Biocide control in papermaking

Abstract

A method for controlling papermaking comprises monitoring (302) a surface level of a fibrous suspension in a container; and identifying (303) that the surface level has been lowered such that at least one emptying criterion is met, and thereafter identifying that the surface level has been raised such that at least one refill criterion is met, and in response to the identifying that the surface level has been raised such that the at least one refill criterion is met. Dosing of a biocide into the fibrous suspension entering the container is initiated. Corresponding devices and computer programs are disclosed.

Description

Technical Field

[0001] The present disclosure relates generally to biocide control in papermaking. The disclosure relates particularly, but not exclusively, to biocide control in papermaking using recycled fibers. Background of the Invention

[0003] This section provides useful background information and is not an admission that any of the techniques described herein represent prior art.

[0004] Recycled fiber, i.e., secondary fiber, can be obtained as raw material from, for example, recycled corrugated boxes. Such recycled fiber materials often contain a lot of starch because it is a common strength additive. Starch, together with various impurities such as from food packaging recycling, can cause a large amount of microbial growth. Linerboard and fluting are components of corrugated boxboard. It is common that the manufacturing process of using recycled fiber to make linerboard or fluting suffers from microbial problems, such as the unintentional production of volatile fatty acids. This easily leads to poor taste in the production environment and the final paperboard. At the same time, the pH is typically reduced and the conductivity is improved. Together, these effects of microbial activity can cause more unstable wet ends and runnability problems, or even some explosive gas emissions. These problems can be accelerated in large process water, fiber suspensions, and damaged storage towers, which tend to have long retention times. Storage towers for recycled fiber suspensions are particularly subject to these problems. The volume of such towers is typically large, for example, varying from hundreds of cubic meters to thousands of cubic meters. The nominal pulp residence time in such towers can be only a few hours. However, the viscosity of the fiber suspension in these towers can be quite high, for example 3 to 12% or even up to 20%. A bottom mixer can be provided to circulate the contents of the tower. However, the influence of the bottom mixer can only reach the very bottom of the tower volume, for example one tenth or one fifth of the tower volume.

[0005] These storage towers are typically filled from the top. In some cases, additional fiber suspension is pumped to the top of the tower with a powerful pump through a pipe system, and the top of the tower can be 10 meters or even up to 30 meters higher than the bottom of the storage tower. At the top of the storage tower, this additional fiber suspension flow is ejected downward with obvious force. This can cause an open circuit (channel ing) effect, that is, at the surface level of the tower, at the impact point, the incoming fiber suspension can move much faster downward than the fiber suspension at the edge of the same tower. It is inferred that these towers, independent of the total volume, can contain only very slow-moving pulp areas, contrary to the main flow of the open circuit through the tower. It should now be understood that such slow-moving areas can contain materials that have been retained for several days. Therefore, such materials can have specific microbial habitats. In such areas, anaerobic bacteria have a good breeding habitat, and fermentation activity can become very high. In addition, the content of anaerobic cellulose degrading bacteria can be increased. The larger and more active these slow-moving areas are, the greater their impact on the open circuit mainstream passing through the tower, because part of these materials are mixed into the mainstream, and the anaerobic core of the slow-moving area continues the fermentation and corruption of the fiber suspension.

[0006] The adverse effects on papermaking caused by microbial growth can become apparent when tower surface levels reach low levels and pulp begins to flow from these slow moving zones, introducing large amounts of deteriorated stock into the papermaking process.

[0007] Unfortunately, once these slow moving zones are formed, their microbial habitat can hardly be altered by adding biocides to the storage tower inlet or directly to the storage tower. It appears that once the slow moving zones are formed, the biocides simply no longer reach these areas and the impact remains in the mainstream, with the risk that the mainstream becomes overly chemicalized. Summary of the invention

[0008] The attached claims define the scope of protection. Any examples and technical descriptions of devices, products and / or methods in the specification and / or drawings that are not covered by the claims are not presented as embodiments of the present invention, but are provided as background technology or examples that can be used to understand the present invention.

[0009] In this document, papermaking may refer to the manufacture of paper, liner, corrugated paper, tissue or paperboard.

[0010] According to a first example aspect, there is provided a method for controlling papermaking, comprising

[0011] monitoring the surface level of the fiber suspension in a storage vessel; and

[0012] identifying that the surface level has decreased such that at least one emptying criterion is satisfied, and thereafter identifying that the surface level has increased such that at least one refilling criterion is satisfied; and

[0013] In response to identifying that the surface level has increased such that at least one refill criterion is met, dosing of a biocide into the fiber suspension entering the container is initiated.

