JP2000161604A - Fluidized bed heat transfer tube and fluidized bed boiler provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluidized bed boiler having a heat transfer tube and a heat transfer tube structure where wear of the heat transfer tube is suppressed, and simultaneously heat transfer to a fluid in the heat transfer tube is prevented from being obscured. SOLUTION: A mesh-shaped material such as a properly opened metal gauze and an expand metal 2 is wound on an external surface of a heat transfer tube 1 used in a fluidized bed boiler and is fixed to the heat transfer tube 1 with a clamp 3 with a proper method. When the service life of the metal gauze or the expand metal 2 is anxious, these surfaces are subjected to calorizing and chromizing and the like, and the surface of the heat transfer tube 1 is hardened to provide wear resistance to the heat transfer tube 1. Further, the service life is prolonged by applying a thin layer of a refractory on the heat transfer tube 1 with the metal gauze and the expand metal 2 taken as a frame.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluidized-bed boiler, and more particularly to a structure for preventing wear of a heat transfer tube arranged in a fluidized-bed of a fluidized-bed boiler.

[0002]

2. Description of the Related Art Fluidized bed boilers use a combustion air introduced from the bottom of a furnace to fluidize lime, silica sand, etc. as a fluid medium, into which solid fuel such as coal is injected from above or below the furnace and burned. This is a steam generator of the type in which the fluid (water) in the heat transfer tube arranged in the fluidized bed is heated by the obtained combustion heat.

[0003] Since the heat exchange by the combustion heat is carried out by bringing the fluid medium into contact with the heat transfer tube provided in the fluid medium, excellent heat transfer characteristics are obtained, and a predetermined heat absorption area is obtained with a small heat transfer area. It has the characteristic of being effective, and its application is expanding in recent years.

[0004] However, since the heat transfer tubes are installed in the fluid medium, the heat transfer tubes are inevitably reduced in wear. Therefore, measures for wear of the heat transfer tubes are indispensable for long-term stable operation. It is. Conventionally, to prevent wear of the heat transfer tube, a method of spraying ceramics such as carbide or oxide on the surface of the heat transfer tube or overlay welding a wear-resistant metal such as stellite to avoid wear reduction has been generally adopted. ing.

[0005] Further, a large number of studs are installed on the heat transfer tubes in the fluidized bed of the fluidized bed boiler, fins parallel to the axial direction of the heat transfer tubes are attached, or a pipe-shaped cover is attached outside the heat transfer tubes. Attempts have also been made to reduce the energy when the fluid medium collides with the heat transfer tubes, and to suppress wear of the heat transfer tubes.

When the heat transfer tube has a bent portion, uneven flow of the fluid medium near the bent portion and so-called blow-through easily occur, and a high wall thinning rate is often observed at the bent portion of the heat transfer tube. Attachment of a protector to the bent portion has been performed as a measure for reducing the thickness of the bent portion. Japanese Patent Laid-Open Publication No. Hei 8-226601 discloses a method of installing such a protector.

Further, after the stud is installed on the heat transfer tube,
A method of constructing a refractory having excellent wear resistance may be applied. This method is generally used to prevent corrosion and thinning of a boiler heat transfer tube due to molten slag, and is often applied to fluidized bed boilers.

[0008] In a fluidized bed catalytic reformer (hereinafter abbreviated as FCC) used when producing gasoline from crude oil or the like, a hex mesh is used on the outer periphery of an air injection ring that is used in a fluidized bed and has severe wear. Anchors are installed and refractories are installed (for example, Fluid Catalytic Cracking
Handbook, R. Sadeghbeigi, Gulf Publishing Company,
Houston, Texas, 1995).

[0009]

Among the above prior arts, the method of applying a high-hardness film or overlay on the surface of the heat transfer tube, or the method of attaching studs or axial fins by welding is appropriate for the heat transfer tube. Although effective in suppressing wall thinning due to wear, it is inevitable that the heat transfer tube will gradually lose its wall thickness as the operation time increases, and the life of the heat transfer tube will soon reach its end.
As the operation time further increases, corrosion fatigue cracks may occur on the inner surface of the heat transfer tube to which the studs or fins are attached due to thermal stress caused by the temperature difference between the studs or fins and the heat transfer tube. Both methods require a great deal of time and attention in construction and processing, and these are factors that increase manufacturing costs.

