JP4223658B2 - Burner diffuser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure of a burner installed in, for example, a boiler, and more particularly to a burner diffuser mounted on the tip side thereof.
[0002]
[Problems to be solved by the invention]
A burner diffuser (also called a flame holder or flame stabilizer) is provided on the tip side of the burner installed in the boiler in order to ensure the shape of the flame generated when the fuel is burned and to stabilize it. A device called is attached.
[0003]
Up to now, burner diffusers made entirely of refractory metals have been used. However, the fuel oil contains a trace amount of corrosive components such as vanadium and sulfur as impurities. For this reason, the conventional metal burner diffuser is easily corroded at a high temperature, and enormous burnout occurs in a short period of time. Therefore, a burner diffuser in which a portion exposed to high heat, that is, a dish part is replaced with a ceramic part (to be precise, the dish part is composed of a plurality of ceramic members) has been proposed (for example, Japanese Utility Model Publication 56). -132417).
[0004]
By the way, as is well known, the coefficient of thermal expansion is significantly different between metal and ceramics. Specifically, the thermal expansion coefficient of a general metal used as a material of a burner diffuser is about 1.15 × 10 ⁻⁵ / ° C., whereas that of ceramic is 3 to 7 × 10 ⁻⁶ / ° C. For this reason, the ceramic member that is constrained over a wide area in the burner diffuser is likely to be damaged due to the difference in the coefficient of thermal expansion of the material. Therefore, how to attach this ceramic member (plate part divided piece) to a metal member (cylindrical main body part) has been a big problem.
[0005]
Therefore, in order to eliminate such problems, a technique has been proposed that can effectively prevent the burner diffuser (particularly ceramic member) from being damaged due to the difference in the coefficient of thermal expansion of the constituent materials (for example, Japanese Utility Model Publication No. 61-34318).
[0006]
In this technology, the ceramic pieces that form the plate portion together are made to have a T-shaped cross section consisting of a fan-shaped main surface portion and leg portions (projections). Furthermore, the cross-sectional shape of the leg portion is a trapezoidal shape that closes toward the main surface portion side, while a groove (concave) corresponding to the cross-section of the leg portion is formed on the top surface of the main body portion. That is, the proposed burner diffuser is configured by fitting individual leg portions of ceramic pieces into a groove on the top surface of the main body (a kind of joint).
[0007]
In a burner diffuser employing such a structure, troubles due to the difference in coefficient of thermal expansion between the constituent materials as described above are unlikely to occur. However, at high temperatures, the gap between the leg of the ceramic piece and the groove on the top surface of the main body becomes excessively large, so that the fixing state of the ceramic piece is deteriorated (that is, play occurs). As a result, the dish part formed from a plurality of ceramic pieces is not in its original shape. That is, the delicate positional relationship between the ceramic pieces is not regular, and the desired flame shape cannot be obtained.
[0008]
Therefore, the problem to be solved by the present invention is a burner that is less likely to be damaged due to a difference in thermal expansion coefficient between members, and that the members constituting the plate portion are always held in a regular positional relationship. Is to provide a diffuser.
[0009]
[Means for Solving the Problems]
This challenge is
A main body having a structure in which an outer cylinder and an inner cylinder existing inside the outer cylinder are connected by a plurality of ribs;
A burner diffuser comprising a plurality of ceramic pieces that jointly form a dish portion covering a region between the outer cylinder and the inner cylinder on one open surface of the main body,
The ceramic piece has a T-shaped cross section having a fan-shaped main surface portion and a leg portion standing on the main surface portion and used for joining to the rib, and the shaft standing on the rib Is inserted through the legs of the ceramic piece,
The ceramic piece is solved by a burner diffuser that is joined to the rib by pressure-bonding the leg to the rib by using a pressing plate through which the shaft inserted through the leg is further inserted. Is done.
[0010]
That is, in the burner diffuser configured as described above, a ceramic member, that is, a ceramic piece is not constrained over a wide area. That is, the ceramic piece is not forcibly deformed by following the thermal expansion of the main body. Therefore, the ceramic piece is extremely unlikely to be damaged due to a difference in thermal expansion coefficient from the main body (difference in thermal expansion coefficient between members). In addition to this, in the burner diffuser having the above-described configuration, even when the temperature is high, no unnecessary gap is generated between the ceramic piece and the main body (that is, no play of the ceramic piece is generated). Therefore, the fixing state of the ceramic pieces is not deteriorated, and the plurality of ceramic pieces constituting the dish portion are always reliably held so as to have a normal positional relationship. As a result, the desired flame shape is stably maintained over a long period of time.