[0014] At least one emptying criterion refers to a partial emptying of the container. At least one emptying criterion may be defined so that when met, the container still contains at least a minimum amount of fiber suspension. The minimum amount may be at least 15, 20, 30 or 40% of the storage capacity. Advantageously, the minimum amount is large enough so that the biocide dosing is performed when the surface level has not yet dropped very close to the bottom of the container. On the other hand, if at least one emptying criterion can be triggered at a high surface level, there may be a risk of unnecessary dosing, where the slow-moving zone cannot be effectively reached by enhancing the biocide dosing. Therefore, 30%, 35% and 40% are considered to be particularly suitable figures for the minimum amount.

[0015] Storage capacity can be at least 200m 3 , more preferably at least 500m 3 , or even more preferably at least 800 m 3 .

[0016] At least one emptying criterion may comprise that the surface level has been reduced to a given lower critical value, for example to a minimum amount. The lower critical value may be defined as a given height. Alternatively, the lower critical value may be dynamically defined as a reduction in the surface level, for example corresponding to a storage capacity of preferably at least 10%, more preferably at least 20%, or even more preferably at least 30%. At least one emptying criterion may also comprise a reduction period, which defines a maximum time (e.g. 1 h or 2 h) during which the reduction must occur.

[0017] The lower critical value can be adaptively defined based on the previous measurement results related to the microbial activity in the container. The microbial activity in the container can be measured continuously, regularly, irregularly or repeatedly. When the suspected microbial activity is increased, the microbial activity can be measured. When the increased microbial activity risk is detected, the microbial activity can be measured. The lower critical value can be adaptively defined based on the microbial activity measurement results performed during the microbial activity measurement period. The microbial activity measurement period can include at least the first 10 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, 24 hours, or 72 hours. The microbial activity measurement period can include at most the first 30 minutes, 1 hour, 6 hours, 12 hours, 24 hours, 72 hours, or 1 week. The microbial activity measurement results can be compared with a predetermined baseline indicating an expected and / or acceptable amount of microbial activity.

[0018] When high and / or increased microbial activity is detected in the container, the lower threshold can be raised. This makes it easier to meet the emptying criteria and promotes earlier biocide dosing. When low and / or reduced microbial activity is detected in the container, the lower threshold can be lowered. This makes it less easy to meet the emptying criteria and is more likely to avoid unnecessary biocide dosing.

[0019] At least one refilling criterion refers to a partial refilling of the container. At least one refilling criterion may include that the surface level has increased to an upper critical value. The upper critical value may be defined as a given height. Alternatively, the upper critical value may be defined as a surface level increment starting from a cycle bottom surface level, which is defined as the minimum surface level between meeting at least one emptying criterion and then meeting at least one refilling criterion. The increment may correspond to 0.1 to 5% of the storage capacity.

[0020] At least one emptying criterion may comprise that a given renewal period has elapsed since the last time the surface level in the container previously met at least one emptying criterion. The renewal period may preferably be at least 24, or more preferably at least 36, or even more preferably 48 hours.

[0021] At least one refilling criterion may include that the surface level increases at a given rate during the incremental period. The given rate at which the surface level increases during the incremental period may correspond to at least 20% to at least 50% of the storage capacity per hour. The incremental period may be at least 30, 60, 180 or 300 seconds. Advantageously, if the rate within the period is large enough, a period of at least 30 seconds may provide a quick indication of the start of filling. An incremental period of at least 60 seconds may better explain the fluctuations in the measurement results and still be relatively fast. An incremental period of 180 seconds further reduces the risk of prematurely starting the dosing of the biocide. In the case of an incremental period of 300 seconds, premature start is still less likely. Although a layer of a certain height may be formed during this period, it is still possible that if the increase is large, the subsequent inflow also has such a rate that the inflow may cause turbulence, which mixes the incoming biocide with the fiber suspension below. Therefore, dosing may extend to a slow moving zone or pocket in the container deep enough.

[0022] When the surface level meets a given stop level threshold, dosing of the biocide may be terminated. The stop level threshold may correspond to at least 80% or 90% of storage capacity, or for example at most 1% or 5% storage capacity below the refill target of the refilling container.

[0023] When the surface level increase meets a given termination increment threshold, corresponding to, for example, at least 20 or 40% of the storage capacity of the container, dosing of the biocide may be terminated.

[0024] The dosing of the biocide can continue for a continuous period. The continuous period can be at least 2 hours, 3 hours, or 5 hours. The continuous period can be up to 3 hours, 4 hours, or 10 hours.

