JP5641007B2 - Method for controlling the amount of internally added chemicals and method for measuring the concentration of suspended substances - Google Patents

Description

  The present invention relates to a method for controlling the amount of internally added chemicals and a method for measuring the concentration of suspending substances in a papermaking process for producing paper from pulp slurry.

  In general, when making paper, the pulp is subjected to processes such as bleaching, beating, mixing, and dilution, and finally prepared into a pulp slurry state, and then sent to a wire part of a paper machine to be dehydrated. When the pulp slurry is dewatered on the wire, the water filtered under the wire is usually called white water. This white water circulates in the papermaking system and raw material system, and is reused as a recovered raw material or as dilution water. However, fine fibers and fillers not captured by the wire in white water, eluate from pulp, and bleaching process Contains the residues of used chemicals.

  When the yield of the raw material in the wire part of the paper machine decreases, the turbidity of white water in the white water pit that collects white water that has passed without being captured by the wire increases. Here, the turbidity of white water mainly depends on the amount of dispersion of insoluble suspension (SS), that is, pulp fibers having a length of 20 μm or more. When the turbidity of white water increases, the fluidity decreases in the piping through which the white water flows, and slime soot is easily generated. When this grows up and adheres to the inside of the white water silo or pipe and peels off, a product defect or a hole defect occurs.

  In this regard, in order to make the yield of insoluble suspension (SS) constant, the concentration of white water generated in the wire part of the paper machine is detected, and the detected white water concentration is operated under a predetermined operating condition. If the white water concentration in the stable state is determined to be the target concentration when it is determined that the stable state has elapsed after the elapse of a predetermined time from the start of the process, the yield improver is set so that the concentration of white water detected thereafter becomes the target concentration There has been proposed a technique for adjusting the amount of addition (see Patent Document 1).

  On the other hand, as the suspending substance contained in the pulp slurry, in addition to the insoluble suspension (SS), fine ash such as calcium carbonate and talc added as a filler (suspension of less than 20 μm in length) Substance). When the yield of ash increases too much, a large amount of ash is incorporated into the product, and the ratio of ash adhering to the surface of the dryer cylinder from the paper surface increases in the dryer part of the next process. As a result, the surface of the dryer cylinder is contaminated in a short time, resulting in product contamination and unevenness in the degree of drying. In addition, the operation rate may be lowered by stopping the paper machine by cleaning the dryer cylinder. Therefore, it is necessary to make the yield constant with respect to the ash as well as the insoluble suspension (SS), but conventionally, there is no method for measuring the ash and it has been difficult to control.

Japanese Patent Laid-Open No. 10-325092

  As described above, the suspending substance contained in the raw material contains ash in addition to the insoluble suspension (SS), so depending on the concentration of white water, that is, the concentration of the insoluble suspension (SS). There is a problem that the yield of ash cannot be controlled by the method of adjusting the amount of internal chemicals added such as a yield improver. In addition, paper mills produce products by switching between multiple brands in a short time, and the optimum yield of ash varies from one brand to another, so quality control is not easy and promptly responds to changes in brands to be manufactured. There is a problem that it cannot be followed.

  The present invention has been made in view of the above circumstances, grasps the concentration of each of the insoluble suspension (SS) and ash, adjusts each yield appropriately according to each product brand, product quality An object of the present invention is to provide a method for controlling the amount of internally added chemicals and a method for measuring the concentration of suspending substances that can stabilize and improve productivity.

  The present inventors have found that the turbidity of white water at the time of stirring correlates with the concentration of the insoluble suspension, and the turbidity of white water at the time of stationary correlates with the concentration of ash, which led to the completion of the present invention. . Specifically, the present invention provides the following.

  (1) A method for controlling the amount of internal additive added in a papermaking process for producing paper from pulp slurry, the step of collecting white water generated in the papermaking process under a predetermined operating condition, and the collected white water Measuring the turbidity as an insoluble suspension equivalent turbidity during stirring, measuring the turbidity of the collected white water as an ash equivalent turbidity at rest, and measuring the insoluble suspension equivalent turbidity And adjusting the addition amount of the internal additive based on the ash equivalent turbidity.

  (2) calculating an insoluble suspension concentration of the collected white water based on the turbidity equivalent to the insoluble suspension measured in the collected white water; and the ash content measured in the collected white water Calculating the ash concentration of the collected white water based on the corresponding turbidity, and further comprising (1).

  (3) The method further includes a step of performing chemical injection control of an internally added chemical capable of adjusting the insoluble suspension yield and the ash content yield in the papermaking process based on the calculated insoluble suspension concentration and the ash content concentration (2). The method described in 1.

