JPH07109281B2 - Cover structure of heat transfer tube in fluidized bed - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cover structure for a heat transfer tube in a fluidized bed, and more particularly to a heat transfer tube in a fluidized bed suitable for preventing wear of the heat transfer tube in a fluidized bed. It relates to a cover structure.

[Conventional technology]

As shown in FIG. 7, the wear amount of the fluidized bed heat transfer tube (hereinafter referred to simply as the in-bed heat transfer tube) of the fluidized bed boiler is as shown in FIG. It heats up rapidly. This is because, as shown in FIG. 8, above the surface of the stationary fluidized bed, the bubbles 14 of combustion gas and flowing air grow while rising inside the fluidized bed 15 and burst at the surface of the fluidized bed 15. This is because the fluidized medium particles 4 in the fluidized bed 15 constantly violently move up and down. Therefore, conventionally, an in-layer heat transfer tube is buried below the surface of the stationary fluidized bed to suppress wear thinning of the in-layer heat transfer tube.

Further, in a fluidized bed boiler, so-called in-furnace that removes SO _x contained in combustion gas when combustion gas rises inside the fluidized bed by mixing limestone powder with fluidized medium particles in the fluidized bed. Desulfurization is in progress. As shown in FIG. 9, the temperature of the fluidized bed was 800 ° C.
The most effective desulfurization reaction occurs. Therefore, the scope of the temperature of the fluidized layer when operating the fluidized bed boiler, including NO _x, are constrained to a range of temperatures that can comply with air quality regulations value.

Therefore, in the fluidized bed boiler, when the load is controlled by the velocity turndown method, it is necessary to prevent the temperature of the fluidized bed from decreasing even if the fuel, that is, the heat input amount decreases as the load decreases. . For this reason, a part of the in-bed heat transfer tube must be exposed from the surface of the fluidized bed whose load has decreased and the height has decreased, so that the heat output from the fluidized bed due to the water supply inside the in-bed heat transfer tube must be reduced. I have to.

Figures 10 (a), (b) and (c) show various arrangements of in-bed heat transfer tubes, and Figure 10 (d) shows the relationship between the load of the fluidized bed boiler and the temperature of the fluidized bed. It is a figure shown for every various arrangement of a heat transfer tube in a layer.

As shown in FIGS. 10 (a), (b), and (c), twelve in-layer heat transfer tubes 1 are three in each of FIG. 10 (a).
Steps 1 to 2 and 4 to 4 above and 3 steps below, and in Figure 10 (b), 4 rows each, row 1 and row 2
In the upper and lower three stages of the stage and the third stage, and in FIG.
They are arranged respectively. And a-1 stage, b-stage and ha
The in-layer heat transfer tube 1 with the first stage, the in-layer heat transfer tube 1 with the second stage, the second stage, the second stage, and the second stage, and the third stage and the low stage.
In-layer heat transfer tubes 1 of three stages are arranged at the same height from the air dispersion plate 5, respectively. Further, the in-layer heat transfer tube 1 in the 4th stage is lower in height from the air dispersion plate 5 than the in-layer heat transfer tubes 1 in the other stages, and is arranged closest to the air dispersion plate 5.

In Fig. 10 (a), (b) and (c), fluidized bed boiler
When 16 loads decrease from rated load to partial load, fluidized bed
The surface of 15 is lowered from the position of surface 11 under rated load to the position of surface 12 under partial load. In this case, a-1 stage and b-1
The in-layer heat transfer tubes 1 of the step and the step c-1 are exposed above the surface 12, but the in-layer heat transfer tubes 1 of the other steps are buried inside the fluidized bed 15. That is, in the case of FIG. 10 (a), there are nine in-layer heat transfer tubes 1 buried in the fluidized bed 15, (b)
Since the number is 8 in the case of and the number is 6 in the case of (c), the heat output taken out from the fluidized bed 15 by the water supply inside the in-layer heat transfer tube 1 is in the order of (a)>(b)> (c). It's getting less.

