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Regular cleaning of the system is an effective supplement to fungicides, dispersants and other resin control agents.
The cleaning of the paper machine includes the flowing part, the Net part, the squeezing part, the sizing part, the drying part and so on.
Component Analysis of dirt in various parts of modern high-speed paper machine production system and formulation of targeted cleaning methods can effectively reduce problems arising from continuous operation of paper machine, improve paper quality and improve system operation performance.
Deposits of paper machines and additive systems can be inhibited by adding fungicides, dispersants and other resin control agents, but due to the influence of system load, low turbulence, dead corners and other factors in production, the system should be cleaned regularly to maintain the best operating performance.
Effective system cleaning can achieve the following benefits:
Reduce paper breakage, holes and defects;
Reduce paper appearance paper disease;
Improve system operation performance;
Increase production and benefits;
Reduce the risk of chemical disposal.
The cleaning of the paper machine shall include all parts from the start of the short process to the roll paper machine.
Cleaning can be physical cleaning, chemical cleaning, or a combination of the two.
It is very important for modern high-speed paper machines to carry out planned cleaning of all parts.
Generally speaking, the sediment on the paper machine mainly has three components: organic matter, inorganic matter and microorganism.
In fact, the precipitation produced by most paper machines is a combination of some or all of these major components.
This can be carried out by a variety of cleaning methods, which can be cleaned online or stopped.
1) cleaning of short process
With the increasing speed of paper machine, the application of fully enclosed paper machine sizing system, the existence of resin in pulp and rubber in waste paper, and the wide use of various chemical additives such as reinforcing agent and Defoamer, as well as the high recycling of the white water system, it promotes the concentration of nutrients and the large number of bacteria. The traditional bacterial control method cannot penetrate the biofilm and kill the microorganisms in the biofilm matrix, and there is no damage to the organic matter in the sediment formed by microorganisms.
In order to eliminate the hotbed of microbial growth, alkali and special biological dispersant are combined to carry out systematic alkali washing at high pH value, in order to prevent cell adhesion by using biological dispersant, thus preventing or slowing down the accumulation of biofilm, the biological dispersant penetrates into the living biofilm to relax and disperse, thus allowing the fungicide to reach the organism.
The cleaning cycle usually depends on the running state of the paper machine and generally changes with the change of the production system. The temperature of the cleaning solution should be controlled at 60~70 ℃, and increasing the temperature can speed up the reaction speed of the cleaning solution and improve the cleaning effect.
If this temperature requirement cannot be met, the concentration of chemicals should be increased or the cleaning time should be extended to obtain the best cleaning effect.
For the temperature, pay attention to the highest temperature that the forming net and the seal can bear. Generally, the highest temperature for cleaning is controlled at 70℃ and the pH is greater than 7 to avoid damaging the forming net.
The cleaning time is controlled at about 4 H. This mainly depends on the type and severity of the sediment. The concentration of cleaning chemicals is generally kept at 1% ~ 10%.
The type and concentration of chemicals also depend on the type and quantity of sediments. Under normal circumstances, a good cleaning effect can be obtained when the chemical concentration of 1% ~ 3% and pH value are 12, and the concentration is generally greater than 1% during alkali washing.
Clear water should be used as much as possible when preparing the cleaning solution, because the organic matter, inorganic matter and microbial particles contained in the white water of the system will consume the chemicals used for cleaning, thus increasing the dosage of chemicals and reducing the cleaning efficiency.
When there is not enough time to completely clean the system, special foam cleaning agent can be used for cleaning. Alkaline foam can efficiently decompose substances on any selected surface and penetrate into any sediment that tightly adheres to the surface of the equipment.
The operation method is to seal the inlet valve of the head sieve and the Weir mouth of the headstock box. The cleaning liquid is added by the head sieve and heated to about 70 ℃ with steam, if the equipment allows, the higher the temperature, the better for cleaning.
The foam generated at the head sieve extends to the headbox, and the foam will soak the surface of the object for as long as possible, at least 30min. Then add water to the pressure screen while running the pump to dilute the cleaning solution and cool the chemical system.
Check the pressure screen and headbox after the cleaning liquid is drained, and wash the residual loose substance with high-pressure water. If the headbox is cleaned separately, foam cleaning agent can be sprayed into the headbox through the weir plate gap (and headbox manhole).
The tip of the tube which is used to spray foam must be wrapped with soft material to avoid scratching the lip plate and the polishing surface inside the headbox.
After the foam effect is 30min, rinse the inner surface of the headbox with clear water. Foam cleaning agent can be repeatedly used as required.
