JPH0459579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring the concentration of suspended pulp in the pulp and paper industry.

(Prior art) Pulp, the raw material for paper, usually has a width of 10 to 15 μm.
It is a wood fiber with a length of 0.5 to 3 mm, and the pulp is subjected to various treatments before being made into sheets in the papermaking process. A typical treatment is a mechanical treatment called beating, in which the fibers are subjected to treatments such as crushing, cutting, and swelling by a beating machine, and the fibers are cleaved, which is called external fibrillation.

Beating is a process in which fibers are subjected to such treatment, and the properties of the resulting paper vary dramatically depending on the degree of beating. In other words, the important factor that determines the properties of paper is the beating process, and depending on the extent to which this process is applied, paper with different properties can be produced even from pulp made from the same raw material, and more than 80% of the paper is due to the beating process. It is said that it will be determined by

The pre-process of this beating treatment includes a disintegration process in which the pulp is disintegrated and dispersed in water, and the post-process includes a mixing process in which the pulp is mixed with chemicals such as fillers and sizing agents. The pulp liquid obtained is diluted to a predetermined concentration and supplied to the papermaking process.

Another important factor that changes the properties of paper is the pulp concentration in the treatment process or papermaking process. Although the pulp concentration in these steps varies depending on the type of paper being made, for example, the following concentration ranges are standard for the pulp concentration in each of the above steps.

Disintegration process: 6 to 15% Beating process: 3 to 15% Mixing process: 3 to 6% Paper making process: 0.1 to 0.8% Conventionally, the method of measuring pulp concentration is based on the fact that the fluid resistance of the suspension depends on the concentration. There are methods that use the principle, and methods that use the principle that there is a correlation between the concentration of a suspension and its light transmission characteristics.

(Problems to be Solved by the Invention) However, these conventional concentration measurement methods tend to measure various disturbance factors at the same time.
Difficult to obtain true pulp consistency.

In the past, there was no suitable measuring method for monitoring pulp density, so it was difficult to obtain treated pulp of a certain quality in the treatment process or to make paper of a certain quality in the papermaking process. It was difficult.

The purpose of the present invention is to solve these conventional problems and to provide a measuring method that can optically, non-contactly, and highly sensitively measure pulp concentration, especially pulp concentration in processes ranging from the mixing process to the papermaking process. Our goal is to provide the following.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the method for measuring the concentration of suspended pulp of the present invention includes a measurement light irradiation device that irradiates measurement light onto a pulp suspension to be measured; An optical measurement unit is constituted by a scattered light intensity measuring device that can measure the measurement light intensity that has passed through the suspension at its front and rear positions, and in the optical measurement unit, By measuring the measurement light intensity at
The pulp density is calculated based on the correspondence with the measured light intensities at the front and rear positions, respectively, and the pulp density calculated based on the respective correspondence is lower than the pulp density of the boundary value obtained from the previous measurement. In the case of high concentration, select the measured light intensity at the front position and use the pulp density calculated from the correspondence with this as the measured value, and in the case of high concentration, select the measured light intensity at the rear position, The gist of this method is to use the pulp density calculated based on this correspondence as the measured value.

(Function) Since there is a correspondence between the measured light intensity that has passed through the suspension and the pulp concentration, by determining this correspondence by measuring various pulp suspensions in advance, it is possible to Pulp density can be calculated from the measured light intensity.

At this time, the correspondence between the measured light intensity and the pulp concentration at the front position is exponential, and the change in the measured light intensity with respect to the change in the pulp concentration, that is, the detection sensitivity of the pulp concentration, is on the side where the concentration is low. is very large, and decreases exponentially as the concentration increases.

On the other hand, the correspondence between the measured light intensity and the pulp concentration at the rear position is linear, and therefore the pulp concentration detection sensitivity hardly changes from the low pulp concentration side to the high pulp concentration side.

