SE530528C2 - Pulp refiner grinding gap calculating system, comprises separate or combined pressure and temperature sensors for providing data combinable with material and process variables - Google Patents

Abstract

Separate or combined pressure and temperature sensors are provided at the refiner grinding segments (12) or in a rail extending along the active radius of the segment. Data from these sensors is combined with material and process variables to create a physical model which includes an independent grinding gap. A system for intermittently calculating the grinding gap in a pulp refiner comprises a number of separate pressure and temperature sensors or combined pressure-temperature sensors, which are located either on or in at least one of the refiner grinding segments, or in a parallelepipedic elongated rail extending along the active radius of the segment. The pressure and temperature data is combined with material variables (e.g. chip or pulp density) and process variables (e.g. motor load, chip and pulp supply, diluting water addition, pressure and temperature of incoming and outgoing flow and hydraulic pressure (5)), and with the aid of a physical model it can be used to minimize the difference between the measured motor load and the integral of the energy distribution across the grinding region (9) calculated using this model, creating an independent grinding gap in the model.

Description

25 30 35 40 530 523 2 The diameter of the grinding wheels varies depending on the manufacturer's make and the producers' production capacity. Previously, the grinding discs were cast in one piece, but today it is more common to modularly manufacture the grinding discs in a number of grinding segments (12 and 13), see Figure 1 and Figure 2. The segments can, for example, extend from the center of the grinding discs to its periphery or be divided into two rings. an inner (14) and an outer ring (15). The zones between the inner and outer rings are often called "breaker bar zone" and peripheral zone, respectively.

The surfaces (16) of the grinding segments are often designed in different ways with characteristic patterns in the form of booms (17) and ponds (18). The booms act as knives and they break the ice or refine the mass formed. In addition to the direct grinding zone, both fibers, water and steam are also transported in the ponds between the barriers. Through different pattern designs, the grinding segments can be made to be fed or alternatively stopped by the mass in order to affect the flow conditions and thereby create special pulp quality. The amount of steam produced is spatially dependent, which is why both water and steam can occur together with fl ice or mass in the malt zone.

There are also other types of grinders such as concavers or grinders where both grinding wheels rotate in the opposite direction or grinders consisting of four grinding wheels, one in the middle rotating rotor has grinding wheels mounted on both sides and two stationary grinding wheels which are pressed together by hydraulic pistons to get two malzoner.

When producing pulp from wood ice or previously refined pulp, the milling discs are compressed so that the gap (10) of the milling zone becomes approximately 0.2-0.7 mm, depending on the type of rafter used.

The grinding gap is a central control variable and an increase or decrease of the gap takes place by means of hydraulic pistons which apply a so-called hydraulic pressure (5) to one or more grinding wheels depending on the type of grinder. If the grinding gap is changed by, for example, 10%, the pulp quality is significantly affected. It is therefore important to have knowledge of the width of the relevant grinding gap. There are grinding gap meters on the market today that are applied directly to the grinding wheels. Usually only one grinding gap sensor is used per grinding zone, mainly to prevent the grinding discs from collapsing and thus not primarily to control the grinding gap.

There are also other systems on the market where the temperature is measured along the grinding zone in order to visualize a temperature profile (19) or pressure profile (20) for control purposes, see Figure 3. In the event of a changed condition in the grinding gap, production (ie ice-alternative pulp supply) and diluent addition changes the temperature which can thus be controlled. Several temperature and / or pressure sensors are commonly used and can be placed directly in the grinding segments or alternatively enclosed in a parallelepiped disk 10 15 20 25 30 35 40 530 528 3 elongate rail (21) extending along the active radius (11) of the grinding segments (12 and 13). see Figure 1, Figure 2 and Figure 4, according to the procedure in EP 0788 407 - Measurement in Malzon. Usually, the parallelepiped rail is implemented between two template segments in the outer ring, see Figure 2.

The design of the grinding segments has proven to be of great importance for the temperature profile along the active radius, which is why it is difficult to determine in advance where the temperature sensors (22) and / or the pressure sensors (22) are to be placed in the rail (21).

Otherwise, there are really no other measuring systems that have been applied in the refiner's malzone. On the other hand, there are instruments that can be placed in the blow line from the generator where the dry content of the flowing mass stream can be calculated using algorithms connected to NIR (Near Infra Red) measurements.

Description of the invention Technical problem: Extensive material regarding electronic control with the aid of dry matter measurement, grinding gap measurement and temperature measurement has been reported in the literature.

The results often show that measurement of the dry content in the blow line shows a clear deviation from the actual dry content, which indicates the degree of difficulty of measuring continuously in these grinding processes. The reason for this is judged to be that the temperature of the mass and the pressure in the blow line as well as other more non-linear process conditions affect the calculation algorithms in such a way that a credible dry matter measure can often not be produced.

