JP3476907B2 - Protection measures for header in water pipe wall of boiler combustion chamber - Google Patents

Description

Description: BACKGROUND OF THE INVENTION In a combustion chamber such as a solid fuel-fired boiler for burning solid fuel such as wood chips, building waste chips, and coal, the furnace wall has a water pipe group. The present invention relates to a method for protecting the header in the water pipe wall of such a boiler combustion chamber. BACKGROUND OF THE INVENTION In a water pipe wall structure of a combustion chamber in a solid fuel fired boiler or the like, if a header which is a connecting portion of a group of water pipes is exposed to the combustion chamber as it is, H in the combustion gas is reduced.
There is a possibility that the header may be corroded by the Cl component and so-called corrosion thinning may occur. There is no problem with water tubes having a small thickness (usually about 3.2 mm) because the temperature difference between the inside and outside of the tube is small.
mm), the temperature difference between the inside and outside of the header becomes extremely large when the thermal load in the combustion chamber is high, and as a result, thermal fatigue cracking due to thermal stress (so-called elephant crack)
Tends to occur. Therefore, the present inventor has previously attempted to solve the above problem by forming a protective layer of an Al ₂ O ₃ -based castable refractory on the combustion chamber side surface of the header. Thus, if such a protective layer is formed, the header surface does not directly come into contact with the combustion gas, so that there is no corrosion. Further, since the temperature inside and outside the header becomes small, the header does not cause thermal fatigue cracking. However, Al ₂ O ₃ castable refractories have low thermal conductivity (about 0.7 Kcal / m · h · ° C.).
Therefore, the surface temperature of the protective layer is inevitably increased, and the clinker may adhere to the surface of the protective layer, which may hinder the operation of the boiler. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in view of the above circumstances. Accordingly, the present invention has been developed for a boiler combustion chamber capable of reliably preventing header corrosion, thermal fatigue cracking and clinker generation. It is an object of the present invention to provide a method for protecting a header in a water pipe wall. In order to achieve the above-mentioned object, in the header protection method of the present invention, in particular, a castable material having a high thermal conductivity is provided on a surface of a combustion chamber side of the header. It is proposed to form a refractory protective layer. [0008] As a constituent material of the protective layer, 60 to 60% of SiC is used.
95% SiC castable refractory or S
It is preferable to use i ₃ N ₄ castable refractories or molded articles thereof. In forming the protective layer, it is preferable that a large number of pin-shaped stud anchors to be buried in the protective layer be protruded from the header in advance. It is preferable to attach a cap made of SiC to all the tip portions of these stud anchors or a part of the selected stud anchors. Of course, such a cap may not be required depending on the combustion conditions such as the fuel used. The combustion chamber side surface of the header is protected by the protective layer made of castable refractory, so that the protective layer can lower the surface temperature of the header. As a result, the temperature difference between the inside and outside of the header becomes small, and thermal fatigue cracking is reliably prevented. Needless to say, unlike the case where the header is exposed in the combustion chamber, there is no danger that the header is corroded and reduced in thickness by the HCl component in the combustion gas. In addition, since the protective layer is made of a SiC-based castable refractory having a high thermal conductivity or a Si ₃ N ₄ -based castable refractory, an Al ₂ O ₃ -based castable refractory having a low thermal conductivity is used. In comparison, the surface temperature of the protective layer is significantly reduced. Therefore, there is no possibility that the clinker adheres to the surface of the protective layer regardless of the combustion conditions. Incidentally, Al ₂ O is used as a constituent material of the protective layer.
_{When a 3} series castable refractory is used, the protective layer needs to be considerably thick (at least about 75 mm) in order to secure a certain layer strength, and has a complicated shape (for example, a V-shape) as a stud anchor. ) Had to be used. However, as described above, when a SiC-based castable refractory or a Si ₃ N ₄ -based castable refractory is used as a constituent material of the protective layer, these materials are stronger than the Al ₂ O ₃ -based castable refractory. Therefore, the thickness of the protective layer can be reduced as much as possible, and the stud anchor can be formed in a simple pin shape. In addition, if necessary, if a cap made of SiC is attached to the tip of all the stud anchors buried in the protective layer or a part of the selected stud anchors, the protective layer at the stud anchor portion is peeled off. Even in the case where the stud anchor is dropped, there is no fear that the tip of the stud anchor made of stainless steel or the like is corroded by contact with the combustion gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the present invention will be specifically described below with reference to the embodiments shown in FIGS. In the solid fuel-fired boiler shown in FIG.
