JPH059883A - Control of cleaning degree of unbleached pulp - Google Patents

Abstract

PURPOSE:To control cleaning degree of pulp so as not to produce pitch in the following processes such as screening process, multi-stage beaching process, papermaking process, etc., by measuring transparency of filtrate from the final step of pulp cleaning. CONSTITUTION:Transparency of filtrate discharged from the final step of a cleaning process of unbleached kraft pulp or an oxygen bleaching process is measured by a turbidmeter, a colorimeter, a photoelectric photometer and is adjusted to 30-100% by using warm water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning degree control method for unbleached kraft pulp. To elaborate further,
TECHNICAL FIELD The present invention relates to a cleaning degree control method for suppressing impurities such as organic substances and inorganic substances accompanying a pulp introduced into a chlorine stage of a multi-stage bleaching step below a certain level and suppressing pitch generation of bleached pulp.

[0002]

BACKGROUND ART Wood chips are kraft cooked with a kraft cooking liquor to efficiently remove and recover water-soluble substances from cooked pulp. It is extremely important in reducing the emission of pollution load on the drainage system.

If the unbleached pulp is not sufficiently washed,
In addition to the above, it causes foaming troubles and pitch troubles in the multi-stage bleaching process, the selection process, and the papermaking process, which causes unstable operation, and the pitch itself exhibits brown or black color, and is mixed in the final product paper as foreign matter. It significantly reduces the quality of the paper.

In order to sufficiently wash the unbleached pulp,
A multi-stage countercurrent cleaning system is adopted, which includes continuous digester pot cleaning, continuous diffuser cleaning, and drum cleaning.

The pulp obtained after the wood chips are digested with a continuous digester is subjected to high heat countercurrent washing in a kettle, or in a digester having no high heat washing zone, without pressure washing in the kettle, pressure type and / or Atmospheric pressure type diffusion washer is used to replace and wash under closed pulp concentration of 10%, and then plastic pieces, metal pieces, coarse foreign matters such as stones mixed in pulp, undigested knots, binding fibers, sand and coarse pitch It is sent to a selective process consisting of a knotter, a flat screen, a centrifugal screen, an overflow screen, and various dehydrators for removing fine foreign matters and processed. The pulp that has been carefully selected is dehydrated with a drum filter to a pulp concentration of 10%,
It is delignified by a known oxygen bleaching process using oxygen and alkali with or without passing through a pulp storage tank, and finally it is again deliquored by a drum filter to a pulp concentration of about 10% and stored in a high concentration tank. If necessary, it is sent to a multi-stage bleaching process.

In some plants, pulp is passed through a knotter and then deliquored by a drum filter, immediately subjected to oxygen bleaching treatment using oxygen and alkali, washed again by a drum filter and deliquored, and then passed through a pulp storage tank or Without being sent, it is sent to the selective process, treated and then deliquored, sent to a high-concentration tank, and sent from there to a multi-stage bleaching process for use. Thus, even with the difference that the pulp selection is done before or after oxygen bleaching,
Alternatively, even if oxygen bleaching is not performed, good or bad cleaning of the pulp is determined by the degree of dirt accompanying the pulp brought into the multistage bleaching process, which is the final stage of the cleaning.
That is, the outlet pulp of the diffusion washer or an additional one stage of the dewatering stage and its filtrate, and when oxygen bleaching is performed, the pulp of the outlet of the one stage of the dewatering stage performed after oxygen bleaching and the stain of the filtrate It is necessary to monitor the degree.

Thus, one indicator of the quality of pulp cleaning is that it is composed of organic substances and inorganic substances that flow into the cleaning system together with the unbleached pulp, and the substances generally called solid substances are not separated to the extent that they adhere to the pulp. It is expressed by a numerical value indicating whether or not the pulp is deliquored, and the liquor separated from the pulp is concretely analyzed. Although indirectly, the filtrate also has a tendency almost similar to that of the liquid contained in the pulp, so that the numerical value can be obtained by concretely analyzing the filtrate at various places.

It is said that the smaller these values are, the more sufficient the cleaning is performed. However, if the values are high, the amount of hot water used in the final stage is increased to perform the cleaning. To be strengthened.