  (4) adjusting the amount of the internal additive added in a feedback manner so that the calculated insoluble suspension concentration becomes the target insoluble suspension concentration and the ash concentration becomes the target ash concentration. Furthermore, the method as described in (3).

  (5) A method for measuring the concentration of a suspending substance in a papermaking process for producing paper from a pulp slurry, the step of collecting white water produced in the papermaking process, and the turbidity of the collected white water in an insoluble suspension. A step of measuring as turbidity equivalent turbidity at the time of stirring; a step of calculating an insoluble suspension concentration of the collected white water based on the measured insoluble suspension equivalent turbidity; and a turbidity of the collected white water A method for measuring the concentration of a suspending substance, comprising: measuring the degree of ash equivalent turbidity at rest, and calculating the ash concentration of the collected white water based on the measured ash equivalent turbidity.

  According to the present invention, the insoluble suspension (SS) concentration and the ash concentration are grasped respectively, the yields of the insoluble suspension (SS) and the ash are appropriately adjusted according to each product brand, and the product quality Stabilization and chemical cost reduction can be performed. Moreover, it is possible to measure the turbidity of the collected white water under conditions different from those at the time of stirring and at rest by effectively using one turbidity unit. In this case, the concentration of insoluble suspension (SS) and The ash content concentration can be properly grasped, and the practical effects such as simplification of the configuration of the measurement system can be achieved.

It is a schematic diagram which shows an example of the paper manufacturing process to which the addition amount control method of the internal medicine which concerns on embodiment of this invention is applied. It is a schematic diagram which shows the outline | summary of the chemical injection system integrated in the papermaking process shown in FIG. It is a figure which shows the rough process sequence of the addition amount control method of the internal medicine which concerns on embodiment of this invention. It is a figure which shows the correlation of the turbidity at the time of stirring by the addition amount control method of the internal medicine which concerns on embodiment of this invention, and the concentration of insoluble suspension (SS) using an analytical instrument. It is a figure which shows the correlation of the turbidity at rest by the addition amount control method of the internal medicine which concerns on embodiment of this invention, and the ash content density | concentration using an analytical instrument. Correlation between Insoluble Suspension (SS) Equivalent Turbidity and Insoluble Suspension (SS) Yield Rate, and Ash Equivalent Turbidity and Ash Content Yield by the Addition Control Method of Internal Additives According to an Embodiment of the Present Invention It is a figure which shows the correlation of a rate. It is a figure which shows the correlation of ash content equivalent turbidity in each product brand by the amount control method of the internal additive which concerns on embodiment of this invention, and ash concentration.

  Hereinafter, although embodiment of this invention is described, this invention is not specifically limited to this.

  FIG. 1 is a schematic diagram of a paper making process 10 according to an example in which the method according to the present invention is implemented. The papermaking process 10 includes a raw material system 40, a preparation / papermaking system 50, a recovery system 60, and a chemical injection system 20.

  The raw material system 40 includes tanks 41, 42, 43 and 44 for storing papermaking raw materials, a mixing chest 47, a machine chest 48, and a seed box 49. On the other hand, the preparation / papermaking system 50 includes a fan pump 51 for sending pulp slurry supplied from the raw material system 40, a screen 52, a cleaner 53, an inlet 54, a wire part 55, and a press part 56. Consists of including. The preparation / papermaking system 50 is provided with a white water silo 58 for storing white water, which will be described later. The recovery system 60 includes a seal pit 61, a recovery device 62, a recovered water tank 63, a disaggregation water pump 64, and a concentrated water pump 65.

  The chemical injection system 20 includes a turbidity measurement unit 30 that measures the turbidity of white water, an arithmetic processing unit 21 that controls the amount of internal chemicals added to the pulp slurry, internal chemical tanks 22a and 22b, Medicine injection pumps 23a and 23b.

  The raw material system 40 includes a chemical pulp tank 41, a recycled pulp tank 42, a broke tank 43, and a recovered raw material tank 44. The chemical pulp tank 41 includes softwood bleached kraft pulp (LBKP), hardwood bleached kraft pulp (NBKP), and the like. Chemical pulp and recycled pulp tank 42 are recycled pulp made from waste paper such as deinked pulp (DIP) and corrugated cardboard transported from the deinking system by used paper pulper 45, and broke tank 43 is slurried by broke pulper 46. The recovered pulp / recovered raw material tank 44 accommodates the pulp obtained by solid-liquid separation of white water by the recovery device 62 as a paper raw material.

  An apparatus for producing and supplying a paper raw material may be provided upstream of the chemical pulp tank 41. That is, upstream of the chemical pulp tank 41, a digester for digesting wood chips, a device for bleaching pulp, a screen for removing foreign matter, and the like may be provided. The broke tank 43 is supplied with broke pulp generated after the press part 56.