Therefore, when the pulp concentration is lower than that, the detection sensitivity is higher at the front position, and when it is higher than that pulp concentration, the detection sensitivity is higher at the rear position than at the front position. There is a boundary value of pulp density. This boundary value can be determined in accordance with the type of pulp, etc., based on the correspondence relationship obtained through the above-mentioned preliminary measurements.

Therefore, if the pulp density calculated from the above correspondence between the front position and the rear position is lower than the above boundary value, the measured light intensity at the front position is selected and calculated based on the correspondence with this. By using the pulp concentration as the measurement value, highly sensitive measurements can be performed.

On the other hand, if the pulp density calculated from the above correspondence relationship between the front position and the rear position is higher than the above boundary value, the measured light intensity at the rear position is selected and calculated based on the correspondence relationship with this. By using the measured pulp concentration as the measured value, highly sensitive measurements can be performed.

The boundary value of the pulp concentration is within the concentration range of the papermaking process from the mixing process to the papermaking process, and therefore the present invention can be applied to such processes.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

Reference numeral 1 is a measurement light irradiation device that irradiates measurement light onto the pulp suspension L to be measured, and 2 is a measurement light intensity measurement device that measures the intensity of the measurement light that has been irradiated and passed through the suspension L. These devices 1 and 2 constitute an optical measurement section A. The measuring device 2 is configured to be able to measure the intensity of the measuring light at the front position a and the rear position b of the suspension L with respect to the irradiation direction of the measuring light, and the suspension L is transparent. The structure is such that measurement is performed by irradiating measurement light while the sensor is housed in the housing section 4.

The minimum measurement position for the measurement light intensity is one point for each of the front position a and the rear position b, but by configuring it so that it can be measured at more points than that, it is possible to perform the measurements described later. The degree of freedom can be increased. To explain a specific example of the latter measuring device 2, the one shown in FIG. A light intensity sensor 3 is disposed at each of the light intensity sensors 3, and each light intensity sensor 3 measures the measurement light intensity at a plurality of positions in each of the positions a and b. As another example, although not shown, a single light intensity sensor is moved circumferentially and the measurement light intensity is measured at consecutive positions or multiple positions from the front position a to the rear position b. You can also do this. Further, the container 4 for storing the pulp suspension L to be measured can be constructed as an independent container as shown in FIG. It can also be configured to measure flowing suspensions.

In the above configuration, the bleached hardwood kraft pulp is now beaten, and the above-mentioned measured light intensity is applied to the pulp suspension with a pulp concentration of 0.5 to 1.5 (%) for each of CSF 217, 416, 437, and 590. The distribution of 0.5, 0.7, 0.9, 1.1, and
The measured light intensity distributions at concentrations of 1.3 and 1.5 (%) are as shown in Figure 3 a, b, c, d, e, and f. Note that the measured light intensity is expressed by the output voltage of the light intensity sensor 3.

From this measurement result, it can be seen that at a constant pulp concentration, a difference occurs in the measurement light intensity due to a change in CSF. For example, as the CSF decreases and beating progresses, the measurement light intensity increases at rear position b. It can be seen that, on the contrary, it is small at the front position a. It is also noteworthy that as the pulp concentration changes, the measured light intensity at the front position a and the measured light intensity at the rear position b significantly change in opposite directions. That is, as the pulp density decreases, the measured light intensity at the front position a increases, and conversely, it decreases at the rear position b.

Next, based on the above measurement results,
For 590 ml of CSF, the relationship between pulp concentration and measured light intensity at front position a (angle 10°) and rear position b (angle 150°) is determined as shown in Figure 4 a, b, and c. , as shown in . In addition, among these figures, a and b correspond to the above-mentioned figure 3 a, b, and the horizontal axis corresponds to the pulp concentration and the vertical axis corresponds to the sensor output voltage.
c, d, e, f, obtained by writing the respective values of front position a (angle 10°) and rear position b (angle 150°), and Figure 4 c is the same as Figure 4 a, b This is a summary of the following.

