JPH076603B2 - Water heater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a feed water heater for thermal power plants and nuclear plants, in which pressure loss inside the fuselage is reduced, and the bottom drain water level is stabilized, thereby significantly improving heat exchange performance. It relates to an improved feed water heater.

[Conventional technology]

In a conventional feed water heater for a thermal power plant or a nuclear power plant, pipe support plates are alternately arranged vertically as described in Japanese Patent Application No. 58-35395, and the structure is such that steam meanders and flows in the body. This structure had a problem that the pressure loss on the steam side was large and the heat exchange performance was significantly reduced.

An example of a conventional feed water heater will be described with reference to FIG. In the figure, the water supply enters the water chamber 1 from the water supply inlet nozzle 2, passes through the U-shaped heating pipe 5, and is discharged from the water outlet nozzle 3. A plurality of U-shaped heating tubes 5 are provided to form a tube group, and penetrate the tube plate 4 to form the water chamber 1.
The tube support plates 6, 6'and the tie rod 7
Is supported by the body 9. Tube support plate 6,
Every other 6'is installed up and down and has the role of supporting the tube group and guiding the steam flow path in a meandering flow. Therefore, the heated steam extracted from the turbine enters the vessel through the steam inlet nozzle 10 and is divided into two parts in the longitudinal direction of the body and flows to the respective end vent discharge ports 8 and 8 '.
These heated steams come into contact with the surface of each tube 5 of the tube group, exchange heat with the feed water flowing in the tubes, condense, and drain.
It is collected at the bottom of the inside of the container and discharged from the drain outlet 14.

In the above-described conventional feed water heater, a large amount of steam, which is about half the amount of steam flowing in, flows toward the tube nests in the front and rear of the fuselage, resulting in a large pressure loss on the steam side and a decrease in the internal pressure of the fuselage and lower drain of the fuselage Generate a water level gradient 15.

In the temperature diagram shown in FIG. 9, the decrease in the internal pressure is due to the saturation temperature TS to the saturation temperature T with respect to the original extraction pressure.
The heat transfer capacity of the feed water heater, which reduces the temperature difference with the feed water, is proportional to the logarithmic average value of this temperature difference, and therefore the drop in the internal pressure of the feed water heater leads to the deterioration of the feed water heater performance. Therefore, it is effective to improve the performance by reducing the pressure loss as much as possible. Further, the generation of the water level gradient in the lower drain of the body causes the heating pipe to be submerged at a high water level portion, which reduces the heating area, which causes a decrease in the internal pressure and a performance deterioration factor of the feed water heater.

In order to eliminate these factors that reduce performance, the steam flow is not made a meandering flow, but a parallel flow that equally divides into each tube nest section has been devised, but even in parallel flow, heated steam flows into the body. It was found that the inertial force collides with the bottom of the fuselage immediately below the steam inlet, causing an increase in pressure loss and a water level gradient.

The increase in pressure loss due to the inertial force at the inflow of steam and the generation of the water level gradient will be described with reference to FIGS. 5 and 6.

FIG. 5 shows the steam nozzle 10 as described above with reference to FIG.
Pipe support plate 6, so that the heating steam introduced from
The feed water heater in which 6'is alternately arranged vertically is shown. Reference numeral 11 denotes an impact prevention plate provided so that the heated steam does not directly collide with the heat transfer tube 5.

FIG. 6 schematically illustrates the feed water heater devised in the parallel flow type.

[Problems to be solved by the invention]

As shown in FIG. 6, the heated steam flows into the body from the steam inlet nozzle 10 and has a high flow velocity of 50 to 60 m / s. Since the amount of steam consumed by each tube section section 16 is fixed,
It was thought that after the steam entered the body, it was quickly distributed in the longitudinal direction of the body and absorbed in each tube nest.
Due to the inertial force due to the high speed of 60 m / s, it was found that almost all of the steam 17 once flows into the tube nest section 16 directly below the steam inflow location, collides with the lower fuselage, and is redistributed to each tube nest section. did. Furthermore, due to this phenomenon, the pressure loss inside the fuselage increases, and the drain water level immediately below the steam inlet locally drops, raising the water level at other points and submerging part of the heating pipe. found.