[0011]
In the burner diffuser of the present invention, two shafts (for example, bolts) are erected adjacent to each other with respect to one rib, and the shafts are spaced apart to the maximum by the thermal expansion of the main body. In particular, it is preferable that at least one of the shafts and the inner peripheral surface of the leg through hole of the ceramic piece through which the shaft is inserted are not in contact with each other. That is, even in a state where the shafts are maximally separated from each other, they are configured so as not to be in pressure contact with the inner peripheral surface of the leg through hole (specifically, the diameter of the leg through hole, the distance between the centers thereof, the shaft It is desirable that the diameter and the interval thereof are optimized.
[0012]
More precisely, even when the shafts are maximally separated by the thermal expansion of the main body, a point on the inner peripheral surface of one leg through hole and an inner peripheral surface of the other leg through hole are The maximum distance between points (the distance along a straight line parallel to the rib surface) is the maximum distance between the points on the peripheral surface of one axis and the points on the peripheral surface of the other axis (also a straight line parallel to the rib surface). It is preferable that it is configured to be larger than (interval along). By doing so, when the distance between the shafts is increased, the leg portion of the ceramic piece does not generate a tensile stress to break it, and the ceramic piece is further prevented from being damaged.
[0013]
Further, in order to increase the cooling efficiency of the ceramic piece and thus the dish part, the air flowing in the space between the outer cylinder and the inner cylinder constituting the main body part is on the side where the leg part is erected on the main surface part of the ceramic piece. It is preferable to be configured to directly collide with a surface and to be ejected from the outer edge side of the main surface portion to the outside of the main body portion. Incidentally, the air flow ejected from the outer edge side of the main surface portion to the outside of the main body portion with a certain spread plays the role of stabilizing the shape of the combustion flame as intended.
[0014]
The ceramic piece can be made of silicon nitride, sialon, silicon carbide, alumina, mullite, or a composite material thereof. However, silicon nitride ceramics are most preferable. This is due to the following reason.
[0015]
The plate portion of the burner diffuser is used in an extremely harsh environment that receives radiant heat from a combustion flame for a long period of time. In addition, when the burner is ignited or extinguished, it receives a thermal shock, and even during the combustion of the fuel, the back side is constantly cooled with air, so the thermal shock caused by this cannot be ignored. Therefore, excellent heat resistance, high temperature corrosion resistance, and thermal shock resistance are required for the plate portion of the burner diffuser. Since the silicon nitride ceramic satisfies these requirements at a higher level than other materials, as described above, the ceramic piece forming the dish portion is composed of the silicon nitride ceramic. Things are the most ideal.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 is an external view of the burner diffuser according to the present embodiment, FIG. 2 is a plan view of the burner diffuser, FIG. 3 is a sectional view of the burner diffuser along line XX in FIG. 2, and FIG. FIG. 5 is a perspective view showing a bonded portion of ceramic pieces in an exploded state.
[0017]
The burner diffuser according to the present embodiment (hereinafter referred to as the present burner diffuser) is mounted on the tip side of the burner and adjusts the flame formed by burning fuel such as heavy oil so as to have an intended shape (and It plays the role of stabilizing it). That is, a burner nozzle is disposed at a position indicated by a one-dot chain line in FIGS. 1 and 2, and fuel is injected from the burner nozzle with a certain spread. The flame formed by this combustion is adjusted by the burner diffuser to have the desired shape.
[0018]
As shown in FIGS. 2 and 3 in addition to FIG. 1, the burner diffuser includes a main body 1 and a plurality of (six in this embodiment) ceramic pieces 2 as main components. To do. In particular, the ceramic pieces 2 are jointly formed in a ring shape and a dish portion having a reverse-shaped cross section. Therefore, it can be said that the present burner diffuser is generally a structure composed of the main body portion 1 and a dish portion composed of a plurality of ceramic pieces 2.
[0019]
Of the above components, the main body 1 has a double cylindrical shape made of a heat-resistant metal (for example, stainless steel). That is, the main body 1 is formed by concentrically connecting a cylindrical outer cylinder 11 and a similarly cylindrical inner cylinder 12 existing inside the outer cylinder 11 by a plurality of (six in this embodiment) ribs 13. It has a connected structure.
