JPS5911718B2 - Dryer steam pressure operation method during paper change in paper machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for operating a dryer vapor pressure during a paper change 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.

Paper making is performed by continuously changing the basis weight and speed per second to new values without stopping the paper 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 dryer DR, and wound onto the reel RL.

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

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 dryer steam pressure operation amount based on the deviation between the measured value and the set value, and sends them to the seed port valve VLV and the dryer steam pressure controller PRC, respectively. and control the basis weight and moisture content to match their respective set values.

When performing a paper change, the calculation control unit CMT controls the head
The flow rate and machine speed of the seeds injected into the box HB, and the amount of steam pressure operation are changed.

Due to the distance between the seed opening valve VLV and the head box HB, there is a dead time before the operation of the seed opening valve VLV affects the raw material concentration in the head box HB.

Therefore, in order to shorten the time required for paper changeover, the seed opening valve is operated prior to changing the papermaking speed by the amount of dead time.

In addition, the dryer system has a large delay time constant, and the steam pressure system that operates it is structured so that it cannot instantly generate a large output. , steam pressure operation is initiated prior to the change in paper speed, depending on expected dryer load fluctuations.

Conventionally, the lead time for steam pressure manipulation has been determined empirically, but this poses a problem from the standpoint of streamlining paper changeover.

An object of the present invention is to provide a rational steam pressure control method that minimizes lead time.

The present invention calculates in advance the steam pressure operation output to match the moisture content of the paper to a target value at the end of the papermaking period when performing papermaking change, and if this output calculation value is within a predetermined limit, For example, the steam pressure is manipulated accordingly, and if this calculated output value exceeds a predetermined limit, a corrected steam pressure manipulated output is calculated with the operation start point advanced enough to bring it within the predetermined limit. The steam pressure was adjusted accordingly.

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

FIG. 2 is a process model focusing on moisture content control.

In Figure 2, the influence of the disturbance V(S) is expressed by the transfer function σ(
S) is expressed as a moisture content change A(S), whereas the intermittent moisture content manipulation output I) by the calculation control device CMT at a fixed period (Z) is a transfer function to the vapor pressure controller PRC. H(S), and its influence is expressed as moisture content change B(S) by the transfer function G(S) of the dryer process, and eventually the moisture content change C(S) is determined as a combination of both.

When changing the paper, changing the load on the dryer causes disturbance V (
S), but since the load is changed linearly, the change in moisture content A(S) is also linear.

Therefore, if the moisture content change B(S) due to operation is made to change linearly in the opposite direction to the moisture content change A(S) due to disturbance, the moisture content change C(S) as a combination of both becomes zero. It can be done.

Moisture content change A(S) due to disturbance! Well, since it can be predicted based on the paper changing schedule, the moisture content change B(S) due to the operation can be determined accordingly, and the operation output for causing such a moisture content change B(S) can be determined. D=
1 (Z) can be found.

The calculation of the operation output I) band (Z) is as follows.

In the process model of FIG. 2, the following equation holds.

D = l (Z) - H (S) ・G (S) = B (S)
(1) Here, when B(S) is expressed in the form of Z transformation, B 屹)=αOZ0+α1Z-1+α2Z-2
+... (2) Since this must change linearly, α.

, α1. α2. ... is an arithmetic sequence. Transfer function H
When (S)・G(S) is expressed in the form of Z transformation, H(S)−
! , is a zero-order hold system, and G(S) is a first-order lag system, so it becomes as follows.

However, ε-er, L: sampling time, T: time constant of the dryer.

Therefore, the operation output D4N(Z) becomes.

However, it is assumed that αo=0. Therefore, the n-th operation output Dn is as follows, and when outputting in differential form, it becomes as follows.

These are general formats of the manipulated output when linearly changing the output of the first-order lag system.

For example, the time course of the operation output is shown in Fig. 3.

In other words, in order to make the moisture content change due to the operation as shown in b, in response to the change in moisture content as shown in a due to paper change,
The operation output will be as shown in C.

Such an operating output has a peak just before the moisture content is stabilized, and then reaches a new steady value smaller than this peak.

The greater the change in moisture content, the greater the peak of the operating output and the greater the difference in output.

This operating output is determined in the calculation control unit CMT prior to carrying out the paper change, and it is checked whether the peak of the operating output exceeds a predetermined limit E.

If the limit has not been exceeded, the moisture content is manipulated using this operating output at the start of paper reshaping, and if the limit has been exceeded, the new operating output is recalculated as follows. , thereby manipulating the moisture content.

If the limit E of the operating output is expressed, for example, as a percentage of the steady operating output after settling, the peak of the operating output must be below this limit.

Since the peak of the operation output is the sum of the absolute value of the steady output value 1/ and the final differential output value ΔDN, the following equation holds true.

Here, and since the inside of the absolute value symbol is negative, the α9 formula is as follows.

That is, if the number N of outputs of the manipulated output is determined so as to satisfy equation (12), the peak of the manipulated output can be made below the limit.

The number of times is expressed as equation (12).

This number of times N is greater than the number of outputs when the peak of the operation output is not limited.

Since the operation cycle is constant, the operation start point is advanced by the increase in the number of operations.

Then, from this earlier point in time, we will change the moisture content by operation as shown by the dotted line in Figure 3, and based on the corresponding new sequence of α, we will calculate the operation output by using equation (8). .

In this case, the operating cage at that time will be, for example, as shown in FIG. 3d, and the peak will be within the limit with the minimum required advance time.

Therefore, when operated at such an output, the steam pressure system can sufficiently respond, and the moisture content matches the predetermined target value at the end of the paper change.

Due to the nature of steam pressure systems, operating power limits may also be specified for the rate of change of power.

In that case, the same concept as above may be applied to the difference in operation output and its limit.

As described above, the present invention calculates in advance the steam pressure operation output to match the moisture content of the paper to the target value at the end of the papermaking period, and calculates the peak of this calculated output value. and or if the rate of change is within predetermined limits,
Manipulate the steam pressure accordingly, and if the peak and/or rate of change of this calculated output value exceeds the limit, correct the steam pressure by advancing the operation start point sufficiently to bring the peak and/or rate of change within the limit. Recalculate the operation output,
The steam pressure was controlled accordingly.

Therefore, rational steam pressure operation can be performed with minimum lead time required.

[Brief explanation of the drawing]

Figure 1 is a conceptual block diagram of a paper machine and its control system, Figure 2 is a process model focusing on moisture content, and Figure 3 is an explanatory diagram of the steam pressure operation according to the present invention. .

Claims (1)

[Claims] 1 In a paper machine controlled by a computer, when performing a papermaking change, the dryer steam pressure operation output is calculated in advance to make the moisture content of the paper match the target value at the end of the papermaking change period, and this output calculation is performed. If the peak value and/or rate of change of the output value is within a predetermined limit, the vapor pressure is manipulated accordingly, and if the peak value and/or rate of change of this calculated output value exceeds the predetermined limit, the peak value and/or change is A dryer steam pressure operation at the time of paper change in a paper machine in which the corrected steam pressure operation output is recalculated so that the operation start point is advanced enough to keep the ratio within a predetermined limit, and the steam pressure is operated accordingly. Method.