• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
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  • 优先权
    • 专利摘要:
    The invention relates to a Method for manufacturing a fibrous web, such as web of paper, board, tissue or the like. The method comprises forming an aqueous fibre suspension comprising cellulosic fibres from one or more raw material flows, and applying at least one chemical and/or physical control measure to the aqueous fibre suspension or at least one of its raw material flows for control of microbial activity in the aqueous fibre suspension or the raw material flow before an inlet of an intermediate residence entity, such as storage tower or broke tower, which has a delay time of at least one hour, preferably at least two hours. In this manner a starting ORP value for the aqueous fibre suspension is obtained. A final ORP value for the aqueous fibre suspension after an outlet of the said intermediate residence entity but before the formation of the fibrous web is measured, and maintained on a target level where the difference between the starting and final ORP values is less than 100 mV, optionally by adjusting the applied chemical and/or physical control measure(s). The aqueous fibre suspension is formed into a fibrous web and drying the fibrous web.
    公开号:FI20175585A1
    申请号:FI20175585
    申请日:2017-06-21
    公开日:2018-12-22
    发明作者:Jaakko Ekman；Marko Kolari；Juhana Ahola
    申请人:Kemira Oyj；
    IPC主号:
    专利说明:

    METHOD FOR MANUFACTURING A FIBROUS WEB
    The present invention relates to a method for manufacturing a fibrous web according to the preamble of the enclosed independent claim.
    Bacterial cells are normally present in the aqueous environments of pulp mills as well as paper and board mills in form of vegetative cells, which multiply by cell division. Growth of the vegetative bacteria in the process is commonly monitored and limited by using various control measures, e.g. by feeding of biocides in the 10 process. However, some genera of bacteria form endospores, which are highly resistant to typical destruction and control methods used for vegetative cells, such as heat, disinfectants, chemical biocides, desiccation, ultraviolet light and ionizing radiation. The transformation of bacterial cells from vegetative form into the resistant endospore form is called sporulation. Mature endospores may remain 15 viable but dormant for prolonged periods, even for years, until the external conditions become favourable, after which the transformation, i.e. germination, of bacterial endospores back to vegetative form takes place.
    The amount of vegetative cells and endospores in the final paper or board product 20 should be as low as possible, especially if the product is intended for hygiene purposes, food or beverage packaging. Conventional manufacture of hygienic paper or board relies on intensive biocide treatment during furnish preparation and in the wet-end of the paper or board making process. The target of the conventional biocide treatment is to minimise or completely eliminate the 25 vegetative bacterial cells and thus inhibit the endospore formation. However, this treatment requires high dosages of biocides which increases the process costs and which may damage process equipment, e.g. cause corrosion. Furthermore, it has been observed that sometimes, even if the biocide dosage is high and the number of vegetative bacterial cells is low, the endospore count in the furnish is 30 increased beyond acceptable levels. Consequently, there is a continuing need to inhibit the formation of endospores during pulp, paper or board manufacture.
    20175585 prh 21 -06- 2017
    It is an object of the present invention to reduce or even eliminate the abovementioned problems appearing in prior art.
    One object of the present invention is to provide a method with which the spore 5 formation during the manufacture of paper, board or the like is minimised.
    In order to realise the above-mentioned objects, among others, the invention is characterised by what is presented in the characterising part of the enclosed independent claim.
    Some preferred embodiments according to the invention are disclosed in the dependent claims presented further below.
    The embodiments mentioned in this text relate, where applicable, to all aspects of 15 the invention, even if this is not always separately mentioned.
    Typical method according to the present invention for manufacturing a fibrous web, such as web of paper, board, tissue or the like, comprises
    - forming an aqueous suspension comprising cellulosic fibres from one or more 20 raw material flows,
    - applying at least one chemical and/or physical control measure to the aqueous fibre suspension and/or at least one of its raw material flows for control of microbial activity in the aqueous fibre suspension and/or the raw material flow before an inlet of an intermediate residence entity, such as storage tower or broke tower, which has a delay time of at least one hour, preferably at least two hours, and obtaining a starting ORP value for the aqueous fibre suspension,
    - measuring a final ORP value for the suspension after an outlet of the said intermediate residence entity but before the formation of a fibrous web,
    - maintaining the final ORP value of the fibre suspension on a target level, where 30 the difference between the starting and final ORP values is less than 100 mV, optionally by adjusting the applied chemical and/or physical control measure(s),
    - forming the aqueous fibre suspension into the fibrous web and drying the fibrous web.