Figure 4a shows that the pulp density and measured light intensity have an exponential correspondence at the front position a, and Figure 4b shows that at the rear position b there is an almost linear relationship. It can be seen that there is a correspondence relationship.

Next, Fig. 5 shows the curves of Fig. 3 a to f together. From this figure, it can be seen that the range of change in the measured light intensity with respect to the change in the degree of beating, that is, the change in CSF590 to 217 (ml), is It can be seen that the range of change in concentration is narrower than 0.2%.

From these facts, it can be seen that by using the correspondence between the pulp density and the measured light intensity, the pulp density can be determined from the measured light intensity at both the front position a and the rear position b.

In particular, in the present invention, the minimum measurement position for the measurement light intensity is one point each at the front position a and the rear position b, and the correspondence relationship between the pulp concentration and the measurement light intensity at each position is shown in FIG. Since they are different as shown in a, b, and c, it is possible to use these to perform an appropriate concentration measurement according to the pulp concentration as shown below.

That is, as shown in Figure 4 a, b, and c, the correspondence between the pulp concentration and the measured light intensity is an exponential function at the front position a, and a linear correspondence at the rear position b. The change in the measured light intensity with respect to the change in concentration, that is, the detection sensitivity of pulp concentration, is very large on the low concentration side and decreases exponentially as the concentration increases. It can be seen that the detection sensitivity of pulp concentration hardly changes from the low pulp concentration side to the high pulp concentration side.

Therefore, when the pulp concentration is lower than that, the detection sensitivity is higher at the front position, and when it is higher than that pulp concentration, the detection sensitivity is higher at the rear position than at the front position. It can be seen that there exists a boundary value of pulp density. In the case of the example, this boundary value is a value around 1.0% pulp concentration, and this pulp concentration is within the concentration range of the process from the mixing process to the papermaking process. That is, in this embodiment, the sensitivities at the front position a and the rear position b are approximately the same at a pulp concentration of about 1%.

Therefore, if the pulp density calculated from the above correspondence between the front position and the rear position is lower than the above boundary value, the measured light intensity at the front position is selected and calculated based on the correspondence with this. Highly sensitive measurements can be made by measuring pulp density.

On the other hand, if the pulp density calculated from the above correspondence relationship at the front position and the rear position is higher than the above boundary value, the assumed light intensity at the rear position is selected and calculated from the correspondence relationship with this. By using the measured pulp concentration as the measured value, highly sensitive measurements can be performed.

That is, an example of such a measuring method is shown in FIG.
This measurement method, which will be explained with reference to specific pulp concentrations shown in b and c, obtains a measured value through the following selection operation, for example. First, the front position a
If the pulp concentration calculated by the correspondence relationship between the front position b and the rear position b is lower than the above boundary value, for example 0.5% and 0.55%, respectively, the pulp concentration is calculated by the correspondence relationship of the front position a, which has higher sensitivity.
The measured value is 0.5%. Conversely, if the pulse concentrations calculated above are higher than the above boundary values, for example 1.5% and 1.55%, respectively, the pulse concentrations are calculated using the correspondence relationship of the more sensitive rear position b.
The measured value is 1.55%. On the other hand, if the pulp concentration calculated above is near the boundary value, for example around 1.0%, one of the calculated values is taken as the measured value.

In addition, in the above selection operation, the calculated pulp concentration is compared with the established value to make a decision, but the value corresponding to this pulse concentration, that is, the value of the sensor output voltage itself, is compared with the set value. It is also possible to judge.

As mentioned in the prior art section, since the pulp concentration in the defibration, beating and mixing steps is 3% or more, the above-mentioned selection operation is not necessarily necessary, but in the steps from the mixing step to the paper making step. ,3
Since the pulp concentration of ~6% is diluted in multiple stages to a concentration of about 0.1 to 0.8%, performing the above-mentioned selection operation to measure the pulp concentration at each stage is essential for highly sensitive concentration measurement. This is a necessary condition.