On the other hand, as the load on the fluidized bed boiler 16 decreases, the amount of fuel injected from the coal feeding pipe 9 into the fluidized bed 15, that is, the amount of heat input also decreases, so the temperature of the fluidized bed 15 decreases by (a)> ( )>
It decreases in the order of (c). The relationship between the temperature of the fluidized bed 15 and the boiler load is shown in FIG. That is, even if the boiler load changes from the rated load to the partial load, the temperature drop of the fluidized bed 15 is the smallest when the arrangement of the in-bed heat transfer tubes 1 is as shown in FIG. .

As described above, in order to prevent the temperature of the fluidized bed from decreasing even if the load is reduced, a large number of in-bed heat transfer tubes are arranged horizontally adjacent to each other at a narrow interval. When the boiler load decreases and the height of the fluidized bed decreases, the number of in-layer heat transfer tubes exposed from the surface of the fluidized bed whose height has decreased may be increased. However, when a large number of in-layer heat transfer tubes are arranged adjacent to each other in a horizontal direction at a narrow interval, combustion gas and flowing air (hereinafter,
The velocity of the gas (which is simply referred to as gas) increases, so that the fluidized medium particles in the fluidized bed flow vigorously, and the amount of wear of the heat transfer tubes in the bed increases. Further, since the superficial velocity of the gas at the rated load is increased in order to maintain the good flow of the fluidized bed at the minimum load, the wear of the in-layer heat transfer tube is promoted.

Therefore, in order to prevent wear of the in-layer heat transfer tubes, in the past, in combination with (1) slumping control, a sufficient space was secured between the in-layer heat transfer tubes as shown in Fig. 10 (a). . However, this causes the temperature of the fluidized bed to decrease when the boiler load decreases, as already explained.
(2) A wear preventing cover was attached to the entire outer surface of the in-layer heat transfer tube. As shown in Fig. 11 which shows the relationship between the heat transfer surface coverage ratio (cover mounting area / heat transfer area of in-layer heat transfer tubes) and the overall heat transfer coefficient and required heat transfer area, Since the heat quantity decreases, the heat transfer area, that is, the number of in-layer heat transfer tubes must be increased, the interval between the arrangement of the in-layer heat transfer tubes becomes narrower, and the velocity of the gas passing between the in-layer heat transfer tubes becomes smaller. It will be very fast. In some cases,
The arrangement shown in Fig. 10 (c) is no longer possible, and the arrangement is made as shown in Fig. 10 (a) or (b) to secure the space between the in-layer heat transfer tubes.

[Problems to be solved by the invention]

In the above conventional technology, that is, in the structure in which the cover is attached to the entire outer surface of the in-layer heat transfer tube arranged above the surface of the stationary fluidized bed when the operation of the fluidized bed boiler is stopped, the in-layer heat transfer tube The outer surface of is not worn uniformly over the entire circumference, and no consideration has been given to the fact that specific locations on the outer surface are heavily worn, and the heat transfer efficiency decreases, so the number of in-layer heat transfer tubes is increased. There was a problem that I had to do.

An object of the present invention is to provide a cover structure for an in-layer heat transfer tube, which effectively prevents wear of the in-layer heat transfer tube and prevents the temperature of the fluidized bed from decreasing even when the boiler load is reduced.

[Means for solving problems]

The above object is achieved by the means described below. That is, of the in-layer heat transfer tubes arranged in a plurality of stages, a cover is attached to the entire outer surface of the uppermost in-layer heat transfer tube. Further, in the in-layer heat transfer tubes other than the uppermost stage, it is achieved by attaching a cover only to the outer surface located on the upstream side of the gas flow rising in the fluidized bed, that is, only the lower outer surface. It

[Action]

FIG. 12 is a diagram showing the relationship between the collision angle of particles and the amount of wear on the collision surface. As shown in Fig. 12, the collision angle of particles is 30
At 0 °, the amount of wear on the impact surface is maximum, and at 0 ° and 90 °, it is minimum.