2) cleaning of network Department
In most cases, the off-machine of the polyester forming net is not because of wear, but because the impurities, fine fibers, glue fillers and various additives and additives in the pulp block the mesh, causing the pasting net, the water filtering performance is reduced, and the machine is changed. Therefore, higher requirements are put forward for the cleaning quality of polyester forming net.
Cleaning of forming net is the key to ensure its service life. Two types of pollutants need to be considered when selecting the cleaning method of the forming net, one is the pollutant filled in the middle of the forming net to reduce the dehydration ability of the net; the other is the pollutant deposited on the surface of the forming net and the joint of the net.
In the paper machine with higher speed, it is required to have a swing high-pressure water washing device, and the spray pipe should have the nozzle facing upwards, so that the probability of impurities blocking the nozzle in the water is significantly reduced, and reduce the chance of increasing single-line fine fibrosis due to the impact of water flow on the friction surface.
The water spray pipe adopts reciprocating needle nozzle, the distance from the forming net is generally 20~40cm, and the swing stroke is generally 15cm or 30cm. For water pressure, the speed should be controlled at 350 ~ 2.5MPa when the speed is 2.0 m/min. When the forming net stops running, the spray water should be turned off immediately. When the speed is less than 400 m/min, the nozzle can wash the forming net vertically, but when the speed of the paper machine is more than 600 m/min, the water spray pipe should be rotated towards the running direction of the forming net, produces an injection angle of less than 90 °.
When the water spray does not work, resulting in poor paper, it can be stopped and cleaned with 10% alkali solution or alkaline chemical cleaning agent to dissolve, emulsify and moisten the adhesive.
If the effect is not ideal, it can be cleaned with 5% ~ 10% oxalic acid solution for about 30min. After washing, it can be thoroughly cleaned with clear water. It is strictly prohibited to rinse the forming net with high-pressure steam.
When cleaning, the forming net is carried out at a lower speed, generally at 60~100 m/min, while closing the high-pressure flushing of each part.
3) cleaning of press department
Dirt filled with pressed fabrics can be roughly divided into five categories:
● alkaline soluble matter. For example, starch, rubber, additives and the like in the ingredients can be removed by dissolving them in strong alkali solution;
● paper powder. Small fibers, miscellaneous cells and other substances in the slurry are trapped by the fabric and block the pores of the fabric. It is insoluble in any chemicals used to wash blankets, and it is best to remove it by physical methods such as high-pressure spray pipes and vacuum suction tanks;
● inorganic substance. Mainly inactive minerals, such as calcium carbonate, titanium dioxide, sediment and calcium and magnesium ions in hard water, which can be removed by controlling the pH value of dilute acid;
● extractable. Resins or polymers soluble in organic solvents, such as turpentine and tar;
● resin. It can be removed before curing by means of alkali washing system, such as synthetic polymer for improving wet strength of paper, etc.
There are physical and chemical methods for cleaning squeezed fabrics. Physical method is mainly spray water pipe, vacuum tube. The amount of water sprayed by the spray pipe and the vacuum degree of the vacuum tube are the key to cleaning the fabric.
The water spray pipe should spray water evenly to the full width of the fabric. Chemical method is used when the cleaning effect of physical method is not ideal. That is, in the process of fabric operation, water washing should be considered first, and chemical washing should only be used as a supplement.
According to the analysis of fabric dirt, fully grasp the type, nature and pollution degree of dirt, and provide basis for selecting chemicals for washing. Chemical washing is divided into continuous washing and intermittent washing. Continuous washing uses fan-shaped nozzles to continuously spray detergent onto the banner of the whole fabric.
When cleaning with chemical method, pay attention to washing with alkali substance (NaOH), wash fully with clear water, and then wash with a certain proportion of hydrochloric acid, make up for the influence caused by the fiber swelling caused by too high pH value after alkali washing and the smaller water filter gap of the fabric. For this reason, soda ash liquid with weak alkalinity is generally used for washing.
Due to the damage to the fibers of the fabric, in recent years, non-ionic alkaline surfactants have been used to compound the special detergent for the fabric, which has the advantages of less dosage, strong decontamination, good wetting effect and less foam, light damage to fabric fibers and other characteristics, but also anti-corrosion, sterilization and other properties.
Due to the complexity of the dirt components on the papermaking fabric, the selection of detergent should be determined according to the main components of the dirt in the fabric, and sometimes two detergents are used for cleaning respectively.
