JPH0361081B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for adjusting the temperature of a fluidized bed boiler.

(Prior art) In general, in a fluidized bed boiler, the temperature inside the fluidized bed varies depending on the type of fuel, the particle size distribution of the fluidized medium forming the fluidized bed, the type of fluidized medium such as sand, limestone, alumina particles, etc., and the operating conditions. The heat transfer characteristics of the heat transfer tubes buried in the pipe change, and the temperature of the fluidized bed changes.

On the other hand, it is necessary to maintain the temperature of the fluidized bed within a certain range in terms of the following points.

In other words, if the temperature of the fluidized bed is too high, the amount of unburned matter, carbon monoxide, and hydrocarbons generated decreases, improving combustion efficiency and improving boiler efficiency, but on the other hand, desulfurization efficiency decreases. and nitrogen oxides increase rapidly.

Conversely, if the temperature of the fluidized bed is too low, combustibility deteriorates, the desulfurization rate further decreases, and the amount of sulfur dioxide discharged increases.

As described above, the temperature of the fluidized bed must be kept within a certain range due to requirements from both combustibility and pollution levels.

Further, the temperature of the fluidized bed is determined by the organic relationship between the amount of heat absorbed by the heat transfer medium flowing through the heat transfer tubes embedded in the fluidized bed and the amount of fuel introduced into the fluidized bed.

Setting the temperature of the fluidized bed is largely influenced by the amount of heat absorbed by the heating medium, but regarding the issue of the amount of heat absorbed by the heating medium, the particle size distribution and type of the fluidized medium, the flow state of the fluidized medium, and the fuel such as the type of
There are still many unresolved uncertainties in heat transfer engineering, and at this stage we have not yet been able to determine the heat absorption amount of a heat medium based on theoretical developments. .

Therefore, to adjust the heat absorption amount of the heat medium, it is necessary to bury heat transfer tubes in the fluidized bed in advance so that they have a large heat transfer surface, and then cut the heat transfer tubes while operating the fluidized bed boiler. Therefore, a method of adjusting the heat absorption amount of the heat medium is being used.

(Problems to be Solved by the Invention) However, when the heat exchanger tube is cut, the following problems occur. For example, if 10 heat transfer tubes are buried in a fluidized bed and 5 of them are cut, the flow rate of the heat medium will double on the downstream side of the cut heat transfer tubes, and the flow resistance (pressure loss ) also doubles, and the film coefficient inside the pipe also increases in proportion to the n-th power of the flow velocity.

In this way, changes in flow velocity, pressure drop, and film coefficient can cause insufficient pump capacity due to an increase in pressure drop, or affect the pressure and temperature of generated steam, causing the entire fluidized bed boiler to become unbalanced. It turns out.

In addition, if 2 or 3 out of 10 heat transfer tubes are cut, or if they are partially cut, the flow velocity, pressure loss, and film coefficient within the tubes of each row of heat transfer tubes buried in the fluidized bed will not be uniform. , Add to this the uncertainties of heat transfer engineering, and the reality is that it is virtually impossible to control the temperature of the fluidized bed.

Furthermore, due to this fact, there is a technical problem in that the temperature of the fluidized bed varies and the combustion efficiency and pollution are not satisfied.

Furthermore, on the other hand, as shown in FIG. 1, there are the following problems in terms of the form of heat transfer within the fluidized bed. In the figure, inside a fluidized bed 1, a large number of heat exchanger tubes 2 are horizontally arranged in a staggered arrangement. In the figure, 2a indicated by a broken line indicates the removed heat exchanger tube.

Air for fluidization and combustion is supplied into the fluidized bed through the air distribution plate 3. This air rises within the layer while forming bubbles 4, and in the process collides with the heat exchanger tubes and is broken, forming small bubbles that activate contact with the twist material and promote combustion.

However, since the bubbles generated in the portion where the heat exchanger tube is removed do not collide with the heat exchanger tube, they grow into large bubbles 4a and rapidly rise within the layer. As a result, the combustibility in this area deteriorates, the layer temperature in that area decreases, and it is not possible to make the layer temperature uniform, which not only makes it impossible to satisfy both flammability and pollution problems, but also However, there is a technical problem in that the heat exchanger tubes are worn out by the fluid medium that is entrained by the rapid rise of bubbles.

