JPH064170Y2 - Desuperheater - Google Patents

Description

[Detailed Description of the Invention] [Field of Use of the Invention] The present invention relates to a desuperheater for effectively lowering the temperature of high temperature steam such as a steam generator by injecting water.

[Background of the invention]

In a boiler plant for driving a steam turbine to extract work by using high-temperature and high-pressure steam, such as a power generation boiler, it is desirable to generate high-temperature and high-pressure steam as much as possible in order to increase plant efficiency. The high-temperature and high-pressure steam is a so-called superheated steam state, which is a state in which the saturated steam state is further heated. In a normal boiler, saturated steam is taken out from a steam / water separator outlet called a so-called steam drum (drum), and further heated in a heat exchange section called a superheater to become high-temperature superheated steam. It is desirable for the temperature and pressure of this superheated steam to be as high as possible from the standpoint of plant efficiency, but if they are too high, the problems described below will occur and actual operation will be hindered. To maintain a constant temperature and pressure.

That is, when the temperature rises too much, the blades (blades) driven by contact with steam in the turbine are thermally expanded and come into contact with peripheral members to damage the blades or members, or to burn these members. is there. In addition, the heat transfer tube temperature of the boiler-side superheater rises and its compressive strength decreases, causing damage such as blast and the like, or ash components (vanadium) and sulfur oxides (SO ₃ ) contained in the combustion gas.
Etc. and cause corrosion damage. Therefore, it is desired that the temperature at the outlet of the superheater be controlled with extremely high accuracy and be as high as possible within the limits that do not cause these troubles.

In order to obtain high-temperature and high-pressure steam, it is natural to pay close attention to the heat transfer area and the materials to be used when designing the boiler plant, but this is the most common method of steam temperature control. There is a method in which the superheater inlet or outlet, or the superheater is divided into two or more stages, and a desuperheater is installed in the middle. That is, this is a method of injecting saturated water or unsaturated water into superheated steam, increasing the amount of water and steam passing with respect to the amount of heat applied in the superheater, and controlling the temperature rise at the outlet. It is desirable that the water thus injected receives heat from the superheated steam and evaporates, and is mixed with the superheated steam to form a uniform steam flow in the superheater tube. Therefore, a spray nozzle is used as a water injection part in the desuperheater. It is desirable that the water droplet size sprayed from this spray nozzle is small, but in order to deal with crack damage due to thermal stress of the nozzle part, shortening of life due to wear, etc.,
A pressure spray type complicated structure is not used, but a swirling spray type simple structure is used. The ratio of the improvement to the nozzle portion that contributes to the improvement of the desuperheater performance is the largest, but the present situation is that there is no best nozzle per se.

FIG. 1 shows an example of the structure of a normally used desuperheater. The water for reducing the temperature is sprayed into the superheated steam from the outlet of the nozzle 4 installed on the central axis of the steam pipe 1.
The speed of the water droplets sprayed here is about several tens m / S, and the average water droplet diameter is 100 to 200 μm. Also, because it is a swirling spray type, it does not become a solid spray pattern,
The spray pattern is an annular spray pattern in which almost no spray water drops go to the center of the pipe. Although there is no example in which the vapor velocity of the water droplet is measured, it is presumed that the water droplet collides with the pipe wall without completing evaporation for 10 m or more and causes so-called erosion. Therefore, most of the sprayed water droplets reach the pipe wall, and thermal stress is generated due to the temperature difference at the steam pipe wall. For the purpose of alleviating thermal stress, it is usual to install a pad 5 called a liner in the steam pipe. However, a water film is formed on the liner wall, and the surface area is further reduced compared to when it is present as water droplets, so the evaporation of water slows down and the water film covers the liner wall thickly.
In some cases, a strong thermal stress is generated in the liner mounting portion, which causes a crack. Therefore, as shown in FIG. 2, there is a liner in which a flow path in the middle of the liner is narrowed to form a venturi type, which promotes mixing of steam and water droplets and prevents backflow of a water film on the liner to a liner mounting portion. However, in this case as well, a water film is formed on the liner, and the evaporation rate remains the same,
A very long liner section is required for water film evaporation. In addition, high pressure steam cannot be obtained due to an increase in pressure loss in the throttle.

[Purpose of device]

An object of the present invention is to provide a compact desuperheater capable of efficiently evaporating spray water for temperature reduction.

[Outline of device]

In the desuperheater of the present invention, a protrusion is fixed to the inner peripheral surface of a metal plate installed in the steam pipe to form a triangular cross section, and one slope of one of the triangles facing the water to be sprayed. Is arranged, fine droplets are returned to the steam by applying the flow generated by the projections, and the mixing of the droplets and the steam is promoted, so that the spray water can be efficiently evaporated.

[Example of device]

An embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS. 3 and 4, a pad 5 forming a liner has a cylindrical shape, and a spray nozzle 4 is installed in the cylinder of the pad 5 at the center of the cylinder axis to spray a spray water droplet 7. It is like this. Protrusions 10 are installed in the pad 5 at right angles to the flow direction 2 of the steam. The projection 10 has a triangular cross section and has both slopes 20 and 30.

Next, the operation of one embodiment of the present invention will be described.