    20175585 prh 21 -06- 2017
    Now it has been surprisingly found that the endospore formation is effectively prevented when the final ORP value of the aqueous fibre suspension after the intermediate residence entity is maintained on target level, where the difference 5 between the starting ORP value and final ORP value is less than 100 mV. In practice this means that the applied control measures before the intermediate residence entity are adjusted to a level which inhibit excessive bacterial growth but which do not fully eliminate the vegetative bacterial cells. In this manner the vegetative bacteria in the process are not induced by environmental stress to form 10 endospores but remain as vegetative cells, which are easily destroyed by the heat in the drying section. The difference between starting and final ORP values of the aqueous fibre suspension provides a parameter with which the correct level of control measure(s) can be determined, maintained and if needed, adjusted. In case the final ORP value deviates from the target level and the difference between 15 the starting and final ORP values exceeds 100 mV, it is possible to adjust the applied control measure(s) before the intermediate residence entity in order to return the final ORP value back to the suitable target level.
    The present invention enables also reduction of costs for control measures. For 20 example, the amount of used biocidal compositions can be decreased as they are not added into the process system for complete or near complete destruction of vegetative bacterial cells. Further, the present invention improves the occupational safety and facilitates the compliance with biocide regulations when the excessive addition of biocides can be avoided. The present invention provides also 25 advantages in view of general environmental and consumer concerns relating to the use of biocides.
    In the present context the term “ORP value” denotes oxidation-reduction potential value of the aqueous fibre suspension. ORP value may be determined or 30 measured by using an ORP probe, such as a redox electrode. These devices are known as such for a person skilled in the art, and not explained in more detail in this application.
    20175585 prh 21 -06- 2017
    The starting and/or final ORP value can be determined or measured continuously, or periodically, or at predetermined time intervals. According to one embodiment of the invention the final ORP value is measured continuously or more often than the obtained starting ORP value, i.e. at shorter intervals than the obtained starting 5 ORP value. According to another embodiment both the starting and final ORP value are measured continuously.
    The method according to the present invention is especially suitable for producing a hygienic fibrous web, such as hygienic web of paper, board, tissue or the like. In 10 the present context the term “hygienic fibrous web” encompasses fibrous webs comprising cellulosic fibres, where bacterial endospore content in the dried web is less than about 1000 CFU/g, preferably less than about 500 CFU/g, more preferably less than about 250 CFU/g. The endospore content is preferably < 1000 CFU/g, preferably < 500 CFU/g, more preferably < 250 CFU/g. According to one 15 embodiment the hygienic fibrous web has a bacterial endospore content in the dried web < 100 CFU/g, preferably < 75 CFU/g, more preferably 50 CFU/g.
    Aqueous fibre suspension is formed from a number of raw material flows, typically a plurality of raw material flows, such as water flow and various pulp flows 20 comprising cellulosic fibres. Raw material flows are combined together and form the aqueous fibre suspension which is fed to the intermediate residence entity. Microbial activity in the aqueous fibre suspension and/or at least one of its raw material flows is controlled by applying at least one chemical and/or physical control measure to the aqueous fibre suspension and/or at least one raw material 25 flows to. For example, the aqueous fibre suspension may be subjected to an addition of a biocidal agent, which inhibits excessive growth of microorganisms in the aqueous fibre suspension. In addition or alternatively, aqueous fibre suspension and/or its raw material flow may be subjected to a physical control measure, e.g. ultrasound or ultraviolet radiation. The control measure(s) may 30 reduce the number of vegetative bacterial cells in the aqueous fibre suspension, but does not eliminate them completely. The applied control measure may also only inhibit the activity or multiplying of the vegetative cells without reducing their
    20175585 prh 21 -06- 2017 actual amount. The control measure(s) is/are applied before the aqueous fibre suspension enters the intermediate residence entity.
    The final ORP value for the aqueous fibre suspension that is used in the control of the process is measured after an outlet of an intermediate residence entity, but before the aqueous fibre suspension exits the headbox or the like and is formed into a web. The intermediate residence entity may be any pulp, water or broke storage tower or tank or corresponding entity, which has a delay time of at least one hour, preferably at least two hours, and before the formation of the web. Delay 10 time is here understood as an average residence time for the aqueous fibre suspension in the intermediate residence entity. The endospore formation requires usually a minimum time, which means that the intermediate residence entities are especially vulnerable points in view of endospore formation. The intermediate residence entity may have a delay time in the range of 1 - 12 h, typically 1 - 8 h, 15 more typically 2 - 7 h. Typically the consistency of the aqueous fibre suspension in the intermediate residence entity is at least 2 g/l, preferably in the range of 10 100 g/l.