As an improvement measure for this, a dummy tube was installed in the section where the heat exchanger tube was cut out to prevent the growth of bubbles, but the flow rate, pressure loss, and film coefficient of the heat medium flowing inside the heat exchanger tube are limited as described above. The problem was not solved, and the overall fluidized bed boiler remained unbalanced, and it was virtually impossible to adjust the temperature of the fluidized bed, resulting in unsatisfactory combustion efficiency and pollution.

The present invention solves the above conventional technical problems,
An object of the present invention is to provide a method for adjusting the temperature of a fluidized bed boiler, which makes it possible to freely and rationally adjust the temperature of the fluidized bed using an extremely simple method, and which can solve the problems of combustion efficiency and pollution at the same time. It is.

(Means for Solving the Problems) The present invention suppresses the contact between the fluid medium and the heat transfer tubes without cutting out the heat transfer tubes, maintains the normal flow of the heat medium in the heat transfer tubes, and reduces the amount of heat absorbed. Therefore, in the method of the present invention, in order to suppress the heat absorption amount of a large number of heat exchanger tubes arranged in a fluidized bed, the surface of the heat exchanger tubes is partially covered. The temperature of the fluidized bed is adjusted by attaching or removing the coating material to the surface of the heat exchanger tube.

Moreover, it is desirable to cover the circumferential surface of the heat exchanger tube using a coating material configured to be detachably attached to the heat exchanger tube.

Alternatively, a predetermined portion of the circumferential surface of the heat exchanger tube may be coated using a coating material configured to be detachably attached to the heat exchanger tube.

(Function) In order to adjust the temperature of the fluidized bed boiler by the method of the present invention, coating materials are attached to the surfaces of appropriate portions of the heat exchanger tubes, and the fluidized bed boiler is trial run in this state. The fluid medium in the fluidized bed is
Through contact with the surface of the heat transfer tube, the retained heat is transferred to the heat medium within the heat transfer tube through the tube wall. At this time, heat transfer is suppressed at the portions of the tube wall where the coating material is attached, so that the temperature of the fluidized bed can be adjusted.

Depending on the results of the trial run, the temperature of the fluidized bed is adjusted by increasing or decreasing the number of locations where the covering material is attached. In this case, it is often easier to install the covering material at a slightly smaller number of locations in terms of work procedure.

When attaching a coating material to the circumferential surface of a heat exchanger tube, for example, a cylindrical coating material with one vertical slit is attached, and the width of the slit is the same as that of the heat exchanger tube. It is spread out on both sides until it reaches a dimension exceeding the outside diameter, passed through the heat exchanger tube, and then wrapped around the circumferential surface of the heat exchanger tube again.

In addition, when coating a predetermined portion of the circumferential surface of a heat exchanger tube, for example, the heat exchanger tube is sandwiched from both sides between a pair of steel plates, and the pair of steel plates are bound together with multiple sets of threaded bolts. This provides partial coverage.

(Example) An example will be described with reference to the drawings. The covering material 6 shown in FIG. It is cut into a cylindrical shape with the same dimensions. In addition, a slit 6' is provided in this covering material 6,
This makes it easy to put on and take off.

Further, the covering material shown in FIG. 3 is made of a pair of steel plates 8 processed to a certain size, which are covered with bolts 9 so as to sandwich the heat exchanger tubes 5 therebetween.

Generally, heat transfer tubes in a fluidized bed are composed of evaporator tubes, superheater tubes, reheater tubes, etc., and the heat transfer coefficients are different because the temperature and velocity of the heat medium (fluid in the tube) in each tube are different. There is. Therefore, even if the coating materials have the same contact area, the effect on the layer temperature will differ depending on the type of heat exchanger tube.

When installing a coating material on a heat transfer tube to adjust the layer temperature, the above characteristics should be taken into account when setting the arrangement, and the installation of the coating material will prevent wear of the heat transfer tube due to friction with the fluid medium. Taking into account the secondary effect of preventing wear, for example, prioritize areas where wear is expected, such as bends.
Next, select a section of the evaporator tube that is subject to relatively high wear, and finally perform the process on the superheater tube or reheater tube, where the tube wall temperature is high, as appropriate. FIG. 4 shows that the bend portion 13 of the heat exchanger tube 5 where the wear is most severe is coated, and the heat exchanger tube 5 located in the upper layer of the fluidized bed where there is a high possibility of bubble growth is coated according to the procedure. do.
The removal order when removing the covering material for temperature adjustment may be performed in the reverse order to the above.