[0025] Dosing can be done in proportion to the input fiber suspension entering the container. Dosing can target a range between 5 mg / l and 300 mg / l. For bronopol, CMIT or MIT, dosing can be between 10 mg / l and 50 mg / l. For glutaraldehyde, dosing can be between 50 mg / l and 200 mg / l.

[0026] Dosing can be directed to the addition of the fiber suspension entering the container. Dosing can be directed to the fiber suspension entering the feed line. Alternatively, or partially additionally, dosing can be directed to the fiber suspension entering the container after entering the container.

[0027] Dosing can be conducted into the fiber suspension in a container.

[0028] The fiber suspension can be introduced into the container through a first end of the container. The fiber suspension can be removed from the container through a second end of the container which can be opposite to the first end of the container.

[0029] The vessel may be a storage tower. The vessel may have a calculated residence time greater than two hours.

[0030] The residence time of the fiber suspension in the container can be monitored. If the residence time meets a first time critical value, such as 4 days, 5 days, 6 days, 7 days, 8 days or 9 days, a first signal can be output. The first signal can indicate a signal cause, such as an aging event. The first signal can be output to a user interface. The first signal can be output to a process control loop to take mitigation measures. Mitigation measures can include at least partially emptying the container. If the residence time meets a second time critical value, such as 48 hours, if the pH or rH changes meet the pH or rH change critical values ​​respectively, a second signal can be output. The second signal can indicate a signal cause, such as an intermediate deterioration risk event. The second signal can be output to a user interface. The second signal can be output to a process control loop to take mitigation measures. Mitigation measures can include at least partially emptying the container.

[0031] The container may be cylindrical, optionally having a height of at least 1, 2, 5 or 10 times the diameter of the container.

[0032] The fiber suspension may comprise cellulose and hemicellulose in aqueous suspension with a dry matter content of up to 1, 2, 10 or 20 weight percent.

[0033] The fiber suspension may comprise cellulose and hemicellulose in aqueous suspension with a dry matter content of at least 0.5, 1, 2, 10 or 15 weight percent.

[0034] The method may include quantifying the anaerobic bacteria in the container. The quantification may be performed continuously. The quantification may be performed periodically, such as once a week or once a month. The quantification may be performed irregularly, such as between 1 and 100 days. The quantification may be performed repeatedly. The quantification may be performed using one or more laboratory tests. The quantification may include using a DNA detection method. The quantification may include detecting the total amount of bacteria. The quantification may include detecting the relative amount or number of a given bacteria.

[0035] The method may also include adjusting the dosing according to the quantification of anaerobic bacteria in the container. The method may also include adjusting the dosing according to the dosing plan. The method may also include adjusting the dosing according to the current surface level. The method may also include adjusting the dosing according to the current filling rate of the filling container.

[0036] Adjustment may include increasing or decreasing the dosing of the biocide. Dosing may be adjusted by modifying the composition and / or concentration of the biocide. The biocide may be produced by mixing two or more biocide ingredients. The biocide ingredients may be individually suitable for biocide use.

[0037] The biocide may include a non-oxidizing biocide. The biocide may include an oxidizing biocide. The biocide may include a non-oxidizing biocide and a non-oxidizing biocide.

[0038] The oxidizing biocide may be selected from the following: monochloramine, MCA; sodium hypochlorite; active chlorine produced from sodium chloride by electrolysis; chlorine dioxide or a stable chlorine compound; wherein the stable chlorine compound comprises the reaction product of a reaction between active chlorine and a nitrogen-containing reactant selected from the group consisting of: ammonium salts; urea; ammonium carbamate or dimethylhydantoin; performic acid; preferably monochloramine; ammonium salts reacted with hypochlorite; urea reacted with hypochlorite; dimethylhydantoin reacted with hypochlorite; performic acid; monohalodimethylhydantoin; dihalodimethylhydantoin; and any combination thereof.

[0039] The non-oxidizing biocide may be selected from the following: glutaraldehyde; bronopol; 2,2-dibromo-3-nitrile propionamide, DBNPA; 5-chloro-2-methyl-4-isothiazolin-3-one, CMIT; 2-methyl-4-isothiazolin-3-one, MIT; 2-n-octyl-4-isothiazolin-3-one, OIT; 4,5-dichloro-2-(n-octyl)-4-isothiazolin-3-one, DCOIT; 1,2-benzisothiazolin-3-one BIT; 2 -(Thio-cyano-methylthio)benzothiazole, TCMTB; methylene dithiocyanate, MBT; tetrakis(hydroxymethyl)phosphonium sulfate, THPS; sodium dimethyldithiocarbamate; didecyl-dimethyl-ammonium chloride, DDAC; alkyldimethylbenzylammonium chloride, ADBAC, preferably glutaraldehyde; bronopol; 5-chloro-2-methyl-4-isothiazolin-3-one, CMIT; 2-methyl-4-isothiazolin-3-one MIT; and any combination of these.

