FI129231B

FI129231B - Method and system of sizing agent cooking circulation

Info

Publication number: FI129231B
Application number: FI20195514A
Authority: FI
Inventors: Janne Heinilä; Christian Prinz; Tuomas Pesonen; Teemu J Nieminen
Original assignee: Valmet Technologies Oy
Priority date: 2019-06-14
Filing date: 2019-06-14
Publication date: 2021-09-30
Also published as: AT522848A2; AT17908U1; DE102020114000A1; FI20195514A1; AT522848A3

Abstract

The invention relates to a method of sizing agent cooking circulation, in which method during cooking of the sizing agent the sizing agent is flown to a converter or slurry container (10), from which converter or slurry container (10) the sizing agent is pumped by a pump (13) to a main line (11), and via which main line (11) the sizing agent is flown to a storage container (15). In the method during a stop in the cooking of the sizing agent a valve (17) of a circulation line (16) connected to the storage container (15) is opened and the sizing agent is flown from the storage container (15) to a circulation line (16) and to the main line (11) and back to the storage container (15) and the sizing agent is circulated until the stop in the cooking ends. The invention also relates to a system of sizing agent cooking circulation, which system comprises a converter or slurry container (10), a main line (11), a pump (13) located in the main line (11), and a storage container (15). The system comprises a circulation line (16) connecting the storage container (15) to the main line (11) for circulating the sizing agent during a stop in the cooking of the sizing agent.

Description

Method and system of sizing agent cooking circulation Technical field In general, present invention relates to producing of fiber webs. More especially the present invention relates to a method according to preamble part of independent method claim and to an arrangement according to preamble part of independent system claim.

Background As known from the prior art in fiber web producing processes typically comprise an assembly formed by a number of apparatuses arranged consecutively in the process line. A typical production and treatment line comprise a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and sections for finishing the fiber web, for example, a sizer, a calender, a coating section. The production and treatment line typically also comprise at least one winder for forming customer rolls as well as a roll packaging apparatus. In this description and the following claims by fiber webs are meant for example paper and board webs. In production of fiber webs, for example of paper or board webs, sizing is used to alter the properties of a fiber web by adding sizing agents, for example starch or other glue chemicals. Sizing can be divided to internal sizing and N surface sizing. In internal sizing the sizing agent is added to pulp in the wet N end of the fiber web production line before forming. In surface sizing the sizing 3 agent is added onto the surface of the fiber web, typically at the dry end of the S 30 fiber web production line. Internal sizing is done in the beginning of the wet z end of the fiber web machine by using different kinds of chemical treatments 3 in order to influence the penetration of a liquid, for example of water into the n fiber web. The sizing agent is typically applied as an agueous slurry containing 3 starch and/or other sizing chemicals for example pigments, retention agents & 35 etc.

The aqueous slurry for the sizing agent is typically prepared in a separate system connected to the sizer and located in connection with the fiber web production line.

A known system of preparing a slurry for a sizing agent known typically as so called enzymatic starch cooking process is in the following described by reference to preparing a starch based slurry but it is applicable in main parts to other sizing agents, as well, as such known by one skilled in the art. Starch is provided to the preparing system in powdered form, typically from a storage container a required amount of starch powder is fed by a conveyor, for example a screw conveyor, via a weighing station to a elutriation container, in which liquid, typically water, is added to the starch powder for elutriating the slurry such, that desired dry solids content is achieved, typically the solids content is around 30 %. There after the aqueous slurry is guided to slurry cooking process, typically via coarse screening, in which coarse impurities are removed from the slurry. The sizing agent cooking begins in a first stage cooking in a first cooker, in which typically enzymes and/or biocatalysts are added to the slurry and the slurry is heated to the required reaction temperature in order to the enzymes and/or the biocatalysts to react and to form sizing agent. After the first stage cooking the sizing agent is fed to a converting container, in which the sizing agent stays for time required for the enzymes and/or the biocatalysts to convert the starch to required form. After converting the sizing agent is fed to a second stage cooking in a second cooker, in which the sizing agent is heated to required temperature in order to stop the converting reaction caused by the enzymes and/or the biocatalysts and additionally a delay time in the required temperature needed to finalize N and to fully stop any reactions caused by the enzymes and/or the biocatalysts N by guiding the sizing agent via a delay pipe. Afterwards, any excessive steam 3 is removed in steam removal stage. Finally, the sizing agent is diluted to the S 30 desired solids content and guided to a storage container, from which, when z needed in the sizing process, the sizing agent is guided to sizing agent / starch 3 application at the sizer.

LO o Another known system of preparing a slurry for a sizing agent known typically as so-called modified starch cooking process where starch has already been modified before it enters the system of preparing a slurry for a sizing agent at the fiber web production line. In the modified starch cooking process only in one cooking stage is needed. Modified starch is commonly used for wet end sizing, but it is also used in many surface sizing applications.

