SU1476000A1 - Method of monitoring the duration of passage of wood stock through vertical continuous-action digester - Google Patents

Abstract

The invention relates to the pulp and paper industry and is intended to increase the efficiency of the operational control and management of the process of continuous sulphate pulping. The purpose of the invention is to improve the accuracy of determining the duration of the passage of wood material in each zone of the digester. This is achieved in that the method determines the time of passage of the working path of the continuous cooking boiler with chips on the basis of estimating the movement parameters of wood material in the liquid phase / speed and concentration at the boundaries of the zones of the cooking boiler / based on the measurements of the level of chips in the boiler, the flow of chips at the inlet , pulp at the outlet of the boiler and additional measurements of pressure drops between zones, temperature drops in the liquor preheaters. Implementing a method for controlling the duration of wood material passing through a digester in automated control systems for continuous brewing plants makes it possible to obtain a continuous estimate of the time to impregnate the chips with alkali, the time of heating and cooking of the chips, the duration of the diffusion washing of the mass, information about the nature of the movement of chips with further use of this information. maintaining an optimal temperature-time schedule of the cooking process and ensuring maximum stationarity of the engine tim wood material. 2 il.s.prokhorov

Description

I

The invention relates to pulp and paper production and can be used to control the movement of a chain package in continuous cooking plants of the Camur type.

The purpose of the invention is to improve the accuracy of determining the time of passage of wood material in each zone of the digester.

Figure 1 shows schematically the zones of the digester; figure 2 shows the device for implementing the method through which the wood material passes during the cooking process (I is the impregnation zone, II is the heating zone, III is the cooking zone, IV is the diffusion washing zone), parameters movements of wood material corresponding to the boundaries of the zones, concentrations C, -, velocity V-, pressure drops along the height of each zone AR, as well as stresses caused by the friction of the wood material on the surface of the sieves of liquor extraction Ts.

The pressure difference dP on the elementary layer with a height dx of the chip package in the boiler, resulting from filtering the liquid phase through the solid, is equal to

dP r (U - V) dx

(one)

where g is the resistivity of the filtering; U, V - velocity of liquid and solid

phases.

From the equilibrium equation of the elementary layer, it follows that the pressure drop over the height of the zone from the cross sections; 1 to x equals x

4P, 4, + S (Ge (x)

(2)

R

B (x)) dx,

de 1 s (x)

Chg

R b (x)

package voltage; the concentration of wood material in cross section x; the weight of 1 kg of the chips shipped in liquid; radius of the boiler section; tangential stress caused by friction of the package against the walls of the boiler;

i (x) K tr (x) - C (x),

where K Tr - coefficient of friction.

Under normal operating conditions, the voltage caused by the friction of the bag against the walls of the boiler should be neglected. However, on the filtering circuits of the circulation, the packet experiences considerable frictional force, which depends

sieves on the state of the surface of the walls, the speed of movement of the package, the consumption of liquor in the circulations, and the filtering properties of the package in this section. The clogging of screening liquor by woody material is accompanied by a sharp increase in the coefficient of friction, and, consequently, of stress in the area of the screen. Hereinafter, bch is understood to mean the average voltage acting in the area of the sieve of the i-th zone of the digester. It follows from equations (1) and (2) that the pressure drops contain not only information about the motion parameters of the wood material, but also information about the motion resistance parameters, i.e.

20

4P; R / C ,, V, -, U, -, 6;)

(3)

The stresses caused by friction affect the movement parameters.

To develop a method for estimating the motion parameters of available measurements based on studies of the compression and filtering properties of wood material during cooking, the dependencies between the motion parameters of the material at the boundaries of the digester, motion resistance parameters and the measured signals are obtained. Under zero initial conditions, the zone equations in the parameter deviations, transformed according to Laplace, have the following form. For the upper zone of the boiler (), the equation for the level of chips in the boiler is:

Px0 + V0 & Ј. , (4.1)

L o

where x 0 is the pillar level deviation

chips in the boiler;

QAp - mass flow rate abs. dry wood supplied to the boiler. Days I zone (i 1):

V0 3iLlx0 + ai4Vf + balUt; (4,2) С, а3, х0 + a34V, + bjiU, (4 3) For other zones (i 2, 3, 4):

V;., A 1; il, 1 Cf., + a; (4 (; ".,) X,

X V; + b j, 4; + Lg;, gi,

4,4)

WITH

 a 2, f, -2 (, 1 x

X V., + b 2, -m,, + b 1; + f, -z U, f

(4.5)

where a | and b i. - transfer functions of complex variable R.