It has also long been a desire to be able to construct a functioning safe absolute measuring grinding column sensor. Physical measurement sensors, based on, for example, inductive technology, are on the market but often provide a relative measurement at the same time as they provide noisy measurement signals that must be filtered in order to be handled for different purposes.

From a maintenance perspective, commercially available grinding column donors rarely exhibit the robustness required.

According to the literature, temperature measurement has proven to be an unusually robust technology for controlling radiators. However, combinatorial measurement techniques, such as grinding gap measurement and / or dry matter measurement, are often required in control to obtain the correct pulp quality.

When measuring the temperature profile in the grinding zone, it has emerged that when production, diluent supply and grinding gap change, the temperature profile is dynamically affected. 10 15 20 25 30 35 40 530 528 4 The dynamic change is suitably illustrated by studying Figure 5a, where a step change of the dilution water affects the temperature profile in different ways depending on where along the radius (11) the course of events is viewed. As the diluent supply increases, the temperature (23) decreases before the temperature maximum (24). After the temperature maximum, the temperature increases (25). The hypothesis has been that the incoming water cools the returning steam at the same time as the forward steam is heated.

When production increases, this usually means that the entire temperature profile (19) lifts to another level (26), see Figure 5b. This usually also applies when the grinding gap (10) decreases, which is equivalent to the hydraulic pressure (5) being applied to the grinding wheels via the hydraulic pistons.

All process conditions, for example increased production or dilution water supply that changes the active volume of the three-phase system (pulp, water and steam) in the grinding zone at constant hydraulic pressure, of course affect the grinding gap. Direct measurement of the grinding gap can not always reproduce this phenomenon, due to said noisy signal content and / or too strong filtration. This means that a compensation for reaching the original template gap after a change by means of some type of control algorithm is not always implemented. This has the consequence that the residence time of the pulp in the grinding zone can vary, which affects the pulp quality.

In connection with a number of research projects carried out at Chalmers University of Technology, a completely new theoretically based physical model has been documented (Berg D., Karlström A., Gustavsson M., 2003, “Deterministic consistency estimation in reining processes”, International Mechanical Pulping Conference, p 361-366 Quebec City June 2003).

The model is general, but in order to be able to use it on-line in process computers or off-line in laboratories, internal conditions such as temperature and / or absolute pressure must be measured in the mold zone in order for the so-called state space to be available for estimating different types of process variables. which previously could only be measured under difficult conditions.

So far, only research has focused on dry matter starvation in the bladder line. Several documented experiments have shown that the estimated dry matter content is more accurate and fast compared with the measured dry matter content in the blow line with the above-mentioned NIR technology. In the published material, however, it has been assumed that the grinding gap is known via filtered information from existing measuring equipment.

The model thus assumes that the temperature and / or the absolute pressure is measured along a segment, preferably along the outer ring in the refiner where the actual refining takes place, in order to mathematically tighten both the material balance and the energy balance in the refiner. What distinguishes the model from previous rudimentary attempts to describe the physics around the grinding process itself is that it calculates both the reversible thermodynarian work and the irreversible refining work carried out on fi brema. 10 15 530 528 5 That is, the model is described from an entropy perspective instead of an enthalpy-based approach.

The dynamic change at different stages in production, dilution and hydraulic pressure is strongly nonlinear, which means that in some situations, for example when low dryness is present in the malt zone, the temperature profile is not significantly affected because other conditions affect the temperature profile dramatically as shown schematically in Figure 5a-Figure 5b. The nonlinearities are also affected by how the grinding segments are designed, which has the consequence that the appearance of the temperature and pressure profiles can vary both spatially and dynamically. This means that it is not always appropriate to control these profiles directly. Instead, other process variables, such as the grinding gap, in the refining zone, may be necessary to follow in combination with, for example, the temperature profile. The problem, however, is that these can seldom be measured with sufficient accuracy, which is why other solutions to the problem must be resorted to. The solution: The present invention is the solution to this problem and relates to a method using robust temperature and / or pressure measurement in combination with available measurement signals from the process and a physical model for estimating the grinding gap in the refiners.

In cases where only temperature measurement is used, according to the procedure in EP 0 907416, the system assumes that the conditions in the malt zone of the malt zone fi are saturated, ie the pressure in the malt zone can be calculated based on the temperature measurement since saturated steam is assumed to occur in the entire mill zone. In cases where overheating may occur, both temperature and pressure must be measured.

To reproduce the nonlinear phenomena in the process, it is assumed that the physical model can describe reality well enough. The main parameters included in the model are production, diluent supply, hydraulic pressure and engine load. In addition, a number of parameters such as incoming temperatures for the chip, pulp, water fl destinies, estimated fl ice density and incoming dry matter, incoming pressure before the malting zone and blow line pressure etc. according to (Berg D., Karlström A., Gustavsson M., 2003, “Deterrninistic consistency estimation in re fi ning processes ”, International Mechanical Pulping Conference, p 361-366 Quebec City June 2003). Some parameters can be set as constants, such as radius position for inner and outer grinding segment rings because others must be measured continuously.