Yet, another known system of preparing a slurry for a sizing agent known typically as so-called oxidation cooking process, in which cooking with oxidation chemical, like hydrogen peroxide or APS (ammonium persulphate), is used to adjust the viscosity. Also, in this oxidation cooking process only one cooking stage is needed.

Above, the systems of preparing a slurry for a sizing agent have been described by reference to preparing a starch-based slurry but they are applicable in main parts to other sizing agents, as well, as such known by one skilled in the art.

During the processes of producing the slurry for the sizing agent there exists needs to stop the process, for example, in case there is too much sizing agent in view of the need of the sizing of the fiber web to be produced i.e. the storage capacity is full or there is a web break. The web breaks and the limited storage tank capacity are key reasons why starch cooking needs to be stopped even though it is designed to run continuously. As the process stops containers, pipes, pumps, cookers etc. of the system need to be flushed before the new start-up to prevent sizing agent, for example starch building-up inside the system, especially when the system is cooling down. During long stops the entire system including the tanks needs to be flushed properly in order to prevent the sizing agent build-up and bacterial problems. Thus, sizing agent and water is wasted, as well as special washing devices might be needed.

N Also, the waste may need to be cleaned due to the possible biohazardous N substances before it enters the wastewater system. In case the process stop 3 takes a long time, for example due to a web break, the temperature of the S 30 slurry container decreases and viscosity of the slurry changes and needs to be E corrected, when the process is started again.

< n Especially, in starch cooking processes the starch itself needs to be washed 3 during stops as the starch increases the BOD/COD (biochemical/biological oxygen demand / chemical oxygen demand) values of wastewater dramatically. The bacteria which is used to clean the wastewater prefers to utilize starch instead of other substances of the wastewater. If starch is present in wastewater treatment the bacteria will focus on the starch and harmful impurities will pass through the wastewater treatment plant. In worst case wastewater treatment plant needs to be shut down because of high starch contamination.

In US patent publication 3321359 is disclosed a continuous starch cooking method for calender stack sizing of paper and an apparatus therefor, in which starch is applied to paper or paperboard, which comprise preparing and maintaining a body of concentrated uncooked starch slurry, continuously blending a stream of water with a stream of said concentrated starch slurry to produce a stream of dilute uncooked starch slurry, continuously pasting said stream of dilute starch slurry with a jet of steam in a uniform immediate manner continuously, introducing the resulting stream of hot cooked starch without quenching into a body of cooked starch having a temperature of at least about 180°F and feeding size boxes of a calender stack with the cooked starch from said body of cooked starch for use in said calender stack sizing operation. An object of the invention is to create a method and a system of sizing agent cooking circulation, in which the problems and disadvantages of prior art are eliminated or at least minimized. Another object of the invention is to provide a method and a system of sizing agent cooking circulation, in which the problems and disadvantages relating to interruptions of the sizing agent cooking circulation due to stops in the process are eliminated or at least minimized. N A particular object of the invention is also to create a method and a system of N sizing agent cooking circulation with the possibility of continuously running 3 sizing agent cooking circulation and thus, with the possibility of continuous S 30 production of the sizing agent for the sizing agent application. = 3 Summary

LO o In order to achieve the above objects and those that become apparent later, the method according to the invention is mainly characterized by the features of the characterizing part of the independent method claim. The system, in turn, is mainly characterized by the features of the characterizing part of the independent system claim. Advantageous embodiments and features are disclosed in the dependent claims. According to the invention in the method of the sizing agent cooking circulation, 5 in which method during cooking of the sizing agent the sizing agent is flown to a converter or slurry container, from which converter or slurry container the sizing agent is pumped by a pump to a main line, and via which main line the sizing agent is flown to a storage container, a valve of a circulation line connected to the storage container is opened and the sizing agent is flown to a circulation line and to the main line and back to the storage container and the sizing agent is circulated until the stop in the cooking ends. According to one advantageous feature of the invention the sizing agent is flown by the pump to a circulation line.

According to one advantageous feature of the invention during the cooking or the sizing agent a valve of the main line is open. According to one advantageous feature of the invention during the flow in the main line the sizing agent is flown through a process equipment part. According to the invention the system of sizing agent cooking circulation comprises a converter or a slurry container, a main line, a pump located in the main line, and a storage container, and a circulation line connecting the storage container to the main line for circulating the sizing agent during a stop in the cooking of the sizing agent.

N N According to one advantageous feature of the invention the pump is provided 3 to flow the sizing agent in the circulation line. 3 30 z According to one advantageous feature the system comprises a valve of the 3 circulation line controlling the flow of the sizing agent in the circulation line.

LO o According to one advantageous feature of the invention the system comprises a valve of the main line.