FIG. 13 is a diagram showing the amount of wear and the place of wear for the in-layer heat transfer tubes having different vertical positions in the fluidized bed. In FIG. 13, whether the intra-layer heat transfer tube 1 is located directly above the surface of the fluidized bed 15 or the intra-layer heat transfer tube 1 buried inside the fluidized bed 15, Of the outer surface of the heat pipe 1, the collision angle with the fluidized medium particles 4 accompanied by the gas rising inside the fluidized bed 15 in the direction indicated by the arrow G is about 30.
The wear amount Δt of the outer surface, which is 0 °, is maximum, as in the case of FIG. 12 already described. However, of the outer surface of the in-layer heat transfer tube 1, the upper half, that is, the fluidized bed 15
For the outer surface located downstream of the gas flow rising in the direction indicated by arrow G, the outer surface having a collision angle of approximately 0 °, and the outer surface having a collision angle of approximately 90 °, the wear amount Δt
The wear amount Δt is minimal.

Therefore, as shown in FIG. 2, of the outer surface of the in-layer heat transfer tube 1, the cover 2 covers the lower half of the outer surface, that is, the entire outer surface located on the upstream side of the gas flow rising in the direction indicated by the arrow G. Or, as shown in FIG. 3, the collision angle is about 30 with respect to the gas rising in the direction indicated by the arrow G.
If the cover 2 is attached to an outer surface having an angle of 0 °, that is, an outer surface having a collision angle of approximately 0 ° and an outer surface having an impact angle of approximately 90 °, the wear of the in-layer heat transfer tube 1 is effectively prevented. can do.

Further, by attaching a cover to the entire outer surface of the uppermost in-layer heat transfer tube, gas bubbles 14 grow and flow inside the fluidized bed 15 while rising inside the fluidized bed 15, as already described in FIG. When bursting on the surface of the layer 15, it is possible to prevent the scattered fluid medium particles 4 from dropping onto the in-layer heat transfer tube and abrading the outer surface of the upper half thereof.

〔Example〕

An embodiment according to the present invention will be described with reference to the drawings. FIG. 1 is a view showing a cover structure of an in-layer heat transfer tube of the present invention.

In FIG. 1, between the position of the surface 13 of the fluidized bed 15 when the operation of the fluidized bed boiler 16 is stopped and the position of the surface 11 of the fluidized bed 15 when operating at the rated load, A plurality of in-layer heat transfer tubes 1 are 1-1 stage, 1-2 stage, 1-3 stage and 1-4 stage.
They are arranged in four rows above and below the row. And the 1-of the top
The first-stage intra-layer heat transfer tube 1 covers the entire outer surface, and the second-stage or lower 1-2-stage, 1-3-stage, and 1-4-stage intra-layer heat transfer tubes 1 are the lower half of the outer surface. Covers 1 are attached to the outer surfaces located on the upstream side of the flow of gas rising in the direction indicated by arrow G, respectively.

As a result, it is possible to effectively prevent the wear of the in-bed heat transfer tube 1 due to the flow of the fluidized medium particles 4 in the fluidized bed 15. Further, when the load on the fluidized bed boiler 16 is reduced and the fuel is reduced, the in-bed heat transfer tube 1 is exposed on the surface of the fluidized bed 15 whose height is lowered, so that the temperature of the fluidized bed 15 is almost reduced. In addition, it is possible to operate at the optimum temperature for desulfurization and denitration in the furnace.

FIGS. 4, 5, and 6 are views showing another embodiment of the present invention.

In FIG. 4, a box-shaped cover 2 is attached to the lower half of the outer surface of the intra-layer heat transfer tube 1, and in FIG. 5, a flat plate-shaped cover 2 is attached to the lower part of the intra-layer heat transfer tube 1. is there.

As a result, in the case shown in FIG. 4, the wear of the in-layer heat transfer tube 1 is, of course, prevented, but the fluid medium particles accompanying the gas rising in the direction indicated by the arrow G and the cover 2 are not separated from each other. Since the collision angles are 0 ° and 90 °, wear of the cover 2 is suppressed. Further, in FIG. 5, the intra-layer heat transfer tube 1
The collision angle between the outer surface and the fluidized medium particles is 0 ° and 90 °
Since the collision angle between the cover 2 and the fluidized medium particles is 90 °, wear of both the in-layer heat transfer tube 1 and the cover 2 is suppressed.