The rate of movement of the liquid phase in the upper part of the boiler to the liquor extraction zone is constant, i.e.

U, Ui U3

The relationship between the zones in the COOT relationship with equations (4.1) - (4.5) is illustrated by the block diagram in Figure 1. For most links, the input signals are the concentration at the top of the zone and the speed at the bottom, and the output signals are the concentration at the bottom and the speed at the top.

The parameters of equations (4.1) - (4.5) can be divided into two categories. The 1st parameters are those that characterize the process of moving the chip package through the boiler. Together, they make up the state vector Y:

x0, V0, C, V, C, Vlf

C3, V

3 С 4

where T is the sign of transportation x0 is the change in the level of chips in the boiler;

Ve, V ,,

Vr, V3 - velocity of movement of the solid phase in sections 0,1,2,3.

T 1

C, C. - concentration of the solid phase in the corresponding sections.

The 2nd category includes the parameters characterizing the external and internal effects (disturbances affecting the process of movement of the package of wood material and independent of this process). They make up the disturbance vector W:

T

fQ 4p & 1 U 3 4

and ,, u4, v4

I

(6)

where Q dr - the massive consumption of wood at the entrance to the boiler;

0

62 s

64 is tangential stress,

caused by friction

the chips on the walls of the boiler in the area of the liquor screen;

U 1 is the speed of movement of the liquid phase in the upper part of the boiler to the liquor extraction zone;

U 4 - the speed of the liquid phase in

a diffusion washing zone moving towards the solid phase;

V4 is the velocity of the wood material in the boiler unloading zone, due to the speed of rotation of the bottom scraper.

Using the notation of the vectors Y and W, equations (401) - (4,5) are written in matrix form.

AY BW, (7)

25 Where A and B are the transfer matrices consisting of the elements a and b, and in the matrix A all the diagonal elements, except the first, are equal to 30, a, -1, i 1.

A system of equations was also obtained that relates the totality of the measurements used with the motion parameters and the resistance parameters to the motion of the wood material.

The first measurement equation is the measurement of the chip level in the boiler.

Z, X0 4- Ј,

(8.1)

40

In the following, we will denote the 1st dimension by Z ;, and the error of the 1st dimension, Ј ;. Then

five

g (ER, h 1i xc + h1 | 3 C,

+ Ј

i

Zb h3, j

0

+ 1

3.1

C, + h 3r 5

61+ Ј3;

Z, UP, bd, C- + h 4.7 С

five

+ 1 4 | s d. s 4- 4

Z5 DR h y C3 + h c, 9

+ 1 f (4 d4 + Ј5 + (8.2)

7 + (8.3)

ъ + (8.4)

f + (8.5)

where Za, Z3,

Z4, Zj - measurements of pressure differences along the height of the boiler zones.

Measuring the load on the bottom fiber determines the mass concentration

I

in the unloading area:

   + Et

(8.6) 10

The measurement of the volume flow rate of the blown mass and its concentration is equal to the current performance of the digester for cellulose Q people, which depends on the concentration of C 4 and the speed V4 of the wood material in the discharge zone:

Z 7 Q

whole - h 7, e 4

+ 1 7i1 V4 + fi (8.7)

The measured values of the temperature difference of the liquor at the inlet and outlet of the heaters of the upper and lower heating zones of the boiler depend on the speed of the solid and liquid phases in these zones:

where Z | fZ (Z4 ...

   II

- measurement vector;

t-llt ,. .. ti

chim

- error vector

measurements;

Y is the vector of the parameters of the state of the process of movement of a solid material;

W is the vector of perturbations;

H and L are transfer matrices consisting of the elements h – n and 1 p k From equation (8) we obtain

W (-A) Y, (10) Then, substituting (1) and (10) we get

Z HY + L (B A) + Ј (H + L (B A)) Y + Ј.

(eleven)

zft at, ha „v. + 1

U. +

S

+ Ј

 lt3 h 9l4v, +

+ E,

(8.8)

Ui +

(8.9)

The measured amplitudes of fluctuations in the temperature of the liquor at the entrance to the preheaters, due to the cyclical switching of the sieves through which the liquor is taken from the boiler to the circulation line, are also functions of the speeds of the solid and liquid phases:

to

 AI h 1M V,

+ 1

fO, 6

U, + Ј,

(8.10)

 A9 h I) 6 V +

+ 1 11.5 U1 + Ј

(8.11)

Equations (8.1) - (8.11) are written in matrix form:

Z HY + LW + E,

(9)

Now one can apply the apparatus of the theory of optimal filtering to equation (11) and obtain the best estimate of the state vector Y:

Y E Y-Z Ch E Z-Z MG g, (12)

where E denotes the mathematical expectation.