  The waste paper pulper 45 and the broke pulper 46 are supplied from the disaggregation water pump 64 with disaggregation water for disaggregating the waste paper and broke. The recycled pulp, broke pulp, chemical pulp, and recovered raw material after being separated by the pulpers 45 and 46 are combined with concentrated water for adjusting the concentration from the concentrated water pump 65 and stored in each tank. As the disaggregation water and concentrated water, in this embodiment, recovered white water is used. However, untreated filtered white water, fresh water, filtrate or squeezed water obtained by dehydrating the slurry of the raw material system 40, surplus in other processes Water may be used.

  The pulp accommodated in the chemical pulp tank 41, the recycled pulp tank 42, the broke tank 43 and the recovered raw material tank 44 is supplied to the mixing chest 47 at an appropriate ratio according to the brand to be manufactured. Mixed. The mixed pulp is transferred to the seed box 49 after the papermaking chemicals are added by the machine chest 48.

  The pulp accommodated in the seed box 49 is sequentially supplied to the screen 52 and the cleaner 53 by the fan pump 51 of the preparation / papermaking system 50 together with the filtered white water from the white water silo 58 to be described later, where foreign matter is removed. Thereafter, it is supplied to the inlet 54. The inlet 54 supplies pulp to the wire of the wire part 55 at an appropriate concentration, speed, and angle. The supplied pulp is dewatered by the wire part 55 and the press part 56, and is produced into paper through a reel winder (not shown).

  The water dehydrated from the pulp by the wire part 55 and the press part 56 is received as white water in the white water pits 57 arranged below the wire part 55 and the press part 56. White water received in the white water pit 57 is introduced into the white water silo 58 through the conduit 59 and stored there. Part of the white water stored in the white water silo 58 is supplied to the fan pump 51 and the rest is supplied to the seal pit 61. The white water supplied to the fan pump 51 dilutes the pulp slurry in the preparation / papermaking system 50. The white water supplied to the seal pit 61 is transferred to the recovery device 62, filtered and solid-liquid separated by the recovery device 62, and the filtrate is recovered to the recovery water tank 63.

  Here, the pulp slurry supplied to the wire part 55 from the inlet 54 is an insoluble suspension (SS) as a suspending substance, that is, calcium carbonate added as a filler in addition to pulp fibers having a length of 20 μm or more. It contains fine ash (suspension material with a length of less than 20 μm) such as talc and talc. These insoluble suspension (SS) and ash are each captured by the wire part 55, and the remainder is filtered under the wire and dispersed in white water. Accordingly, white water is an insoluble suspension (SS) as a suspending substance, that is, pulp fibers having a length of 20 μm or more, and fine ash such as calcium carbonate and talc added as a filler (less than 20 μm in length). Of suspended substances).

  Hereinafter, the drug injection system 20 will be described.

  Downstream of the fan pump 51, the internal medicine tank 22a containing the internal medicine A is supplied via the chemical injection pump 23a, and the internal medicine tank 22b containing the internal medicine B is supplied via the chemical injection pump 23b. Each is connected. The medicinal pumps 23 a and 23 b are electrically connected to the output side of the arithmetic processing unit 21 that constitutes a control unit described later, and the turbidity measuring unit 30 is electrically connected to the input side of the arithmetic processing unit 21. ing.

  The turbidity measurement unit 30 collects white water from the conduit 59 connected to the white water pit 57, measures the turbidity of white water, and transmits the measurement result to the arithmetic processing unit 21. The arithmetic processing unit 21 operates the chemical injection pumps 23a and 23b in accordance with the transmitted measurement results, thereby injecting the internal additive chemical A into the internal slurry tank 22a and the internal additive chemical tank into the pulp slurry. The injection amount of the internal additive B in 22b is controlled.

In the papermaking process, a yield improver, a coagulant, a paper strength agent and the like are used as internal additives. When these addition amounts are changed, the yield of the suspending substance in the wire part 55 changes. That is, for example, when the addition amount of the yield improver is increased, the yield of the insoluble suspension (SS) is improved, and the yield of ash is slightly improved. On the other hand, when the addition amount of the coagulant is increased, both the yield of insoluble suspension (SS) and the yield of ash are improved. (However, excessive use of the coagulant deteriorates the texture of the product.) In addition, when the amount of the paper strength agent is increased, both the yield of insoluble suspension (SS) and the yield of ash are slightly improved.
The internal additive A is appropriately selected from agents capable of adjusting the yield of the insoluble suspension (SS) in the wire part 55 by adjusting the injection amount of the internal additive A, and may be a yield improver. . The internal additive B is appropriately selected from agents that can adjust the yield of ash in the wire part 55 by adjusting the injection amount of the internal additive B, and may be a coagulant.