    According to one embodiment of the invention, in case the process comprises a 20 plurality of intermediate residence entities, such as storage towers, arranged in the series, the starting ORP value may be determined before the inlet of the first intermediate residence entity and the final ORP value is measured after the outlet of the last intermediate residence entity in the series. The intermediate residence entities in the series may be different or similar to each other. Alternatively, a 25 starting ORP value may be determined before the inlet of each intermediate residence entity and a final ORP value is measured after the outlet of the each intermediate residence entity in the series and the final ORP values are individually maintained on a target level for each intermediate residence entity. According to a further alternative, a critical intermediate residence entity in the 30 series, e.g. with the longest delay time or with the most beneficial conditions for spore formation, is recognized and selected, whereafter the starting ORP value may be determined solely before the inlet of the critical intermediate residence entity and the final ORP value is measured solely after the outlet of the critical
    20175585 prh 21 -06- 2017 intermediate residence entity in the series and the final ORP value are maintained on a target level for the critical intermediate residence entity.
    According to one preferable embodiment of the invention the final ORP value is maintained on the target level, i.e. on a level where the difference between the starting and final ORP value is < 100 mV, at least for 90 % of an observance period of 24 hours. In practice this means that under any observance period of 24 hours, when the process is working normally and excluding process start-ups, process down closings, cleaning periods, the difference between the starting and final ORP value does not deviate for long periods and/or regularly outside the limit value of 100 mV. Preferably, the final ORP value is maintained on the target level at least for 95 %, more preferably at least for 97.5 % of the observance period of 24 hours.
    On basis of the measured final ORP value of the aqueous fibre suspension it is possible to adjust, if necessary, the chemical and/or physical control measure(s) to which the aqueous fibre suspension is subjected prior to the intermediate residence entity. According to one preferable embodiment of the present invention the final ORP value may be in the predetermined range of 0 - +350 mV, preferably
    0 - +200 mV, more preferably +50 - +175 mV, even more preferably +100 - +150 mV. The values are obtained by using conventional ORP electrodes comprising a platinum redox sensing electrode and a silver/silver chloride reference electrode in one body. It has been observed that the final ORP value within these predetermined ranges provides conditions where the microbial activity is controlled at a suitable level, avoiding anaerobic conditions, spore formation and/or excessive microbial growth. In case the final ORP value is inside the predetermined range, and at the target level, no adjustment of the control measure(s) is necessary, but the adjustment may be done if deemed necessary on basis of other process parameters.
    Also the obtained starting ORP value for the aqueous fibre suspension may be measured before its entry to the intermediate residence entity, i.e. before the inlet of the intermediate residence entity. The starting ORP value does not only provide
    20175585 prh 21 -06- 2017 a starting level for the determination of the difference between the starting and final ORP values, but it is possible to obtain preliminary information about the effect of the control measure(s) applied on the aqueous fibre suspension and/or its raw material flows and/or changes in the properties of the aqueous fibre 5 suspension itself. For example, the starting ORP may provide preliminary information about the effect of the control measure(s) and/or appropriate level of the control measure(s).
    The starting ORP value before the inlet of the intermediate residence entity and 10 the final ORP value measured after the outlet of the intermediate residence entity are used to determinate the difference between the ORP values. The difference indicates the conditions prevailing in the intermediate residence entity. The target level for the final ORP value sets the difference between the starting ORP value and the final ORP value less than 100 mV, preferably less than 90 mV, preferably 15 75 mV, more preferably less than 50 mV. The smaller the difference between the starting ORP value and the final ORP value, more stable are the conditions in the intermediate residence entity and smaller the risk for stressful environment leading to endospore formation.
    According to one embodiment of the invention bacterial endospore content in the aqueous fibre suspension is determined after the intermediate residence entity. In this manner it can be guaranteed that there is no or only minimal endospore formation occurring in the intermediate residence entity and the applied control measures before the intermediate residence entity are at the appropriate level.
    According to one embodiment of the invention the aqueous fibre suspension may have a bacterial endospore content less than 400 CFU/ml, preferably less than 200 CFU/ml, more preferably less than 100 CFU/ml after the intermediate residence entity.
