JPS5927437B2 - How to change the paper machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a paper changing method in a paper machine.

In the papermaking process, paper basis weight and moisture content are important factors that determine the quality of paper, so the papermaking machine is controlled so that each of these satisfies predetermined standards.

When changing the paper standard, a paper change is performed.

The papermaking change is performed by continuously changing the basis weight and papermaking speed to new values without stopping the papermaking machine.

Control during paper changing is also automated.

A paper machine and its control system are configured as shown in FIG. 1, for example.

That is, the raw material discharged from the head box HB is squeezed by passing through the wire part WP, dried by passing through the pre-dryer DR1 and the after-dryer DR2, and wound onto the reel RL.

White water from the water extraction from the wire par) WP is received by the pi) PT and returned to the head box HB by the fan pump PMP.

The amount of white water returned is proportional to the passing speed of the raw material in the wire part WP, that is, the speed per second.

At the inlet of the fan pump PMP, the seed port valve VLV
As a result, the raw material (seed) in the seed box SB is injected.

Therefore, the concentration of the raw material in the head box HB is
It is determined by the machine speed and the seed injection flow rate.

Before the white water flow rate and the seed injection flow rate affect the concentration of the feedstock in the head box HB, it is necessary to
There is a dead time depending on the distance, and there is also a delay time due to tanks, etc. on the way (not shown).

Generally, dead time is dominant, so the following explanation will focus on this.

At a certain point t, the speed per second is ■, the seed injection flow rate is Fl,
The seed concentration is C1, and the raw material concentration of head box HB is C.
2, the dead time of white water return is LV, and the dead time of product method input is LF, then the relationship of the following equation holds true.

In steady state, It-LV) is constant, so
The dead time Lv is not a problem.

The basis weight and moisture content are measured using measuring device B just before the reel RL.
M and are respectively measured and input to the calculation control unit CMT.

The calculation control device CMT calculates the seed flow rate operation amount and the steam pressure set value of each dryer based on the deviation between the measured value and the set value, and applies them to the seed port valve VLV and the steam pressure controller of each dryer. Give it to PRC1 and PRC2,
The basis weight and moisture content are controlled to match their respective set values.

When performing a paper change, the calculation control unit CMT controls the head
Change the flow rate and machine speed of the seeds injected into box HB.

In that case, conventionally, the seed flow rate and machine speed were changed linearly at a constant rate of change up to a new target value.

However, if this is done, especially when the machine speed changes, there will be a period when the change in white water flow rate due to the change in speed per second does not reach the head box HB due to the dead time of white water return. There are times when the concentration of the raw material in the inlet, that is, the inlet concentration, does not change commensurate with the change in papermaking speed.

In this case, only the papermaking speed changes while the basis weight remains unchanged, and this causes a phenomenon in which the amount of paper produced per unit time temporarily deviates from the expected value.

If the speed per second is increased, this deviation will appear as an unexpected increase in the production amount≧<<, resulting in an increased load on the dryer that controls the moisture content.

However, because the dryer is structurally incapable of quickly dealing with an increase in load, sufficient drying may not be achieved, and in the worst case, there is a risk of paper breakage.

Further, since load fluctuations on the dryer cause a large disturbance to the moisture content control system, the stability of the moisture content after papermaking is changed is also adversely affected.

In addition, due to the dead time of returning to white water, the head box H
Since the stabilization of the raw material concentration in B is delayed, the arrival of the target basis weight is delayed, and the time required for paper changing becomes longer.

The paper during the paper change period is non-standard paper and is waste paper, and the amount of paper lost is proportional to the time required for paper change, so in order to reduce paper waste, the time required for paper change should be as short as possible.

An object of the present invention is to provide a paper machine changing method in which no unexpected deviation in production volume occurs during the paper making change, the moisture content after the paper making change is stable, and the time required for the paper making change is short. It's about doing.