  Here, the internal chemicals A and B are shown as being injected into the preparation / papermaking system 50 downstream of the fan pump 51 when they are added to the pulp slurry. For example, it can be injected into the machine chest 48), can be injected from the raw material system 40 into any of the preparation / papermaking systems 50, or can be injected into a plurality of these.

  FIG. 2 is a schematic diagram showing an outline of the chemical injection system 20 incorporated in the papermaking process 10 shown in FIG.

  The turbidity measuring unit 30 is configured to collect white water from the conduit 59 according to a predetermined procedure, store the white water in the measuring container 31, and measure the turbidity. Specifically, the turbidity measurement unit 30 includes a supply system 37 including a sampling pump 33 for pumping white water flowing through the conduit 59 and supplying the white water to the measurement container 31, and white water having a capacity equal to or greater than the capacity of the measurement container 31. And a circulatory system 38 that flows out of 31 and returns to the conduit 59. The supply system 37 and the circulation system 38 are provided with a supply valve 34 and a circulation valve 35 that are selectively opened and closed by the arithmetic processing unit 21. The turbidity measurement unit 30 is provided with these supply valves 34. The white water flowing through the conduit 59 can be collected in the measurement container 31 by performing the opening / closing control of the circulation valve 35 and the operation control of the sampling pump 33.

  When the sampling pump 33 is of the positive displacement type, the supply valve 34 is unnecessary, and if the measurement container 31 is of an open system and has a structure for overflowing the collected liquid, the circulation valve 35 is also unnecessary. . Here, white water is collected from the conduit 59, but white water may be collected directly from the white water pit 57.

  The number of turbidity measurement units is preferably one as in this embodiment from the viewpoint of simplification of the system configuration, but may be plural. When using multiple turbidity measurement units, the turbidity at the time of stirring and the turbidity at rest are measured in separate containers, so both turbidities can be measured in parallel without waiting for the time to stand still. Can be measured.

  The measuring vessel 31 has a depth of, for example, about 0.3 to 1.5 m and a volume for storing white water of 20 to 1000 L, preferably about 30 to 50 L, and a drainage valve that forms a drainage system at the bottom thereof. 36. Further, a turbidity sensor 32 for measuring turbidity in the upper part of white water stored in the measurement container 31 is provided at an upper part of the inner wall surface of the measurement container 31, for example, at a position 50 to 200 mm below the water surface. As the turbidity sensor 32, for example, an absorbance sensor, a reflected light sensor, a transmitted light sensor, or the like can be used. Further, a water surface sensor (not shown) for detecting that the white water surface has reached the full water position may be provided at the full water position on the inner wall surface of the measurement container 31.

  In the vicinity of the turbidity sensor 32, a cleaning mechanism 39 including a water jet nozzle and a wiper (not shown) for cleaning the periphery of the turbidity sensor 32 and its sensor surface is provided. This cleaning mechanism 39 measures the turbidity of white water collected in the measurement container 31 by the turbidity sensor 32, and then operates selectively after opening the drain valve 36 to drain the white water. The sensor surface and its surroundings are cleaned, and the inside of the measurement container 31 is kept clean.

  Here, the supply speed of the supply system 37 (and the discharge speed of the circulation system 38) [L / sec] and the capacity [L] of the measurement container 31 are the white water flow into which the white water in the measurement container 31 flows from the supply system 37. Is set to be sufficiently stirred.

  As described above, the arithmetic processing unit 21 obtains the injection amounts of the internal additives A and B into the pulp slurry based on the turbidity of white water collected in the measurement container 31 and measured by the turbidity sensor 32. The arithmetic processing unit 21 optimizes and controls the injection amount of the internal medicine A in the internal medicine tank 22a and the injection amount of the internal medicine B in the internal medicine tank 22b.

  FIG. 3 is a diagram showing a schematic processing procedure of the method for controlling the amount of internally added chemical according to the embodiment of the present invention. Hereinafter, the injection amount control of the internal medicine by the arithmetic processing unit 21 will be described with reference to FIG.

  The processing for controlling the injection amount of the internal chemicals is performed by the measurement container 31, the supply valve 34 and the circulation valve 35, and the drain valve 36 as “measurement container 31: empty, drain valve 36: open, supply valve 34 and First, the drain valve 36 is closed, the supply valve 34 and the circulation valve 35 are opened [Step S1], the sampling pump 33 is operated [Step S2], and white water is supplied. It begins by pumping from the conduit 59 via the system 37 and supplying it to the measuring vessel 31. At the same time, when the supply of white water to the measurement container 31 is started, a timer (not shown) provided in the arithmetic processing unit 21 is activated to measure the supply time.