It is important to point out that the model also assumes that the engine load is known.

The motor load can in this context be seen as the power that must be added to the process to refine the mass. However, the motor load does not describe how the power is distributed along the mal zone, but should be seen as a total power, ie an integration of the distributed power along the active radius.

Spatial vectors for the malzone description are also required as input parameters to the model. Examples of such vectors are the temperature and / or pressure profile along the grinding zone as previously mentioned, but the position vector was on the active radius at which these are measured is also necessary to include. In addition, vectorial information about the grinding of the grinding segments must be included in order to be able to calculate the shear between the bars of the grinding segments and the mass in the grinding zone at all.

The first thing that is usually done when using the model is to interpolate the accepted vector elements required to increase the vector size. Usually only temperature and / or pressure are measured in a few positions, eg ten, along the radius.

The purpose is to describe the radial phenomena in the grinding zone as accurately as possible, also taking into account that there are discontinuities which are suitably approximated by a smooth continuous transition (27). Examples of such discontinuities are the transitions from one grinding (28) to another on the grinding segments, see Figure 6.

The total mass fates are then calculated using the input fate parameters, enthalpy and entropy calculations. The total energy distribution along the grinding zone is then calculated with the help of, among other things, knowledge of the grinding segments' grinding, grinding gap and viscosity of the pulp. As the total mass flows and energy distribution in the malting zone are calculated, the fl velocities of water (29) and steam (30) can then be estimated along the active radius, see Figure 7.

The direction of fate is usually defined as positive from the center towards the periphery of the template segments. It is important to point out that the modeled fate direction of the formed steam must be able to be negative or positive depending on where along the active radius the process is viewed, since the refining process allows the formed steam in the malt zone to flow both backwards (in the negative direction) and forwards ( in a positive direction) in the malzone. This means that in cases where the process shows a backward steam somewhere along the radius, the steam velocity must be uncontrollable, ie close to zero, in some area along the active radius. This so-called stagnation point (31) should be in an area around the temperature maximum, but the position of this area has never been detected before.

Recent experiments in a factory environment, where the temperature profile is measured using simultaneous use of a physical model, have shown that the area where the absolute amount of the steam velocity (32) has a minimum corresponds somewhat to the area where the temperature profile has its maximum (24), see Figure 8, under provided that the grinding gap (10) can be released as an independent optimization parameter in the physical model. That is, the optimization algorithm minimizes the difference between the measured radius position for temperature maximum and the position along the radius where the estimated steam velocity is zero by iterating an estimate on the grinding gap that meets these conditions. The latter has not previously been assumed because it is always assumed that the grinding gap must be measured in order for the model to be used on-line for controlling the division of labor between the thermodynamic work and the refining work in the refinery using applied production, supply of diluent and change in hydraulic pressure.

For practical and economic reasons, you always want to minimize the number of temperature sensors at the same time as you want to measure the appearance of the entire temperature profile for other informative control purposes. This thus means that it is unrealistic to place all sensors close to the position where one expects to find the temperature maximum. To deal with this problem, an alternative technology can be used. The technology is to minimize the difference between the actual motor load (33), ie the actual electricity consumption that is measured, and the integral of the model calculated from the model 10 15 20 25 30 35 5GB 528 8 the energy distribution along the grinding zone (34), i.e. required estimated work to refine the mass, instead of seeking the exact position for the temperature maximum. In the same way as before, it is assumed that the grinding gap (10) is an Obßwênåß optimization parameter in the physical model when the difference is minimized, see Figure 9.

This technique also means that a better estimate for the position where the steam velocity is almost zero can be calculated regardless of how accurate the area is around the temperature maximum. The latter can be used to design patterns where the knowledge of the position of the stagnation point on the mesh segment is important.

Knowing where the point of stagnation lies along the radius of the outer periphery, the residence time during which the fibers are in the grinding zone can be calculated before and after the point of stagnation since the vector velocity of the pulp can be calculated.

This means that even if the exact residence time is difficult to predict, a relationship between residence time before stagnation point and the total residence time can be interesting to follow as it provides information on how a statistical measure of how the fibers are processed can be derived.

It is important to point out that the measurement of the temperature or the pressure or a combination of the two is necessary in order to be able to estimate the grinding gap at all with this method.

Since a credible measure of the grinding gap can be calculated, this also means that the estimate can be used for control end needles. The grinding gap is preferably controlled by means of the applied hydraulic pressure but is also affected by other parameters such as dilution water supply and production as these affect the volume in the grinding zone.