[0020]
The heights of the outer cylinder 11 and the inner cylinder 12 are substantially equal. On the other hand, the rib 13 has a triangular portion at the upper end protruding from the open surface of the main body 1 sandwiched between the outer cylinder 11 and the inner cylinder 12, and the ceramic piece as described in detail later. 2 are joined.
[0021]
Next, as described above, the ceramic piece 2 is a joint of a ring-shaped dish portion covering one open surface of the main body 1 (more precisely, a region between the outer cylinder 11 and the inner cylinder 12 on the open surface). Form with. However, the ceramic pieces 2 are not in contact with each other. That is, an appropriate gap is formed between the ceramic pieces 2. This is to avoid a situation in which when the ceramic piece 2 is thermally expanded, the facing end faces come into contact with each other and are pressed against each other. In the present embodiment, the ceramic piece 2 is made of silicon nitride ceramic.
[0022]
The ceramic piece 2 has a T-shaped cross section as can be seen from FIG. 4 showing a state in which a part of the outer cylinder 11 is broken. That is, it has a fan-shaped main surface portion 21 and leg portions 22 erected on the main surface portion 21 and used for joining to the rib 13. In particular, the leg 22 has a through-hole used for joining the ceramic piece 2 to the rib 13 by bolting as shown in FIG. 5 (in FIG. 5, its diameter is R ₁ , center-to-center distance is indicated by D ₁₎ 22a are two forms.
[0023]
On the other hand, two bolts (shafts) 14a and 14b are erected on the upper end portions (triangular portions) of the ribs 13 constituting the main body 1 so as to be adjacent to each other. However, in this embodiment, the heads of the bolts 14 a and 14 b are not fixed to the rib 13. That is, the rib 13 is formed with two through-holes 13a (in FIG. 5, the diameter is R ₂ and the center-to-center distance is D ₂ ). Until the joining, the bolts 14a and 14b are only in the through holes 13a. However, considering the state in which the ceramic piece 2 is completely joined to the rib 13 (the state in which the nut is tightened), the bolts 14 a and 14 b can be regarded as standing on the rib 13.
[0024]
Now, in this burner diffuser, these bolts 14a and 14b are inserted through the leg portions 22 of the ceramic piece 2, more precisely through the through holes 22a formed in the leg portions 22. The ceramic piece 2, a bolt 14a inserted through the leg portions 22, in pressing plate (Figure 5 14b is further inserted, the diameter of the through hole 15a in _{R 3,} also the distance between the centers indicated by _{D 3} ) 15, and the leg portion 22 is bonded to the rib 13 by being crimped to the rib 13. In other words, in this embodiment, the nuts 16 a and 16 b are screwed onto the bolts 14 a and 14 b via the rectangular holding plate 15, and the ceramic pieces 2 are attached to the ribs 13 by sufficiently tightening them. It is connected so as to be separable (common to all ceramic pieces 2).
[0025]
In addition, between the leg part 22 and the rib 13 of the ceramic piece 2, and between the leg part 22 and the pressing plate 15 of the ceramic piece 2 also functions as a kind of cushioning material when the nuts 16a and 16b are tightened. A sheet (not shown) made of inorganic fibers such as alumina is interposed. Further, the pressing plate 15 is made of a metal material, but naturally, the pressing plate 15 is also required to have heat resistance and high temperature corrosion resistance. For this reason, the press plate 15 is made of stainless steel like the main body 1. However, instead of this, high-chromium heat-resistant cast steel such as 45Cr-30Ni steel or Cr50-Ni50 steel or Ni-based alloy may be used.
[0026]
Incidentally, as described above, a total of two bolts 14 a and 14 b are arranged adjacent to each other with respect to one rib 13. In this burner diffuser, even when the bolt 14a and the bolt 14b are separated to the maximum (design limit value) due to thermal expansion of the main body 1, at least one bolt and the bolt are inserted. It is configured to be in a state where it does not come into contact with the inner peripheral surface of the leg through hole 22a (the positional relationship can be in a state where it does not come into contact, and when all the centers do not exist on the same straight line, it comes into contact. Sometimes).