  By supplying white water, the amount of white water stored in the measurement container 31 increases. When the white water stored in the measurement container 31 reaches full capacity, white water exceeding the capacity of the measurement container 31 passes through the circulation system 38 through the conduit 59. To leak. If it will be in this state, the supply amount of the white water supplied to the measurement container 31 and the outflow amount of the white water flowing out of the measurement container 31 will become equal, and the water surface position of the white water in the measurement container 31 will be maintained at a full water position. At this time, the white water stored in the measurement container 31 is in a stirring state as white water is continuously supplied to the measurement container 31.

When the supply time reaches a preset time t1, that is, when white water is supplied over the time t1 and the white water in the measurement container 31 is full [Step S3], the turbidity sensor 32 is turned on. The turbidity of white water (preferably, the absorbance of white water) is measured [Step S4].
As described above, since the white water stored in the measurement container 31 at this time is in a stirring state by continuous supply of white water, the measured turbidity is the “turbidity at the time of stirring”, as described later. Insoluble suspension (SS) has a correlation with white water insoluble suspension (SS) concentration as turbidity.

  Here, the predetermined time t1 is set in advance to a time required for the white water surface position in the measurement container 31 to reach a predetermined full water height based on the volume of the measurement container 31 and the white water supply speed. Also, here, the timer is started at the same time as the supply of white water is started, and it is detected that the surface level of the white water has reached the full water height when a predetermined time t1 has elapsed, but instead of the timer or in combination with the timer Then, the water level sensor (not shown) provided at the full water position of the measurement container 31 may detect that the water surface position of the white water has reached the full water height.

  When the measurement of “turbidity during stirring” of the white water is completed, the sampling pump 33 is then stopped [Step S5], and the supply valve 34 and the circulation valve 35 are closed with the drain valve 36 closed [Step S6]. As a result, the supply of white water to the measurement container 31 and the outflow from the measurement container 31 are stopped. Then, the white water stored in the measurement container 31 is allowed to stand by stopping the supply and outflow of the white water.

  Simultaneously with the start of standing of the white water stored in the measurement container 31, as described above, the white water is used by using the turbidity sensor 32 disposed at the position for measuring the turbidity in the upper part of the white water stored in the measurement container 31. Continuous measurement of turbidity (preferably, absorbance of white water) is started [Step S7]. This continuous measurement of white water turbidity may be performed by sampling the measurement value of the turbidity sensor 32 at a predetermined sampling frequency (for example, sampling frequency = 0.1 to 5 Hz).

  And when sufficient time has passed after the start of measurement and the continuous measurement value of white water turbidity is stable (for example, when the rate of change of the continuous measurement value is below a predetermined value), Step S8], the stable measurement value is set as the “turbidity at rest” of white water [Step S9]. As will be described later, the “turbidity at rest” of white water has a correlation with the ash concentration of white water as ash equivalent turbidity. Note that the turbidity that correlates with the ash concentration is more likely to be obtained when the predetermined rate of change that defines the resting time is lower, but even if it is too low, the increase in correlation is saturated, The waiting time for measuring turbidity is prolonged. For this reason, the specific predetermined value may be set as appropriate based on the balance between the accuracy and efficiency of the required control, but the end point may be, for example, the time point when the rate of decrease is 1 NTU / min or less.

  Thereafter, the drain valve 36 is opened to drain all the white water stored in the measurement container 31 [Step S10], and the cleaning mechanism 39 is further operated to clean the sensor surface of the turbidity sensor 32 and its surroundings. [Step S11] can be restored to the initial state described above.

  Thereafter, the steps described above may be repeated batchwise to control the “turbidity when stirring” and “turbidity when stationary” continuously. That is, the medicinal injection system 20 can continuously measure “turbidity at the time of stirring” and “turbidity at the time of static” generated in the wire part 55 and the press part 56 in real time.

  When the turbidity sensor 32 is used to measure the “turbidity during stirring” of the white water, the arithmetic processing unit 21 obtains the measured value M1 as information for grasping the concentration of insoluble suspension (SS) of white water. This is based on the following reason.

  That is, when the white water is sufficiently stirred in the measurement container 31, both the insoluble suspension (SS) and the ash are dispersed in the white water without settling. Since the particle size of the insoluble suspension (SS) is larger than the particle size of ash, when the turbidity of white water is measured with stirring, the amount of dispersion of the insoluble suspension (SS) (with respect to the measured turbidity) Concentration) is dominant, and the amount of ash dispersion (concentration) is small. Accordingly, since the “turbidity during stirring” of white water has a correlation with the concentration of the insoluble suspension (SS), the measured value M1 of “turbidity during stirring” measured using the turbidity sensor 32. Can be obtained as information for grasping the concentration of insoluble suspension (SS) in white water as “insoluble suspension (SS) equivalent turbidity”.