[0010] On the other hand, the method of constructing a refractory after attaching studs or axial fins to the heat transfer tube does not directly contact the heat transfer tube and the flowing medium until the refractory is exhausted, which is effective in extending the life. However, this method is usually applied to a heat transfer surface such as a membrane structure, and each heat transfer tube is independent, such as a tube in a fluidized bed. When applied to an object that vibrates or deforms somewhat, the refractory may easily come off during operation due to the small anchor effect of the stud. Further, if the size of the separated refractory fragments is larger than a certain size, the fragments may become obstacles when the fluid medium is withdrawn, causing a serious problem. In particular, when the studs and the axial fins are used as anchors, the above-described problems are liable to occur because the fragments become essentially large pieces and are easily separated from the heat transfer tube.

A method using a hex mesh, which is frequently used in the FCC, is intended for a tubular object having a diameter exceeding 150 mm, and cannot be applied to a boiler heat transfer tube having a diameter of about 35 to 50 mm.

Another problem other than wear of the heat transfer tube is that when a relatively thick refractory is applied to the surface of the heat transfer tube, heat transfer to the fluid in the heat transfer tube is hindered by the heat insulating effect of the refractory. Can be For this reason, when using refractories, it is necessary to consider the degree of heat transfer inhibition in product design (calculation of heat transfer surface, etc.) and remodeling of equipment, etc. Have to do it.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, suppress the wear of the heat transfer tube, and at the same time, prevent the heat transfer to the fluid in the heat transfer tube from being hindered. To provide a fluidized-bed boiler equipped with the same.

[0014]

SUMMARY OF THE INVENTION The object of the present invention is to wrap a mesh such as a wire mesh or expanded metal having an appropriate aperture around an outer surface of a heat transfer tube used in a fluidized-bed boiler or the like, and apply these to an appropriate method. It is solved by fixing to the heat transfer tube.

If there is a concern about the life of the wire mesh or expanded metal, these surfaces are subjected to a calorizing treatment, a chromizing treatment, or the like to harden the surface of the heat transfer tube to give the heat transfer tube abrasion resistance. Solvable. In addition, the service life can be extended by thinly applying a refractory material to the heat transfer tube using a wire mesh or expanded metal as a framework.

[0016]

According to the present invention, in a fluidized bed furnace, energy when a fluid medium collides violently with a heat transfer tube is absorbed or dissipated by a mesh such as a wire net or expanded metal wound in a semi-fixed state on the heat transfer tube, The fluid medium is prevented from directly contacting the heat transfer tube, thereby preventing the heat transfer tube from being worn in the fluidized bed. In particular, in the case of this method, the heat transfer tube and the high-temperature gas (combustion exhaust gas) in the fluidized bed are always in contact with each other, so that heat transfer inhibition is very small.

[0017]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the appearance of a state in which the expanded metal 2 shown in FIG. 2 is wound as a mesh on the heat transfer tube 1 and the expanded metal 2 is held by the clamp 3 from above.

The material of the heat transfer tube 1 is made of an alloy ranging from carbon steel to alloy steel, and its size is usually 30 to 6 in outer diameter.
0 mm and a thickness of about 2 to 10 mm. The expanded metal 2 preferably has a thickness of 0.3 to 0.5 mm, a horizontal width of 3 to 4 mm, and a vertical size of 1 to 2 mm. The material of the expanded metal 2 is determined depending on the conditions of use, and a typical example is an austenitic stainless steel such as SUS310S. A ferritic stainless steel containing aluminum may be selected for the reasons described below.

Next, the clamp 3 has a thickness of 1 to 3 mm and a width of 10 mm.
Those having a size of ２０20 mm are preferred. The dimensions are not particularly limited to these. The material of clamp 3 is SUS
310S and the like are typical. FIG. 3 shows a radial cross section of a mounting portion of the clamp 3, in which the clamp 3 is fixed by a welding portion 3 '. The welding material is selected according to the material and dimensions of the clamp 3. Here, the method of fixing the clamp 3 by welding has been described, but the same effect can be obtained with a band using screws.

The maximum value of the aperture of the expanded metal 2 as a mesh-like material (the maximum value of the vertical and horizontal lengths of the aperture) is less than 5 mm, or the equivalent hydraulic diameter of the aperture of the expanded metal 2 is 2 mm. It is desirable to be less than.
This is to prevent coal ash or rock having a diameter of several mm, which may be present in the fluid medium, from passing through the eyes and directly colliding with the heat transfer tube 1 as much as possible.

Whether there is ash or rock having a diameter of more than 2 mm depends on the type of fuel or fluid medium used in the operation, and such large-diameter and hard granular material is often used in fluidized-bed boilers. It is very commonly observed that when the abundance in the fluid medium is large, the wall loss due to wear of the heat transfer tubes and the structure in the layer becomes remarkable. Therefore, the numerical values related to the size of the openings of the expanded metal 2 are set based on such experiences and facts.