[0027]
In other words, in the present embodiment, the diameter R ₁ of the leg through hole 22a, the distance D ₁ between the centers thereof, the diameters of the bolts 14a and 14b (indicated by R ₄ in FIG. 5), and the interval (D in FIG. 5) It is set such as best shown in _4). As a result, even if the bolts 14a and 14b are maximally separated by the thermal expansion of the main body 1, a point on the inner peripheral surface of one leg through hole 22a and the inner periphery of the other leg through hole 22a. maximum distance between the points on the surface (distance along the surface and a straight line parallel ribs 13. in FIG. 5, corresponding to the L ₁₎ includes a point on the circumferential surface of the bolt 14a (virtual circumference), the bolt 14b maximum distance of the peripheral surface of a point on (virtual circumference) (distance along the surface and a straight line parallel ribs 13. in FIG. 5, corresponding to the L ₂₎ has become larger than.
[0028]
Moreover, in this embodiment, the air which flows through the space between the outer cylinder 11 and the inner cylinder 12 which comprise the main-body part 1 is the back surface of the ceramic piece 2 (the side by which the leg part 22 in the main surface part 21 was erected). Directly collide with the surface). Incidentally, this is because the rib 13 is not provided with a flange (so-called a seating surface of the ceramic piece 2) that overlaps the main surface portion 21 of the ceramic piece 2, and the rib 13 is simply a flat plate. Therefore, the cooling air supplied to the present burner diffuser is directly ejected from the outer edge side of the main body 1 after colliding directly with the main surface 21 of the ceramic piece 2 as indicated by a broken line in FIG. Become. By the way, this air flow plays a role in adjusting the shape of the combustion flame to be the desired one and stabilizing it.
[0029]
Now, in the present burner diffuser configured as described above, the main body 1 does not constrain the ceramic piece 2 forming the dish portion over a wide area. That is, the ceramic piece 2 is not easily affected by the thermal expansion on the main body 1 side, and therefore, the ceramic piece 2 is excessively deformed (distracted) in the form of following the large thermal expansion of the main body 1 as in the conventional product. Absent. Therefore, the burner diffuser, particularly the ceramic piece 2 constituting the burner diffuser, is not damaged due to the difference in thermal expansion coefficient with the main body 1.
[0030]
In addition, in the present burner diffuser, no gap is generated between the ceramic piece 2 and the main body 1 (between the joining surfaces) even at high temperatures. That is, no play of the ceramic piece 2 occurs. Therefore, the fixing state of the ceramic piece 2 is not deteriorated, and the plurality of ceramic pieces 2 constituting the dish portion are always reliably held so as to be in a normal positional relationship. As a result, the present burner diffuser can stably maintain the desired flame shape over a long period of time.
[0031]
【Example】
A burner diffuser according to the above embodiment (hereinafter referred to as the present example) was manufactured under the following conditions.
[0032]
Material of main body: Stainless steel (SUS-310S)
Outer diameter of the pan: 200 mm
Material of the ceramic piece forming the dish part: Diameter R ₁ of the leg through hole of the silicon nitride ceramic ceramic piece: 7 mm
Spacing between leg through holes of ceramic piece (distance between centers of through holes) D ₁ : 15 mm
Rib through-hole diameter R ₂ : 6 mm
Rib through-hole interval (distance between through-hole centers) D ₂ : 15 mm
Bolt diameter R ₄ (maximum thread diameter): 6 mm
Tightening of bolts: Space between uniform tightening bolts with a torque wrench (distance between centers) D ₄ : 15 mm
Holding plate material: Stainless steel (SUS-310S)
Presser plate dimensions (length x width x thickness): 35 mm x 15 mm x 4 mm
Diameter of through hole of presser plate R ₃ : 6 mm
Space between through holes of presser plate (distance between centers of through holes) D ₃ : 15 mm
Buffer material: High alumina fiber sheet with a thickness of 2 mm [0033]
For reference, the thermal expansion coefficient of the silicon nitride-based ceramics constituting the ceramic piece is about 3 × 10 ⁻⁶ / ° C., while the thermal expansion coefficient of the stainless steel constituting the main body and the holding plate. Is 17 × 10 ⁻⁶ / ° C. And the temperature of the joint portion (around the bolt) between the rib of the main body portion and the ceramic piece rises to 500 to 800 ° C. during the combustion of fuel. For this reason, if the bolt interval is 15 mm at normal temperature, the interval further increases by about 0.13 to 0.20 mm due to thermal expansion of the ribs at a high temperature. On the other hand, the corresponding part on the ceramic piece side extends only about 0.02 to 0.04 mm. Therefore, the difference between the diameter of the leg through hole of the ceramic piece and the diameter of the bolt is required to be 0.18 mm (however, when the difference in the amount of extension is absorbed at one location. Half of 0.09 mm).