[0040] The method may include dosing a biocide for mitigating the slow moving zone problem in response to meeting at least one emptying criterion and at least one refilling criterion. The method may include additional dosing of the same or another biocide, such as an oxidizing biocide, a non-oxidizing biocide, or an oxidizing and non-oxidizing biocide, to reduce overall microbial activity in a continuous dosing or frequent burst manner. In such a case, the method includes a first biocide treatment and a second biocide treatment, the second biocide treatment being performed in response to identifying that the surface level of the fiber suspension in the container has met at least one emptying criterion and at least one refilling criterion. The first biocide treatment may be performed repeatedly, continuously, regularly, and / or irregularly. The first biocide treatment may be emphasized when performing the second biocide treatment to increase the impact on the formation of the slow moving zone. When the method includes additional dosing of the same or another biocide in response to identifying that at least one emptying criterion and at least one refilling criterion are met, starting dosing may refer to starting dosing conditioned on these criteria. Furthermore, when the method includes additional dosing of the same or another biocide in response to identifying that at least one emptying criterion and at least one refilling criterion are met, stopping dosing may refer to stopping dosing conditional on these criteria.

[0041] The first biocide treatment may be performed using a non-oxidizing biocide, and the second biocide treatment may be performed using a non-oxidizing biocide. The first biocide treatment may be performed using an oxidizing biocide, and the second biocide treatment may be performed using a non-oxidizing biocide. The first biocide treatment may be performed using an oxidizing and non-oxidizing biocide, and the second biocide treatment may be performed using a non-oxidizing biocide. The first biocide treatment may be performed using an oxidizing biocide, and the second biocide treatment may be performed using an oxidizing biocide. The first biocide treatment may be performed using an oxidizing biocide, and the second biocide treatment may be performed using an oxidizing biocide. The first biocide treatment may be performed using an oxidizing biocide, and the second biocide treatment may be performed using an oxidizing biocide. The first biocide treatment may be performed using an oxidizing biocide, and the second biocide treatment may be performed using an oxidizing biocide. The first biocide treatment may be performed using an oxidizing and non-oxidizing biocide, and the second biocide treatment may be performed using an oxidizing biocide.

[0042] In the first biocide treatment using a biocide, the oxidizing biocide may be selected from active chlorine released from sodium hypochlorite; active chlorine generated from sodium chloride by electrolysis; chlorine dioxide or a stable chlorine compound; wherein the stable chlorine compound comprises a reaction product of a reaction between active chlorine and a nitrogen-containing reactant selected from the group consisting of: an ammonium salt; urea; ammonium carbamate or dimethylhydantoin. A preferred first biocide is monochloramine (MCA), a reaction product of a reaction between active chlorine and an ammonium salt.

[0043] The inventors realize that there is only a relatively short time window in which the slow moving zones can be fully affected by the biocide. At this time, these slow moving zones form. At this time, the container begins to fill up, and the volume pressure in the container begins to affect the flow of the stored pulp, possibly producing separate slow moving zones and channel flows. At this time, the incoming flow should be treated with a biocide chemical suitable for affecting the slow moving zones when the slow moving zones form. When so dosing, the biocide concentration in these slow moving zones should remain sufficient to inhibit microbial activity until the process of repeating the surface reduction and refilling with biocide is repeated. Further advantageously, by enhancing dosing during the time window in which these slow moving zones are formed, excessive consumption of biocide can be avoided.

[0044] A more stable papermaking process can be achieved by lowering the storage tower surface, treating the slow moving zone with enhanced biocide dosing when refilling the container, and repeating this process before the slow moving zone gets out of control.

[0045] Further advantageously, by performing such enhancement processing when at least one emptying criterion and then at least one refilling criterion is met, enhancement processing can be performed as needed whenever the appropriate opportunity arises.

[0046] According to a second exemplary aspect, there is provided an apparatus for controlling pulp or paper making, comprising at least one memory including program code and a processor, together configured to:

[0047] monitoring the surface level of the fiber suspension in the container;

[0048] identifying that the surface level has decreased such that at least one emptying criterion is satisfied and thereafter the surface level has increased such that at least one refilling criterion is satisfied; and

[0049] In response to identifying that the surface level has increased such that at least one refill criterion is met, initiation of dosing of a biocide into the fiber suspension entering the container is caused.