Next, the measurement error will be considered as follows.

Figure 6 shows the relationship between the pulp concentration and the measured light intensity at rear position b (angle 150°) by adding the relationship between the pulp concentration and the measured light intensity to a sample of 590 (ml) CSF, and all the remaining CSF values mentioned above, i.e.
Samples of 437, 416, and 217 (ml) are also shown. From this figure, when determining the difference in pulp density due to the difference in degree of beating at the same measurement light intensity, for example, when the pulp density is around 1%, CSF590~
In the range of 217 (ml), it is about 0.1%,
If the intermediate value is used as a reference, it will be approximately ±0.05%.
This results in a measurement error, but the value becomes smaller as the range of beating degree becomes narrower, and therefore, more accurate measurement can be performed. From the above, the correspondence between the measured light intensity and the pulp density can be determined by measuring various pulp suspensions in advance, and by performing the selection operation described above, the pulp density can be measured with high precision from the measured light intensity. I know what I'm getting. The above calculation operations (including selection operations)
This can be easily performed by storing the correspondence relationship as a data table or a function formula in a storage device in a microcomputer or the like.

(Effects of the Invention) As described above, the present invention includes a fixed light irradiation device that irradiates measuring light onto a pulp suspension to be measured, and a measuring light irradiation device that irradiates measuring light onto a pulp suspension to be measured, and a measuring light irradiation device that irradiates measuring light intensity through the suspension at each of its front and rear positions.
An optical measuring unit is constructed from a scattering light measuring device that measures at more than one point, and the optical measuring unit measures the measured light intensity at the front and rear positions and the pulp density. When calculating the pulp density based on the correspondence relationship, the measurement position of the measurement light intensity used to derive the measured value by the above calculation is selected as the front or rear depending on the level of the pulp density. This method has the advantage of being able to perform appropriate measurements depending on the situation, and that it is possible to measure pulp concentration with high sensitivity and high accuracy.
INDUSTRIAL APPLICABILITY The present invention is effective for measuring pulp concentration during the papermaking process, particularly from the mixing process to the papermaking process.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams showing the measurement system of the method of the present invention, Figures 3a, b, c, d, e, and f are diagrams of the optical characteristics measurement results of LBKP using the measurement system of the present invention, Figures 4a and b are explanatory diagrams showing the correspondence between the pulp density and the measured light intensity at the front and rear positions, respectively, based on the measurement results diagram in Figure 3, and Figure 4c
is an explanatory diagram that collectively shows the curves in Figures 4 a and b, Figure 5 is an explanatory diagram that collectively shows the curves in Figure 3 a, b, c, d, e, and f, and Figure 6 is an explanatory diagram that collectively shows the curves in Figure 4 a, b, c, d, e, and f. FIG. 3 is an explanatory diagram showing the curve of sample b plus curves of samples with other freeness degrees. Symbols A: Optical measurement section, L: Pulp suspension, 1: Measurement light irradiation device, 2: Scattered light intensity measuring device, 3: Light intensity sensor, 4: Storage section.

Claims (1)

[Claims] 1. A measurement light irradiation device that irradiates measurement light onto the pulp suspension to be measured, and a scattered light intensity measurement device that can measure the measurement light intensity that has passed through the suspension at positions in front and rear of the measurement light intensity measurement device. A measurement section is configured, and the optical measurement section measures the measurement light intensity at the front and rear positions, and determines the pulp density based on the correspondence with the measurement light intensity at the front and rear positions, respectively. If the pulp density calculated from each correspondence relationship is lower than the pulp density of the boundary value obtained from the previous measurement, the measured light intensity at the front position is selected and the correspondence is made with this. The pulp density calculated from the relationship is used as the measured value, and in the case of high density, the measured light intensity at the rear position is selected, and the pulp density calculated from the corresponding relationship with this is used as the measured value. A method for measuring the concentration of suspended pulp.