[0034]
However, in this embodiment, as described above, the sum of the differences between the diameters of the leg through holes and the bolts is 2 mm. Therefore, there is no problem that both bolts are brought into pressure contact with the peripheral surface of the leg through hole, and tensile stress is generated in the leg portion of the ceramic piece to cause breakage (breakage).
[0035]
Now, the burner diffuser with the above configuration was mounted on the burner of a private power generation boiler, and its utility was examined. As a result, no abnormality was found in the shape of the combustion flame, and it was found that the burner diffuser of this example can maintain a stable combustion state for a long period of time. Furthermore, after using for one year, the burner diffuser was removed, and the members constituting it were closely observed. However, no damage such as looseness or cracks in the ceramic pieces was observed. Furthermore, there was virtually no evidence of high-temperature corrosion of the ceramic piece, and the same soundness as before the start of the test was maintained.
[0036]
For comparison,
(1) The plate is made of metal (Comparative Example 1)
(2) The plate part is composed of a plurality of ceramic pieces and is constrained to the main body part over a wide area (Comparative Example 2),
(3) The plate part is composed of a plurality of ceramic pieces and joined to the main body part by fitting the leg parts (Comparative Example 3)
Was prepared and the same test as described above was performed. The results are as follows.
[0037]
First, in Comparative Example 1, when the dish portion was observed after being used for one year, high-temperature corrosion was progressing so that quick exchange was necessary. On the other hand, in Comparative Example 2, high-temperature corrosion was not generated in the ceramic pieces constituting the dish part, but cracks were observed. Further, in Comparative Example 3, although no damage such as traces of high temperature corrosion and cracks were found on the ceramic pieces, the positional relationship between the ceramic pieces was distorted during fuel combustion, and the desired flame shape was stably maintained. I couldn't.
[0038]
【The invention's effect】
The burner diffuser of the present invention is less likely to be damaged due to the difference in the coefficient of thermal expansion between the members, and is securely held so that the members constituting the plate portion are always in a normal positional relationship, and the desired flame shape is obtained. It can be stably maintained over a long period of time.
[Brief description of the drawings]
1 is an external view of a burner diffuser according to an embodiment of the present invention. FIG. 2 is a plan view of a burner diffuser according to an embodiment of the present invention. FIG. 3 is an embodiment of the present invention taken along line XX in FIG. Cross-sectional view of burner diffuser according to embodiment [FIG. 4] Front view of a joined portion of ceramic pieces [FIG. 5] Perspective view showing a joined portion of ceramic pieces in an exploded state [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main-body part 2 Ceramic piece 11 Outer cylinder 12 Inner cylinder 13 Rib 13a Rib through-hole 14a, 14b Bolt (shaft)
15 Holding plate 15a Through hole 16a, 16b of holding plate Nut 21 Main surface portion 22 of ceramic piece Leg portion 22a of ceramic piece Leg through hole of ceramic piece

Claims (2)

A main body having a structure in which an outer cylinder and an inner cylinder existing inside the outer cylinder are connected by a plurality of ribs;
A burner diffuser comprising a plurality of ceramic pieces jointly forming a ring-shaped dish portion covering a region between the outer cylinder and the inner cylinder on one open surface of the main body,
The ceramic piece, a fan-shaped main surface portion, erected on the main surface portion, be of T-shaped cross-section having a leg portion used for bonding the said ribs, each other for the one of said ribs Two adjacent shafts are inserted through the legs of the ceramic piece,
The ceramic piece is bonded to the rib in the circumferential direction of the dish part by using a pressing plate through which the shaft inserted through the leg part is further inserted. Are joined to the ribs so as to maintain a normal positional relationship with each other.
The rib is formed of a simple flat plate not having the seating surface of the ceramic piece,
Even when the adjacent erected shafts are maximally separated by thermal expansion of the main body, at least one of the shafts and the inner peripheral surface of the leg through hole of the ceramic piece through which the shaft is inserted Is configured to be in a non-contact state,
The burner diffuser according to claim 1, wherein the ceramic piece is joined to the main body portion only by pressure bonding to the rib of the leg portion . The air flowing in the space between the outer cylinder and the inner cylinder constituting the main body directly collides with the surface of the main surface portion of the ceramic piece on the side where the leg portion is erected, and from the outer edge side of the main surface portion The burner diffuser according to claim 1 , wherein the burner diffuser is configured to be ejected outside the main body.

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