    The pH of the aqueous fibre suspension may also be measured, before and/or after the intermediate residence entity. Preferably the pH of the aqueous fibre suspension is stable, around pH 7 - 9, and the maximum difference between the
    20175585 prh 21 -06- 2017 measured pH values is ±1 pH units. Stable pH reduces the risk for environmental stress factors and enables to keep the ORP value within the predetermined range.
    According to one embodiment an rH value of the aqueous fibre suspension after 5 the intermediate residence entity is in the range of 21 - 32, preferably 21 - 27, more preferably 22 - 26, even more preferably 24 - 26. The difference between aqueous fibre suspension’s rH values before and after the intermediate residence entity may preferably be less than 3, preferably less than 2.5, more preferably less than 1.5 rH units.
    It is possible to determine the bacterial endospore content value of the aqueous fibre suspension before and after the intermediate residence entity, whereby the difference between the determined endospore content values is preferably less than 100 CFU/ml, more preferably less than 75 CFU/ml. By determining the values 15 for bacterial endospore content before and after the intermediate residence entity and their difference, information about the actual spore formation in the intermediate residence entity may be obtained. This determination is especially useful if the measured ORP value(s) and/or other parameters are near a predetermined border value or there is otherwise a suspicion about the actual 20 conditions in the intermediate residence entity.
    The aqueous fibre suspension is formed from cellulosic fibres, optional papermaking additives and water. The cellulosic fibres may be virgin fibres obtained by any known pulping process and/or they may be recycled fibres and/or 25 they may originate from broke. For example, the fibre stock may comprise cellulosic fibres obtained by mechanical pulping, chemical pulping, chemithermomechanical pulping or by repulping recycled or recovered fibres. The cellulosic fibres can be refined or unrefined, bleached or unbleached. The cellulosic fibres may be recycled unbleached or bleached kraft pulp fibres, hardwood semi-chemical pulp fibres, grass pulp fibres or any mixtures thereof.
    The aqueous fibre suspension may be formed by combining two or more raw material flows, which may comprise cellulosic fibres from different sources and/or
    20175585 prh 21 -06- 2017 fresh water and/or circulated process water. The chemical and/or physical control measure(s) may be applied to one or more of these raw material flows or to the aqueous fibre suspension after its formation.
    The aqueous fibre suspension may contain one or several known chemical additives used in pulp and paper making.
    According to one embodiment of the invention chemical control measure comprises feeding of a microbial control chemical to the aqueous fibre suspension 10 or to at least one of its raw material flows. The microbial control chemical may be a biocide, reductive chemical or oxidative chemical.
    According to one embodiment the biocide is non-oxidative biocide. Suitable nonoxidative biocide may selected from glutaraldehyde, 2,2-dibromo-315 nitrilopropionamide (DBNPA), 2-bromo-2-nitropropane-1,3-diol (Bronopol), carbamates, 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), 2-methyl-4isothiazolin-3-one (MIT), 1,2-dibromo-2,4-dicyano butane, bis(trichloromethyl)sulfone, 2-bromo-2-nitrostyrene, 4,5-dichloro-1,2-dithiol-3-one, 2-n-octyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, ortho-phthaldehyde, quaternary 20 ammonium compounds (=quats), such as n-alkyl dimethyl benzyl ammonium chloride, didecyl dimethyl ammonium chloride (DDAC) or alkenyl dimethylethyl ammonium chloride, guanidines, biguanidines, pyrithiones, 3-iodopropynyl-Nbutylcarbamate, phosphonium salts, such as tetrakis hydroxymethyl phosphonium sulfate (THPS), dazomet, 2-(thiocyanomethylthio)benzothiazole, methylene 25 bisthiocyanate (MBT), and a combination thereof. Preferably non-oxidative biocide is selected from glutaraldehyde, 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) and 2-methyl-4-isothiazolin-3-one (MIT).