[0050] According to a third exemplary aspect, a computer program is provided, comprising a computer executable program code, which, when executed by at least one processor, causes a device to perform at least the following steps for controlling paper making:

[0051] monitoring the surface level of the fiber suspension in the vessel; and

[0052] identifying that the surface level has decreased such that at least one emptying criterion is satisfied, and thereafter identifying that the surface level has increased such that at least one refilling criterion is satisfied; and

[0053] In response to identifying that the surface level has increased such that at least one refill criterion is met, dosing of a biocide into the fiber suspension entering the container is initiated.

[0054] According to a fourth example aspect, there is provided a computer program product comprising a non-transitory computer readable medium having the computer program of the third example aspect stored thereon.

[0055] According to a fifth example aspect, there is provided an apparatus comprising means for performing the method of any preceding aspect.

[0056] Any of the foregoing storage media may include digital data storage, such as a data optical disk or floppy disk; optical storage; magnetic storage; holographic storage; magneto-optical storage; phase change memory; resistive random access memory; magnetic random access memory; solid electrolyte memory; ferroelectric random access memory; organic memory; or polymer memory. The storage medium may be formed as a device having no other substantial functions besides storing memory, or it may be formed as part of a device having other functions, including but not limited to the memory of a computer; a chipset; and a subcomponent of an electronic device.

[0057] Different unconstrained example aspects and embodiments are described above. The above embodiments are only used to explain selected aspects or steps that can be used in different embodiments. Some embodiments can be presented with reference to only some example aspects. It should be understood that the corresponding embodiments may also be applicable to other example aspects.

[0058] BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Some example embodiments will be described with reference to the accompanying drawings, in which:

[0060] Figure 1 Schematically shows a system according to an exemplary embodiment in four different filling states a) to d) of the fiber suspension;

[0061] Figure 2 shows a block diagram of an apparatus according to an example embodiment; and

[0062] Figures 3a to 3d A flow chart according to an example embodiment is shown.

[0063] Details

[0064] In the following description, the same reference numerals denote the same elements or steps.

[0065] Figure 1 The system 100 according to the exemplary embodiment is schematically shown in four different filling states of the fiber suspension a) to d). The system comprises an inlet line 110, a dosing device 120 for dosing a biocide into the inlet line to enter the fiber suspension, a controller 130 for controlling the dosing device 120, a storage tower 140 and a bottom mixer 150 for mixing the fiber suspension in the storage tower 140. In the exemplary embodiment, the system 100 also comprises a pre-dosing device (not shown) for applying a basic dosing of the biocide independently of the operation of the dosing device 120, which can perform a time-intensive dosing to alleviate the problem of the slow-moving zone 160.

[0066] As the storage tower fills with additional fiber suspension, a slow moving zone begins to form and the volume pressure in the storage begins to affect the flow in the stored pulp. Gradually, the slow moving zone creates a habitat with highly active anaerobic microorganisms, different from the open path main flow through the tower.

[0067] Figure 2 A block diagram 200 of a device according to an example embodiment is shown. Device 200 includes a communication interface 210; a processor 220; a user interface 230; and a memory 240.

[0068] The communication interface 210 includes wired and / or wireless communication circuits, such as Ethernet, wireless LAN, Bluetooth, GSM, CDMA, WCDMA, LTE, and / or 5G circuits in an embodiment. The communication interface can be integrated into the device 200, or provided as part of an adapter, card, etc., which can be attached to the device 200. The communication interface 210 can support one or more different communication technologies. The device 200 can also or alternatively include more than one communication interface 210.

[0069] In this document, a processor may refer to a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), a graphics processing unit, an application specific integrated circuit (ASIC), a field programmable gate array, a microcontroller, or a combination of such elements.

[0070] The user interface may include circuitry for receiving input from a user of device 200, for example via a keyboard, a graphical user interface displayed on a display of device 200, speech recognition circuitry, or an accessory device (e.g., headphones), and for providing output to the user, for example via a graphical user interface or a speaker.

[0071] The memory 240 includes a working memory 242 and a persistent memory 244, which is configured to store computer program code 246 and data 248. The memory 240 may include any one or more of the following: read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), random access memory (RAM), flash memory, data disk, optical memory, magnetic memory, smart card, solid state drive (SSD), etc. The device 200 may include multiple memories 240. The memory 240 may be constructed as a part of the device 200, or as an accessory that is inserted into a slot, port, etc. of the device 200 by a user or by another person or by a robot. The memory 240 may serve only the purpose of storing data, or be constructed as a part of the device 200 (which serves other purposes such as processing data).