As a direct and simple method for obtaining such a numerical value, COD (chemical oxygen demand by the chromium method or the permanganate method) of the liquid adhering to the pulp discharged from the final stage of the washing system is used. , Soda (or sodium)
It is generally practiced to measure the content and the like, and determine the degree of cleaning from the ratio of entering and leaving these cleaning systems.
However, these measurements are usually made with pulp concentrations of 10-
The pulp dehydrated to 15% is manually collected, separated into pulp and liquid, and the separated liquid is analyzed to obtain the result, which makes it difficult for the operator to collect the sample and the result is revealed. It has a drawback that it takes a long time to complete.

On the other hand, it flows into the cleaning system together with the pulp,
A method of estimating the cleaning degree indirectly by continuously measuring the electric conductivity, conductivity, etc. of the filtrate removed in the cleaning system is also commonly used. That is, as a method for easily controlling the degree of washing, the electric conductivity of the filtrate in each washing stage, especially the washing filtrate from the final stage of washing, is continuously measured, and this value and atomic absorption analysis, flame photometric analysis are performed in advance. Etc. or the organic matter content is obtained indirectly by COD analysis, total carbon analysis, etc., and the organic matter content is indirectly obtained from the calibration curve obtained by obtaining the correlation between the soda content or organic matter content and the electric conductivity value. There is known a method of determining the amount or soda content and further calculating the degree of cleaning, or a method of directly judging the quality of cleaning from the vertical fluctuation of the electric conductivity value of the filtrate and controlling the relative degree of cleaning. ..

However, since various kinds of organic substances and inorganic substances are present in the filtrate, there are also fluctuation factors such as the type of material, the Kappa number of pulp, the extraction ratio during washing, and the amount of hot water used. It was not enough to control the cleanliness of the washed pulp by the conductivity alone. In addition, it is difficult to control the occurrence of pitch troubles that occur after the pulp is treated in a multi-stage bleaching process, even if the pulp whose degree of cleaning is controlled in this way is used.

[0012]

DISCLOSURE OF THE INVENTION In view of the above situation, the inventors of the present invention have earnestly studied a method for controlling the degree of washing of unbleached pulp, and as a result, the filtrate obtained from the final stage of each washing is measured with a turbidimeter and a ratio. The value of the transparency of the separated liquid measured using either a color meter or a photoelectric photometer has a very good correlation with the degree of cleaning of the pulp, especially the amount of pitch component accompanying the pulp during multi-stage bleaching. The present invention has been completed and the present invention has been completed.

Accordingly, an object of the present invention is to provide a method for controlling the degree of cleansing of unbleached and oxygen bleached pulp, which can easily and quickly control the degree of cleaning, and which can reduce the pitch component accompanying the pulp during multi-stage bleaching of pulp. To provide.

[0014]

DISCLOSURE OF THE INVENTION The present invention provides a turbidimeter, a colorimeter, a photoelectric photometer, etc. for measuring the optical transparency of a filtrate discharged from the final stage of the washing step of unbleached kraft pulp or the oxygen bleaching step. It is a method for controlling the degree of cleansing of unbleached kraft pulp, which is characterized by setting the transparency in the range of 30 to 100% using any of the above.

Any of known turbidimeters, photoelectric colorimeters, photoelectric photometers and the like, which are known and commercially available, are preferably used for measuring the transparency used for the present invention.

In the present invention, when the pulp discharged from the final stage of each washing or the unbleached pulp is continuously washed with oxygen after bleaching, the concentration of pulp discharged from the dehydrator after the oxygen bleaching treatment is 10 to 15 %, Dehydrated pulp may be collected, and the liquid contained in the pulp may be squeezed to be separated to obtain the liquid transparency.

However, according to the present invention, the filtrate discharged from the final stage of each washing or the filtrate removed after the oxygen bleaching is completed in the case where oxygen bleaching is performed, the turbidimeter, the photoelectric colorimeter, the photoelectric converter It can be preferably carried out by measuring the transparency using one of a photometer and the like. Such a filtrate can be analyzed in an extremely short time because a pipe can be provided in an analysis room near the instrument room to send the filtrate without the operator having to go to the site to collect the filtrate for each analysis.