The position of the liquid spray should be as close as possible to the pressure zone, so that the detergent can react with the dirt for a long time. Then rinse with high-pressure and low-pressure water, and then use vacuum suction tank to suction.
The concentration and dosage of detergent should be selected according to the weight of the fabric, the amount of pollutants and the speed of the vehicle. When cleaning, it is carried out slowly at a crawling speed. At the same time, the vacuum device of the vacuum box is turned off or the vacuum degree is greatly reduced, so that stubborn adhesion can be removed.
Increasing the temperature of the drug can improve the washing effect. When the water temperature rises from 10℃ to 30℃, its viscosity can be reduced by about 60%. Practice shows that it is most appropriate to heat the temperature of detergent to 50 ~ 60℃. Washing of pressed fabrics is closely related to embossing.
A reasonable washing method, such as washing should first wash the reverse side (because the particles and impurities that cause fabric embossing in copying are adsorbed by the front of the fabric and gradually enter the inner layer of the fabric, if it accumulates to a certain extent and causes embossing), after the front face is washed at an angle of 30 degrees towards the running direction of the fabric, impurities and particulate matter are drained away with the water through vacuum suction. When the washing water pipe is blocked, it should be eliminated in time, otherwise it is easy to cause ribbon embossing.
Vacuum suction blanket box can remove some moisture from squeezed fabric. In order to ensure the dehydration effect, the vacuum suction blanket box should be checked regularly to check its contact degree with the fabric (under normal circumstances, the suction mouth should be straight and close to the fabric), the vacuum degree of the vacuum box, whether the connection of the vacuum box and the pipeline are leaking, whether there are sundries in the box, etc., and the problems should be adjusted and repaired in time.
4) cleaning of sizing department
The cleaning of the sizing part is mainly the problem of scaling of pipelines and containers.
-Alkaline cleaning: starch deposits that do not contain polyvinyl alcohol can be washed with 5% ~ 10% hot alkaline solution, and circulating Flushing below 90℃ is generally controlled, which may include special pipelines. However, the use of hot lye requires careful operation.
-Acid cleaning: if polyvinyl alcohol is contained in the stickies, thick deposits will be formed in the pipes and containers, boiling 5% of hot hydrochloric acid solution treated by inhibition can be used to remove dirt through the system for several hours, while thick dirt needs nearly 7-8 hours.
The sizing press roll itself is cleaned with hot water.
5) cleaning of drying section
There are basically four categories of dirt in the drying part:
Paper wool (generally composed of staple fibers and fine fibers);
Turpentine, latex;
Water soluble sizing agent;
Solvent salt or heat setting coating.
The cleaning method of each dirt is different:
-Paper hair is generally removed by blowing device, which can be carried out when the paper is broken or stopped.
-Turpentine, latex and dirt strongly adhering to the fabric should be cleaned outside the machine if it exists.
-For water-soluble sizing agents, they can be cleaned directly with steam hoses, spray pipes or hot water during shutdown. The cleaning cycle depends on the specific situation.
-Solvent salts or heat setting coatings shall be removed before hardening.
Using high-pressure hot water or steam injector to clean inside its circuit can work. If the hole has been blocked, it needs to be cleaned with a special chemical cleaning agent.
Generally speaking, chemical cleaning agents are only used when normal steam or hot water cleaning is ineffective. The cleaning of the fabric to be cleaned is stopped and carried out at room temperature after the dryer cools down.
The cleaning agent should be sprayed on the mesh surface of the fabric in the form of foam, so as to make the cleaning agent adhere to the mesh surface in the form of foam and stay on the mesh surface for a long time, it is not easy to lose the liquid medicine that becomes liquid.
When cleaning, the dryer is carried out at a crawling speed (generally 15 m/min), and foam cleaning is carried out by foam cleaning equipment.
The amount of cleaning agent varies according to the type of pollutants and cleaning degree of the fabric and the structure of the fabric. Generally, the amount of cleaning agent is 0.02 ~ 0.05MPa.
After cleaning, the liquid medicine on the fabric and equipment should be completely washed clean with high-pressure water until the mesh surface of the fabric is not smooth.
For the surface of the dryer and the dirt on the guide roll, the manual soda ash spray method can be used. After the liquid medicine is cleaned, rinse it with clear water.
In short, the paper machine is cleaned regularly, systematically and scientifically, which not only improves the production efficiency and the quality of paper products, but also helps to extend the forming net, the service life of pressed fabric and dried fabric, thus improving the operating performance of the paper machine system.
Practice shows that cleaning is an effective way to control the good operation of modern high-speed paper machine system.
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