the furnace exit is protected from falling lumps of fire-side deposits by positioning the screen-guards so that the falling lumps hit the screenguards and are deflected from their initial direct line of fall.
4. A method according to claim 2 wherein falling lumps of fire-side deposits are deflected from their initial line of fall by hitting a series of tubes positioned in their fall path, above and in line with the sloping portion of the screen tubes which are to be protected.
5. A method according to claim 3 wherein the falling lumps are broken into smaller lumps when they impact with the screen-guards.
6. A screenguard for protecting the sloping part of a screen tube at the furnace exit in a boiler which comprises a protrusion extending above the sloping part of the screen tube and in vertical line with the screen tube.
7. A screenguard according to claim 6 wherein the protrusion is formed by screen tube bent in a zig-zag pattern to form a series of protrusions.
8. A screenguard according to claim 7 wherein the screenguard tube is a furnace wall tube.
9. A screenguard according to claim 7 wherein the screenguard tube is a superheater tube.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 589797 CA1328787C (en) | 1989-02-01 | 1989-02-01 | Method and apparatus for protecting screen tubes in boilers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 589797 CA1328787C (en) | 1989-02-01 | 1989-02-01 | Method and apparatus for protecting screen tubes in boilers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1328787C true CA1328787C (en) | 1994-04-26 |
Family
ID=4139552
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 589797 Expired - Fee Related CA1328787C (en) | 1989-02-01 | 1989-02-01 | Method and apparatus for protecting screen tubes in boilers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1328787C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2205903A2 (en) * | 2007-10-01 | 2010-07-14 | Riley Power, Inc. | Municipal solid waste fuel steam generator with waterwall furnace platens |
| EP3339505A1 (en) * | 2016-12-22 | 2018-06-27 | Valmet Technologies Oy | Chemical recovery boiler |
-
1989
- 1989-02-01 CA CA 589797 patent/CA1328787C/en not_active Expired - Fee Related
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2205903A2 (en) * | 2007-10-01 | 2010-07-14 | Riley Power, Inc. | Municipal solid waste fuel steam generator with waterwall furnace platens |
| EP2205903A4 (en) * | 2007-10-01 | 2011-09-07 | Riley Power Inc | Municipal solid waste fuel steam generator with waterwall furnace platens |
| US8096268B2 (en) | 2007-10-01 | 2012-01-17 | Riley Power Inc. | Municipal solid waste fuel steam generator with waterwall furnace platens |
| EP3339505A1 (en) * | 2016-12-22 | 2018-06-27 | Valmet Technologies Oy | Chemical recovery boiler |
| US10260744B2 (en) | 2016-12-22 | 2019-04-16 | Valmet Technologies Oy | Chemical recovery boiler |
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