  Here, “turbidity during stirring” [NTU] of white water has a positive correlation with the insoluble suspension (SS) concentration [mg / L] of white water, as will be described later. Therefore, in the arithmetic processing unit 21, a calibration curve stored in a memory (not shown) of the arithmetic processing unit 21 based on the measured value M1 [NTU] of “turbidity during stirring” measured using the turbidity sensor 32. To calculate the corresponding insoluble suspension (SS) concentration D1 [mg / L]. Further, according to the calculated insoluble suspension (SS) concentration D1 [mg / L], the insoluble suspension (SS) concentration D1 [mg / L] is a predetermined insoluble suspension (SS) concentration target value T1 [ The optimum injection amount of the internal medicine A that can adjust the yield of the insoluble suspension (SS) by adjusting the injection amount so as to be NTU] is obtained in a feedback manner (step S12). Here, the predetermined insoluble suspension (SS) concentration target value T1 [NTU] is a predetermined numerical value, but may be a predetermined numerical range. And according to this optimal injection quantity, the injection quantity of the internal additive A inject | poured into a pulp slurry is adjusted by controlling the chemical injection pump 23a [step S13].

  On the other hand, when the turbidity sensor 32 is used to measure the “still-time turbidity” of the white water, the arithmetic processing unit 21 obtains the measured value M2 as information for grasping the white water ash concentration. This is based on the reason.

  That is, when white water is allowed to stand, an insoluble suspension (SS) having a relatively large particle size dispersed in the white water quickly settles, while an ash having a relatively small particle size hardly settles. White water is gradually separated into solid and liquid. Therefore, as described above, when the turbidity of the white water (supernatant liquid portion) is continuously measured by the turbidity sensor 32 while the white water stored in the measurement container 31 is left still, the sedimentation of the insoluble suspension (SS) occurs. Turbidity measurements are decreasing. Then, when a sufficient amount of time has elapsed after the start of measurement and the measured value of turbidity is stable (for example, when the rate of change of the continuous measured value falls below a predetermined value), the stable measurement is taken as the end point. The value is the “turbidity at rest” of white water. Accordingly, the “still-time turbidity” of white water is hardly affected by the concentration of insoluble suspension (SS) and has a correlation with the ash concentration. Therefore, the “white turbidity” measured using the turbidity sensor 32 is “ The measured value M2 of “turbidity at rest” can be obtained as information for grasping the ash concentration of white water as “ash equivalent turbidity”.

  Here, the “turbidity at rest” [NTU] of white water has a positive correlation with the ash concentration [mg / L] of white water, as will be described later. Therefore, in the arithmetic processing unit 21, a calibration curve stored in a memory (not shown) of the arithmetic processing unit 21 based on the measured value M2 [NTU] of “still-time turbidity” measured using the turbidity sensor 32. Accordingly, the corresponding ash concentration D2 [mg / L] is calculated. Further, according to the calculated ash concentration D2 [mg / L], the ash content yield is adjusted by adjusting the injection amount so that the ash concentration D2 [mg / L] becomes the predetermined ash concentration target value T2 [NTU]. The optimum amount of the internal additive B that can be adjusted is determined in a feedback manner [step S14]. Here, the predetermined ash concentration target value T2 [NTU] is a predetermined numerical value, but may be a predetermined numerical range. And according to this optimal injection amount, the injection amount of the internal chemical | medical agent B inject | poured into a pulp slurry is adjusted by controlling the chemical injection pump 23b [step S15].

By the way, as described above, it is desired to maintain the quality of the paper manufactured by controlling the yield of the raw material in the wire part 55 at a desired value. The raw material yield rate R (%) in the wire part 55 is approximately expressed by the following equation.
<Formula 1> R = [1- (white water concentration / inlet raw material concentration)] × 100
From this equation, when it is assumed that the inlet raw material concentration in the inlet 54 is controlled to be constant, the insoluble suspension in the wire part 55 is adjusted by adjusting the insoluble suspension (SS) concentration and the ash concentration in white water, respectively. The yield rate R1 (%) of (SS) and the yield rate R2 (%) of ash can be controlled to be constant. That is, it is produced as a result of maintaining a constant amount of pulp and ash that are made up on the wire by stabilizing the insoluble suspension (SS) concentration and ash concentration variation of white water by reducing the fluctuation range. It can be expected that the basis weight of the paper, the pulp fiber and the ash content are stabilized, and the quality of the produced paper is reduced.