In FIG. 6, as in the case shown in FIG. 3 already described, the collision angle is almost 0 ° with respect to the gas rising in the direction indicated by the arrow G on the outer surface of the in-layer heat transfer tube 1. Cover 2 on the outer surface and the outer surface except the outer surface which is almost 90 °
Is attached, but a gap is provided between the outer surface and the cover 2.

As a result, the gas that rises in the fluidized bed in the direction indicated by the arrow G is transferred to the in-layer heat transfer tube 1 and the cover 2 as indicated by the solid arrow.
While flowing through the gap between the fluid medium particles 4 and the fluidized medium particles 4 also gently move through the gap as the gas flows, the amount of heat absorbed by the feed water inside the in-layer heat transfer tube 1 increases and The heat transfer tube 1 does not wear. Therefore, the amount of heat absorbed from the fluidized bed is suppressed from being significantly reduced, and the heat transfer area is smaller than that in the case where no gap is provided.

〔The invention's effect〕

According to the present invention, it is possible to prevent wear of the in-layer heat transfer tube, and since the temperature of the fluidized bed does not decrease even when the boiler load decreases, there is an effect that there is no need to increase the heat transfer area, It has the effect of maintaining the effects of in-furnace desulfurization and denitration. In addition, it has the effect of improving load following performance, and since there is no need for slumping operation when the load changes, cell division, window box partitioning,
This has the effect of eliminating the need for a branch of the air duct, a control device for the amount of fuel and air for each cell, and the like.

[Brief description of drawings]

FIG. 1 is a view showing a cover structure of an in-layer heat transfer tube of the present invention, FIGS. 2 and 3 are detailed views thereof, and FIGS. 4 to 6 are views showing other embodiments of the present invention. FIG. 7 is a diagram showing the relationship between the wear amount of the intra-layer heat transfer tube and the arrangement height of the intra-layer heat transfer tube, and FIG. 8 is a diagram showing the process in which bubbles grow and burst while rising in the fluidized bed, and FIG. The figure shows the relationship between the temperature of the fluidized bed and the SO _x concentration and NO _x concentration in the exhaust gas, and Fig. 10 shows the various arrangements of the in-bed heat transfer tubes and the temperature of the fluidized bed when the boiler load changes. Fig. 11, Fig. 11 is a diagram showing the relationship between the coverage ratio of the heat transfer surface, the overall heat transfer coefficient and the required heat transfer area, and Fig. 12 is a view showing the relationship between the collision angle of particles and the wear amount of the collision surface. FIG. 13 is a diagram showing the amount of wear and the places of wear for the in-layer heat transfer tubes having different vertical positions in the fluidized bed. 1 ... Intra-layer heat transfer tube, 2 ... Cover 4 ... Fluid medium particles, 5 ... Air dispersion plate 6 ... Wind box, 7 ... Air duct, 8 ... Air damper, 9 ... Coal feeding tube ... … Coaling nozzle, 11 to 13… Fluidized bed surface 14… Bubbles, 15… Fluidized bed 16… Fluidized bed boiler

Claims (1)

[Claims] 1. When the load of the fluidized bed boiler is reduced, a part of the heat transfer tubes in the fluidized bed arranged in a plurality of stages is exposed on the surface of the fluidized bed. In a fluidized bed boiler in which some stages of the fluidized bed heat transfer tubes or all the stages of the fluidized bed heat transfer tubes are arranged in the vicinity of the surface of the fluidized bed, Of the heat pipes, the heat transfer pipe in the uppermost stage has the entire outer surface thereof, and the heat transfer pipes in the fluidized beds other than the uppermost stage have a flow of gas rising inside the fluidized bed. A cover structure for a heat transfer tube in a fluidized bed, wherein a cover is attached only to the outer surface located on the upstream side of the.