The present invention has been made based on the above-mentioned research results, and prevents adverse effects due to inertia of the introduced high-speed steam flow, locally lowers the drain immediately below the steam inlet and raises the drain water level at other places. It is an object of the present invention to provide a feed water heater that is not feared, has less pressure loss in the body, and can be downsized in its overall shape.

[Means for solving problems]

The parallel flow type shown in FIG. 6 has less pressure loss in the fuselage than the meandering flow type shown in FIG. 5, but has a remarkable problem of pushing down the drain water surface just below the inlet of the heated steam. The present invention is based on the assumption that the above-mentioned drain water surface pushing-down phenomenon is caused by the inflow of heating steam into the "room in which the tube nest is closed", and the steam channel cross-sectional area on the side of the tube nest is changed. As a result of experiments, it was discovered that the pressure loss was remarkably improved when the flow path cross section exceeded a certain value (ratio to the cross sectional area of the cylinder). This law will be described in detail below with reference to FIGS. 7 and 8.

The crosshatched hatching portion 30 (cross sectional area of the body excluding the tube group 31 and the drain 32) in FIG. 7 is called a parameter A ₃ . Fig. 8 The steam passage hatching portion 33 (inner body cross-sectional area excluding the pipe support plate 6 and the drain 32) is referred to as parameter A ₄ . A ₄ and the ratio alpha = A ₄ / A ₃ and A _3, it has been found related to the increase or decrease of the experimental results the pressure loss.

Figure 10 shows an example of the experimental results. It can be seen that the pressure rises immediately below the steam inflow point (indicated by the arrow) and a pressure gradient occurs at other points. The smaller the above parameter (α = A ₄ / A ₃ ) is, the larger the pressure fluctuation amount becomes.
It can be seen that the larger the α value is, the smaller it becomes, and the pressure loss is alleviated as the α value increases, that is, the steam side passage area A ₄ increases. Therefore, by arranging the relationship between the α value and the pressure loss as shown in Fig. 11 in order to find the economically appropriate value of the α value, it is possible to largely eliminate the pressure loss when the α value is set to about 0.24 or more. found. It can be seen that α = 0.24 should be taken into consideration when designing in order to determine the optimum body diameter that can sufficiently reduce the pressure loss for the existing feed water heater tube nest.

In addition, since the ratio of the shell length and the shell diameter of the feed water heater in the conventional thermal power and nuclear power plants is generally about 5 to 8 times, and the side steam flow passage ratio is about 0.1 to 0.17, α The condition of = 0.24 is applicable.

Further, in consideration of economical efficiency, the feed water heater is provided with as many heating pipes as possible in the body, so that the outer periphery of the tube nest is generally formed into a cylindrical surface along the inner diameter of the body. For this reason, the steam passage area at the outer peripheral portion of the tube nest is reduced, and in addition to this, the steam passage area is further reduced by the pipe support plate, so that the side steam passage ratio is generally 0.10 to 0.17 (10 % To 17%).

If the feed water heater under these conditions is used, the side steam flow path ratio α = 0.24 (24
%) Or more, it is possible to obtain a high-performance feed water heater having a very small fuselage pressure loss, which is the effect aimed at by the present invention.

[Action]

As described above, if the side steam flow channel ratio is set to be larger than the conventional one, the flow rate of the side steam flow 34 in FIG. 6 becomes large.
If this flow rate is set appropriately, when the steam flowing from the steam inlet flows into the tube nest section directly below the steam inlet, the steam is moved and distributed to the side flow passage having a sufficient area before increasing the dynamic pressure. As a result, the increase in pressure loss and the increase in water level gradient are eliminated, and the parallel flow structure, which is a significant improvement in performance efficiency, can be adopted.