  Therefore, the insoluble suspension (SS) concentration target value T1 [NTU] and the ash concentration target value T2 [NTU] are the insoluble suspension (SS) yield rate R1 (%) and the ash content in the wire part 55. It is preferable that each is set based on an appropriate value of the distillation rate R2 (%). In addition, the appropriate values of the insoluble suspension (SS) yield rate R1 (%) and the ash content rate R2 (%) in the wire part 55 differ depending on the operating conditions including the product brand to be manufactured. It is preferable to appropriately correct the insoluble suspension (SS) concentration target value T1 [NTU] and the ash concentration target value T2 [NTU] according to changes in operating conditions including the product brand to be manufactured.

  In addition, when the inlet raw material concentration and flow rate in the inlet 54 fluctuate, the insoluble suspension (SS) concentration target value T1 [NTU] is changed according to the fluctuation of the concentration and flow rate, or is corrected to the optimum injection amount obtained. By multiplying by a coefficient, the condition of the operation control of the medicinal pump 23a based on the calculated insoluble suspension (SS) concentration D1 [mg / L] may be corrected.

  Similarly, the calculated ash content is obtained by changing the ash concentration target value T2 [NTU] in accordance with the variation of the inlet raw material concentration and flow rate in the inlet 54, or by multiplying the obtained optimum injection amount by a correction coefficient. What is necessary is just to correct | amend the conditions of the action | operation control of the chemical injection pump 23b based on density | concentration D2 [mg / L].

  Since the effect may be saturated even if the internal additive A is excessively injected, it is desirable to set an upper limit value for the injection amount of the internal additive A, for example. Similarly, since the effect may be saturated even if the internal additive B is excessively injected, it is desirable to set an upper limit for the injection amount of the internal additive B, for example.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Example 1>
Using the turbidity measurement unit 30 based on this embodiment, the white water concentration was continuously measured batchwise, and the “turbidity at stirring” and “turbidity at rest” were measured. At the same time, the white water insoluble suspension (SS) concentration and ash concentration were measured using an analytical instrument.

  FIG. 4 is a diagram showing a correlation between “turbidity during stirring” and an insoluble suspension (SS) concentration using an analytical instrument according to the method for controlling the amount of internally added chemicals according to an embodiment of the present invention.

  From this result, it was confirmed that the “turbidity during stirring” measured in the stirring state of white water based on the embodiment of the present invention has a positive correlation with the actual insoluble suspension (SS) concentration. In addition, it was confirmed that the concentration of insoluble suspension (SS) can be calculated based on “turbidity during stirring” using the linearity shown in FIG. 4 as a calibration curve. Therefore, if this calibration curve is converted into data and stored in a memory (not shown) of the arithmetic processing unit 21, an insoluble suspension is obtained from the measured value M1 [NTU] of “turbidity during stirring” using the calibration curve. The substance (SS) concentration D1 [mg / L] can be calculated.

  FIG. 5 is a diagram showing the correlation between the “turbidity at rest” and the ash concentration using an analytical instrument by the method for controlling the amount of internally added chemicals according to the embodiment of the present invention. Here, the “turbidity at rest” is a turbidity measurement value when the decreasing rate of the turbidity measurement value continuously measured by leaving white water standing is 1 NTU / min or less.

  From this result, it was confirmed that the “turbidity at rest” measured after leaving white water for a sufficient time based on the embodiment of the present invention has a positive correlation with the actual ash concentration. Further, it was confirmed that the ash concentration can be calculated based on the “turbidity at rest” using the linearity shown in FIG. 5 as a calibration curve. Therefore, if the calibration curve is converted into data and stored in a memory (not shown) of the arithmetic processing unit 21, the ash concentration D2 is calculated from the measured value M2 [NTU] of the “static turbidity” using the calibration curve. [Mg / L] can be calculated.

  FIG. 6 shows the “turbidity during stirring” based on FIGS. 4 and 5, which was prepared on the assumption that the inlet concentration was kept constant, that is, the turbidity equivalent to the insoluble suspension (SS) and the insoluble suspension (SS). FIG. 4 is a diagram showing the correlation between yield rates and “resting turbidity”, that is, the correlation between ash equivalent turbidity and ash yield.

  According to this result, when the inlet concentration is controlled to be constant, the “turbidity during stirring”, that is, the turbidity equivalent to insoluble suspension (SS), It was confirmed that “turbidity”, that is, ash equivalent turbidity has a correlation with the ash yield. Therefore, adjusting the turbidity at stirring (insoluble suspension (SS) concentration) to adjust the insoluble suspension (SS) yield and adjusting the turbidity at rest (ash concentration). It can be seen that the ash yield can be adjusted individually.