According to one advantageous feature of the invention the process equipment part comprises means, for example at least one cooker, for example a jet cooker, and/or at least one mixing device, for example a mixing device for steam and sizing agent to add heat energy, for example steam, to the process to maintain the temperature of the sizing agent in the storage container.

In the method and in the system in accordance with the invention the washing need of lines during production breaks is eliminated or at least minimized due to the circulation possibility provided by the circulation line.

Also, the temperature of the pipes is kept more stabilized due to the hot sizing agent, for example starch, circulation in the pipes provided by the circulation line.

Additionally, the temperature of the storage tank can be maintained at optimum level.

The invention also provides the possibility that content of the storage tank can be cooked again in order to break up raps (reformed amylose particles) and/or lipids, which can build up during a long storage period.

This way it is possible to utilize the content of the storage tank much longer than in connection with storage tanks of the prior art systems, in connection of which it is commonly considered that starch should be discharged from the storage tank after 8-12 h storage period because starch quality is not then any more acceptable.

The discharge stage of the starch storage tank of systems known from prior art causes very big challenges for wastewater treatment plant.

N The invention also provides the advantage that the start procedure of and stop N procedure of the cooking are much shorter and thus, the risk to fail during these 3 procedures is much lower.

In connection with cooking lines known from prior S 30 art it usually takes several minutes before temperature and pressure in the z cooking line have reached the setpoint and starch cooking can be started. 3 During this starting period in the prior art systems, usually water is used to n replace starch and thus all this water will end up to the sewerage.

Also, it is 3 typically in the prior art systems during cooking stops to use water for flushing the cooking line and then for cooling the cooking line before the cooking line is shut down, which procedure takes typically several minutes and also here all water ends up in the sewerage as wastewater.

Additionally, in the prior art system the starting as well as the stopping contaminates the starch with water and the wastewater with starch because separation between starch and water is not fully possible. By the invention it is possible to reduce the starting and stopping times of the process to few seconds. Short starting and stopping times as well as the continuous operation of the cooking are also advantageous as thus there is lower risk of equipment failure during the starting of the cooking. In the prior art systems a common problem is that the post-cooking pump has too little capacity after the cooking pump has cooled down during a long cooking break as capacity of the cooking pump capacity depends strongly on temperature of the substance to be pumped, which causes that it might not be possible to start post-cooking at the correct time and that there might be a viscosity drop due to too long converting time. In many cases a lot of time is lost because pre-cooking stops when the converter tank is full, and the converter tank must either be drained, or the contents of the converter tank cooked to the storage tank with too low viscosity and only afterwards the cooking system can be started again. In worst case this procedure can take so long that storage tank runs empty and sizer is running out of starch. This typically has the same effects than a forced shut down of the fiber web production line or at least leads to significant downgrade of the production quality. The invention also eliminates this problem. Brief description of the drawings In the following the invention is describe in more detail with reference to the N accompanying drawing in which

N 3 Figure 1 shows schematically an advantageous example of a sizing agent S 30 cooking circulation system in accordance with the invention. i < n During the course of the following description relating to figure 1 like numbers 3 and signs will be used to identify like elements according to the different views which illustrate the invention and its advantageous example. In the figure some repetitive reference signs have been omitted for clarity reasons.

Detailed description In the figure 1 is schematically shown an example of a sizing agent cooking circulation system, for example a starch cooking circulation system, which system comprises a converter or a slurry container 10 and a storage container

15. From the converter or slurry container 10 sizing agent is guided to a main line 11 via a valve 12 to control the flow of the sizing agent from the converter or slurry container 10 to and in the main line 11. When the valve 12 is in open position the sizing agent is pumped by a pump 13 to flow along the main line 11 to process eguipment part 14 of the system and after processing the sizing agent by process eguipment part 14 the sizing agent is guided along the main line 11 to the storage container 15. The storage container 15 is connected via a circulation line to the main line 11 such, that the connection of the circulation line 16 to the main line 11 is located in flow direction of the sizing agent in the main line 11 before the pump 13. Thus, the pump 13 is utilized also for pumping from the storage container 15. The circulation line 16 comprises a valve 17 controlling the flow of the circulation line 16.

