JPH0743065B2 - Flow distribution device for paper machine head box - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a flow distribution device of a head box of a paper machine.

(Prior Art) FIG. 3 is a plan view of a conventional head box, and FIG.
It is sectional drawing which shows the AA cross section of a figure. The distribution pipe 1 having a rectangular cross section has a stock material inlet 2 and a passage outlet 3, and the cross-sectional area thereof is gradually reduced from the inlet 2 to the outlet 3, and the branch pipes 4 arranged at equal intervals in the length direction are The length becomes shorter toward the downstream side of the distribution pipe 1.

According to the flow loss of the distribution pipe 1 that increases toward the downstream side of the distribution pipe 1, the length of the downstream side branch pipe 4 is made shorter by ΔZ than the adjacent upstream side branch pipe 4 to reduce the flow loss in the branch pipe. By offsetting the increase in the flow loss in the distribution pipe and the decrease in the flow loss in the branch pipe, each branch pipe 4,4 ...
It is devised so that the flow rates flowing to ... become equal.

In the case of the illustrated example, the length of the branch pipe is adjusted as described above as a countermeasure against the pressure in the distribution pipe 1 linearly decreasing toward the narrow end outlet 3. As described above, it is generally understood that the pressure distribution in the width direction of the distribution pipe (header) has a great influence on the flow distribution in the past, which corresponds to the increase in pipe friction loss that increases toward the header outflow side. hand,
The idea was to adjust the recirculation flow rate to correct it. Then, in order to correct the pipe friction loss, a method of sequentially shortening the branch pipes and a taper angle of the header have been made multistage.

By the way, according to a study by the present inventors, (1) since the pipe friction loss in the width direction of the header is as small as several tens of mmH ₂ O, the pressure distribution in the width direction of the header is a straight header. Even if there is, if the recirculation amount is adjusted, the pressure (static pressure) distribution becomes uniform.

(2) However, even if the pressure distribution in the width direction of the header is made uniform, it does not lead to uniform flow distribution in the width direction.

I knew that. This is shown in FIGS. 5 and 6.

In FIG. 5, the horizontal axis represents the longitudinal (width) direction of the header, the vertical axis represents the pressure difference in the longitudinal direction, and the vertical axis represents the pressure difference in the longitudinal direction. According to Bernoulli's theorem, when the amount of recirculation is reduced, the dynamic pressure component of the fluid is converted into static pressure, and pressure recovery occurs in the flow direction. When the recirculation ratio / (recirculation flow rate / inflow pipe flow rate) is 0%, a pressure recovery larger than the pipe friction loss of the header occurs, and the pressure increases as it flows to the recirculation side. If the recirculation ratio is 5 to 8%, a rectangular straight header with a design recirculation ratio of 9% (
%, The distribution flow velocity was uniform in the width direction), and a substantially uniform static pressure distribution was obtained.

FIG. 6 shows a header in the case of a recirculation ratio of 8% in a flow distribution device in which the side surface of the rectangular straight header obtained in the result of FIG. It is the test data of the flow velocity (flow rate) distribution in the width direction.
As a result, test data showing a unique flow rate distribution which cannot be predicted from the pressure distribution shown in FIG. 5 was obtained.

The horizontal axis of FIG. 6 indicates the longitudinal (width) direction of the header, and the vertical axis indicates the ratio of the flow velocity Vi measured at each portion in the same direction to the average flow velocity Vmean in the longitudinal direction.

Here, in order to eliminate the influence of the velocity distribution due to the jet ejected from the holes of the perforated plate and to measure the flow rate in the width direction,
V _i was measured at the outlet of a mixing chamber provided downstream of the perforated plate. As can be understood from FIG. 6, the flow velocity decreasing portions are recognized on the inflow side and the outflow side of the header, respectively, and moreover, the degree of flow velocity decrease is larger on the inflow side and smaller on the outflow side.

FIG. 7 shows the flow velocity (flow rate) distribution in the width direction of the header when the recirculation amount is changed with the same value as in FIG. In FIG. 5, when the recirculation amount is set to 0%, the pressure in the width direction of the header shifts to the upper right as a whole, and correspondingly, in FIG. 7, the flow distribution pattern also shifts to the upper right as a whole. The flow rate distribution corresponding to the pressure distribution in the width direction of the header can be obtained with other recirculation amounts, and all of them have a pattern on the upper right.