In the present invention, a pulp liquid (pulp concentration 3 to 5) introduced into the chlorine tower when the pulp is bleached in multiple stages is used.
%), The separated liquid can be taken out with a strainer provided with a wire net, and the optical transparency of the liquid can be measured.

FIG. 1 is a photo-colorimeter (PHOTOMRTOR) showing the washing and dewatering filtrate after oxygen bleaching in the production of bleached softwood kraft pulp.
IC COLORIMETER MODEL AE-11, TOKYO ERMA OPTICAL WO
RKSLTD.) Was used to measure the transparency at a wavelength of 660 nm, and this value and hematometer (manufactured by Nippon Kogaku Co., Ltd.)
2 is a graph showing the relationship with the amount of colloidal pitch contained in pulp measured with an optical microscope (1000 times) using a.

Strictly speaking, the amount contained in the colloidal pitch pulp has various factors, and although there are variations, in the case of 35 × 10 7 pieces / cm ³ or more, after the papermaking process, particularly after beating with a refiner, Pitch is generated and adheres to chests, piping and wet presses of paper machines, felts, wires, etc., the frequency of removing the pitch by stopping the operation of the paper machine increases, and It has been found from experience that black foreign matter due to the pitch component is mixed in as impurities.

Although it is not possible to unequivocally determine the value of the transparency by any one of the above liquid turbidity meter, photoelectric colorimeter, photoelectric photometer, etc., when oxygen treatment is performed, it is 30 It is adjusted by increasing or decreasing the amount of warm water used for washing so as to be maintained in the range of ˜70%, preferably 40 to 60%, and in the range of 35 to 80%, preferably 50 to 70% for hardwood pulp.

If the amount is less than these ranges, not only the pitch trouble in the process but also the increase of the black foreign matter due to the pitch on the paper product is not noticeable, and it is desired to obtain the high transparency beyond the range. If so, it is necessary to significantly increase the amount of hot water used for cleaning the oxygen stage, and eventually the amount of liquid sent to the evaporator increases and the load on the evaporator increases, or in some cases evaporation processing becomes impossible. Since there is a limit on the amount of hot water used due to the liquid balance, it is not economically feasible to obtain a transparency that exceeds these values.

As described above, the method of the present invention can be carried out with the liquid of the chlorine stage inlet material of the multi-stage bleaching, but when the unbleached pulp or the oxygen treated pulp is diluted with the chlorine stage white water which is circulated, a considerable coloring substance is produced. The value of the transparency is 70
As high as ~ 95%, the pitch content in the pulp is reduced in proportion to the increase.

On the other hand, when the method of the present invention is applied in the final stage of washing before oxygen treatment, the transparency is adjusted in the range of 20 to 50%, and if it is less than 20%, it is subjected to multi-stage bleaching to make a paper product. However, it is not suitable due to the occurrence of pitch in the process and the inclusion of black foreign matter in the paper product. In this case, if the final stage of cleaning or oxygen bleaching is performed, it is necessary to increase the amount of warm water used in the cleaning / dehydration stage after oxygen treatment to enhance cleaning, while increasing the transparency to 50% or more As described above, the amount of hot water used increases and the burden on the evaporator also increases, which is not economically feasible, which is not suitable.

When the stains of each washing are controlled by the transparency according to the method of the present invention, it is possible to suppress the generation of pitch in the steps after the multi-stage bleaching, reduce the contamination of foreign matters into the paper product, and unnecessary hot water. Since the use of can be efficiently avoided, the economic effect is great.

[0026]

The present invention will be described in more detail with reference to the following examples, but of course the present invention is not limited thereto.

Example 1 Domestic hardwood chips and kraft white liquor were used to cook in a 650T / D Kamiya continuous digester to produce unbleached kraft pulp with a Kappa number of 19.8, followed by the removal of unbleached pulp in an oxygen bleaching facility. Add 1.8% of oxidized white liquor as 2.0% oxygen and alkali to dry weight, reaction temperature 100 ℃, reaction time 30 minutes,
Oxygen bleaching was performed at 650 T / D with a pulp concentration of 10%.