[0072] The skilled person will understand that in addition to Figure 2 In addition to the components shown in the figure, the device 200 may include other components, such as a microphone, a display, and additional circuits such as input / output (I / O) circuits, memory chips, application-specific integrated circuits (ASICs), processing circuits for special purposes, such as source encoding / decoding circuits, channel encoding / decoding circuits, encryption / decryption circuits, etc. In addition, the device 200 may include a disposable or rechargeable battery (not shown) for powering the device 200 if an external power source is not available.

[0073] Reference is now made to a flowchart showing a flow chart according to an example embodiment. Figures 3a to 3d to describe various example embodiments. Figures 3a to 3dThe method includes various possible steps, including some optional steps, and may also include other steps and / or some steps may be performed multiple times:

[0074] 301. A fiber suspension is added to the vessel via inlet line 110, optionally using a base dose of biocide that is independent of surface level changes in the vessel.

[0075] 302. Monitor the surface level of the fiber suspension in the container, for example by the controller 130 tracking pressure and / or surface height measurements of the storage tower.

[0076] 303. Identify that the surface level has decreased such that at least one emptying criterion is satisfied, and thereafter identify that the surface level has increased such that at least one refilling criterion is satisfied, and in response to identifying that the surface level has increased such that at least one refilling criterion is satisfied, cause to initiate dosing of a biocide into the fiber suspension entering the container. Dosing into the fiber suspension entering the container may occur before, as, or after the fiber suspension enters the container. In an example embodiment, in addition to continuously dosing the same or other biocide, which may be continuous, periodic, or non-periodic, initiating dosing of the biocide begins adaptively or conditionally.

[0077] 304. The partial emptying of the container is defined by at least one emptying criterion, such that when met the container still contains at least a minimum amount of fiber suspension. The minimum amount is for example at least 15, 20, 30 or 40% of the storage capacity.

[0078] 305. Using as an emptying criterion that the surface level has dropped to a given lower threshold value, the lower threshold value being defined, for example, as a given height, a reduction in the surface level, or being defined dynamically based on previous microbial activity measurements.

[0079] 306. Partial refilling of the container is defined by at least one refilling criterion, such as such that the surface level has increased to an upper threshold value. The upper threshold value may be defined as a given height or surface level increment starting from a bottom surface level reached before the surface level starts to increase.

[0080] 307. Use as an emptying criterion whether a renewal period has elapsed since the last time the surface level in the container has fallen below a lower threshold value. The renewal period is, for example, at least 48, 60, or 72 hours.

[0081] 308. Use as a refill criterion the surface level increasing at a given rate, e.g., at least 20% to at least 50% of the storage capacity per hour during an incremental period, e.g., at least 30, 60, 180 or 300 seconds.

[0082] 309. The dosing of the biocide is terminated when the surface level meets a given termination level threshold, such as at least 80% or 90% of storage capacity, or such as at most 1% or 5% of storage capacity below the refill target.

[0083] 310. When the surface level increase meets a given termination increment threshold, corresponding to, for example, at least 20 or 40% of the storage capacity of the container, the dosing of the biocide is terminated.

[0084] 311. Continue dosing the biocide for a period of time, such as at least 2 hours; 3 hours; or 5 hours; and / or such as at most 3 hours; 4 hours; or 10 hours.

[0085] 312. Dosing is carried out in proportion to the amount of fiber suspension entering the container, for example several tens or hundreds of mg / l for the fiber suspension.

[0086] 313. The inlet line flow of the fiber suspension directed to the dosing vessel.

[0087] 314. Directing the dose or a portion of the dose to the fiber suspension in the container.

[0088] 315. Receiving a fiber suspension in a container through a first end of the container.

[0089] 316. Outputting the fiber suspension from the container through a second end of the container, wherein the second end is opposite to the first end of the container.

[0090] 317. Use a storage tower, for example one with a calculated residence time greater than two hours, as a container.

[0091] 318. Monitor the residence time of the fiber suspension, for example, if the residence time meets a first time critical value (for example, 4 days, 5 days, 6 days, 7 days, 8 days or 9 days), output a first signal; and / or if the residence time meets a second time critical value (for example, 48 hours), and the pH or rH changes to meet the pH or rH change critical value respectively, output a second signal.

[0092] 319. Using as fiber suspension an aqueous suspension comprising cellulose and hemicellulose, wherein the dry matter content is at most 1, 2, 10 or 20% by weight.

[0093] 320. Using as fiber suspension an aqueous suspension comprising cellulose and hemicellulose, wherein the dry matter content is at least 0.5, 1, 2, 10 or 15% by weight.