However, it has been found that the peculiar decrease in the flow rate on the inflow side and the outflow side in the width direction does not change even if the recirculation amount is changed as shown in FIG.

(Problems to be Solved by the Invention) From the above, in the conventional distribution device of this type, (1) even if the pressure in the distribution pipe is uniform toward the narrow end outlet, its flow rate distribution is peculiar. Deviations in different patterns remain.

(2) Even if the recirculation amount is changed, it is not possible to correct the tendency of the flow rate decrease on the inflow side and the outflow side.

The point turned out to be a problem.

Further, the inventors' studies have shown that if there is a decrease in the flow rate on the inflow side and the outflow side, it causes a lateral flow in the width direction and an unstable flow in the slice chamber from the outlet of the perforated plate to the ejection port. It was

That is, since the flow is generally throttled at the jet outlet, the widthwise flow rate unevenness at the perforated plate outlet is made uniform in the width direction in the slice chamber, and a more uniform flow rate distribution is obtained at the jet outlet.
Although this is preferable in itself, in this case, in order to make it uniform in the width direction, a fluid flow (transverse flow) in the width direction is required.

By the way, in the head box, it is necessary to eject from the ejection port in a uniform flow direction, but the lateral flow causes deterioration of the flow direction of the ejection jet. In addition, the turbulence of the flow due to the lateral flow also hinders the production of a stable weight of paper.

The present invention has been made to solve these problems, and provides a flow distribution device for a paper machine headbox that can obtain a uniform flow distribution in the width direction of the header without deteriorating the flow direction of the jet. Is what you are trying to do.

(Means for Solving the Problems) For this reason, the present invention includes a header pipe that is tapered in the longitudinal direction and has a large number of fluid branch holes formed in the side wall along the longitudinal direction. In a paper machine head box in which the direction of the flow of the raw material liquid flowing through the hole is changed substantially at right angles in the hole portion, the fluid branch hole is opened on at least one of the raw material liquid inflow side and the recirculation side of the header pipe. A flow distribution device for a paper machine head box is characterized in that the porosity is set to be larger than the porosity in the central portion, and this is a means for solving the above problems.

(Operation) Increasing the porosity of the region of the header pipe on the inflow side and / or the recirculation side where the flow rate is small increases the passage area of the fluid.
That is, since the flow rate can be increased by increasing the porosity, the flow rate in the low flow rate region can be made equal to that in the other regions. Therefore, the deviation of the flow rate distribution in the width direction can be reduced in the state where the flow direction is uniform, and ideal flow rate distribution can be achieved.

(Example) Hereinafter, the Example of this invention is described in full detail based on drawing.

FIG. 1 shows a plan view of a head box which is a typical embodiment of the present invention.

In this embodiment, the inlet pipe is provided upstream of the tapered header 10.
11, and a recirculation pipe 12 is connected downstream. The design flow velocity of the inflow pipe 11, the header 10, and the recirculation pipe 12 is set to 2 to 4 m / s. The design recirculation flow rate is preferably about 7 to 12% with respect to the inflow flow rate of the inflow pipe 11. For example, when the recirculation amount is 9%, the taper angle α is determined so that the flow velocity in the header 10 becomes constant in the flow direction. At this time, α is preferably 3 ° to 15 °. The angle β at which the center line of the inflow pipe 11 and the longitudinal direction of the porous plate 13 intersect is generally 0 ° to 15 °, and preferably 3 ° to 15 °.

2 shows the ZZ cross section of FIG. 1, in which the perforated plate 13 is, as an example, the region A of the inlet side 30% with respect to the pond width L in the longitudinal (width) direction of the header 11, the center. It is divided into a 50% area B nearer to it and an area C on the outflow side 20%. The diameter of the drill hole in the region B of the porous plate 13 is d, and the pitch in the width direction is p. At this time, the dimensionless pitch p / d is set to 1.1 to 5.0.