    According to another alternative the biocide may be an oxidative biocide, such as 30 a stabilised active chlorine compound or a peracid. In one embodiment of the invention the oxidative biocide may include an oxidant, which is selected from chlorine, alkali and alkaline earth hypochlorite salts, hypochlorous acid, chlorinated isocyanurates, bromine, alkali and alkaline earth hypobromite salts, hypobromous
    20175585 prh 21 -06- 2017 acid, bromine chloride, chlorine dioxide, ozone, hydrogen peroxide, peroxy compounds, such as peracetic acid, performic acid, percarbonate or persulfate salts, halogenated hydantoins, e.g., monohalodimethylhydantoins such as monochlorodimethylhydantoin, or dihalodimethylhydantoins such as chlorobromo5 dimethylhydantoin, monochloramines, monobromamines, dihaloamines, trihaloamines, or any combination thereof. It is further possible to combine the oxidant with a nitrogen-containing compound in the oxidative biocide. Suitable nitrogenhydrogen compounds may be selected from ammonium salts, such as ammonium sulphate, ammonium bromide, ammonium chloride or ammonium carbamate, 10 ammonia, urea, hydantoin, ethanolamine, pyrrolidone, 2-pyrrolidone, ethylene urea, N-methylolurea, N-methylurea, acetylurea, pyrrole, indole, formamide, benzamide, acetamide, imidazoline, or morpholine. According to one preferable embodiment oxidative biocide comprises urea or ammonium salts reacted with an oxidant. For example, oxidative biocide comprises urea, ammonium bromide, 15 ammonium carbamate or ammonium sulphate which is reacted with an oxidant, e.g., sodium hypochlorite. Preferable oxidative biocides are selected from monochloramine (MCA), chlorine dioxide, performic acid (PFA), peracetic acid, alkali and alkaline earth hypochlorite salts, and N-hydrogen compounds combined with an oxidant. More preferably, oxidative biocides are selected from 20 monochloramine (MCA), chlorine dioxide, performic acid, or a N-hydrogen compound combined with an oxidant, e.g. urea reacted with an oxidant.
    The aqueous fibre suspension is formed into a fibrous web and dried in any suitable manner. The temperature during the drying is preferably at least 100 Ό, 25 preferably at least 110 Ό, for at least 0.3 min, preferably at least 0.5 min, sometimes at least 1 min. This ensures the termination of vegetative bacterial cells and achievement of a hygienic fibrous web.
    EXPERIMENTAL
    Example 1
    This laboratory test compared efficacy of two oxidizing biocides, namely free active chlorine and stabilized active chlorine, in killing of vegetative bacterial cells and in controlling of bacterial spore formation. Test was performed with authentic bacterial population of a broke sample taken from couch pit of a board machine making 3-ply food-packaging board. Broke sample was divided in equal proportions. Two reference samples were stored as such, the “free active chlorine” 5 sample was treated with sodium hypochlorite, and the “stabilized active chlorine” sample was treated with sodium hypochlorite stabilized by 5,5-dimethylhydantoin (mixed in 1:1 molar ratio to form monochloro-5,5-dimethylhydantoin, MCDMH).
    Both forms of active chlorine were dosed at 10 ppm (=mg/l as total active chlorine Ch). Broke samples were stored at +45 Ό without mixi ng. Total aerobic bacteria 10 and aerobic bacterial spores were quantified by using conventional agar plate cultivation methods (Plate Count Agar, incubation at +37 Ό for 2 days) at the beginning of the test (untreated reference samples) and after 1 and 2 days of contact time. Broke pH and Redox (mV) values were also monitored.
    Results are shown in Table 1.
    20175585 prh 21 -06- 2017
    Table 1 Results of Example 1.
    Start of the test1 days storage time2 days storage timeTotal aerobic bacteria (CFU/ml)Bacterial spores(CFU/ml)T Q_redox (mV)Total aerobic bacteria (CFU/ml)Bacterial spores(CFU/ml)T Q_redox (mV)Total aerobic bacteria (CFU/ml)Bacterial spores(CFU/ml)T Q_redox (mV)Reference broke 1, no added Active Chlorine1χ103 807.81497x105 707.81462x107 107.5126Reference broke 2, no added Active Chlorine8x102 707.91386x105 607.81401χ107 307.5120Broke, Na-hypochlorite treatment,10 mg/lNDNDNDND4x105 607.81082x107 6707.668Broke, MCDMH treatment, 10 mg/lNDNDNDND6x104 307.9862x107 607.678
    Results in Table 1 show that in the beginning of the experiment the untreated reference broke samples 1 and 2 contained relatively low amounts of aerobic bacteria (8x102 and 1x103 CFU/ml), and a small amount of aerobic bacterial
    20175585 prh 21 -06- 2017 spores (80 and 70 CFU/ml). During two days of storage the total aerobic bacteria level in the reference samples 1 and 2 increased up to 1 - 2 x107 CFU/ml, whereas the aerobic bacterial spore counts decreased down to 10 and 30 CFU/ml. This indicates, surprisingly, that the aerobic storage conditions (pH 7.5 - 7.9, redox 120 - 149 mV) at a typical board machine temperature favoured vegetative bacterial growth but did not cause any increase in bacterial sporulation. Broke sample treated with free active chlorine (sodium hypochlorite, no stabilizer) showed almost equal content of vegetative bacteria after 1 day storage time. This indicates that at a 10 ppm dosing level the free active chlorine did not demonstrate 10 any longer-term killing effect in the broke sample. However, the treatment with free active chlorine caused a 10-fold increase in the quantity of aerobic spores (60 CFU/ml 670 CFU/ml) due to the stress caused by the free active chlorine. Treatment of broke with a stabilized chlorine (MCDMH, 10 mg/l as active chlorine) showed 1 log unit stronger reduction of total aerobic bacteria content compared to 15 free chlorine (6 χ 104 CFU/ml compared to 4 x 105 CFU/ml) after 1 day of storage.