[0094] 321. Quantify anaerobic bacteria in a container, for example continuously, periodically, irregularly, or repeatedly, and adjust dosing accordingly.

[0095] 322. When adjusting the dosage, the dosage of the biocide is increased or decreased, for example by changing the composition and / or concentration of the biocide.

[0096] 323. Use a biocide comprising a non-oxidizing biocide.

[0097] 324. Using any one or more of glutaraldehyde; bronopol; 2,2-dibromo-3-nitrile propionamide DBNPA; methylchloroisothiazolinone CMIT; and / or methylisothiazolinone MIT as a biocide.

[0098] 325. When surface levels are low or below a given adaptation threshold level, dynamically adjust the composition and / or concentration of the biocide, such as using a more effective composition or a higher concentration, such as increasing by 20% or 50%.

[0099] 326. In dosing control, adjust how much of a given chemical is applied to the fiber solution.

[0100] 327. In dosing control, changing the composition or concentration of chemical reagents.

[0101] 328. Dosing of oxidizing biocides to reduce overall microbial activity or frequent shocks.

[0102] 329. In response to meeting at least one emptying criterion and at least one refilling criterion, dosing a biocide to mitigate slow moving zone problems and additionally dosing an oxidizing biocide to reduce overall microbial activity in a continuous dosing or frequent bursts manner.

[0103] The skilled person will understand that rH corresponds to the oxidation-reduction potential (ORP) adjusted for pH and temperature. In one example, rH can be calculated using the following formula:

[0104] rH=2·pH+2·Eh·F / (2.3026·R·T), where:

[0105] Eh is the redox potential measured using a standard hydrogen electrode (V)

[0106] F is the Faraday constant (96485C·mol -1 )

[0107] R is the gas constant 8.314 J·K-1·mol -1

[0108] T is the temperature in Kelvin (K).

[0109] Tests were conducted to verify the effectiveness of nine different biocides against microbial flora in RCF processes from four different mills. The bronopol-containing biocides Product A (active ingredients DBNPA; bronopol; CMIT; and MIT), Product B (active ingredients bronopol; CMIT; and MIT) and Product C (bronopol) were the most effective preservatives. They prevented the growth of anaerobic bacteria and the drop in pH for several days. When Product A and Product B were used together with an oxidizing agent (monochloramine, MCA), dosing at 10 mg / l to 30 mg / l prevented bacterial growth for at least 7 days. This shows that recycled fiber pulp can also be preserved for several days under mill conditions. This is based on the results that mixing in the recycled fiber pulp tower was insufficient to prevent the formation of slow-moving zones of old pulp. Based on experiments, it seems sufficient to allow the fiber suspension in the tower to reach a low surface level once a week, at which time a biocide boost dose (an additional biocide dosing batch on top of the basic biocide treatment) is applied within the correct time window when the tower starts to refill and may have an impact on the slow moving zone. For example, the basic biocide treatment may include regular treatments (continuous dosing or several batches per day) with an oxidizing biocide (e.g., MCA), and the boost dose may be automatically performed at the right time to reach the slow moving zone. This may occur only 5 to 10 times per month.

[0110] In further comparative tests, it was found that the dosing according to the example embodiment produced improved quality in recycled cardboard while reducing the total consumption of biocides. The average bacterial content in the dry cardboard was reduced by 3.31 times, and the median of the bacterial content was reduced by 1.18 times. These figures are derived from a comparison of 40 analyses of the final cardboard, representing a total of 40 consecutive days of using the dosing according to the example embodiment, compared with 40 analyses of a similar time period using the old dosing strategy (just before switching to the dosing according to the example embodiment). The total consumption of biocide products during the innovation period in use is still 3% lower than that in the comparison period, indicating that bacterial control is improved by concentrating dosing in time rather than increasing the use of biocides. In this experiment, the bacterial content in the dry cardboard was quantified according to ISO standard 8784-1:2014 Pulp, paper and board-Microbiological examination. Part 1: Enumeration of bacteria and bacterial spores based on disintegration.

[0111] Various embodiments are presented.It is to be understood that in this document, the words comprising, including, and containing are each used as open-ended expressions with no intent to be exclusive.

[0112] The above description has provided a complete and useful information description of the best mode currently contemplated by the inventor for implementing the invention by way of non-limiting examples of specific embodiments and implementations. However, it is clear to those skilled in the art that the present invention is not limited to the details of the above-mentioned embodiments, but can be implemented in other embodiments using equivalent means or in different combinations of embodiments without departing from the characteristics of the present invention.

[0113] In addition, some features of the example embodiments disclosed above may be used advantageously without the corresponding use of other features. Therefore, the above description should be considered as merely illustrative of the principles of the present invention, rather than limiting the present invention. Therefore, the scope of the present invention is limited only by the attached patent claims.