<Example 2>
Using the turbidity measuring unit 30 based on this embodiment, the white water concentration was continuously measured batchwise, and the “turbidity at rest” of white water was measured. At the same time, the ash concentration of white water was measured using an analytical instrument.

  FIG. 7 is a diagram showing a correlation between ash equivalent turbidity and ash concentration in each product brand by the method for controlling the amount of internally added chemicals according to the embodiment of the present invention.

  According to this result, `` static turbidity '' measured after leaving white water for a sufficient period of time based on the embodiment of the present invention, that is, ash equivalent turbidity is positively correlated with actual ash concentration in each product brand. It was confirmed that the Moreover, it was confirmed that the ash concentration can be calculated based on the “turbidity at rest” in each product brand by using the linearity in each product brand shown in FIG. 7 as a calibration curve. Accordingly, if the calibration curves for each of the product brands are converted into data and stored in a memory (not shown) of the arithmetic processing unit 21, the “turbidity at rest” measured using the corresponding calibration curve for each product brand. The ash concentration D2 [mg / L] can be calculated from the measured value M2 [NTU].

  Thus, according to the drug injection system 20 based on the present embodiment, white water is collected, and the concentration of the insoluble suspension (SS) is obtained from “turbidity during stirring” obtained by measuring the white water in a stirring state. Based on the concentration, the optimal injection amount of the internal additive A that can adjust the yield of the insoluble suspension (SS) by adjusting the injection amount is obtained in a feedback manner. Also, the optimal injection of internal additive B that can adjust the yield of ash by adjusting the injection amount based on the ash concentration obtained from the “turbidity at rest” measured after leaving white water for a sufficient period of time. We ask for quantity in feedback. Therefore, it is possible to optimize the injection amount of these internally added chemicals and minimize the cost of the chemical solution.

  In addition, since the optimum injection amounts of the internal additive A and the internal additive B are obtained in this way, it is easy to follow the inlet raw material concentration fluctuation and flow rate fluctuation in the inlet 54, and there is no feedback time lag (small). Optimized injection control of internal chemicals can be realized. In particular, it is possible to build an internal chemical injection control system suitable for controlling the optimal injection amount of internal additive in situations where both the insoluble suspension (SS) concentration and the ash concentration vary greatly, such as when switching the product brand to be manufactured. .

  Further, by effectively using one turbidity sensor 32 incorporated in the measurement container 31, the concentration of the sex suspension (SS) is obtained from “turbidity during stirring” obtained by measuring the collected white water in a stirring state. Since the ash concentration is determined from the “turbidity at rest” measured after leaving the collected white water for a sufficient period of time, the physical configuration is simple and effects such as simplification of the device configuration can be achieved. In addition, there are advantages such as reducing the maintenance man-hours of the measuring equipment and realizing simple and efficient operation.

10 Papermaking process 30 Turbidity measurement unit 55 Wire part M1 Turbidity when stirring (turbidity equivalent to insoluble suspension)
M2 Turbidity at rest (ash equivalent turbidity)
D1 Insoluble suspension concentration D2 Ash content

Claims (5)

A method for controlling the amount of internally added chemicals in a papermaking process for producing paper from pulp slurry,
Collecting white water produced in the papermaking process under predetermined operating conditions;
Measuring the turbidity of the collected white water as an insoluble suspension equivalent turbidity upon stirring;
Measuring the turbidity of the collected white water as ash equivalent turbidity at rest;
Adjusting the addition amount of the internal additive based on the measured turbidity equivalent to insoluble suspension and ash equivalent turbidity. Calculating an insoluble suspension concentration of the collected white water based on the turbidity equivalent to the insoluble suspension measured in the collected white water;
The method according to claim 1, further comprising: calculating an ash concentration of the collected white water based on the ash equivalent turbidity measured in the collected white water.   The method according to claim 2, further comprising the step of performing chemical injection control of an internally added chemical capable of adjusting the insoluble suspension yield and the ash content yield in the papermaking process based on the calculated insoluble suspension concentration and the ash content concentration. Method.   The method further includes a step of feedback-adjusting the amount of the internal additive added so that the calculated insoluble suspension concentration becomes a target insoluble suspension concentration and the ash concentration becomes a target ash concentration. Item 4. The method according to Item 3. A method for measuring the concentration of a suspended substance in a papermaking process for producing paper from pulp slurry,
Collecting white water produced in the papermaking process;
Measuring the turbidity of the collected white water as an insoluble suspension equivalent turbidity upon stirring;
Calculating an insoluble suspension concentration of the collected white water based on the measured insoluble suspension equivalent turbidity;
Measuring the turbidity of the collected white water as ash equivalent turbidity at rest;
Calculating the ash concentration of the collected white water based on the measured ash equivalent turbidity.

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