Pulp having a Kappa number of 10.2 after the oxygen bleaching treatment was heated in a single-stage drum filter with an amount of warm water of 5.5 m ³ /
It is washed and dehydrated in an extremely dry pulp ton, and the transparency of the filtrate at this time is measured by a photoelectric colorimeter (PHOTOMETORIC COLORIMETER MODEL AE
-11, TOKYOERMA OPTICAL WORKS LTD.)
The measurement was performed at 60 nm every hour, and the measurement was performed for 48 hours. At this time, the transparency is in the range of 54 to 66%, and the average value is 60.3% (n
= 47). This pulp is further CE / OHD
A pulp having a whiteness of 85% was produced by the usual bleaching sequence of the above, and a high quality paper of 60 g / m ² was produced in the paper machine using this pulp, and the black foreign matter of the paper was measured. The measurement result of the black foreign matter was 1.0 mm ² / m ² (n = 15), which was a level sufficient for practical use. No adhesion of pitch was observed in the papermaking process.

The test methods used in the examples are as follows.

(1) Measurement of transparency by photoelectric colorimeter 10 ml of pure water was put in a glass test tube of 12 mm diameter, put in a sample tank of the photoelectric photometer, and the adjustment dial was turned at a wavelength of 660 nm to 100% of the meter. To match. Next, collect 10 ml of sample in another similar test tube, put it in the sample tank,
Read the shake of the meter.

(2) Method for measuring black foreign matter on paper 10 sheets of 200 cm ² in size are prepared as samples. Place the test piece on a white paperboard, illuminate it with a 50W matte light bulb from a position 1.2m away, and compare the dust to 0.04mm ² or more by comparing it with the foreign matter measurement chart used in JIS P 8208. Record the black foreign matter by area. The test is done on both sides of the paper and recorded in the same way. The area of each measured black foreign matter is tabulated and displayed as the area of black foreign matter per 1 m ² (mm ² / m ² ).

Example 2 Fine paper was produced in the same manner as in Example 1 except that the amount of warm water used was 6.0 m ³ / ton of absolutely dry pulp in a single-stage drum filter for washing and dehydrating pulp having a Kappa number of 10.4 after oxygen bleaching. did. The transparency of the filtrate from the drum filter is
It was in the range of 65 to 76%, and the average value was 70.1% (n = 45). The measurement result of black foreign matter on paper is 0.5 mm ² / m ² (n = 1
In 5), it was a level that could be practically used, and no pitch was observed in the papermaking process.

Comparative Example 1 Fine paper was produced in the same manner as in Example 1 except that the amount of hot water used was 4.5 m ³ / ton of absolutely dry pulp in a one-stage drum filter for washing and dehydrating pulp having a Kappa number of 10.1 after oxygen bleaching. did. The transparency of the filtrate from the drum filter is
It was in the range of 24-29%, and the average value was 26.9% (n = 46). The measurement result of black foreign matter on paper is 2.0 mm ² / m ² (n = 1
In 5), there was a lot of black foreign matter, which was a level that could not be put to practical use. At the time of papermaking, adhesion of pitch was observed on the wet press and felt.

Example 3 Using a softwood chip consisting of 20% Douglas fir and 80% domestic pine and kraft white liquor, a Kappa number of 28.3 by MCC (modified) kraft cooking method in 800T / D Kamiya type 2 vessel liquid phase continuous digester. Of unbleached pulp,
Then, in the oxygen bleaching facility, 2.5% of oxygen and 2.3% of oxidized white liquor were added to the dry weight of unbleached kraft pulp as alkali, reaction temperature 100 ° C, reaction time 30 minutes, pulp concentration 10%, 800T / Oxygen bleaching was performed at D.

Pulp with a Kappa number of 13.5 after oxygen bleaching was washed and dewatered in a single-stage drum filter with 5.5 m ³ of hot water used / ton of dry pulp, and the transparency of the filtrate at this time was the same as that of Example 1. The measurement was performed every hour using a meter, and the measurement was performed for 48 hours. The transparency at this time is in the range of 36-45%,
The average value was 40.2% (n = 46).

The oxygen bleached pulp is then C / DE-O-
Pulp with 85% whiteness was obtained by conventional bleaching of HD. A basis weight of 60 g / m ² in a paper machine using this pulp
The single-sided glossy paper of No. 1 was manufactured and the black foreign matter on the surface of the paper was measured. The measurement result of black foreign matter on paper is 0.5mm ² / m ² (n = 15),
It was a level that could be put to practical use. No occurrence of pitch was observed in the papermaking process.