As shown in FIG. 5, the water droplets ejected from the spray nozzle 4 and reaching the pad (liner portion) 5 climb the slope 20 of the protrusion 10 along the flow 2 of the steam and are refined again at the apex. The atomized water droplets are sent to the center of the steam pipe. The water drop beyond the apex climbs up the slope 30 of the protrusion 10 again due to the backflow 11 caused by the presence of the protrusion 10.
It will be miniaturized. According to an experiment to be described later, the water droplets made into fine particles by this backflow have a maximum of 100 μm or less and an average particle size of about 50 μm or less, which is very small compared to the spray nozzle 4, so that evaporation is fast. The evaporation mechanism of water droplets has been studied for a long time in elucidation of the evaporation process prior to combustion of fuel droplets, elucidation of the evaporation rate of water droplets into the air in a temperature control device, etc. It is proportional to the square of the diameter. That is, it is known to be proportional to the droplet surface area. As mentioned above, the droplet size is 200 μm
Assuming that the water droplet of 50 μm becomes 2
One water droplet of 00 μm has 64 water droplets of 50 μm, and the surface area increases four times. The water droplet diameter of 200 μm is due to the spray from the nozzle and only secures the surface area for a short time until it collides with the liner wall. Since they flow in parallel, there is no shortening of life due to collision. Therefore, the evaporation is promoted at a speed four times faster than the ideal state using the spray nozzle as compared with the evaporation by the water film evaporation of the conventional method, and the length of the desuperheater can be shortened to 1/4. .

Regarding the shape of the protrusions 10, the following conclusions were obtained by the visualization experiment and the measurement of the droplet diameter with a transparent plastic tube using cold air instead of steam. That is, for the slopes 20 and 30 facing the flow of steam, the water film both climbs the slope, but from the tip of the projection 10 it becomes water droplets and scatters, forming an angle θ with the wall of the upstream slope 20 of the steam flow. ₁ and downstream slope 3
The diameter of the scattered water droplets changes depending on the angle θ ₂ formed with the wall of 0. A small particle size is preferable for vigorous evaporation in steam, but an angle θ ₁ of 30 ° to 80 ° is suitable, and about 60 ° is particularly preferable.
° is optimal. The angle θ ₂ is preferably 10 ° to 60 °, and optimally about 20 °. Further, if the height h to the top of the projection 10 is about 1/50 or more of the diameter of the steam pipe, the water droplets 12 become fine as shown in FIG.

In this way, the improvement of the evaporation rate can be expected by the improvement of the nozzle, but the mixing distance can be shortened by turning the projections 10 which can be miniaturized further onto the metal plate 5. The protrusion 10 can re-spray the reattached water droplets by forming not only one mountain but also two or more mountains. It is easier to finish the protrusion 10 into a spiral shape when the inner surface of the liner is cut and processed. Alternatively, a spiral wire may be welded to the inner surface of the liner to form the protrusion 10 as shown in FIG.

In the above embodiment, the protrusions 10 are formed as continuous peaks, but the peaks do not have to be continuous, and even wart-shaped projections are effective for re-scattering of the water film.

Further, in the above-described embodiment, the case where the protrusions 10 each having a triangular shape in cross section are attached has been described. However, even if the protrusions 10 are provided on the inner surface of the pad 5 by welding build-up, the shape is not Although not present, the above-mentioned water droplet miniaturization phenomenon was partially confirmed. In the description of the embodiments, the pad 5 has a straight shape, but the venturi type does not change the effect of miniaturization.

[Effect of device]

As described above, according to the present invention, it is possible to efficiently evaporate and reduce the temperature by refining the water for reducing the temperature by the protrusion. In addition, the length of the liner can be shortened, and erosion due to non-evaporated water droplets generated in the downstream portion of the desuperheater can be prevented. Moreover, since the liquid retention flow rate on the pad is reduced, the temperature difference at the pad attachment portion is reduced, which helps to alleviate the thermal stress, and the cracks of the constituent members can be prevented. Thus, the desuperheater can be downsized, the performance can be improved, and the installation location can be freely selected.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional desuperheater having a straight metal fitting, FIG. 2 is a sectional view of a conventional dehumidifier having a Venturi type metal fitting, and FIG. 3 is a sectional view of the dehumidifier of the present invention. Sectional view, 4th
FIG. 5 is a sectional view taken along the line AA in FIG. 3, FIG. 5 is a diagram showing the atomization phenomenon of water droplets, and FIG. 6 is a sectional view of a desuperheater of another embodiment. 1 ... Steam pipe, 4 ... Spray nozzle, 5 ... Pad (liner), 10 ... Protrusion.

Claims (4)

[Scope of utility model registration request] 1. A desuperheater for reducing a steam temperature, comprising a pad in a steam pipe and a spray nozzle for injecting water into steam inside the gold, and a projection on the inner surface of the pad. , The cross section of the projection is formed in a triangular shape, and one slope of the triangle is arranged so as to face the water to be sprayed. 2. The protrusion triangle has an angle between 30 ° and 80 ° between one side facing the steam flow and the steam flow,
The desuperheater according to claim 1, wherein the apex angle is formed by two sides having an angle between the other side and the flow of steam of between 10 ° and 60 °. . 3. The desuperheater according to claim 1, wherein the protrusions are a plurality of peaks. 4. The desuperheater according to claim 1, wherein the pad has a straight shape or a Venturi shape.