    Further, the MCDMH did not cause any new spore formation in the broke and spore counts remained at 30 - 60 CFU/ml level during the 2 days experiment. After 2 days of storage all samples contained bacteria 1 - 2 χ 107 CFU/ml indicating that none of the oxidizer treatments showed a long-lasting killing effect.
    Example 1 shows, surprisingly, that a biocide treatment is not absolutely necessary for preventing bacterial spore formation in machine broke. Test demonstrated that if broke from of a board machine is stored under suitable conditions, the spore formation can be minimized. This example also showed that 25 if such aerobic broke is treated with free active chlorine, at dosages not providing a complete kill of bacterial cells, it can irritate remaining bacteria to spore formation. Surprisingly, treating the broke in similar manner with stabilized active chlorine is not causing bacterial spore formation.
    Example 2
    This laboratory test was performed with broke sample taken from an alkaline board machine producing 3-ply food-packaging board and the sample included the mill’s authentic bacterial population in it. The sample was divided in two different containers, one stored as such and the second one amended with biocide, 50 mg/l of glutaraldehyde as active agent. Containers were closed and stored at +45 Ό without mixing i.e. under conditions that simulate situation in broke storage tower during a machine shutdown. Total aerobic bacteria and aerobic spore contents 5 were determined by using conventional agar plate cultivation methods (plate count agar, 2 days incubation at +37 Ό) at the beginning of the test and after 3 days of storage time, along with pH and redox measurements.
    Results are shown in Table 2.
    Table 2 Results of Example 2.
    At start of the testAfter 3 days storage timeTotal aerobic bacteria (CFU/ml)Bacterial spores(CFU/ml)I Q.redox (mV)Total aerobic bacteria (CFU/ml)Bacterial spores(CFU/ml)I Q.redox (mV)Untreated broke sample2xl07 1257.91375xl07 8506.9-23Broke, treated with glutaraldehydeNDNDNDND2xl07 807.4145
    20175585 prh 21 -06- 2017
    Results in Table 2 show that during 3 days of storage time, in the untreated broke sample, pH value (7.9 6.9) and redox value (+137 mV -23 mV) dropped markedly indicating that conditions in the broke turned from aerobic to fermentative during the storage time. Total aerobic bacteria counts increased from 2x107 CFU/ml to 5x107 and amount of aerobic spores increased from 125 CFU/ml to 850 CFU/ml.
    Broke treated with 50 mg/l of glutaraldehyde biocide contained total aerobic bacteria 2 χ 107 CFU/ml after 3 days of storage, i.e. 40 % of the untreated reference, indicating that this biocide treatment did not have a long-lasting killing effect. However, the treatment effectively prevented development of anaerobic fermentative conditions, i.e. redox (145 mV) and pH (7.4) remained at high level.
    20175585 prh 21 -06- 2017
    Conditions were not triggering any spore formation in the broke sample and the broke contained only a low amount (80 CFU/ml) of spores after 3 days of storage.
    Example 2 demonstrates that a biocide treatment which is not causing an intensive and long-lasting killing effect of bacterial cells can surprisingly well control spore formation in broke, as long as the biocide treatment is successful in preventing development of anaerobic conditions in the broke.
    Example 3
    This example compares technical performance of two different biocide programs in the broke system of a 3-ply board machine producing food-packaging board. Broke system is a part of the wet-end of the board making process. This board machine has set a hygiene target for the final board that it should contain aerobic bacterial spores less than 1000 CFU, and preferably less than 250 CFU, per gram 15 of dry board.