Claims

1. A method for controlling papermaking comprising: monitoring the surface level of the fiber suspension in the container; and identifying that the surface level has decreased such that at least one emptying criterion is satisfied, and thereafter identifying that the surface level has increased such that at least one refilling criterion is satisfied; and In response to said identifying that said surface level has increased such that said at least one refill criterion is met, dosing of a biocide into said fiber suspension entering said container is initiated.

2. A method according to claim 1, wherein the at least one emptying criterion comprises that the surface level has dropped to a lower critical value, for example corresponding to preferably at least 10%, more preferably at least 20%, or even more preferably at least 30% of the storage capacity of the container.

3. The method according to claim 2, wherein the lower critical value is dynamically defined as a reduction in the surface level, for example corresponding to preferably at least 10%, more preferably at least 20%, or even more preferably at least 30% of the storage capacity.

4. The method according to claim 2 or 3, wherein the lower critical value is adaptively defined based on previous measurements related to microbial activity in the container.

5. The method according to claim 4, wherein the previous measurements relating to microbial activity are based on one or more effects of degradation of the stored fiber suspension, such as reduced pH and / or increased conductivity.

6. A method according to any one of the preceding claims, wherein The at least one refill criterion comprises the surface level being raised by a given increment from a circulating bottom surface level; The circulating bottom surface level is the minimum surface level after the at least one emptying criterion is met; and The given increment corresponds to 0.1% to 5% of the storage capacity of the container.

7. A method according to claim 6, wherein the at least one refilling criterion comprises that the surface level increases at a given rate during an incremental period, for example a rate corresponding to filling at least 20% to 50% of the storage capacity of the container per hour.

8. The method according to any one of the preceding claims, wherein the fiber suspension comprises recycled fibers.

9. The method according to any of the preceding claims, further comprising terminating the dosing of the biocide when the surface level meets a given termination height threshold, for example corresponding to at least 60%, or more preferably 70%, or even more preferably 80%, or most preferably 90% of the storage capacity of the container, or for example at most 1% or 5% of the storage capacity below the refill target of the container being refilled.

10. The method according to any one of the preceding claims, further comprising terminating the dosing of the biocide when the surface level increase meets a given termination increment threshold, for example corresponding to at least 20%, 30% or 40% of the storage capacity of the container.

11. The method according to any one of the preceding claims, wherein the dosing is proportional to the amount of the fiber suspension entering the container.

12. The method according to any one of the preceding claims, further comprising quantifying anaerobic bacteria and adjusting the dosing accordingly.

13. A method according to any one of the preceding claims, wherein the biocide is selected from the group consisting of: an oxidizing biocide comprising monochloramine, MCA; sodium hypochlorite; active chlorine generated from sodium chloride by electrolysis; chlorine dioxide or a stable chlorine compound; wherein the stable chlorine compound comprises the reaction product of a reaction between active chlorine and a nitrogen-containing reactant selected from the group consisting of: ammonium salts; urea; ammonium carbamate or dimethylhydantoin; performic acid; preferably monochloramine, MCA; ammonium salts reacted with hypochlorite; urea reacted with hypochlorite; dimethylhydantoin; performic acid and any combination thereof; and a non-oxidizing biocide comprising glutaraldehyde; bronopol; 2,2-dibromo-3-nitrile propionamide, DBNPA; 5-chloro-2-methyl-4-isothiazolin-3-one, CMIT; 2- methyl-4-isothiazolin-3-one, MIT; 2-n-octyl-4-isothiazolin-3-one, OIT; 4,5-dichloro-2-(n-octyl)-4-isothiazolin-3-one, DCOIT; 1,2-benzisothiazolin-3-one BIT; 2-(thio-cyano-methylthio)benzothiazole, TCMTB; methylene dithiocyanate, MBT; tetrakis(hydroxymethyl)phosphonium sulfate, THPS; sodium dimethyldithiocarbamate; didecyl-dimethyl-ammonium chloride, DDAC; alkyldimethylbenzyl ammonium chloride, ADBAC, preferably glutaraldehyde; bronopol; 5-chloro-2-methyl-4-isothiazolin-3-one, CMIT; 2-methyl-4-isothiazolin-3-one MIT; and any combination of these; and any combination of oxidizing and non-oxidizing biocides.

14. Apparatus comprising means for carrying out the method according to any one of the preceding claims.

15. Computer program comprising computer executable program code which, when executed, is configured to cause a computer to perform the method according to any one of claims 1 to 13.

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