FIG. 1 is a horizontal sectional view of one embodiment of the present invention, and FIG. 2 is a vertical sectional view of the same.

As shown in FIG. 1, a tube group 31 is installed in the body 9 of the feed water heater, and the heating tube is prevented from being damaged by steam flowing from the steam inlet nozzle 10 at the upper part of the tube group 31. Therefore, the impact prevention plate 11 is installed.

A vent plate mother tube 20 is provided in the center of the tube nest, and functions as a collective discharge of the non-condensable gas as a terminal end portion of the steam flowing into the tube nest. A vent guide baffle 21 is attached to the vent extraction pipe, and serves to reliably guide the vapor and the non-condensed gas to the vent extraction pipe. With this vent extraction structure, vents are completely discharged without remaining in the tube nest, contributing to performance improvement. A notch 22 is provided on the outer periphery of the tube support plate 6 to quickly distribute the steam flowing into the tube nest section to each tube nest section in the longitudinal direction to prevent an increase in pressure loss. In addition, the side steam flow path ratio is 24% or more (about 30% in this example) including the above-mentioned pipe support plate outer peripheral cutout 22, and by providing the cutout 22, the pipe support plate is cut from the inside of the body 9. 6 and drain 32,
Cross-sectional area excluding the notch 22, that is, the body 9 shown in FIG.
The area of the inner upper part can be reduced, which allows the body 9 to be downsized.

Here, the basic shape of the pipe support plate is a circle in contact with the inner peripheral surface of the body, but in the pipe support plate of the parallel flow type feed water heater, the above-mentioned basic circular upper end forms the steam flow path. In order to form a drain passage, it is cut into an arc shape (circular segment), and the lower end is cut into an arc shape (see FIG. 8).

In the present invention, the notch of the pipe support plate means the pipe support plate and the inner surface of the body except for the steam flow passage provided at the upper part of the pipe support plate and the drain flow passage provided at the lower part of the pipe support plate. Is a space intentionally provided between the two notches, and both ends of the notch are brought into contact with the inner peripheral surface of the body. The reason is that, when the body is assembled by welding during manufacturing, the tube support plate is supported so as not to move relative to the body.

That is, the notch in the present invention, in the parallel flow type feed water heater, quickly distributes (smoothly diffuses) the heating steam introduced from the heating steam inlet into the body in the longitudinal direction inside the body and is introduced. It is formed in order to suppress the local drop in the water level of the drain, which is affected by the heated steam. In order to achieve the action of this cutout, in the present invention, the drainage is calculated from the inner cavity area excluding the area where a plurality of U-shaped heat transfer tubes having a cross section perpendicular to the longitudinal direction of the body is arranged. The cross-sectional area obtained by subtracting the area occupied by A ₃ is A ₃ , the cross-sectional area A _{4 obtained} by subtracting the area occupied by the pipe support plate and the drain from the internal cavity area, and the ratio α of A ₃ and A ₄ = A ₄ / A
₃ was found to be 0.240 to 0.357.

The above operation will be described in detail with reference to FIG. 2. A plurality of pipe support plates 6 are arranged at equal height to form a parallel flow type feed water heater. A vapor flow section 23 is formed above each tube section section 16. A portion of the vapor stream enters each tube nest section as a distribution stream 24, but each tube nest section is also supplied with a portion of the vapor stream as a tube nest side stream 25. As a result, it is possible to suppress the local drop in the water level of the drain, and it is possible to operate with less pressure loss.

Incidentally, as described above, the impact prevention plate 11 is for preventing the heating pipe from being damaged by the steam flowing from the steam inlet nozzle 10, and is essential for achieving the action by the notch. Not a configuration.

FIG. 3 shows an embodiment different from the above. In the feed water heater of this example, the tube nest shape is arranged in a quadrangle in order to secure a sufficient side steam flow path. With this configuration, it is easy to take a large side passage area.