The manner of winding the expanded metal 2 around the heat transfer tube 1 is determined by the conditions of use and the degree of wear, and may be single winding or multiple winding. Impractical,
As a practical condition, single winding or double winding is preferable.

The material of the expanded metal 2 is typically SUS310S as described above. However, since such an austenitic stainless steel has a large coefficient of thermal expansion, expanded metal 2 is required during operation of the fluidized bed boiler.
If the heat transfer tube 1 cannot be sufficiently protected because it is expanded by thermal expansion, ferritic stainless steel containing aluminum as an alloy component and having high oxidation resistance is suitable.
This is based on the fact that the coefficient of thermal expansion of ferritic stainless steel is much smaller than that of austenitic stainless steel.

As is clear from the above description, the wear prevention structure of the heat transfer tube shown in FIGS. 1 to 3 wraps an expanded metal 2 which is a general industrial product around the heat transfer tube 1 at a portion to be subjected to wear prevention. However, since it is a simple structure that is simply fixed to the heat transfer tube 1 by a normal method, a method that requires a large amount of welding and requires a high level of skill, such as a cover or a stud that has been conventionally applied, or a refractory is used. Abrasion prevention can be achieved very easily and inexpensively as compared with the method of construction.

FIG. 4 shows a second embodiment of the present invention.
This is one in which an expand 2 wound around a heat transfer tube 1 is fixed with a normal stud. FIG. 5 shows a cross-section in the pipe diameter direction of the stud installation portion. The number and arrangement of the studs 4 should be determined by a designer or a constructor as appropriate, and there is no particular limitation. As shown in (1), it is desirable to install the stud 4 also diagonally below the heat transfer tube 1.

In the example shown in FIG. 5, the stud 4 is pressed from above the expanded metal 2 and welded to the heat transfer tube 1. However, the expanded metal 2 is inherently thin. As a result, the purpose of fixing by the stud 4 may be impaired. Therefore, when applying this method, it is desirable to select appropriate welding conditions before construction.

FIG. 6 shows one method for avoiding the above-mentioned problem relating to the fusing of the expanded metal 2. That is, an underplate 5b of an appropriate material is placed in advance on a portion where the stud 4 is to be welded (temporarily fixing the underplate 5b by welding, fixing it to a flammable tape or the like), and then expanding the expanded metal 2 into the expanded metal. After the metal 2 is wound around the heat transfer tube 1, the stud 4 is welded by sandwiching the metal between the heat transfer tubes 1 so that the expanded metal 2 is fixed to the heat transfer tube 1 even if the expanded metal 2 is blown out. Thus, the purpose of preventing wear is achieved.

In the present invention, the size and material of the backing plate 5 are not limited, but it is necessary to select a thickness that allows stud welding. It is desirable to determine the actual thickness after setting the welding conditions of the stud 4 in advance.

The above-mentioned method of fixing the expanded metal 2 with the studs 4 has a disadvantage that the reliability is slightly inferior to that of the clamp method and that the heat transfer tube 1 serving as a pressure-resistant portion is directly affected. There is a merit that it can be applied to a part where ordinary welding is difficult because of its excellent properties.

FIGS. 1 and 4 show examples in which expanded metal 2 is used as a mesh-like material, but the same effect is obtained as shown in FIG.
Can be obtained by winding the wire mesh 6 shown in FIG. For the same reason as in the case of the expanded metal 2 described above, it is necessary that the maximum size (diagonal direction) of the mesh size of the wire mesh 6 be less than 5 mm. In the present invention, the wire diameter of the wire mesh 6 is not limited, but the wire diameter is 0.5 to 1.0 m from the workability of winding and the effect of preventing abrasion.
m is preferable. The material of the wire mesh 6 is SUS31
0S is typical. The wire mesh 6 can be fixed in the same manner as the method shown in FIG. 1 or FIG.

In the method of using the wire mesh 6 as the mesh-like material, even if the wire mesh 6 having a relatively large wire diameter and a small opening is selected from the viewpoint of the service life, the wire mesh 6 is more easily deformed than the expanded metal 2. There is a merit that it is easy to wind around.

When the abrasion of the fluid medium is extremely strong and the life of the expanded metal 2 or the wire mesh 6 is short, various surface treatments are applied to the expanded metal 2 or the wire mesh 6. Representative examples include aluminizing (diffusion and infiltration of aluminum), calorizing (diffusion and infiltration of chromium), siliconizing (diffusion and infiltration of silicon), bolonizing (diffusion and infiltration of boiler), and the like.