In the present invention, the contents are discharged from a head box containing a mixture of seeds supplied through a seed opening valve and white water returned from a pit according to the machine speed, and the water is squeezed using a wire part. In a paper machine that drops white water into a pit and dries the remainder in a dryer, when changing the paper, the value F (to) of the loading flow rate before the paper change using the seed opening valve and the paper speed before the paper change are determined. The speed change pattern V(t) for changing from V(to) to the target speed, and the basis weight BD(t) before changing the basis weight.
Basis weight change pattern B that changes from o) to the target basis weight
When D(t) is given, pattern F is given by the following formula for the loading method inflow rate by the seed opening valve for paper change.
(t) However, the above objective is achieved by the dead time of returning white water to LV.

The present invention will be explained below with reference to the drawings.

FIG. 2 is an explanatory diagram of the operation when changing the papermaking according to the present invention, in which the papermaking speed is increased and the basis weight is reduced in inverse proportion to the papermaking speed.
This is the case when the production amount is kept unchanged.

In FIG. 2, time t.

The machine change is started at , and the machine speed is linearly increased at a constant slope from the previous value V(to) to the prespecified target value V(t3) (FIG. 2a).

In an ideal case where there is no dead time in white water return, the white water return flow rate increases immediately as the speed per second increases, so the seed opening valve VL
Even if the injection flow rate of seeds from V is not changed, the inlet concentration will decrease inversely proportionally to the increase in machine speed at the same time as the machine speed changes. (Dotted line in Figure 2) ) In other words, the production volume should remain unchanged (dotted line in Figure 2 C).

However, due to the dead time, the inlet concentration changes as shown by the solid line in Figure 2, and the production volume temporarily increases as shown in the solid line in Figure 2C.

Therefore, in the present invention, by changing the seed flow rate non-linearly as shown by the dotted line in Figure 2d, the inlet concentration is
As shown by the dotted line in the figure, the change was made to be ideal.

To do this, the ideal inlet density change pattern (
A seed flow rate variation pattern for changing the inlet concentration along this ideal pattern is determined by calculation, and the seed port valve is operated according to the calculation result.

The ideal inlet density change pattern is determined by the machine speed change pattern and the target basis weight value.

If the production volume is kept unchanged during papermaking as shown in Figure 2,
The ideal inlet concentration change is inversely proportional to the machine speed change, but this can be approximated by a straight line.

Once the ideal inlet concentration change pattern is determined, the inlet concentration at each point in time can be determined from that pattern.

Since the inlet concentration is proportional to the basis weight, the inlet concentration will be expressed in terms of basis weight below.

The seed flow rate change pattern is determined as follows.

According to the ideal inlet concentration change pattern, the time t1 when the dead time Lv of white water return has elapsed after the start of paper change.
During this period, the inlet concentration changes from BD(to) to BD(
tl).

Therefore, if such a concentration change can be realized by changing the seed flow rate from F(to) to F(tl), the following equation holds true from the proportional relationship between the inlet concentration, that is, the basis weight and the seed flow rate.

Therefore, the seed flow rate may be changed linearly so that the seed flow rate at time t becomes the value of equation (3).

At time t3 when the speed per second reaches the target value, the inlet concentration must reach the target value BD (t3).

The seed flow rate to match such a target value is set as F(t3
), and assuming that the seed flow rate remains unchanged at F(to) from the beginning, the virtual inlet concentration at time t3 is BD'
(t3), the following equation holds true.

Here, the virtual inlet concentration BD'(t3) corresponds to the papermaking speed V(t2) at time t2, which is the dead time LV before the end of papermaking change, so the mass balance as shown in the following equation is obtained. To establish.

BD'(t3) ・V (t2) = BD(to) ・
V(to) (6) From this equation, it becomes, so by substituting this into equation (5), the following equation is obtained.

Therefore, the seed flow rate may be made to match the value of equation (8) at time t3.

Since this value is almost equal to F(tl), the seed flow rate is kept almost constant from time t1 to t3.

During the period LV from time t3 to t4, the white water return amount continues to increase, but since the inlet concentration has reached the target value, the seed flow rate is increased in order to maintain that concentration.

The seed flow rate is increased at time t4 to match the flow rate F(to) before the paper change.

By controlling the seed flow rate in this manner, the inlet concentration is changed according to an ideal pattern, and the production amount is kept unchanged even during paper changes.

However, in reality, there is a dead time LF before the operation result of the seed opening valve appears in the inlet concentration, so it is necessary to operate the seed opening valve in advance by that amount (Fig. 2e).