Example 4 A single-glossy paper was produced in the same manner as in Example 3 except that the amount of warm water used was 6.0 m ³ / ton of absolutely dry pulp in a one-stage drum filter for washing and dehydrating pulp having a Kappa number of 13.2 after oxygen bleaching. did. The transparency of the filtrate from the drum filter is 47.
The average value was 50.1% (n = 46). The measurement result of black foreign matter on paper is 0.4 mm ² / m ² (n = 1
In 5), it was at a level that was sufficiently practical. No occurrence of pitch was observed in the papermaking process.

Comparative Example 2 A single-glossy paper was produced in the same manner as in Example 3 except that the amount of warm water used in the one-stage drum filter for washing and dehydrating the pulp having a Kappa number of 13.8 after oxygen bleaching was 4.5 m ³ / ton of dry pulp. did. The transparency of the filtrate from the drum filter is 18
The average value was 26.3% (n = 47). The measurement result of black foreign matter on the paper is 0.8 mm ² / m ² (n = 1
In 5), there was a lot of black foreign matter, which was a level that could not be put to practical use. Adhesion of pitch was observed on the wet press and felt during papermaking.

The results obtained in Examples 1 to 2 are shown in Table 1.
Shown in.

[0040]

[Table 1]

[0041]

According to the method of the present invention, the amount of pitch components contained in the filtrate can be determined by measuring the transparency of the washing filtrate. It is possible to maintain a high degree of cleaning, that is, it is possible to suppress the generation of pitch in the multi-stage bleaching process and the papermaking process using bleached pulp, and to prevent the inclusion of black foreign matter due to the pitch in the paper product.

[Brief description of drawings]

FIG. 1 is a perspective view of a cleaning filtrate after oxygen bleaching during the production of bleached softwood kraft pulp, which is contained in the pulp measured by a photoelectric colorimeter and an optical microscope using a hemastometer. It is a graph which shows the relationship with the colloidal pitch amount.

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[Procedure amendment]

[Submission date] August 29, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0019

[Correction method] Change

[Correction content]

[0019] Figure 1 is softwood bleached kraft pulp production during oxygen bleaching treatment after washing draining filtrate photoelectric colorimeter (photom E TOR
IC COLORIMETER MODEL AE-11, TOKYO ERMA OPTICAL WOR
KSLTD.) Was used to measure the transparency at a wavelength of 660 nm, and this value and hematometer (manufactured by Nippon Kogaku Co., Ltd.)
2 is a graph showing the relationship with the amount of colloidal pitch contained in pulp measured with an optical microscope (1000 times) using a.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

Pulp having a Kappa number of 10.2 after the oxygen bleaching treatment was heated in a single-stage drum filter with an amount of warm water of 5.5 m ³ /
It is washed and dehydrated with a ton of dry pulp, and the transparency of the filtrate at this time is measured by a photoelectric colorimeter (PHOTOMETORIC COLORIMETER MODEL AE-11, T
OKYO ERMAOPTICAL WORKS LTD.) Was used for measurement at a wavelength of 660 nm every hour and for 48 hours. The transparency at this time is in the range of 54-66%, and the average value is 60.3% (n = 47)
Met. This pulp was further subjected to a normal bleaching sequence of C / E / O-H-D to produce a pulp having a whiteness of 85%,
Using this pulp, a high-quality paper of 60 g / m ² was produced in a paper machine, and the measurement result of black foreign matter on the paper was 1.0 mm ² / m.
^{The value was 2} (n = 15), which was a level that could withstand practical use. No adhesion of pitch was observed in the papermaking process.

Front Page Continuation (72) Inventor Koji Sakaguchi 1 Oji-cho, Kasugai-shi, Aichi Oji Paper Co., Ltd. Kasugai Mill

Claims (1)

Claims: 1. The transparency of the filtrate discharged from the final stage of the washing step of unbleached kraft pulp or the oxygen bleaching step is either a turbidimeter, a colorimeter, a photoelectric photometer, or the like. Measured using
A method for controlling the degree of cleansing of unbleached pulp, which has a transparency of 30 to 100%.