    In this experiment, for the first period (Days 1-10) the machine was running a biocide program consisting of stabilized active chlorine (MCDMH) and glutaraldehyde. For the second period, the machine was running chlorine dioxide, 20 a non-stabilized oxidizer, as the biocide. It was running for 10 days starting from a shutdown (Days 15 - 25). Third period (Days 26 - 47) was run with the same MCDMH and glutaraldehyde program as the first period. During this experiment technical performance of the two different biocide programs was monitored at selected dates by several means: on-line Redox monitoring system collecting 25 Redox values at every 10 minutes (results are shown as daily average mV values); measuring aerobic spore content of the final board samples; and by measuring aerobic bacterial spore quantities from different process locations by using agar plate cultivation methods (pasteurization at 82 Ό for 20 min, followed by cultivation on Plate Count Agar for 2 days at +37 Ό).
    Results are shown in Table 3.
    Table 3 Results of Example 3.
    Redox (mV) in Couch Pit (daily avg)Aerobic Bacterial Spores (CFU/ml) in processBacterial Spores in Final Board (CFU/g)Low consistency (1-4 w/w-%) broke towerHigh consistency (4-6 w/w-%) broke towerASpore content within the broke systemIncoming PulpDay 1197110270+16080220Day 2192150200+5040240Day 1019180110+3030230Day 15387250440+19020520Day 194926101100+490605530Day 21477NDNDNDND9580Day 25471850950+100ND3210Day 43186280210-7040680Day 4717350170+120ND210
    20175585 prh 21 -06- 2017
    Results in Table 3 show that during the first period (Days 1-10) the produced final board had spore content always <250 CFU/g and thus the board met the 5 hygiene targets. During days 1-10 redox level of couch pit (=tank collecting and sending material to low consistency broke tower) was stable at +190 - 200 mV range. It is seen that during days 1 - 10 the broke system had stable aerobic conditions and Aspore content within the broke system (=difference between inlet and outlet) was generally low, indicating that intensive formation of new spore did 10 not occur. Also other areas of the process, treated with the stabilized oxidizer
    MCDMH, contained generally low amounts of spores. For example, pulp transportation water (15 CFU/ml) and incoming pulp (30 - 80 CFU/ml) possessed low quantities of spores, indicating that the MCDMH biocide program did not trigger intensive spore formation.
    During second period (Days 15-25) the system was treated with chloride dioxide. Dosing of this non-stabilized oxidizer increased Redox values in the system dramatically, e.g. in broke system from +190 mV range up to +492 mV.
    20175585 prh 21 -06- 2017
    Interestingly, spore quantities also showed a strong increase, for example up to 1100 CFU/ml in the high consistency broke tower. Also spore content in the final board increased dramatically, to a magnitude higher values than what is the set hygiene target for final board, the highest value being as high as 9580 CFU/g. This 5 indicates that the strong oxidative stress caused by non-stabilized oxidizer triggered intensive spore formation in the broke system of this board machine.
    During the third period (Days 26 - 47) the process was treated with MCDMH and glutaraldehyde, similarly as during the first period. With a small delay the process 10 conditions stabilized back to similar Redox range as during first experimental period, and interestingly, also spore values in the final board returned back to target level.
    Results from Example 3 support the surprising finding that for the production of 15 food-packaging board with a low content of aerobic bacterial spores, it is more effective to treat the system with biocides such as stabilized-oxidizers and glutaraldehyde in a manner providing stable aerobic conditions with moderate Redox values, compared to treating the system with oxidizing biocides and targeting high +380 to +500 mV Redox values in the broke system.
    Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions 25 within the scope of the enclosed claims.
    权利要求:
    Claims (11)
    [1] 1. Method for manufacturing a fibrous web, such as web of paper, board, tissue or the like, the method comprising
    5 - forming an aqueous fibre suspension comprising cellulosic fibres from one or more raw material flows,
    - applying at least one chemical and/or physical control measure to the aqueous fibre suspension or at least one of its raw material flows for control of microbial activity in the aqueous fibre suspension or the raw material flow before an inlet of
    10 an intermediate residence entity, such as storage tower or broke tower, which has a delay time of at least one hour, preferably at least two hours, and obtaining a starting ORP value for the aqueous fibre suspension,
    - forming the aqueous fibre suspension into a fibrous web and drying the fibrous web,
    15 characterised in
    - measuring a final ORP value for the aqueous fibre suspension after an outlet of the said intermediate residence entity but before the formation of the fibrous web,
    - maintaining the final ORP value of the aqueous fibre suspension on a target level where the difference between the starting and final ORP values is less than 100
    20 mV, optionally by adjusting the applied chemical and/or physical control measure(s).