For example, assume that there is a 10% decrease in flow rate in regions A and C. In the area A of the perforated plate, the drill hole diameter d is the same, and the pitch is changed from 1.00p to 0.9p. That is, the pitch is set to 0 in a region where there is a large degree of insufficient flow rate.
Approximately 9p and 0.99p to 1.00p in the case of a slight flow shortage
To That is, the aperture ratio is increased in correlation with the insufficient flow rate in the area A. As the correction of the aperture ratio, the influence of the smaller pitch may be further considered.

In the region C as well, the pitch is reduced and the aperture ratio is increased as in the above case. Since the decrease in the flow rate in the region C is smaller than that in the region A, it is unnecessary to correct the open area ratio in the region C in some cases. That is, it should be considered whether or not the aperture ratio of the region C should be corrected in consideration of the uniformity of the flow rate distribution in the slice chamber 14 from the perforated plate to the ejection port 15.

In the area A or the area C of the perforated plate, the hole diameter of the drill is set with a constant pitch p. The porosity can be increased by 1.01 to 1.10% by increasing it.

The hole of the perforated plate may be a single hole or a double hole having a large diameter on the downstream side.

The drill holes in the perforated plate can be replaced by tubes.
In this case, it is more advantageous to use the same pipe in terms of cost, and therefore it is preferable to use the above pitch correction.

The tube may be a tapered tube that is tapered toward the outlet of the tube and has a large diameter on the outlet side.

The header may have a circular cross section instead of a rectangular cross section.

As described above, as the embodiment,
Although the case of 10% was explained, the decrease in flow rate is not absolute at 10%, and the degree of decrease in flow rate will change somewhat due to the following factors.

That is, (1) hole pitch (2) header flow velocity (3) header flow velocity and hole inlet flow velocity ratio (4) perforated plate head loss, etc. In general, the degree of decrease in the flow rate is about 3 to 20%, and the correction amount of the open area ratio is about 3 to 20%.

Similarly, regarding the setting range of the area A and the area C, the above (1)
The value changes depending on the design difference of (4). Generally, the range of 30% from the pond side on the inflow side and the range of 20% from the pond side on the outflow side is the correction section of the porosity.

From the above, the correction amount and the correction section of the aperture ratio should be determined according to the design of each distributor, but the aperture ratio is always increased.

(Effects of the Invention) As described in detail above, according to the present invention, the following excellent effects are exhibited.

(1) Good flow distribution with a flow deviation of about ± 1% in the width direction can be obtained.

(2) The lateral flow from the perforated plate outlet to the jet outlet is reduced, and a jet flow with a uniform flow direction is obtained.

(3) Flow instability due to lateral flow is eliminated.

(4) In such a headbox, fine adjustment of the opening degree at the ejection port is small, and it is possible to stably manufacture a uniform amount of paper in the width direction, which greatly improves the quality of the paper and the productivity. Can contribute.

[Brief description of drawings]

FIG. 1 is a plan view of a head box showing a typical embodiment of the present invention, FIG. 2 is a sectional view taken along the line ZZ of FIG. 1, FIG. 3 is a plan view of a conventional head box, and FIG. Fig. 3 is a sectional view taken along line AA, Fig. 5 is a pressure distribution diagram (static pressure) in the width direction of a conventional header, and Fig. 6 is a flow rate (flow velocity) in the width direction obtained using a conventional header and a perforated plate. The distribution diagram, FIG. 7, is a flow distribution diagram with the recirculation amount as a parameter. Description of main parts of the figure 10… Header 13… Perforated plate 14… Slice chamber 15… Spout

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tetsuo Makino 5007 Itozaki-cho, Mihara-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Mihara Mfg. Co., Ltd. Heavy Industry Co., Ltd. Hiroshima Laboratory

Claims (1)

[Claims] 1. A header pipe which is tapered in the longitudinal direction and has a large number of fluid branching holes formed in the side wall along the longitudinal direction, and the direction of flow of the raw material liquid flowing in the longitudinal direction of the header pipe is defined by the holes. In a paper machine headbox that is configured to be changed almost at right angles in the section, the opening ratio of the fluid branch hole is made larger than the opening ratio in the central portion on at least one of the raw material liquid inflow side and the recirculation side of the header pipe. A flow distribution device for a paper machine head box characterized by being set.