1 is a combustion chamber, 2 is a boiler body juxtaposed with the combustion chamber 1, 3
Reference numeral denotes a transfer-type grate disposed at the bottom of the combustion chamber 1, 4 denotes a wind box for supplying combustion air from below the grate 3, and 5 denotes a fuel inlet. The furnace walls 6a, 6b, 6c of the combustion chamber 1 have a water tube wall structure formed by connecting water tube groups which are arranged side by side at a constant pitch by a header. In particular, the method according to the invention is applied to headers 8a, 8b in the side wall 6a and the rear wall 6b which are thermally problematic. That is, as shown in FIGS. 1 and 2, the side wall 6a is formed by connecting the lower ends of the water pipe groups 7a... Arranged in the front-rear direction to the header 8a extending in the front-rear direction. A protective layer 9a made of a castable refractory having high thermal conductivity and excellent strength is formed on the surface of the combustion chamber side. Such castable refractories include S
those things or Si ₃ N ₄ system SiC system containing 60% to 95% of iC is preferred. Of course, it is also possible to use molded articles of these castable refractories. In addition, header 8a
As shown in FIG. 2, a large number of stud anchors 10 are projected to prevent the protective layer 9a from falling off. Each stud anchor 10 has a pin shape, and a cap 11 made of SiC is attached to the tip of each stud anchor 10. Also, the rear wall 6b is, as shown in FIGS.
The lower end portions of the water pipe groups 7b... Arranged in the left-right direction are connected to a header 8b extending in the left-right direction.
In the same manner as described above, a protective layer 9b made of a castable refractory of SiC or Si ₃ N ₄
Are formed, and pin-shaped stud anchors 10 similar to the above are protruded. Of course, also in this case, as shown in FIG. 3, a cap 11 made of SiC is attached to the tip of the stud anchors 10. In this embodiment, of the stud anchor groups 10 embedded in each of the protective layers 9a and 9b, a selected stud anchor 10 is selected.
(The half of all stud anchors) has the cap 11 attached thereto, but the number of stud anchors for attaching the cap 11 can be appropriately set according to combustion conditions and the like. For example, the cap 11 may be attached to all of the stud anchors 10 embedded in the protective layers 9a and 9b. Of course, depending on the fuel, the cap 11 may not be required at all. In this embodiment, each of the water pipes 7a and 7b has an inner diameter of 69.8 mm and an outer diameter of 76.2 mm.
Carbon steel tubes for boiler heat exchangers are used. Each of the headers 8a and 8b has an inner diameter of 267.7 mm and an outer diameter of 31.
An 8.5 mm high temperature carbon steel tube is used. The protection layers 9a and 9b are formed not only on the existing water pipe wall but also on the newly installed water pipe wall after the water pipe wall is completed. Is
For example, well-known techniques such as ironing, spraying, and molding are employed. In this embodiment, the protective layer 9 is
a, 9b were formed. The thickness of the protective layers 9a and 9b and the shape and arrangement (pitch) of the stud anchors 10 are
It is necessary to appropriately set the protection layers 9a and 9b so that the protection layers 9a and 9b do not fall off.
The stud anchors 10 are made of stainless steel pins and are evenly arranged at a small pitch of about 40 mm, and the surfaces of the protective layers 9a and 9b and the upper surface of the cap 11 are substantially equal to each other. It is flush. As described above, when the protective layers 9a and 9b made of the castable refractory of the SiC type or the Si ₃ N ₄ type are formed, as described above, the thermal fatigue cracking of the header and the adhesion of the clinker are surely caused. Although it is prevented, this point has been confirmed by the following experiment. That is, this experiment was conducted using the solid fuel-fired boiler described above, and the protective layers 9a and 9b were used.