    [2] 2. Method according to claim 1, characterised in maintaining the final ORP value on the target level at least for 90 % of an observance period of 24 hours.
    [3] 3. Method according to claim 1 or 2, characterised in that the difference between the starting ORP value and final ORP value is less than 90 mV, preferably less than 75 mV, more preferably less than 50 mV.
    30
    [4] 4. Method according to claim 1, 2 or 3, characterised in that the final ORP value is in the range of 0 - +350 mV, preferably 0 - +200 mV, more preferably +50 +175 mV, even more preferably +100 - +150 mV.
    20175585 prh 21 -06- 2017
    [5] 5. Method according to any of claims 1 - 4, characterised in that an rH value of the aqueous fibre suspension after the intermediate residence entity is in the range of 21 - 32, preferably 21 - 27, more preferably 22 - 26, even more preferably 24 - 26.
    [6] 6. Method according to any of claims 1 - 5, characterised in that the difference between aqueous fibre suspension’s rH values before and after the intermediate residence entity is less than 3, preferably less than 2.5, more preferably less than
    I. 5.
    [7] 7. Method according to any of claims 1 - 6, characterised in that after the intermediate residence entity the aqueous fibre suspension has a bacterial endospore content less than 400 CFU/ml, preferably less than 200 CFU/ml, more preferably less than 100 CFU/ml.
    [8] 8. Method according to any of claims 1 - 7, characterised in determining the bacterial endospore content value of the aqueous fibre suspension before and after the intermediate residence entity, whereby the difference between the determined values is less than 100 CFU/ml.
    [9] 9. Method according to any of claims 1 - 8, characterised in that the bacterial endospore content in the dried web is < 1000 CFU/g, preferably < 500 CFU/g, more preferably < 250 CFU/g.
    25 10. Method according to any of claims 1 - 9, characterised in that the intermediate residence entity has a delay time in the range of 1 - 12 h, typically 1 - 8 h, more typically 2 - 7 h.
    II. Method according to any of claims 1-10, characterised in that the chemical
    30 control measure comprises feeding of a microbial control chemical to the aqueous fibre suspension or to at least one of its raw material flows.
    12. Method according to claim 11, characterised in that the microbial control chemical is a biocide, reductive chemical or oxidative chemical.
    13. Method according to claim 12, characterised in that the biocide is non5 oxidative biocide, preferably selected from glutaraldehyde, 5-chloro-2-methyl-4- isothiazolin-3-one (CMIT) and 2-methyl-4-isothiazolin-3-one (MIT).
    14. Method according to claim 12, characterised in that the biocide is oxidative biocide, preferably selected from monochloramine (MCA), chlorine dioxide,
    [10] 10 performic acid, or an N-hydrogen compound combined with an oxidant, e.g. urea reacted with an oxidant.
    [11] 15. Method according to any of claims 1-14, characterised in that the obtained starting ORP value for the aqueous fibre suspension is measured before its entry
    15 to the intermediate residence entity.
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    FI20175585A|FI128324B|2017-06-21|2017-06-21|Method for manufacturing a fibrous web|FI20175585A| FI128324B|2017-06-21|2017-06-21|Method for manufacturing a fibrous web|
    PCT/FI2018/050479| WO2018234635A1|2017-06-21|2018-06-19|Method for manufacturing a fibrous web|
    EP18739572.8A| EP3642416A1|2017-06-21|2018-06-19|Method for manufacturing a fibrous web|
    KR1020197037866A| KR20200019891A|2017-06-21|2018-06-19|Fiber web manufacturing method|
    RU2019142688A| RU2763929C2|2017-06-21|2018-06-19|Method for producing fibrous material|
    US16/619,109| US20200095730A1|2017-06-21|2018-06-19|Method for manufacturing a fibrous web|
    CA3065643A| CA3065643A1|2017-06-21|2018-06-19|Method for manufacturing a fibrous web|
    CN201880041404.1A| CN110785525A|2017-06-21|2018-06-19|Method for producing a fibrous web|
    BR112019027394-8A| BR112019027394A2|2017-06-21|2018-06-19|process for fabricating a fibrous web|
    AU2018287124A| AU2018287124A1|2017-06-21|2018-06-19|Method for manufacturing a fibrous web|
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