Such an operation prevents an unexpected increase in the production amount during the papermaking period, so that no disturbance is caused to the moisture control system, and the stability of the moisture content after the papermaking change is guaranteed.

Furthermore, since there is no delay due to dead time when the inlet concentration is 1, the paper changing time is shortened by that amount.

When there is no inversely proportional relationship between the target value of machine speed and the target value of basis weight, a change in production volume occurs.

In that case, the machine speed change pattern and the inlet concentration change pattern are determined so that the production amount changes at a constant rate of change that does not cause a large disturbance to the moisture content control system.

The operation in such a case is shown in FIG.

In FIG. 3, if the machine speed is changed as indicated by a and the inlet concentration is varied as indicated by the dotted line b, the production amount can be linearly shifted as indicated by the dotted line C.

In order to change the inlet concentration as shown in the dotted line b, the seed flow rate is changed as shown in the dotted line d, taking into account the dead time LV of white water return.

On the other hand, if the seed flow rate is changed as shown by the solid line d, the production amount changes as shown by the solid line C, which causes a large disturbance to the moisture content control system.

Flow rate F(t, ), F(t
3) is obtained by substituting the values of a and b at each point in time into the above equations (3) and (8).

The final value F(t4) of the seed flow rate is determined by the following equation.

However, BD (t4)...Target value of basis weight at the time of paper change (=
BD(t3)) BD'(t4)・・・Final value of basis weight when seed flow rate remains unchanged at F(to) Mass balance formula at time t4 % formula %() Therefore, the equation (9) becomes as follows.

In other words, the seed flow rate change pattern is based on these F(tl),
A broken line connecting F(t3), F(t4), and F(to) may be used.

Then, the seed opening valve is operated as shown by the dotted line in e, taking into account the dead time LF.

In the above, the seed flow rate change pattern is determined by determining the flow rates at main points in time and connecting them with straight lines, but it can also be determined continuously as follows.

That is, from the above formula (1), F C (t) - B D (t) ・V (t - Ly )
(12), but t just before the paper change.

At the time point, FC(to)−BD(to)・v(t
o) (13)°, °v (to)=v (to-
LV ) (14), so the following holds true.

Then, although it is assumed that the species concentration C remains unchanged before and after the paper change, −K −B D(t)・v(t−Ly) (1
7).

In equation (17), BD(t) is the basis weight change pattern, and v(t-Lv) is the machine speed change pattern translated by the dead time Lv. b and a'.

The result of multiplying these by the magnification is d in the same figure.
The seed flow rate change pattern is as follows.

Comparing Equation (16) with Equations (3), (8), and (11) above at each time point, they match, which means that the same seed flow rate change pattern can be obtained. I understand.

As described above, according to the present invention, there is no unplanned deviation in the production amount during the papermaking change, the moisture content after the papermaking change is stable, and the time required for the papermaking change is short. An automatic paper changing method can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a conceptual block diagram of a paper machine and its control system, and FIGS. 2, 3, and 4 are explanatory diagrams of the paper changing operation according to the present invention. SB... Seed box, VLV... Seed mouth valve, H
B...Head box, WP...Wire part, PT...Pit, PMP...
...Fan pump, DR,. DR2...Dryer, BM...Basic weight/
Moisture percentage needle, RL...Reel, CMT...
・Calculation control device, PRC,, PRC2... Steam pressure controller.

Claims (1)

[Claims] 1. The mixture of seeds supplied through the seed opening valve and white water returned from the pit is discharged from the head box according to the rate of second, and the mixture is squeezed with a wire part. When changing the paper machine, which drains the white water into the pit and dries the remaining water with a dryer, the value p (to) of the loading method input flow rate by the seed opening valve before the paper change, and the paper speed before the paper change. A speed change pattern v(L) that changes the speed from V(tO) to the target speed, and the basis weight B D (t
Basis weight change pattern B that changes from o) to the target basis weight
When D(t) is given, pattern F is given by the following formula for the loading method inflow rate by the seed opening valve for paper change.
(t) A method for changing paper sheets, characterized by changing the paper according to (t). However, LV......the wasted time of returning to Hakusui.