By optimal estimates of the velocities at the boundaries of the zones, one can estimate the residence time of the wood material in each of them.

We take for an estimate of the average velocity of the wood material in the i-th zone, a value equal to

l

V,

Cf

V; - + Vj 2

(13)

50

Then the estimate of the residence time of the material in the i-th zone is equal to

 l

t, H; / Vfc

R

(14)

where is h. - height of the i-th zone (distance between the i-1 and i-th sections).

The cooker contains a boiling kettle 1, a chip dispenser 2 feeding the chips into the boiler, a bottom scraper 3,

pulp unloading, pump 4 circulation lines of the upper cooking zone, pump 5 of the lower cooking zone, pipes 6 and 7 of the liquor circulation line, 8 cellulose blowing line 8, cooking liquor supply line 9, washing liquor 10 supply line washing, line 11 for extraction of lye into the evaporation cyclone, sieve 12 for extraction of lye into the circulation line of the upper heating zone, sieve 13 for the extraction of lye into the circulation line of the lower heating zone, sieve 14 for extraction of the extracted liquor, steam heaters 15 and 16 of the circulating liquor, evaporated cyclone 17.

The chips come to the upper part of the boiler, together with the cooking liquor passes the impregnation zone I, then heating

circulating through 15 passes through the zone heated with liquor through the heater

16 to the cooking temperature, passes through cooking zone III, after which the liquor from it is taken through sieve 14 into line 11. Next, the mass enters the washing zone IV, where it is moved upwards from the bottom to the washing liquor, which extracts organic solution from the mass wood and output through a sieve 14 and line 11 to an evaporative cyclone 17.

The mass is discharged by the bottom scraper 3. When unloaded, the mass is diluted with washing liquor through line 10 and blown through line 8

Each sieve is divided into two. The selection of liquor is carried out alternately from the upper sieve, then from the lower one, with a frequency of about 1 minute.

To control the movement of the material, sensors are used to measure the flow rate of chips 18 at the boiler inlet, the chips damage to the boiler 19, the output of the boiler for the rotation speed of the bottom scraper 20, the load on its drive 21, the mass flow in the blow line 22 and its concentration 23.

For the implementation of the monitoring method, sensors of pressure difference across the height of the zones of the digester are additionally installed: 24 for measuring the pressure drop over the impregnation zone (LR), 25 for measuring the pressure drop at the upper heating zone

76,000

ten

ten

15

25

thirty

35

(DP2), 26 for measuring the differential pressure in the lower heating zone, 27 for measuring the differential pressure in the diffusion washing zone (4P4), and temperature sensors for measuring the temperature difference of the liquor at the inlet and outlet of the heaters for the upper heating zone dT 1 28 and 29, for the lower LTE heating zone 30 and 31, sensors 29 and 31 for measuring the amplitude of fluctuations in the temperature of the liquor when cycling the selection screens (A, A3).

The sensor measurements contain information on the parameters of the resistance to movement of the chip column, the concentration of the material and its velocity in certain zones. The whole set of measurements is connected to a computing device, which calculates the estimation of the vector of parameters of the state of the process of movement of wood material by zones of the digester in accordance with the formula (12) for estimating the average velocities of the material in the zones using the formula (13), the residence time of the material in each zone according to the formula (14). The results of the calculation are presented to the operator in the form of numbers and graphs.

The method of controlling the duration of wood material preservation in the process of continuous cooking can be used as part of an automated control system for the cooking and washing plant for the production of bleached sulphate pulp.

Claims (1)

40 claims The method of controlling the duration of the passage of wood material through a vertical continuous-action digester by measuring the level of material in the boiler, the flow rate of the material at the inlet and outlet of the boiler, characterized in that, in order to improve the accuracy of determining the duration of the passage of wood material in each zone of the digester In addition, pressure differences between the boiler zones, temperature differences in the preheat 55 l x x liquor, amplitudes of temperature fluctuations during cyclic switching of the liquor withdrawal from the upper and lower halves of the circulation sieves and, on the basis of all measured values, the concentration and speed of movement of the wood material at the boundaries of the digester zones are consistently calculated, the average speed of the engine 1 1 neither the material in the zones, and then the duration of the passage of the material through each zone of the boiler and through the boiler as a whole is determined.