As shown in Table 1, in the case of being composed of an SiC castable refractory and the case of being composed of a Si ₃ N ₄ castable refractory, the operating time was 3600 hours, and the combustion chamber temperature (flame temperature) was 1300 ° C. water. The boiler is operated under the condition of the fluid inside the pipe wall: water (280 ° C.), and the temperature of each part of the headers 8a, 8b and the protective layers 9a, 9b and the surface of the protective layers 9a, 9b formed on the headers 8a, 8b. Measured and investigated whether clinker adhered or not. The results were as shown in Table 2. As a comparative example, the protective layer 9
When a and 9b are made of Al ₂ O ₃ -based castable refractories as shown in Table 1 and when the protective layers 9a and 9b are not formed, the boiler operation is performed under the same conditions as in the above case, and the headers 8a and The temperature of each part of 8b and the presence or absence of clinker on the surface of the protective layer were measured and investigated. The results were as shown in Table 2. In Comparative Example 1, a V-shaped stud anchor was used and arranged at a pitch of 200 to 300 mm. [Table 1] [Table 2] As is apparent from Table 2, headers 8a, 8
In Comparative Example 2 where b was exposed, although the outside surface temperature of the header was high and the inside and outside temperatures were large, the combustion chamber side surfaces of the headers 8a and 8b were protected by the castable protective layers 9a and 9b. In Comparative Example 1, regardless of the material of the protective layer, the temperature of the outer surface of the headers 8a and 8b can be significantly reduced regardless of the material of the protective layer. Therefore, there is a possibility that thermal fatigue cracking occurs in Comparative Example 2, but there is no possibility that thermal fatigue cracking occurs in Experimental Examples 1 and 2 and Comparative Example 1. Incidentally, since thermal fatigue cracking does not occur until at least two to three years have passed, it cannot be confirmed by the above-described experimental operation of about 3600 hours. However, those having the same structure as Comparative Examples 1 and 2 have been operated for more than three years under the same conditions as described above. No thermal fatigue cracking occurred at the header of the sample, but a clear thermal fatigue cracking occurred in Comparative Example 2. From the results of the performance survey, it is easily understood that it is effective to reduce the temperature difference between the inside and outside of the header by the protective layer made of the castable refractory in order to prevent thermal fatigue cracking. Further, as is apparent from Table 2, in Comparative Example 1 in which the protective layer was made of an Al ₂ O ₃ -based castable refractory, the surface temperature of the protective layer became extremely high, and clinker adhered to the surface. In contrast, in Experimental Examples 1 and 2,
Since the protective layer was made of a castable refractory having a high thermal conductivity, the surface temperature of the protective layer was significantly reduced, and the clinker did not adhere to the surface. As described above, in Examples 1 and 2, thermal fatigue cracking and clinker adhesion can be effectively prevented.
It has been confirmed that the method of the present invention is effective in protecting the header. The present invention is applicable not only to the combustion chamber of the solid fuel-fired boiler described above, but also to the combustion chambers of various boilers (such as fluidized bed boilers) in which the furnace wall forms a water tube wall. The header in which a layer is to be formed can be appropriately selected according to the boiler type and combustion conditions. As is apparent from the above description, according to the present invention, a protective layer made of a castable refractory having high thermal conductivity and excellent strength such as SiC or Si ₃ N ₄ is provided. By forming them, the corrosion of the header and the thermal fatigue crack can be reliably prevented, and the clinker can be securely prevented from adhering to the surface of the protective layer. Therefore, irrespective of whether the water pipe wall is an existing one or not, it is possible to take thorough measures for protection of the header, and to greatly improve the durability of the water pipe wall and thus the entire boiler.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional side view showing an example of a boiler having a water pipe wall structure in which a method for protecting a header is implemented according to the present invention. FIG. 2 is an enlarged sectional view taken along line II-II of FIG. FIG. 3 is an enlarged detail view showing a portion III in FIG. 1; [Description of Signs] 1 ... combustion chamber (boiler combustion chamber), 6a ... side wall (water pipe wall),
6b: rear wall (water pipe wall), 7a, 7b: water pipe, 8a, 8b
... Header, 9a, 9b ... Protective layer, 10 ... Stud anchor, 11 ... Cap.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-231602 (JP, A) JP-A-2-203194 (JP, A) JP-A-57-164203 (JP, A) 175856 (JP, U) JP 31-152 (JP, B1) JUKI 7-788 (JP, Y1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F22B 37/00 F22B 37 /twenty two

Claims (1)

(57) [Claim 1] In a water pipe wall of a boiler combustion chamber in which water pipe groups are connected by a header, the surface of the header near the combustion chamber
High and high thermal conductivity containing 60-95% SiC
SiC castable refractory or S
By i ₃ N ₄ castable refractories or their molded products
A protective layer is formed, and in forming the protective layer,
Many pin-shaped studs buried in the protective layer
With the Doanka projecting, all stud anchors
At the tip of the stud anchor or some selected stud anchors
A cap made of SiC is attached, and the surface of the protective layer
And the upper surface of the cap are made substantially flush with each other.
That, protection method of tube gathering in the water pipe wall of the combustion chamber.