Figure 10 schematically shows the control of the process. The unit (35) consisting of a computer or similar electronic equipment is fed with the difference between (the setpoints) (36) and (the actual values) on the estimated grinding gap (10). The control unit (35) then controls the hydraulic pressure (5), fl ice or mass fl fate (6) in combination with supplied water (37).

From the process (38), the measured process signals (39) (such as production, diluent supply, hydraulic pressure, temperature profile and / or pressure profile, engine load, inlet and outlet temperature and pressure, incoming dry matter, etc.) are fed intermittently at high sampling rate together with geometric and material characteristic parameters (40) (such as grinding of the grinding segments, position of temperature and / or pressure sensors, density, viscosity, etc.), required for the calculation of the grinding gap (10), into a computer unit (41). The ground pulp is removed from the process at (42).

In cases where a sufficiently accurate grinding sensor is available, the above calculation method can also be used to calibrate the grinding sensor on-line 10 15 20 530 528 9 since the difference between calculated grinding gap and measured grinding gap provides the offset required as a basis for the compensation.

In cases where a credible grinding gap measurement is available and when the absolute viscosity of the pulp is judged to vary within larger areas, such as for CTMP, the model can set the absolute viscosity as an independent variable in order to control the kernel additives in the process online.

The main object of the invention is thus to describe a method which can with great reliability present an on-line alternative off-line based estimation of the grinding gap between the segments in the grinder's grinding zone. The calculation is based on the fact that the temperature profile and / or the absolute pressure profile can be measured in the grinding zone.

In cases where the invention is used on-line, the estimated values (actual values) on the grinding gap are fed into a computer unit where the desired values (setpoints) are entered, from which deviations from (setpoints) are fed into a control unit which regulates the applied pressure on the grinding wheels. and to the fate of ice or mass and water to it, as well as any vapor pressure.

The method according to the present invention is not limited to any device for reading temperature or pressure in the grinding zone. However, such devices are known from, for example, Swedish patent 94037433-9 and EP 0907416.

The invention is not limited to the embodiment shown, but it can be varied in various ways within the scope of the claims. 10 15 20 25 30 530 528 10 Description of the drawing base: Figure 1: Section of a stationary grinding wheel pressing against a rotating grinding wheel.

Figure 2: Two grinding segments with intermediate parallelepiped elongated rail for measuring temperature and / or pressure.

Figure 3: Temperature profile and pressure profile as a function of the malzone radius.

Figure 4: Parallel pipedong elongated rail with discreetly placed temperature and / or pressure sensors.

Figure 5a: The dilution water supply of the temperature profile. appearance before and after an increase in Figure Sb: The appearance of the temperature profile before and after an increase in production.

Figure 6: Grinding gap and grinding as a function of the active radius.

Figure 7: The meadow and water velocities as a function of the active radius.

Figure 8: The absolute steam velocity and the temperature profile as a function of the active radius.

Figure 9: Schematic representation of the independent grinding gap and the difference between motor load and the calculated integral of the energy distribution along the grinding zone as a function of the number of iterations required to achieve a predetermined difference between measured motor load and the model deducted integral of the energy distribution. required estimated work to refine the pulp.

Figure 10: Schematic description of how the process is controlled using an estimated template gap.

Claims (1)

1. 0 15 20 25 30 35 530 528 ll Patent claims: Method for intermittently calculating the grinding gap in a refiner, characterized in that a number of position-specified pressure sensors and / or temperature sensors, located along the active radius of the refiner grinding segments together with spatial information on grinding the grinding segments, are used together with information on process variables their density, incoming dry matter and the electron's measured engine load diluent addition, temperature and pressure on incoming and outgoing fl fates, hydraulic pressure in order to use a physical model to minimize the difference between measured engine load and the integral of the energy distribution calculated by the model by a template gap independent of the model. . Method according to claim 1, characterized in that the estimated grinding gap (actual value) is fed into a computer unit where the desired values (setpoints) are entered, from which the deviations from the setpoints are fed into a control unit which regulates the applied pressure on the grinding wheels in the refiner. fl ice or mass and / or water to this and possibly the vapor pressure. Method according to claim 1 or 2, characterized in that the estimated grinding gap is used to shift the position where the steam velocity in the grinding zone is almost zero back and forth by means of changes in production, water addition or the applied pressure on the grinding wheels or a combination of these control parameters. Method according to one of Claims 1 to 3, characterized in that in cases where a sufficiently accurate grinding gap sensor is available, it is calibrated online by means of the difference between calculated grinding gap and measured grinding gap, which corresponds to the required compensation requirement. Method according to one of Claims 1 to 3, characterized in that the desired values of the temperature profile are entered together with the actual measured temperature profile in a computer unit, from which the deviations from the desired values are entered into a control unit which regulates the estimated grinding gap to reach the desired the temperature profile.