The same effect can be expected by hot-dip aluminum plating. After aluminum spraying, the material to be processed may be rapidly heated to a temperature higher than the melting point of aluminum. In the present invention, the present invention is not limited to the above-described treatment method, and any treatment for curing the surface layer of the material is included in the present invention. In each of these, a layer having a higher hardness than the material is formed on the surface of the object to be treated, so that the abrasion resistance is improved.
Alternatively, it is effective in extending the life of the wire net 6, and the purpose of preventing wear is achieved.

The above embodiments of the present invention are intended to dissipate or absorb the collision energy of the fluid medium by the expanded metal 2 or the wire mesh 6 alone.
When the particle size of the fluid medium is small and fine particles may collide with the heat transfer tube 1 at high speed through the mesh of the expanded metal 2 or the wire mesh 6, the desired effect cannot be obtained. There are cases.

In such a case, a method is adopted in which the expanded metal 2 and the wire mesh 6 are used as a framework and a refractory of a sunshine-bonding type is constructed. If the refractory is applied too thickly, it is easy to peel off, so a few millimeters at most is sufficient. However, it is necessary to add a fine fibrous substance typified by rock wool or the like so that the refractory is firmly held by the expanded metal 2 and the wire mesh 6. The addition amount of the fine fibrous substance is appropriately determined depending on the holding effect and workability.

In applying the present invention, the particle size of the aggregate (rock, etc.) added to ensure the strength of the refractory itself must be sufficiently smaller than the size of the openings of the expanded metal 2 and the wire mesh 6. Needless to say, this must be done.

When a refractory is applied, the heat transfer tube 1 has a disadvantage that the heat transfer inhibition of the heat transfer tube 1 is greater than when the refractory is not applied. This has the effect of reliably preventing the wear of the device.

In the above embodiment of the present invention, the wear of the heat transfer tube 1 in the fluidized bed boiler layer is reliably prevented or suppressed, and the fluidized bed boiler can be operated stably for a long period of time. Since the heat transfer inhibition of the heat transfer tube 1 is small or almost negligible as compared with the method, the influence on the performance of the fluidized bed boiler is small.

In the above embodiment of the present invention, the construction cost can be significantly reduced as compared with the conventional method, and when the conventional method causes wear, repair is difficult or impossible. In addition, there is an advantage that repair can be performed easily and in a short time by replacing a portion where the mesh-like material is damaged or by overlapping the mesh-like material.

[0040]

According to the present invention, wear of the heat transfer tube in the fluidized bed boiler layer can be reliably prevented or suppressed, and the fluidized bed boiler can be operated stably for a long period of time. The impact on the performance of the fluidized-bed boiler is small since it is small or little. According to the present invention,
Not only the construction cost can be reduced than the conventional method, but also when the abrasion occurs, the repair can be performed easily and in a short time.

[Brief description of the drawings]

FIG. 1 is a view showing a structure for preventing wear of a heat transfer tube according to an embodiment of the present invention.

FIG. 2 is a view showing an expanded metal used in the wear prevention structure of FIG. 1;

FIG. 3 is a sectional view of the wear prevention structure of FIG. 1 in a radial direction of a heat transfer tube.

FIG. 4 is a view showing a structure for preventing wear of the heat transfer tube according to the embodiment of the present invention.

5 is a sectional view of the wear prevention structure of FIG. 4 in a heat transfer tube radial direction.

6 is a cross-sectional view in the axial direction of a heat transfer tube showing an example of a stud construction method of the wear prevention structure of FIG.

FIG. 7 is a view showing a wire mesh used for a wear prevention structure of a heat transfer tube according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat transfer tube 2 Expanded metal 3 Clamp 3 'Clamp weld 4 Stud 5a Upper plate 5b Lower plate 6 Wire mesh

Claims (4)

[Claims] A fluidized-bed heat transfer tube fixed to the heat transfer tube by winding a mesh-like material around the outer surface of the heat transfer tube. 2. The fluidized-bed heat transfer tube according to claim 1, wherein the surface of the mesh-shaped material is subjected to a hardening-resistant hardening treatment. 3. The fluidized-bed heat transfer tube according to claim 1, wherein the mesh-shaped material is used as a framework and the refractory is thinly applied to the heat transfer tube. 4. A fluidized-bed boiler comprising the fluidized-bed heat transfer tube according to claim 1 disposed in a fluidized-bed.