In the system the sizing agent is, thus pumped either from the converter or slurry container 10 by the pump 13 through the main line 11 and the process eguipment part 14 to the storage container 15 or it is pumped from the storage container 15 by the pump 13 using the circulation line 16 through the main line 11 and through the process eguipment part 14 back to the storage container

15. There can also be more than one pump, for example two parallel pumps N or two serial pumps.

N 3 The process equipment part 14 typically comprises at least one cooker, for S 30 example a jet cooker, and/or at least one mixing device, for example a mixing z device for steam and sizing agent. In the cooker or the mixing device the sizing 3 agent and steam are mixed as the steam is condensing inside the liquid sizing o agent and the condensation is thus increasing the temperature of the liguid. > N 35 In the system and in the method, there is continuous circulation through the main line 11, the pump 13 and the process eguipment 14. The cooking of the sizing agent from the converter or slurry tank 10 has priority, but in cases when the cooking from the converter or slurry tank 10 is not possible, the circulation continues from the storage container 15 through the circulation line 16, the main line 11, the pump 13 and the process equipment 14 back to the storage container 15. Typical reason why cooking from the converter or slurry tank 10 is not possible is that the storage container 15 is full due to a long web break in the fiber web production. There are also many other reasons: problems with steam or problems with first stage cooking or an empty starch silo or simply maintenance problems. In connection with an enzymatic starch cooking process the above example of the sizing agent production method and system the starch cooking begins in a first stage cooking in a first cooker (not shown), in which typically enzymes and/or biocatalysts are added to the slurry and the slurry is heated to the required reaction temperature in order to the enzymes and/or the biocatalysts to react and to form the sizing agent. After the first stage cooking the starch is fed to the converting container 10, in which the sizing agent stays for time required for the enzymes and/or the biocatalysts to convert the starch to required form. After converting the starch is fed to a second stage cooking in a second cooker in the process equipment part 14, in which the starch is heated to required temperature in order to stop the converting reaction caused by the enzymes and/or the biocatalysts and additionally a delay time in the required temperature needed to finalize and to fully stop any reactions caused by the enzymes and/or the biocatalysts by guiding the slurry via a delay pipe. Afterwards, any excessive steam is removed in steam removal stage. Finally, the starch is diluted to the desired solids content and guided to a storage container 15, from which, when needed in the sizing process, the starch is N guided to starch application at the sizer or the circulation along line 16 is used.

N 3 In connection with a modified starch cooking process or an oxidization cooking S 30 process in the above example of the sizing agent production method and z system there is a slurry container 10. The starch is not heated to inactivate the 3 enzyme, instead the starch is heated in order to swell and unfold the molecule n chains, which in the enzymatic starch cooking process happens in pre-cooking 3 stage i.e. in the first stage cooking. In case of the oxidation cooking process the oxidation chemical would be injected before the pump 13 and then the oxidation chemical would attack and split the molecule chains of the starch after the process equipment part 14 , for example a jet cooker 14 during the cooking time in the main line 11.

In the description in the foregoing, although some functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to the certain example, those features may also be present in other examples whether described or not.

Above only an advantageous example of the invention has been described to which example the invention is not to be narrowly limited and many modifications and alterations are possible within the invention.

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Reference signs used in the drawing: 10 converter or slurry container 11 main line 12 valve of the main line 13 pump 14 process equipment part 15 storage container 16 circulation line 17 valve of the circulation line

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Claims

1. Method of sizing agent cooking circulation, in which method during cooking of the sizing agent the sizing agent is flown to a converter or slurry container (10), from which converter or slurry container (10) the sizing agent is pumped by a pump (13) to a main line (11), and via which main line (11) the sizing agent is flown to a storage container (15), characterized in that, in the method during a stop in the cooking of the sizing agent a valve (17) of a circulation line (16) connected to the storage container (15) is opened and the sizing agent is flown from the storage container (15) to a circulation line (16) and to the main line (11) and back to the storage container (15) and the sizing agent is circulated until the stop in the cooking ends.

2. Method according to claim 1, characterized in that the sizing agent is flown by the pump (13) to a circulation line (16).

3. Method according to claim 1 or 2, characterized in that during the cooking of the sizing agent a valve (12) of the main line is open.

4. Method according to any of claims 1 — 3, characterized in that during the flow in the main line (11) the sizing agent is flown through a process equipment part (14).

5. System of sizing agent cooking circulation, which system comprises a converter or slurry container (10), a to the converter or slurry container (10) connected main line (11), a pump (13) located in the main line (11), = and a to the main line (11) connected storage container (15), a 25 characterized in that the system comprises a circulation line (16) 2 connecting the storage container (15) to the main line (11) for circulating 2 the sizing agent during a stop in the cooking of the sizing agent. z

6. System according to claim 5, characterized in that the pump (13) is x provided to flow the sizing agent in the circulation line (16).

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7. System according to claim 5 or 6, characterized in that the system comprises a valve (17) of the circulation line (16) controlling the flow of the sizing agent in the circulation line.

8. System according to any of claims 5 - 7, characterized in that the system comprises a valve (12) of the main line (11).

9. System according to any of claims 5 - 8, characterized in that the process equipment part (14) comprises means, for example at least one cooker and/or a mixer, to add heat energy, for example steam, to the process to maintain the temperature of the sizing agent in the storage container (15).

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