A trial calculation example in which the performance is improved by a design example in which the steam side channel ratio α is 0.24 or more will be described below.

FIG. 9 shows a temperature diagram of a conventional feed water heater. The feed water flows in at temperature T ₁ and flows out of the device at temperature T ₂ . Feedwater flow is G _W, steam side is the saturation temperature for the fuselage saturation pressure
A constant temperature is maintained at TS. In the feed water heater under such conditions, the required heating area S _CZ (m ² ) is represented by the following formula.

Where h ₂ is the enthalpy (Kca) corresponding to the outlet water temperature t _2.
l / kg) h ₁ : Enthalpy equivalent to inlet feed water temperature t ₁ (Kcal / kg) K _CZ : Thermal conductivity (Kcal / m ² h ℃) θ _m ： Logarithmic mean temperature difference (℃) Required heating area is represented as S _CZ the logarithmic mean temperature difference theta _m
Inversely proportional to. Furthermore, θ _m is the saturation temperature T
Since s' (saturation temperature of pressure obtained by subtracting pressure loss from the extraction pressure from the turbine) increases, the required heating area can be reduced by reducing the internal pressure loss.

The following shows an example of performance comparison between the conventional type and the new type with an α value of 0.24 or more for an example of a feedwater heater for a nuclear power plant.

As described above, the heating area (heat transfer tube area) was reduced by 12% by setting α = 0.3.

〔The invention's effect〕

As described above in detail, when the present invention is applied, the pressure loss of the heating steam in the feed water heater can be reduced, the heat exchange performance can be improved, and the drain water level immediately below the heating steam inflow portion can be reduced. It is possible to prevent the occurrence of problems with it and to transfer the area of the body cavity inside the tube support to the area formed by the notch, which reduces the body diameter and reduces the feed water heater. Can be miniaturized.

[Brief description of drawings]

1 and 2 show one embodiment of the present invention. FIG. 1 is a transverse sectional view and FIG. 2 is a longitudinal sectional view. FIG. 3 is a cross-sectional view of an embodiment different from the above. FIG. 4 is a transverse sectional view of a conventional feed water heater. FIG. 5 is an illustration of a meandering flow type feed water heater, and FIG. 6 is an illustration of a parallel flow type feed water heater.
7 and 8 are explanatory views of the side flow path ratio. FIG. 9 is a temperature diagram for explaining the action and effect of the above embodiment. FIG. 10 and FIG. 11 are charts for explaining the influence of the side channel ratio. 5 ... U-shaped heating tube, 6 ... tube support plate, 7 ... ty rod, 8 ... end vent outlet, 10 ... steam inlet tube base, 15
…… Water level gradient, 16 …… Sections for each tube nest, 17 …… Steam,
18 ...... Lower steam flow path, 19 ...... closed room, 20 ...... vent vent pipe, vent induction bag, 22 ...... tube support plate notch, 23 ...... steam flow section, 24 ...... distributive flow , 25 …… Tube nest side flow, 31 …… Tube group, 34 …… Side steam flow section.

Claims (1)

[Claims] 1. A body having an inlet for introducing heated steam and a drain outlet, a plurality of U-shaped heat transfer tubes provided in the body in a longitudinal direction thereof, and supporting the U-shaped heat transfer tube. In a parallel flow type feed water heater having a pipe support plate, a cutout is formed in at least a part between the periphery of the pipe support plate and an inner surface of the body, and steam from the inlet is formed into the cutout. (A) The cross-sectional area obtained by subtracting the portion occupied by the drain from the lumen area excluding the area in which the plurality of U-shaped heat transfer tubes are arranged is perpendicular to the longitudinal direction of the body. and a _3, that the cross-sectional area obtained by subtracting the portion occupied by the tube support plate and the drain and a _4, sets the a ₄ / a ratio of a ₃ alpha to 0.240 to 0.357 from the lumen area (b) Characteristic water heater.