The operation of this embodiment constructed as described above will now be described. In the example shown in FIG. 4, one heat exchanger tube 5 is bent three times to form a meandering tube, and such meandering tubes are arranged in three rows. In the three rows of meandering heat transfer tubes 5, an amount of heat medium corresponding to the amount of evaporation of the fluidized bed boiler is uniformly distributed and flowing.

The heat retained in the fluid medium is transferred to the heat transfer tube 5 through contact between the heat transfer tube 5 and the fluid medium, and the heat transferred to the heat transfer tube 5 is transferred to the heat medium flowing inside the heat transfer tube 5. .

In this heat transfer process, the heat transfer between the fluid medium and the heat transfer tube 5 is not constant depending on the type of fluid medium or the flow state, and there are many uncertain factors, and the actual situation is clear. Not.

On the other hand, heat transfer between the heat transfer tubes 5 and the heat medium is determined by the flow rate of the heat medium. Therefore, by keeping the flow rate of the heat medium constant and adjusting the amount of heat transfer between the heat transfer tubes 5 and the fluidized medium, the amount of heat absorbed by the heat medium is adjusted.

In the method of the present invention, the amount of heat transfer between the heat transfer tubes 5 and the fluid medium is adjusted by attaching a covering material 6 to the surface of the heat transfer tubes 5 to suppress direct contact between the heat transfer tubes 5 and the fluid medium. This is done by

That is, a constant flow rate of a heat medium is passed through the heat transfer tube 5, and a covering material 6 formed to a constant size is coated.
The area covered by the coating material is increased or decreased by attaching and removing the coating material 6 so that the temperature within the fluidized bed 15 stays within a certain range. In this way, the amount of heat absorbed by the heating medium to keep the temperature of the fluidized bed 15 within a certain range can be determined.
It is very simple and easy to do.

(Effects of the Invention) As detailed above, according to the temperature adjustment method for a fluidized bed boiler of the present invention, (1) on the surface of the heat exchanger tube arranged in the fluidized bed,
By partially coating the surface of the tube by a very simple method of attaching and removing the coating material, the flow rate of the heat medium flowing inside the heat exchanger tube remains constant, and the connection between the heat exchanger tube and the fluidizing medium is maintained. Since it is possible to adjust only the amount of heat transfer between (3) Fluidized bed (4) The composition of the cladding material can now be adjusted reliably and easily, solving both the flammability problem and the pollution problem at the same time, and maintaining the specified performance of the fluidized bed boiler. , the heat exchanger tube has a removable structure that allows the coating to cover the entire circumferential surface of the heat transfer tube, or a removable structure that allows the coating to be applied to a predetermined portion of the circumferential surface of the heat transfer tube. When making adjustments, it has excellent effects such as being able to easily attach and remove the covering material, and temperature adjustments can be made in small steps.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the form of heat transfer in the fluidized bed.
Figures 2, 3, and 4 all show examples of the present invention; Figure 2 is a perspective view of a cylindrical covering material; Figure 3 is a perspective view of a covering material made of two steel plates; Fourth
The figure is a perspective view showing a state in which a heat exchanger tube is coated with a coating material. DESCRIPTION OF SYMBOLS 1... Fluidized bed, 5... Heat exchanger tube, 6... Coating material, 8... Steel plate as coating material.

Claims (1)

[Claims] 1. In order to suppress the heat absorption amount of a large number of heat exchanger tubes arranged in a fluidized bed, a coating material is provided to partially cover the surface of the heat exchanger tubes, and the coating material is applied to the surface of the heat exchanger tubes. A method for adjusting the temperature of a fluidized bed boiler, the method comprising adjusting the temperature of the fluidized bed by attaching or removing the fluidized bed. 2. A method for adjusting the temperature of a fluidized bed boiler according to claim 1, wherein the heat exchanger tubes are coated on their circumferential surfaces using a coating material configured to be detachably attached to the heat exchanger tubes. 3. A method for adjusting the temperature of a fluidized bed boiler according to claim 1, wherein a predetermined portion of the circumferential surface of the heat exchanger tube is coated using a coating material configured to be detachably attached to the heat exchanger tube.